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Commercial-in-Confidence I Report No 6990l05A

August 1997

I I I I I I I ,I I I I I I

DESIGNING CONCRETE MIXES USING LOCAL MATERIALS

Overseas Development I Administration 94 Victoria Street London

UK 1 SWlE5.K

Gifford and Partners Carlton House

Ringwood Road Woodlands

Southampton SO40 7HT

UK

I 1 I I I I I I 1 1 I I I I I I I I I I


Although this report has been commissioned by the British Government under grant aid arrangements, the British Government bears no responsibility for, and is not in any way committed to, the views and recommendations expressed therein.

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C O N T E N T S

INTRODUCTION

DURABLE CONCRETE

2.1 Chemical Exposure 2.2 2.3 Reactive Aggregates 2.4 Freezing and Thawing 2.5 Quality of Materials 2.6 Concrete Construction

AGGREGATES

3.1 3.2 Physical Properties 3.3 Contaminants

CEMENTS

4.1 General 4.2 Portland Cement 4.3 Blended Cement

WATER

5.1 General 5.2 Sea Water 5.3 Industrial Wastewater 5.4 Domestic Wastewater

ADMIXTURES

6.1 General

Corrosion of Reinforcement Embedded in the Concrete

Particle Size, Shape and Grading

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LOCAL ALTERNATIVE MATERIALS

7.1 Alternative Aggregates 7.2 Replacement Materials 7.3 No-fines Concrete 7.4 Local Reinforcing Materials

CONCRETE

8.1 Durability Parameters 8.2 8.3 8.4 8.5

Minimum Standards for Durable Concrete Proportioning Materials for Concrete - General Proportioning Materials for Concrete - Mix Design Proportioning Materials for Concrete - Blending of Aggregates

REFERENCES

STANDARDS

GLOSSARY

LIST OF TABLES

3.1 3.2 4.1 4.2 4.3 5.1 6.1 8.1

8.2 8.3

8.4

8.5 to 8.8

Aggregate Properties Aggregate Contaminants Significant Specification Limits for Standard ASTM and BS Type Cements Portland Cements Relation between CEN Type and BS and ASTM Type Cements Contaminants that can be Present in Local Water Common Admixtures Minimum Cement Content and Maximum WatedCement Ratio for Different Types of Exposure Concrete Mix Design Statistics Approximate Water Contents (kg/m3) Required to give Various Levels of Workability Approximate Compressive Strengths (N/mm2) of Concrete Mixes made with a WaterKement Ratio of 0.5

Concrete Mix Proportioning - Examples 1 to 4

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1 INTRODUCTION

This manual provides practical guidance on how to produce durable concrete in rural environments using local materials. It is written as an aid to qualified engineers working in design offices. A companion pocket-size volume entitled Making Good Concrete is written for technicians working on construction sites and requiring more elementary guidance.

‘Local materials’ is a term used to describe aggregates, cement and water which may fail to meet the requirements of the commonly used British and American Standards. Although they are apparently unacceptable, these materials can often be used to make good concrete provided due care is taken with the mix proportioning and production. In this manual, emphasis is placed on the wisdom of using information from past experience of concrete made from local materials. Also it is important to carry out trial mixes and repeat them if there are any changes in the supply of materials.

Guidance is provided for producing low to medium strength, durable concrete for mass and reinforced concrete structures. Account is taken of environmental conditions, the intended life span of the structure and its intended use. The importance of durability is explained and the different factors influencing it are described. There are sections on the constituent materials required for concrete; aggregates, cements, water and admixtures. There is also a section on alternative and replacement materials not usually recognised in Standards.

A number of example trial mixes are given and the background data are included to permit the user of this manual to proportion his own trial mixes.

Terms shown in italics in the text are defined and explained in a glossary arranged alphabetically at the back of the manual. This enables additional explanations to be given without interruption to the text. The manual is extensively indexed and cross-referenced to enable information to be extracted more easily. A list of the more commonly used British and American Standards is provided. Some of the Indian Standards are also listed because of their relevance to local materials.

Sources of information that have been used include the CIRIA Guide to Construction in the Gulf Region, various publications by the Concrete Society and the former Cement and Concrete Association, reported case studies in developing countries, research reports and first-hand experience of the authors.

Finally, it should be noted that prestressed concrete and pavement concrete are not included as these are special materials requiring higher technology than is appropriate to this manual.

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2 DURABLE CONCRETE

‘Durability’ of concrete is defined as its ability to resist weathering action, chemical attack, abrasion or any other process of deterioration. ‘Durable’ concrete will retain its quality when exposed to weathering and the environment during its lifetime.

It is therefore essential to design a concrete to give a satisfactory performance taking into account the materials to be used, the environment in which the structure is to be built and operational requirements.

It should also be pointed out that, to produce durable concrete, it is essential to have good quality control in its production and a high level of workmanship in placing, compacting and curing the concrete.

In determining the desired properties and quantities of the various materials in a concrete mix, it is important to understand the causes of deterioration that can occur and the mechanism behind them. The major causes of deterioration for a concrete structure are:

8 chemical exposure; 8

8 reactive aggregates; 8 freezing and thawing; 8 poor quality materials; and 8 poor concrete construction.

corrosion of reinforcement embedded in the concrete;

The most common faults and failures in buildings have been reviewed in Reference 1. The various processes of deterioration that fall under each of these categories are briefly described in the following sections.

2.1 Chemical Exposure

2.1.1 Seawater

I I

m See Section 5.2 for Exposure of concrete to seawater can result in corrosion to steel reinforcement due

I to chlorides in the dissolved salts. Damage to the cement paste can be caused by sulphates, also in the dissolved salts.

information On

seawater

Concrete with low permeability is essential to delay the attack from the dissolved salts and to protect the reinforcement. Mass concrete, containing no reinforcement and continuously immersed in seawater, may perform satisfactorily.

2.1.2 Sulphates

Sulphates may occur naturally in the soil or groundwater adjacent to the structure. Evaporation can lead to an accumulation of sulphates on an exposed face of the structure which can accelerate deterioration processes.

See Section 8.2.5

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2.3.3 Oxidation or Hydration of Unstable Elements in Aggregates

Expansive inclusions such as iron pyrites and some sulphides or oxides, such as anhydrous magnesium oxide or calcium oxide, can produce damaging reactions. For instance, the sulphides can be oxidised to form a ferrous sulphate which can then decompose with the sulphate ions reacting with the cement paste. Damage can result especially under warm and humid conditions.

2.3.4 Reaction of Organic Materials

Organic materials such as humus or organic loam, which can be found in aggregates, can interfere with the hydration, thereby affecting the strength and durability of the concrete.

2.3.5 Minimising the Risk of Reaction

The risk of alkali reaction can be minimised by careful selection of the aggregate and use of low alkali cement. A concrete believed to be susceptible should be kept dry and should not be used in places where it can get wet.

Detailed information on minimising the risk of alkali-silica reaction is given in the Concrete Society Technical Report No 30, Reference 2.

2.4 Freezing and Thawing

If wet concrete is subjected to cycles of freezing and thawing, cracking and deterioration can take place. This is because water that has soaked into the concrete expands during the freezing cycle and disrupts the concrete structure.

Only good quality concrete, having low permeability, can resist the actions of freezing and thawing without some deterioration taking place.

If concrete is to be exposed to cycles of freezing and thawing it is important to use a mix having a low waterkement ratio. Coarse aggregate containing particles with relatively high absorption values should be avoided as should those aggregates with a high proportion of flat particles.

The use of an air entrainment admixture improves resistance to freezing and thawing.

2.5 Quality of Materials

The durability of a concrete structure depends on properties of the various constituents of the concrete mix. The effect these properties will have on durability will vary according to the environment and what the concrete is used for.

For aggregates, durability can be affected by the physical properties, particle grading, particle shape and any contaminants present. For instance, if the grading

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See Section 4.1.2 for information on cement soundness

See Tables 3.2 and 5.1 for information on organic contamination

See Sections 3.2.9 and 4.1.8 for information on low-alkali cements

See Table 6.1 for information on air entraining admixtures

See Section 3.1 for information on

I I I I I I 1 I I I 1 B 8 U I I I I I I

It is essential that the construction practices to suit the local conditions are fully understood. For concrete production, this includes the protection of materials from contamination and unacceptable temperatures during delivery and whilst being stored on site. It is also important to provide and maintain an adequate mixing plant and to control the temperature of the materials during mixing.

For transporting and placing, it is essential that the concrete is moved as quickly as possible with little exposure to the environment, otherwise, the workability of the concrete may be affected. Careful consideration should be given to how the concrete is to be placed in order to avoid segregation, settlement and bleeding.

After placing the concrete, it should be compacted as soon as possible and vibrated carefully to ensure adequate compaction and to avoid segregation.

Curing of the concrete is of prime importance if long term durability is to be achieved. If the right treatment to the concrete is not provided during the first weeks, crucial properties of the concrete, such as its permeability, may be affected and defects, such as plastic shrinkage cracking, may arise.

It is essential that the importance of curing and the methods that should be adopted for a particular situation are understood. If inadequate curing is undertaken, any problems that arise in general, must be made good by other treatments.

In hot weather, the constituent materials heat up and the temperature of the fresh concrete becomes higher than normal. The temperature of the concrete also rises due to the heat of hydration being generated at a faster rate. The high temperature causes several problems:

0 the concrete stiffens faster; 0

0

0

as the concrete cools, there is increased thermal contraction; if the climate is hot and dry, evaporation rates are even higher than for hot and humid conditions; and if there are high winds, evaporation rates are higher still and plastic shrinkage can occur.

See Reference 3

information on concreting in hot

The quality of concrete in hot weather can be controlled by a number of actions: for

0 constituent materials should be kept cool; weather 0

0

0

0

0

temperature of concrete should not exceed 40°C when placed; appropriate admixtures may be needed to retard the set and maintain workability; cement content should be as low as is compatible with other requirements; mixing and placing the concrete should be done in the coolest times of the day; and the concrete should be protected from the sim during the curing period and kept cool and moist.



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3.2 Physical Properties

The physical properties of aggregates are described below. Testing procedures and guidance are given in Table 3.1.

3.2.1 Strength

The strength of an aggregate depends on its composition, texture and structure. Hence, a low strength may be due to the weakness of the constituent particles or the particles may be strong but not well bonded. Aggregate strength is rarely tested and generally does not influence the strength of concrete as much as cement paste strength and paste-aggregate bond. However it can limit the strength of the concrete if it is similar to the strength of the cement, rather than being much greater as is the usual case. An example of this is lateritic aggregate, which is common in Africa, South Asia and South America. Laterite can produce concrete having a strength of up to 10N/mm2. This is low but may be adequate for many purposes.

The measurement of aggregate strength is often done indirectly. However, it can be measured directly, if required, by determining its Crushing Value or Impact Value.

3.2.2 Modulus of Elasticity

An aggregate with a high Modulus of Elasticity (Young’s Modulus), will not compress or expand so much when a load is applied. A high Modulus of Elasticity in the aggregate will produce a concrete with a high Modulus of Elasticity, and will also affect the amount of creep and shrinkage of the concrete.

During volume changes in a concrete, a less compressible, rigid aggregate might cause cracking of the cement matrix, whilst a more compressible, flexible aggregate would ‘deform’, allowing such change without cracking. Depending on the situation, therefore, it may be desirable to use an aggregate with a low Modulus of Elasticity, which is often linked to lower strength, rather than one with a high Modulus of Elasticity and high strength.

3.2.3 Specific Gravity

The specific gravity gives valuable information on an aggregate’s quality and properties; generally, the higher the specific gravity, the stronger and harder it will be. Changes in the specific gravity of an aggregate might indicate a change in its nature or source of supply. However, large changes in composition may not necessarily cause a change in specific gravity, therefore measurement of specific gravity alone should not be used for quality control of the aggregate.

3.2.4 Weathering

Weathering of aggregate takes place whilst it is part of the bedrock. During weathering over thousands of years, the rock can break down until it may

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See Table 3.1 aggregate properties

See Sections 3.2.5 on soundness, 3.2.6 on water absorption and 3.2.8 on friability

eventually become soil. In wet places, the upper rock may be weathered so that much of its original minerals have been removed due to rainfall. This produces a weak rock, unsuitable for aggregates. In hot, dry places, where evaporation is greater than rainfall, the upper rock may have additional soluble minerals, removed from below. These may be contaminants such as sulphates, which produce an unsuitable aggregate. Igneous and metamorphic rocks are more likely than sedimentary rocks to have weathered upper rock.

See Table 3.1

National standards, in general, state that weathered rock should not be used for making concrete. However, if an aggregate known to be from a weathered zone has a good record of service in existing structures, it may be possible to continue to use it.

When a new quarry is used, it is important to take careful samples of the rock at different depths to check for weathering. Weathered rock may be recognised by discoloration and sometimes (depending on the type of rock) greater fissuring. Weathered rock should be discarded. Trial mixes should then be carried out to determine the properties of concrete made from the aggregate.

3.2.5 Soundness

Soundness is the ability to resist excessive changes in volume. Causes of volume change include: See Table 3.1

0

0

freeze-thaw cycles and thermal changes above freezing, typically occurring in arid climates; entry of salts into pores which can occur when groundwater containing soluble salts is drawn up into concrete by capillary action, then evaporates from the concrete surface leaving salt in the concrete; wet-dry cycles, typically occurring in tidal areas. 0

Types of aggregates that are unsound and may expand disruptively, and crack the concrete are:

0 limestones containing clay; 0 porous chalk; 0 slate; and 0 weathered rock.

Soundness can best be predicted from past performance of concrete made from these materials.

3.2.6 Water Absorption

Water absorption provides an indication of the durability and strength of an aggregate, and, to a lesser extent, it can affect the permeability of the hardened concrete. The absorption characteristics of an aggregate need to be determined, prior to use, so that the total water content of the concrete mix can be controlled and correct batch weights used.

SeeTable3.1

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Measurement of water absorption is made when the aggregate is Saturated Surface Dry (SSD), that is, when the aggregate is saturated on the inside but dry on the outside. However, when an aggregate is stored in a stockpile, the water it contains will vary depending on the climate, weather and time of day, due to evaporation and absorption of moisture. To account for this, the wetness of the aggregate must be checked at least twice a day in order that the correct watedcement ratio is maintained in the mix.

3.2.7 Thermal Expansion

Thermal expansion and shrinkage occurs with changing temperature. The expansion of aggregates (4-15 microstraid'C) is usually lower than that of the cement paste (1 1-20 microstrain"/C). If the difference is very great, temperature changes can produce tiny cracks where the paste and aggregate meet in the hardened concrete as they try to expand by different amounts. This micro-cracking can increase permeability and lower the durability of the concrete.

See Table 3.1

3.2.8 Friability

A friable aggregate is one which breaks down easily during handling operations and mixing of the concrete. This breakdown increases the surface area of the aggregate particles (known as specific area). These smaller particles then require a higher water content for a given workability. It is therefore necessary to carry out site mixing trials which include the handling operations, so that friability can be taken into account in selecting the mix proportions.

See 3.l

3.2.9 Reactivity

The types of alkali-aggregate reaction are given in Section 2.3. Alkali-silica reaction is the most common; it is the reaction between the active silica parts of the aggregate and the alkalis in the cement. This expansive reaction occurs during and after hardening of the concrete. It is the reaction after hardening which may cause disruption of the cement paste and then cracking in the concrete.

See Table 3.1

see Section 2.3.1

The reaction can occur in a number of aggregates including limestones some quartzites, silicaceous shales and rocks containing opal cherts, schists. It has occurred in concrete in most countries. Serious disruption requiring expensive repairs can occur as soon as six years.

The alkali-carbonate reaction is more rare and occurs in a similar manner to the alkali-silica reaction. It is known to occur with aggregates from calcitic dolomites and limestones.

The rate of these reactions is also affected by how much water is in the cement paste and the cement's constituents which cause it to be alkaline. The reaction is accelerated in humid conditions, by wetting and drying cycles, and in a temperature range between 10°C and 40°C.

See Section 2.3.2

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There are several tests for reactivity. They require special skills and equipment, See Section 4.1.8

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and can take up to a year to carry out. The best way of determining potential reactivity is from experience and knowledge of the local aggregate.

3.3 Contaminants

The suitability of aggregate for making concrete is influenced by the presence of contaminants. These contaminants occur as natural impurities, such as sea salt and shell in sea sand, and as part of stone crushing processes, which produce dust and clay as well as aggregate.

Typical contaminants that can be present in aggregates are:

See Table 3.2

0 Clay, silt and dust 0 Mica e Organic material 0 Shell 0 Absorbent and soft particles 0 Chlorides 0 Sulphates

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Compliance with a Standard gives the designer some assurance as to a cement’s quality, but many of the properties covered by these standards are of no particular relevance to mix design. Even if a cement conforms to a national Standard, it does not ensure that its performance in the concrete will be easily predicted. The cement should be tested for the properties which are important to the user.

It must also be noted that when working with cement from unfamiliar sources, the design mix should be based on the actual measured performance of that particular cement. It should not be assumed that all cements which comply with the same specification will behave the same. For this reason, it should also be ensured that all the cement used for a particular structure comes from the same supplier and the same location.

The significance of some of the cement specifications to the designer is explained below; followed by Table 4.1 which gives some specification limits for BS and ASTM type cements.

4.1.1 Setting Time

The initial and final setting times of cements are usually well within the limits allowed by national Standards, and are not of much practical use in terms of concrete mix design. Setting times of concretes do not correlate directly with those of cement pastes in the laboratory because of the different temperatures and water losses to surroundings. However, the setting times may be used to compare the behaviour of different cements. Setting time tests may also be used throughout a project as a simple quality control on consistency between batches of cement.

See 4.1

It should be noted that speed of setting and speed of hardening (eg gain of strength) are entirely independent of each other.

A simple test for less important works, may be carried out on site without special apparatus, as follows:

Make a stiff paste of pure cement and water and form it into a pat about 75rnm in diameter and 12 to 25mm thick. The pat should start to set in approximately 30 to 60 minutes. In 18 to 24 hours the pat should have hardened enough that a thumb-nail cannot scratch the surface. After 48 hours it should be difficult to break with fingers and it should be fully hard in 7 to 8 days. Note that high temperatures may decrease setting times.

4.1.2 Soundness

Soundness refers to the ability of a hardened cement paste to retain its volume after setting. Lack of soundness is caused by too much magnesia (MgO) or free

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lime (CaO). concrete if they are present in excess.

These hydrate slowly and may cause disruption of hardened See Table 4.1

The quantities of free lime and magnesia may be limited by carrying out Soundness Tests. The Le Chatelier (BS) test detects unsoundness due to free lime only. The Autoclave (ASTM) test can detect unsoundness due to both free lime and magnesia.

A simple test, which may be carried out on site, follows on from that described under Setting Time:

Take a cement pat that has set and boil it in water for approximately five hours. The pat should remain sound and hard, and should not swell, crack or disintegrate, and may show only hair-line cracks. This is a very easy and important site-test to determine the suitability of a cement for construction.

4.1.3 Compressive Strength

Compressive strength of mortar cubes as given by manufacturers of cement is an indication of the potential of the cement for producing strong concrete. For more reliable guidance, the strength of specific mortar cubes of the actual cement should be tested as it arrives on site. The best guide to a concrete's compressive strength may be found by making concrete cubes because this takes into account many of the other important variables such as aggregate characteristics, concrete mix and construction methods.

See Glossary for information on mortar cubetests, also Section 8.7.2

Compressive strength testing may be used throughout a project as a check on quality control between batches of concrete.

4.1.4 Heat of Hydration

Heat of hydration is the heat generated when cement and water react. The rate of heat given out is dependent on the chemical composition of the cement, but it also increases with the fineness of the cement, the temperature of the concrete and with a decreasing watedcement ratio.

SeeTab1e4.1

Cement temperature can be a particular problem in hot climates. As the ambient temperature is raised, the rate of evolution of heat increases which further rises the concrete's temperature. As a result, problems of differential temperature stress and thermal cracking during the early stages of hardening of concrete, can be serious and special precautions to keep the materials cool may be required. Using a Low-heat Portland cement (LHPc) may reduce the problem.

See Tab,e 4,2 for information on L H P ~ and RHPC

In cold climates, a rise in concrete temperature caused by heat of hydration may benefit curing and stop freezing of the concrete which would otherwise be a

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serious problem. In this case, using a richer mix or a Rapid Hardening Portland cement (RHPc), may reduce the problem.

4.1.5 Insoluble Residue and Loss on Ignition

In general neither insoluble residue nor loss on ignition is of particular importance to mix design, but they may be good indicators of its quality relative to a ‘normal’ cement if a local and non-standard cement is being used, for example Rice Husk Ash

See Table 4.1

Loss on ignition is determined by heating a cement sample of known weight to 900-1000°C. When the weight of the sample reaches a constant value it is noted. The percentage weight loss is an indication of prehydration and carbonation.

4.1.6 Sulphate Content

Sulphate (measured as SO, or SO,) is present in gypsum, which is added by makers of the cement, to produce the required rate of setting. There is a restriction as to the amount of sulphate allowed in concrete. The allowable sulphate content of the aggregates to be used is then found by subtracting the amount in the cement (and in mixing water, if any) from this total content.

See Section 8.2.3 for total allowable sulphate

4.1.7 Tricalcium Aluminate (C,A)

If there are large amounts of sulphates in the aggregates to be used, the Tricalcium Aluminate, CJA, content is important. This is because C,A reacts See Section slowly with the aggregate sulphates to form an expansive solid which may 2.1 for further

damage the concrete when hardened. produce this slow reaction after hardening. Reaction between C,A and sulphates in the cement is not a problem.

Sulphates from groundwater may also information on sulphates

If chloride attack of reinforcement in the concrete is likely to be a problem, a higher C,A content may actually be desirable. This is because the C,A will react with and remove some of the harmful chloride ions from the concrete. For this reason, it may not be appropriate to use a sulphate-resisting cement (which has a low C,A content) when both problems occur at once.

See Table 4.2

4.1.8 Alkalis

See Section 3.2.9 on alkali- aggregate reactivity

If alkali-aggregate reactivity is considered to be a problem, then limiting the alkali content of the cement may reduce the occurrence of the reaction. When an alkali limit is specified, the cements are called ‘low-alkali’ cements.

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4.2

4.3

Portland Cement

National standards for Portland cements exist world-wide. The most commonly used are BS and ASTM, whilst all Portland cements are specified by CEN standards as CEM Type 1. Table 4.2 gives specifications and general descriptions of each type.

Blended Cements

Blended cements comprise those which are not wholly based on Portland cement. The replacement materials include blast furnace slag, pulverised fuel ash and silica fume ash.

ASTM standards group all such cements as ‘blended’, with subgroups depending on the constituents of each. CEN standards are given for CEM Types I1 to V, with the type dependent on the proportion of Portland cement clinker (only Type V is specifically referred to as ‘blended’). British Standards classify each cement with a specific name, which depends on a range of proportions of each constituent.

In general, many of the cements have been developed to increase durability of concrete under a range of conditions. Examples of this include increased resistance to:

0 sulphate attack; 0 chloride attack; and 0 alkali-aggregate reaction.

It should be noted that blended cements tend to have a slower gain of strength than Portland cements, but will eventually produce concrete at least as strong and often more durable.

An additional advantage is that the blend constituents are waste materials of industrial processes. The use of them is environmentally attractive.

Table 4.3 provides a grouping of different National Standard cement blend types against the European CEN Standards. Different proportion boundaries between CEN, BS and ASTM standards mean that some BS and ASTM cements fall into several CEM categories. Therefore, the description of the cements most specifically applies to the CEM types, but the ASTM and BS types will be similar. Advantages and disadvantages of the specific types are also given. See Table 4.3

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I I I I I I I I I 1 I I I I I U I I I I

5 WATER

5.1 General

Water is required for hydration of the cement and to lubricate the aggregate particles sufficiently to give a satisfactory workability. It is usually taken from approved sources and commonly from drinking water supplies. Whilst in general drinking water is suitable for making concrete, sometimes the concentration of salts is too high for reinforced concrete. If the taste of the local water supply is even slightly salty, testing should be carried out to assess the salt concentration.

National Standards generally specify that mixing water should not be taken from shallow or stagnant sources, marshes, tidal rivers or the sea. Water should also be free from oils, acids, alkalis and organic matter. However, for unreinforced concrete, brackish water and seawater may be useable.

In some cases it may be difficult to obtain mixing water which complies with all criteria of a particular national Standard. In such circumstances if the effect of the particular contaminant(s) are understood, it may be safe to use this water. The most common contaminants, their effects, limits and advice are given in Table 5.1.

See Tab1e 5.1

In marginal cases, contaminated water may be mixed with clean water to dilute the contaminants to acceptable concentrations. Where there is no alternative, it may be necessary to import water from another location. Some of the more common sources of water, which are ‘non-standard’ are given below:

5.2 Sea Water

The use of sea water for producing unreinforced or mass concrete is generally acceptable. Sea water should not be used in reinforced or prestressed concrete because the chlorides present can cause corrosion of the steel. If reinforced concrete construction is desirable and there is no alternative source of water, a desalination plant could be installed on site to purify the salt water, though this would be expensive.

Sea water or brackish water should not be used in concrete with known alkali- reactive aggregates, even when the cement’s alkali content is low. This is because the potassium and sodium in the salt can react with the aggregate, producing disruptive effects in the hardened concrete.

See Section 3.2.9for information onalkali- aggregate reaction

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Note that, although it may be possible to make a good quality concrete with sea water, any problems due to the presence of salts such as alkali-aggregate reaction would not become apparent until some years after construction.

The contaminants in sea water usually consist of about 78% sodium chloride and 15% magnesium chloride and sulphate. Whilst concrete made with sea water may gain strength earlier than normal concrete, strengths at later stages (after 28 days) are likely to be lower. It is therefore important to carry-out cube strength comparisons with concrete made with clean water, in order to assess any differences in long-term strength. The strength of concrete made with sea water can be compensated by increasing the cement content.

See Section 8.7.2 and the

for mortar cube testing

Concrete made with sea water may suffer persistent dampness and surface efflorescence. Sea water should not therefore be used where the appearance of the concrete is of importance or where a plaster finish is to be applied.

5.3 Industrial Wastewater

Most waters carrying industrial wastes have less than 4000ppm of total solids. If waste water has to be used as mixing water, the reduction in compressive strength is likely to be not more than 10 to 15%. Comparative tests on mortar cubes should be undertaken in order to assess the effects on strength and setting time.

SeeGlossaW for mortar cube testing

Certain wastewaters, such as those from paint factories, coke and chemical plants, mines and mineral dumps may contain harmful impurities. These waters should only be used with extra caution and testing for unusual impurities should be undertaken.

5.4 Domestic Wastewater

It may be possible to use wastewater from sewage treatment plants as a replacement or partial-replacement for clean water in concrete. A wastewater which has higher than acceptable limits of contamination may be diluted by potable water until it falls within the limits. Alternatively, it may be possible to allow a particular contaminant to remain above the normally acceptable limits, depending on its effects on the concrete and the structure’s use.

Comparative tests on mortar cubes should be undertaken to assess the effects on strength and setting time.

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The use of admixtures is not a substitute for good practice, and cannot make a poorly designed or poorly produced concrete good. It is necessary to carefully carry out trial mixes, to check that the performance of the concrete with the admixture is as expected. It is also important to follow the manufacturers’ instructions as to the quantity of admixture to be used and when to use it. On occasions, it may be tempting to exceed the stated amount, but overuse of admixtures can cause considerable problems.

In general, it is acceptable to use both air entrainment and water reducing agents in one mix, but otherwise particular care is needed when using more than one admixture at a time. This is due to the possibility of unexpected and unwanted reactions occurring between the admixtures. Trials mixes should be carried out to assess these effects.

Admixtures should comply with a National Standard. Some of the most widely used standards are:

0 British Standard BS 5075 All types of admixture

0 ASTM Standards ASTM C-494 All types except as below ASTM C-260 Air entrainers ASTM C- 1 - 17 Superplasticisers

0 Indian Standard IS 9103 All except superplasticisers

For more information on admixtures, see the Concrete Society Technical Report No 18 (Reference 10).


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7 LOCAL ALTERNATIVE MATERIALS

In some locations it may be impossible or depending on the type of construction, unnecessary, to use conventional aggregate, cement and reinforcement.

Examples are:

0 Urban development where the natural sources of aggregate are scarce, but alternative aggregates such as crushed brick, recycled concrete or other waste are available and cheap.

0 In areas where the likelihood of alkali-aggregate reaction is considered high due to the type of available aggregate.

See Section 3.2.9 for information on alkali- aggregate

0 In areas where the available aggregate is unsuitable, for example in East Nepal, where sands contain 4 to 30% mica by weight.

reaction

7.1 Alternative Aggregates

In cases where normal aggregates are not available local alternatives could be considered:

7.1.1 Lightweight Materials

These include naturally occurring rocks such as pumice, scoria and volcanic cinders. Other materials are processed such as expanded clays, slates, shales and pulverised fuel ash.

All lightweight materials are relatively weak due to their high porosity which also tends to make them more absorbent. This loss of strength relative to conventional aggregate, can be compensated by increasing the cement content of (he concrete mix, though there is a limit beyond which additional cement will not affect the strength. Generally, the denser the resulting concrete, the stronger it is. ( Ither effects of using lightweight materials in concrete are:

0 mixes tend to be less workable;

may have a lower thermal conductivity (good for thermal insulation); and may have an increased fire resistance.

0 may have a higher drying shrinkage; 0

0

7.1.2 Crushed Brick

("rushed brick is one of the more widely used artificial aggregates in locations where naturally occurring aggregate is not available. It is a good material for

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making plain, mass concrete but should not be used in reinforced concrete if the crushing strength of the brick is less than 30-35N/mm2.

The bricks should be free from lime mortar and from lime sulphate. They should be soaked in water to saturate them before use, so that they do not absorb mixing water. Porous aggregates which absorb more than 10% of their mass after 24 hours soaking in water, are not recommended for concrete construction using Portland cement. It may however, be possible to use lime cement in cases where the aggregate absorbs up to 25% of its weight. Lime concrete is weaker than that produced with Portland cement, but is suitable for many purposes.

Other properties of concrete made with crushed bricks are:

8 poor resistance to abrasion, therefore should not be used for roads or flooring; higher fire-resistance than provided by normal aggregate; and porous so that it is unsuitable for waterproof construction.

8

8

Hard burnt or over-burnt brick may be used in reinforced concrete, provided the stresses are not high. Laterite and overburnt ‘jhamma’ (an Indian aggregate) should not be used where steel reinforced concrete is likely to go through wet and dry cycles. However, adding a pozzolan may ‘use up’ the free lime in the cement, which would cause carbonation of the concrete making it susceptible to corrosion of the steel reinforcement.

Guidance for the use of crushed brick is given in the Indian Standard IS3068 ‘Broken Brick (Burnt Clay) Coarse Aggregates for use in Lime Concrete’.

7.1.3 Recycled Concrete and Masonry

Demolition waste is increasingly being recycled in industrialised and urbanised countries. The two major constituents are concrete and masonry, which can be reused as aggregate in concrete. Recycled concrete and masonry can be used to completely replace or partially replace other aggregates, depending on the requirements.

Research has shown that it is most practicable to separate materials at demolition. It is necessary also to keep crushed masonry and crushed concrete as separate as possible, because their properties differ. Masonry is more friable, porous and variable than concrete.

Contaminants, such as glass, gypsum-based materials, wood, plastics, textiles, organic materials and earth have adverse effects on the finished concrete and should be removed.

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Three factors may affect mix design:

a Workability of the mix may be lower than with natural aggregate due to the angular shape and the higher water absorption of crushed concrete and masonry. Compressive strength may decrease slightly. It has been found that 20% replacement of good quality aggregate by recycled concrete aggregate has little effect on strength, whereas, 100% replacement may reduce strength by 10 to 20%. Masonry concrete may be more susceptible to frost damage. The higher watedcement ratio required may also increase drying shrinkage of the concrete.

~ e ~ . ~ ~ ~ o n informationon

water of aggregate 0

a

Crushed concrete and masonry typically have a lower density than normal aggregate.

7.1.4 Cinders

Cinders can be used to make unreinforced mass concrete of low strength which is light and porous. Cinder concrete has good insulating properties.

See Section 7.2.4 on lime cement

Guidance for the use of cinders is given in the Indian Standard IS 2686 ‘Use of Cinders in Lime Concrete’.

7.2 Replacement Materials

7.2.1 Pozzolans

A pozzolan is a silica-based material which, in itself, has little or no cementitious behaviour but will, if finely ground and in the presence of water, chemically react with constituents of Portland cement or lime to form cement- I i ke substances.

A number of man-made waste materials will act as pozzolans for example pulverised fuel ash, silica fume, ground granulated blast hrnace slag and rice husk ash. These materials are often included in cement when it is manufactured.

SeeTable4.3

Some naturally occurring materials will also act as pozzolans, for example, opal cherts, clays, shales, certain volcanic rocks and pumicites.

I’ozzolans often have properties other than their cement-like behaviour, which are useful in making good, durable concrete.

Guidance on the use of local pozzolans is given in the Indian Standard IS 3144 ‘Calcined Clay Pozzolan’

7.2.2 Waste Ash

Various types of waste ash have been successfully used or have been proposed for making durable concrete. The ash produced is used as a partial replacement of some of the Portland cement (typically 20%) and may come from waste material such as:

e incinerated refuse; e

e burnt oil shale; e burnt rice husks; and e burnt soil.

burnt sludge from sewerage treatment works blended with clay;

Some of these materials have been shown to have pozzolanic activity. Rice Husk Ash has been well researched and is described below.

7.2.3 Rice Husk Ash

Rice husk is an abundant waste material from the rice-growing industry produced in such countries as Thailand, India and the USA. Rice husk ash ( M A ) may be made by burning the rice husk in a basket burner or small incinerator and then grinding it and screening it to produce fine RHA. When burnt at the correct temperature (approximately 700°C for eight hours) RHA can be a highly reactive silica, which may be used to economically replace some of the Portland cement in concrete structures.

RHA cement is a mixture of RHA and lime or Portland cement. Whilst RHA- lime cements are lower in strength than RHA-Portland cements, lime may be a more readily available local material.

Other effects found from RHA cement:

I I

I I

I I I I

I I I

e Reduces alkali-aggregate reaction by ‘using up’ the available alkali in the See Section

cement before it reacts with the aggregate. This may increase durability 3.2.9 for information on alkali- in cases where aggregate reactivity is a problem.

e Reduces segregation and bleeding o f concrete. aggregate Increases water requirement for a given workability and it may therefore reaction be necessary to use super-plasticisers or plasticisers to increase See Table 6.1 workability of the wet concrete. for admixtures

e

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It may be necessary to avoid rapid water evaporation from the surface of the freshly placed concrete to prevent or reduce shrinkage cracking. This may be done by adequate curing of the concrete and avoiding concrete making in hot weather. Some RHA-lime cements are quick-setting. This can be controlled by careful mix design. Whilst setting of concrete made with RHA cements may be more rapid See Section

than with Portland cement alone, the rate of heat of hydration remains 4.1.4for information on heat of unaffected.

Concretes made with RHA have been found to have an increased hydration resistance to acid-attack. RHA-cements tend to produce concrete with a lower permeability than concrete made with Portland cement only. This is likely to improve the overall durability of the concrete. Strengths of concretes made with RHA-Portland cement may be comparable to those made with only Portland cement. Strength has also been found to be increased by using limestone aggregates rather than silicaceous aggregates.

There are, as yet, no comparable standards in the correct use of RHA but there is considerable research being done in order to produce such standards. Whilst this research is being carried out, and where there is no alternative, it will be necessary to carry out a full range of tests on the mix design to make sure that the concrete performance is as required. This may be done by comparison of Portland cement trial mixes with the RHA-Portland cement mixes. Further tests should be carried out at intervals to make sure that the concrete made with RHA- cement maintains the required properties. It must also be noted that the

See Glossary formortar cube testing properties of RHA-cement are likely to be variable.

Further information about RHA-cement is given in the BRE Report OBN 198 (Reference 11).

7.2.4 Lime Cement

Lime is a cementitious material which can be found in limestone deposits (called ‘kunkar’ in some areas), chalk and sea shells and is also produced as a by- product of the sugar industry.

Lime cement is more permeable than Portland cement, has lower strength, and the lime-concrete produced takes longer to set and harden. It produces a less durable structure overall, but for less important works, or those where maintenance would be regular (such as private housing) this may be acceptable. Lime cement may be more readily available and easier to produce locally than Portland cement, and therefore would be economic for low-rise building construction.

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Lime-pozzolan blends (called ‘pozzolime’) have been used in Tanzania, India and Indonesia. Pozzolans used have been ground burnt bricks and tiles, volcanic tuffs and Rice Husk Ash (an interground lime-RHA mixture has been produced called ‘Ashmoh’ cement in South Asia). The use of a pozzolan has greatly extended the use of lime, by improving its cementitious properties.

Guidance is given in the relevant Indian Standards IS 4098 Lime-pozzolan Specifications and IS 5817 Code of Practice for use of Lime-pozzolan Concrete.

7.3 No-fines Concrete

In locations where suitable sand is not available, it may be appropriate to make no-fines concrete. This is a material composed of cement and a notionally single-sized aggregate. The product has uniformly distributed voids giving it a low density of about 66% of conventional concrete.

It has been recommended that the aggregate should have not more than 5% retained on a 19mm sieve and 10% passing a 9mm sieve. Typical mix proportions have a watedcement ratio of 0.4 and cement/aggregate of 1:s. Typical 28-day cube strengths are 4 to 9N/mm2 depending on the type of aggregate.

No-fines concrete has certain advantages over conventional concrete, the density is lower, drying shrinkage is lower and it has good thermal insulation properties. Where there are soluble salts present the concrete may be able to cope better with consequential expansion.

More information is provided in the BRE Overseas Building Note No 166 (Reference 4).

7.4 Local Reinforcing Materials

In areas where either economic considerations or corrosion of steel reinforcement would make it undesirable to use steel, concrete can be reinforced with natural materials. The concrete produced may be less durable overall than well made concrete with reinforced steel, and will be less able to withstand high loads, but could be suitable for less important structures or elements of structures.

Bamboo is used in Nepal in traditional concrete house building where one- and two-storey construction is typical.

Palm tree fronds are available in Egypt. These have been proposed as a replacement for steel reinforcement in roofs, due to their light weight, excellent insulation properties, corrosion resistance and strength.

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8.1.4 Environment

Various forms of deterioration can take place as a result of weathering and ground conditions. Other environmental factors such as industrial pollution or exposure to marine conditions should also be considered. Some knowledge of the conditions in the area would normally be available and it may be possible to ascertain the causes of any deterioration that has taken place in existing structures.

8.2 Minimum Standards for Durable Concrete

Specifications currently in use for structural work provide limits appropriate to the particular environment and usage. Minimum limits are usually given for cement content and maximum limits for waterkement ratio, cement content and for chloride and sulphate contaminants in the mix.

Where concrete is to be buried in the ground, and subjected to sulphate or acid attack, more restrictive limits are given on minimum cement content and maximum waterhement ratio. Restrictions are also provided on the types of cement that can be used and recommendations made on other actions that should be taken.

Examples of these durability limits are given in Table 8.1, but it should be understood that these are only given for guidance. The Engineer will need to specify limits appropriate to the particular environment and usage, taking into account his overall requirements for durability of the structure and the quality of the materials to be used.

See BRE Digest 363 (Reference 12) for information about sulphate and acid resistance of concrete in the ground.

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8.2.1

Table 8.1

Minimum Cement Content and Maximum WaterKement Ratio

Minimum Cement Content and Maximum Water/Cement Ratio for Different Types of Exposure (from Reference 6)

Mass Concrete Reinforced Concrete

Minimum Cement Content (kg/m3)

for Nominal Maximum Size of Aggregate (mm)

Minimum Cement Content (kg/m3)

for Nominal Maximum Size of Aggregate (mm)

klaximum Water/ Cement

Ratio

Maximum Water/ Cement

Ratio Type of Exposure

40 20 14 10 40 20 14 10

Concrete surfaces zxposed to: i abrasive action by

ii water with a pH

Concrete surfaces directly affected by: i de-icing salts ii sea water spray

Concrete surfaces exposed to: i drivingrain ii alternate wetting

sea water

4.5 or less

and drying

Concrete surfaces above ground level and fully sheltered against all of the following: i rain i i de-icing salts iii sea water spray

120 350 370 390 0.45 0.50

0.50

320 350 370 390 Zxtreme

very severe

Severe

Moderate

0.45 !95 325 345 365 295 325 345 365

295 325 345 365 0.50 0.50 !70 300 320 340

0.50 270 300 320 340 0.50 245 275 295 315

Concrete surfaces permanently saturated by water with a p H greater than 4.5

Concrete surfaces completely protected against weather and aggressive conditions, excepl for a brief period oj exposure to normal weathcr conditions during construction.

Mild 245 275 295 315 0.55 0.55 220 250 270 290

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8.2.2 Maximum Cement Content

The cement content should be limited to minimise the risk of cracking due to drying shrinkage in thin sections and higher thermal stresses in thicker sections. In the UK, the Specification for Highway Works limits the cement content to 550kg/m3 whilst in some parts of the Middle East the value is limited to 450kg/m3 because of the hotter climate.

8.2.3 Maximum Sulphate Content

In the UK, the Specification for Highway Works (Reference 6) limits the total acid soluble content of the concrete mix to less than 4% of the mass of cement in the mix. Excessive amounts can lead to expansion and disruption of the concrete. This figure is also the recommended limit in some parts of the Middle East. Any lowering of this limit should only be considered as a result of extensive experience of the behaviour of concrete made from the proposed constituents in a similar environment.

See Tables 3.2, 4.1 and 5.1 for sulphate limits for each concrete constituent

8.2.4 Maximum Chloride Content

For reinforced concrete, Codes of Practice in many countries limit the chloride content of the concrete mix, but there is no consensus on the threshold level for corrosion. In the UK, the Specification for Highway Works (Reference 6) limits the total chloride content to less than 0.3% of chloride ions by mass of cement and this value is also used in some parts of the Middle East, except when the cement contains less than 4% C3A (tricalcium aluminate) where 0.15% is recommended. This lower limit would, for instance, apply to sulphate resisting cement. These limits apply only to concrete using Portland cement.

SeeTables3.2, 4.1 and 5.1 chloride limits for each

constituent

For unreinforced concrete, less guidance is available, but, in some parts of the Middle East, a maximum chloride level of 0.60% of chloride ions by mass of cement is quoted to be a reasonable value under normal conditions. However, it is considered that sea water (which will not comply with this limit) can be used for unreinforced concrete subject to providing resistance to sulphate attack and control Section of the type of aggregates. 5.2 on sea-

8.2.5 Restrictions to Resist Sulphate and Acid Attack on Concrete Below Ground

See

water

Sulphates and acids in the ground can attack the hardened concrete. The level of attack depends on the concentrations of the sulphates and acids within the ground, the level and mobility of the water table and the properties of the proposed concrete. ‘The sulphates and acids can arise from naturally occurring materials or from industrial waste materials.

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8.3

To resist this form of attack it is important that the concrete incorporates an appropriate cement. It should also have a low permeability by restricting the waterkement ratio and having a minimum cement content.

In both the UK and some parts of the Middle East, requirements are specified for different exposure and conditions of use. The greater the resistance required, the more onerous the required minimum cement content and maximum waterkement ratio. In addition restrictions are made on the types of cement that can be used. More information about sulphate and acid resistance of concrete in the ground is given in BRE Digest 363 (Reference 12).

Proportioning Materials for Concrete - General ..

When the Engineer has determined his specific requirements for the strength and durability of the concrete, taking into account the mechanical and physical properties of the proposed materials, trial mixes should be undertaken. Trial mixes are essential to ascertain whether the component materials have the necessary quality to produce concrete with an acceptable cohesiveness and workability.

This section details a method for proportioning the qualities of the materials for a first trial mix, taking into account design requirements for the concrete in terms of strength and durability.

In order to calculate the required mix proportions, the Engineer must determine the required properties of the concrete, as given in the following sections.

8.3.1 Characteristic Strength

This is the value used as the basis for the structural design. If requirements for durability are incorporated in the mix design, the required strength will almost certainly be achieved. However, the trial mix design must establish that the characteristic strength can be achieved and from this a strength standard can be determined against which the quality of the production concrete can be controlled.

For the durability of reinforced concrete structures, it is usual to specify minimum concrete cover requirements for the reinforcement appropriate to the particular environment and usage. Under aggressive conditions, the cover requirements can become onerous and consideration may need to be given to increasing the strength of the concrete. For instance, in the UK, the Code of Practice for Design of Concrete Bridges (Reference 16) reduces the cover requirements for higher strength concrete, and also limits the use of lower grade concrete in severe ciivironments, in order to keep the reinforcement cover to what it considers to be an acceptable level. This is because, if the cover is too large, it may not be

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possible to provide sufficient steel to control crack widths without increasing the member size considerably.

8.3.2 Standard Deviation, Margin, Target Mean Strength

In order to obtain the Target Mean Strength (the strength required to ensure that 95% of results of strength tests should be greater than the characteristic strength) for the trial mix, it is necessary to specify the Standard Deviation. The Standard Deviation is related to the Target Mean Strength by the relationship:

Target Mean Strength Margin

= Characteristic Strength plus Margin, and = 1.64 x Standard Deviation

The Standard Deviation relates to the quality control that can be achieved on production of the concrete. The higher the control, the lower the standard deviation and therefore the lesser the Margin that is required.

Table 8.2 shows the relationship between Control, Standard Deviation and Margin. For ‘good’ control, it is considered that data would have to be available to show that 100 separate batches of concrete of nominally similar proportions of similar materials, have been produced over a period of one year. ‘Average’ would apply where data are available for 40 separate batches over a period not exceeding six months. ‘Poor’ should be used when insufficient data are available.

8.3.3 Cement Type and Content

‘The Engineer should prescribe the type of cement required and the minimum and maximum cement contents applicable to durability requirements. He will need to obtain the speclJc gravity of the cement. If measured values cannot be obtained, a value of 3.15 is reasonable to be assumed.

See Section for cement tYpes

For a given workability and degree of exposure, the cement content should be increased as the aggregate surface roughness increases and the aggregate particle shape becomes more irregular or angular. The cement content should also be increased if the maximum size of the aggregate has to be reduced. This is implied I?y approximate fi-ee-water contents given in Table 8.3.

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Table 8.2 Concrete Mix Design Statistics Relationship between production control, margin and standard deviation for various characteristic strengths

Confidence Level

%

Characteristic 20 25 30 35 40 45 50 Strength

Production Margins(M) and Standard Deviations(SD) Control (N/mm*)

Good M SD

6.67 4.07

M I I SD

8.34 10.0 11.67 13.34 15.0 16.67 5.08 6. I 7.11 8.13 9.15 10.16

I I I 75 I AverageyD Average M

SD M I 70 I SD

I 65 I Poor FD

1.05 I 1.32 I 1.58 I 1.84 1 2.11 I 2.37 I 2.63 0.64 0.80 0.96 I . 12 1.28 1.44 1.61

3.53 5.29 7.06 7.94 3.77 4.30

5.00 I 6.25 I 7.5 I 8.75 1 1:;; 1 11.25 1 12.5 3.05 3.81 4.57 5.34 6.86 7.62

t3S; 1 10.: 1 1:::; I b5i! 1 17.14 1 19.29 1 21.43 10.45 11.76 13.07

10.77 13.46 16.15 18.85 21.541 24.23 26.92 6.57 9.85 11.49 3.13 14.78 16.42

Note: 90% confidence level implies 95% of results of strength tests greater than characteristic strength

8.3.4 Slump

The Engineer should determine the workability requirement for the concrete by providing an acceptable range for the slump test. He should take into account what the concrete is to be used for. For instance, for mass concrete construction and lightly reinforced sections, a low slump is probably acceptable to achieve the required workability. Some national standards give specific slump requirements tor different types of work, but it is advisable to specify the requirement on the basis of the lowest slump compatible with the conditions of placement. (A low value of slump implies a low waterkement ratio and consequently low permeability and good strength).

The mix design procedure checks the workability requirement against ranges of slump as detailed in Table 8.3.

I:or a given cement and water content, an increasing fineness of the sand content in the blended aggregate will cause the mix to become sticky and have poor workability. This must be compensated by increasing the quantities of medium and coarse aggregate content so that the total aggregate content, as determined by the design process, remains unaltered.

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Maximum

Size of Aggregate

(mm)

10

20

40

Increasing the water content in order to improve the workability on site is a common error which can lead to the production of concrete having lower strength and poor durability.

Water Content kg/m2

Type of Slump (mm) Aggregate

0.10 10-30 30-60 60-1 80

Uncrushed 150 180 205 225 Crushed 180 205 230 250



There may be occasions when it is necessary to use an admixture to achieve the See Table 6.1 admixtures required workability for a low specified water content.

8.3.5 Maximum WatedCement Ratio

The maximum watedcement ratio can be specified to satisfy durability requirements. If no value is specified, then the watedcement ratio will be calculated as part of the mix proportioning with no restriction on the value.

It is important to understand that water hydrates the cement grains leading to strength and durability of the concrete; and lubricates the aggregate particles sufficiently to give the concrete a satisfactory workability.

Table 8.3 Approximate Water Contents (kg/m3) Required to give Various Levels of Workability

Note: When coarse and fine aggregates of different types are used, the water content is estimated by the expression:

*/3 w, + '13 w, where and

W, is the water content appropriate to the type of fine aggregate W, is the water content appropriate to the type of coarse aggregate

8.3.6 Aggregate Selection

The Engineer should determine what aggregates to use taking into account durability requirements, the advice given in this manual and any data available concerning these materials. Once the aggregates have been selected the following should be determined:

See Section for aggregates

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I

i)

For mix proportioning, it is usual to consider the aggregates as being in the saturated and surface dry (SSD) state and any variation from this must be allowed for in the mix design procedure.

Their spec& gravity (SG) can be determined as follows:

SG where A

B C

Saturated and Surface Dry (SSD) Aggregates

See Section 3,2,6for information on SSD condition

See Section 3.2.3 for information on aggregate specific gravity

= A/[A-(B-C)] = weight in mix of the aggregate sample in the SSD condition = weight of a container plus water plus the aggregate sample = weight of the same container plus water only.

ii)

The gradings of the coarse and fine aggregates should be obtained using 40mm, 20mm, 1Omm and 5mm sieves for the coarse sizes and 5mm, 2.4mm, 1.2mm, 0.6mm, 0.3mm and 0.15mm sieves for the finer sizes.

It is possible to combine two or more individual aggregates using the method detailed in Section 8.5 to achieve the desired combined aggregate grading for the concrete. Obviously, for each individual aggregate selected, it is necessary to provide its grading as detailed above.

Grading of the Coarse and Fine Aggregates

See Section 3.1. for further information

Manual methods of grading aggregate are described in the TRRL Report SR 503 (Reference 13).

Proportioning Materials for Concrete - Mix Design

8.4.1

8.4

Background to the Method of Proportioning

The method detailed below is for proportioning the quantities of materials needed for a first trial mix. The method has been based on the publication Design of Normal Concrete Mixes (Reference 14) but has been broadened so as to take account of aggregate materials and gradings which do not conform to British Standard 882 - Specification for Aggregates from Natural Sources for Concrete. In addition, greater account has been taken of some of the measures needed to ensure the durability of the concrete.

This method of proportioning takes account of some of the mechanical and physical properties of the aggregates that can affect the workability and the quality of the hardened concrete.

The method is based on the absolute volume of materials in the hardened concrete and on the aggregates being in the SSD condition.

I I

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If surface wet aggregates are used, then allowance must be made for the surface water by determining the surface water content, in kg/m3, and subtracting this amount from the water to be added.

If the aggregates are dry, then their absorption after 30 minutes soaking should be measured. From this it will then be possible to determine the amount of additional water that should be incorporated in the concrete mix.

For small jobs and only when dry aggregates are to be used, they may be volume batched, if it is more convenient to do so. For volume batching, reference should be made to Figure 8.4.

Volume batching should not be used for damp or wet aggregates because of the risk of the bulking of the finer materials.

As part of the method, the selected aggregates are blended to produce a combined grading close to one of the gradings given in Figures 8.5, 8.6 and 8.7. These gradings are in no sense ideal but represent those used in tests from which data have been obtained. Four gradings are provided for each of three nominal maximum sizes of aggregates. The four areas represent differing proportions of fine particles, 1 being the coarsest and 4 being the finest.

8.4.2 Method for Mix Design

The method for mix design consists of the following steps:

Use the data obtained from the sieve analysis of the aggregates to work out the proportions in which they are to be blended in order to reach agreement with the desired overall grading of all particle sizes.

See Section 8.5

From Table 8.4 obtain a value for the strength of a mix made with a watedcement ratio of 0.5 according to the specified age, the type of cement and the aggregate to be used. This strength value is then plotted on Figure 8.1 and a curve is drawn from this point and parallel to the printed curves until it intercepts a horizontal line passing through the value on the y-axis representing the Target Mean Strength. The corresponding value for the watedcement ratio can then be read from the x-axis. For the proportioning of mixes where the watedcement ratio is specified, the value used in the mix design should be the lower of that specified and that determined from Figure 8.1.

Some calibration may be needed to the data in Table 8.4 for local cements which may have different fineness or hydration characteristics. Small variations of the specific gravity of the cement can be ignored.

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Use the watedcement ratio and the water content given in Table 8.3 for the desired workability to calculate the cement content in kg/m3. Check the cement content with the minimum and maximum values specified.

0 From Figure 8.2 find the wet density of the concrete mix in kg/m3.

Work out the aggregate content in kg/m3 by subtracting the cement and water contents from the wet density. (The aggregatekement ratio may be checked by reference to Figure 8.3).

0 Use the aggregate blending proportions to calculate the content of all the aggregate materials needed for the first trial mix.

0 The Engineer should then check that the mix proportions comply with any other durability requirements that may be specified. For instance, if the materials in the mix are contaminated with chlorides, does the chloride content of the proposed trial mix comply with a restriction on the total chloride content for the concrete? Similarly, if the proposed aggregate is susceptible to alkali- silica reaction, a limitation on the alkali content of the mix may be required.

0 Make the first trial mix and measure the workability and strength of the concrete.

0 If the first trial mix fails to provide the required workability or strength, adjust the proportions of the materials and make a second trial mix.

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2

3

22 27

4 6 8 10 12 0

7 28 91

30 42 49 36 49 56

Aggregate/Cement Ratio by Weight

Ordinary Portland or sulphate- resisting Portland

lb/yd3 200 400 600 800 1000

Uncrushed Crushed

loo 200

~ ~

Rapid-hardening Portland

300 400 500 600

~~

Uncrushed 37 48 54 ~ I iz I 43 1 55 I 61 Crushed

Cement Content - kg/m3

Figure 8.3 AggregateKement Ratio by Weight

‘Table 8.4 Approximate Compressive Strengths (N/mm2) of Concrete Mixes Made with a WaterKement Ratio of 0.5 (from Reference 14)

Type of Cement Type of Coarse

Aggregate

8.5 I’roportioning Materials for Concrete - Blending of Aggregates

‘ 1 ’ 0 determine the proportions in which two or more aggregates can be blended, a graphical method can be used as follows: (Note that Figure 8.8 provides an csample, following steps 1 to 9)

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2. Draw a diagonal straight line through the origin at any slope until percentage passing at 100% (already marked on proforma, Figure 8.9).

3. Choose the desired combined grading. Mark percentages passing each sieve as horizontal lines (red in example, Figure 8.8) to intersect the diagonal line.

4. Through each of the intersection points along the diagonal draw a vertical line to intersect the horizontal axis. Label each intersection with the sieve size corresponding to the desired combined grading.

5. Determine the individual gradings of the aggregates to be used. In the example, a fine sand, a 5 to lOmm coarse aggregate and, a 10 to 20mm coarse aggregate are used. The individual gradings of these aggregates can be entered into the Table in Figure 8.8.

6. Plot the individual gradings on the non-uniform graph (blue in example). Draw the steepest straight line (I, I1 and I11 in example) through the points representing each aggregate, ignoring points lying near the 0 and 100% passing lines.

See Figure 8,8

7. Draw a straight line between the 0 and 100% passing sieve sizes of adjacent aggregate types (green in example).

8. Draw a horizontal line (brown dashed in example) back to the vertical axis fiom the intersection between the original diagonal (black) and the new 0 to 100% lines (green).

9. The horizontal intersections with the vertical (brown dashed) give the proportions by weight of each grading:

Therefore, according to the graph given in the example for Grading Curve 3 in Figure 8.7, proportions should be as follows:

3 9% fine sand -

5 to 10 mm coarse (62-39) = 23% 3 8% 10 to 20 mm coarse

-

- -

Add these to the table as percentages of the original gradings. The values may be checked for accuracy by comparing the sum total of the combined aggregates for each sieve size, against the desired combined grading.

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I

100

90

80 U

f 7 0 VI VI 2 6 0

U 5 0 < c Z 4 0 w

W

U a 30 W &

2 0

10

n

150p 3 0 0 p 6OOpm 118mm 2.36mm 5mm 10mm (No 100) (No. 5 2 ) (No 2 5 ) (No 14) (No. 7 ) ( A in.) ( 1 in.)

B S SIEVE S I Z E

Figure 8.5 Grading Curves for 10mm Maximum-size Aggregate (Reference 15)


100

90

2 6 0

5 0 < Z 4 0 c Y

U 5 30 4

2 0

10

0

1 S O p m 3 0 0 ~ 6 O O p m 1 1 8 m m 2 . 3 6 m m 5 m m 1Omm 20- 3 7 - 5 m (No. 100) (No. 52) (No. 25) (No. 14) (No. 7 ) (A in.) ( 1 in.) (1 in) (li in.)

B S S I E V E S I Z E


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1

Project Job Ref

Element Date

Engineer

Sheet No

MIX No

Aggregate Name I Oescription Source Other"

Combined Grading

0 m

e n

f

Description Other Notes

6 Passing 1015

Desired Grading of individual Aggregate Grading of combined Aggregate

% Passing Sand 20110 39% Sand 23% 1015 35% 20110

Sieve Size Combined Grading % Passing

Proforma

;heck results ?h Passing

Sieve Size

Figure 8.9 Proforma



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THIS PAGE IS INTENDED TO BE BLANK

Example Mix Proportioning for Low Strengt Low Slump Concrete, loderate Exposure

Work out the proportions of materials needed for a trial mix of concrete and having the following target properties:

Characteristic strength 22N/mm2 Reference Section 8.3.1 Nominal maximum size of aggregate 20mm Reference Section 8.3.6

Standard Deviation 5N/mm2 Reference Section 8.3.2 Workability 10 to 30mm slump Reference Section 8.3.4 Cement type and SG Reference Section 8.3.3 Specific durability requirements:

Portland cement 3.1 5

Minimum cement content 300kg/m3 Reference Section 8.3.3 Maximum cement content 450kg/m3

Maximum watedcement ratio 0.5 Reference Section 8.3.5

The aggregates have been selected from locally available crushed rock and natural sand and are clean and free of chemical contaminants. They are petrologically sound, are not susceptible to alkali reaction and are available in three sizes. They have been blended to Curve 2 in Figure 8.6 by means of the method shown in Section 8.5 and the SG has been measured.

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Example 2 Mix Proportioning for Chloride Exposure and Sulphate Attack, Extreme Exposure

0 Work out the proportions of materials needed for a trial mix of concrete having the following

target properties:

Characteristic strength

Nominal maximum size of aggregate

Standard Deviation

Workability

Cement type and SG

Specific Durability Requirements:

Minimum cement content

Maximum cement content

Maximum waterlcement ratio

3 2N/mm2 Reference Section 8.3.1

20mm Reference Section 8.3.6

5N/mm2 Reference Section 8.3.2

30 to 60 mm slump Reference Section 8.3.4

Portland cement 3.1 5 Reference Section 8.3.3

350kglm3

45 Okg/m3

0.45

Reference Section 8.3.3


0 The aggregates have been selected from locally available crushed rock and natural sand and are

clean and free of chemical contaminants. They are petrologically sound, are not susceptible to

alkali reaction and are available in three sizes. They have been blended to Curve 3 of Figure 8.6

as shown in the aggregate blending example detailed in Section 8.5 and the SG has been

measured (See 8.3.6).

0 A minimum cement content of 350kg/m3 has been specified to provide the concrete with the

necessary durability to resist chloride and sulphate attack.

-



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Example 4 Mix Proportioning for Poor Quality Aggregates of High Absorption and Low SG - Dry

Batched for Concrete Exposed to Driving Rain and Alternate Wetting and Drying, Severe

Exposure

A concrete is to be made from aggregates of low SG and high water absorption. It is proposed to

batch all the materials in the perfectly dry (oven dry) state.

The aggregates have been selected and blended to Curve 3 in Figure 8.6 as shown in the example

detailed in Section 8.5.

A sample has been soaked for 24 hours and the saturated and surface dry SG has been found.

This is needed for the mix design method which is based on aggregates being in the SSD

condition.

To obtain kg/m3 of the oven dry aggregates, when aggregates are to be batched in an oven dry

condition, the kg/m3 of the SSD aggregates as found from the charts are multiplied by loo/( 100 + A) where A is the percentage by weight of water needed to bring the dry aggregates to the SSD

condition.

Characteristic strength

Nominal maximum size of aggregate

Standard deviation

Workability

Cement type and SG

Specific durability requirements:

Minimum cement content

Maximum cement content

Maximum water cement ratio

SG of the aggregates

Water absorption of the aggregates - fine

- coarse

3 2N/mm2

20mm

5N/mm2

30 to 60mm slump

Portland cement, 3.15

3 25 kg/m3

450kg/m3

0.5

2.2

8%

5 yo

Reference Section 8.3-1






ii.eference Section 8.3.5

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I I

Slump Degree of Workability

mm

0-25 Very low

25-50 Low

50-100 Medium

100- 175 High

It has been argued that the slump test provides a rather poor indication of workability. Nevertheless, it is easy to do and the equipment is cheap and simple.

The American variant of the slump test is to ASTM C124-39. Other types of test include the compaction factor test, Vebe, and the flow table.

8.7.2 Compressive Test

Compressive strength tests are carried out on cubes of 15Omm size to BS 1881 Part 3 or cylinders of 15Omm diameter and 300mm long to ASTM C192-76.

The procedure is to place and compact concrete in the mould according to requirements of BS 1881. It is stored for 24 hours at a temperature of 18 to 21°C and a relative humidity of 90%. It is then removed from the mould and stored in water at 19 to 21°C. The compression test is most commonly carried out at 28 days. Additional tests may be called for at three days or seven days if the rate of gain of early strength is required.

There is no unique relationship between cube strength and cylinder strength but it has been suggested that cylinder strength is 80% of the cube strength as a rough guide.

Compressive strength provides an indication of other properties, for example high strengths indicate high modulii of elasticity and are usually, but not always, associated with high density and hence low permeability.

Achieving compressive strength for mix design is not usually a problem. However, maintaining consistency of strength and workability sometimes requires re-adjustment of the mix proportions.

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9 REFERENCES

(1) Building Research Establishment. Avoiding Faults and Failures in Building. BRE OBN 177, 1977, UK

(2) Concrete Society. Alkali-silicate Reaction: Minimising the Risk to Concrete. Technical Report 20, UK, 1995

(3) FIP. Concrete Construction in Hot Weather: Guide to Good Practice. Thomas Telford, 1986. ISBN 0727702572

(4) Building Research Establishment. No-fines Concrete. BRE OBN 166, UK, 1976

( 5 ) CIRIA. Guide to Construction in the Gulf Region. Special Publication 3 1, UK, 1984

(6) Highways Agency (UK). Manual of Contract Documents for Highway Works, Vol 1. Specification for Highway Works. HMSO, 1994

(7) Indian Practical Civil Engineers Handbook. Engineers Publishers, New Dehli, 13 Edition, 1994

(8) Cement and Concrete Association. Effect of Mica in the Fine Aggregates on the Water Requirements and Strength of Concrete. Technical Report TRA 370, 1963

(9) Portland Cement Association. Design and Control of Concrete Mixes. US, 1992

(1 0) Concrete Society. Guide to Chemical Admixtures for Concrete. Technical Report 18, UK, 1980

(1 1) Building Research Establishment. Alternatives to OPC. BRE OBN 198, UK, 1993

(12) Building Research Establishment. Sulphate and Acid Resistance of Concrete in the Ground. BRE Digest 363

(1 3) Transport Research Laboratory. Some Manual Methods of Screening Aggregates for Labour- intensive Road Construction. TRL Report SR 503, UK, 1979

(14) Building Research Establishment. Design of Normal Concrete Mixes. BRE Report 106, UK, 1988

(1 5 ) Cement and Concrete Association. Concrete Constituents and PFA Properties. C&CA Report, 1974

(1 6) British Standards Institution. Steel, Concrete and Composite Bridges. BS 5400, 1990

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10 STANDARDS

BRITISH STANDARDS LGGREGATES IS 812 Parts 2 - 124 )S 882

Testing aggregates Specification for aggregates from natural sources for concrete

i S 1377 : Parts 1 - 9 i S 877 : 2

Methods of test for soils for civil engineering purposes (withdrawn) Specification for forced or expanded blast furnace slag

I

3s 1047 lightweight aggregate for concrete Specification for air-cooled blast furnace slag aggregate for use in construction

3s 3797 Specification for lightweight aggregates for masonry units and structural

3s 1165 concrete (withdrawn) Specification for clinker and furnace bottom ash aggregates for concrete

3s 3681 (withdrawn) Methods of sampling and testing of lightweight aggregates for concrete

ZEMENT 3s 12 3s 1370

Specification for Portland cement Specification for low heat Portland cement

3s 4027 3s 146 3s 6588 3s 6610 BS 4550 : Parts 0 - 6

Specification for sulphate-resisting Portland cement Specification for Portland blastfurnace cement Specification for Portland pulverised-fuel ash cements Specification for Pozzolanic pulverised-fuel ash cement Methods of testing cement (Partially replaced by BS EN 196 but still ir wide use) Methods of testing cement

Methods of test for water for making concrete (including notes on tht

BS EN 196 : Parts 1 - 7 WATER BS 3 I48

suitability of the water) Methods of testing water used in industry Water quality General methods of chemical analysis - Method for determination c

BS 2690 : Parts 1 - 125 BS 6068 : Parts 0 - 6 BS 6337 : Part 4

BS 3993 BS 3903

BS 5634 BS 6075 : Part CP i 1 O : l

chloride ions by potentiometry Specification for hydrochloric acid, commercial types 1 and 2. Methods of test for sulphuric acid, oleum and liquid sulphur trioxide

Methods of test for potassium hydroxide Methods of sampling and test for sodium hydroxide for industrial use (Superseded) Code of Practice for the Structural use of Concrete Design Materials and Workmanship (Replaced by BS 8 1 10)

Concrete Admixtures ADMIXTURES BS 5075 : Parts 1 - 3

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AMERICAN STANDARDS kGGFtEGATES 4STM C-88 Test Method for Soundness of Aggregates by Use of Sodium

4STM C-33 (-81) 4STM C- 13 1

4STM C-535

ASTM C-294 ASTM C-295 ASTM C-289 ASTM C-227

ASTM C-586

ASTM C- 142

Sulphate or Magnesium Sulphate. Specification for Concrete Aggregates Test Method for Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine Test Method for Resistance to Degradation of Large-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine Descriptive Nomenclature of Constituent of Natural Mineral Aggregates Guide for Petrographic Examination of Aggregates for Concrete Test Method for Potential Reactivity of Aggregates (Chemical Method) Test Method for Potential Alkali Reactivity of Cement- Aggregate Combinations (Mortar-Bar Method) Test Method for Potential Alkali Reactivity of Carbonate Rocks for Concrete Aggregates (Rock Cylinder Method) Test Method for Clay Lumps and Friable Particles in Aggregates

ASTM C-40 CEMENT

Test Method for Organic Impurities in Fine Aggregates for Concrete

ASTM C- 150 ASTM C-595/595M ASTM C- 19 1 ASTM C-151 ASTM C- 109/109M

ASTM C- 1 86 ASTM C-114 WATER

Specification for Portland Cement Specification for Blended Hydraulic Cements [metric] Test Method for Time of Setting of Hydraulic Cement by Vicat Needle Test Method for Autoclave Expansion of Portland Cement Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2in or 50mm cube Specimens) [metric] Test Method for Heat of Hydration of Hydraulic Cement Test Methods for Chemical Analysis of Hydraulic Cement

ASTM STP-169C :

ASTM C-99 AASHTO T26 : AS'I'M D-5 16 ASTM D-5 12 ADMIXTURES ASTM C-494 ASTM C-260 ASTM C-1017

Significance of Tests and Properties of Concrete and Concrete Making Materials Test Method for Modulus of Rupture of Dimension Stone Method of Test for Quality of Water to be Used in Concrete Test Methods for Sulphate Ion in Water Test Methods for Chloride Ion in Water

Specification for Chemical Admixtures for Concrete Specification for Air-Entraining Admixtures for Concrete Specification for Chemical Admixtures for Use in Producing Flowing Concrete

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INDIANSTANDARDS 4GGREGATES [S 2386 [S 5816 [S 6461 [S 7861 [S 383

[S 456 [S 516 WATER IS 3025

Methods of Test for Aggregates for Concrete Method of Test for Splitting Tensile Strength of Concrete Glossary of Terms Relating to Cement Concrete Code of Practice for Extreme Weather Concreting Specification for Coarse and Fine Aggregates from Natural Sources for Concrete Code of Practice for Plain and Reinforced Concrete Methods of Test for Strength of Concrete

Methods of Sampling and Test (Physical and Chemical) for Water used in Industry

IS 3550 ADMIXTURES

Methods of Test for Routine Control for Water used in Industry

IS 9103 CEMENT IS 455 IS 269 IS 1489 IS 8041 IS 12330 OTHER MATERIALS IS 5817

IS 2686 IS 3068 IS 4098 Lime-Dozzolan Mixture

Specification for Admixtures in Concrete

Specification for Portland Slag Cement Specification for Ordinary and Low Heat Portland Cement Specification for Portland Pozzolona Cement Specification for Rapid Hardening Portland Cement Specification for Sulphate Resisting Portland Cement

Code of Practice for Preparation and Use of Lime Pozzolan Concrete in Buildings and Roads Cinder as Fine Aggregates for Use in Lime Concrete Broken Brick (Burnt Clay) Fine Aggregates for use in Lime Concrete

CANADIAN STANDARDS AGGREGATES MTO LS 606 OPSS 1002 LS GO4 WATER OPSS 1302 ADMIXTURES OPSS 1303

Soundness of Aggregate by Use of Magnesium Sulphate Material Specification of Aggregates - Concrete Reflective Density and Absorption of Coarse Aggregate

I EUROPEAN STANDARDS I CEMENT - PORTLAND CEM Standards

CEM Standards CEMENT - BLEND

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11 GLOSSARY

air entraining admixture

acid

admixlure

aggregate shrinkage

alkali

alkali-uggregate reaction

alkali carbonate reaction

alkal i-s il ica

all-in uggregate

batch

batching

blast jiirnace slag

bleedittg

bulking

calcitic

capilhry action

Admixture that allows a controlled quantity of bubbles to be dispersed evenly during mixing and remain after hardening. See Table 6.1.

An aqueous solution with a pH less then 7.0. See Table 5.1.

A material added in small quantities during the mixing process to modify the properties of the mixture.

Aggregates with high absorption characteristics may have high shrinkage on drying. See Section 3.2.6.

An aqueous solution with a pH greater than 7.0. See Table 5.1.

See Sections 2.3.1 and 3.2.9.



Aggregate consisting of a mixture of coarse aggregate and fine aggregate, usually occurring naturally.

Quantity of concrete mixed in one cycle of operations of a concrete mixer, or the quantity of concrete transported ready-mixed in a vehicle.

The making of a batch of concrete. Two methods exist: batching by weight and batching by volume. Whilst volume batching is widely used on less important structures, weight batching is the recommended method for the production of durable concrete, because it allows greater quality control.

See ground granulated blast firnace slag.

Separation of water from fresh concrete.

The increase in the volume of a given weight of the fine aggregate, caused, if water is present, by the films of water pushing the particles apart.

A rock in which one of the primary minerals is calcium

The rising of fluid in tiny voids above the level of the fluid, caused by surface tension. The zone of saturation above the water table is called the capillary fringe. It may extend for many metres, depending on the size of the voids in the ground and the temperature and dryness of the atmosphere.

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carbonation

characteristic strength

chloride

cinders

clinker

coating

cohesiveness

compacting/cornpaction

compressibility

compressive strength

concrete cube tests

contaminatiodcontaminants

corrosion

creep

curing

de-ionised water

A process by which carbon dioxide from the air penetrates the concrete or cement and reacts with hydroxides to form carbonates. It increases shrinkage drying and lowers alkalinity of the concrete which can lead to corrosion of steel reinforcement.

See Section 8.3.1.

A contaminant of concrete constituents. May also attack the finished structure. See Section 8.2.4.

Waste material produced when coal is burnt. See Section 7.1.4.

When the raw materials used in the manufacture of cement have been ground and then mixed together and burnt, the resultant material has sintered and partially fused into balls known as clinker.

Covering layer - eg paint.

A property closely related to workability. A cohesive mix provides for uniform and well-compacted concrete. Depends largely on the proportion of fine particles in the mix.

Process of removing air from fresh concrete and ensuring that a dense homogeneous material is produced. Can be done by hand, though for higher quality concrete, a mechanical vibrator is usually used.

The ease with which a material can be compressed or shortened by applying a force. Related to elasticity.

The resistance expressed in force per unit area of a structural material at failure in a compression test.

See Section 8.7.2.

Impurity that is contained in the material or that penetrates the material from an external source.

The gradual removal or weakening of metal from its surface by chemical attack.

The time dependent deformation of concrete which begins as soon as it is loaded and continues at a decreasing rate for as long as the concrete remains loaded.

Operation to ensure the hardening of concrete by preventing excessive evaporation of water and extremes of temperature. Curing may be accelerated by the use of steam or super-heated steam. Adequate curing is of prime importance if a durable concrete is to be produced.

Water which by the use of an ion exchanger has less than 1 ppm solid particle contamination. See Section 5.1.

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desal inisation

distilled water

drying shrinkage

durability

eflorescence

elongated aggregate

exposure trials

$as h-set

Jocculution

the removal of salt from water to enable its use in reinforced concrete, or for drinking.

Water which has been purified by boiling it, removing the steam which is produced at 100°C and then condensing it.

Contraction of hardened concrete caused by evaporation of water from its mass. May cause shrinkage cracks.

Refers to the ability (of concrete) to fulfil its purpose, in the environment for which it was designed, for a required service life.

A chalky white salt deposit which occasionally forms on the surface of concrete, caused by the leaching of lime compounds. See Section 5.2.

Coarse aggregate in which there are particles which have a long length (largest dimension) in relation to the size fraction to which they belong.

Durability tests on concrete cubes, in which the cubes are placed in the same environment as that of the finished concrete structure. Exposure trials will typically take at least 90 days.

Premature stiffening of the mortar in a concrete immediately after mixing, which can be corrected by reworking without adding water.

Coarse aggregate in which thickness (least dimension) they belong.

Stiffening of a mix which water. It is caused by a irreversible.

there are particles which have a small in relation to the size fraction to which

occurs very quickly after mixing with lack of gypsum in the cement and is

Merging together of the cement particles. If flocculation can be prevented the particles have a greater mobility and water is freed to infiltrate the mix and improve workability.

fiee lime See Section 4.1.2.

j?iable/j+iability See Section 3.2.8.

graded aggregate

grading

Aggregate containing selected proportions of different particle sizes, usually chosen to form a concrete of maximum density.

The percentage by weight of different particle sizes in a sample of aggregate, expressed on a grading curve.

ground granulated blast furnace slug

Abbreviated to GGBS, a by-product of iron manufacture. Has a chemical composition similar to Portland cement but cannot be used on its own as it requires ‘activation’. GGBS may be used to replace up to 90% of the Portland cement. The use of GGBS as a replacement has been recommended as a method of reducing the

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hardening

likelihood of alkali aggregate reaction. See Section 4.3

The time dependent increase in strength of a mortar or concrete. Not to be confused with setting.

heat of hydration

hydration

The heat produced when cement reacts with water.

The combination of water with cement or lime in a chemical reaction.

hydraulic cement

igneous rocks

impregnation treatment

A cement that sets and hardens by chemical reaction with water, and is capable of doing so under water.

When molten rock material (magma) cools, either within the earth or on the surface as lava, it produces igneous rocks.

The application of an impregnating material to the surface of the concrete to provide an effective water repellent but vapour is a permeable layer.

in situ cast concrete Concrete which is placed fresh in its permanent position.

insoluble residue A measure of the impurities in cement. National Standards limit the amount allowed. See Section 4.1.5.

lean mix A concrete mix which has a high aggregatelcement ratio.

lightweight aggregate

lightweight concrete

lime

low-alkali cement

loss on ignition

Aggregate having a bulk density of not more than l2OOkg/m3 for fine aggregate or 1 OOOkg/m3 for coarse aggregate. See Section 7.1.1.

Concrete that has an air dry density of more than 2OOOkg/m3. See Section 7.1.1.

A hydraulic material, produced from the burning of limestone, sea shells, chalk etc. See Section 7.2.4.

Cement with a low alkali content, which reduces the risk of alkali- aggregate reaction.

A measure of the prehydration and carbonation. National Standards limit the amount allowed. See Section 4.1.5.

magnesia See Section 4.1.1.

masonry Stone or brick building blocks. See Sections 7.1.2 and 7.1.3.

mass concrete Concrete that is without reinforcement and is usually of large bulk.

minerrrl

metamorphic rocks

Minerals are the solid, crystalline constituents of rocks, which have a particular chemical composition and structure.

Rocks which have changed their structure and mineral content as a result of great pressure and heat.

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mix design

modulus of elasticity

mortar cube tests

oven dry

oxidat ion

permeability

petrographic examination

PH

placing

plastic shrinkage

The process of selecting suitable Constituents of concrete and determining their relative quantities with the object of economically producing concrete of certain properties, notably strength and durability.

For any material it is the ratio of the stress applied (force per unit area) to the strain produced (deformation per unit length). It is a constant up to the point of plastic yield - where the material no longer behaves elastically.

Mortar cubes can be made by the method described in BS 4550, or cylinders by the methods in ASTM C-31 and C-192. These can be used to compare the effects of impurities in water on strength and time to set, with a mortar made with ‘pure’ constituents. BS 3148 states that water will have no effect on the setting and hardening characteristics if: a the initial setting times of the mortar blocks do not differ by

more than 30 minutes b the average compressive strength of the test cubes is not less

than 90% of that of the control cubes. AASHTO 726 describes a similar procedure. These tests can be extended to compare the behaviour of aggregates, cements and admixtures, by comparing either mortar or concrete cubes, and by setting a limit on the acceptable variation between the control and tested concrete or mortar.

Condition where aggregate has no internal moisture nor external moisture and therefore is fully absorbent.

The reaction of a substance with oxygen from the air.

Refers to the rate of water migration through concrete when the water is under pressure or to the ability of the concrete to resist penetration of water or other substances (liquid, gas, ions etc). The more permeable a concrete is, the less watertight and usually less durable it is.

The method by which a microscope is used for studying thin sections of rocks, to determine the minerals which they contain and their particle size.

A measure of the hydrogen ion concentration. The pH of neutral water is 7.0; values below 7.0 indicate acidity and those above 7.0 alkalinity.

Putting fresh concrete into its permanent position or mould.

Contraction which occurs whilst the concrete is still in the plastic state caused by hydration of the cement. The heat produced during hydration also contributes by increasing evaporation of water. Cracking of the concrete can result. May be reduced by preventing or reducing evaporation. Cracking especially develops over obstructions such as reinforcement.

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plasticising admixture

plum concrete

porosity

pozzolan

precast concrete

prehydration

prestressed concrete

pulverisedfiel ash

quality control

rice husk ash

rich niix

sand

saturuled surface dry (ssd)

sedinicwtary rocks

segegtrtion

setting

Admixture that increases workability at a given water content. See Table 6.1, or permit the water content to be reduced for a given workability.

Concrete in which large boulders (called ‘plums’) are placed in order to reduce the overall concrete quantity. Sometimes used in large foundations, the plums must be sound and durable.

The ratio of the volume of voids to the total volume. A concrete with a high porosity will also generally have a high permeability.

See Section 7.2.1

Concrete which is cast and partly matured on site or in a factory before being put into position in a structure.

Hydration of the cement from moisture, prior to use. This usually occurs due to prolonged storage, inadequate storage or through incorrect handling during transport.

Concrete in which internal stresses are deliberately induced, usually by tensioned steel, prior to loading a structure.

A fine powder resembling cement, which results from the combustion of pulverised coal in electric power generating plants. It is pozzolanic and is used as a partial replacement of Portland cements. See Section 7.2.1 and Table 4.3.

Control of variations in the properties of the mix ingredients and the control of accuracy of all operations which affect the strength or consistency of concrete: batching, mixing, placing, curing and testing.

A waste product of rice. It can be highly pozzolanic and may be used as a partial replacement of Portland cement or lime. See Section 7.2.3.

A concrete mix with a low aggregatekement ratio.

Fine material resulting from natural break-down of rock. Often fine aggregate is called ‘sand’ - which means particles passing a 0.06mm sieve.

Condition where aggregate is saturated on the inside but dry on the outside. Therefore it neither absorbs water nor adds water to the concrete mix.

Rocks which form when sediments of sand, mud or organic material are laid down and harden.

Separation of the constituents of fresh concrete, usually during transport, placing or compacting.

The stiffening of a cemendwater mix upon hydration.

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settlement

sheltering

silica *me

silicaceous

silt

slump

sodium oxide equivalent

soundness

specific gravity

standurd deviation

sulphule

sulphute-resisting cement

superplasticising admixture

tanking

tensile strength

thernitrl conductivity

Concrete settlement over reinforcing bars or coarse aggregate tends to occur in hot weather, with wet mixes and with poor mixing and compact ion.

Using a separate structure to provide some form of protection to the new structure.

A grey powder, which results from the manufacture of silicon and ferrosilicon alloy. It is pozzolanic and is used in the partial replacement of Portland cement. See Section 7.2.1 and Table 4.3.

A rock in which one of the primary minerals is silica.

Material finer than sand but coarser than clay, that is, from 0.002 to 0.06mm. It feels gritty between the fingers, but the particles are difficult to see. Often a contaminant of aggregates and water.

See Section 8.7.1.

Expressed as Na2 0 + 0.658 K20


The weight per unit volume of a substance compared with the weight of the same volume of water at a given temperature. See Section 3.2.3.

Defined as the square root of the average of the squares of the deviations of all the values. It measures the spread of the values, and is used in quality control. See Section 8.3.2.

A contaminant of concrete constituents, which may also attack the finished structure. See Sections 8.2.3 and 8.2.5.

A cement with a low tricalcium aluminate (C3A) content, which reduces sulphate attack.

Admixture that provides for a very high concrete workability. Can be used to reduce water content whilst maintaining workability. See Table 6.1.

Waterproofing the concrete.

The resistance expressed in force per unit area of a structural material at failure in a tension test.

A measure of a material's ability to conduct or transfer heat. A material which is not conductive is called an insulator.

thernrr rl expansion See Section 3.2.7.

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trial mix

tricalcium aluminate

water absorption

waterkement ratio

water reducing admixture

weathering

workability

Trial concrete mixes are made using calculated or estimated proportions of each constituent. The properties of these mixes are checked and adjustments made to the mix proportions until a satisfactory mix design is reached.

A constituent of cement. See Section 4.1.7.

See Section 3.2.6.

The amount of water compared with the amount of cement per unit weight. A crucial factor in the mix design it is one of the primary factors which determines the strength and durability of a concrete.

See plasticising admixture.

See Section 3.2.4.

The ease with which a concrete can be placed and compacted. Can be measured by the slump test. See slump test, Section 8.7.2.

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