Influence of compressivestren

gth of recycled aggregates in

acidic condition.Md abu sayem,Md minhaj uddin,Md naeem uddin,mdsayem.sayem@gmail.com ,+8801926002783

ABSTRACT

A major consequence of environment degradation is the adverse effect of pollution on building materials. With the growing contamination of water by industrial and domestic waste, building materials, especially concrete and mortar are becoming increasingly prone to aggressive chemical attack. Concrete is susceptible to acid attack and Acetic acid is very aggressive as their calcium salts are really soluble and removed from the attack front .Sulfuric acid is very damaging to concrete as it combines with acid and leads to sulfate attack .

Recycled aggregates are comprised of crushed, graded inorganic particles processed from the materials that have been used in the constructions and demolition debris. The aim

for this ongoing project is to determine the compressive strength of recycled aggregates in acidic environment and strength characteristics of recycled aggregates for application in concrete structure, which will give a better understanding on the properties of concrete with recycled aggregates, as an alternative material to coarse aggregate in structural concrete.

In the present investigation, a comparative study was carried out on behavior of concrete cube of recycled aggregates exposed to acidic water. The 4 inch cubic specimens of concrete were cast with three mix ratio of 1:1.5:2.5, 1:1.5:3, 1:2:3 and placed in three types of concentration of H2SO4 (1%, 2% & 3%) and in normal water. The test is carried out at the different ages for 7, 14, 21, 28, 60 & 30 days. The result of the test specimen under the above exposures was compared to those of specimens placed in normal water. The concrete specimen obtains about 71.7% to 93% of maximum compressive strength of normal water in different concentration of sulfuric acid. Compressive strength of concrete specimen gradually decreases upto 42% in acidic environment in accordance with acid intensity. But in normal water strength increases gradually. Volume change (decrease) of concrete specimen is about 4.46 to 13.92% in acidic environment and increases with acid intensity. Mass loss of concrete specimen is about 1.94 to 5.74% in acidic environment and increases with acid intensity. But in normal water volume gradually increases upto 2.46% and mass gain upto 1.11% .

Keywords: Compressive Strength.

INTRODUCTION

1.1 BACKGROUND

Recycling is the act of processing the used material for use in creating new product. The usage of natural aggregate is getting more and more intense with the advanced development in infrastructure area. In order to reduce the usage of natural aggregate, recycled

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aggregate can be used as the replacement materials. Recycled aggregate are comprised of crushed, graded inorganic particles processed from the materials that have been used in the constructions and demolition debris. These materials are generally from buildings, roads, bridges, and sometimes even from catastrophes, such as wars and earthquakes.

  On the other hand, a major consequence of environmental degradation is the adverse effect of pollution on building materials . Acidic environment caused by industrial wastes or chemical residues in the ground could influences the durability of the Portland cement concrete .Acid rain is another major cause to create acidic environment. When the cement binder in the concrete is exposed to an acid, the corrosion process is started.

 

Concrete can be subjected to attack by various minerals acids which include sulfuric acid, nitric acid, hydrochloric acid and phosphoric acid. In waste water stream, the corrosion of the concrete structures is caused by sulfuric acid and it is a major problem in most areas around the world. By a biologically influenced process, hydrogen sulfide is converted into sulfuric acid. When concrete is in contact with this acid, the sulfuric acid react with concrete to from gypsum Concrete will expand and spall.

1.2 STATEMENT

Recently, a huge number of building construction projects (from six-storied to twenty storied) have been undertaken in the major cities of Bangladesh.

So that, every year we need a large amount of aggregate for construction purpose.

In Bangladesh, the volume of demolished concrete is increasing due to the deterioration of many low- rise buildings by relatively high-rise buildings due to the booming of real estate business.

Disposal of the demolished concrete is becoming a great concern to the developers of the buildings.

If the demolished concrete is used for new constructions, the disposal problem will be solved, the demand for new aggregates will be reduced, and finally consumption of the natural resources for making aggregate will be reduced.

Concrete is often exposed to water which may contain domestic and industrial effluents. With the growing contamination of water by industrial and domestic waste building material, especially concrete and mortar are becoming increasingly prone to aggressive chemical attack. So a comparative study was carried out on behavior of concrete cubes exposed to acidic water environment.

For those reasons we felt investigations are needed for recycling of demolished concrete & a study was carried out on behavior of concrete cubes exposed to acidic water environment.

1.4 OBJECTIVES:

The objectives of this project are specified below-

• To determine and compare the strength of concrete by using of recycled aggregates in different types of acidic environment.

• To study the dimensional stability (volume change, mass change) .

• To determine the mix ratio which give maximum strength of concrete.

• To compare the test results of specimens test under acidic water and normal water.

• Establishment of relationship between mechanical behaviour & dimensional stability

1.5 SCOPE OF THE WORK:

The experimental project has been divided into some tasks to achieve the above objectives-

• Making of the acidic solution according to Concentration of the industrial effluents.

• Casting of the Concrete cubes of size 4 inch and placing them in normal and three types of acidic solution.

• Testing of the specimens for the physical properties such as compressive strength, porosity, water absorption.

• Carrying out of the test at different ages such as 7 days, 14 days, 21 days, 28 days,2 months and 3 months.

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• Comparing the results of tests conducted on specimens under acidic solutions with those of specimen’s places in normal water.

1.6 WORK PLAN

2.1 CONCRETE

Concrete is an artificial kind of stone manufactured from mixture of binding materials and inert materials with water known as concrete.

Concrete = binding materials + Inert materials + water

Concrete is considered as a chemically combined mass where the inert material acts as filler and the binding materials acts as a binder. The inert materials used in concrete are termed as aggregates. The aggregates are two types-

1. Fine aggregate

2. Coarse aggregate

2.1.1 Fine aggregate:

Aggregates of size smaller than 3/16 inch or 4 mm in dia is known as coarse aggregate. Sand and surki are commonly used as fine aggregate.

2.1.2 Coarse aggregate:

Aggregate of size larger than 3/16in or 4 mm in dia is known as coarse aggregate. Brick, khoa, broken stone, gravels, pebbles, cinders etc of size 3/16 inch to 2 inch are commonly used as a coarse aggregate in making concrete.

2.2 FUNCTIONS OF AGGREATES IN CONCRETE

The aggregate give volume to the concrete. In case of concrete, the voids of coarse aggregate is filled up with fine aggregate, then the voids in the fine aggregate is filled up with materials. Finally the binds the individuals units of aggregate into a solid mass with the help of water.

2.3 QUALITES OF AGGREGATES:

The quality of aggregate is very important for concrete because it occupies about three quarters of its volume. Weak aggregate can never produce strong concrete. The properties of aggregate not only limit the strength of concrete but also greatly affect the durability performance of concrete.

Aggregate is considered as an inert materials but actually it acts as a binding materials

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connected into a cohesive whole by means of cement paste in manner similar to the masonary construction. In fact aggregate are not truly inert. Their Physicals, chemical and thermal properties influence the structural performance of concrete. Aggregate are cheaper than cement. So it is economical to use much amount of aggregates as possible.

2.4 FUNCTION OF WATER IN CONCRETE

To wet the surfaces of aggregate to develop adhesion.

To prepare a plastic mixture of various ingredients.

To impart workability to concrete to facilitate placing in the desired position.

Water also needed for the hydration of the cementing materials to set and harden during the period of curing.

2.5 PROPERTIES OF CONCRETE

The following are the desirable properties of concrete –

1. Strength2. Elastic properties3. Fatigue4. Durability 5. Impermeability6. Workability

2.5.1 Strength:

It is considered as its (concrete) important property. Strength usually gives the overall picture of quality of concrete.

Strength of concrete are of following types:

a. Compressive Strengthb. Tensile Strengthc. Flexural Strengthd. Shear Strength

a. Compressive strength: Generally two specimens are used in our country- cube and cylinder. The cube specimen of concrete is cast in steel or in cast iron moulds, normally 6 inch in size. The standard practice is to fill the cube mould with concrete in three equal layers. Each layer of concrete is compacted 35 strokes by a 1 inch squre steel punner. Ramming is continued until sufficient compaction

has been achieved. The top surface of cube is to be finished smooth by means of towel.

The standard cylinder specimen of concrete is 6 inch in diameter and 12 inch high. It is cast in mould made of cast iron. Cylinder specimens are also made in na similar way to the cube. Except it is compacted either in three layers using a 5/8 inch diameter steel rod or in two layers by means of an immersion vibrator.

b. Tensile strength: The tensile strength of concrete is much lower than the compressive strength, largely because the cracks created by tensile loads can propagate very easily.

c. Flexural strength: The stress that caused by the bending moment are known as flexural strength of plain concrete is almost wholly dependent upon the tensile strength

d. Shear strength: It is that type of strength that is caused by forces acting along or parallel to the area of resisting the forces. It is also known as tangential strength. Pure shear is probably never encountered in concrete structures.

2.5.2 Elastic properties:The elastic property of concrete is very important. Its importance is not only because of their bearing of load under restricted but also for the design of reinforced concrete. For designing reinforced concrete it is necessary to known the relative stress in the steel and concrete under same distortion.

2.5.3 Durability: It is essential that concrete should withstand the condition for which it has been designed without deterioration over a period of years’ such type of concrete is known durable concrete. The absence of durability may be caused by the environment to which the concrete is exposed or by internal cause within the concrete itself.

2.5.4Fatigue: Plain concrete when subjected to flexural exhibits fatigue. The flexural resisting ability of a concrete of a given quality is indicated by an endurance limit, whose value depends upon the number of repetitions of stress. This is known as fatigue of concrete.

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2.5.5 Impermeability: Penetration of external material from solution of side concrete may adversely affect is durability. This penetration depends on the permeability of concrete.

2.5.6 Workability: The strength of concrete of given mix proportion is very seriously affected by the degree of compaction. So the consistency of the mix such that the concrete can be transported placed and finished sufficiently easily and without segregation. A concrete satisfying these condition is known as workable.

2.6 WHY CONCRETE RECYCLE

1. Protecting the environment by reducing the need to extract virgin material from the ground.

2. Reduce the waste going to landfill.3. Reducing project costs by using

materials fit for purpose.4. Concrete and construction waste is

currently being utilized for a broad number of applications including, road base, fill, and hardstand areas. It has also been used as the main aggregate source in new concrete in a number of cases

Figure 2.6.1: Recycled Aggregate

2.7 DEMOLISHED CONCRETE

When demolished concrete is crushed, is certain amount of mortar and cement paste from the original concrete remains attached to atone particles in recycled aggregate. This attached mortar is the main reason for the lower quality of RCA compared to natural aggregate (NA). RCA compared to NA has following properties:

-increased water absorption

-decreased bulk density

-decreased specific gravity

-increased abrasion loss

-increased crushability

-increased quantity of dust particles

-increased quantity of organic impurities if concrete is mixed with earth during building demolition.

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-possible concrete of chemically harmful substances, depending on service conditions in building from which the demolition and crushing recycled aggregate is obtained.

Available test results of recycled aggregate concrete vary in wide limits, sometimes are even opposite, but general conclusions about the properties of concrete with recycled coarse aggregate compared to concrete with natural aggregate are:

-increased drying shrinkage up to 50%

-increased creep up to 50%

-Water absorption increased up to 50%

-decreased compressive strength up to 50%

-decreased splitting and flexural tensile strength up to 10%

-decreased modulus of elasticity up to 45%

-Same or decreased frost resistance

Technology of RAC production is different from the production procedure for concrete with natural aggregate. Because of the attached mortar, recycled aggregate has significantly higher water absorption than natural aggregate. Therefore, to obtain the desired workability of RAC it is necessary to add a certain amount of water to saturate recycled aggregate before or during mixing, if no water- reducing admixture is applied. One option is to first saturate recycled aggregate to the condition, water saturated surface dry and the other is to use dried recycled aggregate and to add the additional water quantity during mixing. The additional water quantity is calculated on the basis of recycled aggregate water absorption in prescribed time.

2.8 ACID ATTACK ON CEMENT CONCRETE:

2.8.1 GENERAL:

Durability is an important engineering property of concrete, which determines the service life of concrete structures significantly. Due to the interactions of concrete with external influences, the mechanical and

physical properties of concrete may be threatened and lost. Among the threatening factors like freezing and thawing, abrasion, corrosion of steel, chemical attack may also deteriorate concrete within time.

ACI committee Report 201 (2008) has classified chemical attacks into several types that include; acidic attack, alkali attack, carbonation, chloride attack, leaching and sulfate attack. It can be accepted as a general rule that acids are deleterious to concrete. The spectrum of aggressive acidic media is wide.

2.8.2WHAT IS ACID ATTACK:

Concrete is subjected is to acid attack because of its alkaline nature. The components of the cement paste break down during contact with acids. Concrete structures are also used for storing liquids, some of which are harmful for concrete. In industrial plants, concrete floors come in contact with liquids which damage the floor. In damp conditions SO₂ and CO₂ and other acid fumes present in the atmosphere affect concrete by dissolving removing part of the set cement. In fact, no Portland cement is acid resistant. Concrete is also attacked by water containing free CO₂. Sewerage water also very slowly causes deterioration of concrete.

Acids such as nitric acid, hydrochloric acid and acetic acid are very aggressive as their calcium salts are rapidly soluble and removed from the attack front. Other acids such as phosphoric acid and humic acid are less harmful as their calcium salt, due to their low solubility, inhibits the attack by blocking the pathways within the concrete such as interconnected cracks, voids and porosity. Sulfuric acid is very damaging to concrete as it combines an acid attack and sulfate attack.

An acid attack is diagnosed primarily by two main features:

Absence of calcium hydroxide in the cement paste.

Surface dissolution of cement paste exposing aggregates.

Acid attack increase with

Increase in acid concentration Higher temperature Higher pressure Constant and fast renewal of acidic

solution at the concrete/liquid interface.

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2.9 ACID CORROSION:

Cement mortar and concrete are mechanically very strong bur because of the presence of some free lime (CaO), it becomes highly susceptible to chemical attack, especially in acidic water (pH<7). In acidic water, the lime present in the mortar and concrete dissolves and makes the concrete weak in strength. Moreover lime is more soluble in soft water that hard water. Consequently concrete undergoes decay or deterioration it soft water than hard water. Consequently concrete undergoes decay or deterioration in contact with acidic water and soft water. Hence, decay is quicker as the pH of water decreases and softness of water increases from hard to soft.

Acid corrosion is provoked by any acid. The possible destruction of concrete in an aqueous medium is determined by the magnitude of the pH value. The final decay products of the constituents of mortar & concrete are silicic gel, calcium and aluminum salts of the acid attacking the cement stone or when acid is involved the gel of aluminum hydroxide.

Formation of silicic gel:

mCaO.SiO2.aqueous+ nH2O i SiO2.aqueous + Ca(OH)2

Formation of Aluminium hydroxide gel:

qCaO.Al2O3.aqueous + pH2O i2AI(OH)3 + qCa(OH)2

Figure2.9.1: Corrosion of concrete block due to 3% H₂SO₄ solution after 90 days curing

Figure 2.9.2 : Corrosion of concrete block due to 3% H₂SO₄ solution after 60 days curing

2.10 CHEMISTRY OF ACID ATTACK:

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The deterioration of cementations materials, and therefore concrete, by acids is mainly due to the reaction between acids and the calcium hydroxide found in the formation of water-soluble solution in mortar/concrete decreases, contributing to the instability of the hydration products in the cement matrix. The quality of the matrix structure is deteriorated and the results are loss of mass, strength and rigidity (softness).

In the case of the presence of sulfate ions, addition deterioration occurs because of decalcification of C-S-H, or even un\hydrated C3S and C2S, in the presence of sulfate ions. This supplies Ca2+to promote the formation of either calcium sulphoaluminate(ettringite) or gypsum. That type of attack (gypsum formation and decalcification of C-S-H) will lead to expansion, elastic properties and strength loss due to a reduction in binding capacity.Due to sulphate attack, damage usually starting at the edges and corners and followed by cracking and spalling of the concrete.

Gypsum is added to the cement clinker to prevent flash set by the hydration of the C₃A.Butsulphates react with both Ca(OH)₂ and the hydrated C₃A to form gypsum and ettringite. MgSo₄ has a more damaging effect than other sulphates because it leads to the decomposition of the hydrated casio₃ as well as of Ca(OH)₂ and of hydrated C₃A; hydrated MgSiO₃ is eventually formed and it has no binding properties.

Natural soft water containing aggressive CO2may be very aggressive to the cementations materials. The majority of natural waters contain certain qualities of dissolved CO2 in equilibrium with calcium carbonate and bicarbonate. Aggressive CO2 reacts with calcium hydroxide in the cement matrix, forms highly soluble calcium bicarbonate, which is gradually leached out. This process leads to the limited values of aggressive CO2that will lead to a significant rate of real attack. It has been concluded in some studies, that water containing more than 20 ppm of aggressive CO2 can result in rapid decomposition and in the case of freely moving waters; the limit could be 10 ppm. Generally, cement and cementitious materials cannot withstand lengthy exposure to acids. Portland cement concrete is not resistant to pH values below 6.0 and it is considered that concrete made with

any type of cement where the pH values are less than 3 are at a high risk of damage.

2.11 FACTORS AFFECTING ACID CORROSION:

2.11.1 Chemical character of anions present: The degree of aggressivity of an acid is dependent on the chemical character of anions present. The strength of acid, dissociation degree in solutions and mainly, the solubility of the calcium salts formed are dependent on the chemical character of anion.

2.11.2 Leaching of the constituents of cement matrix: The acidic attack is affected by the processes of decomposition and leaching of the constituent of cement matrix.

2.11.3 pH and acid concentration: An acidic media may achieve pH values under 7, predominantly 6and lower. However, pH values give no correct information about the real quantity of the acid in the solution, because the pH value is dependent on the dissociation degree of acid. Besides for the aggressivity of acidic solutions, the real concentration of acid is more significant than pH value.

2.11.4 Type of aggregate: Aggregate type also affects the performance of mortars against acid attack. Limestone aggregate is more vulnerable to acid attacks. However, aggregates like river gravel and similar silicious materials are more resistant.

2.11.5 Type of cement: The type of cement is another factor affecting the performance of concrete in an aggressive environment. It is known that acids are always hazardous on any type of cement .The integrity of hardened Portland cement binders is highly dependent on maintaining the high levels of alkalinities which normally stabilize the gel compound responsible for cementitious properties. Acids react with alkaline components of the binder (calcium hydroxide, calcium silicate hydrates and calcium aluminates hydrates) lowering the degree of alkalinity. In extreme cases, acids may completely neutralize the alkalinity. These chemical changes are the most vulnerable cement type to acidic attack, since they contain a high proportion of calcium hydroxide released during hydration of the calcium

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silicates. It should also be considered that, the efficiency of blending for acid resistance may be affected by other factors e.g.

-the type of cement used for blending,

-the amount and fineness of pozzolan used and

- Especially curing conditions.

2.11.6 Other factors: There exist a number of factors that control hardened cement pastes deterioration in acid solutions. These include the type, the concentration and pH of the acidic solution, the mobility of the solution, the water/cement ratio, the type of cement and mineral admixtures.

2.12 SOURCES OF ACID ATTACK ON CEMENT:

Industrial process:Petroleum refineries and other oil related industries and their effluent. Various acids such as sulfuric acid, nitric acid and phosphoric acid plant are the sources of acid attack on concrete.

Natural sources:Natural exposure condition may cause acid attacks. Free acids in natural waters are rare. Exceptions are carbonic waters and sulfuric acids in peat waters. Concrete can produce sulfuric acid which reacts with acid. Several organic and inorganic acids may occur in shallow regions of sea-water as a consequence of bacteriological activity. Significant quantities of free acids in plants and factories may be found.

Unsafe disposal of wastes: Landfills remain the major method used for the disposal of hazardous industrial wastes. Despite continuing efforts to promote waste reduction, recycling, reuse and clean manufacturing technologies, some wastes will always require safe disposal to landfill. Pre-landfill treatment of hazardous industrial waste is therefore likely to be required in order to ensure its long-term safe disposal.

Acid rain: The combustion of any sulfur containing material produces SO2and SO3. With the present of sufficient water vapor, SO3 and water combine to from droplets of H2SO4 which may found in the atmosphere. Similarly NO2 react awithe hydroxyl radicals (HC) in the atmosphere to from nitric acid (HNO3). These acids are washed out of the atmosphere as acid rain.

Sewage in sewers: Hydrogen sulfide gas (H2S) is often generated in sewers particularly those having a low gradient, low volume and a high BOD (Biological Oxygen Demand) value. In poorly ventilated sewers, bacterial action in the most environment oxidizes the hydrogen sulfide gas (H2S) to from sulfuric acid (H2SO4). H2S gas is normally generated from human wastes and other human activities. These acids attack the concrete sewer. Again bacterial actions in sewers- anaerobic bacteria produce sulfur dioxide which dissolves in water and then oxidizes to form sulfuric acid.

Bricks:In masonry, sulfates present in bricks and can gradually released over a long period of time, causing sulfate attack of mortar, especially where sulfates are concentrated due to moisture environment.

Laboratory investigation: Various tests use certain acids which in turns come in contact with concrete.

Carbonation by contact with water:Natural water usually have a pH of more than 7 and seldom less than 6. Even waters with a pH greater than 6.5 may be aggressive if they contain bicarbonates. Any water that contains bicarbonate ion also contains free carbon dioxide, which can dissolve calcium carbonate unless saturation already exists. Water with this aggressive carbon dioxide acts by acid reaction and can attack concrete and other Portland cement products whether or not they are carbonated.

Other sources:Dairying, fruit processing certain vegetables processing, wine manufacturing, fish and meat processing, wool scouring and other industries all produce various forms of acids a in solution which will attack concrete .

2.13 EFFECT OF ACID ATTACK:

Loss of alkalinity Loss of mass. Loss of strength and rigidity. Expansion.

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Loss of bond between the cement paste and aggregate.

Major cracking: Calcium hydroxide reacts with the acid and form gypsum and ettringite. This causes the concrete to expand. When tensile stress caused by concrete expansion exceeds the failure tensile strength of the coating, cracking occurs. Generally, specimens which have larger cracks first. Good bonding will prevent migration of acid along the interface resulting in smaller blisters.

Spalling : When a coating can not resist sulfuric acid attack itself or sulfuric can easily penetrate through the coating and affect the concrete at multiple locations, spalling occurs. In this situation, sulfuric acid rapidly reacts with calcium hydroxide on the surface of the specimen.

Blistering: This type of failure occurs on coating/lining with good ductility. When concrete expand, coating/lining deform without cracking. In some cases, blisters also occur under the coating film.

Eroding: In some coatings, the sulfuric acid directly attacks the coating film first resulting in the removal (erosion) of coating.

So mainly the durability property of the concrete is reduced, which is very important for any type of structures.

2.14 CORROSION DUE TO VARIOUS ACIDS:

A comparative loss due solidified soil waste, which normally contain Pb(OH)2 and Cr(OH)3 are specified below.

Corrosion due to acids: Weight change data of cement based solidified wastes exposed to 0.5 acetic is a function of time. The percentage weight loss from the samples gradually increased with increasing exposure duration, but at a decreasing rate, a cement based solidified waste consists of the hydration products of various constituents, mainly CSH gel and calcium hydroxide, waste components, unreacted cement clinker phases and the residue of the water-filled pores. These pores in the solidified waste formed the capillary porosity. The ingression of an aggressive acetic acid leachant into the pore water disturbs the

chemical equilibrium formed with the surrounding solids and this may result in solubilization of insoluble components.Ca(OH)2is the most readily available alkali material in solidified waste and is solubilized when the pH drops below 12. The dissolution of Ca(OH)2results in an increased degree of capillary pore connectivity and leads to further ingression of the acid leachent. As a result an extensive dissolution of Ca(OH)2 and decalcification of CSH gels occurred. This led to the formation of macro pores and macro cracking in the corroded layer. It was observed that weight loss from the solidified wastes increased with rising concentrations of Pb(OH)2 and Cr(OH)3in the mixes. The increased concentration of Pb(OH)2 and Cr(OH)3: resulted in a decreased cement content and therefore the ability of the solidified waste matrices to neutralize acid was reduced. In addition the interfering effects of Pb(OH)2 and Cr(OH)3: on OPC hydration could induce a poor microstructure development of the solidified wastes.[16] As a result, the resistance of a cement matrix to acid corrosion was reduced.

Corrosion due to nitric acid: Similar effects on all cement-based solidified waste after exposure to 0.5 N nitric acid was observed, but at a greater rate of weight loss than acetic acid. Nitric acid is a strong mineral acid, which dissociates completely, and form highly soluble calcium nitrate. According to the higher solubility of calcium nitrate (266.0g/100g water ) compared to calcium acetate (43.6g/100g water ), calcium nitrate was likely to precipitate in the porous corroded layer of the solidified waste less than calcium acetate. This resulted in a lower diffusion resistance of the corroded layer and a greater rate of corrosion caused by nitric acid was observed.

Corrosion due to sulfuric acid: Weight change data of cement-based solidified waste at different exposure durations in 0.5N sulfuric acid. A gain in weight of cement – based solidified wastes after exposure to sulfuric acid was observed. Similar observation was reported by several researchers that the weight gain was caused by the deposition of gypsum on the surface and in the porous corroded layer of the solidified wastes.

Ca(OH)2 + H2SO4i CaSO4+ 2H2O

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Gypsum, which is formed by the reaction between sulfate iron and calcium hydroxide, has very low solubility (0.22 g/100 g water). Formation of his insoluble gypsum layer can prevent the solidified waste matrices from further deterioration upon contact with sulfuric acid. However, this gypsum layer was loosely connected with the solidified waste and fell off spontaneously. This implies that the solidified waste was substantially deteriorated, although at a much slower rate compared to acetic and nitric acid.

Corrosion due to hydrochloric acid:The action of HCI on cement hydration products, in particular Ca(OH)2and the resulting products are presented in the following chemical equations:

Ca(OH)2 + 2HC1 iCaC12+2H2O

From equation it can be seen that, consumption o0f Ca(OH)2 results with formation of salts of CaC12. By the help of water these soluble salts may easily be transported to the outer parts and increased pore volume speed up the rate of reaction.

2.15 PREVENTION OF ACID ATTACK ON CONCRETE:

Portland cement concrete usually does not have good resistance to acid. Some weak acid however can be tolerated, particularly if the exposure is occasional. There are essential three ways to improves concrete resistance to acids:

Choosing the right concrete composition to make it as impermeable as possible.

Isolating it from the environment by using a suitable coating.

Modifying the environment to make it less aggressive to the concrete.

Acids attack concrete by dissolving both hydrated and unhydrated cement compound as well as calcareous aggregate. In most cases, the chemical reaction from soluble calcium compounds, which are then leached away.

Siliceous aggregates are resistant to most acids and other chemicals and are sometimes specified to improve the chemical resistance of concrete.

Acid resistance increases with

High Ca2+content in a dense hardened cement paste ( low water-cement ratio)

Low proportions of soluble components of concrete

Creation of a durable protective layer of reaction products with low diffusion coefficient (transport properties).

Concrete deterioration increases as the pH of the acid decreases from 6.5 in fact, no hydraulic cement concrete, regardless of its composition, will hold up for long if exposed to a solution with a pH of 3.0 or lower. To protect concrete from such severely acidic environments, surface protective treatments are available such as-

Use of slag in cement: The durability of alkali-activated slag (AAS) concrete exposed to acid attack was investigated. To study resistance of AAS concrete in acid environments, AAS concrete was immersed in an acetic acid solution of pH = 4 . The main parameters studied were the evolution of compressive strength products of degradation, and micro structural changes.

It was found that AAS concrete of Grade 40 had a high resistance in acid environment, superior to the durability of OPC concrete of similar grade.

Use of admixtures: The degradation of concrete sewer pipes by sulfuric acid attack is a problem of global scope, resulting in substantial economic losses each year. In this study, five admixtures, which offer a range of potential improvement mechanisms, were used at various dosages to enhance the resistance of concrete made with Type 50E cement to chemical sulfuric acid attack .The resistance to sulfuric acid of concrete specimens incorporating these admixtures was measured and compared to that of control specimens. An attempt was made to determine whether there is a relationship between the effect of the various admixtures on mechanical strength and porosity and the resistance of concrete to H2SO4attack. Results indicate that reduce the mass loss of concrete specimens due to immersion for eight weeks in H2SO4 solution and having concentrations of 70% and 3% (by

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volume) by 38% and 25% respectively, compared with that of the control specimens. Other admixtures (OCI, Caltite and Xypex) reduced the mass loss of concrete specimens in the range 12-20% for the 7% H2SO4solution and in the range 9-16% for the 3% H2SO4 solution. Although silica fume effectively increased compressive strength and reduced the porosity of concrete, its contribution to the resistance of concrete to chemical sulfuric acid wad minor. No clear relationship could be established between the mechanical and physical properties of concrete (compressive strength and porosity) and its resistance to sulfuric acid attack. It was also found that the decline in compressive strength of concrete specimens subjected to H2SO4 attack was directly proportional to their mass loss, following a linear relationship.

Use of acid resistance concrete and mortar: The present invention relates to concrete, mortar and other harden able mixtures comprising cement and fly ash use in construction and other applications, which harden able mixtures, demonstrate significant levels of acid and sulfate resistance while maintaining acceptable compressive strength properties. The acid and sulfate harden able mixtures of the invention containing fly ash comprise cementitious materials and a fine aggregate. The cementitious materials may comprise fly ash as well as cement. The fine aggregate may comprise fly ash as well as sand. The total amount of fly ash in the harden able mixture ranges from about 60% to about 120% of the total amount of cement, by weight, whether the fly ash is included as a cementitious materials, fine aggregate or an additive, or any combination of the foregoing.

Lowering the permeability: German researchers tried to improve acid resistance of concrete pipes exposed to long term acid attacks aim a pH range between 4.5 to 6.5 . The fundamental solution of increasing chemical resistance by lowering concrete’s permeability was used to optimize concrete mix designs. The objective was use to keep the erosion rate so low that a service life of about 100 years could be achieved. It was found that a significant improvement in acid resistance can be achieved by carefully controlled use of fine supplementary cementitious materials.

The main reason for the increased acid resistance of the concrete investigated was the formation of a very dense hardened cement paste and aggregate interface with very low porosities.

CHAPTER - 3

LABORATORY INVESTIGATION

3.1 SIEVE ANALYSIS OF FINE AGGREGTE (FRESH)

3.1.1FINENESS MODULUS OFSYLHET SAND

Weight of sample = 500gm

Table 3.1.2 : Determination of fineness modulus of Sylhet sand

Seive

size

Opening

(mm)

Weight of materials retained(gm)

% Retained

Cumulative

%retained

%Finer

No.4

4.75 0 0 0 100

No.8

2.36 8.4 1.68 1.68 98.32

No.16

1.18 67.2 13.44

15.12 84.88

No.30

0.6 152 30.4 45.52 54.48

No.50

0.3 169 33.8 79.32 20.68

No.100

0.15 97.3 19.46

98.78 1.22

Pan 6.1 1.22 100 0

Fineness modulus of sylhet sand = =2.40

xii

3.2 SPECIFIC GRAVITY, ABSORPTION CAPACITY & MOISTURE CONTENT OF FINE AGGREGATE (SYLHET SAND)

Data from experimental work

Weight of air dry sample,X=500gm Weight of oven dry sample, A=491gm Weight of pycnometer, B =155.6gm Weight of pycnometer+ SSD sample,

C=666.9gm Weight of pycnometer+ SSD sample +

Water up to mark, D=949.2gm Weight of pycnometer+ Water up to

mark, E=652.3gm Weight of SSD sample,F=511.3gm

CALCULATION:

Specific gravity = =

=2.29

Absorption capacity = *100 = *100

= 4.13%

Moisture content = *100 = *100

= 1.833%

3.3 SPECIFIC GRAVITY & ABSORPTION CAPACITY OF COARSE AGGREGATE (RECYCLED)

Data from experimental work:

Weight of oven dry sample,A=1940gm

Weight of SSD sample in air,B=2050gm

Weight of air saturated sample in air ,C=1210gm

CALCULATION :

Bulk specific gravity = =

= 2.284

Absorption capacity = *100

= *100

=5.67%

3.4 MOISTURE CONTENT OF COARSE AGGREGATE(RECYCLED)

Data from experimental work:

Weight of air dry sample,A =2000gm

Weight of oven dry sample,B=1940 gm

CALCULATION:

Moisture content = *100 = *100 =3.1%

3.5 UNIT WEIGHT OF COARSE AGGREGATE (RECYCLED)

Data from experimental work:

Weight of cylinder ,A=4 kg Weight of cylinder

+sample,B=23.2kg Volume of cylinder,V=0.5

ft³

CALCULATION:

Unit weight =

= kg/ft³

=1355 kg/m³

xiii

Figure 3.6.1: Cubical mould (4in*4in*4in)

Figure3.6.3: Placing in suitable position after casting

Figure 3.6.4: Concrete specimen block

CHAPTER – 4

RESULT AND DISCUSSION

4.1 COMPRESSIVE STRENGTH OF CONCRETETable 4.1.1: Volume change(decrease), mass loss & compressive strength of concrete in 1% H₂SO₄ Solution

No of block

Ratio Curing Days

volume change ( %)

Avg. (%)

Mass Loss (%)

Avg. (%)

Comp. Strength (psi)

4

1:1.5:2.5

90 7.7269

7.7

3.3725

3.46

4095.8

57.7739

3.5527

4177.7

67.6106

3.4441

4095.8

28 1:1.5:3.0

7.162 6.87 3.1128

3.04

3768.1

xiv

296.6843

3.0584 3850

306.7628

2.9528 3850

52

1:2.0:3.0

6.3393

7.2

2.8862

3.18

3276.5

537.6923

3.3333

3194.6

547.5686

3.3058

3112.7

76

1:1.5:2.5

60

6.2802

6.23

2.6639

2.73

4341.6

775.8934 2.625

4095.8

786.5094 2.887

4177.7

100

1:1.5:3.0

6.2749

6.15

2.7273

2.69

4013.9

1016.4672

2.8511

3768.1

1025.7143 2.5 3850

124

1:2.0:3.0

6.4193

5.81

2.7269

2.56

3522.3

1254.9553

2.4016

3604.2

1266.0488 2.541

3440.4

157

1:1.5:2.5

28

4.8113

4.81

2.1074

2.1

3768.1

1584.7529

2.0747 3850

1594.8525

2.1162

3768.1

181

1:1.5:3.0

4.8479

4.46

2.1171

1.94

3440.4

1824.3907

1.8992

3358.5

1834.1451

1.7978

3358.5

205 1:2.0:3 4.588 4.66 2.016 2.0 3030.

xv

.0

9 8

6

7

2064.7259

2.0991

3112.7

207 4.682.0693

2948.8

Table4.1.2:Volume change(decrease), mass loss & compressive strength of concrete in 1% H₂SO₄ Solution

No of Block

RatioCuring Days

volume change ( %)

Avg. (%)

Mass Loss (%)

Avg. (%)

Comp. Strength (psi)

217

1:1.5:2.5

21

4.1007

4.05

1.811

1.78

3440.4

2184.0112 1.77

3440.4

2194.0404 1.76

3358.5

241

1:1.5:3.0

3.7801

3.78

1.66

1.67

2948.8

2423.7771

1.674

3030.7

2433.7893 1.68

3112.7

265

1:2.0:3.0

3.5556

3.65

1.581

1.62

2703

2663.6381

1.612

2621.1

2673.7684

1.667

2457.2

295

1:1.5:2.5

14 2.7514

2.63

1.213

1.16

2703

2962.8571

1.262

2457.2

2972.2948

1.016

2621.1

3191:1.5:3.0

2.5688

2.62

1.134

1.15

2375.3

320 2.7514

1.218

2293.4

xvi

3212.5316

1.107

2375.3

343

1:2.0:3.0

2.4545

2.42

1.083

1.07

2375.3

3442.2604 1

2211.5

345 2.541.131

2539.2

364

1:1.5:2.5

7

1.6457

1.5

0.722

0.65

2129.5

3651.3263

0.583

2211.5

3661.5355

0.654

2129.5

388

1:1.5:3.0

1.1324

1.23

0.492

0.54

2047.6

3891.3112

0.574

2047.6

3901.2411

0.541

1965.7

412

1:2.0:3.0

1.1054

1.33

0.481

0.58

1965.7

4131.0934

0.478

1883.7

4141.7807

0.782

2129.5

Figure 4.1.4: Crack developed in concrete block specimen due to compressive load

Table4.2.1 :Volume change(decrease), mass loss & compressive strength of concrete in 2% H₂SO₄ Solution

No of Block

RatioCuring Days

volume change (%)

Avg. (%)

Mass Loss (%)

Avg. (%)

Comp. Strength (psi)

1 1:1.5: 90 8.9962 8.9 3.911 3.8 3276.

xvii

2.5

1

2

1

7

5

29.17782

3.9588

3440.4

38.58951

3.7402

3358.5

25

1:1.5:3.0

8.21394

7.86

3.5685

3.44

2948.8

267.76965

3.4316

3030.7

27 7.60493.3055

2948.8

49

1:2.0:3.0

8.01843

7.83

3.551

3.47

2457.2

507.73381

3.4538

2621.1

517.74194

3.4146 2703

73

1:1.5:2.5

60

7.04633

7.16

2.9918

3.1

4013.9

747.14286

3.1224

3768.1

757.27969

3.1799 3932

97

1:1.5:3.0

7.23938

7.41

3.1915

3.24

3522.3

987.52475 3.29

3604.2

997.46411 3.25

3686.2

121

1:2.0:3.0

7.27449

7.02

3.2051

3.1

3112.7

1226.84444

3.0315

3194.6

1236.93161

3.0738

3276.5

1601:1.5:2.5

28 5.23311

5.25

2.2822

2.29

3522.3

1615.22814

2.2822

3440.4

162 5.2980 2.314 3276.

xviii

1 5

184

1:1.5:3.0

5.00864

5.23

2.1723

2.27

2948.8

1855.10753

2.2093

3030.7

1865.58229

2.4268

3112.7

208

1:2.0:3.0

5.4211

5.32

2.3649

2.34

2866.9

2095.17891

2.3051 2785

2105.35373

2.3529 2703

Table4.2.2 :Volume change(decrease), mass loss & compressive strength of concrete in 2% H₂SO₄ Solution

No of Block

RatioCuring Days

volume change (%)

Avg. (%)

Mass Loss (%)

Avg. (%)

Comp. Strength (psi)

220

1:1.5:2.5

21

4.87132

4.84

2.1721

2.12

3030.7

2214.89182

2.1399

2948.8

2224.76636 2.04

3112.7

244

1:1.5:3.0

4.56897

4.77

2

2.09

2703

2454.80226

2.0988

2539.2

2464.95238

2.1757

2621.1

268

1:2.0:3.0

4.73214

4.74

2.0949

2.1

2129.5

2694.71349

2.0988

2293.4

2704.77941

2.1138

2211.5

292 1:1.5: 14 3.225 3.2 1.42 1.4 2129.

xix

2.5

81

1

14

2

5

2933.17741

1.4063

2211.5

2943.2381

1.4298

2129.5

316

1:1.5:3.0

2.84404

2.97

1.2551

1.3

2047.6

3173.09478

1.3496

1965.7

3182.98373

1.3049

2047.6

340

1:2.0:3.0

3.18182

3.25

1.4034

1.44

1965.7

3413.07414 1.36

1801.8

3423.48071

1.5501

1883.7

367

1:1.5:2.5

7

2.61375

2.43

1.146

1.06

2047.6

3682.28728

1.0012

1965.7

3692.37877

1.0408

2047.6

391

1:1.5:3.0

2.1777

2.29

0.9459

0.99

1965.7

3922.21631

0.9667

1883.7

3932.46679

1.0638

1883.7

415

1:2.0:3.0

2.267

2.35

0.9926

1.03

1801.8

4162.43674 1.07

1801.8

4172.34962

1.0318

1883.7

Table 4 .3.1 :Volume change(decrease), mass loss & compressive strength of concrete in 3% H₂SO₄ Solution

xx

No of Block

RatioCuring Days

volume change (%)

Avg. (%)

Mass Loss ( %)

Avg. (%)

Comp. Strength (psi)

7

1:1.5:2.5

90

17.5202

13.2

7.6471

5.74

2375.3

812.5977

5.3817

2457.2

99.55535

4.1909

2375.3

31

1:1.5:3.0

10.5986

10.3

4.5957

4.441

2047.6

329.92579

4.2126

2211.5

3310.4187

4.5148

2129.5

55

1:2.0:3.0

11.9284

10.7

5.1282

4.637

1556

569.83917

4.2798

1719.9

5710.2355

4.502 1638

79

1:1.5:2.5

60

8.10811

7.93

3.4426

3.431

3440.4

808.01158

3.5021

3030.7

817.66284

3.3473

3276.5

103

1:1.5:3.0

8.01158

8.09

3.5319

3.527

2948.8

1048.13397

3.5417

2866.9

1058.11623

3.5065

3112.7

127

1:2.0:3.0

7.28889

7.7

3.2283

3.406

2621.1

1288.05044

3.547

2866.9

1297.7634

3.4426 2703

163 1:1.5: 28 5.988 6.0 2.61 2.62 2948.

xxi

2.5

59

2

41

4

8

1645.84906

2.562

3030.7

1656.20821

2.6971

3112.7

187

1:1.5:3.0

5.625

5.73

2.4514

2.484

2539.2

1885.3913

2.3221

2539.2

1896.15977

2.6778

2457.2

211

1:2.0:3.0

5.72233

5.99

2.5566

2.65

2375.3

2126.04027

2.6616

2211.5

2136.21415

2.7311

2293.4

Table 4.3.2: Volume change(decrease), mass loss & compressive strength of concrete in 3% H₂SO₄ Solution

No of Block

RatioCuring Days

volume change (%)

Avg. (%)

Mass Loss (%)

Avg. (%)

Comp. Strength (psi)

223

1:1.5:2.5

21 5.23416

5.3266

2.28

2.32

2621.1

2245.55556

2.3849

2539.2

2255.18999

2.3045 2703

247

1:1.5:3.0

4.89691

5.0333

2.1509

2.22

2293.4

2485.19358

2.3013

2211.5

2495.00928

2.2222

2293.4

271 1:2.0:3 5.3308 5.236 2.357 2.3 2047.

xxii

.0

8

8

7

2

6

2725.22388 2.314

1883.7

2735.15556

2.2925

1965.7

289

1:1.5:2.5

14

3.82409

3.7485

1.6821

1.65

1883.7

2903.70697

1.6406

2047.6

2913.71429 1.64

1965.7

313

1:1.5:3.0

3.72137

3.7938

1.6304

1.66

1801.8

3144.06872

1.7794

1883.7

3153.59116

1.5815

1883.7

337

1:2.0:3.0

3.81818

3.7706

1.684

1.67

1801.8

3383.72727

1.6446

1965.7

3393.76648

1.6764

1883.7

370

1:1.5:2.5

7 2.67142

2.8388

1.176

1.25

1801.8

3712.83883

1.2415

1883.7

3723.00619

1.3214

1965.7

394

1:1.5:3.0

2.75404

2.7638

1.1866

1.2

1883.7

3952.83688

1.2374

2047.6

3962.70035

1.1729

1965.7

4181:2.0:3.0

2.72556

2.6282

1.1969

1.15

2047.6

4192.63605

1.1477

1801.8

420 2.5231 1.103 1801.

xxiii

3 8 8

Table 4 .4.1 :Volume change(increase), mass loss & compressive strength of concrete in plain water

No of Block

RatioCuring Days

volume change (%)

Avg. (%)

Mass gain (%)

Avg. (%)

Comp. Strength (psi)

10

1:1.5:2.5

90

2.4752

2.46

1.1728

1.11

4669.3

112.4952

1.0892

4505.5

122.4209

1.0669

4587.4

34

1:1.5:3.0

2.4713

2.46

1.0938

1.08

4259.7

352.4952

1.0943

4259.7

362.4141

1.0656

4341.6

58

1:2.0:3.0

2.4186

2.44

1.0744

1.08

3932

592.4412

1.0693

4013.9

602.4725

1.0914

4013.9

82

1:1.5:2.5

60

1.7241

1.73

1.1297

0.88

4341.6

831.7375

0.7595

4423.5

841.7391

0.7377

4423.5

106 1:1.5:3.0

1.7085 1.7

40.766 0.7

5

4013.9

107 1.782 0.732 4177.

xxiv

2 8 7

1081.7391

0.7531

4095.8

130

1:2.0:3.0

1.756

1.76

0.7377

0.78

3850

1311.7621

0.7451

3768.1

1321.7476

0.8511

3768.1

166

1:1.5:2.5

28

1.5123

1.51

0.7438

0.69

4013.9

1671.5195

0.6639

4013.9

168 1.5080.6612

3276.5

190

1:1.5:3.0

1.5399

1.54

0.6695

0.64

3604.2

1911.5233

0.6202

3768.1

1921.5544

0.6367

3604.2

214

1:2.0:3.0

1.5296

1.52

0.7563

0.7

3276.5

2151.5066

0.6706

3522.3

2161.5267

0.6757

3194.6

Table 4 .4.2 : Volume change (increase), mass loss & compressive strength of concrete in plain water.

No of Block

RatioCuring Days

volume change (%)

Avg. (%)

Mass gain (%)

Avg. (%)

Comp. Strength (psi)

2261:1.5:2.5

21 1.2037

1.26

0.53

0.56

3686.2

227 1.297 0.5 3604.

xxv

5 8 2

2281.29032

0.56

3686.2

250

1:1.5:3.0

1.27119

1.24

0.57

0.55

3276.5

2511.22757

0.54

3440.4

2521.21269

0.53

3358.5

274

1:2.0:3.0

1.28676

1.19

0.57

0.53

3030.7

2751.21156

0.54

2948.8

2761.06667

0.47

3112.7

298

1:1.5:2.5

14

1.04762

1.05

0.46

0.46

2866.9

2991.05163

0.46 2785

3001.05914

0.47

2948.8

322

1:1.5:3.0

1.01289

1.05

0.45

0.46

2539.2

3231.04364

0.46 2703

3241.08499

0.47

2621.1

346

1:2.0:3.0

1.03481

1.06

0.46

0.47

2457.2

3471.09091

0.48

2293.4

3481.04265

0.46

2375.3

361

1:1.5:2.5

7 0.96805

0.97

0.42

0.43

2703

3620.97259

0.43

2621.1

3630.97952

0.43 2703

385 1:1.5: 0.958 0.9 0.4 0.4 2375.

xxvi

3.0

19

6

2

2

3

3860.96154

0.42

2457.2

3870.94967

0.41

2457.2

409

1:2.0:3.0

0.92515

0.93

0.4

0.41

2293.4

4100.93633

0.41

2375.3

4110.93197

0.41

2211.5

0 10 20 30 40 50 60 70 80 90 1000

500100015002000250030003500400045005000

PLAIN WATER

1:1.5:2.51.0:1.5:3.01:2.0:3.0

Age (days)

Com

pres

sive

str

engt

h (p

si)

Mix Ratiocement:sand:aggregate

Figure 4.5.1: Age VS Compressive strength for plain water

xxvii

0 10 20 30 40 50 60 70 80 90 1000

500100015002000250030003500400045005000

1%H₂SO₄

1:1.5:2.51.0:1.5:3.01:02:03

Age(days)

Com

pres

sive

stre

ngth

(psi

)

Mix Ratio cement:sand:aggregate

Figure 4.5.2: Age VS Compressive strength for 1%H₂SO₄

0 10 20 30 40 50 60 70 80 90 1000

50010001500200025003000350040004500

2%H₂SO₄

1:1.5:2.51:1.5:3.01:2.0:3.0

Age(days)

Com

pres

sive

stre

ngth

(psi

)

Mix Ratiocement:sand:aggregate

Figure4.5.3: Age VS Compressive strength for 2%H₂SO₄

xxviii

0 10 20 30 40 50 60 70 80 90 1000

500

1000

1500

2000

2500

3000

3500

4000

3% H₂SO₄

1:1.5:2.51:1.5:3.01:2.0:3.0

Age(days)

Com

pres

sive

stre

ngth

(psi

)

Mix Ratiocement:sand:aggregate

Figure4.5.4: Age VS Compressive strength for 3%H₂SO₄

0 0.5 1 1.5 2 2.5 3 3.50

50010001500200025003000350040004500

28 DAYS CURING

1:1.5:2.51:1.5:3.01:2.0:3.0

Concentration of H₂SO₄(%)

Com

pres

sive

stre

ngth

(psi

)

Mix Ratiocement:sand:aggregate

Figure4.6.1: Concentration of H₂SO₄ VS Compressive strength for 28 days curing

xxix

0 0.5 1 1.5 2 2.5 3 3.50

500100015002000250030003500400045005000 60 DAYS CURING

1:1.5:2.51:1.5:3.01:2.0:3.0

Concetration of H₂SO₄ (%)

Com

pres

sive

stre

ngth

(psi

)

Mix Ratiocement:sand:aggregate

Figure4.6.2: Concentration of H₂SO₄ VS Compressive strength for 60 days curing

0 0.5 1 1.5 2 2.5 3 3.50

500100015002000250030003500400045005000

90 DAYS CURING

1:1.5:2.51:1.5:3.01:2.0:3.0

Concentration of H₂SO₄ (%)

Com

pres

sive

stre

ngth

(psi

)

Mix Ratiocement:sand:aggregate

Figure4.6.3: Concentration of H₂SO₄ VS Compressive strength for 90 days curing

xxx

1:1.5:2.5 1:1.5:3.0 1:2.0:3.035003600370038003900400041004200430044004500

60 DAYS CURING

plain water

MIX RATIO

Com

pres

sive

stre

ngth

(psi

)

Figure4.7.1: Mix Ratio VS Compressive strength for 60 days curing in plain water

1:1.5:2.5 1:1.5:3.0 1:2.0:3.00

500

1000

1500

20002500

30003500

40004500

5000

60 DAYS CURING

1% H2SO4

MIX RATIO

Com

pres

sive

stre

ngth

(psi

)

Concentration

Figure4.7.2: Mix Ratio VS Compressive strength for 60 days curing in 1%H₂SO₄

xxxi

1:1.5:2.5 1:1.5:3.0 1:2.0:3.00

500

1000

1500

2000

2500

3000

3500

4000

4500

60 DAYS CURING

2% H2SO4

MIX RATIO

Com

pres

sive

stre

ngth

(psi

)

Concentration

Figure 4.7.3: Mix Ratio VS compressive strength for 60 days curing in 2%H₂SO₄

1:1.5:2.5 1:1.5:3.0 1:2.0:3.00

5001000150020002500300035004000

60 DAYS CURING

3% H2SO4

MIX RATIO

Com

pres

sive

Str

engt

h(ps

i)

Concentration

Figure 4.7.4: Mix ratio VS compressive Strength for 60 days curing in 3% H₂SO₄

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0 1 2 3 4 5 6 70

500100015002000250030003500400045005000

MIX RATIO1:1.5:2.5

1% H2SO42% H2SO43% H2SO4

Mass loss (%)

Com

pres

sive

stre

ngth

(psi)

Concentration

Figure 4.8.1: Mass loss VS compressive strength for mix ratio of 1:1.5:2.5

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

50010001500200025003000350040004500

MIX RATIO1:1.5:3

1%H2SO42%H2SO43%H2SO4

Mass loss (%)

Com

pres

sive

stre

ngth

(psi)

Concentration

Figure 4.8.2: Mass loss VS compressive Strength for mix ratio of 1:1.5:3

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0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

5001000150020002500300035004000

MIX RATIO1:2:3

1%H2SO42% H2SO43% H2SO4

Mass loss (%)

Com

pres

sive

stre

ngth

(psi)

Concentration

Figure 4.8.3: Mass loss VS compressive Strength for mix ratio of 1:2:3

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.20

500100015002000250030003500400045005000

PLAIN WATER

1:1.5:2.51:1.5:3.01:2.0:3.0

Mass gain (%)

Com

pres

sive

stre

ngth

(psi)

Cement :Sand:Aggregate

Figure 4.8.4: Mass gain VS compressive Strength in plain water

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0 2 4 6 8 10 12 140

500100015002000250030003500400045005000

MIX RATIO1:1.5:2.5

1% H2SO4

2% H2SO4

3% H2SO4

Volume loss(%)

Com

pres

sive

stre

ngth

(psi

)

Concentration

Figure 4.9.1: Volume loss VS compressive strength for mix ratio of 1:1.5:2.5

0 2 4 6 8 10 120

50010001500200025003000350040004500

MIX RATIO1:1.5:3

1%H2SO42%H2SO43%H2SO4

V olume loss(%)

Com

pres

sive

stre

ngth

(psi)

Concentration

Figure 4.9.2: Volume loss VS compressive strength for mix ratio of 1:1.5:3

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0 2 4 6 8 10 120

5001000150020002500300035004000

MIX RATIO1:2:3

1%H2SO42% H2SO43% H2SO4

Volume loss(%)

Com

pres

sive

stre

ngth

(psi)

Concentration

Figure 4.9.3: Volume loss VS compressive strength for mix ratio of 1:2:3

0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.60

500100015002000250030003500400045005000

PLAIN WATER

1:1.5:2.51:1.5:3.01:2.0:3.0

Volume gain (%)

Com

pres

sive

str

engt

h (p

si)

Mix Ratio Cement :Sand:aggregate

Figure 4.9.4: Volume gain VS compressive strength in plain water

4.10: DISCUSSION ON TEST RESULT:

4.10.1 RESULTS:

For mix ratio 1:1.5:2.5 (cement : sand: aggregate) :

Concrete block gain maximum compressive strength (4669.3 psi) in plain water after 90 days curing and 86% ; 94.7% of

maximum strength are obtained after 28days and 60days curing. From graph volume gain are obtained 1.51% ; 1.73% ; 2.46% after 28days ; 60days ; 90days curing and mass gain are obtained 0.69% ; 0.88% ; 1.11% after 28days ; 60days ; 90days curing.

From graph 82.46% ; 93% ; 89.5% of maximum strength are obtained after 28days ;

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60days and 90days curing in 1% solution of H₂SO₄ . Volume loss are obtained 4.81% ; 7.2% ; 7.7% after 28days ; 60days and 90 days curing and mass loss are obtained 2.1% ; 2.73% ; 3.46% after 28days ; 60days ; 90days curing.

From graph 75.44% ; 85.96% ; 73.68% of maximum strength are obtained after 28days ; 60days and 90days curing in 2% solution of H₂SO₄. Volume loss are obtained 5.25% ; 7.16% ; 8.92% after 28days ; 60days ; 90 days curing and mass loss are obtained 2.29% ; 3.1% ; 3.87% after 28days ; 60days ; 90days curing.

From graph 66.66% ; 73.68% ; 52.62% of maximum strength are obtained after 28days ; 60days and 90days curing in 3% solution of H₂SO₄. Volume loss are obtained 6.02% ; 7.93% ; 13.2% after 28days ; 60days ; 90days curing and mass loss are obtained 2.62% ; 3.43% ; 5.74% after 28days ; 60days ; 90days curing.

For mix ratio 1:1.5:3 ( cement : sand: aggregate) :

Concrete block gain maximum compressive strength (4341.6 psi) in plain water after 90 days curing and 86.8% ; 96.22% of maximum strength are obtained after 28days and 60 days curing. Volume gain are obtained 1.54% ; 1.74% ; 2.46% after 28days ; 60days ; 90days curing and mass gain are obtained 0.64% ; 0.75% ; 1.08% after 28days ; 60days ; 90days curing.

From graph 79.24% ; 92.5% ; 88.77% of maximum strength are obtained after 28days ; 60days and 90days curing in 1% solution of H₂SO₄ . Volume loss are obtained 4.46% ; 6.23% ; 6.87% after28days ; 60days and 90 days curing and mass loss are obtained 1.94% ; 2.69% ; 3.04% after 28days ; 60days ; 90days curing.

From graph 71.7% ; 84.9% ; 69.8% of maximum strength are obtained after 28days ; 60days and 90days curing in 2% solution of H₂SO₄. Volume loss are obtained 5.23% ; 7.41% ; 7.86% after 28days ; 60days ; 90 days curing and mass loss are obtained 2.27% ; 3.24% ; 3.44% after 28days ; 60days ; 90days curing.

From graph 58.5% ; 71.7% ; 51% of maximum strength are obtained after 28days ; 60days and 90days curing in 3% solution of H₂SO₄. Volume loss are obtained 5.73% ; 8.09% ; 10.3% after 28days ; 60days and 90days curing and mass loss are obtained 3.48% ; 3.53% ; 4.44% after 28days ; 60days ; 90days curing.

For mix ratio 1:2:3 ( cement : sand: aggregate) :

Concrete block gain maximum compressive strength (4013.9 psi) in plain water after 90 days curing and 87.75% ; 96% of maximum strength are obtained after 28 days and 60 days curing. Volume gain are obtained 1.52% ; 1.76% ; 2.44% after 28days ; 60days ; 90days curing and mass gain are obtained 0.77% ; 0.78% ; 1.08% after 28days ; 60days ; 90days curing.

From graph 77.5% ; 89.8% ; 81.6% of maximum strength are obtained after 28days ; 60days and 90days curing in 1% solution of H₂SO₄ . Volume loss are obtained 4.66% ; 6.15% ; 7.25% after 28days ; 60days and 90 days curing and mass loss are obtained 2.o6% ; 2.56% ; 3.18% after 28days ; 60days ; 90days curing.

From graph 71.42% ; 81.63% ; 75.5% of maximum strength are obtained after 28days ; 60days and 90days curing in 2% solution of H₂SO₄. Volume loss are obtained 5.32% ; 7.02% ; 7.83% after 28days ; 60days and 90 days curing and

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mass loss are obtained 2.34% ; 3.1% ; 3.47% after 28days ; 60days ; 90days curing.

From graph 58.5% ; 71.7% ; 51% of maximum strength are obtained after 28days ; 60days and 90days curing in 3% solution of H₂SO₄. Volume loss are obtained 5.99% ; 7.7% ; 10.7% after 28days ; 60days and 90 days curing and mass loss are obtained 2.65% ; 3.41% ; 4.64% after 28days ; 60days ; 90days curing.

4.10.2 DISCUSSION:

Concrete is subjected is to acid attack because of its alkaline nature. The components of the cement paste break down during contact with acids. Concrete structures are also used for storing liquids, some of which are harmful for concrete. In industrial plants, concrete floors come in contact with liquids which damage the floor. In damp conditions SO₂ and CO₂ and other acid fumes present in the atmosphere affect concrete by dissolving removing part of the set cement. In fact, no Portland cement is acid resistant. Concrete is also attacked by water containing free CO₂. Sewerage water also very slowly causes deterioration of concrete.

The deterioration of cementations materials, and therefore concrete, by acids is mainly due to the reaction between acids and the calcium hydroxide found in the formation of water-soluble solution in mortar/concrete decreases, contributing to the instability of the hydration products in the cement matrix. The quality of the matrix structure is deteriorated and the results are loss of mass, strength and rigidity (softness)

Acids such as nitric acid, hydrochloric acid and acetic acid are very aggressive as their calcium salts are rapidly soluble and removed from the attack front. Other acids such as phosphoric acid and humic acid are less harmful as their calcium salt, due to their low solubility, inhibits the attack by blocking the pathways within the concrete such as Interconnected cracks, voids and porosity. Sulfuric acid is very damaging to concrete as it combines an acid attack and sulfate attack.

In the case of the presence of sulfate ions, addition deterioration occurs because of decalcification of C-S-H, or even un\hydrated C3S and C2S, in the presence of sulfate ions. This supplies Ca2+to promote the formation of either calcium sulphoaluminate (ettringite) or gypsum. That type of attack (gypsum formation and decalcification of C-S-H) will lead to expansion, elastic properties and strength loss due to a reduction in binding capacity. Due to sulphate attack, damage usually starting at the edges and corners and followed by cracking and spalling of the concrete. Acid attack increase with increase in acid concentration. SO we can say that compressive strength of concrete decrease with increase in acid concentration and volume loss or mass loss increase with increase in acid concentration. We can observed from our project work compressive strength of concrete is minimum in acid concentration of 3% H₂SO₄ and volume loss or mass loss is high in acid concentration of 3% H₂SO₄.

But in plain water; volume , mass and compressive strength of concrete increase with increase in curing periods. Due to hydration of cement; Ca(OH)₂ and various salts are formed which are very less soluble in water and do not react with plain water.

CaO + H₂O = Ca(OH)₂

MgO + H₂O = Mg(OH)₂

This hydration products fill up internal void in concrete which is responsible to increase the volume and mass of concrete with increase in curing period. From our project work; we can also observed that compressive strength, volume and mass gain is maximum for concrete for which mix ratio is 1:1.5: 2.5(cement: sand :aggregate).

CONCLUSION AND RECOMMENDATIONS

5.1 CONCLUSION:

This project determined the factors that influence the properties of concrete with high concentration of acid (H₂SO₄) and produced

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guidelines to ensure the safe and appropriate use of concrete in acidic environment.

The conclusion of the project is as follows:

Compressive strength of concrete block increases with time upto 60 days curing and after then strength decreases with time in acidic water. Concrete for mix ratio 1:1.5:2.5 (cement:sand:aggregate) gives the maximum strength in various concentration of acidic solution and mix ratio 1:2:3 gives the lowest compressive strength.

Compressive strength of concrete block increases with time in plain water.Concrete for mix ratio 1:1.5:2.5 (cement:sand:aggregate) also gives the maximum strength in plain water.

Compressive strength decreases with the increase of acidic concentration. Concrete blocks for mix ratio 1:1.5:2.5 (cement:sand:aggregate) are obtained 89.5% ; 73.68% ; 52.62% of maximum compressive strength after 90 days curing in 1% ; 2% ; 3% H₂SO₄ solution.

Corrosion of concrete block increases with the increase of acidic concentration.

Mass loss of concrete block increases with the increment of acidic concentration.Concrete blocks for mix ratio 1:1.5:2.5 (cement:sand:aggregate) occurred in mass loss are 3.46% ; 3.87% ; 5.74% after 90 days curing in 1% ; 2% ; 3% H₂SO₄ solution.

Mass gain of concrete block increases with time in plain water.

Volume loss of concrete block increases with the increase of acidic concentration. Concrete blocks for mix ratio 1:1.5:2.5 (cement:sand:aggregate) occurred in volume loss are 7.25% ; 7.83% ; 10.73% after 90 days curing in 1% ; 2% ; 3% H₂SO₄ solution.

Mass gain and volume gain of concrete block increases with time in plain water.

In ACI method of mix design, the mix ratio of 1: 1.5: 2.5 gives the maximum compressive strength in acidic water as well as plain water.

5.2 RECOMMENDATIONS:

After completion of the project, the following recommendations for further research of concrete with regards to high concentration of acidic environment are outline below.

This investigation may be carried out by curing the specimens in the sewage water directly and also in the acidic water sample made by those acids which are present in the waste water.

As curing periods affects the durability of concrete, the same investigation may be done for several months more to examine.

The deterioration conditions of concrete under acidic environment.

The experiment has been carried out with fully recycled aggregate (100%), if it is done with different percentages of natural aggregate and recycled aggregates such as 70-30,60-40,50-50 concrete may give better strength.

Similar study may be carried out for concrete specimens with different mix ratios and different types of cement which may be effective for future research.

Annual testing of the indoor and outdoor exposed concrete specimens produced for this project should be continued for next 5 years in acidic environment. Rate of volume change, mass change and decreasing rate of compressive strength predictive model developed for this project should be updated as annual data become available.

Field studies should be conducted on concrete structures built within relatively high concentration of acidic environment to determine strength, corrosion and permeability of concrete in the field.

Effect of curing in acidic environment on the rate of strength , volume change further investigation.

The effects of on freeze-thaw resistance, acid scaling resistance and drying shrinkage, creep of concrete should be investigated.

1. REFERRENCES2. Properties of Concrete – By Neville –

Durability of concrete:acid attack &

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sulfate attack on concrete, Mechanism of attack.

3. Concrete Technology - By Neville –Permeability & Durability : sulfate attack& acid attack..

4. Concrete Technology – By Gambhir –acid attack on concrete.

5. Influences of various acids on the physio- mechanical properties of pozzolanic cement mortar, By S.Turkel, B.Felekogin and S.Dulluc,Department of Civil Engineering, DokuzEylin University.

6. Engineering Materials – By Dr. M.A. Aziz.

7. Temper B.(1931). The effect of acidic water on concrete . ACI journal.Vol.28:1-32

8. BRE Digest 363, sulfate & Acid Resistance of Concrete in Ground, Building Research Establishment, UK ,1996.

9. Dr. B.K. Sharma- Industrial Chemistry (including Chemical engineering). Meerut: Goel publishing house,1985.

10. Corrosion of cement based solidified wastes due to different acid attack, By SuwimolAsavapisit, ManopBoonjam, Environment Technology Division, School of energy and materials, King Mongkut’s University of Technology, Thonburi, Bangkok, Thailand.

11. Online –Google Search, Wikipedia, the free Encyclopedia.

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