Faculty of EngineeringAlexandria UniversityCivil EngineeringStructural Department

Lightweight Aggregate Concrete

Babylon, Iraq, built by Sumerian

Pyramids in Mexico, built during the Mayan period A.D. 624987.

U.S.S Selma ship

San Francisco Oakland Bay Bridge

Literature Review

What is Lightweight Concrete?

Lightweight concrete is manufactured on account of its low density or lower unit weight concrete.

Unit Weight range from 0.4~1.8 t/m3

Advantages of light weight concretes

Provide a very good thermal insulation. Satisfactory durability. Sound insulation. Cheaper unit cost of transport.

Disadvantages of lightweight concretes More expensive than ordinary concretes.Mixing, handling and placing require more care and attention than ordinary concrete.

However for many purposes the advantages of lightweight concrete outweigh its disadvantages.

Methods to produce lightweight concreteNo-Fines concreteAerated concreteLightweight Aggregate concrete

Classification of Lightweight Aggregate Concrete According to the ACI 213 there are three types:

Low density concretes.Moderate strength concretes.Structural concretes

Classification of Lightweight Concrete

Lightweight AggregatesLightweight aggregate (LWA) can be divided in two categories:Naturally and are ready to use only with mechanical treatment, i.e., crushing and sieving.Produced by thermal treatment from either naturally occurring materials or from industrial by-products, waste materials, etc.

Production Processes of Lightweight Aggregates Rotary KilnSintered StrandVertical Shaft Kiln

Rotary Kiln

Properties of Lightweight Aggregates Unit Weight Absorption Bulk Specific Gravity Particle Shape and Surface Texture

The main factor affecting Unit Weight, Absorption and Bulk Specific Gravity is the Cellular Structure of the aggregates.

Properties of different types of Aggregates

Particle Shape and Surface Texture

Peculiarities of Light Weight Concrete Mix Proportioning Preliminary Mix Trial Mix Final Mix

The Steps of the Proportioning Procedure

Precautions in Manufacture of Lightweight Concrete Moisture Content of the Lightweight AggregateSlump and Air Entrained Of the Lightweight AggregatePumped Concrete and Its Design

Physical Properties of Lightweight Aggregate Concrete

Compressive StrengthDensityModulus of ElasticityTensile and Flexural StrengthEffect of sand replacement Elastic compatibilityDrying ShrinkageCreepThermal Conductivity

Compressive StrengthThe type of lightweight aggregate is the primary factor controlling the compressive strength

Compressive strength of lightweight aggregate concrete was not much affect neither by increasing of Cement content, by replacing Cement by Silica Fume, nor by using natural sand as partial replacement of the lightweight sand.

DensityThe density of the concrete is mainly governed by the particle density of the aggregate mixtureThe compressive strength is directly proportionalto the aggregate density

Modulus of ElasticityThe modulus of elasticity of concrete depends on the modulus of elasticity of both the matrix and the aggregate

Tensile and Flexural Strength The splitting tensile strength of all lightweight concrete varies from approximately 70~100 % that of the normal weight concrete at equal compressive strength.

Effect of sand replacement

Partial or complete replacement of lightweight fines with natural sand generally provides improvements in the workability and finishability of the plastic concrete, and also many physical properties of the hardened concrete.

Elastic compatibility Concrete can be considered a composite material in which the coarse aggregates act as a spherical inclusion in an infinite matrix of mortar.

The primary reason for the lack of bond cracks may be due to the similarity of elastic modulus of the LWA and the mortar fraction.

Drying Shrinkage

Drying shrinkage is an important property that affects extent of cracking, pre-stress loss and effective tensile strength.

For equal cement paste content the shrinkage of lightweight aggregate concrete is usually slightly greater than normal weight concrete

Creep

Generally higher creep strains are produced in lightweight aggregate concrete than in normal weight concrete due to lower E-value of aggregate.

The basic creep of lightweight aggregate concrete is approximately 15% higher than the normal weight concrete.

Thermal Conductivity Lightweight concrete has a smaller thermal conductivity than normal weight concrete. Due to its pores structure or air-void system.

The air-pore system in the LWAC depends upon the binder system and the chemical admixtures used. With the addition of silica fume and fly ash, thermal conductivity is decreased

Durability Durability in concrete is defined as its ability to resist weathering action, chemical attack, occurrence of extreme temperature or any other process of deterioration

Permeability

Fire Resistance

The performance of building materials under fire exposure is of significant importance. One phenomenon that must be considered during fire is the risk of explosive spalling, which may cause much of the concrete cover to disappear leaving the reinforcing bars directly exposed to fire

FIRE TEST Fire endurance tests of four types of concrete were conducted in a gas-oil furnace

LWAC, 3L-concrete, (Swedish Leca)structural LWAC (strength 350 kg/cm2)LWAC modified with chemical admixtureshigh strength LWAC (Silica fume)

specimens A comparison was done with normal weight concrete made with the addition of a polymer fire test was performed on:

2.5 cm thick plates of normal concrete 2.5 cm thick plates of LWAC 5.0 cm thick slab of LWAC 15 cm thick reinforced concrete beam of LWAC

Gas-oil Fired Furnace

ConclusionNormal concrete plates from two sides resulted in destructive spalling at about 125175C

Concretes made with the polymer addition, no spalling was observed when heated from both sides, even after 30 minutes.

Tests performed on the 5 cm slabs and the LWAC reinforced beam (b h = 0.15 0.3 m 3 ) did not show any damage for 1 hour after heating when the temperature in the middle of the specimens observed was 850C

Chemical ExposureChemical durability is defined as the resistance of concrete against the gases, chemicals, and temperature variations which interact chemically with the binder components of the concrete causing deterioration The following are varies types chemical attacks:

Acid ResistanceCarbonation and CorrosionChloride Ion PenetrationSulphate resistance

Acid ResistanceConcrete is susceptible to acid attack because of its alkaline nature The components of the cement paste break down during contact with acids according to the following reaction:

2 HX + Ca(OH)2 -> CaX2 + 2 H2O Decomposition of the concrete depends on porosity of the cement pastethe concentration of the acid the solubility of the acid calcium salts

Carbonation and CorrosionCarbonation occurs in concrete because the calcium bearing phases present are attacked by carbon dioxide of the air and converted to calcium carbonate

Ca(OH)2 + CO 2 CaCO3 + H 2 O

CaCO 3 + CO 2 + H 2 O Ca(HCO 3 ) 2

Ca(HCO 3 ) 2 + Ca(OH)2 2CaCO 3 + 2H 2 O

Chloride Ion PenetrationChloride ions penetrate concrete and react with calcium hydroxide and calcium aluminates.

calcium hydroxide calcium chloride (soluble)calcium aluminates C3A.CaCl2.H2O

If the concentration of CaCl2 is higher than the surroundings. It leads to microcrack formation making easy penetration of chloride ions.

Cont. Chloride Ion PenetrationIn the presence of chloride, a basic iron chloride is formed, 3Fe(OH)2 FeCl2, which later decomposes and forms FeOH (akaganite). Leaching of salt increases the porosity and permeability of concrete and weakens the bond between the aggregate and the cement paste.

Sulphate ResistanceSulphate Attack Cement Paste

Gypsum and Ettringite formed during the external sulfate attack may cause concrete to crack and scale

Materials & Experimental Program

Materials & Experimental ProgramIn the following part three points are discussed. Materials Experimental programMix design

CEMENT

WE HAVE BEEN USING ORDINARY PORTLAND CEMENT ,CEMENT CONTENT WERE 300,350,400 AND 450 KG/m3

Fine LecaIt has been delivered from national cement companyThe compacted unit weight = 0.71 & the loose unit weight = 0.66

SANDWe used natural siliceous sand as replacement of fine leca

Coarse aggregateThe coarse aggregate used in this study was coarse lecaMaximum size was 3/8inchCompacted unit weight =0.376Loose unit weight =0.36

Silica fumeIs a by product resulting from the reduction of high-purity quartz with coal or coke and wood chips .

Silica fume produced from ferro silicon alloys

FoamFoam is a by product of the petroleum industry

We used it as a percentage of 10,20,30and 40% of the mix vol.

ADMIXTURES Superplasticizer Type F has been used in all concrete mixes in constant dosage of 1.25 % of the cement weight.

This type is known as "sikament 163M" delivered from a local company.

Design of lightweight concrete & mix proportions To design the mix there are two methods: 1.Weight method

Where:C = wt. of cementC.L = wt. of coarse lecaF.L = wt. of fine lecaS = wt. of sandW = wt. of waterA = wt of adm.Y= unit wt.

2. Volumetric method

Where:C = wt. of cement S = wt. of sandW = wt. of water F = Foam = volume of foam used in cement content

Experimental Program

Properties of LWACFresh Concrete:Fresh unit weightSlump

Hardened Concrete:Hardened unit weightCompressive strengthSplitting tensile strengthFlexural StrengthBond strengthModulus of elasticityShrinkage

Results and Discussion

Introduction

In this chapter we will discuss the results of different tests which were carried out during our study .

Properties of fresh concrete

Fresh unit weight

As observed the unit weight varies between (1.16 to 1.632)

Slump

The slump value for the different concrete mixes has an average of 11cm.This was achieved by adding the 1.25% dosage of the super plasticizer.

Properties of Hardened Concrete

Hardened unit weight

It can be observed that the compressive strength increases as the unit weight increases

The hardened unit weight increases as the replacement percentage of fines with sand increases. Hardened unit weight and sand%

Compressive strengthEffect of sand replacement

The increase of sand replacement increase the cube compressive strength.

The increase of sand replacement increase the cube compressive strength. Compressive strength and sand%

Relation between fcu28&fcu7

Chart1

46.79

59.275

74.1

90.72

97.76

C = 400

Fcu 28 Days

Fcu 7 Days

Fcu 7 = 0.8324 Fcu28 + 3.8082

Sheet1

60.6746.79

86.5059.28

96.0074.10

106.5090.72

100.0097.76

143.00

Sheet2

Sheet3

Samples of tested cubes

Effect of sand replacement The splitting tensile strength increases with the increase of sand replacement percentage. Splitting tensile strength

Splitting tensile strength and compressive strengthThe increase of the compressive strength leads to the increase of the splitting tensile strength.

Samples of tested cylinders

Flexural strengthEffect of sand replacementFlexural strength increases with increase of sand replacement percentage

Flexural strength and compressive strength

The flexural strength increases with the increase of the compressive strength

Bond StrengthEffect of sand replacementThe bond strength increases with increase of sand replacement percentage

Bond strength and compressive strength

Sample of tested cylinders

Modulus of ElasticityModulus of elasticity and the percentage of sand

Modulus of Elasticity and Compressive strength

Shrinkage Drying

Drying shrinkage of LWAC made and cured at normal temperatures ranges from slightly 30% than that of some normal weight concrete. lightweight aggregate usually give higher shrinkage because it has low modulus of elasticity.

Effect of replacement percent of fines with sand

Sand replacement percentage increases the drying shrinkage decreases.

Presence of Silica Fume

ConclusionWe have found some results &conclusions regarding all the experimental work done

The fresh unit weight increases with the increase of the sand replacement percentage and with increase of cement content, ranges between (1.15-1.75).The slump value for the different concrete mixes has an average of 12 cm. This was achieved by adding the 1.25%-2.00% dosage of the super plasticizer The compressive strength (55 to 170 kg/cm2)increases as the unit weight increases (1.15 to 1.75 t/m3).

ConclusionThe increase of sand replacement increases the cube compressive strengthThe splitting tensile, bond, flexural strength increases with the increase of sand replacement percentage.Increase of cement content leads to increase of the splitting tensile strength this is due to increase of the cement paste and mechanical bond between coarse aggregate and cement paste.light weight concrete is a non structural concrete but have got low unit weight which Leads to many benefits as decreasing costs, having good thermal & sound insulation.