Concrete Technology HINDUSTAN CONSTRUCTION CO. LTD. HINCON HOUSE, L. B. S. MARG, VIKHROLI (WEST), MUMBAI – 400 083. INDIA.

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Presentation transcript:

Concrete Technology HINDUSTAN CONSTRUCTION CO. LTD. HINCON HOUSE, L. B. S. MARG, VIKHROLI (WEST), MUMBAI – INDIA.

Concrete is a mix of cement, fine aggregate, coarse aggregate, water, chemical admixtures and sometimes supplementary cementitious materials like Fly Ash, GGBS, Silica Fume etc. which, when placed in the skeleton of forms, allowed to hydrate and cured form a hardened mass with very high compressive strength. Introduction

Basic Ingredients of concrete

Cement Supplementary Cementitious Materials (Fly Ash, GGBS, Silica fume) Water Coarse Aggregates Fine Aggregates (Crushed & Natural) Admixtures Basic ingredients of concrete

Cement is the most important ingredient of concrete as it forms the binding medium for the discrete ingredients Cement

Cement

Cement portland cement + water  calcium silicate hydrate (CSH) + calcium hydroxide [Ca(OH) 2 ] Hydraulic reaction

Water Water is an important ingredient of concrete as it actively participates in the chemical reaction with cement. Since water helps to form the strength giving cement gel,the Quantity and Quality of water is required to be maintained. A popular yardstick to measure the suitability of water for mixing concrete is that, if water is fit for drinking it is fit for making concrete.

Aggregate Aggregates are important constituents in concrete & give body to the concrete Reduce shrinkage & Effect economy Occupy % of volume of concrete Classification Aggregates can be classified as: Normal weight aggregates Heavy weight aggregates

Aggregate Fine aggregates: Natural or manufactured sand with particles up to 10mm. Generally, sand particles almost entirely pass the 5mm sieve and are predominantly retained on the 75µm sieve. Coarse aggregates: Natural gravel or manufactured material. The particles are predominantly retained on the 5mm sieve.

Aggregate Size of Aggregates: MAS that can be used are governed by the following factors: Thickness of section Spacing of reinforcement Clear Cover Mixing, Handling, & placing techniques. MAS of 20mm is widely used for structural & Road Works. MAS of 10mm is used in shotcrete. MAS of 80 to 150mm is used for mass concreting.

Aggregate Shape of Aggregates: The shape of aggregates is an imp. characteristic since it affects the workability of concrete. Flaky particles have influence on workability, cement requirement, interlocking, strength, & durability.

Aggregate The grading, the shape and the texture of aggregates can significantly influence concrete workability. The amount of water required for a target workability is related to aggregate properties: Nominal maximum size of the coarse aggregate. Shape and texture of particles of fine and coarse aggregates. Grading of coarse aggregate.

Aggregate Angular sand (manufactured sand) can significantly increase the water demand and the cement content for a required slump. Very coarse sands and coarse aggregates can produce harsh, unworkable mixes. Changes in grading (or the shape / texture) of the aggregates can cause changes in the water demand of concrete, segregation and affect uniformity of concrete from batch to batch.

Aggregate Grading The fundamental idea is that finer stones fill up gaps between larger stones, and remaining space is filled by cement paste.

Admixtures Admixture can be defined as a chemical product which, is added to the concrete batch immediately before or during mixing or during an additional mixing operation prior to the placing of concrete for the purpose of achieving specific modifications to the normal properties of concrete. Admixtures are commonly classified by their function in concrete but often they exhibit some additional action.

Admixtures The different type of chemical admixtures are: Water Reducing Admixtures Retarding Admixtures High Range water reducing admixtures Accelerating Admixtures Air Entraining admixtures

Admixtures The purpose of use of admixtures is: To increase workability without increasing water content or to decrease water content at the same workability. To accelerate the rate of strength development at early ages To increase the strength. To retard or accelerate the initial setting To retard or reduce heat of hydration To increase durability or resistance to severe conditions of exposure.

Water Reducing Admixtures These are principally surface active agents (surfactants). Fine cement particles being very small clump together and flocculate when water is added to concrete. Plasticizers induce negative charge on the individual cement particles such that fine cement particles are dispersed due to inter particle repulsion.

Water Reducing Admixtures

Supplementary Cementitious Material Cementitious materials are finely divided siliceous or siliceous & aluminous materials having little or no cementitious properties and that will react chemically with calcium hydroxide (released from the hydration of portland cement), in the presence of moisture, to form compounds possessing cementing properties The common cementitious material used are: Fly Ash Ground Granulated Blast Slag Microsilica

How pozzolana reacts? pozzolan + Ca(OH) 2 + water  calcium silicate hydrate (CSH) Pozzolanic reaction Reacts with

Mix Design of concrete

Mix Design The objective in designing concrete mixtures is to determine the most economical and practical combination of available materials to produce a concrete that will satisfy the performance requirements under particular conditions of use. To fulfill this objective, a properly proportioned concrete mix will possess these qualities: Acceptable workability of freshly mixed concrete Durability, strength, and uniform appearance of hardened concrete Economy

Mix Design The design of concrete mix is based on the following factors: Grade of concrete Type of cement Maximum size of aggregate Maximum water-cement ratio Workability Minimum cement content

Steps for finalizing a mix design Step 1 – Compute the target strength for the desired grade of concrete as per requirements Step 2 – Select the workability requirements i.e., slump for the concrete appropriate for the work. The slump should be such that the concrete can be consolidated properly. Step 3 – Select the maximum size of aggregate. Step 4 – Estimate the amount of mixing water required for producing the desired slump.

Steps for finalizing a mix design Step 5 – If admixtures are added the appropriate reduction in water depending upon the type of admixture used must be done. Step 6 – Select the appropriate W/C or W/Cm ratio required for the achieving the desired target strength. Check that the W/Cm ratio is less than that specified in the codes for durability aspect Step 7 – Calculate the cement or cementitious material content. Check that the cement content calculated is more than the minimum cement content as specified in the codes for durability aspect.

Steps for finalizing a mix design Step 8 – Estimate the total aggregate content. Select the desirable proportion of coarse and fine aggregate depending upon the type of concrete. Step 9 – Conduct trial batches and check the fresh and hardened concrete properties. Step 10 – Adjust the mix proportions if required to get the desired results.

Properties of concrete

Portland Cement + Water + Sand + Gravel Cement Paste Mortar Concrete Paste = “Binder” or Continuous Phase Aggregate = Inert Filler or Discontinuous Phase Cement + Water Results in a Chemical Reaction (i.e. Hydration)

Composition of concrete VOL. %WT. % Air Water Portland Cement Sand ~75 Coarse Aggregate Portland Cement - Ceramic material made to precise mineralogical requirements Concrete - Composite material

Properties of concrete Plastic State Workability Slump Pumpability Finishability Air Content Mixing Uniform Property Transitional State Rate of Slump Loss Air Loss Setting Time Segregation Rate of Hardening Plastic Shrinkage Strength Drying Shrinkage

Properties of concrete Hardened State Compressive Strength Tensile Strength Flexural Strength Shear Strength Fracture Toughness Elasticity Poisson’s Ratio Porosity Pore Size Distribution Permeability Shrinkage Creep Fatigue Dynamic Properties Chemical Reactivity Abrasion Resistance Thermal Vol. Change Heat Capacity Thermal Conductivity Electrical Conductivity Density Texture Air Void System

Properties of concrete 3 Sources of failure of concrete Hydrated cement paste Interface between the hydrated cement paste and the aggregate Aggregate In order to increase compressive strength steps must be taken to strengthen these three sources

Properties of concrete Improving the strength of hydrated cement paste Compressive strength decreases with increasing pore size Compressive strength increases with decreasing grain size Microstructural inhomogeneities are a source of loss

Properties of concrete Increasing the strength of the transition zone Reducing water/cement ratio Using supplementary cementitious materials Use of smaller sized aggregates leads to homogenous distribution of water

Properties of concrete Search for strong aggregates Strength of natural aggregate depends on the nature of the parent rock Process particles to contain minimum amount of micro-cracks Single phase rocks are superior, ex. Limestone, dolomite, limestone, granite Avoid rocks with weak cleavage planes or severely weathered

Effect of use of supplementary cementitious material in concrete

Fly Ash Fly Ash is a finely divided residue that results from combustion of pulverised coal & it transported from the combustion chamber by exhaust gases.

Advantage of Fly Ash to fresh concrete Improved workability. The spherical shaped particles of fly ash act as miniature ball bearings within the concrete mix, thus providing a lubricant effect. This same effect also improves concrete pumpability by reducing frictional losses during the pumping process and flat work finishability.

Advantage of Fly Ash to fresh concrete

Decreased water demand. The replacement of cement by fly ash reduces the water demand for a given slump. When fly ash is used at about 20 percent of the total cementitious, water demand is reduced by approximately 10 percent. Higher fly ash contents will yield higher water reductions. The decreased water demand has little or no effect on drying shrinkage/cracking. Some fly ash is known to reduce drying shrinkage in certain situations.

Advantage of Fly Ash to fresh concrete

Reduced heat of hydration. Replacing cement with the same amount of fly ash can reduce the heat of hydration of concrete. This reduction in the heat of hydration does not sacrifice long-term strength gain or durability. The reduced heat of hydration lessens heat rise problems in mass concrete placements.

Advantage of Fly Ash to fresh concrete

Ease in Pumping – More paste volume and spherical shape of fly ash particles aids in easy pumping of the concrete. Improved Finishing – More paste volume and lesser bleeding and segregation of concrete mix during placement and compaction leads to better finishing.

Advantage of Fly Ash to fresh concrete Reduced Bleeding & Segregation – Improved cohesiveness of fly ash concrete reduces bleeding and segregation. Fewer bleed channels decreases porosity and chemical attack. Reduce Slump Loss – More dependable concrete allows for greater working time, especially in HOT WEATHER conditions as in our country.

Advantage of Fly Ash to fresh concrete

Advantage of Fly Ash to hardened concrete Increased ultimate strength. The additional binder produced by the fly ash reaction with available lime allows fly ash concrete to continue to gain strength over time. Mixtures designed to produce equivalent strength at early ages (less than 90 days) will ultimately exceed the strength of straight cement concrete mixes.

Advantage of Fly Ash to hardened concrete

Aggregate – Matrix Interface – The weakest link in the concrete micro structural chain is the aggregate matrix transition zone. This happens because, at the transition zone, the no. of surface irregularities allows for collection of water.Therefore, this is the prime site for the formation of CH crystals. These crystals are oriented and fail easily. On addition of fly ash, the interface is strengthened because the Calcium Hydroxide is consumed in the pozzolanic activity and there results the Cementitious binding gel CSH.

Advantage of Fly Ash to hardened concrete

Decreased Permeability Reduced Water demand, Increased density and long term pozzolanic action of fly ash, which ties up free lime, results in fewer bleed channels and decreases permeability. Lower permeability offers resistance to chloride ion penetration and prevents corrosion of reinforcement.

Advantage of Fly Ash to hardened concrete

Improved durability. The decrease in free lime and the resulting increase in cementitious compounds, combined with the reduction in permeability enhance concrete durability. This affords several benefits:

Advantage of Fly Ash to hardened concrete Improved resistance to ASR. Fly ash reacts with available alkali in the concrete, which makes them less available to react with certain silica minerals contained in the aggregates.

Advantage of Fly Ash to hardened concrete

Improved resistance to sulfate attack Fly ash consumes the free lime making it unavailable to react with sulfate The reduced permeability prevents sulfate penetration into the concrete Replacement of cement reduces the amount of reactive aluminates available Improved resistance to corrosion. The reduction in permeability increases the resistance to corrosion.

Advantage of Fly Ash to hardened concrete

Ground Granulated Blast Slag Non-metallic product, consisting essentially of silicates and alumino-silicates of calcium and other bases, that is developed in a molten condition simultaneously with iron in a blast furnace used in steel making. Molten slag floating above the denser molten iron which consists of calcium and magnesium from the fluxing stone, alumina and silica from the iron ore, and the ash from the coke. The molten slag is then drawn off the furnace & cooled rapidly.

Benefits of using GGBS Increased compressive and flexural strengths Reduced permeability Improved chemical resistance Reduced Alkali Silica Reaction expansion Increased workability Lower heat of hydration Improved de-icer scaling resistance Lighter color

Chemical Composition

Silica Fume Silica fume is a by-product in the production of Silicon or Ferro Silicon industry Silica fume has a very high Specific Surface Area: 13, ,000 m 2 /kg versus m 2 /kg for cement Due to its high fineness it is highly pozzolanic in nature

Benefits of using Silica Fume Water demand: Silica fume has a very high sp. surface area, which results in having a greater water demand Increased water demand of SF concrete can be overcome by using HRWRA Bleeding: Reduced bleeding. Expected, because of high water demand of SF, results in very little water left in mixture to bleed Cohesiveness: More cohesive, less prone to segregation.Thus, advantageous in “flowing” and “pumped” concrete.

Benefits of using Silica Fume Plastic shrinkage: Cracking associated with curing conditions.Result of faster evaporation of water from surface than water replaced by bleeding from underneath. Since SF reduces bleeding, SF concrete is prone to plastic shrinkage cracks. High wind velocity and high temperature pose a serious problem

Benefits of using Silica Fume Compressive Strength: Due to its high pozzolanic reactivity, SF concrete gain very high strengths in early ages. Very helpful for precast concrete Permeability: Significant decrease in permeability. Attributable to fine pore structure and refined ITZ

Benefits of using Silica Fume Durability Aspects Control of Alkali Aggregate Reactivity (AAR): Very effective in reducing AAR. Fine SF particles react rapidly with cement alkalis, leaving little or none to react with Aggregates. Furthermore, SF reacts with CH, thus lowers the pH of pore solution. Increased Chemical and Sulfate Resistance: Chemical resistance increased - SF reacts with CH. So, no CH available to leach out. Modified pore structure and decreased permeability

Durability of concrete

Durability of concrete can be defined as the resistance of concrete to deteriorating influences which may be inside the concrete itself or which may be present in the environment to which it is exposed Durability of concrete largely depends on the ease with which fluids, both liquids and gases, can enter into and move through the concrete. This property is known as permeability of concrete.

Durability of concrete Concrete Deterioration PhysicalDeteriorationChemicalDeteriorationReinforcementCorrosion

Durability of concrete Concrete Deterioration PhysicalDeteriorationChemicalDeteriorationReinforcementCorrosion Carbonation Chlorides

Carbonation In presence of moisture CO 2 present in air reacts with Ca(OH) 2 to form CaCO 3 Carbonation causes the reduction in pH of pore water from between 12.6 to 13.5 to about 9 Steel embedded in concrete forms a thin passivity layer of oxide which remains only with high pH As the pH reduces the oxide layer is removed and the corrosion of steel starts, its volume increases and creates tensile stresses in concrete

Chloride attack The primary action in chloride attack is the corrosion of steel and consequently damage to surrounding concrete As long as the oxide film on steel is present, the steel remains intact Chloride ions destroy the film and in presence of water and oxygen corrosion occurs Corrosion does not occur in dry or fully submerged concrete, but occurs in alternate wetting & drying and in relative humidity of 70-80%

Chloride attack Chlorides can be present in concrete through use of contaminated aggregates, sea water or chlorides in admixture I.S. code states that total chloride content in cement should not be exceed 0.05% by mass of cement I.S states that total chloride content in concrete should not exceed 0.4 & 0.6 kg/m 3 for prestressed and reinforced / plain concrete containing embedded metal respectively

Durability of concrete Concrete Deterioration PhysicalDeteriorationChemicalDeteriorationReinforcementCorrosion SulphateAcid Sea water Alkali-aggregatereactionLeaching

Sulphate attack Sulphates present in solution react with hydrated cement paste Common sulphates present in soil and ground water are sodium, potassium, magnesium, calcium Sodium sulphate attacks Ca(OH) 2 and gypsum is deposited. Ca(OH) 2 can also be completely leached out Magnesium sulphate attacks calcium silicate, calcium aluminate hydrates & also Ca(OH) 2

Sulphate attack Ettringite formed has a higher volume and causes expansion in concrete Calcium sulphate attacks calcium aluminate hydrate (C 3 A) forming ettringite Preventive measures Use cement with less C 3 A content i.e, to use sulphate resistant cement Reduce the quantity of Ca(OH) 2 by using Fly ash or GGBS

Sulphate attack Specimens are stored in solution of sodium or magnesium sulphate and subjected to alternate wetting and drying This accelerates the damage due to crystallization of salts in the pores of concrete The effect of exposure can be estimated by the loss in strength of specimen

Alkali-Aggregate Reactivity Reaction between active silica constituents of aggregates and alkali in cement forms alkali-silicate gels in planes of weakness or either in pores or surface of aggregates The reaction starts with attack on siliceous minerals in aggregates by alkaline hydroxides in pore water derived from the alkalis (Na 2 O or K 2 O) in cement This gel is of unlimited swelling type, absorbs water and causes increase in volume

Alkali-Aggregate Reactivity I.S Part VII states two tests for determining the potential reactivity of aggregates: Mortar Bar Test Chemical methods

Durability of concrete Concrete Deterioration PhysicalDeteriorationChemicalDeteriorationReinforcementCorrosion Cracking FrostAttrition Fire

4 essential C’s for durability of concrete Ensure design Cover is maintained Ensure sufficient Cementitious material and proper w/c ratio Ensure adequate Compaction so there is no honeycombing Ensure good Curing so that design strength is attained (esp. At surface)

CONCRETE AT OUR SITE WE ARE USING HIGH PERFORMANCE CONCRETE HIGH DENSITY CONCRETE NORMAL CONCRETE HIGH VOLUME FLY ASH CONCRETE SELF COMPACTING CONCRETE

HIGH PERFORMANCE CONCRETE HIGH PERFORMANCE CONCRETE IS THE ONE WHICH IS THE ONE SPECIALY DESIGNED TO PERFORM AT SPECIFIED REQUIRMENTS IN BOTH ITS FRESH AND HARDENDED STATE. MAIN PARAMETRES ARE HIGH STRENGTH AND IMPERMEABILTY IN ITS HARDENDED STATE.

TESTS FOR HIGH PERFORMANCE CONCRETE

Thank You