Concrete : Its Ingredients and Properties

WHAT IS CONCRETE? Vinod Kumar Singh Co-Founder, Happho https://happho.com https://happho.comis an Online Marketplace for Construction Material & One Stop Solution for Bungalow Construction & Interiors © Happho

CONCRETE Basic Definition: Concrete is a composite material that essentially consists of a binding medium (typically cement paste) embedded with Fine-Aggregate (typically sand) and Coarse Aggregate (typically gravel) with or without chemical and mineral admixture. • Constituents: • Mixture of aggregate and paste • Cement paste - 30 to 40% • Portland cement + Mineral Admixture 7% to 15% by Vol. • Water + Chemical Admixture 14% to 21% by Vol. • Aggregates - 60% to 70% • coarse aggregates • Fine aggregates © Happho

CONCRETE – Typical Ingredients Proportion (By Volume) © Happho

CONCRETE – Universal Construction Material • Concrete is neither as strong nor as tough as steel, so why is it the most widely used engineering material? There are at least three primary reasons. • Concrete possesses excellent resistance to water • The second reason for the widespread use of concrete is the ease with which structural concrete elements can be formed into a variety of shapes and sizes • The third reason for the popularity of concrete with engineers is that it is usually the cheapest and most readily available material on the job Quantity of concrete consumed by humankind is next only to water. © Happho

Basic Concrete Ingredients CEMENT NATURAL SAND Coarse Aggregate WATER © Happho

CONCRETE – IN FRESH STATE © Happho

Cement – As Concrete Ingredient Portland cement, the basic ingredient of concrete, is a closely controlled chemical combination of calcium, silicon, aluminium, iron and small amounts of other ingredients to which gypsum is added in the final grinding process to regulate the setting time of the concrete. Lime and silica make up about 85% of the mass. Common among the materials used in its manufacture are limestone, Bauxite, laterite, shells, shale, clay, slate or , silica sand, and iron ore. © Happho

Cement – As Concrete Ingredient Portland Cement • Dry powder of very fine particles • Forms a paste when mixed with water • Chemical reaction with water-Hydration • Forms Gel • Paste coats all the aggregates together • Hardens and forms a solid mass Primary role is to give binding property & strength to concrete © Happho

Cement – As Concrete Ingredient Types of Portland Cement • Ordinary Portland Cement (IS 12269) Typically 95% Clinker & 5% Gypsum - 43 Grade (IS 8112) [less grinding, low surface area, strength target 43MPa+) - 53 Grade (IS 12269) [high grinding, high surface area, strength target 53MPa+) • Portland Pozzolana Cement (IS 1489) Typically 85 to 65% clinker, Fly Ash (by product of thermal power plant) 15 to 35% & 3 to 5% Gypsum) • Portland Slag Cement (IS 455) Typically 65 to 30% clinker, GGBF Slag (by product of iron industries) 35 to 70% & 3 to 5% Gypsum) As all cement differ (chemically, physically & mineralogically) in their formulation, they can’t be substitutes to each other in a given concrete mix. © Happho

With increase in Cement Content : Concrete At a given Water/Cement ratio, higher workability can be achieved with addition of more cement(because of high paste content, ball bearing affect) Cement – As Concrete Ingredient © Happho

With increase in Cement Content : Concrete Strength increases (w/c ratio constant) Cost Increases Volume instability( chances of plastic and drying shrinkages increases) being the most reactive ingredient. Cement content has to be kept bear minimum( considering all design requirements) to get a economical & good concrete. Cement – As Concrete Ingredient © Happho

Water – As Concrete Ingredient Water : • Needed for two purposes: • Chemical reaction with cement • Workability • Only 1/3 of the water is needed for chemical reaction • Extra water remains in pores and holes • Results in porosity • Good for preventing plastic shrinkage cracking and workability • Bad for permeability, strength, durability. Primary role is cement hydration Water is necessary evil in a concrete mix © Happho

Aggregate – As Concrete Ingredient Aggregate: • Economical Inert filler material • Hard material • Provide volume stability • Reduce volume changes • Provide abrasion resistance Basic role is to give volume stability ,higher the cement content concrete is more prone to shrinkage. © Happho

Aggregate – As Concrete Ingredient Aggregates are generally classifiedaccording to particle size, bulk density, or source). • Coarse aggregate is used to describe particles larger than 4.75 mm. • Fine aggregate (Sand) is used for particles smaller than 4.75mm; typically, Fine aggregates contain particles in the size range 75 µm to 4.75 mm, and coarse aggregates from 4.75 to about 50 mm, except for mass concrete which may contain particles up to 150 mm. Fine Aggregate and Coarse Aggregate are proportioned in a concrete mix to give maximum packing density (Grading of each aggregate would influence there proportion among each other ) Generally, aggregate properties affect not only the concrete mixture proportions but Also the behavior of fresh and hardened concrete. © Happho

Aggregate – As Concrete Ingredient A knowledge of certain aggregate characteristics (i.e., density, grading, and moisture state) is required for proportioning concrete mixtures. Porosity or density, grading, shape, and surface texture determine the properties of plastic concrete mixtures. Size and Grading : • There are several reasons for specifying grading limits and maximum aggregate size, the most important being their influence on workability and cost. For example, very coarse sands produce harsh and unworkable concrete mixtures, and very fine sands increase the water requirement (therefore, the cement requirement for a given water-cement ratio is uneconomical). • Aggregates that do not have a large deficiency or excess of any particular size produce the most workable and economical concrete mixtures. © Happho

Size and Grading : Larger the particle size, the higher the slump for a given paste content. (Larger particles, less surface area, thicker coating, easy sliding (ball bearing affect) of particles. Smaller particles, more surface area, thinner coating, interlocking of particles. Shape: Flakiness Index: Thickness being 0.6 times their mean dimension, contributes more surface area for a unit volume occupied. Elongation Index: Greatest dimension being 1.8 times their mean dimension, contributes more surface area for a unit volume occupied. High flaky and elongated aggregates (>25%) requires high cement content to produce a required workable mix. Angular/spherical shape of aggregate are best for concrete making Aggregate – As Concrete Ingredient © Happho

Fineness Modulus (F.M): Empirical factor called the Fineness modulus is often used as an index of the fineness of aggregate. The fineness modulus is computed from screen (sieve) analysis data by adding the cumulative percentages of aggregate retained on each of a specified series of sieves, and dividing the sum by 100. The sieves used for determining the fineness modulus are: No. 100 (150 µm), No. 50 (300 µm), No. 30 (600 µm), No. 16 (1.18 mm), No. 8 (2.36 mm), No. 4 (4.75 mm), 10 mm,20mm,40mm etc. Sand with Fineness Modulus in the range of 2.4 – 3.0 are best for concrete preparation Higher the F.M the greater proportion of fine aggregate in a given concrete mix Example : F.M = 2.6 : Sand = 35% ,C.A = 65% F.M = 3.0 : Sand = 40% ,C.A = 60% Aggregate – As Concrete Ingredient © Happho

Slit Content :Material finer than 75-µm (No. 200) sieve are generally called slit. They affect the workability as water demand increases, strength is also influenced along with bonding. IS (Indian Standard) limit is 3% by weight. → 1% Silt can reduce concrete strength by 15% GENERAL ACCEPTACE CRITERIA BY VOLUME: After 10mins = 12% After 2hrs. = 8% For durable concrete washed sand is advisable, with zero silt in sand considerable amount of cement content can be reduced. Aggregate – As Concrete Ingredient © Happho

Aggregate primarily acts as a inert filler, but has secondary influences on various concrete properties. Awareness about the role played by aggregate in concrete can be instrumental in exploiting the use of the same in achieving concrete properties as per intended requirements, which would be of high performance and economical. It is inappropriate to treat the aggregate with any less respect than cement. Aggregate – As Concrete Ingredient © Happho

Admixtures are material other than cement, aggregates & water that are added to concrete either before or during mixing to alter its properties & performance in fresh (workability, setting time etc) and hardened state (strength, durability etc.) CONCRETE ADMIXTURES ARE BROADLY DIVIDED INTO TWO TYPES i.e. 1.Chemical Admixtures (Water Reducers, Super plasticizers, Retarders, Accelerators etc.) 2.Mineral Admixtures (Fly Ash, GGBFS, Metakaoline, Silica Fumes etc.) Admixtures – As Concrete Ingredients © Happho

Typically incorporated to improve the following concrete properties Protect Against Freeze Thaw Cycles –Improve Durability Water Reduction in the Mix Mid- Range water reducers High-Range water reducers – superplasticizers High Strength Concrete Corrosion Protection Set Acceleration Strength Enhancement Set Retardation Crack Control (shrinkage reduction) Flowability Self leveling Finish Enhancement Admixtures – As Concrete Ingredients © Happho

Chemical Admixtures – As Concrete Ingredients • Chemical admixtures are used to improve the quality of concrete during mixing, transporting, placement and curing. They reduce the cost of construction, modify properties of hardened concrete, ensure quality of concrete during mixing/transporting/placing/curing, and overcome certain emergencies during concrete operations. • They are basically chemical compounds. Dosage ranges from 0.2% to 2% by weight of cement. They fall into the following categories: • Air entrainers • Water reducers • Set retarders • Set accelerators • Super-plasticizers • Specialty admixtures: which include corrosion inhibitors, shrinkage control, alkali-silica reactivity inhibitors, and coloring. © Happho

Chemical Admixtures – As Concrete Ingredients • Air entraining Admixtures: Air-entraining agents entrain small air bubbles in the concrete. The major benefit of this is enhanced durability in freeze-thaw cycles, especially relevant in cold climates. • Retarding Admixtures: Retarding admixtures slow down the hydration of cement, lengthening set time. Retarders are beneficially used in hot weather conditions in order to overcome accelerating effects of higher temperatures and large masses of concrete on concrete setting time • Accelerating admixtures: : Accelerators shorten the set time of concrete, allowing a cold-weather pour, early removal of forms, early surface finishing, and in some cases, early load application. © Happho

Chemical Admixtures – As Concrete Ingredients • Water Reducing Admixtures : Water reducing admixtures require less water to make a concrete of equal slump, or increase the slump of concrete at the same water content. Typical water reduction is the range of 10 – 15%. • Superplasticizers : High range water reducers are admixtures that allow large water reduction or greater flowability (as defined by the manufacturers, concrete suppliers and industry standards) without substantially slowing set time or increasing air entrainment. • Specialty admixtures: Include corrosion inhibitors, shrinkage control, alkali-silica reactivity inhibitors, and coloring. © Happho

Chemical Admixtures – As Concrete Ingredients Using a Water Reducer: Option 1 • To get a stronger and more durable concrete from a given amount of cement by allowing reduction of water-cement ratio • Most regular water reducers will permit 5-15% reduction water Example: • Original mix: 330 kg cement, 181.5 kg water, w/c = 0.55 strength at 28 days = 30 MPa • Mix with water reducer 330 kg cement, 165 kg water, w/c = 0.5 strength at 28 days = 36 MPa © Happho

Chemical Admixtures – As Concrete Ingredients Using a Water Reducer: Option 2 • For a given w/c a mix may turn out to be unworkable • Add water reducer to increase slump without making adjustment to mix proportions • Results in better workability of the mix and slight increase in strength © Happho

Chemical Admixtures – As Concrete Ingredients Using a Water Reducers: Options 3 • Economy: a concrete with the same w/c and same strength can be produced with less cement. • Normally the extra cost for the water reducer is more than offset by savings in cement. Example →Original Mix 330 kg cement, 165 kg water, w/c =0.5 →Mix with WR (10% water reduction) 150 kg water, For w/c = 0.5 cement required = 300 kg. ÎSave 30 kg cement/m 3 of concrete) © Happho

Mineral Admixtures – As Concrete Ingredients • Mineral admixtures affect the nature of the hardened concrete through hydraulic or pozzolanic activity. Pozzolans are cementitious materials and include natural pozzolans (such as the volcanic ash used in Roman concrete), fly ash, Silica Fume, Metakaolin, Rice Husk Ash, GGBFS. • Mineral admixtures make mixtures more economical (enables reduction in total cement content), reduce permeability, increase strength, and influence other concrete properties. • They can be used with Portland cement, or blended cement either individually or in combinations. © Happho

Mineral Admixtures – As Concrete Ingredients • Fly Ash (By product of Thermal Power Plant) : • Derived from burning coal, fly ash is a valuable additive that makes concrete stronger, more durable and easier to work with. • Fly ash aids the formation of cementitious compounds to enhance the strength, impermeability and durability of concrete. • →Two main classes of fly ash are used in concrete, Class F, and Class C. • Class F • Reduces bleeding and segregation in plastic concrete. In hardened concrete, increases ultimate strength, reduces drying shrinkage and permeability, lowers heat of hydration and reduces creep. • Class C • Provides unique self-hardening characteristics and improves permeability. Especially useful in pre-stressed concrete and other applications where high early strengths are required. Also useful in soil stabilization. © Happho

Mineral Admixtures – As Concrete Ingredients • Fly Ash (By product of Thermal Power Plant) : • In addition to economic and ecological benefits, the use of fly ash in concrete improves its workability, reduces segregation, bleeding, heat evolution and permeability, inhibits alkali-aggregate reaction, and enhances sulfate resistance. • Even though the use of fly ash in concrete has increased in the last 20 years, less than 20% of the fly ash collected was used in the cement and concrete industries • One of the most important fields of application for fly ash is PCC pavement, where a large quantity of concrete is used and economy is an important factor in concrete pavement construction. © Happho

Mineral Admixtures – As Concrete Ingredients • Silica Fume (By product of Silicon and Ferro-Silicon Alloy) : • When measured by nitrogen absorption techniques, its particles are approximately 100 times smaller than the average cement particle. Because of its extreme fineness and high silica content, Silica Fume is a highly effective pozzolanic material • Silica fume can make a significant contribution to early-age strength of concrete. One kilogram of silica fume produces about the same amount of heat as a kilogram of Portland cement, and yields about three to five times as much compressive strength. • Silica fume improves concrete in two ways – the basic pozzolanic reaction, and a micro filler effect. Addition of silica fume improves bonding within the concrete and helps reduce permeability, it also combines with the calcium hydroxide produced in the hydration of portland cement to improve concrete durability. © Happho

Mineral Admixtures – As Concrete Ingredients • Silica Fume (By product of Silicon and Ferro-Silicon Alloy) : • As a microfiller, the extreme fineness of the silica fume allows it to fill the microscopic voids between cement particles. This greatly reduces permeability and improves the paste-to-aggregate bond of the resulting concrete compared to conventional concrete. • Silica Fume is used in concrete to improve its properties. It has been found that Silica Fume improves compressive strength, bond strength, and abrasion resistance; reduces permeability; and therefore helps in protecting reinforcing steel from corrosion. • Caution: • The higher percentage of silica fume used, the higher the amount of super plasticizer needed - but mix can become "sticky“. © Happho

Mineral Admixtures – As Concrete Ingredients • Ground Granulated Blast Furnace Slag (By product of Iron Industries) : • Ground granulated blast-furnace slag is the granular material formed when molten iron blast furnace slag is rapidly chilled (quenched) by immersion in water. It is a granular product with very limited crystal formation, is highly cementitious in nature and, ground to cement fineness, hydrates like Portland cement. • Concrete containing GGBFS as a partial cement replacement has longer-lasting workability and low slump loss during hot weather construction. • Concrete containing GGBFS exhibits a lower heat of hydration than conventional Portland cement concrete. • The use of GGBFS as a partial replacement for Portland cement can reduce available alkalies and can reduce the reaction between certain siliceous components of concrete aggregates and the alkalies in the concrete • Use of GGBFS as a partial cement replacement gives concrete moderate resistance to sulfate attack © Happho

Mineral Admixtures – As Concrete Ingredients • Metakaolin: • Calcination of Kaolin (a fine, white clay mineral), results a highly pozzolanic material called matakaolin • Rice Husk Ash : • Rice milling generates a by product know as husk . This surrounds the paddy grain. During milling of paddy about 78 % of weight is received as rice , broken rice and bran .Rest 22 % of the weight of paddy is received as husk . This husk is used as fuel in the rice mills to generate steam for the parboiling process • This husk contains about 75 % organic volatile matter and the balance 25 % of the weight of this husk is converted into ash during the firing process , is known as rice husk ash ( RHA ). This RHA in turn contains around 85 % - 90 % amorphous silica © Happho

Mineral Admixtures – As Concrete Ingredients • Mineral and Chemical Admixture play a very important role in concrete, its judicious selection improves its fresh and hardened concrete properties & enhances its long terms performance. • New age concrete like Self Compacting Concrete, High Volume Fly Ash Concrete, High Performance Concrete etc, would not have been realized without the availability / incorporation of mineral and chemical admixture. • Mandatory use of mineral and chemical admixture should be encouraged in order to attain true sustainable development. © Happho

Placing, Compaction & Curing of Concrete Planning: Spaces to receive concrete are clear free from debris and free from water. Foundations to be concreted in layers of thickness not exceeding 300mm. Columns to be cast in one or maximum 2 lifts between the floors(window to restrict concrete free fall to 1.5m), lift height not exceeding 3.0m for individual lifts. Slabs to be cast in strips and not in alternate bays. Construction joint locations should be approved or as shown in drawings Items like insert, pipe sleeves, water stop, pipe, bolt & other fixtures should be provided as given in the good for construction drawing. All works should be true to level, plumb and square and all corners and edges in all cases should be unbroken & neat. © Happho 36

Placing, Compaction & Curing of Concrete Transportation & Placing All concrete should be transported with the help of transit mixers to the place of laying as rapidly as possible. When a truck mixer of agitator is used for transporting concrete, the concrete should be delivered to the site of work and discharge should be complete within 3 hrs from plant exit. Acceptable temperature of concrete, air temperature & shade temperature etc. should be as per specifications and verified by supplier before delivery. Placing of concrete should generally be done using pumps to achieve necessary heights wherever required. In case of deep trenches/footings, it may be done with the help of chutes or directly from transit mixers from the reasonable height. © Happho 37

Placing, Compaction & Curing of Concrete Transportation & Placing In columns it can be placed manually with the help of staging. Concrete from wheel barrows should be dumped into the face of concrete already in place. Suitable platform should be provided for working wherever required. © Happho 38

Placing, Compaction & Curing of Concrete Transportation & Placing The concrete should be deposited as nearly as practicable in its final position to avoid re-handling. The concrete should be placed and compacted before initial setting of concrete commences and should not be subsequently disturbed. Concrete should be placed in layers. Bottom layer should not finally set before the top layers are placed. Methods of placing should be such as to avoid segregation. Care should be taken to avoid displacement of reinforcement or movement of formwork. Formwork should be continuously watched during and after the concreting. In case of leakages, bulging or sagging immediate action should be taken before initial setting of the concrete. © Happho 39

Placing, Compaction & Curing of Concrete Compaction • Concrete should be thoroughly compacted and fully worked around the reinforcement, around embedded fixtures and into corners of the formwork. Note: If no care is taken during vibration, it may result in honey combing. Remember 5 % Voids in Concrete , reduces strength of concrete by 30% © Happho 40

Placing, Compaction & Curing of Concrete Precautions: Don’t use a vibrator to move concrete horizontally Don’t start a job without a spare vibrator Concrete should not be over vibrated Stop vibrating concrete when the concrete surface takes on a shining appearance Stop vibrating concrete when larger air bubbles no longer escape Stop vibrating concrete when there is a change in the pitch or tone of the vibrator. © Happho 41

Placing, Compaction & Curing of Concrete Precautions: Take extra precautions in locations of abrupt section change Set concrete not to be disturbed by successive vibration. Remember Cube test cannot check degree of compaction achieved in-situ. Poor vibration may take all the difference between good and poor quality concrete. Vibration is a skilled job. Insist on a qualified operator. It will be good for the concrete and make the operator take pride in his work. © Happho 42

Placing, Compaction & Curing of Concrete After Pouring Precautions Finishing: Roof should be troweled even & smooth with wooden float before concrete begins to set. Surface that will receive plaster should be roughened immediately. Surface in contact with masonry should be roughened immediately. Surface that will receive floor finishes, tiling etc. should be roughened while it is still green. Freshly laid concrete should not be disturbed For ramps and basement concrete should be broom finished. © Happho 43

Placing, Compaction & Curing of Concrete After Pouring (Placing Concrete) Precautions. After removal of formwork from vertical members, the concrete surface is checked for defects if any. All minor defects if appeared, to be rectified immediately. Hessian cloth should be wrapped on the surface of columns for curing. After 24 hrs of laying of concrete, the surfaces should be cured by either ponding or covering with moist Hessian cloth for period of 7 days. © Happho 44

New Generation Concrete High Performance Concrete (HPC): The American Concrete Institute defines HPC as concrete that meets special performance and uniformity requirements that cannot always be obtained using conventional ingredients, normal mixing procedures, and typical curing practices. High Performance Concrete is a specialized series of concrete designed to provide several benefits in the construction of Concrete Structures. © Happho

New Generation Concrete Self Compacting Concrete (SCC): • Self-compacting concrete (SCC) is an innovative concrete that does not require vibration for placing and compaction. It is able to flow under its own weight, completely filling formwork and achieving full compaction, even in the presence of congested reinforcement. • The hardened concrete is dense, homogeneous and has the same engineering properties and durability as traditional vibrated concrete. MIX DESIGN • High Cementitious Content • Low Coarse Aggregate Content & Increase Fine Aggregate Content • Smaller Maximum Aggregate Size. • High Range Water Reducing Agent • Viscosity Modifying Agent © Happho

New Generation Concrete Self Compacting Concrete (Continued): Benefits. • Faster construction (Rapid speed of concrete placement) • Reduce noise pollution (no vibrators used) • Superior level of finish • Less energy required • Less labor required. • SCC often designed with low water cement ratio has potential of high strength and durable concrete etc. Application: • Elements with thin wall. • Area of dense reinforcement • Drill Shaft etc. © Happho

New Generation Concrete HIGH VOLUME FLY ASH CONCRETE (HVFA): • Incorporates high volumes of fly ash (~50% by weight of total cementitious content) • Low water and OPC content. • Superplasticizer being mandatory to achieve high slump. ADVANTAGES: • Use of a byproduct otherwise wasted-disposal problem. • Economical • Better Concrete • Conservation of resources • Reduction in CO2 emission. APPLICATIONS: • Mass Concrete • Structural and non-structural purposes. • Severe to very severe environments. © Happho

New Generation Concrete OTHERS: Fiber-Reinforced Concrete. A new approach to reinforcing concrete is the use of steel fibers, about 0.014 inch in diameter and 1.5 inches long, uniformly distributed and randomly directed throughout the concrete mix. Such fibers can be utilized either in ordinary reinforced concrete or pre-stressed concrete to increase the tensile strength and resistance to cracking. © Happho

Concrete : Its Ingredients and Properties