Aggregates should be hard, strong and durable. They must also be free of clay, loam, vegetable and other foreign materials. As far as possible, flaky and elongated pieces of stone should be avoided.
Proportions of concrete
Selection of materials Selecting the right building material is crucial for any construction. Although the contractor may be arranging the material, yet it is advisable for you as the house owner to be aware of methods to ascertain the quality of the material being used. This is especially important if you are not using ready-mix concrete.
Cement The cement used shall be any of the following and the type selected should be appropriate for the intended use: 33 grade OPC (IS 269) 43 grade OPC (IS 8112) 53 grade OPC (12269) Other types,Portland slag cement conforming to IS 455 Portland pozzolana cement (fly ash based) IS 1489 (Part 1) Portland pozzolana cement (calcined clay based)IS 1489 (Part 2) Hydrophobic cement conforming to IS 8043 Low heat Portland cement conforming to IS 12600 Sulphate resisting Portland cement conforming to IS 12330
Different Tests on cement Fineness (IS 4031 ) Soundness: Le-Chatelier Consistency of Standard Cement Paste Initial & final setting time Compressive Strength
Sand In technical language, sand is referred to as Fine Aggregates. Size of particles is less than 5 mm. River sand is cheapest source of natural aggregates. It should be free from dust, clay, silt and organic impurities. You can conduct a simple field test for sand: Hold some of the sand in hand, rub it and just throw it. Check your palm. Good sand will not stick to the palm.
COARSE AGGREGATESCrushed hard stone and gravel arecommon materials used as coarseaggregates for concrete work in India.Aggregates are available in sizes of40mm, 20mm and 10mm. For residentialslab, beam and column work, 20mm and10mm size of aggregates are generallyused
Tests on Aggregates(IS 2386)Part 1 particle size and shapePart 2 Estimation of deleterious & organicImpuritiesPart 3 specific gravity, Density, Voids,bulkingAbsorption.
WATERMunicipal water supplied for drinkingpurpose is generally considered fit forconstruction purpose. Additionally, youcan check if the water is free of oil,acids, salts and organic impurities. Sea-water and ground water shouldpreferably not be used for constructionpurposes.
IS Recommendations forWater To neutralize 100 ml sample of water, using phenolphthalein as an indicator, it should not require more than 5 ml of 0.02 normal NAOH IS 3025 (Part 22). To neutralize 100 ml sample of water, using mixed indicator, it should not require more than 25 ml of 0.02 normal H2O,. The details of ‘test shall be as given in 8 of IS 3025
BRICKS Bricks should be sound, hard and well burnt. They should be free from effloresces and be uniform in size, shape and colour. The bricks when struck together should produce a good metallic ringing sound. They must not break when dropped from a height of approximately a meter.
Steel IS 432 Mild steel and medium tensile steel bars and hard-drawn steel wire for concrete reinforcement : Mild steel and medium tensile steel bars IS 1789 High Strength Deformed Steel Bars and Wires for Concrete Reinforcement
Concrete Concrete is a composite construction material composed primarily of aggregate, cement, and water admixtures. Concrete has two main stages 1)Fresh Concrete 2)Hardened Concrete
Admixtures Accelerating admixtures Retarding admixtures Water-reducing admixtures and super plasticizers Air-entraining admixtures Foaming agents
Mixing, placing, finishing and curing of concreteMIXINGInvolves weighing out all the ingredients for a batch of concrete and mixing them together - A six-bag batch contains six bags of cement per batch - Hand-mixing (tools used) - Mixing with stationary or paving mixer - Mixing with truck mixers - Rated capacities of mixers vary from 2cu.ft. to 7cu.yd.
Segregation & Bleeding Segregation can be defined as separating out of the ingredients of a concrete mix, so that the mix is no longer in a homogeneous condition.Bleeding is due to the rise ofwater in the mix to the surfacebecause of the inability of thesolid particles in the mix to holdall the mixing water duringsettling of particles under theeffect of compaction.
POURING AND CONSOLIDATION Formwork must be in good condition to prevent leakage. limit of vertical free fall not more then .5m Care was taken to ensure that concrete is not over vibrated so as to cause segregation
Pumping and placing Concrete is conveyed to the construction site in wheel barrows, carts, belt conveyors, cranes or chutes or pumped (high- rise building) - Pumps have capacities to pump concrete Concrete should be placed as near as possible to its final position - Placed in horizontal layers of uniform thickness (6” to 20”) and consolidated before placing the next layer
Finishing: The concrete must be leveled and surface made smooth/flat -Smooth finish; Float/trowel finish; Broom finish; Exposed aggregatefinish
FINISHING CONCRETE SURFACE a) All concrete while being poured against form work was worked with vibrator rods & trowels as required so that good quality concrete is obtained. b) All exposed surface of RCC lintels, beams, columns etc. were plastered to match with adjoining plastered face of walls after suitably hacking the concrete surface.
Terms related to concrete Compressive Strength Tensile Strength(8-12% CS) Shear Strength (12-13% CS) Bond Strength (10% CS)
RMC concrete Vs Site mix concrete The quality of concrete is a critical factor in determining the durability and life of your construction. In case of site-mix concrete, the quality is variable and depends upon the limited expertise of the construction supervisor. The process is manual and non-standardised, and hence prone to human error.
Curing of concrete Curing requires adequate — Moisture Temperature Time
Methods of curing Ponding and Immersion Wet Coverings Fogging and Sprinkling Plastic Sheets Steam Curing Electrical, Oil, Microwave, and Infrared Curing
Proportions of concrete Use/Application Proportion on volumetric basis Cement Sand Stone AggregatesPlain Cement Concrete (PCC) 1 3 6RCC footing column, beam, slab, 1, 1 1.5, 2 3, 4(5,3)(M20) etc.Brick Masonry (23 cm and above) 1 6 -Brick Masonry (Less than 23 cm) 1 3 -Cement plaster on wall 1 4 -Cement plaster on ceiling 1 3 -Ceramic tiles fixing 1 4 - Flooring 1 2 4Cement concrete for 1 1.5 3footpath/internal roads in housingsocieties
Deshuttering periodDeshuttering period relates to the maturity of concrete anddepends on the ambient temperature. Forms shall not struckuntil the concrete has reached strength at least twice the stressof which the concrete may be subjected at the time of removalof form work.Assuming standard conditions of workmanship and quality ofmaterials, you can refer to the following time-frames for theremoval of forms.
Deshuttering period Form Summers Winters (Temp <18° C)Walls, columns and vertical faces of 24 hrs. 48 hrs.structural membersRemoval of props under slab 7 days 14 daysSpanning up to 4.5 mRemoval of props under beams and 14 days 28 daysarches spanning up to 6 m