Good Construction Practices Part II This report is solely for the internal use. No part of it may be circulated, quoted, or reproduced for distribution outside the company organization without prior written approval from ACC Limited. This material was used during an oral presentation; it is not a complete record of the discussion.
Curing Very necessary for strength and durability of concrete structure Do not start plastering before completion of Brickwork curing. 2
Curing By Hessian Clothes for columns & sides of beams Ponding on flat horizontal surface. 3
Curing 4
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Strength and Curing Strength 100% moist cured entire time in air after 7 days in air after 3 days in air entire time 28 time 7
Brickwork How to choose Bricks? All bricks should be of same size and color Bricks should be properly baked. If a brick is dropped from a height of 1 m, it should not break. Correct Practice: Bricks should be immersed in water at least two hours before use. Cement to sand proportion should be 1:5. Use the Mixed material within half n hour of mixing, otherwise it start loosing strength. Maximum 1 m work should be done in a day. All joints should be raked properly. 8
Mortar and Plaster Even though mortar makes up as little as 7% of the total volume of a masonry wall, it plays a crucial role in the performance of the structure. It not only bonds the individual units together, but it also seals the building against moisture and air penetration. It can be used to bond to anchors, ties or reinforcing. The mortar is literally the glue that holds the wall system together. The primary ingredient in mortar is Portland cement. Since Portland cement is also used in concrete, we need to make a few distinctions here. 9
Mortar Concrete is formulated to become a solid monolithic wall system by itself. The most important characteristic of concrete is compressive strength. Mortar, on the other hand, is formulated to bind masonry units together. There are several properties of mortar that can influence bond strength and durability. The most important qualities of mortar are bond strength and durability. 10
Requirements of mortar The single most important property of mortar is bond strength,. It is critical that this bond be complete, strong, and durable. The mechanical bond between individual bricks, blocks, or stones unifies the wall as a system, provides resistance to tensile stress, and seals against the penetration of moisture. 11
Factors affecting mortar properties The strength and extent of the bond are affected by many variables of material and workmanship. Complete and intimate contact between the mortar and the unit is essential, Workability influences the ease with which the mortar spreads and covers the surfaces. Rough units have a very porous surface that is highly receptive to the wet mortar and increases adhesion 12
Factors affecting mortar properties The moisture content and suction of the units, the water retention of the mortar. Curing conditions such as temperature, relative humidity, and wind combine to influence the completeness and integrity of the mechanical and chemical bond. Voids at the mortar-to-unit interface offer little resistance to water infiltration and facilitate subsequent disintegration In aligning the masonry, laboratory tests show that tapping the unit to level will increase bond strength 50 to 100% over hand pressure alone 13
Factors affecting mortar properties Often overlooked is the size/shape of mortar joints in that the ultimate compressive load capacity of a typical 3/8 in. bed joint will probably be well over twice the value obtained when the mortar is tested as a 2 in. (50.8 mm) cube. Mortars should typically be weaker than the masonry units, so that any cracks will occur in the mortar joints where they can more easily be repaired. 14
Factors affecting mortar properties Compressive strength of mortar increases with an increase in cement content and decreases with an increase lime, sand, water or air content. Retempering is associated with a decrease in mortar compressive strength. The amount of the reduction increases with water addition and time between mixing and retempering. It is frequently desirable to sacrifice some compressive strength of the mortar in favor of improved bond, consequently retempering within reasonable time limits is recommended to improve bond. 15
RCC Band at 1 m height which should be of 4 thick with two bars of minimum 8 mm Avoid corner windows in Load bearing structures 16
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Surface Preparation Before plastering concrete surface should be hacked properly ( Minimum 50 per sq.ft.) It is advisable to apply a base coat of cement paste on concrete surface, and cure it for three days to have a better bonding. A brick wall should be made wet a day before plastering 19
Surface Properties required The surface to be plastered should be accurately positioned overall and zones should not deviate excessively from a plane (or curved) surface. Ideally, the substrate should be rough; absorbent to a limited extent; strong; and clean, i.e. free of any film, such as dust, oil or paint, that could impair bond between plaster and substrate.. Roughness improves adhesion by providing a positive key for plaster to grip. Absorption removes the water film, between substrate and plaster, that would tend to weaken adhesion. Excessive absorption will however dry out the The strength of the substrate material should be greater than, or equal to, that of the hardened plaster. 20
Surface Preparation Background surfaces should ideally be at least as rough as coarse sandpaper or rough-sawn timber. Surface roughness can be achieved in one of the following ways: Using formwork with a rough surface, Stripping formwork early and wire brushing concrete Hacking Abrasive blasting (e.g. sand blasting) Applying a spatter dash layer 21
Surface Preparation Spatter dash is a mixture of one part of cement to one and a half parts of coarse sand with enough water for sluggishly pourable consistence. The mixture is thrown forcibly on to the wall, using a scoop or a brush with long, stiff bristles. (The impact drives out the water film at the interface between spatterdash and substrate and hence improves adhesion.) The Spatterdash should cover the substrate surface completely and form a rough texture with nodules about5 mm high. Spatterdash must not be allowed to dry out for at least three days. 22
Absorption Assess absorptiveness by throwing about a cupful of water against the surface. The surface will fall into one of the three categories: No water is absorbed. Some water is absorbed but most runs off. Most of the water is absorbed. First type of surfaces, include hard-burnt clay face bricks, glazed bricks and very dense high-strength concrete, should be prepared by applying a spatter dash Second type of surfaces should not require any treatment to control suction. Third type of surfaces should be wetted thoroughly and then allowed to become surface dry before the plaster is applied. 23
Surface - Monolithic concrete. Provide a rough surface by using rough-textured formwork, early stripping of formwork and wire brushing the concrete, hacking or abrasive blasting. (If none of these is practicable, apply a spatter dash coat after ensuring that the surface is clean.) Ensure that no form-release oil is left on the surface to be plastered. Clean down by water jetting or vacuuming. Conventional structural concrete should not require wetting to control suction. High-strength concrete may require the application of a spatter dash coat. 24
Surface - Brickwork Burnt clay brickwork If the surface is dusty, clean by brushing, water jetting Burnt clay stock bricks normally have a very high suction; pre-wet the wall and allow it to become surface dry before applying the plaster. Sun dried or poorly burnt soft clay brickwork This type of walling may be found in very old buildings, usually when restoration or repairs are being done. Care should be taken when removing the old plaster so as not to damage the bricks. Protect the wall from rain water once the bricks are exposed. Rake out the joints about 10 mm deep (the mortar is normally very soft). Brush down the wall to remove any loosely adhering material. Lightly dampen the wall and apply a spatter dash coat that improve adhesion. 25
Very Smooth Surface Result in to Poor Bonding. Use Bonding agent Or Hack the surface at close spacing 26
Surface making. 27
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