This should be prepared by mixing coarse aggregate and lime mortar in the specified proportions with required quality of water.
i) Proportioning: The proportions of aggregate to lime mortar should be done by volume. Generally lime is prepared by mixing 100 parts of 40 mm nominal size graded stone aggregate, gravel or brick aggregate as specified and 40 parts of lime mortars of the specified mix.
ii) Mixing: Mixing of concrete should be done in a mechanical mixer. Before mixing brick aggregates should well soaked with water for at least 2 hours and mortar 10-15 mm thick composed of cement and sand in the same proportion in the concrete mix. This should be freshly prepared and applied immediately before placing of
concrete.
Where the concrete has not fully hardened, all maintenance should be removed by scrubbing with wire brushes and the surface should be thoroughly wetted without leaving any free water. It should be coated with cement slurry at the rate of 2 kg of cement per sq.m.
iii) Concreting under special conditions should be done as per the procedure set out in IS:7861 (Part I and Part 11). Below 40 OC concreting should not be done. In cold weather it should be protected against frost. During hot weather the temperature of the wet concrete should be kept below-38 OC.
For under water concreting 10% additional cement should be added. Under water concreting should be done with prior approval of engineer-in-charge regarding the method equipment, materials and mix. Concrete should be deposited continuously until it is brought to required height. The concrete should be deposited under water by one of the approved methods such as tremie method, drop bottom bucket, bags, grouting etc. as per IS 456-1978. The concrete should not be disturbed after placing a till it has set.
iv) Curing: Depending on the weather as the concrete begins to harden within two to three hours after compaction, the exposed surface should be kept damp with moist gunny bags, sand or any other material. After 24 hours after stone aggregate and gravel should be washed with water to remove dirt and dust. Measured quantity of coarse aggregate and wet ground mortar for one batch should be poured in the drum of the mixer while it is revolving. Water should then be added gradually and wet mixing should be done at least for two minutes in the drum till uniform colour and consistency is achieved. Hand mixing should be allowed only in exception cases with the prior approval of the engineer-in-charge. It should be ensured that mortar did not separate from the coarse aggregate.
v) Placing and compaction: Concrete should be laid not thrown in layers of about 20 cm thickness while it is quite fresh. Each layer should be thoroughly rammed with 4.5 kg to 5.5 kg iron rammer and consolidated before the succeeding layer is placed. Joints should be staggered in different layers. Ramming should be done till a skin of
mortar covers the surface completely.
vi) Curing: After about 24 hours of compaction when the concrete had started hardening it should be kept damp with moist gunny bag:;, sand, or other approved methods for a minimum period of 7 days. Till then masonry over the foundation should not be started.
i) Proportioning: The proportions of aggregate to lime mortar should be done by volume. Generally lime is prepared by mixing 100 parts of 40 mm nominal size graded stone aggregate, gravel or brick aggregate as specified and 40 parts of lime mortars of the specified mix.
ii) Mixing: Mixing of concrete should be done in a mechanical mixer. Before mixing brick aggregates should well soaked with water for at least 2 hours and mortar 10-15 mm thick composed of cement and sand in the same proportion in the concrete mix. This should be freshly prepared and applied immediately before placing of
concrete.
Where the concrete has not fully hardened, all maintenance should be removed by scrubbing with wire brushes and the surface should be thoroughly wetted without leaving any free water. It should be coated with cement slurry at the rate of 2 kg of cement per sq.m.
iii) Concreting under special conditions should be done as per the procedure set out in IS:7861 (Part I and Part 11). Below 40 OC concreting should not be done. In cold weather it should be protected against frost. During hot weather the temperature of the wet concrete should be kept below-38 OC.
For under water concreting 10% additional cement should be added. Under water concreting should be done with prior approval of engineer-in-charge regarding the method equipment, materials and mix. Concrete should be deposited continuously until it is brought to required height. The concrete should be deposited under water by one of the approved methods such as tremie method, drop bottom bucket, bags, grouting etc. as per IS 456-1978. The concrete should not be disturbed after placing a till it has set.
iv) Curing: Depending on the weather as the concrete begins to harden within two to three hours after compaction, the exposed surface should be kept damp with moist gunny bags, sand or any other material. After 24 hours after stone aggregate and gravel should be washed with water to remove dirt and dust. Measured quantity of coarse aggregate and wet ground mortar for one batch should be poured in the drum of the mixer while it is revolving. Water should then be added gradually and wet mixing should be done at least for two minutes in the drum till uniform colour and consistency is achieved. Hand mixing should be allowed only in exception cases with the prior approval of the engineer-in-charge. It should be ensured that mortar did not separate from the coarse aggregate.
v) Placing and compaction: Concrete should be laid not thrown in layers of about 20 cm thickness while it is quite fresh. Each layer should be thoroughly rammed with 4.5 kg to 5.5 kg iron rammer and consolidated before the succeeding layer is placed. Joints should be staggered in different layers. Ramming should be done till a skin of
mortar covers the surface completely.
vi) Curing: After about 24 hours of compaction when the concrete had started hardening it should be kept damp with moist gunny bag:;, sand, or other approved methods for a minimum period of 7 days. Till then masonry over the foundation should not be started.
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