cThis concrete has less density compared to the conventional concrete. Light-weight concrete may be prepared (i) by omitting the fine aggregate, (ii) by using light-weight concrete or (iii) by aerating concrete.
The concrete prepared by omitting the fine aggregate is called no-fine concrete. It has low drying shrinkage. This is used for cast-in-situ external load-bearing walls, small retaining walls, where repetitive loads are expected to occur, etc. This has better insulating properties.
The light-weight aggregates used are pumice, expanded slates, furnace clinker, etc., and the fine aggregates used are crushed light-weight aggregate or natural sand. This type of light-weight concrete has better insulating and fire-resistant properties, is highly water absorptive and economical. This can be used for all the works stated above.
The light-weight concrete obtained by aeration is known as gas, porous or foamed concrete. This is prepared by (i) mixing air-entraining agents with cement or cement mortar in high-speed machines, (ii) mixing a specified quantity of pre-formed foam with cement or cement mortar in an ordinary mixer or (iii) adding aluminium or zinc powder to cement mortar or hydrogen peroxide to concrete. It has a very high drying shrinkage and is used for the manufacture of building blocks.
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