Proper Cement Content is Important to Concrete Quality
Diskuzní fórum (povinná reklama)Cement is an intermediate product while the actual construction products are concrete or mortar. The quality and quantity of cement significantly affect the ultimate performance of concrete and the durability of the structure. Keeping this fact in view, the Bureau of Indian Standards (BIS) has issued a revised Code IS:456-2000 for plain and reinforced concrete in which a separate chapter has been devoted to durability of concrete. The different grade designations of concrete and proportions of ingredients specified for each grade are given in this Code and are briefly indicated in Table-11.1 below. These proportions are for nominal mixes only
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For concrete mixes above M-20, the mix design should be adopted as per approved procedure.
a) Minimum cement content ?
The Code has classified environments to which concrete will be exposed into five levels of severity, namely, mild, moderate, severe, very severe and extreme. Depending upon the exposure conditions concrete pumps, the minimum cement content and the minimum grade of concrete have been specified in the Code. Irrespective of the grade and type of cement, the minimum cement content specified in the Code must be used while producing concrete for a particular environmental condition.
b) Maximum cement content ?
IS: 456-2000 also stipulates that cement content (not including fly ash and ground granulated blast furnace slag) in excess of 450 kg/m3 should not be used in concrete. In special cases, where due consideration has been given in design to the increased risk of cracking due to drying shrinkage, etc., a higher proportion of cement can be used but precautionary measures have to be taken before doing so. Excess cement over the actual requirement is harmful as it is likely to induce micro-cracks in concrete. These micro-cracks, on the one hand, reduce the compressive strength of concrete and are a potential cause for reducing the durability of the structure, on the other