Concrete Materials

The success of concreting is dependent on the quality of concrete materials  used in making it and the efficiency with which they are batched and mixed at site/plant and transported to the construction site. The concrete materials are cement, coarse aggregate, fine aggregate, water  and admixtures, if  used. It is  necessary that  proper checks are carried out on these concrete materials  to ensure their compliance with specified standoffish so that the final product i.e. concrete is of desired quality. We will examine each of these concrete materials now. 

Cement 

• The properties of cement should comply with relevant IS Code. You should attempt to obtain total quality of cement from a single source and obtain producer's certificate for each consignment stating that it conforms to the specified I.S. Code. 
• Cement should be stored  over  dry platforms at least 20 cm high in  such a manner as to prevent deterioration due to moisture or intrusion of foreign matter. In case of store rooms, the stack should be at least 20 cm away from floors and walls. The height of stack should be such that it does not lead to setting of lower bags. This height is generally restricted to 7 bags. You should carry out inspection of stored cement at least  once a day. 
• Different brands  and consignments should be  stored separately. Tested and untested cement should also be distinguished. The principle of first in, first out should be  used so that there is no  old  cement. 
• Use of any cement which has  deteriorated should not be allowed. 
• Carry out the specified test  for  different consignments. Some of these tests are, Fineness test, soundness test, initial set, final  set, compressive strength and chemical composition. A record should be kept for these tests. 
• Certain field tests such as cc>lour of the cement, fineness of cement, absence of visible lumps in the bag etc may  be done to ascertain freshness of cement and the absence of adulteration. 
• The site engineer  should be aware of the properties of OPC/33 grade, 43 grade and 53 grade cement which are now available and  make use of them appropriately keeping in view  their cost/benefit ratio. Depending upon the location of  the project, he should also decide whether to use portland pozzolana cement, blast furnace slag cement, sulphate resisting cement or ordinary Portland cement to obtain durable concrete.