coal chert silt rock dust material finer than 75 microns organic material unsound and friable particles Cement In present day concrete cement is a mixture of lime stone and clay heated in a kiln to The information is revised as per IS 456 The compressive strength of concrete is given in terms of the characteristic coal chert silt rock dust material finer than 75 microns organic material unsound and friable particles Cement In present day concrete cement is a mixture of lime stone and clay heated in a kiln to The information is revised as per IS 456 The compressive strength of concrete is given in terms of the characteristic