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Questions on cement and concrete Mr John Park, writing to us from London, makes two observations on British Standards on which he would welcome comments from our readers. These are: Firstly: BS 12 states that ordinary Portland cement shall have a minimum specific surface (fineness) of 225 m2/kg while rapid-hardening Portland cement shall have a minimum of 325 m2/kg. Cement from other countries may have values higher than this. Should they then be regarded as rapid-hardening and be rejected if OPC has been specified? What would be the effects on the structure of using higher values? Presumably early drying shrinkage will increase. What extra precautions should be taken if the contractor offers cement with a fineness of 300 m2/kg in one part of the structure and, say, 350 m2/kg in another? Should a maximum value be specified? If so, what should it be? Verulam