The effect of phosphate on the constitution and hardening of portland cement

Abstract

Abstract The effect of phosphorus pentoxide on the burning of Portland‐cement clinker and the setting and hardening of the resultant cement has been investigated, using both synthetic mixtures and the raw materials which it is proposed to use for cement manufacture in Uganda. It is shown that the P 2 O 5 forms a solid solution with the 2CaO,SiO 2 of the cement clinker and reduces the content of 3CaO,SiO 2 . Consequently the early strength falls as the P 2 O 5 increases until, when the P 2 O 5 reaches 2·25% of the clinker, the cement fails to meet British Standard requirements. Formulae are given from which the percentage of compounds present in the clinker can be calculated, and the procedure for determining the proportion of clay in the raw mix is described. Test data on concrete are given; cement high in P 2 O 5 is affected more markedly than normal cement by an increase in water: cement ratio.