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

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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 P2O5 forms a solid solution with the 2CaO,SiO2 of the cement clinker and reduces the content of 3CaO,SiO2. Consequently the early strength falls as the P2O5 increases until, when the P2O5 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 P2O5 is affected more markedly than normal cement by an increase in water: cement ratio.

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