Effect of insoluble residue on properties of Portland cement

Abstract

Insoluble residue is a non-cementing material which is present in Portland cement. This residue material affects the properties of cement, especially its compressive strength. To control the non-cementing material in Portland cement, ASTM standard allows the insoluble residue to be not higher than 0.75%. This limitation is much lower than the allowance provided by the British standard which is 1.5%. To verify the effect of insoluble residue on the properties of Portland cement, artificial insoluble residue was prepared and replaced in Portland cement type I. Finely crushed sand was extracted to represent artificial insoluble residue. Setting times and compressive strengths of cement mortar mixed with insoluble residue were investigated. The Portland cement was replaced by insoluble residue which varied in amounts of 0%, 0.5%, 1.0%, 1.5%, 2.0%, 3.0%, 5.0% and 7.0% by weight. The results showed that the addition of the insoluble residue from 0.0% to 7.0% by weight in Portland cement did not affect the normal consistency or setting times of cement. However, the compressive strength of cement mortar was affected during the early age, but the figure reduced as the cement mortar was older. With 7.28% of insoluble residue in the mortar at 1 day, the compressive strength was reduced by 11.5%, but after 60 days, the strength of the same mortar was only reduced by 5.5% as compared to the control mortar. It was also found that the compressive strength of Portland cement mortar with insoluble residue provided by ASTM standard or British standard was still higher than the compressive strength of Portland cement mortar type I allowed by the standards. The limit of insoluble residue given by ASTM standard as 0.75 is rather low and can possibly be increased to 1.5% according to British standard, or even slightly higher, without significantly reducing the compressive strength of cement.