High strength cement pastes

Abstract

The microstructures of high strength cements containing polymer (sometimes known as MDF cements) has been examined. They are basically composed of either clinker or clinker plus hydration products embedded in an amorphous polymeric matrix. Cement pastes based on ordinary Portland cement (OPC) contain the usual hydrates but lack the pronounced fibrillar morphology of hydrate gel often observed in conventional pastes. In contrast, pastes based on the high alumina cement Secar 71 did not contain the normal cyrstalline hydrate phases. Energy dispersive microanalysis of the polymeric phase in Secar 71 material revealed the presence of calcium and aluminium while calciumrich interstitial material was found in OPC pastes. These results indicate that the organic component plays a more active role than that of an inert rheological aid. The effect of prolonged reaction with hot water is to cause the formation of crystalline hydrate products in Secar 71 paste with a permanent loss in strength of the order of 50%. OPC based pastes appear to be less affected by a similar treatment.