Compatibility of PCP with Portland Cement Replaced with Natural Pozzolan and Fly Ash

摘要

The use of materials able to develop pozzolanic reaction as main constituents in cement production is not new to the construction industry but has gained increasing importance in the last years for its contribution to sustainable development and durability improvement of concrete. Nevertheless basic in-depth examination of blended cements with comb-type superplasticizers is an issue, which still deserve attention to further enhance the application of these binders and solve some problems of compatibility. The paper investigates the behavior of a commercial comb-polymer dispersant (PCP) of the last generation with two groups of laboratory-prepared blended cements, the former obtained by partial substitution of Portland cement with natural pozzolan the latter with fly ash. The action of superplasticizer on blended cement is studied by gas and liquid adsorption, intrusion mercury porosimetry, mini slump and mechanical test. According to BET experiments, natural pozzolan has very high specific surface compared to that of fly ash and this explains the differences between adsorption isotherms of the two additions. Intrusion mercury porosimetry provides data on cumulative volume and pore size distribution. This information can be used to evaluate compressive strength results also in the light of conduction calorimetry measurements. Clear effects of progressive increasing amount and types of addition on cement structure and performances are shown and discussed.