Studies on blended Portland cements containing Santorin earth

Abstract

Although pozzolans, such as the Santorin earth, have been in use for over two thousand years for making cementitious products, the mechanism by which pozzolanic reactions contribute to the strength and chemical durability of mortars and concretes is not fully understood. Reported here are the results of an investigation in which portland pozzolan cements containing 10, 20, or 30 weight percent Santorin earth were used. Performance of the cements was evaluated with respect to strength development, drying shrinkage, sulfate resistance, and alkali-silica activity. The cement containing 20 percent pozzolan showed the highest compressive strength at 1 year, and the cements containing 20 or 30 percent pozzolan showed the least permeability and best resistance to sulfate attack. Microstructural investigations involving scanning electron microscopy, X-ray diffraction analysis, determination of free Ca(OH) 2 present, and pore-size distribution were conducted on hydrated cement pastes for the purpose of understanding the factors responsible for the observed behavior of the cements. From the results, it is concluded that the process of pore refinement associated with pozzolanic reactions plays an important part in enhancing the strength and chemical durability of portland pozzolan cements. It is suggested that the rate at which pore refinement occurs in a hydrating pozzolan cements is not only useful as a measure of the activity of the pozzolan presen, but also for a more reliable prediction of the performance characteristics of the cement.