Research into mineral additives in New Zealand

This paper describes the recent work with a fine waste pumice and Microsilica 600 (MS600) where tangible benefits can be obtained from their use. Up to 30% cement replacement can be made with pumice before the effects of the replacement are noticed with a drop off in compressive strength. A similar effect was noted with MS600. By following how cement reacts by measuring the rate of heat output with an isothermal calorimeter it has been found that while pumice addition reduces heat output as the pozzolanic reaction is slow, hydration is not slowed with MS600 and there is no reduction in heat. The usual explanation of the pozzolanic reaction is the siliceous additive reacts with Ca(OH)2 formed from hydrating cement.
One of the issues when using a pozzolans is usually water demand. The use of a water reducer is almost essential if high replacement levels are used. However, the addition of admixtures to the two cements commonly available in New Zealand can give different results, even though the two cements behave similarly when admixtures are not used. Understanding why this occurs could help advance the use of cement replacements in New Zealand.

Author: A. Durant, C.H. Bigley, N.B. Milestone

Section: Science and production

Keywords: cement, pozzolana, fly ash, pumice, microsilica.