New Zealand Pozzolans-An Ancient Answer to a Modern Dilemma

The New Zealand cement industry has, thus far, been able to achieve reductions in carbon dioxide emissions in line with government expectations through process change and the wider use, and acceptance, of cement extenders. However, a continued improvement is required to meet the nation's commitment under the Kyoto Protocol. Sitting astride the junction of the Pacific and Australian tectonic plates, for millions of years these islands have been the scene of major volcanic activity. The legacy of this volcanism and upheaval is a range of materials, widely distributed, possessing pozzolanic properties ideally suited to cementing applications. These materials could play an important part in assisting the country to meet its undertakings. The purpose of this paper is to review the past limited use of these natural pozzolan materials and, using modern internationally accepted methods, look at the performance of binders of varying composition. The materials examined include an amorphous silica of geothermal origin, a pumicite from the Bay of Plenty region and two diatomites from the central North Island. These materials were selected and prepared at two different fineness levels. Substitution levels between 5% and 40% were achieved. Further, they were interground with cement clinker to determine the efficacy of the two different blending methods. The paper will outline the results of this major investigation into the performance of New Zealand pozzolans. It will also give a guide as to the possible substitution levels to deliver adequate compressive strengths.