Microstructural Development in Pore Reduced Cement (PRC)
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MICROSTRUCTURAL DEVELOPMENT IN PORE REDUCED CEMENT (PRC) D.E. Macphee, E.E. Lachowski , A.H. Taylor and T.J. Brown CSIRO Division of Building, Construction and Engineering,P.O. Box 56, Highett, Victoria 3190, ýustralia. Department of Chemistry, University of Aberdeen,Meston Walk, Old Aberdeen AB9 2UE, Scotland.
ABSTRACT Pore Reduced Cement (PRC) is a high density, high strength material which may have specialist use in the construction industry. It is produced by the high pressure processing of Ordinary Portland cement (OPC) pastes, or blends of OPC with certain supplementary cementing materials, such that effective water/cement ratios (w/c) are significantly reduced relative to those used for mixing. A previous paper [I] describes the mechanical properties of PRC (patent pending) during the early stages of product development and more recent data show that improved preparative techniques are leading to increasing densities and strengths. However, fundamental data on the microstructure, mineralogy and durability properties have not previously been reported. The present paper is directed towards the study of microstructural development in the closely compacted matrix using electron microscopy. Mineralogical and porosity data are also presented. INTRODUCTION Pore Reduced Cement (PRC) is obtained from the high pressure processing of hydrating cementitious materials. The products based on Portland cement only have densities increased by around 30% relative to normally processed cement pastes and this has an important influence on their mechanical properties. The pressing techniques applied permit the recovery of a portion of the mixing water from a set paste so that resulting water/cement ratios (w/c) can be significantly reduced from those which were required to meet the rheological requirements of the fresh cement mix. Preliminary data on properties [I] show compressive and tensile strength improvements of up to 3 and 6 times respectively. Modifications to the pressing procedure have increased these factors of improvement to 3.6 and 7. Figure 1 summarises the measured physical and mechanical properties of the products. Pressed cement materials are not new. lsostatic pressing and isostatic hot pressing techniques have been applied 12,3,4] to Portland cements, aluminous cements and cements with silica fume mixed at low w/c to produce very high strengths. Concrete product properties have also been improved by pressing 15]. In the present approach, the cements are mixed with water at normal w/c and the water contents are reduced after the paste has achieved an initial set. It is suspected that the residual fluid retained in the setting product can permit continued hydration so that new hydration products can form and fill the significantly reduced void space within the product. This would correspond to the substantial density increase mentioned above. Also, hydration under conditions of compaction and reduced water availability may lead to changes in hydration product composition and morphology. Electron microscopy tech
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