Hot Pressed DSP Cement Paste
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HOT PRESSED DSP CEMENT PASTE Ping LU* and J. Francis YOUNG Center for Cement Composite Materials University of Illinois at Urbana-Champaign Urbana IL 61801, U. S. A. ABSTRACT DSP cement paste is prepared by hot-pressing technique in this study in order to improve its particle packing and chemical composition, and to investigate the relationship between its solid phase microstructure and mechanical strength at the porosity close to zero. The addition of silica fume improves strength development, although capillary porosities are not changed significantly. Results obtained indicate that the highest compressive strength reached are 800 MPa after 28 days hydration and oven drying at 2000C. The strength has better relation with degree of hydration or the physical density of C-S-H. the silicate anion polymerization closes not appear to influence strength. INTRODUCTION DSP (Densified by Small Particles) cement is a low porosity binder which consists of Portland cement with silica fume packed between the cement grains. Bache[l] first proposed the use of silica fume which is not only a filler in pore structure of the paste, but also reacts with the paste, resulting in improvement of its intrinsic properties. Hjorth[2] and Wise et al.[3] developed a series of new applications of this material. Roy Lt.nL[4] reported the effects of hydrothermal and heating processes on the strength of DSP mortar. Typically, use of superplasticizer makes the paste castable in very low W/C ratio, but in spite of the densified system, castable DSP materials still have not achieved porosities approaching zero[5]. On the other hand, using hot-press technology, Roy and Gouda[6, 7] prepared compacted cement paste with compressive strength of as high as 650 MPa. Theporosity of these pastes was much lower than that of ordinary paste or cast DSP cement paste[5]. The goal of this study is to use
*Permanent address: Department of Materials Science and Engineering, Tongji University, Shanghai 200092, China.
Mat. Res. Soc. Symp. Proc. Vol. 245. ©1992 Materials Research Society
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hot pressed DSP system to improve its particle packing and chemical composition, and to investigate the relationship between solid phase microstructure and behaviour of this paste at porosities close to zero.
EXPERIMENTAL PROCEDURES Starting Materials and Sample Preparation The ordinary Portland cement (Type 1) used in this study is microfine cement (MC300) supplied by Geochemical Corporation, Ridgewood, NJ. Its Blaine surface area is about 10,000 cm 2 /g. Silica fume used is microsilica (Grad 983U, Elkem Chemical, NORWAY) with a surface area of 20-25 m2 /g. It was added to the cement at 5, 10 and 15 wt% levels(HFPx). The procedure of sample preparation is the same as that used by Roy and Gouda[6]. The experiment parameters for hot pressing are given in Table 1. After hot pressing, samples were immersed in water at room temperature until tested. Table 1
Conditions for Preparing Hot Pressed Cement Compacts Condition A
w/s ratio Pressure(MPa) Temperature(OC) Pressing Time(mi
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