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Deformation tests have been made on hardened cements. A difference from unhardened ones, which show considerable plastic (viscous) deformation, is that the hardened ones show mainly elastic strain with a small inelastic component at a temperature exceeding the preliminary heat treatment value.The next stage in our research was testing hardened alumophosphate cement compositions [19, 22]. The specimens had been heat treated at 300 and 600°C (series 4 and 5 respectively [23]). After heat treatment, the cement contained the hydrated phosphates 3AlPO 4 × 5H 2 O and 2AlPO 4 × 3H 2 O, a mixture of cristobalite and tridymite forms of AlPO 4 , and also an amorphous phase. The preliminary treatment temperature was determined from the previously described experiments, which showed that the solidification temperature of this cement was at 200 -220°C, as was evident from the increase in the compressive strength from 0.95 to 26.6 MPa on heating from 20 to 300°C. Above 120°C, the specimens contained the high-temperature form of the orthophosphate AlPO 4 (cristobalite), which had a positive effect on the strength. The porosities and densities of specimens heat treated at 300°C hardly altered after heating in the range 300 -1200°C (Fig. 6, curves 2 and 3 ). The sharp increase in strength (curve 1) and density, and the considerable reduction in porosity in the interval 1300 -1400°C, are due to sintering of the alumophosphate cement stone.The deformation curves for cement specimens solidified at 300°C (series 4) were obtained with a primary heating cycle up to 500°C and cooling without load or under loads of 0.3 and 0.6 MPa, and also we repeated heating-cooling cycles unloaded for a specimen tested in the first cycle of 20 -500 -20°C under a load of 0.3 MPa, as shown in Fig. 7a. Deformation curves 1 -3 indicate certain deviations from a linear dependence characteristic of thermal expansion. As the load is increased, the elongation of the specimens was reduced, and at 500°C it was 0.58 and 0.47% at loads of 0.3 and 0.6 MPa respectively; without load, it was 0.78% (maximal expansion). All the curves show kinks in the range 200 -300°C, which are due to dehydration and are usually observed on primary heating associated with hardening of the cement; only at the ends of curves 1 -3 is there a certain deviation from a linear dependence characteristic of alumophosphate cement. On cooling, residual deformation was observed only on specimens tested at a load of 0.6 MPa, but it was slight and was only 0.05%. On repeating the heating-cooling cycle, the specimen without load (Fig. 7a, curve 4 ) after primary testing in a heating-cooling cycle at a load of 0.3 MPa showed expansion increasing to 0.62%, while residual strain was not observed.

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