The Structural Engineer > Archive > Volume 48 (1970) > Issues > Issue 5 > Discussion on High-strength Concrete: Manufacture and Properties by A.J. Harris
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Discussion on High-strength Concrete: Manufacture and Properties by A.J. Harris

Mr. C. D. Lawrence: ‘Fig D1 shows the high pressure die that was used to produce the high-strength cement paste referred to by Mr. Harris. It was found necessary to use a rather elaborate method of releasing the cylindrical compact from the die because the compact was very fragile immediately after pressing; the residual lateral stresses present after removing the axial compacting pressure had to be released uniformly over the whole length of the compact. We have now found that it is possible to release the residual lateral stresses by just pushing the compact out of a coned die but this works only for rather thin compacts. The compressive strengths obtained at different compacting pressures are shown in Fig D2; 32 mm (1.26 in) diameter cylindrical specimens were examined which were pressed dry and then evacuated and flooded with water. Larger specimens are not so readily saturated by this technique but one can press moist paste containing sufficient water to fill the voids after compaction, and get very similar strengths; this latter procedure also avoids the effects of the large initial heat generation which occurs on contact between dry cement and water, i.e. large temperature rises causing cracks to develop.