Ultra-high performance pastes under pressure curing

Abstract Compaction pressure has positive effects on the development of the microstructure and mechanical properties of hardened cementitious mixtures. However, the benefits have been studied at high-pressure levels or combined with thermal curing. This article is part of a research project that proposed an alternative equipment to promote both pressure and thermal curing, in conditions that are easy to reproduce. The paper reports the results obtained from the study of the isolated effect of the pressure applied in the first hours of hydration, with loads of 0,1 MPa, 5 MPa and 10 MPa. The relationship between pressure increments and mechanical performance was checked by means of density, modulus of dynamic elasticity and compressive strength tests. Scanning electron microscopy, porosimetry and thermogravimetry analyses were carried out. They showed the influence of pressurizing on the development of a compact and homogeneous matrix, but with an increase in microporosity and a decrease in the amount of hydration products formed. The results indicate that a satisfactory mechanical performance does not depend exclusively on the degree of hydration of the cement, but on the synergy between hydration products and changes in the pore structure.