The internal relative humidity of the control paste decreases and stabilizes at approximately 83% RH within one week of hardening. The values obtained for the control and SF pastes, 83% and 90%, respectively, are in reasonable accordance with the literature [46, 47, 53, 54]; the RHA pastes values are 87% and 88%, respectively for the RRHA and the CRHA.
Fig. 5 indicates a marked influence of the silica-content on the reached level of equilibrium relative humidities (see Table 1).The higher RH of pastes with mineral admixtures, when compared with control mixture, is explained by the lower water consumption during hydration.
The autogenous shrinkage results indicate that the use of RHA (RRHA and CRHA) has a positive effect, which may be due to its porous cellular structure, Fig. 1. The RHA probably acts as an internal reservoir, providing a source of curing water to the paste volume in its vicinity. The control mixture has the same amount of internal water, but mixtures with RHA may provide more homogenous distribution of large pores, that feed the capillary pores.Assuming that RHA provides a homogenous distribution of large pores, a decrease of capillary tension may be also expected, according to the Kelvin–Laplace equation.
Table 3 shows the compressive strength at the age of 1, 7 and 28 days on 50 mm cubes under sealed conditions. As expected, all the pastes show an increase in strength with age. From the results it arises that the compressive strength of RRHA pastes exhibit an excellent performance at ages of 7 days and over.
It is known that CRHA provides a positive effect on the compressive strength at long term [37, 42]; the results of this study show that the behavior of pastes with RRHA is not inferior. No significant changes in long term compressive strength were observed by RRHA or SF incorporation.
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