5. Results and discussion
The measured autogenous deformation for the mixtures is provided in Figs. 3 and 4. Deformations were recorded for 28 days. The deformations were zeroed at the moment of final setting time, according Table 2. The inflections of the curves that occurred between 1 and 2 days may be due to the following effects; reabsorption of detrimental bleeding water accumulated at very early age between paste and the corrugated tube; ettingite needles growth; crystals of calcium hydroxide growth; topochemical reaction of C3S. However, the origin of this swelling was not investigated.
As shown in Fig. 3, RHA could decrease the autogenous deformation. With no RHA, a considerable autogenous deformation, approximately 600 lm/m, is developed during 4 weeks of sealed hardening. Replacement of 5% and 10% of Portland cement by RHA lead to a successive reduction of this autogenous deformation. At 10% RHA could decrease the autogenous deformation after 4 weeks by 250 lm/m.
RRHA provides a positive effect on the autogenous deformation, since early ages (1–2 days) which is attributed to the filler effect, when compared with the hydration effect of an equal dosage of Portland cement. The humidity measurements, Fig. 5, confirm a higher humidity of paste with RRHA. The cement substitution by CRHA at early age increases the autogenous deformation due to the pozzolanic effect, since chemical shrinkage of the silica reaction is much higher than Portland cement reaction; but with time ,probably due to its cellular structure the autogenous deformation decreases in comparison with that of the paste without RHA (control).In the long time the behavior of the pastes with CRHA was similar to those of RRHA pastes. The lower strength of mixtures with CRHA is an indication of higher porous structure which may lead to lower capillary stresses in these pastes. The humidity values of the CRHA paste are higher than RRHA paste, which may also result of changes on porous structure. In fact, assuming that only Portland cement consumes water during hydration, the higher relative humidity of CRHA, when compared with RRHA, may be explained by the existence of larger pores in the CRHA paste.
|
