Influência do cloreto de cálcio nas propriedades reológicas de pastas de cal com adições pozolânicas

Abstract

Lime mortars are indicated for restoration and conservation interventions of historic buildings, however, the slow hardening of these mortars does not favor their use and dissemination in the current construction scenario. This hardening time tends to be shorter when lime is mixed with pozzolans, but the results achieved are not close to those found in conventional Portland cement mortars. In addition, few works focused on the rheology of lime pastes are found. Therefore, this research aimed to evaluate the performance of hydrated lime pastes and two different metakaolins, one commercial metakaolin (MK) and other from the calcination of kaolin in the laboratory (CC). In order to reduce the hardening time percentagens of 5% and 10% of calcium chloride (CaCl2) were tested. The mixtures were studied in the fresh state for hardening time using the Vicat test and semi-adiabatic calorimetry, and for rheological behavior using mini-slump and rheometry tests. As for the hardened state, microstructural characteristics were investigated by means of XRD and SEM at the ages of 3 and 7 days. The pastes without and with 10% of CaCl2 were reproduced in mortars for analysis of mechanical performance. From the results obtained from rheological characterization, it is observed that the lime and CC pastes resulted in more fluid pastes than those with MC and that CaCl2 also increased the fluidity of the pastes. In general, the pastes adjusted to the pseudoplastic behavior, however the more fluid ones approached the Bingham model. Regarding the hardening time, CaCl2 accelerated the hardening process in lime and MC pastes differently from those with CC. The main hydration product observed in the diffractograms of all pastes was monocarboaluminate. The mechanical strengths of lime and CC mortars were higher than those of lime and MC, and the compressive strength reached a value of 19.96 MPa. The CaCl2 improved the strength in the mortar with MC and reduced in that with CC.