Mortars produced with an environmentally sustainable rice HUSK silica: Rheological properties

Abstract

This paper presents an experimental study on the rheological behavior of commercial mortars with a high percentage of Rice Husk Silica (RHS). RHS was used to replace 5%, 10%, 15%, 20% and 30% by mass of Portland cement. The use of the waste material from burning rice husk in the mixtures contributes to a cleaner and more sustainable environment. The rheological behavior of fresh mixtures was investigated along with the time (15, 60, 120 e 180 min) by flow table test, modified Vicat and squeeze flow tests. In this research, an extension version of squeeze flow test was proposed, in which the samples are submitted to load and unload test (tensile test). The flow table results obtained showed that the workability of the mortars decreases as the RHS content increases. About 4% of the workability loss is related to the granular structure of mortars, and 96% about the porous structure of the RHS. In the Modified Vicat test, lower cone penetrations were observed as the RHS content increased, indicating the increase in the viscosities of mortars. Through the squeeze flow test, it was observed an increase in the mortar stiffness with the increase in RHS content and the increase in time. The maximum tensile load obtained in the unload squeeze flow test was higher as the replacement of Portland cement by RHS increased. Therefore, the mortars with higher RHS content are possibly able to retain more water, which may increase the adhesion with the substrate in the hardened state. In sum, the study shows that it is possible to produce eco-friendly mortar with a high quantity of RHS by increasing the time for application.