Profile of internal relative humidity and depth of drying in cementitious materials containing superabsorbent polymer and nano-silica particles

Abstract

This paper aims to characterize and model the internal relative humidity profiles and drying depth in hardened cement pastes containing superabsorbent polymers (SAP) and nano-silica (NS) particles. Five different cement pastes were considered with the incorporation of SAP, NS, and simultaneous SAP and NS to reference mixtures with different water/cement ratios. Characterization of mass loss history, the evolution of the diffusion coefficient, and modeling of relative humidity profiles were performed for the five cement pastes in three different ages and three drying times. This paper also proposes a low-cost apparatus to monitor the mass loss history of thin specimens of cement pastes. The characterization was determined by the drying process with a gradual variation of the RH environment from 100% to 43%. The diffusion coefficient and the profile of the internal relative humidity through the drying depth in specimens of different ages and drying periods were estimated by the mass loss evolution. The results show that the pastes containing SAP presents a higher mass loss, higher diffusivity and deeper drying depths for all ages and drying periods investigated. Although the incorporation of NS to the reference paste improved their performance, this improvement is observed only in 28-day old pastes with SAP.