Hybrid binders based on volcanic pumice: Effect of the chemical composition on strength and microstructures

Abstract

This research focused on pastes of hybrid binders (HB-VP) based on precursors of Volcanic pumice (VP, 25–75 %) and portland cement (PC, 25–75 %), activated with 4–12 wt% Na2SO4 and Ca(OH)2 in various molar ratios Na2SO4:Ca(OH)2. The experimental work and results were based on the surface response method and statistical tools, which indicated that the %VP influenced the early strength for up to 28 days and that the activators influenced the 90 and 180-day strength. SEM, EDS, XRD, FTIR and NMR indicated heterogeneous microstructures, with complex mixtures of cementitious gels like C-S-H with ettringite; HB-VP with 50 % VP showed Al into bridging positions in C-A-S-H, while for 75 % crosslinked C-(A)-S-H structures were noted. The chemical composition of the reaction products varied depending on the surrounding precursor. The CO2 emissions and strength of the HB-VP are competitive relative to other reported binders, and appear to be a suitable sustainable replacement of the Portland Cement.