Advances in understanding R³ chemical reactivity in various traditional and emerging pozzolans: Chemical, mineralogical and calorimetric dimensions

Development of the ASTM C1897-based R³ test facilitates faster, more accurate and more effective assessment of the chemical reactivity of natural and industrial pozzolans. While this methodology has been validated for conventional pozzolans (i.e. metakaolin, silica fume, fly ash, calcined clays and granulated slags), its robustness when applied to emerging eco-pozzolans has yet to be confirmed. This paper presents new evidence on chemical reactivity in a wide range of emerging supplementary cementitious materials (e.g. minerals recycled from construction and demolition waste, calcined paper sludge, biomass ash, rice husk ash and sugar cane bagasse ash) and statistically evaluates the consistency and correlation of methods A and B employed in R³ testing based on the different samples’ fundamental chemical composition (XRF) and amount of amorphous mineral content (XRD–Rietveld). The results reveal strong correlations between the amorphous material content of the 12 pozzolans examined and the cumulative heat release at 168 h (R² = 87 %) and with methods A and B. An excellent correlation (R² =99.7 %) is likewise evident between the combined water method and the thermogravimetry technique. Based on these findings, four ranges of chemical reactivity are proposed according to the cumulative heat release at 168 h (determined as per ASTM C1897 Method A): low 25–100 J/g; moderate 100–180 J/g; high 180–360 J/g and very high > 360 J/g. Finally, for certain types of biomass ash with high potash and sulphate content, the chemically combined water content is determined in two steps: (i) from 40 °C to 105 °C and (ii) from 105 °C to 350 °C, verifying that the B/A ratio exceeds 1.0.