Assessment of Various Natural Pozzolans, Recycled Glass Powder, and Reclaimed Fly Ash as Supplementary Cementitious Materials for Concrete Mixtures

Abstract

The increasing demand for reducing the CO2 emissions associated with Portland cement production in the concrete industry has increased the need for the use of supplementary cementitious materials (SCMs) to partially replace the Portland cement. Such a demand, in addition to the decline in the availability of Class F fly ash, necessitates exploring alternative SCMs. This study aimed to fill this gap by assessing the performance of different natural pozzolans and industrial wastes/by-products as SCMs for concrete mixtures. The SCMs included a medium- and a high-grade metakaolin (MMK and HMK), diatomaceous earth (DE), pumice, wollastonite, recycled glass powder (RGP), and reclaimed fly ash (RFA), all sourced from North America. The research first explored the effect of these SCMs in cement paste and mortar, when used at 20% by weight of cement, with DE at 10%. The rheology and heat of reaction were measured in cement paste, and the flow table and compressive strength were assessed in mortar. Reactivity of these SCMs was also tested according to RILEM TC 267-TRM. The SCMs that met the threshold for the 7-day heat release and bound water content were then used in concrete at the same content as that used in cement paste and mortar. The concretes were tested for fresh properties, compressive strength, and durability parameters, including depth of water penetration, water sorptivity, chloride penetrability, and bulk and surface electrical resistivity. The results showed that the selected natural pozzolans (MMK, HMK, and DE) had similar or improved compressive strengths over the reference concrete with no SCMs at all testing ages (3 to 91 days), however, they reduced the workability of the concrete. Concretes with these natural pozzolans also had the highest resistance to water and chloride penetration out of all the concretes tested, indicating improved durability. Concretes with RFA and RGP had reduced early-age strength, however, achieved comparable late-age strengths to the reference concrete and the concrete containing Class F fly ash, with improved or similar workability to the reference concrete. The concrete with RGP did not perform as well as the concretes with the natural pozzolans, however, it provided enhanced strength and durability compared to the concretes with RFA and Class F fly ash. The findings from this research contribute to a deeper understanding of the effectiveness of these SCMs across various applications in the concrete industry.