Evaluating the use of diatomaceous earth waste and by-products as a supplementary cementitious material

In recent years, the use of supplementary cementitious materials (SCMs) in building materials has increased due to concerns about CO₂ emissions from the cement industry. On the other hand, the scarcity of traditional sources of SCMs in certain regions exacerbates the issue of high demand for these materials in concrete production. In this context, this article explores the chemical, mineralogical, morphological, and physical properties and pozzolanic activity of two types of diatomaceous earth (DE) obtained from industrial waste and by-products. The waste was classified into two categories: low-density DE (DE-LD) and high-density DE (DE-HD), representing particles attached to the cyclone wall and those lacking suitable characteristics for use as filter material and/or loading agent, respectively. Results showed that both DE types are rich in silicon oxide and have a highly porous surface. DE-LD and particles smaller than 0.075 mm of DE-HD contain more amorphous phases. DE-HD consists of a mixture of quartz sand and DE particles. Both DE types have a lower apparent specific mass compared to cement, with DE-LD standing out for its high specific surface area (~ 8.7 times that of cement) and uniform particle size distribution. Pozzolanic activity tests indicate that DE-LD exhibits greater reactivity, whereas the < 0.075 mm fraction of DE-HD displays latent hydraulic behavior, likely due to the presence of amorphous silica. Based on these findings, DE-LD can serve as SCMs due to its pozzolanic characteristics, while DE-HD (< 4.75 mm) can be used as fine aggregate in concretes and mortars or as SCMs after sieving to obtain particles smaller than 0.075 mm. Thus, these waste materials show potential for use in the production of pozzolanic cements, mortars, and concretes, contributing to the valorization of waste that would otherwise be disposed of improperly and helping to address SCMs shortages.