A preliminary study of mechanical treatments’ effect on the reactivation of hydrated cement paste

Abstract

Abstract More than 4.4 billion metric tons of cement were produced in 2021 [1], making it one of the most common building materials. Unfortunately, excessive cement use brings up several environmental concerns, one being the enormous volumes of CO2e (carbon dioxide equivalent) created as a by-product. CO2e is a standard unit for measuring carbon footprint and can be calculated for all greenhouse gases using global warming potential. Reducing CO2 and other greenhouse gas emissions is crucial in modern cement manufacturing, as 0.9 kg of CO2e is produced for every kg of cement. Cement manufacturing contributed by releasing 3.96 Gt of CO2e into the atmosphere in 2021. This issue is often remedied using recycled materials in the fresh concrete mix as supplementary or pozzolanic additives. Some researchers have focused on regaining the activity of hydrated cement paste by grinding and thermally activating it [2–5], but a low-strength binder would also work for many applications. A low-strength binder recovered with as little energy as possible (only grinding, no heat treatment) could be considered a more sustainable and less energy-intensive way of recovery of the cement binder matrix. This study investigated a technique for recycling hydrated cement paste by mechanical treatment to disintegrate the hydrated cement conglomerate to reveal the unhydrated cement particles [6] that can be used as a recovered cementitious binder from processing waste from the production of wood-cement boards. Processing waste is defined as cement particles containing hydrated and unhydrated cement [7] and spruce wood fibres. The partly hydrated cement in the waste stream was mechanically processed in a planetary mill to reactivate it and restore its cementitious characteristics. The binder was characterized by density and mechanical compressive strength.