Effect of raw and calcined sediments on mechanical and rheological behaviour of grout cement paste

Construction consume enormous amounts of materials, the manufacture of which generates significant greenhouse gas emissions. The use of municipal waste from street sweeping as a component of backfill grout offers the potential to reduce both environmental impacts and costs. However, its heterogeneity and organic matter content can negatively affect rheology in the fresh state and hydration . In this study, the effects of raw (S2) and calcined (S1) sediments used as substitutes for sand and partial cement, respectively, on the flow, structure formation and early hydration of compactable grouts were investigated. Class F fly ash (FA) was added to optimise particle settling. A fly ash content of 10% by weight and a water/binder ratio of 0.27 minimised both the static elasticity limit and apparent viscosity through improved settling due to a ball-bearing effect. Calcined sediments used as partial cement substitutes increased structural strength (Athix) and immediate bearing index (IBI) up to a substitution level of 15%, and then decreased to levels around 40% due to the dilution effect. Isothermal calorimetry, thermogravimetry, and X-ray diffraction indicated increased formation of early ettringite and carboaluminate phases with calcined sediments, as well as a reduction in portlandite content as substitution increased. The results demonstrate a practical window for low-carbon grouts that meet the objectives of fluidity and early bearing capacity.