Coupling evaluation of carbon emissions and strength: Early carbonation curing of cement mortar containing incinerated sewage sludge ash (ISSA)

A superposition of wastes utilization and early carbonation curing is attracting attention as a novel way for reducing carbon emission of cement production. In this work, the effects of early carbonation curing on the early properties and microstructure of mortars containing incinerated sewage sludge ash (ISSA) were explored, and the total carbon emissions of 1 m3 cement mortar products during the whole life cycle were calculated and evaluated by introducing the definition of “carbon-to-strength ratio”. The findings showed that early carbonation curing can partially compensate for the strength loss and increase in total porosity of cement mortars caused by incorporating ISSA. Microstructural analyses revealed that the hydration products (Ca(OH)2) and unhydrated clinker (C2S and C3S) were consumed during the early carbonation curing, while carbonation products that was mainly calcite was formed. Further calculations showed that the CO2 uptake of mortars with 30 wt% ISSA through the early carbonation curing was 11.0 wt%, which had the highest carbonation degree. Compared with the mortar product without ISSA, the total carbon emissions of 1 m3 carbonation-cured mortar products with 10 wt% - 30 wt% ISSA were reduced by 7.7–40.5%, respectively. The proper addition of ISSA can promote the carbonation reaction, and the dosage of ISSA is suggested to be no larger than 20 wt% by considering the coupling evaluation of carbon emissions and strength. •Early carbonation curing partially compensated the negative effect of ISSA on mortar.•Microstructure revealed a significant amount of calcite in carbonation-cured mortar.•The largest CO2 uptake through carbonation curing was 11.0 wt% based on TG-DSC.•A proper dosage of ISSA can promote the carbonation reaction of mortar.•The largest dosage of ISSA was 20 wt%, considering carbon-to-strength ratio.