Assessment of CO2 reduction of alkali-activated concrete

Although alkali-activated (AA) concrete is generally regarded as one of the most effective concrete technologies for reducing CO2 emissions, very few investigations have been carried out on the assessment of the CO2 reduction of such concrete. The present paper reports an evaluation procedure for the CO2 reduction of AA concrete. The studied system considers all of the steps from the cradle to pre-construction. CO2 reduction for secondary precast concrete products is also evaluated with reference to practical examples wherein ground granulated blast-furnace slag (GGBS) cement is replaced with AA GGBS binder. Comparisons of the performance efficiency indicators, binder and CO2 intensities, reveal that the contribution of the binder to the total CO2 emission is more significant in ordinary Portland cement (OPC)-based concrete than in AA concrete, whereas the contribution of aggregate transportation becomes more critical in AA concrete than in OPC-based concrete. The reduction rate of CO2 emission of AA concrete relative to OPC concrete commonly ranges between 55 and 75%. In addition, the CO2 reduction rate in secondary precast concrete products that use AA GGBS binder instead of GGBS cement can be evaluated as approximately 20% when the total aggregate-to-binder ratio ranges between 3.0 and 4.0. On the other hand, Ca(OH)2-based AA GGBS concrete shows a CO2 intensity that is approximately 2.4 times lower than that of OPC concrete. Overall, the slope of the increasing rate of the CO2 intensity against the binder intensity is lower in Ca(OH)2-based AA GGBS concrete than in OPC-based concrete.