Energy and CO2 emission assessments of alkali-activated concrete and Ordinary Portland Cement concrete: A comparative analysis of different grades of concrete

Research has shown that alkali-activated concrete (AAC) is comparable to ordinary Portland cement concrete (OPCC) in terms of mechanical properties and may offer ecological benefits compared to OPCC. This study evaluates the energy and emission of AAC and OPCC across different classifications of concrete compressive strength (40, 60, and 100 MPa). Analysis indicates that the selection of constituent materials can substantially affect the energy and emission of AAC and OPCC. Ordinary Portland cement (OPC) is the principal contributor to the energy and emission of OPCC, accounting for 80% of energy and 91% of emissions of OPCC. The activating solution, meanwhile, is the main contributor to the energy and CO2 emission of AAC. Normal strength AAC (40 MPa) shows 46% less energy and 73% less CO2 emission than OPCC. However, high-strength AAC (60 MPa), using metakaolin as a base material, experiences higher energy (8%) than OPCC yet the emission is 40% less than OPCC. A substitution of fly ash for metakaolin results in superior efficiency of AAC compared to OPCC. Two mixtures of ultra-high-strength AAC (100 MPa) result in contradictory findings. One mixture with a sodium hydroxide and silica fume activating solution shows 5% and 30% less energy and CO2 emission, while the other mixture with a sodium hydroxide and sodium silicate activating mixture is less efficient than OPCC.