Studies have indicated that alkali-activated concrete (AAC) is comparable to ordinary Portland cement concrete (OPCC) in terms of mechanical properties (eg. compressive strength, tensile strength, flexural strength, and modulus of elasticity) and can deliver environmental advantages compared to OPCC. This research assesses the energy and CO2 emissions associated with OPCC and AAC. Three grades of concrete were selected; 40, 60, and 100 MPa to cover a wide range of concrete that can be used for several purposes. The 40 MPa is considered standard strength concrete, and it is common for most structural uses where exceptional compressive is not required. On the other hand, the 60 MPa is high strength concrete with compressive strength > 55 MPa. Finally, the 100 MPa is ultra-high- strength concrete with compressive strength ≥ 100 MPa. Analysis shows that the selection of constituent materials can considerably influence the energy and emission of AAC and OPCC. Ordinary Portland cement (OPC) is the primary contributor to the energy and emission of OPCC, accounting for 80% of energy and 91% of emissions of OPCC. The activating solution of AAC, 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 sodium hydroxide and silica fume activating solution shows 5% and 30% less energy and emission, whereas the other mixture with a sodium hydroxide and sodium silicate activating mixture is less efficient than OPCC.
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