Evaluation of high-volume fly ash (HVFA) concrete modified by metakaolin: Technical, economic and environmental analysis

Incorporating high-volume fly ash (HVFA) to concrete is one of the effective means to reduce the carbon footprint of buildings, but it also leads to problems such as the slow performance development of concrete. In this study, metakaolin (MK) as a calcined clay mineral is used to modify HVFA concrete, and the multi-scale characteristics of concrete are studied. The results show that compared with plain concrete, the mechanical properties and the volume fraction of hydration products of HVFA concrete are reduced, and the microstructure becomes loose. When 20% of MK is used to replace FA, the 90-d compressive strength of HVFA concrete are similar to those of plain concrete, and the drying shrinkage and porosity are relatively lowest, and the microstructure is relatively dense. The performance enhancement of MK-modified HVFA concrete is attributed to the increase of C-S-H phase and the decrease of the content of pore phase. Meanwhile, incorporating an appropriate amount of MK can reduce the carbon footprint and cost of HVFA.(c) 2022 Elsevier B.V. All rights reserved.