Cement Equivalence of Metakaolin for Workability, Cohesiveness, Strength and Sorptivity of Concrete

A series of concrete mixes with metakaolin (MK) content ranging from 0 to 30% and water/cementitious materials (W/CM) ratio varying from 0.30 to 0.50 were produced for performance testing. The results showed that adding MK up to 20% as ordinary Portland cement (OPC) replacement best improved the 28-day and 70-day cube strengths, whereas adding MK up to 30% as OPC replacement always increased the cohesiveness and decreased the sorptivity, but impaired the workability. Moreover, the cement equivalent factor (CEF), i.e. the equivalent mass of OPC per mass of MK added, for each performance attribute, including workability and cohesiveness, was evaluated. Whilst the actual CEF of MK was generally higher at a higher W/CM ratio and lower at a higher MK content, overall, the average CEFs were found to be 1.98, 2.17, 3.83, 1.93, 2.12, and 4.70 for slump, flow, cohesiveness, 28-day cube strength, 70-day cube strength, and sorptivity coefficient, respectively. These CEF values indicated that the MK is a highly effective cementitious material for improving the cohesiveness, strength, and durability. Moreover, it has been demonstrated that the CEFs for workability and cohesiveness are useful parameters in aiding the mix design of MK concrete.
This research was funded by National Natural Science Foundation of China (grant number 51678161), Research Project of Guangdong Provincial Education Department of China (grant number 2018GXJK197), Guangdong Provincial Education Department Educational Reformation Project (grant number 595 in year 2018), Research Centre of Green Building Materials and Modular Integrated Construction Technology of Guangdong Province of China (grant number ZCZX201803), Featured and Innovative Project for Colleges and Universities of Guangdong Province (grant number 2017KTSCX061) and Pearl River S&T Nova Program of Guangzhou City (grant number 201906010064)