Effects of metakaolin on mechanical and microstructural properties of ultra-high performance cement-based composites

The effects of metakaolin (MK) on the mechanical and microstructural properties of ultra-high performance cement-based composite (UHPCC) were studied in this paper. The microstructure of UHPCC was investigated via XRD, SEM, nanoindentation, X-ray CT, and other different analytical testing methods. The results indicated that the mechanical performance of UHPCC was improved with the adding of MK. Blended mortars with 10% MK showed the highest compressive and flexural strengths in comparison to the others. As a result of Ca(OH)(2) consumption through the pozzolanic reaction of MK, the interface was strengthened with the increase of curing time and the microstructure of MK blended mortar was denser than the mortar without addition of MK. Nanoindentation results revealed that most hydrated products of MK blended mortar was UHD C-S-H and a large quality of unhydrated cement existed in the mortar. X-ray CT results indicate that MK conduced to the distribution of steel fiber, thus improved the mechanical properties of UHPCC.