Influence of metakaolin on the conversion and compressive strength of quaternary phase paste

Application of calcium aluminate cement in construction faces the challenges of high manufacturing cost and volumetric instability associated with hydrates conversion. This work introduces a newly developed high‐performance Ca 20 Al 26 Mg 3 Si 3 O 68 (Q phase)‐metakaolin (MK) composite binder. The influence of MK on the conversion and strength development of Q phase paste cured at 40°C was investigated. The mechanism of MK on the stability of synthetic hydrate was studied by solution chemistry, XRD, and NMR. The pure Q phase paste experiences a significant strength reduction due to hydrates conversion, whereas the Q phase paste containing 15% MK exhibits a continuous increase in strength. MK promotes the formation of CAH 10 , contributing to the refinement of pore structure and enhanced mechanical property. The Al V and Al IV dissolved from MK increase the Al(OH) 4 ‐ concentration in the pore solution, and then the solubility of CAH 10 decreases due to the common‐ion effect, thus inhibiting the subsequent precipitation of C 3 AH 6 . In addition, the release of dissolved alumina from MK considerably impedes silica dissolution, and consequently, the formation of C 2 ASH 8 is hindered at a higher content of MK.