Study on the efflorescence behavior of concrete by adding metakaolin

Abstract

This study utilized the equivalent replacement technique to substitute cement with metakaolin, examining its role in mitigating efflorescence commonly found on concrete building surfaces. Efflorescence was quantified through measurements of the efflorescence area, ionic concentration, and pH in the leach solution. The effect of metakaolin on the hydration products and microstructure was analyzed using X-ray diffraction, scanning electron microscopy, simultaneous thermal analysis, and proton nuclear magnetic resonance. For concrete samples with 20% metakaolin substitution, the efflorescence area decreased from 60.16% to 30.27%, the ion concentration of the leachate decreased from 259.18 mol/L to 174.60 mol/L, and the pH level declined from 11.40 to 10.69. In samples with a 15% metakaolin substitution rate, the concentrations of calcium hydroxide and calcium carbonate diminished, giving rise to additional hydration products. The incorporation of metakaolin also enhanced the pore structure of the concrete, elevating the mesopore proportion by 57.6%. Furthermore, the compressive strength after a standard 28-d curing period increased from 45.1 MPa to 53.3 MPa. Overall, the study demonstrates that the introduction of metakaolin produces favorable effects in attenuating concrete efflorescence and augmenting mechanical properties through mechanisms involving pozzolanic activity, nucleation effects, and microaggregate filling.