Effects of metakaolin on sulfate and sulfuric acid resistance of grouting restoration materials

Abstract

• Sulfate attack caused the internal expansion and disintegration of the sample. • Sulfuric acid attack caused the outer layer of the sample to fall off layer by layer. • The appearance characteristics and microstructure of sulfate and sulfuric acid in different attack periods. In this paper, the effect of metakaolin on the durability of grouting materials with the composition of natural hydraulic lime (NHL), sulfoaluminate cement (SAC), water-based epoxy resin (WER) and metakaolin (MK) in 5 % sodium sulfate solution and sulfuric acid solution (PH = 1) was investigated. A comprehensive study was carried out for sulfate and sulfuric acid solution attacked samples by the measurement of compressive strength, X-ray diffraction (XRD), scanning electron microscopy (SEM) etc. The results showed that the addition of MK could effectively enhance the resistance of sulfate and sulfuric acid. For samples immersed in sulfate solution, larger ettringite crystals were formed inside and the crystals were cross-supported with each other, causing macroscopic expansion and cracking. Due to the attack of sulfuric acid, the calcium carbonate in the outer layer converted into gypsum, which caused the outer layer of the samples fell off layer by layer. The addition of MK could consume calcium hydroxide through pozzolanic reaction during curing. The reduction of calcium hydroxide was beneficial to hinder the conversion of monocarboaluminate to ettringite. In addition, the addition of MK could reduce the carbonization depth, which closely linked to the number of layers that fell off during sulfuric acid attack.