Mechanical and durability properties of metakaolin blended with slag geopolymer mortars used for pavement repair

Abstract

Metakaolin (MK)-based geopolymers are usually treated with heat curing for variable lengths of time, which limit their application to areas beyond prefabricated components. In this paper, an experimental investigation was carried out to study the compressive, flexural, and bond strengths, as well as the dry shrinkage, durability, and microstructural characteristics of MK-based geopolymer mortar cured at ambient conditions for pavement repair with the inclusion of ground granulated blast furnace slag (GGBS) at replacement ratios of 0%–40%. Changes in the mass and strength of the geopolymer and ordinary Portland cement (OPC) mortars subjected to 3.5% sodium chloride solution, 5% sodium sulfate solution, and sulfuric acid solution (pH = 1) were used to investigate durability. In addition, a field application case of alkali-activated MK–GGBS mortar repair material indicated desirable construction based on visual observations and ground-penetrating radar scanning. The microstructures were studied by field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The results demonstrated that when the GGBS replacement ratio reached 30%, the mortar performed better than many pavement repair materials, with a desirable compressive strength (75.9 MPa), flexural strength (12.2 MPa), and bond strength (6.42 MPa). It also had a much lower dry shrinkage of 1/4–1 than that of OPC at 28 days with 10% GGBS inclusion. Further, it had superior durability under chemical environments, which can be attributed to fine void-filling particles and the formation of N-A-S-H-type and C-S-H-type gels. The degradation mechanism of the alkali-activated MK–GGBS binary system in a sulfuric acid environment was found to be based mainly on the leaching of metal cations, the destruction of alumina–silicate bonds, and the micro-expansion microcracks of the gypsum phase. A field application of the repair material indicated that it is desirable for construction, allowing for a quick reopening within 6 h, while the repaired pavement still performed well after 4 months of service.