Durability performance of waste glass powder and calcium oxide added sodium carbonate-activated slag mortar

Abstract

Cement manufacturing consumes large quantities of natural resources, emits considerable amounts of greenhouse gases, and brings harm to the environment. Alkali-activated cementation materials are promising candidates to replace ordinary Portland cement. However, Na2CO3-activated slag mortars suffer from long setting times, low early strengths, and poor durability. In this study, CaO and recycled waste glass were added to Na2CO3-activated slag mortars to overcome these issues. Accordingly, in this experiment, the effects of the CaO and glass powder (GP) contents on the setting time, fluidity, compressive strength, drying shrinkage, chloride ion electric flux, sulfate erosion, and fire resistance of Na2CO3-activated slag mortar were investigated. X-ray diffraction and nuclear magnetic resonance were used to characterize the reaction products and pore structure. It was found that the initial setting time and final setting time of slag mortar activated by sodium carbonate are more than 3 days. The setting time and fluidity of mortar decrease with the increase of calcium oxide. When 4% calcium oxide was added, the initial and final setting time was reduced to 95 min and 160 min, and the fluidity was reduced to 170. However, after GP replaced part of the slag, the setting time and mobility increased. The effect of CaO content on compressive strength and drying shrinkage of sodium carbonate activated slag mortar is similar (increasing first and then decreasing). The main reason may be that when CaO content is less than 6%, the calcite generated in the reaction fills the pores, which makes the number of pores in smaller pores (less than 50 nm) increase and the structure becomes more dense. GP is good for reducing drying shrinkage, but not good for early compressive strength. CaO is beneficial to improve the chloride ion erosion resistance of sodium carbonate activated slag mortar, which is related to the porosity and the adsorption of hydrotalc. The addition of GP has no effect on the improvement of chloride ion erosion resistance of CaO and sodium carbonate composite activated slag mortar, but the chloride ion electric flux is lower than 1200 C at 28 d. CaO and GP are beneficial to improve the resistance of alkali-excited slag mortar to sulfate attack. The effect of CaO on the resistance to sulfate attack is mainly related to the porosity and the content of hydrotalcite. The effect of GP on the resistance to sulfate attack is mainly related to the silicon and aluminum separated by GP. CaO and GP are beneficial to improve the fire resistance of alkali-excited slag mortar. The increase of fire resistance is related to decomposition temperature and content of reaction products. The combination of CaO and Na2CO3 to activate the slag and the addition of GP were significantly better than the use of only Na2CO3 to activate the slag.