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[Display omitted] • The addition of CaO and SO 3 can increase the strength of geopolymer cured at ordinary temperature; • The CaO and SO 3 increase the water immersion expansion rate of geopolymer; • Ettringite and calcium silicate hydrate gel are formed in fly ash based geopolymer; • The slight expansion of ettringite effectively reduces the drying shrinkage of geopolymer. Fly ash based geopolymer is a green cementitious material with the potential to replace portland cement. Due to the changes of raw coal and coal combustion technology in recent years, the fly ash often has high CaO and SO 3 contents. The action mechanism of CaO and SO 3 on the mechanical properties and dimensional stability of fly ash-based geopolymers is not clear, which restricts its application. The influence of CaO and SO 3 content on the flexural strength, compressive strength, water immersion expansion rate and drying shrinkage rate of fly ash based geopolymer were studied, and X-ray diffractography (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and 29Si nuclear magnetic resonance (NMR) were used to study the influence mechanism of calcium and sulfur on the geopolymer. The results show that the mechanical properties of fly ash based geopolymers increase initially and then decrease with the increase of CaO and SO 3 content. When the contents of CaO and SO 3 are 11% and 4% respectively, the properties of geopolymer prepared at ordinary temperature (20 ℃) are the optimum. The 28d flexural strength and compressive strength can be increased by 17.91% and 15.56% respectively, and compared with the unmodified fly ash based geopolymer, the drying shrinkage is reduced by 60.65%. Microscopic test results show that the addition of CaO and SO 3 promoted the geopolymer reaction, increased the gel products and generated ettringite, which enhanced the strength of the matrix and compensated the shrinkage of geopolymer. [ABSTRACT FROM AUTHOR]

• Alkali-activated slag modified by chitosan was used to prepare pervious concrete. • The volumetric structural parameters of pervious concrete were optimized. • The pervious concrete with water purification was designed. A kind of alkali-activated slag pervious concrete (AAS-PC) was designed to purify rainwater to prevent it from polluting groundwater resources. The pervious concrete was designed from two aspects: the cementitious material and the volumetric structure parameters of pervious concrete. Chitosan was used in the cementitious material paste to enhance the adsorption capacity for heavy metal ions and other pollutants. In consideration of adsorption, composition parameters of the cementitious material paste such as the chitosan content, the mole ratio of SiO 2 /Na 2 O, and the concentration of alkali activator wereoptimized by orthogonal experiment. The influences of the bulk porosity of aggregate (BPA) and the ratio of paste to aggregate (P/A, mass ratio) on water purification capability, water permeability, and mechanical properties of the AAS-PC were investigated. It is found that, with the BPA increasing, the adsorption to Pb2+ and the compressive strength of pervious concrete decreased gradually but its water permeability improved; meanwhile, with the P/A increasing, its adsorption to Pb2+ and the compressive strength increased, but its water permeability decreased. There is a negative correlation between the water purification and the water permeability of the pervious concrete. Considering the water purification, water permeability and strength properties of the pervious concrete, the optimum BPA was 30% and the optimum P/A was 0.25. [ABSTRACT FROM AUTHOR]