Using industrial byproducts to replace cement is an important way to reduce carbon emissions from the cement industry. In this study, the effects of two industrial byproducts, fly ash (FA) and quartz powder (QZ), as supplementary cementitious materials (SCMs) on the macroscopic properties and microstructure of cement-based materials were experimentally investigated. The results of the compressive strength and ultrasonic pulse velocity experiments showed that QZ significantly mitigated the decrease in strength and ultrasonic pulse velocity caused by the reduction in cement dosage in the early stage. Moreover, the 28-day compressive strength of the FA group was comparable to that of the control group, and regression analysis indicated a negligible effect of FA addition on 28-day compressive strength. X-ray diffraction and Fourier transform infrared spectroscopy experiments showed that QZ can promote the hydration reaction in the early stage. Scanning electron microscopy images revealed that a layer of hydration products can form on the surface of FA after 28 days of hydration. Hydration heat experiments indicated that FA significantly reduces the release of hydration heat, while QZ promotes the formation of ettringite through nucleation effects in the early stage of hydration, thereby accelerating the release of hydration heat. Thermogravimetric analysis after 28 days showed that the amount of hydration products and calcium hydroxide produced decreased with the addition of cementitious materials. Finally, the use of FA and QZ was analyzed for carbon emissions and energy consumption. The results showed that using these two cementitious materials significantly reduces carbon dioxide emissions and energy consumption.

Groundwater seepage is influenced by various anthropogenic factors during urban construction, among which subsurface structures and surface hardening are two key factors. This study employed numerical simulations to investigate the impacts of rainfall infiltration on groundwater seepage under the effect of urban construction. A numerical model was established to predict groundwater level (GWL) in the phreatic aquifer (Aq0), incorporating the actual distribution of impervious surfaces and subsurface structures for a representative urban area in Shanghai. The model accounted for land surface conditions through rainfall infiltration coefficients, while subsurface structures were parameterized using equivalent hydraulic conductivity ( K eq ) derived from effective medium theory. Validation results show that the model achieved a maximum error of only 1.7%, demonstrating reliable performance in predicting groundwater seepage. There is 23.23% area with GWL declining more than 0.4 m in the actual scenario with 93% impervious surface hardening comparing without surface hardening. Prediction scenarios with varying reduction rates of impervious surface compared with the actual scenario ( R a ) were conducted to investigate the impact of surface hardening on GWL. The results indicate average GWL of the study area presents exponential decay with the impervious surface ratio. Further, the variations in GWL of Aq0 were investigated by reducing hardened surfaces in different locations with the same R a . As the proportion of underground structures in the reduced impervious surface increases, the area with the same increment of GWL decreases. Prioritizing low impact development in areas with lower subsurface structure density can significantly enhance the efficiency of groundwater recharge by rainfall infiltration.