Li Yang

The declining availability of fly ash has intensified the need to identify alternative supplementary cementitious materials (SCMs) capable of maintaining engineering performance while improving durability and reducing greenhouse gas (GHG) emissions. This study evaluates three locally sourced natural pozzolans (NPs) as potential regional alternatives to fly ash (FA), with particular emphasis on alkali–silica reaction (ASR) mitigation performance, hydration behavior, mechanical properties, setting characteristics, and embodied carbon reduction. Physical and chemical characterization revealed high silica contents (65–71%) and relatively fine particle size distributions (d50 between 10 and 14 μm). Accelerated mortar bar testing demonstrated that the natural pozzolans provided substantially greater ASR mitigation than FA. While the FA mixtures continued to exhibit noticeable expansion growth during the testing period, NP1 and NP3 maintained expansion values near or below the commonly used 0.10% mitigation threshold and exhibited significantly reduced visible surface cracking, indicating superior resistance to ASR-related deterioration. Isothermal calorimetry indicated slightly lower early-age heat release for the NP systems compared with OPC and FA, reflecting reduced clinker content and moderate pozzolanic reactivity. Although the natural pozzolans generally exhibited lower early-age strength and stiffness than FA, all NP systems demonstrated continuous long-term mechanical development. At 91 days, compressive strength and dynamic modulus reached up to 83% and 92% of OPC, respectively, with NP1 showing the closest overall mechanical performance to FA. In contrast to FA, the natural pozzolans accelerated both initial and final setting times. A cradle-to-gate life cycle assessment further showed that SCM incorporation significantly reduced embodied carbon emissions, with natural pozzolans achieving greater carbon reduction than FA at equivalent replacement levels. Overall, the results demonstrate that locally available natural pozzolans, particularly NP1 and NP3, can serve as promising alternatives to fly ash by combining superior ASR mitigation performance, meaningful long-term mechanical properties, and substantial carbon reduction potential.

Supersulfated cement (SSC) is an environmentally friendly cementitious material with a low clinker content, in which industrial byproduct gypsum serves as the sulfate source, thereby enabling the valorization of solid waste. The hydration process, pore structure, microstructure, and hydration products were investigated using paste samples by means of isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TG–DTG), Fourier transform–infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM), while compressive strength was evaluated using mortar specimens. Compared with ordinary Portland cement (OPC), SSC offers clear advantages in reducing energy consumption and greenhouse gas emissions. In this study, the effects of titanium gypsum (TG) and flue gas desulfurization gypsum (FGD) on the hydration behavior, fluidity, mechanical properties, and microstructural evolution of an anhydrite (AH)–phosphogypsum (PG)-based SSC were systematically investigated. The results indicate that the incorporation of 11% TG and FGD mitigates the strong sulfate environment caused by the rapid dissolution of soluble AH, thereby regulating the hydration process. As the proportion of TG and FGD increased, the cumulative heat release within 72 h gradually decreased. When AH was completely replaced, the cumulative heat release of TG4 and FG4 decreased by approximately 19.7% and 28.6%, respectively. TG and FGD exhibited opposite effects on the fluidity of SSC while both promoting strength development. Among all mixtures, TG2 and FG2 showed the best performance, with the highest 28-day compressive strengths of 50.15 MPa and 51.95 MPa, respectively. Microstructural analysis reveals that differences in particle size distribution and dissolution kinetics among gypsums governed the sulfate release characteristics and slag activation mechanisms, thus leading to distinct hydration pathways, pore structure evolution, and microstructural densification. This study provides a theoretical basis for the efficient utilization of various industrial byproduct gypsums and offers important guidance for the controllable design of SSC performance.

Pervious concrete is challenged by the inherent trade-off between permeability and mechanical strength. This study presents a systematic optimization of its mix design to achieve a balance between these properties. Single-factor experiments and an L₉(3³) orthogonal array test were employed to evaluate the effects of target porosity (14–26%), water–cement ratio (0.26–0.34), sand rate (0–10%), and VMA dosage (0–0.02%). Additionally, Spearman rank correlation analysis and nonlinear regression fitting were utilized to develop quantitative relationships correlating the measured porosity to material performance. The results revealed that increasing target porosity enhances permeability but reduces compressive and splitting tensile strengths. The optimal water-to-cement ratio (w/c) was found to be 0.32, balancing both permeability and strength. An appropriate sand content of 6% improved mechanical properties, while a VMA dosage of 0.01% effectively enhanced bonding strength and workability. The orthogonal experiment identified the optimal mix ratio as a w/c ratio of 0.3, VMA dosage of 0.12%, target porosity of 14%, and sand content of 7%, achieving a compressive strength at 28-days of 43.5 MPa and a permeability coefficient of 2.57 mm·s⁻¹. Empirical relationships for the permeability coefficient and mechanical properties as functions of the measured porosity were derived, demonstrating a positive exponential correlation between the measured porosity and the permeability coefficient, and a negative correlation with compressive and splitting tensile strengths. This research provides a systematic framework for designing high-performance pervious concrete with balanced permeability and mechanical properties, offering valuable insights for its development and application in green infrastructure projects.