Bo Li

As tangible witnesses and cultural carriers of the evolution of Chinese civilization, earthen heritage sites embody outstanding historical, cultural, and scientific value. However, due to the heterogeneity among sites and their long-term exposure to complex environmental and anthropogenic pressures, their conservation faces numerous challenges. This paper provides a comprehensive review of the deterioration mechanisms of earthen heritage sites in China induced by environmental and anthropogenic factors, with particular emphasis on the effects of individual factors, such as salt-induced erosion, wetting–drying cycles, wind erosion, microbial activity, freeze–thaw cycles, and human activities, as well as the coupled actions of multiple factors. It further summarizes recent progress in protective technologies developed in response to these mechanisms, as well as integrated conservation strategies for coping with coupled deterioration effects. In recent years, the intrinsic linkage mechanisms between external environmental conditions and the engineering performance of earthen heritage sites have become a research focus. This review aims to deepen the understanding of environmental degradation processes in earthen heritage sites and to provide theoretical and technical support for the scientific formulation of targeted preventive conservation, repair, and strengthening measures.

The utilisation of excavated soil with high moisture and high viscosity faces challenges such as complex dehydration processes and difficult material dispersion. Controlled Low-Strength Material (CLSM) provides a feasible pathway for its dehydration-free resource utilisation. To enhance sustainability, alkali-activated materials can replace Portland cement as the binder in CLSM. However, the influences of activator concentration on CLSM performance remain unclear, and the dispersibility of high-viscosity soil needs further improvement. Therefore, this study develops a novel CLSM using high-viscosity excavated soil and alkali-activated slag, with coal bottom ash (CBA) introduced to improve its dispersibility. Through flowability, setting time, and compressive strength tests, the influences of binder content, alkaline dosage, silicate modulus, soil-to-aggregate ratio, and wet-dry cycles on CLSM performance are systematically investigated, followed by hydration heat and thermogravimetric analyses to reveal the underlying mechanisms. The results demonstrate that increasing the binder content promotes hydration and enhances the mechanical properties of CLSM. CBA can effectively improve flowability but has limited effects on hydration and strength enhancement. Increasing the alkaline dosage accelerates early hydration and increases 7-day compressive strength but may retard later-stage strength development. Reducing the silicate modulus is beneficial to early hydration and performance, whereas a high modulus presents higher later-stage compressive strength. Wet-dry cycles exert dual effects on CLSM through promoting hydration and inducing internal crack propagation, ultimately resulting in strength degradation under wet-dry cycles. This paper provides a theoretical basis and technical reference for the efficient and low-carbon resource utilisation of high-viscosity excavated soil as filling material.

The widespread application of alkali-activated soil-based artificial aggregates (AAs) is limited by their low early strength and high-water absorption, creating an imperative for effective enhancement methods. This study...

Ultra-high-performance concrete (UHPC) often faces challenges due to its low water-to-binder ratio. In this case, cement particles will be unable to fully hydrate, resulting in a high degree of initial dimensional instability. As a promising solution, superabsorbent polymers (SAP) and natural zeolite have potential in mitigating shrinkage and achieving self-stressing properties. Despite prior research on strength, shrinkage, and hydration of UHPC, no systematic study has examined the effects of SAP and natural zeolite on porosity and pore structure. To address this gap, a holistic testing program was established in this study to investigate how these materials affect the microstructural properties of UHPC, especially porosity and pore distribution. This included compressive strength, drying shrinkage, and autogenous shrinkage. The hardened mixtures were also characterized using mercury intrusion porosimetry, while nuclear magnetic resonance (NMR) technology was used to evaluate the pore parameters. The results show that UHPC incorporated with zeolite experiences less autogenous shrinkage than SAP due to the internal curing effect of zeolite particles. The compressive strength, however, is reduced attributed to a more porous microstructure. The outcome of this study provided valuable insights into optimizing the balance between durability and mechanical performance, paving the way for more sustainable and cost-effective applications of UHPC in modern construction practices.