This study examines the effects of three polymer binders—polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyacrylic acid (PAA) on the mechanical properties and dry–wet cycle corrosion resistance of cement mortar at different dosages (1–4%). Mechanical testing combined with scanning electron microscopy (SEM) and molecular dynamics (MD) simulations was conducted to validate the experimental findings and reveal the underlying mechanisms. Results show that polymers reduce early-age strength but improve flexural performance, and at low dosage, enhance compressive strength. PVA and PAA exhibited a pronounced improvement in mechanical strength while PVA and PEG showed a significant improvement in wet cycle corrosion resistance. SEM observations indicated that polymers encapsulate cement particles, enhancing interfacial bonding while partially inhibiting hydration. MD simulations revealed that PVA and PAA interact with Ca²⁺ via Ca-O coordination, while PEG primarily forms hydrogen bonds, resulting in distinct water-binding capacities (PEG > PVA > PAA). These interactions explain the enhanced mechanism of mechanical and dry–wet cycle resistance properties. This work combined experimental and molecular-level validation to clarify how polymer–matrix and polymer–water interactions govern mechanical and durability, respectively. The findings provide theoretical and practical guidance for designing advanced polymer binders with tailored interfacial adhesion and water absorption properties to improve cementitious materials.

In this study, cellulose nanocrystals (CNs) were utilized to enhance the mechanical properties and sulfate corrosion resistance of engineered cementitious composites (ECCs). The results of compressive strength and uniaxial tensile tests demonstrated that the incorporation of CNs significantly improved the compressive strength, strain rate, tensile strength, and sulfate corrosion resistance of ECC specimens. Scanning electron microscopy (SEM) observations revealed that the addition of CNs facilitated the formation of increased amounts of ettringite and calcium silicate hydrate (C-S-H) in the matrix, enhancing the hydration degree of the cementitious system and increasing the overall density of the ECC structure. Molecular dynamics simulations were employed to investigate the interactions between CN, C-S-H, water molecules, and sulfate ions (SO₄²⁻) while also calculating the kinetic parameters of atoms at the interface. These simulations provided insights into the microstructural strengthening mechanism of CNs in improving the sulfate corrosion resistance of ECCs. The results indicated that CNs adsorb onto C-S-H via Ca-O and H-O coordination, forming a protective layer that inhibits the penetration of SO₄²⁻ and water molecules into the C-S-H structure. Additionally, CNs form hydrogen bonds with SO₄²⁻ and water molecules, which restricts their diffusion and reduces their coordination with the C-S-H interface and the dissolution of SO₄²⁻ and water to the hydration product, thereby enhancing the sulfate corrosion resistance of ECCs.

In this work, the indoor thermal environment and indoor air quality of rural houses in Northern China were investigated in detail. The current heating situation in rural areas, the causes of indoor air pollution, and the indoor ventilation habits of residents were analyzed. The indoor thermal environment and indoor air quality were improved by upgrading the thermal insulation of the rural housing envelope and installing indoor ventilation systems with heat recovery, leading to an average indoor temperature increase of 6 °C. The Predicted Mean Vote reached approximately 1.0, so the human body heat sensation was more moderate. The air age was greatly reduced, and the indoor air quality was significantly improved. The Predicted Percentage of Dissatisfied dramatically decreased to 15%. Thus, when focusing on heat source renovation in rural areas, priority should be given to improving the energy efficiency of buildings, especially the building envelope insulation performance. Ventilation and air exchange systems with heat recovery are inexpensive and effective, and they are suitable for rural dwellings where the temperatures are not as high as they should be but where the indoor air quality is poor and ventilation is urgently needed.

Glass-enclosed courtyards are common in self-built rural housing, but their summer retrofit value is uncertain because temperature attenuation may coexist with overheating or moisture accumulation. This study compared three south-facing brick-concrete dwellings with glass-enclosed courtyards in Qingdao, China, and integrated matched field measurements with a 64-household survey. Outdoor-normalized temperature offsets, sampled range differences, psychrometric variables, moist-air enthalpy, and courtyard-room temperature separation were analyzed. Mean courtyard–outdoor temperature differences across 18 observations were +1.34, +0.64, and −0.12 °C for Cases 1–3. On 15 July, Case 2 reduced the sampled courtyard temperature range to 0.9 °C compared with 7.9 °C outdoors, while its mean courtyard humidity ratio remained 2.86 g/kg higher than outdoors. This contrast shows that attenuation of dry-bulb temperature variation does not necessarily imply a reduction in absolute air-moisture content. The survey showed that 55.6% of valid respondents reported hot-side summer sensations, while 47.6% identified improved summer ventilation and cooling as a desired retrofit outcome. The survey provides complementary implementation context, while shading, courtyard ventilation, and courtyard–room air-exchange control are identified as candidate measures for future intervention testing rather than as validated retrofit solutions.