This work provides a case study on the indoor environment and ventilation rate of naturally ventilated research student rooms in Chinese universities. In the measured room, air temperature, relative humidity and carbon dioxide (CO₂) concentration were monitored during the heating period for 4 weeks. The number of indoor occupants, occupied time of the room and window/door-opening cases were simultaneously recorded. Results showed the research student room was occupied for an average of 12.0 h each day. Due to a large indoor and outdoor temperature difference during the heating season, and occupants’ adaption to indoor environment, indoor occupants seldom open windows/doors for ventilation. Air exchange of the room only by air infiltration cannot meet the ventilation requirement. As a result, an average of 77.6% of measured CO₂ data each day exceeded 1000 ppm during occupied time. In fact, according to CO₂ data, it was observed that window/door opening could effectively decrease indoor CO₂ concentration. Therefore, intermittent window/door opening or CO₂-based demand-controlled ventilation facilities were suggested for improving indoor air quality of such rooms. Additionally, special attention should be paid to other possible outdoor pollution.

Residual mortar on recycled fine aggregate contains pores and microcracks that weaken mortar strength and resistance to water ingress. This study treated recycled fine aggregate with 5 wt.% KH570 silane and used waste ceramic micropowder, at 4–12% of the total recycled fine aggregate mass, to replace an equal mass of the fraction not exceeding 0.6 mm. At a constant water-to-cement ratio and comparable flowability, compressive strength, flexural strength, 28 d water absorption, and maximum water pressure without visible leakage were evaluated, together with SEM, XRD, and MIP analyses. Mortar strength first increased and then decreased with increasing ceramic micropowder content, whereas water absorption showed the opposite trend. Among the tested replacement levels, SCR8 achieved the most favorable mean performance, with 28 d compressive and flexural strengths of 42.4 and 6.0 MPa, respectively, 38.6% and 25.0% higher than those of the unmodified recycled mortar. Its water absorption decreased by 36.4% to 7.48%, and it sustained 0.6 MPa without visible leakage. Microstructural results indicated fewer local defects, improved interfacial continuity, lower cumulative mercury intrusion, and a shift toward smaller pore throats. These improvements could be associated with combined regulation of aggregate wettability and pore-throat structure.

Polypropylene (PP) fiber-reinforced soil slopes undergo progressive resistance degradation under wet–dry cycling (WDC), while stochastic seismic loading introduces additional uncertainty, challenging deterministic seismic assessment. This study develops a time-dependent seismic reliability framework integrating the probability density evolution method and the equivalent extreme value event method. The cohesion and internal friction angle of unreinforced soil measured at different WDC states are represented as cross-correlated lognormal random fields and combined with random fiber configurations and weighted nonstationary stochastic ground motions in a nonlinear dynamic model. The main contribution is a unified uncertainty-propagation scheme that incorporates experimentally characterized WDC degradation and multiple uncertainty sources into the evolution of response probability and multilevel first-passage reliability. With increasing WDC number and PGA, the extreme displacement distributions shift toward larger values, accompanied by increased response dispersion, tail risk, and reliability loss. The reliability evolution exhibits three stages, namely initial stability, rapid degradation, and residual convergence, during the 70 s excitation. PP fiber reinforcement improves reliability, although the marginal gain becomes limited when the fiber content exceeds 0.15% under the present numerical conditions. The proposed framework provides a probabilistic basis for the seismic assessment and deformation control of PP fiber-reinforced soil slopes at different WDC degradation states.