Study on the cohesion and adhesion of hot-poured crack sealants

Filling crack sealant is a main method to repair cracking of pavement. The cohesion and adhesion of crack sealant directly determine its service performance and durability. However, the competitive mechanism of cohesion and adhesion failure modes is not clear currently. This research proposed two methods to evaluate cohesion and adhesion of crack sealant, and analyzed the influence of temperature on cohesion and adhesion. The effect of moisture on low- temperature performance of crack sealant was also be evaluated by conducting a soaking test. Results show that with the decrease of temperature, the cohesion force of crack sealant increases significantly, while the adhesion force changes little. There is a critical temperature at which the cohesion force equals the adhesion force. When the temperature is higher, the adhesion force will be greater than cohesion force, and the cohesion failure will happen more easily. In contrast, the adhesion failure will happen more easily when the temperature is lower than the critical value. Soaking in 25 ℃ water for 24-48 hours will slightly improve the low-temperature tension performance of crack sealant. However, soaking in 60 ℃ water for 24 hours will decrease the failure energy of low-temperature tension and damage the durability of crack sealant.

Local and regional contributions to PM_(2.5) in the Beijing 2022 Winter Olympics infrastructure areas during haze episodes

The 2022 Winter Olympics is scheduled to take place in Beijing and Zhangjiakou,which were defined as OIAs(Olympic infirastructure areas)in this study.This study presents the characteristics and source apportionment of PM_(2.5) in the OIAs,China.The entire region of China's Mainland,except for the OIAs,was divided into 9 source regions,including four regions in the BTH(Beijing-Tianjin-Hebei)region,the four provinces surrounding the BTH and the remaining areas.Using CAMx/PSAT,the contributions of the nine regions to the PM_(2.5) concentration in the OIAs were simulated spatially and temporally.The simulated source apportionment results showed that the contribution of regional transportation was 48.78%,and when PM_(2.5) concentration was larger than 75μg/m^(3) central Hebei was the largest contributor with a contribution of 19.18%,followed by Tianjin,northern Hebei,Shanxi,Inner Mongolia,Shandong,southern Hebei,Henan and Liaoning.Furthermore,the contribution from neighboring regions of the OIAs was 47.12%,which was nearly twice that of long-range transportation.Haze episodes were analyzed,and the results presented the importance of regional transportation during severe PM_(2.5) pollution periods.It was also found that they were associated with differences in pollution sources between Zhangjiakou and Beijing.Regional transportation was the main factor affecting PM_(2.5) pollution in Zhangjiakou due to its low local emissions.Stagnant weather with a low planetary boundary layer height and a low wind velocity prevented the local emitted pollutants in Beijing from being transported outside,and as a result,local emissions constituted a larger contribution in Beijing.