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• The addition of SPOP improved the W-D cycle resistance of the low-grade sand. • SPOP membranes provided a combination of adhesive, filling, and bridging effects for treated sand. • Cyclic wetting and drying damage the bridging effect of polymer membranes. • The porosity increased, and micropores were developed to mesopores and macropores after 20 W-D cycles. Polymer materials are finding increasing application in soil stabilization, but little is known about the changes in performance and microstructure of polymer membranes under wetting–drying (W-D) cycles. This paper introduced a self-developed porous organic polymer material (SPOP) to investigate the mechanical properties of treated sand under various SPOP contents (1 %, 2 %, 3 %, and 4 %) and W-D cycles (0, 4, 8, 12, 16, and 20) using uniaxial compression tests and triaxial tests. The changes in the microstructure of SPOP-sand mixtures were observed by scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The results indicated that the addition of SPOP significantly increased the mechanical strength, elastic modulus, and cohesion of natural sand under W-D cycles. The mechanical properties exhibited an upward trend before decreasing as the increment of SPOP contents and peaked at 3 % SPOP content. Specimens with high SPOP content were more susceptible to moisture. On the other hand, the mechanical properties of SPOP-sand mixtures decreased significantly for all specimens under the first 4 cycles, followed by a decrease with increasing cycles exponentially. The NMR test showed the proportion of micropores within the specimens decreased by 27.81 %–48.09 % after wetting. The micropores were transformed into mesopores and macropores, and the porosity of specimens was increased. Based on the SEM images, there were three mechanisms of polymer strengthening sand, including wrapping, pore filling, and bridging effects. Alternate W-D cycles damaged the inter-particle bridging effect, thus weakening the bonding strength between the polymer membrane and sand particles. Soil aggregates inside the specimens were loosened, and polymer membrane was softened and broken under cyclic wetting and drying, causing the unstable structure of the specimen when applied external pressure. [ABSTRACT FROM AUTHOR]

• The structure and properties of coarse slag and fine slag have obvious difference. • Residual carbon from slag hinders the cementitious reaction of slag and cement or lime. • Active mineral phases from slag contribute significantly to the pozzolanic reactions between slag and cement or lime. • The binding properties of slag mortar were promoted by adding an appropriate amount of lime. In order to extend the utilization of slag in concrete, it is a key to understand the reaction mechanism of coal gasification slag with cement or lime. This article focus on the characteristics of gasification slag and hydration products of slag with cement or lime by analyzing microstructure, elements, mineral composition and slag mortar strength. The microstructure and composition were determined by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS), transmission electron microscopy (TEM) with energy dispersive X-ray (EDX) and X-ray diffractometry (XRD). The results show that the content of residual carbon in the fine slag is evidently more than that of coarse slag and residual carbon hinders the cementitious reaction between slag and cement or lime. In addition, many hydrated products, such as ettringite, okenite and C-S-H gels, are detected in the mortar mixed coarse slag, which indicates that there is positive interaction between the coarse slag with the cement. The abundant active mineral phases in the coarse slag can facilitate the cementitious reaction, and enhance the mortar strength. It is also found that the lime can effectively activate the SiO 2 and Al 2 O 3 mineral phases in the coarse slag to form hydration products, and the calcite from hydration reaction is favorable to improve the strength of mixtures. [ABSTRACT FROM AUTHOR]

• The compositions of five different bitumens were analyzed before and after aging. • The composition of the "bee" structures in bitumen is correlated with the presence of resins and asphaltenes. • The surface morphology is greatly influenced by the composition. • Some correlations between composition and micro-structure evolution during aging were observed. Aging is an important cause of the performance decline for bitumen. Research on the composition and micro-structure contributes to a better understanding of the bitumen aging. In this study, five bitumens from different oil sources were chosen for the aging tests and then separated into four compositions. Gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) were utilized to test molecular weight, prominent function groups and surface morphology of single composition, respectively. Moreover, prominent function groups and surface morphology of the five bitumens before and after aging were investigated by FTIR and AFM. Based on the experimental evidences, it was found that light compositions were evolved into heavy compositions and prominent function groups increased after aging. The "bee" structures observed by AFM on bitumen surface probably originated from asphaltenes and partial resins and they became gradually indistinguishable after aging. Besides, some sunken regions or micro-cracks appeared around the "bee" structures after aging. There are some correlations between composition variation and micro-structure evolution during aging. The greater the colloid index decreased, the faster the indexes of the carbonyl functions and the sulfoxide functions grew, and the peak height and roughness of surface morphology on bitumen decreased with the decline of the colloid index. [ABSTRACT FROM AUTHOR]