Geopolymers are prepared by alkali solution‐activated natural minerals or industrial waste materials, which have been widely used as new sustainable building and construction materials for their excellent thermal and mechanical properties. The thermal and mechanical properties of geopolymers at high temperature have attracted great attention from many researchers. However, there are few systematic works concerning these two issues. Therefore, this work reviewed the thermal and mechanical behaviors of geopolymers at high temperature. Firstly, the thermal properties of geopolymers in terms of mass loss, thermal expansion, and thermal conductivity after high temperature were explained. Secondly, the mechanical properties of residual compressive strength and stress‐strain relationship of fly ash geopolymers and metakaolin geopolymers after high temperature were analyzed. Finally, the microstructure and mineralogical characteristics of geopolymers upon heating were interpreted according to the changes of microstructures and compositions. The results show that the thermal properties of geopolymers are superior to cement concrete. The geopolymers possess few mass loss and a low expansion ratio and thermal conductivity at high temperature. The thermal and mechanical properties of the geopolymers are usually closely related to the raw materials and the constituents of the geopolymers. Preparation and testing conditions can affect the mechanical properties of the geopolymers. The stress‐strain curves of geopolymer are changed by the composition of geopolymers and the high temperature. The silicon‐type fillers not only improve the thermal expansion of the geopolymers but also enhance mechanical properties of the geopolymers. But, they do not contribute to reducing the thermal conductivity. the different raw materials, aluminosilicate precursor and reinforcement materials, result in different geopolymer damage during the heating. However, phase transitions can occur during the process of heating regardless of the raw materials. The additional performance enhancements can be achieved by optimizing the paste formulation, adjusting the inner structure, changing the alkali type, and incorporating reinforcements.

Modified cement mortar was prepared by incorporating a superabsorbent polymer (SAP) with two kinds of dosing state, dry powdery SAP and swelled SAP (where the SAP has been pre-wetted in tap water), respectively. The mechanical properties, drying shrinkage and freeze–thaw resistance of the mortars were compared and analyzed with the variation of SAP content and entrained water-to-cement ratios. Additionally, the effect of SAP on the microstructure of mortar was characterized by scanning electron microscopy (SEM). The results indicate that agglomerative accumulation is formed in the voids of mortar after water desorption from SAP and there are abundant hydration products, most of which are C-S-H gels, around the SAP voids. The incorporation of the powdery SAP increases the 28 d compressive strength of the mortars by about 10% to 50%, while for the incorporation of swelled SAP, the 28 d compressive strength of the mortar can be increased by about −26% to 6%. At a dosage of 0.1% SAP and an entrained water–cement ratio of 0.06, the powdery SAP and the swelled SAP can reduce the mortar shrinkage rate by about 32.2% and 14.5%, respectively. Both the incorporation of powdery and swelled SAP has a positive effect on the freeze–thaw resistance of cement mortar. In particular, for powdery SAP with an entrained water-to-cement ratio of 0.06, the mass loss rate after 300 cycles is still lower than 5%.

Low atmospheric pressure (LAP) can enormously affect properties of cement concrete in plateau areas. There are fewer studies and attendances on this issue than those of cement concrete in normal atmospheric pressure (AP), because of the limitations of both environmental conditions and instruments. In order to improve properties of cement concrete under LAP, influences of LAP on properties of cement concrete were reviewed in this work. The influence rules and mechanism on properties of cement concrete were summarized. The corresponding mechanism and techniques were put forward for enhancing the properties of cement concrete. The results of researchers show that LAP can significantly reduce the air entraining ability of the air entraining agent (AEA). Air content in concrete linearly decreases with the decrease of AP when other conditions are constant. If the initial air content is high, the decrease rate of air content increases with the decrease of AP. When the initial air content in cement concretes is similar, the greater the slump of cement concrete, the stronger its resistance to the decrease of air content caused by the decrease of AP. In addition, the condition of the bubble characteristics of hardened cement concrete under LAP is worse than that under normal AP. Therefore, the change of concrete properties under LAP is mainly attributed to these bubble characteristics, such as air content, bubble spacing coefficient, bubble radius and bubble specific surface area. In this work, nano-silica (negative charges) with cationic oligomeric surfactants is recommended as a new type of AEA to optimize the bubble characteristics under LAP in plateau areas.

To address the increasing air pollution caused by vehicle exhaust, environment-friendly pavement materials that possesses exhaust-purifying properties were prepared using common cement concrete and porous cement concrete as the base of photocatalyst nano-titanium dioxide (TiO₂), respectively. Firstly, Fe³⁺-doped TiO₂ powder was prepared by applying planetary high-energy ball milling in order to improve the efficiency of the semiconductor photocatalyst for degrading vehicle exhausts. Two nano-TiO₂, namely the original and modified nanomaterials, were adopted to produce the photocatalytic cement concretes subsequently. The physicochemical properties of the modified powder, as well as the mechanical and photocatalytic properties of TiO₂-modified concrete, were characterized using a suite of complementary techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), compressive strength and degradation efficiency tests. The results show that the ball milling method not only successfully doped Fe³⁺ into catalysts but also caused significant changes in: (1) decreased particle sizes, (2) more amorphous morphology, (3) decreased percentage of the most thermodynamically stable crystal facet, and (4) increased percentage of other high gas sensing crystal facets. Both the original and modified nano-TiO₂ can improve the concrete strength while the strengthening effect of modified nanomaterials is superior. It is pronounced that the photocatalytic property of the modified nano-TiO₂ is much better than that of the original nano particles, and the degradation rate of porous concrete is also better than common concrete when exposed to the same photocatalyst content. In a comprehensive consideration of both mechanical performance and degradation efficiency, the recommended optimum dosage of TiO₂ is 3% to 4% for exhaust-purifying concrete.

To investigate the properties of antifreeze asphalt mixtures (AFAC), the dense-graded and gap-graded asphalt mixtures, AC-13 and SMA-13, containing 2, 4, 5, 6, and 4 % by weight and 5, 6, 7, and 8 % by weight antifreeze filler, respectively, were used in this paper. In the experiments, Marshall, rutting, bending beam, and immersion Marshall tests were used to study the engineering performances of AFAC. In addition, a conductivity test was carried out to evaluate the salt releasing law under static state condition. Results show that the properties of AFAC are affected by the gradation composition and content of antifreeze filler. It is suggested that the content of antifreeze filler is $3\sim 6\%$ by weight according to the Marshall test. The composition type of asphalt mixture is an important factor in AFAC because the durability of SMA-13 is worse than that of AC-13. Moreover, the salt releasing process is divided into three steps based on the conductivity test.