The low atmosphere-pressure in plateau regions will affect the bubble stability, thus affecting the air-void structure and frost resistance of air-entrained concrete. The effect of atmosphere pressure on the pore structure of freshly mixed air-entraining mortar was investigated via constructing a self-built low atmosphere pressure mixing device. The results show that the decrease of atmosphere pressure can decrease the initial air content of air-entrained mortar, increase the bubble spacing coefficient as well as air content loss through time, and deteriorate the pore structure. The mechanism of low atmosphere pressure effect on the pore structure of air-entrained mortar is mainly since the reduced atmosphere pressure accelerates the Ostwald ripening process of the bubble system, which makes the small bubbles smaller until they disappear and the large bubbles larger until they break, and the average pore size of the bubble system increases, thus accelerating the destabilization rate of the bubble system. These findings have important implications for understanding the mechanism of bubble destabilization under a low atmosphere pressure and developing the corresponding bubble stabilization techniques.

The chloride resistance of blended cementitious materials can be improved by incorporating a high volume of supplementary cementitious materials (SCMs), thereby improving the durability and service life of concrete structures. However, their mechanical properties decrease significantly, especially at early age. To improve the early-age mechanical properties and chloride resistance, the type and addition of cementitious materials in the fine, mid-size, and coarse fractions were optimized based on particle close-packing and pore fillability during hydration. The blended cement pastes with greater chloride binding capacity and pore tortuosity are obtained due to the pore refinement of fine particles and efficient hydration of both clinker and SCMs. In addition, a blended cementitious material with 3-day compressive strength of 27.3 MPa and 28-day chloride diffusion coefficient of 0.36×10^-12 m²/s was prepared using only 59% clinker with a size range of 4-55 μm. The results provide a deeper insight in the microstructural optimization and durability improvement of cement-based materials.

To reveal the difference of corrosion mechanism of steel bars in concrete under Cl^- and SO₄^2- action, and provide the theoretical basis for the control of concrete corrosion resistance under chloride and sulphate attack, the electrochemical behavior of reinforcement subjected to Cl^- and SO₄^2- in concrete pore solutions was investigated, and the competitive adsorptions of corrosive ions (Cl^-, SO₄^2-) and passive ions (CaOH⁺, OH^-) on the Fe (100) surface were analyzed by the density functional theory based on the first-principles. The results show that the corrosion potential and polarization resistance of steel reinforcement in concrete pore solution with SO₄^2- both are lower than those in concrete pore solution with Cl^-, indicating that the steel reinforcement corrosion occurs more easily in concrete pore solution with SO₄^2-. The inhibition effect of SO₄^2- on the reaction of OH^- and iron surface is slightly stronger than that of Cl^-. Moreover, SO₄^2- can promote the elongation of Ca-OH bond, and block the interaction of the OH group in CaOH⁺ and surface Fe atom, showing that the inhibition effect of SO₄^2- on the reaction of CaOH⁺ and iron is stronger than that of Cl^-. The results reveal the corrosion mechanism of steel reinforcement under the attack of Cl^- and SO₄^2- in concrete.

To further understand the influence of climate environment on the microstructure of concrete materials in northwestern China, the microstructure characteristics of concrete under different temperature and humidity curing conditions were investigated by a nano-indentation technology. The results show that the lack of curing temperature and humidity leads to the increase of capillary pores and low-density calcium silicate hydrate (C-S-H) gel content in cement mortar. The indentation modulus and hardness of concrete interfacial transition zone (ITZ) under different curing conditions were statistically analyzed. It is indicated that the average thickness of concrete ITZ is increased by 5 μm and 10 μm when the curing conditions are 10 ℃-70% relative humidity (RH) and 3 ℃-50% RH, respectively, compared with that the curing condition is 20 ℃-95% RH.

The orientation of steel fibers has an effect on the mechanical properties of steel fiber reinforced concrete (SFRC). In elements or structures such as slabs, floors and pavements, vertical steel fibers are useless but harmful to the structures. In this case, the optimal distribution of steel fibers is two-dimensional (no vertical, but random in the plane) dispersion. In this paper, the steel fibers were aligned using a rotating uniform magnetic field, and the 2D aligned steel fiber reinforced concrete (2D-SFRC) was prepared to enhance the mechanical properties of SFRC and the efficiency of reinforcement of steel fibers. The splitting tensile performance, flexural behavior of prism and circular plate specimens of 2D-SFRC were tested and compared with those of the specimens with randomly distributed steel fiber reinforced concrete (RD-SFRC). Besides, the mechanism of reinforcement of 2D-SFRC was investigated from the perspective of fiber distribution characteristics and acoustic emission signals. The results show that the mechanical properties of 2D-SFRC are significantly improved, compared with RD-SFRC. The fiber distribution statistics and acoustic emission analysis indicate that the increased amount of steel fibers in the fracture surface and enhanced fiber orientation effective factor are the main reasons for the improved mechanical properties of 2D-SFRC. The 2D-SFRC has the characteristics of high performance and low cost, which is of great significance for improving the engineering quality and reduce the materials consumption.

It is essential to ensure the concrete construction quality of high arch dam via comprehensively collecting multi-source heterogeneous information in the concrete vibration construction and timely and objectively analyzing vibration quality. For incomplete information perception and undesirable data quality in current space-ground perception technology during concrete vibration construction, an intelligent sensing scheme with space-air-ground integration for concrete vibrating construction information was established to realize the stereoscopic perception of multi-source, multi-modal and multi-scale construction information in the concrete pouring process. On this basis, the Kalman-based denoising method for positioning data of Global Navigation Satellite System (GNSS), improved Faster R-CNN-based video analysis method and DebrGAN-v2-based surface image deblurring method were proposed, respectively, for numerical type, video stream, and image information. Taking Yangfanggou hydropower station as an example, the intelligent analysis and monitoring of concrete vibration quality can be realized by the proposed space-air-ground integration sensing method.

Anti-thermal cracking is one of key issues for construction quality control of mass concrete. This paper introduced an intelligent monitoring technology of anti-thermal cracking for mass concrete. The temperature cooling process was optimized by thermal stress tests conducted on the temperature-stress testing machine. The real-time evaluation and prediction models targeting on adequate concrete temperature were established based on the real-time collected information at different stages of mixing, casting, cooling and insulation. The models can achieve precise index monitoring and dynamic warning of concrete temperature, and control concrete parameters such as temperature automatically and intelligently. The technology shows a good application effect on the mass concrete temperature control optimization and real-time monitoring, and it can be popularized in the similar projects.

Carbonatable binder is a developed type of cementitious material that reacts with CO₂ and is capable of binding other ingredients to form a monolith with mechanical strength. Manufacturing carbonatable binder-based carbonated products is an important route for the utilization of CO₂ as a research hotspot. This review elucidated the definition of carbonatable binder and its mineral composition, analyzed the carbonation reaction mechanism, microstructure evolution and the mechanical performance along with the multi-species transport mechanism, and introduced the three main categories of carbonatable binders and their applications. In addition, the future research areas and the application prospects were also given.

The ultra-high performance concrete materials (UHPC) are developed rapidly and are widely used in bridge engineering and other fields. The corresponding advantages involve the reducing dead weight, simplifying reinforcement details, shortening construction period, and improving durability. The comprehensive economic and technical benefits are achieved. This review represented recent development on the UHPC building structures. The characteristics of UHPC structure and the current engineering application were summarized, and the basic design principles and methods were analyzed. Recent studies on the UHPC building structural components and joints were introduced, including lightweight thermal insulation sandwich roof panels, sandwich floor/wall panel-based prefabricated structures, two-way waffle slabs, post-poured beam-column joint in precast reinforced concrete frame, prefabricated frames based on the UHPC connections, etc.. Some methods and benefits of UHPC application in building structures were concluded. In addition, the future research aspects of UHPC building structure were also given to promote the application of UHPC in building structure and improve its comprehensive performance and quality.

As a key mineral of low carbon and high corrosion resistant cement clinker, ferrite phase plays an important role in improving the burnability of cement raw meal, the formation and hydration of clinker, and the ability of cement to corrosion resistance. This review represented recent work on the physicochemical properties of ferrite phase and the influence of ferrite phase on Portland cement and calcium sulphoaluminate cement. The effect of ferrite phase on the mineral formation, hydration rate and hydration product, mechanics and corrosion resistance of two cement clinker was emphatically discussed. In addition, some issues that need to be solved urgently and the application prospect of low-carbon high corrosion resistant cement were also represented.