The effects of xenon lamp and wear on the waterproofing effect of silicone emulsion were investigated. The results show that the surface impregnated treatment with silicone resin on concrete can improve the hydrophobicity of concrete, and reduce the capillary water absorption of concrete, and the effect becomes dominant with the increase of coating amount. After 90-d xenon lamp test, the contact angle of the surface impregnated concrete and the water absorption curve of the surface impregnated concrete do not change much. The surface impregnated concrete after aging still shows a good hydrophobicity. The existence of the main chain of Si-O-Si leads to a good aging resistance of silicone resin. The hydrophobicity of surface impregnated concrete with silicone resin decreases gradually with the increase of worn depth.

The dynamic characteristics of cement paste samples with different contents (mass ratio to cement) of carbon nanotubes (CNTs) under impact loads were investigated by a split Hopkinson pressure bar (SHPB) apparatus, and the microscopic characteristics of cement paste with CNTs were revealed by scanning electron microscopy. The results show that the dynamic compressive strength, elastic modulus and peak toughness of the samples all firstly increase and then decrease with the increase of CNTs content. When the CNTs content is 0.10%, the three samples reach the maximum values, and the increments are 34.1%, 70.0%, and 15.4%, respectively. However, the damage degree of the sample shows an opposite change law. The sample with 0.10% CNTs content has the lowest degree of crushing, and the fractal dimension is reduced by 22.3%, compared to the blank sample. Adding an appropriate amount of CNTs can improve the pore size distribution of cement matrix, and fill and bridge pores and cracks to make it denser, but the excessive amount of CNTs addition can cause aggregation and deteriorate the mechanical properties of cement-based composites.

The effect of restraint (i.e., expansion restraint and shrinkage restraint) on the surface damage of single-side salt freezing and thawing (SSFT) of concrete and its mechanism were investigated. After every four SSFT cycles and the strain during the cooling phase of the first SSFT cycle, the surface scaling was measured on the restrained concrete with a water-cement ratio of 0.40, and the tensile stress in the ice on the concrete surface was calculated. The results show that the surface scaling of restrained concrete is greater than that of free concrete, and it increases with the increase of the expansion restraint stress, but has little relationship with the shrinkage restraint stress. Compared to the free concrete, the tensile stress in the ice on the restrained concrete's surface is greater, and it is influenced by the expansion restraint stress positively. The results calculated based on the theory of "glue-spall" indicate that the expansion restrains cause the ice to crack more easily and more serious surface damage to concrete under the ice.

Incorporating multi-walled carbon nanotubes (MWCNTs) into concrete can improve the fracture toughness of concrete. The fracture properties of MWCNTs reinforced concrete were examined via three-point bending beam fracture tests. The fracture parameters of MWCNTs reinforced concrete were analyzed by using the double K fracture parameters. The results show that MWCNTs can improve the fracture toughness of concrete. When the content of MWCNTs is 0.10%, the 28-d compressive strength and splitting tensile strength of concrete are increased by 1.7% and 11.7%, respectively. When the content of MWCNTs is 0.15%, the initial fracture toughness, unstable fracture toughness and fracture energy of concrete are increased by 31.0%, 32.4% and 24.6%, respectively. It is indicated that MWCNTs delay the propagation of micro-cracks by bridging across the micro-cracks in concrete and strengthening the interfacial transition zone.

The effects of CaO-MgO blended expansive agent (CMEA) and temperature rising inhibitor (TRI) on the hydration of cement paste were investigated by low-field nuclear magnetic resonance spectroscopy. The results show that the transversal relaxation (T₂) intensity increases in the dormant period and decreases in the steady period with the increase of CMEA content. The change of cement paste containing CMEA and TRI with CMEA content is similar to that of cement paste containing CMEA addition only. However, the duration of the acceleration period and deceleration period increase, and the hydration rate decrease evidently with increasing the TRI content. Moreover, curing temperature has an effect on the hydration with the combination of CMEA and TRI, and a high curing temperature promotes the dissolution and diffusion of TRI, resulting in a further decrease of hydration rate in the acceleration period.

To investigate the mechanical behavior and failure mechanism of coral aggregate concrete (CAC) under static and dynamic load, this paper proposed a 3D random mesoscale model composed of three mesoscale components, i.e., aggregate, mortar matrix and interfacial transition zone (ITZ). Using the 3D random convex particle model into the characterization of the random features of broken coral aggregates, i.e., shape and spatial distribution, was proposed. Based on the developed model and corresponding material models, i.e., CONCRETE_DAMAGE_REL3 and HOLMQUIST-JOHNSON-COOK, the static- and dynamic responses of CAC were analyzed in terms of stress-strain relation, failure pattern and process, strain rate effect, etc. The failure mechanism of CAC under different loading conditions was discussed as well. The results indicate that there is a high reliability for the developed 3D random mesoscale model in simulating the static- and dynamic properties of CAC, particularly in its failure patterns and fracture processes, which is of great significance for the failure mechanism analysis of CAC under various loading conditions.

Nano-structural change of calcium(sodium) aluminium silicate hydrates (C(N)-A-S-H) gel in alkali-activated slag (AAS) mortars after wetting-drying cyclic attack in 5 % (mass fraction, the same below) and 10% sulphate solutions was investigated. The structural and compositional changes of aluminosilicate chains in the main binding phases (C(N)-A-S-H) in AAS mortars were analyzed by Fourier-transform infrared spectroscopy, thermogravimetry-differential scanning calorimetry, ²⁹Si magic angle spinning nuclear magnetic resonance, backscattered scanning electron microscopy and transmission electron microscopy-energy dispersive X-ray spectroscopy. The results show that the sulphate attack increases the degree of reaction of ground granulated blast-furnace slag regardless of sulphate salt type. The main corrosion products in MgSO₄ solutions are gypsum, which is not detected in the samples subjected to Na₂SO₄ solutions. The C(N)-A-S-H with longer chains prefers to be attacked in MgSO₄ solutions, whilst the end-members of the chains or short chains of C(N)-A-S-H are broken in Na₂SO₄ solutions. The C(N)-A-S-H after cyclic water attack is a mixture of tobermorite/jennite dimer to undecamer (T/J2-T/J11), while the Na₂SO₄ solutions attack results in the destroy of shorter chains and the increase of protonation (or Na-balanced ratio), thus forming a new C(N)-A-S-H gel.

3D concrete printing is a rapid prototyping technology based on 3-dimensional building information model. 3D printing has attracted more attention in the latest decade due to its none-framework, low labor cost and quick construction. Fiber reinforced concrete (FRC) possesses a superior tensile property, a crack control ability, and some advantages in shapeability and cost control as conventional concrete. 3D-FRC printing thus becomes a hot research topic. Review, recent development on 3D-FRC printing was comprehensively represented, including, category of 3D printable FRC, workability of 3D printable FRC during printing and their mechanical property in hardened state. In addition, the future opportunities and current challenges in 3D printable FRC technology were also discussed.

Fe₃O₄@calcium silicate hydrate (CSH) nanosheets composite adsorbents were obtained through electrostatic interaction. And an "adsorbent-to-photocatalyst" transformation strategy was proposed: the harmful heavy metal ions from the polluted water were removed by Fe₃O₄@CSH adsorbents, after which they were recycled and reused as photocatalysts for CO₂ reduction. The results demonstrated that: benefiting from ultrahigh surface area and strong ion exchange ability of CSH nanosheets, heavy metal ions including Zn²⁺, Cu²⁺, Co²⁺, Ni²⁺, and Pb²⁺ could be efficiently removed by Fe₃O₄@CSH adsorbents. The maximal adsorption capacities were 83, 142, 150, 179, 343 mg/g, respectively. Fe₃O₄@CSH adsorbents containing heavy metal ions could efficiently reduce CO₂ to CO under visible light. Particularly, Fe₃O₄@CSH-Ni after adsorption of Ni²⁺ showed the best catalytic activity. The CO generation rate was up to 3 310 μmol/(g·h) with a high selectivity of 99.3%. Besides, the magnetic property of Fe₃O₄ enabled the rapid recovery of Fe₃O₄@CSH during the adsorption and photocatalysis processes.

A series of graphitic carbon nitride (g-C₃N₄) nanosheets with controllable thicknesses were prepared by a thermal polymerization method with different ratios of precursor melamine and urea. The nanosheets were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, specific surface area measurement, ultraviolet-visible spectroscopy and photoluminescence, respectively, which were used for the photocatalytic degradation of Rhodamine B (RhB). The results show that g-C₃N₄ is the thinnest (1∶8-CN) with the thickness of 3.5 nm when the ratio of melamine to urea is 1∶8. Its specific surface area is 6 times greater than that of g-C₃N₄ prepared using only melamine (assigned as M-CN). The photoelectric analysis indicates that 1∶8-CN has a higher separation efficiency of photogenerated carriers. Under the visible-light, the photocatalytic degradation rate of RhB by 1∶8-CN can reach 96.2%, which is 1.9 times greater than that of M-CN. Besides, the photocatalytic degradation mechanism of 1∶8-CN toward RhB is since the electrons generated by the separation of photogenerated electron-hole pairs combine with O₂ to generate·O₂^-, and then·O₂^- oxidizes RhB into CO₂ and H₂O, and the holes do hardly participate in the reaction.