Corrosion behavior and evolution of steel reinforcement in simulated concrete pore solutions subjected to different corrosive ions (i.e., chloride, sulfate, chloride-sulfate, and simulate sea water) were investigated. Corrosion products induced with chloride and sulfate ions were also analyzed, respectively. The results show that the presence of sulfate ions in co-existence scenario of chloride-sulfate ions lead to a lower polarization resistance and a higher corrosion current density. The steel corrosion potential is correlated to the polarization resistance evolution as a power function relationship. Corrosion products induced by chloride and sulfate ions depicts a slight difference, mainly containing γ-FeOOH, α-FeOOH, Fe(OH)₃, Fe₂O₃ and FeO.

To ascertain the influences of bentonite and its content on the printability of 3D printing mortar, the extrudability of mortar was evaluated via fluidity, and its buildability was evaluated by height retention rate and penetration resistance. Also, the rheological behavior of cement pastes with bentonite was characterized via dynamic and static shear tests. Effects of bentonite and its content on the printability of mortars were analyzed via rheology. The results show that the fluidity of printable mortars is linearly correlated to the plastic viscosity of cement pastes and logarithmically to the dynamic yield stress of cement pastes. Besides, there is an exponential relationship between the height retention rate of printable mortars and the static yield stress of cement pastes. The addition of bentonite in the mortar increases the plastic viscosity and dynamic yield stress of cement pastes, resulting in a decrease in the extrudability of mortar. Also, the addition of bentonite improves the static yield stress and structural rebuilding rate of cement pastes, thereby improving the buildability of mortar. Therefore, appropriate amount of bentonite can make the mortar maintain good extrudability while improving its buildability. A width ratio between the top and bottom layers of the printed sample with 2% bentonite is 0.96.

The hydration degree and mechanical properties of ultra-high performance concrete (UHPC) specimens with hybrid steel fibers cured in air and hot water (1 d, 60℃ hot water + 2 d air), respectively, were investigated via ignition loss tests and uniaxial tensile and compressive tests. Also, the surface cracking characteristics of tensile specimens were characterized by digital image correlation technique and optical microscopy, and the microstructures were analyzed by scanning electron microscopy. The results show that compared with the results obtained in air curing, hot water curing accelerates the hydration reaction progress of the UHPC matrix, and an increase in temperature mainly contributes to the promotion of hydration reaction, thus improving the initial cracking, tensile and compressive strength of the UHPC specimens in hot water curing. However, the tensile strain capacity changes slightly. In general, the maximum crack width of the specimen decreases, the matrix becomes denser, and the interface bonding between the fibers and the matrix is stronger. The tensile strain of UHPC increases with the increase of fiber content, in which the tensile strains of the specimens with 2.5% (volume fraction) of fibers (a ratio of long fibers to short fibers is 1.25∶1.25 and 1.5∶1.0, respectively) are more than 2 ×10^-3, the specimen with 1.5% long fibers and 1.0% short fibers produces more tensile cracks with the width of < 50 μm in hot water curing. The uniaxial tensile strains predicted by DIC are in reasonable agreement with the strains measured.

Ultra-high performance concrete (UHPC) prismatic specimen with different water-binder ratios, coarse aggregate contents, steel fiber volume fractions, and specimen dimensions were prepared. The influences of water-binder ratio, coarse aggregate content and steel fiber volume fraction as well as the scale effect on the flexural tensile strength of UHPC containing coarse aggregate were investigated. The results show that the flexural tensile strength of UHPC containing coarse aggregate decreases with the increase of the water-binder ratio and the coarse aggregate content. The scale effect on the flexural tensile strength of UHPC containing coarse aggregate is greater than that of UHPC without coarse aggregate. The scale effect on the flexural tensile strength of UHPC containing coarse aggregate decreases gradually with the increase of water-binder ratio. The scale conversion coefficient of flexural tensile strength of UHPC containing coarse aggregate and the parameter calculation formula of scale effect law were proposed for predicting the flexural tensile strength of UHPC with coarse aggregate.

To improve the working performance of ultra-high performance concrete (UHPC), two kinds of water reducers with different structures, i.e., polyoxyethylene (EO) polyether (PCE-1) and propylene oxide block polyoxyethylene (EO/PO) polyether (PCE-2), were prepared. The performance of cement-silica fume slurry in a low water-binder ratio with two water reducing agents was evaluated via slurry fluidity, slurry viscosity test, total organic carbon test, and surface tension test, and the relevant mechanism was discussed. The results show that at PCE-2 in the slurry at 0.16 of water-binder ratio and 5%-25% of silica fume content (in mass fraction) has an adsorption-dispersion effect on silica fume rather than PCE-1, thus increasing the fluidity of cement-silica fume slurry. The block polyether structure of water reducer can adjust the surface tension and viscosity of the interstitial fluid, and reduce the viscosity of the cement-silica fume slurry.

Cement-based materials are brittle and easy to crack, which are concerned as the key problems to be solved in engineering application. The microscale brittleness of the material phases of cement-based materials needs to be investigated, and a relationship between the micro-scale brittleness and the overall brittleness needs to be established for the toughening design of cement-based materials. In this work, the fracture toughness-displacement curves were obtained via micro-scratch test, and the phases corresponding to the scratch area were analyzed by high resolution scanning electron microscopy, thus charactering quantitatively the fracture toughness of cement paste and its material phases, and establishing the relationship between the overall brittleness of cement paste and the brittleness of calcium silicate hydrate gel.

Carbonatable calcium silicate cementitious material is a novel low-carbon building material with a great potential for development. γ-dicalcium silicate is one of the most carbonation reactive minerals among calcium silicates. In this paper, a wet powder of γ-dicalcium silicate was used as an experimental material. The influences of reaction duration, particle size, relative humidity, temperature, partial pressure and water-to-solid ratio on the degree of carbonation were investigated. The carbonation kinetic equation was proposed based on the modified shrinking-core model and empirical equation. It is indicated that the data predicted by the kinetic model are in reasonable agreement with the experimental results. The obstruction of ions diffusion attributed to the coating of carbonation products is a major factor of controlling the carbonation reaction.

The thermal conductivity of cement paste with different water-cement ratios and curing ages were measured. Moreover, the thermal conductivity of cement paste was predicted by parallel model, series model, Maxwell model, MT model, EMT model and SC model, respectively. In addition, the thermal conductivity of each phase in cement paste was calculated by a molecular dynamics method. The results show that the thermal conductivity of cement paste decreases with the increase of curing age and water-cement ratio. SC model can be used to predict the thermal conductivity of cement paste at different water-cement ratios or curing ages, and the relative error between the predicted and the experimental values is 0.3%-4.7%. The Maxwell model and MT model can be used to calculate the thermal conductivity of cement paste at a large water-cement ratio and a long curing age.

The fatigue properties of ultra-high performance concrete (UHPC) at 20 ℃ and -10 ℃ were investigated via flexural fatigue tests under different stress levels. The results show that, the degradation of UHPC flexural fatigue performance and the fatigue strength decrease under a cyclic load with the decrease of temperature due to the cold brittleness characteristics of steel fibers at the cracked section. Compared with the test results at 20 ℃, the fatigue strength of UHPC at -10 ℃ is decreased by 15.6%. Although the fatigue strength of the specimens at a low temperature is lower than that of the specimens at normal temperature, their fatigue deformation modulus ratios (E_n/E₀) corresponding to their fatigue strengths are similar, which are 0.48. The residual strength of UHPC specimens undergoing 2 million cycles without flexural fatigue failure is close to the static strength under monotonic loading, at normal temperature or low temperature. Based on the results, a model of predicting the fatigue life of UHPC at 20 ℃ and -10 ℃ was proposed, and the predicted results could be used as reference in the practical application.

The residual effect of fractured glass, which is greatly affected by its fracture morphology, is correlated to the post-fracture performance of laminated glass. For tempered glass in laminated glass, its fracture morphology is affected by some major variables such as surface compressive stress, thickness, and fracture point. However, a few previous work concerning the fracture morphology characterization are reported. In this paper, fragmentation tests were firstly conducted on 81 tempered glass specimens. The fracture morphology and spatial distribution, including fragment area, perimeter, circularity and distribution intensity, were analyzed. The fracture morphology and spatial distribution obtained at the given variables (i.e., surface compressive stress of 60-105 MPa, thickness of 6-12 mm, three fracture points) were discussed. Also, a new seeds generation approach for the centroid of fragments to control nearest neighbor distance and global distribution intensity of fragments was proposed, which was combined with the Voronoi tessellation to characterize the fracture morphology of tempered glass. The proposed method has a satisfactory accuracy in generating the fracture morphology.