Ordinary concrete target, ultra-high performance concrete (UHPC) target and functionally graded concrete target composed of different kinds of UHPC were prepared. The penetration and explosion experiments were performed on different types of concrete targets. The numerical simulation analysis was carried out by finite element method. The results show that in terms of the failure mode, the functionally graded concrete target has the smallest fracture depth, and the crater depth does not exceed the range of the anti-penetration layer under the coupled load of penetration and explosion. In terms of damage distribution, the concrete damage is mainly concentrated on the front surface and around the projectile channel and transmitted diagonally on the rear surface. Fiber reinforced targets maintain a good integrity. From the perspective of energy, the ability of absorbing projectile kinetic energy of high-strength coarse aggregates in anti-penetration layer is greater than that of concrete matrix. UHPC with a functionally graded structure has a superior anti-penetration and explosion ability.

To investigate the constitutive model of ultra-high performance concrete confined by steel tube, axial compressive experiments were conducted on 42 confined UHPC and 3 unconfined UHPC specimens. Failure modes and stress-strain curves were obtained. Effects of steel fiber volume fraction and aspect ratio, polypropylene fiber volume fraction and aspect ratio and steel tube thickness on the stress-strain curves were analyzed. The results show that steel tube thickness is a main affecting factor. The peak stress and corresponding strain increase with the increase in the thickness. Fibers are beneficial to the improvement in the peak stress and strain. Steel fiber volume fraction has an obvious effect on the peak stress and strain. At a proper volume fraction of polypropylene fiber, the peak stress increases and the peak strain first decreases and then increases with increasing steel fiber volume fraction. In addition, the corresponding constitutive models were also proposed based on the typical stress-strain curves of confined UHPC.

Explosive spalling behavior and microstructure of ultra-high performance concrete (UHPC) prepared with four different curing regimes (i.e., 20 ℃ water curing, hot water curing, dry air heating and hot water-dry air combined curing) were investigated. The results indicate that the combined curing is efficient to enhance resistance of UHPC to explosive spalling under high temperature. No spalling occurs on the UHPC cured by 90 ℃ hot water curing for 2 d and 250 ℃ dry air heating for 3 d. Such a combined curing is a novel approach to prevent explosive spalling of UHPC at elevated temperature, which is different from adding polypropylene fiber usually employed. It can be attributed to an internal free water minimizing mechanism. During dry air heating within the combined curing, a high-temperature steam environment can be established inside UHPC. Thus, further hydration of residual cement and pozzolanic reaction of mineral admixtures both can be activated to form massive dense hydrates. Meanwhile, most of internal free water has been consumed, so that the vapor pressure inside UHPC under high temperature is decreased, hence prohibiting the spalling occurrence efficiently.

Ultra-high performance concrete (UHPC) and common mortar were prepared using simulated sea sand at different chloride ion contents. The electrochemical indexes of the internal reinforcement during passivation period were measured by linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and cyclic polarization. The passivation evolution of reinforcement and the effect of chloride ion on the growth of passivation film were investigated, and the passivation behavior difference between UHPC and ordinary mortar was compared. The experiment results show that the corrosion rate of reinforcement in UHPC decreases with the increase of age. The corrosion rate is accelerated, but its effect is limited, and it has no effect on the density of passive film when chloride ion content in sea sand is increased. When the content of chloride ion in the sea sand is below 0.448%, the steel bars could be passivated within 10 d, and the corrosion rate is the similar after passivation.

For the degradation of oil well set-cement under CO₂ sequestration condition, the thermodynamic conditions of pure minerals related to hydration products degradation were determined based on the equilibrium constant theory, and the resistance difference was investigated. The mass change of hydration products was simulated based on the Gibbs free energy minimization principle. The results show that the order of degradation resistance of related pure minerals or end members is 4Mg(OH)₂·2Al(OH)₃·3H₂O, 0.83CaO·0.67SiO₂·1.83H₂O, 0.67CaO·SiO₂·1.5H₂O, 6CaO·Al₂O₃·3SO₄·32H₂O, 6CaO·Al₂O₃·3SO₄·30H₂O, 1.33CaO·SiO₂·2.17H₂O, 3CaO·0.5Al₂O₃·0.5Fe₂O₃·0.84SiO₂·4.32H₂O, 3CaO·Fe₂O₃·0.84SiO₂·4.32H₂O, 1.5CaO·0.67SiO₂·2.5H₂O, Ca(OH)₂. The order of mass decrease in set-cement degradation process is Ca(OH)₂, calcium silicate hydrate solid solution, Si-hydrogarnet solid solution, ettringite solid solution, and M₄AH₁₀. The number of moles and the proportion of end member minerals changes and the quality of solid solution decreases, but the change is inconsistent with its relative degradation resistance.

Calcium aluminate cement (CAC) has a superior resistance to seawater erosion. In order to further develop the application potential of CAC in marine environment, the effect of seawater on the hydration of CAC with different calcium monoaluminate/calcium dialuminate (CA/CA₂) ratios was investigated. The results show that in the early hydration stage, seawater retards the hydration of CAC, and the lower the CA/CA₂ ratio is, the more significant the retarding would be. In the late hydration stage, seawater promotes the hydration of CAC, and the amount of monocalcium aluminate decahydrate (CAH₁₀) in the paste increases and the pore structure optimizes, resulting in a prominent increase in the CAC strength, compared to that mixed with tap water. Moreover, a lower CA/CA₂ ratio leads to a more improvement of the CAC strength. However, compared to tap water, the compressive strength of CAC strength decreases in the late stage when the CAC is mixed with seawater. Regardless of mixing with tap water or seawater, CAH₁₀ is the main hydration product of CAC, and chloride ions are mainly bound by the physical adsorption. No hydration products related to sulfate and magnesium attack appear.

A calculation framework was proposed to transform the chemical action of reinforcement corrosion in concrete into mechanical action, leading the chemical reaction of reinforcement corrosion to the macroscopic mechanical behavior. A calculation equation of current density i_corr was obtained by the corrosion rate model under different humidity conditions. A relationship between corrosion layer thickness δ and reinforcement corrosion rate i_corr was thus determined based on the Faraday law. Also, a relationship between the corrosion expansion stress q and the corrosion layer thickness δ was obtained by the uniform corrosion expansion model. Based on the numerical results, the corrosion current density, corrosion layer thickness and corrosion expansion stress in the calculation frame could be in reasonable agreement with the reported values, thus indicating that the framework of chemical mechanical transformation is feasible.

Alkyl sulfate surfactants with different hydrophobic chains (i.e., C8-C14) and surfactants with different anionic groups (i.e., sulfate, sulfonate and phosphate) were analyzed, and the effects of hydrophobicity and ionic groups on the surface activity, foam behavior and air-entraining performance in cement mortars were investigated. The results show that the more intense interfacial self-assembly behavior of surfactants can reduce the interfacial free energy and increase the surface activity, thus resulting in a greater foaming property of aqueous solutions and a higher air entraining performance in cement mortars. Sodium lauryl sulfate has the maximum interfacial self-assembly density, the minimum interfacial free energy, and the superior air entraining performance in aqueous solutions and cement mortars, as well as the optimum air-void adjustment performance of hardened cement mortars.

A nano-modification method is proposed to improve the performance of alkali activated cementitious materials (AAM). This paper reviewed the effects of nano-particles (i.e., silica particles) and nano-materials (i.e., cabon nano-tube) on the workability, setting and hardening behavior, mechanical property and durability of AAM. The acceleration of geopolymerization, the more compact matrix, the higher strength and the lower permeability of nano-modified AAM occur due to the presence of soluble silica in alkali solution from silica nanoparticles and the nucleation site effect, filling effect derived from other nano-particles such as TiO₂ nanoparticles. The modified AAM with a higher toughness and a lower brittleness is available for the incorporation of carbon nano-tube or graphene oxide. Furthermore, the carbon nano-tube or graphene oxide modified AAM exhibits some functional characteristics like the self-sensing capacity to detect its own structural damage and the photocatalytic performance to treat wastewater. Some controversial issues on the flowability and setting time of fersh mixtures, strength and permeability of hardened samples containing silica nanoparticles in previous studies were also represented. The reason for the controversial issues above could be due to the interaction bewteen silica nanoparticles and alkaline solution and the initial chemical reaction between silica nanoparticles and Ca²⁺ ions in solution. In addition, some further research works on nano-modified AAM were also given.

An indicator named as water absorption ratio of super-absorbent polymer (SAP) was proposed. The effect of SAP water absorption ratio on the absorption kinetics of SAP in centrifugal liquid from cement slurry (CLCS), rheological property of fresh concrete with internal curing, compressive strength and shrinkage of hardened concrete with internal curing was investigated. The results indicate that the absorption of SAP in CLCS exhibits a law of rapid increase, gradual decrease and final stability. The peak value of absorption and the release time increase, the yield stress of fresh concrete gradually increases and the plastic viscosity gradually decreases as the SAP water absorption ratio increases. SAP reduces the early strength and shrinkage of concrete significantly, and has little impact on the long-term strength. SAP also has no impact on the compressive strength and shrinkage of hardened concrete evolved with curing time when the water absorption ratio is 1.94-6.16.