There are two inherent drawbacks in designing ultra-high performance concrete (UHPC) by the modified Andreasen-Andersen (MAA) model, i.e., unproven reliability under wet conditions and ignorance of disturbing effect of steel fiber on particle packing skeleton. In this work, the D-optimal mixture design model and the equivalent spherical diameter of steel fires were adopted to verify and optimize the MAA model, and the properties of the optimized UHPC were utilized to verify the feasibility of the new proposed method. The results reveal that the MAA model is also suitable to be utilized under wet conditions. Moreover, the equivalent spherical diameter of steel fibers (L=13 mm, d=0.2 mm) is 5.65 mm, which is determined by evaluating the effect of screening particles and steel fibers on wet packing density. In addition, the employed steel fibers that are treated as spheroidal particles can be implanted into the MAA model for the optimized design of new UHPC, which has a densely packing structure and an admirable compressive strength.

A nano-, micron-, and millimeter-sized multi-scale fiber composite reinforced ultra-high performance concrete (UHPC) was proposed. The mechanical properties of UHPC can be improved by suppressing the defects of different sizes with different fibers. Carbon nanotubes, micron-sized calcium carbonate whiskers, and millimeter-sized steel fibers were used to design 7 groups of UHPC specimens. The axial tensile and compressive stress-strain curves of UHPC were measured. The results show that the initial crack strength and strain of UHPC are determined by the millimeter-sized steel fiber in a macro-scale. However, micron- and nano-sized fibers have little effect on the initial crack strength and strain. The addition of calcium carbonate whiskers and carbon nanotubes changes the tensile behavior of UHPC specimens after cracking, thus enhancing the strain hardening capability. The tensile and compressive properties of UHPC with different sizes of fibers are similar. The addition of calcium carbonate whisker has a positive effect rather than that of carbon nanotube when mixing with steel fiber. The effect becomes optimum when adding calcium carbonate whiskers and carbon nanotubes.

Direct tensile tests were carried out on three types of ultra-high performance concrete (UHPC) specimens with different thicknesses of arc-shaped dog bone shape, and the relationship among axial tensile stress, strain, and crack of UHPC was analyzed. The results show that the tensile strength of UHPC increases slightly, the ability to limit crack development increases, the strain capacity decreases significantly, and the strain softening rate increases as the specimen thickness decreases from 100 mm to 30 mm. When the crack width is less than 0.2 mm, the post-crack stress of UHPC increases slightly. After the main crack forms, the crack development rate and the post-crack stress decline rate increase correspondingly. The tensile strain value is fitted from the main crack width, and it is indicated that the main crack development process of UHPC specimen be in reasonable agreement with the strain softening stage.

Ultra-high performance concrete (UHPC) was designed with different replacement percentages of manufactured sand, i.e., 0%, 25% 50%, 75%, and 100% (in mass fraction). The properties of the UHPC, including the quasi static and dynamic mechanical properties, were examined. The results show that the compressive strength of UHPCs with manufactured sand as fine aggregates is similar to that of the reference mixture with only river sand. The UHPC with manufactured sand has superior dynamic mechanical properties. The UHPC with manufactured sand has an effect on its strain rate, and the dynamic increase factor has a logarithmic function relation with the strain rate. In addition, the finite element method was also employed to simulate the impact process of the UHPC with manufactured sand.

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.

The effects of borax, sodium gluconate and L(+)-tartaric acid on the hardening behavior and strength development of rapid-hardening calcium sulphoaluminate cement mixed with calcium chloride solution at -10 ℃ were investigated. The results show that the initial and final setting time of rapid-hardening calcium sulphoaluminate cement mixed with calcium chloride solution prolonge to 25 min and 28 min with 0.6% borax at -10 ℃, respectively. However, the setting time of pastes with sodium gluconate or L(+)-tartaric acid does not extremely change. The strength gradually decreases in the samples with increasing the dosages of borax and sodium gluconate at different ages. A maximum reduction of 25.5 MPa occurs in those samples. The strength of samples containing L(+)-tartaric acid sharply decreases. A reduction of 10.9 MPa in 3-day samples containing 0.3% tartaric acid and 27.3 MPa in 28-day samples containing 0.6% tartaric acid occur. The presence of 0.6% borax does not change the morphology of ettringite at 1 d, but decreases the amount of ettringite by 5.31%. A short column-like ettringite in the samples with sodium gluconate and a needle-shaped-like ettringite in the samples with L(+)-tartaric acid are detected, respectively. However, the amount of ettringite in those two samples above has no remarkable change. Borax is a suitable retarder for calcium sulphoaluminate cement at -10 ℃ because of the feasibility of setting prolongation and the acceptable strength reduction. Sodium gluconate and L(+)-tartaric acid have a slight effect on the setting time but change the ettringite morphology and deteriorate the strength.

It is necessary to concern the safe utilization of the fluorine-containing sludge disposed in landfills due to its possible leaching toxicity. The effect of physicochemical performance of fluorine-containing sludge, used in cement kiln on the cement properties and environmental safety was investigated by X-ray fluorescence, X-ray diffraction, scanning electron microscopy, immersion extraction and leaching toxicity tests. The results show that the fluorine content of fluorine-containing is 15.3% with a small amount of heavy metal ions (e.g. Cr, Mn, Ni, Cu, Zn, etc.). Fluorite is the major mineral phase, and secondary mineral phases are sphalerite and nantokite. Fluorine in fluorine-containing sludge is mostly calcium fluoride, and its content (mass fraction) reaches approximately 30.0% in the sludge. In addition, the leaching toxicity of F and Cr is below the toxicity restriction. However, the leaching toxicity of Ni, Cu and Zn is above the toxicity restriction. Therefore, the fluorine-containing sludge is subordinate to a heavy metal solid hazardous waste. Also, the incorporation of fluorine-containing sludge assists the formation of alite, and improves slightly the compressive strength of cement mortars. Meanwhile, 2.0% (mass fraction) fluorine-containing sludge doped cement could not cause the secondary environment risk after curing age of 28 d.

The measurement scheme of rheological parameters of fresh cement-based materials and the processing method of measured data were given. The feasibility of different methods, i.e., using of the shear stress and shear strain rate displayed on rheometer, some approximate equations and solution to the Couette inverse problem was analyzed for calculating the rheological parameters of fresh cement-based materials. The analysis results show that the solution to the Couette inverse problem as a reasonable method can be used to obtain the rheological parameters of fresh cement-based materials. The corresponding calculation procedure was given. The influence of plug flow on the calculation of rheological parameters of fresh cement-based materials could be considered. The calculation of rheological parameters of fresh cement-based materials could be more accurate for the measured data in the absence of plug flow.

Ultraviolet labeling technology was used to enhance the ultraviolet absorption of polycarboxylate, and then the technology of ultraviolet absorption spectrum and total organic carbon analysis is used together to effectively distinguish respective adsorption behavior of polycarboxylate and quaternary ammonium salt cation molecules when they exist at the same time, and the interaction between three typical quaternary ammonium salt cations and polycarboxylate in cement montmorillonite system is studied systematically. The results show that the adsorption of polycarboxylate on the cement surface is not affected by the small molecular quaternary ammonium salt, the Gemini quaternary ammonium salt can promote the adsorption of polycarboxylate, the polymer quaternary ammonium salt can inhibit the adsorption of polycarboxylate water reducer on the cement surface. And the three quaternary ammonium salts can effectively inhibit the adsorption of polycarboxylate water reducer on the surface of montmorillonite when doped as 2.5×10^-4. The effect of Gemini quaternary ammonium salt and polymer quaternary ammonium salt is more obvious. The inhibition effect of Gemini quaternary ammonium salt is stronger at low dosage, while the inhibition effect of polymer quaternary ammonium salt at high dosage is better.

A zeolite molecular sieve was synthesized with oil shale ash from Yaojie, China. The effects of liquid-solid ratio (A), crystallization time (B) and crystallization temperature (C) on the cation exchange capacity (Y) of synthesized zeolite were investigated based on the Box-Behnken Design (BBD) of a response surface method. The results show that the model established by the response surface method has a good predictability for the Y value of zeolite, and the Y value of zeolite is improved after optimization. Each factor and their interaction have effects on the Y value of synthesized zeolite, and the order of the factor effect is A, C, and B and the order of interaction effect is AC, BC, and AB. The Na-X zeolite can be synthesized under optimum conditions (i.e., alkali melting temperature of 650 ℃, ash-alkali ratio of 1∶1.7 g/g, liquid-solid ratio of 4.5∶1 mL/g, crystallization time of 25.2 h, and crystallization temperature of 83 ℃). The Y value of zeolite synthesized under optimum conditions is 52.44 mg/g.

A flexible expanded vermiculite (FEV) with a high expansion ratio was prepared by a chemical-microwave method with industrial vermiculite as a raw material. The optional process and relationship between expansion rate and flexibility were investigated. The results show that the expansion ratio of FEV prepared by chemical-microwave heating is up to 36.36. The screen tailings yield of FEV samples is negatively correlated to the expansion rate, and the sharp expansion action can improve the exfoliation ability of expanded vermiculite particles, thereby reducing the flexibility of FEV sample particles. The interior of FEV is loose and porous, the pores are evenly distributed and the intact layered structure is still maintained. The thickness of the inner wall forming the narrow slit is 50-200 nm. The FEV is a low-cost precursor of vermiculite nanomaterial, which can be mechanically exfoliated to prepare vermiculite nanomaterial based on its lamellar dissociation characteristic.

Hexagonal mesoporous silica (H-mSiO₂) particles were prepared via an alcohol/water mixed reaction system using cetyltrimethyl ammonium bromide as a template. The resultant products were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform spectroscopy, thermogravimetric analysis-differential scanning calorimetry, and nitrogen adsorption/desorption measurements. As an alcohol/water volume ratio decreases slowly, the morphologies of samples change from spherical/ellipsoidal to spherical and then to necked or peanut-like. Based on the polishing tests over oxide films (about 208 nm), the developed H-mSiO₂ abrasives contribute to the reductions of surface roughness and topographical variation, compared to non-porous sphere SiO₂ (sSiO₂) particles. The root-mean-square roughness of oxidized silicon wafers reduces from (1.27±0.15) nm to (0.25±0.01) nm after polishing with H-mSiO₂ containing spherical and ellipsoidal particles. The maximum asperity height in sectional profiles decreases from 3.59 nm to 0.72 nm, and the maximum valley depth also reduces from 3.16 nm to 0.69 nm. Moreover, H-mSiO₂ abrasives with uniform spherical shapes achieve a removal rate of (223±17) nm/min.

An acid leaching solution containing aluminum ions was obtained by a sulfuric acid leaching process after calcining clinkers using coal fly ash as a raw material. Aluminum hydroxide was precipitated through adjusting the pH value of solution and used as an aluminum source. Magnesium aluminum hydrotalcite was synthesized via hydrothermal reaction with magnesium oxide and sodium carbonate. Based on the results by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy, magnesium-aluminum hydrotalcite with a good crystallinity, a pure phase and a complete lamellar structure can be synthesized under the hydrothermal conditions (i.e., mole ratio n(MgO)∶n(Al(OH)₃)∶n(Na₂CO₃) of 2∶1∶1, at 160 ℃ for 14 h). In addition, the feasibility of adsorbing phosphorus by Mg-Al hydrotalcite was also investigated. The removal rate can reach 97.4% when the concentration of phosphorus solution is 20 mg/L, the dosage of Mg-Al hydrotalcite is 0.7 g and pH value is 4-10.

The As₄₀S₆₀ core and As₃₉S₆₁ inner and outer cladding glasses were fabricated with the dynamic distillation purification process and melt-quenching method. The cladding tube was prepared by a computerized numerical control precision drilling machine, and then the fiber with the cladding and core diameter of 124 μm and 5 µm was produced by the combination of the secondary tube in rod method. The refractive index of core and cladding, cross-section dimensions, loss and bending loss of the fiber was measured and analyzed. The results show that the N_A of the fiber is less than 0.425 in the wavelength range of 2.5-10.0 µm and its concentricity between core and cladding is good. The fiber has the minimum loss of 1.7 dB/m at 1 550 nm, and single-mode mode in the wavelength range of >2.5 µm. The fiber transmission losses increase sharply when the bending radius reduces to 20 mm.