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The fact that high-strength concrete is easily to crack has a significant negative impact on its durability and strength. This paper gives an optimum design method of high-strength concrete for improving crack resistance based on orthogonal test artificial neural networks (ANN) and genetic algorithm. First, orthogonal test is operated to determine the influence of the concrete mix proportion to the slump, compressive strength, tensile strength, and elastic modulus, followed by calculating and predicting the concrete performance using ANN. Based on results from orthogonal test and ANN, a functional relationship among slump, compressive strength, tensile strength, elastic modulus, and mix proportion has been built. On this basis, using the widely used shrinkage and creep models, the functional relationship between the concrete cracking risk coefficient and the mix proportion is derived, and finally genetic algorithm is used to optimize the concrete mix proportion to improve its crack resistance. The research results showed that, compared with the control concrete, the cracking risk coefficient of the optimized concrete was reduced by 25%, and its crack resistance was significantly improved.

This paper investigated the electromagnetic shielding properties and the mechanisms of tricalcium silicate (C3S) paste with three water-cement (W/C) ratios after long-term curing. The C3S pastes with three W/C ratios were tested by XRD and other tests for the qualitative and quantitative analysis of the individual phases. The electromagnetic shielding properties and electromagnetic parameters of the specimens were obtained using the waveguide method. Finally, the microscopic mechanism of the variation of electromagnetic shielding properties of C3S paste affected by the W/C ratio was dissected based on the individual phases. The results show that the volume fraction of pore, calcium silicate hydrate (C–S–H) gel, calcium hydroxide (CH), and calcite (CaCO3) in the specimen increases with the rise of the W/C ratio, and the unhydrated C3S decreases; the electromagnetic shielding of the paste specimen increases; the complex relative permittivity gradually increases. The mechanism of the W/C ratio affecting the electromagnetic shielding performance of C3S paste is that, on the one hand, both the volume fraction of C–S–H and the relative permittivity in the solid phase, which have the greatest influence on the electromagnetic shielding performance, gradually increase with the increase of W/C ratio. On the other hand, as the W/C ratio increases, the volume fraction and area fraction of the mesopores in the specimen increase, which increases the internal loss of electromagnetic waves. [ABSTRACT FROM AUTHOR]

This paper investigated the influence of water-borne epoxy resin emulsion (WER) dosage on the properties of modified emulsified asphalt and analyzed the modification mechanism of WER on emulsified asphalt. Water-borne epoxy modified emulsified asphalt was used to prepare MS-2 micro-surfacing mixture, and dispersed demulsifier was introduced to improve the construction performance of the mixture. The best content of each component and the best asphalt -aggregate ratio were obtained through orthogonal test. The results show that 6% water-borne epoxy emulsion asphalt has the best compatibility and storage stability. With the increase of water-borne epoxy content, the low-temperature performance of water-borne epoxy emulsion asphalt becomes worse and the anti-aging performance increases. The optimum asphalt-aggregate ratio of MS-2 micro-surfacing is 7.5%. When the added water is 3%, the cement content is 1%, and the dispersed demulsifier content is 0.25%, the prepared micro-surfacing has good water damage resistance, rutting resistance, tensile strength and cohesiveness, which can meet the normal use requirements of pavement. [ABSTRACT FROM AUTHOR]

Polycarboxylate superplasticizer (PCE) is widely used in concrete, but the clay content in the aggregate is increasing at present, which seriously weakens the dispersing function of PCE. Therefore, in order to lower the sensitivity of PCE to the clay, β‐cyclodextrin (β‐CD) was used for synthesizing anti‐clay polycarboxylate superplasticizers (AC‐PCE). Firstly, the clay tolerance property of AC‐PCE was explored by the fluidity and rheological test; then, the PCE was mixed with montmorillonite (MMT), and interaction mechanism was studied. The results showed that compared with the conventional polycarboxylate superplasticizer (CO‐PCE), an increase of 19.5% and 14.9% was observed in the fluidity of cement paste and mortar for AC‐PCE, indicating that the sensitivity of AC‐PCE to the clay was lower than that of CO‐PCE. Both CO‐PCE and AC‐PCE were adsorpted on MMT. XRD results showed that intercalation adsorption had occurred for both CO‐PCE and AC‐PCE. N2 adsorption results showed that although AC‐PCE was also inserted into the interlayer of MMT, its adsorption amount was lower than that of CO‐PCE due to steric hindrance from β‐CD, which increased the sorption level of the AC‐PCE on the cement clinkers particles. Therefore, the clay tolerance of PCE was enhanced significantly by β‐CD. [ABSTRACT FROM AUTHOR]

Two kinds of layered double hydroxides (LDHs), MgAl-NO2 (N-LDH) and MgAl-CO3 (C-LDH), were incorporated to study the durability of mortar and concrete. The LDH contents of mortar were 1%, 2%, and 4% by mass and the LDH contents of concrete were 0.5%, 1%, 2%, 4%, respectively. The effect of LDHs on sulfate resistance of mortar was studied through dry-wetting cycle test, compressive strength test, and flexural strength test. In addition, the effects of LDHs on pore structure, chloride resistance, carbonation resistance, shrinkage, and creep of concrete were investigated by SEM, mercury injection test, XRD, chloride ion diffusion coefficient test, chloride salt corrosion depth test, carbonation depth test, shrinkage test, and creep test. The results showed that LDHs can improve the ability of resisting ion corrosion, carbonization, shrinkage, and creep, reduce the pore content, and optimize the pore structure of mortar and concrete to some extent. Moreover, 4% LDHs had a better effect on improving the durability of mortar and concrete compared to 0.5%, 1%, and 2% LDHs, and the effect of C-LDH was better than N-LDH. [ABSTRACT FROM AUTHOR]