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• An inverse analysis algorithm considering local response was proposed. • Complete load-CMOD curve was accurately reproduced and the σ-w curve was evaluated. • Tri-linear model was recommended after considering the accuracy and convergence. • Applicability to various materials and specimen configurations was investigated. This study presents an inverse analysis algorithm for deriving the softening relationship of concrete. The algorithm can not only reproduce the influence of local response on the σ - w curve by introducing additional load criteria but also reduce the dependence of optimization results on the initial guesses by combining global best-fitting with the automatic parameter updating technique, improving the prediction accuracy and lowing the possibility of obtaining pseudo-solutions. Then, the fracture tests were carried out on the wedge splitting specimens. The validity and versatility of the algorithm were verified using experimental data. The findings show that the simulation responses agree well with the test ones in all regions of the load-CMOD curve, and the values of fracture energy determined by the load-CMOD and σ - w curves are consistent. The derived σ - w curve is independent of the initial guesses of parameters. The widely used bi-linear σ-w curve tends to overestimate the load in the post-peak of load-CMOD, and the tri-linear model is recommended after considering the accuracy, computation time, and convergence. The tensile strength evaluated by the inverse analysis method is 75% of the splitting tension test and 91% of the fracture theory method. Further, the proposed algorithm exhibits outstanding versatility, applying to various concrete materials and specimen configurations. [ABSTRACT FROM AUTHOR]

Highlights • The effect of curing conditions on concrete fracture properties was investigated. • An innovative humidity rate function was introduced. • A maturity model considering coupling effect of temperature and humidity is proposed. • In-place applicability of model was evaluated using four variable curing conditions. • Fracture properties of concrete can be accurately predicted by the proposed model. Abstract In this study, a new maturity model that considers the coupling effect of curing temperature and humidity is proposed. An innovative humidity rate function was introduced into the model to evaluate the influence of humidity on the fracture properties of concrete, which makes the maturity method more robust. Thereafter, fracture tests were performed on wedge-splitting specimens exposed to different constant and varying temperature and humidity to calibrate the parameters and validate the established model. The results indicated that the new model can accurately predict the fracture properties of concrete exposed to any curing condition with an error of less than 6%. In addition, although the temperature inversion phenomenon in the fracture properties of concrete was observed at all the humidity levels investigated, at low humidity, the phenomenon was not as pronounced as that at high humidity. Furthermore, the threshold age for the temperature crossover effect decreased as the curing humidity decreased. [ABSTRACT FROM AUTHOR]

This study investigates the influence of curing humidity on concrete fracture properties. Concrete fracture energy, effective fracture toughness, and characteristic length were tested at five different ages using wedge splitting specimens exposed to four different relative humidity values (30%, 50%, 70% and 98%). Four environmental chambers capable of automatically controlling temperature and relative humidity were constructed. A data averaging method for companion specimens was introduced. The test results show that at the early age, fracture energy, effective fracture toughness, and characteristic length remained almost constant during drying. As time elapsed, however, the influence of curing humidity on the concrete fracture properties became increasingly pronounced; larger values of fracture energy, effective fracture toughness, and characteristic length were measured by concrete specimens kept at high humidity. The concrete fracture mode also gradually changed from ductile to brittle with curing humidity decreasing and hydration time elapsing. [ABSTRACT FROM AUTHOR]

• Failure stress is lower than the tensile strength for concrete thermal cracking. • The unsuitable failure criterion is the main reason for occurrence of concrete thermal cracking. • Stress-Strain combined criterion has demonstrated in evaluating thermal cracking. • Both restrained stress/strain and direct tensile strength/strain are required. The thermal cracking of massive concrete, especially for the dam concrete, due to the complex temperature histories and restraint conditions jeopardizes the structure's safety and durability. Suitable failure criterion is one of the critical factors for preventing thermal cracking. The eligible failure criterion depends on the full understanding of the failure mechanism, which further relies on convincing experimental techniques. Though the mechanisms and experimental techniques of thermal cracking have been extensively studied, their relations to failure criteria are rarely established. Thus this state-of-the-art review focuses on the thermal failure criteria, related to mechanisms and temperature stress test (TST) methods. The TST researches show the restrained concrete exhibits lower failure stress than its direct tensile strength tested by the free specimen, while has a larger failure strain than its tensile strain capacity, leading to disqualification of the conventional tensile strength/strain capacity criterion. The development of a multiple TST machine system enables the establishment and verification of a Stress-Strain combined criterion. Meanwhile, more verifications experiments considering the material compositions, temperature histories, restrained degrees, loading durations should be conducted. Moreover, the three-dimensional failure criteria and TST methods are suggested for future research. [ABSTRACT FROM AUTHOR]

The inconsistency in strength parameters between full-graded dam concrete and wet-sieved concrete is primarily attributed to variations in curing conditions, member size, and aggregate size. To ensure more reliable strength parameters for the structural analysis of the Baihetan Dam, comprehensive strength tests were conducted on site-casting full-graded and wet-sieved concrete. Full-graded concrete specimens and a portion of wet-sieved concrete specimens underwent natural curing on site or in close proximity to the laboratory, while the remaining wet-sieved concrete specimens were cured in seven large environmental chambers with controlled temperatures and relative humidity. The quantitative effects of curing conditions, specimen size and maximum aggregate size on the compressive and splitting tensile strength of dam concrete were obtained through strength tests. Subsequently, based on the test results, by introducing the equivalent age-adjusted coefficient C ea , the member size-adjusted coefficient C ms and the aggregate size-adjusted coefficient C as , a strength determination method for full-graded concrete that can consider the above three factors was proposed and validated. Finally, according to the measured temperature and relative humidity history of the dam concrete and ambient environment, the real strength parameters of the full-graded concrete of Baihetan dam were determined by the proposed method. The validation and practical application of the proposed method indicate that this method can meet the actual use requirements of the Baihetan dam project, and can provide more reliable full-graded concrete strength parameters for dam structure analysis than traditional methods. • Curing conditions, specimen size and aggregate size effects on dam concrete strength should be considered. • The equivalent age, member size and aggregate size adjusted coefficients are derived. • A strength determination method for dam concrete is proposed and validated. • The strength determination method meets Baihetan dam's application requirements. [ABSTRACT FROM AUTHOR]

• Restrained cracking for concrete is determined by stress and strain together. • The restrained cracking has a lower failure stress and larger failure strain. • A combined stress–strain failure criterion for concrete restrained cracking. The failure behavior of restrained cracking induced by temperature and/or shrinkage differs from that of direct tensile failure. To study the restrained cracking behavior and criterion, a self-developed temperature stress testing machine (TSTM) was utilized and found to have good performance when examining concentric deformation and reproducibility. Restrained cracking experiments were performed considering different mixtures, temperature histories, shrinkages, and loading ages. The results indicated that concrete would crack when the restrained tensile stress exceeded 76% of the direct tensile strength, while the failure strain was 103%–137% of the tensile strain capacity. A combined stress–strain failure criterion was proposed under the assumption of linearity, and the prediction errors range from −7.61% to 12.89%. The proposed criterion will aid evaluations of the safety of restrained concrete. [ABSTRACT FROM AUTHOR]

For ultra-light geopolymer foam, it is challenging to maintain excellent mechanical properties and foaming stability while continuously reducing the density. In this study, basalt fibers (BF) and hollow microspheres (HM) were used to prepare a basalt fiber-reinforced metakaolin (MK)-based geopolymer foam (FRGF) and the workability, microstructure, physical properties, high-temperature performance, and shrinkage characteristics were systematically investigated. Results indicate that incorporating 50% HM into FRGF significantly reduces the fluidity by 31.2% and reaction rate of the geopolymer paste, slows down the decomposition rate of hydrogen peroxide, and enhances the stability of the foaming process. Additionally, the incorporation of HM increases the total porosity of the FRGF from 75.4% to 86.3%, lowers the bulk density from 0.42 g/cm3 to 0.34 g/cm3, and decreases the thermal conductivity to 0.0681 W/(m⋅K). Concurrently, the introduction of BF significantly enhances the mechanical properties of FRGF, with a 28-day compressive strength reaching 2.49 MPa. After treatment at 1000 ℃, the FRGF transformed from an amorphous gel structure to a crystalline structure. The sintering between BF and the matrix notably enhances the performance of interfacial transition zone (ITZ), further increasing the energy absorption capability and decreasing the linear shrinkage of FRGF at high temperatures (1000 °C) by 55.2%. In conclusion, 50% HM and 0.6% BF demonstrated superior mechanical properties, thermal insulation, and high-temperature performance. It offers a strategy to resolve the contradiction between the density, mechanical performance, and stability of geopolymer foams and has potential applications in the field of high-temperature insulation. • A novel geopolymer foam containing HM reinforced by BF was developed. • BFs enhance the compressive strength of FRGF. • Developed FRGF exhibits superior ITZ after high-temperature treatments. • HMs reduce the thermal conductivity of FRGF at room temperature. • BFs improve the shrinkage performance at room and high temperatures. [ABSTRACT FROM AUTHOR]

To solve the seepage problem of roller-compacted concrete (RCC) gravity dams, grout-enriched vibrated RCC (GEVR) and immersion vibrated RCC (IVRCC) have been widely used as the primary impervious materials. However, the vibration process required for these materials severely impedes the rapid construction of RCC dams. To reduce the construction disturbance on RCC impervious structures, we propose a new type of self-compacting concrete (SCC), namely, high-fluidity impermeable and anti-cracking concrete (HIAC). HIAC is formed by partially replacing cement with an equal amount of expansion agent and by adjusting the mixture proportions through trial testing. The comprehensive performance of HIAC was studied using tests on its compressive strength, elastic modulus, permeability and, in particular, the mechanical properties of the interface between HIAC and RCC, using a large roller-compacted specimen. The results indicated that HIAC meets the basic requirements of hydraulic concrete. The compressive strength reached 1.52 times the design strength, and the permeability grade of the HIAC was greater than W34. In addition, the interfacial properties between HIAC and RCC were favorable. Relative to RCC, higher splitting strength was measured at the interface of HIAC and RCC. Therefore, using HIAC as the impervious material instead of GEVR facilitates simpler, faster and higher-quality construction. These advantages signify that HIAC is a promising material in hydraulic engineering. [ABSTRACT FROM AUTHOR]

• Nano-clay particles are new types of nano-materials with high pozzolanic activity. • Appropriate content of nano-clay improves properties of cement-based materials. • Mechanism for the effects of environmental condition was summarized. Nano-clay and calcined nano-clay are new types of nano-materials with high pozzolanic activity. In recent years, numerous studies have been done about the effects of nano-clay and calcined nano-clay. However, a comprehensive review is lacked to better understanding their mechanism. Therefore, properties including workability, mechanical properties, durability, shrinkage, hydration and microstructure of cement-based materials incorporating nano-clay and calcined nano-clay are reviewed in this paper. Based on the results of various literatures, the mechanism of nano-clay and calcined nano-clay are summarized. Furthermore, in view of problems existing in the current studies, some suggestions are put forward for the future research. The results show that appropriate content of nano-clay or calcined nano-clay has beneficial effects on improving the properties of cement-based materials, which is mainly attributed to their filling effect, pozzolanic effect, nucleation effect, bridging effect and barrier effect. [ABSTRACT FROM AUTHOR]

This article presents a nonlinear analysis to explore mechanical properties of the membrane structures made of laminated woven fabrics by numerical simulation and experiments. Stresses-moduli response surfaces are created with the data of stress-strain curves measured from the biaxial test. To apply this method into finite element method (FEM) analysis, complete cubic polynomials of these surfaces are obtained and created the nonlinear material model under user defined subroutine UMAT of ABAQUS. A cruciform specimen is analyzed adapting the nonlinear model, which is subjected to biaxial tensile under the condition of stress ratio of 1:1, 1:2, 2:1, 3:1, 1:3, 0:1 and 1:0. It is shown that the results of nonlinear material model agree well with experimental results. [ABSTRACT FROM AUTHOR]

Highlights: [•] The influence of lateral tension on the bond behavior of plain round bars. [•] The regression analysis of bond parameters with the effect of lateral tension. [•] The bond stress–slip relationship with the consideration of lateral tension. [Copyright &y& Elsevier]

• Preparation of a novel hydrophobic agent. • Enhancement of freeze–thaw resistance of concrete. • Improvement of splitting tensile strength and compressive strength of concrete. • The formation of harmful pores is restrained in concrete. An innovative hydrophobic agent named YREC (Yellow River Engineering Consulting) was adopted in this study. The substrate is mica powder, which is treated with silane coupling agent and polydimethylsiloxane. By comparing hydrophobicity of the hydrophobic agent with different dosages of polydimethylsiloxane and temperatures, the optimum processing scheme of hydrophobic agent was provided. A series of hydrophobic concrete with different water to cement ratios and YREC contents were prepared. Freeze-thaw (F-T) resistance and mechanical properties of concrete were investigated. Meanwhile, microstructure was determined by means of water adsorption test and mercury intrusion porosimetry. The results show that the YREC provides hydrophobic functional group and improves pore network to inhibit the invasion of water, which further enhances the F-T resistance and mechanical properties of concrete significantly. The pore size characterizations indicate that the addition of YREC increases the quantity of transition pores while decreases that of macro-pores, and the mechanical properties of concrete are reduced obviously due to the decrease of macro-pores. Compared with adjusting water to cement ratio, YREC is more conducive to refine pore structure of concrete. [ABSTRACT FROM AUTHOR]

• Electrically conductive roller-compacted concrete is proposed for overwintering layer of dams. • ERCC layer provide a new way to solve the thermal crack problem of RCC dams. • The electro-thermal properties and resistivity variation of ERCC are evaluated. • The compaction properties of ERCC are assessed by rolling compacted device. • Larger density and strength shows the superiority of rolling construction method. To solve the thermal crack problem of overwintering layer of roller-compacted concrete (RCC) dams. A new type of intelligent hydraulic concrete, namely electrically conductive roller-compacted concrete (ERCC), was designed. ERCC layer could provide a new way to control the temperature distribution and reduce the cracking likelihood of RCC dams by its electro-thermal properties, closely related to the variation of resistivity of ERCC. Thus, the relationships between design factors and the resistivity were investigated to obtain the real resistivity of ERCC layer of RCC dams. Then the temperature increase of ERCC layer with the size of 3000 × 700 × 200 mm was measured under 30 V direct current voltage. The temperature rises 14 ~ 16 ℃ within 235 min. It means that the electro-thermal properties of ERCC are enough to resist cold waves in winter. On the other hand, the mechanical and compaction properties of ERCC were investigated through experiments to evaluate whether the roller compaction method can overcome the poor fluidity and improve the construction quality of ERCC. So the density and strength of roller compacted device formed ERCC were compared with those of vibration formed ERCC, which shows the superiority of rolling construction method. According to unit compaction energy and parameters of the roller machines, the onsite compaction passes N S are calculated, which provides guidance for the construction of overwintering layer. In summary, selecting ERCC as the overwintering material instead of traditional thermal insulation materials could provide a more flexible and intelligent temperature control way for RCC dams in the severe cold areas, signifying ERCC is a promising material in hydraulic engineering. [ABSTRACT FROM AUTHOR]

• Higher temperature or wind speed, or lower humidity affected interlayer properties of concrete negatively. • Mechanism for the effects of environmental condition was discussed. • Relationship between damage degree and loss rate of tensile splitting strength was established. Dam concrete is usually poured layer by layer. Interlayer as a "weak section" or "defect" inside the concrete, may lead to an increase in the risks of seepage and bedding slip of dams. This study investigated effects of environmental condition (i.e. ambient temperature, relative humidity and wind speed) on interlayer properties of dam concrete, in terms of tensile splitting strength, resistance to chloride ion penetration and pore structure. In addition, damage degree of concrete caused by the interlayer was evaluated by means of ultrasonic non-destructive test. The results show that increasing temperature or wind speed on the lower layer surface decreases the interlayer tensile splitting strength and resistance to chloride ion penetration of concrete significantly. Meanwhile, reducing relative humidity has an adverse effect on the interlayer properties of concrete. It is attributed to that higher temperature or wind speed, or lower relative humidity can accelerate water evaporation, reducing surface water content and speeding up hardening process of the lower layer concrete obviously. It causes not only a worse bonding quality but also a pore-structure coarsening effect near the interlayer. Moreover, the reduction of surface water content of the lower layer concrete may decrease final degree of hydration reaction, which should be responsible for the decrease in the interlayer properties as well. Furthermore, there was a linear relationship between the damage degree and loss rate of tensile splitting strength of concrete. Therefore, the damage degree calculated from wave velocity can be adopted to predict the loss rate of tensile splitting strength effectively. [ABSTRACT FROM AUTHOR]

• A new water-repellent additive (YREC) improved dry-cured concrete performance. • Dry-cured concrete with YREC had higher strength, and lower shrinkage. • By blocking pore channels, YREC retains moisture and improves pore structure. Severe environments worsen the performance of concrete. To increase the cracking resistance of concrete cured in dry environments, a water-repellent additive (YREC) was developed by surface treating mica powder with a silane coupling agent and polydimethylsiloxane. The strength, shrinkage, and restrained cracking characteristics of concrete with and without the YREC additive, named OPC-YREC and OPC, were investigated. The results showed that the OPC-YREC had a higher strength at 30% RH and a comparable strength at 50–70% RH compared to OPC. This advantage can maintain when the temperature ranges from 10 °C to 40 °C. In addition to the lower shrinkage, resulting in higher cracking resistance of OPC-YREC than OPC in dry curing environments. Microscopic analyses showed that the YREC retained moisture and strengthened the pore structure by providing a water-repellent barrier between pore channels. [ABSTRACT FROM AUTHOR]