Materials and Structures最新文献

Based on the strain reduction coefficient methodology, which enables an analysis of a beam with external or internal unbonded tendons as a beam with bonded tendons, and using the age-adjusted effective modulus method for time analyses of prestressed concrete members under long-term loads, this paper proposes an equation for the calculation of prestress loss in simply supported beams with internal unbonded tendons. The proposed equation takes into account the effects of concrete creep, concrete shrinkage, relaxation of the prestressing steel, and the presence of a bonded, non-prestressed reinforcement. The main goal of this study is to reduce a relatively complex problem, in which it is necessary to analyse the member as a whole, to one of sectional analysis. As our main conclusion, we find that the loss of prestress obtained by applying the proposed equation has an accuracy that is comparable with the results of previous studies and with the application of existing formulations.

A straightforward mixing approach that involves incorporating glass fiber into cement-based materials is frequently carried out at construction sites. This practice can have adverse effects on both the fresh and hardened properties of cement mixtures. The lack of quality control measures often leads to the production of fiber-reinforced cement mixtures that do not perform as intended. Additionally, the inherent variations in commercially available glass fibers of the same type add complexity to mixing, making it difficult to consistently reproduce desired effects for in situ casting. Therefore, this research aims to accomplish three main objectives. Firstly, characterizing E-glass and AR-glass fibers to enable a practical replication of performance using these specific variants. Secondly, assessing the impact of five different mixing methods on water absorption, flowability, setting time, compressive, and flexural strength in cement mixtures embedded with these glass fibers. Lastly, evaluating the fiber-matrix interaction within the hardened samples for each mixing method. The results revealed that various mixing methods yielded distinct advantages in the fresh and hardened properties. This highlights the variability in mixing approaches, indicating that the choice of method should be tailored to meet the specific construction requirements of engineers. In essence, the study underscores the importance of selecting an appropriate mixing technique based on the desired outcomes for both the fresh and hardened states of cement mixtures.

The utilization of engineered wood products is becoming more and more important when it comes to carbon sequestration and sustainable building. Among them, Cross-laminated timber (CLT) has emerged as a popular mass timber product, offering enhanced structural properties and environmental benefits. This study investigates the potential of incorporating small-diameter trees as corrugated wood-strand composite panels into CLT, developing a cellular cross-laminated timber (CCLT). A systematic investigation was carried out to assess the impact of core geometry on the flexural stiffness of CCLT panels utilizing the finite element method. Six cases involving combinations of fixed and variable geometrical parameters were examined to determine the effect of each geometrical parameter. The findings revealed a substantial positive effect of corrugation depth, while bond length and unit cell length exhibited a negative influence on bending stiffness. Other geometric characteristics play a minor, supportive role. Considering the insights derived from the parametric study and considering manufacturing constraints, a corrugated geometry was designed and fabricated using an aluminum matched-die mold. The CCLT panels, constructed using these corrugated panels, were evaluated against predictions from a finite element model, demonstrating close agreement. Moreover, the CCLT exhibited a higher value of normalized modulus of elasticity by density compared to conventional CLT.

This study introduces a novel non-prestressed concrete precast bottom slab with a section steel and two ribs, designated as NPBS2R. The research aimed to evaluate the effect of section steel form and steel trusses on the flexural performance of NPBS2R. A comprehensive analysis, including three-point static loading tests and numerical simulations, was conducted on five full-scale specimens. The findings reveal that all NPBS2R specimens satisfy the free support construction requirements. Compared to conventional non-prestressed precast bottom slabs with steel trusses (NPB), the NPBS2R’s cracking moment improved by 43.5–59.5%. The section steel, remaining unyielded in tests, demonstrates potential for reuse, with its form exerting minimal impact on the overall flexural stiffness of NPBS2R. The presence of steel trusses was observed to marginally enhance the flexural behavior, contributing to a 15.0% increase. The numerical study highlights that the section size of the section steel, the chord diameter of the steel truss, and the truss quantity significantly influence NPBS2R’s flexural performance. The theoretical values derived from the study closely align with the experimental and numerical outcomes, confirming the established calculation formula’s accuracy and reliability for practical engineering applications.

Most of the roads constructed in the early days have entered the phase of repair and maintenance, leading to an accumulation of large stockpiles of recycled asphalt pavement material (RAP) and posing significant challenges for environmentally sound disposal. Moreover, the low rate of reuse of RAP contributes to the excessive waste of pavement materials. This study focuses on the use of RAP in recycled cement-stabilized aggregates as the primary research subject. Proportion designs for RAP and the base course with inorganic recycled aggregates (RAI) are conducted at ratios of 1:1 (1# recycled base), 1:2 (2# recycled base), and 1:4 (3# recycled base), respectively. Subsequently, mechanical parameters are tested. Using ABAQUS software, a structural model of the reclaimed base course with cement-stabilized aggregate is created. The mechanical properties of the reclaimed base course with varying amounts of cement are analyzed under the influence of dynamic vehicle loading, taking into consideration the potential for cracking at the tip of the base course. The results indicate that under dynamic loading, the vertical stress of the recycled subgrade with 4% cement is significantly better than that of the recycled subgrade with 5% and 6% cement. Among the various recycled base cement, the 4% recycled base exhibits superior shear resistance and the lowest peak horizontal stress at the crack tip, making it less prone to cracking. In terms of vertical strain, shear strain, and horizontal strain of the recycled base layer with different cement dosages for 1# under dynamic load, the strain gradually increases as the distance between the dynamic load and the crack tip of the recycled base layer decreases, reaching the maximum value at the top of the crack tip. The sensitivity of vertical, shear, and horizontal strains at the crack tip to dynamic vehicle loading increases with the cement dosage, with larger strains occurring at a cement dosage of 6%. Therefore, while increasing the amount of cement does not effectively enhance strain at the crack tip, reasonable control of the cement amount can improve the integrity of the base course and reduce crack expansion.

Waste glass is a high-quality siliceous material for autoclaved material, but its effect as the substitution for quartz sand is variable and not sufficiently clarified. To better apply the waste glass in the autoclaved material, the single and combined effect of waste glass and quartz sand as siliceous material on compressive strength is evaluated, and the transformation of hydration products and microstructure is ascertained based on the comprehensive analysis of XRD, FTIR, TG-DSC and ²⁹Si NMR tests. The results indicate that the compressive strength of the autoclaved materials with waste glass is generally higher than that with quartz sand, and the optimum Ca/Si ratio for the waste glass autoclaved material is 0.7, lower than 0.9 for quartz sand autoclaved material. As a single siliceous material, waste glass inhibits the formation of tobermorite and benefits the production of amorphous and highly polymerized C-S–H. At the fixed Ca/Si ratio of 0.7, the partial substitution of waste glass improves the compressive strength of quartz sand autoclaved material by increasing the yield of tobermorite, and the compressive strength reaches the maximum value at the substitution ratio of 20%. A higher waste glass replacement ratio will then be adverse to the formation of tobermorite and decrease the compressive strength. With the increase of the waste glass replacement ratio, the compressive strength presents a three-stage development process. Boosting the formation of tobermorite at a low replacement level of waste glass or highly polymerized C-S–H at a high enough replacement level of waste glass are two feasible approaches to enhancing the strength of autoclaved materials.

Nano-attapulgite (ATP) is a layered silicate mineral with abundant reserves, large specific surface area, and low cost. The unique structure of ATP has attracted wide attention in the field of adsorption. In this study, a preparation technology of ATP grafting basalt fiber (BF) was proposed by chemical grafting method based on the idea of plant root bionics. The optimal preparation process of ATP grafting BF was determined through the tests of asphalt absorption performance, thermal stability performance, and segregation dispersion performance. The mechanism of ATP grafting BF was analyzed by micro-morphology, functional group changes, and elemental composition. Finally, the adsorption performance of ATP grafting BF was investigated on the basis of adsorption kinetics model and molecular dynamics simulation. The study results indicated that ATP-BF_HCl had better compatibility and wettability with asphalt. The quasi-second-order kinetic equation could better fit the adsorption process of ATP-BF_HCl on asphaltene, which indicated that ATP-BF_HCl adsorbed asphaltene with chemisorption or ion exchange. The diffusion coefficient and diffusion activation energy of the saturate and the aromatic were larger, indicating a smaller molecular weight and faster movement, and lightweight components of asphalt are more easily adsorbed on the surface of ATP. The diffusion activation energy of asphaltene is the smallest and the reaction is the easiest to take place, which indicates that it is the first to react during temperature increase. The research results can provide a theoretical basis and technical support for BF surface treatment technology.

This study determines how untreated recycled concrete aggregates (URA), thermally treated recycled concrete aggregates (TRA), and recycled concrete aggregates developed through an integrated thermomechanical treatment process (T_mRA) perform in concrete relative to each other. A concrete composed of 100% recycled aggregates (RCA) with Portland pozzolana cement has been successfully developed in the present study. The compressive strength, split tensile strength, flexural strength, fracture energy, and modulus of elasticity of T_mRC is observed higher than URC by 18.62%, 8.20%, 40.72%, 24.18%, and 54.99%, and those TRC by 7.54%, 28.57%, 29.78%, 24.12%, and 34.35%, respectively. The split tensile strength, flexural strength, fracture energy, and modulus of elasticity of these concretes are strongly correlated with their compressive strength. T_mRC material properties match NAC, standard requirements, and reported values closely. URC and TRC chloride-ion penetrations are around 3.51- and 2.42-times greater than T_mRC. Among these concretes, only T_mRC meets corrosion protection requirements like NAC. The abrasion resistance of T_mRC is observed 52.03% greater than URC and 43.07% greater than that of TRC. T_mRC has substantially lower sorptivity compared to URC and TRC and is close to NAC. T_mRC has around 32.65% and 16.67% less weight loss in drying than URC and TRC, respectively. URC and TRC have around 1.99- and 1.82-times less abrasion resistance than T_mRC. An optimal reduced adhered-mortar volume, the minimized porosity and microcracks, dense and uniform surface texture, strengthened interfacial transition zones leads the performance of T_mRA superior to URA and TRA, and close to or superior to parent aggregates.

This paper presents an investigation on the seismic behavior of RC frames with masonry infills retrofitted by precast Ultra-Lightweight Insulated Cementitious Composites plates under cyclic loading. The objective was to provide an easy retrofit approach for concurrent seismic behavior and energy efficiency upgrading of existing RC frames. Three scaled RC frames were built including a control frame and two frames with different retrofit schemes. The experiments were conducted to investigate the effect of different retrofit schemes over the failure patterns, hysteretic curves, energy dissipation abilities, skeleton curves, and characteristic loads and displacements. The retrofitted RC frames provided higher carrying capacities, energy dissipation abilities, and displacement ductility. Retrofit schemes proposed can prevent severe damage of masonry infills, and alleviate shear failure of columns significantly. Based on the test results, ULICC plates influenced on the flexural moments of columns and beams, and base shear distribution were analyzed. Interactions between retrofitted infills and surrounding frames were discussed. A theoretical model based on equivalent strut was proposed to obtain initial lateral stiffness and carrying capacity of retrofitted RC frames. The experiments have demonstrated that precast ULICC plates retrofit strategy can enhance the seismic performances under low-frequency cyclic loading.