摘要：
To repair reinforced concrete beams efficiently in a limited building space, the four-sided application of a reinforcing thin layer of reactive powder concrete ("RPCTL") was proposed to improve the bending capacity of the members. Static flexural tests of one comparison beam and five reinforced beams were completed on a four-point centralized loading device. Changes in deflection, cracks, stresses, and damage characteristics of the specimens were measured under various levels of loading. The test results showed that the damage patterns of the reinforced specimens were dominated by the yielding of longitudinal tensile reinforcement at the bottoms of the beams and the crushing of the cementitious material in the top compression zones of the beams. The cracking load greatly increased by 1.42 to 7.12 times, and the ultimate bearing capacity increased by 0.29 to 1.41 times. The distribution characteristics and dynamic changes in the displacement, stress, and damage of the specimens were dynamically simulated by finite element software. The effects of reinforcement and initial load-holding level on the reinforcement effect were investigated. A bending capacity calculation formula for RPCTL reinforcement technology is proposed that aligns with the test results and can provide a reference for the design of RPCTL reinforcement.
摘要：
<jats:p>The huge demand for sand and gravel resources in road engineering construction leads to excessive consumption of resources and environmental damage. Recycling waste concrete and industrial solid waste as a road material is a promising alternative. In order to explore the application of these solid wastes in the road base, this paper studies the effect of adding lithium slag activated by an alkaline activator, fly ash (FA) and a combination of the two on the compressive strength, splitting strength and shrinkage performance of recycled cement-stabilized macadam mixture (RCSM). The optimum content of recycled aggregate (RA), alkali-activated lithium slag (AALS) and FA in composite-improved RCSM was optimized using a response surface method (Box–Behnken), and the microscopic characteristics of the mixture were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the optimum dosage of AALS, FA and RA determined by the response surface method is 15%, 10% and 40%, respectively. Compared with the cement-stabilized macadam mixture (CSM) with 40% RA, the 28 d compressive strength and 28 d splitting strength of the composite-improved RCSM are increased by 26.8% and 22.9%, respectively, and the dry shrinkage coefficient and average temperature shrinkage coefficient are decreased by 25.8% and 14.8%, respectively. Microscopic tests show that AALS and FA participate in the hydration reaction, generate more hydrated silicate (C-S-H) and ettringite (AFt), refine pores, effectively improve the performance of the internal interface transition zone of the mixture, make the microstructure of the mixture denser, and improve the strength and shrinkage performance of RCSM. This study provides technical support for the reuse of resources and the sustainable development of road construction.</jats:p>
摘要：
This paper has investigated the effects of the six factors of concrete volume density, polystyrene particles, water-cement ratio, sand rate, glass powder, and silicon ash on the thermal properties of polystyrene granular concrete, analyzed the degree of influence of various factors through the principal component method, established a comprehensive index where the thermal conductivity of polystyrene granular concrete, is affected by multiple factors and determined a model equation for the standard value of the thermal conductivity. On this basis, the conclusion has been reached. Specifically, the polystyrene particle content has the most significant effect on the thermal conductivity of the polystyrene particles, followed by the bulk density of concrete, with glass powder having the most negligible impact. When the replacement rate of silicon ash is greater than 10%, the thermal conductivity of polystyrene granular concrete could be reduced to improve its thermal performance. When polystyrene granular concrete is prepared using silicon ash, its thermal conductivity is reduced by 22%. When the replacement rate of glass powder does not exceed 20%, it exerts a positive effect on reducing the thermal conductivity of polystyrene granular concrete. Among them, when the glass powder replacement rate is 10%, the thermal conductivity reaches a minimum value, which is 16.1% lower than that of the control group. With the increase of the sand rate, the thermal conductivity of polystyrene granular concrete increases, and the higher the bulk weight of the concrete, the smaller the increase in thermal conductivity.
摘要：
Shotcrete is widely used in mine and civil engineering as supporting structure. A new type of ultra-high-strength shotcrete (UHSSC) with viscosity-enhancing agent was taken as the research object in this paper. A microstructure model of UHSSC under different curing conditions (standard curing, natural curing and film curing) was reconstructed using X-ray computed tomography (X-CT). The grey theory was used to analyze the correlation between pore characteristics and strength of UHSSC. The results showed that the porosity and the pore size of UHSSC were significantly reduced, the compressive strength was obviously improved by the new spraying process. The effects of curing conditions on the pore characteristics and compressive strength of UHSSC were obvious. Under natural curing, the hydration degree was the highest, the maximum pore size was the smallest, and the compressive strength was the highest, reaching 95.8 MPa, but the porosity was the highest. The curing condition had a certain influence on the sphericity distribution of UHSSC pores. Under film curing, the proportion of special-shaped pores (S < 0.4) was the largest and compressive strength was the smallest. There was a good correlation between pore characteristic parameters and the compressive strength of UHSSC under different curing conditions. In particular, the large pore size (D ≥ 5000 µm) and special-shaped pores (S < 0.4) had obvious effects on the strength of UHSSC, and the grey correlation coefficients were 0.8539 and 0.8080, respectively. Additionally, the pore direction of UHSSC had obvious directionality, and the anisotropy of UHSSC may be more prominent than poured specimen. The results will lay a foundation for the study of its mechanical properties and durability.
摘要：
Shotcrete is widely used in civil engineering as a supporting structure. In this paper, the compressive behavior of ultra-high-performance shotcrete (UHPSC) with different steel fiber content by volume (0, 0.5%, 0.75%, 1%, 1.25%, 1.5%) was investigated. The results showed that the failure pattern of UHPSC was changed from brittle failure to ductile failure with the increase in steel fiber content. The compressive strength, peak strain and compressive toughness of UHPSC increased with the increase in steel fiber content, but the elastic modulus and Poisson's ratio did not change significantly. With content of 1.5% steel fibers, its axial compressive strength, peak strain and compressive strain energy were 122.7 MPa, 3749 mu epsilon and 0.269 MPa, respectively, increased by 14%, 23.5% and 55.5% compared with those without steel fiber. The peak strain and compressive toughness were higher than that of ultra-high-performance concrete (UHPC), while the elastic modulus of UHPSC was lower than that of UHPC. Based on the experimental data, the relationship between compressive strength, peak strain, compressive toughness and the change in the characteristic value of steel fiber content (lambda f) were revealed. The uniaxial compressive constitutive model of UHPSC with different steel fiber content was established and reflected the change rule of the shape parameter of alpha (constitutive model ascending section) and beta (constitutive model descending section) with lambda f. The experimental results were in good agreement with the model calculation results, which can provide theoretical support for the structural design of UHPSC.
摘要：
Hollow structures reduce weight without compromising load-bearing capacity and are widely used. The new Glass-Fiber-Reinforced Polymer high-strength thin-walled inner mold simplifies internal cavity construction and boosts structural performance. This study first investigates the influence of a GFRP high-strength thin-walled circular tube on the cross-sectional load-carrying capacity of hollow slabs. Then, a formula for the bending load-carrying capacity of the section under the action of the tube is derived. The results indicate that when the height of the concrete compression zone meets certain conditions, GFRP high-strength thin-walled circular tubes can improve the ultimate load-carrying capacity of the hollow floor slabs. In order to achieve a more economical design, the bending moment modification of a GFRP high-strength thin-walled circular tube of a continuous slab was studied. Research has found that the bending moment modulation limit for a continuous slab is 35.65% when it is subjected to a load of Pu=24 kN. Experimental analysis has shown that the results are generally consistent with the calculations. In practical engineering, the application of a GFRP high-strength thin-walled circular tube of continuous slabs has limitations. Therefore, this study investigated a GFRP high-strength thin-walled honeycomb core slab and found that its ultimate load-bearing capacity is greater compared to waffle slabs. In addition, the stress performance of the GFRP high-strength thin-walled honeycomb core internal mold is superior, making it more promising for practical applications.
作者机构：
[Yu, Zhouping; Cai, Jiahang] Yuan College, Shaoxing University, Shaoxing;312000, China;[Yang, Weijun] College of Civil Engineering, Changsha University of Science and Technology, Changsha;410076, China;[Yu, Zhouping] 312000, China<&wdkj&>College of Civil Engineering, Changsha University of Science and Technology, Changsha
摘要：
In this paper, glass powder (GP) was used as a partial replacement of cement and the effects of different levels of GP replacement on the mechanical and durability properties of modified polystyrene particle concrete were investigated, and the mechanism of action was analysed using x-ray diffraction, scanning electron microscopy and CT techniques. The study results show that GP reduces the early strength of modified polystyrene particle concrete. When the substitution rate of GP is not more than 20%, it can improve the late compressive strength and splitting tensile strength of modified polystyrene granular concrete and enhance the chloride ion permeability and frost resistance. When the substitution rate of GP reaches 30% and above, it is unfavourable to the mechanical properties and durability of modified polystyrene granular concrete.20% is the best substitution rate of GP in modified polystyrene grainy concrete. The thermal conductivity of modified polystyrene particulate concrete tends to decrease and then increase with the increase of the GP substitution rate. The best thermal performance is achieved when the GP substitution rate is 10%. It can be attributed to the fact that the appropriate amount of GP can improve the internal microstructure of the modified polystyrene particle concrete and optimise the pore structure.
作者机构：
[Ye, Xin; Yang, Jianyu; Yang, Weijun] Changsha Univ Sci & Technol, Sch Civil Engn, Changsha 410114, Peoples R China.;[Li, Rongjun] Gen Contracting Co CCSED, Changsha 410114, Peoples R China.
通讯机构：
[Jianyu Yang] S;School of Civil Engineering, Changsha University of Science & Technology, Changsha 410114, China<&wdkj&>Author to whom correspondence should be addressed.
关键词：
stray current;water environment;corrosion of steel bars;calcium ion erosion;compressive strength damage
摘要：
The construction of subways, hydroelectric stations and water substations is exposed to stray currents, which can accelerate concrete corrosion. The influence of stray currents on reinforced concrete structures is unclear. In this paper, the influence of concrete strength grade, reinforcement diameter and stray current intensity on the extent of reinforcement corrosion and calcium ion dissolution were investigated, and the damage of reinforcement and calcium ion corrosion to concrete strength was investigated by simulating a stray current environment and conducting an electrified acceleration test. The test results show that the higher the strength grade of concrete, the lower the stray current intensity and the smaller the corrosion rate and calcium ion dissolution rate of reinforcement; with the increase in the diameter of reinforcement the corrosion rate decreases, but the calcium ion dissolution rate is not affected by reinforcement diameter. The damage effect of reinforcement corrosion on concrete compressive strength is more obvious than that of calcium ion corrosion.
作者机构：
[Yang Weijun; Ye Xin; Yang Jianyu] Changsha Univ Sci & Technol, Sch Civil Engn, Changsha 410114, Peoples R China.;[Jiang Cong] China Construct Technol Hunan Co Ltd, Changsha 410114, Peoples R China.
通讯机构：
[Yang Weijun] S;School of Civil Engineering, Changsha University of Science & Technology, Changsha 410114, China<&wdkj&>Author to whom correspondence should be addressed.
关键词：
steel bar;energized corrosion;corrosion efficiency;chloride ion;current density
摘要：
As the main problem of the durability deterioration of concrete structures, the corrosion of steel bars is usually made by the method of electrified corrosion with a short cycle and low cost. However, there is a big difference between the actual corrosion depth and the theoretical corrosion depth after the reinforcement is electrified. In this paper, through the accelerated corrosion test of steel bars, the change law and influence factors of corrosion efficiency of steel bars in concrete simulated pore solution and NaCl solution are studied. The test results show that the corrosion efficiency of reinforcement in the NaCl solution is higher than that in the concrete simulated pore solution, and the corrosion efficiency in the NaCl solution changes in two stages with the corrosion degree of reinforcement. The corrosion efficiency of concrete in the simulated pore solution decreases with the increase of corrosion degree of reinforcement, which is more significant than that in the NaCl solution. Under the same conditions, the corrosion efficiency is higher in the chloride ion solution with high concentration, and the influence of chloride ion concentration change in the simulated pore solution of concrete on the corrosion efficiency is more significant. The corrosion efficiency of reinforcement under low current density is higher than that under high current density.
通讯机构：
[Weijun Yang] S;School of Civil Engineering, Changsha University of Science and Technology, Changsha 410014, China<&wdkj&>Author to whom correspondence should be addressed.
摘要：
Autoclaved aerated concrete wallboard (AACW) has been widely used as a building envelope component in the infill walls of frame structures, which has broad prospects for development and utilization. However, the cracking of AACW has become a pressing problem, and this problem needs be solved or relieved effectively. We need an effective control method to reduce the cracking problem of AACW. It is necessary to study the interrelationship between the moisture content and the dry shrinkage of AACW. In this paper, a moisture content test and a drying shrinkage test of AACW were conducted, to understand the effect of the moisture content on the drying shrinkage performance of AACW. In addition, the moisture content of AACW with time was explored, and changes in the dry shrinkage value of AACW with the moisture content of AACW were obtained. According to the results and the conditions and the hypothesis of the test, the drying shrinkage value of AACW increases with time, and the drying shrinkage speed was fast in the early stage and tended to be stable in the later stage. In AACW, the drying shrinkage value and the relative humidity have a notable negative correlation. In addition, there was a positive correlation between the drying shrinkage value and the initial moisture content and the ambient temperature. When the AACW lost water from its initial moisture content to the equilibrium moisture content, the accumulated dry shrinkage value of AACW increased with the water loss. Moreover, a time-varying model of the moisture content and a prediction model of the equilibrium moisture content of AACW were established, and time-varying models of the drying shrinkage value of AACW with different initial moisture contents were proposed. The results provide a scientific basis for the reasonable maintenance and profitable control of drying shrinkage cracking of AACW.
