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The purpose of this study is to develop a method for highway tunnel performance evaluation using combined weight theory and fuzzy multi-criteria decision-making analysis (FMCDM). This study takes the MWP highway tunnel as the research object, and analytic hierarchy process (AHP), entropy theory (ET), game theory (GT), and FMCDM theory were used to study the tunnel performance. The evaluation index system and the classification value limits are determined, the key factors affecting the tunnel performance level were analyzed, and the subjective and objective weights of each index are calculated using AHP and ET. By applying the membership function of FMCDM theory to solve the single index membership of each index at different levels, and combining GT to obtain the comprehensive weights, and the weights of lining structure and Communication Systems is the largest among all index, 0.389 and 0.214, respectively, and in line with engineering practice. The multi-index comprehensive membership evaluation value and target comprehensive membership evaluation vector of the tunnels based on FMCDM theory at different levels are obtained. According to the principle that with the larger the value, the performance is better, the tunnel performance is comprehensively evaluated. Finally, the scientific of the evaluation method is tested in combination with the MWP tunnel case, and the deterioration model of the tunnel performance is proposed based on the structure reliability theory, and the model results are compared with actual observations during tunnel inspection. The results show that the degradation model has strong operability and high accuracy and can effectively predict and ensure the safety of the tunnel structure. The performance evaluation method has objectivity, relevance, and intuitiveness. It can identify the key links of the evaluation and enable construction planners and managers to improve the robustness and safety of the tunnels.

To achieve the ambitious goal of carbon neutrality, more carbon sequestration channels need to be developed. In this study, we tried to combine biochar with cold-bonded artificial lightweight coarse aggregate (ALCA) which is made from municipal solid household waste incineration bottom ash (MSWIBA).The strong carbon capture ability of biochar was used to attract external CO

The pore structure of alkali-activated fly ash mortar (AAFAM) under different mix ratios and curing system was measured by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Based on the fractal theory, the integral shape dimension of the pore surface of the AAFAM is obtained and discussed its relationship with total porosity, proportion of gel pores, transition pore, capillary pores and macropores, average pore diameter, median pore diameter, pore surface area, pore size distribution, and the influence of mass ratio of alkali activators, curing temperature, and curing age on pore structures. In addition, data regression analysis (DRA) is a statistical tool and applied to study the relationship between microscopic pore parameters and the fractal dimension of the AAFAM mixtures. The results show that the fractal dimension of the AAFAM is between 2.6 and 2.9, and the pore size distribution has a linear relationship with the fractal dimension, and the internal pore diameter of the AAFAM will gradually decrease and AAFAM’s matrix gradually becomes denser and the microstructure integrity is more stable as the curing age and temperature increases, and the mechanical strength will be higher. The AAFAM mixture composed of Na2SiO3/NAOH with a mass ratio of 1.0 and 100% fly ash is considered the most suitable mixture. AAFAM can make full use of industrial by-products (fly ash) and seems to be a suitable candidate for green environmental protection materials for engineering applications.

To investigate the influence of curing conditions and raw materials on the performance of engineered cement-based composites (ECCs), polypropylene fiber engineered cement-based composites (PP-ECCs) were designed and manufactured. The mathematical relationships between the fly ash content, curing temperature and PP-ECC tensile properties were explored by a uniaxial tensile test and by scanning electron microscopy. The results show the following: 1) with the increase in fly ash content and curing temperature, the ultimate tensile strain, ultimate tensile stress and tensile toughness index of the PP-ECC show a trend of first increasing and then decreasing, while the modulus of elasticity increases. 2) The optimum temperature is 20°C for the hydration reaction of the cementitious material inside the PP-ECC matrix. 3) When the fly ash content is 40% and the curing temperature is 20°C, the tensile mechanical parameters, ductility and toughness index of the PP-ECC are the best. This set of variables is recommended as a reference for PP-ECC engineering applications. 4) A mathematical relationship among the tensile strength, tensile strain and elastic modulus of the PP-ECC and coupling variables (fly ash content and curing temperature) is established.

Polypropylene engineered cementitious composites (PP-ECC) exhibit superior strength and strain hardening under tensile deformation, which is expected to enhance the anti-cracking performance and self-confinement of the plastic hinge region in structural columns. However, there is still a lack of fundamental studies on the compressive behavior of a reinforcement-confined PP-ECC column. This paper presents a proof-of-concept experimental study on the confined PP-ECC column and hybrid normal strength concrete (NSC)-ECC column. Two sets of reinforcement-confined columns were designed: a pure PP-ECC column and a hybrid C30-PP-ECC column. Then, static compression tests were carried out to prove the effectiveness of the confinement in enhancing the peak strength of the hybrid column with respect to pure PP-ECC columns. However, the deformability improvement was not remarkable, with an increase of only 3.2% from samples containing no stirrups to those containing stirrups at a volumetric ratio of 1.6%. An equation was proposed to predict the peak strength of the confined PP-ECC columns. This equation considered the contribution from the tensile capacity of PP-ECC to the circumferential confining effect of the columns. The hybrid column delivered better deformability but smaller peak strength compared with the pure PP-ECC columns. Some mechanical features of the hybrid column were discussed.

The municipal solid waste incineration bottom ash (MSWIBA) contains amounts of hazardous elements or composition, and its disposal to landfills may pose a serious threat to the ground water and soil. To reduce the environmental impact of MSWIBA, a novelty application into the utilization of MSWIBA for the manufacture of cold-bonded aggregates (CBAs) was investigated in this study. This study explored the impacts of curing systems on the comprehensive properties of CBAs. Furthermore, the hydrating phases of the designed CBAs were studied by X-ray diffractometer, and the micro characteristics of CBAs was analyzed by Scanning Electron Microscopy. The results show that CBAs produced from the MSWIBA had good properties with density of 1.75-1.98 g/cm

Since municipal solid waste incineration bottom ash (MSWIBA) contains some heavy metals that are harmful to the groundwater and soil, this study proposes an effective and new approach to deal with high-volume MSWIBA. Selecting 70% MSWIBA, 10% ordinary Portland cement (OPC), 10% fly ash/ground granulated blast furnace slag (FA/GGBFS), and 1% volume of polypropylene (PP) fiber as the raw materials, this project designed and manufactured cold-bonded fiber aggregates (CBFAs) and applied them into sustainable concrete. It was found that the water absorption of CBFAs was between 12 and 14%, the bulk density was between 900 and 1100 kg/m

Due to the current deterioration of the environment, the performance degradation of reinforced concrete rainwater drainage pipes (RCRDPs) has become increasingly serious. Aiming at these pr...

Chloride ions are known as one of the most crucial factors for rebar corrosion in reinforced concrete (RC) structures exposed to marine environments under drying-wetting cycles. In this condition, the chloride ion content in unsaturated concrete will change under the coupled effect of diffusion and capillary suction. This study simulates the atmosphere zone of the marine environment to explore the law of the chloride transmission behavior under the context of constant temperature and humidity. To analyze the effect of different drying-wetting ratios on the chloride ion profile in the concrete by conducting the dry-wet cycle tests. It is found that the most unfavorable drying-wetting ratios for RC structures in this study is 1:5.5. A finite element numerical model of chloride ion transmission based on Fick's Ⅱ law was established by COMSOL Multiphysics. It can be used to predict the range of concrete surface chloride ion concentration, and dynamic change of the distribution of chloride ion concentration inside the RC structures under different drying-wetting cycles over time. The comparison of experiment data and simulation results verify that the chloride diffusion prediction model has a good correlation.

This study aims to explore the mechanical and micro performance of seawater and sea sand concrete under accelerated carbonization environment. This study designed a total of 8 mix ratios, mainly to explore the effects of different water-cement ratios and different mineral admixtures (FA and LC2) on the properties of seawater and sea sand concrete after carbonization. To better evaluate and understand the mechanical properties, the micro morphology analysis was carried out by SEM, the hydration product analysis was carried out by TGA and XRD, and the pore structure was studied by MIP. The results show that the standard curing of seawater and sea sand concrete for 28 days can increase the compressive strength by about 10% compared with ordinary concrete, but the final mechanical strength is similar to ordinary concrete under the condition of long-term accelerated carbonization. The carbonation resistance performance of seawater and sea sand concrete is approximately twice that of ordinary concrete, but when FA and LC2 are added, the property of carbonation resistance will be reduced by more than two times. The large amount of chloride ions added into the concrete by seawater and sea sand will reduce the total porosity of the concrete by about 13% and improve the pore size distribution. In general, to improve the current shortage of natural resources such as river water and river sand, it is feasible to consider adding seawater and sea sand into ordinary concrete.

The durability of concrete reinforced by cellulose fiber (CTF), polyvinyl alcohol fiber (PF) and polyolefin fiber (VS) is comprehensively studied in this paper. Relevant durability tests are conducted to explore the effect of different fiber types and dosages on durability performance demonstrated in the resistance to drying shrinkage, water permeability, crack, carbonization and chloride ion penetration. Besides single fiber reinforced concrete, synergistic effect of hybrid fibers on durability is also studied, and the service life of fiber reinforced concrete in carbonization environment and chloride ion corrosive environment is further predicted. In addition, the structure of fiber reinforced concrete is analyzed from the micro perspective by using the optical and electron microscope. The results showed that: (1) The addition of CTF can effectively enhance the all five aspects of durability performance, including the resistance to drying shrinkage, water permeability, crack, carbonization and chloride ion penetration. The addition of PF can enhance the durability properties except for chloride ion penetration resistance. Generally, though with few exceptions, the increased dosage of CTF or PF would improve the strengthening effect on the durability of single fiber reinforced concrete. The addition of VS can either enhance or weaken the above five aspects of durability properties, and its effect varies much with the fiber dosage. (2) Hybrid fiber is found to have a positive synergistic effect and enhance the above five aspects of durability properties of concrete. The concrete reinforced with the hybrid fiber combination of 1.2 kg/m3 CTF, 2.0 kg/m3 PF and 2.0 kg/m3 VS may achieve the optimal durability properties. (3) CTF, PF and VS, especially their hybrid combinations, are found to effectively prolong the service life of concrete structure in the carbonization and chloride ion corrosive environment. The research findings obtained in this paper can supplement the study on the durability of fiber reinforced concrete, and provide suggestions for suitable fiber type and dosage selection in actual engineering designs of fiber reinforced concrete.

Reinforced Concrete (RC) structures eroded by chloride ions will reduce the chloride ion concentration on the concrete surface under the effect of sustained rainfall dilution and erosion, and there will be rainfall convection areas and peak chloride ion contents. In this study, the influence of rainfall environment on the transporting behavior of chloride ions in concrete is studied through capillary absorption test and rainfall experiment. A numerical prediction model of chloride ion transporting behavior in concrete was established by COMSOL Multiphysics based on the rainfall tests. The chloride behavior is analyzed and studied. It is found that the numerical simulation results are in good agreement with the experimental results, and the predicted models of chloride ion diffusion under different rainfall conditions are obtained, and the transporting behavior of chloride ions can be effectively predicted. The results also show that with the increasing of rainfall intensity and rainfall time, the chloride ion contents on the concrete surface decreases obviously. When the rainfall time and rainfall intensity increase, the chloride ion contents of concrete decreases, and the binding capacity of chloride ions in the matrix weakens. This research provides some resulting information of RC structures in rainy marine areas.

In order to solve the degradation problem of rock bolts and the safety of a support structure for a high geothermal tunnel in a dry heat environment, various tensile tests of rock bolts were conducted at different temperatures and different levels of roughness of the surrounding rocks in this paper. The roughness of the surrounding rocks was simulated through different types of steel tubes, and dry heat environment was simulated through different temperatures of a drying oven. Based on the first interface (bolt to grout interface) and the second interface (grout to pipe interface) pullout tests, the load-displacement curves of rock bolts were obtained at different temperatures and roughness. The results showed that temperature had little effects on the failure mode, but roughness of the surrounding rock had a great influence on the pullout strength. With an increase in roughness, the tensile strength increased, and the bolting effect was enhanced. For the non-threaded specimens, the interface bond strength of the first interface was larger than that of the second interface, and the second interface showed a kind of shear failure. Finally, it was revealed that the dependence of ultimate tensile force on temperature and roughness of surrounding rocks obeyed a cubic and quadratic polynomial function, respectively.

The low temperature of ice and snow all year round in Sweden leads to the common use of deicing salt to melt the roads, but the splash of the deicing salt on the reinforced concrete (RC) on both sides of the roads brings about the deterioration of the durability of RC components. The chloride ions diffusion coefficient is an important parameter to evaluate the durability of RC. By adopting the rapid chloride migration method (RCM) and replacing chloride ions with iodide ions, the samples of concrete blocks exposed on the side of the highway for 20 years were taken. This is directly beneficial to study the influence of the type, content, and water-cement ratio of mineral additions on the diffusion and distribution of iodide ions in concrete and analyze the surface environmental effect depth of concrete. The influence of chloride ions on the pore structure and microscopic morphology of concrete also were studied by scanning electron microscope-energy dispersive spectrum and X-ray diffractometer. The results show that as the water-cement ratio increases, the surface environmental effect depth of concrete and the diffusion area of iodide ions gradually increase. Silica fume and ground granulated blast furnace slag (GGBF slag) have an impediment to the diffusion of iodide ions, especially with the high volume of the GGBF slag (about 50%), the diffusion of iodide ions is very low. In general, this research is helpful to provide some empirical ideas and suggestions for the manufacturing and durability design of concrete structures in marine environments or deicing salt road environments.

Reinforced concrete (RC) structures located in coastal salt spray areas are subjected to rainfall erosion and chloride ion corrosion throughout the year. Consequently, this study simulates a rainfall environment with artificial rainfall simulation devices and applies a potentiometer to determine the chloride ion concentration. The microstructures and chemical compositions of the concrete were revealed through microscopic experiments. The research results show that with a greater rainfall intensity, the surface chloride ion concentration decreases more obviously, the surface chloride ion loss is more serious, and the chloride ion binding capacity becomes weaker. As the saturation decreases, the binding capacity of chloride ions also decreases. This study can provide some theoretical ideas for the durability design of PC structures in rainy environments.

This paper studies crack features of steel fiber reinforced concrete (SFRC) tunnel segments subjected to eccentric compression. An experiment is conducted in which 56 SFRC beam specimens of different steel fiber type and dosage are cast and loaded. Both qualitive observation and quantitative analysis are made to shed light on crack features of SFRC beams which are demonstrated by crack patterns, the development of crack width and length as well as the energy absorbed during the cracking process. Based on the cracking features of SFRC tunnel segment under eccentric compression obtained in this paper, an improved design method applicable to the SFRC tunnel segment is proposed. The results show that: (1) Two different crack patterns would occur for SFRC beams under compressive loads of different eccentricity, which is different from that of reinforced concrete (RC) beams, and the two patterns differ in how cracks gradually develop. (2) SFRC beam specimens are safer when subjected to compressive loads of small eccentricity. Dramix 5D SFRC tunnel segments are more suitable for loads of smaller eccentricity (0.1 m) since it exhibits better anti-cracking capacity in that scenario. (3) The Boltzmann fitting formula can properly reflect the development of crack length with the increase of the crack width. (4) Using the obtained experimental results, the rationality of the improved design method is well verified.

Mechanical properties of concrete reinforced with cellulose fiber (CTF), polyvinyl alcohol fiber (PF) and polyolefin fiber suitable for various spray (VS) are experimentally studied. The individual impact of single fiber as well as synergistic effect of hybrid fiber on axial compressive strength, splitting tensile strength and shear strength of concrete are investigated. Microstructures of fiber reinforced concrete specimen as well as its stress–strain relationship is also observed. The results show that CTF alone enhances axial compressive strength of concrete but weakens splitting tensile strength; VS weakens splitting tensile strength as well but has little impact on the other two strength; PF has a negative effect on all the three mechanical strength. Synergistic effect of hybrid fiber varies with dosage, and only with the appropriate fiber dosage can hybrid fiber has positive synergistic effect on mechanical properties. 1.5 kg/m3 cellulose fiber with 1.0 kg/m3 polyvinyl alcohol fiber is found to be optimal combination of CTF-PF hybrid fiber to achieve the best synergistic effect. Practical implications of CTF, PF and VS are also put forward.

Aiming at the problems of complicated data processing, large amount of calculation, perplexing results of the orthogonal test, and the uncertain multi-index decision-making matter that the decision-making index value is difficult to be refined, this paper studies the mixed multi-index gray target decision-making model with three data types of real value, interval number and triangular fuzzy number. According to the basic connotation of decision gray target and uncertain decision information, a hybrid ellipsoid gray target is defined, and a mixed gray target decision model is established. Then through the mechanical, durability, workability and other performance, the lightweight aggregate shotcrete (LWAS) was selected for the optimization of the mix ratio, and then compared with the traditional orthogonal results, and applied in the tunnel engineering. Therefore, the feasibility of applying LWAS in tunnel bolting and shotcreting supporting was explored to provide a theoretical reference for the application of LWAS in tunnel lining. The results show that: (1). The unit water consumption has some influences on the compressive strength, Splitting tensile strength, bonding strength and resistance to chloride ion permeability of the LWAS, and the optimal range of water consumption is 180–200 kg/m3. (2). The water-binder ratio has a significant effect on the compressive strength, splitting tensile strength and electric flux of LWAS, and has a small effect on the bonding strength. (3). The compressive strength, splitting tensile strength and electric flux of concrete increase with the decrease of water-binder ratio. (4). When the fly ash content is 0%, the 28 d compressive strength, splitting tensile strength and bonding strength of LWAS are the largest, and the electric flux is the smallest. (5). When the water-cement ratio is 0.42 with pure cement, the combination of gray targets has the best comprehensive decision-making performance, and it is recommended as the tunnel lining concrete ratio.