Search Results (143)

The present study highlights the critical role of surface type, insect species, and exposure duration in determining the efficacy of surface-applied insecticides in stored-product pest management. Four insecticides were sprayed and evaluated on different surfaces (concrete, metallic, plastic, and ceramic) against two beetles: the red flour beetle and the tobacco beetle. Alpha-cypermethrin and spinosad exhibited rapid and high efficacy, particularly on non-porous surfaces such as metal and ceramic, whereas pirimiphos-methyl was less effective initially and required extended exposure to achieve complete mortality, especially against Tribolium castaneum. In contrast, Lasioderma serricorne showed greater susceptibility across all insecticides and surfaces. Spinosad maintained high efficacy across all surface types, suggesting broader applicability under variable conditions. The reduced performance of insecticides on concrete surfaces underscores the influence of substrate porosity on insecticide bioavailability. Additionally, the observed delayed mortality effect in all treatments indicates that even brief exposure can result in lethal outcomes, emphasizing the long-term potential of these applications. These findings underscore the need for surface-specific application strategies and support the integration of surface treatments into comprehensive pest management programs. Further research is warranted under simulated field conditions to assess residual efficacy over time and in the presence of food, thereby enhancing the relevance of laboratory findings to real-world storage environments. Full article

The spray-applied pipe lining (SAPL) method, extensively employed in the trenchless rehabilitation of reinforced concrete pipes (RCPs) due to its operational versatility, remains constrained by an incomplete understanding of the failure behavior of rehabilitated pipelines, thereby impeding optimal design strategies. This study proposes an analytical approach to evaluate the structural performance of pipes with fiber-reinforced mortar lining, with a particular focus on interface failure and its consequences. Two RCPs with an inner diameter of 1000 mm, repaired with 34 mm and 45 mm centrifugally sprayed fiber-reinforced mortar liners, were subjected to three-edge-bearing (TEB) tests. The elastic limit loads of the two pipes were 57% and 39% of their pre-rehabilitation conditions, while the ultimate loads were 45% and 69%. A thicker liner exhibits a greater susceptibility to interface failure, leading to wider cracks around the elastic stage during loading. Once the interface failure occurs, load redistribution allows the liner to resist further cracking and sustain higher capacity, demonstrating enhanced bearing performance. Critical factors influencing the failure process were analyzed to inform design optimization, revealing that improving the interface takes precedence, followed by thickness design. Full article

This study examines freeze–thaw deterioration patterns and predicts the service life of wet-sprayed concrete with composite cementitious materials in cold-region tunnels. The microstructure and particle size distribution of four materials (cement, fly ash, silica fume, and mineral powder) were analyzed. Subsequent tests evaluated the rebound rate, mechanical properties, and durability of wet-sprayed concrete with various compositions and proportions of cementitious materials, emphasizing freeze–thaw resistance under cyclic freezing and thawing. A freeze–thaw deterioration equation was developed using damage mechanics theory to predict the service life of early-stage wet-sprayed concrete in tunnels. The results indicate that proportionally combining cementitious materials with different particle sizes and gradations can enhance concrete compactness. Adding mineral admixtures increases concrete viscosity, effectively reducing rebound rates and dust generation during wet spraying. Concrete incorporating binary and ternary mineral admixtures shows reduced early-age strength but significantly enhanced later-age strength. Its frost resistance is also improved to varying degrees. The ternary composite binder fills voids between cement particles and at the interface between paste and aggregate, resulting in a dense microstructure due to a ‘composite superposition effect.’ This significantly enhances the frost resistance of wet-mixed shotcrete, enabling it to withstand up to 200 freeze–thaw cycles, compared to failure after 75 cycles in plain cement concrete. The relative dynamic modulus of elasticity of wet-shotcrete follows a parabolic deterioration trend with increasing freeze–thaw cycles. Except for specimen P5 (R² = 0.89), the correlation coefficients of deterioration models exceed 0.94, supporting their use in durability prediction. Simulation results indicate that, across all regions of China, the service life of wet-shotcrete with ternary admixtures can exceed 100 years, while that of plain cement concrete remains below 41 years. Full article

Addressing the shortcomings of currently available concrete reinforcement techniques, a new method using sprayed Glass Fibre Epoxy Mortar (GFEM) reinforcement is proposed. To investigate the effect of this method on the frost durability of concrete, a total of 156 specimens in four groups were designed, and related freezing and thawing cycle tests were conducted. The apparent morphology, mass loss rate, ultrasonic velocity, freeze–thaw damage, and strength loss rate of each group of specimens after different freeze–thaw cycles were analysed comparatively. The test results show that the concrete specimens reinforced with GFEM have a better mass loss rate after freeze–thaw cycles and ultrasonic wave velocity than the unreinforced concrete specimens. The compressive strength of specimens in group A is 24.04 MPa, and the compressive strengths of specimens in groups B, C, and D are 35.28 MPa, 35.73 MPa, and 36.37 MPa, respectively, which is higher than that of group A by 46.76%, 48.63%, and 51.29%, respectively, and 46.76%, 48.63%, and 51.29% higher than group A, respectively. It can be seen that the concrete specimens reinforced with sprayed Glass Fibre Epoxy Mortar can effectively improve the frost durability of concrete; the reinforcing effect is obvious, and in a certain range of fibre mixing, the larger the better the frost resistance. The integration of GFEM is cost-effective and improves viscosity, and the best glass fibre mix percentage is about 0.8%. A freeze–thaw damage model for GFEM-reinforced concrete was developed using the Weibull distribution theory, and an improved strength attenuation model under freeze–thaw cycles was established. By correlating the strength attenuation model with the freeze–thaw damage model, a damage evolution equation for the reinforced specimens was formulated, allowing for the prediction of freeze–thaw damage based on the number of cycles and the relative compressive strength. Full article

The high water head of some pumped storage power stations will induce the cracking of the concrete lining of their diversion tunnel and the leakage of high-pressure water, which will affect the safety of the tunnel and the surrounding rock. At present, there is no solution to the problem of impermeability of concrete materials after cracking. This paper proposes a composite lining to solve this problem. The composite lining with modified polydimethylsiloxane coating can effectively prevent high-pressure water, but its crack resistance needs to be further studied. Therefore, the tensile mechanical properties, constitutive relationship of modified polydimethylsiloxane impermeable coating, and the crack resistance mechanical properties of modified polydimethylsiloxane impermeable composite lining were studied by laboratory tests and numerical simulations. The results show that the true fracture elongation of the modified polydimethylsiloxane impermeable coating is as high as 118.98%, and its mechanical behavior can be described by a simplified polynomial hyperelastic constitutive model. The in situ stress will affect the crack width of the concrete lining. When the lateral pressure coefficient is less than 1, the crack width decreases with the increase in the lateral pressure coefficient. When the lateral pressure coefficient is greater than 1, the crack width increases with the increase in the lateral pressure coefficient. To prevent the cracking of modified polydimethylsiloxane coating, its spraying thickness needs to increase with the increase in crack width. The ratio of the coating’s thickness to crack width is recommended from 0.162 to 1.930 for internal water pressure from 1 MPa to 10 MPa, respectively. The suggestion provides a reference for designing the impermeable composite lining structure subjected to high internal water pressure. Full article

Cement-based materials used in China’s coastal and salt lake areas in the northwest are exposed to long-term chloride corrosion, which deteriorates the materials and substantially reduces the durability of the structures. This study investigates the chlorine ion erosion resistance in salt spray environments of cement-based materials made with iron ore tailings (IOTs) as an aggregate (namely, IOTCs). The compressive strength, mass loss, and relative dynamic elastic modulus (RDEM) macroscopic performance of IOTC undergoing different chloride diffusion times (0–180 d) were explored in detail. Chloride ion profiles at 0–180 d were analyzed via chemical titration, while X-ray computed tomography (CT) and scanning electron microscopy (SEM) were employed to characterize microstructural evolution. The results demonstrate that IOTC exhibited superior chloride resistance compared to conventional concrete (GC). While both materials showed early strength gain (<60 d) due to hydration and pore-filling effects, IOTC experienced only a 23.9% strength loss after long-term exposure (180 d) significantly less than the 37.2% reduction in GC. Chloride profiling revealed that IOTC had 43.5% lower free chloride ions (C_f) and 32% lower total chloride ions (C_t) at 1 mm depth after 180 d, alongside reduced chloride diffusion coefficients (D_a). The CT analysis revealed that IOTC exhibited a significantly denser and more uniformly distributed pore structure than GC, with a porosity of only 0.67% under chloride-free conditions. SEM confirmed IOTC’s more intact matrix and fewer microcracks. Full article

In order to solve the problems of stress concentration in the roadway peripheral rock and poor support effect in a wide range of high-stress areas under the high-stress environment of MaKeng Iron Mine, this study is based on the theory of loose circle support, combined with the calculation of the anchor suspension theory to determine the reasonable length of pipe slit anchors and other key parameters. Through the two methods of punching and bonding, we examined the destructive effect to determine the thickness of the spray concrete and, finally, put forward the pipe slit anchor mesh spraying support technology program. The numerical model was constructed by using three-dimensional numerical simulation software (FLAC3D 5.0), and the support effect analysis of the support scheme was carried out systematically. The research results show the following: under the high-stress environment dominated by external horizontal tectonic stress, the use of pipe slit anchor net spray support technology can significantly improve the distribution characteristics of the plastic zone, stress field and displacement around the roadway; after the support, the deformation and displacement of the surrounding rock around the empty zone are significantly reduced, effectively preventing the destruction of the surrounding rock under the high-stress environment. The program not only unifies the mine support form and support parameters but also specifies the support construction method and construction quality inspection standard, which provides a scientific technical guarantee for mine shaft support and has an important reference value for the support design and construction of a mine roadway under a similar high-stress environment. Full article

Straw as a building material alternative is in line with sustainable development goals. To make effective use of straw resources such as rice and corn stalks in rural areas, a kind of steel wire mesh-reinforced straw concrete sandwich panel (SCSP) was developed. The SCSP was composed of cold-drawn low-carbon steel-wire mesh (SWM), fine gravel concrete (FGC), and straw. The used type of FGC was shotcrete. A cold-drawn low-carbon SWM was arranged on the upper and lower sides of the SCSP, and a vertical wire tie was arranged between the upper and lower cold-drawn low-carbon SWMs. The FGC was sprayed on the SWM to make the SCSP layer work together. The loading process of the SCSP could be divided into three stages: elastic working state, cracking state, and failure state. The results of the four-point loading test show that the maximum flexural moment of the SCSP can be up to 7.5 kN·m in the elastic range. The ultimate bearing capacity of SCSP reaches 10.9 kN·m, and the maximum crack width can reach 3~4 mm. At the same time, based on the assumption of the flexural section of SCSP, two simplified calculation models of SCSP bearing capacity were established. The average error was 2.99% and 9.41%, respectively, by comparing the experimental values with the two calculated values. The results obtained by using the two models were in good agreement with the experimental results. Full article

To address the challenges of low automation in tunnel wet-spraying jumbos and the heavy reliance on manual expertise for ensuring the spraying quality, this study proposes a novel task planning method for tunnel spraying operations. First, the tunnel surface to be sprayed is aligned with the designed contour using a vehicle navigation method, enabling the estimation of the overbreak and underbreak volumes. These volumes are then utilized to hierarchically plan the spraying tasks (e.g., patching, filling, and surface smoothing). A concrete coating thickness prediction method is developed, incorporating static and dynamic coating accumulation models with key process parameters—spraying flow rate Q, air pressure P, and spraying distance H—as independent variables. Based on the required thickness for each task layer, operational parameters such as the spraying duration t and nozzle movement speed v are optimized. By analyzing the spray gun action combinations and integrating hierarchical task planning with parameter optimization, a Planning Domain Definition Language (PDDL) domain file and problem file are designed to generate the spray gun action sequences and paths via a planner. The experimental results demonstrate that the overbreak volume on the sprayed tunnel surface is reduced to approximately 3 cm after applying the planned sequences. The proposed method autonomously generates the task hierarchies and the corresponding spray gun actions based on the 3D morphology of the tunnel surface, effectively ensuring the spraying quality while significantly reducing the dependence on manual intervention. This approach provides a practical solution for enhancing automation and precision in tunnel spraying operations. Full article

The research presented in this article seeks to identify the possible causes of reinforcement shadows (RS) on the surface of concrete test specimen produced under laboratory conditions. Different hypotheses about RS were selected based on factory practices and simulated in the study. The test specimens were cast horizontally in contact with steel form-facing surfaces coated with a water-soluble release agent. In addition, two scenarios were analysed during specimen production: reinforcing mesh was fixed using plastic spacers or tie wire. The analysis of the reinforcement shadows was based on visual inspection, taking photos, surface moisture content measurements, and colour variation analysis using the Natural Colour System. It was concluded that RS, which are typically characterized by darker lines, can be defined by the percentage of black colour present in the shadowed area compared to the percentage of black colour in the surrounding area. This percentage can be quickly assessed on a factory scale using digital colour readers that provide timely information. The reduced concrete cover thickness from 35 mm to 10 mm revealed light horizontal dark lines on the exposed surface. It was hypothesised that the gap of less than 10 mm between the reinforcing bars and the steel form-facing plate, along with the sieving effect of the fresh concrete, can retard the cement paste hydration process, resulting in unhydrated ferrite phases that contribute to the dark colour of the unhydrated cement. The release agent sprayed on the steel form-facing surface straight through the reinforcing mesh created a RS effect of the reinforcement on the exposed concrete surface. The absence of a release agent under steel rebars decreased the wettability at the interface between the formwork and fresh concrete, resulting in dark lines during the curing process. It is important to avoid such cases when manufacturing precast reinforced concrete elements. Quantitatively assessing RS and proposing a standardized method for calculation and categorization could be a new research direction in the future. Full article

Conventional shotcrete systems face critical limitations in adverse geological environments, including a delayed strength development (<5 MPa at 3 h), excessive rebounds (15–25%), and permeable macropore networks (>50 μm), often resulting in support failure for deeply buried tunnels. To address these challenges, this study systematically investigates the mechanical properties and pore characteristics of a manufactured sand-based sprayed UHPC at different spraying positions under simulated tunnel conditions. Our results demonstrate that the high-pressure air (0.8 MPa) driven spraying process optimizes its pore distribution, reducing large pores (>10 μm) and increasing harmless pores (<100 nm). Furthermore, the sprayed UHPC incorporating manufactured sand derived from tunnel slag not only maintains a 28-day compressive strength of 110.9 MPa but also reduces material costs and enhances sustainability. Field tests validate its low rebound rate (<5%) and rapid strength development (achieving a compressive strength of 30 MPa within 1 day), confirming its adaptability to complex geological conditions such as high-stress zones, thereby providing a novel method for support in complex geological conditions. Full article

Traditional stone masonry walls are structural elements in most historic buildings. To preserve them and improve their ability to withstand extreme events, such as earthquakes, it is necessary to implement effective reinforcement solutions. This paper presents the modeling of traditional Portuguese rubble stone masonry walls, reinforced with external steel mesh, sprayed micro-concrete layers and transverse confinement by steel connectors, which were developed and tested experimentally in uniaxial compression. The modeling is carried out using micro-modeling through a 2D particle model (PM). The process of calibrating the properties of both micro-concrete and concrete is presented, the methodology for generating the numerical models is described and the numerical response is compared with the experimental results. The numerical results show that the PM can adequately reproduce the experimentally observed behavior of this type of reinforcement solution. Full article

In order to explore a model for the deterioration rate law and mechanism of concrete performance in salt lake water or sea water, the mixed sand concrete test of different forms of chloride ion erosion under a dry–wet cycle was simulated in the laboratory. The compressive strength and penetration depth were used to characterize the structural degradation degree of mixed sand concrete. The performance degradation of mixed sand concrete was analyzed through field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetry (TG), and nuclear magnetic resonance (NMR) testing. Experimental investigations have revealed that, at an age of 140 days and under alternating wet–dry conditions, liquid chloride ion erosion results in a 17.47% reduction in the compressive strength of blended sand concrete, accompanied by an erosion depth of 28.077 mm. This erosion progresses from the exterior towards the interior of the material. Conversely, gaseous chloride ion erosion exhibits a bidirectional penetration pattern. When subjected to gaseous chloride ion erosion, the compressive strength of blended sand concrete decreases by 31.36%, with an associated erosion depth of 38.008 mm. This exposure subjects the structure to heightened crystalline pressures, leading to severe deterioration of both the micro-porous structure within the concrete and the dense structure of hydration products. Consequently, the overall extent of structural damage is more pronounced, and the rate of degradation progression is accelerated. Under the action of liquid chloride ion erosion, the degradation of mixed sand concrete structure is caused by dry–wet fatigue, crystallization pressure, chloride salt erosion and calcium ion dissolution. Under the action of spray-born chloride erosion, the degradation of the mixed sand concrete structure is caused by dry–wet fatigue, crystallization pressure, chloride salt erosion, and calcium ion dissolution, among which crystallization degradation plays a major role. In line with the engineering standards for the utilization of vast desert resources in Inner Mongolia and the long-term service of concrete in the Hetao Irrigation District, our approach contributes to the achievement of sustainable development. Full article

Based on the tensile strain hardening characteristics of fiber-reinforced cementitious composites (FRCC), this study experimentally investigated the mechanical properties of reinforced concrete (RC) beams reinforced with FRCC, both with and without precast cracks. The spraying process was applied, and different thicknesses of FRCC reinforcement layers were considered. Additionally, crack identification based on Digital Image Correlation (DIC) technology was employed in the study. The results indicated that as the ratio of the thickness of the FRCC reinforcement layer to the beam height increased, the initial cracking load, yield load, and ultimate load of the RC beams after reinforcement also increased. Moreover, the FRCC layer effectively controlled the development of cracks. When considering the damage to existing RC beams, the application of sprayed FRCC reinforcement improved the ultimate flexural capacity of the beams with precast cracks by over 20%. Specifically, a 30 mm FRCC reinforcement layer restored the flexural capacity of damaged RC beams to more than 85% of their uncracked state. Additionally, the use of DIC technology improved the identification of cracks in images and verified the process of damage and cracking in RC beams. Hence, the utilization of sprayed FRCC as formwork-free reinforcement presents significant value in terms of enhancing durability and mechanical properties. Full article

Wood is the most commonly used material for framing single-family houses in the USA, yet alternative materials like Insulated Concrete Forms (ICFs) offer potential advantages in energy efficiency and thermal performance. This study evaluates ICFs as a viable alternative by analyzing the energy performance and indoor temperature stability of five single-family houses in Oklahoma, USA, monitored over 12 months. The sample included a total of five single-family houses: two wood-framed houses with blown fiberglass insulation, one wood-framed house with spray foam insulation in the attic, and two houses with ICF exterior walls. Results demonstrated that ICF houses consumed up to 41% less electricity and at least 5% less natural gas compared to wood-framed houses, with improved indoor temperature stability. Occupants also saved approximately USD 270 annually on energy costs, highlighting the advantage of ICF’s efficiency. This study provides empirical evidence of the benefits of ICF construction, which previously relied heavily on simulations or anecdotal claims. However, findings are limited by the specific geographic focus of the study. Future research should expand on these findings by incorporating a wider range of climates and housing designs to better understand the broader applicability of an ICF as an alternative to conventional wood-framed construction. Full article