Search Results (136)

Transient thermal strain (TS) is a unique compressive strain that reactive powder concrete (RPC) experiences during temperature rise. RPC has a more rapid TS development than normal concrete (NC) during temperatures of 300 °C~800 °C, and under the same load level, the TS of RPC is 40% to 60% higher than that of NC. However, while TS is known to be significant in RPC, its quantitative influence on the structural fire response and ultimate fire resistance of RPC columns remains insufficiently understood and inadequately modeled, posing a potential risk to fire safety design. In this study, a method for modelling the fire response of RPC columns with due consideration to TS was developed using ABAQUS. The Drucker–Prager model was applied to assess the impact of TS on the fire resistance of RPC columns. The results indicate that ignoring the effect of TS could lead to unsafe fire resistance predictions for RPC columns. The influence of TS on the fire resistance performance of RPC columns increases with the increase in cross-sectional dimensions. When the cross-sectional dimension of RPC columns increases from 305 mm to 500 mm, the influence of TS on the fire resistance of RPC columns increases from 22% to 43%. Under the same load, the influence of TS on the fire resistance of RPC columns is 31.3%, which is greater than that on NC columns. When the hydrocarbon heating curve is used, if the influence of TS is not considered, the fire resistance will be overestimated by 18.2% and 37.7%. Under fire, the existence of TS will lead to a further increase in the compressive stress of the RPC element in the relatively low temperature region, resulting in a greater stress redistribution, and accelerating the RPC column to reach the fire resistance. Therefore, it is crucial to clearly consider TS for the accurate fire resistance prediction and safe fire protection design of RPC columns. Crucially, these findings have direct significance for the fire protection design of actual projects, such as liquefied petroleum stations. Full article

The objective of this study was to evaluate the technical properties and assess the durability of a novel high-performance concrete with aggregates composed entirely of reactive powders derived from chalcedonite—a mineral previously not utilized in HPC technology. Since there is insufficient information on chalcedonite-based concretes in the scientific literature, the presented research aims to address these knowledge gaps. The characterization of the chalcedonite powder involved the determination of specific gravity, particle size distribution, specific surface area, and particle morphology through microscopic analysis. The hardened chalcedonite-based and reference quartz-based high-performance concretes were subjected to a comprehensive suite of tests to determine their physical properties (bulk density, water absorption, and capillary absorption) and mechanical properties (flexural and compressive strength). Durability was further assessed based on compressive strength criteria, including frost resistance and carbonation resistance. To simulate long-term performance and better evaluate the durability of the high-performance concretes, specimens were tested following standard water curing and after additional maturation processes, including thermal treatment, which in the extreme case resulted in a seven-day compressive strength of 176.9 MPa, a value higher by 56.7 MPa (corresponding to an increase of 47.1%) compared to the strength of the identical concrete not subjected to thermal treatment. To explore the potential for architectural applications, particularly in outdoor environments, capillary absorption testing was of particular importance, as it provided insight into the material’s resistance to eventual pigment leaching from the mineral matrix. Full article

Aiming at the lightweight design of a bridge-shed integration structure, this paper presents a three-layered absorbing system in which a part of the sand cushion is replaced by expanded polystyrene (EPS) geofoam and the reinforced concrete (RC) protective slab is arranged above the sand cushion to enhance the composite system’s safety. A three-dimensional Smoothed Particle Hydrodynamics–Finite Element Method (SPH-FEM) coupled numerical model is developed in LS-DYNA (Livermore Software Technology Corporation, Livermore, CA, USA, version R13.1.1), with its validity rigorously verified. The dynamic response of rockfall impacts on the shed slab with composite cushions of various thicknesses is analyzed by varying the thickness of sand and EPS materials. To optimize the cushion design, a specific energy dissipation ratio (SEDR), defined as the energy dissipation rate per unit mass (η/M), is introduced as a key performance metric. Furthermore, the complicated interactional mechanism between the rockfall and the optimum-thickness composite system is rationally interpreted, and the energy dissipation mechanism of the composite cushion is revealed. Using logistic regression, the ultimate stress state of the reactive powder concrete (RPC) slab is methodically analyzed, accounting for the speed and mass of the rockfall. The results are indicative of the fact that the composite cushion not only has less dead weight but also exhibits superior impact resistance compared to the 90 cm sand cushions; the impact resistance performance index SEDR of the three-layered absorbing system reaches 2.5, showing a remarkable 55% enhancement compared to the sand cushion (SEDR = 1.61). Additionally, both the sand cushion and the RC protective slab effectively dissipate most of the impact energy, while the EPS material experiences relatively little internal energy build-up in comparison. This feature overcomes the traditional vulnerability of EPS subjected to impact loads. One of the highlights of the present investigation is the development of an identification model specifically designed to accurately assess the stress state of RPC slabs under various rockfall impact conditions. Full article

The demand for super-tall buildings and long-span bridges has driven concrete development toward higher strength and durability. Therefore, this study investigated the impact of composition of materials (aggregates, admixtures, and steel fibers) on the mechanical performance and economic feasibility of coarse aggregate reactive powder concrete (CA-RPC). The goal is to identify optimal combinations for both performance and cost. Scanning electron microscopy (SEM) and pore structure analysis were used to assess microstructural characteristics. The results demonstrated that replacing quartz sand with yellow sand as the fine aggregate in CA-RPC effectively reduced construction costs without compromising compressive strength. The use of basalt as the coarse aggregate led to higher mechanical strength compared to limestone. Incorporating 20% fly ash reduced the 7-day compressive strength, while the 28-day strength remained unaffected. The addition of 10% silica fume showed no obvious effect on the early strength but significantly improved the 28-day strength and workability of the concrete. Moreover, the incorporation of steel fibers improved the flexural strength and structural integrity of CA-RPC, shifting the failure mode from brittle fracture to a more ductile cracking behavior. SEM observations and pore structure analyses revealed that the admixtures altered the hydration products and pore distribution, thereby affecting the mechanical performance. This study provides valuable insights into the strength development and underlying mechanisms of CA-RPC, offering a theoretical basis for its practical application in bridge deck pavement and tunnels. Full article

To address the engineering issues of difficult quality control, complex construction processes, and long construction periods in cast-in-place protective walls for manually excavated piles, a prefabricated protective wall structure is proposed. This study aims to investigate its mechanical properties and key influencing parameters through experiments. Six groups of prefabricated wall segment specimens with different wall thicknesses (50 mm, 65 mm) and concrete strengths (C50 concrete, reactive powder concrete RPC) were designed, and two-point bending tests were conducted to systematically analyze their failure characteristics, crack development patterns, and strain distribution laws. The test results show that the peak vertical bending displacements at mid-span of the specimens are 11–18 mm (1.83–2.71% of the radius). The 65-mm-thick specimens exhibit 3–10% higher flexural strength than the 50-mm-thick ones, and reactive powder concrete (RPC) specimens of the same thickness show an 8.3% increase in strength compared to C50 concrete specimens. When the load reaches 80% of the ultimate load, abrupt changes in concrete strain occur at the mid-span and loading points, while the strain at the fixed end is only 15–20% of the mid-span strain. The prefabricated protective wall demonstrates superior deformation resistance, with vertical displacements (3–5% of the radius) significantly lower than those of cast-in-place walls. This research clarifies the influence of wall thickness and concrete strength on the mechanical properties of prefabricated protective walls, providing key mechanical parameters to support their engineering applications. Full article

This study investigates the effects of supplementary cementitious materials (SCMs) on the material performance of foamed concrete containing lightweight coarse aggregates, namely hydrophobically modified expanded perlite (EP). The EP aggregates were treated with a sodium methyl silicate solution to impart water-repellent properties prior to being incorporated into the foamed concrete mixtures. Ordinary Portland cement (OPC) was partially replaced with various SCMs, namely, silica fume (SF), mineral powder (MP), and metakaolin (MK) at substitution levels of 3%, 6%, and 9%. Key indicators to evaluate the material performance of foamed concrete included 28-day uniaxial compressive strength, thermal conductivity, mass loss rate under thermal cycling, volumetric water absorption, and shrinkage. The results noted that all three SCMs improved the uniaxial compressive strength of foamed concrete, with MP achieving the greatest improvement, approximately 97% at the 9% replacement level. Thermal conductivity increased slightly with the addition of SF or MP but decreased with MK, highlighting the superior insulation capability of MK. Both SF and MK reduced the mass loss rate under thermal cycling, with SF exhibiting the highest thermal stability. Furthermore, MK was most effective in minimizing water absorption and shrinkage, attributed to its high pozzolanic reactivity and the resulting refinement of the microstructures. Full article

Waste glass powder (WGP) faces challenges in recycling and regeneration, which is used as a partial substitute for concrete components, with its macro-mechanical properties being investigated. This study aims to elucidate the extent to which various variables affect the unconfined compressive strength (UCS) and alkali–silica reactivity (ASR) of waste glass incorporated concrete. Initially, in the experimental procedure, 291 data points for the UCS and 485 data points for the ASR were obtained from laboratory tests. Subsequently, four machine learning models were introduced, including Gradient Boosting Regressor, Random Forest, Hist Gradient Boosting Regressor, and XGBoost. Their performance was analyzed and compared based on evaluation indexes. The findings reveal that Gradient Boosting Regressor accurately models the actual data distribution, generating reliable synthetic data. Partial dependence plots (PDPs) were used to understand the impact of individual features on glass concrete UCS and ASR, and Shapley additive explanation (SHAP) values were used to analyze the predictive output influenced by the contribution of each feature. The feature interaction effects analyzed through PDP indicate that UCS is highest when WGP is 202.5 kg/m³, and ASR is maximized when WGP is 708.75 kg/m³. The SHAP value analysis results reveal that the “alkali” feature exerts the most pronounced influence on the UCS model predictions. Conversely, in the case of the ASR model, the “curing duration” feature emerges as the primary driver of its predictions. Full article

Over 2 million tonnes of ceramic waste are generated annually in South Africa, with the majority disposed of in landfills, contributing to environmental degradation. Meanwhile, researchers are actively seeking sustainable alternatives to Portland cement (PC), which is associated with significant environmental challenges. Ceramic waste powder (CWP) refers to finely milled ceramic waste and powder derived from the polishing and finishing stages of ceramic production. This review examines the potential of CWP as a partial replacement for PC in concrete, focusing on its effects on workability, mechanical durability, and microstructural properties. The findings indicate that moderate replacement levels (up to 20%) enhance the compressive and flexural strengths of concrete. However, these benefits are not consistently reported across all studies. Additionally, CWP improves the microstructural properties of the concrete. This is probably due to the pozzolanic reactions of CWP, which result in a denser concrete matrix and enhanced long-term durability. Notable durability benefits include reduced water absorption, increased resistance to chemical attacks, and improved thermal insulation. However, the performance of concrete with higher CWP replacement levels (above 30%) remains unclear. Some studies have reported strength reductions and increased susceptibility to durability loss at this level. Further studies should focus on clarifying its pozzolanic reactivity, durability in aggressive environments, and optimum replacement percentage. Full article

This study investigates the influence of various cementitious materials on the performance of alkali-activated green ultra-high performance concrete (GUHPC). Alkali-activated GUHPC was prepared by substituting cement, quartz powder, and limestone powder with slag powder and fly ash. The mechanical properties, durability, hydration products, and microstructure were systematically analyzed. The results demonstrate that, with a cement dosage of 264 kg/m³, the alkali-activated GUHPC incorporating 40% slag powder and 28% fly ash as cement replacements exhibited superior mechanical performance, achieving compressive and tensile strengths of 165.3 MPa and 7.7 MPa, respectively, after curing. The GUHPC displayed a dense internal structure with an extremely low porosity of 6.76%, along with superior impermeability and frost resistance compared to conventional UHPC. Slag powder exhibited high pozzolanic reactivity under alkali activation, enabling effective cement replacement. These findings provide valuable insights for the formulation of alkali-activated GUHPC. Full article

To investigate the influence of repeated loading on the bond behavior between steel bars and reactive powder concrete (RPC), this study conducted repeated loading tests on eight beam specimens and one static loading test as a control. The effects of stress levels and the number of repeated loading cycles on the bond behavior between steel bars and RPC were examined. The results indicate that the static failure mode was characterized by steel bar pull-out accompanied by significant plastic deformation, with no propagation of cracks in the RPC after their initiation, demonstrating the excellent crack control capability of RPC. After 10,000 cycles of repeated loading at a high stress level (Z = 0.9), the ultimate bond strength decreased by only 3.68%, indicating the superior fatigue resistance of the steel–RPC interface. Based on the analysis of slip accumulation effects, a constitutive model considering stress levels and the number of repeated loading cycles was established. This model can serve as a basis for the design of steel anchorage in RPC structures subjected to cyclic loading. Full article

It is difficult to obtain efficient flowability of reactive powder concrete (RPC) mix due to a low water/binder ratio. The improvement of material flowability could be achieved by using the latest generation polycarboxylate superplasticizers (SPs), as well as by changing the mixing procedure. This paper presents two different superplasticizers’ effect on a fresh mix and hardened reactive powder concrete properties. Results of systematic experimental studies (including physicochemical and spectroscopic tests) and molecular modelling suggest that superplasticizer chemical structure plays a key role in shaping the properties of the concrete mix. It has been demonstrated that SP containing more carboxylate salt groups -COO⁻ Me⁺ improves fluidity of the RPC mix and causes its better deaeration. In contrast, hardened concrete exhibits lower porosity and consequently greater strength. On the other hand, a change in ingredients mixing from a three-stage to a four-stage procedure increased the mix flowability and the RPC strength. The chemical structure of SP and the mixing procedure had no significant impact on cement hydration progress. Our results could be useful both from the point of view of the basic science of materials and the applied field of planning of cement composites in construction. Full article

This paper the flexural and compressive strengths of the reactive powder concrete (RPC) with steel scoria and quartz sand containing NaCl are investigated. Moreover, the RPC’s mass, the chloride ion permeability and the carbonation depth (D_c) are determined. The mass ratios of steel scoria and the NaCl are 0%~20% and 0%~0.25% by mass of binder materials and the quartz sand respectively. The RPC specimens are exposed to the NaCl erosion environment. The scanning electron microscope-energy dispersive spectrometer (SEM-EDS) and X-ray diffraction (XRD) spectrum are acquired for analyzing the mechanism of RPC’s performance. Results show that the flexural strength, the compressive strengths, the mass and the dynamic modulus of elasticity (RDME) of RPC decrease in the form of cubic function with the mass ratio of NaCl. When the mass ratio of steel scoria is 10%, the mechanical strengths and the RDME are the highest. The RPC’s flexural strength, the compressive strength and the RDME decrease by rates of 4.94%~42.28%, 5.11%~48.65% and 8.72%~226.1% after NaCl erosion. Meanwhile, the corresponding mass loss rate, the chloride ion permeability, the D_c are increased by rates of 1.32%~27.63%. RPC with 10% steel scoria shows the lowest performance degradation. The SEM-EDS results show that the pores and cracks inner RPC and the Cl and Ca elements are increased by the NaCl. The Fe and Ca elements are increased by the added steel scoria. The addition of steel scoria exhibit decreasing effect and the added NaCl shows increasing effect on the Ca (OH)₂ crystals respectively. Full article

Reactive powder concrete (RPC) is widely used in ultra-high-rise buildings, hydropower stations, bridges, and other important infrastructures. To study the dynamic response and damage characteristics of RPC columns and frames considering coupled fire and explosions, an analytical model of RPC columns and frames with coupled fire and explosions was established by using ABAQUS (2021) finite element software. The dynamic response and damage degree of RPC columns under coupled fire and explosions were investigated to reveal the influence laws of parameters such as cross-section size, axial compression ratio, reinforcement rate, and fire duration on the dynamic response of RPC columns at high temperatures. The dynamic response of the frame structure was analyzed when the explosion load was applied to the bottom corner columns, side columns, and top beams, respectively. The results show that the fire severely weakened the blast resistance of RPC columns; the maximum mid-span deformation and residual deformation of RPC columns decreased with the increase in cross-section size and longitudinal bar reinforcement ratio and increased with the increase in fire duration and axial compression ratio. When the explosion load was applied to the corner columns of the bottom floor of the frame, the bottom corner columns were almost completely destroyed, and there was a significant risk of the structure collapsing. Based on the results of the data analysis, a method to enhance the explosion resistance of RC frame structures using RPC materials at high temperatures is proposed. Full article

China has an existing building area of 80 billion square meters, where reinforced concrete structures have a large quantity and a wide surface area. The risk of structures being subjected to blast loading is relatively high. Reactive powder concrete has the specialties of ultra-high toughness, super strength, and a high strength to ponderance ratio. Reinforced concrete (RC) structures strengthened by RPC are called RPC-RC structures, which can easily elevate the explosive load resistance of building structures while also strengthening the building. It is a significant method used in avoiding the collapse of structures under explosive loads. The dynamic reaction and damage evaluation approaches of RPC-RC columns under explosive load have not been deeply studied. For addressing this issue, numerical simulation of RPC strengthened RC columns under explosive load was carried out by LS-DYNA (R10), and the correctness of the numerical simulation was verified by comparing it with relevant experimental results. In this paper, a finite element model of an RPC-RC column was established, and the main factors affecting the anti-explosion performance of an RPC-RC column were studied. The influence of the RPC reinforcement layer parameters (RPC thickness, RPC strength, longitudinal reinforcement ratio, and stirrup ratio) on the dynamic reaction and damage degree of RPC-RC columns was examined. The consequences indicated that the failure mode of the columns after RPC reinforcement can alter from bending shear damage to bending damage. As the thickness and strength of the RPC increases, the longitudinal reinforcement ratio increases, the stirrup ratio increases, and the maximum horizontal deformation of the center point of the RPC reinforced RC columns decreases. For RPC-RC columns with a height of 3–4 m and a width of 300–400 mm under blast loading, columns with an axial compression ratio greater than 0.3 will collapse, while columns with an axial compression ratio less than 0.3 are less likely to collapse. In the light of the calculation outcomes, a formula for reckoning the damage index of RPC-RC columns was proposed, taking into account factors such as proportional distance, axial compression ratio, RPC thickness, longitudinal reinforcement ratio, and stirrup ratio. Full article

During shield tunnel construction, waste mud is a significant source of urban construction waste. However, the disposal of waste mud has always been a challenge in engineering. Addressing the challenge of harmlessly disposing of, or repurposing, mud cakes formed after pressure filtration of shield mud remains a pressing issue for many cities. To address the challenge of shield mud disposal and explore the utilization technology of this resource, this study focuses on shield mud obtained from the Shenzhen subway tunnel. Calcined shield mud powder (CSMP) was prepared by activating its potential pozzolanic properties through a calcination process. Compressive strength tests revealed that, while CSMP exhibits some pozzolanic activity, its performance is limited. When 30% of the cement is replaced, the mortar’s maximum strength activity index (SAI) is only 82.6%, which makes it unsuitable as a supplementary cementitious material for concrete applications. At the same time, CSMP was also evaluated as a partial replacement for fly ash in the formulation of synchronous grouting materials, with performance metrics including fluidity, bleeding rate, hardening rate, setting time, and compressive strength systematically tested. The experimental results showed that, while CSMP reduces the fluidity of grouting, it significantly improves volumetric stability, shortens setting time, and enhances mechanical performance. Compared to the fly ash used in the study, CSMP exhibited better pozzolanic reactivity, promoting the formation of C-S-H and C-A-S-H phases, optimizing the pore structure, and increasing the density and overall performance of the grouting material. When the substitution rate is below 60%, the performance of grouting meets standard requirements, indicating the strong feasibility of utilizing CSMP to replace fly ash in synchronous grouting materials. Full article