https://jcr.guilan.ac.ir/ Concrete Research en daily 1 Sat, 21 Mar 2026 00:00:00 +0330 Sat, 21 Mar 2026 00:00:00 +0330 https://jcr.guilan.ac.ir/article_9763.html Concrete is a brittle material with low strength and strain capacity. In recent decades, fibers have been used to enhance concrete and overcome these limitations. In this study, macro twisted, and PP fibers were used in a hybrid form to produce traffic concrete overlays. In 21 different mixtures, the volumetric ratio of macro fibers ranged from 0 to 0.165%, and polypropylene (PP) fibers ranged from 0 to 0.604%. The mixtures were tested for compressive strength, tensile strength, flexural strength, impact resistance, and shrinkage. The results showed that adding fibers had little effect on compressive strength, but it significantly improved tensile and flexural strength. Additionally, the impact resistance of fiber-reinforced concrete increased by up to 5 times. Finally, a software with python was developed in order to optimization the valume of fibers and thickness of the slab. As a result,, the optimal mixture contained 0.110% macro fibers and 0.165% polypropylene fibers was recommended. https://jcr.guilan.ac.ir/article_9764.html In this study, the effect of replacing powdered materials with recycled glass, rubber, and ceramic materials on the compressive, tensile, and flexural strength performance of reactive powdered concrete was investigated. For this purpose, the effect of replacing 10%, 20%, and 40% of powdered materials with recycled materials was investigated through laboratory tests. The sample used for the compressive test was a cube with dimensions of 10 cm, the tensile test was a cylinder with a diameter of 10 cm and a height of 20 cm, and the flexural test was a sample with dimensions of 50 × 10 × 10 cm3. The results showed that replacing recycled materials will reduce the compressive strength of reactive powdered concrete. So that by replacing 40% of powdered materials with rubber, the compressive strength will decrease by 49%. Replacing recycled rubber materials up to 20% with powdered materials will cause a slight increase in tensile strength. Replacing recycled glass with powdered materials has the best effect on the flexural strength of reactive powdered concrete, such that by replacing 10% of powdered materials with recycled glass, the flexural strength will increase by 8%. https://jcr.guilan.ac.ir/article_9766.html This study aims to develop an Artificial Neural Network (ANN) model to predict the axial capacity of Concrete-Filled Steel Tubular (CFST) columns under axial loading. A comprehensive database comprising 95 experimental specimens from reliable sources was compiled to capture a wide range of geometric and material characteristics. A multilayer feedforward ANN with optimized architecture was designed and trained to model the nonlinear relationships between input parameters and the axial capacity of CFST columns. The model demonstrated high accuracy, with correlation coefficients of 0.9968, 0.9663, and 0.9612 for the training, validation, and test datasets, respectively. Evaluation using an independent dataset further confirmed the model’s reliability, yielding a correlation coefficient of 0.9994. Sensitivity analysis based on Garson’s method indicated that the diameter-to-thickness ratio had the greatest influence (31.39%), while the column slenderness ratio had the least (13.99%). Additionally, a practical computational framework was developed based on the trained ANN weights and biases, allowing direct calculation of axial capacity without rerunning the network. Finally, goodness-of-fit tests suggested that the Generalized Extreme Value distribution provides the best match to the experimental data, serving as an optimal probability distribution function for the axial capacity of CFST columns. The proposed ANN model and computational framework provide an efficient, accurate, and generalizable tool for predicting the axial performance of CFST columns in structural design and assessment. https://jcr.guilan.ac.ir/article_9767.html Geopolymer concrete, as a sustainable alternative to Portland cement, is produced through the alkaline activation of pozzolanic materials. This type of concrete offers several environmental advantages, notably the reduction of CO₂ emissions. However, one of its main drawbacks is its relatively low flexural strength. The incorporation of fibers can enhance its ductility and reduce brittleness by bridging cracks and increasing deformation capacity.In this study, six geopolymer concrete mix designs were prepared using 8, 10, and 12 molar sodium hydroxide solutions for pozzolan activation. To improve mechanical properties, recycled tire cord fibers were incorporated into the mixes. The specimens were cured under three different conditions: ambient temperature, 60°C, and 100°C. Compressive strength, flexural strength, fracture energy, and elastic modulus were measured for each case.The results showed that increasing the concentration of the sodium hydroxide solution led to a 7 to 32% reduction in compressive strength, flexural strength, and modulus of elasticity, while the 8-molar solution exhibited the best performance. Using 1% recycled tire cord fibers increased the compressive strength and modulus of elasticity by 9 to 50% compared to the 2% dosage. In contrast, specimens containing 2% fibers improved the flexural strength and fracture energy by 2 to 6%, indicating enhanced toughness. Curing at temperatures of 60 and 100°C accelerated strength development, achieving 88 to 95% of the ultimate strength within 72 hours. The obtained results indicate that geopolymer concrete has the potential to replace conventional concrete, and recycled tire cord fibers improve its performance. https://jcr.guilan.ac.ir/article_9768.html In recent decades, the adverse environmental impacts associated with Ordinary Portland Cement (OPC) production have encouraged researchers to investigate sustainable and environmentally friendly alternatives such as geopolymer materials. One of the main challenges in the application of geopolymer mortars is the evaluation of their performance in aggressive environments, particularly acidic conditions. In this study, the effect of incorporating microsilica at weight replacement levels of 5%, 10%, 15%, and 20% as a partial substitute for metakaolin in geopolymer mortar was investigated. Sodium hydroxide was employed as the alkaline activator at two molar concentrations of 6 M and 12 M, and all specimens were subjected to an accelerated curing regime. To assess durability, the specimens were immersed in a sulfuric acid solution with a pH of 1 for 28 days after the initial curing period. The compressive strength test results indicated that increasing the microsilica replacement level and the sodium hydroxide concentration effectively enhanced the 28-day compressive strength. Replacing 20% of the binder with microsilica at a molarity of 12 M increased the compressive strength by more than 55% and the flexural strength by more than 37% compared with the sample without microsilica. Furthermore, the results demonstrated that the incorporation of microsilica significantly improves the durability of geopolymer mortars and minimizes the reduction in compressive strength caused by acidic exposure. These findings highlight the potential application of geopolymer mortars in aggressive environments. https://jcr.guilan.ac.ir/article_9720.html Due to the high energy consumption and carbon emissions associated with cement production, finding alternative mixtures with mechanical performance comparable or superior to that of cement under harsh environmental conditions such as freeze-thaw cycles has become a necessity. This study investigates the mechanical performance of mixtures containing industrial wastes, including lime kiln dust, silica fume, and waste carpet fibers, in comparison with a cement sample under freeze-thaw cycle conditions. The main objective is to achieve a stable and durable mixture with suitable replaceability for cement in geotechnical applications in cold regions. For this purpose, the effects of lime kiln dust (up to 10%), silica fume (up to 100% as a replacement for lime kiln dust), and carpet fibers (up to 2%), along with cement-containing mixtures (up to 10% cement), were evaluated. The results indicated that the optimal mixture, consisting of 5% lime kiln dust, 50% silica fume, and 1% carpet fibers, achieved a compressive strength exceeding 7000 kPa and a tensile strength of 600 kPa, demonstrating significantly superior performance compared to the reference cement sample. After 8 freeze-thaw cycles, this mixture retained over 97% of its initial strength, indicating its superior resistance compared to the cement sample under successive freeze-thaw conditions. Carpet fibers, by providing bridging across microcracks, significantly enhanced the tensile strength of this mixture. Overall, the introduced optimal mixture exhibits considerable superiority in terms of mechanical performance and durability compared to the cement sample and can be considered an environmentally friendly and efficient alternative. https://jcr.guilan.ac.ir/article_9719.html Abstract: Carbon nanotubes, owing to their high electrical conductivity, large aspect ratio, and excellent mechanical properties, are among the most important additives used in self-sensing concrete. However, the strong tendency of these nanomaterials to aggregate and form clusters due to van der Waals attractive forces is one of the major obstacles to achieving desirable electri-cal and piezoresistive performance in cementitious composites containing carbon nanotubes. The use of surfactants, as one of the most common dispersion methods, plays an important role in improving the distribution of carbon nanotubes and enhancing their efficiency in cementitious environments. In this study, the experimental behavior of self-sensing cementitious composites containing carbon nanotubes was investigated. Subsequently, four commonly used surfactants, namely sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), carboxyme-thyl cellulose (CMC), and cetyltrimethylammonium bromide (CTAB), were compared from mo-lecular and mechanistic perspectives. For this purpose, molecular models of carbon nanotubes and surfactants were developed, and their interactions were analyzed using molecular dynamics simulation. Interaction energy, molecular arrangement on the carbon nanotube surface, and the stability of the formed structures were considered as evaluation criteria. The results showed that, under the investigated conditions, CMC exhibited a greater capability for stabilizing carbon nanotubes due to its more favorable arrangement around the carbon nanotube and more effective contact with the CNT surface. However, the performance of surfactants in real cementitious en-vironments depends on a range of factors, including compatibility with the cement matrix, air-entraining effects, compressive strength, density, electrical response, and long-term stability. https://jcr.guilan.ac.ir/article_9765.html Nowadays, heavyweight concrete is widely used in structures such as buildings, bridges, power plants, and medical facilities. The aim of this study is to evaluate the strength of self-compacting heavyweight concrete using non-destructive tests and to investigate the properties of fresh concrete. In this research, the replacement ratio of heavyweight magnetite aggregate (0, 50, and 100%), with a maximum size of 15 mm, was considered as the main variable at different concrete ages (3, 7, 28, and 90 days). Additionally, silica fume was used at 6% by weight of cement as a dual-purpose material (filler and reactive), and limestone powder was employed at 25% replacement of sand as filler. In total, six mix designs were prepared, including three without silica fume and three with silica fume, and all specimens were cured in a moist environment. The results showed that the use of silica fume improved the filler effect and increased the compressive strength of both normal and heavyweight self-compacting concrete by about 8%. The 50% magnetite aggregate replacement demonstrated the best performance, increasing the 90-day compressive strength by about 10 MPa compared to the control sample, whereas 100% replacement only resulted in an increase of about 5 MPa. Moreover, the ultrasonic pulse velocity increased with concrete age; at 90 days, replacing 50% of the natural aggregate with heavyweight aggregate resulted in an increase of about 1.7% compared to the natural aggregate. In addition, the incorporation of silica fume improved the pulse velocity by 2–3% in all mixtures.