In this research, the effect of the presence of MWCNTs treated by 0.01 and 0.02 weight percentages carboxylic group were studied. The Concrete nanocompsite samples were prepared by uniform distribution of nanotubes in cement/sand in water. The effects of CNTs on mechanical behavior were studied by compression and flexural strength analysis of Concrete nanocomposite and their Microstructures investigated by SEM analysis. In presence of CNTs, the compression and the flexural strength of Concrete composites increased more than 30% and 13%, respectively. Also, CNTs lead to improvement of Microstructure porosity of Concrete composite and therefore more solid and more compressed Concrete composite will be created. The treated CNTs in Concrete composite will generate more contact surface to transferring of forces. As a result, these lead to better CNT’s surface bonding with Concrete matrix to prevent it from growth of defects.

Soldering plays a crucial role in the electronics industry, driving the need for constant improvements in physical and mechanical properties and the management of intermetallic compound formation. Research in composite materials aims to achieve a uniform distribution of reinforcing particles within solder matrix to enhance their performance. This study investigates the integration of cobalt microparticles into SAC0307 lead-free soft solder alloy using the accumulative roll bonding (ARB) method. Microstructural analysis confirmed a homogeneous dispersion of cobalt particles within the solder after three ARB passes. Moreover, increasing cobalt content led to a reduction in the size of Cu6Sn5 intermetallic compounds, from 9 µm to 5 µm with 1% cobalt by weight. Examination of β-Sn grain morphology revealed the impact of cobalt particles on recovery and recrystallization kinetics in the solder. Mechanical testing indicated a 20% decrease in interlayer strength within composite solder sheets. Tensile tests showed a 28% increase in strength and a 31% decrease in elongation for composite solder alloy containing 1% cobalt. Differential scanning calorimetry (DSC) results revealed minimal change in the melting temperature of composite solder foil.

Heat, both in transient and steady state, changes the physical and chemical properties of Concrete. In addition, the use of slag with Portland cement is very effective on development of Concrete Microstructure. The main products of hydration process are cement paste and slag, which plays important role in increasing Concrete strength, C-S-H and C-A-Fe-H Microstructures. Based on this, this paper has focused on the Concrete containing varying degrees of steel slag in order to get a deeper perception of the changing behavior of C-S-H and C-A-Fe-H due to being exposed to high temperature. In this regard, 150 cubic samples of Concrete with zero, 5%, 10%, 15% and 20% replacement of steel slag to Portland cement were treated for 28 days in a moisture bath. Then, all samples were exposed for 1 hour to 25 to 800 º, C. The percentage of weight change, compressive strength and cracking behavior of samples were investigated. Furthermore, in order to evaluate the microstructural behavior of test samples in different temperatures, SEM photos and EDS were used. Based on the results, the behavior of Concrete samples depends on the variations of C-S-H and C-A-Fe-H Microstructures under high temperature. The compressive strength of samples containing 5 to 15% steel slag increased as compared to conventional Concrete sample. Based on SEM photos, the reason for this increase is higher density of C-S-H and C-AFe-H Microstructures and FeO(OH).

One of the important issues in the production of Concrete is environmental variability that affects the Concrete and elements constructed from this material. Due to the importance of different characteristics of Concrete in short- and long-term conditions, this article aims to investigate the influence of initial temperature conditions of self-compacting Concrete on its long-term characteristics and determine the initial optimal temperature of Concrete. For these purposes, several experiments under three temperature conditions of 5, 20, and 40 degree-of-Celsius were conducted to evaluate the rheology and mechanical properties of fresh Concrete in the range of 7 and 28 days. In these experiments, alternative mineral admixtures of cement such as micro-silica, fly ash, and zeolite were used to build the Concrete specimens. Results demonstrate that the mechanical properties of the specimens increase with increasing initial temperature in the short term, while such properties significantly decrease in the long term compared to the specimens constructed under lower initial temperature. Moreover, the fluidity of self-compacting Concrete increases with increasing initial temperature.

Today, the construction of highly critical structures (such as military and nuclear structures, hospitals and infrastructures), with high resistance to impact loads and high temperatures, is of particular importance in the field of passive defense. In this regard, the production of high-strength and nature-friendly Concrete as the main material used in these types of structures plays a significant role. In this paper, the laboratory properties of the slag geopolymer Concrete containing 0 to 8% nanosilica and 1 to 2% polyalphin fibers have been investigated. The Concrete samples made at 90 days of curing age at 25 and 500 °C Celsius underwent weightlifting, weight loss, scanning electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, and X-ray fluorescence (XRF) at 25 °C. At the age of seven days, the processing was performed on the Concrete samples. The results indicate the weakening of the Microstructure of Concrete exposed to high temperatures. Also, the improvement of test results in the geopolymer Concrete compared to ordinary Concrete is evident. The best and worst performance in the weight loss test of the samples belonged to the geopolymer Concrete containing 8% nanosilica and the geopolymer Concrete containing 8% nanosilica and 2% fibers, by 0. 061% and 0. 12% weight loss of the sample, respectively. The best performance in the energy absorption of falling weight at 25 and 500 degrees Celsius belongs to the geopolymer Concrete (containing 8% nanosilica and 2% fiber) at 2928. 25 and 773. 44 joules, respectively. The highest and lowest energy loss of Concrete samples at 500 °C compared to 25 °C belong to the ordinary Concrete and the geopolymer Concrete (containing 8% nanosilica) by 83. 33% and 53. 33%, respectively.

One of the common ways to increase the life of Concrete is the use of pozzolans, some pozzolans that have higher reactivity than ordinary cement lead to greater resistance and less permeability of Concrete by reducing Concrete pores. Structures made with ordinary Portland Concrete generally do not have proper performance in harsh environmental conditions and destructive aggressive factors. Sulfate attack is the process of Concrete destruction due to the expansion caused by sulfate reactions inside the Concrete, and in the long term, it causes a decrease in cohesion, occurrence of cracks and collapse in the Concrete structure, one of the effects of which is the reduction of Concrete strength. The addition of metakaolin reduces the porosity in Concrete, as a result, Concretes containing metakaolin have lower permeability compared to normal Concrete. In this research, calcined clay was used as pozzolan, first the soil was heated to a temperature of 700 degrees Celsius for 3 hours so that the calcination process takes place, then calcined clay along with a percentage of limestone powder and microsilica was replaced by cement. The purpose of this combination for cement materials is to achieve a mixture design that the Concretes made by it have better resistance than normal Concretes against aggressive and corrosive environmental conditions. In this study, ettringite crystals were formed on the samples processed in sodium sulfate solution, which were less in the pozzolanic samples than in the control sample. At early ages, the capillary absorption coefficient for samples containing calcined clay is higher than the control samples, but this difference is greatly reduced as the samples age and the pozzolanic reactions become more complete. The electrical resistance values of the samples also increased with the passage of time and the increase in pozzolan replacement percentage. Also, in all the experiments, the addition of microsilica fills the empty spaces in the Concrete, because the microsilica particles, being smaller than the pozzolan particles of the clay used and the faster reactivity of microsilica produces more silicate gel in a shorter period of time than clay pozzolan and makes the Concrete denser. In this research, 10 mixed designs were used in 2 ratios of water to cement materials: 0.35 and 0.4. In each proportion of clay in percentages of 10 and 20%, limestone powder in percentages of 30 and 20%, respectively, and microsilica along with the combination of soil and lime in 7% by weight as powder materials were replaced by cement. In order to check the properties of the prepared soil, XRD test was performed to ensure the amorphousness of the soil particles and the presence of pozzolanic compounds on it. Also, to check and analyze the durability of Concrete, sulfate resistance, capillary absorption and electrical resistance tests were used on 10 cm cube samples at the age of 28 and 90 days. In this research, designs containing 20% calcined clay, 20% lime, and 7% microsilica have the best performance in pozzolanic designs and are introduced as optimal pozzolanic designs in the conducted experiments.

Industrial activities, particularly in petrochemical and refinery sectors, have introduced a wide range of organic pollutants into the environment, leading to the pollution of aggregate materials with crude oil or petroleum products. This study investigates the influence of aggregate materials contaminated with crude oil and diesel on the cement hydration process and Concrete properties. Around 90 Concrete samples with polluted aggregates were evaluated over a 6-month period. Compressive strength tests and water absorption percentage tests were conducted at different ages. Microstructural analysis through SEM, structural analysis via EDX, and XRD analysis for hydration product characterization were performed. Results showed a significant reduction in compressive strength (47% and 31%) for samples contaminated with crude oil and diesel, respectively, compared to the control. Water absorption and permeability increased in polluted samples. SEM, and XRD, results indicated increased ettringite production, decreased nanostructure C-S-H, reduced strength and durability, and increased water absorption and permeability in the Concrete. This study highlights the detrimental effects of organic contaminants on Concrete properties, emphasizing the need for pollution management in aggregate materials for sustainable construction practices.

Ultra-high performance Concrete (UHPC) is a new type of composite materials that can develop a compressive strength up to 200   MPa and high tensile strength around 10 MPa, given the low water-to-binder ratio (W/B). The fracture energy of UHPC can vary from 8560 to 40, 000  J/m2, which is approximately 220 times greater than that of conventional mortar. Due to its superior properties, Ultra-high performance Concrete has received great attention among researchers recently. Very high compressive strength leads to a significant weight loss of the structure and makes it possible to build slender structural elements. In this paper, the ultra-high performance fiber reinforced Concrete specimens exposed to two different curing regimes, a 23° C limewater tank, and a 70° C hot-water tank. Then, the compressive and flexural strength and the electrical behavior of specimens were evaluated. Mechanical strength at the age of 28 days and six months were measured, in order to in conjunction with durability-related properties offer an overall view of UHPFRC characteristics. Results showed that the PVA fiber affected the mechanical strengths by preventing the propagation of cracks and by increasing the total porosity of the matrix. Moreover, its influence on resistivity was highly dependent on the concentration of silica fume particles.