Recently, polymer concrete (PC) has been widely used in many civil engineering applications. PC shows superiority in major physical, mechanical, and fracture properties comparing to ordinary Portland cement concrete. Despite many suitable characteristics of thermosetting resins related to processing, the thermal resistance of polymer concrete composite is relatively low. This study aims to investigate the effect of incorporating short fibers on mechanical and fracture properties of PC under different ranges of high temperatures. Short carbon and polypropylene fibers were added randomly at a rate of 1 and 2% by the total weight of the PC composite. The exposure temperatures cycles were ranged between 23 to 250 °C. Various tests were conducted including flexure strength, elastic modulus, toughness, tensile crack opening, density, and porosity to evaluate the effect of addition of short fibers on fracture properties of PC. The results show that the inclusion of short fiber lead to an increase in the load carrying capacity of PC by an average of 24% and limits the crack propagation. On the other hand, the enhancement of fracture properties of based PC containing short fibers is vanished at high temperature (250 °C), but still more efficient than ordinary cement concrete. This work could lead to broader applications of polymer concrete exposed to high temperatures.

Although ultra-high-performance concrete (UHPC) presents superior mechanical properties and durability compared to conventional concrete; its spalling resistance to elevated temperatures is much lower compared to conventional concrete due to the high compactness and absence of capillary pores. This paper investigated the influence of lightweight aggregate (LWA) on the strength properties and microstructure of UHPC to enhance its resistance to elevated temperatures. UHPC specimens prepared with LWA as a partial replacement of silica sand were produced. The study evaluated the compressive and flexural strengths, failure mode, mass loss, and microstructure of the specimens, using SEM. The results showed that the compressive strength of the UHPC specimen was reduced with increasing the content of LWA at ambient temperature, but the compressive strength of the UHPC specimens prepared with LWA improved when exposed to elevated temperatures. The replacement of 10% of the silica sand with LWA led to an increase in the compressive strength from 100 MPa to 110 MPa after exposure to 200 °C; however, the flexural strength decreased from 23.6 MPa to 18.3 MPa. On the contrary, the flexural strength of UHPC increased with the inclusion of LWA at an ambient temperature but reduced with high-temperature exposure. The failure mode of UHPC was not significantly affected by the variation in LWA content and temperature. In addition, the SEM result confirms that LWA is an effective internal curing material for enhancing the microstructure and compressive strength of UHPC

Date palm fiber (DPF) has been reported to have many advantages when used in concrete, however, its major disadvantage is that it causes a reduction in compressive strength. In this research, powdered activated carbon (PAC) was added to cement in the DPF-reinforced concrete (DPFRC) to lessen the loss in strength. PAC has not been properly utilized as an additive in fiber reinforced concrete even though it has been reported to enhance the properties of cementitious composites. Response surface methodology (RSM) has also been utilized for experimental design, model development, results analysis, and optimization. The variables were DPF and PAC as additions each at proportions of 0%, 1%, 2%, and 3% by weight of cement. Slump, fresh density, mechanical strengths, and water absorption were the responses that were considered. From the results, both DPF and PAC decreased the workability of the concrete. DPF addition improved the splitting tensile and flexural strengths and reduced the compressive strength, and up to 2 wt% PAC addition enhanced the concrete’s strength and lowered the water absorption. The proposed models using RSM were extremely significant and have excellent predictive power for the concrete’s aforementioned properties. Each of the models was further validated experimentally and was found to have an average error of less than 5.5%. According to the results of the optimization, the optimal mix of 0.93 wt% DPF and 0.37 wt% PAC as cement additives resulted in the best properties of the DPFRC in terms of workability, strength, and water absorption. The optimization’s outcome received a 91% desirability rating. The addition of 1% PAC increased the 28-day compressive strength of the DPFRC containing 0%, 1% and 2% DPF by 9.67%, 11.13% and 5.5% respectively. Similarly, 1% PAC addition enhanced the 28-day split tensile strength of the DPFRC containing 0%, 1% and 2% by 8.54%, 11.08% and 19.3% respectively. Likewise, the 28-day flexural strength of DPFRC containing 0%, 1%, 2% and 3% improved by 8.3%, 11.15%, 18.7% and 6.73% respectively with the addition of 1% PAC. Lastly, 1% PAC addition led to a reduction in the water absorption of DPFRC containing 0% and 1% DPF by 17.93% and 12.2% respectively.

The use of corrugated webs in steel beams has become one of the most practical ways to increase the efficiency of beams in resisting loads, natural frequencies, and their resulting displacements. Such a practice has the benefit of achieving the same efficiency as beams with a flat web with a greater thickness. Consequently, the effect of the types of corrugated webs on the flexure mode shapes and natural frequencies in the steel beams has been investigated by analyzing 23 beams with flat and corrugated webs using the finite element (FE) numerical analysis technique. Hence, two flat web steel beams with and without stiffeners were experimentally tested and compared to FE numerical modeling results. Moreover, three types (trapezoidal, rectangular, triangular) of corrugated webs were tested and studied in addition to other parameters such as thickness, width, length, and angle. The investigation results show that FE numerical analysis is very highly accurate in predicting the natural frequencies and flexure mode shape changes of beams with corrugated webs. Accordingly, a saving of at least 33% in thickness could be realized as compared to the flat type. The triangular corrugated web is more efficient in the 1st mode shape, while rectangular is better for the other modes. The effectiveness of the angle for the triangular type in resisting mode shape and frequencies was clearly noticed, and decreases of 0.60 and 0.78, respectively, were recorded. It is also perceived that the effect of thickness and angle is linear for specified cases.

Date palm fiber (DPF) is one of the abundant solid waste materials in the agriculture sector in Saudi Arabia, and it is gaining great attraction due to its advantages compared to synthetic and other natural fibers. For proper utilization of DPF in cementitious composites, its performance under high temperatures needs to be understood. This is because DPF is a cellulose-based agricultural fiber material and is expected to degrade when subjected to high temperatures. This will cause a significant loss in strength and structural integrity of the composites. The use of Pozzolanic materials has been reported to reduce the loss in mechanical properties of cementitious composites under high temperatures. With powdered activated carbon (PAC) being a low-cost material compared to other Pozzolanic materials, this study utilized PAC as an additive to the DPF-reinforced concrete to mitigate its loss in mechanical strength when exposed to elevated temperature. The experiment was designed using response surface methodology (RSM), which was used to construct mathematical models for estimating the strengths of the concrete exposed to high temperatures. The DPF was added at proportions of 1%, 2%, and 3% by weight of cement. Similarly, the PAC was added at 1%, 2%, and 3% by weight of cement to the concrete. The concrete was subjected to elevated temperatures of 300 °C, 600 °C, and 900 °C for a 2 h exposure period. The degradation of the concrete in terms of mass loss and the compressive strength of the concrete after heating were measured. DPF in the concrete led to an escalation in weight loss and reduction in strength, which was more pronounced at a temperature of 600 °C and above. The addition of PAC resulted in an enhancement in the strengths of the concrete containing up to 2% DPF at 300 °C, while at 600 °C the improvement was minimal. The models developed for predicting the mass loss and strengths of the DPF-reinforced concrete under high temperatures were statistically significant with a high correlation degree. Based on the optimization results, DPF-reinforced concrete produced with 1% DPF, and 2.27% PAC as additives and subjected to a temperature of 300 °C for 2 h yielded the lowest mass loss of 2.05%, highest residual compressive strength and relative strength of 45.85 MPa and 106.7% respectively.