Papers by Keyword: Elevated Temperature

Abstract: The article addresses the issue of determining the dependence between the tensile strength of GFRP (Glass Fiber Reinforced Polymer) reinforcement and temperature. Figuring out this dependence is crucial for designing reinforced concrete structures exposed to fire. The newly published generation of standards does not specify any material characteristics of FRP reinforcement at elevated temperatures. The design equations are derived only for steel reinforcement, although this standard allows for the use of FRP reinforcement in the design of concrete structures. For this reason, and based on the available and published experimental data, a robust database of results expressing the decrease in GFRP reinforcement tensile strength as a function of temperature was created and supplemented by the results of our own tests. The characteristic value of the tensile strength was determined as 5% quantile according to the requirements of current a new standard by using two methods: data binning and quantile regression. The resulting (characteristic) dependence of the decreasing tensile strength of GFRP reinforcement on temperature shows zero strength at 550 °C and considers the effect of polymer matrix degradation on the behavior of the reinforcement. The determined curve can be used as a basis for the design of GFRP reinforcement in structures exposed to fire in accordance with EN standards.

Abstract: This research investigated the mechanical properties, impact resistance, and behavior under elevated temperatures of Fiber Rubberized High-Strength Concrete (FRHSC), which incorporates Waste Steel Fiber (WSF) and Crumbed Rubber (CR) obtained from waste tires. The study involved five different concrete mixtures to explore the impact of WSF and CR. WSF was consistently mixed in a ratio of 0.3% by volume of the concrete. CR was used to partially replace the fine aggregate in proportions of 10%, 20%, 30%, and 40% by volume. The study examined various characteristics of both the fresh and hardened FRHSC, including slump, unit weight, compressive, tensile, and flexural strengths, as well as its impact resistance. The effects of elevated temperatures at ambient, 200 °C, 400 °C, and 600 °C for a period of 2 hours were also analyzed, focusing on the failure shape, and residual compressive strength. Findings indicated that as the quantity of rubber in the concrete samples increased, there was a noted gradual decline in their mechanical properties. Concurrently, this increase in rubber content contributed to an enhancement in the ductility of the samples. The energy absorption by the rubberized specimens was found to be consistent, regardless of the variation in rubber content due to the presence of WSF. The residual compressive strengths of FRHSC subjected to elevated temperatures improved with the addition of CR. The presence of CR led to an increase in the concrete's porosity, and exposure to high temperatures resulted in more cracks due to CR evaporation and the replacement of air voids, causing a notable reduction in compressive strengths. Keywords Fiber reinforced Concrete; Crumb rubber; waste steel fiber; waste tires, Rubberized concrete; Impact energy; Mechanical properties; Elevated temperature.

Abstract: Chitosan/clay materials derived from periwinkle shells and clay soil at a 50:50 ratio were prepared as adsorbents, characterized, and used for the adsorption of CO₂ from flue gas at elevated temperatures (500°C - 5000°C) in a fixed bed column (1.5 m in length and 0.02 m in internal diameter). The flue gas, with a composition of Methane (0.003), Ethane (0.002), Hydrogen (0.05), CO2 (0.15), Water Vapor (0.02), and Nitrogen (0.76), at a pressure of 49 KPa, a temperature of 5000°C, and a flow rate of 75 L/min from the exhaust tank, entered the fixed bed column for the adsorption process, where the adsorbent had already been placed. Fourier Transform Infrared spectroscopy revealed the presence of halogen, alcohol, nitro, and amine compounds in the nanoparticles, indicating a strong affinity for CO₂ particles in the flue gas. Additional analysis showed the presence of elements (Ca, Si, Al, and Sr) in significant compositions (0.470, 0.202, 0.186, and 0.092, respectively), suggesting that the adsorbent was resistant to high temperatures. X-ray diffraction analysis of the adsorbent identified Ca(OH)₂, CaCO₃, and TiO₂ with compositions of 0.78, 0.19, and 0.026, respectively, further confirming the strong affinity of the adsorbent for CO₂. Surface morphology analysis revealed that the adsorbent’s surface was rough and contained a variety of pores or holes with different capacities, indicating that more CO₂ was captured and accommodated within the surface. Thermal analysis using the Barrett-Joyner-Halenda method showed that the adsorbent could withstand high temperatures of up to 9000°C. At this temperature, the adsorbent accounted for only about 18% of the material that entered the fixed bed column for adsorption, but 100% of it could remain active within the temperature range of 0°C - 3000°C. The characterization of the adsorbent showed that a pore width of 5.283 nm, a pore diameter of 2.64 nm, a micropore surface area of 434.7 m²/g, a pore volume of 0.202 cc/g, and a porosity of 56.73% were the optimal values for the adsorbent. Finally, it was revealed that 95% of CO₂ was adsorbed at optimal conditions within the temperature range of 500°C - 3500°C, time range of 0.5 - 5 hours, and bed height range of 1 - 6 cm.

Abstract: In this study concrete block was produced with waste crushed clay bricks (CCB). CCB is used as a conventional coarse aggregate replacement with the range of 0, 25, 50 and 75%. Physical and mechanical properties of concrete blocks were examined at room temperature (25°C) and elevated temperatures of 400, 600 and 800°C. The results indicated that concrete specimens with 50% CCB exhibited the greatest flexural strength characteristics compared to that containing natural aggregates, whereas a slight decline indicated at the density and compressive strength. However, the specimens with 75% CCB have the highest residual strength at an elevated temperature of 800°C. Accordingly, it is suitable for load-bearing wall application when exposed to elevated temperature in confirmation to ASTM-C55. Keywords: Concrete Masonry Units; Crushed Clay Bricks; Elevated Temperature; Coarse Aggregate Replacement.

Abstract: The increasing rate of fire disaster especially in the developing countries has renewed the demand for utilization of more economically sustainable materials for built environment. In this paper, the effect of calcined Ebonyi shale (CES) incorporated as partial replacement (15%) of cement on the thermo-mechanical properties of high strength concrete were investigated. The preparation of the CES was carried out by calcining the Ebonyi shale at a temperature of 900 °C. Both raw Ebonyi shale (RES) and calcined Ebonyi shale (CES) were analyzed using scanning electron microscope (SEM) and X-ray fluorescence (XRF). After curing time of 28days, several samples were exposed to varying temperatures. A comparison of the results showed that incorporation of CES enhanced high strength properties of concrete at elevated temperature. Consequently, economical and eco-friendly mixes that reduces CO₂ emissions of the overall cement production of clinker were achieved.

Abstract: The ability to improve the tendency of hardened concrete in compression at elevated temperature was studied. Five mixes of fly ash were cast with a replacement amount of 0%, 10%, 20%, 30%, and 40% by cement mass. They were exposed to 400°C and held for 2 hours after water curing. The specimens have been cooled down to room temperature and then undergo a compressive test. This research aims to study the physical and mechanical properties of fly ash concrete after being exposed to elevated temperatures. A digital microscope was used to analyse the formation mechanism of microstructure in concrete. Fly ash was used to produce high fire resistance concrete with 100 mm x 100 mm x 100 mm concrete cube. Sample 4 with 30% fly ash has the highest compressive strength with 26 MPa after 28 days and 21 MPa after exposed to 400°C. The results show that concrete containing a high amount of fly ash has several improvements when exposed to elevated temperature. The concrete specimens were used to validate an interfacial transition zone (ITZ) in concrete. The microstructure features were discussed concerning their influence on the strength development of concrete.

Abstract: The research aims to investigate the effect of elevated temperature on the compressive strength of concrete containing waste tile aggregate. Two water-to-cement ratios (w/c = 0.4 and 0.6) and three replacement ratios of waste tile aggregate (0%, 50% and 100%) were selected for producing concrete specimens. Experiment results showed that the slump of concrete were increased with the increase of the replacement ratio of waste tile aggregate. The compressive strength of concrete decreased with the increase of waste tile aggregate. The concrete with higher w/c of 0.6 can present equivalent compressive strength for that of the replacement ratio of waste tile aggregate under 50%; on the contrary, the concrete with lower w/c of 0.4 can have higher compressive strength for the replacement ratio increased to 100%. In addition, when the subjected temperature exceeded 440°C and raised to 800°C, the compressive strength of concrete decayed seriously and the residual strengths was almost the same at 800°C. Consequently, the fire resistance of waste tile aggregate concrete may be comparable to that of natural aggregate concrete.

Abstract: This paper presents experimental studies on the post-fire performance of concrete-filled steel tube (CSFT) columns under uni-axial load. The structural responses and axial load capacity of CSFT columns after exposure to elevated temperatures are investigated and discussed. All of the specimens are 750 mm in height, the nominal cross-section of the specimen is 150 mm x 150 mm, and have cylinder compressive strength of 18 MPa. The primary test parameters to be measured during the uni-axial compression test are wall thicknesses of the square tube (3.0 mm, 4.5 mm and 6.0 mm) and three different exposure to elevated temperatures (400°C, 600°C and 800°C). The results showed that the load-axial shortening relationship of the CSFT columns have a linear elastic response up to 80-90% of axial load capacity. After the axial load capacity is reached, the load-axial shortening curves are rarely becoming a nonlinear manner. It is also shown that the axial load capacity and ductility of the post-fire test columns are decreased significantly compared to the columns at ambient temperature, depending mainly on the elevated temperature. In addition, by comparing the axial load capacity of the test results with those obtained from the ACI design equation, the comparison results indicate that calculation formula in ACI code unconservative predicts the axial load capacity of the CSFT columns after exposure to elevated temperatures. Finally, the residual strength ratios are modified to both strength of concrete and steel tube under ambient temperature, and analyzed to evaluate the effect of post-fire behavior on the axial capacity of CFST columns.

Abstract: The objective of this research is to evaluate the temperature dependent strengthening mechanism of 0.5 wt.% carbon nanofiber reinforced glass fiber/epoxy (CNF-GE) as a function of environmental temperature. Flexural response of the CNF-GE composite has been studied at 30°C, 70°C and 110°C temperatures and compared over control glass fiber/epoxy (GE) composite. When flexural test was conducted at room temperature, CNF-GE composite exhibited about 29% improvement in strength, over control GE composite. With increase in environmental temperature, the extent of strength enhancement continued to decrease and at 110°C, the strength of the CNF-GE composite was found to be about 12% lower than control GE composite. Visco-elastic properties of CNF-GE and control GE composites have also been studied in the temperature range of 40 to 200°C.

Abstract: In the case of exposure of reinforced concrete structure to accidental fire, an assessment of its residual capacity is needed. Bond strength of concrete was observed under elevated temperatures (150°, 250°, 350° and 500°C) in this study. Cylindrical specimens were prepared for pull-out tests to find out the bond behavior and to observe the mechanical properties of concrete. All the specimens were 100 mm diameter and 200 mm height. The pull-out specimens contain a 10 mm steel bar at its center. The specimens were tested at 52 days age following a 28 days water curing. Samples were preheated for 3 hours at 100°C temperature and then put into the furnace for 1 hour at the target temperature. Samples were tested before preheating as controlled specimens. In case of mechanical properties and the bond strength of concrete, there were no remarkable changes due to elevated temperature up to 150°C. However, the mechanical properties and bond strength were decreased gradually after 150°C temperature. Maximum reduction of bond strength observed was 52.13% and 49.8% at 500°C for testing within 1 hour and after 24 hours of heating respectively when compared to the controlled specimens. Bond strength was found to reduce at a greater rate than compressive strength due to the elevated temperature.