دراسة تأثير درجات الحرارة المرتفعة على سلوك الاعتاب الخرسانية ذات الخرسانة المستدامة

Study of the Elevated Temperature Effect of Sustainable Reinforced Concrete Beams

Abstract

Many concrete structures may be exposed to extreme conditions during their service life, one of which is fire. The elevated temperatures caused by the fire put additional strains and stresses on the structures that weren’t considered during the designing process. However, there is little information available regarding how high temperatures affect the behavior and modes of failure of sustainable reinforced concrete beams.
The behavior and failure modes of sustainable reinforced concrete beams at elevated temperatures are examined experimentally in this study. Experimental tests were conducted on fifteen sustainable RC beams in dimensions of 150mm × 200 mm (width ×height); and 1400 mm total length. Three samples were not exposed to temperatures and were not tempered and twelve sustainable RC beams were exposed to different elevated temperatures and all beams were then subjected to two vertically concentrated loads, each load at one-third of the beam until it failed. Every RC beam specimen was designed in compliance with ACI Committee 318-2019. Connections among temperature and time, as well as load and deflection, were illustrated. The failure types and crack patterns were noted and observed. Two main aspects were the focus of the experimental investigation. The first is the weight replacement ratio of cement; 30 % of ground granulated blast furnace slag (GGBS) and 5%, 10% and 15% of silica fume (SF) were used to replace cement. The second is to study the effect of elevated temperatures of 300 and 400 °C on the sustainable concrete with reinforcement beams and their strengthening using carbon fiber reinforced polymer (CFRP) sheets under flexural load. A U-shaped strengthening scheme was used along the beam to strengthen them.
The results showed that the ideal percentage of silica fumes used in the sustainable concrete mix is 10%. The results also showed that replacing cement with a perfect combination consist 30% blast furnace slag (GGBS) and 10% silica fume (SF) increases the mechanical characteristics (compressive, tensile and flexural strength) by 10.91%, 15% and 16.67% and decreases when exposed to temperatures of 400°C by 12.52%, 22.56 and 33.46% respectively compared to the replacement ratios of 30% to blast furnace slag and 5% to silica fumes. It was also noted that the ideal combination increased the final load of the sustained beam by 12.28%.
The results also showed that exposure of the sustainable beams to high temperatures leads to a decrease in the load capacity, as the beams consisting of 30% furnace slag and 10% silica fume decreased by 5.93% and 7.47% when exposed to a temperature of 300 and 400 °C, respectively, compared to the beams not exposed to heat.
The effects of carbon fibers reinforced polymer (CFRP) sheets on reinforced beams were shown by the experimental results. In comparison to beams exposed to heat and not strengthened, U-shaped carbon fibers for beams made of 30% blast furnace slag and 10% silica fume and exposed to temperatures of 300 and 400 °C increased load capacity by 46.29% and 46.87% and decreased displacement by 26.3% and 0.5%, respectively.
Nonetheless, it was determined that high temperatures cause the concrete to peel, which causes the chunks of concrete to separate as the heating process progresses.