Investigation of the physical-mechanical properties and durability of high-strength concrete with recycled PET as a partial replacement for fine aggregates

In this study, PET plastic waste, which is a type of polymer commonly used in the manufacture of plastic bottles, has been incorporated into concrete by partially replacing the natural fine aggregate. An experimental study was conducted by casting and testing 90 concrete cylinders and 54 concrete cubes. A concrete mixture was designed in which the natural fine aggregate was substituted partially with PET plastic waste (PW) at a ratio of 0%, 25%, and 50%, with various w/c ratios of.40,.45, and.55. Physical, mechanical, and durability properties were assessed. The downside of the test results show degradation in each of the following characteristics: slump, compressive strength, splitting tensile strength, ultrasonic pulse velocity, water absorption, and porosity. The degradation of these characteristics increased with the increase in the volume of plastic aggregate (PA) and the w/c ratio. While the positive side of the results showed that with the increase of the PA volume and the w/c ratio, the fresh and dry densities decreased further, and by using 50% PET, the dry density became below 2000 kg/m3. Therefore, it is classified as lightweight concrete. Moreover, the fracture of concrete changed from brittle to more ductile compared to control concrete. Also, the thermal conductivity decreased significantly (11%–47%), and by using 50% of PET, the thermal conductivity became less than.71 W/mK, and accordingly, classified as a bearing insulator

Strengthening of fire-damaged bridge columns using CFRP fabrics

In recent years the introduction of CFRP composites for strengthening concrete structures has received considerable attention and popularity in structural applications. This is due to their high strength-toweight and stiff-ness-to-weight ratios, high corrosion resistance, good fatigue behavior, and their ability to form and to shape to the existing structure. This paper presents the results of an experimental investigation on concrete specimens, both damaged and undamaged by elevated temperatures, then retrofitted with externallybonded CFRP fabrics under axial compression. For this purpose, six identical experimental tests were carried out on 204 × 750mm RC columns and six identical plain cylinders 100 × 200mm. Four of the cylinders were subjected to high temperatures, but only two were confined with CFRP sheets. The experimental parameters included the number of CFRP sheet layers and damaged and undamaged concrete. The results of this experimental investigation indicate that CFRP can significantly increase the residual strength of undamaged columns and post-heated concrete cylinders. The test results also confirm that using CFRP fabrics is an effective way to restore some or even the full strength of concrete after damage by heating. The results compare well with the available codes and guidelines for strengthening

Effectiveness of CFRP strengthening of fire-damaged concrete

It is well known that the mechanical properties of concrete deteriorate after exposure to a fire/elevated temperatures. This study investigated the effects of heating temperature and cooling on the residual strength reduction of heat-damaged concrete. A method for improving the degree of strength recovery using carbon fibre reinforced polymers (CFRPs) is discussed. FRP materials have been applied successfully to strengthen existing concrete members by means of confinement, with remarkable increases of strength and ductility (energy absorption), as indicated by numerous published studies. This paper provides the results of an experimental study to predict the axial strength of unconfined, postheated unconfined and post-heated CFRP-confined concrete cylinders under axial monotonic compression. For this purpose, fourteen (65 x 150 mm) smaller concrete cylinders and six (100 x 200 mm) concrete cylinders were tested. The experimental results indicate that the residual compressive strength of concrete decreases with heating temperature above 300oC and after cooling. In addition, it was found that the application of the CFRP to the surface of heat-damaged concrete cylinders significantly improves the residual compressive strength

Confinement of heat-damaged RC circular columns using CFRP fabrics

The confinement of concrete with fibre-reinforced polymer (FRP) composites can significantly enhance its strength and ductility. This is due to their high strength-to-weight and stiffness-to-weight ratios and their ability to be readily formed into various cross-sectional shapes. Most of the available ambient temperature studies for achieving the compression strength and ductility of confined concrete have been done on standard cylinders. However, there is a lack of knowledge on confinement of circular RC columns, in which the concrete is damaged by fire and then uniformly confined using carbon fibre-reinforced polymer (CFRP) sheets. This paper presents a residual confinement study based on 10 identical circular RC columns with dimensions of Ø 204 × 750mm, previously damaged by elevated temperatures and retrofitted externally using CFRP fabrics and then tested under axial compression. The testing involved the RC columns being loaded during both the heating and cooling phases as would be the case with real structural elements in a fire. The results indicate that CFRP fabric can considered an excellent technique for strengthening heat-damaged RC columns