In general, plastic waste has been growing remarkably. Numerous waste plastic products are generated by manufacturing processes, service industries, and municipal solid waste (MSW). The increase in plastic waste increases concern about the environment and how to dispose of the generated waste. Thus, recycling plastic waste becomes an alternative technique to the disposal of plastic waste in a limited landfill. One of the solutions is to use plastic waste as recycled material in concrete construction to produce what is called green concrete. This research illustrates a summary of studies that utilized polyethylene terephthalate (PET) in concrete as a volume ratio or concrete aggregate replacement. It presents data with regard to mixing design and concrete behavior when PET is used. Moreover, using PET in concrete industries may reduce environmental pollution such as the emission of carbon dioxide and plastic waste disposal problems.

In recent decades, several studies have considered the use of plastic waste as a partial substitute for aggregate in green concrete. Such concrete has been limited to non-structural applications due to its low strength. This raises whether such concrete can be enhanced for use in some structural applications. This paper reports an attempt to develop a structural-grade concrete containing plastic waste aggregate with high proportions of substitution and confined with carbon fiber reinforced polymer (CFRP) fabrics. Experimental research was conducted involving the casting and testing 54 plain and confined concrete cylinders. A concrete mixture was designed in which the fine aggregate was partially replaced by polyethylene terephthalate (PET) waste plastic at ratios of 0%, 25%, and 50%, and with different w/c ratios of 0.40, 0.45, and 0.55. The results show that confinement has a substantial positive effect on the compressive behavior of PET concrete. The enhancement efficiency increases by 8–190%, with higher enhancement levels for higher substitution ratios. Adding one layer of CFRP fabric raises the ultimate strength of samples that have lost compressive strength to a level close to that of unconfined samples not containing PET. This confinement is accompanied by an increase in the slope of the stress-strain curve and greater axial and lateral strain values at failure. For the specimens confined by CFRP fabric, PET aggregate can be used as a partial substitute for sand at a replacement ratio of up to 50% by volume for structural applications. This paper also considers the ability of existing models to predict the strength of confined-PET concrete circular cross-sections by comparing model predictions with experimental results. The strength of confined PET concrete elements can’t be accurately predicted by any of the models that are already out there. It’s important to come up with a new model for these elements.

Enhancing concrete's mechanical properties has become a prominent field in recent years. Numerous studies investigated the possibility of enhancing the mechanical properties of concrete by adding additive materials. Few studies investigated the effects of copped CFRP on the tensile strength of normal-strength concrete (NSC) and low-strength concrete (LSC). In this study, the effects of Chopped Carbon Fiber Reinforced Polymer (CCFRP) on the mechanical properties of LSC and NSC were investigated. The method of the study was experimentally investigating the effects of CCFRP on the mechanical properties of LSC and NSC. Different volume fractions (0%, 0.25%, 0.5%, and 0.75%) of chopped carbon fibers were added to the concrete mix for the 13 MPa and 28 MPa concrete grades, and five mix trials were conducted to achieve concrete with 13 MPa and 28 MPa. The ratios (1:1.5:2.5) for the normal strength mix and (1:2.6:4.1) for the low strength mix were chosen. Three tests were conducted to evaluate the effects of chopped CFRP on the mechanical properties of concrete: compressive strength, tensile strength, and flexural strength. A total of 120 pieces were cast, including 24 beams, 48 cubes, and 48 cylinders. The casted cubes were 15 × 15 × 15 cm and the cylinders were 15 cm in diameter and 30 cm in length. Prism beams with a 15 × 15 cm cross-section and a 56 cm length were tested under a single point load. The samples were tested at 7 and 28 days of age, and the sample density was recorded. The results revealed that adding 0.25% CCFRP increased the compressive strength of LSC from 9.5 MPa to 11.2 MPa which is about 10% enhancement and slightly affected the compressive strength of NSC by about 5%. On the other hand, adding 0.25% CCFRP to both LSC and NSC increased split tensile strength from 2.5 MPa to 3.6 MPa which is about 44% enhancement for NSC and 16.6% for LSC. Similar improvements were made in flexural strength of normal strength increased from 4.5 MPa to 5.4 MPa. Whereas the effects on LSC were unremarkable. As such, this study recommends 0.25% CCFRP fiber as the ideal dosage.

The strength models for fibre reinforced polymer wrapped columns available in the research literature were developed at ambient temperatures. To date, no experimental or analytical data have been available on the behaviour of large-scale reinforced concrete circular columns loaded during heating and cooling and subsequently wrapped with carbon fibre reinforced polymer fabrics. This paper deals with the development of new design-oriented strength models to predict the compressive strength of unheated and heat-damaged reinforced concrete columns confined with carbon fibre reinforced polymer. In this paper, 18 Ø 204 mm × 750 mm identical reinforced concrete columns were fabricated and tested, of which 12 were subjected to elevated temperatures under stress and then subsequently confined with carbon fibre reinforced polymer sheets after air cooling. The variables considered in these tests included the level of heat exposure and the number of carbon fibre reinforced polymer sheet layers. The digital image correlation technique and conventional foil gauges were used to determine the axial strain of carbon fibre reinforced polymer coupons and axial and lateral strains over the surface of unheated and heat-damaged carbon fibre reinforced polymer-wrapped columns. It was found that it is possible to repair heat-damaged concrete even to the extent of achieving the original compressive strength prior to heating through the use of appropriate carbon fibre reinforced polymer materials. The developed models were compared with the strength of columns obtained from test results of both unheated and heat-damaged carbon fibre reinforced polymer-wrapped columns and also with the existing ambient temperature strength models.

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