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The improvement in the compressive strength (CS) and ductility of plain concrete always remained an active area for advanced research. The present study aims to enhance the strength of low strength hybrid fiber reinforced concrete (HFRC) cylinders confined with different number of carbon fiber reinforced polymer (CFRP) sheets by examining the axial CS, axial compressive strain, and compressive stress–strain behavior of low strength HFRC cylinders confined with CFRP sheets. The HFRC consisted of steel fibers and polypropylene fibers. Two groups of low strength HFRC specimens (12.5 MPa and 16.5 MPa) were fabricated to investigate the effect of CFRP confinement on the different CS of HFRC. The experimental outcomes depicted that the lateral CFRP confinement of concrete significantly improved the CS, axial compressive strain, and axial stiffness of low strength HFRC specimens. The improvements of 115.7% and 130.7% occurred in the CS of 12.5 MPa group for single and double CFRP layers, respectively. Similarly, the improvements of 37.4% and 112.6% occurred in the CS of 16.5 MPa group for single and double CFRP layers, respectively. Therefore, the CFRP confinement is more effective for low strength HFRC as compared with high strength HFRC in terms of axial CS and axial compressive strain.

The objective of this research study is to demonstrate the axial compressive behavior of GRFC columns by fabricating five circular columns (1150 mm high and 250 mm in cross-section) and testing them under axial concentric loading. Two different kinds of fibers, that is, polyvinyl alcoholfibers (PVA) and polypropylene fibers (PPF) were incorporated into the concrete. Two types of transverse confinement (GFRP hoops and GFRP spirals) were provided. The efficiency of GFRP hoops was explored by providing them at the spacing of 75 mm, 150 mm, and 250 mm, respectively. The efficiency of GFRP spirals was examined by keeping the spacing of 38 mm and 75 mm, respectively. The GRFC columns confined with GFRP spirals portrayed higher axial strength and higher ductility indices. Furthermore, an extensive finite element modeling (FEM) was performed by considering the effect of hybrid fibers using a modified concrete damaged plastic (CDP) model. The proposed FEM captured the axial response and cracking behavior of GRFC columns with high accuracy. This study also proposed a new empirical model for capturing the axial strength of GRFC columns by considering the influence of GFRP bars and lateral confinement of GFRP hoops/spirals.

The increased quantity of construction and demolition waste and the high carbon footprint of cement production is creating significant environmental problems. This study explored the use of recycled coarse aggregates (RCA) in geopolymer concrete (GPC) and reinforced with glass fiber reinforced polymer (GFRP) bars and spirals to fabricate novel and structural GRAGC columns. A total of 9 GRAGC columns with 1150 mm in height and 250 mm in diameter were tested to failure under axial compression. The influence of a different number of longitudinal GFRP bars and spiral spacing on the cracking behaviour, ductility, and axial load-carrying capacity (LCC) were investigated. A nonlinear finite element model (FEM) was implemented to predict the axial compressive response of GRAGC columns. The experimental results depicted that an improvement in the ductility and lateral confinement was observed by decreasing the spacing of GFRP spirals. GRAGC columns with eight longitudinal GFRP bars portrayed the highest LCC. All tested GRAGC columns portrayed similar failure modes with the damage at the central region of the specimens. The theoretical model suggested over a database of 225 GFRP reinforced columns showed a high accuracy compared with the previous models. The present study suggests an efficient and environmental-friendly compression member.

Structural members comprising geopolymer recycled aggregate concrete (RAC) reinforced with glass fiber-reinforced polymer (GFRP) bars have not been investigated appropriately for axial compressive loading cases. The present study addresses this knowledge gap by evaluating the structural efficiency of GFRP-reinforced geopolymer recycled aggregate concrete (GGRAC)-based members subjected to axial compressive loading. A total of nine compressive members (250 mm in cross-section and 1150 mm in height) were constructed to examine the effect of the number of longitudinal GFRP bars and the vertical spacing of transverse GFRP hoops/ties. The experimental results portrayed that the ductility of GGRAC compressive members improved with the reduction in the pitch of GFRP hoops. The axial load-carrying capacity (LCC) of GGRAC compressive members increased by increasing the number of GFRP bars up to eight (corresponding to a reinforcement ratio of 2.11%) while it decreased by using ten longitudinal GFRP bars (corresponding to a reinforcement ratio of 2.65%). Additionally, an empirical model was suggested to predict the axial LCC of GGRAC compressive members based on a large amount of experimental data of similar members. The experimental results and related theoretical predictions substantially prove the applicability and accuracy of the proposed model. The proposed column represents a feasible structural member in terms of material availability and environmental sustainability.

The reuse of industrial wastewater and the recycling of construction and demolition waste material produced by the construction industry will lead to a sustainable environment by reducing the exploitation of the new natural resources and the waste deposit areas. The present study endeavors to investigate the mechanical and durability performance of recycled aggregate concrete (RAC) made with five different kinds of wastewater taken from domestic sewerage, fertilizer factory, textile factory, sugar factory, and service station. The potable water was completely replaced with each kind of wastewater for the mixing of concrete to examine its effect on compressive strength (CS) and split tensile strength (STS), water absorption (WA), chloride penetration (CP), and resistance against sulfuric acid attack of RAC at various testing days. The results show that using the wastewater taken from the textile factory in the production of RAC presents the maximum CS (32.2 MPa) and STS (3 MPa) that were 19% and 16% higher than that of the RAC made with potable water. The use of wastewater taken from domestic sewerage for the mixing of RAC presented the highest WA (13.88%). The usage of wastewater taken from the fertilizer factory in the production of RAC depicted the maximum mass loss (19.62% at 120 days of testing) due to an attack of 4% H2SO4 and the highest CP (16.49 mm at 28 days of testing). The statistical analysis depicted a considerable difference among the CS and CP of RAC mixes while no considerable difference was depicted by the statistical tests for the WA, STS, and acid attack for various RAC mixes.

To develop a sustainable environment and to alleviate the problems of the large annual production of construction and demolition waste, the recycled aggregate concrete (RAC) has been used in the columns reinforced with glass fiber reinforced polymer (GFRP) bars. This study explores and compares the structural behavior of GFRP reinforced recycled aggregate concrete columns (GRAC columns) and steel bars reinforced recycled aggregate concrete columns (SRAC columns) under concentric and eccentric loadings. 18 circular concrete columns having a diameter of 250 mm and a height of 1150 mm were manufactured from which 9 samples consisted of GFRP reinforcement and the other 9 samples consisted of steel bars. The test measurements portrayed that the GRAC columns showed lower axial strength (up to 7.79%) with higher ductility indices (up to 4%) compared with SRAC columns. Both GRAC and SRAC columns showed similar failure modes and cracking patterns. Furthermore, both GRAC and SRAC columns presented significant reductions in the axial strength due to the loading eccentricities. The present study proposed a three-dimensional nonlinear finite element model (FEM) for predicting the structural response of GRAC and SRAC columns using ABAQUS 6.14. The simulation of RAC was carried out using a modified concrete damaged plasticity (CDP) model and that of GFRP bars was carried out using a linear elastic model. A theoretical model for predicting the axial strength of GRAC columns was given based on a large database of 270 GFRP reinforced concrete columns. The close agreements were observed among the experimental results, numerical simulations, and theoretical predictions for GRAC columns.