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This study presents an analytical model for the load-moment (P-M) interaction diagrams of circular geopolymer concrete (GPC) columns reinforced with glass fiber-reinforced polymer (GFRP) bars and GFRP helices. The analytical P-M interaction diagrams of GPC columns were developed using the layer-by-layer numerical integration method. The analytical predictions of GFRP reinforced GPC columns were then validated against the experimental results on the behaviour of GFRP reinforced GPC columns under different loading conditions. It was found that the developed analytical model predicted the load and moment capacities of GFRP reinforced GPC columns with good accuracy. Further, a parametric study showed that the influence of increasing the compressive strength of GPC was more pronounced on P-M interaction diagrams of GPC columns under concentric and low levels of eccentric axial loadings. Also, the increase in longitudinal and transverse reinforcement ratios resulted in significant improvements in the load and moment capacities of GPC columns reinforced with GFRP bars and GFRP helices.

This paper presents an experimental investigation into the behavior of Glass Fiber-Reinforced Polymer (GFRP) bar reinforced high strength concrete and ultra-high strength concrete beams. In total, twelve GFRP bar reinforced concrete beams (GFRP-RC beams) were constructed and tested. Six GFRP-RC beams were tested under static loading. Higher strength concrete was found to influence the overall behavior of GFRP-RC beams under static loading in terms of load carrying capacity, deflection, and post-cracking bending stiffness. Six GFRP-RC beams were tested under impact loading at various levels of impact energy. The GFRP-RC beams displayed a shift in the failure mode (from shear failure to flexure failure) as a result of the use of ultra-high strength concrete under impact loading.

The behaviour of Glass Fibre-Reinforced Polymer (GFRP) bar reinforced concrete beams varies significantly from the behaviour of traditional steel bar reinforced concrete beams. This paper numerically investigates the response of GFRP bar reinforced concrete (GFRP-RC) beams under monotonic loads. This paper also presents the details of a three-dimensional Finite Element (FE) model for GFRP-RC beams under monotonic loads. The results of the numerical modelling have been validated against the experimental results of nine GFRP-RC beams. The results of the FE analysis have been found to be in very good agreement with the experimental results. Furthermore, a parametric study is carried out to investigate the effects of the reinforcement ratio, compressive strength of concrete, and shear span to effective depth ratio on the response of GFRP-RC beams. The effects of these parameters on the load-midspan deflection behaviour, energy absorption capacity, and failure modes of GFRP-RC beams have been adequately discussed in this paper.

In this study, a new equation is proposed to compute the maximum axial load carrying capacity of FRP bar reinforced concrete columns under axial compression. The equation proposed in this study was critically compared with the equations proposed in the previous research studies using a wide range of experimental data taken from the available literature. In general, it was found that computing the contribution of the FRP longitudinal bars in concrete columns based on the modulus of elasticity (stiffness) of the FRP bars provides more rational predictions than computing the contribution of the FRP longitudinal bars based on the ultimate tensile strength of the FRP bars. It was also found that using a concrete compressive strength-based empirical equation in estimating the axial strain in the FRP longitudinal bars in concrete columns provides more accurate predictions of the contribution of the longitudinal FRP bars in the axial load sustained by the FRP bar reinforced concrete columns.

This study investigates the potential of the use of recycled glass powder in foam concrete as a sustainable solution for future construction. The effects of cement and recycled glass powder contents, water to cement ratio and volume of foam on the plastic density, dry density, and compressive strength of foam concrete were investigated. The compressive strength of foam concrete without and with recycled glass powder increased with the increase in the plastic density and dry density of foam concrete. The direct replacement of cement with recycled glass powder (20% by mass) increased the compressive strength of foam concrete. Refereed/Peer-reviewed

Fly ash-based geopolymer (FAGP) and alkali-activated slag (AAS) concrete are produced by mixing alkaline solutions with aluminosilicate materials. As the FAGP and AAS concrete are free of Portland cement, they have a low carbon footprint and consume low energy during the production process. This paper compares the engineering properties of normal strength and high strength FAGP and AAS concrete with OPC concrete. The engineering properties considered in this study included workability, dry density, ultrasonic pulse velocity (UPV), compressive strength, indirect tensile strength, flexural strength, direct tensile strength, and stress-strain behaviour in compression and direct tension. Microstructural observations using scanning electronic microscopy (SEM) are also presented. It was found that the dry density and UPV of FAGP and AAS concrete were lower than those of OPC concrete of similar compressive strength. The tensile strength of FAGP and AAS concrete was comparable to the tensile strength of OPC concrete when the compressive strength of the concrete was about 35 MPa (normal strength concrete). However, the tensile strength of FAGP and AAS concrete was higher than the tensile strength of OPC concrete when the compressive strength of concrete was about 65 MPa (high strength concrete). The modulus of elasticity of FAGP and AAS concrete in compression and direct tension was lower than the modulus of elasticity of OPC concrete of similar compressive strength. The SEM results indicated that the microstructures of FAGP and AAS concrete were more compact and homogeneous than the microstructures of OPC concrete at 7 days, but less compact and homogeneous than the microstructures of OPC concrete at 28 days for the concrete of similar compressive strength.

This study provides new insight on the compressive behaviour of partially fibre reinforced polymer (FRP) confined concrete with either strain-hardening or strain-softening responses. Fully FRP confined concrete, partially FRP confined concrete with different strip gaps, and unconfined concrete were tested under axial compression. Four types of axial load-axial deformation behaviours were observed for specimens with different strip gaps. Even though a high volumetric ratio of FRP was applied, the confinement effectiveness was negligible when the strip gap exceeded the diameter of the specimens. Moreover, the axial stress-axial strain behaviours of wrapped and non-wrapped concrete were observed to be different, and significant strain localization was observed within the non-wrapped region. Based on the experimental observations and an extensive literature review, a confinement effectiveness coefficient was proposed for partially FRP confined concrete. A stress-strain model was then developed by considering the proposed confinement effectiveness coefficient. The developed stress-strain model provided better predictions than other existing stress-strain models.

A series of pullout tests were carried out to characterize the interface bond between steel fibre and magnesium phosphate cement (MPC) based matrix. The effect of the mixture proportions, curing time and end-hook of fibre on the interface bond properties between the steel fibre and the MPC-based matrix was investigated. The mixture proportions investigated include the mole ratio of magnesium oxide to potassium dihydrogen phosphate, mass ratio of sand to cement, mass ratio of water to cement and dosage of silica fume. The effect of different types of cement on the interface bond properties was also investigated.

This paper presents the mechanical properties of micro-steel fibre (MSF) reinforced magnesium potassium phosphate cement (MPPC) composites with multi-composite retarder. The compressive strength, flexural strength, flexural toughness and flexural ductility of the MSF reinforced MPPC composite (MSFRMC) were experimentally explored. The variables of the experiment included sand-cement mass ratio, water-cement mass ratio, curing time and fibre volume fraction. In addition, the effect of different types of cement on the mechanical properties of MSF reinforced composites was investigated. It was found that with the increase of water content in the MPPC paste, the average compressive strength, flexural strength and flexural toughness of MSFRMC decreased significantly and the ductility of MSFRMC increased slightly. With the increase of MPPC content in the paste, the flexural toughness of MSFRMC increased significantly and the flexural ductility of MSFRMC increased moderately. With the increase of the addition of MSF, the compressive strength, flexural strength, flexural toughness and flexural ductility of MSFRMC improved significantly. The compressive strength, flexural strength, flexural toughness and flexural ductility of MSFRMC were high at the early stage of curing, especially during the first 3 days. The addition of MSF in MPPC composite improved the compressive strength, flexural toughness and flexural ductility significantly more than the addition of MSF in sulphoaluminate cement and ordinary Portland cement composites.

In this study, the efficiency of Glass Fibre Reinforced-Polymer (GFRP) bar reinforced normal strength concrete (NSC) and high strength concrete (HSC) columns in sustaining axial and flexural loads was analytically investigated. Experimental data from available literature were used as benchmarks for the analytical investigations conducted in this study. In addition, a comprehensive parametric study was carried out to investigate the effect of different parameters (i.e., compressive strength of concrete, mechanical properties and reinforcement ratio of GFRP bars, and slenderness ratio of the columns) on the performance of concrete columns reinforced with GFRP bars. It was observed that under concentric axial load, the improvements in the axial load carrying capacity due to increasing GFRP longitudinal reinforcement ratio were more pronounced in GFRP bar reinforced NSC columns than in GFRP bar reinforced HSC columns. It was also observed that HSC columns reinforced longitudinally with GFRP bars with small longitudinal reinforcement ratio or low tensile modulus of elasticity might experience a tensile failure of the GFRP bars located on the tension side of the column cross-sections, especially if the columns are subjected to a high level of axial load eccentricity.

A simplified analytical model has been developed for the axial load-axial deformation behaviour of self-compacting concrete (SCC) columns reinforced with steel tubes. The developed analytical model takes into account the contribution of the steel tubes, unconfined concrete cover, confined concrete core and confined concrete inside the steel tube. The results of the analytical model have been compared with experimental results of four SCC column specimens. The results of the analytical model are in good agreement with the experimental results. A parametric study has been conducted to investigate the influences of the compressive strength of SCC, tensile strength of steel tube, wall thickness of steel tube and pitch of steel helix on the axial load-axial deformation behaviour of SCC columns reinforced with steel tubes. The ductility of SCC columns has been found to be significantly influenced by the increase in the compressive strength of SCC and the pitch of steel helix.

This study investigates the behaviour of ambient cured geopolymer concrete column specimens reinforced with steel fibres under different loading conditions. Three types of steel fibres (straight micro steel fibre, deformed macro steel fibre and hybrid steel fibre) were used in reinforcing the geopolymer concrete column specimens. Also, geopolymer concrete column specimens without steel fibre were tested as reference column specimens. Sixteen circular geopolymer concrete column specimens of 150 mm diameter and 600 mm height were cast and tested. The influences of the addition of different types of steel fibres and the loading conditions (concentric axial load, eccentric axial load and four-point bending) on the performance of the geopolymer concrete column specimens were investigated. The test results showed that the peak axial load and bending moment of fibre reinforced geopolymer concrete column specimens were higher than those of the geopolymer concrete column specimens without steel fibres under different loading conditions. Also, the addition of different types of steel fibres resulted in significant improvements in the ductility of the geopolymer concrete column specimens. The addition of hybrid steel fibre showed the highest improvement in the peak axial load, bending moment and the ductility of ambient cured geopolymer concrete column specimens.

This study investigates the effect of the location of Carbon Fibre Reinforced Polymer (CFRP) strips on the performance of partially wrapped square reinforced concrete (RC) columns under axial compression. Three column specimens with 150 mm × 150 mm cross-section and 800 mm height were tested. One specimen was the reference RC specimen, one specimen was partially wrapped with CFRP strips without considering the location of the steel ties, and the other specimen was partially wrapped with CFRP strips located in between the steel ties. The experimental results showed that wrapping the square RC column specimens with CFRP strips enhanced the strength and ductility under axial compression. For the similar amount of CFRP strips, the specimen partially wrapped with CFRP strips located in between the existing steel ties showed higher strength and ductility than the specimen wrapped with CFRP strips without considering the location of the steel ties. In addition, post-peak axial load-axial deformation response changed from descending to ascending response when the CFRP strips were located in between the existing steel ties.

This paper investigates the effect of corrosion on the bond between reinforcing steel bars and fibre reinforced geopolymer concrete. An accelerated corrosion method was used to corrode the reinforcing steel bars embedded in geopolymer concrete. Three types of steel fibres including straight micro steel fibre, deformed macro steel fibre, and hybrid steel fibre were used in this study. A total of ten geopolymer concrete mixes were used to evaluate the effect of corrosion of steel bar on the bond between steel bar and fibre reinforced geopolymer concrete. The pull-out test specimens were composed of concrete cubes with a side length of 160mm and reinforced with a deformed steel bar of 16 mm diameter located at the centre of the specimens. The test results showed that the addition of steel fibres in geopolymer concrete (fibre reinforced geopolymer concrete) significantly enhanced the bond strength of reinforcing steel bar. The bond strength of reinforcing steel bars embedded in steel fibre reinforced geopolymer concrete specimens reduced due to corrosion of reinforcement. However, the reduction of bond strength in steel fibre reinforced geopolymer concrete specimens was less than the reduction of bond strength in plain geopolymer concrete specimen.

In this study, a new cement-based composite with high early strength and toughness was developed by the addition of micro-fine steel fibre (MSF) in sulphoaluminate cement (SAC). The new composite is termed as MSF reinforced SAC composite (MSFRSC). The mechanical behaviour of MSFRSC was experimentally investigated, the flexural toughness and ductility of MSFRSC was evaluated. It was found that the compressive strength, flexural strength, shear strength, flexural toughness and ductility of MSFRSC were significantly influenced by the curing time and volume fraction of MSF. The compressive strength, flexural strength and shear strength of MSFRSC increased with the increase of curing time, especially during the first three days. The flexural strength and shear strength of MSFRSC improved significantly with the increase of the volume fraction of MSF. The flexural toughness of MSFRSC significantly improved and the ductility slightly improved with the increase of the volume fraction of MSF from 0.0% to 2.0%. The flexural toughness slightly increased and the ductility slightly decreased with the increase of the curing time from 1 day to 28 days. Also, the recommendations of different codes for the evaluation of the flexural toughness and ductility of MSFRSC were compared. The recommendations in ASTM C1609 fully reflected the flexural toughness and ductility of MSFRSC. The recommendations in JG/T 472-2015 distinguished the influence of MSF on the pre-peak and post-peak flexural load-deflection behaviours of MSFRSC. A simplified approach based on JG/T 472-2015 was proposed to evaluate the flexural ductility of MSFRSC.

This paper investigates axial and flexural behaviour of circular reinforced concrete (RC) columns strengthened with reactive powder concrete (RPC) jacket and fibre reinforced polymer wrapping. The experimental results of 16 circular RC column specimens have been presented. The specimens were divided into four groups of four specimens. Column specimens of the first group were the reference RC specimens without any strengthening, specimens of the second group were strengthened by wrapping with two layers of carbon fibre reinforced polymer (CFRP), specimens of the third group were jacketed with a 25 mm thick layer of RPC and specimens of the fourth group were jacketed with a 25 mm thick layer of RPC then wrapped with a single layer of CFRP. Test results demonstrated that jacketing with a thin layer of the RPC enhanced significantly the ultimate axial and flexural loads as well as energy absorption of circular RC column specimens. Wrapping the RPC jacketed specimens with CFRP improved the ultimate axial load, ductility and energy absorption of the specimens.

This study investigates the behaviour of square reinforced concrete (RC) columns partially and fully wrapped with CFRP under different loading conditions. The experimental results of twelve specimens with 150 mm × 150 mm cross-section and 800 mm height tested under concentric axial load, eccentric axial loads and four-point bending are presented in this study. The experimental results showed that partial and full wrapping increased the strength and ductility of square RC column specimens. The increase in the strength and ductility of fully wrapped square RC column specimens was higher than the increase in the strength and ductility of partially wrapped square RC column specimens under all loading conditions. However, the increase in the axial load eccentricity (concentric, 25 mm eccentric and 50 mm eccentric axial loads) resulted in a significant decrease in the maximum axial load with the largest reduction observed for fully wrapped specimens compared to partially wrapped specimens. The experimental axial load-bending moment interaction diagrams showed the better performance of partially and fully CFRP wrapped square RC specimens compared to non-wrapped square RC specimens.

The axial and flexural behaviors of Concrete Filled Carbon Fiber Reinforced Polymer Tube (CFRP-CFFT) columns have received significant research attention in the last two decades. One of the most attractive advantages of Carbon FRP (CFRP) tube is the high confinement which results in substantial increase in peak axial and flexural loads and deformations. Despite large research efforts, the behavior of CFRP-CFFT with and without CFRP reinforcing bars under different applied axial load eccentricity has not yet been adequately investigated. This study investigates the experimental and analytical axial-flexural ( P − M ) interactions of CFRP-CFFT columns with and without CFRP reinforcing bars. A total of 12 specimens of 204–205 mm outer diameter and 800–812 mm height were tested under concentric axial load, 25 mm and 50 mm eccentric axial loads and four-point load. The effectiveness of CFRP reinforcement (tube and bar) was observed to be reduced with the increase in the applied axial load eccentricity. Analytical P − M interactions were constructed using available FRP confined concrete design codes which matched well with the experimental P − M interactions. The parametric study showed that the actual confinement ratio, orientation of fibers and CFRP bar reinforcement ratio have significant influences on P − M interactions of CFRP-CFFT specimens.

This study experimentally investigated the behavior of glass fiber-reinforced polymer (GFRP) reinforced hollow-core concrete specimens under concentric axial compression . The effect of the type of concrete (non-fibrous concrete, i.e., normal concrete without the addition of fibers; polypropylene fiber concrete; and glass fiber concrete) and pitches of the GFRP helices on the behavior of GFRP bar-reinforced hollow-core concrete specimens were investigated. The experimental program consisted of seven circular hollow-core specimens with an outer diameter of 214 mm, an inner circular hole diameter of 56 mm, and a height of 850 mm. The failure modes, axial load carrying capacity, and ductility of GFRP bar-reinforced hollow-core concrete specimens were investigated. The experimental results showed that, for a similar amount of reinforcement, the GFRP bar-reinforced hollow-core polypropylene fiber concrete (GFRP–HC–PFC) specimen achieved 2% higher maximum axial load and 19% higher ductility than the GFRP bar-reinforced hollow-core non-fibrous concrete (GFRP–HC–NFC) specimen. For a similar amount of reinforcement, the GFRP bar-reinforced hollow-core glass fiber concrete (GFRP–HC–GFC) specimen achieved 14% lower maximum axial load but 9% higher ductility than the GFRP–HC–NFC specimen. The axial load carrying capacity and ductility of the specimens enhanced with the close pitch of the GFRP helices. A simplified equation was developed for GFRP bar-reinforced hollow-core concrete columns, which predicted the axial load capacity of the specimens with reasonable accuracy.

This paper investigates the effect of graphene on the properties of slag and fly ash-based ambient cured geopolymer paste and mortar. Graphene was added with five percentage (0.0%, 0.1%, 0.5%, 1.0% and 1.5%) of aluminosilicate materials by weight. The initial and final setting times of geopolymer pastes were reduced. The workability of geopolymer paste and mortar was slightly decreased with graphene. The 7-day and 28-day compressive strength of geopolymer mortar with 1.0% addition of graphene increased by 25% and 10%, respectively. The addition of 1% graphene could be considered as optimum proportion to improve the compressive strength of geopolymer mortar.

In some special applications at low temperature, high ductility, deformation, and durability are required for cement-based composites. Magnesium phosphate cement (MPC) possesses unique properties, including fast hardening at a temperature below 0 °C, high early-strength, and durability. This study investigated the influence of the water-to-binder (W/B) ratio, sand-to-binder (S/B) ratio, and various proportions of fly ash (FA) (as a substitute for MPC) on the workability, compressive strength , and tensile properties of high-ductility MPC-based composites (HDMPCC) incorporating polyvinyl acetate (PVA) fibre and cured at low temperatures. The experimental results revealed that the incorporation of up to 30% FA by mass significantly improved the ductility of the HDMPCC. For an S/B ratio of 0.2, strain corresponding to ultimate tensile stress was found to be more than 1.5%, resulting in better strain-hardening behaviour. Moreover, the HDMPCC composite with 30% FA, W/B ratio of 0.14, and S/B ratio of 0.12 exhibited the highest strain corresponding to peak tensile stress at 0 °C. The strain corresponding to peak and ultimate tensile stress ranged from 0.41% to 2.22%. The highest ultimate tensile stress of about 1.28 MPa was observed for HDMPCC specimens cured at 0 °C, –5 °C and –10 °C.

This study investigated the behaviour of short square concrete filled fibre reinforced polymer tube specimens under concentric, uniaxial eccentric, biaxial eccentric and four-point bending loads. Seven concrete filled glass fibre reinforced polymer (GFRP) tube specimens (GFRP-CFFT) and seven traditional steel bar reinforced concrete (steel-RC) specimens of 200 mm x 200 mm cross-section were tested. The GFRP-CFFT specimens obtained a larger P-M interaction surface (higher maximum axial loads and higher bending moments) than the steel-RC specimens. In addition, the GFRP-CFFT specimens exhibited a lower average reduction in ductility under eccentric axial loads than the steel-RC specimens.

In this study, the load moment (P-M ) interaction behavior of geopolymer concrete (GPC) filled fiber reinforced polymer (FRP) tube circular columns internally reinforced with FRP bars was analytically investigated. An analytical model for the P-M interaction behavior of the column was developed and validated against the experimental investigation results. The analytical model incorporates the confined GPC strength and the contribution of FRP bars in the load and moment capacities. In addition, a parametric study was conducted to investigate the influence of the compressive strength of the GPC, longitudinal reinforcement ratio and confinement ratio on the P-M interaction behavior of the column. The developed analytical model conservatively predicted the P-M interaction behavior of the column. It was found that the compressive strength of the GPC, the longitudinal reinforcement ratio and the confinement ratio significantly influenced the P-M interaction behavior of the column. All the tested parameters resulted in the linear increase of load and moment capacities with the increase in the tested parameter.

Steel-concrete composite structures have been widely used in the on-site constructions due to the benefit of composite actions provided by the steel and concrete. However, prefabricated steel–concrete composite constructions for building structures are not very popular in practice due to insufficient research studies and the lack of information on the connection systems, especially for the connection of prefabricated composite slabs. Prefabricated slabs are usually designed and constructed as simply supported and discontinuous elements. However, on-site composite slabs are continuous and connected to steel beams using shear connectors. Hence, the capacity of the composite slab constructed on-site is higher than that of conventional prefabricated slabs. Therefore, there is a significant need to develop a prefabricated continuous composite slab system to utilise the full benefit of the composite action. This study proposes interlocking connection systems for prefabricated steel–concrete composite slabs. The proposed prefabricated composite slabs with an interlocking system are analysed using finite element (FE) modelling and compared the results with the conventional slabs such as simply supported non-composite slabs, non-composite continuous slab and composite continuous slab. The ultimate load capacity of the proposed prefabricated composite slabs with the interlocking connection system has been found to be 40% higher than that of simply supported non-composite slabs and 10% lower than that of the continuous composite slab.

© 2017 Elsevier Ltd A new composite column named concrete-encased concrete-filled fibre reinforced polymer tube (CCFT) column has been proposed in this study. This composite column consists of an inner concrete-filled fibre reinforced polymer (FRP) tube, outer concrete confined with polymer grid, and concrete cover. In this study, a total of 16 concrete stub columns were cast and tested under axial compression. Columns were divided into eight groups, which included one group of plain concrete columns, two groups of FRP confined concrete columns, and five groups of CCFT columns. For FRP confined concrete columns, one layer and two layers of carbon FRP (CFRP) sheet were wrapped, respectively. For CCFT columns, glass FRP (GFRP) tube was used to confine the inner concrete, and polymer grid was used to confine the outer concrete. The test results show that considerable increase in strength and ductility can be obtained for CCFT columns. An analytical model has been developed to predict the axial compressive behaviour of CCFT columns. The analytical results have been found to be in good agreement with the experimental results. Based on the analytical model, the influences of different parameters on the axial compressive behaviour of CCFT columns have been investigated through parametric analyses.

Small diameter steel tubes are used in many civil engineering applications. Recently, the behaviour of concrete columns reinforced with small diameter steel tubes was experimentally and analytically investigated. This study explores the effect of unsupported length to the outside diameter ( L / D ) ratio on the axial compressive behaviour of small diameter steel tubes, which has not yet been adequately investigated. Galvanized and cold-formed steel tube specimens with L / D ratio of 2 to 12 were tested. It was observed that for specimens with L / D ratio of 2 and 4, the compressive failure occurred due to local elephant's foot buckling. However, the compressive failure mode changed to global buckling for specimens with L / D ratio≥6. The ultimate compressive strength was found to be lower than the ultimate tensile strength for specimens with L / D ratio≥6.

Circularizing a square column by bonding concrete segments onto the sides of the column and then wrapping with fibre reinforced polymer (FRP) is considered an effective technique in strengthening square solid columns. This paper investigates the suitability of the circularization technique for strengthening square hollow concrete specimens. Eight specimens in two groups (four solid specimens and four hollow specimens) were cast and tested under axial compression. The first specimen from each group was the reference specimen. The corners of the second specimen were rounded to 20 mm radius and wrapped with two layers of carbon fibre reinforced polymer (CFRP). The third specimen was circularized with full length concrete segments and wrapped with two layers of CFRP. The fourth specimen was circularized with concrete segments shorter than the length of the specimen and wrapped with two layers of CFRP. The test results demonstrate that circularization of hollow specimens similar to the circularization of solid specimens reduces the stress concentration at the corners and enhances the ultimate load carrying capacity and ductility. The circularization with short concrete segments is more effective for hollow specimens than the circularization with full length concrete segments when the ductility is of main concern.

In this paper, the Taguchi method has been used to design optimum mix proportions for geopolymer concrete with ground granulated blast furnace slag (GGBFS) as aluminosilicate source at ambient curing condition. The influences of binder content, alkaline activator to binder content (Al/Bi) ratio, sodium silicate to sodium hydroxide (SS/SH) ratio, and sodium hydroxide (SH) concentration on the geopolymer concrete were investigated. A total of nine mix designs were evaluated. It was found that specimens with a binder content of 450 kg/m3, Al/Bi ratio of 0.35, SS/SH ratio of 2.5, and SH concentration of 14 M produced the highest 7-day compressive strength (60.4 MPa). However, the setting time was found to be short. Hence, fly ash (FA), metakaolin (MK), and silica fume (SF) were used as partial replacement of GGBFS in different proportions to increase the setting time. It was found that the setting time improved for the partial replacement of GGBFS with FA, MK, and SF.

This paper investigates the compressive behaviour of prefabricated concrete-filled steel tube (CFST) columns with prefabricated column–column (PCC) connections. The innovative PCC connections are designed using conventional structural bolts instead of expensive blind bolts to connect two prefabricated CFST columns, simplifying the construction process and rendering the construction cost-effective. The compressive behaviour of prefabricated CFST columns with or without PCC connections has been investigated numerically. Parametric studies have been conducted to investigate the effect of different parameters of PCC connections, including connection configurations, horizontal and vertical stiffeners of connections, diameter of the coupling bolt, steel tube thickness, yield strength of steel tube, and compression strength of concrete, on the compressive behaviour of CFST columns with PCC connections. The prefabricated CSFT columns with the developed PCC connections are able to achieve similar compressive strengths that are achieved by the CFST columns without connections. Therefore, the developed PCC connections can be used to construct prefabricated CFST columns for the prefabricated steel–concrete composite structures.

This study proposes a new strain model for concrete with discrete fiber-reinforced polymer (FRP) confinement. An energy absorption factor for discretely FRP confined concrete and a strain reduction factor of FRP were proposed. The energy absorption factor and strain reduction factor in conjunction with an available strength model of concrete with FRP confinement were then used to develop a new strain model for concrete with discrete FRP confinement based on the strain energy balance principle. The new strain model was compared with available strain models suggested for concrete with FRP confinement. It was found that the strain model proposed in this study was more accurate than the available strain models in predicting the ultimate axial strain of concrete with discrete FRP confinement.

This study presents the results of an experimental investigation on high strength concrete (HSC) and steel fibre high strength concrete (SFHSC) circular column specimens reinforced longitudinally and transversely with Glass Fibre-Reinforced Polymer (GFRP) bars and helices, respectively. The Influence of the type of the reinforcement (steel and GFRP), the pitch of the transverse reinforcement, the addition of the steel fibres and the loading condition (concentric, eccentric and four-point loading) on the performance of the specimens was investigated. The study showed that the GFRP bar reinforced HSC (GFRP-HSC) specimen is as efficient as the steel bar reinforced HSC (steel-HSC) specimen in sustaining concentric axial load. However, the maximum load sustained by the GFRP-HSC specimens under eccentric axial load was 10–12% lower than the maximum load sustained by the steel-HSC specimens. GFRP bar reinforced SFHSC (GFRP-SFHSC) specimens sustained 3–13% higher axial load and 14–27% greater ductility than GFRP-HSC specimens under different loading conditions. Furthermore, reducing the pitch of the GFRP helices in GFRP-SFHSC specimens resulted in a significant improvement in the ductility and the post-peak axial load-axial deformation behaviour of the specimens.

FRP bars are considered alternatives to steel bars for reinforcing concrete structures in harsh environments. FRP bars are non-corrosive, light weight, non-magnetic and have high longitudinal strength and low thermal and electric conductivity. This paper experimentally investigated the flexural behaviour of high strength concrete (HSC) and ultra-high strength concrete (UHSC) beams reinforced with glass fiber reinforced polymer (GFRP) bars that has not been addressed in the literature before. Beams of 2400 mm long, 100 mm wide and 150 mm high were tested under quasi-static loading (three point loading). Influence of reinforcement ratio and compressive strength of concrete (HSC and UHSC) on the load carrying capacity, deflection, energy absorption, strains in the concrete and reinforcement, and failure modes were investigated. Test results found that over-reinforced HSC and UHSC GFRP bar reinforced concrete (GFRP-RC) beams showed an amount of pseudo “ductility” compared to under-reinforced HSC and UHSC GFRP-RC beams, where failure was brittle, without any prior warning. Energy absorption capacities were found to be higher for UHSC GFRP-RC beams for the same amount of reinforcement compared to HSC GFRP-RC beams. FRP design recommendations in ACI (2015) and CSA (2012) were compared with experimental data. FRP design recommendations for the calculation of flexural strength were found to be conservative (load-carrying capacity was under-predicted by 36% for both HSC GFRP-RC beams and UHSC GFRP-RC beams). However, FRP design recommendations for the calculation of deflection at the load carrying capacity were found to be un-conservative (deflections were under-predicted by an average of 10–22% for the HSC GFRP-RC beams and UHSC GFRP-RC beams).

Fiber Reinforced Polymer (FRP) composites have emerged as a viable alternative of steel reinforcement due to higher ultimate tensile strength to weight ratio and corrosion resistance of FRP composites. Concrete Filled Fiber Reinforced Polymer Tube (CFFT) technique for new column construction has attracted significant research attention. This paper investigated the axial and flexural behavior of Concrete Filled Carbon FRP Tube (CFRP CFFT) columns with and without CFRP bar and concrete filled Glass FRP (GFRP) tube columns with and without GFRP bar. The test results of 16 circular CFFT and four steel Reinforced Concrete (RC) specimens of 203–205 mm diameter and 800–812 mm height have been reported in this paper. The test results showed a larger reduction in the confinement effectiveness of FRP tube than steel helices under increasing applied load eccentricity. FRP bar reinforced CFFT specimens exhibited higher axial loads, flexural loads, and deformations at peak loads than unreinforced CFFT and steel RC specimens. Experimental axial load-bending moment interaction curves of tested specimens also showed the improved performance of FRP bar reinforced CFFT specimens.