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Glass transition temperature (Tg) of the bond between CFRP and steel influences on the service and fire performance of strengthened members. A total of eighty-two CFRP/steel double strap joints were prepared and tested under elevated temperature. They were cured under a range of elevated temperature conditions in the control laboratory environment and in the open environment which is practically feasible in large civil engineering structures. The test results showed a similar trend of reductions in the bond strength, Poisson’s ratio and Elastic modulus of CFRP/steel joint with the exposure to the elevated temperature. More than 50% reduction in the Poisson’s ratio, elastic modulus and the bond strength was noted when the bond line temperature exceeds Tg + 15 °C, irrespective of the curing time and curing conditions. Initial elevated temperature curing also causes for shifting the curves in the right-skewed direction. A significant increase in Tg of bond was noted with 4 h initial curing at 75 °C, i.e. Tg + 20 °C. more...

The rice processing industry generates a significant amount of rice husk ash (RHA) waste, which is considered as cost-efficient and environmentally friendly pozzolanic material . This study used RHA as a replacement for filler material/fine aggregate in the mortar. The mechanical, thermal, and environmental performance of mortar comprising RHA waste as a replacement of river sand in different contents (0, 10, 20, 30 and 50% by weight of river sand) were investigated through experimental tests and environmental impact assessment . The RHAs were obtained from both controlled burnt (CBRHA) and opened burnt (OBRHA) processes and used to produce the mortar mixtures. Results show that OBRHA can be used as a partial replacement for river sand for up to 30% of weight to improve the thermal performance by reducing thermal conductivity up to 62% while keeping the adequate compressive strength . Further, the replacement of 30% weight of sand with OBRHA in conventional mortar production significantly reduces greenhouse gas emissions (i.e. 13% reduction per kg) and cost (4% reduction per kg). more...

This paper reports a detailed test programme conducted on enhancing the flexural performance of Carbon Fiber Reinforced Polymer (CFRP) strengthened reinforced concrete beams to ensure prolonged composite action between CFRP laminate and concrete. The effects of surface preparation and alternative bonding techniques on the composite performance were investigated. In this regards, a total of 28 small-scale CFRP strengthened and non-strengthened reinforced concrete beams were tested using the three-point bending test method. This study clearly shows the importance of surface preparation and level of roughness on bond performance of CFRP/Concrete composites. The results also indicate the better performance in CFRP/epoxy/Polyester mesh hybrid arrangement when compare with CFRP strengthened concrete beams. more...

The behaviour of Carbon Fibre Reinforced Polymer (CFRP) strengthened vertically curved beams of Steel Circular Hollow Sections (SCHS) was studied. Sixteen numbers of curved beams with 1200 mm span having four radii of curvatures; 0 mm, 2000 mm, 4000 mm and 6000 mm were tested under three-point bending tests. A range of CFRP lengths up to 1000 mm was selected. The maximum performance was noted when the ratio between CFRP length to total length of beams is 0.625. Four types of failure modes were observed in the strengthened beams. A theoretical model was also developed and validated to predict the load–deflection behaviour of CFRP strengthened tubular vertically curved beams in the elastic region using the Maxwell-Mohr integral method. more...

The energy used to maintain the thermal comfort of buildings significantly contributes to the GHG emissions and global warming. In this study, a sustainable and cost-effective rice husk ash (RHA)-based mortar for wall plastering has been developed to provide better thermal insulation, reduce the operational energy and enhance the thermal comfort. Consequently, RHA was partially replaced with the sand in the conventional mortar to produce the RHA-based plaster. Initially, compressive strengths and thermal conductivities of the selected mortar mixes were assessed. The results highlight that the RHA can be replaced up to 30% instead of sand in mortar to produce the thermally enhanced wall plaster. Further, two identical prototype model houses were constructed with RHA-based (i.e. 30% of RHA) and conventional plasters to evaluate their heat transfer, heat flux, and the characteristics of internal and external wall surface temperatures in open weather conditions. It was noted that the average peak heat flux reduction formed by the RHA-based plaster was 10%. The average daily heat transfer reduction across the wall with RHA-based plaster was about 26%. Results also show that RHA-based plaster can reduce the energy that required to maintain thermal comfort by about 9% than the conventional plaster. Moreover, the environmental impact analysis was also conducted to assess the sustainability performance of RHA-based mortars. The environmental impact assessment revealed that the RHA-based plaster has less environmental impact than the conventional mortar. Furthermore, the CO2 emission generated by the production of RHA-based mortar is about 14% less than the conventional plaster. more...

A total of fifty two CFRP strengthened concrete specimens were tested. In preliminary investigation, ten specimens were tested at ambient conditions with varying bond length. This indicated the effective bond length is in the range between 100 mm and 150 mm. The bond length of 150 mm was considered and forty two specimens were prepared for detailed investigation. Thirty of them were conditioned under a range (0–50%) of sustained loading. All specimens were subjected to the temperature cycles of 20–50 °C and constant relative humidity (30%) during conditioning. These specimens were tested using the single-lap shear test method at ambient conditions after 1800 h and 2250 h exposure for accelerated ageing. The conditioned specimens showed the maximum strength reduction of 24%. The test results indicate that the concrete/epoxy interface as the weakest part of the composite in service life. Reduction in peak bond stress was noted from conditioned specimens with exposed level of sustained loading. more...

This paper reports on the long-term performance of CFRP strengthened concrete members subjected to 20–50 °C cyclic temperature, 60% constant humidity and sustained loading. The induced sustained stress was imposed through a range of loading values from 0% to 35% of the ultimate strength of specimens subjected to normal environmental conditions. The behaviour of CFRP/concrete lap shear specimens prepared using two types of commercially available two-part epoxy adhesives was investigated. Three different curing conditions were taken into account. more...

In strengthening systems, the CFRP (Carbon Fibre Reinforced Polymer) materials typically have excellent resistance against environmental conditions; however, the performance of adhesives between CFRP and steel is generally affected by various environmental conditions such as marine environment, cold and hot weather. This paper presents the comparative durability study of CFRP strengthened tubular steel structures by using two different adhesives such as MBrace saturant and Araldite K630 under four-point bending. The program consisted of testing twelve CFRP strengthened specimens having treated with epoxy based adhesion promoter, untreated surface and one unstrengthened specimen and conditioned under cold weather for 3 and 6 months to determine the environmental durability. The beams were then loaded to failure in quasi-static manner under four-point bending. The structural responses of CFRP strengthened tubular steel beams were compared in terms of failure load, stiffness and modes of failure. The research findings show that the cold weather immersion had adversely affected the durability of CFRP strengthened steel members. Design factor is also proposed to address the short-terms durability performance under cold weather. more...

The sudden punching shear failure of flat slabs is a critical issue. The combined effects of externally strengthened Carbon Fiber Reinforced Polymer (CFRP) flexural reinforcements and post-installed CFRP shear reinforcements which explain the real behavior in the strengthening phase of a shear deficient slab, on the punching shear performance are not fully explained. In this study, the flat slab panels of 1200 mm × 1200 mm × 100 mm were retrofitted with seven alternative bonding arrangements of CFRP to investigate the combined effects of shear dowels and flexural reinforcements. A transient load was applied using a stub column, size 100 mm × 100 mm located at the center of the slab. The non-strengthened specimens failed in punching shear. The strengthened specimens showed a maximum punching shear capacity enhancement of 120%. A numerical model was also developed to identify the load transfer behavior of post-installed CFRP shear dowels. Further, the effects from the end anchorage of external CFRP and the refilling material at drilled locations to install CFRP shear strengthening scheme were also determined. more...

Fibre reinforced polymer (FRP) systems have emerged as one of the most promising and affordable solutions for strengthening civil engineering infrastructure. Nowadays, this application is widely used in outdoor structures such as bridges, silos and towers. The major challenge in composites applications for outdoor structures is the long-term durability of bond between FRP and substrate under different environmental conditions. Elevated temperature and humidity are common issues that may have adverse effects on the polymer matrix, especially on thermosetting adhesives such as epoxies. This paper presents the results of long-term bond performance of carbon fibre reinforced polymer (CFRP) strengthened concrete members. CFRP-plated concrete specimens were exposed to combination of cyclic temperatures (20-50 C) and 90% constant humidity. In addition to environmental exposure, some of the specimens were subjected to sustained loading. At the end of the exposure period, the residual strength was measured using single lap shear test method. more...

International audience; This paper presents the results of an experimental and numerical program to investigate the circular hollow section (CHS) beams, strengthened using Carbon Fibre Reinforced Polymer (CFRP) sheets. The circular hollow shaped steel beams bonded with different CFRP layer orientations were tested under four-point bending. The mid-span deflection, service load and failure load were recorded. The LHL (where L, first inner longitudinal layer, H, second hoop layer and L, third outer longitudinal layer) and LLH (where L, first inner longitudinal layer, L, second longitudinal layer and H, third outer hoop layer) layer oriented strengthened beams perform slightly better than HHL (where H, first inner hoop layer, H, second hoop layer and L, third outer longitudinal layer) layer oriented strengthened beams. The LHL and LLH layer oriented treated beams showed very similar structural behaviour. Numerical analyses were then conducted on the CFRP strengthened steel CHS beams. The validity of the models has been assessed by comparing the failure loads and mid-span deflections. The effects of various parameters such as bond length, section types, tensile modulus of CFRP, adhesive layer thickness and adhesive types have been studied. more...

Fire related structural degradation is a challenge to the safe design of structural members. Carbon fibre reinforced polymer (CFRP) strengthened concrete members show degradation of bond properties with temperature. Therefore, a detailed investigation of heat effects on composites is required before further application of this system can be effective. This paper focuses on a 3D model developed to predict the behaviour of CFRP–concrete composites under fire. Heat transfer analysis was employed to predict the temperature within the adhesive layer of epoxy, which is the most critical part of the member at high temperature. The model showed that the epoxy reached the failure point within a short time under standard fire. The model was also used to predict the required insulation thickness requirement for two-hour and three-hour fire resistance levels. The effects of rate of temperature increase on bond strength of composite structures are demonstrated through numerical analysis. The model results were validated with experimental data. more...

The use of circular hollow steel members has attracted a great deal of attention during past few years because of having excellent structural properties, aesthetic appearance, corrosion and fire protection capability. However, no one can deny the structural deficiency of such structures due to reduction of strength when they are exposed to severe environmental conditions such as marine environment, cold and hot weather. Hence strengthening and retrofitting of structural steel members is now very imperative. This paper presents the findings of a research program that was conducted to study the bond durability of carbon fibre-reinforced polymer (CFRP) strengthened steel tubular members under cold weather and tested under four-point bending. Six number of CFRP-strengthened specimens and one unstrengthened specimen were considered in this program. The three specimens having sand blasted surface to be strengthened was pre-treated with MBrace primer and other three were remained untreated and then cured under ambient temperature at least four weeks and cold weather (3 C) for three and six months period of time. Quasi-static tests were then performed on beams to failure under four-point bending. The structural response of each specimen was predicted in terms of failure load, mid-span deflection, composite beam behaviour and failure mode. The research outcomes show that the cold weather immersion had an adverse effect on durability of CFRP-strengthened steel structures. Moreover, the epoxy based adhesion promoter was found to enhance the bond durability in plastic range. The analytical models presented in this study were found to be in good agreement in terms of predicting ultimate load and deflection. Finally, design factors are proposed to address the short-terms durability performance under cold weather. more...