Search

This study focuses on the development of an insulating cementitious adhesive for bonding Carbon Fibre Reinforced Polymer (CFRP) fabrics to a concrete surface. The epoxy adhesive which is the generally used adhesive for CFRP shows a low thermal performance. As a potential solution, Engineered Cementitious Composite (ECC) mortar was modified as a cementitious adhesive with improved thermal insulation. The ECC adhesive was developed using locally available class F fly ash, silica sand and Polyethylene terephthalate (PET) fibres other than the generally used cement and water (PET-ECC). The selected mix proportion for PET-ECC achieved a low thermal conductivity of 0.145–0.180 W/mK which limited the heat transfer through the adhesive layer. The effective bond length of the developed PET-ECC adhesive was 125 mm and the corresponding bond strength was 224.9 MPa. The respective bond strength was further enhanced up to 570.28 MPa by sticking river sand on top of CFRP fabric using epoxy adhesive before bonding it to the concrete surface using the PET-ECC adhesive. The use of PET-ECC as the bonding agent to strengthen compression members with CFRP confinement yielded an average strength enhancement of 34%.

Partially replacement of constituent materials in cementitious products using waste materials leads to reduce the CO2 emissions while saving the natural resources and minimize the environmental hazards caused by waste disposal. Development of such an alternative for conventional plaster with better thermal performance, strength and durability characteristics will result in energy savings in the construction and operational phases of buildings. A composite plaster was developed by dry mixing of fine aggregate, bottom ash (BA), Portland cement and poly-carboxylic ether-based admixture. Their phase composition and microstructure morphologies were evaluated using XRD and SEM for a range of compositions and comparisons were made by varying water to cement ratios on the development of the best composition. The results indicate that the morphology and grain dimensions of the developed composite plaster can save 60 % of fine aggregate with effective replacement of bottom ash while maintaining the water to cement ratio of 1.15. A reduction of thermal conductivity by 76 % was noted concerning to the conventional plaster. The application of this waste based composite plaster in model units indicated good adhesion properties with better surface texture and good water resistance characteristics. No thermal or shrinkage cracks appeared in the operational phase of the models under outdoor exposure of two years to the tropical environment. A numerical model was also developed to predict the indoor wall temperature variation of a compartment finished with the said composite plaster and a comparison was made with the measured temperature cycle during outdoor exposure. A parametric study was conducted to compare the heat balance of the developed models with available systems and different climate variations.

The use of green materials in building construction has become trendy to improve the thermal comfort within the buildings with minimized natural resources. This paper presents the development of a cementitious insulated plaster using Expanded Polystyrene (EPS) as partial replacement for fine aggregates. An experimental program was conducted by replacing the fine aggregates in the conventional plaster with EPS in the range of 0–200% by volume. A reduction up to 69% and 53% were noted in thermal conductivity and density, respectively due to the replacement of aggregates with EPS in the conventional mortar. From a trial and error process, the mix with 125% replacement by EPS was selected as the ideal mix for optimum thermo-mechanical performance. A numerical model was developed to examine the heat transfer behaviour through a wall/Plaster composite and the predicted results were in a satisfactory agreement with the experimental results. A reduction of 18% in the decrement factor and an increment of 20% in time lag were noted in the wall panels with the developed EPS-Cement plaster.

EPS (Expanded Polystyrene) is a well-established insulation material in the Civil Engineering Industry. This paper presents an experimental and numerical investigation of cementitious insulation developed using EPS for Carbon Fiber Reinforced Polymer (CFRP) – Concrete composites. An EPS blended insulation was applied to the CFRP/Concrete composites and tested at elevated temperatures. A numerical model was also developed to predict the heat transfer behavior of the CFRP/Concrete composites with the developed insulation under standard fire conditions. The simulations showed that the bond line has reached the glass transition temperature within a short period of time while the insulated members withstood more time. The model results indicated that the CFRP/Concrete which composites with coarser EPS can achieve 75% to 94% of fire resistance, and composites with finer EPS can achieve 83% to 99% of fire resistance than the insulation materials already commercially available.

Epoxy adhesive used as the bonding agent in the Carbon Fibre Reinforced Polymer/concrete bond shows poor thermal performance. Therefore, this experimental study focused on modifying the epoxy adhesive by blending recycled Polyethylene terephthalate (PET) fibres to enhance thermal performance. The single-lap shear test was conducted by varying the fibre content in the epoxy adhesive to determine the optimum PET fibre to develop the modified epoxy adhesive. The optimum PET fibre content was selected as 30% of the volume of epoxy. The modified adhesive showed a successful bond strength enhancement in both ambient and elevated temperature conditions when compared to the pure epoxy adhesive. The mechanical properties were tested for the developed epoxy-based adhesive. The modified epoxy adhesive achieved an average bond strength of 827.31 MPa (at 30 °C) for 150 mm bond length. Although the glass transition temperature of pure epoxy was between 60 °C and 80 °C, it was between 120°C and 150 °C for the modified epoxy adhesive.

Application of insulation on Carbon Fiber Reinforced Polymer (CFRP) strengthened concrete members in building s is essential to preserve the structural integrity during the fire. Investigation on suitable bonding techniques to minimize the usage of insulation without affecting the structural performance may lead to a cost optimum solution for re trofitting projects. An experimental program was conducted to compare the thermal and structural performance of groove d and external bonding techniques. A total of 15 CFRP - Concrete members were exposed to different fire scenarios with and without insulatio n. A numerical model was also developed to predict the effects of sensitive parameters on the thermo - mechanical performance of CFRP/Concrete composite s under standard fire. The results indicated that the application of CFRP laminates in a groove within the nominal cover of the member can save up to 36% of the insulation than the external bonding technique. This study provides d esign recommendations in the form of charts for easy guidance to select a suitable bonding technique, insulation type and applicatio n depending on the feasibility of the project.

Rice Husk (RH) is an agricultural waste which is produced in huge amounts from the milling process of paddy rice. Rice Husk Ash (RHA) is a by-product material obtained from the combustion of rice husk. The amorphous silica-rich RHA (84-90 wt%) has a wide range of applications. This research focused on the possibility of utilizing RHA in the process of developing a mortar with low thermal conductivity to enhance the thermal comfort in concrete and masonry buildings. The thermal conductivity of mortar was determined by Lee’s Disc method, and the results were compared to the data for conventional mortar as well as commercial thermal insulation materials. The results indicate a significant reduction in thermal conductivity in the mortar developed with RHA

The use of Carbon Fibre Reinforced Polymer (CFRP) composites have become a prominent solution for retrofitting the concrete structures. Though CFRP composites have superior mechanical properties, resistance of CFRP/Concrete composites to fire remains unsolved. The degradation of the epoxy resin at elevated temperature makes the FRP composites weaker due to the low glass transition temperature of epoxy resin. A review on CFRP-concrete composites at elevated temperature and available insulation systems are presented in this paper. The paper summarises the results obtained from experimental and numerical studies on the fire performance of CFRP-concrete composites. Hence, it was concluded that by providing appropriate insulation system, the CFRP-concrete members can be protected from fire. However, there are several drawbacks with available insulation systems, such as high cost, addition of dead load, and less aesthetic appearance which are also discussed in this paper.

Strengthening of deteriorated steel elements using Carbon Fiber Reinforced Polymer (CFRP) materials is widely gaining appeal. Since the majority of applications can be seen in outdoor structures, the evaluation of long-term behaviour under various environmental conditions is an important aspect. In the present study, the bond performance of CFRP strengthened steel double strap joints immersed in distilled water at ambient (28 °C) and elevated (40 °C) temperatures for six months was examined. A total of twelve specimens were tested including four control specimens and eight number of conditioned specimens. A numerical model was also developed. The model results are in good agreement with experimental results. The bond shear stress – local slip curves were then developed for each environmental condition using model predicted strain readings. The bond-slip models showed a bond shear strength degradation of about 24 % at 28 °C and 30 % at 40 °C within the exposure duration of six months.

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.

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).

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.

Elevated temperature curing increases the glass transition temperature of the polymeric bond between CFRP and steel. Fire performance of an elevated temperature cured and ambient temperature cured CFRP strengthened steel I beam was evaluated using a numerical model. The effects of a range of thicknesses and conductivities of insulation layers were also analyzed. Model results are in good agreement with the theoretical results. Insulation is a compulsory requirement for CFRP strengthened steel I sections. On average, a 35% increase in fire performance was noted at elevated temperature cured CFRP strengthened I beams compared to the ambient cured I beam.

Carbon Fiber Reinforced Polymer (CFRP) retrofitted application has become widespread in the last decade due to its unique advantages. This paper presents the punching shear strength enhancement of flat slabs which can be achieved with CFRP by embedding it through the slab section and attaching it externally on the tension surface. A common anchorage system that would optimise the use of CFRP has been introduced in CFRP shear reinforcement. The maximum capacity increment in punching shear was 22% and further improvements to achieve even higher load capacities have been discussed. Theoretical expressions have also been compared with the experimental results with recommendations.

A numerical model was developed to investigate the flexural performance of Carbon Fibre Reinforced Polymer (CFRP) strengthened concrete curved beams subjected to outof-plane bending. In this study, near surface mounted (NSM) technique has been used to strengthen the curved beams due to easy of application in curved beams subjected to out-of-plane bending. A commercially available finite element analysis software was used to simulate a numerical model and a nonlinear analysis was carried out. Alternative bonding arrangements were considered. The results indicate the highest strength performance in the curved beams with CFRP strip bonded in the radial direction of the beams. Further, it was revealed that the CFRP thickness, Elastic Modulus of CFRP, Concrete Grade, and the beam curvature affect the strength enhancement.

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.

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.

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.

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.

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.

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.

Retrofitting of slab-column connections has become a crucial concern as they are highly vulnerable to fail in punching shear failure. External strengthening is practically feasible rather than the post-installation of shear reinforcement in deteriorated slab-column connections. Hence, the behavior of medium scale slab-column junctions strengthened with alternative arrangements of Carbon Fiber Reinforced Polymer (CFRP) was studied. Numerical models were also developed to analyze bond behavior. The model predicted performances are in good agreement with the test results. The maximum average punching shear enhancement of 46% was observed from the specimens with CFRP plates attached to the tension face of the specimens with steel end anchors. Keywords: CFRP, External strengthening, Numerical modeling, Punching shear enhancement, Slab/column interface

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.

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.

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.

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.