High-temperature Resistance Performance of An Inorganic Adhesive for Concrete Structures Strengthened with CFRP Sheets

Organic epoxy matrices have been widely used in the FRP reinforcing technique, but they have serious disadvantages of poor high-temperature resistance. An inorganic adhesive is invented to replace the organic adhesive. For the inorganic adhesive at normal temperature and different high temperatures, the microstructure and phase composition are investigated by means of X-ray diffraction （XRD） and SEM respectively. Results show that inorganic adhesive can resist at least 600 ℃ high temperature. Fire-resistance performance of inorganic adhesive can meet the requirements of fiber reinforced polymer （FRP） strengthened RC structures.

Experimental research on refractory performance of reinforced concrete beams strengthened with CFRP sheets bonded with an inorganic adhesive

To meet the requirement of fire endurance for concrete structures strengthened with CFRP sheets, this study develops an inorganic adhesive whose strength at 600 ℃ is not lower than that at normal room temperature. The inorganic adhesive is then used to bond CFRP sheets on reinforced concrete beams in order to strengthen them. The fire protection of the CFRP sheets is done using the thick-type fireproofing coatings for tunnel ( TFCT) and steel structure ( TFCSS) respectively. Four specimens are tested in the furnace together. Specimens are exposed to fire for 1. 5 h in according to the ISO834 standard fire curve,and then naturally cooled for 1 h. In the tests,the largest displacements at the mid-span positions of specimens are only from 1 /1400 to 1 /318 of actual span corresponding to the highest temperatures from 300 ℃ to 470 ℃. After the specimens are naturally cooled to the normal temperature and the fireproofing coatings are then removed,it can be seen that the CFRP sheets keep in a good state,which indicates that CFRP sheets can be tightly bonded on the concrete and work well together with the concrete beams during and after fire. Besides,the tests also verify that the fire performance of TFCT is superior to TFCSS for the strengthened beams.

Flexural behavior of composite beams after the ultimate limit state externally strengthened with CFRP sheets bonded with high-temperature resistant matrix

In this paper the alkali-activated slag cementitious materials(AASCM)which strength at 600 ℃ is larger than that of AASCM at room temperature,were prepared to paste CFRP sheets to strengthen four simply supported unbonded prestressed composite beams encased circular steel tube truss after ultimate limit state.Test on flexural behavior of these four beams was performed.Moreover,normal section load-bearing capacity of these beams and the curve load-deflection at mid-span were obtained.Experimental results show that it is feasible to strengthen concrete members with CFRP sheets bonded with AASCM.Based on the experimental results and theoretical study,computational method of stiffness is proposed for calculating bending rigidity and normal section load-bearing capacity of concrete simply supported beams strengthened with CFRP sheets bonded with AASCM.Formula of bending rigidity calculation was founded which results are in good agreement with testing data.

Numerical Determination of Shear Strength of Steel Reinforced Concrete Column Strengthened by CFRP Sheets

The earthquake resistant property of reinforced concrete members depends on the interaction between reinforcing bars and surrounding concrete through bond to a large degree. In this paper a general system aimed at dealing with the failure analysis of reinforced concrete columns strengthened with carbon fiber reinforced plastic (CFRP) sheets including bond slip of the anchored reinforcing bars at the foot of the columns is presented. It is based on the yield design theory with a mixed modeling of the structure, according to which the concrete material is treated as a classical two dimensional continuum, whereas the longitudinal reinforcing bars are regarded as one dimensional rods including bond slip at the foot of the columns. In shear reinforced zones both the shear CFRP sheets and transverse reinforcing bars are incorporated in the analysis through a homogenization procedure and they are only in tension. The approach is then implemented numerically by means of the finite element formulation. The numerical procedure produces accurate estimates for the loading carrying capacity of the shear members taken as an illustrative application by correlation with the experimental results, so the proposed approach is valid.

Seismic retrofitting of severely damaged RC connections made with recycled concrete using CFRP sheets

An experimental and numerical program is carried out in this research to investigate the influence of CFRP sheets on the cyclic behavior of unconfined connections made with recycled concrete.Cement is partially replaced by silica fume,iron flling and pulverised fuel ash using two different percentages:15%and 20%.Each specimen is partially loaded at the first stage and then specimens are repaired using CFRP sheets.The repaired specimens are then laterally loaded until failure.In addition,a finite element model is built in ABAQUS and verfed using the experimental results.The experimental results have shown that the repaired specimens have regained almost double the capacity of the un-repaired specimens and hence the adopted repair configuration is recommended for retroftting seismically vulnerable RC connections.Increasing cement replacement percentage by silica fume,fuel ash or iron flling from 15%to 20%has reduced joint carrying capacity and weakened the joint.It is recommended using 15%pulverised fuel ash or silica fume as cement partial replacement to enhance the strength and ultimate drift of beam-column joints under cyclic loading.Iron filling concrete is also recommended but the enhancement is relatively less than that found with pulverised fuel ash concrete and silica fume concrete.

Square concrete columns strengthened with carbon fiber reinforced plastics sheets at low temperatures

Twenty-one square concrete columns were constructed and tested. The testing results indicate that bonded carbon fiber reinforced plastics(CFRP) sheets can be used to increase the strength and improve the serviceability of damaged concrete columns at low temperatures. The failure of the specimens,in most cases,takes place within the middle half of the columns. And the failure of strengthened columns is sudden and explosive. The CFRP sheets increase both the axial load capacity and the ultimate concrete compressive strain of the columns. The ultimate loads of strengthened columns at-10,0 and 10 ℃ increase averagely by 9.09%,6.63% and 17.83%,respectively,as compared with those of the control specimens. The axial compressive strength of strengthened columns is related to the curing temperatures. The improvement of axial compressive strength decreases with reducing temperature,and when the temperature drops to a certain value,the improvement increases with falling temperature.

Bonding Characteristics and Flexural Stiffening Effect of Carbon Fibre Reinforced Plastics Strand Sheets Bonded to Steel Beams

Corrosion of steel structures is unavoidable and the structural performance decreases dramatically due to the corrosion. As a repairing method for corroded steel members, bonding carbon fiber sheets with resin had been developed. The purpose of this study is to propose the flexural strengthening method for steel members by using CFRP （carbon fiber reinforced polymer） strand sheets. In order to clarify the stiffening effect and the debonding characteristics of CFRP strand sheets, and to optimize the strengthening design specifications, the flexural tests using high tension steel beams strengthened with CFRP strand sheets are performed. Two cases of experiments are carried out. In Experiment 1, the result from previous research is reflected in the strengthening design. Moreover in Experiment 2, the debonding characteristics obtained from Experiment 1 are reflected. As a result, it was clarified that CFRP strand sheets have stiffening effect equivalent to the theoretical value and its debonding property is practically high enough when FRP （fiber reinforcement polymer） sheets have an appropriate bonding length.