Study On Key Parameters And Anchorage Mechanism Of Pull-out And Tensile Performance Of C-FRCM Composites

Fabric-reinforced cementitious matrix(FRCM)is a new cementitious composite made of the mortar and the dry fiber fabric.As an externally bonded strengthening composite system,FRCM has been proved to be an effective alternative to strengthen and repair reinforced concrete(RC)structures or masonry structures in recent years due to its excellent compatibility with existing concrete structures.However,it is found that the non-uniform bonding properties of the fiber-mortar interface remain to be solved,which causes the fiber slippage failure and induces the lower fiber bundle efficiency,and thus the mechanical properties of the fiber cannot be utilized efficiently.Therefore,how to develop a simple,fast and efficient method to improve the bonding properties of the fiber–mortar interface and increase the fiber bundle efficiency,and thus enhance the performance of the FRCM becomes a key technical problem to be solved at present.This paper developed a novel method,which is fiber bundle end bending anchorage,intending to improve the fiber-mortar interface bonding performance and the basic mechanical properties of FRCM composites.A series of experiments have been carried out based on the fiber-mortar interface level and the macro-mechanical level of the FRCM through the pull-out test and the uniaxial tensile test.The main research contents and results in this paper include:(1)Investigated the pull-out performance of carbon fiber bundles.The influence of various bond lengths,anchorage lengths,anchorage angles,the number of fiber bundles and the mortar strength on the fiber bundle peak pull-out stress were investigated by the pull-out test with 275 specimens,which has confirmed the effectiveness of the fiber bundle end bending anchorage system to enhance the synergetic behavior in fiber bundles,and therefore the fiber bundle efficiency of carbon-FRCM is improved.The test results highlighted that: i)The anchorage angle has a significant effect on the peak pull-out stress of the specimen,the peak pull-out stress of the specimens showed an increasing trend with the increase of the anchorage angle,and the fiber bundles were subjected fractured failure accompanied with the maximum peak pull-out stress and fiber bundle efficiency when the anchorage angle was 180°.ii)Moreover,the bond length and the anchorage length jointly affect the peak pull-out stress: the anchorage length has little effect on the peak pull-out stress in the case of the anchorage length larger than the effective anchorage length.Besides,the end bending anchorage system affects the peak pull-out stress and fiber bundle efficiency more significantly at relatively short bond length.Compared with those specimens which were of the same total length but without bending anchorage,the peak pull-out stress in different series specimens with bending anchorage increased between 49%~165%.iii)Furthermore,the specimens with five fiber bundles showed lower peak pull-out stress than those specimens with a single fiber bundle,which indicated that peak pull-out stress decreases as the number of fiber bundles increases.iv)Finally,ESEM images showed the increased ratio of the fractured fiber filaments to the pull-out fiber filaments within bending anchorage specimens,which reveals the positive effect of end bending anchorage.(2)Investigated the uniaxial tensile performance of C-FRCM.The tensile stress-strain properties of carbon-FRCM composites were studied by the uniaxial tensile test.The tabs contact lengths,the number of fabric mesh layers,the strength of the mortar,and the end bending anchorage of the fiber bundles were assessed based on the test results of 48 specimens.In particular,different effects of partly parameters between the pullout test and the uniaxial tensile test are discussed.The test results indicated that: i)The ultimate tensile stress and fiber bundle efficiency of the specimens with fiber bundles end bending anchorage is higher 10.4%~ 21.1% than those specimens without fiber bundles end bending anchorage,although the load response stages are similar.ii)Moreover,the ultimate tensile stress of the carbon-FRCM increases with the tabs contact length,while it showed only a slight effect under the tabs contact length larger than 150mm;iii)The crack distribution and mechanical properties of the uniaxial tensile specimens were affected by the number of fiber fabric mesh layers.Additionally,the ultimate load increases with the number of fiber fabric mesh layers,and the T4 series specimens showed smaller crack space and higher ultimate stress than the T1 and the T2 series specimens.iv)A different effect of the mortar strength on the fiber bundles pull-out performance and the carbon-FRCM uniaxial tensile properties are discussed.The mortar strength showed significant effects on the peak pull-out stress of the fiber bundles and the carbon-FRCM uniaxial tensile crack load,but the effect on the carbon-FRCM ultimate tensile stress is marginal.(3)The numerical simulation of the pull-out performance of carbon fiber bundles has been carried out based on the trilinear bond-slip constitutive relationship,which is in good agreement with the experimental results.