Carbon Fabric Reinforced Cementitious Matrix Research Articles

Mechanical performance and crack pattern analysis of aged Carbon Fabric Cementitious Matrix (CFRCM) composites

We discuss the effect of environmental exposure on mechanical performance of impregnated Carbon Fabric Reinforced Cementitious Matrix (CFRCM) composite. Following the recently published ICC-ES AC434 guidelines, mechanical performance of prismatic composite specimens is determined on the basis of tensile uni-axial tests. Exposure to saline and alkaline aqueous solutions is considered at 28- as well as 60-day curing time. Special emphasis is placed on crack pattern evaluation as a mean to gain better insight into matrix/fabric bond quality. To this aim, the evolution of the average crack spacing and of the average crack width is determined as a function of strain for all test environments and curing times. It is found that curing time plays a significant role in mitigating the detrimental effect of aggressive environments. Furthermore, the average crack spacing provides a very reliable measure of matrix/fabric bond degradation at all test stages.

Hybrid NSE/EB technique for shear strengthening of reinforced concrete beams using FRCM: Experimental study

The externally bonded (EB) fabric reinforced cementitious matrix (FRCM) has successfully been used as a structural strengthening for various applications including flexural and shear strengthening of reinforced concrete (RC) beams, flexural strengthening of RC slabs and column confinement. However, the EB-FRCM system is characterized by poor FRCM/concrete bond leading to premature debonding of FRCM off the concrete substrate, particularly for thicker FRCM. The present paper reports on an experimental study on the efficacy of a pioneer form of hybrid near surface embedded and externally bonded technique using FRCM composites (NSEEB-FRCM) for shear strengthening of RC beams. With such a technique, higher thickness of FRCM composites can be applied with less likelihood of debonding that is normally experienced when using the EB-FRCM system. Thirteen shear-deficient medium-scale RC beams were constructed, strengthened in shear and tested under three-point bending test. The test parameters were: (a) FRCM type (polyparaphenylene benzobisoxazole, carbon, and glass), (b) strengthening configuration (full versus intermittent strips), and (c) number of fabric layers.The percentage enhancement in the shear capacity of the beams ranged from 43% to 114% indicating the successful implementation of the strengthening methods provided. An average enhancement in shear capacity of 83%, 72% and 62% were observed in carbon FRCM, glass FRCM and PBO-FRCM, respectively. The failure mode of the strengthened specimens was sensitive to the type and configuration of FRCM in addition to the number of FRCM layers. The strengthening systems also resulted in higher deflection at failure and energy absorption value of the strengthened beams with an average of 94% and 204% relative to the reference specimen, respectively.

Impregnated Carbon Fabric–Reinforced Cementitious Matrix Composite for Rehabilitation of the Finale Emilia Hospital Roofs: Case Study

AbstractIn this paper, the mechanical performance of concrete beams strengthened by an impregnated carbon fabric–reinforced cementitious matrix (CFRCM) composite is investigated. The study is aimed...

Effect of the Fiber Type and Axial Stiffness of FRCM on the Flexural Strengthening of RC Beams

The use of externally-bonded fiber-reinforced polymer (FRP) sheets has been successfully used in the repair and strengthening of both the shear and flexural capacities of reinforced concrete (RC) beams, slabs and columns since the 1990s. However, the externally-bonded FRP reinforcements still present many disadvantages, such as poor performance in elevated temperature and fire, lack of permeability and strength degradation when exposed to ultraviolet radiation. To remedy such drawbacks, the fiber-/fabric-reinforced cementitious matrix (FRCM) has been recently introduced. The FRCM system consists of a fiber mesh or grid embedded in a cementitious bonding material. The present research investigates the flexural strengthening of reinforced concrete (RC) beams with FRCM. The experimental testing included eight large-scale concrete beams, 150 mm × 250 mm × 2400 mm, internally reinforced with steel bars and strengthened in flexure with FRCM. The investigated parameters were the internal steel reinforcement ratio and the FRCM systems. Two steel reinforcement ratios of 0.18 and 0.36 of the balanced reinforcement ratio, as well as three FRCM systems using glass, carbon and PBO fibers were investigated. Test results are presented in terms of load-deflection, load-strain and load-crack width relationships. The test results indicated that the PBO FRCM significantly increased the ultimate capacity of the strengthened RC beams with both low and moderate internal reinforcement ratios compared to the glass and carbon FRCM.

On the effect of curing time and environmental exposure on impregnated Carbon Fabric Reinforced Cementitious Matrix (CFRCM) composite with design considerations

Abstract This paper investigates the effect of curing time and aggressive environmental exposure on the mechanical performance of impregnated Carbon Fabric Reinforced Cementitious Matrix (CFRCM) composite. Following the recently published IIC-ES AC434 guidelines, saltwater, distilled water, alkali and acid resistance are investigated together with freeze-thaw cycles. Mechanical characterization is based on tensile uni-axial tests under deformation control of rectangular-base prismatic specimens. 28- and 60-day curing times are considered for the control environment as well as for saltwater and alkali resistance. Deformation is monitored via digital acquisition. Besides uni-axial tests, experimental results comprise optical and scanning electron microscopy, crack pattern analysis and failure mechanism assessment. Focus is set on the determination of the design limits for the composite system at failure for the tested environments and curing times. In particular, a comparison is drawn with established design criteria already coded for FRP systems, which introduce the concept of safety (or partial) factors. Environmental conversion factors are also defined and calculated on a statistical basis in a twofold manner, as a mean to determine the design strain and strength limits of exposed specimens from the control (unexposed) data. It is found that they provide a convenient method for assessing the composite vulnerability to the aggressive environments at different curing times.

Effectiveness of Fabric-Reinforced Cementitious Matrix in Strengthening Reinforced Concrete Beams

AbstractThis paper reports on the efficiency of fabric-reinforced cementitious matrix (FRCM) in enhancing the flexural capacity and deformational characteristics of RC beams. In the main experimental part of the paper, 12 RC beams, 2,500 mm long, 150 mm wide, and 260 mm deep, were fabricated. The beams had two different steel reinforcement ratios, namely, ρsD12=0.72% and ρsD16=1.27%, representing typical underreinforced beam sections. The strengthened beams utilized two FRCM types, carbon and polyparaphenylene benzobisoxazole (PBO) FRCM systems. In the second part of the work, tensile material characterization tests were performed on the FRCM coupons to determine the tensile characteristics of the FRCM composites. The beams were tested in flexure under four-point loading until failure. Two beams without FRCM strengthening were used as a benchmark. Six beams were externally strengthened using one, two, and three layers of carbon FRCM system. Four beams were strengthened with one and two layers of PBO FRCM ...

Bond characteristics of carbon fabric-reinforced cementitious matrix in double shear tests

This study examined the bond characteristics between fabric-reinforced cementitious matrix (FRCM) systems and concrete. Twenty-seven double-shear specimens were tested under direct shear loading. Two types of cementitious mortars (FRCM specimens) and one type of epoxy (FRE specimens) were used as a matrix. Fabric delamination governed the failure of the FRCM specimens without debonding at the concrete/matrix interface. The FRCM specimens experienced cracking prior to failure whereas the FRE specimens failed suddenly by fabric rupture without cracking. The bond stress of the FRCM specimens at failure was on average 28% lower than that of the FRE specimens. For the same width of the bonded area, the bond stress at failure typically decreased with an increase in the bonded length of the fabric. Similarly, for the same bonded area, the bond stress at failure tended to decrease by increasing the bonded length. This reduction in the bond stress at failure was more pronounced in the FRE specimens than in the FRCM specimens.

FRCM Strengthening of Shear-Critical RC Beams

AbstractThis paper presents the results of an experimental study conducted to investigate the effectiveness of different types of fabric-reinforced cementitious matrix (FRCM) composite systems to strengthen shear critical reinforced concrete (RC) beams. Seven shear-critical RC beams were tested. The test variables included the strengthening material (glass FRCM or carbon FRCM) and the strengthening scheme (side bonded or u-wrapped). The test results revealed that FRCM strengthening is effective in enhancing the load-carrying capacity of shear-critical RC beams. The increase in load-carrying capacity of the FRCM-strengthened beams ranged between 19 and 105%. Both strengthening schemes (side bonded and u-wrapped) exhibited similar behavior, suggesting that the excellent bond of the FRCM to concrete may not require u-wrapped applications for anchorage. The experimental results were also compared with theoretical predictions according to fiber-reinforced polymer (FRP) design guidelines in North America with s...