RC BEAMS SHEAR-STRENGTHENED WITH FABRIC-REINFORCED-CEMENTITIOUS-MATRIX (FRCM) COMPOSITE

The interest in retrofit/rehabilitation of existing concrete structures has increased due to degradation and/or introduction of more stringent design requirements. Among the externally-bonded strengthening systems fiber-reinforced polymers is the most widely known technology. Despite its effectiveness as a material system, the presence of an organic binder has some drawbacks that could be addressed by using in its place a cementitious binder as in fabric- reinforced cementitious matrix (FRCM) systems. The pur- pose of this paper is to evaluate the behavior of reinforced concrete (RC) beams strengthened in shear with U-wraps made of FRCM. An extensive experimental program was undertaken in order to understand and characterize this composite when used as a strengthening system. The labo- ratory results demonstrate the technical viability of FRCM for shear strengthening of RC beams. Based on the experi- mental and analytical results, FRCM increases shear strength but not proportionally to the number of fabric plies installed. On the other hand, FRCM failure modes are related with a high consistency to the amount of external reinforcement applied. Design considerations based on the algorithms proposed by ACI guidelines are also provided

Flexural Strengthening of Two-Way RC Slabs with Textile-Reinforced Mortar: Experimental Investigation and Design Equations

The application of textile-reinforced mortar (TRM) as a means of increasing the flexural capacity of two-way reinforced concrete (RC) slabs is experimentally investigated in this study. The parameters examined include the number of TRM layers, the strengthening configuration, the textile fibers material (carbon versus glass), and the role of initial cracking in the slab. For this purpose six largescale RC slabs were built and tested to failure under monotonic loading distributed at four points. It is concluded that TRM increases substantially the precracking stiffness, the cracking load, the postcracking stiffness, and eventually the flexural capacity of two-way RC slabs, whereas the strengthening configuration plays an important role in the effectiveness of the technique. Simple design equations that provide good estimation of the experimental flexural moment of resistance are proposed

Single-lap shear bond tests on Steel Reinforced Geopolymeric Matrix-concrete joints

YesNowadays Fiber Reinforced Polymers (FRPs) represent a well-established technique for rehabilitation of Reinforced Concrete (RC) and masonry structures. However, the severe degradation of mechanical properties of FRP under high temperature and fire as well as poor sustainability represents major weak points of organic-based systems. The use of eco-friendly inorganic geopolymeric matrices, alternative to the polymeric resins, would be highly desirable to overcome these issues. The present work aims to investigate the bond characteristic of a novel Steel Reinforced Geopolymeric Matrix (SRGM) strengthening system externally bonded to a concrete substrate having low mechanical properties. SRGM composite material consists of stainless steel cords embedded into a fireproof geopolymeric matrix. Single-lap shear tests by varying the bonded length were carried out. The main failure mode observed of SRGM-concrete joints was debonding at the fiber-matrix interface. Test results also suggest the effective bond length. On the basis of the experimental results, a cohesive bond-slip law was proposed.Part of the analyses were developed within the activities of Rete dei Laboratori Universitari di Ingegneria Sismica (ReLUIS) for the research program funded by the Dipartimento di Protezione Civile (DPC), Progetto DPC/ReLUIS 2016–AQ DPC/ReLUIS 2014–2016

Textile-reinforced mortar (TRM) versus fibre-reinforced polymers (FRP) in flexural strengthening of RC beams

The aim of this paper is to compare the flexural performance of reinforced concrete (RC) beams strengthened with textile-reinforced mortar (TRM) and fibre-reinforced polymers (FRP). The investigated parameters included the strengthening material, namely TRM or FRP; the number of TRM/FRP layers; the textile surface condition (coated and uncoated); the textile fibre material (carbon, coated basalt or glass fibres); and the end-anchorage system of the external reinforcement. Thirteen RC beams were fabricated, strengthened and tested in four-point bending. One beam served as control specimen, seven beams strengthened with TRM, and five with FRP. It was mainly found that: (a) TRM was generally inferior to FRP in enhancing the flexural capacity of RC beams, with the effectiveness ratio between the two systems varying from 0.46 to 0.80, depending on the parameters examined, (b) by tripling the number of TRM layers (from one to three), the TRM versus FRP effectiveness ratio was almost doubled, (c) providing coating to the dry textile enhanced the TRM effectiveness and altered the failure mode; (d) different textile materials, having approximately same axial stiffness, resulted in different flexural capacity increases; and (e) providing end-anchorage had a limited effect on the performance of TRM-retrofitted beams. Finally, a simple formula proposed by fib Model Code 2010 for FRP reinforcement was used to predict the mean debonding stress developed in the TRM reinforcement. It was found that this formula is in a good agreement with the average stress calculated based on the experimental results when failure was similar to FRP-strengthened beams

Masonry Walls Strengthened with Fabric-Reinforced Cementitious Matrix Composite Subjected to In-Plane and Out-of-Plane Load

A natural evolution of ferrocement has been the replacement of the reinforcing steel with new composite materials. Not only has this addressed the issue of possible durability problems associated with steel corrosion, but has opened the possibility of using thin-section cementitious products as repair materials. Fabric-reinforced cementitious matrix (FRCM) is a class of composite systems that has recently emerged as an alternative to traditional retrofitting methods like fiber-reinforced polymers (FRP), steel plate bonding, section enlargement, and external post-tensioning for repairing and strengthening reinforced concrete (RC) and masonry structures. FRCM consists of a reinforcing phase (fabrics) embedded into a matrix (cementitious mortar) adhered to concrete or masonry structural members and acts as supplemental, externally-bonded reinforcement. The goal of this dissertation is to experimentally and analytically investigate the effectiveness of FRCM to retrofit existing masonry structures; to evaluate the flexural and shear capacity of FRCM walls; to develop structural design procedures; and, to compare FRCM and FRP externally strengthened masonry walls. The dissertation is articulated in three studies. The first study (Study 1) investigates masonry walls externally strengthened with FRCM subjected to diagonal compression; the second (Study 2) focuses on FRCM strengthened walls subjected to out-of-plane loading; and the third (Study 3) presents a comparison between experimental results in this research program and other research programs using FRP systems when the normalized shear or flexural capacity is related to a calibrated reinforcement ratio

Shear strengthening of un-reinforced concrete masonry walls with fabric-reinforced-cementitious-matrix

In this paper, the in-plane behavior of un-reinforced concrete masonry walls externally strengthened with a fabric-reinforced cementitious matrix (FRCM) system is investigated. The experimental program consists of testing nine un-reinforced concrete masonry walls strengthened on both sides with two different FRCM schemes (one and four reinforcement fabrics). The analytical model as per ACI 549-13 is used to predict the shear capacity of the strengthened walls. The effects of design limitations in the approach proposed by ACI 549-13 are also discussed. Finally, experimental data from other research programs using fiber-reinforced polymer (FRP) composites are presented to demonstrate that when normalized shear capacity is related to a calibrated reinforcement ratio, the two overlay strengthening technologies match well

Out-of-plane strengthening of URM walls with fabric-reinforced-cementitious-matrix (FRCM)

Masonry as a building technology meets many of the attributes of sustainable construction, thus an economical alternative to demolish-rebuild existing deficient masonry structures is to retrofit them with novel strengthening systems. Current retrofit techniques used to improve flexural capacity of un-reinforced masonry (URM) walls include both internal and external reinforcement with common materials, namely: steel bars, plates, and most recently fiber-reinforced polymers (FRPs). However, significant margins exist to advance these rehabilitation systems by addressing economic, technological, and environmental issues. This paper investigates the effectiveness of strengthening URM walls using carbon fabric-reinforced cementitious matrix (FRCM) as a technique to enhance pseudo-ductility and flexural capacity. The paper reports on the results obtained by testing a total of 18 masonry walls made of clay bricks and concrete blocks strengthened with two different FRCM schemes (one and four fabrics) subjected to uniformly distributed out-of-plane loading were tested. Experimental data from other research programs using FRP system are also presented to show that when normalized flexural capacity is related to a calibrated reinforcement ratio, the two technologies provide similar enhancements

In-plane behavior of unreinforced masonry walls strengthened with fabric-reinforced cementitious matrix (FRCM)

Un-reinforced masonry (URM) walls have proven to have low shear strength to withstand in-plane loads caused by earthquakes. Retrofitting masonry walls with novel materials such as fiber-reinforced composites has shown to increase the in-plane shear capacity of the walls and minimize damage by enhancing pseudo-ductility. In this study, a new fabric-reinforced cementitious matrix (FRCM) composite system is applied to URM walls to determine its feasibility as an externally-bonded retrofitting technique. The experimental program consists of testing under diagonal compression a total of 18 wall specimens, made from clay bricks and concrete blocks with two FRCM strengthening reinforcement schemes (one and four plies fabric). The experimental results demonstrate the effectiveness of FRCM strengthening on improving the shear capacity of masonry walls. Experimental data from other research programs using fiber reinforced polymer (FRP) composites are presented to demonstrate that when the normalized shear capacity is related to a calibrated reinforcement ratio, the two technologies show similar enhancements