The use of carbon fiber reinforced polymer (CFRP) composites has been investigated in the past few years as a means to rehabilitate aging concrete structures. The detection of disbonds and delaminations between CFRP laminate and the concrete substrate is a critical issue in this area, as the presence of such defects adversely affects the effectiveness of the reinforcement. Thus, the development of a nondestructive testing (NDT) technique to detect these types of defects is of great interest in this field. Furthermore, any such method should also be capable of verifying the quality of the repair of such defects. Near-field microwave NDT techniques, utilizing open-ended rectangular waveguides, have shown great potential in the past for detecting delaminations and disbonds in complex composite structures. Microwave NDT techniques have the added advantages of providing real-time, noncontact, one-sided, rapid, and robust measurements. This paper presents the experimental results of detecting disbonds in a spec...

Rehabilitation of existing structures with carbon fiber reinforced polymers (CFRP) has been growing in popularity because they offer resistance to corrosion and a high stiffness-to-weight ratio. This paper presents the flexural strengthening of seven reinforced concrete (RC) beams with two FRP systems. Two beams were maintained as unstrengthened control samples. Three of the RC beams were strengthened with CFRP fabrics, whereas the remaining two were strengthened using FRP precured laminates. Glass fiber anchor spikes were applied in one of the CFRP fabric strengthened beams. One of the FRP precured laminate strengthened beams was bonded with epoxy adhesive and the other one was attached by using mechanical fasteners. Five of the beams were tested under fatigue loading for two million cycles. All of the beams survived fatigue testing. The results showed that use of anchor spikes in fabric strengthening increase ultimate strength, and mechanical fasteners can be an alternative to epoxy bonded precured laminate systems.

A series of framed unreinforced masonry (URM) infill walls were retrofitted with modern materials to evaluate the abilities of these materials to mitigate blast effects. The walls were constructed from traditional and alternative masonry materials to assess the applicability of using a wood-fiber fly ash material for infill construction. The walls were tested in the laboratory under static conditions and were evaluated using several criteria: energy absorption, out-of-plane load resistance, out-of-plane deformability, and the reduction of masonry debris scatter upon collapse. Due to the presence of the surrounding frame structure, all of the walls in this program experienced some form of an arching mechanism. The use of a spray-on polyurea material was found to be highly effective in improving URM energy absorption and reducing masonry fragmentation. Infill walls retrofitted with a combination of fiber-reinforced polymer (FRP) grids and polyurea material were found to fail prematurely due to a lack of anc...

The development and advancement of cement-based composites has shown promise in recent years. It is important to examine new materials and technologies so that they can satisfy the ever-changing repair and strengthening application needs in the structural engineering field. This paper presents an experimental study on the behavior of reinforced concrete beams strengthened in shear using an externally applied fiber-reinforced cementitious matrix (FRCM). The first aim of this study is to investigate the effectiveness and the performance of the polyparaphenylene benzobisoxazole fiber-reinforced cementitious mortar (PBO-FRCM) system for shear strengthening. The second aim is to study the shear performance of the PBO-FRCM system in terms of the availability and absence of internal transverse shear reinforcements. A comparison study with previous experimental work and the relevant code is done to evaluate the shear performance of the PBO-FRCM system. The test results include the observed shear contribution of the PBO-FRCM system, the failure mode of the strengthened beams, and the influence of the internal transverse shear reinforcements on the shear performance of the PBO-FRCM system.

Recent research has been conducted to evaluate the benefits provided by externally-applied discrete fiber-reinforced polyurea (DFRP) coating systems. This coating was proposed to allow for ease of construction in repair-retrofit situations and to provide multihazard benefits, ranging from blast or impact fragmentation mitigation to seismic reinforcement and general strengthening. This phase of research investigated the flexural and shear reinforcement capabilities of the systems. Testing parameters included type of structural failure, polyurea, and fiber volume fraction. Additionally, the effects of the thickness of the composite system were considered. Concrete beam specimens were fabricated and coated per the designed test matrix and subjected to four-point bending. Analysis was based on ultimate capacity, deflection, overall ductility, and the qualitative observations of coating adhesion and fragmentation confinement. In addition, a theoretical model was developed and validated to describe the ...