NSM FRP STRENGTHENING RC BEAMS USING HIGH TG FRPS &amp; CEMENTITIOUS ADHESIVES – RESPONSE AT AMBIENT AND ELEVATED TEMPERATURE
Creators: name: Del Prete, Iolanda
Publisher: name: Università degli Studi di Napoli Federico II
Year: 2015

description: The aging of the built heritage and infrastructures throughout the civil and industrialized world, as well as their deterioration due to environmental effects, and/or changing in service demand, lead to increasing interest in novel techniques aimed to design, maintain and rehabilitate concrete structures.
Among the available strengthening techniques for improving the performance of concrete structures, the strengthening with Fibre Reinforced Polymers (FRP) gained huge and fast popularity during the last twenty years in the field of civil engineering. 
In the field of external strengthening of RC members the strengthening technique that experienced a widespread in the recent years is the Near Surface Mounted (NSM) strengthening system, in which the FRP is placed into the groove, cut into the surface of structural members, and bonded through an adhesive (epoxy resin or cement mortar). Several studies demonstrated that NSM with epoxy adhesive exhibits a better bond behaviour than EBR. Moreover, NSM is less prone to external attack, since the FRP is completely embedded in the adhesive. Despite that, the effectiveness of epoxy adhesive may be affected by high temperature, whereas cementitious adhesive may offer better performance than epoxies, keeping low the temperature in the FRP.
The available literature about the behaviour of NSM FRP strengthened RC members is still limited, if compared to that available for EBR strengthening technique. Even worse is the knowledge about NSM with cementitious adhesive in not ordinary condition (fire). For this reason, very limited indications are available in the current codes for designing and predicting the capacity of the NSM strengthened members.
Keeping that in mind, the thesis shows a research project undertaken on a high T_g FRP strengthening system bonded in a groove (NSM) with cementitious adhesive, aimed to define its response at ambient and at elevated temperature.
The Chapter 2 of the Thesis presents a review of available literature on the behaviour of both NSM and EBR flexural strengthening applications for reinforced concrete members. Firstly, an overview of the main thermal and mechanical properties of the commercial FRPs and adhesives is reported. Then, the most recent experimental activities conducted on EBR and NSM, both at ambient and high temperature are summarized. Finally, the available international and national codes and guidelines are cited.
Chapter 3 provides information about the techniques commonly used to assess the main thermal and mechanical properties of structural materials. Particularly, the most common techniques for measuring the thermal properties, such as Tg and Td of polymeric materials are shown. Moreover, the results of the tests, e.g., Dynamic Mechanic Analysis (DMA), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC), conducted on a novel commercial CFRP bar are shown. In addition, the results of thermal conductivity tests of CFRP and cementitious grout are discussed. Finally, the results of the tests conducted for the mechanical characterization of the concrete, the steel bars, the cementitious grout and the CFRP bar, used to manufacture the above-mentioned beams, are shown.
The Chapter 4 summarizes the results of the bond pull-out tests conducted on the new commercial cementitious-bonded CFRP NSM strengthening system, by varying the bond affecting parameters. Moreover, a comparison between the performances of this strengthening system and the performances of a resin-bonded CFRP NSM strengthening system is also shown.
The Chapter 5 shows the design of the un-strengthened and strengthened beams with a prediction of their flexural capacity by means of cross sectional analyses. Moreover, a photographic report of the manufacturing and strengthening stages, the test setup and of the instrumentation of the beams is also shown. Particular attention is dedicated to the Digital Image Correlation (DIC), nowadays considered as innovative and powerful technique for displacements and strains measuring. Finally, the results of the tests of NSM FRP strengthened reinforced concrete beams, performed at both ambient and elevated temperature, by varying also the heating configuration, are discussed. 
The Chapter 6 reports a detailed description of the finite element models implemented in SAFIR 2011 for the thermal analysis of the tested NSM FRP strengthened RC beams, subjected to both the non-standard heating history recorded during the experimental tests and to the standard fire curve ISO834. The results of the thermal analyses, compared with the experimental results, are also provided and discussed. Finally, useful fire safety design criteria of NSM FRP strengthened RC beams are provided, based on the results of thermo-mechanical analysis, conducted on this structural typology.