1、 1 Structural Rehabilitation of Concrete Bridges with CFRP Composites-Practical Details and Applications Riyad S. ABOUTAHA1, and Nuttawat CHUTARAT2 ABSTRACT: Many old existing bridges are still active in the various highway transportation networks, carrying heavier and faster trucks, in all kinds of
2、 environments. Water, salt, and wind have caused damage to these old bridges, and scarcity of maintenance funds has aggravated their conditions. One attempt to restore the original condition； and to extend the service life of concrete bridges is by the use of carbon fiber reinforced polymer (CFRP) c
3、omposites. There appear to be very limited guides on repair of deteriorated concrete bridges with CFRP composites. In this paper, guidelines for nondestructive evaluation (NDE), nondestructive testing (NDT), and rehabilitation of deteriorated concrete bridges with CFRP composites are presented. The
4、effect of detailing on ductility and behavior of CFRP strengthened concrete bridges are also discussed and presented. KEYWORDS: Concrete deterioration, corrosion of steel, bridge rehabilitation, CFRP composites. 1 Introduction There are several destructive external environmental factors that limit t
5、he service life of bridges. These factors include but not limited to chemical attacks, corrosion of reinforcing steel bars, carbonation of concrete, and chemical reaction of aggregate. If bridges were not well maintained, these factors may lead to a structural deficiency, which reduces the margin of
6、 safety, and may result in structural failure. In order to rehabilitate and/or strengthen deteriorated existing bridges, thorough evaluation should be conducted. The purpose of the evaluation is to assess the actual condition of any existing bridge, and generally to examine the remaining strength an
7、d load carry capacity of the bridge. 1 Associate Professor, Syracuse University, U.S.A. 2 Lecturer, Sripatum University, Thailand. One attempt to restore the original condition, and to extend the service life of concrete bridges is by the use of carbon fiber reinforced polymer (CFRP) composites. In
8、North America, Europe and Japan, CFRP has been extensively investigated and 2 applied. Several design guides have been developed for strengthening of concrete bridges with CFRP composites. However, there appear to be very limited guides on repair of deteriorated concrete bridges with CFRP composites
9、. This paper presents guidelines for repair of deteriorated concrete bridges, along with proper detailing. Evaluation, nondestructive testing, and rehabilitation of deteriorated concrete bridges with CFRP composites are presented. Successful application of CFRP composites requires good detailing as
10、the forces developed in the CFRP sheets are transferred by bond at the concrete-CFRP interface. The effect of detailing on ductility and behavior of CFRP strengthened concrete bridges will also be discussed and presented. 2 Deteriorated Concrete Bridges Durability of bridges is of major concern. Inc
11、reasing number of bridges are experiencing significant amounts of deterioration prior to reaching their design service life. This premature deterioration considered a problem in terms of the structural integrity and safety of the bridge. In addition, deterioration of a bridge has a considerable magn
12、itude of costs associated with it. In many cases, the root of a deterioration problem is caused by corrosion of steel reinforcement in concrete structures. Concrete normally acts to provide a high degree of protection against corrosion of the embedded reinforcement. However, corrosion will result in
13、 those cases that typically experience poor concrete quality, inadequate design or construction, and harsh environmental conditions. If not treated a durability problem, e.g. corrosion, may turn into a strength problem leading to a structural deficiency, as shown in Figure1. Figure1 Corrosion of the
14、 steel bars is leading to a structural deficiency 3 Non-destructive Testing of Deteriorated Concrete Bridge Piers In order to design a successful retrofit system, the condition of the existing bridge should be thoroughly evaluated. Evaluation of existing bridge elements or systems involves review of
15、 the asbuilt drawings, as well as accurate estimate of the condition of the existing bridge, as shown in Figure2. Depending on the purpose of evaluation, non-destructive tests may involve estimation of strength, salt contents, corrosion rates, alkalinity in concrete, etc. Figure2 Visible concrete di
16、stress marked on an elevation of a concrete bridge pier Although most of the non-destructive tests do not cause any damage to existing bridges, some NDT may cause minor local damage (e.g. drilled holes & coring) that 3 should be repaired right after the NDT. These tests are also referred to as parti
17、al destructive tests but fall under non-destructive testing. In order to select the most appropriate non-destructive test for a particular case, the purpose of the test should be identified. In general, there are three types of NDT to investigate: (1) strength, (2) other structural properties, and (
18、3) quality and durability. The strength methods may include； compressive test (e.g. core test/rebound hammer/ ultrasonic pulse velocity), surface hardness test (e.g. rebound hammer), penetration test (e.g. Windsor probe), and pullout test (anchor test). Other structural test methods may include； con
19、crete cover thickness (cover-meter), locating rebars (rebar locator), rebar size (some rebar locators/rebar data scan), concrete moisture (acquameter/moisture meter), cracking (visual test/impact echo/ultrasonic pulse velocity), delamination (hammer test/ ultrasonic pulse velocity/impact echo), flaw
20、s and internal cracking (ultrasonic pulse velocity/impact echo), dynamic modulus of elasticity (ultrasonic pulse velocity), Possions ratio (ultrasonic pulse velocity), thickness of concrete slab or wall (ultrasonic pulse velocity), CFRP debonding (hammer test/infrared thermographic technique), and s
21、tain on concrete surface (visual inspection). Quality and durability test methods may include； rebar corrosion rate field test, chloride profile field test, rebar corrosion analysis, rebar resistivity test, alkali-silica reactivity field test, concrete alkalinity test (carbonation field test), concr
22、ete permeability (field test for permeability). 4 Non-destructive Evaluation of Deteriorated Concrete Bridge Piers The process of evaluating the structural condition of an existing concrete bridge consists of collecting information, e.g. drawings and construction & inspection records, analyzing NDT
23、data, and structural analysis of the bridge. The evaluation process can be summarized as follows: (1) Planning for the assessment, (2) Preliminary assessment, which involves examination of available documents, site inspection, materials assessment, and preliminary analysis, (3) Preliminary evaluatio
24、n, this involves: examination phase, and judgmental phase, and finally (4) the cost-impact study. If the information is insufficient to conduct evaluation to a specific required level, then a detailed evaluation may be conducted following similar steps for the above-mentioned preliminary assessment, but in-depth assessment. Successful analytical evaluation of an existing deteriorated concrete bridge should consider the actual condition of the bridge and level of deterioration of various elements. Factors, e.g. actual
