Dr D Pearson-Kirk, M S Lever & I S Motyl, Mouchel Limited, Exeter, UK
Despite the use of design procedures and construction practices that have been developed over many years, the failure and unexpectedly early deterioration of structures has become a matter of considerable concern in many countries. One effect of this problem is that significant expenditure has to be diverted from capital works to the management of existing structures.
The paper contains a review of the performance of structures and the benefits of inspections of higher risk structures being accompanied by targeted testing. A phased approach is described that enables higher risk structures to be identified and prioritised for investigation. Investigations need to be carried out by well-qualified dedicated technical staff, with results being interpreted by experienced engineers. The condition of structures can then be accurately assessed, the extent, severity and causes of any deterioration determined, and any appropriate management actions identified with confidence.
Case studies from Europe and the United States are presented that cover the identification of higher risk structures, determining the causes, extent and severity of defects, avoiding mis-diagnoses and determining appropriate courses of action. Subsequent changes may then be made to design standards, specifications, construction procedures and to the training of staff that will assist in maintaining the best value of the assets.
Certain of the ideology currently used in the management of structures needs to be changed in order to avoid failures and unexpectedly early deterioration of structures in the future. Design and maintenance engineers need to be educated as to the benefits of condition monitoring in the identification of causes of deterioration, together with an improved understanding of the assessment and control of deterioration.
It is well known that steel corrodes and, when embedded in concrete, this expansive reaction cracks the concrete and forces the cover concrete to spall away. Stopping this process is more complex than chipping back the loose concrete and replacing it. Whilst this may fix the direct area of repair it does nothing to improve the situation in adjacent parts of the structure and may even make matters worse. This paper will look at the basic electro-chemical corrosion mechanism with steel embedded in concrete and examine the impressed current cathodic protection systems which have been implemented on three recent contracts to arrest further rusting.
1202
HYBRID ELECTROCHEMICAL TREATMENT OF PASTON INTERCHANGE BRIDGES, UK
A Higson, D Dudeney, M Burrows, Balvac, Sutton Weaver, N Davison, S Holmes, M Davison CP-Tech, Nottingham, UK
Chloride induced corrosion on bridge structures is well documented. Common options to deal with the corrosion attack are to repair spalled concrete and/or utilise electrochemical treatments. Paston interchange comprises two over-bridges that carry the A47 over the A15 in Peterborough: both of which have suffered extensive concrete damage from chloride induced corrosion. This paper details the installation of a hybrid electrochemical treatment system to offer long term protection to the two bridges. The hybrid treatment system utilises a discrete anode in an initial short term impressed current re-passivation phase, then a galvanic phase to offer long term protection. The design of the hybrid system, installation procedure and monitoring data obtained following installation are detailed.
EXPERIENCE WITH EVALUATING BRIDGE DECK DETERIORATION WITH GROUND PENETRATING RADAR
A P Annan & J D Redman, Sensors & Software, Mississauga, ON, Canada
Ground penetrating radar (GPR) has been promoted as an effective means for assessing the state of concrete deterioration in bridge decks for several decades. The method has met with mixed success and is still not adopted widely. Constant development is making high speed GPR mapping more affordable and systems more widely available and easier to deploy. For the many years, we have developed highway speed ground coupled GPR surveying platforms with one of the main applications being rapid examination of bridge decks. American Society for Testing and Materials (ASTM) standards proscribe a procedure that should be followed. The standard was written primarily for air launched GPR measurements and then modified to ground coupled GPR. Our experience indicates the much higher resolution ground coupled enable more exact analysis incorporating both velocity and attenuation properties. Further, the proscribed process ignores the impact of depth and other variables in the analysis which advanced practitioners know are major limitations.
Using both the high speed ground coupled GPR system as well as small scale surveys using cart mounted and handheld GPR’s, we have extensively tested ground coupled measurements and evolved processing to provide cost effective deck deterioration mapping. In this paper, we will describe the work flow we have evolved and demonstrate successful application of the methodology.
1368
USING 3D GPR, LASER SCANNER AND HIGH PRECISION THERMAL CAMERA TECHNIQUES IN CONCRETE BRIDGE DECK CONDITION SURVEYS
A Leppala, T Saarenketo, P Varin & P Maijala, Roadscanners Oy, Tampere, Finland
Ground penetrating radar (GPR) has been promoted as an effective means for assessing the state of concrete deterioration in bridge decks for several decades. The method has met with mixed success and is still not adopted widely. Constant development is making high speed GPR mapping more affordable and systems more widely available and easier to deploy.
For the many years, we have developed highway speed ground coupled GPR surveying platforms with one of the main applications being rapid examination of bridge decks. American Society for Testing and Materials (ASTM) standards proscribe a procedure that should be followed. The standard was written primarily for air launched GPR measurements and then modified to ground coupled GPR. Our experience indicates the much higher resolution ground coupled enable more exact analysis incorporating both velocity and attenuation properties. Further, the proscribed process ignores the impact of depth and other variables in the analysis which advanced practitioners know are major limitations.
Using both the high speed ground coupled GPR system as well as small scale surveys using cart mounted and handheld GPR’s, we have extensively tested ground coupled measurements and evolved processing to provide cost effective deck deterioration mapping. In this paper, we will describe the work flow we have evolved and demonstrate successful application of the methodology.
1138
STRUCTURAL EVALUATION OF SLAB REHABILITATION BY METHOD OF HYDRODEMOLITION AND LATEX MODIFIED OVERLAY
Concrete overlays of concrete bridge decks are common practice for many transportation authorities and are expected to increase the service life of the underlying concrete deck on the order of 20 years. Nonetheless, many authorities do not permit the overlay to be accounted for in the structural load rating of the repaired deck. This effectively restricts overlays to being relatively thin thereby limiting the utility of overlays as a tool for maintaining a sustainable bridge infrastructure. The authors challenge the assertion that overlays must remain non-structural. The objective of this work is to provide laboratory-based experimental verification and assessment of the performance of reinforced concrete bridge deck slabs rehabilitated by means of hydrodemolition (HD) followed by the application of a latex modified concrete (LMC) overlay. The fundamental objective is to determine whether the overlay may be considered composite with the residual deck and under what conditions composite behaviour may be assumed in eventual load rating of the rehabilitated deck.
Tests of ten full-scale laboratory specimens and four decommissioned bridge slabs (having marked existing damage) are presented. The principal parameter investigated is the depth of HD and subsequent LMC overlay. Depths ranging from 7% to 50% of the original slab depth are considered and, in all but the thinnest cases, the overlay does not increase the overall depth of the slab (an important consideration on existing bridges that must be compatible with existing roadway elevations). Results are considered in terms of overall slab performance including cracking, moment-curvature response and, importantly, behaviour and performance of the LMC-concrete interface. In all cases, LMC-repaired slabs demonstrated analytically-predictable behaviour marginally superior to control monolithic slabs. The results clearly demonstrate that not only is composite action between the overlay and residual slab established and maintained, the interface, when constructed correctly, does not affect slab behaviour.
1274
GPR ANALYSIS OF BRIDGEDECK CONSTRUCTION AND THE DETECTION OF DELAMINATION
E Carrick Utsi & V Utsi, Utsi Electronics Ltd, Cambridge, A Birtwisle, Atlas Geophysical Ltd, Rugby, UK
Ground Penetrating Radar (GPR) is a commonly used investigation technique for examining the structure and potential structural faults in bridgedecks. In order to detect delamination at an early stage, it is useful to deploy a very high frequency GPR. Although this limits the depth of penetration, since the upper asphaltic layers tend to be thin, the finer target resolution is very useful.
Simulations and the practical results of commercial GPR surveys are used to illustrate the detection of delamination within the first 200mm of surface using a 4GHz antenna. Potential problems such as the limitations of frequency and the use of materials unsuited to GPR are briefly discussed.
It can be useful to carry out this type of survey at speed although this requires the antenna to be lifted off the bridgedeck surface. In theory horn antennas are more efficient than other types of antenna for this mode of operation as they should not require ground coupling. The effect of increasing antenna height above the surface is described and illustrated with reference to a 4GHz horn antenna used to detect the position and depth of bridgedeck reinforcement. The conclusions reached are that good ground coupling is essential for optimum detection unless a very high frequency horn antenna is used; that it is important to select the right frequency for the task; and that very high frequency antennas are useful for examining delamination in the wearing course, allowing such surveys to be completed at traffic speeds.
1168
REPAIR AND MAINTENANCE OF DELAMINATED REINFORCED CONCRETE DECKS CAUSED BY DEICING SALTS IN HOKURIKU EXPRESSWAY IN JAPAN
Y Ishikawa & N Arima, Central Nippon Highway Engineering, Ishikawa, Kanazawa, M Nagai & E Iwasaki, Nagaoka Univ of Technology, M Moriyama, Central Nippon Expressway, Ishikawa, Japan E Iwasaki,
The use of deicing salt has dramatically increased in the Hokuriku expressway in Japan because of the studded tires banned in 1990. The use of deicing salt is able to keep the safety condition of icy road. However, as an opposite result, the highway structures will be significantly damaged by salt attack. Especially, reinforced concrete bridge decks and bridge girder ends have been damaged by deicing salt. In this paper, the field investigations are carried out at 5 cases of the delaminated reinforced concrete bridge deck in the Hokuriku Expressway. In order to evaluate the condition of reinforced concrete bridge decks, the various non-destructive examinations, hereinafter NDE, are used in the field. NDE are able to detect the delaminated areas in slight condition. In addition, we propose the evaluation of reinforced concrete bridge decks at the top with NDE and at the bottom surface with visual survey is proposed. However, that investigation results aren’t always accurate. Thus, it becomes necessary to cover the inaccuracy of NDE results. In order to cover NDE inaccuracies, we develop a fast accelerate set concrete named as FACET. FACET is concrete mixed directly with chemical powder in a mixer truck. FACET is a low cost concrete which has a flexible supply system that can cover shortage of NDE results. In addition, we carried out feasibility study on FACET in a total area of about 1,000m2. In result, it becomes possible to evaluate the condition and implement comprehensive repairing works for the reinforced concrete decks in the Hokuriku Expressway.
Jakob Kunz & Camiel de Smet, Hilti Corp, Liechtenstein + Norbert Randl, Hilti Development, D-86916 Kaufering, Germany
The placing of concrete overlays has gained in importance as a result of the more frequent need to strengthen existing structures. In order to obtain monolithic structures, the shear transfer between the concrete layers must be guaranteed. The state of the art connecting procedures and design method are briefly introduced. From an analysis of the load-bearing behaviour of the interface, optimization criteria concerning the static behaviour of connectors are derived. Numerical models which allow to simulate a splitting test and a shear test have been set up and calibrated. By simulating various connector geometries in the splitting test, an optimized shape could be defined. Simulation of the shear test confirmed the improved behaviour of the new shape compared to traditional connectors. An analysis of the placing procedures has shown that the new shape also offers a clear advantage in terms of time required for setting the elements.
1275
EUROPEAN GPR ASSOCIATION: ITS PRESENT & FUTURE ROLES IN ENGINEERING,
E Carrick Utsi, Utsi Electronics Ltd, Cambridge, UK
The European GPR Association (EuroGPR) grew up originally from the UK based Impulse Radar Users Association (IRUA). The change of name and extension across the continent resulted when it became evident that a licensing framework for the use of a transmitting technology would be required not only within the UK but also across Europe.
The initial focus of the organisation on licensing issues has resulted in a workable frame of reference for all of the major GPR manufacturers, EN302 066 01 and the adoption of the Association’s own Code of Practice as an European Telecommunications Standards Institute official document.
Standards and guidelines for all types of GPR survey including utility detection and engineering investigations are becoming of increasing concern both to GPR surveyors and to the engineers who employ them. The Association has contributed to the issue of the Survey Association guidelines, the formation of the Utility Mapping Association, and the drawing up of PAS128, due to be issued in Spring 2014. It also issues its own guidance on the use of GPR.
Even for those not based within Europe, the Association welcomes collaboration, technical input and continues to hold its members accountable for their expertise.
FRP Bridge Strengthening
1326
LONG-TERM DURABILITY ASSESSMENT OF PRESTRESSED CONCRETE GIRDERS WITH FRP SHELL,
M Shafqat Ali, M Saeed Mirza & L Lessard, McGill Univ, Montreal, Canada
This paper presents the results of a preliminary study on design of FRP-reinforced bridge girders for durability over a long service life, when subjected to an aggressive environment. This system of three materials - FRP composites, concrete and prestressing steel, have their individual durability problems and the associated deterioration mechanisms, which can range from superficial surface problems to disintegration of the FRPs, concrete and prestressing steel within the member. The FRP composite shell, acting as a barrier, showed significant resistance against chloride ingress by significantly slowing down the chlorides ingress rate and the total amount of chloride ions. Based on Fick’s second law of diffusion, the predicted profiles for a prestressed concrete girder without FRP shell showed that chloride ingress from the exterior surface can reach the prestressing steel strands within a period of about 45 years. For a prestressed concrete girder with an FRP composite shell, the accumulated time for chloride ions reaching the level of prestressing steel strands was predicted to more than 135 years. These results suggest that the FRP shell can be quite effective in improving the durability characteristics of prestressed concrete girders and can significantly extend their service life.
1303
TESTS OF CRACKED, R.C. BEAMS STRENGTHENED WITH NEAR-SURFACE-MOUNTED FIBER-REINFORCED POLYMER STRIPS
EA. Bertolotti, Hartzell Engine Technologies, Montgomery, AL, R Barnes, WB Childs & AK Schindler, Auburn Univ, AL, USA
A standard State of Alabama (USA) reinforced concrete highway bridge type has been judged to have deficient negative-moment capacity under current loading standards. A near-surface-mounted fiber-reinforced polymer (NSM FRP) strengthening system was proposed to repair the deficiency. A survey of relevant literature regarding the intermediate-crack (IC) debonding of NSM FRP revealed only tests with reinforcement ratios and concrete compressive strengths greater than those present in the deficient bridge; furthermore, few previous tests involved flexural specimens that were cracked prior to strengthening. To generate experimental data for direct correlation with this standard bridge type, a series of laboratory tests was conducted to study the performance of the proposed NSM system.
Eight specimens were designed to represent realistic ranges of (a) existing steel reinforcement and (b) newly installed NSM FRP. In order to mimic actual bridge conditions, the specimens were fabricated with 50 ksi [340 MPa] steel reinforcement and 3000 psi [20 MPa] concrete, pre-cracked, and then repaired with NSM FRP strips. Flexural tests included service-load cycles, followed by monotonic loading until failure. A nonlinear, layer-by-layer flexural analytical model—to account for strain hardening in the steel, and the cracked nature of the specimens during repair—was developed to compute expected performance data for comparison to the experimental results. Results were also compared to the strength predictions resulting from the limiting design values recommended by ACI 440 (2008), Standards Australia (2008), and others.
Analysis of the data obtained from both the service-load cycles and the monotonic loading showed no evidence of bond degradation; examination of the specimens after failure and all experimental results indicated functional bond until achievement of ultimate strength. The capacities predicted according to the evaluated design methods proved conservative. The viability of the recommended design was confirmed.
