WTI

Validation of Rehab Strategies to Extend the Service Life of Concrete Bridge Decks

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Project Objective

The objective of this research is to investigate the long-term effectiveness of Caltrans’ preservation and rehabilitation strategies for concrete bridge decks. Caltrans currently employs high molecular weight methacrylate (HMWM)-based crack sealing and polyester overlay. This research will also explore the value of Portland cement concrete (PCC) and asphalt concrete (AC) overlays on bridge decks, and identify the appropriate treatment time and frequency for these strategies.

Project Abstract

Concrete box girder bridges with integral decks are the predominant bridge type in California. Instead of unreliable and expensive deck replacement, Caltrans currently employs preservation and rehabilitation strategies, mainly using HMWM-based crack sealing and polyester overlay. The current state-of-the-practice relative to rehabilitating bridge decks using these methods, as well as PCC and AC overlay, will be assessed by reviewing existing literature. Critical factors and variables that influence the effectiveness and durability of these practices in California will be identified. As critical parameters are identified, a series of laboratory experiments will be conducted to obtain load cycle vs. deterioration relationships for deck slabs under various conditions before and after protective treatment. A laboratory-based accelerated tester will be fabricated to test deck slabs under rolling loads and well-controlled environmental conditions. The load cycle vs. deterioration relationships will address strength loss and reinforcement corrosion of the deteriorated concrete, which are two of Caltrans’ primary concerns for its bridge decks. A two-dimensional (2D) finite element method (FEM) model will be developed to simulate the ingress of chloride and moisture into deck slabs. The load cycle vs. wheel-path stiffness, chloride permeability and moisture permeability curves obtained from the laboratory test will then be combined with the 2D FEM model to predict the service life of each rehabilitation strategy. A life-cycle cost analysis will be performed to determine the most cost-effective rehabilitation strategies for Caltrans bridge decks.

Task Descriptions

1. Literature Review
   1. The research team will conduct a comprehensive literature review to gather existing information related to this project, including mechanisms of bridge deck cracking, reinforcement corrosion, and other relevant distresses. Information will also be collected regarding previous and state-of-the-practice bridge deck protection strategies, deterioration mechanisms of bridge deck protection systems centered on HMWMs as crack sealants and polyester/PCC/AC overlays, identification of critical factors and variables that influence their performance. Methods used to detect, characterize, and mitigate/prevent the distresses of HMWM sealants, polyester/ PCC/AC overlays and the repaired bridge decks will be documented.
2. Experimental Setup for a Laboratory Accelerated Tester
   1. To successfully fulfill the project objectives, both intact and HMWM or overlay treated deck panels need to be cyclically loaded to failure to study and characterize their deterioration behavior under typical in-service loads. To this end, an accelerated test apparatus will be developed that is capable of applying rolling loads to a deck panel in the laboratory using a full-size track wheel, of which the wheel load and tire pressure will be representative of trucks running on Caltrans bridges decks.
3. Experimental Design
   1. The experimental test matrix will be carefully developed to optimize the information collected from the finite number of deck panels that can be tested. The HMWM crack sealants and polyester/PCC/AC overlays are influenced by many factors, and obviously this investigation must focus on the important ones. A comprehensive laboratory evaluation of the impacts of all the potential factors/variables is impracticable in light of the time and resources that would be required. Instead, this research will focus on the important factors/variables that are related to the three primary distresses faced by Caltrans bridge decks—i.e., loss of structural stiffness, loss of resistance to chloride permeability, and loss of resistance to moisture permeability. A literature review will be conducted first to identify the potential factors/variables that could affect the Caltrans bridge deck protection systems. Using Analytical Hierarchy Ranking (AHR) analyses applied with due consideration of typical characteristics of Caltrans bridge decks and the environments in which they are deployed, the scope will be narrowed down as much as possible to those factors closely related to the three primary bridge deck distresses of interest.
4. Laboratory Investigation
   1. Deck panels will be fabricated to Caltrans bridge design specifications in custom-designed wooden molds and cured in specified conditions. Great care will be taken to ensure the quality of concrete panels and to avoid the presence of crevices and micro-cracks. Concrete mixes will be prepared and sampled in accordance with applicable ACI and ASTM standards to ensure proper and complete mixing. Applicable mix design parameters and concrete properties such as material batch weights, air content, unit weight, and slump will be recorded for each mix. All tests will start after the 28-day strength is gained. Strength and moisture content of the slab concrete will be determined at the beginning of the tests and periodically, thereafter. Newly cast concrete slabs will be subjected to accelerated testing under controlled environmental conditions. One deck panel will be loaded under the rolling wheel until failure to acquire a life-span load cycle vs. surface deterioration level (crack size and crack density) curve. Up to ten more slabs will also be tested, and each will be stopped at a different level of surface cracking from 10 percent to 100 percent. At the different levels of surface cracking, the in-situ stiffness will be monitored and at least two concrete samples will be extracted and each subjected to a chloride permeability test and a moisture permeability test, respectively. By testing these slabs, the load cycle vs. deterioration data relationship will be established for an unprotected deck panel, including four curves: a load cycle vs. surface deterioration level (cracking for untreated deck panels) curve; a load cycle vs. stiffness curve; a load cycle vs. chloride permeability curve; and a load cycle vs. moisture permeability curve. To evaluate the effectiveness of HMWM crack sealing, a batch of five concrete slabs will be subjected to the accelerated rolling wheel test. Each panel will be “precracked” to surface cracking levels of 20, 40, 60, 80, and 100 percent. The panels will then be treated with HMWM sealant using a typical Caltrans procedure. After complete curing, each of the five deck panels will be loaded to different levels (from 0 percent to 100 percent) of the previously determined maximum allowed load repetitions to obtain the results of surface deterioration, stiffness, and chloride and moisture permeability. Thus, four load cycle vs. deterioration curves (surface deterioration, stiffness reduction, chloride permeability, and moisture permeability) will be determined for each of the five panels. Following the same procedures used in evaluating the HMWM treatment, performance curves (i.e., load cycle vs. deterioration) will be established for each of the other practices: partial-removal polyester overlay, non-removal thin polyester overlay, partial-removal PCC overlay and AC overlay. Six panels will be tested for each of the four overlay treatments, leading to four load cycle vs. deterioration curves (surface deterioration, stiffness reduction, chloride permeability, and moisture permeability) for each treatment. Therefore, for one influential factor/variable, a total of 40 panels will be tested. The total number of tests that should be conducted, however, will be dependent on the number of influential factors/variables that need to be evaluated, and on how thoroughly the factors need to be tested to reasonably characterize the performance curves.
5. Service-Life Modeling and Lifecycle Cost Analysis
   1. An FEM analysis will be conducted to predict the evolution of the chloride and moisture concentration profiles for each case—intact concrete slab, deteriorated slab, HMWM sealed slab, and polyester/PCC/AC overlaid slabs—under different traffic and environmental conditions. This numerical analysis will be based on a two-dimensional (2D) FEM model developed by the PI of this proposal to simulate moisture movement and transport of ionic species in a concrete matrix. With the load cycle vs. deterioration curves measured in the laboratory, and the FEM model to predict the service life of bridge decks at different levels of deterioration, the life-cycle cost analysis involving life-cycle cost comparison of different rehabilitation strategies can be performed for a bridge deck rehabilitation project to find the most cost-effective strategy to follow.

Milestones, Dates, Schedule

Student Involvement

True

Relationship to Other Research Projects

False

Technology Transfer Activities

True

Transportation Research Board Keywords

Fatigue Cracking of Reinforced-Concrete Bridge Decks, Protection Sealant and Overlay, Rolling Wheel Load Evaluation

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