Results from Visual Inspection and Laboratory Testing for ASR in Existing Concrete Cores from Bridges and Pavements in California
The overall goal of this project was to evaluate with available cores the presence of alkali-silica reaction (ASR) in California bridges and pavements, to develop procedures for evaluation of ASR by Caltrans staff, and, potentially, to investigate several locations suspected of having ASR damage. This report summarizes the creation of an inventory for cores taken from bridges and pavements in previous projects, the results of visual inspection and strength testing to identify the potential presence of ASR, and the development of a draft approach for Caltrans staff to evaluate the potential for ASR in bridges and pavements. A spreadsheet database was prepared for storing inventory data for 265 pavement cores with four inch (100 mm) diameter and 311 bridge cores with two inch (50 mm) diameter. Most of the bridge cores were from the San Francisco Bay Area, while the pavement cores were collected from across the state. Visual inspection was performed on 259 of the pavement cores (including multiple samples from some of the pavement cores) and 80 of the bridge cores (those with lengths greater than the three-inch minimum required for evaluation of ASR) using the Damage Rating Index (DRI) method. None of the cores showed the likelihood of an ASR issue, as defined by a DRI greater than 2,000, although a few cores showed a small number of ASR features. Comparison of the ages of the bridges and the ASR damage rating index for the cores showed almost no trend, and showed no apparent differences between cores from bridges built before and after 1995, approximately when Caltrans changed specifications to reduce the risk of ASR. Most of the pavement cores tested had unconfined compressive strength (UCS) less than 8,700 psi (60 MPa) and the median of the UCS of the pavement cores was approximately 6,100 psi (42 MPa). Most of the pavement cores tested had densities less than 156 pcf (2,500 kg/m3 ) and the median of the UCS of the pavement cores was approximately 147 pcf (2,350 kg/m3 ). No significant correlation was found between the UCS and the density of the pavement cores tested, although the UCS strengths generally increased with increased density. The bridge cores were too small in diameter for strength and density testing. An integrated spreadsheet database was prepared for storing all relevant data for all cores, including test results from all tasks (DRI, UCS, and density). A draft guideline was developed for visual inspection of concrete cores to identify signs of potential ASR-related distresses and to support decisions regarding the need for a further detailed investigation for ASR. The guideline describes step-by-step inspection procedures and selection criteria for a further detailed examination, with relevant example pictures showing different severity levels of potential ASR distresses.