Impact of environmental exposure on concrete strength in highway bridges in Uganda

Deterioration of concrete structures is a worldwide problem. Environmental exposure is known to affect concrete strength in structures. While moisture affects rebound values by lowering them, carbonation does the opposite. The aim of the study was to determine the in-situ concrete strength of three bridge elements, namely, pier, abutment and deck and evaluate the environmental conditions such as moisture and abrasive forces on the near surface of concrete. Acknowledging that destructive tests on concrete are expensive and time consuming, this research used rebound hammer test -a non-destructive test (NDT) method. The easiness, simplicity and portability of the rebound hammer made it possible to cover all 13 highway bridges in a period of two months. All the study sites were under the management of Uganda National Roads Authority (UNRA). The choice of test locations was based on BS 1881: Part 202. Rebound hammer tests were done on main elements of bridges namely, decks, piers and abutments. Where possible a maximum of 3 test points were chosen for every single test location. In addition to the universal machine calibrations, the rebound values were correlated to the standard concrete cube compressive strength using old concrete factors. Preliminary results show that although there is significant variation in concrete strength in both pier and abutment, the variation is relatively more pronounced in latter. The paper recommends a combined methodology involving the use of several NDTs to come up with sufficiently reliable results. In conclusion, the development of a formal Bridge Management System (BMS) to enable collection of data through regular monitoring and inspection programs would facilitate prioritization of Maintenance, Repair and Rehabilitation (MR&R) strategies.