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Bridge repairs are usually done considering many factors. In many jurisdictions, bridge repairs are contracted to repair companies that have the capability and prowess in the area. Bridge repairs that don't necessitate a full extension of repairs along the width of a bay or multiple bays are categorized as partial-depth repairs. The repairs are often shallow, and damage is limited to the bridge deck. These types of repairs can be done without closing the underpasses below bridges. Although partial-depth repairs are the most common forms of repairs done on bridges, they often tend to exhibit failure quite fast. These failures may be attributed to the following factors.
De-bonding between patching material and the substrate
When repair material is spread thinly over a large surface, the bond between the repair material and the substrate surface might loosen easily as the repair material dries up, leading to failure. To avoid this, the contractor should first dig the area requiring partial-depth repair beyond the topmost steel layer. The steel layer serves the purpose of mechanically bonding the repair material to the substrate base. Excavating a layer also serves to ensure sufficiently thick portions of the repair material is laid, enough to deter quick failure.
Increased Cement Content
Repair material for bridges is composed of cement. Exact ratios of cement, water, and aggregate need to be met when preparing bridge construction and repair material. Some contractors use excessive cement when preparing this mixture. Cement paste is the component in concrete that goes through excess shrinking during drying and curing. Aggregate, on the other hand, does not shrink. It also has a lower thermal expansion coefficient. Excess cement will, therefore, shrink more and leave the other components in an easily disturbed state. High cement content also leads to a higher heat of hydration. This increases the risks of thermal cracking. Good bridge repairs contractors should calculate maximum effective ratios for each component of the repair material matrix, and even factor in air content.
Rapid curing to result in rapid return to service rates
Bridge repairs necessitate the closure of lanes and even complete bridges. To minimize the detrimental effects of such closures, especially in urban areas, many contractors use rapid strength gain materials. While these are useful for quick return to service times, rapid curing often results in uneven distribution of hydration products. This results in regions of weakness that will soon give in to external stress factors. Even when done correctly, rapid return to service can result in stress-induced micro-cracks within the repair work. These will quickly widen with time and will need repair again.
It is finally important for contractors to use appropriate machinery when carrying out partial-depth bridge repairs. Use of extremely heavy equipment during the excavation of repair patches, or even digging beyond applicable limits during surface preparation, can result in the future need for full-depth bridge repairs.
Share3 November 2015
