When damage or deterioration is detected in concrete structures, it is important to consider multiple potential causes. Modern concrete technology incorporates the use of admixtures and advanced materials, which can enhance the durability of concrete and protect it against various causes of damage. However, even with these advancements, concrete can still experience deterioration. Therefore, it is crucial to identify and address all possible causes of damage, as failure to do so may result in inadequate repairs and reduced serviceability. It is likely that a combination of factors contribute to the deterioration of concrete, and thorough investigation and mitigation of all potential causes is necessary for effective repair and maintenance of concrete structures.
Figure 1: Results of multiple cause concrete damage.
The concrete shown in Figure 1 is experiencing cracking due to alkali-aggregate reaction, which has been further exacerbated by freeze-thaw deterioration on the surface. Additionally, faulty design or construction techniques have resulted in the electrical conduits being placed too close to the exterior surface of the concrete, causing damage. The use of air entraining admixtures in modern concrete has generally improved its resistance to freeze-thaw deterioration, and such damage should not occur under normal conditions. However, before blaming freezing and thawing conditions, it is important to investigate why the air entraining admixture did not provide effective protection. This can be determined through examination of mix records and aggregate quality test results to identify issues such as poor proportioning or low-quality aggregate. Construction inspection records can also reveal inadequate placing and finishing techniques. Petrographic examination of the affected concrete may uncover additional factors such as alkali-aggregate reaction, sulfate exposure, or induced chlorides weakening the concrete and allowing freeze-thaw damage to occur. These findings may indicate that the problem is more extensive than initially thought, requiring more comprehensive preventative or corrective action beyond simple replacement of the deteriorated concrete.
There are various factors that contribute to low durability in concrete, including the use of excessive mix water, improper type of Portland cement, poor construction practices, improper mixture proportioning, dirty or low-quality aggregate, and inadequate curing. Concrete with low durability may have reduced resistance to weathering and other hazards. Therefore, selecting the appropriate methods and materials for repairing concrete damaged by multiple causes depends on identifying the weakening cause and the accelerated cause. Once the weakening cause is fully understood, preventative measures may need to be taken to protect the remaining original concrete from further damage. This can include applying concrete sealing compounds or thin polymer concrete overlays. If preventative measures are not feasible, repairs can be made using suitable methods, but it should be anticipated that the repaired concrete may have a shorter service life and may experience future damage.