Concrete structures can suffer from a variety of damages and deteriorations. When such issues arise, it is important to consider multiple potential causes. Fortunately, modern concrete technology offers various admixtures and advanced materials that can prevent damage. However, if concrete has already deteriorated, it is likely that several causes are at play. To effectively repair the damage, it is crucial to identify and address all the contributing factors. Failing to do so will likely result in subpar repair serviceability.
The concrete shown in Figure 1 is suffering from multiple causes of damage, including alkali-aggregate reaction cracking and accelerated freeze-thaw deterioration of the surface. Additionally, faulty design or construction techniques placed electrical conduits too close to the exterior surface, causing further damage. However, the use of air entraining admixtures in modern concrete has significantly increased its resistance to freeze-thaw deterioration, except in unusually severe exposures.
Despite this, freeze-thaw deterioration is often still blamed for concrete damage. It is better to first determine why the air entraining admixture did not provide effective protection. This can be done by examining mix records and aggregate quality test results to determine if the concrete was poorly proportioned or if low-quality aggregate was used. Construction inspection records can also reveal if placing and finishing techniques were inadequate. Petrographic examination of the concrete can reveal if alkali-aggregate reaction, sulfate exposure, or induced chlorides have weakened the concrete, allowing freeze-thaw damage to occur.
If any of these findings are present, the problem may be more extensive than initially thought and require more extensive preventative or corrective action than simply replacing the deteriorated concrete. 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 can all contribute to low durability in concrete, making it more susceptible to weathering and other hazards.
When repairing concrete damaged by multiple causes, it is essential to determine the weakening cause and the accelerated cause. Preventative measures may be necessary to protect the remaining original concrete from additional damage, such as the application of concrete sealing compounds or a thin polymer concrete overlay. If these preventative measures are not possible, repairs can be made using suitable methods, but it is important to anticipate a short repair service life and the possibility of future damage.