SPALLING: WHAT IS IT, REALLY?
WHAT IS SPALLING? The condition shown in the image below is common in older buildings, bridges, and other concrete structures. Buildings on the KZN coast, are particularly susceptible to spalling, due to the extreme coastal weather conditions. The term “spalling” is used to describe this condition and specifically refers to the delaminating or fragmenting of the concrete surface.
SPALLING CAUSES:
Spalling in concrete can be triggered by several causes: The most prominent cause in KZN is sea salt or sodium chloride. Salt acts as a catalyst to enhance the reaction between the oxygen in the water and the iron in reinforcing steel. The resultant oxidation (rusting) causes the reinforcing steel to enlarge which creates high internal stresses within the concrete and, ultimately, the fracturing of the concrete surface. Rusted steel can expand up to five times its original size. Surface cracking can be generated by the reaction between atmospheric carbon dioxide and the alkalis present in the concrete mix itself. These surface cracks can then admit rainwater or condensation.
WHY IS SPALLING A PROBLEM?
Concrete spalling can result in a variety of undesirable outcome: Spalls on the underside of concrete decks (bridges, general slabs etc.), can cause damage below as well as unsafe conditions. Falling concrete debris is also unsafe where pedestrians travel, (especially to spalling on vertical surfaces of buildings) and in parking areas. Spalled surfaces can lead to rapid degradation of reinforcing steel which would jeopardize the integrity of structures and necessitate costly repairs. Spalls are also unsightly and indicate a lack of maintenance on the part of facility owners or managing agents.
SPALLING REPAIRS IN ACTION: Casablanca – Durban:
Chipping & Priming: Once the spalling area has been chipped until fresh rebar has appeared, the concrete as well as the rebar are pre-saturated and primed.
Packing & Cross-Hatching: The primed area is then packed with a cementitious mortar and cross-hatched to allow for proper grip when skimming.
Skimming & Finish: The final product is then skimmed and smoothed off which can then be primed and painted.