Municipalities and transportation authorities use rock salt on roads during the winter to lower the freezing temperature of water and melts ice to make roads safe for commuters. Deicing rock salt contains highly acidic chemicals like Calcium Chloride (CaCl), Magnesium Chloride (MgCl) and Potassium Acetate (CH3CO2K) (Ccee Chan, 2006). Those chemicals are transported along with water from the road into the concrete floors of the parking facilities attacking aggressively the concrete. As a function of time the concrete starts to erode in the circulation and maneuvering zones of the floors and travels through the concrete capillaries all the way to the steel reinforcement to initiate the corrosion process.
The main failure for the parking facilities concrete slabs is corrosion of steel bars. Corrosion results in a volume increase in the steel rebars which in turn imposes pressure on the concrete section and consequently cracks start to occur (Deif, 2010). As corrosion causes the steel bar size to decrease which in turn decreases the value of the designed strength which leads to weakening the entire structural strength. An alkaline chemical environment is provided by the alkali reserve (KOH, NaOH) and Portlandite (CaOH) contained in the Portland cement creates a protective casing for the steel reinforcement. The PH value for the cement in the concrete section in normally ranges between 11 and 13 which provides a non-corrosive environment for the entire section. Once the concrete is exposed to atmosphere it reacts with Co2 and therefore Calcium Silicate Hydrate (CSH) of the hardened cement paste becomes progressively carbonated and the pH gradually decreases from 13 down to 8.5 which is no longer a passive environment that subjects the steel reinforcement to the danger of corrosion( Tatematsu 2003). Parking facilities is a rich environment of Co2 due to the automobile emissions which make it a severe environment to unprotected concrete elements as carbonation process starts to take place actively and in massive magnitude.
Most of indoor parking projects require minor to major repair work to be done to the concrete slabs in prior of installing protective waterproofing membrane. For more information please check our CONCRETE REPAIR SECTION.