Case 3

Introduction

Type of Building: Car-park (Residential)

In this case, the concrete floor in a basement of a carpark is cracked as shown. Reinforced concrete may be a durable material under tropical conditions as steel reinforcement is chemically protected from corrosion by the alkaline nature of the good- quality reinforced concrete. However, due to many external factors such as honeycombs, concrete can be carbonated even before reaching its life span. This, in turn, reduces its alkaline nature and hence, corrosion of reinforcement may inevitable. Corrosion of the steel produces iron oxides and hydroxides, which have a volume greater than the volume of the original metallic iron. This increase in volume (may be up to 8 times) develops tensile stresses around reinforcement bars. Concrete is weak in tension and hence, these stresses will cause cracking.

In this case, it is possible that the concrete could have been carbonated by the carbon dioxide from vehicle exhaust. Hence, the alkaline protective environment is neutralized. Corrosion takes place in the presence of moisture within the basement or from the moisture brought in by vehicles. It is also possible that moisture from the soil causes the corrosion induced crack. It may be due to the excessively porous concrete, which exposes the reinforcement.