Concrete cover is the outer concrete layer serves to protect the rebar in RC structure. Its thickness and density dictates both the protection performance and fire – resisting ability. The extract from the research paper by Albert K.H. Kwan in Department of Civil Engineering, University of Hong Kong , the concrete cover will become much permeability to water once the “water to cement ratio” exceeds 0.4. Adversely does the high water to cement ratio happen in many concreting process in Hong Kong. To account the reason behind , it is the slump of the concrete or the workability of the concrete affects the entire concreting process. The drawback from high permeability is very obvious . The concrete cover becomes lesser defensive against the water nor air penetration . The alkaline environment around the rebar is diminished along with the carbonation due from the air pollution
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