Question
If contractor suggests increasing concrete cover beyond contractual such as 40mm to 70mm shall engineers accept suggestion?

Answer
In contractual part, based on requirement of General Specification of Civil Engineering Works, tolerance of concrete cover is involving +5mm and -5mm and engineers must not believe sub-standard work as they do not possess an authority to change acceptance criteria. In that case where engineers think contractor suggestion acceptable in technical point of view, consent has to be required from employer regarding changes in receiving criteria.

From practical point of view, effect on cracking because of an enlarge in concrete cover have to be considered. In general, there are three major parameters which govern crack width, namely tensile damage at the point considered, distance of longitudinal bar to concerned point and depth of tension zone.

For second factor, as in proximity of longitudinal bars to point of part, closer a bar is to this point; smaller is crack width. So, closely spaced bars with smaller cover determination give narrower cracks than extensively spaced bars with larger cover. So, with an increase of concrete cover, crack width will add to that is undesirable.