Handbook for Bridge Inspections - TSP2

9.2 CONCRETE ELEMENTS
204 Cracks in Concrete Elements
Description
Thi s category covers all hamlful cracks a nd fi ssures in concrete. Thus cracks in concrete which
have been subject to stress from flexura l or tensile forces are normal. However, these cracks must
fall within certain limits.
Bridges containing pl ai n steel reinforcement bars can be subject to large cracks more widely spaced
apart than is the case for ribbed reinforcement bars. Pre-stressed constructions do not nonnally suffer
from cracking.
Cause of Damage
* Design fault - insufficient reinfo rcement! hi gh tension in the reinforcement during in-service
condition.
* Materials fault - an incorrect concrete mixture can produce shrinkage cracks. Aggregates which
react to alkali can therefore react with alkali contained in cement and water and in the long tenn
produce an expansion in the volume of the concrete. This can lead in turn to cracks.
'" Construction fau lts - both an inadequate casting process and faulty finishing treatment may cause
cracks during curing, cracks resulting from loss of plasticity, wastage due to dehydration or
cracks caused by the heat of the curing process Itemperature gradients.
'" Inadequate day-to-day maintenance - badly cleaned out joints may result in
unforeseen loads.
'" Environmental impact - hostile environment, e.g. cracks caused by chloride induced corrosion on
reinforcement.
'" Impacts from traffic, subsidence etc ..
'" Accidental impacts - traffic collisions.
'" In-service impacts - secondary damage.
Possible Measurements
'" Measuring the width and pattem of cracks
'" Removal of concrete specimens, drilling out cores or thin sli cing.
Degree of Damage/Consequences
The degree of damage should be assessed in relation to the location of the cracks, extent, cause,
probable development and the amount of stress the elements have been subjected to. In addition,
climate impact may be of importance here.
Handbook for Bridge Inspections 153