Assessing the age at cracking of concrete repair mortars

The amount of concrete infrastructure needing repair and rehabilitation is increasing worldwide. The bonded overlay technique, which involves removal- of a damaged concrete layer on an existing concrete base (substrate) and replacing it with a new layer is one of the most widely used techniques. Due to thermal and hygral differences in the two composites, differential shrinkage occurs. This leads to overlay shrinkage restraint by the relatively mature substrate. Restrained shrinkage in bonded overlays can cause stress build up and may result in cracking. Cracking due to restrained deformation is a major problem as it may lead to durability concerns. Overlay resistance to crack initiation, development and propagation depends on a number of time-dependent properties of the concrete. To be able to predict the onset of cracking requires knowledge of the different material properties and how they interact with each other. In this study, an investigation was carried out on whether the performance with respect to cracking of concrete overlays can be adequately predicted from tests such as ring test, free shrinkage strain, tensile strength test, tensile relaxation and elastic modulus. Five concrete mortar types i.e. three commercially available mortars and two laboratory mixed mortars with water-tocement ratio (w/c) = 0.45 and w/c = 0.6 were used in the ring test and material property tests. The influence of curing on the crack resistance of overlays was also investigated. An analytical madel for predicting age at cracking in bonded overlays based upon time-development of overlay material properties and the superposition principle was developed. Results from the model were compared with results from the ring test. Results indicate that crack resistance of repair mortars depends upon the combined influence of the different material properties. In particular tensile stress relaxation appears to have a large influence. Curing was observed to delay the onset of cracking. Results also indicate that although the ring test will give the correct order of cracking, it will not give the actual age at cracking when assessing materials for crack resistance.

Grantor dc:publisher.institution

Department of Civil Engineering

Year dc:date.issued

2012

Author dc:creator

• Chilwesa, Masuzyo

Advisors dc:contributor.advisor

• Beushausen, Hans-Dieter
• Moyo, P

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/5054

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/5054