Early-Age Cracking in Reconstructed Concrete Bridge Barrier Walls

An assessment of newly reconstructed reinforced concrete barrier walls on a highway bridge near Montreal indicated intense transverse cracking only a few days after concreting. Subsequent inspection of other concrete bridges in urban areas confirmed that such cracking is not uncommon. Analytical models, together with field and estimated data, were used to study the magnitude and roles of the factors that are the probable cause of this cracking. The results indicate that a combination of factors, such as temperature gradients, differential shrinkage and vibration due to traffic circulation, generated stresses that exceeded the low tensile strength of the young concrete. Résumé: Une inspection des parapets en béton armé nouvellement reconstruits d’un pont d’autoroute près de Montréal a révélé une fissuration transversale intense seulement quelques jours après le bétonnage. Une inspection subséquente d’autres ponts en béton situés dans des régions urbaines a confirmé qu’une telle fissuration n’était pas inhabituelle. Des modèles analytiques, supportés par des données in-situ et estimées, ont été utilisés afin d’étudier l’importance et le rôle des facteurs qui sont la cause probable de cette fissuration. Les résultats indiquent qu’une combinaison de facteurs, tels les gradients de température, le retrait différentiel et la vibration due à la circulation, a produit des contraintes qui ont excédées la faible résistance en tension du jeune béton. RESEARCH SIGNIFICANCE Major factors that contributed to the early-age cracking of a reconstructed concrete bridge barrier wall were evaluated using analytical models from the CEB (1993a) and ACI 209 (1997) design codes along with measured field data and finite element modeling. A sound understanding of the early-age cracking problem is important because it may lead to ingress of moisture and salt, reinforcement corrosion, concrete spalling and, ultimately, to a reduced inservice performance of the bridge. The conclusions obtained from this study can also be applied to newly constructed barrier walls since they are often built several weeks or months after the bridge slab. Institute for Research in Construction’s Paper NRCC 43373 Page 2 of 16