Title:
Cracking in Precast, Prestressed Deck Planks in Two Bridges: Causes of Cracking, Concrete Characteristics, and Rehabilitation Options
Author(s):
Ahmad Shayan and Howard Morris
Publication:
Materials Journal
Volume:
99
Issue:
2
Appears on pages(s):
165-172
Keywords:
alkali-aggregate reaction; crack; expansion; prestressed concrete.
DOI:
10.14359/11709
Date:
3/1/2002
Abstract:
Precast, prestressed concrete (PSC) planks in the decks of two Roads and Traffic Authority (RTA) bridges, referred to as MC and BC bridges, exhibited cracking in the soffit of the planks, and alkali-aggregate reaction (AAR) was suspected. Two PSC planks from each bridge were examined to identify the causes of the cracking and determine their remedial needs based on the residual strength and residual expansion properties. Based on petrographic examination and scanning electron microscopy, strong AAR was found to be the cause of cracking for both bridges. Investigation of strength properties of the concrete cores showed that significant loss in strength properties had occurred of approximately 30% in compressive strength and up to 50% in elastic modulus. Residual expansion of the cores was determined in the laboratory under conditions of elevated temperature and humidity, and it was found that the expansion potential of the cores examined was relatively small. The cast-in-place columns of the MC bridge were also examined and found to be free of AAR, of adequate strength, and in sound condition. Options for the rehabilitation of the structures are discussed. Remedial action would need to consider the economy of replacement of the whole deck. Strengthening of the affected planks using recently developed retrofitting techniques may not be a desirable long-term option for these particular structures.