Early-age cracking of concrete bridge deck slabs reinforced with GFRP bars
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Date
2015-07-02
Authors
Ghatefar, Amir
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Abstract
Since concrete bridge deck slabs are much longer in the traffic direction, they experience transverse early-age cracks due to volumetric instability and restraint. In the last decade, the lower cost of the non-corrodible Glass Fiber Reinforced Polymer (GFRP) bars, as alternative to steel reinforcement, has made them attractive to the bridge construction industry. However, low modulus of GFRP bars may lead to wider cracks in GFRP-RC structures. This serviceability issue can be aggravated by harsh environmental conditions. Hence, the main objective of this thesis is to investigate the effect of early-age cracking in restraint bridge deck slabs reinforced with GFRP bars subjected to different environments. This research consists of two phases: an experimental investigation and a numerical study. In the experimental phase, four full-scale cast-in-place slabs reinforced with different longitudinal GFRP reinforcement ratios (0.30, 0.50, 0.70 and 1.1%) and one with steel reinforcement ratio of 0.7% measuring 2500 mm long × 765 mm wide × 180 mm thick were constructed and tested in the laboratory. Three environmental conditions were implemented; normal (laboratory) adiabatic conditions as well as freezing-thawing and wetting-drying cycles. The main test results are presented in terms of cracking pattern, width and spacing, and strains in the reinforcement and concrete. Test results indicated that the minimum reinforcement ratio (0.7%) recommended by CHBDC for bridge deck slabs reinforced with GFRP bars satisfied the serviceability requirements after being subjected to the simulated exposures of normal laboratory conditions, freezing-thawing, and wetting-drying cycles. In the numerical phase of this research, a finite element model (FEM) was constructed using ATENA software package (ver. 5) to simulate the behaviour of the test specimens. According to the FEM results, a reinforcement ratio of 0.45% Carbon FRP (CFRP) can control the early-age crack width and reinforcement strain in CFRP-RC members subjected to restrained shrinkage. Also, the results indicated that changing the bar surface texture (sand-coated and ribbed bars) or concrete cover had an insignificant effect on the early-age crack behavior of FRP-RC bridge deck slabs subjected to shrinkage. However, reducing bar spacing and concrete strength resulted in a decrease in crack width and reinforcement strain.
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Keywords
Early-Age Cracking, GFRP, Deck Slab, Bridge