United States Department of Transportation
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TRIS Online Accession Number:01115780
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Edition:Final Report
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Abstract:The research objective was to investigate the causes of premature deterioration of concrete bridge barriers with the goal of developing strategies for corrective actions. The synthesis of all the data collected in various tasks revealed that barrier deterioration starts with early formation of vertical cracking as a result of the tensile stress due to early-age thermal load. Volume change of concrete due to temperature and shrinkage occurs simultaneously. An increase in drying shrinkage arising from delays in curing also affects the barrier cracking. Additionally, drying shrinkage, beyond the very early ages, increases the width of cracks that have formed due to thermal loads. Penetration of moisture and other corrosive agents through the cracks causes reinforcing steel corrosion leading to horizontal cracking and finally the delamination and spall. Insufficient consolidation of concrete often observed in slipformed barriers accelerated the deterioration. Concrete parameters controlling the thermal load are the cement type, content, and fineness, ambient temperature at the time of concrete placement, and the time of inception of curing. From field inspection data and the finite element results it was found that the minimum possible full-length vertical crack spacing is equal to barrier height. One of the most important recommendations drawn from this study is the implementation of crack arrestors at about 3-feet intervals. The crack arrestors, some with cracks formed at full length, should be sealed with durable silicone-based flexible material during first scheduled maintenance cycle. Additional recommendations include the substitution of cement with mineral admixtures and the development of detailed specifications for barrier construction.
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