Effects of curing on shrinkage cracking in bridge deck concrete

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Title: Effects of curing on shrinkage cracking in bridge deck concrete
Author: Aamidala, Hari Shankar G
Abstract: Shrinkage cracking is a critical factor affecting the durability of concrete bridge decks . Since cracks in reinforced concrete decks provide a path for corrosive agents to enter the concrete , thereby accelerating the deterioration of the reinforcing steel . Concrete undergoes volumetric changes due to variation in temperature and moisture . When concrete is prevented by a surrounding structure from undergoing these volumetric changes freely , tensile stresses are developed . Depending on the amount of restraint applied , these tensile stresses potentially lead to cracks in the structures . This type of cracking can be reduced by providing rebars in the form of mesh to take the tensile stresses and /or the use of shrinkage -reducing admixtures (SRAs ) . Recent studies performed on SRAs show that the use of such admixtures is an effective method to reduce shrinkage cracking . Simulating restraint experienced in highway pavements and bridge decks is a challenge to researchers . This challenge has led to the development of different methods to assess the potential of restrained shrinkage cracking . Currently , there exists no standard test to assess cracking due to restrained shrinkage , though several researchers have simulated the effects of restraint in various ways to better understand the behavior of concrete shrinkage . The objective of this research is the evaluation of the different concrete mix designs used in bridge decks in Texas . Specifically , the influence of curing duration on the cracking potential of concrete bridge decks has been investigated based on the unrestrained (free ) linear shrinkage measurements of prismatic specimens . In addition to free shrinkage tests , tests have been performed to study the weight loss , modulus of elasticity and split tensile strength of the concrete mix designs . Using the data obtained from these tests , shrinkage stresses developed due to full -restraint (100 % -restraint ) have been estimated and compared with the split tensile strength to estimate the age at which a first crack can be observed in the concrete . The approach presented assists in better understanding the effect of shrinkage on the cracking of bridge decks under full -restraint . Using the weight loss measurements and weight of oven -dried specimens , internal moisture content was tracked . This data is used to compare the behavior of the material to the development of shrinkage strains . Comparing the different curing durations did not indicate a significant difference in the development of either modulus of elasticity or split tensile strength . However , a favorable correlation was observed between the tensile strength of concrete and shrinkage stresses developed due to full restraint based on different curing durations . The results did not show a significant delay in the age of first crack with increase in curing duration from 4 days to 7 days . Thus , based on the research to date , one can conclude that 4 day curing suffices for durability of bridge decks from a shrinkage cracking perspective .
URI: http : / /hdl .handle .net /2346 /14276
Date: 2003-12

Citation

Effects of curing on shrinkage cracking in bridge deck concrete. Master's thesis, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /14276 .

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