Restrained shrinkage behavior of high-performance concrete containing slag.

摘要

Many high-performance concrete (HPC) bridge decks have been observed to exhibit cracking even after a couple days from casting. The shrinkage of concrete is one of the main causes of why bridge decks crack. Since bridge decks tend to restrain concrete from shrinkage, tensile stresses build up and cause the concrete to crack. Other factors also such as loading cause concrete to crack as well. It is important to test various HPC mixes under restrained conditions to analyze their cracking behavior and severity.;The AASHTO test (PP 34-06, The Passive or Restrained Ring Test) is utilized to measure the shrinkage of HPC mixes containing slag under restrained conditions. Cracking patterns are also investigated as well. The use of six Vibrating Wire Strain Gages (VWSGs) have been added in order measure the strain in the concrete ring directly and to detect the actual cracking day. Other tests including the free shrinkage and mechanical properties tests (compressive strength, tensile strength, and elastic modulus) were performed on each mix. The shrinkage performance and cracking behaviors were reported and compared based on total cementitious content, coarse aggregate content, and the coarse aggregate to fine aggregate ratio. It was found that the total cementitious content, coarse aggregate content and its ratio to fine aggregate can significantly affect shrinkage and make that mix more or less likely to crack. Mixes with low coarse aggregate content and highest cementitious content crack the earliest and have the most severe cracking. Mixes with lower cementitious content and a higher coarse aggregate content and ratio tend to crack later and some have a least one ring specimen free of any cracking. Complementary linear free shrinkage blocks were also tested to correlate the free shrinkage performance with the restrained shrinkage performance of each mix. Any mix with a free shrinkage strain less than 450 microstrains day 56 tends to perform best under restraint conditions. Those mixes contain the lower cementitious contents (less than 700 lbs/cu yd), a higher coarse aggregate content (1800 lbs/cu yd), and a higher coarse aggregate to fine aggregate ratio of 1.6.