Date of Award
Master of Science
Civil, Construction, and Environmental Engineering
Peter C. Taylor
The work presented in this thesis involves the study of deterioration of concrete caused by using deicers. This thesis includes two papers resulting from the study: 1). Scaling resistance and evaluation of concrete containing slag cement and 2). Effect of the Interfacial Transition Zone on Joint Deterioration of Concrete Pavements. In the first paper, an alternative test method was proposed to evaluate scaling resistance of concrete containing SCMs, which is believed to better represent the field performance, and both standard method and alternative method was performed and compared. The relationship between air system and scaling resistance and the methods to test air system are also studied. In the second paper, deicer deterioration of interfacial transition zone is observed by Scanning Electron Microscopy, to study the mechanism behind the deterioration of joint of concrete pavements.
In Paper 1, Scaling resistance and evaluation of concrete containing slag cement has been studied. Slag cement (slag), has long been used as a supplementary cementing material in concrete mixtures. With the addition of slag, concrete generally exhibits good long-term strength and durability. However, various authors have expressed concern about the scaling resistance of concrete containing slag cement, especially when the dosage is high. Much of the concern to appears to be based on the results from laboratory scaling tests (ASTM C672), which tend to overestimate damage when compared to field observation and results. The reasons for this are thought to be because at high replacement levels, SCM mixtures can take longer to set and develop their properties, but neither of these factors is considered in the finishing and curing procedure of laboratory tests. As a result, a modified test which takes these variables into account has been drafted and used in this project (Hooton 2012).
The experimental research focused on the evaluation of scaling resistance tests, including the new test and the ASTM C672 test with normal curing and an accelerated curing regime used by VA DOT. A total of 28 concrete mixtures were studied using high alkali cement and low alkali cement, Grade 100 and Grade 120 slag with 0, 35, and 50 percent slag replacement by mass of total cementing materials. The objective of the paper is to recommend a test method that is more representative of field performance for concrete in a salt scaling environment. It is recommended that the proposed test method be submitted to ASTM for acceptance as a new test method.
In Paper 2, Effects of the Interfacial Transition Zone on Joint Deterioration of Concrete Pavements is studies. In the Midwestern region of the U.S., some concrete suffers from deterioration of sawn joints, generally related to freezing and thawing of saturated concrete. One form of the distress occurs as cracks forming about one inch from, and parallel to, the free surface. These cracks are observed to go around the coarse aggregate and leave little or no paste adhering to it.
It is hypothesized that a mechanism for this observation is that when joints are sawn, the cut exposes the interfacial transition zone (ITZ) around coarse aggregate particles. Water or salt solution subsequently held in the saw-cut can be wicked around the coarse aggregate particles through the ITZ. Subsequent freezing and thawing action can lead to the aggregate being separated from the paste, and a crack propagating to the surface. Once the now-loose piece is removed by traffic loading, the cycle is repeated. The mechanisms behind the separation of aggregate and paste are not clear and may include freezing expansion of water, salt crystallization and dissolution of the ITZ. This paper describes an experimental program aimed at investigating this hypothesis and to assess what mechanism(s) can be responsible or the observed behavior. It was found that chemically induced expansion of the paste likely caused a stress concentration around the non-expanding aggregate, so resulting in a crack in the ITZ.
Wang, Xin, "Evaluation of de-icer deterioration of concrete" (2014). Graduate Theses and Dissertations. 14260.