Use of Class AA Concrete Modified with a High-Range Water Reducing Admixture in aFull-Depth Bridge Deck Slab, US 127, Lincoln County

摘要

Because it is desirable for bridge deck concrete to be strong and durable, theKentucky Department of Highways chose to use a high-range water reducer to modify the properties of a conventional Class AA concrete mixture to be placed in a full-depth concrete bridge deck on US 127 in Lincoln County. A high-range water reducer is a chemical admixture that when added to low-to-normal slump concrete produces a high slump to flowing concrete. The higher slump enhances placement properties in areas of closely spaced and congested reinforcing steel such as that encountered in the corners of a skewed bridge structure. The addition of a high-range water reducer permits reductions in mix water in the range of 12 to 30 percent. The reduction in mix water lowers the water-to-cement ratio leading to increased strength properties. The Kentucky Department of Highways specified an admixture dosage rate of 10.42 mL per kilogram of cement (16.0 oz per 100 lbs of cement). Test results indicated that this dosage rate would facilitate the desired 15 percent reduction in the available mix water. The use of a high-slump concrete enhances placement properties in areas of closely spaced reinforcing steel such as a skewed bridge. structure. Data obtained during this study indicate that the high-range water reducing admixture also enhances durability and strength properties of concrete. The magnitude of cracking was slightly more for the experimental deck concrete but the severity of the cracks appeared to be higher in the control deck. The inability to adhere to the specified admixture rate compounded by the finishing characteristics of the concrete mixture contributed to the poor results achieved with the experimental deck. The admixture representative present during the experimental deck placement could not provide the suitable proportioning of the admixtures necessary for both a good finishing mix that also met the requirements of the project. It is recommended that consideration be given again to the use of high-range water reducers to modifiy conventional bridge deck concrete in situations where the placement properties can be enhanced or where it is desired to enhance strength and durability properties.