Evaluation of Internal Curing of Concrete Bridge Decks

Especially in cold regions, the long-term performance of concrete bridge decks is a function of the quality of concrete curing. During the weeks immediately following deck construction, high degrees of moisture saturation are desirable to ensure good concrete curing necessary for the development of both strength and durability, including the reduction of cracking. One method of maintaining high degrees of moisture saturation in concrete immediately following deck construction is the use of pre-saturated, lightweight fine aggregate. This aggregate has a much higher absorption than that typical of conventional aggregate, and the absorbed water can be gradually released into the cement paste over time to extend the cement hydration process even after the bridge deck is opened to traffic. For this reason, this process of “internal curing” is expected to yield a stronger and more durable concrete bridge deck. The Mountain View Corridor (MVC) Project Team of the Utah Department of Transportation (UDOT) will be constructing four new bridges, two at 8200 South and two at Dannon Way. At each location in the spring of 2012, one bridge deck will be constructed using a conventional concrete mixture, and one will be constructed using a concrete mixture containing a portion of pre-saturated, lightweight fine aggregate. Inclusion of pre-saturated, lightweight fine aggregate will facilitate internal curing of the concrete. The objective of the proposed research is to evaluate and compare the two concrete mixtures. This project is expected to generate field data that demonstrate the benefits of utilizing concrete containing pre-saturated, lightweight fine aggregate for construction of concrete bridge decks. Design engineers may then consider specifying such concrete mixtures to improve the strength and durability of bridge decks. Some of the work performed for this contract will take place on properties or rights-of-way owned by UDOT. These locations include the area of the MVC Project at 8200 South and at Dannon Way. Tasks associated with the above research objective are described in the following sections: Task 1: Instrumentation. The proposed field work includes instrumentation of each of the four bridges with between two and five sensors and a data logger equipped with cellular service. The sensors will measure the moisture content, electrical conductivity, and temperature of the concrete on hourly intervals. The moisture content will reflect on the availability of water for cement hydration in the concrete, and electrical conductivity will be a useful surrogate measure of permeability, since electrical conductivity is affected by many of the same factors that affect hydraulic conductivity in porous media. Temperature measurements will allow for documentation of environmental conditions, including number of freeze-thaw cycles, for example, and will also allow the researchers to account for temperature effects on electrical conductivity readings. At least two sensors will be installed in each deck at the level of the top mat of reinforcing steel as displayed in Figure 1, and cabling for each sensor will be routed out of each deck, through or around the wing walls, and then through conduit down the face of the given wall to an elevation at which the wires can be conveniently terminated. Task 2: Initial Distress Survey. A distress survey will be completed on each deck after construction, ideally before the onset of winter weather and before application of any planned deck overlay. Traffic control for this field work will be provided by UDOT using monetary resources outside of this contract. Task 3: Laboratory Testing and Field Monitoring. If they are available, extra concrete cylinders cast by the MVC team during construction of each bridge deck will be evaluated in compression testing and also in the rapid chloride permeability test. Such testing will continue in parallel with the field monitoring, with evaluations performed on regular intervals to track the development of strength and durability over time and to allow comparison of the two different kinds of concrete. Monitoring of the sensor data will continue through April 2014, at which time the data loggers will be removed from the site by BYU. Task 4: Data Analysis. All field and laboratory data will be analyzed using statistics to compare the conventional concrete with the concrete containing pre-saturated, lightweight fine aggregate. Task 5: Presentation of Results. Memoranda and oral presentations will be developed and provided to UDOT with the research procedures and results.