U.S. Concrete Builds A Nuclear Family

In the never-ending pursuit of new markets in which concrete can be a viable or preferred commodity, Dunkirk, Md.-based U.S. Concrete On-Site Inc. (USCOS)

In the never-ending pursuit of new markets in which concrete can be a viable or preferred commodity, Dunkirk, Md.-based U.S. Concrete On-Site Inc. (USCOS) Û the mobile plant division of U.S. Concrete Û has added several new operations to its lineup in the past few years. Jobs requiring fast-track mobilization, custom designs, high security demands, and an environmental awareness have been chief among the company’s varied offerings.

Since 2006, USCOS has secured on-site work in various sectors of high performance concrete, but the company’s most prestigious project to date is the MOX Fuel Fabrication Facility in Aiken, S.C., under contract with Shaw AREVA MOX Services. The job is a U.S. Department of Energy (USDOE) undertaking and the first nuclear-type project in the United States in more than 25 years. With the award of this contract and the approval of the USCOS’s Quality Assurance (QA) Plan for the project, the company has become the only ready mixed producer in the nation that is approved and producing Nuclear Quality Level 1 concrete under its own Quality Assurance plan in accordance with the most rigid regulations and requirements set forth by the Nuclear Regulatory Commission’s (NRC) Quality Assurance Criteria for Nuclear Power Plants and Fuel Processing Plants.

On this project, where traceability is of paramount importance, the company chose to pursue approval of its own QA plan versus the option taken by most other subcontractors to operate as a participant to the plan in place by the general contractor. You have to submit a program with implementing procedures for every action and process in our operations and administration Û from qualifying our raw materials, receiving material at the site, loading and releasing a truck, adding admixtures or water, and documenting everything that took place every operating day, explains Amanda Shepherd, USCOS contract administrator and director of business development. As part of our plan, we had formalized 65 detailed Implementing Procedures, only a small number of which were developed after the project’s start.

Typically for a job this size, we would send 10-12 transmittals to the general contractor for information, project records, and/or approval for work items including submittals and test results on raw materials, storage, testing methods, quality control, and safety plans, to name a few. As of the end of December, we have sent 167 transmittals for this MOX job, all of which go into Documentum for the project.

Compliance with all procedures was documented and addressed using Condition Reports and Non-Conformance Reports, which were administered by the firm’s Quality Assurance manager, David Crowley. In evaluation of all of the CR’s and NCR’s, the most addressed source of rejection in a plastic state was due to slump tolerance, and that only equated to 0.3 percent of the loads of concrete supplied, he says.

That margin of error is phenonmenal for this level of quality assurance. If it’s wrong or even questionable, you dump it on the ground, and adding to that record, we have had zero yards of rejected concrete in place, confirms Shepherd.

The operations and technical acumen of the project team are anchored by the firm’s three leaders, who together have more than 80 years combined experience in the industry, and have been working and thinking outside of the box since the early 90’s when Diana Havenner Bowling owned and operated DYNA Corp. For USCOS, Havenner Bowling runs the business as its general manager; Roberto Talavera serves as operations manager; and, technical services are directed by Stephen Youngerman. Adding to the expertise of the group is company Senior Plant Manager Chuck White, who has been working with Havenner Bowling since 1988. Since finishing his duties on the MOX project, White is currently managing the company’s critical expansion of the Walter Reed Medical Hospital in Bethesda, Md.

To meet the scope of the work and the accelerated mobilization schedule for the MOX project, USCOS brought in the proven services of Material Services, Inc. to design and layout a customized manufacturing system. The system is anchored by two new Vince Hagan HT12400C central mix horizontal plants with 10-yd. batching capacity, which worked along with five mixer trucks to produce and deliver 1,300 yd. of ready mix on busy days.

USCOS had to meet a rapid mobilization schedule. We had 17 weeks to specify, submit for approval, order, have the plants built, and get them delivered and installed to meet the critical path schedule, says Shepherd. In March 2007, our team and our subcontractors stepped up to the plate, and by mid-July, we had fully developed and engineered the site, built foundations, installed our equipment, designed and tested mix designs, hired a new operating staff, and secured all approvals to begin production.

The original scope of work required a single plant operating and the second plant for backup. But as soon as we started production, Shepherd adds, the client realized that they could benefit from higher production rates, and engaged us in a change order to enhance the system to meet 200 yd./hour. A simple task in the standard commercial world, not so simple in the nuclear world.

The peak one-day pour was 1,601 yd., delivered and placed at less than 85_F, despite South Carolina temperatures that often top 100_. In addition, USCOS supplied a controlled low-strength material (flowable fill), which also had to meet NQA1 CLSM specifications.

With all concrete materials either pumped or chute poured for this phase of the work, the production rate required was only 100 yd./hour for most pours, and 200 yards per hour for the larger basemat pours. All totaled, more than 53,000 yd. of ready mixed were delivered, including incidental concrete, with an additional 41,000 yd. of NQA1 CLSM, which were used around the structure in lieu of engineered fill, saving significant costs in placement.

Another value-engineered change provided by USCOS involved the design and testing of a modified basemat mix, which reduced heat of hydration and controlled shrinkage to the point that MOX was able to modify their construction methods to allow for a single, 6.5-ft.-deep mat pour, in lieu of the two-lift configuration that was in the original specifications and design. Using maturity meters and simulating the basemats thru 10-plus-yd. mock-up cubes, USCOS, with engineering support from BASF, provided real-time test data that was the catalyst for changes in mix designs and construction methods, resulting in an estimated $1 million-plus savings for the project.

We showed that if the mix was adjusted, the heat of hydration could be minimized, Shepherd adds. We also showed that the engineered increase in the quantity of fly ash being used in the modified mixes not only supported cost-saving construction methods, but also responsibly disposed of more than 7,000 tons of coal-burning byproduct by using more fly ash in the mixes.

Extensive training for all personnel was critical for this project on every possible level. The batching operation for any NQA1 concrete produced was considered critical pours, especially in the case of a dual-plant operation. The QA procedures dictated the detailed tasks involved in every facet of the operation, including the oversight of a Design Controller for every critical pour. That person was responsible for the plastic characteristics of the concrete and for any adjustments that needed to be made to hold back water and/or admixtures in accordance with the approved mix design limits as well as the process (implementing) procedures.

During the course of the project, the maximum water/cement ratio was never compromised above its limits, every batch documented, and every gallon of water added to the concrete or ounce of admixture was recorded on tickets and reports. This was accomplished by the enforcement of the detailed procedures, along with the use of moisture probes on all aggregates Û fine and course Û and an ice system that weighed the shaved ice and, through the batch system, automatically deducted the amount of ice in pounds from the water in the load, to provide full accountability and recordation of all water and ice included in every load. Furthermore, the constituent ingredients had to stay within the tolerances provided by the specifications.

With the successful completion of USCOS’s contract on the MOX project, no project is too technical or demanding for its capabilities, and forecasts for 2009 and beyond are strong, despite an economy that contradicts business growth for most of the construction industry.
Û The article was adapted from material supplied by U.S. Concrete On-Site Inc., 410/286-3500