The National Veteran’s Memorial and Museum pays tribute to the nation’s 22 million living veterans. Slag cement played an integral role in constructing one of the most complex concrete structures ever built in Ohio.
Mass concrete placements are increasingly common in contemporary building and construction projects. (Mass concrete is defined as concrete that experiences thermal issues attributable to the heat of hydration; cracking, strength reduction and other problems can result when the internal temperature of curing concrete becomes too high.) According to the Portland Cement Association (PCA), “mass concrete has been historically associated with large structures such as dams, bridge piers, and other large volume placements. However, due to the increasingly common use of fast-track construction practices and high-performance concretes…mass concrete issues are being experienced in typical bridge and building placements.”
One recent building project that involved mass concrete is the National Veterans Memorial and Museum in Columbus, Ohio. A key part of the museum’s design is a geometric arrangement of intersecting concrete rings that, according to designers at Allied Works Architecture, represent the branches of service, supporting and strengthening one another. There are no load-bearing columns in the building; it uses 28 million pounds of concrete, reinforced with 1100 tons of rebar, to create a load-bearing frame—a fact that Amy Taylor, Chief Operating Officer of the Columbus Downtown Development Corporation points out is symbolic of the self-reliance of the veterans themselves. The concentric design is also symbolic of the continual, unbroken level of service veterans offer, even once they return to their homes and communities. The concrete arcs serve a functional purpose, too: they are processional ramps that lead to a rooftop sanctuary.
The building’s frame is one of the most complex concrete structures ever built in Ohio. To prevent potential issues with heat of hydration in the concrete, all mixes utilized slag cement supplied by Skyway Cement Company, varying between 35-65 percent replacement for portland cement. Using slag cement reduces thermal stresses in mass concrete in several ways, according to the Slag Cement Association (SCA): the increased strength of slag cement leads to a reduction in the total cementitious content of the mix; portland cement content is reduced by the percentage of slag cement used; and the hydration characteristics of slag cement are such that the early rate of heat generation and peak temperature of the concrete are reduced.
“We wanted to slow the set time of the mass concrete placements in the Veterans Memorial,” said Rod Jenkins, Quality Control Manager, Anderson Concrete Corp. “Anderson has successfully accomplished this in the past by using slag cement. We worked with Baker Concrete [the concrete contractor] and Turner Construction [the general contractor] to achieve the proper mix design. Rob Ford, the Estimating/ Precon Manager at Baker, worked with us in our lab on multiple occasions, testing the self-consolidating concrete mix.”
Self-consolidating concrete was used to give the exposed surfaces an aesthetically-pleasing finish. The concrete was pumped into forms from the bottom up to force air out of the cavities and prevent surface defects in the finished concrete. Slag cement also contributes to a smoother surface, reducing blemishes and improving the uniformity of the finish.
Slag cement helped the mix achieve good early and late concrete strength, as well, with nearly all mixes achieving design strength within seven days.
The design of the National Veterans Memorial and Museum has achieved national acclaim, receiving an ENR Midwest Best Project Award of Merit and an SCA award for innovative application. Originally planned as a state memorial to serve Ohio’s 900,000 living veterans, the project’s scope eventually expanded to become a national memorial, serving 22 million living veterans. The building’s prominent location along the Scioto River in downtown Columbus makes it not only important in celebrating members of the U.S. military, but gives it an integral role in the city’s recently revitalized urban center.
Project Team: Franklin County Commissioners, Baker Concrete, Turner Construction, Allied Works Architecture, Anderson Concrete, Skyway Cement