Success and the ability to produce the touted benefits of tilt-up result from everyone's involvement in ensuring that fresh and hardened concrete perform as they should. Dennis Ahal, chairman of the board/CEO of concrete subcontractor Ahal Contracting Co. of Bridgeton, Mo., says he believes that superplasticizers have their place, but he recommends using only the minimum amount needed to get the strength desired. He also says that using a well-graded aggregate reduces the amount of paste required, providing equal or higher strength with less water and reducing shrinkage.
Although the ACI 551 Tilt-Up Construction Committee also is in the process of developing a tilt-up specification, the Tilt-Up Concrete Association (TCA) specification currently is the only industry standard. Mix design, test panels, and quality control are all key tenets of the revised TCA specification. Mike Sugrue, P.E., vice president of Con/Steel Tilt-Up Systems, Dayton, Ohio, says that although cylinders are crucial for assessing the strength of concrete in service, beams are needed to ascertain flexural strength prior to lifting.
TCA's revised specification calls for no fewer than four cylinders and three beams for each class of concrete, each 150 cubic yards (114.7 cubic meters) or a fraction thereof, each day concrete is cast, or each 5000 square feet (464.5 square meters) of panel area. The article also describes a joint TCA-ACI tilt-up technician certification program and how to investigate low-strength test results.