In 2010, PPL Holtwood, LLC (PPL) began construction on a project to expand the 100-year-old Holtwood Hydroelectric Station, on the Susquehanna River in Lancaster County, PA. The goal of the $434 million project was to increase production capacity by 125 megawatts and improve migratory fish passage. The existing 108 megawatt power station will be supplemented with the addition of two new hydroturbines in a new powerhouse, more than doubling the station output.
General contractor Walsh Construction turned to CTLGroup to develop thermal control plans and specialized mass concrete mixtures for construction of the powerhouse.
CTLGroup reviewed existing concrete mixture designs and suggested alternate options that would allow for better thermal control. Our experts developed workable self-consolidating mass concrete mixtures optimized for flowability, low heat and long term durability. We assisted in the selection of constituent materials, and performed laboratory tests to verify the fresh and hardened properties of our concrete mixtures before implementation in the field. Once on-site, CTLGroup assisted in fine-tuning and troubleshooting the batch plant to obtain the optimum concrete performance.
By developing innovative flowable low heat mixtures, CTLGroup allowed the client to avoid cooling pipes and expedite the construction process by pumping the concrete into place, instead of using the time consuming crane-and-bucket approach. The team used the maturity method for determination of in-place concrete strength, combined with performance-based temperature limits to enhance thermal control without cutting durability.
The successful outcome of the work done by CTLGroup has saved the client time and money when compared to a traditional mass concrete approach.