Cement Manufacturer Builds Storage Dome with PLC
In Indiana, one cement company upgraded one of its facilities to bring state-of-the-art technology to cement manufacturing, including the latest environmental controls. But they did more than just improve equipment; they chose a more sustainable concrete mix for the structural work. As part of the new plant, a storage dome was needed to house the clinker after production and prior to entering the grinding mills.
This provided a good opportunity to introduce more environmentally friendly materials like the manufacturer’s own portland-limestone cement (PLC), an ASTM C595 Type IL material. PLC contains up to 10% more unfired limestone than ASTM C150 portland cement (PC) for a lower carbon footprint yet provides equivalent performance in concrete mixes.
The dome required 7000 cubic yards of concrete; establishing performance of fresh concrete was important so that construction could progress smoothly. The PLC mixes underwent extensive testing to confirm they’d work well with the shotcrete application method. Shotcrete requires that mixes be sprayed out of a gun using high pressure air, and pumpability is a key consideration to assure ease of placement. The dome contractor had never used PLC mixes before, so they ran extensive field testing on mockups and test panels. The contractor also performed strength tests and took core samples to confirm that the strength of the resulting concrete was adequate. After confirming there were no visible differences during the testing phase, the contractor was ready for construction. They found the PLC mixes to be comparable to their typical portland cement mixes for the shotcrete application.
Per ACI 506R-16, Guide to Shotcrete, shotcrete is a cost-effective way to build structures. For structural work, compressive strength should be specified as 4000 psi (28 MPa) or greater. It is suited to thin layer construction. Shotcrete can be placed without traditional formwork, as was the case for this dome. After the foundation work was completed, the contractor inflated a PVC membrane and placed reinforcement inside the exterior skin before placing concrete in layers via the shotcrete method, a process that results in a monolithic dome. The result is a strong, resilient structure with a high tolerance for differential settlement.
At 66.8 m (219 ft) in diameter and 502 m (164 ft) tall, this is the largest storage dome in North America built using PLC mixes. The lower carbon concrete was suited to the goal of improving the environmental performance of the facility. While PLC was chosen for its contribution to concrete sustainability, this project demonstrated that PLC is acceptable for structural uses and compatible with the shotcrete method of placement.