Engineer recommends removing gym slab, using structural foam to stabilize Carrie Matthews Recreation Center floor

A consultant told Decatur City Council that the gymnasium floor at the Carrie Matthews Recreation Center has settled and recommended removing the settled slab, stabilizing the subgrade and rebuilding the floor over structural foam to prevent future settlement.

The consultant, identified in the meeting only as a structural consultant, said the center — built in 1968 — shows varying voids beneath the slab, including a 3.25-inch void at one core location and a six-inch void at another. “The final conclusion, our conclusion, is that the gymnasium floor, the half of it that has not been removed, half has been removed, needs to be removed and smooth down some soil, cut down, and then replaced with what's called a structural Styrofoam,” the consultant said.

The recommendation calls for excavating the settled portion of the slab, smoothing and recompacting soils and installing two layers of structural foam (four-by-eight-foot blocks) totaling about one foot of foam beneath the new slab. The consultant described the product as lightweight and used in landslide repairs and bridge-repair work, saying it keeps slab weight from adding to soil settlement.

Why it matters: Council members heard that the condition is more complex than visible surface settlement. The consultant said testing showed weaker soils near the surface and firmer soils about five feet down in the tested locations, with substantial variation across the gym. Council members pressed for confidence that the foam approach would hold long-term; the consultant answered that his report gives specific design numbers and he is confident in the recommendation.

Supporting details and scope: The consultant provided preliminary budget estimates delivered to council members before the meeting: roughly $250,000 for the gym repairs and about $100,000–$150,000 for grouting elsewhere in the building. He warned those estimates do not include probable repairs to utilities that lie under the slab: “I am highly confident that the sewer lines in the building have settled and probably don't drain. And I think that this the cost that I have does not include things as the sewer lines, the water lines, part of the electrical lines were cut when they removed the floor slab.”

Council members and staff discussed next steps. The consultant said he can assist in recommending architects with experience on similar repairs and advised getting an architect to prepare a full bid package that addresses the slab, partition walls and the utility work.

Questions and caveats: Councilmember Justin asked whether the structural foam and the recommended grouting would prevent recurrence in five to 10 years; the consultant replied, “That's correct. I am,” and said he provided specific numbers in his report. The consultant also emphasized the variation across core locations — one core showed an 8.5-inch gap beneath the slab while another showed a 2-inch gap — and said that grouting quantities will vary by cubic foot and the grouting likely must extend down to about five feet in some places.

Next steps: The consultant said he forwarded his report and cost estimate to council and staff. He recommended engaging an architect to produce bid documents that also address the sewer, water and electrical repairs that were not included in his slab estimates. The consultant offered to assist in architect selection and in preparing the scope for bidding.

Ending: Council members thanked the consultant for the study and noted the need to bring back a comprehensive repair scope and formal bid package before funding or construction begins.