Question: Hi my name is Ervin. I own a small flatwork business in Eastern Pennsylvania. Two years ago we poured a pole barn floor for one of our contractors. The building houses truck tires. They use a forklift to handle up to 10 tires at a time. The floor was poured 6 inches thick and 4000 psi, with standard fibermesh that the contractor specified. When they drive their forklift across the sawcuts, you can see the floor move, with the worst being1/8to1/4inch. The customer is concerned, and rightfully so. I found some curling at the sawcut joints, which were on 4-foot centers. The average curl is maybe about1/4to3/8inches. The customer provided his own excavator and the job was done in early spring on a wet jobsite. I say the floor was under engineered and on a soft base. The contractor says it is a workmanship problem between me and the excavator. What are your thoughts on this and how should I go about repairing it? The contractor suggested pumping grout under the floor at the joints, but I don't think that is a good idea and not a permanent fix. Any comments or suggestions would be appreciated. Thanks.
Answer: It sounds like you've had quite a bit of curling, which is generally worse with wetter mixes. Even if the mix didn't have particularly high water content, the wet jobsite could contribute to the curling you've experienced. Aggregate gradation can influence how much curling occurs. Although adding fibers helps control shrinkage and cracking early in the slab's life, I'm not sure it does anything to limit curling over time—especially at low dosages.
You might want to look into something developed by the Somero Matson Group, their SD-7 join stabilizing system. Someromatsongroup.com has some good explanations, including animations of how curling affects forklift traffic and how their joint stabilization system can help.
Somero Matson has a downloadable PDF that talks about how Pep Boys has used the system.
I hope this is enough to get you started.