Pavement Preservation

Fly ash grouts are used for sealing voids beneath pavement slab sections. The unconfined compressive strength requirements for a grout mixture will usually exceed 8,300 kPa (1,200 psi) at 28 days and will range between 4,100 and 5,500 kPa (600 and 800 psi) at 7 days.

This strength profile for grouts differentiates them from flowable fill materials inasmuch as the flowable fill definition (or controlled low strength material) sets an unconfined compressive strength limit of 8,300 kPa (1,200 psi) at 28 days. Furthermore, the relatively small size of the void filled with the grout mixture further differentiates this application from the larger voids where the lower strength flowable fills are utilized.

The principal requirements for a slab stabilization material is that it can flow to fill very small voids and still have adequate strength to support the slab. A good stabilization material should remain insoluble, incompressible, and not erode after it has been placed and hardened. It should also have sufficiently low internal friction to flow into very small voids and water channels. If the material is too stiff, it will create a seat below the grout hole and not fill all voids. If it is too wet, it will not have enough strength to support the slab and may have a large amount of shrinkage. Finally, it should have sufficient body to displace free water from under the slab and develop adequate strength and durability.