If the subgrade bearing surface is aggregate, contractors have different methods of ensuring optimum compaction and a high standard of care for the final grading. More often, the subgrade system is prepared low, and either with shim stacks or levelling devices, precast foundations are set to proper elevations and flowable material is pumped through openings in the foundation until it flows out all sides ensuring full and uniform bearing. Early ABC (Accelerated Bridge Construction) projects used non-shrink grout for this fill. This is not recommended as it is very expensive. Typical bearing pressures under footings are less than 1000 psi. Therefore, there is no need to use a high strength grout for this purpose. The more common material now in use is flowable fill, which flows easily, is much less expensive, and has adequate capacity.