Fabric forming offers exceptional advantages for underwater work where conventional rigid forms are very expensive and concrete placement by the tremie method further adds to the cost. Normally a sand-cement mortar, occasionally with pea gravel added, is simply pumped into a bag tailored to whatever shape is required. The fabric acts as a separator between surrounding water and the concrete as it flows into the fabric container, preventing segregation of the concrete.
IMPROVEMENT OF WATER-CEMENT RATIO
Any fabric of suitable strength may be used. A refinement of the fabric forming technique uses a highly water permeable fabric which is designed to serve as a filter as well as a form. This fabric is woven of high-strength industrial nylon which has been textured to provide improved filtering as well as adhesion to the mortar. The mortar is pumped into the form and pressure is maintained on the mortar after the form is full. Excess mixing water is squeezed through the fabric causing a pronounced reduction in the water-cement ratio for a distance up to 6 inches or more from the surface of the fabric.
EROSION CONTROL REVETMENTS
The most important application of fabric forming is in the construction of erosion-control revetments. Here two layers of fabric are woven together forming an envelope-like configuration into which structural mortar is injected to form nylon encased concrete armoring to protect the shorelines of waterways, lakes or reservoirs or as drainage channel lining to prevent erosion.