Joints in a floor slab can allow liquids to leak out of a tank – creating the possibility of adversely affecting the environment and/or undermining the structure’s foundation. Joints can also allow substances to seep into the tank and potentially contaminate the contents.

VSL’s DuraStor™ tank floors are cast in a single placement with no joints or dowels. The floor is a highly reinforced ductile concrete membrane, normally five inches thick, that can tolerate differential movements while maintaining watertightness. The tendons are "stage-stressed" within 48 hours of casting the floor slab to eliminate shrinkage cracks by providing immediate precompression to the concrete.

Below is a comparison of tank floor slabs (AWWA D110-04 / AWWA D115-06). 
View full comparison.

Floor Slab	AWWA D110-04 Code	Wrapped Prestressed Tank	AWWA D115-06 Code	Tendon Prestressed Tank
Minimum Thickness	3.8.2	four inch for non-prestressed, no prestressed option - ACI 350 allows three inch thickness if reinforced with WWF	3.6	5" if prestressed, 6" if non-prestressed
Concrete Placement	3.8.2	multiple placements - shrinkage cracking and joints that are a potential for leakage and maintenance		single placement is standard practice - no joints or penetrations
Reinforcement		mild steel only	3.6	prestressed with 200 psi residual each direction
Minimum Reinforcement Ratio		0.005 - mild reinforced only - # 5 at 15.5" maximum	3.6	.0015 in addition to prestressing
Concrete Cover on Reinforcement	3.8	none specified - ACI 350 H.4 allows 1.5" top and 1.5" bottom - less for 3" slabs	3.11	1.5" top, 2" bottom