The calculator first computes the volume of concrete needed for the countertop with a ramp sink basin. The formula for the volume of concrete in a countertop with a ramp sink basin is:
V = T* L*W - (0.5 * sWid * sLen * sDep)
where:
V = volume of concrete in the sink
L = Length of Countertop
W = Width of Countertop
T = Thickness of Countertop
sWid = Sink Width
sLen = Sink Length
sDep = Sink Depth
Based on the volume of concrete, the following recipe is used for 1 cubic foot of concrete to compute the volume of materials for the countertop:
32 pounds of Portland cement
8 pounds of Alto-Pozz
90 pounds of 50-50 sand / aggregate mix
14.5 pounds of water (1.737 gallons)
200 grams of fiber mesh (PVA 8mm fibers)
120 ml plasticizer (Optimum 380 premium superplasticizer)
30 ml defoaming additive (C-64 defoaming & densifying additive)
Thanks to Everything About Concrete and Mike Day for the recipe above. His site provides valuable additional information and guidance.