Advanced Foundation

Basics

Compacted rock foundations are much less energy intensive than concrete. A good example of a solid gravel base is the railroad track - which sustains very heavy loads of 86 tons [1] - and is only 20" thick at max. By maximizing the quantity of rock, the quantity of concrete can be minimized.

Concrete is 10-15 percent cement. Cement is typically 1:2:3 or 1:3:3 [2]. 1:3:3 is 13% cement.

Embodied energy of cement - 5.6 MJ/kg. Concrete trucks get 3 mpg [3].

One gallon of gasoline can produce 20kg of cement, or 1 weight of gasoline produces 5 weights of cement. Thus, one weight gasoline produces 35 weights of concrete - which is a strong case for using more rock, less cement.

Gasoline is 121 MJ per gallon. [4]

Embodied energy of rock from gravel pit - aggregate seems to be 1/10 the embodied energy of concrete [5].

Conclusions

Just to haul gravel - we are spending say 3 mpg, 25 mile haul - 8 gal - or equivalent of 1 ton of concrete in embodied energy. 10 dumps of gravel have same embodied energy as a concrete truck. Thus, say we minimize the concrete required by using more rock: say instead of 6" of rock, we use 20" of rock (4x more). Then we still come out ahead as opposed to using concrete - in embodied energy. However, a truck of concrete is $1500. 4 trucks of gravel are comparable. Thus, cost is comparable. Embodied energy of rock is smaller.

Local solar concrete can cut down the transportation costs and fuel significantly.