Green strength is a continuing concern of most brick manufacturers. Once the column leaves the die, there is no way that it can be made any better, although it can be ruined in many ways. Flaws not only remain, but generally get worse and/or cause related problems down the line. Although ASTM procedure C-67-5 for determining modulus of rupture does exist, it is not required. Very few plants use the method, and even fewer keep records of green strength.
Determining the effect of a change in the mix on green strength is an interesting, but tricky, process. For example, assume that you have tested brick made with mix 1 and found its green modulus of rupture averaged 35 psi, while brick made with mix 2 averaged 40 psi. Which mix produced the strongest brick? Did you choose mix 2? How can you be sure that it was the mix that produced a stronger brick and not some other condition?
To make that determination, you need to know the precise amount of water of plasticity in the test brick. You need to know the rate of extrusion, the power consumption of the extruder, the …
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