We have decided to use ASTM C-1272-05a, "Standard Specification for Heavy Vehicular Paving Brick" as our standard
for making an adequate brick. This is a good standard for this project because paving bricks are generally smooth, without hollow cores or frogs, and we can only make smooth bricks. The two physical requirements we will try to meet are Breaking Load and Cold Water Absorption.
Cold water absorption gives us the resistance to freeze/thaw and a sense of whether the brick is fully fired. High porosity often correlates to low strength. The standard for cold water absorption is an average of 6.0 percent for 5 bricks. In our initial absorption tests we determined that we can get below 6 percent absorption by firing 50 percent glass bricks to 1850F. We also determined that we can prevent visible cracks by firing to 1850 in ninety minutes, then holding at 1850 for 30 minutes.
So our standard time/temperature curve looks like this:
Vertical Scale is Degrees F, Horizontal Scale is hours/minutes
So we make ten bricks using the profile above. The absorptions of the ten glass/clay bricks are:
Average absorption is 4.1%, with a remarkably narrow variance. It was also notable that there were no rejections, that is, none of the bricks made using this profile had visible cracks.
Ultimately, this project is about determining how much energy is takes to make a glass/clay brick vs. a grog/clay brick, so now we have to find an equivalent absorption using the same clay and regular grog. In a screening test, the gradation of the glass we are using looks like this:
