was 144 3 pounds cubic foot 3896 pounds cubic yard two samples were cast in 4 inch diameter u00d7 8 inch long cylinders a third specimen was a rectangular plate all three specimens were heated on one edge of the finished side using a propane torch approximately 1800 u00b0 c flame temperature and on the opposite edge using a mapp gas torch approximately 5300 u00b0 c flame temperature the areas were heated for 2 minutes at a distance of about 2 inches from the tips of the torches all three specimens produced a slight red glow when heated with the propane and a more intense glow when heated with the mapp gas no violent pop outs or spalling were observed in the test specimens in contrast to the behavior expected from a typical concrete sample those skilled in the art of concrete will appreciate that the optimal composition of the mix will vary depending on the particular application for example the amount of ground expanded perlite replacing the cement may vary from 2 to 25 preferably from 2 to 15 and more preferably from 4 to 15 for a standard 5000 psi concrete the preferred amount of ground expanded perlite will range from about 25 to 100 pounds per cubic yard in general for many applications the amount of cement plus perlite will be about 13 to 18 percent by weight of the total mix for adequate strength in structural applications such as airport runways a suitable coarse aggregate is needed some examples of suitable aggregate materials include gravel limestone and crushed granite the coarse aggregate preferably has a size range from u215c to u00be inch and preferably comprises about.