Concrete Test ASTM C39 Cylinder Mold

thingiverse

This two-part mold is filled with concrete to create compression testing cylinders, for determining the PSI or MPa compressive strength of your concrete or mortar or geopolymer or alkali activated cement mix. The halves of the mold are identical, they can be held together with rubber bands or spring clamps during curing, and they peel off the cured cylinder so they can be reused for multiple tests. Consolidate your mix carefully for maximum strength--it's easy to leave big voids that severely impact strength. I printed these in PETG and coated them in baby oil so they release from the concrete easily. The tiny 25mm diameter size only needs about 25cc / 50 grams of concrete or mortar to fill. The 100mm diameter size needs about 1.6 liters / 3 kg of concrete to fill. To determine your sample's compressive strength, add rubber or foam pads on both ends (to avoid fracturing it via point loading) and apply force directly between the ends. This is easiest with a hydraulic press. Use Google to do the unit conversion for your final compressive strength, for example if a 25mm diameter cylinder survived to 78 kgf load, the strength is "78 kgf / ((25mm/2)^2 \* pi) in MPa" == 1.55 MPa. In US units, if the small sample survived a 1500 lb load, its strength is "1500 lb / ((25mm/2)^2 \* pi) in pounds/square inch" == 1971 psi. These cylinder dimensions are used by ASTM C39 compressive strength test, though in these scaled-down versions you might need to use Weibull theory to estimate how the strength will change at full scale.