Shape characteristics of coarse aggregates are important to performance of materials or mixes. Proportional Calipers are timesaving devices. Use either for rapid determination of percentages of flat and elongated particles in coarse aggregate fractions of 3/8in (9.5mm) or larger. Proportional Calipers are constructed of durable aluminum, precision tooled for accuracy.
For shape determination of flat particle sizing, set the width of a particle in the larger end of the Caliper, then tighten the pivot screw. Without adjusting the Caliper, determine the thickness of the same particle in the smaller measuring end of the Caliper. If the particle fits within the smaller gap, it is considered flat. Elongated particle determination uses the same steps. If the particle is larger than the small measurement in both situations then the particle is considered neither flat nor elongated.
Budget Proportional Caliper consists of a 6x16in (152x406mm) base plate with two fixed posts and a 13in (330mm) pivoting arm mounted between the posts so that there is an opening at each end of the arm. The pivoting arm adjusts by securing a pivot screw at one of four threaded positions to provide end opening ratios of 1:2, 1:3, 1:4, or 1:5.
Meets Test Method:
ASTM D 4791