Development of a Laboratory Microcracking Procedure for Full-Depth Recycled Cement Stabilized Materials

Microcracking of full-depth recycled cement stabilized layers can be an effective method to mitigate the effect of reflective drying shrinkage cracks. To date, no effective method of performing microcracking in the laboratory has been developed. This is needed to determine appropriate levels of microcracking in the field, and to understand how the material will perform after microcracking. This paper covers the development and validation of a nondestructive laboratory procedure that can induce microcracking in specimens to controlled levels. The test setup used in this work was identical to that for the resilient modulus test, which facilitates stiffness measurement before and after microcracking. The use of on-specimen linear variable differential transducers is recommended to exclude end effects that can affect the stiffness result. The results indicate that: stiffness loss is a function of applied energy, and independent of the stress sequence; stiffness should only be calculated at low stress sequences, when the backbone of the stress-strain curve is linear, to accurately represent the stiffness of the material; microcracking effectively reduces the stiffness of the material; the microcracking test is a repeatable and nondestructive test; the stiffness reduction level is controllable; and the test can replicate microcracking effectively in the laboratory to represent microcracking in the field.