Modulus of Rubblized Portland Cement Concrete from Surface Wave Testing

Several Interstate portland cement concrete (PCC) pavement sections in New Jersey are being rubblized by multihead breaker equipment; the rubblized concrete is later compacted by several passes of vibratory Z-grid and rubber-wheel static rollers. To evaluate the modulus of the rubblized PCC and to compare it to the modulus of a typical dense graded aggregate base material, nondestructive evaluation using surface waves, implemented in a portable seismic property analyzer, was conducted. The elastic modulus is evaluated from the average velocity of surface waves, from the shortest measurable wavelength (about 2 in.) to one equal to an approximate thickness of the rubblized concrete (about 10 in.). In addition to the average velocity (modulus), the variation of the surface wave (phase) velocity with wavelength can be related to the variation of modulus with depth. The modulus obtained from seismic testing is a low-strain modulus, and appropriate corrections (reductions) should be provided to describe it as a resilient modulus. The modulus variation is largely constrained between 550 and 2,800 MPa (80 and 400 ksi), with an average modulus between 1,100 and 1,400 MPa (160 and 200 ksi). Significant modulus variation is attributed to the rubblization process, which provides the highest crushing of concrete near the surface; near the bottom, rubblized concrete appears more like fractured rock and can form an uneven interface between the two zones. In general, the modulus of rubblized PCC is higher than the modulus of a typical granular base.