Evaluation of Optimum Rubblized Depth to Prevent Reflection Cracks

Reflection cracking is a common distress in asphalt overlays on cracked concrete pavements. Rubblization, which can minimize reflection cracks, has been used as an efficient rehabilitation method for aged concrete pavements in the United States. When applying the rubblization method, it is typical for the upper layer of aged concrete pavement to be rubblized to $40–70\mathrm{mm}$ in size, while the lower layer of the aged concrete pavement remains at a larger size, often over $300\mathrm{mm}$ . For thick concrete slabs, it is difficult to rubblize the entire depth of thick concrete slabs in terms of both construction and cost. The high impact energy necessary to rubblize the entire depth may cause degradation of the structural capacity of the pavement substructure. Korean highways are typically paved with thick concrete pavement slabs ( $30–33\mathrm{cm}$ concrete slabs with $15\mathrm{cm}$ lean concrete bases on granular subbases). This study conducted in Korea determined the minimum depth of effective $40–70\mathrm{mm}$ size rubblization to deter a reflection crack. An indoor simulation experiment was designed to assess the effects of the depth of the $40–70\mathrm{mm}$ rubblized layer on the prevention of reflection cracks. The experiment simulated two modes of reflection crack initiation: Mode I (bending failure) and Mode II (shear failure). Modes I and II tests were carried out for rubblization depths of 0, 10, and $20\mathrm{cm}$ . Reflection cracking did not occur with the simulated rubblization depths of $10\mathrm{cm}$ or $20\mathrm{cm}$ .