Analyses of top-down cracking in rubblized and flexible pavements

Rubblization is one of the rehabilitation options for deteriorated concrete pavements. The main objectives of rubblization are to destroy the integrity of the concrete slabs and joints and to debond the temperature steel as to eliminate future reflective cracking potential. However, field investigation revealed that reflective cracks, top-down cracks (TDC) and segregation are the dominant distresses on rubblized pavements. TDC were also reported on conventional flexible pavements.; Recognizing the problems, this study was conducted to determine the causes of the underperformance of rubblized pavements and the causes of TDC. The research activities include field and laboratory investigations of rubblized and flexible pavements, backcalculation of pavement layer moduli and 2- and 3-dimensional analyses of stresses induced in the AC layer of rubblized and flexible pavements.; The field investigation consisted of two phases; during the rubblization operation and after construction. In the first phase 15 rubblized pavement projects were investigated whereas 87 rubblized and 10 flexible pavement projects were investigated after the completion of construction. Results of the former indicated that the rubblized concrete slabs consisted of two layers; a rubblized material and fractured concrete with uneven interface between them. Further, in the majority of cases, the temperature steel was not debonded. In the latter, nondestructive deflection tests (NDT) were conducted and cores were extracted from rubblized and flexible pavements. The deflection data were used to backcalculate the layer moduli while the cores were used for TDC verification and for laboratory investigation. To overcome the problems (more than 5-layers and uneven interface between the layers) in the backcalculation of layer moduli of rubblized pavements, a backcalculation procedure and a procedure to estimate the depth to stiff layer were developed and implemented in this study.; Mechanistic analyses were conducted using finite element programs to determine the load-induced stresses in the AC layer. Whereas thermal stresses were calculated using the relaxation constitutive equation and the measured pavement temperatures. Results of the analyses indicated that, in certain scenarios, the potential of longitudinal TDC at the edges of the wheel paths is higher than that for bottom-up cracking and longitudinal TDC are caused by high stress ratio (the ratio of the tensile stress to the tensile strength) at the AC surface and are likely to initiate during summer. The high thermal tensile stresses in winter increase transverse TDC initiation potential and accelerate the propagation of TDC.; Based on the results of field and laboratory investigations and of mechanistic analyses, a guideline to determine TDC based on field observation was developed. Further, it was shown that when the rubblization objectives are not fully satisfied, premature distresses would occur. Consequently, two procedures were developed for the selection of candidate projects for rubblization and for the calibration of the rubblizing equipment as to improve the quality of the rubblization operation.