CRACK FORMATION IN CONTINUOUSLY-REINFORCED PAVEMENTS

RESULTS OF A SERIES OF LABORATORY EXPERIMENTS ON SIMULATED CONTINUOUSLY REINFORCED CONCRETE SLABS ARE GIVEN, WITH THOSE RESULTS PERTAINING TO THE FORMATION OF CRACKS BEING EMPHASIZED. THE FINDINGS OF THESE LABORATORY EXPERIMENTS ARE CORRELATED WITH THE FIELD OBSERVATIONS REPORTED IN THE LITERATURE. SOME OF THE MORE IMPORTANT CONCLUSIONS REACHED AS A RESULT OF THIS RESEARCH, SUBJECT TO THE LIMITATIONS IMPOSED BY THE RANGE OF VARIABLES STUDIED, ARE AS FOLLOWS: (1) THE EFFECTS OF CONCRETE SHRINKAGE, TEMPERATURE CHANGES, AND WHEEL LOADS ON CRACK FORMATION IN CONTINUOUSLY REINFORCED PAVEMENTS CAN BE ADEQUATELY SIMULATED IN THE LABORATORY WITHOUT PRODUCING ACTUAL TEMPERATURE CHANGES IN AN INFINITELY LONG PAVEMENT SLAB. (2) THE FORMATION OF COMPLETE CRACK PATTERN IN A CONTINUOUSLY REINFORCED PAVEMENT IS THE RESULT OF A SUPERPOSITION OF THE EFFECTS OF CONCRETE SHRINKAGE, TEMPERATURE CHANGES AND LIVE (WHEEL) LOADS. (3) CRACK SPACING IN A CONTINUOUSLY REINFORCED PAVEMENT WITH SOME AGE AND USE VARIES INVERSELY WITH THE PERCENTAGE OF LONGITUDINAL STEEL REINFORCEMENT, IF THE STEEL IS PLACED AT MID-DEPTH, WITH A MINIMUM AVERAGE CRACK SPACING OF ABOUT 2 FT IN A SLAB HAVING 0.768 PERCENT LONGITUDINAL STEEL. (4) IT IS GENERALLY AGREED THAT A CONTINUOUSLY REINFORCED PAVEMENT SLAB MUST BE REINFORCED WITH LONGITUDINAL STEEL IN SUFFICIENT AMOUNT TO MAINTAIN ALL TRANSVERSE CRACKS IN A TIGHTLY CLOSED CONDITION. FOR MID-DEPTH REINFORCEMENT THIS CONDITION IS MET WHEN INCREASING LONGITUDINAL FORCES CAUSED BY TEMPERATURE DROPS, IN COMBINATION WITH LIVE LOADS, TEND TO CAUSE ADDITIONAL CRACKS RATHER THAN TO OPEN EXISTING CRACKS FOREVER WIDER. (5) THE SUGGESTED DESIGN CRITERION IS SATISFIED FOR AN 8-IN. PAVEMENT RESTING ON A SUBGRADE HAVING A MODULUS OF 160 PCI, BY 0.45 PERCENT LONGITUDINAL REINFORCEMENT EITHER IN THE FORM OF DEFORMED BARS OR WELDED WIRE FABRIC REINFORCEMENT PLACED AT MID-DEPTH IN THE SLAB. /AUTHOR/