Book Description
Residual stresses in rigid pavements diminish a pavement's ability to sustain its designed load. When capacity is reduced by residual stress, a pavement is vulnerable to premature failure necessitating costly repairs or replacement. A test method for measuring residual stresses has already been developed for steel wherein a small hole is drilled adjacent to an affixed surface strain gage (ASTM E837 2008). Based on the geometry of the test procedure, the change in strain reading is correlated to a residual stress in the steel material. While rigid pavements are as detrimentally affected by the formation of residual stresses as steel, no similar testing method exists for concrete. Recent research conducted by the Federal Aviation Administration's (FAA0́9s) National Airport Pavement Test Facility (NAPTF) investigated the strain relaxation of cantilevered concrete beams when a blind-depth hole using core drilling is made in the vicinity of an affixed strain gage. Initial findings indicated that the testing procedure partially quantified the residual stresses. Research at the University of Illinois at Urbana-Champaign (UIUC) improved the testing procedure using cantilevered concrete beams by instead sawing a linear notch near one end of the strain gage and sawing two linear notches near both ends of the strain gage. Results for the doubly notched concrete beam proved to be a much improved method for measuring residual stresses when compared to the core-drilled test procedure. The current project further improved test procedures and completed additional lab and field testing on in-situ plain concrete pavements. The test procedure was altered in order to observe the strain relaxation in three directions while four saw cuts are made surrounding the strain rosette. When this area of concrete had been appropriately isolated from load-induced stresses, simple calculations determine the residual stress of the material. Three dimensional Finite Element Model (FEM) analyses of these tests further corroborates the findings suggesting that the residual stresses in plain concrete pavements can be reliably measured.
