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Title:Characterizing effective built-in curling and its effect on concrete pavement cracking
Author(s):Rao, Shreenath P.
Director of Research:Roesler, Jeffery R.
Doctoral Committee Chair(s):Roesler, Jeffery R.
Doctoral Committee Member(s):Lange, David A.; Darter, Michael I.; Carpenter, Samuel H.
Department / Program:Civil and Environmental Engineering
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
concrete pavement cracking
Abstract:Differential expansion and contraction between the top and bottom of a concrete slab results in curling. Curling affects stresses and deflections and is an important component of any mechanistic-empirical design procedure. A significant portion of the curling can be attributed to the combined effects of nonlinear "built-in" temperature gradients, irreversible shrinkage, moisture gradients, and creep, which can be represented by an effective built-in temperature difference (EBITD). Several instrumented test sections with various design features were constructed and evaluated using the Heavy Vehicle Simulator (HVS) in Palmdale, California. These instrumented slabs were loaded with a half-axle edge load without wander, to study the effects of curling and to fail the slab sections under accelerated pavement testing. A procedure for estimating EBITD using loaded slab deflections was developed using the HVS results. The advantages are that they can be used for measuring EBITD of slabs with high negative built-in curl and can also be adapted for a Falling Weight Deflectometer, making it an efficient and cost-effective procedure to backcalculate EBITD of in-service pavements. Differences in restraints and variability in concrete material properties resulted in EBITDs ranging from -5 octo greater than -30 °C. The HVS field tests were also used to examine Miner's hypothesis along with various fatigue damage models. Results indicate test slabs cracked at cumulative damage levels significantly different from unity. New models that incorporate both stress range and peak stresses were developed to account for transverse cracking, longitudinal cracking, and comer breaks. For slabs susceptible to high shrinkage gradients, microcracking resulting from early-age restraint stresses that can vary considerably from one slab to another is proposed as a factor that significantly affected the nominal strength of individual slabs, resulting in variability in cracking performance. A procedure to model slab strength reduction and slab size was developed using nonlinear fracture mechanics principles. A parameter called "effective initial crack depth" was introduced to characterize the early-age surface microcracking.
Issue Date:2005
Genre:Dissertation / Thesis
Rights Information:Copyright 2005 Shreenath P. Rao
Date Available in IDEALS:2012-03-01

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