Pavement Review Test 2

Pavement Review Test 2 - MEPDG Mechanistic Empirical...

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MEPDG – Mechanistic Empirical Pavement Design Guide 1 psi = 6.9 kPa Constant stress = creep Constant strain = relaxation Know equations: 7.29, 7.30, 7.40, 7.45, 7.51 Forces Resulted From Friction and Steel Reinforcement between concrete slab and its foundation o tensile stresses in concrete and tie bars effect of volume change on concrete o caused by variation of temperature and moisture o induces tensile stresses and causes concrete to crack o causes joint to open and decreases efficiency of load transfer concrete stress frictional stresses occur b/t slab and subgrade amount of friction depends on relative movement o zero = at center (no movement occurs) o max = some distance from center where movement is fully mobilized tensile stress greatest at center independent of slab thickness joint opening decreases efficiency of load transfer steel stress o steel used in concrete as reinforcements, tie bars, and dowels reinforcements wire fabric or bar mats may be used for control of temperature cracking don’t increase structural capacity of slab but used for o increase joint spacing o tie cracked concrete together and maintain load transfers through aggregate interlock assumed all tensile stresses taken by steel alone amount of steel required proportional to length of slab o same amount used throughout allowable stress generally 2/3 of yield strength welded wire fabric o prefabricated reinforcement
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o parallel series of high-strength, cold-drawn wires welded together in square or rectangular grids o subjected to bending and tensile stresses at cracks tie bars placed along longitudinal joint to tie slabs together joint will be tightly closed to ensure load transfer across joint Joints and Functionality provided in concrete pavements to prevent premature cracking due to moisture and temperature four types of joints o contraction joints transverse joints used to relieve tensile stresses spacing based upon location since type of coarse aggregate materials vary from place to place and have a significant effect on the coefficient of thermal expansion. joint spacing should not exceed twice the slab thickness dummy grooves dummy grooves formed by placing a metal strip on the fresh concrete, which is later removed and sealed with a plastic dowels needed if joint spacing is large or if panels located near the edge of the pavement, and unnecessary if the spacing is small premolded strips permanent and placed in fresh concrete either a felt asphalt ribbon or asphalt board strip
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Pavement Review Test 2 - MEPDG Mechanistic Empirical...

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