Lecture 31 AASHTO Design MethodThis method developed out of the AASHTO road test in the 1960s and has been refined several times. AASHTO Design Guide . The equation from the 1986 Guide iswhereZR = Standard normal variantSo = overall standard deviationW18 = 18 kip ESALD= thickness in inchesDPSI = serviceability lossPi = initial serviceabilityPt = final serviceabilityEc = elastic modulus of concreteSc = modulus of rupture of concreteJ = load transfer coefficient = 3.2 (assumed)Cd = drainage coefficientK = modulus of sub grade reactionChange in performance, PSI usually 2 to 2.5Requires corrections forThickness of sub baseLocation of bedrockMOR-varies with concrete mix in the range from 500-800 psiModulus of elasticity- typical value 4000000 psiLoss of sub grade supportLecture 31 AASHTO Design MethodThis method developed out of the AASHTO road test in the 1960s and has been refined several times. AASHTO Design Guide . The equation from the 1986 Guide is))//(42.18(132.1(63.215log)32.022.4())1/()10624.1((1))5.15.4/((log06.0)1(log35.7log25.075.075.0'1046.8710101810kEDDJCSPDxPSIDSZWcdttoRwhereZR = Standard normal variantSo = overall standard deviationW18 = 18 kip ESALD= thickness in inchesDPSI = serviceability lossPi = initial serviceabilityPt = final serviceabilityEc = elastic modulus of concreteSc = modulus of rupture of concreteJ = load transfer coefficient = 3.2 (assumed)Cd = drainage coefficient K = modulus of sub grade reactionData needed to solve the equation for pavement thickness.Change in performance, PSI usually 2 to 2.5Modulus of sub reaction Modulus of Sub Grade Reaction Test Requires corrections for Seasonal effectsThickness of sub baseLoss of supportLocation of bedrockTraffic – by ESALConcrete propertiesMOR-varies with concrete mix in the range from500-800 psiModulus of elasticity- typical value 4000000 psiDrainage coefficient as in the flexible pavement designReliability- depends on the functional classification 50%-99.9%Standard deviation-0.4 to 0.5Load transfer – RJCP = 3.2, PJCP = 3.8Loss of sub grade support CTB = 0 to 1Granular = 1 to 3Fine granular = 2 to 3Solution to equation shown in AASHTO Design Guide for Pavement Structures or Fig 21.13 A Calculator for determining concrete pavement thickness is available at Calculator for Concrete Surfaced