Improving the Foundation Layers for Concrete Pavements: Assessment of Seasonal Variations in Concrete Pavement Foundation Layers – TPF-5(183) Multiple Test Sections in Iowa -

(2016) Improving the Foundation Layers for Concrete Pavements: Assessment of Seasonal Variations in Concrete Pavement Foundation Layers – TPF-5(183) Multiple Test Sections in Iowa -.

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Abstract

This technical project report is one of the field project reports developed as part of the TPF-5(183) and FHWA DTFH 61-06-H00011:WO18 studies. In cold climates, pavement surfaces and foundation layers are subjected to seasonal temperature variation and freeze-thaw cycles. The number and duration of freeze-thaw cycles in foundation layers can significantly influence pavement performance. Seasonal variation in foundation layers is accounted for in pavement design by empirically adjusting foundation layer moduli values. This paper presents results from in situ falling weight deflectometer (FWD) and dynamic cone penetrometer (DCP) tests conducted over a two-year period at five sites in Iowa; at one of these sites, temperatures of the foundation layers were continuously monitored during the testing period. FWD testing was conducted to determine modulus of subgrade reaction (k) values, and DCP testing was conducted to estimate California bearing ratio (CBR) values of the foundation layers. Temperature data was analyzed to determine freezing and thawing periods and frost penetration in the foundation layers. Seasonal variations observed in the mechanistic properties of the foundation layers were compared with assumed design values, and empirical relationships between the mechanistic properties were explored. For the five sections tested in this study, there were no significant differences in the k values obtained from the FWD in thawed conditions and summer. At four of the five sites, there were no significant differences in the CBR values obtained from DCP tests during thawed and summer conditions. The k values from FWD during frozen conditions were about 10% to 56% higher than in summer at four of the five sites. At one test site, the values were about the same at all testing times. At two of the five sites, k values from FWD were about 1.5 to 2 times lower than the design assumed k value (41 kPa/mm) in thawed condition and in summer. Empirical relationships presented in the design guides to convert CBR to k or Mr to k showed much higher values compared with measured values. Pavement age, k values, and subgrade CBR values were all strongly correlated to the pavement condition index (PCI) values.