Evaluating stiffness and strength of pavement materials

Current mechanical empirical-based pavement design requires use of the mechanical properties of pavement materials. For quantitative evaluations of the mechanical properties (i.e. stiffness and strength), field tests are emphasised. In this paper, a recently developed instrument called the soil stiffness gauge (SSG) and the dynamic cone penetrometer (DCP) have been used to assess respectively the in-situ stiffness and strength of natural earthen materials, industrial by-products, and chemically stabilised soils from ten highway construction sites around the state of Wisconsin, USA. The SSG and DCP survey data were analysed to develop a relationship between the SSG stiffness and DCP penetration index (DPI) values for individual material types and for all materials combined. A simple linear semi-logarithmic model is obtained between the SSG stiffness and DPI values, with the coefficient of determination, R-2, ranging from 0(.)47 to 0(.)75 for individual material types and an R-2 value of 0(.)72 for all materials combined. The SSG stiffness and DPI values can be also correlated with the modulus (E) and California bearing ratio (CBR) of the materials respectively. A good relationship is obtained between E from the SSG and CBR from the DCP, and is compared with the well-known equations developed by Powell et al. and AASHTO as well as other available correlations from different in-situ tests: the falling weight deflectometer, German light drop weight, and plate load tests. Finally, the proposed power model is validated with a data set from two other test sites. Either or both devices show good potential for future use in pavement and subgrade materials evaluation. The in-situ stiffness and strength properties of various materials can be rapidly and directly monitored in companion with the conventional compaction control tests during pavement construction. The modulus of pavement and subgrade materials is uniquely related to CBRs regardless of soil type and site, and their relationship is also applicable to both as-compacted and post-construction states.