Stabilization Option for Soil Subgrade in Low Volume Bituminous Pavements

Abstract

Poor sub grade soil conditions can lead to inadequate pavement support and reduce pavement life. Soils may be improved by soil stabilization by stabilizing by lime, fly ash, cement, rice husk, etc. which are generally waste products and they create disposal problems. These additives can be used with a variety of soils to help improve their engineering properties. The effectiveness of these additives depends on the soil treated and the amount of additive used. The sub grade strength is mostly expressed in terms of California Bearing Ratio (CBR). Weaker sub grade essentially requires thicker layers whereas stronger sub grade goes well with thinner pavement layers.

The pavement and the sub grade mutually must sustain the traffic volume. This work attempts to understand the strength of sub grade in terms of CBR values subjected to different types of stabilizers. Treatment with lime and fly ash was found to be an effective option for improvement of soil properties, based on the testing conducted as a part of this work. It was found that with the addition of stabilizers i.e. lime and fly ash, the C.B.R. increased up to a certain limit but after that the C.B.R. decreased even on the further addition of stabilizers. Long-term performance of pavement structures is significantly impacted by the stability of the underlying soils. In situ sub grades often do not provide the support required to achieve acceptable performance under traffic loading and environmental demands. Although stabilization is an effective alternative for improving soil properties, the engineering properties derived from stabilization vary widely due to heterogeneity in soil composition, differences in micro and macro structure among soils, heterogeneity of geologic deposits, and due to differences in physical and chemical interactions between the soil and candidate stabilizers. These variations necessitate the consideration of site -specific treatment options which must be validated through testing of soil -stabilizer mixtures. This report addresses soil treatment with the traditional calcium-based stabilizers: Portland cement, lime, and fly ash. The report describes and compares the basic reactions that occur between these stabilizers and soil and the mechanisms that result in stabilization. The report presents a straightforward methodology to determine which stabilizers should be considered as candidates for stabilization for a specific soil, pavement, and environment. The report then presents a protocol for each stabilizer through which the selection of the stabilizer is validated based on mixture testing and mixture design. The mixture design process defines an acceptable amount of stabilizer for the soil in question based on consistency testing, strength testing, and in some cases (resilient) modulus testing. Within each additive validation and mixture design protocol, an assessment of the potential for deleterious soil-additive reactions is made.