Development of an Evaluation Protocol for Self-Cementing Secondary Road Base Materials

Abstract

In congested areas around the world, traffic has significantly grown beyond expectation in terms of both volume and weight. Any hinder to the traffic causes severe delays resulting not only in economic loss but also in extra pollution of the environment. Therefore, the number of times maintenance work have to be performed should be reduced as much as possible. Application of self-cementing, secondary materials such as Blast Furnace Slag (BFS) for base courses is one of the methods to reduce the need for maintenance, since such base courses can provide an increase of the stiffness and the strength of the pavement structure. The long-term performance of this type of self-cementing, secondary material is however not fully understood. Because this type of stabilization appears to be associated with undesired deformations and distresses such as heaves formation and cracking. These undesired defects, which appear at random in terms of severity and moment of occurring, requires an assessment of the long-term physical and mechanical performance of these materials. However, long-term behaviour is often difficult to predict. In general, field-scale trials monitored over a long period of time, are needed to provide information whether these materials can be used without significant risk or not. As an alternative to field trials, which are time consuming and expensive, reliable methodologies are needed to estimate the long-term physical and mechanical performance within a short period of time. In this research, a protocol is proposed as a means of exploring the long-term mechanical and physical performance of secondary materials. A slag mixture which is routinely used in the Netherlands in road (sub-)bases was selected as study material. The slag mixture consisted of fresh Air-cooled Blast Furnace Slag (AC-BFS), steel slag and Granulated Blast Furnace Slag (GBFS) sand. The A32 motorway in the Netherlands was used as a source of field aged Blast Furnace Slag and steel slag materials. The pavement structure of this motorway experienced serious failure after about 20 years of service life and the base layer material caused this failure. In order to prevent similar problems to occur in the future, this research suggests different methods to detect at an early stage potential poor material performance. The first step of exploring the long-term performance of self-cementing materials in road applications implies obtaining a better understanding of the physical, mechanical and microstructural features of the materials when used as road base material and to analysis its possible effects on the pavement performance. Consequently, the influence of different potential degradation conditions, which can be mimicked in the laboratory was investigated. Numerous failure mechanisms have been hypothesized, including chemical reactions and increased stresses due to obstructed deformations. Additionally, other physical failure mechanisms including frost action damage were investigated. The results show that there is a linkage between the secondary material performance and temperature, moisture, chemical composition and time. The measured data indicate a relationship between some major chemical compositions and the mechanical properties of slags. The response of the laboratory prepared samples to the proposed tests were similar to the A32 base material failure, suggesting that the evaluation method did a reasonable job of producing in an accelerated way in the laboratory a material which behaves similar as the A32 material. The developed procedure (protocol) suggests that it is possible on the basis of material characterization, steam aging tests and freezing – thawing tests to trace in a rather short period of time materials which may attribute to the failure process of base layers in pavements.Structural EngineeringCivil Engineering and Geoscience