Durability of cementitiously stabilized aggregate bases for pavement application.

Abstract

Cementitious stabilization has been extensively used to improve the performance of pavement materials. In the past, emphasis has been placed on observing the macromanifestation of stabilized pavement materials, but to the author's knowledge, very little effort has been directed toward the micro-manifestation. In this study, selective existing techniques, namely, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), are used to assess the micro-structural development of cementing compounds in stabilized aggregate specimens. Specifically, the reference intensity ratio (RIR) method is employed to semi-quantify the mass percent of minerals and cementing compounds in the mixtures. Results reveal the formation of cementing compounds (due to stabilization) such as ettringite, calcium silicate hydrate (C-S-H), calcium aluminum hydrate (C-A-H) and calcium aluminum silicate hydrate (C-A-S-H), which are responsible for the increase in strength. Findings from this study shed light on the use of semi-quantification techniques in cementitious stabilization. These techniques would provide a better understanding of cementitious reactions related to their short- and long-term roles. (Abstract shortened by UMI.)

In this study, the effect of durability, namely, W-D and F-T cycles, on the resilient modulus (Mr) of stabilized aggregate bases is examined. A total of four aggregates commonly used in Okalahoma are utilized. Cylindrical specimens are stabilized with cement kiln dust (CKD), class C fly ash (CFA) and fluidized bed ash (FBA), and then cured for 28 days. After curing, specimens are subjected to W-D or F-T cycles prior to testing for Mr. Results show that the changes in Mr values due to W-D or F-T cycles depend on the stabilizing agent properties and physical properties represented by maximum dry density and optimum moisture content.

In addition, the effect of F-T cycles on the flexural behavior of CFA-stabilized aggregate beams is investigated. This study is motivated by the fact that stabilized aggregate bases are subjected to flexural stresses under wheel loading. Thus, the flexural strength (represented by modulus of rupture) becomes another important design parameter in designing a pavement within the mechanistic framework. Beam specimens are prepared by compacting aggregates mixed with CFA and water, and then cured for 1 hour, 3 days and 28 days. After curing, specimens are subjected to F-T cycles and then tested for resilient modulus in flexure (Mrf) and modulus of rupture (MOR). It is found that both Mrf and MOR exhibit a decrease as F-T cycles increase. Among other benefits, this study helps enrich the database on the durability of stabilized aggregate bases. Also, the test procedures employed in this study are expected to benefit future studies in this area.