Evaluation of the Impact of Fines on the Performance of Lightly Cement-Stabilized Aggregate Systems

Abstract

The impact of increasing fines content on the performance of unbound (unstabilized) and lightly stabilized aggregate systems was evaluated. The aggregate systems analyzed varied in amount of mineral fines, the moisture state during curing and at the time of testing, and the amount of portland cement used to stabilize the blend. The evaluation was based on measurements of anisotropic resilient properties, permanent deformation, and unconfined compressive strengths of aggregate systems. In addition, the nonlinear anisotropic resilient properties of the aggregate blends were used in a finite element program to determine critical pavement responses. Aggregate systems with higher fines content were, as expected, more sensitive to moisture than control systems with standard fines content. The increase in the fines content in the unbound systems when molding moisture was wet of optimum dramatically diminished the quality of performance. However, the aggregate systems with higher fines benefited considerably from low percentages of cement stabilizer. It was found that with the proper design of fines content, cement content, and moisture, the performance of the stabilized systems with high fines content can perform equivalent to or even better than the systems with standard fines content. This was clearly evinced by enhancing the resilient properties (increase in stiffness and decrease in anisotropy), decreasing the rate and magnitude of permanent deformation, and increasing compressive strength. The beneficial use of mineral fines will result in benefit to the aggregate industry.Approximately 75 to 80 million tons of fines smaller than the number 200 sieve (75 µm) are produced annually in the United States. These materials are not successfully marketed and therefore add to stockpiles and storage ponds. These waste fines total approximately 400 million tons in the United States (1, 2). Well-characterized aggregate layers containing higher fines content than currently permitted are an attractive means by which to use more fines and reduce stockpiles of fines. Achieving this objective would have significant economical and environmental impacts.Several researchers have studied the resilient behavior of high fine unbound systems. These studies reported a decrease in the resilient modulus caused by an increase in fines content (3-5). Gray (3) reported that in unbound aggregate bases with 25.4 mm maximum particle size, the highest strength was achieved through using a maximum of

Characterization of Cementitiously Stabilized Layers for Use in Pavement Design and Analysis

“…Increasing the cement content increases the UCS and resilient modulus values (Arora and Aydilek 2005). Increasing the fines content up to 30% increases the resilient modulus of lightly stabilized soil and the UCS (Ashtiani et al 2007).…”

Evaluation of Characterization and Performance Modeling of Cementitiously Stabilized Layers in the Mechanistic–Empirical Pavement Design Guide

“…For example, the elastic modulus is expressed in terms of unconfined compressive strength through statistical correlations for LCB and CTB (1). This information could be exploited to the benefit of CSM modeling in MEPDG, because the unconfined compressive strength test is the most widely adopted method of testing (6,(11)(12)(13)(14)(15)(16)(17)(18)(19). Although these generic correlations can lead to mistaken design values in very rare instances, by and large, they effectively estimate relevant elastic parameters.…”

“…MEPDG does not require a direct input of compressive strength of CSMs for its modeling. However, the unconfined compressive Existing research discusses the application of the UCS test to soil cement (11,13,14) and cement-stabilized aggregates (6,12,(15)(16)(17)(18)(19) to correlate compressive strength with other properties such as tensile strength, elastic modulus, resilient modulus, and shrinkage. Much of this research also studies the effect of repeated loading, freeze-thaw, and wet-dry cycles on compressive strength.…”

“…The effect of cement content and moisture content on unconfined compressive strength varies considerably depending on the test conditions, although the general trend suggests that the stiffness and strength increase with the increase of cement content. Although an optimum stabilizer-fines ratio has been found to result in maximum compressive strength, increasing the cement content also leads to an increase in the water content, which in turn causes increased shrinkage because of drying and temperature changes (17). Ventura recommended that a maximum limit be placed on unconfined compressive strength to deal with excessive shrinkage and cracking for CTB and LCB (15).…”

Material Factors that Influence Anisotropic Behavior of Aggregate Bases

“…They established correlations between shear strength ratios and anisotropic modular ratios and reported that "good quality" aggregate systems have higher modular ratios (horizontal modulus-vertical modulus) or are less anisotropic, and "poor quality" materials have lower modular ratios or are more anisotropic. The study conducted by Salehi et al (7) on high fine content aggregate systems emphasized that the analysis should consider all anisotropic material properties and not modular ratios only. They showed that despite the fact that unstabilized high fine systems are less anisotropic, they performed poorly and developed significant plastic strains when subjected to repeated loading at elevated saturation levels.…”