Tuncer B. Edil

The purpose of this study is to evaluate the performance, costs, energy, and greenhouse gas emission of cementitious high-carbon fly ash (CHCFA)-stabilised recycled pavement materials (RPMs) as base course. Three test road cells were built in Minnesota. These cells have the same pavement structure except different base courses: conventional crushed aggregates, untreated RPM, and CHCFA-stabilised RPM. Results of laboratory and field tests were used in the Mechanistic-empirical pavement design guide (MEPDG) to predict the pavement performance. MEPDG performance prediction indicated that Cell 79 containing CHCFA-stabilised RPM had the longest service life in the three cells. The life-cycle analysis indicated that the usage of the CHCFA-stabilised RPM as the base of the flexible pavement can significantly reduce the life-cycle cost, energy consumption, and greenhouse gas emission.

Data from bench-scale composite liner experiments were compared with predictions made with two models, a finite-difference model and a semianalytical model, used to predict volatile organic compound (VOC) transport through composite liners. Transport parameters for the geomembrane and clay for five common VOCs were measured independently and used as input. Predictions from both models for all five VOCs were essentially identical. Excellent agreement was obtained between the predicted and measured concentrations for all five VOCs without model calibration. However, inherent variability in measured transport parameters has a significant effect on predictions. Volatile organic compound concentrations in the clay liner near the geomembrane-clay interface depend primarily on transport parameters for the geomembrane. However, this becomes less significant as the distance from the geomembrane-clay interface increases.

The effectiveness of fly ash use in the stabilization of organic soils and the factors that are likely to affect the degree of stabilization were studied. Unconfined compression and resilient modulus tests were conducted on organic soil–fly ash mixtures and untreated soil specimens. The unconfined compressive strength of organic soils can be increased using fly ash, but the amount of increase depends on the type of soil and characteristics of the fly ash. Resilient moduli of the slightly organic and organic soils can also be significantly improved. The increases in strength and stiffness are attributed primarily to cementing caused by pozzolanic reactions, although the reduction in water content resulting from the addition of dry fly ash solid also contributes to strength gain. The pozzolonic effect appears to diminish as the water content decreases. The significant characteristics of fly ash that affect the increase in unconfined compressive strength and resilient modulus include CaO content and CaO/SiO2...

Bentonite was modified at the nanoscale so that low hydraulic conductivity would be maintained under adverse conditions. Nanoscale modification consisted of polymerizing acrylic acid within a bentonite slurry to form a stable interconnected structure. This modified material is referred to as a bentonite-polymer nanocomposite (BPN). The BPN was then air dried and ground to simulate the granule-size distribution of granular bentonite in geosynthetic clay liners (GCLs). Index property tests indicate that BPN has different behavior than natural sodium bentonite (Na-bentonite). For example, free swell tests with natural Na-bentonite swelled to approximately 30 mL in deionized water, whereas BPN swelled to more than 70 mL in the same solution. GCLs were assembled and directly permeated with a range of calcium chloride (CaCl₂) solutions known to cause large increases in the hydraulic conductivity (k) of natural Na-bentonite. Low hydraulic conductivities (k < 3 x 10^–10 cm/s) were maintained by BPN for all solutions tested. In contrast, natural Na-bentonite tested under the same conditions had k more than 4 orders of magnitude higher (k > 2 x 10^–5 cm/s). Additional study of the properties and the underlying mechanisms of BPN are ongoing.

A smear zone, i.e., a disturbed zone is considered to form during installation of a prefabricated vertical drain (PVD) using a mandrel and this zone retards the horizontal consolidation of soft clays in the vicinity of PVD. The characteristics of the smear zone, such as its extent and hydraulic conductivity remain discrepant among investigators. This study attempts to determine the extent of the smear zone and to measure the hydraulic conductivity of the smear zone directly by laboratory tests. For this purpose, a Smear Zone Model (SZM) test is described. The tests indicate that two soil zones are identifiable in the soil mass surrounding the PVD after the PVD installation using the mandrel. The extent of the smear zone is about 3 to 4 times the equivalent radius of the mandrel depending on soil type. The smear zone permeability ratio was measured to be about 1.03 to 1.25 for the soils tested. However, the test conditions employed were least conducive to generating a highly disturbed zone.

The effects of deformation on PVD discharge capacity remain discrepant among investigators. This study investigates the discharge capacity behavior of deformed PVDs using a laboratory performance test. Four different PVDs were tested, and two different soils were used for confinement. The reduction of the discharge capacity of PVDs varied with the type of PVD and percentage settlement, and reached up to 99% at a maximum percentage settlement of 41%. Hydraulic gradient also appreciably affects discharge capacity, owing to the non-steady-state flow in the core of the PVD. Soil type impacts on the deformation pattern of PVDs, but its effect on discharge capacity appears to be slight in this study. Soil type, however, has a significant influence on required discharge capacity. For a 20 m long drain in example calculations, one of the PVDs would result in restriction of water flow and cause significant increases in time for consolidation. Additionally, if soils with a higher hydraulic conductivity, such as 1 × 10⁻⁸ m/s occur at a site, significant increases in consolidation time could occur at percentage settlements in excess of approximately 30% for all drains tested.

In-place recycling of asphalt pavement is an inexpensive and sustainable pavement rehabilitation method. Existing Hot Mix Asphalt (HMA) layer is pulverized and blended with some of or the entire base course to form a broadly graded material referred to as recycled pavement material (RPM). RPM can be compacted as the new base course and overlaid by a new layer of HMA. Additives may be added to improve the properties of RPM base course, such as cement or fly ash. In this study, three flexible pavement sections with different base materials were constructed at MnROAD test facility to evaluate the RPM with and without fly ash additive and to compare them with conventional crushed aggregate base course, Minnesota Department of Transportation Class 6 aggregates. The fly ash used was a high carbon and high calcium content off-specification self-cementitious fly ash. Various field tests were conducted, using dynamic cone penetrometer, lightweight deflectometer, soil stiffness gauge, and falling weight deflectometer. The backcalculated modulus of base materials from these field tests were compared with each other and with the resilient modulus from laboratory tests. It was found that there are significant differences in the moduli from different test methods. It is believed that this is due to the stress and strain dependence of these materials. However, in any case, the fly ash stabilized RPM has higher modulus than RPM, followed by Class 6.