Engineering properties and construction guidelines for soil stabilized with self-cementing fly ash

Thomas, Zach
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Civil, Construction, and Environmental Engineering

Research was initiated to evaluate the engineering properties and to observe the short and long-term behavior of soil stabilized with self-cementing fly ash. Typically Iowa soils have low strength due to high fines content. Five Iowa soils ranging from ML to CH were used in this study as well as self-cementing fly ash from eight Iowa power plants. Fly ash addition had a profound effect on the compaction characteristics of the soils. The influences of fly ash content, moisture content, and compaction delay on compressive strength were observed for samples molded with ISU 2-in x 2-in apparatus as well as standard 4-inch diameter Proctor equipment. Long-term strength gain was evaluated for samples that were over 2.5 years old. California Bearing Ration (CBR) of fine-grained soils was also increased substantially with the addition of fly ash. Strength gain was also tested for samples cured in various environments. Freeze-thaw and wet-dry durability of soils were increased and reductions in plasticity characteristics were observed with fly ash addition. The morphology of soil-fly ash mixtures was studied as well as the clay mineralogy of the soils used in the study. In addition to the study of soil-fly ash mixtures, previous ISU research involving hydrated and conditioned fly ash was continued. The research utilized four sources of hydrated fly ash (HFA) and two sources of conditioned fly ash (CFA) from Iowa. Moisture content, curing temperature and time all had an impact on the strength gain of HFA and CFA. Shear strength parameter values for these materials were also determined. In addition to evaluating the strength of HFA and CFA alone, these two types of materials were also tested as soil stabilizers. The final part of research was to use the information determined in the previous tests to develop construction guidelines. Three construction guidelines were developed for use in Iowa. Two of these guidelines described the procedures for using HFA and CFA as select fill under pavement structures, while the third set of guidelines was developed for constructing sections of self-cementing fly ash stabilized soil.