SGER: Are High Carbon Fly Ashes (HCFAS) Effective Stabilizers for Soft Organic Soils?

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Cementitious Class C fly ashes, as well as other cementing agents, have been found to be very effective stabilizers for soft inorganic soils, but are essentially ineffective at stabilizing soft organic soils. However, preliminary test data developed by the PIs has shown that soft organic soils can be effectively stabilized with cementitious high-carbon fly ashes (HCFAs), i.e., fly ashes with organic carbon content > 3%. The objective of this SGER is to explore the feasibility of using HCFAs for stabilizing soft organic soils. This concept is novel because a long-standing unsolved problem (stabilization of soft organic soil) is being solved by a new approach with a material (HCFA) that is currently landfilled. The concept is also high risk, because a very limited data set has been developed showing that HCFAs are indeed effective stabilizers for soft organic soils. However, the potential rewards are substantial. Successful results from this study could make HCFAs the material of choice for stabilizing soft organic soils (a problem heretofore unresolved), foster sustainable development and sustainable construction practices, reduce construction costs, and improve the environment by reducing the volume of fly ash being landfilled. The hypotheses to be tested are as follows: (i) soft organic soils can be effectively stabilized with HCFAs and (ii) the organic carbon in HCFAs is the primary factor responsible for successful stabilization of organic soils with HCFAs. A research program consisting of four tasks is proposed to test these hypotheses. The tasks include physical and chemical characterization of three soft organic soils and three HCFAs that represent a broad range of organic matter (soil) and organic carbon (fly ash) contents, unconfined compression testing of mixtures of the organic soils and HCFAs, microstructural analyses to evaluate cementation in these mixtures, and an evaluation of curing rates to indirectly assess how the organic matter content and organic carbon content affect cementation kinetics.