Beneficial Utilization of Lime Sludge for Subgrade Stabilization : a Pilot Investigation
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2010-06-30
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Edition:Final report; Mar. 2009-July, 2010.
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Abstract:Water plants annually produce thousands of tons of lime sludge from the water treatment procedures. The lime sludge
is then discharged into a retention pond. When the storage limit is reached, lime sludge is usually disposed into
landfills, where they are treated as solid wastes. The large amount of lime sludge available (the quantity of lime sludge
is estimated to be millions of tons for Ohio alone), the inexpensive (essentially free) material is very attractive if it can
be used for soil stabilization in transportation constructions.
In order to use efficiently lime sludge as subgrade stabilization, proper design procedures for lime sludge introduction
need to be followed to achieve the optimal performance. Besides, the long term performance of lime sludge modified
soils needs to be verified. The purpose of this study was to determine the feasibility of using lime sludge as subgrade
stabilization. The study focused on the feasibility of using lime sludge as a substitute of regular lime used in road
construction, design issues such as, method of lime sludge introduction, the optimum content of lime sludge and the
long term performance etc. Experimental study was conducted on five typical types of subgrade soils in Ohio as well as
a high plastic clay soil in Cleveland area.
Common procedures for determining the optimal lime content for soil stabilization based on pH values are found not
applicable for lime sludge. Instead, performance criteria based on unconfined compression tests need to be utilized.
Lime sludge was found to increase the soil deformation modulus and reduce the plastic behaviors. Wet mix and dry
mix methods do not appear to significantly affect the strength of lime sludge modified soil. Considering of the
economic factors associated with drying lime sludge, lime sludge can be introduced in the slurry format via the wet mix
procedure. The existing testing data indicated that lime sludge does not significantly improve the unconfined soil
strength. Lime sludge however demonstrated the positive effects in reducing the plasticity of soils and improve the
freeze/thaw durability. The long term performance evaluation could provide data to quantify the effectiveness of lime
sludge as an economic and sustainable material.
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