How Much Quicklime to Use?

[ih8xc]

We have a large site with a substantial amount of silty clay (some sand) soil that needs to be reused onsite, however it is currently well above optimum moisture for compaction. The soil is currently in a number of stockpiles and we've thoroughly measured it's moisture throughout (~25%). We do not have the space nor the time to spread it and wait for it to dry, and therefore we are looking to use quicklime to reduce the moisture content to a compactible level. What I'm wondering is how to quantify how much quicklime will be required to reduce the moisture by a certain amount (for example to 15% from 25%). I understand that there are a number of processes occurring that change both the moisture content and the optimum moisture for compaction. Looking at it solely as a chemical reaction it seems like each kilogram of water would require about 3 kg of CaO to fully react. Does this seem accurate? Do the evaporative effects of the exothermic reaction play a major role in the moisture reduction?

And as a final note, there is likely to be a substantial amount of sulphur in the soil. I'm unsure if this would also affect the reaction and stabilization process.

 

[Ron]

How do you plan to mix the lime into the soil?

 

[Panars]

For drying fine grained soil, you are probably going to need 2-4% lime measured by weight and compared to the dry unit weight of the soil in question. This percentage is usually determined from a test program where you take samples, mix them with different amounts of lime and then compact them in a standard Proctor mold. I suggest you look to the National Lime Association and Carmeuse for detailed information. You can find their websites at

http://www.lime.org

and

http://www.limestabilization.com

.

Yes, sulfur (actually sulfates) are going to cause problems. But it depends on the application whether it will be problem or not. Sulfates and calcium and water will create ettringite, which expands. If your treat with lime, compact the soil, and then place pavement above it, the swelling will cause buckling and heaving of the pavement. But if you mix the lime, wait a week or couple days, and then compact the soil into an embankment, you will probably be okay. There is information about sulfates on the Lime association and Carmeuse websites too. In the USA, Texas DOT probably has the most information about sulfate heaving, followed by Colorado and Ohio DOTs. (DOT is Department of Transportation).