Affects of gypsum in laboratory testing of soils

[Jaden1017]

I'm inquiring if there is someone who knows what affect gypsum has to laboratory testing. For example if i run a proctor with significant gypsum content. What would be the effect to my test results if I dry back my moistures in high heat versus low heat.

 

[emmgjld]

The presence of significant amounts of gypsum WILL affect the moisture content of affected soils. I deal with this problem a lot. You need to be running comparative tests between the drying methods for suspected, and sometimes, non suspected soils.

Gypsum can also affect atterburg limits, though usually to a small degree.

 

[Jaden1017]

how about expansion will it effect how expasive a material will be?

 

[iandig]

Yes, it will affect the potential of the soil to expansion if you are also using lime modification/stabilisation. Gypsum is a sulfate and it will react with lime, silica or allumina in the soil and water to form expansive materials [Thaumasite/ettringite].
I have also experienced problems with testing soils with gypsum for permeability, as the crystals appear to grow [with undisturbed samples it is not possible to determine the size of the crystals prior to testing] under saturated conditions impacting on the test.

 

[msquared48]

As a primitive gardener, besides a structural engineer, you use gypsum to break up clay soil along with sand, rendering the soil mass suitable for agriculture. Hence it has the effect of rendering better drainage in the area too. Hence the drying effect you mention.

Mike McCann
McCann Engineering