Pavement heave due to sulphite expansion

[Pete Franklin]

Not sure where the best place for this is but as it is chemistry related I think the science forum is possibly the best area

This is relating to highway construction: I am currently looking at a situation where there is pavement heave, believed to be caused by sulphite expension in a previously stabalised layer.

Seeing as the effect has already taken place, what is the likelyhood that it will continue happening? I assume with things like Pyrite oxidation, there is only a certain amount of material that will react and when it has reacted the problem will stop occuring? I appreciate that the condition of that material may or may not be structually sound afterwards though.

we are trying to come up with a cost effective solution to the problem. Avoiding costly structural work would be best.

Any advice or experience would be great.

Thanks

Pete

[kiteless]

IME, this occurs when soil below a highway or other construction has been "engineered" with lime to create a solid substrate in lieu of excavating out and replacing with stone (say 6F2). This is in areas of the country where the indigenous soil is primarily clay, and of course subject to heave thus cracking the structure / highway / floor slab built over it.

Lime stabilisation of clay soils does work; once cured, the "engineered" soil does turn as hard as an equivalent stone layer. However if there is a significant quantity of sulphites in the original clay, these sulphites - when wet - react with the lime and create the same heave as if the soil had not been treated.

Remediation can be costly. One solution I have seen is to excavate out all of the affected "engineered" soil, stockpile it in a different location, then mix with huge quantities of PFA (pulverised fuel ash). Or, even more costly, fetch out all of the affected soil and just replace it with 6F2 stone.