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Re: Free Lime

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Vijay,

        The idea of completely soaking the fill material scares me!  I fear that the excess water might saturate the soil below the footings and cause an even worse problem than you already have.  I would advise you not to do this without advice from a geotechnical engineer familiar with the materials which have been used as well as the foundation conditions.

Regards,

H. Daryl Richardson

Vijay Patil wrote:

I recently came across a peculiar problem. I designed a medium span single storey structure in steel.Upper 1.5 metres of the soil was black cotton soil (expansive soil). So it was decided that upper two metres of the entire soil be removed and filled in with good soil as filler. The foundation of the main structure were taken upto 2m below existing ground which was firm soil. Since the client was steel manufacturing company they have a lot of LD slag as their by product. This slag was used for filling the two metres for the plinth filling topped with  PCC and further with a grade slab to carry all the internal walls. After a few days the partition walls started cracking and even the grade slab cracked. The entire floor had become uneven.It was the filling which was expanding. We found out that the LD slag contains 4 to 8% free lime(CaO). Free lime when comes in contact with water forms calcium hydroxide which may expand upto 150 to 200% of original volume. (As the foundation of the structure goes right upto stable ground the structure is not damaged at all. It is only the grade slab and all the internal walls that are damaged.) The only solution I can think of is 1. Saturate the fill with water by drilling holes in the grade slab and continously pouring water in it.   This may damage the walls and the slab further as the free lime which has not reacted till now may react with the water to form CaOH2.  The damaged walls and the grade slab can be repared as one assumes that the fill below is stable.    The catch here is that entire component of the free CaO is may not be converted  in to CaOH2 knowing that the reaction some time takes years. 2. Break open the entire grade slab and replace the fill with other stable fill such as Granulated slag ( this does not contain free CaO).      This would be safe but too expensive and time cosuming as almost all the walls are completed and plastered will have to be broken down.  Is there any third solution or any way the first solution given here be made foolproof.??? Thanks in Advance. Vijay Patil