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There are some solution to this problem. One of them is using cement type 2 or 5 mixed with pozzolan which can be anti sulphate. Low amount of w/c may help in this regard. Also, applying insulation like bitumen might be beneficial.
Use Type 2 or type 5 cement. These type of cement are Sulphate Resistant Cement, it is recommended to use Sulphate Resistant Cement for the concrete which is in contact with the soil that has high content of sulphate.
1. The quality of concrete, specifically a low permeability, is the best protection against sulfate attack.
2. The use of sulfate resisting cements provide additional safety against sulfate attack
A waterproofing system must be used the to insulate the concrete and avoid any contact with the soil. Adhesive waterproofing membrane can be applied to the substructure and covered with a layer of protection board to protect the membrane from tearing while backfilling and compaction. Another waterproofing type can be used which is applying bituminous paint ; several coats must be applied to achieve the required thickness, and then must be covered with polythene sheet to protect the coating while backfilling and compacting. Different systems can be used for different conditions and structures. It is preferable to use stainless steel reinforcement and stainless steel ting wires for structures constructed deep in aggressive soil such as piles.
it is not clear in your question if this is a new construction or you are doing maintenance for old structure.
Anyways; Your best deal is working on insulating the concrete from the soil. Before pouring the concrete lay nylon sheet on the compacted soil, after pouring the concrete, and after removing the forms, you will need to water the concrete a couple of times to assure good curing. before dumping soil, paint the concrete with good quality pitmen and make sure you paint any part covered with soil.
One, the concrete can be broken out and removed; (Note that the affected concrete must not be used as hardcore under the replacement or for any other concrete work. The fill material will remain in place, but has to be further compacted if necessary, install a DPM over the fill, turn it up at the perimeter and laid the new concrete on the newly placed DPM. Therefore the new slab will be isolated from any sulfates remaining in the fill material. Only ensure that the area under consideration is fully covered by the DPM.
Secondly, remove the concrete and the hardcore to a reasonable depth, lay sand blinding and cover with DPM, place new hardcore from an inert source (such as crushed limestone) that is free from significant amounts of sulfate, sulfide and other deleterious substances. Place and compact in layers following usual good practice. Lay sand blinding again and cover with a second DPM. Ensure by good detailing and workmanship that this DPM is moisture tight. Construct a new concrete over the DPM.
All these must be done following approved procedures in your standard of choice and good construction practices.
