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The expensive soils change in volume by an increase or decrease the moisture content. This research study presents suggest treatment for swelling problem; the treatment aims reducing swelling ratio and elevate the rate of infiltration, the treatment based on chemical additive such as chloride sodium, that is available and cheap and waste material phosphogypsum which is detrimental to both human and environment and it is also available and inexpensive. The utilization of salt and phosphogypsum, both provides a significant contribution solution of the environmental pollution problems and to our economy.
The research conducted an experimental program for a standard commercial expansive soil, bentonite (as an alternative of swelling soil) with adding NaCl and phosphogypsum. The study started by groups of mixes, those mixes were tested by Liquid limit, plastic limit, and plasticity index, free swell, longitudinal and normal shrinkage. Then twenty-two mixes were selected for infiltration and swelling tests as discussed in chapter 3 and 4. Later on, six mixes were selected for conducting odometer test. And finally, three physical models were tested for determining the swelling ratio for a large scale model.
The main findings from this study are as follows:
• Standard laboratory tests on Bentonite mixed with (NaCl , Pg ) mix and distilled water show that the liquid limit, Plasticity index, and free swell index are significantly reduced by (76%, 85%, 90%) respectively , while the shrinkage limit increase by (55%) .
• ‘‘The swelling infiltrometer’’ test used to measure the swelling ratio and infiltration rate, the results confirm that the effect of the NaCl and Pg is increasing the infiltration and decrease the swelling potential.
• NaCl has a greater effect on swelling ratio than PG. Also the mix of NaCl and PG improve the performance of PG on decreasing the swelling ratio.
• XRD analysis show that the addition of the (Nacl – PG) mix to the bentonite leads to create non swelling material such as (kaolin , microcline) which reduce the swelling behavior of the Bentonite.
• PG is a waste product from industries that can be used as additives to clay soil and this would help to solve the conventional problem of their disposals.
• The utilization of material such as (Salt & Phosphogypsum) could decrease both treatment’s cost and time.
5.3 Recommendations for Future Study
It should be considered that this was a study for this: phosphogypsum, sodium chloride and bentonite (the alternative of expansive soil). The chemical reactions depend on the chemical composition and index properties of sodium chloride, phosphogypsum, and expansive soil. Therefore, for better estimating the behavior of treated samples, instead of distilled water, tap water or sea water can be used to see the effect of water on the test results. Radioactivity of phosphogypsum should be checked before using in soil stabilization. The strength development and more mechanical properties can be further studied in detail, in addition to Scanning Electron Microscopy studies to corroborate the proposed mechanism. The risks imposed on the environment by possible geotechnical applications of phosphogypsum must be carefully weighed against creating new pollution sources elsewhere.