IMPROVIG OF SAND DUNES USING THE CARBONATED CEMENT KILN DUST (CCKD) AND ULTRA-PURE SODIUM HYDROXIDE SOLUTION (NaOH)

Sand Dunes are one of the most common types of desert soil formations which are very abundant especially in Western Desert of Egypt. This soil represents difficult obstruction against urban development in those places. It causes problems for structures because of its low strength, excessive settlement, obstruction and difficulty of compaction in field due to its permanent movement, high permeability and uniformity of its small particles. This research aims to study the possibility of using dune sand after improving their properties in various projects rather than importing sand from distant quarries so as to reduce the cost, especially in road projects where the sources of the materials used is one of the most important factors affecting the cost. In this study, one of the waste materials for cements industry, carbonated cement kiln dust (CCKD) brought from Helwan Cement Company in Egypt, was used with the purpose of preserving the environment and reducing the costs. Also, ultra-pure sodium hydroxide solution (NaOH) purchased from LOBA Chemical Company in India was added. Three different ratios of (CCKD), 10%, 20%, and 30% by the weight of soil, in addition of 10% of (NaOH) by the weight of (CCKD) were added to a dune sand soil brought from Wadi El Rayan, Fayoum governorate. Compacted specimens were prepared using the optimum moisture content. These specimens have been cured for 1, 7, and 28 days in air. Tests were carried out to determine the unconfined compressive strength (UCS), direct shear parameters (c and Ø), collapsibility index (Ie), and California bearing ratio (CBR) after soaking. The results of laboratory tests indicated significant increases in the unconfined compressive strength. More enhancements occurred at late ages. If 20% CCKD or more is mixed in addition of 10% NaOH and allowed to cure for a certain period of time (say 7 days), the mixture has an unconfined compressive strength that is much higher than that of very stiff or hard clays. The bearing capacity provided by such mixtures will be sufficient to support a moderate-rise building. Cohesion of the mixture was increased with the increasing of the CCKD ratio, while, the angle of internal friction (غ) was not affected by the CCKD ratio. The increase of CCKD content achieved considerable increase for CBR. Dune sand stabilized with 10% or more of CCKD with 10% NaOH had CBR more than 40% which can be used as sub-base layers for roads. In general, all CCKD ratios appeared negligible collapsibility.