Stabilization of Sabkha soil using Cement Kiln Dust (CKD)

Roads designers are often faced with the challenge to design a stable solid foundation on top of Sabkha soil, which has high salt content, very low bearing capacity and loosing of its strength upon wetting. Roads constructed on this type of soil are mainly facing problems of settlement due traffic loads and very low bearing capacity of Sabkha soft soil. This type of soil need to be stabilized using one of the stabilization techniques. The aim of this paper is study and evaluate the sabkha soil problem, which exist in North-West of Libya, where the main road connecting Libya with Tunis passed. This paper illustrates the results of using Cement Kiln Dust (CKD) in Sabkha soil stabilization. The results show a considerable improvement of sabkha soil properties based on tests conducted specially CBR values.


Introduction
Sabkha is an Arabic term that describe recent coastal sediments with a high salt content and are characterized by very low bearing capacities.Sabkha soils are widely distributed over the world, like in India, Australia, USA and Southern Africa as well as the Arabian Peninsula [1].The geotechnical problems caused by sabkhas are now well definite and although several standard soil improvement methods are broadly used.One of the economical methods of soil stabilization used in roads and highways is the chemical stabilization by adding materials like lime or cement.Cement Kiln Dust (CKD) are used in this study as additive to improve the Sabkha soil properties.It is estimated that 15 to 20% is generated from the produced cement, which means that millions of metric tons of CKD are produced [2].There are many studies used CKD as soil stabilizer to improve its geotechnical properties.Examples of these studies are shown in This paper presents the test results carried out on Sabkha soil stabilized by using Cement Kiln Dust (CKD) to improve their bearing capacity and reduce plasticity, swelling, and shrinkage.

Properties of Sabkha soil
Sabkha soil can be divided into two categories [9]: • Muddy sabkhas: These soils are located near the cost, on depths ranging between +2m to -6m from the sea level.
• Sandy sabkhas: often successive layers of sand and silt and sandy located at great distances from the beach up to tens of kilometers.Table (2) illustrate the properties of both sabkha types.To construct, Muddy Sabkha soil considered more problematic comparing with the sandy type.

Aim of the study
To improve the sabkha soil properties by using Cement Kiln Dust (CKD) to improve their strength and reduce plasticity, swelling, and shrinkage.

Methodology 1 Location of the study selection and soil properties characteristics
Samples used in this study were obtained from the port of Zuwarah's road, which is located about 100 km west of Tripoli, the capital.This road were selected because there was settlement problems on the road surface that can be noted clearly.

Sample collection
Disturbed and undisturbed sample were collected.The samples were Muddy Sabkha soil with brown color.High water table has been observed with a high percentage of salts.
3 Studying the characteristics of soil used A number of tests were carried out according to ASTM standards to measure the engineering properties of soil samples.Tests results are shown in (Table 3).Cement dust has been selected for use in the stabilization process of the soil, because it contains the main chemical compounds that work to stabilize the soil.CKD were obtained from Cement Factory -Al-Khoms,Libya.

Laboratory tests
Cement kiln dust mixing ratios of 8%, 12% .16%was selected, and then conducting laboratory tests on a mixture of soil and cement kiln dust (CKD) after mix them and left them for 24 hours exposed to air at the Laboratory temperature.A number of laboratory tests were carried out according to ASTM standards to investigate the properties of the plain soil and after adding the decided percent of CKD.These tests include pH value, Plasticity index, maximum dry density, optimum moisture content, unsoaked CBR and soaked CBR.pH are measured, since it is one of the factors that help to success of the lime treatment process [3].The high values of pH (because of lime) help in forming cementnous material that help to increase soil strength.The pH values are shown in table 5.The plasticity index was decreased with increasing of CKD percent added to the soil.(Fig. 1) illustrates the relationship between the proportion of cement dust added and plasticity index.Also, swelling index was reduced with increasing of the CKD added.(Fig. 2) shows the relationship between the proportion of cement dust added and the swelling index.Small increase in maximum dry density was noticed as the percent of CKD added increase.(Fig. 3) illustrate the relation between Maximum dry density and percent of CKD added.Samples of the plain sabkha soil subjected to soaked CBR tests are prepared with the dosages of CKD, and tested according to ASTM standard in addition of the plain Sobkha soil.The samples were sealed and cured for 7 days at laboratory condition of (25) °C.Then, they are soaked in tap water for 4 days before testing.Figure 3 illustrates the relationship between the proportion of cement dust added and the CBR value.Noticeable improve in CBR values as the percent of CKD increased.(Fig. 4) illustrates the relationship between the proportion of cement dust added and the CBR value.

Fig 1 :
Fig 1: Relation between CKD and plasticity index

Fig 2 :
Fig 2: Relation between CKD percent added and swelling index

Fig 3 :
Fig 3: Relation between CKD percent added and maximum dry density

Table 4 : Chemical composition of Cement Kiln Dust
2 K