Submit Manuscript | http://medcraveonline.com Introduction Black cotton soil (BCS) is an expansive fne-grained soil which is considered problematic because of its characteristics. BCS contain high montmorillonite clay mineral content. It is considered as a problematic soil since it challenges the engineers during construction. BCS shows large volume changes because of fuctuations in moisture content. When water or moisture is exposed to this soil, the soil either shrinks or swell. Shrinking is whereby the soil increases in its volume whereas swelling is whereby the volume of the soil increases. Excessive swelling of black cotton soil leads to a process called heaving and shrinking of the soil leads to a process known as subsidence. 1,2 Black clays or black cottons are known to be potentially expansive soils which are “black” or “greyish black” or in their eroded phase “greyish white” heavy loam or clay (usually 50 %), with predominant clay mineral of the smectite group, rich in alkali earth elements and the horizons sometimes contain calcium carbonate or magnesium oxide concentrations. Black cotton soils are susceptible to detrimental volumetric changes with moisture. 3 The black soils are formed when volcanic rocks and some sediments are weathered under humid, alkaline conditions. Because of poor drainage, these soils are rich in soluble bases and silica. The parent materials of expansive soils could also be classifed into two groups. The frst group comprises basic igneous rocks. Here pyroxene mineral of the parent rocks decomposes to form montmorillonite which is the predominant mineral of expansive soil and other secondary minerals. The second group comprises sedimentary rocks that contain montmorillonite. 3 South Africa, Morocco, Mexico, Israel, Spain, Turkey, Iran, India, the United Kingdom, Ethiopia, Ghana, Australia, the United States, and Argentina are among the countries that have reported ES damages. The cost of expansive soils repairing construction damage in South Africa is projected to be R100 million per year. ES damages are estimated to be about £400 million each year in the United Kingdom. According to the American Society of Civil Engineers, ES causes damage to almost a quarter of all houses. ES damages result in a greater annual fnancial loss than hurricanes, foods, tornadoes, and earthquakes combined. 4 According to Buruga et al., 5 black cotton soil belongs to the smectite group, and incorporates montmorillonite, a highly expansive and the most troublesome clay mineral in construction. Montmorillonites incorporate a central octahedral sheet sandwiched among twofold tetrahedral sheets and it forms a three-layer element. Weak bonds between the elements leads to swelling and they can be broken down when water is absorbed. As stated by Metry & Polli, 6 the chemical composition of BCS changes depending on components such as parent rock, generic characteristics of soil (transported or residual), degree of weathering, etc. However, BCS are generally rich in silica, lime, iron, magnesia and alumina. It also contains titanium oxide in small concentrations, which is liable for the black color of the soil. The organic matter components of black cotton soils are low. According to Chen, 7 the following are ways of identifying black cotton soil, usually have a color of black or grey, wide or deep shrinkage cracks, high dry strength and low wet strength, Stickiness and low trafc ability when wet, cut surfaces have a shiny appearance, the appearance of cracks in nearby structures. Arid and semiarid areas are particular trouble spots because of large variations in rainfall and temperature. Black cotton soil has proved itself as a source of harm to the property and economical loss. Expansion and contraction of black cotton soil causes various issues to the civil engineers not only during construction but also throughout the life of structures. Uneven contraction and swelling decreases the serviceability of the structures. It causes the rise of hairline cracks, diferential settlements, and sometimes even serious cracks, which may lead to the collapse of structures, railway lines and roadways. Decrease in the availability of suitable soil for construction has forced analysts to look for an appropriate strategy to improve the performance of locally available MOJ Civil Eng. 2023;7(1):1‒6. 1 ©2023 Firoozi et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and build upon your work non-commercially. Assessment of lime stabilization of black cotton soil for roads construction projects Volume 7 Issue 1 - 2023 Ali Akbar Firoozi, Ali Asghar Firoozi Department of Civil Engineering, Faculty of Engineering & Technology, University of Botswana, Gaborone, Botswana Correspondence: Ali Akbar Firoozi, Department of Civil Engineering, Faculty of Engineering & Technology, University of Botswana, Gaborone, Botswana, Email Received: March 15, 2023 | Published: March 28, 2023 Abstract The design foundation (i.e., pavements) on black cotton soil has always been a difcult task for the engineers as the structure resting on black cotton soil cracks without any warning. This research evaluates the efect of lime (anhydrous sodium sulphate) on engineering properties of black cotton soil which are considered highly problematic to civil engineering works. Black cotton soil brings about signifcant geotechnical and structural engineering challenges to property and infrastructure development around the world. The objective of the study is to investigate the use of lime-stabilized black cotton soil as subbase material in fexible pavements. Black cotton soil procured from the local area in Gaborone, Botswana, tested for suitability as subbase material, turned out to be unsuitable as it resulted in very less CBR value (4.8%). The black cotton soil-lime mix was checked for consistency limits, compaction, CBR for diferent proportions of lime (i.e., 0, 5, 10 and 15%). It was observed that the plasticity index of the soil shows a substantial decrease upon addition of the lime whereas CBR values show a marked increase with unsoaked CBR. The addition of 5%, 10% and 15% of lime produced some desirable soil properties. It can be concluded lime could be one of the best alternative stabilizer materials for highly expansive clayey. Keywords: black cotton soil, lime, CBR, swelling, shrinkage, optimum moisture content, maximum dry density MOJ Civil Engineering Research Article Open Access