The extensive geological spread of swelling clays around the globe presents a key challenge to engineers, especially in areas where construction and land development activities are intended. Engineering structures intended for clay-rich soils of high plasticity would be at serious risk of failure if little or no solution is sought to salvage the foundation soil. What has become even more challenging nowadays is the continuous rise in world population and housing needs, thus making land development and construction activities on areas of weak or problematic soils unavoidable. High-plasticity soils have continued to present geotechnical engineers with key challenges such as swelling and shrinkage due to their undesirable swelling and/or shrinkage characteristics. Soils with smectite clay minerals, such as montmorillonite, tend to swell during moisture ingress or shrink in extremely dry conditions, and are therefore termed swelling clays. The extensive geology of these soils has made them become practically unavoidable especially in areas where their deposits are very large (Nelson et al.
2015; Lin and Cerato
2012). Both man-made and periodic environmental factors work to trigger intrinsic mineral properties of expansive soil, with a resulting increase or decrease in the soil’s volume (Nelson and Miller
1992). These soils are very problematic and almost impossible to compact during construction unless they are treated with cement or a combination of cement and other cementitious by-product materials (Abbey et al.
2015,
2016,
2017,
2018; Rahgozar et al.
2018; Ta’negonbadi and Noorzad
2017; Pourakbar et al.
2015). Soil stabilisation involves the improvement of the engineering properties of weak soils mechanically, physically or by mixing with binders to achieve some predetermined objectives. The use of additives to stabilise soils has been a major concern in the improvement of engineering characteristics of problematic soils such as soils susceptible to swelling (Kilic et al.
2016). Calcium-based hydraulic stabilising agents such as lime and cement are commonly used to chemically improve the engineering properties of highly plastic clays. The effect on soil of using lime and cement has been regarded as very similar in many respects (Al-Rawas et al.
2005), although cement-treated soils seem to have the least impact on the environment because of less chemical leaching, and they can provide greater sustainable strength for longer periods (Muhunthan and Sariosseiri
2008; Puppala et al.
2015). The strength properties of Portland cement (PC)-treated soils have been studied by several authors (Consoli et al.
2015; Caraşca
2016). Chen et al. (
2016) examined the variation in strength of marine clay treated with cement during a wet deep mixing work at the Marina Bay Financial Centre in Singapore and found that the strength of the improved clay varied from 0.7 MPa to about 5 MPa. In addition, according to Chen et al. (
2016), the strength distribution in deep mixing-improved soils is affected by in situ soil properties and the chemical reactions between soil and cementitious constituent. The addition of either cement or lime to soils triggers a series of reactions including hydration, cation ionic exchange, flocculation and agglomeration and the production of pozzolanic reaction products (Nelson and Miller
1992). Soil stabilisation with cement is particularly desirable in terms of durability enhancement and provision of adequate resistance against cycles of freezing and thawing, which are common phenomena in cold climates. Just as in construction activities involving the use of concretes, cold weather can be regarded as one of the obstacles militating against soil stabilisation with cement, especially in temperate regions. One technical solution that can accommodate soil stabilisation during the cold weather season is the use of a high-early-strength cement. High-strength PC helps to counteract the effects of the cold conditions by increasing the early-stage heat of hydration. The presence of tricalcium sulphate (C
3S) added to the cement clinker during its production is what enhances the early strength development. Undoubtedly, cement-soil mixing techniques have been widely employed in the construction field for strength enhancement and improved compressibility (Farouk and Shahien
2013; Gaafer et al.
2015) and the beneficial outcome on the performance of cement-treated soils has been extensively documented in literature (Praticò and Puppala
2012; Åhnberg et al.
2001; Kitazume et al.
2015; Pakbaz and Alipour
2012). The application of cement in treatment of weak and problematic soils have resulted in improved performance such as reduction in plasticity and swell potential, substantial strength gain, increase in elastic modulus and resistance against the influence of moisture.
Bell (
1993) suggested that cement addition up to 2% can modify soil properties, while much larger quantities could have a more considerable effect. Also, cement content may range from 3 to 16% of the soil’s dry weight and depends on soil type and required properties. It was also stated elsewhere that the quantity of cement needed to stabilise expansive soils could range from 2 to 6% by dry weight of the soil (Chen
1975), and the higher the soil plasticity, the greater the quantity of cement to be used (PCA
1992). The American Association of State Highway Transportation Officials (AASHTO) cement requirement by dry weight for soils of high plasticity ranges from 9 to 15%. The U.S. Army Corps of Engineers have recommended a range of 7–20% of cement by dry weight of a silty or clayey soil. The seeming lack of a unified standard as to the quantity of cement required goes to show that stabilisation with cement does depend on several factors, not least the soil type and the field conditions encountered (Sarkar and Islam
2012). Few studies have evaluated the engineering behaviour of stabilised expansive soils by utilising some amount of different cement types to obtain an optimum proportion relying on several conditions (Sivapullaiah and Lakshmikanthay,
2010; Jamsawang et al.
2017; Cokca
2001; Latifi et al.
2015; Yilmaz and Civelekoglu
2009; Raftari et al.
2014; Kumar et al.
2014; Solanki et al.
2017; Kechouane and Nechnech
2015; Tilak et al.
2015; Consoli et al.
2010; Iravanian and Bilsel
2016; Abdelkader et al.
2013; Alrubaye et al.
2017; Asma Muhmed,
2013; Ghobadi et al.
2014). Geotechnical engineering design relying on assessment of the behaviour of clay-bentonite mixed soils treated with cement or other cementitious materials could find useful and broad application ranging from engineered clay barriers to subgrade construction materials (Wagner
2013; Lakshmikantha and Sivapullaiah
2006; Guler and Bozdey,
2001). However, few studies have focused on the determination of important engineering properties of kaolinite-bentonite mix modified by the addition of cement (Por et al.
2017; Jamsawang et al.
2017; Raftari et al.
2014). Therefore, the present study has investigated the swell and microstructural characteristics of high-plasticity clay soils (kaolinite-bentonite mix) to evaluate and promote a better understanding of the geotechnical properties of these soils.