## 1 Introduction
Chemical treatments using a single product may be associated with some deficiencies, such as a slow reaction process or leachability in a wet environment. Lime or calcium chloride-treated soils are frequently prone to the leaching of the additive, leading to less concentration of the stabilizer and leaving some voids that affect the general mixture performance [17]. The decrease in the rate of pozzolanic reactions and increase in hydraulic conductivity can be influenced by the dose of the additive and the mineralogy of the soil. Ordinary Portland cement (OPC) is expected to hold particles together when some parts of calcium chloride are washed out. The microstructure and interaction between the clay particles and cement can be observed by high magnification scanning electron microscopy (SEM) images. The formation of voids within expansive soils, if not excessive, may help in reducing the swell pressure and swell potential. [PERSON] et al. [18; 19] investigated the effect of the addition of chloride salts on the index properties of expansive soils as well as the extent of reduction in swell pressure and swell potential for other selected chloride salts (e.g., AlCl\({}_{3}\), FeCl\({}_{3}\), and NH\({}_{4}\)Cl). Calcium chloride salt can absorb water greater than its weight, and in a highly humid environment, calcium chloride can absorb water greater than 16 times its weight [20]. This property can reduce the exposure of expansive clay to water, thereby decreasing the expansion and swelling. As calcium chloride is a soluble salt, it creates voids and spaces for swelling to occur internally. [PERSON] and [PERSON] [21] stated that the plasticity index of the clay bed decreased by 7-15% and 40-60% with lime and calcium chloride treatments, respectively. The use of combined additives including calcium chloride is rare in the literature. The works of [PERSON] and [PERSON] [22] suggested using calcium chloride and alcofine. This study is aimed at using a small amount of cement (2%) to improve the calcium chloride stabilization of expansive soil. The combined effect of the two stabilizers is presented as an alternative to a single additive. Higher cement content needed for good stabilization may result in a stiff and non-workable soil mixture. The use of a low amount of the strong binder (2%) is suggested for two reasons. (1) The higher amount of cement is expected to produce very stiff lumps that are not easily compacted. Moreover, the delay of compaction may be a significant factor that affects field operations. (2) The cost of using excessive cement as an additional binder will impact the budget of the stabilization process. [PERSON], 2022 [23], considered using cement at 2% as a cementing agent to the PUMICE foam additive to expansive soils. The plasticity index was reduced by nearly 30% when 2% cement and 12% PUMICE foam material is added. [PERSON], 2019 [24], confirmed that the addition of cement has immediate and long-term effects on the consistency limits and improves the strength and stiffness of the untreated soil. The call for using a low amount of a strong binder, namely, cement along with the calcium chloride is expected to perform well and reduce the level of leaching by preventing the disintegration of weakly cemented lumps formed as a result of the pozzolanic reaction. Calcium chloride with little cement is expected to give better results than other stabilization methods using lime or calcium chloride alone. This research is conducted using highly plastic expansive soil obtained from Al-Qatif region in the eastern province of Saudi Arabia.