## 1 Introduction  
Sulphate-bearing soils are present in critical areas of the globe where the construction of civil engineering structures or similar land-based developments are unavoidable. Sulphates commonly found in soils such as sodium sulphate or Glauber's salt (Na\({}_{2}\)SO\({}_{4}\)), hydrated calcium sulphate or gypsum (CaSO\({}_{4}\).2H\({}_{2}\)O), and magnesium sulphate or epsomite (MgSO\({}_{4}\)) are either naturally occurring or imparted on the soil through some secondary sources [1, 2]. Research has shown that the use of calcium oxide- (or hydroxide)-based agents (such as lime and cement) for the stabilisation of sulphate-bearing clays can lead to unwanted heavy (or sulphate-induced heaving) when inundated with water [3, 4]. Researchers have also highlighted that sulphate-bearing soils may be prone to loss of strength, stability, and durability as a result of the generation and propagation of expansive reactions when stabilised with calcium oxide-based agents [5, 6, 7, 8, 9]. It is known that, within the mechanism of sulphate soil-binder reaction, a suitable pH condition (between 11 and 13) can develop and lead to the formation of an expansive mineral called \"etriting\" ((Ca\({}_{6}\)[Al (OH)\({}_{6}\))\({}_{20}\).24H\({}_{2}\)O] (SO\({}_{4}\))\({}_{2}\) H\({}_{2}\)O) or \"thaussite\" (Ca\({}_{6}\) [Si (OH)\({}_{6}\)]\({}_{20}\) (SO\({}_{4}\)) (CO\({}_{3}\))\({}_{2}\).24H\({}_{2}\)O) in the hydrated system. Studies on the suppression of the deleterious effects of etrtingtites and their formation mechanisms by the use of GGBS and other sustainable means in the stabilisation of sulphate soils rich in calcium oxide or (hydroxide) (such as cement and lime) are life [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 4, 6]. It has been reported that high proportions of GGBS (up to 80%) compared to another calcium oxide (or hydroxide) agent (e.g., cement and lime) are required in the stabilised soil mix to effectively prevent attacks by sulphates [11]. Although numerous investigations have been conducted in the past on the use of GGBS for the prevention of unwarranted linear or volumetric deformation of calcium oxide-based treated sulphate soils as noted above; however, studies that relate to the strength capacity of these stabilised sulphate-bearing soils are quite limited [5; 6; 15; 16; 21; 24]. Earlier studies carried out by [PERSON] [16] explored the effect of GGBS on the unconfined strength of lime-treated kaolinite in the presence of sulphates. Gypsum (4%) was used to mirror the influence of sulphate in the kaolinite while the minimum quantity of lime used was 4% with varying proportions relative to that of the GGBS utilised but maintaining an overall total of 10% of both (lime and GGBS) by weight of the soil. The samples were moist-cured for 7 and 28 days at 300 \({}^{\circ}\)C and 100% humidity. Results indicated an increase in strength corresponding to an increase in the GGBS-to-lime ratio in the absence of gypsum. However, with the sulphate added, an increase in the GGBS-to-lime ratio produced a \"non-systematic\" variation in strength. A further examination of the lime-gypseous soil-GGBS system was conducted by [PERSON] et al. [24] but with the total percentage of GGBS and lime in the mix being 6% and gypsum varying between 1% and 2% by dry weight of the soil. Testing was carried out under the same conditions as [PERSON] [16], with the results suggesting that the development of strength was dependent on the proportion of the additives used and curing. For instance, the most significant improvement was due to high lime/low GGBS in the presence of gypsum at 28 days. However, at 7 days, the greatest strength experienced by the treated sulphate soil was made possible by a high lime-to-GGBS ratio. [PERSON] et al. [15] recently studied the effect of sample soaking on the unconfined compressive strength of lime/GGBS-treated sulphate soil. Three weight ratios of lime and GGBS (1:9, 2:8, and 3:7) were used, and the treated soils compacted at optimum conditions.