A road can fail not because its soil is too weak, but because the repair material makes it swell. This study finds a different mixture that strengthens the ground while sharply reducing that dangerous expansion. Roads and other structures depend on knowing how treated soil will behave.

The safety and durability of facilities built on engineered earth materials depend directly on correctly modelling that behaviour. But sulphate-rich soil creates a difficult trap: treating it with cement or lime has produced expansion and drying cracks, while sulphate can also leave the treated ground weaker, more permeable, and unstable in volume.

The gap was not simply whether the soil could be treated. There was insufficient information about how a lime-and-furnace-slag mixture would behave in highly gypsum-rich clay. So the study compared ordinary cement with the lime-and-furnace-slag mixture across the properties that matter for pavement design, including strength, resistance to penetration, swelling, water absorption, and the material’s internal structure.

Here is the core idea. Think of loose soil particles as a pile of separate building blocks: a good treatment needs to make them grip one another and leave fewer open spaces between them. The treated clay with the lime-and-furnace-slag mixture formed a denser structure, while the cement-treated soil had more open spaces and more isolated clay plates.

Adding gypsum made the soil-and-binder phase more sealed. But strength is only half the story. When soaked, the lime-and-furnace-slag-treated soils expanded much more slowly and had a lower total volume change by the end of soaking. Even though strength-producing compounds formed alongside expanding crystals, the crystals’ tendency to expand in water was significantly reduced compared with the ordinary-cement-treated samples.

Water entering treated gypsum-rich ground can make it heave enough to threaten lightweight roads: one treatment reached about nineteen percent swelling, while the lime-based alternative stayed close to the ground’s original size even after soaking. The strength results point in the same direction.

After longer curing, the lime-and-furnace-slag-treated samples performed better than the ordinary-cement-treated samples, as stronger bonds formed over time. At seven days, the UCS of the lime-and-furnace-slag-treated samples performed better than that of the ordinary-cement-treated samples, showing the advantage was already present early in curing.

By twenty-eight days, the lime-and-furnace-slag-treated samples performed better than the ordinary-cement-treated samples, continuing the same strength advantage at the later curing period. Under soaked conditions, the four percent lime and eight percent GGBS treatment showed better performance, offering the most resistance against penetration overall.

The results also suggest that the best balance between gypsum and binder may exist at a particular mixture ratio, although that needs further investigation. Both treatments improved the compressive strength of gypsum-rich soil. But the lime-and-furnace-slag-treated soils showed higher strength than the ordinary-cement-treated samples at both curing stages and across every gypsum content tested.

The wet-condition result matters because ordinary cement showed more swelling than the lime-and-furnace-slag mixture. That makes the alternative mixture better suited to reducing sulphate-driven heave in soil beneath roads. In practical terms, the lime-and-furnace-slag combination enhanced the treated soil’s performance when soaked, even though the chemistry still produced some expanding minerals.

The paper’s final practical message is that the lime-and-furnace-slag mixture is a suitable alternative to ordinary cement for pavement construction, with the added advantage of a lower carbon footprint. For road construction over sulphate-rich ground, after twenty-eight days all lime-and-furnace-slag-treated samples exceeded CB1 strength requirements and proved suitable for CS, CB1, and CB2 applications.

Lime combined with a furnace by-product strengthened gypsum-rich clay more effectively than ordinary cement and reduced swelling in wet conditions. That could make road foundations more reliable where sulphate-rich ground is a problem.