Cement kiln bypass dust (CKBD), a CaO-rich by-product of the cement industry, exhibits significant potential for soil stabilization and the construction of pavement sublayers. This study investigated three material groups: pure CKBD, fly ash with CKBD additions (10–50%), and clayey soil with CKBD (5–20%). The geomechanical properties of the mixtures were evaluated through Proctor compaction tests, unconfined compressive strength, swelling, and California Bearing Ratio (CBR) tests. Results indicate that pure CKBD provides high compressive strength and CBR values with minimal swelling. The addition of CKBD to fly ash activates pozzolanic reactions, significantly enhancing compressive strength and CKBD, with an optimal content of 20%. Stabilization of clayey soil with CKBD led to a compressive strength increase of up to 75% and a reduction in swelling by over 80%, while maintaining stable CBR values under wet conditions. Water durability tests confirmed the structural stability of CKBD-containing mixtures, whereas untreated fly ash exhibited partial degradation. The findings suggest that CKBD, either alone or in combination with fly ash and clayey soil, is an effective material for improving geotechnical properties and is suitable for application in pavement subbase layers.

Stone “Tenelija” is categorized as oolitic limestone. This stone was used to build a number of constructions in Herzegovina, and one of the most famous is the “Old Bridge” in Mostar. The stone is characterized by its specific physical and mechanical characteristics. Stone “Tenelija” has low uniaxial compression strength, low modulus of elasticity, large porosity, big influence of water on its uniaxial strength, and yet many objects that were built hundreds of years ago, form this rock, still stand. The paper presents the laboratory testing of physical and mechanical characteristics of the samples of various sizes, with all specificities. Also, mutual correlations of the results was analyzed and presented.