High plasticity clayey soils present significant challenges in engineering projects due to their unstable properties and high susceptibility to volumetric changes. This study investigates the effect of adding quarry sand at different percentages (10% and 20%) and the effect of curing time (0, 3, and 7 days) on the compaction properties of clayey soil. The laboratory results showed that the addition of quarry dust significantly improved the physical properties of the soil. The Plasticity Index (PI) decreased from 33% in the natural sample to 23% and 22% with the addition of 10% and 20% quarry sand, respectively, changing the soil classification from High Plasticity Clay (CH) to Low Plasticity Clay (CL). Compaction parameters also improved at zero curing time (immediate compaction), showing an increase in Maximum Dry Density (MDD) and a decrease in Optimum Moisture Content (OMC). However, the results of the compaction tests indicated that increasing the curing time (delay in compaction) led to a gradual decrease in the MDD and a gradual increase in the OMC. The rate of decrease in the MDD was found to be greater for the 20% addition compared to the 10% addition over time. Based on these findings, it is recommended to use a mixture of 20% quarry dust for medium to heavy load projects, provided that the compaction process is carried out immediately after mixing to avoid the deterioration of properties caused by delaying the compaction................. Keywords: .................Clayey Soil, Quarry Dust, Curing Time, Compaction Properties, Maximum Dry Density, Optimum Moisture Content, Plasticity Index.