Cement kiln dust(CKD) a hazardous waste product from cement kiln burning process was evaluated for its potential as a limestone substitute in cement making circular chemistry. CKD XRF elemental chemical analysis is similar to that of limestone making it a suitable replacement of limestone. The quantity of CKD waste generated is estimated to be 15-20% of the cement produced at Khayah Cement Limited Zimbabwe. Substitution of limestone with low-cost waste CKD will avoid environmental pollution, enhance waste utilisation, minimise land fill and reduce cement-making cost. Experimental laboratory research design was used to make cement by substituting limestone with CKD. Ten batches of cement were made by milling 0 to 45% CKD as limestone substitute, limestone, clinker and gypsum using quantities obtained from Bogue cement making calculations. For each batch of cement milled full chemical analysis were performed using XRF before milling in order to calculate the Bogue clinker chemical parameters for cement making and after milling to verify compliance of cement specifications parameters of the cement produced. Cement strength and setting time tests results were evaluated in accordance with the Standards Association of Zimbabwe Specifications (SAZS) EN 196 and 197 test methods using the bricks made from the milled cement. The results obtained from the cement strength and setting time demonstrated that substitution of limestone with CKD up to 20% maximum produced a cement equivalent to Portland cement of 32.5 R and substitution up to 10% maximum produced a cement equivalent to 42.5 R (Superset). The cement test results obtained of up to 20% of limestone substitution with CKD complies with SAZS EN 196 and 197 cement specification requirements. CKD limestone substitution in cement making can be used to conserve limestone mining and lower the cost of cement making thus making a contribution to the resilient Zimbabwe circular economy

Keywords: cement kiln dust, limestone, cement, substitute, milling.