An investigation of the hydration chemistry of ternary blends containing cement kiln dust

During the manufacture of Portland cement, dust is generated composed of particles of feedstock and condensed volatilised inorganic salts. Due to its highly alkaline soluble fraction, the dust can be used as an activator in blends containing pozzolanic materials or hydraulic slags, allowing them to undergo cementitious reactions. The inclusion of Portland cement in such blends enhances strength development further, although careful proportioning of materials will be required to obtain optimum performance. Ternary systems containing cement kiln dust, pulverised-fuel ash and Portland cement were characterised in this paper in terms of strength development and hydration products. For a given Portland cement content, optimum strength was achieved in blends containing approximately 10% cement kiln dust for Portland cement levels up to 80%. Beyond this level a CKD/PFA ratio of one was optimal. Isothermal conduction calorimetry results and measurements of calcium hydroxide levels indicated that this was due to an acceleration of the reactions of the blend constituents by the dust. Additionally, the chemical composition of the optimal blends promoted the production of calcium aluminate and ferrite hydrates of a type conducive to maintaining the integrity of the cementitious matrix.