The sustainable utilization of weathered cement kiln dust in the cleaner production of alkali activated binder incorporating glass sludge

Abstract

It is recognized that the presence of amorphous aluminosilicates, which have high ability to interact with alkalis, is one requirement for synthesizing conventional alkali-activated cements. This paper presents an innovative method for preparing alkali-activated calcium carbonate (CaCO3)-based cement, in which weathered-cement kiln dust (W-CKD) is the main precursor. Sodium oxide (Na2O) source (sodium hydroxide, sodium silicate, and sodium aluminate), Na2O-content (1.93, 3.87, 5.82, and 7.75 wt%), type of mixing water (tap and sea water), and the content of lead glass sludge (LGS: 10, 30, and 50 wt%) are the main compositional factors, which strongly affect the performance of the prepared cement. Pirssonite double salt CaCO3.Na2CO3·2H2O is alone main binding phase within sodium hydroxide-activated W-CKD with modest 28-day compressive strengths (~2–9 MPa). A significant enhancement in 28-day compressive strength (~15–21 MPa), which associated with the formation of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) was observed when sodium silicate and sodium aluminate used as alkali activators. On the other hand, mixing sea water with alkali activators results in the formation of nano materials with high effectiveness in the improvement of the mechanical performance of the prepared cement. Incorporating LGS within sodium aluminate-activated W-CKD enhances the formation of C-S-H accompanied by a significant improvement in the compressive strength of the hardened cement (25–52 MPa at 28-day of air curing). Moreover, all hardened W-CKD/LGS mixtures exhibit low Pb-leachability in acidic media. This strongly reflects on the safe application of these mixtures in the construction works.