Study On CKD As Cementitious Materials Combining Industrial Wastes

Cement kiln dust(CKD) is produced in the cement manufacturing processes. Although some amount can be reintroduce into the kiln as a raw feed, a substantial amount cannot. It was estimated that 100 million tons were produced worldwide in 2005. The demand for better methods of disposing of waste CKD is increasing. One method may be to use CKD as a supplementary material in concrete; however, limited work has been done on this subject due to its high alkali, sulfur, and chloride content. To control these undesirable effects, CKD is frequently incorporated in concrete with pozzolanic materials such as slag and fly ash.The present research investigates characteristics of a binder system containing CKD, slag, fly ash(FA) and Ordinary Portland Cement (OPC). The influence of the different compositions on the early hydration and hardening of cement pastes was studied using a new non contact resistivity meter together with the measurement of hydration heat. Other techniques such as thermogravimetry, differential thermal analysis, scanning electron mirocscopy had been used to investigate the microstructure of the samples. In the end, adopt the electrochemical method to investigates the chloride binding capacity in different system.Through above-mentioned research , have got the following conclusion:(1) It' s not effective to activate CKD through grinding regimes.(2) The main hydration product of mortar combined 15% CKD is calcium sulfoaluminate hydrate and C-S-H. Aft is stability after formed and contribute to the development of strength.(3) The test of resistivity showed that, when mixed CKD and fly ash or slag, fly ash and slag can on the certain degree balance the alkali in the CKD material system. And the alkali in the CKD can activate the fly ash and slag. Compared with the single admixture of the fly ash cement and slag cement, CKD can improve the early strength of the high content mixture cement based composite materials obviously.(4) CKD has a certain activity, but high alkalinity and high Cl^-, SO₃ content will affect it's upper limit as mixture or direct dust feedback directly. When increase the content of the CKD, the strength of the sample trend to decrease.(5) A CKD-slag specimen made without Portland cement also displays satisfactory compressive and flexural strength. This indicates that alkalis released from CKD may activate slag hydration.(6) Under the conditions of this experiment the cement concrete components' and mineral functional materials' original capability of binding the chloride are as follows: cement>fly ash>slag, while the output of calcium aluminate chloride hydrate and the chemical adsorption is the main factor of the hydrate's capability of binding the chloride.