Ozonation for the Chemical Modification of Carbon Surfaces in Fly Ash

Coal combustion fly ash is a useful additive in concrete due to its pozzolanic property — i.e. its ability to react with calcium in concrete mixes to contribute to the formation of the cementitious matrix [1]. Through this mechanism, fly ash serves as a partial replacement for Portland cement, yielding cost savings as well as a variety of concrete property enhancements. A practical problem with this recycling technology is the tendency of residual carbon in ash to interfere with the air entrainment process in concrete. Porous carbon adsorbs the chemical surfactants used in concrete pastes, making them unavailable for the stabilization of a desirable micro-void system. Our earlier work identified nonpolar carbon surface as the primary adsorption sites for the surfactant [2]. The present paper describes a new concept for suppressing the surfactant adsorption by the introduction of polar functionalities by reactive treatment at ambient temperature and in the dry state.