Utilizing thermal activation treatment to improve the properties of waste cementitious powder and its newmade cementitious materials

The low activity of waste cementitious powder from construction and demolition waste (CDW) is the main reason that limits its application in cementitious materials, and thus, this work investigates the utilization of thermal activation treatment in improving the properties of waste cementitious powder and its newmade mortar. The untreated waste powder mainly consists of inert hydrated products, quartz or calcite, and new active components are formed in thermal-activated waste powder, and the utilization of thermal-activated waste powder promotes the hydration reaction of new cementitious materials. The waste powder has an irregular micro-structure, but it becomes smooth after 1200 degrees C activation. When the thermal activation temperature on waste powder is 600-800 degrees C, the properties of mortar including thermal-activated waste powder are better than those of mortar with un-treated waste powder, and specifically, the activity index of waste paste powder ranges from 71.7% to 90.1% when the activation temperature ranges from 20 degrees C to 600 degrees C. But the properties of mortar including 1200 degrees C thermal-activated waste powder are generally inferior to those of mortar with other thermal-activated waste powders. The 600-800 degrees C thermal-activated temperature is suggested to improve the properties of waste cementitious powder by taking energy consumption and thermal-activated efficiency into consideration. And although higher than untreated waste powder preparation, the costs and energy consumption for preparing thermal-activated waste powder still has advantages in contrast with cement preparation. Replacing partial cement with thermal-activated waste powder in new cementitious materials is feasible and beneficial.