Reuse of ceramic sludge in the production of vitrified clay pipes

The use of various wastes in the manufacture of different ceramic products has proved to be beneficial from both economic and environmental points of view. In the present paper, the simultaneous reuse of ceramic sludge waste (from 0% to 6.2%) and cullet (from 0% to 10%) in the production of vitrified clay pipes has been investigated. Samples were pressed at 15 MPa, dried and subsequently fired at three different temperatures (1050, 1150 and 1250 °C) and soaking times (1, 2 and 3 h). A two-level factorial design was applied to study the effect of the various parameters on the properties of fired bodies. It was concluded that an economic recipe can be prepared involving the use of 6.2% sludge (dry basis) and 5% cullet with the balance clay + grog followed by firing the dried body at 1050 °C for one hour only. The produced fired specimens yielded bending strength exceeding the minimum requirement for any size of soil embedded pipes and for 8″ and larger concrete cradled pipes. The suggested composition makes use of an environmentally polluting waste (sludge) and broken glass waste (cullet) and involves firing for one single hour at a temperature about 200 °C lower than commonly used.