Strength and Chemical Resistance of Mortars Containing Brick Manufacturing Clays Subjected to Different Heat Treatments


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Title: Strength and Chemical Resistance of Mortars Containing Brick Manufacturing Clays Subjected to Different Heat Treatments

Author(s): M. O'Farrell, B.B. Sabir, and S. Wild

Publication: Special Publication

Volume: 207


Appears on pages(s): 33-50

Keywords: chemical resistance; compressive strength; ground brick; heat treated clay

Date: 10/7/2002

The use of calcined clay as a pozzolanic partial cement replacement material in concrete is currently receiving increased attention. Previous work by the authors has demonstrated the effectiveness of utilising ground waste clay bricks in mortar and concrete. This paper presents the results of an investigation of the properties of mortar in which a calcined clay was employed as a pozzolan. The clay was heated in crucibles to 800°C with a heating ramp of 100°C per hour. The furnace environment was then kept constant at 800°C for a period of two hours. After heat treatment the clay was cooled in two different ways. One batch was allowed to cool naturally to room temperature and the second was water quenched with the crucible lid on. Mortars were prepared using either the heat treated clay or ground waste clay bricks (from the same clay subjected to 1000°C calcining) as a pozzolanic partial replacement for cement at replacement levels of 10, 20 and 30%. The compressive strengths of the mortars were monitored up to 90 days and the resistance to sodium sulfate solution and synthetic seawater was monitored up to 300 days. The specimens were also monitored for weight changes. Partially replacing cement by ground brick or heat-treated brick clay gives early strengths that are lower than that of the control. At 90 days, however, the strengths are the same as or greater than that of the control. Heat-treated clay is effective in reducing expansion during exposure of the mortar to sulfate solution and synthetic seawater. The rapidly cooled clay gives better performance, in terms of strength development and resistance to harmful solutions, than the slow cooled clay.