Calcined Attapulgite Clay as Supplementary Cementing Material: Thermal Treatment, Hydration Activity and Mechanical Properties

The present paper studied the effects of calcination temperatures (200-800 degrees C) on the appearance, mineral composition, and active SiO2 content in attapulgite and investigated the effects of attapulgite before and after calcination on the chemically bonded water content, the degree of reaction of cement paste, and the mechanical properties such as the flexural strength, compressive strength, and splitting-tensile strength of cement mortar. The results indicate that the calcination temperature changes the mineral composition of attapulgite, thereby affecting the hydration activity of cement-based materials. The attapulgite calcined at 500 degrees C (AT500) has the best enhancement on the hydration activity of cement-based materials. The calcination at 500 degrees C is most beneficial to the dissolution of SiO2, and the content of SiO2 reaches 20.96%. The contents of chemically bonded water in the samples incorporated with calcined attapulgite reduced and that of the samples incorporated with AT500 at 28 d is the same as that of the control group. The reaction degree of AT500 is 78.61% at 28 days. Calcined attapulgite clay can reduce the energy consumption of the cement industry and promote the sustainable development of attapulgite clay.

Automated summary

The present study investigates the effects of different calcination temperatures on the appearance, mineral composition, and active SiO2 content in attapulgite. It also examines the influence of calcined attapulgite on the chemically bonded water content, hydration degree of cement paste, and mechanical properties of cement mortar. The results suggest that a calcination temperature of 500 degrees C yields the best enhancement in cement-based materials' hydration activity. This study highlights the potential of using calcined attapulgite clay to reduce energy consumption in the cement industry and promote the sustainable development of attapulgite clay.