Impact of the mineralogical composition of natural pozzolan on properties of resultant geopolymers

Abstract

This article presents a comparison between the impact of different mineralogical compositions of natural pozzolans for geopolymer synthesis. Beyond an optimum silica modulus, the compressive strength either increases on low rate or decreases with age. The presence of zeolite minerals enhances the reactivity of natural pozzolans. In contrast, the presence of calcite can lead to the incorporation of calcium into the reaction products. At the same time, the carbonate can enhance the formation of sodium carbonate, which can deplete the alkalis and water from binder gel, thereby reducing the rate of compressive strength development. In severe cases, the crystallization pressure of sodium carbonate can cause a complete disintegration of the structure. These effects are pronounced for samples outside the optimum silica modulus range and for low reactive pozzolans.

Keywords:

• Natural pozzolan
• compressive strength
• degree of reaction
• crystalline mineral
• calcite
• sodium carbonate

Disclosure statement

No potential conflict of interest was reported by the authors.

Acknowledgments

Authors are thankful to Dr. Yury Andrés Villagrán-Zaccardi for fruitful discussion. The authors are thankful to Tubag quick-mix Gruppe GmbH & Co. KG and Märker Zement GmbH for providing samples.

Additional information

Funding

This study was supported by the German Academic Exchange Service and Higher Education Commission of Pakistan (Programme ID: 57245990).