Compositional Dependence of Pore Structure, Strengthand Freezing-Thawing Resistance of Metakaolin-Based Geopolymers.

Dongming Yan,Qiang Zeng,Shaoqin Ruan,Lingjun Xie,Xiaoqian Qian

doi:10.3390/ma13132973

Abstract

The understanding of the composition dependent properties and freezing-thawing (F-T) resistance of geopolymer materials is vital to their applications in cold regions. In this study, metakaolin-based geopolymer (MKG) mortars were fabricated by controlling the Si/Al ratio and the Na/Al ratio. The pore structure and strength were measured by mercury intrusion porosimetry and compression tests, respectively, which both showed obvious correlations with the material composition. Mass loss, strength loss, visual rate, and microscopic observation were adopted to assess the changes of the material properties and microstructure caused by F-T loads. The results showed that the strength-porosity relationship roughly followed a linear plot. Increases of the Si/Al ratio increased the capillary pore volume, but decreased the gel pore volume and the F-T resistance. Increases of the Na/Al ratio decreased the gel pore, but roughly enhanced the F-T resistance. The MKG mortar at the Na/Al ratio of 1.26 showed the lowest total pore volume and the best F-T resistance. The mechanisms of our experimental observations were that the abundantly distributed air voids connected by the capillary pores facilitated the relaxation of hydraulic pressures induced by the freezing of the pore liquid. The findings of this work help better clarify the compositional dependence of the pore structure, strength, and freezing-thawing resistance of MKG materials and provide fundamental bases for their engineering applications in cold regions.

Highlights

The great amount of CO2 emissions from the production of ordinary Portland cement (OPC), around 0.8 kg CO2 per kg OPC [1], provides significant engineering, social-economic, and ecologic incentives to replace OPC with green cementitious materials with low CO2 emissions
Experimental tests on the metakaolin-based geopolymer (MKG) mortars verified the compositional sensitivity of the strength and pore structure
A linear relationship was found between the compressive strength and total porosity (Figure 4)

Summary

Introduction

The great amount of CO2 emissions from the production of ordinary Portland cement (OPC), around 0.8 kg CO2 per kg OPC [1], provides significant engineering, social-economic, and ecologic incentives to replace OPC with green cementitious materials with low CO2 emissions. The economical and environmental benefits would be further raised when geopolymers are synthesized with solid wastes with high value added applications [4,5,6,7,8,9]. Al-O-Si bonds and to generate continual material skeletons that enable high strengths [10]. With those advantages, geopolymer-based materials possess a series of excellent performances with promising potentials in engineering applications, including high mechanical strength, great fire resistance, enhanced leaching resistance, and improved contaminate stabilization [11,12,13,14,15]

Objectives

Methods

Findings

Conclusion