Early-stage geopolymerization revealed by 27Al and 29Si nuclear magnetic resonance spectroscopy based on vacuum dehydration

Abstract

The geopolymerization process affects the mechanical properties and chemical durability of geopolymer cement by forming alkali aluminosilicate gels of varying degrees of polymerization. An integrated and accurate analysis of geopolymerization process cannot be easily achieved due to the restriction of in-situ detection. In this work, vacuum dehydration is demonstrated to be an efficient and reliable method to arrest geopolymerization of pulpy and paste samples for nuclear magnetic resonance (NMR) analysis. Consistent and reliable results on inchoate geopolymerization can be obtained by one single test with constant instrumental parameters. Four stages of geopolymerization are identified, including dissolution, orderly polymerization in the short range, structural rearrangement, and unordered condensation. Each stage is differentiated by the reaction duration and Qm(nAl) evolution. The results support the existing geopolymerization theories but also provide new insights into the mechanisms by which free water loss affects structural rearrangement of geopolymers.