Development of grouting materials with application to the protection of the geological relics of the Weng’an Biota

Abstract

The Weng’an Biota, a fossil Konservat-Lagerstatte in South China that is c. 570 – 609 myr old, preserves the world’s oldest zoolite and provides a unique empirical record for studying animal origins and early evolution. Due to geological disasters caused by the exploitation of the local phosphate mine, part of the fossilized records and the geological sections of the Weng’an Biota have been seriously damaged. Protection of this unique fossil area is urgently required. In this research, an innovative scheme for the protection of the geological relics of the Weng’an Biota is proposed by backfilling the mine cavity with specially formulated grouting materials. In view of the shortcomings of the current grouting materials, such as the high proportion of water separation, the low stone percentage and high cost, newly developed grout materials consisting of mixtures of cement-fly ash-expansion agent (C-F-E) were systematically studied by a combined method of theoretical analysis and experimental study. Firstly, new grouting materials (C-F-E) were developed using selected proportions of (1) Portland cement (P·O 32.5), (2) external admixture (Fly ash), (3) expansion agent (NV) and (4) admixture (DFZ). Then, the properties of new grouting materials (C-F-E), such as stability, stone percentage, rheology, fluidity, setting time and compressive strength were evaluated by laboratory tests. Finally, a new model of the hydration process was proposed for these newly developed grouting materials based on a detailed scanning electron microscopy (SEM) study of their microstructural development. These research results will provide an effective solution to the protection of the geological relics of the Weng’an Biota. Additionally, these grouting materials may prove suitable for solving similar problems in the management of most mine cavities requiring stabilization in the future.