Improving the rheological, mechanical, thermal, and geoenvironmental behavior of cemented backfills to derive the benefits

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Backfilling of large underground voids created by mine ore removal is an essential technology to provide ground support and regional stability, thereby facilitating ore removal from nearby regions. This study investigates two types of backfill: 1) cemented past backfill (CPB), a mixture of filtered tailings, binder, and water; and 2) cemented paste aggregate fill (CPAF), or tailings paste incorporating crushed waste rocks. Binder is added in sufficient quantity to strengthen CPB mixtures, and water is simultaneously added to facilitate transport flow through pipelines and drill holes and to prevent plugs from forming. To avoid using large quantities of water, which negatively impact strength, superplasticizers (SP) currently used in concretes can be used. SPs allow obtaining flowable and easily pumpable CPBs with low water content (or high solids content), thereby reducing the binder content and shortening the time to achieve the required strength. The most effective polycarboxylate SPs are expensive. Hence, the first objective of this study is to investigate the use of more affordable dispersants and to develop effective and convincing tools to promote their regular use in mine backfill operations under different climatic conditions. CPAF is another promising backfill technology when superior mechanical properties are required compared to classical CPBs. Few studies to date have addressed the flowability of these materials, their behavior during pipeline transport, or the conditions to be met to prevent sedimentation of aggregates, which produces heterogonous CPAFs. The second study objective is therefore to develop design tools for optimal recipe formulation and pipeline transport of non-segregating CPAF. Backfilling in voids excavated in the permafrost raises additional design challenges: CPB hardens under decreasing temperature due to heat exchange with the permafrost, and advanced numerical design tools are needed to address this issue. The third study objective is therefore to develop robust design tools for backfilling voids excavated in the permafrost. CPB and CPAF mix proportioning is generally based on extensive laboratory testing of a large number of mixes. To date, no standardized mixing procedure has been developed to account for the variable mixing times, mixer load mass, mixing speeds, and types of mixers used at different laboratories. Hence, the influence of the mixing energy and several other factors on CPB and CPAF properties will also be investigated. Advanced and innovative scientific knowledge will be developed in order to derive the maximum of technological, economic, and environmental benefits. The newly developed tools will be disseminated to potential users, including the scientific community, backfill engineers in the mining industry and at engineering consulting firms, designers of new adjuvants in the dispersants industry, and ministries and governmental agencies.