Mix Development and Performance of Concrete with Treated Slag from Copper Production as Cement and Sand Replacement

By incorporation of MFS-slag (modified iron-silicate slag) in concrete mixtures at high cement and/or aggregate replacement levels, the DUSC project strives for (i) maximum residue valorisation and avoidance of waste disposal, and (ii) more durable and sustainable reinforced concrete structures, with a low carbon footprint, high service life and good recyclability. MFS-slag based concrete (‘MFS-concrete’) is targeted which can be used as ready-mix concrete for structural applications, such as beams, columns and slabs of buildings and infrastructure. The study focusses on demonstrating the equivalent performance of the MFS-concrete, compared to traditional concrete, in terms of workability, mechanical and durability behaviour. The project deals with two different cement replacement levels. On one hand, MFS-slag will be used as supplementary cementitious material in concrete to replace at least 25% of OPC (Ordinary Portland Cement) (= MFS-CS concrete). At the other hand, MFS-slag will be used in concrete at high (70%) OPC replacement levels by the additional use of an activator (or accelerator) (= MFS-CA concrete). In addition to the replacement of the cement, both types of concrete also apply coarse aggregate replacement. The DUSC project scientifically substantiates the use of MFS-slag in concrete: (i) to investigate and adopt the most appropriate production process parameters, (ii) to determine cement/aggregate replacement levels, (iii) to develop compatible and efficient chemical admixtures and (iv) to evaluate and model the workability, mechanical, durability, sustainability and recyclability performance of MFS-concrete. The objectives as presented below will be achieved through intensive collaboration between all partners. Objective 1: To develop insights into the compositional parameters of MFS-slag and modelling its variability in the function of the plasma fuming process parameters. To retain the most favourable conditions for MFS-slag production to be used as cement/aggregate replacement. The quality and homogeneity will comply to the use in structural concrete, with equivalent mechanical and durability performance as traditional concrete. Objective 2: To develop improved reactivity tests to screen the applicability of MFS-slag as the supplementary binder material in concrete (with or without activator). Objective 3: To maximize the use of MFS-slag as cement and aggregate replacement in concrete. For MFS-CS, minimum 25% cement and 50% coarse aggregate replacement are targeted. For MFS-CA, the target is to increase the cement replacement to 70%, combined with 25% aggregate replacement. The final replacement levels will be derived from equivalent concrete performance in terms of fresh and hardened concrete properties (both mechanical and durability), in reference to ready-mix C35-RC-EE2/3/4. Objective 4: To increase the efficiency of chemical admixtures (air-entraining agents, accelerators, superplasticizers) in MFS-concrete by adapting its formulations and investigating its impact on performance-based MFS-concrete. The admixtures will be fully compatible with the MFS-slag, to guarantee equivalent workability, mechanical and durability performance with respect to traditional concretes. Objective 5: To scientifically substantiate the durability and sustainability performance of MFS-concrete. Durability will be assessed by equivalent concrete performance testing and service life prediction. Sustainability will be evaluated by life-cycle assessment, including end-of-life related impacts. Objective 6: To evaluate the recyclability of MFS-concrete. Recycled MFS-concrete aggregates are targeted which comply to conformity requirements in accordance to NBN EN 206 and NBN B15-001. Objective 7: To demonstrate MFS-concrete in a large-scale testing setting, for further proof of principle.