*4.4.1 Cooper slag as a partial replacement of concrete fine aggregates*

Copper slag (CS) is a vitreous substance generated in the copper smelting process. Globally, the copper industry produces approximately 24.6 million tonnes of slag [118]. In this regard, Chile is the world's largest copper producer [119, 120], generating 2.2 tonnes of CS for one tonne of copper produced. This creates significant accumulations of slag, negatively impacting the environment.

Considering the mechanical and chemical characteristics of CS, their use in concrete mixes as a partial replacement of aggregates has been evaluated. In fact, studies indicate that replacing up to 40% of fine aggregate in concrete samples results in higher or equivalent strengths compared to samples without slag [121–123]. Similar results were reported by Al-Jabri et al. [124] and Borkowsky [125] on mortar samples with 40% and 50% fine aggregate replacement, respectively. This percentage of replacement were experimentally verified by Pérez [126] for Chilean cement and aggregates. In addition, and in order to quantify the environmental benefits of this technique, a sustainability assessment based on the five-step method of Ashby et al. [30] was performed by Pérez [126] as well. The assessment estimates the percentage of CS that could be recycled, and then, the reduction of sand demand of cement mortars and concrete. Different scenarios were considered in the analysis that the copper smelters and the aggregate extraction plants are at similar distances from the concrete plants.

The results of the sustainability analysis indicate that in the most optimistic scenario, it is possible to reuse between 58% and 64% of the CS volume produced annually. This represents an annual saving of approximately 0.7 million tonnes of sand and an annual energy saving of 210409 GJ,1737905 kg CO2 eq, 11.89 kg Sb eq, 23549348 MJ ADP, 0.08 kg CDC-11 eq, 704.14 kg C2H4 eq, 12016 kg SO2 eq and 1563 kg PO4–3 eq. For instance, shows the benefits achieved for one of the cases evaluated (**Figure 6**).

These results are relevant since, in Chile, approximately 60% of building surfaces are made of concrete and 12% of masonry [127]. Therefore, there is a great opportunity to reuse this industrial waste.

**Figure 6.** *Percentage of recycled CS [126].*

Currently, the investigation continues at the concrete laboratory of Universidad de Concepción, with promising results in replacing more than 50% of the of the fine aggregate with CS.

#### *4.4.2 Recycled plastics as a partial replacement of concrete fine aggregates*

Various types of plastic waste have been incorporated into concrete to avoid direct contact with the environment [128–130]. In particular, in the Biobio region of Chile, the acrylonitrile butadiene styrene (ABS) is not being recycled and then its incorporation into concrete as a partial replacement of fine aggregate has been studied at the concrete laboratory of the Universidad de Concepcion (Biobio Region)*.*

The ABS is a plastic used in the production of computer keys, appliance and power tool housings, plastic plug protectors and automotive parts such as dashboards and bumpers [131]. However, in Chile, the ABS accounts for only 2% of national plastic recycling [132], which can lead to serious waste disposal problems.

Preliminary results show that it is possible to replace up to 50% of the fine aggregate for applications as lean concrete, simple foundations, false floors and subfloors. However, optimal results were obtained when replacing 25% of the fine aggregate with ABS plastic.

Considering that concrete is a material with a high demand for natural aggregates, the strategy of using products with post-consumer recycled content, such as ABS plastic to replace sand in concrete, reduces the environmental impacts resulting from the initial stage of the concrete life cycle, extraction and processing of virgin materials.
