How does civil engineering use recycled materials?

A recent article published in the journal Materials reviewed the innovative use of recycled materials in civil engineering applications.

Study: Materials recycled in civil and environmental engineering. Image Credit: M2020/Shutterstock.com

Background

Proper waste management can ensure a continuous and sustainable supply of energy and materials over the years. Waste management mainly includes all activities of the whole waste management process, such as reuse, treatment, transport, recycling and waste collection. These activities reduce the adverse effects of waste on human health and the environment.

The proper management of non-hazardous and hazardous waste generated by industrial and civil operations is a fundamental requirement to promote a circular economy. Thus, the entire waste cycle must be regulated, from production to disposal, with particular attention to recycling and recovery.

In this study, recent innovative studies that demonstrated the use of recycled/secondary raw materials in civil engineering applications were reviewed. All of these studies aimed to identify ways to reduce waste generation and maximize the value of recycled materials that can be easily reused for various applications.

Waste recycled in civil engineering

Renewable resources derived from recycling industrial waste, such as ilmenite chlorination kiln slag, water quenched blast furnace slag and reclaimed asphalt paving material (RAP), have been used in a further study to produce recycled aggregate (RA) materials for construction and concrete applications.

The influence of mixing and processing methods on recycled aggregate concretes (RAC) obtained after different techniques was investigated in a study. A statistical study was carried out after evaluating the results of concrete compressive strength tests designed with the equivalent mortar volume method (EMV) and the absolute volume method (AVM) and containing silica fume (SF ), RA and natural aggregates (NA).

Machine learning (ML) techniques such as bagging regressor, decision tree, and gradient boosting have been used by researchers to predict the compressive strength of RACs. Statistical tests and correlation coefficients were performed to assess the performance of the ML methods, while error dispersions and k-fold evaluation were performed to confirm their validity.

Cellulose fibers obtained from recycling waste paper have been used to produce durable cement mortars. The approach represents a technically and economically feasible and environmentally friendly way of managing the waste generated by indoor applications. Additionally, the composites produced provided healthy living solutions because the cellulose aggregates in the cement regulated the humidity inside the buildings.

Prior concretes (PC) prepared from recycled brick aggregates (RBA) were characterized using porous structure distribution analysis and mechanical testing. In addition, the influence of particle size and replacement rate on the pore characteristic and structural performance of PC has also been investigated using image processing techniques and laboratory tests.

Agricultural and industrial by-products, such as wheat straw and end-of-life tire rubber, have been used as aggregates in a study to produce unconventional cement mortars through an environmentally friendly and good production process. market. The synthesized composites were thermally insulating in nature compared to the sand-based references.

The addition of another aggregate, perlite, improved the mechanical strength of the composites without harming their thermal conductivity. Additionally, composites with wheat straw exhibited high sound absorption and impact resistance, while composites with end-of-life tire rubber exhibited hydrophobic behavior due to low water absorption. Thus, these composites can be used in non-structural insulation products for interior applications.

Steel-concrete-steel (SCS) sandwich panels, consisting of two thin, high-strength steel plates separated by a thick, low-strength, low-density concrete core, were studied by the researchers. The core was synthesized using steel fiber concrete (SFC), normal strength concrete and recycled coarse aggregate. The results of the study showed that the use of SFC in the concrete core improved the ductility ratio and shear strength of the sandwich panels.

The mechanical and physical properties of economical and environmentally friendly products based on coconut fibers have been studied to produce mortars with two different binders. The use of coconut fibers improved the cracking behavior of the mortars, while the volume fraction of the binder and the fibers improved the brittleness of the composite. A lime-cement binder with a high content of coconut fibers showed the highest fracture toughness, which demonstrated the feasibility of using these fibers for cement-air-lime mortars and reinforcing cement.

Self-luminescent composites based on high density polyethylene (HDPE)/strontium aluminate were synthesized and analyzed in terms of phosphorescence and mechanical characteristics. The results of the study demonstrated that the addition of two strontium aluminate-based fillers extended the remanence time and improved the mechanical characteristics of HDPE composites. Thus, these composites can be used effectively in applications such as lamps and roadside night displays.

In another study, soil-cement blocks were produced using waste tire steel fibers (WTSF) and studied. Three mixtures with 10% Portland cement and 1.5%, 0.75% and 0% WTSF were synthesized. The greatest increase in mean compressive strength was observed in soil-cement blocks with 1.5% WTSF. In addition, all the results of the samples studied complied with the minimum requirements of the different standards considered in the study.

To sum up, recycled materials have demonstrated significant potential in different civil engineering applications. However, further research is needed to further expand the application of recycled materials in civil engineering to reduce waste generation.

Source

Notarnicola, M., Petrella, A. Recycled materials in civil and environmental engineering. Materials 2022. https://www.mdpi.com/1996-1944/15/11/3955

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