Development of construction materials using nano-silica and aggregates recycled from construction and demolition waste

Effective method for upcycling construction and demolition waste into concrete: A life cycle approach

Different property enhancement techniques have already been established to support upcycling of construction and demolition waste as aggregate in concrete. However, the most suitable and sustainable method is still unknown. Quality improvement of recycled coarse aggregate (RCA) after any treatment method and its environmental impact is estimated using life cycle analysis (LCA). This article compares the environmental impacts of such treatment methods on RCA and aims to find out the most suitable method with minimum impacts. The functional unit of this study is considered the preparation of 1 tonne of treated aggregate (recycled), considering reduction in water absorption after the treatment. An LCA is carried out using the SimaPro software (https://simapro.com/) followed by ISO 14040/44 guidelines. Based on the LCA environmental profiles, thermal treatment is the highest emission contributing removal method followed by mechanical grinding. In strengthening of attached mortar methods, accelerated carbonation process is the major emission contributing method followed by a specific microbial treatment. Moreover, a sensitivity analysis was performed by varying the energy mix with a focus on renewable-based energy mix. The sensitivity analysis shows a shift on selection for the suitable treatment method and other possibilities considering renewable-based energy mix. A preliminary assessment and probable impact prediction could be conceptualized before the adoption of any treatment method on RCA for a particular location.

Experimental investigation on the effect of nano-silica on reinforced concrete Beam-column connection subjected to Cyclic Loading

Beam-column joints are crucial load transmission zones because they face concentrated forces from both the beams and the columns. High shear and axial stresses caused by these concentrated forces in the area of the joint may result in decreased joint strength. This article proposes a new beam-to-column connection developed for precast concrete-resisting frames. Concrete mixtures are enhanced mechanically by adding nano silica as it increases compressive strength, flexural strength, and abrasion resistance. Within the concrete, it creates a solid, gel-like matrix that fills voids and strengthens the whole construction. In this study, three reinforced concrete beam-column joint specimens were cast with fly ash, the other three with nano-silica and fly ash, and one sample with nano-silica and a control mix without admixtures was cast. Specimen cast using fly ash and nano-silica is subjected to cyclic loading after 28 days of curing. A load capacity of 100 kN was imposed on the column during testing. It was observed that a gradual increase in fly ash decreased the compressive and flexural strength of the beam-column joints. This decrease in strength was addressed by adding 2.5% nano-silica. Nano silica acts as a nucleus to bond tightly with cement particles during hydration. The results showed that the flexural strength equivalent to that of a controlled specimen can be achieved by adding nano-silica at 2.5% and fly ash at 60%. The highest loading of 38.1 kN can be applied to the specimen with nano-silica without fly ash. Although a higher axial compression ratio can improve the bearing capacity and initial stiffness, it can also reduce deformation capacity and flexibility.

Recent Advancements in the Nanomaterial Application in Concrete and Its Ecological Impact

At present, nanotechnology is a significant research area in different countries, owing to its immense ability along with its economic impact. Nanotechnology is the scientific study, development, manufacturing, and processing of structures and materials on a nanoscale level. It has tremendous application in different industries such as construction. This study discusses the various progressive uses of nanomaterials in concrete, as well as their related health risks and environmental impacts. Nanomaterials such as nanosilica, nano-TiO₂, carbon nanotubes (CNTs), ferric oxides, polycarboxylates, and nanocellulose have the capability to increase the durability of buildings by improving their mechanical and thermal properties. This could cause an indirect reduction in energy usage and total expenses in the concrete industry. However, due to the uncertainties and irregularities in size, shape, and chemical compositions, some nanosized materials might have harmful effects on the environment and human health. Acknowledgement of the possible beneficial impacts and inadvertent dangers of these nanosized materials to the environment will be extremely important when pursuing progress in the upcoming years. This research paper is expected to bring proper attention to the probable effects of construction waste, together with the importance of proper regulations, on the final disposal of the construction waste.