# Hybrid Binders Through Alkaline Activation of Fine Construction and Demolition Waste

## TL;DR

This study explores using construction and demolition waste as a sustainable cement alternative through alkaline activation, showing promising results for reducing construction waste and improving material properties.

## Contribution

The study introduces a method to optimize alkali-activated systems using construction and demolition waste as a sustainable binder.

## Key findings

- Higher NaOH content reduced setting times for ceramic and concrete waste-based mortars.
- Increased Na2SiO3 content led to greater drying shrinkage in both waste types.
- Compressive strengths of 7.6 to 8.2 MPa were achieved at 28 days.

## Abstract

The use of construction and demolition waste (CDW) as an alternative binder to ordinary Portland cement presents a promising solution through alkaline activation. This study evaluates the physical, mechanical, and microstructural behaviour of pastes and mortars produced with CDW—specifically concrete (RH) and ceramic (RC) waste—activated with NaOH and Na2SiO3 (SS) solutions. Mortars were prepared with NaOH/SS ratios of 0.2 and 0.3 and an activator-to-precursor (AA/P) ratio of 0.2. Results showed that higher NaOH content accelerated alkaline activation, reducing setting times from 6.2 h to 3.7 h for RC and from 4.6 h to 3.2 h for RH. Conversely, increasing Na2SiO3 content led to greater drying shrinkage, from −0.42% to −0.49% in RC and from −0.46% to −0.52% in RH. Compressive strength values at 28 days ranged from 7.6 to 8.2 MPa. X-ray diffraction (XRD) revealed the presence of non-reactive crystalline phases in both precursors, while Fourier transform infrared (FTIR) spectroscopy indicated the formation of CASH, CSH, and/or (N)CASH gels. This study highlights the potential of CDW as a sustainable alternative binder and the usefulness of the proposed method for optimising alkali-activated systems, contributing to circular economy strategies in the construction sector.