Stabilising CDW recycled aggregates with alternatives to Portland cement

The use of ordinary Portland cement for the stabilisation of granular materials in road construction undermines the effort on sustainability made by using recycled aggregate in substitution of natural ones. This requires the use of low-impact binders so that the road construction industry complies with the prevailing environmental regulations. This study compares the mechanical and environmental properties of construction and demolition waste (CDW) aggregates stabilised with different binders: (i) a Portland-limestone cement as a reference, (ii) a pozzolanic cement, (iii) an experimental pozzolanic cement containing waste clay from the lightweight aggregate production, and (iv) a binder with alkali-activated CDW fines. In the laboratory experiments, both strength and resilient properties were considered, while the environmental impact was assessed in a cradle-to-gate scenario through a life cycle analysis (LCA). The stabilised mixture with pozzolanic cement achieved comparable strength and stiffness while exhibiting a lower environmental impact than the mixture containing Portland-limestone cement. The addition of waste clay to the pozzolanic cement significantly reduces its environmental impact albeit more binder is required to compensate for the lower mechanical properties. The alkaline activation of the fine particles in the CDW aggregate enabled the creation of a stabilised mixture with high strengths and resilient modulus. However, this alternative stabilisation technique requires further optimisation to mitigate the significant environmental impact. The engineering evaluations of the stabilised granular mixtures studied have considered both mechanical and environmental factors intending to contribute to the scientific debate on how to make roadworks sustainable and conserve natural resources. • Recycled aggregates make cement-stabilised granular materials more sustainable. • Ordinary Portland cement counteracts the benefit of recycled aggregates. • Pozzolanic cements preserve mechanical properties and enhance sustainability. • The addition of waste clay to pozzolanic cement reduces the environmental impact. • Alkali-activated binders require further optimisation to decrease environmental harm.