Stabilisation of construction and demolition waste with a high fines content using alkali activated fly ash

This paper deals with the stabilisation of the fines portion of Construction and Demolition Waste (CDW) produced by a Portuguese recycling company. The recycled aggregate was analysed with and without the addition of a well-known precursor – fly ash (FA), considering different CDW/FA weight ratios. The resulting mixtures were activated with a solution based on sodium hydroxide and sodium silicate, and their microstructure and mechanical behaviour were extensively characterised, using XRD, FTIR, SEM, BSEM/EDX and uniaxial compression strength (UCS) tests. Results obtained showed that the presence of fly ash improves compression strength and elasticity module, reaching UCS values higher than 8 MPa, after 28 days of curing at ambient temperature and relative humidity. Such values are above any kind of threshold considered for geotechnical works such as road and railway foundations or infrastructure embankments, which are regarded as effective applications for recycled CDW. The products resulting from the alkali activation of the CDW/FA mixtures were characterised as a mixture of the gels NASH and CASH, which was attributed to the initial high content of amorphous Si, Al and Ca of these mixtures.Peer reviewe