Page 45 - New Trends in Green Construction

MULTISCALE LABORATORY INVESTIGATION INTO GEOPOLYMERIZED CONSTRUCTION AND DEMOLITION WASTE AGGREGATES IN STRUCTURAL ROAD PAVEMENT LAYERS
Luca Tefa, Paola Palmero, Marco Bassani
Keywords: stabilized road pavement layers, construction and demolition waste, alkali-activation. 1. Introduction
Construction and demolition wastes (CDW) are produced on a large scale in the European Union (EU) with negative consequences for the environment. The EU Commission has developed several policies aimed at maximising the reuse of CDW in civil constructions as an alternative aggregate source. The main use of CDW aggregates is in road constructions. However, due to their limited physical/mechanical properties, they are generally used in backfilling applications and where the deteriorating effects of traffic and the environment are lower (i.e., road embankments, subgrades). In recent years, they have also been used in the formation of subbases for low-traffic volume roads (Jiménez et al., 2012). Their employment in subbases and granular bases of trafficked roads has been made possible with an improvement in their mechanical properties (through stabilization) which serve to enable an adequate response to higher stress conditions and more severe degradation phenomena (Bassani et al., 2016; Mohammadinia et al., 2014).
This paper introduces a new stabilization technology based on the alkali-activation (AA) of aluminosilicates present in the finest size class of CDW mixed recycled aggregate (MRA). The AA was triggered by adding an alkaline solution (AS-100%) to CDW aggregates. The AS-100% was obtained by diluting sodium silicate and sodium hydroxide in water. This technology avoids the use of common industrial solid binders (i.e., Portland cements, lime) as well as other by-products (i.e., fly ash, blast furnace slags) to limit costs and environmentally harmful consequences.
2. Materials and methods
CDW aggregate obtained from a recycling plant close to Turin (Italy) was investigated. A preliminary chemical characterization (XRD, Table 1) of fine particles (< 63 m) included in the CDW (named UND) revealed the presence of significant amounts of aluminosilicates (56.8%), and a lower content of minerals from the mica group (22.7%), carbonates (11.8%), and quartz (14.7%). The same analysis was carried out on powders (Figure 1) obtained from the four main CDW constituents: recycled concrete (RC), recycled asphalt (RA), brick and tiles (BT), and natural aggregate (NA). UND, RC, RA, BT, and NA fines smaller than 0.125 mm were mixed with the AS-100%. Flexural and compressive strength tests on hardened samples (with a liquid/solid mass ratio equal to 0.4) were carried out on prismatic (80×20×20 mm) specimens after 28 days of curing at room temperature.
A mechanical characterization (i.e., unconfined compression strength UCS, resilient modulus RM) was also carried out on a larger scale on cylindrical specimens of 100×200 mm (d×h) made up of CDW aggregates in the particle size range 0-25 mm. In this case, CDW aggregates were stabilized by adding a quantity of AS-100% within ± 2% of the optimal moisture content (ww,opt = 8.6%). The mechanical properties of the mixtures were measured after 7, 28 and 60 days of curing at
45
New Trends in Green Construction