Use of recycled mortar as fine aggregates in pavement concrete applications.

The use of recycled aggregates derived from construction and demolition wastes increased in the concrete construction industry. While the coarse fraction (i.e., from 5 to 20 mm) was successfully recycled, the fine fraction (i.e., from 0 to 5 mm) is hardly recyclable given its heterogenous nature and poor physical properties. This paper assesses the feasibility of recycled mortar aggregate (RMA) in pavement concrete applications requiring superior resistance to weathering and wearing effects. Three concrete strength grade categories prepared with different water-to-binder ratios (w/b) of 0.4, 0.5, and 0.6 are investigated; the natural sand replacement levels by RMA varied from 0 % to 60 % by volume, at 20 % increment rates. Test results showed that the detrimental RMA effect on durability depends on the concrete strength category, requiring proper adjustment of the maximum replacement rate to maintain acceptable losses in performance. Hence, the higher strength grade mixtures prepared with 0.4 w/b were found to yield significant drops in durability reaching 25 % in water sorptivity, 18 % in abrasion, and 22 % due to freeze/thaw (F/T) cycles. In contrast, the lower strength grade concrete made with 0.6 w/b exhibited marginal degradation in strength and durability, despite the incorporation of 60 % RMA. The resulting losses in sorptivity, abrasion, and F/T cycles were limited to 13 %, 8 %, and 12 %, respectively.

Durability of self-consolidating concrete containing natural waste perlite powders.

Perlite is a natural glassy volcanic rock used in construction applications requiring improved lightweight, thermal, and acoustic properties. During processing of raw perlite (i.e., cutting and fractioning to different sizes), large amounts of powders are collected and stored as waste materials. This paper evaluates the effect of waste perlite (WP) powders on durability and long-term transport properties of self-consolidating concrete (SCC). Different mixtures prepared with 580 kg/m3 powder using various combinations of WP, limestone filler (LF), metakaolin (MK), and silica fume (SF) are tested over 2-years period. Test results showed that WP confers particular benefits to the SCC compressive strength and its evolution over time, particularly when used in combination with MK and SF. Water permeability, carbonation, and chloride ion migration curtailed when WP concentration reached 220 and 260 kg/m3. In contrast, the resistance against freeze/thaw remarkably improved, given the pozzolanic reactions and porous nature of such powders that accommodated the disruptive expansive stresses resulting from frost attack.