Effects of mix composition on the mechanical, physical and durability properties of alkali-activated calcined clay/slag concrete cured under ambient condition
Samuel De Carvalho Gomes, Quang Dieu Nguyen, Wengui Li, Arnaud Castel
Abstract
Alkali-activated concrete (AAC), a possible alternative to ordinary Portland cement (OPC), provides increased environmental advantages, notably lower carbon emissions. Likewise, similar to OPC, it faces durability problems under severe environments. This study evaluated the effectiveness and durability of alkali-activated concretes containing low-grade calcined clay and granulated blast furnace slag (GGBFS), using NaOH/KOH as activators and MgO and superabsorbent polymer (SAP) as additives. The study's focus was on their physical-mechanical characteristics and performance under accelerated carbonation and chloride diffusion. Findings showed that calcined clay-GGBFS alkali-activated concretes exhibited a compressive strength range of 41.2–53.3 MPa, positioning them as a viable concrete for many structural usages. Nevertheless, the modified-RCPT (10 V) and NT Build 492 tests showed all concretes falling into the "high chloride penetrability" category, with values exceeding 350 coulombs and 13.5 (×10 −12 m 2 /s) for the non-steady-state migration coefficient (D nssm ). NaOH and sodium silicate led to higher compressive strengths compared to KOH. Furthermore, the chloride migration coefficient of alkali-activated concrete blends ranged from 55.68 to 121.14 (× 10 −12 m 2 /s). The incorporation of 0.6 % SAP decreased compressive strength but improved the non-steady-state migration coefficient (D nssm ). Lastly, MgO-enriched samples showed the lowest water absorption and carbonation depth, attributed to the buffering action of magnesium phases, reducing carbonate formations, as revealed by XRD analysis. • Concretes cured at ambient conditions show suitable compressive strength for structural use, even in severe environments. • NaOH with sodium silicate as the activator produced superior compressive strength compared to KOH. • GGBFS content played a significant role in the properties of calcined clay/GGBFS alkali-activated concretes. • Higher GGBFS reduced carbonation depth; higher calcined clay kept pH higher after carbonation. • MgO reduced the carbonation depth due to a chemical buffering mechanism.