Carbonation resistance of alkali-activated GGBFS/calcined clay concrete under natural and accelerated conditions
Luís Urbano Durlo Tambara Júnior, Astrid Hirsch, Frank Dehn, Gregor J. G. Gluth
Abstract
The carbonation resistance of alkali-activated materials (AAMs) is a crucial parameter for their applicability in concrete construction, yet the parameters influencing it are insufficiently understood to date. In the present study, the carbonation resistance of alkali-activated concretes with varying fractions of ground granulated blast furnace slag (GGBFS) and calcined clay ( i.e ., high, intermediate, and low Ca contents) were assessed under natural and accelerated conditions. Corresponding hardened AAM pastes were studied using X-ray diffraction, thermogravimetry, Raman microscopy, and mercury intrusion porosimetry. The carbonation resistance of the concretes at natural CO 2 concentration depended principally on their water/(CaO + MgO eq + Na 2 O eq + K 2 O eq ) ratio. The remaining variability for similar ratios was caused by differences between the pore structures of the AAMs. For concrete with favorable water/(CaO + MgO eq + Na 2 O eq + K 2 O eq ) ratio and pore structure, the carbonation resistance was comparable to that of Portland cement concrete. The relationship between carbonation coefficients obtained under accelerated and natural conditions differed for concretes with high and low fractions of calcined clay, indicating that accelerated carbonation testing is less suitable to study the carbonation of low-Ca AAMs. • AAMs based on GGBFS and calcined clay exhibit high carbonation resistance. • The carbonation resistance can be approximately predicted using a single parameter. • The remaining scatter is influenced by the pore structure of the AAMs. • Accelerated carbonation testing of low-Ca AAMs deviates from predicted behaviour.