Title: Transport and Durability Properties of Alkali-Activated Natural Pozzolan/Slag Concrete
Author(s): Meysam Najimi and Nader Ghafoori
Publication: Materials Journal
Appears on pages(s): 81-94
Keywords: acid attack; activator combination; alkali activation; corrosion; frost resistance; natural pozzolan; precursor combination; slag; sodium hydroxide concentration; transport properties
The current study aims to assess the transport and durability properties of alkali-activated concretes made with hybrid aluminosilicate precursors having different proportions of natural pozzolan as a low-calcium precursor and ground-granulated blast furnace slag as a high-calcium precursor, which are activated with different concentrations and combinations of sodium hydroxide and sodium silicate. The studied parameters included precursor combination (natural pozzolan/slag combinations of 30/70, 50/50, and 70/30), sodium hydroxide concentration (1, 1.75, and 2.5 M), and activator combination (sodium hydroxide/sodium silicate combinations of 70/30, 75/25, and 80/20). The resulting concrete mixtures were tested for slump flow, setting time, compressive strength, absorption, rapid chloride penetration, rapid chloride migration, resistance to sulfuric acid attack, chloride-induced corrosion, and frost resistance. Mercury intrusion porosimetry and X-ray diffraction were used to justify the observed behaviors. The performance of alkali-activated natural pozzolan/slag concretes was also compared with that of a reference concrete made with solely portland cement binder. In view of overall performance, an equal proportion of natural pozzolan and slag (50/50) and a 30/70 combination of sodium silicate and sodium hydroxide proved to be the optimum precursor and activator combinations. The optimum sodium hydroxide concentration was dependent on the precursor and activator combinations as well as the expected fresh, strength, transport and durability performance. In terms of the measured transport properties (that is, absorption, chloride penetration depth, and passing charges) and resistance to acid attack and chloride-induced corrosion, all the studied alkali-activated concretes performed considerably superior to the reference portland cement concrete. In the case of frost resistance, only alkali-activated concretes with 50 and 70% slag performed superior to the reference portland cement concrete.