The Effect of Aluminum in Solution on the Dissolution of Amorphous Silica and its Relation to Cementitious Systems

Abstract

One of the most serious causes of degradation of concrete is the alkali–silica reaction. Amorphous silicates present in certain aggregates react with the alkaline pore solution of the concrete to form a gel, which absorbs water and swells, leading to the expansion of the concrete. It is known that the deleterious effects of ASR can be suppressed by the incorporation of supplementary cementitious materials in the concrete, but the mechanisms operating are not clear. In this article, we study a model system of amorphous silica plates in simulated pore solutions by X‐ray photoelectron spectroscopy (XPS), to demonstrate that aluminum in solution can directly suppress the dissolution of amorphous silica under the highly alkaline conditions found in concrete. XPS shows that aluminum species are incorporated into the framework of the silica structure. Scanning electron microscope (SEM) and atomic force microscope (AFM) images confirmed the reduction in dissolution of silica in solutions containing aluminum.

Alkali–silica reaction: Current understanding of the reaction mechanisms and the knowledge gaps

“…• Reducing silica dissolution rate from aggregates, by Al adsorption on the surface of reactive silica and/or formation of a diffuse zeolite barrier [180][181][182]; • Reducing the pore solution pH by formation of C-A-S-H, which improves alkali binding capacity over C-S-H [183]; • Reaction with and consumption of portlandite to form calcium aluminate phases; • Reducing swelling of ASR gel; • Densifying pore structure, and reducing permeability of concrete.…”

“…Chappex and Scrivener [182,184] demonstrated that presence of aluminum in pore solution can limit the dissolution of silica from aggregates. Two potential mechanisms have been suggested to explain how Al may impact the dissolution of silica in alkaline environments.…”

Silica fouling in coal seam gas water reverse osmosis desalination

“…Especially in the field of osmotic membrane separation, it has been noted that only small amounts of cations impurities may impose different deposition structures , Cob 2012. Moreover, there has been considerable speculation on the role of aluminium in aluminosilicate deposition (Chappex 2012, Iler 1976, Bergna 1994). …”

Transport- and surface reaction-controlled SON68 glass dissolution at 30°C and 70°C and pH=13.7

“…Several investigators have shown the inhibitory effect of Al(OH) 4 À on the dissolution of silicate materials in highly alkaline solutions (Bickmore et al, 2006;Chappex and Scrivener, 2012;Snellings, 2013). According to the authors, Al(OH) 4 À would co-adsorb with Na + on silanol sites and passivate the surface of silicate materials.…”