Barium carbonate and supplementary cementitious materials to counteract thaumasite sulfate attack in mortars: Effect of aggregate composition

P.M Carmona-Quiroga,M.T Blanco-Varela

doi:10.1016/j.conbuildmat.2021.122583

Abstract

Abstract Supplementary cementitious materials (SCMs) have been shown to have a beneficial impact on carbonate-bearing mortar and concrete resistance to sulfates in general and thaumasite sulfate attack (TSA) in particular, although the effect is limited in some cases. In pursuit of improved sulfate-resistance formulations that inhibit thaumasite formation, this study added barium carbonate, both as mineral addition and as aggregate, to cements blended with SCMs. The aim was to immobilise sulfates via conversion to barite, a practically insoluble form of barium sulfate. The study was conducted on standardised mortars prepared with CEM I 52.5 N-SR 5 (reference, Ref) cement, laboratory-blended CEM III/C-SR (with slag) or CEM IV/B-SR (fly ash-bearing) cements. Mixes were also prepared with the latter two cements in which the slag or fly ash filler was partially replaced with barium carbonate. Barium or calcium carbonate sands were used as aggregate in the respective mortars, all of which were soaked in a Na2SO4 solution at 8 °C for 6 months and monitored for variations in mass, compressive strength, ultrasonic velocity, soundness (expansion) and mineralogy. The findings showed that at such low temperatures the amount of Ba2+ solubilised did not suffice to effectively immobilise the external sulfates in the blends containing SCMs. The fly ash-bearing samples, particularly where the addition was partially replaced with barium carbonate, deteriorated severely or very severely (substantial expansion and mass loss) because thaumasite precipitated even in the presence of the barite formed. The low cement content, slag-bearing blends exhibited greatest sulfate resistance, irrespective of the presence of barium carbonate as addition or aggregate. In mortars made with commercial, low C3A content (Ref.) sulfate-resistant cement, barium carbonate sand inhibited gypsum and ettringite formation, whereas both products precipitated in analogous and less porous mixes bearing limestone aggregate.

Highlights

Sulfate attack is one of the primary causes of cementitious material deterioration, for it induces expansion, strength loss and decohesion [1,2]
As all the mortars were batched to a wt/wt water/binder ratio of 1/2 and a binder/sand ratio of 1/3, the higher density of barium carbonate determined a lower volume of sand in the experimental than the limestone sand (Table 3)
System fluidity was significantly greater in the presence of barium carbonate sand, where spread values of 120 mm to 150 mm and higher porosity were observed (Table 4)

Summary

Introduction

Sulfate attack is one of the primary causes of cementitious material deterioration, for it induces expansion, strength loss and decohesion [1,2]. 12.45 and a suitable sulfate concentration, thaumasite (CaSiO3ÁCaCO3ÁCaSO4Á15H2O) may precipitate [3,4,5]. First described as a product of sulfate attack in concrete in 1965 [6] and slow-growing, by favouring C-S-H disintegration that salt may induce more severe damage than gypsum (CaSO4Á2H2O) and/or (secondary or delayed) ettringite (3CaO∙Al2O3∙3CaSO4Á∙32H2O) that precipitate in the more usual or characteristic form of sulfate attack.

Methods

Results

Conclusion