Effect of magnesium and sulphate ions on the sulphate resistance of blended cements in low and medium-strength concretes

Abstract

Structural concrete components undergo degradation when e.\posed to sulphate-bearing environments. Diffusion of sulphate ions through concrete pores causes the formation of expansive products such as gypsum and ettringite in the internal microstructure of concrete. This chemical change leads to a significant reduction of strength in structural components. In the literature it has been reported that in blended cements, because of the reduction of calcium hydroxide, magnesium sulphate ions directly react with the cementitious calcium-silicate-hydrate (C-S-H) gel and convert this into non-cementititous magnesium-silicate-hydrate (M-S-H) gel. However, in the present investigation it was observed that, in low-strength concrete (20 MPa), blended cements show more resistance than ordinarv Portland cement (OPC) because of the pozzolanic and dilution effect of added fly ash and slag. In this concrete, the expansive product. namely gypsum, densifies the porous pore structure and does not cause any cracking. In the case of medium-strength concretes (30 and 40 MPa), the po::.::.olanic and dilution effects of blended cements are not very significant and hence they did not show any increase in sulphate resistance compared with OPC cement. In these medium-strength concretes b.ecause of their pore structure, the expansive products cause micro-cracks. The inferior performance of concretes with blended cements due to magnesium ion attack is mainly attributed to the formation of ettringite and gypsum. as in the case of sodium sulphate, and these cause more micro-cracks in comparison with OPC cement. Thermal analysis also confirms this. structural components as well as decreasing the extended to the calcium-silicate-hydrate (C-S

Performa Beton Dengan Ground Granulated Blast Furnace Slag Terhadap Sulfate Attack

“…Struktur beton yang kontak langsung dengan air tanah (groundwater) rentan terhadap serangan sulfat karena air tanah merupakan sumber sulfat alami. Sulfat juga umumnya terkandung dalam tanah dan air laut (Vedalakshmi et al, 2005;Whittaker and Black, 2015). Degradasi beton akibat external sulfate attack terdiri dari physical sulfate attack, yaitu pengendapan garam sulfat dalam pori beton, dan chemical sulfate attack, yaitu masuknya ion sulfat ke matriks semen (Whittaker and Black, 2015;Panesar, 2019).…”