Chloride Ingress in Chemically Activated Calcined Clay-Based Cement

Abstract

Chloride-laden environments pose serious durability concerns in cement based materials. This paper presents the findings of chloride ingress in chemically activated calcined Clay-Ordinary Portland Cement blended mortars. Results are also presented for compressive strength development and porosity tests. Sampled clays were incinerated at a temperature of 800 ∘ C for 4 hours. The resultant calcined clay was blended with Ordinary Portland Cement (OPC) at replacement level of 35% by mass of OPC to make test cement labeled PCC35. Mortar prisms measuring 40 mm × 40 mm × 160 mm were cast using PCC35 with 0.5 M Na 2 SO 4 solution as a chemical activator instead of water. Compressive strength was determined at 28th day of curing. As a control, OPC, Portland Pozzolana Cement (PPC), and PCC35 were similarly investigated without use of activator. After the 28th day of curing, mortar specimens were subjected to accelerated chloride ingress, porosity, compressive strength tests, and chloride profiling. Subsequently, apparent diffusion coefficients ( app ) were estimated from solutions to Fick's second law of diffusion. Compressive strength increased after exposure to the chloride rich media in all cement categories. Chemically activated PCC35 exhibited higher compressive strength compared to nonactivated PCC35. However, chemically activated PCC35 had the least gain in compressive strength, lower porosity, and lower chloride ingress in terms of app , compared to OPC, PPC, and nonactivated PCC35.

Effect of Sulphate and Chloride Ingress on Selected Cements Mortar Prisms Immersed in Seawater and Leather Industry Effluent

“…is was observed in this study. Chlorides are known to be accelerators of compressive strength development in mortars or concrete [1]. On the other hand, WLI was found to have a higher sulphate concentration than SW. Mortar prisms subjected to it were expected to suffer more from sulphate attack [36][37][38]; this was observed in this study.…”

“…Long-term durability of concrete structures is the main concern for safety and economic reasons. Deterioration of concrete structures is generally caused by ingress of aggressive agents into the concrete [1]. A large number of concrete structures such as harbors, decks, piers, floating offshore platforms, power plants, and waste disposal facilities are generally subjected to environments which contain aggressive agents [2].…”

“…Sulphate attack is considered a major deteriorative problem occurring when the cement-based materials, such as concrete, mortars, and buildings, are exposed to sulphate ions environment [12]. e sources of aggressive ions to the mortar/concrete may include deicing salts, seawater, groundwater, bacterial action in sewers, wastewater from industries, use of sulphate or chloride contaminated mix water, and natural gypsum in the aggregate, among others [1,[13][14][15][16].…”

“…Ordinary Portland cement (OPC) is the main cement used in buildings and civil structures such as dams and bridges in Kenya [1]. It is mostly preferred to blended cements due to the fact that it exhibits shorter setting times and achieves high early strength (28 days) than blended cements [1,20]. However, it is more prone to attack by aggressive media, for example, chlorides and sulphates, among others.…”

“…is is attributed to the fact that the hydration of OPC results in production of about 20 percent by weight of Ca(OH) 2 , which makes it highly susceptible to the aggressive ions [1].…”