Chapter 6 deals with the durability performance of mortar containing ceramic tile waste exposed to sulphate attack. The introduction discusses the latest development regarding this subject as no case study has been found where ceramic tile waste was actually used in the field. This study investigates the sulphate resistance of ceramic mortar by using sulphate solution and tested the visual appearance of specimens, mass loss, residual compressive strength, and microstructure analysis up to 18 months of sulphate exposure. The ceramic mortar demonstrated superior advantages with respect to visual appearance and mass change with low values of strength loss upon exposure to sulphate solutions. Therefore, ceramic waste in the form of fine aggregates and fine powder can be used in mortar production with comparable strength and improvement in the fresh and hardened state properties of the mortar as compared with the OPC mortar.
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Limited research was carried out on the blended cement mortars incorporating ceramic powder exposed to sulphate attack. Generally aggressive chemicals such as sodium sulphate (Na2SO4), magnesium sulphate (MgSO4) and calcium sulphate (CaSO4) which are available in some soils or groundwater will attack cement paste in concrete or mortar. These chemicals will degrade and/or deteriorate the cement paste. In soil, these aggressive agents are in the form of salts where, when dissolved in water will react with Ca(OH)2 present in ordinary Portland cement paste. According to periodic table of elements, sodium ions (Na+1) are more reactive than calcium ions (Ca+2) and can be more harmful to cement paste. The reaction between these aggressive agents and cement paste cause an expansion and swelling which will consequently crack the concrete or mortar. One of the main issues related to concrete or mortar is the attack by sulphate ions (SO4-2) which would decrease the compressive strength over a long period of time. The decrease in compressive strength of concrete in infrastructures can be a critical issue related to serviceability of structure. Series of researches have been conducted to fully understand the mechanism of sulphate ions (SO4-2) reactions (Bhutta et al., 2013). According to the findings reported by Mehta and Monteiro (1998), the reaction of sulphate ions (SO4-2) with cement paste of concrete occurred in two phases. In the primary phase, the sulphate ions (SO4-2) react with calcium hydroxide (Ca(OH)2) and produce gypsum (CaSO4.2HO2) which fills the pores in concrete or mortar. In the secondary phase, the concentration of sulphate ions (SO4-2) increases and results in the transformation of mono-sulpho-aluminate into long needle-shaped crystals of ettringite (3CaO. Al2O3. 3CaSO4·32H2O). The ettringite causes expansion in concrete or mortar which consequently reduces the compressive strength. In fact, not only sulphate ions (SO4-2) in the solution reacts with calcium hydroxide (Ca(OH)2), other ions like magnesium ions (Mg+2) also react with cement components and cause additional deterioration to concrete structures.
Usually, to improve the resistance of structures exposed to sulphate attack, pozzolanic materials are added in concrete or mortar mixtures. Extensive literature studies are available on the beneficial use of pozzolanic materials such as fly ash, palm oil fuel ash, rice husk ash, metakaolin, and silica fume to improve the resistance of concrete or mortar against sulphate attack (O’Farrell et al., 2006; Ramadhansyah et al., 2012b; Budiea et al., 2010; Jaturapitakkul et al., 2007). Such pozzolanic materials decrease the permeability of concrete and mortars by two mechanisms; firstly by reducing water requirements for mixture (using fly ash). Secondly, all pozzolanic materials contain high amount of amorphous silicate (SiO2) which react with calcium hydroxide and produce calcium silicate hydrate. The calcium silicate hydrate gives denser structure to concrete which provide high resistance against sulphate attack.