Publication: Development and evaluation of room temperature cured silicomanganese fume-based alkali activated binder
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Date
2021-12-01
Authors
Najamuddin, Syed Khaja
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Abstract
Silicomanganese (SiMn) fume is an industrial waste whose potency in the synthesis of alkaline activated mortar/concrete is yet to be explored. The major constituents of SiMn fume are oxides of silica, manganese and potassium (SiO2, MnO2 and K2O). Percentage of calcium oxide (CaO) is very low. Precursors with low CaO needs elevated curing to develop the strength. Concentration of this study was to develop room temperature cured binder despite low CaO to make it adaptive for in-situ construction by proper synthesis of available ionic elements in SiMn fume. SiMn fume based mortar cured at room temperature (23+2° C) was synthesized with sodium hydroxide (NaOH) of varying molarities (4, 8 and 12) and sodium silicate (Na2SiO3) as alkaline activators with different ratios of Na2SiO3/NaOH (2, 2.5 and 3). The effect of SiMn fume content (370, 470 and 570 kg/m3 ) and alkaline solution content (33, 43 and 53%) was also investigated. Initially, the alkali activated SiMn fume (AASiMnF) mortars were evaluated by means of flow, compressive strength and flexural strength. Based on the evaluation, the optimum mixes were selected and silica fume (SF) was incorporated at different dosages (1, 3, 5 and 7%) to further improve the properties of the binder. Further, the mortars with optimum SF content were again selected to study the mechanical and durability properties of AASiMnF concrete. The engineering mechanical and durability properties such as setting time, compressive/flexural/split tensile strength, water absorption, volume of permeable voids, apparent density, and resistance to acid and sulfate attack were ascertained. Microstructural features and mineral compositions were studied by X-Ray diffraction, scanning electron microscope, Energy dispersive X-Ray spectroscopy xxi and Fourier-transform infrared spectroscopy analyses. The findings show that the combination of Na2SiO3 and NaOH have shown better results compared to NaOH alone as activator. With optimum Na2SiO3/NaOH ratio of 2.5 and 12M NaOH, the maximum 28-day compressive strength of room temperature cured mortar was 36 MPa. The AASiMnF binder showed longer setting time than the OPC. The optimum content of precursor and activator (at NaOH concentration of 8 and 12M) were 470 kg/m3 and 43% respectively. The incorporation of SF has improved the properties of binder and the optimum amount of SF was 5%. The maximum compressive strength of mix 12SF5 AASiMnF concrete was 57.6 MPa. The fine particle size and larger surface area of SF has reduced volume of permeable voids and water absorption. There was an increase in the apparent density of the AASiMnF concrete. AASiMnF concrete had better strength retention during acid and sulphate attack compared to OPC mix. Except the mix 12SF5 in acid exposure there was no deterioration and change in the cross-section of the AASiMnF concrete cubes. Its ability to develop good strength at room temperature (23±2° C) curing makes it adaptive to real life applications and helps to reduce carbon dioxide (CO2) foot print.