Aziz, Nurhanim Abdul
(2018)
Removal Of Sulphate In Waste Recycle Aggregate Using Bacillus Subtilis.
PhD thesis, Universiti Sains Malaysia.
Abstract
Waste concrete aggregate (WCA) is highly potential to be re-utilised as a recycled material as it is applicable to numerous functions. Attached cement paste on WCA surface has limited the potential WCA to be recycled as a part of raw construction materials. Low density, high in water absorption and sulphate content are identified as the major contributing factors for this limitation. The sulphate content in delayed ettringite formation (DEF) from high water absorption of attached cement paste leads to DEF expansion and forms a micro-crack, causing a mass loss and affects the mechanical strength (compressive strength) of the concrete. The main objective of the present study was to treat WCA by incorporating the use of Bacillus subtilis before it was reused in recycled cement mortar (RCM) production. The characteristics of WCA were previously identified prior to the B. subtilis adhesion test. The efficiency of B. subtilis to treat WCA was evaluated based on four variable factors i.e. B. subtilis concentration, B. subtilis: WCA ratio, zeta potential, and retention time. Treated WCA (TWCA) from the WCA treatment by B. subtilis was reused as a part of RCM production. The compressive strength of RCM was subsequently evaluated to determine its quality. Results revealed that WCA had a low density, high water absorption, carbonated by attached cement paste and rich in ettringite. WCA contained 0.53 ±0.06 % of soluble sulphate and 47.76 ±8.43 % of attached cement paste. Leaching behaviour of inorganic element demonstrated Ca and SO42- as major elements, ranging from 10.06 mg L-1 to 149.15 mg L-1 and 30.78 mg L-1 to 38.90 mg L-1, respectively.
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