Sulphate reduction in waste concrete aggregate using Bacillus subtilis

Nurhanim Abdul Aziz, . and Putri Anis Syahira Mohamed Jamil, . and Mohd Zarir Yusoff, . and Norli Ismail, . (2024) Sulphate reduction in waste concrete aggregate using Bacillus subtilis. Journal of Sustainability Science and Management (Malaysia), 19 (4). pp. 10-27. ISSN 2672-7226

Waste concrete aggregate (WCA) can be re-utilised as a recycled material as it applies to numerous functions. High sulphate content in attached cement mortar was identified as a weakness of recycled material due to the developed expansion of delayed ettringite formation (DEF). The DEF results in micro-crack formation, which affects the compressive strength. The main objective of the present study was to treat WCA by Bacillus subtilis before being reused in recycled concrete mortar (RCM) production. The DEF of WCA was identified using X-ray diffractometric (XRD) techniques and soluble sulphate tests. The efficiency of B. subtilis in treating WCA was evaluated based on sulphate reduction on three variable factors, i.e., B. subtilis concentration, B. subtilis: WCA ratio, 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 RC was subsequently evaluated to determine its durability. Results revealed that WCA was rich in ettringite and contained 0.53% sulphate. The sulphate content in WCA was successfully reduced to 81.5% by B. subtilis when B. subtilis concentration was at 0.2 x 10⁸ CFU mLˉ¹, the B. subtilis: WCA ratio was 1:1 and the retention time was increased up to the 4ᵗʰ day. The construction of RCM using TWCA can potentially replace the natural concrete aggregate due to its higher compressive strength (26 MPa) compared to control (20 MPa). The study indicated that B. subtilis efficiently reduced sulphate in WCA to avoid micro-crack formation on the RC surface.

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Abstract

Waste concrete aggregate (WCA) can be re-utilised as a recycled material as it applies to numerous functions. High sulphate content in attached cement mortar was identified as a weakness of recycled material due to the developed expansion of delayed ettringite formation (DEF). The DEF results in micro-crack formation, which affects the compressive strength. The main objective of the present study was to treat WCA by Bacillus subtilis before being reused in recycled concrete mortar (RCM) production. The DEF of WCA was identified using X-ray diffractometric (XRD) techniques and soluble sulphate tests. The efficiency of B. subtilis in treating WCA was evaluated based on sulphate reduction on three variable factors, i.e., B. subtilis concentration, B. subtilis: WCA ratio, 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 RC was subsequently evaluated to determine its durability. Results revealed that WCA was rich in ettringite and contained 0.53% sulphate. The sulphate content in WCA was successfully reduced to 81.5% by B. subtilis when B. subtilis concentration was at 0.2 x 10⁸ CFU mLˉ¹, the B. subtilis: WCA ratio was 1:1 and the retention time was increased up to the 4ᵗʰ day. The construction of RCM using TWCA can potentially replace the natural concrete aggregate due to its higher compressive strength (26 MPa) compared to control (20 MPa). The study indicated that B. subtilis efficiently reduced sulphate in WCA to avoid micro-crack formation on the RC surface.

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Item Type:	Article
AGROVOC Term:	Bacillus subtilis
AGROVOC Term:	industrial wastes
AGROVOC Term:	concrete
AGROVOC Term:	microorganisms
AGROVOC Term:	waste utilization
Geographical Term:	Malaysia
Uncontrolled Keywords:	sulphate reduction, Compressive strength testing
Depositing User:	Mr. Khoirul Asrimi Md Nor
Date Deposited:	10 Mar 2025 02:31
Last Modified:	10 Mar 2025 02:31
URI:	http://webagris.upm.edu.my/id/eprint/2473

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