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Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Chemical and Biochemical Engineering

Collaborative Specialization

Environment and Sustainability

Supervisor

Xu, Chunbao C.

Abstract

Concrete water reducers are chemical ingredients added to concrete before or during mixing to reduce the required quantity of water, which produces increased workability and flowability in freshly mixed concrete and improved mechanical strength, and durability in hardened concrete. Recently, there has been a growing interest in bio-based concrete water reducers because they are renewable, abundant, and simple to source and produce. Also, the increased awareness of the deleterious environment and health impacts of producing and using petroleum-based concrete water reducers has further increased the demand for bio-based water reducers. In the present study, a new bio-based concrete water reducer is produced from the dual consecutive esterification (with maleic anhydride, MA) and sulphonation (with sodium sulphite, SS) of crude cellulose (CC) obtained from fractionated pinewood sawdust. The effects of various reaction conditions on the Degree of Substitution (DS), product yield and Sulfonation Degree (SD) were investigated to optimize the process conditions. The optimal reaction conditions of the esterification process have been determined as: 140oC, 5h, 3:1 MA/CC molar ratio, 4% ZnCl2 catalyst loading, using N, N Dimethylformamide (DMF) as solvent in a solvent/substrate ratio of 60:40 (w/w), where the obtained crude cellulose maleate (CC-MA) product has a DS of 1.3 and 90% yield. The CC-MA was further functionalized by a sulphonation reaction with sodium sulphite (SS) performed at room temperature overnight, or at 60-70 oC for 2h, with an SS/CC-MA molar ratio of (0.95´DS):1 using water as solvent at a solvent/substrate ratio of 70:30 (w/w) to produce crude cellulose-based water reducers. The crude cellulose-based water reducer derived from the CC-MA 1.3DS (denoted as 1.3WR) demonstrated better and comparable plasticizing and mechanical properties relative to the commercial lignin-based product. At a dose of 0.6 wt.% of cement weight, the 1.3WR sample showed better performance in cement fluidity and concrete slump than the commercial lignin-based water reducer and comparable performance in setting time and compressive strength measurements.

Summary for Lay Audience

Concrete water reducers are chemical substances that are added to concrete before or during mixing to reduce the amount of water needed in its preparation. The addition of this ingredient increases the ease at which the freshly mixed concrete can be poured, flowed, and transferred without adding more water which therefore produces stronger and durable hardened concrete. The interest and demand for bio-based concrete water reducers has grown considerably in our present time because they can be sourced from abundant and renewable raw materials. They can also be produced via simple and environmentally benign processes compared to their synthetic counterparts (petroleum-based products) that pose potential health and environmental challenges. In the present study, bio-based concrete water reducers have been produced from crude cellulose fractionated from wood sawdust via chemical modifications. The effects of various reaction conditions on the products’ properties and yields were investigated to optimize the process conditions. The effects of the new bio-based water reducer on cement fluidity, concrete slump, setting time and compressive strength were studied and compared to those of a commercial water reducer. The result showed that the cellulose-based water reducer obtained at the determined optimal conditions attained comparable or better concrete plasticizing and mechanical properties than the commercial water reducer when tested for cement fluidity, concrete slump, setting time and compressive strength.

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