Experimental study on grade 30 concrete slump behaviour and compressive strength after re-dosing with medium-range superplasticizer subjected to delayed casting

Teong, Kai Jian (2024) Experimental study on grade 30 concrete slump behaviour and compressive strength after re-dosing with medium-range superplasticizer subjected to delayed casting. Final Year Project, UTAR.

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Abstract

With concrete usage being common in the construction industry, there are more issues encountered on-site such as slump loss due to delayed casting. This research investigates the impact of medium-range superplasticizer dosage on the workability and strength properties of concrete. The study aims to identify the optimal dosage of medium-range superplasticizer that enhances concrete performance without compromising its strength quality. A series of tests, including slump, Vebe time, compacting factor, density, and compressive strength measurements, were conducted on Grade 30 concrete mixes with varying dosages of medium-range superplasticizer. The trial mix stage of this study was performed by testing the performance of various mixes to produce a control mix proportion that satisfies the workability and strength requirements of Grade 30 concrete. Desired slump value and the cube compressive strength at 28-day were set at 100 mm and 30 MPa respectively. In the actual mix stage, the results indicate that an increase in medium-range superplasticizer dosage generally improves workability. However, beyond a certain threshold (0.40% medium-range superplasticizer), excessive fluidity leads to segregation, negatively affecting the concrete's overall quality. The study identifies 0.20% as the optimal dosage, offering a balanced combination of workability, strength, and stability. This dosage provides a 28-day compressive strength of 31.76 MPa (35.03% higher than mix C2) and slump of 160 mm, making it ideal for practical applications in the construction industry. The findings contribute to a better understanding of how medium-range superplasticizers improve concrete performance, particularly in scenarios where re-dosing is necessary due to on-site delays.

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