An experimental investigation exploring the effects of delayed casting on grade 30 concrete slump behavior and compressive strength subsequent to re-dosing with low-range superplasticizer

Chan, Man You (2024) An experimental investigation exploring the effects of delayed casting on grade 30 concrete slump behavior and compressive strength subsequent to re-dosing with low-range superplasticizer. Final Year Project, UTAR.

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Abstract

Chemical admixtures are vital in concrete construction for enhancing workability and strength. However, delayed casting can reduce slump below desired levels. While adding water to restore slump is common on-site, but it will compromises compressive strength. However, research on re-dosing with superplasticizer after delayed casting is limited. This research investigates the impact of delayed casting on Grade 30 concrete's slump behavior and compressive strength, focusing on the effects of re-dosing with a low-range superplasticizer, MasterGlenium Ace 8333, and the implications of water addition. The superplasticizer dosages used ranged from 0.1% to 0.7%, with 0.1% increments. The tests conducted were slump, Vebe time, compacting factor, fresh density, air content, hardened density, and compressive strength. Results show that delayed casting reduced the 7 and 28 days compressive strengths by approximately 26% and 24% compared to the control mix. When water was added after delayed casting, compressive strength further decreased by about 4% at both 7 and 28 days. Re-dosing with a superplasticizer, particularly at a dosage of 0.2%, successfully restored the original slump and improved the 7 and 28 days compressive strengths, achieving the required strength. However, as the superplasticizer dosage increased, slump values continued to rise, peaking at 220 mm for a 0.7% dosage, while the initial slump for delayed casting was only 48 mm, representing a significant improvement. This study highlights the importance of optimizing superplasticizer dosage to enhance concrete performance under delayed casting conditions, emphasizing careful management to maintain concrete quality in construction scenarios with frequent delays.

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