An experimental study investigating the impact of delayed casting on the slump behavior and compressive strength of grade 30 concrete after re-dosing with high-range superplasticizer

Soo, Hui Wen (2024) An experimental study investigating the impact of delayed casting on the slump behavior and compressive strength of grade 30 concrete after re-dosing with high-range superplasticizer. Final Year Project, UTAR.

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Abstract

Concrete is ideally placed immediately after mixing, but delays are common in the ready-mixed concrete industry due to factors like long transportation distances, traffic congestion, and placement delays. These delays often cause the concrete to stiffen by the time it arrives at the site, leading to a significant reduction in workability, which can make placement difficult and negatively impact the concrete's strength. To address this, superplasticizers can be used to restore the concrete's plasticity, or, as a common approach, extra water is sometimes added to the mixture before discharge. This study aims to examine the effects of casting delays (slump reduction from 100mm to 50mm) on the slump behaviour and compressive strength of grade 30 concrete. It also explores the effects of retempering with water and the impact of re-dosing with varying dosages of the high-range superplasticizer, MasterGlenium ACE 8538, in dosages from 0.05% to 0.30% at 0.05% intervals. Workability tests revealed that a 0.1% dosage of high-range superplasticizer was sufficient to restore the workability of the control mix, while a 0.15% dosage achieved the highest workability before segregation occurred. It was also found that although retempering with water can improve workability, it may significantly reduce compressive strength. In contrast, re-dosing with an appropriate amount of superplasticizer improves both workability and compressive strength, making it the more favorable retempering method. This study also identified the optimal dosage as 0.1% for regaining slump and 0.15% for achieving the best balance of workability and strength.

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