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Enormous success has been achieved in recent decades in the advancement of chemical admixtures for concrete. Most efforts have concentrated on improving the properties of concrete and studying the factors that influence on these properties. Since the compressive strength is considered a valuable property and is invariably a vital element of the structural design, especially high early strength development which can provide more benefits in concrete production, such as reducing construction time and labor and saving the formwork and energy. However the incompatibility issue between cement and chemical admixtures is also observed. Specifications calling for the use of admixtures in concrete often results in strange occurrences, i.e. rapid set, retardation, accelerated stiffening etc.
Therefore, a research has been conducted to study the effect of superplasticizer (SP) and retarder on the properties of fresh and hardened concrete. This paper presents the findings of the research that made an effort to explore several basic characteristics of superplasticized and retarded concrete chiefly related to workability, setting time and compressive strength. The prime focus of the study was on the combined effect of superplasticizer and retarder in concrete made with three different types of cement- Ordinary Portland Cement (BDS EN 197-1: 2003, CEM Ι 52.5N), Portland Composite Cement (BDS EN 197-1:2003, CEM ІІ/B-M (V-S-L), 42.5N) and Portland Limestone Cement (BDS EN 197-1:2003, CEM ІI/B-L, 42.5N) were used. Polycarboxylate ether (PCE) based superplasticizer and ASTM C 494 Types B, D and G retarder were used. Consequently, within the scope of the work, SP and retarder dosage was varied in the mixes but the Nominal mix design was kept unchanged. Encouraging results were observed for workability, setting time and compressive strength with significant increase in capacity. The test results revealed that the single and combined effects of superplasticizer (SP) and retarder on properties of a given concrete mix are not only dependent upon their dosage but also the types of cement used. In case of combination of SP & Retarder combined dosage, PCC and PLC show better result than that of OPC and PCC shows the highest IST & FST with maximum dose which is 27.76% higher than the Nominal mix. With increase of time & dosage, compressive strength gain is always less than the nominal mix for OPC, almost similar to the nominal mix for PCC and more similar to the nominal mix for PLC. |
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