International Research Journal of Engineering and Technology (IRJET) Volume: 12 Issue: 09 | Sep 2025
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e-ISSN: 2395-0056 p-ISSN: 2395-0072
Investigation into the Role of Different Accelerators in Enhancing Concrete Strength Parameters Akshay Gupta1, Dr. Ravindra Gautam2, Suraj Mishra3 1M. Tech Scholar, Dept. of Civil Engineering, Technocrats Institute of Technology – Excellence 2Professor, Dept. of Civil Engineering, Technocrats Institute of Technology – Excellence 3Assistant Professor, Dept. of Civil Engineering, Technocrats Institute of Technology – Excellence
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Abstract - Concrete, being the most widely used construction material, often requires modification of its fresh and hardened
properties to meet specific construction demands, particularly where rapid setting and early strength development are essential. Among various chemical admixtures, accelerators play a significant role in enhancing the rate of hydration, thereby improving the early-age strength of concrete. The present experimental study was undertaken to investigate the effect of different accelerators on the strength parameters of concrete, with special reference to M20 and M30 grade mixes. In this work, three commonly used accelerating admixtures, namely Calcium Nitrite, Sodium Nitrite, and Potassium Carbonate, were incorporated in concrete mixes, and their influence on compressive strength and flexural strength was examined at different curing ages of 1, 3, 7, 14, and 28 days. The primary objective was to identify the most effective accelerator for enhancing strength characteristics and to compare the performance of accelerators in normal-strength (M20) and medium-strength (M30) concretes. The experimental findings revealed that Calcium Nitrite emerged as the most effective accelerator, yielding maximum percentage gains in both compressive and flexural strength parameters across all curing ages for both grades of concrete. In terms of compressive strength, M20 grade concrete showed a remarkable 30% increase at three days of curing, while M30 grade concrete recorded a maximum gain of more than 20% at seven days when Calcium Nitrite was used. However, at 28 days, the variation in compressive strength between accelerated and non-accelerated mixes was marginal for all three admixtures, indicating that the primary benefit of accelerators lies in early-age strength enhancement. Flexural strength analysis further supported these trends. The highest improvement was observed with Calcium Nitrite, showing a 14% gain at one day in M20 and a similar gain at three days in M30 grade concrete. In contrast, Potassium Carbonate exhibited negligible improvement in flexural strength, while Sodium Nitrite showed moderate effectiveness, particularly in the early curing stages. The comparative performance demonstrated that accelerators had a more pronounced effect on M20 mixes than on M30, especially during the initial curing period. From the overall investigation, it can be concluded that Calcium Nitrite is the most reliable and efficient accelerator for achieving rapid early-age strength in concrete, making it highly suitable for applications where early formwork removal, accelerated construction schedules, or cold-weather concreting is required. The study also highlights that while accelerators significantly influence the initial strength development, their impact at later ages is relatively minor. These findings can serve as a useful reference for the construction industry in selecting appropriate admixtures for practical applications involving accelerated strength gain. Key Words: Concrete, Accelerators, Calcium Nitrite, Sodium Nitrite, Potassium Carbonate, Compressive Strength, Flexural Strength, Early-age Strength Development
1. INTRODUCTION Cement properties can be modified either by varying the proportions of its fundamental constituents or by partially substituting cementitious or aggregate phases. In recent years, increasing attention has been given to achieving high early strength and reducing construction time, particularly in infrastructure projects. Rapid-setting concrete mixtures are especially beneficial for highway rigid pavement slab replacements, as they enable early opening to traffic. However, such practices also pose challenges, primarily due to the elevated heat of hydration, which can increase the likelihood of cracking. Since a minimum strength must be attained before the pavement can be opened to vehicles, the use of accelerating admixtures has become common to meet strength requirements within limited timeframes. It is noteworthy that while there are prescribed minimum strength thresholds for such applications, no maximum strength limitations exist for pavement slab replacement works. Accelerators achieve faster strength gain by enhancing the hydration process, but their use often results in higher concrete temperatures and greater thermal gradients. Such conditions arise because these mixes typically employ high cement content, heated mixing water, and sun-warmed aggregates, producing what are often termed as “hot mixes.” These mixes exhibit shorter workability periods and an increased risk of early-age cracking, as the fresh concrete temperature can approach 100°F (≈38°C) even before the accelerator is introduced. The central objective of the present study is to examine the effects of different accelerators—Potassium Carbonate, Sodium Nitrite, and Calcium Nitrite—on the
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