Development of Mix Proportions for Different Grades of Met Kaolin Based Self-Compacting Concrete

Abstract

Concrete is the most widely used construction material because of its mould ability into any required structural form and shape due to its fluid behavior at early ages. Thorough compaction, using vibration, is normally essential for achieving workability, the required strength and durability of concrete. Inadequate compaction of concrete results in large number of voids, affecting strength and long term durability of structures. Self-Compacting Concrete (SCC) provides a solution to these problems. As the name signifies, it is able to compact itself without any additional vibration. However, wide spread applications of SCC have been restricted due to lack of standard mix design procedure and testing methods. It is gaining wide acceptability because no vibration is needed and noise pollution is eliminated. The construction process is safer and more productive.

This study presents the performance of M40 grade SCC by using Ordinary Portland cement, fine aggregate from Krishna river sand sieved through 600µm, 10-12.5 mm crushed gravel, mineral admixtures like Metakaolin (MK), Fly ash (FA), Ground granulated blast furnace slag (GGBS)and chemical admixture named Master Glenium Sky 8234 used as a superplasticiser. MK is produced by heating kaolin, one of the most abundant natural clay minerals, to temperatures of 650-900°C. The performance of MK in SCC is not well documented, particularly over a wide range of grades. In particular, the effects of MK as a high surface area mineral addition on the workability as well as mechanical properties of SCC need to be fully recognized. So, the present study is an effort to characterize the fresh and hardened properties of SCC containing MK. The another supplementary cementitious material used in this study was Fly ash (FA) which can be obtained as finely divided residue that results from the combustion of ground or powdered coal and is transported by flue gases from the combustion zone to the particle removal system. Slag is a non-metallic product consisting essentially of glass containing silicates and aluminates of lime and other bases, as in the case of blast furnace slag, which is developed simultaneously with iron in blast furnace or electric pig iron furnace. Granulated slag is obtained by further processing the molten slag by rapidly chilling or quenching it with water or steam and air. Master Glenium Sky 8234 is an admixture of a new generation based on modified poly carboxylic ether. It is free from chloride and is compatible with all types of cements.

This experimental study demonstrates that MK, FA, GGBS can be successfully used as an admixture in the preparation of SCC. In order to prepare suitable mix proportion for M 40 grade for MK, FA, GGBS based SCC, investigations were undertaken replacing cement with 0%, 10%, 15%, 20%, 25% and 30% of MK, FA, GGBS and with adjusted dosage of super plasticizer (Master Glenium Sky 8234). As per the European guidelines for Self-compacting concrete, slump flow test, V-funnel test and L-box test have been carried out on fresh properties of MK, FA, GGBS based SCC. The compressive strength, split tensile strength and flexural strength of the specimens have been analyzed for 7-days and 28 days curing. And finally optimized mix proportions have been recommended for M40 grade of MK, FA, and GGBS based SCC. The fresh concrete test results revealed that by substituting different percentages of MK, FA, and GGBS in SCC satisfactory workability properties can be achieved, even though no viscosity modifying agent was needed.

The test results for acceptance characteristics of self-compacting concrete such as slump flow test; V-funnel test and L-Box test were satisfactory as per EFNARC for developed mix proportions of M40 grade SCC mix. Further, compressive strength, tensile strength and flexural strength at the age of 7 and 28 days were also determined and 10% to 15% replacement of MK, 20 to 25 % replacement of FA, and 30 to 35 % of GGBS can be regarded as a suitable replacements and optimized mix proportions have been recommended for M40 grade of MK, FA, GGBS based SCC from this experimental study.