Testing of Strength of Recycled Aggregate Concrete using MicroSilica and its Applicability

I. INTRODUCTION

Concrete rubbles generated from construction and demolition waste comprises of sand,gravel,concrete,stone,bricks,wood,metals,glass,plastic,paper etc; Recycling and reusing the waste (Recycled Aggregates) may save landfill space and also may reduce the natural resources (Virgin Aggregates) for the production of fresh concrete. Recently lot of research work is carried out on recycling and reuse of recycled aggregates as a part of waste management. Waste arising out of construction and demolition structures are increasing day by day and approximately 50% of this waste comprises of concrete rubbles which may be the good source of recycled aggregates. So, there is an urgent need to establish a technology to reuse recycled aggregates as a substitute to virgin aggregates in production of fresh concrete. Recycled aggregates were collected from different sources and the mixes were varied by replacement of virgin aggregates with recycled aggregates upto 100% by weight with or without admixture , MicroSilica . Results projects that the replacement of virgin aggregate by coarse recycled aggregate with MicroSilica upto 50% has better compressive strength as compared to the normal concrete but higher levels of replacement reduces the compressive strength.

Testing programme was carried out replacing virgin aggregates by recycled ones with replacement percentages of 25%,50%,75% and 100% alongwith admixture MicroSilica. Concrete cubes were casted in moulds with machined faces of 15cmx15cmx15cm.Cubes were tested after 7 and 28 days. Various concrete mixes (Cement: Sand: Aggregates) in proportion 1:2.36:3.2 were taken with water cement ratio 0.55 . NCRA0 - Normal concrete with 0% replacement by recycled aggregates.NCRA10-Normal concrete with 10% replacement by recycled aggregates.NCRA0MS10-Normal concrete with 0% replacement by recycled aggregate and 10% addition of Microsilica .CF-Compaction Factor. It is observed that the strength achieved with the addition of Microsilica (10%) by weight of cement is less than the strength of normal grade concrete ( NCRA0) and further study is carried out with same design mix with replacement of MicroSilica to 15%. Replacement ratio of recycled aggregates with virgin aggregates is maintained same and cube strength is tested after 7 and 28 days of curing at room temperature.

Average compressive strength after 7 days of curing with 50% replacement of virgin aggregate by recycled ones is quiet greater than the normal grade of concrete NCRA0.

From Table 3 it is obvious that compressive strength decreases with the addition of recycled aggregates. Decrease in strength is due to the adhered mortar to recycled aggregates. Adhered mortar makes bonding with the new mortar which leads to poor recycled aggregate concrete performance which eventually leads to decrease in compressive strength. Increase in compressive strength of recycled aggregate concrete is obvious in percentage replacement ratio of 25% and 50% along with the admixture MicroSilica as compared to fresh concrete after 28days of curing. Gain in strength is due to the unhydrated mortar adhered to recycled aggregates and MicroSilica added as admixture.

Based on test results, recycled aggregate concrete with admixture MicroSilica is giving better compressive strength as compared to fresh concrete with replacement percentages of 25% and 50%.Recycled aggregate concrete mixes is giving bigger compressive strength as compared to fresh concrete at replacement percentages of 25% and 50% due to gel formation because of admixture MicroSilica. Workability decreases with percentage increase of recycled aggregates because of water absorption by the adhered mortar. Recycled aggregates can be termed as raw material which can be economic assets in future for the construction industry. Results are awesome and

Author is thankful to Hon. Chairman Dr. Rajeev Kumar, Hon. Chancellor Dr. Sandeep Arora, Registrar Dr. Sandeep Gandhi and Dean Research Dr. A. Rajshekhar for providing support and facilitating to conduct this study.

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Research Scholar, Kalinga University, Naya Raipur, Chhattisgarh, India profdhapekar@gmail.com