An Experimental Investigation on Influence of Mixing and Compaction Temperature on Air Voids in Bituminous Mix

Abstract

The air void content and long-term performance of pavements are significantly impacted by the mixing and compaction temperature of bituminous mixtures, leading to potential failures such as premature aging, reduced durability, and issues like fatigue life, raveling, rutting, and vertical consolidation in Hot Mix Asphalt (HMA) pavements. To achieve optimal production and placement of HMA, it is crucial to carefully consider the mixing and compaction temperatures of the binder (bitumen) used. Notably, these temperatures vary based on the grade and origin of the bitumen, as different sources exhibit distinct properties affecting the mixing and compaction characteristics. Selecting an appropriate mixing and compaction temperature is vital to ensure effective aggregate coating and achieve the desired density. This experimental study aims to determine a reliable method for estimating the mixing and compaction temperatures for both modified and unmodified bitumen, thereby enhancing the overall performance and longevity of asphalt pavements.

Introduction

I. INTRODUCTION

The bituminous mix has been using for road construction since 1870’s and 70% of pavements are made of bitumen. The mixing and compaction temperature of bitumen is an important factor affecting the performance of the bituminous pavements. To estimate the appropriate temperature, approximations from field experiences are currently used. The mixing and compaction temperature is not identical for all grades of bitumen. Depending on the origin of bitumen, there will be change in properties and this influences the mixing and compaction temperature. The mixing and compaction temperature influences the air voids and causes failures by accelerating the aging and decreasing the durability, affects fatigue life, raveling, rutting and vertical consolidation. The correct mixing and compaction temperature is correlated to the viscosity of the material. If the viscosity of bitumen is high, there will be difficulty in mixing while a low viscosity results in drain down from the mix. Hence an appropriate viscosity has to be determined to be correlated to the mixing and compaction temperature. The mixing and compaction temperature for modified binder is higher when compared with the unmodified binders. Currently, the use of modified binder is about 20% of the total pavement construction. Some recommendations have been made regarding the mixing and compaction temperature. It has been said that the temperature should not exceeds 182°C while mixing and the temperature should be 149°C when discharged from hauling in the case of modified binders.

II. METHODOLOGY

From the common source, required grades of bitumen are chosen. Steady shear and shear rate sweep tests are performed at 120°C, 135°C and 160°C. Corresponding viscosity for each method is determined using various tests such as Equiviscous, Low shear viscosity & High shear viscosity. From the result of various methods, a mould is made and volumetric properties are determined.

III. EXPERIMENTAL INVESTIGATION

A. Introduction

For determining mixing and compaction temperature the experiments required are

1. Rotational viscometer

a. Introduction: From the name we can determine that viscometer is an equipment use to determine the viscosity of the material.  Viscometer measures both Newtonian and non-Newtonian fluids.

b. Principle: From the name we can determine that viscometer is an equipment use to determine the viscosity of the material.  Viscometer measures both Newtonian and non-Newtonian fluids.

c. Methods: Steady shear: constant shear rate is used; Shear rate sweep: shear rate is varied over a range

d. Procedure: Viscometer, thermostat and the computer are connected with each other. The bitumen is placed in the cylindrical container and fixed at the bottom plate of viscometer. The spindle is made to suspend on the hook. The temperature and torque values are fixed and let the bitumen to melt and to reach the desired temperature. The spindle is partially immersed in the cylindrical container to maintain the equilibrium for 5 minutes. Start the viscometer, the spindle will tend to rotate and data are taken. Viscometer works by getting the measurements of the torque on a vertical stand that rotates the spindle in an anti-clockwise direction. The rotation of the spindle is usually proportional to how viscous the sample is.

2. Marshall Apparatus

a. Introduction: The test is intended for the measurement of the resistance to plastic flow of cylindrical specimen of bituminous paving mixture loaded on the lateral surface. The procedure consists of determining the Marshall stability and flow value analysis, property of the mix and maximum binder content. With the help of phase diagram calculations are made.

b. Procedure: The Marshall mould of 102 mm diameter and 64 mm height with a base plate and a collar is taken. In concern with mix design grading and mixing have been made and the mix is placed in the mould in three layers and compacted in the rammer of weight 4.5 kg is made to drop from the height of 175 cm. The compaction is made on the other side of the mould by keeping the mould in an inverse manner. Sample is extracted with the help of sample extractor. The mould is placed between the curved path and breaking head. The load is applied on the mould and the value will be displayed in the dial gauge, then the stability and the flow value is measured.

VI. ACKNOWLEDGMENT

First and foremost, I would like to thank the Almighty God for giving me the power to believe in myself and achieve my goals.

I sincerely remit my due respect to my project guide Mrs.Suganya, M.E. Assistant Professor in Civil Engineering for her

encouragement and guidance throughout the project.

I extend my sincere thanks to all faculty members, non-teaching staff and my friends for their help and support in completing this project work.

Conclusion

From the guidance of NCHRP the mixing and compaction temperature of VG20 grade is obtained using equiviscous and zero shear viscosity. The mould is made at mixing and compaction temperatures then the volumetric properties are determined. The volume of air voids is 4% the pavement gets rectify from the stress caused by the vehicle with sufficient bitumen content of 4.7%. The stability is 15 kN much higher than the expectation, where as specified value is 8kN. So it with stand larger amount of weight with very low deformation of 8 mm. The value of VMA is good and value of VFA is excellent, so the pavement made at mixing and compaction temperature will last for decades and obtained volumetric properties lie within the specification, so it should be the best mixing and compaction temperature. This is the field laying mixing and compaction temperature, depends on the distance the temperature may vary.

References

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Copyright

Copyright © 2023 Reshma Ravikumar, Mrs. Suganya R, Mrs. Archana M. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.