EVALUATION OF BOND PERFORMANCE OF AN ULTRA-RAPID SETTING EMULSION FOR TACK COAT APPLICATIONS  

ABSTRACT

The purpose of this study was to evaluate the bond performance of a new ultra-rapid setting emulsion (URS) relative to that of a cationic rapid setting emulsion (CRS-1h), through a host of laboratory tests. URS is a proprietary, ultra rapid-setting emulsion used as a bituminous tack coat for pavement applications. The product exhibits a very fast set time feature which distinguishes it from regular rapid setting emulsions. This is achieved by the introduction of certain additives, which speed up the water evaporation. The rapid set time is beneficial for fasttrack paving projects and hence could prove to be highly cost effective. However, the adoption of such a new product as an approved replacement to typical tack coats used by PennDOT is contingent on it exhibiting bond characteristics similar to those exhibited by other rapid setting emulsions. The results indicated that the URS delivered shear strength comparable with that from the CRS-1h. Considering the fact, that the tested CRS-1h has been commonly used in construction’s tack coat applications, it appears that the URS could be reliably used in such applications with the gained benefit of faster setting.

 

 

 

 

 

 

 

 

 

 

Table of Contents

List of Figures………………………………………………………………………………………………………… v

List of Tables………………………………………………………………………………………………………… vii

Acknowledgements……………………………………………………………………………………………….. viii

Introduction……………………………………………………………………………………………………………. 1

Study Objective………………………………………………………………………………………………………. 3

Literature Review……………………………………………………………………………………………………. 4

Tack Coats: Composition and Construction…………………………………………………………….. 4

Evaluation of Tack Coat Adhesion………………………………………………………………………… 7

Adhesion Testing Methods and Equipment……………………………………………………………… 8

URS…………………………………………………………………………………………………………….. 17

Methodology………………………………………………………………………………………………………… 18

Modified Marshall Test…………………………………………………………………………………….. 18

SST (Simple Shear Test)…………………………………………………………………………………… 21

Sample Preparation………………………………………………………………………………………….. 25

Tack Coat………………………………………………………………………………………………………. 26

Testing Plan…………………………………………………………………………………………………… 30

Results and Analysis………………………………………………………………………………………………. 32

Modified Marshall Test…………………………………………………………………………………….. 32

SST……………………………………………………………………………………………………………… 34

Statistical Analysis………………………………………………………………………………………….. 36

Interpretation of Results……………………………………………………………………………………. 37

Comparison with Field Stress Levels……………………………………………………………………. 38

Conclusions………………………………………………………………………………………………………….. 42

References……………………………………………………………………………………………………………. 44

Appendix A – Core Data………………………………………………………………………………………….. 48

Appendix B – Testing Results…………………………………………………………………………………… 49

Appendix C – Fixture Drawings ………………………………………………………………50

Chapter 1

Introduction

 

An asphalt tack coat is a film of bituminous emulsion that is used to enhance adhesive bonding between an existing layer and a new layer. Adhesion between pavement layers is a key factor affecting the proper stress distribution among the pavement layers. The use of tack coat ensures that the layers act as a monolithic system, preventing slippage on the interface between layers. Improper bonding between layers can cause a deficient transfer of radial tensile and shear stresses into the entire pavement structure. It can also cause a stress concentration at the bottom of the wearing course (Louay et al., 2002). The lack of tack coat can lead to de-bonding of the overlay, slippage between layers, and premature fatigue cracking (WSDOT, 2002). The only exception for the use of tack coat is when an overlay is placed after 1 or 2 days on a new asphalt layer that has not yet been opened for traffic. Mrawira and Damude (1999) compared the shear strength of an interface between overlays placed over fresh pavements (1 to 2 days old) with and without tack coat by applying a shear load of 1 mm/min (0.04 in/min). The authors have found that the tack coat doesn’t improve shear strength.

Normally, hot liquid asphalt, emulsified asphalt, or cutback asphalt are used for tack coat. The application process consists of spraying the material on the surface of an existing pavement prior to an overlay. Tack coats are also used where the asphalt mixture comes in contact with the vertical face of curbs, gutters, cold pavement joints, and structures. The object of study in this work is a proprietary ultra-rapid setting emulsion, (URS) used as a bituminous tack coat for pavement applications. The product exhibits a very fast set time feature that distinguishes it from regular rapid-setting emulsions. The faster setting (15 minutes) is achieved by the introduction of two additives, one prior and one after the application of the emulsion itself. The rapid set time is beneficial for fast-track paving projects and hence could prove to be highly cost effective given the economy in time due to a faster setting process.

EVALUATION OF BOND PERFORMANCE OF AN ULTRA-RAPID SETTING EMULSION FOR TACK COAT APPLICATIONS  

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