International Research Journal of Engineering and Technology (IRJET) Volume: 11 Issue: 06 | Jun 2024 www.irjet.net
e-ISSN: 2395-0056 p-ISSN: 2395-0072
The Bond Between the Bituminous Paving Layers: Lab Scale Assessment. Aruan Kumar PG Scholar Department of Civil Engineering, Mewar University, Gangrar Rajasthan 312901 ------------------------------------------------------------------------***------------------------------------------------------------------------Abstract A bituminous surface is a multi-layered structure consisting of surfacing, base, and subbase courses on a subgrade. An interface is defined as a boundary between any two consecutive layers. As a result, adequate bonding between the layers at the interfaces is required to ensure that multiple layers function as a single composite structure. In the case of nonbituminous or bituminous-non-bituminous layers, an adequate bond is formed because of the mechanical interlocking of the aggregate surfaces. However, the state of the bond at the interface of any two bituminous layers has a significant impact on the stress distribution across pavement layers under traffic loads, as well as the pavement's overall performance. Bituminous tack coats are applied before overlay to improve adhesion or bonding between the two bituminous layers. This study assesses the interface bond strength of two types of bituminous layer mixtures in the laboratory. The cylindrical specimens were tested for bond strength at four normal service temperatures, 250, 300, 350, and 400C, using different types of tack coats at varying application rates. The specimens were prepared according to the normal Marshall Procedure, first for the underlying layer, then for the tack coat, and finally for the top layer in the same mould. Two types of layer combinations have been tried, namely (i) Bituminous Concrete (BC) layer on Dense Bituminous Macadam (DBM) samples and (ii) Semi Dense Bituminous Concrete (SDBC) layer on Bituminous Macadam (BM) samples. Similarly, different types of tack coat materials namely bitumen, Cationic Rapid Setting with low viscosity (CRS-1) and Cationic Medium Setting with high viscosity (CMS-2) emulsions have been used for the interface bond between the said bituminous layers. The prepared samples were tested using a bond strength device attached to the loading frame of the Modified Marshall Testing Apparatus. The interlayer bond strength is observed to be temperature-dependent, and it decreases as the test temperature increases. It has also been observed that the bond strength is affected by the type of tack coat used and the conditions of the type of combination. The optimal amount of tack coat varies depending on the type of tack coat used and the layer combination.
Keywords: Interlayer Bond strength, Tack coat, Bituminous layer combination, Bond strength device. Introduction Highways are the foundation of a country's progress and development. All developed and developing countries typically have an ongoing strategy of maintaining and building road infrastructure or improving existing roads. To improve the existing road infrastructure in response to increased traffic, reinforce the existing pavement layer by combining it with another layer of the appropriate material composition and thickness. Flexible pavements are typically designed and builtin multiple layers to ensure effective stress distribution across the layers under varying heavy traffic loads. The viscous nature of the flexible pavement allows its various layers to withstand significant plastic deformation, despite distresses caused by repeated heavy loading over time, which is the most common failure mode. The flexible pavement functions as a single structure due to good bonding between the different layers interfacing. The adhesion conditions at the layer interface are thought to have a significant impact on the pavement stress distribution. Poor adhesion at the layer interface can reduce the structural strength of the pavement system and lead to premature failures. Bituminous tack coats are applied before overlay to improve layer bonding. Bituminous emulsions are typically used as tack coats. Despite their widespread use, pavement engineers disagree about the effectiveness of tack coats in improving adhesion between the two layers. This tack coat is also made of a thin layer of bitumen residue, and its purpose is to provide adequate adherence between the layers. If the quantity of bituminous emulsions used is greater or less than the required one, the interface bonding will not be satisfactory. 1.1 Failures arise due to inadequate bonds. Several premature pavement failures have been caused by a loss of bond between two layers of hot mix asphalt (HMA). Poor adhesion between pavement layers has been widely observed to contribute to significant pavement overlay distresses and many premature failures. Slippage failure and layer delamination. Slippage failure worsens as the pavement layers slide against one another, and the top layer typically separates from the lower layer. This type of failure occurs
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