Cohesive zone modeling of EAF slag-included asphalt mixtures in fracture modes I and II

doi:10.1016/j.tafmec.2021.102918

Theoretical and Applied Fracture Mechanics

Volume 112, April 2021, 102918

https://doi.org/10.1016/j.tafmec.2021.102918 Get rights and content

Highlights

•
The fracture toughness of EAF slag-included asphalt mixes were studied.
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The 2D FEM model was appropriately used for determining the SIF and fracture energy.
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The CZM modeling results were in agreement with what was determined experimentally.
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The augment in the EAF slag content led to increase in crack initiation resistance.
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The fracture energy of Mode II were successfully predicted using Weibull distribution.

Abstract

Fracture properties of asphalt mixtures containing fine and coarse Electric-Arc Furnace (EAF) aggregates were determined at low-temperature conditions by implementing Cohesive Zone Modeling (CZM). Semi-Circular Bending (SCB) test was conducted in both fracture Mode I and II (opening tensile and in-plane shear, respectively), and the bi-linear traction separation law was used to obtain the coefficients of cohesive elements. To determine the fracture failure probability concerning the adopted testing parameters, the two-parameter Weibull distribution curve was fitted on the FEM results. Based on CZM simulation modeling, it was observed that the simulated curves were promisingly consistent with the experimental results. Weibull distribution analysis revealed that the inclusion of fine EAF slag aggregates increases the fracture failure probability compared with those containing coarse aggregates. A statistically predictive model was introduced, based on the Weibull distribution results, to predict the in-plane shear (Mode II) fracture properties using those of Mode I.

Introduction

The Asphalt concrete, as the most typical pavement material, plays a vital role in road infrastructure due to its inherent properties, availability, and economic benefits. Cracking and its associated deterioration as the major failures in flexible pavement, occur due to cyclic traffic loading and environmental conditions. The asphalt pavement is usually subjected to different load configurations, whereas the risk of cracking due to combined tensile-shear loads is greater than the pure tensile or shear loading conditions [1]. Thermal cracking, generated by subjecting to the low temperatures in the cold regions, is another major distress in asphalt pavement that often causes untimely deterioration needing maintenance earlier than anticipated. Previous studies have classified the thermal cracking into two categories [2]; 1) thermal fatigue cracking induced by repeated thermal stress and 2) thermal contraction cracks caused by extremely low-temperature conditions. Subzero conditions may result in brittle fracture responses that increase the possibility of crack initiation and propagation, which can be addressed using the Linear Elastic Fracture Mechanic (LEFM) [2], [3]. In this regard, Stress Intensity Factors (SIF) can be appropriately used to examine the possibility of fracture failure in asphalt pavements [4], [5].

Numerous studies have been conducted to reach a better understanding of the cracking phenomenon and propose a proper fracture test procedure and related models to predict the possibility of this failure. Various geometry-based test including Three-Point Bending (3PB), Semi-Circular Bending (SCB), Disk-Shaped Compact Tension (DCT), and Edge Notched Disc Bend (ENDB) tests, are commonly used for this purpose [6], [7], [8], [9], [10]. Type of the asphalt binder or adopted additives, testing temperature, mineral aggregate properties and composition, and different air void contents are the well-known factors the effect of which on the fracture properties of asphalt mixtures can be determined through the mentioned geometries. The SCB geometry enabled scholars a thorough investigation of Mode I, II and I&II combined [11].

Special emphasis has been placed on the sustainable, comprehensive development concept in construction, especially in pavement industries, with a focus on recovering equilibrium among substantial construction aspects including economy, environment, social issues, and security, to conserve the nature for future generations. Road construction has a crucial role in the development of a country’s transportation system. To satisfy the sustainable development principles, much attention has been paid to a new approach that diminishes emission, adverse environmental effects, and construction costs. Since asphalt pavements are compatible with this issue, attention should be paid to (1) the required heat source for road building materials processing, which results in release greenhouse gases; the Warm Mix Asphalt (WMA) is an innovative technology that causes lower plant emission, reduces mixing and compaction temperature, causes quicker turnover to traffic and saves costs, (2) cost of asphalt components (binder and aggregate); a wide range of waste and by-product resources (e.g., Construction and Demolition Wastes (CDW), Reclaimed Asphalt Pavement (RAP), Electric Arc Furnace Steel Slag (EAFSS)) can be used to reduce dumped waste disposal and preserve the natural nonrenewable materials [12], [13], [14], [15], [16].

Thriving steel-making industries and steel production growth have led to a remarkable rise in the disposal of steel slag and, consequently, its adverse environmental effects. Crystalline Slag (CS), Granulated Slag (GS), and Expanded or Foamed Slag (ES) are three slag types Considering the cooling method [14]. Angular or roughly cubical shape of slag is required and desirable to be used as asphalt aggregates. Crystalline steel slag has a cellular or vesicular structure caused by gas bubbles formed in the molten mass. Its chemistry and morphology depend on the solidification process, categorizing by the refinery process into Electric-Arc Furnace (EAF), Basic-Oxygen Furnace (BOF), and Siemens-Martin (SM) [17].

Numerous research studies have been conducted on asphalt applications to investigate the use of EAF steel slag as a substitute for mineral coarse and fine aggregates. Its physical characteristics, sharp edges, proper particle shape, and rough surface texture might result in improved asphalt binder-aggregate skeleton adhesion increasing the friction coefficient in asphalt surface courses [18]. Such characteristics plus proper particle size distribution will result in enhanced elasticity modulus, Marshall Stability, rutting resistance, and reduced Poisson’s coefficient [19], [20], [21], [22], [23], [24], [25]. It is worth noting that steel slag aggregates’ volume fraction in the asphalt mixture should be selected regarding the compaction assessment. A main drawbacks of steel slag-included asphalt mixtures is the higher asphalt binder they need due to the higher specific surface area and porosity of steel slag aggregates which lead to excessive asphalt absorption and, hence, increase the asphalt production costs [18].

The authors’ previous study on the fracture properties of EAF steel slag-included asphalt mixtures revealed that the fracture energy in WMA mixtures was significantly reduced due to the presence of EAF steel slag aggregates [18]. However, the simultaneously use of EAF steel slag and Sasobit in WMA mixtures caused a promising synergic effect on reducing thermal sensitivity of asphalt mixtures. Accordingly, the present research study was drawn aimed to measure the fracture properties of HMA and WMA mixes containing coarse and fine EAF steel slag aggregates performing Semi-Circular Bending (SCB) test. Investigations were based on testing under 0 and −20 °C temperatures and fracture modes I and II. The Cohesive Zone Modeling (CZM) was carried out through the two-dimensional Finite Element Modeling (FEM) to model and assess the fracture evolvement in the mixtures at both Modes I and II. The Weibull distribution probabilistic statistical analysis was performed to determine the exact impacts of the test variables, and a statistical model was, consequently, proposed based on the FEM results to predict Mode II fracture parameters considering the parameters under Mode I loading

Section snippets

Theoretical background

Used for modeling the crack evolution at the tip of a pre-existing crack for a variety of materials, CZM is a well-known method developed in the damage mechanic framework utilizing the concept of fracture mechanics [26], [27]. Its definition is based on observations wherein the cohesion forces gradually tend to an ascending trend as the distance between two atomic planes increases. Once the maximum value is reached, the cohesion forces experience a severe drop by the rise of separation [27].

The

Materials

Table 1 shows the physical characteristics of the EAF slag and virgin siliceous aggregates. The EAF slag was collected from Isfahan province, Iran, and left outdoor more than a year to reduce the adverse effect of its free-CaO and MgO that expand in asphalt mixtures. It is worth mentioning that the presence of free-CaO contents increase the resistance of EAF slag-included mixtures against stripping and improve the aggregates- asphalt binder internal adhesion [18]. Fig. 2 shows the XRD pattern

Crack trajectories in mode I and II

Fig. 8 shows the crack trajectory envelopes for HMA and WMA specimens at 0 and −20 °C under Mode I and II applied loading. Each notch tip was assumed as a benchmark to build up an envelope, and the GIS was used to obtain the crack trajectory envelopes (grey pixels in the picture of the broken SCB specimens - spectrum response in G, R and B wavelengths). As shown, the SCB specimen’s crack path is parallel to the load applied under both modes I and II, and is consistent with the assumed direction

Summary and conclusions

This study was performed to evaluate the fracture properties of HMA and WMA asphalt mixes containing fine and coarse EAF slag, at 0 and −20 °C, under different fracture modes using the SCB test. A 2D FEM simulation, the cohesive zone modeling, was conducted to assess the fracture parameters of the designed mixes. To this end, the SCB geometry was simulated under opening tensile and in-plane shear fracture modes, and the fracture toughness and fracture energy were determined. A statistical

CRediT authorship contribution statement

S.M. Motevalizadeh: Conceptualization, Methodology, Investigation, Software, Validation. H. Rooholamini: Conceptualization, Methodology, Formal analysis, Data curation, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Citation Excerpt :
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Cohesive zone modeling of EAF slag-included asphalt mixtures in fracture modes I and II

Highlights

Abstract

Introduction

Section snippets

Theoretical background

Materials

Crack trajectories in mode I and II

Summary and conclusions

CRediT authorship contribution statement

Declaration of Competing Interest

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