Sustainability

Research

19 pages, 5947 KiB

Open AccessArticle

Hot In-Place Recycled Asphalt Mixtures: RAP Analysis, Compaction Characteristics and Field Evaluation

by Teng Wang, Xin Zhao, Lele Zheng, Chengxin Mao, Li Wang, Augusto Cannone Falchetto and Dedong Guo

Sustainability 2024, 16(3), 1064; https://doi.org/10.3390/su16031064 - 26 Jan 2024

Viewed by 1797

Abstract

The substantial accumulation of reclaimed asphalt pavement (RAP) poses a pressing issue in road construction. The hot in-place recycling (HIR) technique has garnered widespread attention due to its high recycling rates of RAP and minimal environmental hazards. This study focuses on the RAP [...] Read more.

The substantial accumulation of reclaimed asphalt pavement (RAP) poses a pressing issue in road construction. The hot in-place recycling (HIR) technique has garnered widespread attention due to its high recycling rates of RAP and minimal environmental hazards. This study focuses on the RAP analysis, compaction characteristics, and field evaluation of hot in-place recycled asphalt pavements (HIRAP). Firstly, a novel test method of RAP analysis was proposed to evaluate the suitability of RAP. Subsequently, compaction tests reveal the compaction characteristics of hot in-place recycled asphalt mixture (HIRAM). Finally, the field performance of HIRAP was assessed. The research findings indicate that the RAP analysis method can accurately characterize the status of RAP. Increasing the RAP temperature improves the compaction characteristics of HIRAM. The field tests show that using HIR technology improves the performance of the pavement, in particular with a compaction of 99.7%. This study will establish a theoretical foundation for further promoting the HIR technique. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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15 pages, 3717 KiB

Open AccessArticle

A Sustainable Superhydrophobic and Photothermal Coatings for Anti-Icing Application on Concrete with a Simple Method for CNTs/SiO₂ Modification

by Shuai Li, Yanwei Li, Yiqiu Tan, Jilu Li, Di Wang, Dongdong Yuan and Jianli Zhang

Sustainability 2023, 15(22), 15865; https://doi.org/10.3390/su152215865 - 12 Nov 2023

Cited by 1 | Viewed by 1478

Abstract

Ice formation on concrete surfaces significantly challenges productivity, economic growth, and safety in diverse industrial sectors. Superhydrophobic coatings represent an effective solution to delay ice formation, although their functionality deteriorates under repeated freeze–thaw cycles. To address this issue, carbon nanotubes (CNTs) are frequently [...] Read more.

Ice formation on concrete surfaces significantly challenges productivity, economic growth, and safety in diverse industrial sectors. Superhydrophobic coatings represent an effective solution to delay ice formation, although their functionality deteriorates under repeated freeze–thaw cycles. To address this issue, carbon nanotubes (CNTs) are frequently employed due to their exceptional photothermal conversion and mechanical properties, which contribute to extending the sustainability of the superhydrophobic coatings. However, the chemical inertness of CNTs often necessitates complex reactions to modify their functionalization. In this study, we have invented a simple method involving the sequential growth of silica on the surface of CNTs and the hydrophobic modification of the silica surface to enhance CNT functionality. These CNTs/SiO₂ functionalized nanoparticles were then incorporated into an epoxy resin using a simple spray technique, resulting in a superhydrophobic and photothermal coating on concrete. To fine-tune the coating’s properties, we explored the effects of varying the doping levels of the nanoparticles on the surface morphology, roughness, and wettability of the CNT/SiO₂-EP coatings. The optimal level of hydrophobicity was achieved by doping the coatings with 300 mg of functionalized nanoparticles, yielding an impressive contact angle of 159.6°. The integration of functionalized nanoparticles into the epoxy matrix not only enhances hydrophobicity but also improves mechanical robustness and abrasion resistance by creating multiscale surface roughness. Additionally, the coating exhibits outstanding chemical stability even under extreme conditions. One of the most significant advantages of these coatings is their ability to extend the ice nucleation time significantly. This effect is primarily attributed to the superior superhydrophobicity of the nanoparticles and the remarkable photothermal conversion capability of the CNTs. Upon exposure to Xenon lamp radiation, the ice droplets rapidly melt, underscoring the impressive performance of these coatings in preventing ice formation. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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19 pages, 4265 KiB

Open AccessArticle

Preparation and Properties of High-Viscosity Modified Asphalt with a Novel Thermoplastic Rubber

by Teng Wang, Zhirong Chen, Jinlong Hong, Zhen Liao, Di Wang, Dongdong Yuan, Yufei Zhang and Augusto Cannone Falchetto

Sustainability 2023, 15(16), 12190; https://doi.org/10.3390/su151612190 - 9 Aug 2023

Cited by 1 | Viewed by 1560

Abstract

With the increasing demand for improved road performance and sustainable development, modified asphalt is increasingly being used in pavement construction. This study investigates the preparation and properties of a novel high-viscosity modified asphalt. Firstly, different contents of novel thermoplastic rubber (NTPR) were mixed [...] Read more.

With the increasing demand for improved road performance and sustainable development, modified asphalt is increasingly being used in pavement construction. This study investigates the preparation and properties of a novel high-viscosity modified asphalt. Firstly, different contents of novel thermoplastic rubber (NTPR) were mixed with neat asphalt to prepare high-viscosity modified asphalt (HVA). Then, the basic physical properties containing penetration, a softening point, ductility, and viscosity were conducted. Moreover, the rheological properties of the HVA before and after aging were analyzed via a dynamic shear rheometer test and a bending beam rheometer test. Finally, the dispersity of the modifier in HVA was analyzed via fluorescence microscopy. The results show that adding the NTPR restricts the flow of asphalt to a certain extent and improves the high temperature performance of asphalt. Furthermore, the apparent viscosity of HVA with various contents increases less and is always less than 3 Pa·s. Although adding NTPR makes the asphalt brittle, the HVA can meet the requirements when the NTPR is from 6% to 11%. With the increase in the NTPR, the modifier forms a mesh structure in the asphalt, enhancing its stability. Considering the above results, HVA with 10~11% of NTPR is recommended because it has better comprehensive properties. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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18 pages, 2909 KiB

Open AccessArticle

Effect of Blending Behavior on the Performance of Hot Recycled Asphalt Mixtures

by Teng Wang, Xianwu Ling, Jun Lin, Bing Xiang, Dongdong Yuan, Wentong Wang, Di Wang and Dedong Guo

Sustainability 2023, 15(15), 11723; https://doi.org/10.3390/su151511723 - 29 Jul 2023

Viewed by 1194

Abstract

Blending behavior is the main factor influencing hot recycled asphalt mixtures’ actual and design performance. The following steps were taken to investigate the above issues. Firstly, the component changes of asphalt mixtures were studied by thin-layer chromatography, with flame ionization detection to obtain [...] Read more.

Blending behavior is the main factor influencing hot recycled asphalt mixtures’ actual and design performance. The following steps were taken to investigate the above issues. Firstly, the component changes of asphalt mixtures were studied by thin-layer chromatography, with flame ionization detection to obtain the mechanism of asphalt aging and recycling. Secondly, according to the difference in the recycled asphalt components, the hot recycled asphalt mixtures were optimized based on the Marshall design method. Lastly, the hot recycled asphalt mixtures for the three mixing processes were prepared using the optimized design method described above. Laboratory tests were conducted to evaluate the correlation between the degree of blending (DoB) and the high-temperature stability, low-temperature crack resistance, water stability, and fatigue performance. The test results indicate that reducing light components (saturates and aromatics) and increasing heavy components (asphaltenes and resins) are the main reasons for asphalt aging, and asphalt recycling is an inverse process. Additionally, the performance of hot recycled asphalt mixtures is improved with an increase in DoB. Specifically, the DoB is only 50% to 60% under a normal mixing process, but by adjusting parameters the DoB will increase to 80% to 90%. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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19 pages, 7151 KiB

Open AccessArticle

Experimental Study of Permeable Asphalt Mixture Containing Reclaimed Asphalt Pavement

by Jingjing Xiao, Teng Wang, Jinlong Hong, Chong Ruan, Yufei Zhang, Dongdong Yuan and Wangjie Wu

Sustainability 2023, 15(13), 10676; https://doi.org/10.3390/su151310676 - 6 Jul 2023

Cited by 4 | Viewed by 1780

Abstract

The current focus of research attention on reclaimed asphalt pavement (RAP) utilization is expanding the applications of RAP. This study aims to analyze the road performance of recycled permeable asphalt mixtures (RPAMs), which represents a novel direction for utilizing RAP. Firstly, the Marshall [...] Read more.

The current focus of research attention on reclaimed asphalt pavement (RAP) utilization is expanding the applications of RAP. This study aims to analyze the road performance of recycled permeable asphalt mixtures (RPAMs), which represents a novel direction for utilizing RAP. Firstly, the Marshall design method was used to carry out the material composition design of the RPAM with varying RAP contents (10%, 20%, and 30%). Subsequently, the performance of the RPAM with different RAP contents (10%, 20%, and 30%) and preheating temperatures (120 °C, 130 °C, 140 °C, 150 °C, and 160 °C) was tested with a permeable asphalt mixture containing 12% high-viscosity asphalt as the control group. The mixture’s performance included high-temperature stability, low-temperature crack resistance, water stability, anti-raveling performance, and dynamic mechanical properties. The results indicate that the higher the RAP content, the better the high-temperature performance of the RPAM, while the low-temperature performance, water stability, and anti-raveling performance deteriorate. At 30% RAP content, its pavement performance is comparable to that of the control group mixture. However, increasing RAP preheating temperature can improve low-temperature and water stability but may reduce high-temperature performance. The optimal RAP preheating temperature for pavement performance is between 140 and 150 °C. The dynamic modulus test showed that the higher the RAP content, the greater the dynamic modulus of the RPAM, leading to better high-temperature stability but reduced low-temperature crack resistance. The influence of RAP preheating temperature is the opposite. These test results demonstrate the feasibility of utilizing RAP for paving permeable asphalt pavement under controlled RAP content and preheating temperature conditions. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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20 pages, 22377 KiB

Open AccessArticle

Analysis of Modulus Properties of High-Modulus Asphalt Mixture and Its New Evaluation Index of Rutting Resistance

by Guojing Huang, Jiupeng Zhang, Bing Hui, Hongfei Zhang, Yongsheng Guan, Fucheng Guo, Yan Li, Yinzhang He and Di Wang

Sustainability 2023, 15(9), 7574; https://doi.org/10.3390/su15097574 - 5 May 2023

Cited by 8 | Viewed by 2546

Abstract

High-modulus asphalt mixture (HMAM) is one of the most effective materials to enhance the rutting resistance of asphalt pavement and upgrade pavement sustainability. The objectives of this study are to investigate the modulus properties of different HMAMs and their correlation with the rutting [...] Read more.

High-modulus asphalt mixture (HMAM) is one of the most effective materials to enhance the rutting resistance of asphalt pavement and upgrade pavement sustainability. The objectives of this study are to investigate the modulus properties of different HMAMs and their correlation with the rutting resistance, to propose reasonable modulus evaluation indicators, and to analyze the rutting resistance mechanisms of different materials (hard asphalt, polyethylene, dissolved polyolefin). The effect of three HMAMs and two styrene-butadiene-styrene (SBS) modifiers on asphalt mixtures’ rutting resistance were evaluated by dynamic modulus test and wheel track test, and the results were simulated and further analyzed via ABAQUS. The results indicate that the dynamic modulus of the mixtures showed a gradual increase and decrease with the increase of loading frequency and testing temperature, respectively. The ratio of dynamic modulus in low frequency to that in high frequency correlates well with dynamic stability under high-temperature conditions, and the wider the frequency coverage, the higher the correlation between this ratio and dynamic stability. The rutting resistance of asphalt pavements can be improved by reducing the frequency sensitivity of HMAMs under high temperatures or by increasing the modulus’ absolute value of the pavement structural layer. Therefore, two indicators, the absolute value of the modulus and the ratio of 0.1 Hz dynamic modulus to 25 Hz dynamic modulus at 55 °C, are recommended for the evaluation of rutting resistance of HMAMs. Based on the evaluation indexes proposed in this paper, a comparative analysis of the rutting resistance mechanism of HMAMs prepared with different materials was carried out, and it was concluded that the mixture with high-modulus agents had the best rutting resistance, which is consistent with the test road observations, thus verifying the feasibility of the modulus evaluation indexes recommended in this paper for the evaluation of the rutting resistance of different types of HMAMs. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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14 pages, 4764 KiB

Open AccessArticle

Investigation of Viscoelastic Properties of Polymer-Modified Asphalt at Low Temperature Based on Gray Relational Analysis

by Zhongcai Huang, Rong Lu, Zhiyu Fu, Jingxiao Li, Pengfei Li, Di Wang, Ben Wei, Weining Zhu, Zujian Wang and Xinyu Wang

Sustainability 2023, 15(8), 6858; https://doi.org/10.3390/su15086858 - 19 Apr 2023

Cited by 1 | Viewed by 1259

Abstract

As the investigation indexes of low-temperature viscoelastic properties of polymer-modified asphalt (PMA) are unclear at present, in this paper, the creep stiffness (S), creep rate (m), low-temperature continuous classification temperature (T_C), ΔT_C, m/S [...] Read more.

As the investigation indexes of low-temperature viscoelastic properties of polymer-modified asphalt (PMA) are unclear at present, in this paper, the creep stiffness (S), creep rate (m), low-temperature continuous classification temperature (T_C), ΔT_C, m/S, relaxation time (

λ

), and dissipation energy ratio (

W_{d} (t) / W_{s} (t)

) were taken as a comparison sequence. The maximum flexural tensile strain (ε_B) of porous asphalt mixture (PAM) in a low-temperature bending test was selected as a reference sequence. Gray relational analysis was used to investigate the PMA’s low-temperature viscoelastic properties based on a bending beam rheometer (BBR). The results show certain contradictions in investigating the low-temperature properties of PMA when only considering the low-temperature deformation capacity or the stress relaxation capacity. The modulus and relaxation capacity should be considered when selecting the investigation indexes of the low-temperature viscoelastic properties of PMA. When rheological method is used to evaluate the low-temperature of polymer modified asphalt, T_C and m/S are preferred. When only S or m is contradictory, m should be preferred. ΔT_C can determine whether the low-temperature performance of PMA is dominated by S or m. The result can better guide the construction of asphalt pavement in areas with low temperatures. Asphalt can be selected quickly and accurately to avoid the waste of resources. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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13 pages, 1460 KiB

Open AccessArticle

Viscoelasticity of Recycled Asphalt Mixtures with High Content Reclaimed SBS Modified Asphalt Pavement

by Kunpeng Zheng, Jian Xu and Jie Wang

Sustainability 2023, 15(3), 2515; https://doi.org/10.3390/su15032515 - 31 Jan 2023

Cited by 7 | Viewed by 1589

Abstract

For the concerns of investigating the viscoelastic properties of recycled asphalt mixtures incorporating high content reclaimed styrene-butadiene-styrene (SBS) modified asphalt pavement (RAP-SBS), asphalt mixture performance tester (AMPT) was applied to analyze the dynamic modulus and phase angle of recycled mixtures by the influence [...] Read more.

For the concerns of investigating the viscoelastic properties of recycled asphalt mixtures incorporating high content reclaimed styrene-butadiene-styrene (SBS) modified asphalt pavement (RAP-SBS), asphalt mixture performance tester (AMPT) was applied to analyze the dynamic modulus and phase angle of recycled mixtures by the influence of RAP-SBS content, temperature, loading frequency, long-term aging (LOTA), and the incorporation of a rejuvenating agent. Master curves of recycled asphalt mixture regarding dynamic modulus and phase angle are developed, and the viscoelastic properties of recycled mixtures within a wide frequency range are characterized with the Christensen–Anderson–Marastean (CAM) model. Eventually, the one-way analysis of variance (ANOVA) was applied to investigate the role of factors on the viscoelasticity of recycled mixtures. The research indicates that (1) the elastic component of recycled mixtures elevates with the increasing of RAP-SBS content and loading frequency; as a result, the high-temperature stability of it enhances, while it is prone to cracking at low temperatures; (2) RAP-SBS content should be selected according to specific characteristics of pavement. For most cases, a content of 50% is recommended; (3) the recycled mixtures incorporating high-content RAP-SBS mixed with a rejuvenating agent has outstanding aging resistance performance; (4) RAP-SBS content is observed to have a significant influence on the viscoelasticity of recycled mixtures. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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Graphical abstract

12 pages, 3337 KiB

Open AccessArticle

Evaluation and Technical Requirements of the Initial Anti-Wear Performance of an Emulsified Asphalt Cold Recycled Mixture: A Case Study in Northern China

by Weidang Duan, Tao Liu, Qiuping Li, Jian Xu, Jialin Zhang, Yongchun Qin, Jie Wang and Rong Chang

Sustainability 2022, 14(22), 15469; https://doi.org/10.3390/su142215469 - 21 Nov 2022

Cited by 1 | Viewed by 1314

Abstract

Considering the initial strength evaluation method of a cold recycled asphalt emulsified mixture, the abrasion test was selected as the evaluation method. The comparison test was designed to determine the key parameters of the test, including the molding method, the curing temperature, the [...] Read more.

Considering the initial strength evaluation method of a cold recycled asphalt emulsified mixture, the abrasion test was selected as the evaluation method. The comparison test was designed to determine the key parameters of the test, including the molding method, the curing temperature, the curing relative humidity, and the curing time. The influence of different emulsifiers, the emulsifier dosage, the asphalt dosage, the cement dosage, and the mineral aggregate gradation on the initial anti-wear performance of the mixture was analyzed. The technical requirements for the emulsified asphalt cold recycled mixture were put forward. We analyzed the significance of different influencing factors using analysis of variance. The results shows that the abrasion test is simple and reliable. It can be used to evaluate the initial abrasion resistance of the emulsified asphalt cold recycled mixture. The curing conditions had a great impact on the abrasion loss. With the increase in temperature or the extension of the curing time, the abrasion loss gradually decreased. With the increase in relative humidity, the abrasion loss gradually increased. The testing protocols, namely 25 °C with a relative humidity of 70%, the curing time was 4 h, followed an active Chinese standard (JTG/T 5521). The results indicate that the factors that affect the initial performance of the cold reclaimed mixture of emulsified asphalt are in the following order: cement dosage, cement strength grade, emulsifier type, mineral aggregate gradation, emulsified asphalt dosage, mixture moisture content, and emulsifier dosage. The cement dosage, emulsifier type, and mineral aggregate gradation had significant effects on the initial strength of the cold recycled mixture. An abrasion loss of less than 3.5% was selected as the basis for optimizing the design of the emulsified asphalt cold recycled mixture. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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16 pages, 4995 KiB

Open AccessArticle

Effect of Sandy Soil Partial Replacement by Construction Waste on Mechanical Behavior and Microstructure of Cemented Mixtures

by Diego Manchini Milani, José Wilson dos Santos Ferreira, Michéle Dal Toé Casagrande, Avacir Casanova Andrello and Raquel Souza Teixeira

Sustainability 2022, 14(19), 12438; https://doi.org/10.3390/su141912438 - 29 Sep 2022

Cited by 1 | Viewed by 1461

Abstract

The large amounts of construction waste (CW) generated yearly and its high landfilled proportion worldwide motivate the search for sustainable solutions. Thus, the effect of sandy soil partial replacement for construction waste in cemented mixtures was assessed in the present work in terms [...] Read more.

The large amounts of construction waste (CW) generated yearly and its high landfilled proportion worldwide motivate the search for sustainable solutions. Thus, the effect of sandy soil partial replacement for construction waste in cemented mixtures was assessed in the present work in terms of mechanical behavior and microstructure. Distinct cement contents, compaction efforts, and curing periods were evaluated from soil-waste proportion of S75W25, S50W50, and S25W75. Tests of unconfined compression strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity, water absorption, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) were conducted. The presence and increase in the amounts of cement and construction waste increase the optimum moisture content of the mixture. In contrast, only the CW content significantly affects maximum dry density. Both S75W25 and S50W50 mixtures resulted in similar UCS and ITS values, which was proven to be statistically equal by analysis of variance (ANOVA) at a 0.05 significance level, favoring CW replacing soil up to 50%. MIP and SEM results explained the sharp mechanical behavior transition obtained in 75% of CW. Cementation reactions resulted in macropores peak reduction and/or peak area translation to the left of the horizontal axis of the PSD curve, while its translation to the right indicates the cement mainly acting as filler, which was supported by SEM tests. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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16 pages, 3132 KiB

Open AccessArticle

Comparison of Rubber Asphalt with Polymer Asphalt under Long-Term Aging Conditions in Michigan

by Dongzhao Jin, Kwadwo Ampadu Boateng, Siyu Chen, Kai Xin and Zhanping You

Sustainability 2022, 14(17), 10987; https://doi.org/10.3390/su141710987 - 2 Sep 2022

Cited by 14 | Viewed by 1911

Abstract

The objective of this study is to compare the long-term aging performance of dry-processed rubber-modified asphalt mixture with styrene–butadiene–styrene polymer-modified asphalt mixture on heavy traffic volume roads in the wet-freeze environment of Michigan. The rutting performance was evaluated using the Hamburg wheel track [...] Read more.

The objective of this study is to compare the long-term aging performance of dry-processed rubber-modified asphalt mixture with styrene–butadiene–styrene polymer-modified asphalt mixture on heavy traffic volume roads in the wet-freeze environment of Michigan. The rutting performance was evaluated using the Hamburg wheel track device. The disc-shaped compact tension test was used to assess the fracture energy. The dynamic modulus experiment was used to estimate the load and displacement relationship. The asphalt binder properties were evaluated using multiple stress creep recovery and the linear amplitude sweep test. The pavement distresses were evaluated using the pavement mechanistic–empirical design. All three types of asphalt mixture show excellent rutting resistance after long-term aging conditions, while the fracture energy of the rubber mix is 17.1% to 30.5% higher than that of the control mix and 6.8% to 9.1% higher than that of the polymer mix. The rubber and polymer incorporated with the asphalt binder improved the resistance to permanent deformation and improved the fatigue life of the asphalt binder. In summary, the rubberized asphalt technology using the dry process shows better cracking resistance and fatigue life. Therefore, rubberized asphalt using the dry process will exhibit adequate performance when used for high-volume roads in the wet-freeze environment of Michigan. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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16 pages, 2187 KiB

Open AccessArticle

Bio-Degradable Wax to Modify Asphalt Binder for Warm Mix Asphalt

by Tess Sigwarth, Johannes Büchner and Michael P. Wistuba

Sustainability 2022, 14(16), 10219; https://doi.org/10.3390/su141610219 - 17 Aug 2022

Cited by 5 | Viewed by 1887

Abstract

In order to reduce production and compaction temperatures, as well as to increase the resistance to permanent deformation, synthetically refined waxes are commonly used as additives in asphalt pavements. This study focuses on the capability of replacing synthetically refined wax with bio-degradable wax. [...] Read more.

In order to reduce production and compaction temperatures, as well as to increase the resistance to permanent deformation, synthetically refined waxes are commonly used as additives in asphalt pavements. This study focuses on the capability of replacing synthetically refined wax with bio-degradable wax. Ten different bio-waxes (called Biomer) with varying melting ranges and composition, as well as three conventional waxes (Sasobit^®, Licomont^®, and Asphaltan) are mixed with a virgin bitumen of standard type 50/70. Different conventional and rheological properties are determined for these viscosity-modified binders to evaluate the effect of the waxes. Two promising Biomer waxes (BIT111 and BIT140) were identified, which show almost identical results compared to Sasobit^® and Licomont^®, respectively. The results indicate that replacement of synthetic wax by bio-degradable wax is technically feasible. Additionally, the potential of asphalt pavements to form a source of microplastic is evaluated in this study. It is found that bitumen and wax cannot be considered as a source of microplastic. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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24 pages, 4971 KiB

Open AccessArticle

Eco-Friendly Optimum Structural Concrete Mix Design

by Najib N. Gerges, Camille A. Issa, Elias Sleiman, Sara Aintrazi, Jad Saadeddine, Remi Abboud and Marc Antoun

Sustainability 2022, 14(14), 8660; https://doi.org/10.3390/su14148660 - 15 Jul 2022

Cited by 17 | Viewed by 2991

Abstract

Concrete, the most consumed man-made material worldwide, has shaped the environment and the modern world. Even though concrete is a major contributor to the carbon footprint, it is indispensable for building the sustainable world of tomorrow. Researchers have been exploring ways to reduce [...] Read more.

Concrete, the most consumed man-made material worldwide, has shaped the environment and the modern world. Even though concrete is a major contributor to the carbon footprint, it is indispensable for building the sustainable world of tomorrow. Researchers have been exploring ways to reduce the carbon footprint and to implement strategical waste management plans in which wastes are repurposed. Pollution has been a challenge for almost all countries, especially with the increase in the release of greenhouse gases in the atmosphere and the emissions resulting from wastes in unmanaged landfills. Additionally, the areas available for landfills have become scarce. Daily all around the world, generated are wastes such as wood ash, waste glass, used tires, construction debris, and demolition wastes. These wastes usually accumulate in landfills for years, as they are mostly nondecomposable. This research explores a solution to this twofold problem in which concrete components are replaced by wastes and by-products, which in return reduces the need for raw materials that have a significant carbon footprint and repurposes wastes as part of a circular economy. In this research, wood ash is used as a partial replacement of cement and sand, fine crushed glass and crumb rubber as partial replacements of sand, and crushed glass and recycled concrete aggregates as partial replacements of gravel. The optimum eco-friendly structural concrete mix was determined to be the combined mix consisting of 5% wood ash as a partial replacement of cement; 20% wood ash, 20% fine crushed glass, and 2% crumb rubber as partial replacements of sand; and 5% crushed glass and 50% recycled concrete aggregates as partial replacements of coarse aggregates. By mass, the recycled waste materials constituted 32% of the mix, translating into 34% of its volume. Additionally, identified were mixes that may be used for structural applications. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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21 pages, 8578 KiB

Open AccessArticle

Investigation of Parking Lot Pavements to Counteract Urban Heat Islands

by Laura Moretti, Giuseppe Cantisani, Marco Carpiceci, Antonio D’Andrea, Giulia Del Serrone, Paola Di Mascio, Paolo Peluso and Giuseppe Loprencipe

Sustainability 2022, 14(12), 7273; https://doi.org/10.3390/su14127273 - 14 Jun 2022

Cited by 14 | Viewed by 2922

Abstract

Urban heat islands (UHI) are one of the unequivocal effects of the ongoing process of climate change: anthropized areas suffer extreme heat events that affect the human perception of comfort. This study investigated the effects of road pavements as a passive countermeasure by [...] Read more.

Urban heat islands (UHI) are one of the unequivocal effects of the ongoing process of climate change: anthropized areas suffer extreme heat events that affect the human perception of comfort. This study investigated the effects of road pavements as a passive countermeasure by comparing the air temperature (AT) and the predicted mean vote (PMV) for different surface materials used to pave a historical square in Rome, Italy. The software ENVI-met has been used to compare, for the whole year 2021, the performances of the existing asphalt pavement with five alternative solutions composed of light concrete, bricks, stone, wood, and grass. This paper proposed a new methodology to summarize the multi-dimensional results over both temporal and spatial domains. The results of the simulations in the evening of the hottest month showed the existing asphalt pavement gives the worst performance, while the light concrete blocks and the grass pavement ensure the coolest solutions in terms of AT (the average AT is 32 °C for the asphalt pavement and 30 °C for the modular one) and PMV (the maximum PMV value is 4.6 for the asphalt pavement and 4.4 for the modular and grass ones). Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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15 pages, 6383 KiB

Open AccessArticle

Feasibility of Using Coal Ash for the Production of Sustainable Bricks

by Ahmad Mukhtar, Asad Ullah Qazi, Qasim Shaukat Khan, Muhammad Junaid Munir, Syed Minhaj Saleem Kazmi and Asif Hameed

Sustainability 2022, 14(11), 6692; https://doi.org/10.3390/su14116692 - 30 May 2022

Cited by 10 | Viewed by 4436

Abstract

In this research study, environmentally friendly unburnt coal ash (CA) bricks were investigated as an alternative to conventional burnt clay bricks. In this research study, various physical and mechanical properties of unburnt CA bricks were investigated. The unburnt CA bricks were prepared by [...] Read more.

In this research study, environmentally friendly unburnt coal ash (CA) bricks were investigated as an alternative to conventional burnt clay bricks. In this research study, various physical and mechanical properties of unburnt CA bricks were investigated. The unburnt CA bricks were prepared by using 60% CA and 10% lime by weight. In these unburnt CA bricks, varying cement contents (5%, 10%, and 15%), sand contents (10% and 15%), and quarry dust contents (5% and 10%) by weight were used. A forming pressure of 29 MPa was applied through an automatic pressure control system either for 3 s or 6 s. The prepared bricks were moist cured for 28 days. The experimental results exhibited that unburnt CA bricks with 10% cement, 10% sand, and 10% quarry dust subjected to forming pressure for 3 s exhibited the highest compressive strength of 19 MPa and flexural strength of 2.1 MPa. The unburnt CA bricks exhibited reduced water absorption, reduced efflorescence, and lower weight per unit area than the conventional clay bricks. A cost comparison of unburnt CA bricks and clay bricks exhibited that unburnt CA bricks are cost-effective compared to clay bricks. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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18 pages, 5181 KiB

Open AccessArticle

Crack Propagation Assessment of Time-Dependent Concrete Degradation of Prestressed Concrete Sleepers

by Dan Li, Ruilin You and Sakdirat Kaewunruen

Sustainability 2022, 14(6), 3217; https://doi.org/10.3390/su14063217 - 9 Mar 2022

Cited by 4 | Viewed by 2697

Abstract

As prestressed concrete sleepers are continuously exposed to various environmental and loading conditions, it is increasingly crucial to analyse their current and future serviceability performance. In practice, the main cause of cracking in prestressed concrete sleepers is usually induced by impact loads. The [...] Read more.

As prestressed concrete sleepers are continuously exposed to various environmental and loading conditions, it is increasingly crucial to analyse their current and future serviceability performance. In practice, the main cause of cracking in prestressed concrete sleepers is usually induced by impact loads. The most heavily influenced sections are the midspan and rail-seat area of sleepers. This paper investigates the effects of time-dependent concrete strength degradation on the capacity of prestressed concrete sleepers. The factors affecting concrete strength degradation are analysed in order to evaluate the crack behaviour of prestressed concrete sleepers. A finite element modelling approach is developed for prestressed concrete sleepers, which is used to assess the effects of structural behaviour in railway sleepers. The sleeper model has been calibrated and validated. This research firstly discusses time-dependent behaviour using load–crack length responses. It is shown that various cracking modes cause an overall increase in the maximum cracking length as prestressed concrete sleepers age. This paper demonstrates that initial cracking loads and ultimate crack lengths have significant change in first 20 years. After 40 years of service life, the crack resistance of prestressed concrete sleepers becomes very weak which is only 61.32% of the new sleeper. In long term, the initial cracking load keeps reducing, and the crack propagation rate becomes sharp. The presented methodology and results can greatly assist in decision-making for the repair or replacement of prestressed concrete sleepers and aid in the design of new prestressed concrete sleepers considering their future performance. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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24 pages, 34135 KiB

Open AccessArticle

Suitability Assessment of Marble, Glass Powders and Poly-Propylene Fibers for Improvement of Siwalik Clay

by Syed Zishan Ashiq, Aziz Akbar, Khalid Farooq, Syed Minhaj Saleem Kazmi and Muhammad Junaid Munir

Sustainability 2022, 14(4), 2314; https://doi.org/10.3390/su14042314 - 17 Feb 2022

Cited by 3 | Viewed by 2160

Abstract

Raising of the Mangla Dam in Pakistan submerged about 15,780 acres of land, resulting in the relocation of 8020 inhabitants to a newly developed town named New City. The new site, consisting of 1300 acres, is in the sub-tropical zone and comprises badland [...] Read more.

Raising of the Mangla Dam in Pakistan submerged about 15,780 acres of land, resulting in the relocation of 8020 inhabitants to a newly developed town named New City. The new site, consisting of 1300 acres, is in the sub-tropical zone and comprises badland topography. The parent soils (Siwalik clay) pose infrastructure serviceability issues, causing immense loss to property. The study aims to improve the properties of Siwalik clay (base soil) using industrial wastes like marble and glass powders (5 to 20%) and polypropylene fibers (0.25 to 1.25%) as modifiers. Laboratory tests including grain size distribution, Atterberg limits, standard Proctor compaction, unconfined compression, indirect tensile strength, swell potential, and California bearing ratio were conducted on the control and modified clay samples. The results showed that unconfined compressive strength (UCS) and swelling strains (SS) were increased by 43% and 8% at 1.57 kPa pressure with 15% replacement of marble powder. However, the addition of the 20% glass powder and 0.5% polypropylene fibers not only improved UCS by 110% and 39%, but also reduced SS by 27% and 86%, respectively. The capital construction cost of 1 km long road with modified subgrade using 15% glass powder was reduced by 16% whereas it increased for marble powder and polypropylene fibers by 22% and 17%, respectively. All modifiers had very low hazard to adjoining aqueous environment. Conclusively, glass powder and polypropylene fibers can be used as environmentally-friendly soil improvement modifiers, leading towards sustainable solutions of the serviceability problems. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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21 pages, 7944 KiB

Open AccessArticle

Effect of Gasification Char and Recycled Carbon Fibres on the Electrical Impedance of Concrete Exposed to Accelerated Degradation

by Alessandra Mobili, Gloria Cosoli, Nicola Giulietti, Paolo Chiariotti, Giuseppe Pandarese, Tiziano Bellezze, Gian Marco Revel and Francesca Tittarelli

Sustainability 2022, 14(3), 1775; https://doi.org/10.3390/su14031775 - 4 Feb 2022

Cited by 9 | Viewed by 1633

Abstract

This paper aims to evaluate the effect of carbon-based conductive recycled additions, i.e., recycled carbon fibres (RCF) and gasification char (GCH), on the mechanical, electrical, and durability properties of concretes. The obtained results show that the compressive strength of concrete is not affected [...] Read more.

This paper aims to evaluate the effect of carbon-based conductive recycled additions, i.e., recycled carbon fibres (RCF) and gasification char (GCH), on the mechanical, electrical, and durability properties of concretes. The obtained results show that the compressive strength of concrete is not affected by conductive additions, whereas electrical impedance, measured according to Wenner’s method, is significantly reduced (6%, 30% and 74% with RCF, GCH, and their combination, respectively) to the advantage of self-sensing properties. As durability is concerned, conductive additions slightly increase capillary water absorption, whereas they decrease chloride ingress through diffusion and do not significantly modify carbonation resistance. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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22 pages, 5620 KiB

Open AccessEditor’s ChoiceArticle

Comparative Investigations into Environment-Friendly Production Methods for Railway Prestressed Concrete Sleepers and Bearers

by Ruilin You, Jijun Wang, Sakdirat Kaewunruen, Meng Wang and Na Ning

Sustainability 2022, 14(3), 1059; https://doi.org/10.3390/su14031059 - 18 Jan 2022

Cited by 3 | Viewed by 2997

Abstract

Prestressed concrete sleeper is a safety-critical track component widely used in ballasted railway tracks. The performance, endurance and quality of prestressed concrete sleepers can detrimentally affect the serviceability and durability of a railway track. An optimal production method is an important criterion underpinning [...] Read more.

Prestressed concrete sleeper is a safety-critical track component widely used in ballasted railway tracks. The performance, endurance and quality of prestressed concrete sleepers can detrimentally affect the serviceability and durability of a railway track. An optimal production method is an important criterion underpinning quality and durability over the entire service life of prestressed concrete sleepers. At present, the research work of the sleeper mainly focuses on the dynamic load, bearing capacity and structural design method, etc. However, there exists a lack of research on the specific advantages and disadvantages of the sleeper production process and the improvement of the sleeper process research. This study is the world’s first to collect and analyse the technical data and characteristics of modern production methods of prestressed concrete sleepers, including the long-line system method, pre-tensioned long-mould flow method, pre-tensioned short-mould flow method, post-tensioned short-mould flow method and instant-demoulded short-mould flow method. The precautions for these prestressed concrete sleepers are highlighted in the paper as well. The research results show that the long-line system method, pre-tensioned short-mould flow method, post-tensioned short-mould flow method and instant-demoulded short-mould flow method have a higher automation level and lower efficiency than the pre-tensioned long-mould flow method. The production method of the pre-tensioned long-mould flow method has high efficiency and low cost of equipment, but more workers are needed. Through a comparative analysis, this paper also determines the environmental impacts and provide new references and suggestions for the development and progress of sleeper production technologies. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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21 pages, 6967 KiB

Open AccessArticle

Chemical, Thermal, and Rheological Performance of Asphalt Binder Containing Plastic Waste

by Rosa Veropalumbo, Francesca Russo, Cristina Oreto, Giovanna Giuliana Buonocore, Letizia Verdolotti, Herminio Muiambo, Salvatore Antonio Biancardo and Nunzio Viscione

Sustainability 2021, 13(24), 13887; https://doi.org/10.3390/su132413887 - 15 Dec 2021

Cited by 8 | Viewed by 2785

Abstract

In order to meet the environmental needs caused by large plastic waste accumulation, in the road construction sector, an effort is being made to integrate plastic waste with the function of polymer into asphalt mixtures; with the purpose of improving the mechanical performance [...] Read more.

In order to meet the environmental needs caused by large plastic waste accumulation, in the road construction sector, an effort is being made to integrate plastic waste with the function of polymer into asphalt mixtures; with the purpose of improving the mechanical performance of the pavement layers. This study focuses on the effect of a recycled mixture of plastic waste on the chemical, thermal, and rheological properties of designed asphalt blends and on the identification of the most suitable composition blend to be proposed for making asphalt mixture through a dry modification method. Thermo-gravimetric analysis, differential scanning calorimetry, and Fourier transform infrared spectroscopy analysis were carried out to investigate the effect of various concentrations and dimensions of plastic waste (PW) on the neat binder (NB). The frequency sweep test and the multiple stress creep and recovery test were performed to analyze the viscoelastic behavior of the asphalt blends made up of PW in comparison with NB and a commercial modified bitumen (MB). It has been observed that the presence of various types of plastic materials having different melting temperatures does not allow a total melting of PW powder at the mixing temperatures. However, the addition of PW in the asphalt blend significantly improved the aging resistance without affecting the oxidation process of the plastic compound present in the asphalt blend. Furthermore, when the asphalt blend mixed with 20% PW by the weight of bitumen is adopted into the asphalt mixture as polymer, it improves the elasticity and strengthens the mixture better than the mixture containing MB. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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17 pages, 1400 KiB

Open AccessArticle

Machine Learning Application to Eco-Friendly Concrete Design for Decarbonisation

by Abigail Lavercombe, Xu Huang and Sakdirat Kaewunruen

Sustainability 2021, 13(24), 13663; https://doi.org/10.3390/su132413663 - 10 Dec 2021

Cited by 12 | Viewed by 3504

Abstract

Cement replacement materials can not only benefit the workability of the concrete but can also improve its compressive strength. Reducing the cement content of concrete can also lower CO₂ emissions to mitigate the impact of the construction industry on the environment and [...] Read more.

Cement replacement materials can not only benefit the workability of the concrete but can also improve its compressive strength. Reducing the cement content of concrete can also lower CO₂ emissions to mitigate the impact of the construction industry on the environment and improve energy consumption. This paper aims to predict the compressive strength (CS) and embodied carbon (EC) of cement replacement concrete using machine learning (ML) algorithms, i.e., deep neural network (DNN), support vector regression (SVR), gradient boosting regression (GBR), random forest (RF), k-nearest neighbors (kNN), and decision tree regression (DTR). Not only is producing an optimal ML model helpful for predicting accurate results, but it also saves time, energy, and costs, compared to conducting experiments. Firstly, 367 pieces of experimental datasets from the open literature were collected, in which cement was replaced with any of the cementitious materials. Secondly, the datasets were imported into the ML models, whose parameters were tuned by the grid search algorithm (GSA). Then, the prediction performance, the coefficient of determination (R²), the prediction accuracy, and the root mean square error (RMSE) were employed to indicate the prediction ability of the ML models. The results demonstrate that the GBR models perform the best prediction of the CS and EC. The R² of the GBR models for predicting the CS and EC are 0.946 and 0.999, respectively. Thus, it can be concluded that the GBR models have promising abilities for design assistance in cement replacement concrete. Finally, a sensitivity analysis (SA) was conducted in this paper to analyse the effects of the inputs on the CS and EC of the cement replacement concrete. Pulverised fuel ash (PFA), blast-furnace slag (GGBS), Expanded perlite (EP), and Silica fume (SF) were noticed to affect the CS and EC of cement replacement concrete significantly. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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14 pages, 4274 KiB

Open AccessArticle

Research on the Viscosity-Temperature Properties and Thermal Stability of Stabilized Rubber Powder Modified Asphalt

by Qingwei Ma, Zhongyin Guo, Ping Guo, Fayong Yang and Haibin Li

Sustainability 2021, 13(24), 13536; https://doi.org/10.3390/su132413536 - 7 Dec 2021

Cited by 5 | Viewed by 2646

Abstract

A stabilized rubber powder-modified asphalt was provided for the field of rubber asphalt, and the optimal blending amount of stable rubber powder was determined from indicators, such as penetration, penetration index, ductility, softening point, and viscosity at 135 °C. The viscoelastic curve was [...] Read more.

A stabilized rubber powder-modified asphalt was provided for the field of rubber asphalt, and the optimal blending amount of stable rubber powder was determined from indicators, such as penetration, penetration index, ductility, softening point, and viscosity at 135 °C. The viscoelastic curve was measured, and the thermal storage stability test showed that the stabilized rubber powder-modified asphalt has significant thermal storage stability. The specific surface area, scanning electron microscope, and differential scanning calorimeters were used to analyze the dispersion state and aggregation state of the rubber powder particles in the stabilized rubber powder-modified asphalt, etc. The swelling state and reaction mechanism of the rubber powder in the stabilized rubber powder-modified asphalt have been characterized. The results show that the temperature sensitivity of the asphalt was improved after the stabilized rubber powder was added. The content of the stabilized rubber powder was determined to be 30%, which effectively reduces the viscosity at 135 °C, and the workability is improved; the impact of rubber powder-modified asphalt was less than that of ordinary rubber asphalt, but the temperature should be strictly controlled to ensure the viscosity of stable rubber powder-modified asphalt; the specific surface area comparison test shows that the stable rubber powder has better performance than ordinary rubber powder and asphalt matrix. The advantage of having a larger contact area enhances the compatibility of stabilized rubber powder with asphalt; scanning electron microscopy and differential scanning calorimeters test results show that the stable rubber powder-modified asphalt is mainly based on the compatibility mechanism, and a series of processes, such as oil absorption swelling-high temperature shear-compatible dispersion, occur. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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20 pages, 1898 KiB

Open AccessArticle

Life Cycle Sustainability Assessments of an Innovative FRP Composite Footbridge

by Timothy Jena and Sakdirat Kaewunruen

Sustainability 2021, 13(23), 13000; https://doi.org/10.3390/su132313000 - 24 Nov 2021

Cited by 12 | Viewed by 3731

Abstract

Sustainable construction and the design of low-carbon structures is a major concern for the UK construction industry. FRP composite materials are seen as a suitable alternative to traditional construction materials due to their high strength and light weight. Network Rail has developed a [...] Read more.

Sustainable construction and the design of low-carbon structures is a major concern for the UK construction industry. FRP composite materials are seen as a suitable alternative to traditional construction materials due to their high strength and light weight. Network Rail has developed a prototype for a new innovative footbridge made entirely from FRP with the aim of replacing the current steel design for footbridges. This study conducted a life cycle analysis of this novel composite footbridge design to quantify the cost and environmental benefits. An LCA and LCC analysis framework was used to analyse the environmental impacts and cost savings of the bridge throughout its lifespan from raw material extraction to its end of life. From the results of the LCA and LCC, the FRP footbridge sustainability was reviewed and compared to a standard steel footbridge. Due to the uncertainty of the fibre-reinforced plastic (FRP) structure’s lifespan, multiple scenarios for longevity at the assets-use stage were studied. The study revealed that the FRP bridge offered substantial economic savings whilst presenting potentially worse environmental impacts, mainly caused by the impact of the production of FRP materials. However, our study also demonstrated the influences of uncertainties related to the glass-fibre-reinforced plastic (GFRP) material design life and end-of-life disposal on the whole life cycle analyses. The results show that if the FRP footbridge surpasses its original estimation for lifespan, the economic savings can be increased and the environmental impacts can be reduced substantially. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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25 pages, 27008 KiB

Open AccessArticle

Study on the Aging Resistance of Polyurethane Precursor Modified Bitumen and its Mechanism

by Liang Zhang, Pengfei Li, Guanfeng Hu, Sufeng Zhang, Bin Hong, Haopeng Wang, Dawei Wang and Markus Oeser

Sustainability 2021, 13(17), 9520; https://doi.org/10.3390/su13179520 - 24 Aug 2021

Cited by 14 | Viewed by 2657

Abstract

As an environmentally friendly alternative for the production of high-performance modified asphalt by chemical reactions, a liquid-state polyurethane-precursor-based reactive modifier (PRM) was developed and employed in the asphalt modification. In contrast to the traditional solid bitumen modifier, for example, rubber and thermoplastic elastomers, [...] Read more.

As an environmentally friendly alternative for the production of high-performance modified asphalt by chemical reactions, a liquid-state polyurethane-precursor-based reactive modifier (PRM) was developed and employed in the asphalt modification. In contrast to the traditional solid bitumen modifier, for example, rubber and thermoplastic elastomers, the PRM as a liquid modifier has more significant advantages in reducing energy consumption and improving asphalt performance, which has attracted widespread attention. However, the aging resistance and its mechanism are not clear. In view of this, the aging performance of two PRM-modified bitumen (PRM-70 and PRM-90), under the short-term thermo-oxidative aging, long-term thermo-oxidative aging, and ultraviolet (UV) aging conditions, was investigated through chemical and mechanical methods. The results show that the PRM-90 is more susceptible to the thermos-oxidative aging and UV aging. The use of low-penetration-grade bitumen and ensuring an adequate reaction are beneficial to enhance the aging resistance of PRM-modified bitumen. The impact of aging on high-temperature performance of PRM-modified bitumen is great, followed by the low-temperature performance and the anti-fatigue performance. The mechanic-relevant rheological aging index (RAI) and fracture energy index (FEI) are recommended to evaluate aging properties for PRM-modified bitumen. This study not only provides support for further research on the relationship between the aging properties and mechanical performance of PRM-modified bitumen, but also provides a reference for conducting mechanism analysis. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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16 pages, 3391 KiB

Open AccessArticle

Laboratory Investigation of Compaction Characteristics of Plant Recycled Hot-Mix Asphalt Mixture

by Jiangang Yang, Chen Sun, Wenjie Tao, Jie Gao, Bocheng Huang and Jian Zhang

Sustainability 2021, 13(6), 3005; https://doi.org/10.3390/su13063005 - 10 Mar 2021

Cited by 11 | Viewed by 2153

Abstract

In this study, the compaction characteristics of recycled hot-mix asphalt (RHMA) were evaluated using the void content (VV), compaction energy index (CEI), slope of accumulated compaction energy (K), and lock point (LP). Then, the effects [...] Read more.

In this study, the compaction characteristics of recycled hot-mix asphalt (RHMA) were evaluated using the void content (VV), compaction energy index (CEI), slope of accumulated compaction energy (K), and lock point (LP). Then, the effects of the compaction parameters, including the gradation of the RHMA, reclaimed asphalt pavement (RAP) content, temperature of gyrations, and number of gyrations, on the compaction characteristics of RHMA were investigated. An orthogonal experiment was designed and the data collected were analyzed via range analysis; then, a regression model was generated relying on a quadratic polynomial. Furthermore, the regression model was used for the comparison and prediction of the mixture’s compactability during the material design. Finally, the compaction mechanism of RHMA was discussed from the perspective of the void content of RAP particles. The results showed that a finer aggregate gradation, a higher gyration temperature, a greater number of gyrations, and a higher RAP content were effective for increasing the compactability of RHMA. The range analysis results suggest that the gradation of RHMA has the greatest influence on compactability, followed by the RAP content. The RAP aggregate cannot diffuse to a new mixture completely, so the remained RAP particle reduces the void content of RHMA. Therefore, a higher RAP content up to 50% can help RHMA to achieve the designed void content with higher efficiency. Full article

(This article belongs to the Special Issue Sustainable Organic Materials Used in the Construction Sector)

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