Application of Dechlorinated MSWI Fly Ash in Asphalt Mixtures

Special Article - Chlorine

Austin Environ Sci. 2021; 6(2): 1058.

Application of Dechlorinated MSWI Fly Ash in Asphalt Mixtures

Hu T1,3, Zhao K2, Chen D1,3 and Hu Y1,3*

¹Thermal and Environmental Engineering Institute, Tongji University, 1239 Siping Road, Yangpu District, Shanghai, China

²Electromechanical Design and Research Institute, Xuhui District, Shanghai, China

³Shanghai Engineering Research Center of Multi-source Solid Wastes Co-processing and Energy Utilization, 1239 Siping Road, Yangpu District, Shanghai, China

*Corresponding author: Yuyan Hu, Professor, Institute of Thermal and Environmental Engineering, Tongji University, 1239 Siping Road, Yangpu District, Shanghai, China

Received: May 19, 2021; Accepted: June 14, 2021; Published: June 21, 2021


The application of Municipal Solid Waste Incineration (MSWI) fly ash in asphalt mixtures is an efficient way to utilize fly ash. The feasibility of applying various kinds of dechlorinated fly ash in asphalt mixtures was comprehensively discussed in the study. The effects of types and amounts of dechlorinated fly ash on the performances of prepared asphalt mixtures were explored. Additionally, their environmental risks and economic values were further evaluated. The water absorption coefficient and porosity of fly ash-asphalt mixtures were respectively in the ranges of 0.15-0.5% and 3-4%, which met the application requirements of asphalt. The replacement of Raw Fly Ash (RFA) and Dechlorinated Fly Ash (DFA) improved Marshall stability, split strength, and Tensile Strength Ratio (TSR) of asphalt mixtures. DFA realized the more significant improvements. The leaching concentrations of heavy metals in all the prepared asphalt mixtures were lower than the detection limit, indicating that there was no risk of leaching toxicity.

Keywords: Dechlorinated MWSI fly ash; Asphalt mixture; Water stability; Leaching of heavy metals


Due to the rapid economic development in China, the production of municipal solid wastes in China has increased year by year. Since 2015, China has replaced the USA and became the country with the largest waste production in the world [1,2]. Municipal Soil Waste Incineration (MSWI) technology with significant advantages, such as volume reduction, stabilization and resource utilization, has been developing rapidly in recent years in China. Municipal Soil Waste Incineration produces fly ash (MSWI fly ash), which is equivalent to 3 to 5% of the mass of original wastes [3-5]. Incinerated fly ash contains heavy metals (such as Zn, Cu, Pb, and Cr), a large amount of soluble salts (mainly chlorides), and persistent organic pollutants (such as dioxins). It is an internationally recognized hazardous waste [6-10]. In the HJ1134-2020 standard [11], the recommended fly ash treatment processes includes washing, curing/stabilization, molding technology, low-temperature thermal decomposition, high-temperature sintering, high-temperature melting, etc. and it is pointed out that the soluble chlorine content in fly ash treatment products should be controlled [11,12]. The most widely used dechlorination method is the washing process, which can not only remove soluble chlorides, but also bring heavy metals and other ions contained in fly ash into water to form intractable wastewater with high concentrations of salts [13,14]. In this study, the heat treatment method was used as the dechlorination pretreatment way of fly ash since it could largely remove soluble and insoluble chlorides and wrap heavy metals in a silicate-based glass matrix in order to achieve the purpose of stabilizing heavy metals [6].

In accordance with the JTG F40-2004 standard [15], it is recommended that fly ash, steel slag, ore slag, etc. can be used as fillers together with mineral powder in asphalt mixtures. Since physical and chemical properties of MSWI fly ash are close to those of coal fly ash and ore slags, some researchers have proposed to apply MSWI fly ash in asphalt mixtures in recent years [16-18]. In the study, the feasibility of the application of fly ash in asphalt mixtures was evaluated in two aspects: the pavement performance and leached heavy metals of asphalt mixtures.

Materials and Methods

Experimental materials

Raw Fly Ash (RFA) samples used in the experiment were from a grate furnace in an incineration plant in East China, where the process utilizing quicklime, activated carbon and bag filter was used for flue gas purification. RFA samples were placed in an oven at 105±5 °C and dried for 24h to remove water. After grinding and filtering through a 150-mesh sieve, pebbles, gravels and other impurities with larger particle diameter were removed. The chemical composition of RFA samples is shown in Table 1. Other physical and chemical properties of RFA samples were compared with mineral powder and dechlorinated fly ash in the following sections. In the experiment, natural basalt produced by Raofeng Stone Sale Company in Jinshan District, Shanghai was used as the aggregate and limestone ore powder (≥99.9%) was used as slag powder. In addition, SK 70# ordinary asphalt for pavement was used as asphalt.