# Laboratory Evaluation of Wear Particle Emissions and
###### Abstract  
This study aims to evaluate the tire-road-wear particles (TRWPs) and suspended dust generated based on the nominal maximum aggregate size (NMAS) of the polymer-modified stone music asphalt (SMA) mixtures indoors. The SMA mixtures containing styrene butadiene styrene (SBS) polymer and the NMASs of 19, 13, 10, 8, and 6 mm were used. Dust was generated from the wear of the tires and the pavement inside the indoor chamber by using the laboratory tire-road-wear particle generation and evaluation tester (LTRWP tester) developed by Korea Expressway Corporation (KEC). In this method, a cylindrical asphalt-mixture specimen rotates in the center, and a load is applied using three tires on the sides of the test specimen. During the test, a digital sensor was used to measure the concentration for each particle size. After the test was completed, the dust was collected and weighed. According to the test results, the generated TRWP emissions were reduced by approximately 0.15 g as the NMAS of the SMA mixture decreased by 1 mm. TRWP emissions decreased by 20% when using the 6 mm SMA mixture compared to the 13 mm SMA mixture. For practical application, a predicted equation of TRWP emissions estimation was developed by using the concentration of suspended dust measured by the digital sensor in the LTRWP tester. LTRWP can be used as an indoor test method to evaluate pavement and tire materials to reduce the amount of dust generated from tire and pavement wear. tire-road-wear particle emissions; suspended dust; SMA mixture; nominal maximum aggregate size +
Footnote †: journal: Medical  
determines the relationship between TRWPs and various asphalt mixtures and driving environments is required. TRWPs are generally discussed in terms of their contribution to particulate matter (PM) in the atmosphere and the amount of TRWP emissions [2; 3; 5]. TRWPs refer to the fine particles generated from the wear and tear of road surfaces and tires. Factors affecting the generation of TRWPs include tire characteristics (such as size, tread depth, structure, air pressure, temperature, and contact area), road surface characteristics (such as pavement type, aggregate, binder, texture, porosity, and humidity), vehicle operation characteristics (such as speed, acceleration, and braking), and vehicle characteristics (such as vehicle weight, load distribution, wheel position, power output, steering, braking system, and suspension condition). For example, highways built with asphalt material generate more suspended dust from the friction between tires and the pavement surface compared to highways built with cement material [5]. Among the influencing factors, the nominal maximum aggregate size (NMAS) of pavement determines the road surface condition in contact with tires and has a relatively high impact on TRWP generation [3]. Several studies have analyzed the effect of NMAS on TRWP generation. Some studies have theoretically deduced that smaller NMASs lead to less tire wear. [PERSON] et al. verified through the Cantabro test that asphalt mixtures with small NMASs had higher pavement wear resistance than asphalt mixtures with large NMASs [6]. However, there are also studies with results contradicting this research finding. [PERSON] et al. empirically stated that the larger the NMAS, the higher the wear resistance of the pavement [7]. [PERSON] et al. utilized the Prall test and road simulator to support the aforementioned hypothesis [8]. The contradicting results of these two theories are based on how the conditions of the tires contacting the road pavement surface have been considered [9]. In the relationship between the NMAS and the mean profile depth (MPD), which describes the texture scale of the pavement surface, the MPD decreases as the NMAS decreases, making the texture of the pavement surface smoother [10]. Therefore, in the case of mixtures of small particles with small NMASs, the contact area between the road surface and the tire increases, which disperses the contact pressure.