ABSTRACT
Cold-In place-Recycled (CIR) pavements are an environmentally friendly option for road rehabilitation operations on aged pavements. These pavements are generally employed as base layers, and a surface treatment is performed on them. However, the design of new additives and enhancements in the technique for constructing CIR pavements have enabled such pavements to be used as wearing courses in some cases. In this context, research on the functional characteristics of CIR pavements is required for characterizing their performance and, therefore, broaden their knowledge and use as a noise mitigation measure. The aim of this study is to analyze some of these functional characteristics: tire/pavement sound levels, texture, and dynamic stiffness. An experimental test track section was evaluated during the pavement curing process (very short term) by means of laboratory and field auscultation. Different measurement campaigns were conducted at different stages of the pavement curing process. According to our results, the changes in the pavement during curing lead to higher tire/pavement sound levels due to the evolution of the dynamic stiffness of the pavement. The increase in tire/pavement noise levels is mainly located at the peak frequencies (800-1250 Hz) of the sound spectra, with values from 76.2 dB(A) to 81.5 dB(A) at 800 Hz. The differences among the mean values of the macrotexture (Mean Profile Depth - MPD) do not explain the different overall tire/pavement noise levels measured at the different stages of curing. However, the texture spectrum undergoes an evolution. The initial texture levels, with wavelengths between 100 mm and 500 mm decrease during the curing process.
ABSTRACT
Tire/pavement noise is produced by the interaction between a tire and the road surface. Complex noise generation mechanisms are involved in this process. Dynamic stiffness (or mechanical impedance) is considered as a related reduction/amplification mechanism. Despite its potential importance, in conventional hot bituminous mixtures this mechanism has little influence on tire/pavement noise. This is because the dynamic stiffness of tire treads is significantly lower than that of the hot bituminous mixes (conventional road surfaces). This paper presents a field assessment of the dynamic stiffness of five experimental sections with different characteristics: from the environmentally friendly mixes such as the Cold-In place-Recycled (CIR) pavement to the gap graded hot bituminous mixtures with crumb rubber (CR) from end of life tires (ELTs). The obtained dynamic stiffness spectra are fitted using a Boltzmann Sigmoid function. The relationships between the fitting coefficients and a few pavement construction characteristics are assessed in order to model the pavement dynamic stiffness as a function of these characteristics. In addition to dynamic stiffness, several surface characteristics such as the Close ProXimity (CPX) sound levels from the tire/pavement interaction, macrotexture in terms of the Mean Profile Depth (MPD), unevenness in terms of the International Roughness Index (IRI), and acoustic absorption are studied. According to our results, lower dynamic stiffness values are related to lower noise levels at high frequencies. No relationship was observed between the low dynamic stiffness values and noise attenuation at medium frequencies in this research work.
ABSTRACT
Environmental noise is a worldwide problem that has an adverse effect in the quality of life of urban population. Some work has shown that there is a correlation between environmental noise and health issues as sleep disturbance or annoyance. This study presents the time evolution of a test track fabricated with an asphalt mixture with 20% of crumb rubber by weight of bitumen, added by the wet process. A complete surface characterization has been performed by determining tire/pavement sound levels, road texture profiles, in-situ dynamic stiffness and sound absorption of compacted and extracted sample cores. Two measurement campaigns were performed: just after mixture laying and after 3 years in service. This study confirms that the use of crumb rubber as a modifier of bituminous binders (CRMB) can improve the pavement characteristics: gap-graded mixtures with crumb rubber can be used in the action plans as urban rehabilitation measure to fight noise pollution. However, this noise reduction seems to decrease with age at a rate of approximately 0.15 dB(A) per year.
