Measuring of noise and wearing of quiet surfaces

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96, [7]
TKK dissertations, 7
When using surfaces with special qualities, there is a need for tools to assess these qualities. Two methods, SPB (Statistical Pass-by) and CPX (Close Proximity), have been used for testing the noise properties of the surfaces in the other countries. Both of these methods had to be modified to suit the Finnish environment. SPBmod-method adheres to the ISO-standard quite closely. It was decided that heavy vehicles are not included in the test, as stipulated in the standard. The normalisation speeds used are 60, 80 and 100 km/h which are not the same as in the standard. There is only a draft standard for the CPX-method. In this standard it is suggested that four different tyres representing different vehicle types should be used. In Finland the method was modified so that measurements are done with one slick tyre (ASTM E 524). This method is called CPXmod. In this research it was recommended that SPBmod-method should be used. Noise levels of the different products can be expressed by comparing them to the virtual references. Virtual reference is an average of several SPBmod-results of different SMA 16 surfaces of different ages. Virtual references are: 60 km/h, 76 dB; 80 km/h, 80 dB; 100 km/h, 83.5 dB. According to the standard, measurements can be taken when the air temperature is 5-30 °C. It was noticed that in Finland there is a seasonal variation in the results. The variation is smaller during the summer months. That is why it was suggested that in Finland the measurements should be taken during June, July and August. Standard also suggests that results should temperature corrected to the reference temperature (20 °C). There is also no common understanding at the moment about the formula of the temperature correction. That is why it is suggested that the measurements should be taken as close to the reference temperature as possible. Measurements should be taken after the first winter. Because of studded tyres the wearing of surfaces has been a problem in Finland. With the "normal" asphalt surfaces a commonly used method is the Prall method. It was found out that this test does not predict almost at all the wearing of quiet surfaces. One problem was that the test was too "rough" for the core samples and they got broken during the test. The Prall test was modified a little to keep the samples whole but the result was the same. It did not predict the wearing measured from the roads. The only way to evaluate the wearing of the quiet surfaces is to compare the profilometer results with the results of the "normal" asphalt products on the same road. Based on the test roads it seems that during the HILJA-project contractors have succeeded in developing surfaces which have good noise reducing qualities (even over 6 dB less noise than the virtual reference) and do not wear more than the normally used asphalt surfaces on the same roads. The enquiries show that there is still need and willingness to use these surfaces in future.
asphalt, surface, noise, wearing, measuring method, SPB, CPX, Prall
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