Effect of aggregates and layer height on the acoustic absorption of pervious concrete

We analyzed pervious concrete with regard to its acoustic absorption behavior. For this purpose, we casted pervious concrete test series using different coarse aggregates varying in its shape (crushed vs. rounded) or size (2-5 mm (0.08 0.20 in.), to 8-11 mm (0.31 0.43 in.)). All test series were compacted in a gyratory compactor with variable intensities to reach an aimed total porosity of 25.0, 22.5, and 20.0 % by vol. and thus to evaluate the effect of the amount of the porosity beside the effects of aggregate shape and geometry on the acoustic absorption. Furthermore, we quantified the effect of the pervious concrete layer height on its acoustic absorption by a stepwise alternate cutting and measuring of the specimens at layer heights from 100 mm (3.94 in.) to 40 mm (1.74 in.). We used the first maximum of the absorption coefficient, its frequency, and the sound wave propagation speed in the porous material to evaluate the acoustic absorption. In general, a higher porosity, bigger grain size, the use of rounded aggregates and higher cylinder height increases the acoustic absorption. A characteristic pore structure factor was found, which allows a prediction of the frequency in dependence of the cylinder height.