| Summary: | The porous concrete layer is an open pore material placed on the noise incident face
of a sound barrier structure on the road. Pore characteristics such as diameter, area and
distribution are the main characteristics of porous concrete different from conventional concrete
and play a dominant role in sound absorption properties. Factors affecting the pore structure of
typical porous concrete have been discussed. The effects of macroscopic properties on sound
absorption properties such as maximum sound absorption coefficient (SAC max), noise
reduction and noise average were reviewed. The porous concrete containing other types of
aggregate such as recycle, waste material, and lightweight in porous concrete innovation were
discussed. Consequently, the effect of thickness, two layers and multiple layers of porous
concrete to improve sound absorption at low frequencies. Finally, the guidances were proposed
for the mixture composition for producing porous layer for good sound absorbing properties
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