Acoustically efficient concretes through engineered pore structure

Three classes of specialty cementitious materials were evaluated for their potential benefits in sound absorption including a Foamed Cellular Concrete (FCC) with density ranging from 400 – 700 kg/m³, Enhanced Porosity Concrete (EPC) incorporating 20-25% open porosity, and a Cellulose Cement Composite (CCC) with density 1400 – 1700 kg/m³. Cylindrical specimens of these materials were tested for acoustic absorption in an impedance tube. The FCC specimens showed absorption coefficients ranging from 0.20 to 0.30, the higher value for lower density specimens. The closed disconnected pore network of FCC hinders sound propagation, thereby resulting in a reduced absorption, even though the porosity is relatively high. The most beneficial acoustic absorption was observed for EPC mixtures. When gap-graded with proper aggregate sizes, these no-fines EPC mixtures dissipate sound energy inside the material through frictional losses. The cellulose fiber cement composites use cellulose fibers at high volume fractions (~7.5%), which are believed to provide continuous channels inside the material where the sound energy can be attenuated. By engineering the pore structure (by careful aggregate grading as in EPC, or incorporating porous inclusions like morphologically altered cellulose fibers) cementitious materials that have the potential for significant acoustic absorption could be developed.