Sound absorption of porous cement composites: effects of the porosity and the pore size

We prepared sound absorbing cement-hydrogel composites using a hydrogel slurry templating technique. We air-dried the wet cement composites containing a varying percentage and size of entrapped hydrogel microbeads to produce a porous cement with a controlled porosity and pore size matching the hydrogel bead distribution. The composites porosity, mass density, compressional strength and sound absorption properties were analysed. SEM analysis showed residual domains from the dried hydrogels beads within the voids created by the hydrogel bead evaporation in the cement samples. The sound absorption coefficient of the composite varied with the templated hydrogel bead size and the overall porosity. The composite samples made with hydrogel beads of average size 0.7 mm showed high absorption coefficients between 0.5 and 0.80 for 500-800 Hz for 50 vol% porosity. Samples produced by templating hydrogels of 1 mm bead size and 70 vol% porosity showed an increased absorption over the sound frequency range 200-2000 Hz. Templating a mixture of the 1.6 and 1.0 mm hydrogel beads slurries with cement slurry did not appear to yield synergistic effect in the sound absorption of the produced porous composites compared to samples made from the separate slurries. The mechanical strength of the obtained porous cement composites decreased with the increase of porosity. Such low fabrication-cost and environmentally friendly composites have a potential to be used as passive sound absorbers by the building and transport industries.