Investigation and improvement of sound absorption performance in plaster surfaces prepared with crushed brick aggregate used in historical buildings

In historical buildings, it can be necessary to enhance the sound absorptive properties of plaster surfaces to improve interior acoustic conditions. The sound absorption performance of plaster layers prepared with crushed brick aggregate was investigated to enhance the material properties of historical buildings. The effects of gradation type, binder properties, and additive materials on sound absorption were examined. For comprehensive analyses, sound absorption, open porosity, compressive and flexural strengths, density, capillary water absorption, and luminance factor tests were conducted to determine the effects of content changes. Aggregate analysis results show that using a uniformly graded aggregate rather than a well-graded aggregate can enhance sound absorption while reducing compressive and flexural strengths, and that particle sizes between 0 and 1 mm can reduce sound absorption at high frequencies. Binder analyses indicate that increasing the binder ratio can reduce sound absorption while increasing mechanical strength, and using a natural hydraulic lime binder or a calcium lime binder instead of a portland cement binder can improve the sound absorption. In the additive analysis, incorporating flax fiber or crumb rubber into the mixture can enhance sound absorption between 100 and 630 Hz, and flax fiber is generally more effective than crumb rubber at high frequencies. Mortar mixture types were recommended based on test results to obtain high sound absorption, and analysis results demonstrate that plaster content modifications reduced the estimated reverberation time in the case study of a room. This research showed that sound absorption can be remarkably increased by modifying the mixtures.