A new type of microperforated panel absorber (MPA) that has holes of multiple sizes instead of uniform size is experimentally investigated. The objective of this research is to obtain a wide band sound absorber that is thin, durable, clean, and healthy. The first step of this research is to investigate the performance of MPA having two different sizes and the same numbers of holes. The investigation is then extended to a combination of three and four different sizes of holes with various spatial arrangements and various densities or percentages of each size of holes on panels. The hole diameters vary between 0.4 mm and 1 mm and the cavity depths vary between 10 mm and 15 mm. The results show that a multi-size MPA enhances the absorption rate and widens the effective frequency band. This study also proves that a multi-size MPA when compared with a uniform size MPA has better sound absorption characteristics with respect to the absorber thickness and absorption bandwidth. These results make it possible to build thin, single layer sound absorbers that are effective in wide frequency bands and have the advantage of being tunable.
In this study, the development of carbonation resistance in blast furnace slag (BFS) mortar when using silicone oil (SO) is investigated. Moreover, the influence of SO on drying shrinkage and frost resistance are investigated. The results indicate that SO tends to improve the carbonation resistance of BFS blended mortar and reduces drying shrinkage; however, it decreases frost resistance. The water repellency of SO has a positive effect on carbonation and drying shrinkage. Furthermore, there is a possibility that SO prevents the consumption of calcium hydroxide (CH) by carbonation and hydration in portland blast furnace slag cement type B (BB) samples. SO exists in the form of oil droplets in hardened cement pastes and inhibits the relaxation of water pressure at freezing. This is a probable cause for why SO decreases frost resistance.
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