Influence of Aggregate Size and Gradation on Acoustic Absorption of Enhanced Porosity Concrete

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Title: Influence of Aggregate Size and Gradation on Acoustic Absorption of Enhanced Porosity Concrete

Author(s): Adam Marolf, Narayanan Neithalath, Eric Sell, Kristy Wegner, Jason Weiss, and Jan Olek

Publication: Materials Journal

Volume: 101

Issue: 1

Appears on pages(s): 82-91

Keywords: absorption; aggregate; grading; porosity

Date: 1/1/2004

Abstract:
This paper presents results from an investigation aimed at identifying whether enhanced porosity concrete (EPC) may have the potential to be used for sound mitigation purposes. Toward this end, EPC mixtures were prepared using single-sized aggregates as well as blends consisting of two different aggregate sizes. In addition, mixtures were prepared to determine the influence of sand content and silica fume on the measured acoustic characteristics and mechanical properties of EPC. All mixtures were tested for sound absorption using an acoustic impedance tube and flexural strength using three-point bending. An image analysis procedure was used to characterize the total porosity and the size of the pores for each mixture. Differences in aggregate grading were observed to result in variations in both the acoustic absorption and flexural strength. These variations are directly related to both total porosity and pore size. The results of this research indicate that EPC mixtures with single-sized aggregates provide substantial improvement to sound absorption as compared with conventional concrete. Blending aggregates in correct proportions enables the pore size and overall porosity to be controlled, resulting in an improvement in the acoustic absorption. The influence of specimen length on the frequency at which maximum absorption is achieved is discussed and a simple conceptual model is used to illustrate the influence of pore structure on the sound absorption properties.