FIA 2018 XI Congreso Iberoamericano de Acústica; X Congreso Ibérico de Acústica; 49º Congreso Español de Acústica -TECNIACUSTICA’18- 24 al 26 de octubre AN EXPERIMENTAL STUDY OF THE INFLUENCE OF MOISTURE CONTENT IN ACOUSTIC ABSORPTION OF POROUS CONCRETE PACS: 43.50.Gf Enrique Ramis 1 , Matheus Pereira 1 , Fernando G. Branco 1 , Luís Godinho 1 , Paulo Amado Mendes 1 1 ISISE, Departamento de Engenharia Civil, Universidade de Coimbra Rua Luís Reis Santos, Pólo II da FCTUC, 3030-788, Coimbra, Portugal E-Mail: { eramiscla@uc.pt, uc2016211184@student.uc.pt, fjbranco@dec.uc.pt, lgodinho@dec.uc.pt, pamendes@dec.uc.pt } Keywords: Moisture effect. Concrete acoustic barriers. Sound absorption. Impedance tube method ISO 10534-2. Expanded clay. ABSTRACT This work presents a study of the variation in the acoustic absorption characteristics of a material widely used in acoustic barriers according to the variation of the humidity and the amount of water retained inside. To analyse this behavior, an experimental monitoring of the normal incidence absorption coefficient for consolidated samples with different aggregate grain size, thickness and quantity of cement was made. Results reveal an important influence of moisture in the sound absorption of tested samples. RESUMEN Este trabajo presenta un estudio de la variación en las características de absorción acústica de un material ampliamente utilizado en barreras acústicas de acuerdo con la variación de la humedad y la cantidad de agua retenida en el interior. Para analizar esto, se realizó un monitoreo experimental del coeficiente de absorción de incidencia normal para muestras consolidadas con diferente tamaño de grano agregado, espesor y cantidad de cemento. Los resultados revelan una influencia importante de la humedad en la absorción del sonido de las muestras analizadas. 1. INTRODUCTION Porous materials based on concrete are generally used as an engineering solution for the absorption of sound outdoors, for example, in acoustic barriers. However, the sound absorption provided by such materials can be influenced by atmospheric conditions, and in particular by the presence of water (due to rain). Although this is known, scarce publications exist quantifying the variation of the absorption properties in the presence of humidity. The present work aims to contribute to enhance the knowledge on this topic, and shows a study of the variation in