On the use of lightweight mortars for the minimization of impact sound transmission Fernando G. Branco a,⇑ , Luís Godinho b a INESC – Coimbra, Department of Civil Engineering, University of Coimbra, Portugal b CICC, Department of Civil Engineering, University of Coimbra, Portugal highlights  Development of technical solutions for improving impact sound insulation.  Development of lightweight mortar underlays to reduce impact sound transmission.  Expedite and low-cost test methods for quantifying impact sound reduction. article info Article history: Received 13 August 2012 Received in revised form 5 March 2013 Accepted 1 April 2013 Available online 4 May 2013 Keywords: Impact sound reduction Simplified testing method Lightweight mortars abstract Most recent European acoustic design codes and regulations establish a maximum value for impact sound insulation on pavement slabs. These requirements demand the implementation of technical solu- tions such as floating floors, with the introduction of a resilient layer under the finishing pavement layer. Technical solutions such as floating concrete slabs (placed over synthetic foam or natural fibers layers), or floating pavements (like wooden floors built over synthetic foam layers) became quite common on recently built constructions. A possible alternative solution to floating pavements is the use of light- weight soft layers, applied over the structural concrete slab. These lightweight materials may present high quality results on the reduction of impact sound transmission. In the present work, lightweight mor- tar slabs were tested, and the impact sound insulation for different materials was quantified. Different types of cement mortar containing expanded polystyrene, expanded cork and expanded clay granulates were compared. The acoustical performance of these solutions was evaluated through laboratory tests, using an acoustic chamber with small dimensions, which allows comparing several solutions, on similar test conditions, in an expedite way. The influence of the type floor covering used over the lightweight mortar layer was also analysed. Different types of materials were tested. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Along the last decades, the requirements concerning comfort and safety in buildings have increased substantially. Indeed, tech- nical standards and building regulations all over Europe impose stricter demands than before, requiring the development of more advanced technical construction solutions. To ensure the best performance on acoustic insulation, against either airborne or impact sounds, research is necessary in two do- mains: the development of new materials and systems to imple- ment higher acoustic insulation in buildings, and also testing methods to characterize their acoustic performance. The standard characterization of impact sound reduction solu- tions requires the application of the test methods defined in stan- dards EN ISO 140-8 [1] and ISO 717-2 [2], and the requirements to be met by the test laboratory must follow standard ISO 140-1 [3]. According to the standard procedures, the test must be performed on a reference reinforced concrete slab 140 mm thick (40 mm, +20 mm), presenting a minimum surface area of 10 m 2 . The test specimen is subjected to standard sequences of impacts, in differ- ent points of the slab, and the sound level in the receiving chamber, located under the slab, is registered. The impact sound reduction is then quantified as the difference between the registered sound lev- els for two testing conditions: the reference slab tested without any coating, and the technical solution whose performance is being characterized. The analysis is carried out in 1/3 octave bands or oc- tave bands. The standard procedure requires high volume testing 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.04.001 Abbreviations: AC, expanded cork granulates size 3/10; ALF, expanded clay granulates size 2/4; ALG, expanded clay granulates size 3/8; APE, expanded polystyrene granulates; BET, standard weight concrete. ⇑ Corresponding author. E-mail address: fjbranco@dec.uc.pt (F.G. Branco). Construction and Building Materials 45 (2013) 184–191 Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat