ORIGINAL ARTICLE Porosity–density relations in stone and brick materials Christopher Hall • Andrea Hamilton Received: 18 July 2013 / Accepted: 5 December 2013 Ó RILEM 2013 Abstract The open porosity of a specimen of stone or brick material is often measured using a gravimetric method based on Archimedes’ principle. This widely used technique also allows both the bulk density and the solid density of the specimen to be determined, although the solid density is not often reported. We discuss the relation between the porosity and density, both for single specimens and for groups of specimens of similar materials, using for illustration data on limestones, sandstones and fired-clay bricks. The significance of the solid density can be overlooked but it is informative both as a material property and as a method of identifying errors in data. We emphasize how the solid density depends on mineralogy and on closed porosity. Keywords Porosity  Density  Fired-clay brick  Limestone  Sandstone 1 Introduction The relationship between the bulk density q b and the volume–fraction porosity f may seem to be of little interest since the equation q b ¼ Cð1  f Þ; ð1Þ with C ¼ q s ; the solid density, is exact for any single sample of material. Equation 1 is the basis of the gravimetric or Archimedes method of determining the porosity of inorganic construction materials, a method which goes back at least to Purdy and Moore [1], and which is still widely used. Often the porosity alone is reported, sometimes the porosity also with the bulk density but rarely with the solid density. When Eq. 1 is applied to groups of similar materials, such as a set of limestones or a set of production bricks, the solid density provides useful information on the mineral composition and microstructure. Similar analyses on some UK fired-clay bricks are presented in [2] (see also [3]), and then discussed more generally in [4]. Now we discuss porosity–density relations in more detail to draw attention to some overlooked features of Eq. 1, especially the significance of the quantity C, and to review porosity– density data on stone and brick materials. 2 Methods In the gravimetric method, three independent quanti- ties are measured. These are the dry weight w d , the C. Hall (&) School of Engineering, University of Edinburgh, Edinburgh EH9 3JL, UK e-mail: christopher.hall@ed.ac.uk A. Hamilton Department of Civil and Environmental Engineering, University of Strathclyde, Glasgow G4 0NG, UK e-mail: andrea.hamilton@strath.ac.uk Materials and Structures DOI 10.1617/s11527-013-0231-1