Water content dependence of the porosity, density and thermal capacity of laterite based bricks with millet waste additive Harouna Bal a , Yves Jannot b,⇑ , Nathan Quenette b , Alain Chenu b , Salif Gaye a a LEA, BP 5085 Dakar Fann, Senegal b LEMTA, Nancy-Université, CNRS, 2, Avenue de la Forêt de Haye, BP160, 54504 Vandoeuvre Cedex, France article info Article history: Received 6 September 2010 Received in revised form 21 December 2011 Accepted 23 December 2011 Keywords: Composite porous medium Humidity Model Porosity Density Thermal capacity abstract Millet waste is traditionally and empirically mixed with laterite for bricks fabrication in Sahelian coun- tries, particularly in Senegal. The aim of this paper was to characterize the porosity, the density and the thermal capacities of these bricks as a function of their water and millet contents. Samples having ﬁve different millet mass contents Y (from 0 to 0:122 kg mi kg 1 la ) with dimensions 10  10  3 cm 3 were ﬁrst fabricated. A pycnometer suited to the samples dimensions was constructed and calibrated. Then, it was used to measure the porosity of the ﬁve dried samples. An asymmetrical hot plate device was used to measure the thermal capacity of these samples with their water content varying from 0 to a maximum value of 0:1 kg dm kg 1 w . An adapted device was developed to prevent water evaporation on the lateral faces of the samples. Both density and thermal capacity were modeled and the experimental results were processed to evaluate separately the density and the thermal capacity of laterite and of millet. The mod- els enabling the estimation of the density and of the thermal capacity of the samples as a function of the millet and water contents was found to be in good agreement with the experimental results. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Adding an insulating component into a building material is one of the simplest process to improve its thermal insulating proper- ties. This process is traditionally used in several Sahelian countries particularly in Senegal where millet waste is added to laterite to make bricks used as building materials. Millet waste addition is ex- pected to highly modify laterite based bricks thermal capacity since it is a very low density material (cf. picture on Fig. 1). It is available in great quantities at a very low cost. Some studies concerning the thermal properties of earth-based materials have already been published. Bouguerra et al. [1] studied the inﬂuence of the water content on the thermal properties of wood cement-clay based composites. Nevertheless, only thermal effusivity was investigated. Adam and Jones [2] studied the ther- mal properties of stabilized soil building blocks but they did not investigate the inﬂuence of the water content. Meukam et al. [3] studied the evolution of the thermal properties of stabilized soil building blocks with pouzzolane or sawdust addition as a function of the water content. Nevertheless, no interpretation of the results based on the structure of the material was presented and no pre- dicting model was proposed. Khedari et al. [4] studied the thermal properties of coconut ﬁber-based soil–cement blocks and Omubo- Pepple et al. [5] studied cement stabilized lateritic bricks with sea shell addition but the inﬂuence of the water content was not inves- tigated in these two studies. The same remark may be done con- cerning the work of Goodhew and Grifﬁths [6] concerning unﬁred clay bricks with straw and wood chippings. The aim of this study was ﬁrst to estimate how much the mix- ing of millet waste with laterite modiﬁes the thermal capacity compared to pure laterite bricks. Since these bricks are use for building and are exposed to very different meteorological conditions, it is also very important to know how their thermal properties vary with the water content. The variation of their thermal capacity with the water content has thus been experimentally determined. Finally, to be able to predict their thermal behavior in various meteorological conditions, a model enabling the calculation of the density and of the thermal capacity as a function of the millet waste mass content Y and of the water content X has been devel- oped and experimentally validated. Another work studying the thermal conductivity in the same manner will be further presented. 2. Experimental devices and principle of the methods 2.1. Samples preparation The laterite powder used was extracted directly from the soil in the region of Matam in north Senegal, with a maximum grain size of 1 mm. The laterite powder is ﬁrst mixed with a chosen quantity of millet waste. Then water is added until mixing lead to a consistent paste. This paste is pressed in a moud with internal 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.12.063 ⇑ Corresponding author. Tel.: +33 383595627; fax: +33 383595551. E-mail address: yves.jannot@ensem.inpl-nancy.fr (Y. Jannot). Construction and Building Materials 31 (2012) 144–150 Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat