United Nations Educational Scientific and Cultural Organization and International Atomic Energy Agency THE ABDUS SALAM INTERNATIONAL CENTRE FOR THEORETICAL PHYSICS MODELING OF HEAT AND MASS TRANSFER IN LATERITIC BUILDING ENVELOPES

Abstract The aim of the present work is to investigate the behavior of building envelopes made of local lateritic soil bricks subjected to different climatic conditions. The analysis is developed for the prediction of the temperature, relative humidity and water content behavior within the walls. The building envelopes studied in this work consist of lateritic soil bricks with incorporation of natural pozzolan or sawdust in order to obtain small thermal conductivity and low-density materials, and limit the heat transfer between the atmospheric climate and the inside environment. In order to describe coupled heat and moisture transfer in wet porous materials, the coupled equations were solved by the introduction of diffusion coefficients. A numerical model HMtrans, developed for prediction of heat and moisture transfer in multi-layered building components, was used to simulate the temperature, water content and relative humidity profiles within the building envelopes. The results allow the prediction of the duration of the exposed building walls to the local weather conditions. They show that for any of three climatic conditions considered, relative humidity and water content do not exceed 87 % and 5% respectively. There is therefore minimum possibility of water condensation in the materials studied. The durability of building envelopes made of lateritic soil bricks with incorporation of natural pozzolan or sawdust is not strongly affected by the climatic conditions in tropical and equatorial regions. MIRAMARE -TRIESTE Introduction Construction materials made from recycled sources are becoming widely available and can minimize a new building's impact on the environment. For home and small commercial buildings, construction using inexpensive natural materials, such as earth blocks, is also becoming more commonplace in many regions in Africa. In terms of the energy performance of a building, the materials used in the building envelope are the most crucial, since the building envelope defines how the building interacts with the external environment. The development of heat transfer analysis for the prediction of the thermal behavior of structural walls is a problem of a fundamental concern in a broad range of engineering applications. The envelope of a building protects the indoor environment from outside. Building components like walls, in service conditions, are subjected to variable climatic conditions, which are different between their exposed sides. The building envelopes are exposed to two different climates, which can create a hygrothermal transfer within their components. Many building walls are made of hygroscopic materials. The building envelope may have moisture sources, people and their activities in case of tanks in attics, water evaporation from the ground if it is not covered, plumbing leaks in wall cavities, etc. It will also have air exchanges into and out of the building volume. In porous building materials, water can be in liquid or gaseous phase. The phase changes and the migration of moisture are always linked to heat transfer. The moisture behavior of exposed building elements has a predominant influence on their durability because water is often the major reason for damage and decay. Therefore, the vapour and liquid transport properties of porous materials are of great practical importance. There are now many numerical models that are capable of describing heat and moisture transfer within the building envelop

Simplified Estimation Method for the Determination of the Thermal Effusivity and Thermal Conductivity Using a Low Cost Hot Strip,” Meas.

Abstract This paper presents the study of a hot strip made of thin rectangular electrical resistance with a thermocouple placed on its centre. The purpose was to simultaneously estimate thermal effusivity and conductivity in a limited time (t 2 < 180 s) using a low cost probe. Heat transfer has been modelled with the quadrupole formalism to simulate the evolution of the temperature at the centre of a hot strip set between two samples of material to be characterized when a heat flux step is applied. Simulation is used to fix the optimal dimensions of a hot strip that behaves as a hot plate (1D transfer) during a minimal time t 1 (>20 s) and that has higher sensitivity to the thermal conductivity between t 1 and t 2 (2D transfer). The thermal effusivity is estimated between 0 and t 1 by minimization of the quadratic errors between the experimental curve and the curve calculated by the classical hot plate model. The thermal conductivity is estimated between t 1 and t 2 but using the complete 2D model. To validate the model and the estimation process, experimental tests were realized on three materials with low diffusivities (a < 2 × 10 −7 m 2 s −1 ) and having typical area of 6 cm × 4 cm and typical thickness of 1.5 cm. Keywords: hot strip, transient method, thermal quadrupoles, effusivity, conductivity, parameter estimation method half-width of the hot strip (m) c s thermal capacity of the hot stri

Performance Evaluation of Newly Developed Sustainable Blocks for Affordable Housing in Malaysia

The thermal design of affordable housing in Malaysia could be ineffective and resulting from this, the majority of their occupants are not satisfied with the thermal comfort levels provided. To overcome this issue of thermal performance of building envelope, the development of sustainable blocks has been done. The blocks have been developed using locally available sustainable waste materials. The materials utilized were mainly procured from agro-industrial waste (oil palm industry) and municipal waste (waste glass). The aim of the research was to provide a better performing material for low cost houses replacing the conventional red clay bricks. In this research, the physical, mechanical and thermal performance of the sustainable building blocks were examined and compared with existing conventional building blocks. The experimental findings revealed that the newly developed Sustainable blocks have better thermal performance as compared to conventional burnt clay bricks. However, the physico-mechanical performance complies with various standard practices thus proving to be a sustainable wall material

Engineering properties, phase evolution and microstructure of the iron-rich aluminosilicates-cement based composites: Cleaner production of energy efficient and sustainable materials

This paper investigates the direct transformation of laterites (natural iron-rich aluminosilicates) to cementitious composites with principal mineral phases being Gismondine and Stratlingite. The effects of particles size distribution and cement content (2 to 8 wt%) on the mechanical properties and microstructure of laterite-cement composites are assessed. Four grades of granulometry with various percentages of fine and coarse particles were considered. The Environment Scanning Electron Microscopy (ESEM), Mercury Intrusion Porosimetry (MIP), Fourier Transformed Infrared Spectroscopy (FT-IR) and X-ray Powder Diffractometry (XRD) were performed after 1, 90 and 365 days, to assess the phase's evolution, mechanical performance and the microstructure of the laterite-cement composites. It is found that fines particles, essentially pozzolanic and amorphous, are responsible for the bonding strength while coarse particles improve the compressive strength. Dense and compact microstructure, water absorption under 18% and flexural strength above 6 MPa (compressive strength > 30 MPa) could be achieved as from 4 wt% of cement making the laterite-cement composite appropriate as building and construction materials. The choice of a highly corroded class of laterite and the selection of the particle size distribution allows the production of optimum composite that is presented as energy-efficient and sustainable. Thus, corroded or indurated laterites are considered as “green metakaolins” which do not require any energy for their transformation unlike clayey materials

Valorisation des briques de terre stabilisées en vue de l'isolation thermique de batiments

Ce travail porte sur la valorisation de matériaux locaux au Cameroun en vue d'améliorer leurs performances en isolation thermique. Il s'agit dans un premier de temps de mettre au point de nouveaux matériaux locaux pour l'enveloppe de bâtiment. La pouzzolane naturelle et la sciure de bois qu'on trouve en abondance au Cameroun ont servi à réaliser des briques de terre plus légères et de meilleures performances thermiques que celles utilisées actuellement dans la construction des maisons. Les résultats expérimentaux portant sur les propriétés therrnophysiques montrent que les briques de terre en latérite+pouzzolane et en latérite+sciure de bois sont plus légères et possèdent de meilleures performances d'isolation thermiques que les briques en latérite simple. Les mesures de la résistance en compression faites sur des BTS incorporant de la pouzzolane naturelle et sur celles incorporant une quantité limitée de sciure de bois donnent des valeurs satisfaisantes. Ces résistances mécaniques sont de même ordre de grandeur que celles des BTS actuellement utilisées. La conductivité thermique et de la diffusivité thermique de ces matériaux augmente avec en teneur en eau. L'augmentation de la teneur en ciment dans les BTS étudiées entraîne une augmentation de la conductivité et une baisse de la diffusivité thermique. La modélisation des transferts couplés de chaleur et d'humidité a permis de déterminer les profils de température, d'humidité relative ct de teneur en eau. à travers une enveloppe de bâtiment faite de ces matériaux. Les faibles teneurs en eau relevées dans les différents cas permettent de conclure qu'il y a une faible possibilité de condensation de vapeur d'eau dans ces matériaux et par conséquent leur durabilité n'est pas mise en cause.In this work, an experimental study was carried out in order to determine the properties of local materials used as construction materials. The thermal properties of lateritic soil based materials were deterrnined. The effect of addition of natural pozzolan or sawdust in lateritic soil brick on the thermal properties is examined. It was shown that the effect of incorporation of natural pozzolan or sawdust is the decreasing of the thermal conductivity and density. The moisture content of these materials can modify their thermal performance. Thus a study of the influence of the water content on the thermal conductivity L and the thermal diffusivity a is presented. The effect of the increasing of cement content is to increase the thermal conductivity and to decrease the thermal diffusivity. The composite materials used for building shielding present sufficient mechanical strength and are suitable for constructions. The analysis is developed for the prediction of the temperature, relative humidity and water content behaviour within the walls. A numerical model HMtrans, developed for prediction of heat and rnoisture transfer in multi-Iayered building cornponents, is used to simulate the temperature, moisture content and humidity profiles within the building envelopes. The results allow the prediction of the duration of the exposed building walls to the local weather conditions. There is therefore minimum possibility of water condensation in the materials studied. The durability of buiIding envelopes made of lateritic soil bricks with incorporation of natural pozzolan or sawdust is not strongly affected by the climate conditions in tropical and equatorial regions.CERGY PONTOISE-BU Les Cerclades (951272104) / SudocCERGY PONTOISE-BU Neuville (951272102) / SudocSudocFranceF