Hygrothermal Properties of Raw Earth Materials: A Literature Review

Abstract

Raw earth historic and contemporary architectures are renowned for their good environmental properties of recyclability and low embodied energy along the production process. Earth massive walls are universally known to be able to regulate indoor thermal and hygroscopic conditions containing energy consumptions, creating comfortable interior spaces with a low carbon footprint. Therefore, earth buildings are de facto green buildings. As a result of this, some earthen technologies have been rediscovered and implemented to be adapted to the contemporary building production sector. Nevertheless, the diffusion of contemporary earthen architecture is decelerated by the lack of broadly accepted standards on its anti-seismic and thermal performance. Indeed, the former issue has been solved using high-tensile materials inside the walls or surface reinforcements on their sides to improve their flexural strength. The latter issue is related to the penalization of earth walls thermal behavior in current regulations, which tent to evaluate only the steady-state performance of building components, neglecting the benefit of heat storage and hygrothermal buffering effect provided by massive and porous envelopes as raw earth ones. In this paper, we show the results of a paper review concerning the hygrothermal performance of earthen materials for contemporary housing: great attention is given to the base materials which are used (inorganic soils, natural fibers, and mineral or recycled aggregates, chemical stabilizers), manufacturing procedures (when described), performed tests and final performances. Different earth techniques (adobe, cob, extruded bricks, rammed earth, compressed earth blocks, light earth) have been considered in order to highlight that earth material can act both as a conductive and insulating meterial depending on how it is implemented, adapting to several climate contests. The paper aims to summarize current progress in the improvement of thermal performance of raw earth traditional mixes, discuss the suitability of existing measurement protocols for hygroscopic and natural materials and provide guidance for further researches.

Computational Prediction of Susceptibility to Biofilms Growth: Two-Dimensional Analysis of Critical Construction Details

“…It can be also seen in Figure 12b that moisture is kept around the beam end for a longer period of time after it penetrates through the surface. It happens due to a high value of the hygroscopic moisture content of the wood (0.0342 m 3 •m −3 , see Table 1), which makes it more capable to absorb and retain moisture. Fungi colonization, mold growth, and wood decay might then appear, especially when the relative humidity is kept above 81% and 90%, respectively [53].…”

“…where ρw (kg•m −3 ) is the water density, w (m 3 •m −3 ) is the water content, pv (Pa) is the partial pressure of water vapor in the air, t (s) is the time, Dw (m 2 •s −1 ) is the moisture diffusivity, δp (s) is the water vapor permeability, H (J•m −3 ) is the enthalpy density, T (K) is the temperature, λ (W•m −1 •K −1 ) is the thermal conductivity, Lv (J•kg −1 ) is the latent heat of evaporation of water, and A, B ϵ <0;1> are transition coefficients between the liquid and gaseous phases of water, which give the weight to each phase according to the current moisture content. The model was developed, calibrated, and validated based on experimental results obtained using a laboratory semi-scale experiment.…”

“…The summary is given in Table 1 and Figures 6 and 7. Hygroscopic moisture content (m 3 •m −3 ) 0.0036 0.0342 0.0144 0.0003 see Figure 7 0.0031 see Figure 7 Figure 6 depicts the thermal conductivity of mineral wool and wood fibers as a function of moisture content. These results were obtained experimentally on a set of samples.…”

“…The stringent requirements on thermal insulating properties of building envelopes have resulted in utilization of modern building materials with high thermal resistance such as modern bricks [3,4], autoclaved aerated concretes [5], various types of excellent thermal insulations, or the construction and operation systems of houses have been improved to reach low energy or even passive standards [6,7]. At the same time, old buildings have been retrofitted by means of the addition of extra insulation layers.…”

“…is the water density, w (m3 •m −3 ) is the water content, p v (Pa) is the partial pressure of water vapor in the air, t (s) is the time, D w (m 2 •s −1 ) is the moisture diffusivity, δ p (s) is the water vapor permeability, H (J•m −3 ) is the enthalpy density, T (K) is the temperature, λ…”