Earth-based Materials Research Articles

Hydric and structural approaches for earth based materials characterization

The earth-based material considered in this work is called Stabilized Earth Bick (SEB). Two distinguish type of SEB were examined: SEB5-Tu and SEB5-Te; their difference refers to the freestone, or the red earth composition. Firstly, a morphological characterization has been done by comparing two different approaches: the water porosity test and the mercury porosimetry which provide access to the material porosity and the pore size distribution.Then, the sorption-desorption isotherm were carefully evaluated for each SEB type. The dynamic gravimetric method was selected for such measurement. Further, theoretical modeling of the sorption desorption isotherm was investigated; here the model parameters allow more accurate interpretation of experimental results.Most of these measurements provided the hygric and structural characteristics relating to the SEB materials and a comparison of their characteristics depending on the variation of their compositions.

Clay particles as binder for earth buildings materials: a fresh look into rheology of dense clay suspensions

In the ceramic industry and in many sectors, clay minerals are widely used. In earthen construction technique, clay plays a crucial role in the processing. The purpose of this research is to understand and modify the clay properties in earth material to propose an innovative strategy to develop a castable earth-based material. To do so, we focused on the modification of clay properties at fresh state with inorganic additives. As the rheological behaviour of clays is controlled by their surface charge, the addition of phosphate anion allows discussing deep the rheology of concentrated clay suspensions. We highlighted the thixotropic and shear thickening behaviour of a dispersed kaolinite clay suspensions. Indeed, by adding sodium hexametaphosphate the workability of clay paste increases and the behaviour is stable during time after a certain shear is applied. Moreover, we stress that the aging and the shift in critical strain in clay system are due to the re-arrangement of clay suspension and a decrease of deformation during time. The understanding of both effect: thixotropy and aging are crucial for better processing of clay-based material and for self-compacting clay concrete. Yet, studies need to pursue to better understand the mechanism.

Applicability of scaling behavior and power laws in the analysis of the magnetocaloric effect in second-order phase transition materials

In recent years, universal scaling has gained renewed attention in the study of magnetocaloric materials. It has been applied to a wide variety of pure elements and compounds, ranging from rare earth-based materials to transition metal alloys, from bulk crystalline samples to nanoparticles. It is therefore necessary to quantify the limits within which the scaling laws would remain applicable for magnetocaloric research. For this purpose, a threefold approach has been followed: a) the magnetocaloric responses of a set of materials with Curie temperatures ranging from 46 to 336 K have been modeled with a mean-field Brillouin model, b) experimental data for Gd has been analyzed, and c) a 3D-Ising model ---which is beyond the mean-field approximation--- has been studied. In this way we can demonstrate that the conclusions extracted in this work are model-independent. It is found that universal scaling remains applicable up to applied fields which provide a magnetic energy to the system up to 8\% of the thermal energy at the Curie temperature. In this range, the predicted deviations from scaling laws remain below the experimental error margin of carefully performed experiments. Therefore, for materials whose Curie temperature is close to room temperature, scaling laws at the Curie temperature would be applicable for the magnetic field range available at conventional magnetism laboratories ($\sim 10$ T), well above the fields which are usually available for magnetocaloric devices.

Building Heritage In The Alto Douro Wine Region, Portugal – Tabique Wall Nails Characterization

Abstract The Alto Douro Wine Region, a region located in the northeast of Portugal, presents an abundant building heritage which consists of tabique constructions, a vernacular construction technology. This technology uses raw materials such as stone, an earth-based material and wood, besides metal nail sensure the timber connections and the required structural safety. Previous research works have shown that most of the existing tabique buildings, in this region, present signs of marked deterioration and some of them are clearly near collapse. This reality is justified, among others, by the non-engineered character of this construction technology and subsequent loss through time of the associated empirical technical knowledge, consequently, conservation and repairing works are urgently needed. These aspects, added to the dearth of knowledge related to this building heritage have motivated this research work which is focused on studying the nails traditionally applied in those tabique buildings. In this article, and for the first time, a nail geometrical and material characterization is presented and discussed. The results highlight a wide nail dimensional variety, being iron the main chemical element identified. Beyond that, this study demonstrates that those nails should no longer be maintained in service and that new nails should be applied in future conservation and strengthening works. Finally, some guidelines regarding tabique rehabilitation and nail rusting prevention are mentioned.

Strength and Fracture Toughness of Earth-Based and Natural Fiber-Reinforced Composites

This paper presents the results of a combined experimental and theoretical study of the strength and fracture toughness of earth-based materials. They include mixtures of laterite, clay and straw that is stabilized with controlled levels of Portland cement. The compositional dependence of compressive, flexural strength and the fracture toughness is explored for different proportions of the constituent materials. Composites and fracture mechanics models are used to estimate the strength and fracture toughness of the resulting composites. The applications of the results are discussed for the design of earth-based building materials for affordable housing.

Overview of Amorphous and Nanocrystalline Magnetocaloric Materials Operating Near Room Temperature

The observation of a giant magnetocaloric effect in Gd5Ge1.9Si2Fe0.1 has stimulated the magnetocaloric research in the last two decades. However, the high price of Gd and its proclivity to corrosion of these compounds have prevented their commercial use. To reduce raw materials cost, transition metal-based alloys are investigated to replace rare earth-based materials. Environmental considerations, substitution for scarce and strategic elements, and cost considerations all speak to potential contributions of these new materials to sustainability. Fe-based soft amorphous alloys are believed to be promising magnetic refrigerants. Efforts in improving the refrigeration capacity (RC) of refrigerants mainly rely on broadening the magnetic entropy change. One promising technique is to couple two phases of magnetic materials with desirable properties. Second is the investigation of nanoparticle synthesis routes, with ball milling being the most widely used one. The motivation for the nanoparticles synthesis is rooted in their inherent tendency to have distributed exchange coupling, which will broaden the magnetic entropy curve. As proven with the cost analysis, the focus is believed to shift from improving the RC of refrigerants toward finding the most economically advantageous magnetic refrigerant with the highest performance.

Rare Earth Silicate Formation: A Route Towards High-k for the 22 nm Node and Beyond

Over the last decade there has been a significant amount of research dedicated to finding a suitable high-k/metal gate stack to replace conventional SiON/poly-Si electrodes. Materials innovations and dedicated engineering work has enabled the transition from research lab to 300 mm production a reality, thereby making high-k/metal gate technology a pathway for continued transistor scaling. In this paper, we will present current status and trends in rare earthbased materials innovations; in particular Gd-based, for the high-k/metal gate technology in the 22 nm node. Key issues and challenges for the 22 nm node and beyond are also highlighted.

Effect of Jointing Mortar on Structural Behaviour of Wall Panels Made of Eco-blocks

Inspired by the global need for sustainable development earth(soil) is re-emerging as the grand eco-material for building construction for the 21st century due to its availability, environmental/cultural appropriateness, structural adequacy, familiarity to the local people, “breathability”, amongst others. Accordingly, both developed and developing countries have embarked on initiatives to develop and promote earth-based construction materials for building construction, especially for use in masonry wall construction. On-going studies conducted clearly demonstrate that eco-blocks made of stabilized soil and quarry dust have comparable or higher strength than conventional dressed stone blocks used in Nairobi or coral stone blocks used in Mombasa. This paper focuses on evaluating the realistic structural behavior of prototype walls made from eco-blocks (earth-based blocks) with the goal of seeking to provide economical alternative material for masonry wall construction. The main variable is the type of jointing mortar used in walls, whereby wall panels made from eco-blocks and various mortars were loaded to failure on a loading frame while monitoring strains on the wall surface as well as load increments up to failure. The walls failed by developing wide cracks whose pattern depended on the type of mortar used. Further, the results confirmed that walls constructed from mortar of comparable strength to that of the blocks have higher load carrying capacity than walls constructed from mortar of higher strength than that of the blocks, attributable to the extent of homogeneity for each tested wall type. It is concluded that wall panels made from stabilized eco-blocks ought to be jointed in mortar of comparable characteristics to that of the eco-blocks, to avoid excessive cracking, reduced load carrying capacity and wasteful design.

A fractal model of the porous microstructure of earth-based materials

Soils with a clay component have been widely used as construction materials since the earliest times and now it continue to be used in some developing countries and in the so-called bioarchitecture. This paper presents the experimental porosimetric data obtained for 13 different earth-based materials using the mercury intrusion technique. The porous microstructure is geometrically described by means of two models based on fractal geometry, the Menger’ sponge and an original P’ sponge proposed here. The P’ sponge is constructed using an aggregation process of granular components, resembling the formation and texture of soil. The fractal dimension of the experimental data set is determined following Pfeifer and Avnir’s approach. Generally the fractal range spans two to three orders of magnitude, from 20 to 0.02 μm. The results show the P’ sponge to be more representative than the Menger’ sponge.

Surface wear resistance of chemically or thermally stabilized earth-based materials

The paper is concerned with the wind erosion resistance of earth-based building materials. With the spatial extent of drylands likely to increase, this aspect will become ever more important for present settlements and the conservation of archaeological site. Experiments were conducted on a soil with high kaolin content, adding sand, hydraulic cements, lime and organic polymers or on the same earth modified by means of low (below ceramization) temperature heat treatment. The stabilization practices currently performed or tested are designed primarily to improve water stability and compressive strength of this class of humble materials. However, very little is known about the effects that these modifications actually produce on surface erosion resistance. An experimental set up designed to simulate the erosive effects of wind-borne particles is described. The experimental data obtained make it possible to clearly discriminate between the different types of material used and indicate that some of the most commonly used earth stabilization products actually have a negative effect on surface durability.

Modeling of Brick Properties for Earth-Based Domes Structures

The use of earth-based materials is becoming increasingly popular, particularly in the rural areas of developing countries. One example is the introduction of an earth dome for low-cost housing in the rural areas of Mozambique [1], although this project is still at a research level. The earth bricks used in building the dome are a type of composite material, consisting of porous soil and possibly cement. The brick properties depend on the proportions of soil, cement and air-filled pores. For economic reasons, the amount of the stiffer and stronger cement phase needs to be minimized. Here, some initial experimental results and the results of a simple numerical model for estimating the stiffness and strength of the bricks are presented. The numerical analyses use a 3D linear elastic finite element program to calculate the effective elastic properties of the brick and a failure stress under uniaxial compression is calculated based on a Drucker-Prager type condition for cohesive materials.

Long-term performance evaluation of an earthen grouting mortar: the Nuraghic complex of Genna Maria, Sardinia

This paper presents a critical assessment of the long-term performance of an earth-based material employed nine years ago in conservation work on a building of massive, Cyclopean-style construction at the Genna Maria Nuraghic complex in central-southern Sardinia (Italy). The material was used for filling the large gaps between stones in the masonry walls to create a barrier to ingress of water into the masonry walls. In situ observations and laboratory analyses were conducted on samples of the grouting material to assess its condition after nine years.