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Earth has been used as construction material since prehistoric times, and it is still utilized nowadays in both developed and developing countries. Heritage conservation purposes and its intrinsic environmental benefits have led researchers to investigate the mechanical behaviour of this material. However, while a lot of works concern with rammed earth, CEB, and adobe techniques, very few studies are directed towards cob, which is an alternative to the more diffused rammed earth and adobe in specific geographic conditions. Due to this lack, this paper presents an experimental program aimed at assessing the failure mode and the main mechanical properties of cob earth walls (compressive strength, Young’s modulus, and Poisson’s ratio) through monotonic axial compression tests. Results show that, if compared with CEB, adobe, and rammed earth, cob has the lowest compressive strength, the lowest modulus of elasticity, and Poisson’s ratio. Differences are also found by comparing results with those obtained for other cob techniques, underlining both the high regional variability of cob and the need of performing more research on this topic. A strong dependence of material properties on loading rate and water content seems to exist too. Finally, the ability of a common analytical method used for masonry structures (an FEM macromodelling with a total strain rotating crack model) to represent the mechanical behaviour of cob walls is showed. [ABSTRACT FROM AUTHOR]

The will of reducing environmental and social impact of building industry has led to a renewed interest in earth construction. Most of earth construction literature dealt with rammed earth or adobe techniques, but very little with cob. Yet, cob participates in the diversity of vernacular earth construction processes that value local materials and is an alternative to rammed earth and adobe in specific geographical conditions. Conservation of cob heritage also requires a better knowledge of this vernacular construction process. This bibliographical analysis gathered extensive data on cob process and summarized the different cob process variations, attempting to take into account their diversity. This analysis allowed us to provide novel data on cob process, and more specifically, (1) a clear definition of cob with regard to other earth construction processes, (2) a first summarized description of cob process that clearly distinguished its variations, (3) a list of fibres traditionally employed, (4) values and, if possible, average and standard deviation for fibre length, fibre content, manufacture water content, drying times, lift heights and wall thicknesses, (5) a summary of the strategies to manage shrinkage cracks, (6) a criterion on the quality of implementation and/or earth for cob, based on slenderness ration of lifts and (7) a discussion on the evolution of cob process with regard to societal evolutions. [ABSTRACT FROM AUTHOR]

In rainy climates, the external surfaces of earthen buildings suffer water erosion. In this paper, the properties of earth plasters have been investigated considering the specific relationship with the underlying substrate. Ten typologies of earth plasters containing different admixtures and surface treatments, a cob wall and a rammed earth wall were produced in laboratory. The aim is to evaluate the effectiveness of the coatings in protecting the earthen walls against weathering. An in situ procedure consisting of a shrinkage test followed by an adhesion strength test was performed in order to identify the earth/sand ratio optimal for the plaster manufacturing. Then, a series of tests was carried out both on the plasters and the two walls: compression, water vapor permeability, surface color, wettability, water absorption and erosion. The results demonstrate that all the plasters are physically and mechanically compatible with the earthen substrates and that the most important differences are in the specific relationship with water. The earth plaster treated with the silane–siloxane product was found to be the best one: it is fully compatible, water-repellent and highly resistant to water erosion. Hence, there is a potential for the use of earth plasters for the protection of earthen buildings against weathering. [ABSTRACT FROM AUTHOR]

Highlights: [•] Compression and diagonal compression tests of earthen wallettes were performed. [•] Manufacturing practice is one of the key factors affecting performances of earth block masonry. [•] Earth block masonry and rammed earth show a brittle mechanical behaviour under compression. [•] Cob shows relatively ductile post peak behaviour under compression due to fibres content. [•] Cob presents a relatively good performance as far as shear behaviour is concerned. [Copyright &y& Elsevier]

Abstract: Tabique construction is one of the main Portuguese traditional building techniques that use earth based building materials. It is peculiar building technique which uses corn''s cob as a filling material for the external tabique walls. The existing tabique construction in Trás-os-Montes e Alto Douro region of northeast Portugal was studied to learn from it for modern day construction. The research showed that corn''s cob, an agricultural waste, has the potential to be used as a sustainable building material for thermal insulation. An experimental work concluded that there are significant similarities between the corn''s cob and the extruded polystyrene (XPS) material in terms of microstructure and chemical composition. Furthermore, the results obtained from an expeditious experimental thermal procedure indicate that the corn''s cob may have adequate thermal properties for building purpose. [Copyright &y& Elsevier]

Abstract: Chain-like and rod-like Co-B nanomaterials are prepared by chemical reduction method in cetyltrimethylammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) aqueous solution, respectively. XRD patterns demonstrate that the two materials both have amorphous structures. SEM and TEM images show that the chain-like Co-B constructs of one-by-one tactic ball-like particles with nanoflakes on the surface, whereas the rod-like Co-B alloy possesses a porous nanostructure. The results of electrochemical measurements indicate that, as negative electrode materials of Ni-MH batteries, their electrochemical properties are both better than those of regular Co-B alloy. At the discharge current density 25mAg−1, the discharge capacities of the chain-like and the rod-like Co-B alloys are 314mAhg−1 and 292mAhg−1 after 50 cycles, respectively, which are both higher than that of regular Co-B alloy. XRD patterns of the electrodes on different charge–discharge states illustrate that the discharge capacity is attributed to hydrogenation of Co-B alloy. [Copyright &y& Elsevier]

Abstract: Cr-modified Co–B (Co–Cr–B) catalyst alloy powders have been synthesized by chemical reduction of cobalt and chromium salt at room temperature to study the hydrogen production by catalytic hydrolysis of NaBH4. The Cr/Co molar ratio was varied in the catalyst in order to study the effect of Cr doping on surface modification and catalytic efficiency of Co–B catalyst. The resulting catalyst powders were characterized by scanning electron microscopy, X-ray diffraction, X-photoelectron spectroscopy, and BET surface area measurement. When the molar ratio χ Cr =Cr/(Cr+Co) exceeds 9% the BET surface area of the Co–Cr–B catalyst increases by one order of magnitude as compared to that of Co–B catalyst. The catalytic activity of the Co–Cr–B for hydrogen production depends on Cr concentration: specifically, the activity increases by increasing χ Cr up to about 4% and then it gradually decreases by further increasing χ Cr. We established that the increased catalytic activity is related to the formation of chromium oxide on the catalyst surface, with the oxide favoring the dispersion of Co–B particles resulting in high catalyst surface area. However as χ Cr exceeds 4%, Cr starts to cover the Co active sites and the corresponding catalytic activity decreases. The highest catalytic activity was obtained at the optimum Cr-content, χ Cr =4%, in Co–Cr–B catalyst, showing nearly 4 times higher H2 generation rate than that of pure Co–B catalyst. Kinetic studies on the hydrolysis reaction of NaBH4 with Co–Cr–B catalyst reveal that the concentrations of both NaBH4 and NaOH have essentially no effects on hydrogen generation rate. The promoting effect of Cr in Co–Cr–B catalyst results in lower activation energy for hydrogen production, which is 37kJmol−1 as compared to 45kJmol−1 obtained with pure Co–B powder. Finally, the possible role of Cr3+ species in the electron exchange mechanisms involved in NaBH4 hydrolysis with the Co–Cr–B catalyst has been discussed. [Copyright &y& Elsevier]

The article presents a study which investigates the ability of cob materials to resist flooding as well as documents basic failure mechanisms. The study uses the form of a literature review as well as case study underpinning laboratory experiments. The study reveals that the cob walls have the ability to resist total failure on flood situations as it is suitably straw reinforced, suitably compacted, and composed and manufactured of the correct materials.

Abstract: Magnetic properties of peculiar structural-type borate Cu2NiB2O6 are investigated by means of ac susceptibility, dc magnetization, and heat capacity measurements. This material is isostructural to Cu2CoB2O6, of which the structural configuration is composed of quasi-one-dimensional six-columns ribbons. Our experimental results show that this material displays an antiferromagnetic phase transition at ∼15K, which differs from Cu2CoB2O6 showing spin-glass behavior below 5K. The different magnetic ground states in these compounds may be attributed mainly to the subtle balance of the exchange energy in the scalene triangles. [Copyright &y& Elsevier]

The article discusses efforts to improve the efficiency and reduction of waste in the housing construction sector. It tackles the social, political, and economic conditions that encourage or obstruct eco-construction. It features the eco-housing projects in such countries as Great Britain, Spain and Argentina. It presents as example the cob houses in Devon, England that is inspired by cob building specialist Kevin McCabe.