M. Quéneudec

Polymer biodegradation: Mechanisms and estimation techniques – A review

Within the frame of the sustainable development, new materials are being conceived in order to increase their biodegradability properties. Biodegradation is considered to take place throughout three stages: biodeterioration, biofragmentation and assimilation, without neglect the participation of abiotic factors. However, most of the techniques used by researchers in this area are inadequate to provide evidence of the final stage: assimilation. In this review, we describe the different stages of biodegradation and we state several techniques used by some authors working in this domain. Validate assimilation (including mineralisation) is an important aspect to guarantee the real biodegradability of items of consumption (in particular friendly environmental new materials). The aim of this review is to emphasise the importance of measure as well as possible, the last stage of the biodegradation, in order to certify the integration of new materials into the biogeochemical cycles. Finally, we give a perspective to use the natural labelling of stable isotopes in the environment, by means of a new methodology based on the isotopic fractionation to validate assimilation by microorganisms.

Influence of the proportion of wood on the thermal and mechanical performances of clay-cement-wood composites

Abstract The introduction of wood aggregates to produce low density composites is an interesting technique allowing the reuse of wastes from both the aggregate-mining and wood processing industries. This paper describes the influence that the proportion of wood aggregates has on the thermal and mechanical performance of a clay-cement-wood composite. First, the composite material and its production technique are presented. Then, the thermal conductivity, mechanical strengths and the porosity of the matrix are experimentally evaluated. Finally, it is shown that the addition of wood to clayey concrete improves its insulation characteristics, reduces its mechanical strength and increases its deformability.

Influence of storage conditions on the carbonation of powdered Ca(OH)2

Abstract The influence of relative air moisture, temperature and concentration of CO 2 on the carbonation of Ca(OH) 2 have been examined under normal climatic conditions. The calcium hydroxide used for this original work is a granular material. The importance of the hydrated state of Ca(OH) 2 has also been studied in order to obtain complete carbonation. A three steps mechanism of carbonation has been proposed to help explain the observed phenomena. This work was carried out with the view to defining the optimal conditions for the storage of slaked lime.

Application of image analysis to measure screw speed influence on physical properties of corn and wheat extrudates

Extruded products are usually studied with the respect to their mechanical and sensorial properties. Computer image analysis has been used to provide information on internal structure of a variety of products. In the current study a digital image technique was used to determine structural properties of two types of extruded flour products as screw speed changed. The extrusion cooking of corn and wheat flour was carried out in a twin-screw corotating extruder. Sectional and longitudinal expansion were measured and water solubility and absorption were also determined. The increase in screw speed resulted in products possessing greater longitudinal expansion, higher water solubility and smaller structural patterns. However, differences between the corn and wheat extrudates were also evident at the various screw speeds examined.

Effect of rubber aggregates on the physico-mechanical behaviour of cement-rubber composites-influence of the alveolar texture of rubber aggregates

Abstract The study presented herein has been undertaken in order to examine the physico-mechanical properties of cement–rubber composites by use of two types of rubber aggregates, in the aim of developing a highly deformable material. The results obtained highlight the importance of the alveolar feature and the elasticity of the rubber aggregates in helping improve the flexural strength and deformability of the material. An optical analysis reveals the best level of bonding between the expanded rubber aggregates and the cement matrix.

Transport of fluids in cement–rubber composites

Abstract The transport properties of building materials exposed to an aggressive environment represent the essential parameters affecting their durability. Furthermore, the deterioration process of materials is highly related to the movement of water contained in a porous volume, whether in liquid or vapour form, and to the air permeability. The present study has been undertaken to examine the influence of rubber aggregates on the durability factors of cement–rubber composites. Results reveal the importance of the cellular character of rubber aggregates with respect to the composite’s behaviour in contact with fluids.

Hydromagnesite development in magnesian lime mortars

Abstract The bond which develops during curing in lime paste mortars in the presence of Mg(OH)2 or MgO and moisture in lime paste is a result of the growth of a new phase. Scanning electron microscopy studies along with X-ray analyses show this new phase to consist of common hydromagnesite (Mg5(CO3)4(OH)2,4H2O). This development is accompanied by an increase in the mechanical strengths of lime mortars.

PROPERTIES OF WOOD-BASED COMPOSITES FORMULATED WITH AGGREGATE INDUSTRY WASTE

Abstract The option of using vegetable-based materials is not only one potential response to the lack of aggregate resources in certain regions, but also a way of helping to preserve the environment. These reasons have incited some authors to address the issue of waste reuse in the form of insulating composites. The work presented herein, once the influence of components has been examined, will focus on the influence of various processes on the performances of hardened composites. Aggregate processing by boiling water, followed by a hydraulic binder coating, enables the minimization of the composites dimensional variations to a larger extent. This processing technique allows the achievement of an excellent compromise in material properties, although it increases density and, hence, thermal conductivity.

Reuse of waste oils in the treatment of wood aggregates

Abstract In this work, oil intended for disposal is used to impregnate wood shavings at room temperature and atmospheric pressure. Experimental results show a sizable decrease in the absorption of water by these wood shavings and the generation of a wood–cement–mineral fines composite from industrial waste. The composites dimensional variations can be reduced by half without any of the mechanical properties or thermal conductivity being adversely affected. An oil intended for disposal is more efficient than linseed oil in reducing the extreme dimensional variations.

Influence of Filler Addition on Mechanical Behavior of Cementitious Mortar-Rubber Aggregates: Experimental Study and Modeling

AbstractThis work focuses on the feasibility of reusing and valorizing rubber aggregates from shredded worn tires in cement paste. This kind of eco-material could be used, for example, in special buildings, roads or pavement, or recreational areas. Fractions of the volume of sand were substituted by the same volume of rubber aggregates. The volume contains the ratio of rubber aggregates ranging from 0 to 50%. Nevertheless, compressive and flexural strengths decrease when the volume ratio of rubber aggregates increases in mortar-rubber aggregate mixtures. A solution to the decrease in mechanical strengths consists of adding mineral particles, such as siliceous or limestone fillers. Experimental characterization of the mechanical behavior of mortar-rubber aggregates containing either siliceous or limestone fillers is developed in this paper. It is observed that the use of either siliceous filler or limestone filler enhances mechanical properties. Modeling is developed to predict compressive and flexural str...