The aim of this paper is to find out new alternative materials that respond to sustainable development criteria. For this purpose, an original utilization of straw for the design of lightweight aggregate concretes is proposed. Four types of straw were used: three wheat straws and a barley straw. In the present study, the morphology and the porosity of the different straw aggregates was studied by SEM in order to understand their effects on the capillary structure and the hygroscopic behavior. The physical properties such as sorption-desorption isotherms, water absorption coefficient, pH, electrical conductivity and thermo-gravimetric analysis were also studied. As a result, it has been found that this new vegetable material has a very low bulk density, a high water absorption capacity and an excellent hydric regulator. The introduction of the straw in the water tends to make the environment more basic; this observation can slow carbonation of the binder matrix in the presence of the straw.

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Thermogravimetric analyzer coupled to a mass spectrometer (TGA-MS) was used to study the thermochemical behavior of eight samples. Two varieties of straw (wheat and barley) and two others of binder (lime and plaster) have employed to design four composites. These composites can be considered as innovative insulation materials for buildings. The thermal degradation of the different specimens was studied from a temperature of 50 to 1000ºC using increased temperature of 20ºC/min. This thermal degradation is an important element to evaluate the fire behavior and predict the evolution of smoke emitted during an accidental fire for building application. Using MS analyzer, the ion currents evolutions of 16 molecule groups (shared by a m/z ratio) were followed as functions of temperature. TG curves show that the thermal decomposition of composite samples is more complex (3-4 mass loss steps) than the one of the basic materials (1-2 mass loss stages) and seems to be mostly affected by the binder nature. The highest amount of gas in pyrolysis products is associated to m/z=28 ratio and presents more than two thirds of the total quantity. The kinetic parameters were evaluated for the more important mass loss of each sample and their values are in the ranges of 8.29-64.86 kJ/mol, 0.4-3.36 and 1.78 x 10^3 -1.63 x 10^7 min^-1 for respectively the activation energy, the reaction order and the pre-exponential factor.Peer ReviewedPostprint (author's final draft

This paper presents an investigation on the use of new light-weight construction material, composed of lime, water and cereal straw fiber. Two types of fibers were used: wheat and barley straw. The influence of some parameters such as fiber types, binder types (lime and/ or lime-cement), fiber to binder ratio (F/B) and Water to Binder ratio (W/B) on the mechanical and thermal properties is studied. Compressive strength, thermal conductivity and density of the material were investigated. The results indicated that the thermal conductivity of the straw-lime composites decreased with increasing straw content. The result comparisons also revealed that the composite reinforced by wheat straw fibres has the highest compressive strength.