Contribution of hybrid fibers on the improvement of sand concrete properties: Barley straws treated with hot water and steel fibers

This study is a continuation of previous work undertaken on a sand concrete lightened by barley straws treated with hot water. Indeed, this type of lightweight concrete presented good thermo-physical properties. But on the other hand, its mechanical properties have been slightly reduced. In order to mechanically strengthen the material, it was decided to incorporate steel fibers in the cement matrix. Thus, we have to develop a new lightweight sand concrete based on hybrid fibers: barley straws and steel fibers. The main objective is therefore to improve the mechanical properties of a lightweight sand concrete, without greatly affecting its thermo-physical properties. Since the effect of the barley straws has already been studied in previous works, the present study mainly focuses on the effect of the steel fibers addition. In order to determine the best compromise between the effect of barley straws and that of steel fibers, different percentages of steel fiber (0%; 0.5%; 1%; 1.5% & 2%), as vol. %, have been investigated. The obtained results showed interesting improvements in the physico-mechanical properties of the studied concrete; these findings were confirmed by a microstructural analysis. The optimal proportion of steel fibers that constitutes the best compromise between the studied properties is 1%. In addition, the compressive strength at 90 days has been improved by about 18%, while slight increases in the thermal conductivity and density have been recorded. The thermal diffusivity has been reduced by about 2% and the specific heat has been increased by about 15%. As for the shrinkage, a reduction of about 30% has been noted. It should be noted that, according to the obtained results, the material still retains its qualities of lightweight concrete. Finally, a microstructural study has revealed that the adhesion between the used fibers and the cement matrix is very good. (C) 2019 Elsevier Ltd. All rights reserved.