Study of concrete properties with vegetal and polypropylene fibers for use in structural walls

ABSTRACT The properties with addition of vegetal fibers (sisal and ramie) and of polypropylene for use in structural walls was studied in this research. An evaluation of the performance of the concrete with an addition of vegetable fibers and of polypropylene fiber was carried out, to verify the possible displacement. Were evaluated, the shrinkage under restrained conditions by ring test, as well the mechanical properties (compressive strength, splitting tension and static modulus of elasticity) and physical properties (specific mass, voids, immersion and capillary absorption). The contents used were 0.25 % and 0.5 % for the vegetable fibers and for the polypropylene fiber or 0.25 % content. In relation to the shrinkage under restrained conditions, it was observed that the addition of 0.25 % of fibers did not result in an increase in performance compared to concrete without fiber addition, but the addition of 0.5 % of vegetal fibers showed satisfactory results, being superior to the reference concrete. The mechanical properties of the concrete with fiber addition, generally lower than the reference concrete, did not undergo major changes, except for concrete with the highest ramie content, which did not present adequate fibers dispersion. The concrete with 0.25 % ramie presented the highest absorption and voids, among all the concretes studied. In relation to the absorption by capillarity, the concretes with addition of the vegetal fibers demonstrated better performance, that is, reduction of the absorption by capillarity. It was concluded that the substitution of polypropylene fiber by vegetal fibers, especially sisal, is plausible.摘要 本研究针对添加植物纤维（剑麻（sisal）、苎麻（ramie））与聚丙烯纤维的材料用于结构墙体的性能展开了探究。本研究对掺加植物纤维及聚丙烯纤维的混凝土性能进行了系统评估，以验证其可能产生的位移变形。通过圆环试验测试了约束条件下的收缩性能，同时评估了其力学性能（抗压强度、劈裂抗拉强度与静态弹性模量）及物理性能（表观密度、孔隙率、浸水性能与毛细吸水性能）。植物纤维的掺量分别为0.25%与0.5%，聚丙烯纤维的掺量为0.25%。针对约束收缩性能，研究发现掺加0.25%纤维的混凝土性能未优于素混凝土；而掺加0.5%植物纤维的混凝土表现出优异性能，优于基准混凝土。掺加纤维的混凝土力学性能整体低于基准混凝土，但未出现显著劣化；仅苎麻掺量最高的试样未实现纤维的均匀分散，性能表现欠佳。在所有受试混凝土中，掺加0.25%苎麻纤维的混凝土吸水率与孔隙率最高。就毛细吸水性能而言，掺加植物纤维的混凝土表现更优，即有效降低了毛细吸水量。研究表明，以植物纤维（尤其是剑麻纤维）替代聚丙烯纤维具备切实可行性。