Experimental Research on New Sustainable Geopolymer Concretes Reinforced and not Reinforced with Natural Fibers

Abstract

The paper describes experimental research voted to verify the mechanical characteristics of very sustainable geopolymer concretes and to try to improve their mechanical characteristic using natural fibers. Particularly, there were used and tested geopolymer concretes using a geopolymer matrix obtained from very cheap and sustainable fly ashes (as they come from the waste recycling). About the natural fibers, they were used hemp short fibers as they are very durable and sustainable. It was designed and performed a bending test program for six reference samples of geopolymer concrete beams without fibers. Then, it was designed and performed the bending test program for six samples of geopolymer concretes with the addition of hemp short fibers. All the samples are beams 15x15x60 cm, to perform four-point bending tests; then it was also designed to use the same beams, after their cracking in the bending tests, to obtain cubic samples (after a regularization of the faces) for compression tests. Thus, they were twelve reference cubic samples without fibers and twelve cubic samples with fibers, for the compression tests. The firsts results show geopolymer concretes with performances like those of a Portland concrete with fck between 25MPa and 30MPa, and tensile strength 1/10 of compression strength, but with a lower elastic modulus. The fibres used not cause significative modification in the mechanical characteristics, but they improve ductility.