フライアッシュをベースとしたジオポリマーコンクリート梁の曲げ性状と構造部材としての可能性

抄録

　Geopolymer concrete has the potential to be an eco-friendly alternative to cement concrete because CO₂ emissions in its production process can be reduced and industrial by-products such as fly-ash can be used effectively.

　The present study investigates flexural behavior of fly-ash based geopolymer concrete beams before yielding and its applicability as a flexural member. Eight beams consisting of four fly-ash based geopolymer concrete beams and four ordinary Portland cement concrete beams were cast and tested under four-point flexural loading. The experimental variables are combinations of reinforcing bar diameter and number of reinforcing bars, compressive strength and concrete types. In addition, non-linear three-dimensional finite element analyses were carried out.

　Bending moment-deflection behavior, crack width, crack space and number of cracks were examined. The experimental results were compared with the proposed equations provided by the AIJ design standard for reinforced concrete. The deflection and maximum crack width of the fly-ash based geopolymer concrete beams subjected to bending moment based on long/short-term allowable stress were similar to those of ordinary Portland cement concrete beams, and, therefore, they have an applicability as flexural members. The flexural behavior of fly-ash based geopolymer concrete beams prior to flexural yielding, except for the yielding deflection, could be predicted using the AIJ design standard. Making modifications to the coefficients related to the Young’s modulus ratio improved the accuracy of the prediction of yielding deflection.

　Although Young’s modulus of fly-ash based geopolymer concrete was lower than that of ordinary Portland cement concrete, the post-cracking stiffness of fly-ash based geopolymer concrete beams were not largely different from that of ordinary Portland cement concrete beams. The results suggested that the effect of tensile strength on the flexural behavior of the beams was greater than that of Young’s modulus of concrete.

　In addition, the crack width of the fly-ash based geopolymer concrete beams was similar to that of the ordinary Portland cement concrete beams, and could be predicted by the AIJ design standard for reinforced concrete.