Steel fibres for reinforcing concrete, esp. sprayed concrete - have very short length with oval cross=section to increase tensile strength of concrete

摘要

The fibres have an oval cross-section of which the axial ratio is 1:2-4, pref. 1:2.5-3.3, and esp. 30-40:100 mu m. The fibre length is 2-6 mm, pref. using an average length of 3 mm. The concrete pref. contains >=4 wt.% of the fibres in a dry mixt. of P-300 or P-400 concrete, in which the grain size of the aggregate is 0-12 mm. The aggregate employed for sprayed concrete pref. contains by wt. 22% sand (0-1 mm), 22% sand (1-4 mm), 24% gravel (4-8 mm), and 32% gravel (8-12 mm). The pref. concrete is made by dry mixing the aggregate, cement and steel fibres for >=30 secs. in a concrete mixer; the gravel sand mixt. pref. has a specific surface of ca. 9.5 m2/kg; and the water/cement factor is pref. >=0.45. The tensile strength of the concrete is almost doubled as compared with concrete contg. no fibres.