Gripping of Anchor Fiber of Ukrainian Production with Fine- Grain Concrete

Abstract

The results of tests for drawing anchor fibers with a length of 50 mm and a diameter of 1 mm, laid at the end of concrete prisms 50x50x100 mm made of fine-grained concrete of classes C 20/25, C25/30 and C 30/35 are presented. From the tests of 50 fibers, the average value of tensile strength was determined, which is equal to 1242 MPa with a coefficient of variation of 2.1%. Prisms were made of fine-grained concrete, which included cement with an activity of 41.2 MPa for concrete class C 20/25 and an activity of 50.8 MPa for concrete classes C 25/30 and C 30/35. Sand with a modulus of size 2.1 was used as a filler. The concrete mixture was prepared in a forced concrete mixer, and the concrete was compacted on a vibrating platform. Simultaneously with these prisms, cubes with dimensions of 150x150x150 mm and prisms with dimensions of 100x100x400 mm were made to determine the bottom and prism strength of concrete. The length of laying fibers into concrete was 10,15 and 25 mm. It is shown that the forces perceived by the end anchors and the smooth part of the fibers rise with increasing strength of concrete. The results of tests for drawing fibers from concrete prisms are given in tables 1 - 3. For the length of laying fiber 10 mm into prisms with strength fcm,cube = 29.31MPa and fcm,prism = 23.15MPa the maximum stresses during drawing were 515.30 - 549.04 MPa (average value - 532.10 MPa). At the same length of laying fiber into concrete prisms with strength fcm,cube = 34.76MPa and fcm,prism = 27.11MPa, these stresses were equal to 554.47 - 588.54 MPa (average value - 569.70 MPa). For the length of laying the fiber 10 mm into prisms with strength fcm,cube = 38.96MPa and fcm,prism = 31.14MPa, the maximum tensile stresses were 590.51 - 621.72 MPa (average value - 606.81MPa). At the specified strengths of the prism concrete, the maximum values of the average stresses for fiber drawing were on average 13.37 MPa for concrete of class C20/25, 14.34 MPa for concrete of class C25/30 and 15.27 MPa for concrete of class C30/35. With a fiber laying length of 15 mm into prisms with concrete strength corresponding to class C20/25, the maximum tensile stresses were 575.80 - 607.64 MPa (average value - 587.10 MPa). With such a length of laying fiber into prisms made of concrete class C25/30, these stresses were equal to 614.44 - 680.25 MPa (average value - 638.95 MPa). At the length of laying the fiber 15 mm into the prisms of concrete class C30/35, the maximum stresses during drawing were 681.14 - 692.99 MPa (average value - 685.44 MPa). The maximum values of average stresses for fiber drawing were on average 9.87 MPa for concrete of class C20/25, 10.70 MPa for concrete of class C25/30 and 11.52 MPa for concrete of class C30/35. At a fiber laying length of 25 mm into prisms with concrete strength corresponding to class C20/25, the maximum tensile stresses were 645.44 - 735.03 MPa (average value - 692.76 MPa). With such a length of laying fiber into prisms made of concrete class C25/30, these stresses were equal to 736.58 - 773.25 MPa (average value - 752.37 MPa). With the length of laying fiber 25 mm into prisms made of concrete class C30/35, maximum stresses during drawing were equal to 780.27 - 839.49 MPa (average value - 809.12 MPa). The maximum values of the average stresses during fiber drawing were on average 6.97 MPa for concrete of class C20/25, 7.57 MPa for concrete of class C25/30 and 8.12 MPa for concrete of class C30/35. The coefficient of anchoring capacity η, which under Ukrainian standards of fibroconcrete structures designing is equal to 0.9, as shown by the data of our experiments, is not constant, so it is necessary to take this into account in the formula for determining the tensile strength of fibroconcrete.