Issue34

A. Satoh et alii, Frattura ed Integrità Strutturale, 34 (2015) 397-405; DOI: 10.3221/IGF-ESIS.34.44 398 This paper aims at obtaining such crack path with revealing the mechanisms for it with the help of fractographic observation and FEM analysis, which leads to enhancing the strength of the repair-substrate mortar (concrete). It also contributes to the improvement of ductility as well, because repair material can contain many types of fiber which can enhance ductility when the crack path extends in repair material. The concrete-repair interface is made of two interfaces: mortar-repair and coarse aggregate-repair interface. To simplify the problem, mortar-repair interface is addressed in this study, which is an outset of enhancement of mechanical performance of concrete-repair interface. M ECHANICAL PROPERTIES OF REPAIR AND REPAIRED MORTAR he authors investigated the mechanical properties of repairs and the mortar specimens repaired with them. The dimension of the specimen is 40 x 40 x 160 mm. In the case of repaired specimens, half depth notch is incised in the center of the specimen, which is the interface between substrate and repair. The attributes of specimens are listed in Tab. 1, where 4 types of repair and 2 types of repaired ones are listed. The used aggregate is iron sand which is commercially available for steel shot grit (diameter is 0.1 mm) with low cost. The substrate is ordinary mortar whose Fb is 5.05 MPa and GF is 77.8 N/m. The roughening treatment for the surface to be repaired was conducted with 3 minutes of wire brushing after one day after the casting of the substrate. The mechanical properties are listed in Tab. 2 and 3 measured under the setup depicted in Fig.1. From Tab. 2, one can see the clear tendency that Fb is dependent to Young’s modulus (E) but GF is not. E depends on the content of steel fiber and iron sand. FRRs in Tab. 3 are almost above 0.9 meaning the crack path extends in the repair. Though GF is almost the same in the two cases, Fb in the case with iron sand is about 8% higher than the case without it. Then it is suggested that Fb is improved with high modulus aggregate (iron sand) in both cases of the repair and the repaired mortar. Name of Volume fraction (-) Type specimen W/C Steel fiber Aggregate Repair C4S-1,2,3 0.4 0.00 0.00 material C4S10-1,2,3 0.4 0.01 0.00 CS-1,2,3 0.5 0.00 0.00 CS10-1,2,3 0.5 0.01 0.00 CS10Fa10-1,2,3 0.5 0.01 0.10 Repaired H2dC4S10Fa10-1,2,3 0.4 0.01 0.10 mortar H2dC4S10-1,2,3 0.4 0.01 0.00 Figure 1 : Specimen and test setup. Table 1 : Attributes of repairs used for specimens. Name of GF (N/mm) Fb (MPa) Young's Bulk Type specimen Data Average Data Average modulus (GPa) density Neat repair C4S-1 0.006 1.621 (W/C=0.4) C4S-2 0.006 0.006 1.494 1.528 14.00 2.13 C4S-3 0.006 1.468 Repair C4S10-1 2.571 6.757 with fiber C4S10-2 2.755 2.426 7.630 7.136 15.86 2.19 C4S10-3 1.953 7.021 Neat repair CS-1 0.005 0.910 (W/C=0.5) CS-2 0.005 0.005 0.949 0.930 13.96 2.08 CS-3 (-) (-) Repair CS10-1 2.739 4.890 with fiber CS10-2 2.064 2.247 4.303 4.347 15.82 2.14 CS10-3 1.938 3.848 Repair CS10Fa10-1 2.308 5.488 with fiber CS10Fa10-2 2.430 2.353 5.180 5.723 32.56 2.66 and aggregate CS10Fa10-3 2.321 6.500 Table 2 : Mechanical properties of repair materials. T