In this study, an alkali activate slag cementless fiber composites(AASFC) with low carbon dioxide emissions was developed and manufactured as eco-friendly and high-ductile mechanical characteristics. The analysis of mixing design, mechanical characteristics, and performance evaluations of structural members according to the fiber mixing rate of AASFC showed the following results.
For fresh AASFC, Slump flow was measured 540~770mm, For hardened AASFC, compressive strength was 32.60~35.50MPa and tensile strength was 3.01~4.69MPa. Moreover, ultimate tensile strain was recorded 2.88~4.96% for direct tensile test and flexural strength was 8.14~12.29MPa. Shear strength was measured 5.01~7.04MPa for push-off shear test, and shear strength was 4.58~5.48 MPa for biaxial pure shear test. Based on an revised model of the Modified Compression Field Theory (MCFT) for AASFC, nonlinear analysis of AASFC panel for biaxial shear performances showed a difference of 8.29~9.53% compared with experiments with 1.95~5.01MPa. Experiments with AASFC-applied bending-type beams showed a maximum load of 127.51kN, a deflection of 11.13mm, and an AASFC-applied experiment with a maximum load of 140.41MPa~158.10MPa, and a deflection of 31.53~42.60 mm. Flexural strength of beams applied with AASFC has a performance improvement of about 10.11~23.99% compared with a specimen of reinforced concrete beam. The performance improvement effect was 13.14~39.07% as a rate of tensile reinforcement reduction, with a reduction of up to 39.07% from 2.00% fiber mixing rate. Experiments with shear-type beams showed that the conventional reinforced concrete beam had a maximum load of 69.15kN, a deflection of 2.22mm, and the AASFC beam had a maximum load of 94.10~122.95MPa, and a deflection of 4.01~4.91mm. The shear strength of beams applied with AASFC showed a performance improvement of approximately 36.08~77.80% over the reinforced concrete beam. The performance improvement effect was 23.63~54.23%, which was reduced by up to 54.23% from 2.00% fiber mixing rate. The proposed flexural strength design equation resulted in a 7.22~9.23% difference in value and a 3.68~12.72% difference in value in the shear strength design compared to the experiment. The proposed beam design equation well calculated the maximum load capacity and the increase in strength with the fiber mixing rate of AASFC compared to the experimental results. Results of nonlinear fiber sectional analysis showed that for the maximum load capacity according to the fiber mixing rate of the AASFC was well estimated with a difference of 0.55~9.74% compared to the experiment. Nonlinear finite element analysis of beams showed that the difference in values was 0.71~9.99% compared to the experiment, predicting the overall load-displacement behavior according to the fiber mixture rate of AASFC, and approximately estimating the load-displacement behavior after maximum load capacity. Results of nonlinear finite element analysis predict the maximum load capacity of beams according to the fiber mixing rate of AASFC. The behavior of each load step of the beam can be effectively predicted through a nonlinear finite element analysis program. In the shear wall normal rebar type, the ordinary concrete experiment showed a maximum load of 160.91kN, a displacement of 10.40mm, the AASFC applied with a displacement of 292.70MPa, and a displacement of 4.42mm. In the minimum reinforcement ratio type, the ordinary concrete experiment showed a maximum load of 160.91 kN, a deflection of 10.40 mm, and the AASFC applied with a maximum load of 292.70MPa and a deflection of 4.42mm. Experiments applied with AASFC showed a higher maximum load of 81.90% for normal reinforcement type and 80.69% for minimum reinforcement type compared to regular concrete type, indicating that it is effective in improving shear wall performance due to fiber mixing. The design strength of the shear wall applied with the design equation that reflects the AASFC material characteristics showed a difference of 3.07~10.54% of the maximum load compared to the experiment, which well predicted the strength of the shear wall. The nonlinear finite element analysis results showed a difference in values from 0.87~7.20% compared to the experiment, and similarly estimated the behavior after the maximum load. Nonlinear finite element analysis programs can effectively predict the behavior of shear walls for each load step.
The alkali-activated slag cementless fiber composites developed in this study has excellent mechanical performance, so it is effective for performance improvement when applied to structural members and has advantages such as the effect of reducing the amount of rebar. It is considered that structural members can be applied as high-ductility/high-performance materials by supplementing the problems of high shrinkage rate and rapid carbonation of alkali-activated slag binders and lowering of surface hardness and applying various types of reinforcing fibers according to various compressive strengths. AASFC is expected to be able to offset the price problem of reinforcing fibers with the effect of reducing rebar and carbon emission by reducing reinforcing bars and reducing carbon emissions. In addition, alkali activated slag cementless fiber composite is effective for crack width and crack control, excellent deformation performance and strength improvement, so it is considered to be advantageous for field application when applied to precast members.