Flexural and fracture performance of fiber reinforced self compacting alkali activated concrete– A DOE approach

Owing to their much-reduced carbon footprint and lower embodied energy, compared to conventional Portland Cement (OPC-based) Concrete mixes, Alkali Activated Concrete (AAC) mixes represent a pivotal advancement towards achieving sustainability goals. The fracture properties were investigated using Three-Point Bending Tests (3-PBT) under the mode I failure mechanism. This study utilises Taguchi analysis to analyse and optimise Self-Compacting Alkali-Activated Concrete (SAAC), focusing mainly on its flexural strength and fracture characteristics. An L-16 orthogonal array of experiments with three input parameters − replacement of Blast Furnace Slag (BFS) with Fly ash (FA) (0 %, 30 %, 40 %, and 50 %), Steel Fibers (SF) volume content (0 %, 0.25 %, 0.5 % and 0.75 %) and Notch to Depth (a₀/d) ratio (0.2,0.3,0.4 and 0.5), at four levels each, was adopted. The Work of Fracture Method (WFM) and Double K Fracture Criterion (DKFC) were utilised to determine the Fracture Energy (G_F) and fracture toughness, respectively. The results obtained from all the sixteen mixes showed that the F0-S0.75-N0.5 mix demonstrated better values in several parameters, such as flexural strength of 7.82 MPa,${\text{K}}_{\text{IC}}^{\text{ini}}$ of 0.928 MPa√m, ${\text{K}}_{\text{IC}}^{\text{uns}}$ of 6.99 MPa√m and ${\text{K}}_{\text{IC}}^{\text{ini}}$/ ${\text{K}}_{\text{IC}}^{\text{uns}}$ of 0.133. A maximum G_F of 2350 N/m was obtained with F50-S0.75-N0.2 mix. However, all the inferior values of these parameters were observed with F50-S0-N0.5 mix, which recorded a flexural strength of 4.90 MPa, ${\text{K}}_{\text{IC}}^{\text{ini}}$ of 0.612 MPa√m,${\text{K}}_{\text{IC}}^{\text{uns}}$ of 1.16 MPa√m, ${\text{K}}_{\text{IC}}^{\text{ini}}$/ ${\text{K}}_{\text{IC}}^{\text{uns}}$ of 0.528 and G_F of 125 N/m. Through Taguchi analysis, the optimal combination for flexural strength was identified as FA 0 %, SF 0.75 %, and a₀/d 0.5 and for both Initial Fracture Toughness (${\text{K}}_{\text{IC}}^{\text{ini}}$) and Unstable Fracture Toughness (${\text{K}}_{\text{IC}}^{\text{un}\text{s}}$) at FA 0 %, SF 0.75 % and a₀/d 0.4. For both the ratio of initial to unstable fracture toughness (${\text{K}}_{\text{IC}}^{\text{ini}}$/ ${\text{K}}_{\text{IC}}^{\text{un}\text{s}}$) and fracture energy (G_F), the optimum combination was FA 0 %, SF 0.75 % and a₀/d 0.2. Furthermore, the results indicate that FA significantly influences ${\text{K}}_{\text{IC}}^{\text{ini}}$, while SF predominantly affects all other parameters. The predictive performance of the regression equations demonstrates good agreement with experimental outcomes.