Acoustic emission and microstructural insights into a ternary OPC-SAC-UFA cementitious grout

Area of Science:

• Materials Science
• Civil Engineering
• Construction Materials

Background:

• Conventional cement-based grouting materials often exhibit poor injectability, delayed setting, and insufficient early strength.
• Addressing these limitations is crucial for improving the performance and application range of grouting materials in various engineering projects.

Purpose of the Study:

• To develop a ternary composite grout by incorporating calcium sulfoaluminate cement (SAC) and ultra-fine fly ash (UFA) into ordinary Portland cement (OPC).
• To investigate the effects of SAC-to-UFA ratio, polycarboxylate superplasticizer (PCE) dosage, and water-to-binder ratio on the grout's workability, mechanical properties, and damage characteristics.
• To elucidate the relationship between microstructural evolution and macroscopic performance.

Main Methods:

• Systematic investigation of workability (fluidity, viscosity), mechanical properties (compressive strength), and acoustic emission (AE) damage characteristics.
• Microstructural analysis using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).
• Optimization of the SAC-to-UFA mass ratio (mSAC:mUFA), PCE dosage, and water-to-binder ratio.

Main Results:

• Increasing mSAC:mUFA ratio accelerated setting time and increased early strength but reduced later strength and fluidity.
• An optimal PCE dosage of 0.3% maximized fluidity and compressive strength across all curing ages.
• The water-to-binder ratio significantly impacted viscosity, bleeding, and 28-day strength, with higher ratios leading to lower viscosity but increased bleeding and degraded strength.
• Grout failure modes and AE characteristics were governed by the interplay of mSAC:mUFA ratio, PCE dosage, and water-to-binder ratio, with specific ratios leading to tensile or shear crack dominance and distinct AE patterns.
• Microstructural analysis revealed SAC's role in early strength, UFA's contribution to fluidity and densification, and PCE's function in dispersion and hydration regulation.

Conclusions:

• The developed ternary composite grout successfully balances fluidity, setting time, and strength development through synergistic effects of SAC, UFA, and PCE.
• The sequential action of SAC for early skeleton formation, UFA for fluidity and densification, and PCE for workability optimization achieves superior performance compared to conventional grouting materials.
• This novel grout formulation offers a promising solution for addressing the limitations of traditional cement-based grouting materials.