Optimization of mix proportion and performance research of composite shrinkage-reducing agent for aeolian sand concrete based on response surface methodology

To address the issues of early-age high shrinkage and the consequent strength deterioration in fully aeolian sand-based high-performance concrete, which arise from its low water-to-binder ratio and absence of coarse aggregate, this study designs and optimizes a ternary composite shrinkage-reducing agent (SRA) with synergistic "shrinkage reduction and strength enhancement" effects using the response surface methodology (RSM). With diethylene glycol monobutyl ether (DGBE), 2-amino-2-methyl-1-propanol (AMP-15), and triisopropanolamine (TIPA) as key components, a quadratic polynomial regression model is constructed based on the Box-Behnken experimental design principle, taking the 28-day shrinkage rate, compressive strength, and flexural strength as response variables. The reliability of the model is confirmed through analysis of variance and experimental validation. The results indicate that the three established response models exhibit high predictive accuracy, with correlation coefficients (R²) of 0.9831, 0.9876, and 0.9811, respectively. Multi-objective optimization yields the optimal formulation of the composite SRA: DGBE 1.4%, AMP-15 1.1%, and TIPA 0.7%. Validation experiments demonstrate that, with this formulation, the 28-day shrinkage rate of the concrete is reduced to 597.3×10^-6, while the compressive and flexural strengths reach 103.3 MPa and 21.1 MPa, respectively, with all prediction errors below 5%. Pore solution performance tests reveal that the composite agent significantly reduces the surface tension of the pore solution to 41.5 mN/m and increases the solution-pore wall contact angle to 37.8°, providing a mechanistic explanation for its excellent shrinkage-reducing efficacy. The high-efficiency ternary composite SRA developed in this study not only significantly mitigates the risk of shrinkage cracking in high-performance concrete with fully aeolian sand replacement but also compensates for the strength loss associated with single-component SRAs, thereby providing a theoretical foundation and data support for the synergistic design and performance regulation of admixtures for fully aeolian sand high-performance concrete.