Towards Ultra-Rapid and High-Toughness Cementing: A Synergistic Acceleration Leveraging Aluminum Sulfate and Sodium Alginate Copolymer Along with Glass Fibers

This study synthesizes two highly water-soluble copolymers, <i>p</i>(SA-<i>co</i>-SMAS) and <i>p</i>(SA-<i>co</i>-SMAS-<i>co</i>-AMPS) using sodium alginate (SA), sodium 2-methylprop-2-ene-1-sulfonate (SMAS), and 2-acrylamido-2-methylpropane sulfonic acid (AMPS, with or without addition) as precursors. Under ball milling, these copolymers are blended with aluminum sulfate and glass fibers to produce two series of cement admixtures. Compared to systems without admixtures or with pure aluminum sulfate as sole admixture, the admixture obtained from <i>p</i>(SA-<i>co</i>-SMAS) and aluminum sulfate significantly shortens the initial setting time (4.47 vs. 33.59 and 29.51 min) and final setting time (8.46 vs. 45.26 and 35.12 min), while markedly improving compressive strength (9.2 vs. 3.5 and 4.3 MPa) and flexural strength (3.5 vs. 1.0 and 1.1 MPa). This enhancement is attributed to the formation of a unique boehmite (AlO(OH)) phase in synthesized admixture, which rapidly reacts with tricalcium silicate, gypsum, and water in cement to form ettringite (Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O). The ettringite interlocks with the two-dimensional C-S-H gel, creating a stable three-dimensional network. Further blending this admixture with 200-mesh glass fibers yields a new admixture containing Al₄SO₄(OH)₁₀·36H₂O. Compared to boehmite, this phase further reduces setting times and increases average compressive strength (10.2 vs. 9.2 MPa). The admixture derived from <i>p</i>(SA-<i>co</i>-SMAS-<i>co</i>-AMPS) and aluminum sulfate shows even better performance: setting times are further shortened and flexural strength is significantly enhanced, owing to the presence of the more effective Al₄SO₄(OH)₁₀·36H₂O phase. Incorporating 200-mesh glass fibers into this system results in the shortest setting times (initial: 2.24 min, final: 5.73 min) and an excellent 24 h compressive strength (9.4 MPa), likely due to a unique and unexpected pore-filling effect. In contrast to conventional uses of sodium alginate as a retarder, glass fibers as mere reinforcements, and aluminum sulfate as a strength-impairing accelerator, this work demonstrates a synergistic strategy, which enables an ultra-rapid and high-strength cement setting process, offering highly significant scientific and practical value.