The accelerating and hardening as well as toughening cement hydration derived from microencapsulation of potassium titanate with Al₂(SO₄)₃·18H₂O and coordinating copolymers as admixture

This study develops a series of functional admixtures for ordinary Portland cement based on a synthesized water-soluble terpolymer and its ball-milled composites with aluminum sulfate. The foundational admixture significantly accelerates cement setting, achieving an initial setting time of 4.33 min and a final setting time of 7.98 min, performance that exceeds the Chinese National Standard GB/T 35159–2017 requirements for flash-setting admixtures (which specify ≤5 min for initial setting and ≤12 min for final setting), while delivering a 24-hour compressive strength of 5.0 MPa and flexural strength of 1.6 MPa. The acceleration mechanism is attributed to the in-situ formation of the active intermediate (H₃O)Al₃(SO₄)₂(OH)₆. Incorporating potassium titanate whiskers—A3 derived from anatase (TiO₂) and A4 from metatitanic acid (TiO₂·H₂O)—forms microcapsule-structured composites that further enhance performance. The A3-based composite reduces initial setting time to 3.83 min and final setting time to 7.10 min, while significantly improving mechanical strength, achieving a 24-hour compressive strength of 6.8 MPa that nearly meets the GB/T 35159–2017 standard requirement of ≥ 7.0 MPa at 24 h. A4-based whiskers provide comparable acceleration and demonstrate superior long-term flexural strength, reaching 5.1 MPa at 28 days. Mechanistic analysis reveals aluminum species drive rapid setting while whiskers enhance strength through distinctive phase transformations during hydration. Furthermore, 3-aminopropyltriethoxysilane-modified whiskers (both A3 and A4) produce admixtures that function as potent set retarders while simultaneously increasing 24-hour compressive and flexural strengths by 113 % and 91 % respectively compared to plain cement mortar, demonstrating exceptional superplasticizer characteristics. A key finding is the whisker-specific optimization strategy: silane pretreatment benefits A3 for achieving both accelerated setting and high strength, whereas unmodified A4 performs better in the same application. This work elucidates the design principles and mechanisms of tunable multifunctional cement admixtures, establishing strategic pathways for developing advanced construction materials suitable for applications ranging from shotcrete to oil well cementing.