The Encapsulation of Illite Powders with Al2(SO4)3·18H2O and Hydrophilic Copolymers: Accelerating and Toughening Cement Hydration Through the Proliferation of 54CaO·MgO·Al2O3·16SiO2 Clinker

Two hydrophilic copolymers containing functional groups such as carboxyl, amido, and sulfonic acid are synthesized using ammonium persulfate-catalyzed free radical polymerization in water. Aluminum sulfate is then introduced, resulting in two polymer complexes that exhibit reduced cement setting times (initial, 1.16-2.44 min; final, 2.02-3.14 min) and improved compressive (24 h, 5.81-7.25 MPa) and flexural (24 h, 2.80-2.99 MPa) strengths compared to pure aluminum sulfate-facilitated cementing (initial, 19.11 min; final, 37.05 min; compressive, 24 h, 5.51 MPa; flexural, 24 h, 2.56 MPa). Following this, ball-milled illite powder is added, and the resulting admixtures further display slightly prolonged setting times (initial, 2.35-2.99 vs. 1.16-2.44 min; final, 3.98-4.35 vs. 2.02-3.14 min), along with comparable compressive strengths (5.85-7.11 vs. 5.81-7.25 MPa) and enhanced flexural strengths (3.92-5.83 vs. 2.80-2.99 MPa). Notably, a unique adhesive pozzolanic clinker, Ca₅₄MgAl₂Si₁₆O₉₀ (54CaO·MgO·Al₂O₃·16SiO₂), emerges in the presence of illite-based admixtures, contributing to the mechanical strength development of the hydrated mortars. Although illite itself is hydrophobic, the coating of ball-milled illite powder with aluminum sulfate and copolymers facilitates its dispersion into the gaps and pores of the cement matrix during setting, thereby increasing the flexural strength. This work presents an interesting approach to utilizing illite materials in cement applications, which is significant for reducing CO₂ emissions during cement production and use.