Mechanism of Pozzolanic Activity of an Additive of Highly Dispersed Wollastonite Stabilized With Polycarboxylate Ether

A method for increasing the activity of natural β-wollastonite is proposed, implemented by ultrasonic dispersion of the feedstock in an aqueous solution of polycarboxylate ether stabilizer at a frequency of 35 kHz for 5 minutes. The degree of pozzolanic activity of the developed highly dispersed fine-grained concrete modifier is 87.3 mg/g, which is more than 25 times higher than that of its initial components. The mechanism of the activation process of natural β-wollastonite is presented, which consists in leaching the crystal surface by replacing calcium ions in its crystal lattice, leading to hydrolysis of the unstable silicate framework with the rupture of Si-O-Ca bonds and subsequent protonation of silicate groups to silicic acids, the presence of which is confirmed by the most characteristic analytical feature based on the formation of a complex silicamolybdenum heteropolyacid and its reduction by tin chloride to molybdenum blue. At the same time, the improvement of the reactivity of β-wollastonite by increasing the specific surface area, as well as the removal of passivation from the surface of its crystals, are determined by the action of ultrasound, which at the same time enhances the hydrolysis of polycarboxylate ether in the reactions of substitution and protonation of carboxylate groups due to the active formation of diprotic maleic acid, fixed on the differential curve of potentiometric titration with an intense peak at pH = 9.55, and its copolymer in the form of monobasic acrylic acid, detected by excluding methacrylate according to the Mano reaction. The use of the developed additive of highly dispersed wollastonite makes it possible to manufacture products from fine-grained concrete with a compressive strength of 58.5 MPa, a bending strength of 6.8 MPa, a water absorption of 1.9%, and a frost resistance of F500. X-ray phase analysis of cement stone revealed a noticeable weakening of the peaks of portlandite by 18.2%, which is explained by its transformation into poorly soluble compounds as a result of acid-base exchange reactions induced by the hydrolysis products of the modifier components.