Preparation of specialized plastering mortar for foam concrete using low silica iron tailings

Abstract

The mismatch in physical properties between traditional mortar and the porous substrate of foam concrete (FC) leads to poor adhesion and cracking, limiting the wider application of FC. In order to address this issue and alleviate the storage pressure of low silica iron tailings (LSIT), this study developed an advanced plastering mortar system for foam concrete blocks through systematic optimization of LSIT. A comprehensive evaluation was conducted on six critical parameters, including the water-cement ratio, the aggregate ratio of LSIT to sand, the content of cement, hydroxypropyl methyl cellulose (HPMC), re-dispersible latex powder (RDP), and polypropylene fiber (PPF), establishing their quantitative impacts on mortar performance. The optimal performance was achieved with a water-cement ratio of 0.84, aggregate ratio of 11:3, cement content of 30%, HPMC content of 0.4%, RDP content of 1.5%, and PPF content of 0.15%, yielding a mortar density of 1447.9 kg/m³, 28 d compressive strength of 8.21 MPa, and 104 mm consistency, parameters fully compliant with the M8 grade specifications in JC/T 890-2017. Advanced microstructural characterization (XRD, SEM, and hydration heat analysis) demonstrated that LSIT particles refined the granulometric distribution through microaggregate effects. In addition, C₃S dissociation was retarded by HPMC through Ca²⁺ chelation, extending the induction period of hydration. Moreover, the RDP facilitated interfacial cross-linking via transesterification, forming the core–shell structures of C–S–H and polymer, compared with the control sample, the portlandite content was slightly reduced. Furthermore, the PPF reinforcement is achieved through crack-deflection and bridging mechanisms. The modification system of multi-component materials therefore exhibits a three-fold synergistic action, including the gradation optimization of particles, the regulation of hydration kinetics, and the toughening of the interfacial. These findings establish a viable pathway for high-value utilization of iron tailings in construction materials and simultaneously elucidate the physicochemical mechanisms underlying the interactions of composite modifiers in cementitious systems. Furthermore, the modified additive system serves as a viable template for valorizing diverse solid wastes.

Graphical abstract