Preparation of a Novel Cement from Red Mud and Limestone

Red mud (RM) is an industrial waste obtained from the Bayer process which is usually discharged into marine or disposed into a landfill causing pollution for the surrounding water, air, and soils. Thus, disposal of RM is an environmental concern, and it should be recycled effectively. Because RM consists of iron- and aluminum-rich phases, it is possible to be processed into cementitious material and utilized for construction purposes. This research fabricated a type of cement from the mixture of RM and limestone. The mixture was sintered at temperature of 1180 °C to obtain the clinker of the novel hydraulic cement with C2S, C3A, and C4AF minerals. In which, C2S, C3A, and C4AF are respectively belite, alite, and tetra-calcium aluminoferrite compounds that are characteristic hydraulic minerals of Portland cement clinker. The specifications of this cement were tested and evaluated in this study such as chemical and mineralogical compositions, fineness, specific surface area, mechanical strength after 3, 7, and 28 days.

Influence of Dimethacrylate Monomer on the Polymerization Efficacy of Resin-Based Dental Cements—FTIR Analysis

The degree of polymerization for dimethacrylate resin-based materials (BisGMA, TEGDMA, UDMA, HEMA) ranges from 55 to 75%. Literature data indicate that polymerization efficacy depends, among other factors, on the type of methacrylate resin comprising the material. The aim of this study was to evaluate the polymerization efficacy of four dental cement materials characterized by different polymerization mechanisms using FTIR analysis. In the present study, the FTIR method was adopted to analyze the degree of polymerization efficacy of four resin-based dental cement materials, two of which were self-cured and two were dual-cured cements. The IR spectral analysis was performed 24 h after the polymerization of the cementitious material. RelyX ARC cement exhibits the lowest polymerization efficacy (61.3%), while that of Variolink II (85.8%) and Maxcem Elite is the highest (90.1%). Although the efficacy of self-cured cements appears to be superior, the difference is not statistically significant (p = 0.280). Polymerization efficacy largely depends on the chemical structure of the material in terms of the presence of a particular methacrylate resin and less on the polymerization mechanism itself, i.e., whether it is a self-cured or dually cured dental cement. Thus, in clinical practice, cementitious materials with a higher proportion of TEGDMA compared with BisGMA are recommended.

Mechanical Properties and Deterioration Instability of Filling Body with Gangue-Cement Material Based on AE Experiment

Gangue materials have been used to solve mine disasters with a support tunnel along the goaf and filling mining. Mastering the properties and damage characteristics of filling materials is an important basis for effective implementation. Based on the conventional uniaxial compression acoustic emission (AE) test, the effects of cementitious materials, ratio between water and cementitious material, gangue particle size, and grading parameters on the mechanical properties of gangue-cement samples were analyzed. The stage characteristics of compression deformation were studied. The fracture propagation characteristics and rock mass failure types induced by different graded gangues were revealed. The fracture forming mechanism from clustered damage and failure was interpreted. The results show that the compressive strength of the backfill increases with the increase of cementitious material; however, it decreases with the increase of water binder ratio. Controlling the proportion and dosage of materials was the key factor to realizing pumpability and stability. Combined with the deformation and AE characteristics, the failure stage of the backfill body is divided into three stages: linear deformation-low energy changing, block compression-high energy changing, and gentle stability-stable energy changing. Affected by the gangue distribution, the load in each stage will induce fracture to produce five distribution modes of single, turning, breakthrough, bifurcated, and collapsed surrounding gangue. In the process of loading failure, different gradation and particle sizes will also change its stress concentration characteristics, resulting in the transformation of rock failure types. The surface structure and roughness of gangue play an important role in the compressive performance of cement paste. The research results try to provide some guidance for efficient filling mining.