The Optimization of Mix Proportions for Cement Paste Backfill Materials via Box–Behnken Experimental Method

Multi-Objective Function Optimization of Cemented Neutralization Slag Backfill Strength Based on RSM-BBD

Tailings produced in the beneficiation of Carlin-type gold deposits are characterized by fine particle size and high mud content. When neutralized with wasted acid generated by pressurized pre-oxidation, the tailings turn to neutralized slag and perform as a novel backfill material. To understand the influential behavior of variable factors on the strength and its optimization of cemented neutralization slag backfill, RMS-BBD design test was carried out with 56–60% slurry mass fraction, 12.5–25% cement/(neutralization slag + waste rock) (i.e., C/(S+R)) and 30–40% waste rock content. A modified three-dimensional quadratic regression model was proposed to predict the strength of cemented neutralization slag backfill. The results showed that backfill strength predicted by the modified ternary quadratic regression model was in high coincidence with the data of backfill mixture tests. C/(S+R) was predominant in backfill strength with regard to every single influential factor throughout the curing age, and the mass fraction of slurry had a significant effect on the later strength. From the perspective of economic and engineering operation, a multi-objective function method was further introduced to optimize the backfill strength. The optimal mixture proportion of cemented neutralized slag backfill slurry was: 58.4% slurry mass fraction, 32.2% waste rock content, and 20.1% C/(S+R). The backfill strength of this mixture proportion on days 7, 28 and 56 was verified as 0.42, 0.64 and 0.85 MPa, respectively. RSM-BBD design and multi-objective function optimization proposed a reliable way to evaluate and optimize the strength of neutralized slag backfill with high mud content.

Optimising the Workability and Strength of Concrete Modified with Anacardium Occidentale Nutshell Ash

Strength failure persists both in structural and mechanical analysis. One of its prominent characteristics is the adequate provision for parameters that minimise or maximise strength objectives while satisfying boundary conditions. The previous optimisation of concrete strength usually neglects mix design mechanisms induced by optimisation. Recent efforts to accurately optimise the concrete compressive strength have factored in some of these mechanisms. However, optimising concrete strength modified with high silica and alumina precursors, and crucial mix design factors are rare. Consequently, this paper optimised the concrete workability and strength, incorporating binding, water/binder ratio, binder/aggregate ratio, and curing mechanisms using the Box–Behnken design approach (BBDA). A waste material, anacardium occidentale (cashew) nutshell ash, was valorised and used at 5, 10, and 15 wt.% of cement. The composites were made, cured and tested at 14–90 d. The results revealed a high precision between the experimental slump and the optimisation slump at 97% R2. In addition, a 5% increase in compressive strength was obtained compared with the target compressive strength. Besides, the correlation between the model equation obtained from this study and predictions of previous studies via BBDA yielded a strong relationship.

A review of additives used in the cemented paste tailings: Environmental aspects and application

A large amount of mine wastes is generated every year through mining and mineral processing operation. The management of mine tailings is an attractive topic for researchers from both environmental and economic aspects. Mine tailings have shown a capacity as a raw material for the construction industry or a substitution for previous materials to produce the cement. It is applied in some specific environments such as offshores or massive projects like large bridges and tunnels. However, the cement industry has caused a variety of environmental issues. The production of Portland cement on an industrial scale increases the greenhouse effects and generates acidic rains. It releases greenhouse gases by the generation of carbon dioxide. In recent years, strict environmental regulations led to more efforts from mining industries to manage their tailings. A new approach to decrease the environmental issues, improve cement technology and obtain economic benefits is the use of mine tailings for cement production. Mine tailings in the cement mixtures decrease the initial hydration, retard the setting time, and lower the product mechanical strength. These problems can be fixed by the use of additives. Additives as chemical compounds are added to a cemented paste to change its properties and improve its performance. Therefore, the additives in cemented paste tailings can increase the pump-ability, reduce the water-to-cement ratio, increase density, or even adjust setting time and hydration according to the desired purposes. However, the amount of additives in the cemented paste tailings changes based on the type of additive. It should be optimized to cause a positive effect on the cement properties. Furthermore, the additives and their adaptation to the physical and chemical characteristics in cement and tailings is an important issue that should be investigated. In this paper, the usage of several chemical additives was studied, which can strengthen the properties of cemented paste tailings during backfilling operation. It can cause a better condition to decrease the environmental problems for the cement industry and mine tailings. A review of previous works is presented with an explanation of the gaps in previous studies.