Optimization of the Mix Formulation of Geopolymer Using Nickel-Laterite Mine Waste and Coal Fly Ash

A state-of-the-art review of the structure and properties of laterite-based sustainable geopolymer cement

Portland cement is the primary material in the field of construction. Despite its importance, its production remains an energy-consuming and polluting operation. Research on alternatives to Portland cement has become an international concern, and these alternatives include geopolymers. With the evolution of the research on geopolymers during the last decade, it is necessary to work on raw materials that are abundant in nature and less expensive and provide sustainable construction materials. The present paper reviews the research on the use of laterites as a precursor in synthesizing sustainable geopolymers. The effect of the nature of activators, the calcination temperature of laterites, and the effect of additives on the properties of laterite-based geopolymers are also examined. The characterization results of laterite-based geopolymers show that laterite is a promising precursor for synthesizing sustainable geopolymers with high physical-mechanical characteristics. Finally, perspectives and recommendations for advancing laterite-based geopolymers are discussed at the end of the paper.

Mining tailings and alkali activation: a comprehensive bibliometric review

Significant amounts of mining tailings are generated and disposed of every year in dams, leading to potentially serious environmental and safety problems. To identify alternatives for the disposal of these wastes, research works involving their potential application as precursors in the development of alkaline-activated materials have been published in recent years. In this context, the objective of this paper is to present an overview of the main contributions already made on the subject, identified through a bibliometric review and content analysis in the Scopus and Web of Science databases. There was an exponential growth of interest in the subject in the period 2019-2021, when more than 50% of the papers were published. The most used tailings and sub-areas of research were also identified.

Use of Fluidized Bed Combustion Fly Ash as a Partial Substitute for Cement in Underwater Concrete Mixes

Despite limitations to coal combustion energy production, many countries face the still-unresolved problem of utilising the wastes from fluidised bed coal combustion. One direction of rational utilisation can be using these wastes in the building materials industry. The study aimed to analyse the possibility of using fluidised bed combustion fly ashes as a partial substitute for cement in the underwater concrete (UWC). Two groups of concrete mixes were tested, containing 20 to 50% of fluidised bed combustion fly ashes. Investigations of the rheological properties of the concrete mixes and the mechanical performance of the hardened concrete confirmed the possibility of replacing cement in UWC with fluidised bed combustion fly ash up to 30% of the cement mass. The higher content of the fly ashes significantly worsens the UWC strength as well as the consistency and wash-out loss of the concrete mixes, excluding its use in underwater concreting.

Development of Ceramic Tiles from Philippine Nickel Laterite Mine Waste by Ceramic Casting Method

Siltation is the biggest environmental challenge associated with nickel laterite mining in the Philippines. The amount of silt generated is huge and one mitigation strategy currently employed by the mining companies is the construction of siltation ponds where the bulk of the clayey- and silt-sized surface runoffs is collected. However, this poses several serious environmental hazards such as landslides due to heavy rainfall and the potential release of hazardous heavy metals. A promising approach to reduce the risks associated with long-term storage of nickel mine waste (NMW) is to employ circular economy by repurposing it for ceramic applications. While generating useful materials with economic value out of a mine waste, it will result in a reduction in volume of waste for disposal. In this study, the method employed to produce NMW-based ceramic wall and floor tiles is slip casting as it is the most appropriate method in forming tiles with complex surface features. Five formulations of NMW-based slips were made for the casting of ceramic tiles and each slip was characterized for its suitability as raw material. The results of NMW characterization show that NMW could be utilized as raw materials for both ceramic wall and floor tiles and the addition of feldspar can enhance casting and physical properties.

The Influence of Composition and Recipe Dosage on the Strength Characteristics of New Geopolymer Concrete with the Use of Stone Flour

Currently, considering global trends and challenges, as well as the UN sustainable development goals and the ESG plan, the development of geopolymer binders for the production of geopolymer concrete has become an urgent area of construction science. This study aimed to reveal the influence of the component composition and recipe dosage on the characteristics of fine-grained geopolymer concrete with the use of stone flour. Eleven compositions of geopolymer fine-grained concrete were made from which samples of the mixture were obtained for testing at the beginning and end of setting and models in the form of beams and cubes for testing the compressive strength tensile strength in bending. It was found that the considered types of stone flour can be successfully used as an additive in the manufacture of geopolymer concrete. An analysis of the setting time measurements showed that stone flour could accelerate the hardening of the geopolymer composite. It was found that the addition of stone waste significantly improves the compressive strength of geopolymers in comparison with a geopolymer composite containing only quartz sand. The maximum compressive strength of 52.2 MPa and the tensile strength in bending of 6.7 MPa provide the introduction of potassium feldspar in an amount of 15% of the binder mass. Microstructural analysis of the geopolymer composite was carried out, confirming the effectiveness of the recipe techniques implemented in this study.

Developing Environmentally Sustainable and Cost-Effective Geopolymer Concrete with Improved Characteristics

Improving the efficiency and quality of construction mainly depends on the cost of building materials, which is about 55–65% of total capital-construction costs. The study aimed to obtain geopolymer fine-grained concrete with improved quality characteristics that meet the construction field’s sustainable development criteria and that have environmental friendliness, economic efficiency, and advantages over competing analogues. The dependences of strength characteristics on various compositions of geopolymer concrete were obtained. It was found that the most effective activator is a composition of NaOH and Na2SiO3 with a ratio of 1:2. The increase in the indicators of the obtained geopolymer concrete from the developed composition (4A) in relation to the base control (1X) was 17% in terms of compressive strength and 24% in tensile strength in bending. Polynomial equations were obtained showing the dependence of the change in the strength characteristics of geopolymer concrete on the individual influence of each of the activators. A significant effect of the composition of the alkaline activator on the strength characteristics of geopolymer fine-grained concrete was noted. The optimal temperature range of heat treatment of geopolymer concrete samples, contributing to the positive kinetics of compressive strength gain at the age of 28 days, was determined. The main technological and recipe parameters for obtaining geopolymers with the desired properties, which meet the ecology requirements and are efficient from the point of view of economics, were determined.

Investigation on the Compressive Strength and Time of Setting of Low-Calcium Fly Ash Geopolymer Paste Using Response Surface Methodology

Approximately 2.78 Mt of coal fly ash is produced in the Philippines, with a low utilization rate. Using fly ash-based geopolymer for construction will lessen the load sent to landfills and will result in lower GHG emissions compared to OPC. It is necessary to characterize the fly ash and optimize the geopolymer components to determine if it can replace OPC for in situ applications. The activator-to-precursor ratio, the water-to-solids ratio, and the sodium hydroxide-to-sodium silicate ratio were optimized using a randomized I-optimal design from the experimental results of 21 runs with five replicates, for a total of 105 specimens of 50 mm × 50 mm × 50 mm paste cubes. The engineering properties chosen as the optimization responses were the unconfined compressive strength (UCS), the initial setting time, and the final setting time. The samples were also ambient-cured with the outdoor temperature ranging from 30 °C to 35 °C and relative humidity of 50% ± 10% to simulate the on-site environment. Runs with high unconfined compressive strength (UCS) and short setting times were observed to have a low water-to-solids (W/S) ratio. All runs with a UCS greater than 20 MPa had a W/S ratio of 0.2, and the runs with the lowest UCS had a W/S of 0.4. The initial setting time for design mixes with a W/S ratio of 0.2 ranged from 8 to 105 min. Meanwhile, five out of seven design mixes with a W/S ratio of 0.4 took longer than 1440 min to set. Specimens with an alkali activator ratio (NaOH/WG) of 0.5 (1:2) and 0.4 (1:2.5) also had significantly lower setting times than those with an alkali activator ratio of 1. The RSM model was verified through confirmatory tests. The results of the confirmatory tests are agreeable, with deviations from the expected UCS ranging from 0 to 38.12%. The generated model is a reliable reference to estimate the UCS and setting time of low-calcium FA geopolymer paste for in situ applications.

Editorial for Special Issue “Novel and Emerging Strategies for Sustainable Mine Tailings and Acid Mine Drainage Management”

Climate change is one of the most pressing problems facing humanity this century [...]

Geopolymers vs. Cement Matrix Materials: How Nanofiller Can Help a Sustainability Approach for Smart Construction Applications-A Review

In the direction of reducing greenhouse emissions and energy consumption related to the activities of the cement and concrete industry, the increasingly popular concept of eco-sustainability is leading to the development and optimization of new technologies and low impact construction materials. In this respect, geopolymers are spreading more and more in the cementitious materials field, exhibiting technological properties that are highly competitive to conventional Portland concrete mixes. In this paper, the mix design, mechanical properties, microstructural features, and mineralogical properties of geopolymer mixes are discussed, investigating the influence of the main synthesis parameters (curing regime, type of precursors, activator molarity, mix design) on the performance of the final product. Moreover, recent developments of geopolymer technology based on the integration of functional nanofillers are reported. The novelty of the manuscript is to provide a detailed collection of past and recent comparative studies between geopolymers and ordinary Portland concrete mixes in terms of strength properties, durability, fire resistance, and environmental impact by LCA analysis, intending to evaluate the advantages and limitations of this technology and direct research towards a targeted optimization of the material.