Use of Flue Gas Desulfurization Gypsum, Construction and Demolition Waste, and Oil Palm Waste Trunks to Produce Concrete Bricks

Application of the Industrial Byproduct Gypsum in Building Materials: A Review

The industrial byproduct gypsum is a general term for byproducts discharged from industrial production with calcium sulfate as the main ingredient. Due to the high number of impurities and production volume, the industrial byproduct gypsum is underutilized, leading to serious environmental problems. At present, only desulfurization gypsum and phosphogypsum have been partially utilized in cementitious materials, cement retarders, etc., while the prospects for the utilization of other byproduct gypsums remain worrying. This paper mainly focuses on the sources and physicochemical properties of various types of gypsum byproducts and summarizes the application scenarios of various gypsums in construction materials. Finally, some suggestions are proposed to solve the problem of the industrial byproduct gypsum. This review is informative for solving the environmental problems caused by gypsum accumulation.

Modification of Recycled Concrete Aggregate and Its Use in Concrete: An Overview of Research Progress

The differences in physical properties, chemical properties, and mechanical properties between reclaimed concrete aggregate and natural aggregate are discussed in this paper. In this paper, the commonly used improvement techniques of recycled concrete aggregate are reviewed. Physical modification involves peeling the attached mortar layer using mechanical and thermodynamic means, including mechanical grinding and shaping, heat treatment, and microwave or electric pulse treatment. Chemical modification is based on the chemical reaction of some materials with recycled aggregate attached mortar, including acid treatment removal, water glass strengthening, carbonation strengthening, inorganic slurry strengthening, and polymer strengthening. Microbial modification is mainly based on the metabolic activity of specific microorganisms that induce carbon deposition modification. The results show that the reinforced technology of recycled aggregate has made some progress in improving the performance of recycled aggregate, but there are still some problems, such as inconsistent strengthening effects and the unstable compatibility of composite materials. In this paper, future research directions, such as the development of new strengthening materials and the integration of multi-functional strengthening technology, are described in order to provide some theoretical support for the utilization of recycled concrete aggregate.

Panel Products Made of Oil Palm Trunk: A Review of Potency, Environmental Aspect, and Comparison with Wood-Based Composites

Oil palm plantations have expanded rapidly in Southeast Asia, particularly in Indonesia and Malaysia. A lot of products, including food and other edible products, oleo-chemicals, cosmetics, personal and household care, pharmaceutical products, and biodiesels are derived from palm oil, thus making them one of the most economically important plants. After 25-30 years of age, the palms are felled and replaced due to declining oil production. Oil palm trunks (OPT) are considered significant waste products. The trunks remain on the plantation site for nutrient recycling or burning. This increases insect and fungi populations causing environmental problems for the new palm generation or air pollution due to the fire. Up till now, OPT has received less attention in research studies. Therefore, this review summarizes the utilization of OPT into products made of oil palm fibers mainly derived from OPT and its application as the substitution of wood panel products. Some research works have been carried out on oil palm fibers that are derived from OPT for exploiting their potential as raw material of composite panel products, which is the objective of this review. Areas of development are processed into various conventional composite panel products such as plywood and laminated board which are usually predominantly made of wood and bonded by synthetic resins, particleboard with binder, or binderless and cement board which is arranged with wood as a minor component. All of the products have been presented and described technically according to best knowledge of the authors and literature review.

Effect of the Composition of Mixed Recycled Aggregates on Physical–Mechanical Properties

Recycled aggregates (RA) from construction and demolition waste are an alternative to natural aggregates in the construction sector. They are usually classified according to their composition. The main constituent materials are separated into the following categories: unbound natural aggregates, ceramic particles, cementitious particles, bituminous materials, and other materials considered impurities, such as glass, plastic, wood, or gypsum. In this research, a large number of samples of RA were collected from three different recycling plants and their properties were studied. After that, 35 samples were selected randomly, and their RA constituents were separated under laboratory conditions. Cementitious particles were differentiated into two subcategories: masonry mortar and concrete particles. Subsequently, their physical–mechanical properties were measured. The statistical analysis carried out exhibited that the constituents had a statistically significant influence on the physical–mechanical properties studied. Specifically, masonry mortar particles had higher water absorption and worse mechanical properties than concrete and ceramic particles. Secondly, multiple regression models were performed to predict the physical–mechanical properties of RA from their composition since mean absolute percentage error (MAPE) ranged between 0.9% and 8.6%. The differentiation in the subcategories of concrete and masonry mortar particles in compositional testing is useful for predicting the physical–mechanical properties of RA.

Production and resource utilization of flue gas desulfurized gypsum in China - A review

Flue gas desulfurized gypsum (FGD gypsum), mainly originates from thermal power plants, smelters, and large-scale enterprise boilers. This article reviews the production in China and the latest beneficial utilizations of FGD gypsum. China is a large coal-consuming country and has always had serious SO₂ emissions. Therefore, the Chinese government has implemented a large number of desulfurization measures since 2006. With continually increasing energy consumption and increasingly stringent environmental requirements, the production of FGD gypsum has exceeded 10⁸ tons. The basic properties and the current beneficial applications of FGD gypsum are summarized here. The practical application of FGD gypsum in four fields-building materials, agriculture, material synthesis, and soil-and its impact on the environment, are analyzed. Finally, a new direction is proposed for the future utilization of FGD gypsum.

Calcination of Calcium Sulphoaluminate Cement Using Pyrite-Rich Cyanide Tailings

Pyrite-rich cyanide tailings (CTs) are industrial hazardous solid wastes arising from the gold mining industry. Every year, hundreds of millions of tons of cyanide tailings are produced and discharged to tailings dams. It is of great significance to dispose of cyanide tailings harmlessly and resourcefully. The feasibility of calcination of calcium sulphoaluminate (CSA) cement clinker using pyrite-rich cyanide tailings as Fe2O3 and SO3 sources was investigated for this paper. The behavior of pyrite during the calcination of cyanide tailings under various calcination conditions and the properties of calcium sulphoaluminate cement clinker were examined. The results show that it is feasible to produce calcium sulphoaluminate cement clinker using pyrite-rich cyanide tailings. The optimal conditions for the calcination of calcium sulphoaluminate cement using pyrite-rich cyanide tailings are confirmed. During the calcination process, the cyanides decompose into carbonate, CO2, and N2. The pyrite decomposes into Fe2O3 and SO2, and they react with CaO and Al2O3 to form the intermediates of CaSO4, 2CaO·Fe2O3, and CaO·2Al2O3, which further react to form 3CaO·3Al2O3·CaSO4, 4CaO·Al2O3·Fe2O3, and 12CaO·7Al2O3. The calcium sulphoaluminate cement prepared by pyrite-rich cyanide tailings exhibits excellent mechanical properties and meets the compressive strength criteria of 42.5 grade calcium sulphoaluminate cement.