Waste Foundry Sand in Concrete Production Instead of Natural River Sand: A Review

Sustainable concrete production using toxic foundry sand and its subsequent effect on water contamination

Amid growing concerns about diminishing river sand resources and escalating environmental apprehensions related to toxic landfill waste, this study explores the potential of Toxic Foundry Sand (TFS) as a substitute for Standard Fine Aggregate (SFA) in concrete production. The investigation into various TFS replacement ratios in M20 concrete focuses on their impact on workability and compressive strength. Although TFS exhibits properties similar to fine aggregate, making it a promising candidate for partial replacement, differences in bulk density and fineness modulus compared to river sand suggest that TFS should be utilized as a partial replacement only. The study proposes an optimal replacement ratio of 30 % TFS and 70 % SFA to achieve satisfactory compressive strength in M20 concrete. The workability of fresh concrete remains unaffected in both nominal and 70:30 mixes, ensuring ease of mixing on the job site. As an innovative aspect, the study includes testing the water exposed to TFS-infused concrete for portability. Prolonged exposure to water on TFS-infused concrete (70:30 mix) raises concerns, as certain parameters such as chloride and hardness exceed acceptable limits. Therefore, careful control and treatment of Toxic Foundry Sand Contact Water (TFSCW) are deemed crucial on job sites to address potential water quality issues and ensure overall environmental safety.

Evaluating Cement Treated Aggregate Base Containing Steel Slag: Mechanical Properties, Volume Stability and Environmental Impacts

Steel slag has been commonly used in road engineering as cementitious material; however, its application in base course is not widely reported. Four contents of steel slag (0%, 30%, 50%, 75% by volume) were blended into different cement (3%, 4%, 5%, 6% by weight)-treated aggregates. Mechanical properties, volume stability, economic benefits and environmental influences of steel slag mixtures were investigated for the feasibility of applying steel slag in semi-rigid base course. Abrasion, crushing and elongated particle content were compared against limestone aggregate, showing that steel slag has the potential of replacing natural aggregate in concrete. Steel slag is beneficial for reinforcement of the strength and stiffness. The mixture has the highest strength and stiffness when bended with 50% steel slag at 4% cement content. By treating steel slag with CH3COOH or adding silica fume, volume expansion of steel slag can effectively be controlled. Larger size steel slag (>4.75 mm) and higher cement content are recommended due to heavy metal leaching risk, especially in salty humid areas. Steel slag has sound economic benefits due to the relatively low price. Environmental benefits can also be achieved given that the transport CO2eq emission of steel slag is accounted for. With proper control in production process, steel slag is a very promising alternative material to be utilized in cement-stabilized base course in road engineering.

Physicochemical and microbiological characteristics of waste foundry sand used in landfills

Biodegradation of solid waste is a process that depends on the characteristics of waste and soil, and these characteristics may create a waterproof barrier in the landfill, changing its performance. Some residues, such as waste foundry sand (WFS), whose final destination is the sanitary landfill, can create waterproofing and alter the performance of the landfill. This study was carried out to test this hypothesis by evaluating two prototypes composed of layers of organic residues, one covered by a mixture of 30% clay soil + 70% WFS and the other covered only with clay soil, monitored for 24 months. The generated leachate was analyzed regarding the parameters of chemical oxygen demand (COD), pH and electrical conductivity. In addition, after the monitoring period, semi-undeformed samples were collected for quantification of microorganisms and physical-chemical analysis (pH, electrical conductivity, moisture content and images with scanning electron microscopy). In the soil prototype, there was the formation of a waterproofing barrier in its deepest layer (soil₃). Factors such as the clay-mineral portion, moisture content (33,18%) and amount of microorganisms influenced this formation (650.000 and 15.000 CFU/g bacterial and fungal biomass, respectively), showing that WFS avoids the formation of this waterproofing barrier, as indicated for covering organic waste in landfills.

Properties and Microstructural Characteristics of Manganese Tailing Sand Concrete

In this work, manganese tailing sand concrete (MTSC) was prepared using manganese tailing sand (MTS) in replacement of river sand (RS) to alleviate the shortage of RS resources and achieve clean treatment and high-value resource utilization of manganese tailing stone. The effects of MTS content on the slump, mechanical strength, air void characteristics, hydration products and micromorphology of MTSC were studied experimentally. The leaching risk of harmful substances in MTSC was also explored by testing the concentration of Mn²⁺. The results show that the utilization of MTS reduces the slump of MTSC to a certain extent. When the MTS content is lower than 40%, the gypsum introduced by MTS and C₃A in cement undergoes a hydration reaction to form ettringite, which decreases the number of pores with a diameter less than 0.1 mm and promotes strength development in MTSC. Additionally, when the MTS content exceeds 40%, the large amount of gypsum reacts to form more ettringite. The expansive stress generated by the ettringite severely damages the pore structure, which is not conducive to the mechanical properties of MTSC. In addition, the leaching of hazardous substances in MTSC is insignificant, and the incorporation of cement can effectively reduce the risk of leaching hazardous substances in MTSC. In summary, it is completely feasible to use MTS to replace RS for concrete preparation when the substitution rate of MTS is less than 40%, with no risk of environmental pollution. The results and adaptation in the concrete industry can reduce the carbon footprint, which is in line with the current trend in civil and materials engineering.

Reuse or Disposal of Waste Foundry Sand: An Insight into Environmental Aspects

From a circular economy perspective, the recovery and reuse of waste plays a fundamental role. Foundries purchase hundreds of millions of siliceous sands every year to create molds and cores that give shape to the casting. These sands, after several uses, become waste that must be properly recovered or disposed of; they are called waste foundry sands (WFS). The reuse of WFS leads to a reduction in: (i) the consumption of raw materials; (ii) the emissions into the atmosphere; and (iii) the amount of waste sent to landfill—on the other hand, the impact that their use generates on the environment and human health must be carefully assessed. Leaching tests are a fundamental tool for establishing the hazardousness of a waste and its release of contaminants into the environment. This paper presents an analysis of the scientific literature regarding the chemical characteristics of WFS and their release following leaching tests carried out in the laboratory; the environmental standards adopted by the countries that have issued guidelines regarding the reuse of WFS will also be presented.