Utilization phosphogypsum as a construction material for road base: a case study in Vietnam

Abstract

Phosphogypsum (PG) is a by-product of the production of fertilizers from phosphate ores, and it contains some harmful substances to the environment. Thus, it is necessary to stabilize/solidify pollutants when using PG as a filling material. The purpose of this study is to investigate and verify the use of PG as a filling material for a road base through laboratory tests for a case study in Vietnam. In this study, PG incorporated with fly ash was stabilized with cement and lime. The specimens of these mixtures were then prepared and cured under wet and dry conditions. The mechanical properties of specimen were investigated through the unconfined compressive strength (UCS), California bearing ratio (CBR), and modulus of elasticity. The physical property of this stabilization was examined using scanning electron microscopy. A toxicity characteristic leaching procedure test was also conducted to assess environmental impact. The results showed that when PG was replaced partially by other materials such as cement, fly ash, lime, or sand, the maximum dry densities of specimens were increased, and their optimum moisture contents were decreased. The inclusion of 10% of FA and 10% of cement or 20% of FA, 5% of lime, and 5% of cement significantly enhanced the UCS of specimens using PG at the ages of 28 days. The compressive strength under the dry condition was higher than that under the wet condition. Additionally, all mixtures showed a higher modulus of elasticity and CBR value than the requirement of road base material. The utilization of original PG can be successfully used as raw material in stabilization for applying in the pavement layers of road construction. The obtained results in the present work showed that the physico-mechanical properties in terms of unconfined compressive strength, modulus of elasticity, CBR of PG specimens could satisfy the requirement for the subgrade, subbase, or base course of road construction even when the content of PG comes up to 90%.

Study on Synergistic Effect of Xanthan Gum and Sodium Methylsiliconate on Mechanical Strength and Water Stability of Phosphogypsum Road-Based Materials

“…This surpasses the strength of traditionally stabilized inorganic PG materials at the 7-day In comparison, Meskini et al [32] utilized fly ash and lime to stabilize PG roadbed material, achieving strengths below 1 MPa at 7 days and ranging from 1-3 MPa at 30 days. In Ngo et al's study [33], the strength of the cement: PG = 10:90 mixture was less than 1 MPa at day 7 and remained less than 2 MPa at day 28. Shen et al's research [34] reported curing strengths of 2 MPa at 7 days and 8 MPa at 28 days for slag-fly ash-PG solidified material.…”

“…Meskini et al [32] found that the incorporation of fly ash and lime can increase the unconfined compressive strength and enhance durability of the PG composite due to the formation of ettringite as the main hydration product responsible for strength development. Ngo et al [33] demonstrated that the stabilization of a PG and fly ash mixture, along with curing using cement and lime, leads to improved mechanical properties of PG. This approach confirms the practical feasibility of employing PG as a filling material for road base construction.…”

Bioremediation of Modified Phosphogypsum to Cultivable Anthrosol via Peanut Growth

“…Japan sets a good example as it reuses 100.0% of its phosphogypsum: 60.0% as gypsum materials in the building industry, 30.0% as a cement retarder, and 10.0% as materials for the medical and food industries . Although phosphogypsum has been widely used in construction, such as cement retarder, , building materials like construction plaster and plastering mortar, and road paving materials, the size of the phosphoric industry and transportation costs have limited its reuse, with a global average reuse rate below 40.0% . , Therefore, innovative and reliable utilization strategies are essential to balance use and production and to maintain a sustainable development of phosphoric industry.…”

Preparation and properties of phosphogypsum based plastering mortar

“…Some harmful gases, such as chlorine fluoride, will enter the atmosphere. After being washed by rain, the soluble impurities in phosphogypsum will dissolve in rain and enter the soil, and then enter the surface water and groundwater through the soil [15]. At present, there are some environmental problems around phosphogypsum storage yard, such as poor water quality, abnormal toxic gas content in the atmosphere, excessive heavy metals in the soil, which seriously endanger the living environment of human beings.…”