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A new civil engineering material: normal temperature modified phosphogypsum embedded filler

100%

Wang C.-q. , Liu D.-s. , Huang Q.

Archives of Civil and Mechanical Engineering

2021

tom Vol. 21, no. 1

76--88

Phosphogypsum (PG) is a by-product from the industry of phosphate fertilizer industry. Approximately 5 tonnes of PG are generated for per ton of phosphoric acid production. The accumulation of PG occupies huge amounts of land resources and results in serious environmental risks. In this study, a new civil engineering building material product, normal temperature-modified PG-embedded filler, was successfully prepared from original PG, supplemented by fly ash, desulfurized ash, quicklime and silica fume. The basic physical properties and microscopic hydration process of the product were systematically studied. To further ensure its environmental safety, the leaching performance of the product was also analyzed. The final research results showed that, the heavy metals in PG, such as Pb, Cd, Hg, As and Cr in PG, were undetected, and Cu, Zn, and Ni have no obvious pollution characteristics. However, the lixivium contents of P and Ba are 2372 mg/kg and 733.6 mg/kg, which can be considered as the particular pollutants. The best ratio of the embedded filler was: 65% original phosphogypsum, 20% Fly-ash, 6% desulfurized ash, 6% quicklime, 3% silica fume and right amount of water. The basic physical properties of the PG-embedded filler prepared met the Chinese technical specification: gypsum filler for cast-in-situ concrete hollow structure (JC/T 2472-2018). In addition, the test results of the leaching solution showed that all the heavy metals met the standard requirements. In a word, the performance of normal temperature-modified PG-embedded filler is satisfied and its production cost in this research is by far lesser than that of the same volume of reinforced concrete which has excellent application foreground.

Interfacial enhancement technology in high‑volume fly ash foam concrete: microscopic mechanism and heavy metal safety assessment

63%

Huang D. m. , Liu K. , Wang C.-q. , Shen B.-h. , Zhao H. , Huang Q.-c. , Zhu Y. , Shui Z. h.

2023

tom Vol. 23, no. 1

art. no. e17, 2023

Applying a large amount of fly ash to foam concrete can greatly reduce the engineering cost, but the proportion of fly ash is limited due to insufficient pozzolanic activity and heavy metal pollution. Therefore, this study used fly ash, portland cement, fly ash ceramsite, foaming agent, etc. as raw materials to design the mix ratio of large-volume fly ash foam concrete. The micro-interface enhancement mechanism was deeply analyzed, and a multi-method pollution assessment system was finally established for the risk assessment of heavy metals. The dry bulk density of the fly ash foam concrete prepared in this study was 894.5 kg/m3, the compressive strength was 4.22 MPa, and the thermal conductivity is 0.2213 W/(m K). These parameters all met the requirements of the Chinese standard “Foam Concrete” (JG/T 266-2011). The microscopic analysis results showed that, compared with the fly ash content of 60%, the foam concrete with 40% fly ash content had more rodlike ettringite at the interface of the pore wall, and its hydration products were distributed more uniformly. Similarly, the interface between the ceramsite mixed with 40% fly ash and the cement stone was more closely combined, the distribution of hydration products between the interfaces was more uniform, and the interface quality was higher. After adding thickener, the pore distribution of fly ash foam concrete was tight, and there were a lot of small pores between the pores, and the pore structure had better connectivity than when no thickener was added. The evaluation results of foamed concrete with 40% fly ash content with the aid of the multi-method pollution assessment system showed that the harmful heavy metals in fly ash were stably solidified in the silicate structure, resulting in low leaching efficiency. Finally, the performance of the high-volume fly ash foamed concrete slab produced according to the mix ratio designed in this study met the requirements of “Light weight panels for partition wall used in buildings” (GB/T 23,451-2009). Therefore, it is a safe and environmentally friendly high-performance building product.