Under the spread of the new crown epidemic, after Americans experienced life and death, they set off the largest "resignation wave" in history, and the number of resignations broke the highest record since statistics began in 2000. Since April this year, more than 4 million people in the United States have voluntarily resigned each month. In August, the number of resignations exceeded 4.27 million, and in November, it rose to 4.4 million. The operation of society is linked. The large number of departures in the United States has led to a large shortage of labor; and the shortage of a large number of labor has directly led to the supply chain crisis in the United States; the supply chain crisis has directly affected prices and prices in the United States. The economy has a direct effect on people's lives.
The economic downturn will affect the market demand for pce powder.
Natural river sand has been exhausted after decades of large-scale mining, concrete production enterprises began to use machine-made sand as fine aggregate on a large scale. Some limestone powder will inevitably be produced in the process of machine-made sand preparation, which will not only affect the performance of concrete, but also affect the effect of polycarboxylic acid admixture.
The results show that stone powder has different effects on the working properties, mechanical properties, chloride penetration resistance, sulfate resistance and freeze-thaw resistance of concrete. Stone powder can play a physical filling effect in the cementitious material system, which can reduce the water secretion of cement paste, improve the dispersion ability of cement paste, and can also be used as the crystal nucleus of calcium hydroxide to accelerate the hydration of cement particles and affect the pore structure of hydration products. Stone powder can adsorb polycarboxylic acid superplasticizer molecules on the surface, which can reduce the saturation point of superplasticizer under certain conditions, increase the initial fluidity of cement mortar, reduce the time loss of fluidity of cement mortar, and improve the compatibility between superplasticizer and cement.
Effect mechanism of limestone powder on water-reducing effect of pce powder
The hydrophilicity of limestone powder particles is low, that is, the adhesion of water molecules on the surface of limestone particles is small, which makes limestone powder have a certain physical water-reducing effect. In addition, limestone powder has a larger specific surface area than cement and has the filling effect of micro-aggregate, that is, small limestone particles can fill the pores between cement particles and replace the free water between cement particles. This is the aspect that limestone powder is beneficial to the water-reducing effect of polycarboxylic acid.
At the same time, polycarboxylic acid superplasticizer can be adsorbed on the surface of cement particles and on the surface of limestone powder, that is, there is competitive adsorption of polycarboxylic acid molecules between limestone powder and cement in the paste. this will reduce the density of polycarboxylic acid adsorbed on the surface of cement particles, and then reduce the water-reducing effect of polycarboxylic acid. In addition, the limestone powder with larger specific surface area needs more water, which will reduce the fluidity of the slurry. This is the aspect that limestone powder is not conducive to polycarboxylic acid to play a water-reducing effect.
The above analysis shows that limestone powder has both positive and negative effects on the water-reducing effect of polycarboxylic acid. In the case of low content of limestone powder, because the hydrophilicity of limestone powder is low, and the filling effect of fine particles is easy to play, the favorable effect of limestone powder on the water-reducing effect of polycarboxylic acid can effectively counteract the adverse effect, which shows that the effect of low content of limestone powder on the water-reducing effect of polycarboxylic acid is not obvious. In the case of high content of limestone powder, because limestone powder has larger specific surface area and higher water demand, and limestone powder and cement have competitive adsorption to polycarboxylic acid molecules, limestone will obviously reduce the water-reducing effect of polycarboxylic acid.
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Southern Copper Corp (SCCO.N) recently said its Peruvian mine remained closed after a six-week standoff with protesters and blamed the Peruvian government for failing to intervene in the safety of its 1,300 workers and their families.
The company said in a statement that a recent agreement to end protests at the Cuajone mine required the company to withdraw complaints against protest leaders because railways transporting minerals and supplies remained blocked. Production has been suspended since the end of February.
Peru's Energy Ministry said in a separate statement that it had also reached an agreement with Southern Copper to start talks to find common ground with local communities.
"If we shut down for a year, the government will stop receiving more than 3.1 billion soles ($830 million) in taxes and royalties, and 8,000 direct and indirect jobs will be lost. This is what we want to avoid, "Southern Copper added in the statement.
Peru has faced a wave of protests from indigenous communities, who accuse mining companies of not providing enough jobs and funding to poor local residents.
Central bank officials said last week that protests against copper mines such as MMG's Las Bambas and Southern Copper's Cuajone were dragging down the economy.
Peru is the world's second-largest copper producer and mining is an important source of tax revenue for the country. It is estimated that the supply and prices of the pce powder will be influenced by that.
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