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Effect of Limestone Powder in Machine-made Sand on PCE powder

The purchasing pace at the demand end of the international thermal coal market continues to slow down and the international thermal coal price continues to decline. Prices for thermal coal at major international ports continued to fall last week as buyers in Europe slowed in recent days for April, coupled with weaker-than-expected import demand from End users in China. According to China Coal Market net monitoring:  Australia Newcastle port thermal coal price index was 253 USD/ton, compared with 309.02 USD/ton, down 56.02 USD/ton, down 18.13%. South Africa's Port Richards thermal coal price Index was $264.5 / mt, down the US $62.72 / mt or 19.17% from US $327.22 / mt. The European ARA Tri-port thermal coal price Index was $281.8 / ton. Does the price of thermal coal in major international ports continue to decline to affect the price of the 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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Gas prices in European countries are expected to triple if Russian supplies are restricted, according to a press release from Rystad Energy, a Norwegian Energy consultancy.  

The price of natural gas in Europe was $1,200 per 1,000 cubic meters on Tuesday. The benchmark price is already 300 percent higher than a year ago. European gas prices are expected to continue to soar to $3,500 per 1,000 cubic meters if Russian supplies are restricted, according to Analysis by Monitor.

In 2021, Russia delivered 155 billion cubic meters of gas to Europe, accounting for 31 percent of its gas supply, according to an analysis by Monitor Advisors. It would be difficult for Europe to replace Russian gas, which would also destabilize the global LNG market and have a profound impact on Europe's population and economy.

The analysis also said that if Russia stopped supplies now, Europe's current gas reserves would be exhausted by the end of the year, setting in for a cold winter.

In addition, affected by the geopolitical factors, the supply of the pce powder is erratic and thus its prices are expected to go higher in the future.

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