Effect of Limestone Powder in Machine-made Sand on PCE powder
Since 2022, Russia-Ukraine geopolitical conflicts have intensified, and global energy prices have risen sharply, with international natural gas prices hitting historic highs. As the most important transitional energy source in the transition from fossil energy to non-fossil energy, the share of natural gas in primary energy has increased from 14.6% in 1965 to 24.7% in 2020. The global gas price indices showed a unilateral downward trend from 2018, bottomed out in 2020, and remained low for a long time. However, since July 2020, the global gas prices have gradually fluctuated upward, and the impact of geopolitical events made the Dutch TTF gas price even hit record highs repeatedly.
An analyst of a securities company believes that the core catalyst of this round of global gas market lies in the lack of investment in upstream oil and gas resources caused by long-term low prices. Since 2020, although the epidemic has led to a decline in demand, the decline in supply has been faster, resulting in a large inventory consumption. In 2021, demand will recover faster than supply (the supply-side is less sensitive to prices, which will be reflected in investment).
As the world's two largest gas pce powder are also expected to change significantly.
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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The development of the Russia-Ukraine conflict will continue to dominate the commodity prices such as the pce powder in the future. If the conflict eases or cools, Russia and Ukraine go back to negotiate, commodity prices would fall. However, if the situation between Russia and Ukraine deteriorates further, or evolves into a full-scale war, the price of the pce powder is predicted to see further improvement over the coming days.