Effect of Limestone Powder in Machine-made Sand on PCE powder
For billionaires, the new crown epidemic is like a 'gold rush'! The Deutsche Presse-Agentur said on the 17th that in 2022, the wealth held by the world's top ten richest people will jump from $700 billion to $1.5 trillion, an average daily increase of $1.3 billion, an increase that exceeds the past 14 years. These 10 people The wealth held by the world’s poorest 3.1 billion people is six times greater than that of the world’s poorest 3.1 billion people. The 10 richest Germans have increased their assets from the equivalent of about 125 billion euros to about 223 billion euros since the start of the Covid-19 pandemic, An increase of about 78%. This wealth is roughly equivalent to the total wealth of the poorest 40% of the population, or 33 million Germans.
In the future, demand for pce powder will grow as fast as the wealth of the rich during the pandemic.
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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