Influences of Concrete Water Reducer on Different Kinds of Cement (1)
Analysts at JPMorgan recommended selling or "underweight" emerging market local currency sovereign debt because of the global impact of the Ukraine-Russia crisis.
JPMorgan estimated that fixed-income assets in emerging markets have lost 6-9 percent of their value since Russia invaded Ukraine a month ago, with nervousness about the war and its impact on global energy and food prices adding to existing pressures.
Some leading emerging market central banks are signaling that interest rates now need to rise faster than previously expected, which fuels fears of "stagflation". Stagflation means when high inflation and higher interest rates undermine economic growth.
With both the U.S. Federal Reserve and emerging market central banks raising interest rates, JPMorgan also said it made sense to "underweight" emerging market assets by taking advantage of the recent pullback in local currency bond yields relative to TREASURIES.
JPMorgan said major metals exporters such as South Africa, Chile, and Peru could still do well, but warned that emerging market fixed income assets now faced a more "stagflationary" trajectory.
The markets and prices of many commodities, metals, chemicals like the concrete water reducer still face uncertainty.
The water-reducing agent or concrete water reducer is a kind of concrete admixture that can reduce the water consumption under the condition of keeping the slump of concrete basically unchanged. It has a dispersive effect on cement particles, can improve its workability, reduce water consumption per unit, improve the fluidity of concrete mixture, or reduce the amount of cement per unit, saving cement.
Because different cement has different mineralized compositions, in addition to the variety of mixed materials, the effect of admixtures for different types of cement is very different.
In this article, we will talk about the problems when water reducer meets different kinds of cement and solutions.
1. High-alkali Cement
Soluble alkali in cement is usually expressed as Na2O equivalent, which mainly comes from the clay and mixture of cement production. An appropriate amount of soluble alkali is conducive to promoting cement hydration and is more conducive to the early strength development of concrete. The results show that the fluidity of cement concrete increases with the increase of alkali content. However, when a certain amount of cement is reached, the cement will hydrate rapidly and the fluidity of cement slurry decreases greatly. Plasticizing effect decreased obviously after adding water reducing agent. When the water reducing agent is used in the construction of concrete and pumped concrete, the loss rate of slump increases.
It is generally believed that alkali in cement promotes the dissolution of tricalcium aluminate (C3A). At this time, cement forms certain AFt crystals quickly with the help of coagulant CaSO4, which wraps on the surface of C3A, inhibits the direct hydration of C3A to form calcium aluminate, and improves the fluidity of cement slurry. However, if the alkali content in cement is too high, due to the formation of a large number of AFt crystals at the beginning, the fluidity will decrease, and the adaptability of water reducing agent to the above cement will inevitably decrease, for example, the water reduction rate is not enough, the plasticizing effect is poor, and the slump loss rate is high.
For high alkali cement, the effect of the water reducing agent with low sulfate content is poor, while the use effect of higher sulfate content of water reducing agent (sodium sulfate content of more than 20%) will be significantly improved. Primarily, low water reducing agent CaSO4 is contained in the synthesis and production, it has good properties of water-soluble. Gypsum in cement before it a large number of soluble in water, dissolved when higher alkali to speed up the C3A dissolution, because the water has a large number of SO3, reaction with C3A, form the AFt, to prevent the liquidity caused by the formation of calcium aluminate. And the slump loss is reduced. It is not difficult to see, that the water reducing agent with high content of sodium sulfate can adapt to high alkali cement more.
The PH value of many polycarboxylate water reducing agents is low, such as with citric acid and other acid retarder combined with high alkali cement is difficult to adapt. It is mainly because when acid admixture is mixed with cement of high alkali, it can produce acid alkali quickly neutralize exothermic reaction, temperature rises sharply, which not only make cement hydrate rapidly, heat of a large number of hydrate is put more can produce vicious circle, the concrete that place makes up not only fluidity is poor, slump falls to spend very likely disappear inside a very short time. Using other kinds of alkaline retarders can avoid these problems.
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