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How is the high strength of concrete achieved?

Recently, covid 19 outbreak spreads in Shanghai, China. There are more than 25,000 new asymptomatic domestic infections every day. China is implementing a dynamic zero-out policy. A leading respiratory expert said the key to COVID-19 prevention and control is to minimize transmission and fatality rate. Omicron has a low case fatality rate but is highly transmissible and can still claim many lives in large outbreaks. "Total openness is not applicable in China.  For China, we should keep to the dynamic zero-out and gradually open up."  

However, "dynamic zero clearance" is not the pursuit of complete "zero infection".  As the Novel Coronavirus has its own uniqueness and strong concealment, there may be no way to prevent the detection of cases at present, but rapid detection and prompt treatment must be carried out, as soon as one case is found, one case will be dealt with.  

The situation in Shanghai is serious. As the financial center of China, Shanghai is a very important city, and the outbreak of the epidemic in Shanghai will put a great impact on China's economy.  The current task is to contain the spread of the epidemic as soon as possible, to achieve social zero so that Shanghai's life and economy quickly return to normal.  

As China plays an important role in the global supply chain, the outbreak will have a significant impact on the supply and prices of many concrete foaming agent.

Concrete is classified as high-strength concrete based on 28-day strength. Until the 1970s, concrete with a strength of more than 40Mpa was classified as high-strength concrete.  The benchmark for high-strength concrete is raised to 55Mpa or higher when concrete mixtures of approximately 60Mpa and above are produced commercially. 

 

High strength concrete has a history of about 35 years, from the development of superplasticizer admixtures in the late 1960s, Japan using "naphthalene sulfonate" high strength prefabricated products, and Germany using "sodium benzenesulfonate" underwater concrete, which was a pioneer in this technology. 

 

How is the high strength of concrete achieved? 

Higher concrete strength can be achieved by using one or a combination of some or many of the following methods: 

High cement content 

Reduce water-cement ratio 

Better machinability and therefore better compaction 

 

Requirements for high-strength concrete require a high content of cementitious material in the concrete mixture, which can be in the range of more than 400 kilograms per cubic meter. Higher cementitious content leads to higher thermal shrinkage and dry shrinkage, and there is a stage where further cementitious material addition does not affect strength.  As for durability, the minimum and maximum cement content in concrete is regulated by law, and reducing the water-cement ratio has its limitations, especially under field conditions. The desire for higher strength leads other materials to achieve the desired effect, thus showing the contribution of cementitious materials to concrete strength. 

 

The addition of pozzolanic mixtures such as pozzolanic fly ash (PFA) or granular blast furnace slag (GGBS) contributes to the formation of secondary CSH gel thereby increasing strength.

 

The addition of pozzolans admixtures (such as fly ash used as an admixture) reduces the strength gain of concrete for the first 3 to 7 days and displays the gain after 7 days and provides higher strength over the long term. 

Add mineral mixtures such as silica fume or metakaolin or rice husk ash. 

 

Silica fume or highly reactive volcanic ash mixtures such as metakaolin and rice husk ash (RHS) will begin to function in about 3 days.  RHS has an advantage over PFA because RHS is more reactive. 

Using chemical admixtures such as superplasticizers or superplasticizers, controlling admixtures will help achieve higher strength in concrete. 

 

Research and experience have shown that admixtures based on polycarboxylic ether (PCE), known as high plasticizers, are best suited for this job as they have a water reduction capacity of 18 to 40 percent relative to control or reference concrete. 

A combination of all or more of the above to achieve the desired strength.


With HSC accompanied by some complexity, such as higher shrinkage rates, higher hydration heat, etc., combinations of at least some of these methods are now unchanged, all of which need to be neutralized or controlled.  Most problems are handled by PFA or a combination of GGBS and PCE mixtures.


Steam curing is also used to speed up cement hydration, but this may not result in higher strength.  Substituting some fine aggregate with fly ash or blast furnace slag can achieve early strength gains without increasing the water requirement of the concrete mixture. 

 

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Twitter recently announced that it had reached an agreement with Musk to take full ownership of the company for $54.20 per share, or about $44 billion in cash.  After the deal, Twitter will become a privately held company. The deal, which has been unanimously approved by Twitter's board but still requires shareholder and regulatory approvals, is expected to close in 2022.  

After Tesla CEO Elon Musk's acquisition of Twitter was finalized, Twitter founder Jack Dorsey sent out a series of six tweets expressing his expectations for Musk.  

Dorsey called Twitter his biggest regret, saying, “The idea and service is all that matters to me, and I will do whatever it takes to protect both. Twitter as a company has always been my sole issue and my biggest regret. It has been owned by Wall Street and the ad model. Taking it back from Wall Street is the correct first step.  

"In principle, I don't believe anyone should own or run Twitter," Dorsey goes on. He thinks the service is a public good.

He called Musk a "singular solution" to Twitter's problems, "Elon's goal of creating a platform that is" Maximally trusted and inclusive "is the right one." He wrote, "Thank you both for getting the company out of an impossible situation. This is the right path...  I believe it with all my heart."

Besides, because of the ever-changing international situation, the supply and prices of international bulk concrete foaming agent are still very uncertain.

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