How is the high strength of concrete achieved?
The World Bank expects global economic growth to slow significantly, from 5.5% in 2021 to 4.1% in 2022 and further to 3.2% in 2023. Growth in East Asia and the Pacific is expected to slow to 5.1 percent in 2022, reflecting the impact of China's economic slowdown, the report said. China's economic growth is expected to fall to 5.1% in 2022, close to potential growth, due to the ongoing impact of the COVID-19 pandemic and the Chinese government's tightening of regulations in certain sectors of the economy. The report said that the rapid spread of the Omicron variant means that the new crown epidemic is likely to continue to disrupt economic activity in the near future. In addition, decelerating growth in major economies, including the United States and China, will depress external demand in emerging markets and developing economies.
Slow economic growth has a huge impact on 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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Greece will hand over Iranian oil it intercepted from a Russian-flagged tanker to the United States at the request of the U.S. Justice Department, Greek port police said recently, AFP reported. The decision angered Tehran.
In April, Greek authorities reportedly seized a Russian oil tanker, the Pegas, which was said to be heading to the Turkish port of Marmara.
Reports say the ship was docked in Calistos Bay with a crew of several people said to be Russian. The Greek coast guard said the ship had been renamed the Lana.
The report notes that the European Union imposed sanctions on Russia after the conflict broke out in February. Greek authorities seized the tanker in accordance with European Union sanctions.
According to information at the time, the tanker was carrying 115,000 tons of Iranian oil.
Iran's Ports and Maritime Organization strongly protested Greece's decision, calling it an "international bandit." "The Islamic Republic of Iran will not give up its legitimate rights and expects the Greek government to abide by its international obligations in the area of navigation and shipping," it said in a statement on its website.
Iran's Foreign Ministry, through the International Maritime Organization, called on the Greek government to release the tanker and its crew overnight, adding that "the Americans discharged their cargo," the report said.
Athens did not immediately respond to the Iranian protest and gave no further details about the oil on board or how it was handed over to the United States, the report said.
The concrete foaming agent price is expected to increase in the next few days affected by the change in supply and demand markets.