What should be paid attention to when using concrete admixtures?
The Rhine, which flows through Switzerland, Germany, France and the Netherlands, is an important shipping channel in Europe, and tens of millions of tons of goods are transported between countries through the Rhine every year. The persistent drought and lack of rain in Europe this summer has led to a drop in the water level of the Rhine, which has seriously affected shipping and exacerbated the energy crisis in Europe.
Argentina's economy minister and director of the National Social Security Agency recently announced that pensions for most of the country's retirees will rise by 15.53% from September. In addition, starting from September, retirees will receive an additional grant for three consecutive months, ranging from 4000 Argentine pesos to 7000 Argentine pesos.
It is understood that the range of people who can enjoy the pension increase is limited to those whose monthly income does not exceed twice the minimum social average wage (43353 Argentine pesos), which is expected to cover 85 per cent of the country's retirees.
The minister of economy said the increase in pensions is to help people cope with rising prices brought about by inflation. Argentina's monthly inflation rate in July has not yet been announced, and several agencies expect it to reach about 8 per cent, while Argentina's annual inflation rate is likely to exceed 100 per cent by the end of the year.
Because of the turbulent international situation, the supply and prices of many international bulk concrete foaming agent are still very uncertain.
1. Choose suitable admixture according to engineering characteristics
Admixtures can be used for almost all kinds of concrete, but suitable admixtures must be selected according to engineering needs, construction conditions and construction technology. For example, ordinary superplasticizer is mainly used for general concrete, superplasticizer is used for early strength and high strength concrete, water reducer with high air entraining property is mixed with water reducer when air temperature is low, single retarding superplasticizer is generally not used, compound early strength superplasticizer is often used, in order to improve the water resistance of concrete, waterproofing agent is used, pumping agent should be used when pumping concrete is used in high-rise buildings, in order to give full play to the characteristics of various admixtures. Should not be substituted for each other. At the same time, the admixture has the problem of adaptability to different cement, which must be tested and controlled in use.
2. The quality of admixtures
Admixtures must be tested according to the standard before use, and only the admixtures that meet the requirements of the standard can be used to prepare concrete.
3. The types of cement
Among the raw materials, cement has the greatest influence on the admixture, and the water-reducing and strengthening effects of superplasticizers are different with different types of cement, especially on the water-reducing effect. Superplasticizer is more selective to cement, and the water reducing rate of different cement varies greatly. Cement mineral composition, admixture, pour point regulator, alkali content, fineness and so on will affect the effect of superplasticizer. For example, the cement mixed with anhydrite will produce quick hardening for some concrete mixed with superplasticizer or greatly shorten the initial setting time of concrete, in which naphthalene superplasticizer has little effect, molasses will cause quick hardening, and wood calcium will prolong the initial setting time. Therefore, the effect of the same kind of superplasticizer is obviously different because of different cement under the same dosage. In some cement, some superplasticizer will cause abnormal setting phenomenon. For this reason, when cement is available, the cement that is more suitable for superplasticizer should be selected to improve the effect of superplasticizer. When the superplasticizer is available, the more suitable superplasticizer for construction cement should be selected. in order to make the superplasticizer play a better effect, cement selection test should be carried out in combination with the project before use.
4. Carry out the test before use
In order to ensure the engineering quality, according to the existing standards, for example, the homogeneity test should be carried out before the superplasticizer is used, and the water reducing rate and solid content (moisture content) should be determined, and then the concrete should be tested, such as testing the performance of the superplasticizer concrete, slump, water reducing rate, air content and compressive strength should be measured.
5. Pay attention to the content
Each admixture has a suitable amount, even if the same admixture, different uses have different appropriate amount. If the mixing amount is too large, it is not only economically unreasonable, but also may cause quality accidents. For the superplasticizer with air entrainment and retarding effect, special attention should be paid not to over-dosage. If the amount of wood calcium is more than 0.5% of the weight of cement, excessive air will be introduced to slow the initial setting and reduce the strength of concrete. If the dosage of superplasticizer is too small, it will lose its high efficiency, while if the dosage is too large, the quality will be affected by water secretion. The limitation of chloride salt is well known, and excess will cause steel bar corrosion. The amount of antifreeze is related to temperature, and it is stipulated according to the effect of strength. in short, there are many factors that affect the amount of admixture, such as the method of adding water reducer, the variety of cement, the initial popularity of the mixture and the curing system, etc.
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The Italian farmers' association pointed out that Italian household food consumption increased by an average of 564 euros in 2022 due to high energy prices, rising prices and drought leading to poor harvests. Among them, the most expensive food for Italians is bread, pasta and rice, with annual spending rising by nearly 115 euros.
TTF natural gas futures in the Netherlands, the European gas benchmark, rose more than 20% at one point to 295 euros per megawatt hour, about 15 times higher than in the same period last year, and German electricity prices exceeded 700 euros per megawatt hour for the first time in German history.
Gazprom announced earlier in August that it would suspend natural gas supplies through the Beixi No. 1 pipeline from August 31 to September 2. Although Gazprom stressed that once the work was completed and there was no technical failure, natural gas transmission would return to 33 million cubic meters per day (20 per cent of the full capacity of the pipeline), but it still caused panic in the market, and many people feared that the supply might not be restored on time.
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