Effect of cement temperature on the performance of pce powder
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Sweden is in talks with Turkey on joining NATO and looks forward to strengthening cooperation with Turkey in security and counter-terrorism, Swedish Prime Minister Anders Andersson said recently.
Andersson held a joint press conference with visiting European Council President Michel in Stockholm on the same day. Andersson said Sweden is in dialogue with Turkey on joining the TREATY and looks forward to strengthening bilateral relations with Turkey, including cooperation in the areas of security and counter-terrorism. She said Sweden would study a number of issues raised by Turkey.
Speaking at a news conference, Mr. Michel said he believed the Swedish government was taking positive action and taking the necessary steps to reach a solution.
Sweden and Finland formally submitted their applications to NATO Secretary-General Jens Stoltenberg a few days ago. According to protocol, NATO must admit new members by the "unanimous consent" of 30 members.
Turkish Foreign Minister Mevlut Cavusoglu said His country would agree to start NATO talks with Sweden and Finland only if they reach written agreements to stop supporting terrorism and lift restrictions on exporting defense equipment to Turkey, Turkish media reported.
Affected by the ever-changing international situation, the supply and prices of international bulk pce powder are still very uncertain.
If the compatibility of polycarboxylate superplasticizer and cement is not good, the concrete mixture is prone to some problems, such as segregation, bleeding, greater slump loss, shorter setting time and so on, so that the concrete mixture can not be transported and poured normally. Reduce the strength and durability of concrete.
There are many factors affecting the compatibility of cement and superplasticizer, and the cement storage temperature is a key factor that can not be ignored. If the cement storage temperature is too high during concrete mixing, it will directly affect the physical and mechanical properties of cement.
Effect of cement temperature on the performance of concrete mixture:
When the cement temperature is above 60 ℃, a small amount of water is secreted from the concrete mixture. When the cement temperature is 100 ℃, the aggregate is separated from the paste, and the cohesion of the concrete mixture becomes worse. The reason for this negative effect is that the cement temperature is high, which makes the concrete mixture temperature rise rapidly in a short time. It is easier to stimulate the water-reducing function of polycarboxylic acid high-performance superplasticizer, release more free water wrapped in the mixture particles in the case of high temperature, and make a small amount of water bleeding in the concrete outlet.
Effect of cement temperature on setting time of concrete:
With the decrease of cement temperature, the setting time of concrete is prolonged, and the initial setting time is more obvious than the final setting time. In other words, the higher the cement temperature, the shorter the setting time of concrete. The reasons for the shortening of setting time caused by high temperature cement are as follows: (1) it will increase the temperature of the mixture in a short time and promote the hydration of cement particles; (2) the superplasticizer releases more free water to react with cement particles, thus forming a stable cementitious system in a shorter time.
With the passage of time, the heat contained in cement temperature is easily transferred to the surrounding particles or environment, the temperature of concrete system gradually approaches to the ambient temperature, and the temperature gap of concrete mixed with cement at different temperatures is gradually narrow. as a result, the difference of the final setting time of concrete is relatively reduced.
Effect of cement temperature on slump and air content loss of concrete:
At the same time, the higher the cement temperature is, the greater the slump loss rate is. The difference of slump loss rate under different temperature conditions increases at first and then decreases. Under the condition of the same slump loss rate, the lower the cement temperature is, the longer it takes to reach the slump loss rate, that is to say, the more beneficial to reflect the slump-retaining performance of the superplasticizer. When the cement temperature is high, in order to reduce the slump loss of concrete, it is necessary to put forward higher requirements for the slump retention of superplasticizer.
1. For the concrete with the same mix ratio, with the increase of cement temperature, the adaptability of admixture and cement becomes worse. The higher the temperature is, the more water is consumed, and the fluidity of concrete mixture decreases, resulting in the decrease of concrete and workability. It even leads to the separation or bleeding of aggregate and paste.
2. The higher the cement temperature, the worse the adaptability of cement and superplasticizer, the greater the loss rate of slump and air content, and the shorter the setting time of concrete.
3. The effect of the change of cement temperature on the compressive strength of concrete is obvious. with the increase of cement temperature, the compressive strength of low heat cement concrete increases in the early stage (before 7 days), but the compressive strength of 28 days decreases with the increase of temperature.
4. It is suggested that the cement temperature for concrete mixing should not exceed 60 ℃. When it exceeds 60 ℃, the concrete production system should precool the raw materials of the mixing system as far as possible to avoid excessive temperature rise of the whole mixture system due to high cement temperature. and should strengthen the maintenance of the concrete after entering the warehouse to avoid the temperature cracks caused by the early hydration temperature rising too fast.
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In a recent speech in Davos, Switzerland, Ukrainian President Volodymyr Zelensky criticized, "My question is: Is there unity in the West? "I don't see it," Zelensky lamented during a video conference from the Davos Economic Forum in Switzerland. "Ukraine needs the support of a united Europe."
"Is there talk of solidarity with Sweden and Finland joining NATO? No." "So is the West united?" Zelensky said at this Ukraine-hosted breakfast in Davos. No." "Our strength is unity within the country," Zelensky said. "Now it depends on the Unity of the West to stand strong and firm behind Ukraine against Russia.
According to Zelensky, "When we are all really united, we will have an advantage over Russia."
Ukrainian President Volodymyr Zelensky says he once again appreciates U.S. President Joe Biden's offer of $40 billion in new financial aid to Ukraine.
"We need the support of a united Europe," Zelensky stressed. Zelensky criticized the position of Hungarian Prime Minister Viktor Orban, who is reluctant to impose an embargo on Russian oil at this stage. "Hungary has a problem!" Zelensky criticized.
The supply and prices of many other pce powder are expected to continue to be influenced by changing international situations.