Chile's government is considering phasing in a proposed ban on glacial mining to limit projects high in the Andes by some big copper companies. Chile's constitutional assembly has approved a proposal to ban mining in glaciers, protected areas, and areas vital to protecting the country's water system.
Chile's mining minister, Marcela Hernando, said about 20 mines had been identified in protected areas, some close to glaciers, including Codelco's El Teniente and Andina projects and Anglo American Plc's Los Bronces project.
The new measures for glaciers and other protected areas will put about a fifth of Chile's copper pce powder prices are predicted to increase in the next few days.
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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Maximo Pacheco, chairman of Codelco, Chile's state copper company, said in a recent interview that he expects copper prices to remain 'very strong in the future,' despite the recent drop. Codelco is the world's largest copper producer.
Copper prices suffered their biggest weekly drop in a year this week on concerns that tightening policy by central banks will dampen global growth and reduce demand for industrial metals. With its wide range of industrial and construction uses, copper prices are often seen as a bellwether of economic activity.
London copper closed at $8,325 a tonne on Friday after touching $8,122.50 a tonne, down 25 per cent from its Peak in March and its lowest level since February 2021. In addition to copper, other industrial metals also fell sharply. Tin, for example, fell nearly 15% at one point on Friday, bringing its losses for the week to about 25%.
"We may be in a temporary short-term turbulence, but what is important is the fundamentals and the balance of supply and demand [currently] looks very favourable for those of us with copper reserves," Mr. Pacheco said. Chile is the world's largest copper producer.
Mr. Pacheco adds that in a world where copper is the best conductor and there are not many new reserves, copper prices look very strong because the future is very favourable for electrification.
Luoyang Tongrun Nano Technology is a trusted chemical supplier and manufacturer providing high-quality chemicals and Nanomaterials. If you are looking for the pce powder, please feel free to contact us and send an inquiry.
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