The influence of the compatibility between cement and admixtures on the quality of concrete:
(1) When the alkali content in cement is high, over time, the fluidity of concrete will decrease and the slump loss will increase, especially when water-reducing agents with low sulfate content are used. The effect is more obvious, and water-reducing agents with high sulfate content can significantly improve this situation. This is mainly because the calcium sulfate contained in low-concentration water-reducing agents is produced during the synthesis and neutralization process and has excellent water solubility. Therefore, when using high-alkali cement, adding a certain amount of sodium sulfate and hydroxy acid salt retarder when preparing the water-reducing agent can improve the fluidity and slump of concrete.
(2) When the alkali content of cement is relatively high and the pH value of polycarboxylate superplasticizers is relatively low, the concrete will first undergo an acid-base neutralization reaction. Not only will the temperature of the concrete rise, but it will also accelerate the hydration of the cement. The fluidity and slump of concrete will show significant losses in a short period of time. Therefore, when encountering similar cement, it is best not to use citric acid retarders but to use alkaline retarders such as sodium hexametaphosphate and sodium polyphosphate, which will have better effects.
(3) When the alkali content in cement is low, the fluidity of concrete is also relatively poor. The effect of appropriately increasing the dosage is not very obvious, and the concrete is prone to water seepage. The main reason for this phenomenon is the insufficient content of sulfate ions in cement, which reduces the hydration inhibition effect of tricalcium aluminate in cement. At this point, a certain amount of sodium thiosulfate and other sulfates should be added during the preparation process to replenish the soluble alkali in the cement.
(4) When the concrete seeps out yellow slurry with many pinholes and bubbles, it can basically be determined that the mother liquor and cement are difficult to adapt to each other. At this point, ethers, esters, aliphatic and other different mother liquors can be compounded. At the same time, it is necessary to consider reducing the amount of pure water reduction mother liquor, adding melamine and sodium hexametaphosphate, and then using an appropriate amount of defoamer. Avoid using thickeners and other products. The use of thickeners will prevent bubbles from emerging, resulting in excessive air content, a significant reduction in concrete density and strength. Tannic acid or yellow lead can be added when necessary.
(5) When the foaming component of the grinding aid in the cement is relatively high, the concrete is also prone to yellowing after being left to stand for about 10 seconds, and its condition is extremely poor. Sometimes, it is mistakenly believed that the water-reducing rate of the water-reducing agent is too high or that too much air was added during the formulation. In fact, this is a problem with the cement grinding aid. When encountering this problem, defoamers must be used based on the foaming amount of the grinding aid. Air-entraining agents must not be used when in combination.
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