The influence of cement and admixture compatibility on concrete quality

(1) When the alkali content in cement is high, the fluidity of concrete will decrease and the slump loss will increase over time, especially when using water-reducing agents with low sulfate content. The effect is more obvious, while the water-reducing agent 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 synthesis and neutralization, and has excellent water solubility. Therefore, when using high-alkali cement, adding a certain amount of sodium sulfate and hydroxyhydroxy acid salt retarders when compounding the water-reducing agent will improve the fluidity and slump of the concrete.

(2) When the alkali content of cement is high and the pH value of polycarboxylate  water-reducing agent is low, the concrete will first produce 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 the concrete will show a relatively large loss in a short period of time. Therefore, when encountering similar cements, it is best not to use citric acid retarders but to use alkaline retarders instead, such as sodium hexametaphosphate, sodium polyphosphate, etc., which are more effective.

(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 bleeding. The main reason for this phenomenon is that the sulfate ion content in cement is insufficient, which reduces the effect of inhibiting the hydration of tricalcium aluminate in cement. At this time, a certain amount of sulfates such as sodium thiosulfate should be added during compounding to supplement the soluble alkali in cement.

(4) When the concrete oozes yellow slurry, has many pinholes and bubbles, it can be basically determined that the mother liquor and cement are difficult to adapt to each other. At this time, 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-reducing mother liquor, adding melamine and sodium hexametaphosphate and then using an appropriate amount of defoaming agent. Avoid using products such as thickeners. Using thickeners will not make bubbles come out, resulting in excessive air content, reduced concrete density and obvious strength reduction. If necessary, tannic acid or yellow lead can be added.

(5) When the foaming component of the grinding aid in cement is high, the concrete is also prone to yellowing and the state is extremely poor after being still for about 10 seconds. Sometimes it is mistakenly believed that the water reduction rate of the water reducer is too high or too much air is added during compounding. In fact, it is a problem with the cement grinding aid. When encountering this problem, the defoamer must be used according to the foaming amount of the grinding aid, and the air entraining agent cannot be used during compounding.