High-performance concrete is becoming more and more widely used in current engineering applications, and high-performance water reducing agents are an essential component in the preparation of high-performance concrete.In recent years, polycarboxylate water reducers have received increasing attention due to their low dosage, high water reduction rate and good retention.Although the performance of polycarboxylate superplasticizer is excellent, in actual engineering applications, various raw materials have different effects on their use effects.Such as the adsorption of cement particles, the mud content of sand and gravel minerals, and the adsorption of impurities, etc.
1、Alkali content of cement
The alkali content of cement mainly refers to the content of Na2O and K2O in cement.The alkali content has a great influence on the adaptability of cement and water reducing agent.As the cement alkali content increases, the plasticizing effect of the water reducing agent becomes poor.An increase in the cementitious content will also result in a reduction in concrete setting time and an increase in slump loss.
2、Mixed material in cement
At present, more than 80% of China's cement is blended with a certain amount of mixed materials, such as volcanic ash, fly ash, slag powder and coal gangue.The test shows that the plasticizer has better plasticizing effect on cement with fly ash and slag than pure Portland cement; the water reducing agent has poor plasticizing effect on cement mixed with volcanic ash or coal gangue.Therefore, for the latter two kinds of cement, in order to achieve a better water reducing effect, it is necessary to increase the amount of the water reducing agent.
3、Fineness of cement
The cement particles have relatively strong adsorption to the water-reducing agent molecules. In the cement slurry with the water-reducing agent, the finer the cement particles, the larger the surface area and the larger the adsorption amount of the water-reducing agent molecules.Therefore, in the case of the same amount of water reducing agent, the plasticizing effect is worse for cement with higher fineness.Nowadays, some cement manufacturers are trying to improve the fineness of cement in order to achieve the early strength of cement. For such cements, in order to achieve better plasticizing effect, it is necessary to increase the amount of water reducing agent.
4、Cement freshness and temperature
The fresher the cement, the worse the plasticizer effect of the water reducing agent is. This is because the positive cement of fresh cement is stronger and the adsorption capacity of the water reducing agent is larger.
The higher the temperature of the cement, the worse the plasticizer effect on the plasticizer and the faster the concrete slump loss.Therefore, when some commercial concrete production plants use concrete that has just been milled and still lose heat, the water reduction rate is low and the slump loss is too fast.Some even appear abnormal condensation in the mixer, which should be taken seriously and avoided.