People all know cement and know that it is a powdery hydraulic inorganic cementitious material. After adding water and stirring to form a slurry, it can harden in air or water and is used to cement sand, stone and other granular materials into mortar or concrete. Mainly used in building decoration. With the acceleration of urbanization, more and more places require cement products. So how much do you know about the production of cement products? In the production of cement products, in addition to the necessary cement, stones and other raw materials, we also Some auxiliaries need to be added. As people’s requirements for the quality of cement concrete increase, the application of cement concrete admixtures is increasing. Adding different admixtures improves the rheological properties of cement concrete from freshly mixed to the mechanical properties and durability after hardening. Therefore, in highway cement concrete projects, many engineering teams will select and use appropriate admixtures to improve the construction quality of buildings, tunnels, and roads.
Cement admixtures are added during the use of cement. There are more than ten kinds of commonly used concrete admixtures, and the dosage varies greatly. Air-entraining agent 0005-0015%, water-reducing agent 02-15% , accelerating setting agent 2-6%, expansion agent 6-15%. The Chinese meaning of “Tian” in cement additives is to add a small amount. In addition, it is necessary to distinguish between cement additives and widely used mixing materials (added in cement production) and admixtures (added in cement use).
Compatibility of cement and water-reducing admixture
(1) Judging from the use results, mix a certain admixture that has been tested to meet the requirements of relevant standards with cement. If it is prepared in In concrete or mortar, if the test can produce the desired performance effect, it indicates that the admixture has good compatibility (or adaptability) with the cement; conversely, if the effect of the admixture is significantly lower than that of the original cement If the test results are abnormal or abnormal phenomena occur after the admixture is mixed into cement, it is called poor compatibility or incompatibility. (2) When measuring the compatibility index between cement and water-reducing agent, the following situations will occur: ① The saturation dosage of water-reducing agent (means that as the dosage of water-reducing agent increases, the initial fluidity of the clean slurry is no longer obvious The increased dosage) point is clear, and the saturation dosage is not high; ② The initial fluidity of the clean slurry at the recommended dosage of water-reducing agent is larger; ③ The fluidity loss of the clean slurry over time (60 minutes) is small; ④ A certain water-reducing agent The water retention of the pure slurry is good at the dosage. If there is no obvious bleeding, it means that the compatibility between the cement and the water-reducing agent is good. (3) Compatibility is divided into chemical compatibility and dose compatibility based on nature. When chemical incompatibility occurs, such as between gypsum and wood alcohol or sugar-based retarding water-reducing admixtures, it is chemically incompatible, and the type of admixture needs to be replaced; when there is dose incompatibility, such as between water-reducing agents and water-reducing agents with high C3A content. For cement or pozzolanic mixed materials, the cement has a strong adsorption capacity for the water-reducing agent and is not suitable. This is a dose incompatibility. You can consider increasing the amount of water-reducing agent or adjusting the cement type.
Retarder is a special admixture that delays the setting and hardening of fresh cement concrete. Generally, acids are selected as retarder for cement concrete, such as ordinary water reducing agents, such as calcium lignosus and calcium sugar. etc. Its biggest role in cement concrete projects is to delay the initial setting time and ensure the quality of fresh cement concrete. Especially in the summer heat. High-strength cement concrete requires the use of high-efficiency water reducing agents. Cement is a highly alkaline material. When we use it, we need to reduce its alkalinity to achieve the effect of retarding setting. If the retarded water-reducing agent is combined with a high-efficiency water-reducing agent, the effect is better than that of a simple retardant. Usually when we make slipform paving cement concrete, retarder is needed when the cement concrete is mixed in the mixing station and during long-distance concrete transportation. Therefore, adding admixtures to cement products is a necessary means in the production process of cement products, but there are certain regulations on the use of admixtures. It is not acceptable to add too much or too little, so as not to affect the quality of cement products.
The reaction principle of the retarder is to reduce the hydration rate of cement or gypsum and generate hydration heat, which can extend the hydration hardening time and allow the concrete to maintain its plasticity for a longer period of time when it is freshly mixed. .
It will eventually lead to a longer setting time, and it can be used for continuous pouring of concrete under high temperature conditions.
Adding concrete admixtures to cement products is a popular and trend. It has to be added. , but please pay attention to relevant precautions
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