Blog
Concrete additives are used in small dosages (0.005%-5% of the cement mass); their effects are significant, so accurate calculation is necessary. The weighing error should not exceed 2%. Determine the variety and dosage of admixtures through experiments based on concrete performance requirements, construction and climatic conditions, raw materials, and mix proportions. When using solution form, include the water in the solution in the total mixed water. When two or more additives are used in combination and cause solution coagulation or precipitation, prepare the solutions separately and add them to the mixer separately.
To ensure uniform mixing, add water-reducing agents in solution form, and increase the dosage as temperature rises. Add water-reducing agents to the mixing water. When transporting concrete with a mixer truck, add water-reducing agents before unloading and mix for 60-120 seconds. Ordinary water-reducing agents are suitable for concrete construction when the minimum daily temperature is 5 ℃ or above.
When the temperature is below 5 ℃, use them in combination with early strength agents, and pay attention to vibration and air removal during use. Concrete mixed with water-reducing agents should undergo enhanced initial curing, and steam curing can be applied only after it reaches a certain strength. Many high-efficiency water-reducing agents cause a significant loss of slump when used in concrete, with a 30%- 50% loss after 30 minutes. Attention should be paid during use.
Mix concrete with high freeze-thaw resistance requirements with air-entraining agents or water-reducing agents, and do not use air-entraining agents for prestressed concrete or steam-cured concrete. Add the air-entraining agent in solution form to the mixing water first. Air-entraining agents can be used with water reducers, early-strength agents, retarders, and antifreeze agents, and the prepared solution must be fully dissolved. If coagulation or precipitation occurs, melt it by heating. Mechanically mix concrete with an air-entraining agent, and keep the mixing time between 3 and 5 minutes. Shorten the time from discharge to pouring as much as possible, and do not vibrate for more than 20 seconds to avoid losing air content.
Add it as a solution. If there are many insoluble substances, mix thoroughly before use. Mixing time can be extended by 1-2 minutes, and it can be used with other additives. Water and cure it after the concrete has fully set. Do not use the retarder for concrete construction when the daily minimum temperature is below 5 ℃, and do not use it alone for concrete with early strength requirements or steam-cured concrete.
Some are added directly as a dry powder, while others should be prepared as a solution. Follow the instructions for use. If used as a dry powder, dry-mix with cement and aggregate first, then add water. Do not mix for less than 3 minutes. For solution preparation, use hot water at 40-70 ℃ to accelerate dissolution. After pouring, cover with plastic film for curing. In low-temperature environments, cover with insulation materials. After final setting, pour water immediately to maintain moisture. When steam-curing concrete mixed with an early-strength agent, determine the steam-curing system through experiments.
Antifreeze agents have specified temperatures of -5 ℃, -10 ℃, -15 ℃, etc. When using them, select based on the lowest daily temperature. Concrete mixed with antifreeze should use Portland cement or ordinary Portland cement with a strength grade of not less than 42.5 MPa, and high-alumina cement is strictly prohibited. Chloride, nitrite, and nitrate antifreeze agents are strictly prohibited in prestressed concrete engineering. Heat concrete raw materials before use, and do not let the mixer outlet temperature fall below 10 ℃; strictly control the antifreeze dosage and water-cement ratio; extend the stirring time by 50% compared to room-temperature mixing. After pouring, cover with plastic film and insulation material, and do not water during curing at negative temperatures.
Before construction, conduct a trial mix to determine the dosage and ensure an accurate expansion rate. Use mechanical mixing; mixing time should be at least 3 minutes and 30 seconds longer than for concrete without admixtures. Mechanically vibrate compensated shrinkage concrete to ensure compactness; do not use mechanical vibration to fill expansive concrete with a slump of 150mm or more. Cure expanded concrete in a damp state for at least 14 days, and cure the latter by spraying a curing agent.
When using accelerators, pay close attention to their compatibility with cement, and ensure you understand the dosage and application conditions. If the cement has high C3A and C3S content, pour or spray the quick-setting concrete mixture within 20 minutes. After the concrete forms, keep it moist and cure it to prevent drying and cracking.
Study on the Effects of Water Reducing Agents and Expanding Agents on Concrete Shrinkage
Blog Study on the Effects
Product information, specifications & applications — sent directly to your email.
*Your information is kept confidential and will only be used to contact you regarding our products.
