Strength-Enhancing And Set-Accelerating

Strength-Enhancing And Set-Accelerating mainly focus on improving the speed of early strength development and do not change the normal setting time of concrete. Accelerators mainly accelerate the setting and hardening process of concrete, shorten the setting time by promoting cement hydration reaction, and make concrete reach the design strength faster. Sometimes, certain additives can improve early strength and promote cement hydration reaction, and these products are often used in concrete construction in cold weather.

Benefits:

• Rapid strength development.
• Useful in cold weather conditions.
• Shorten construction schedules and improve early formwork removal.

Applications:

Suitable for ready-mixed and precast concrete of all strength grades. When utilising this product series in the production of precast pipe segments and precast concrete components, the steam curing stage can be omitted, achieving zero-energy curing. For high-strength precast concrete components such as PHC pipe piles, employing this product series eliminates the need for high-pressure steam curing, substantially reducing curing costs and energy consumption. Concrete performance enhancers are accelerators that promote concrete strength development by directionally stimulating cement mineral hydration. They markedly improve the mechanical properties of concrete at all ages, aid in optimising concrete mix designs, conserve cementitious materials, and reduce concrete production costs. They are also suitable for the production of precast concrete components such as pipe segments and precast concrete  elements.

Commonly used earlyaccelerators are primarily classified into the following three categories:
(1)Chloride-based earlyaccelerators, such as CaCl₂,Calcium Formate , are cost-effective and easy to use, effectively enhancing early concrete strength while promoting setting and providing freeze protection. However, they may cause corrosion to reinforcing steel. Therefore, in reinforced concrete, the CaCl₂ dosage must be limited to less than 1% of the cement quantity and is typically used in combination with sodium nitrite as a rust inhibitor.
(2) Sulfate-based earlyaccelerator, such as sodium sulfate (Epsom salt), a white powder with an optimal dosage of 0.5%-2%. These agents often appear in composite forms, like NC, which is finely ground from sodium sulfate, calcium sulfate, and quartz sand.
(3) Organic earlyaccelerators primarily include triethanolamine, triisopropanolamine, methanol, and ethanol, with triethanolamine being the most commonly used. It is a colorless or pale yellow transparent oily liquid, highly soluble in water, with a recommended dosage of 0.02%-0.05%. This type of earlyaccelerator has a retarding effect and is typically not used alone but combined with other earlyaccelerators.

The effects of earlyaccelerators on concrete performance include the following:

(1) Significantly enhance early-stage concrete strength without adversely affecting later-stage strength. For instance, chloride salts and sulfates increase 3-day strength by 30%–40% or more (composite earlyaccelerators can boost it by 50%–80%), while 7-day strength rises by 15%–30% (composite strength agents can increase it by 20%–30%).

(2) Altering concrete’s resistance to sulfate attack. Calcium chloride reduces sulfate resistance, while sodium sulfate enhances it.

(3) Accelerating reinforcement corrosion. Earlyaccelerator must be strictly limited to below 1% of cement mass during use.

(4) Sodium salts in sulfates may trigger alkali-aggregate reactions in concrete, while excessive sulfate ions compromise volumetric stability. Usage must be strictly limited to 4% of cement mass.

(5) Slightly increases concrete volume in early stages, while enhancing drying shrinkage and creep in later stages.

Concrete earlyaccelerator, as an admixture, is designed to enhance the early strength of concrete without significantly adversely affecting its long-term strength. Its primary mechanism of action lies in accelerating the hydration process of cement, thereby promoting the development of early strength in concrete. According to the national standard “Admixtures for Concrete” (GB 8076-2008), the difference in setting time between concrete containing an earlyaccelerator and the reference concrete without it should be controlled within ±90 minutes. This requires that the effect of the earlyaccelerator on concrete setting time be kept within a specified range. Simultaneously, the standard imposes strict requirements on the compressive strength ratio of concrete, mandating that the compressive strength ratio at all ages meet certain standards.

On the other hand, concrete accelerators are admixtures that enable rapid setting and hardening of concrete while minimizing adverse effects on long-term strength. According to the National Standard for Shotcrete Accelerator (JC 477-2005), the initial setting time of cement paste containing accelerators must not exceed 5 minutes, and the final setting time must not exceed 12 minutes. Additionally, the compressive strength of cement mortar with accelerator added should not be less than 6 MPa at 1 day, and the compressive strength ratio at 28 days should reach over 70%.

By definition, earlyaccelerator and Shotcrete accelerator are two distinct types of concrete admixtures with different functions. Earlyaccelerator primarily focuses on enhancing concrete’s early strength while striving to maintain stable setting times. Shotcrete accelerator, on the other hand, concentrates on rapidly adjusting the setting time of cement paste. The standards for both admixtures explicitly stipulate compressive strength requirements for concrete or mortar, particularly setting strict minimum thresholds for early strength. Nevertheless, their evaluation systems exhibit significant differences and should not be conflated.