Flash setting admixture for concrete is a chemical additive that significantly shortens the setting time of concrete. It is primarily used in applications such as sprayed concrete, urgent repair projects, and low-temperature construction, where fast hardening is required. The key components of the admixture can be classified into two types based on their chemical properties: alkaline flash setting admixtures and non-alkaline (low-alkali) flash setting admixtures. The admixture accelerates the hydration reaction of cement, rapidly promoting cement setting and shortening the setting time. This allows concrete to set within a short period, making the construction process more efficient, especially in projects like sprayed concrete, where the setting time is critical.
Recommended dosage: Typically, 6%–8% of the total weight of the binder material (specific dosage should be determined based on product specifications and tests).
Feeding sequence
Wet spraying method: Mix cement, aggregates, and water thoroughly, and then add the flash setting admixture (to avoid premature reaction).
Dry spraying method: Pre-mix the flash setting admixture with cement and aggregates, then spray them together with water at the nozzle.
Mixing time: After adding the flash setting admixture, mix quickly for 30–60 seconds to ensure uniform dispersion.
Temperature
Best temperature: 10–25°C, with an appropriate increase in dosage when the temperature is lower than 5°C.
High temperature (>30°C): May shorten the workable time, requiring faster construction speed.
Humidity: The environment humidity during spraying should be >70% to prevent rapid evaporation of moisture.
When using flash setting admixture for concrete, it is important to pay attention to the following points to avoid negative impacts:
Avoid Adding Admixture During Mixing: Flash setting admixture should not be added during the mixing phase of concrete, especially if sand and aggregate are not completely dry. If the sand and aggregate contain moisture, contact with the admixture may prematurely decompose its setting components, destabilizing the setting time and negatively impacting the concrete’s strength and spraying quality.
Cement Selection and Testing: Before using flash setting admixture for concrete, it is essential to conduct trial mixes according to the type of cement used and determine the optimal dosage and admixture ratio. Cement that is expired or does not meet national standards should be avoided, as it may react adversely with the admixture, degrading the concrete's quality.
Storage Conditions: Flash setting cement admixture should be stored properly to prevent moisture absorption, which can cause it to clump and lose its effectiveness. The storage environment should be kept dry to preserve the admixture's efficacy.
Curing Measures: Although the flash setting admixture accelerates the concrete's setting time, curing remains critical. During the early stages of construction, especially in sprayed concrete applications, extra attention should be given to water curing to ensure proper strength development in the concrete over time.
Water-to-Cement Ratio and Water Permeability: It is essential to strictly control the water-to-cement ratio during construction, as a high ratio can reduce the concrete's strength. In projects involving water seepage, it is recommended to slightly increase the dosage of the flash setting admixture to ensure rapid setting and adequate strength.
English
العربية
