Adding a small amount of concrete admixtures to concrete can greatly improve its performance and reduce costs, making full use of resources and contributing to environmental protection. This article will provide you with a detailed introduction to the role of concrete admixtures.
By incorporating air-entraining and water-reducing concrete admixtures, the flowability of concrete can be enhanced, improving its workability. Because of this improvement in workability, the quality of the concrete is guaranteed, energy consumption can be reduced, and working conditions can be improved.
Adding pumping agents to pumped concrete ensures good pumpability, preventing bleeding and segregation, and increasing the flowability and stability of the mixture. Additionally, this reduces the friction resistance within the pipeline, lowering energy loss during transportation and enhancing the compactness of the concrete.
When pouring high-flowability concrete, slump loss can often affect construction quality. The use of high-efficiency water-reducing agents, such as polycarboxylate-based admixtures, effectively reduces slump loss, facilitating construction and ensuring concrete quality.
In underwater concrete construction, to resist underwater segregation of concrete and increase the mixture's cohesion, underwater anti-washout admixtures can be incorporated to keep the concrete in a flocculated state.
Increasing Concrete Strength
By incorporating various types of water-reducing concrete admixtures into concrete, with the mixture workability and cementitious material content unchanged, the water content can be reduced, thereby lowering the water-cement ratio and increasing the concrete strength.
Adding 0.25% lignosulfonate (such as calcium lignosulfonate) can reduce water content by 5% ~ 15%; adding molasses-based water reducers can reduce water content by 6% ~ 11%; adding high-efficiency water reducers can reduce water content by 15% ~ 30%.
For ultra-high-strength concrete, the water reduction rate can even reach 40%. The enhancement effect of water reducers ranges from 5% to 30%, or even higher. Using high-efficiency water reducers can lower the water-cement ratio to around 0.25, achieving a compressive strength of over 100 MPa for the concrete.
Incorporating air-entraining concrete admixtures into concrete can lower the interfacial tension between air and water. The mechanism involves the air-entraining agent comprising molecules with a polar functional group at one end and a non-polar group at the other. The polar end aligns with the dipole of the water molecules, while the non-polar end points towards the air, thus introducing a large number of air bubbles into the concrete during mixing.
These fine air bubbles can exist uniformly and stably within the concrete, partly due to the formation of a molecular layer with opposite charges around the bubbles, and partly because the hydration products from cement hydration adsorb onto the bubbles' surface, increasing their stability. Numerous tiny bubbles in the concrete can alleviate the expansion pressure from freezing water in pores and osmotic pressure from supercooled water migration to capillaries, thereby giving air-entrained concrete high frost resistance.
The hydration of cement is an exothermic reaction. In the early stages of the reaction, a large amount of heat is released quickly over a short period and accumulates inside the structure, causing a rapid temperature rise within the concrete. Depending on the structure size, the internal temperature of the concrete can reach as high as 70°C to 80°C. Concrete is a poor thermal conductor and exhibits thermal expansion and contraction. At this stage, the interior of the concrete is under compressive stress, which generally prevents cracking. After some time, the internal temperature of the concrete reaches its peak and starts to cool gradually.
Due to the limited heat exchange efficiency, the temperature on the exterior surface drops more rapidly than the interior, creating a temperature differential that grows over time, inducing tensile stress within the concrete structure. The resulting cracks are known as temperature cracks. Hydration heat-reducing admixtures can effectively lower the early exothermic peak of ordinary Portland cement at a low dosage, without significantly affecting the total heat release and strength development in later stages, thus effectively mitigating temperature cracking in large-volume concrete.
As a professional concrete admixture company, ARIT has a professional R&D team that can provide customized concrete admixtures based on the specific materials and performance requirements of their clients.
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