Silica fume, a vital active mineral admixture employed in concrete, exhibits several properties that contribute significantly to the improvement of concrete composition and durability. This article explores the enhancing, filling, and plasticizing effects of silica fume, as well as its role in fortifying concrete durability.
Silica fume, employed as an active mineral admixture in concrete, plays a pivotal role in enhancing the composition of the cementitious material. Its ability to reduce and eliminate free lime is noteworthy. The SiO2 in silica fume engages in a volcanic ash reaction with free lime and high alkaline hydrated calcium silicate, yielding lower alkaline hydrated calcium silicate with superior strength and stability. This process significantly increases the quantity of cementitious material and greatly improves the interface structure between cement stone and aggregate, consequently boosting the strength of the concrete.
In concrete mixes incorporating an appropriate amount of ultrafine mineral admixture, specifically silica fume with an average particle size of 0.10-0.26um, the filling effect is pronounced. Silica fume, with its significantly smaller particle size compared to fly ash and slag, efficiently fills the voids between fly ash and slag particles. This not only enhances the denseness of the cementitious material particles but also contributes to a further increase in strength. Moreover, the filling effect enhances the overall denseness of concrete, thereby improving its durability.
In the mixing process, the synergistic interaction of silica fume with a high-efficiency water-reducing agent is crucial. The surface of minute spherical silica fume powder particles becomes coated with a layer of surface-active material, forming a barrier with cement particles and other mineral admixture particles. This results in electrostatic repulsion between the particles. Given that spherical silica fume particles are much smaller than cement particles, they assume a “ball” role between cement particles, enhancing the fluidity of the cement slurry. This makes pumping and filling more efficient, effectively reflecting the enhancement effect.
Improvement of Concrete Durability:
Active silica fume, upon hydrating in concrete, generates a significant amount of low-alkaline hydrated calcium silicate gel. This gel has the capacity to absorb and fix a large number of ions such as Na+ and K+, leading to a substantial reduction in the effective alkali content of the concrete pore solution. Consequently, the harmful effects of alkali-aggregate reactions are greatly diminished. Additionally, silica fume fills voids between cement particles and interfaces, significantly improving the permeability of concrete. This impedes the entry of water and erosion mediums into the concrete interior, resulting in a remarkable enhancement of concrete durability.
In conclusion, the multifaceted effects of silica fume on concrete, spanning enhancement, filling, plasticizing, and improved durability, underscore its indispensable role in optimizing the performance and longevity of concrete structures. The judicious incorporation of silica fume not only advances concrete technology but also aligns with sustainable construction practices, promoting robust and enduring infrastructure.