Using Colloidal Silica in Concrete: Rules for Use in Ready-Mix Trucks
The use of colloidal silica in cement composites stretches back to work done by the US Army Corp of Engineers back in the early 2000 (Green 2004, 2012). This versatile material has become increasingly popular in the construction industry due to its numerous benefits, including increased strength and durability of concrete structures. In this article we outline rules for using colloidal silica admixtures in concrete, specifically in the back of industrial ready-mix trucks.
Rules for Using Colloidal Silica Admixtures
Here are four rules we recommend sticking to for optimal performance:
1. Proper Ratio: When mixing colloidal silica admixtures into concrete, the water cementitious ratio needs to be above 0.35. If too much water is used, it will impact the strength of the concrete. If too little is used, cracking and shrinkage will occur. It is important to adjust the amounts of accelerators and high range water reducers to make sure the colloidal silica is dispersed through the concrete.
2. Mixing Timing: Colloidal silica admixtures require longer mixing times compared to traditional concrete admixtures. Colloidal silica is most efficient when mixed at the tail end of the mixing process. This is similar to a polycarboxylate style high-range water-reducer, where all the cement particles need to be wetted before the colloidal silica goes into the back of the mixer truck.
3. Dilution Timing: The timing of dilution before mixing is incredibly important. When diluting colloidal silica into the back of a ready-mix truck, sequence it at the same time as, or just after, the tailwater.
4. Proper Dispersion: It is important to get as close to universal dispersion of the colloidal silica into the concrete as possible. We recommend using a polycarboxylate polymer, or a polycarboxylate ether style high-range water reducer to ensure appropriate dispersion. Colloidal silica has a very specific and, and even sensitive, chemistry. If the chemistry is not conducive to dispersion, the benefits and performance features of the colloidal silica will be diminished.
Conclusion
Colloidal silica is a valuable admixture that can significantly improve the performance of concrete. However, it is important to follow the rules outlined above to achieve optimal results. By understanding how colloidal silica works and using it correctly, we can produce stronger and more durable concrete structures that will stand the test of time.