Compositions For Improved Concrete Performance

What is this patent about?

’658 is related to the field of concrete preparation, specifically addressing the challenges of achieving optimal compressive strength and minimizing defects like cracking, curling, and shrinkage during the curing process. Traditional concrete mixing involves a delicate balance of water content to ensure both workability and proper hydration, but excess water can lead to structural weaknesses. The use of silica additives to improve concrete properties is known, but often increases water demand, exacerbating the problem of capillary and void formation.

The underlying idea behind ’658 is to introduce nanosilica particles with a high surface area into the concrete mix *after* the initial wetting of the dry cement and aggregate components. This delayed addition, in contrast to conventional methods where silica is added earlier, surprisingly reduces water loss during curing, leading to improved workability, reduced defects, and enhanced compressive strength. The key insight is that the timing of nanosilica addition significantly impacts its effectiveness in controlling water retention and promoting complete hydration.

The claims of ’658 focus on a process for preparing concrete installations. This process involves combining a dry cement mix, water, nanosilica particles (0.1 to 7.0 ounces per hundredweight of cement, with a particle size of 1-55 nm and/or a surface area of 300-900 m²/g), and aggregate/sand (400-700 wt % bwoc). The water is added either in its entirety after which the mix is agitated for a time t a prior to the addition of the amorphous silica, after which the concrete mix is then agitated for a time t b ; or in portions, with the nanosilica added after an initial portion of water has been mixed with the cement and aggregate/sand. The claims specify various mixing times (t 11 , t 12 , t 13 , t 21 , t 22 , t 23 , t 31 , t 32 , t a , t b ) for different addition sequences, followed by pouring the concrete mix to form the installation.

In practice, the process involves first mixing the dry cement, aggregate, and a portion of the water (or all of it) in a Ready-mix or similar mixer. After a period of agitation to ensure the dry components are thoroughly wetted, the nanosilica, often in the form of a colloidal suspension, is added. A final mixing stage ensures the nanosilica is evenly distributed throughout the concrete. This delayed addition is crucial; adding the nanosilica before or during the initial wetting can compromise the concrete's workability and increase the likelihood of defects. The resulting concrete exhibits improved water retention, allowing for more complete hydration and a denser, stronger final product.

This approach differentiates itself from prior art by recognizing the importance of the *timing* of nanosilica addition. While silica has been used in concrete for some time, the conventional wisdom was that it could be added at any point during the mixing process. ’658 demonstrates that adding nanosilica *after* the initial wetting of the dry components leads to significantly better results. This is believed to be due to the nanosilica's ability to immobilize water and prevent its premature evaporation, promoting more complete hydration and reducing the formation of capillaries and voids. The result is a concrete that is more durable, resistant to cracking and shrinkage, and possesses a higher compressive strength, even under adverse environmental conditions.