Is colloidal silica the most efficient technology among curing agents?

If you're reading this article, you might be in the polished concrete industry or interested in understanding which materials are most efficient for polished concrete floor construction. From a chemical perspective, many in the industry don't fully grasp the necessity of using a densifier between grinding and polishing. The densifier plays a crucial role in creating an attractive and durable polished concrete surface, yet it is often underestimated. In the 1990s, many concrete floors used polishing techniques but skipped the densifier step. Over time, these surfaces quickly deteriorated and lost their shine. As a result, the importance of the densifier became recognized as a crucial step in the polishing process. However, many contractors still do not understand why a densifier is needed. To comprehend its importance, we first need to understand all the technical aspects of densifiers. Colloidal silica technology was introduced to the polished concrete industry nine years ago and has proven to be a reliable tool. Yet, confusion about this technology persists, leading to misunderstandings. This article will clarify the functions, technology, and role of densifiers.

First, it's important to clarify key terms and definitions in the industry. Silica (Silicon Dioxide) consists of 47% silicon and 53% oxygen and is a major component of Portland cement. When water is added to cement powder, it produces calcium silicate hydrate (CSH) and as a by-product, lime, which does not enhance concrete strength.

Colloidal silica consists of a mixture of liquid and nano-sized silica particles, which remain suspended without dissolving. The manufacturing process involves stripping sodium from sodium silicate and suspending pure silica in a low-surface tension liquid. Colloidal silica should not be confused with silica fume, a dry powder additive.

### How do densifiers harden concrete surfaces?

All densifiers react with unreactive calcium hydroxide in concrete to produce effective calcium silicate hydrate, making the concrete denser and harder. Some companies claim densifiers produce crystalline CSH, which is incorrect as CSH is a gel-like substance, not crystalline.

### Different Types of Silica

All concrete densifiers aim to deliver active silica into the micro-capillary system of the cement paste. The difference lies in the form of silica and how it is suspended in the densifier liquid. Colloidal silica delivers pure silica in nano-particle form, allowing deeper penetration and higher reactivity compared to silicates.

In capillaries, colloidal silica forms new CSH, bonding with existing CSH in concrete. It can also bond with other silica, even reacting with itself. This bonding provides additional reactions, a feature not present in silicate densifiers.

Silicate densifiers contain high proportions of mineral salts and require thorough cleaning to prevent efflorescence. Colloidal silica, being 99.95% pure, avoids this issue.

By using advanced technology, colloidal silica enhances concrete hardness, allowing direct polishing and saving labor.

### Performance Hardening

Though there is no global standard, abrasion resistance, and surface hardness measure densifier performance. Third-party tests have shown that colloidal silica formulas excel in polishing and densifying concrete surfaces. They prevent dusting and enhance durability while being environmentally friendly and labor-saving.

Author: Steven H. Miller  
Translator: Chen Chen