What is Colloidal Silica

Although colloidal silica has been around for years, it is recently gaining traction in the concrete and construction industry due to it’s proven benefit to concrete strength and durability. This article explores the history of colloidal silica and various performance indicators of colloidal silica in concrete.

History

Colloidal silica, originally patented in 1959, was first brought to the United States by Bryan H. Green from the U.S. Army Corps of Engineers at the Engineering Research and Development Center in Vicksburg, Mississippi. In 1989, Green introduced colloidal silica as a viscosity modifying admixture for rock-matching grout. Prior to this, he encountered challenges with a very fluid grout that contained hematite sand, which tended to fall out of solution. To address this issue, Green experimented with dextrose and xanthan gums, but these additives made the grout tacky and difficult to work with. Eventually, Green discovered that colloidal silica not only kept the hematite sand in solution, but also densified it, reduced permeability, increased strength, and reduced wave attenuation, among other benefits.

Definition

The word colloidal means "stays in solution". An example of a colloidal suspension is milk, which contains fat and proteins in a dispersed form. Colloidal silica refers to a universal dispersion of nano silica particles, with nano being defined as particles ranging from 1 to 100 nanometers in diameter. To put it into perspective, a single strand of human hair has a diameter of approximately 100,000 to 150,000 nanometers.

Why Colloidal Silica?

Colloidal silica is utilized to effectively manipulate the molecular kinetics of cement hydration, thereby enhancing the strength and durability of concrete. By consuming calcium hydroxide, colloidal silica minimizes pore sizes, pore solution, and pore connectivity, resulting in reinforced concrete that is stronger and longer-lasting.

Strength

Strength is an important factor to consider. It refers to the stress level at which things fail. The goal is to increase the stress level so that failure is prevented. In our lab, we have conducted numerous tests that demonstrate this concept. To benchmark, we use a standard ASTM C94 mix which consists of water, sand, and cement at approximately 4000psi. We compare this reference mix to a variation where colloidal silica is added. The results are impressive. For compressive strength, we observe a significant increase of 15%-30%, especially during the first week (1-7 days). The significant increase in early strength is ideal for pavements and strip forms. After that time frame, the increase in strength becomes less substantial, particularly at 28, 56, and 90. Nevertheless, the strength is still higher compared to the reference mix.

Strength Regression

Years ago, Intelligent Concrete worked on a fast-track pavement project for the Colorado Department of Transportation. The pavement mix used provided excellent results. Within 4-6 hours of placement, a strength of 3500psi was achieved, allowing for open traffic to flow smoothly on the highway. However, issues were encountered with the accelerators employed, such as calcium nitrite, nitrate, sodium thiocyanides, and chlorides, as they tended to create a porous microstructure. As a result, higher early strengths were attained, but a reduction in strength at 28 days was observed. Moreover, this porous microstructure made the pavement more vulnerable to chemical attack from deicing salts and brine. By implementing colloidal silica, shorter curing times were achieved while simultaneously creating denser microstructures. Additionally, the flexural strength, which is essentially a tension measurement, at 28 days, increased 20% when compared to the reference.

Modulus of Elasticity

Using excessive amounts of colloidal silica in concrete can have various effects on its properties. When conducting fractal and brittle tests, it has been observed that using large particles of colloidal silica can make the concrete more brittle. Additionally, there is a reduction in tensile strength and ductility when higher dosages of colloidal silica are used.

Reasonable amounts of colloidal silica in the mixture can result in a steeper line, indicating a slightly stiffer and stickier mixture. However, in terms of linear elasticity, the proportion limit and strain at the proportion limit are higher, preventing brittleness. Colloidal silica is a remarkable technology that addresses various issues related to concrete durability. Unlike common approaches that involve adding more cement, reducing water, or using accelerators, colloidal silica offers a solution to problems such as alkali-silica reaction (ASR), deicing attack, and steel corrosion. Excessive cement content, microstructure, environmental factors, and other materials contribute to durability challenges, which can be mitigated by incorporating colloidal silica.

Abrasion

Abrasion is a notable example of increased performance with colloidal silica in concrete. Intelligent Concrete has conducted various abrasion tests, including the standard abrasion tests that involve applying pressure from steel balls. These tests simulate scenarios such as warehouses and workforce lifts, where pressure is exerted on concrete surfaces. Comparing the results obtained using the reference and colloidal silica, a significant reduction in abrasive wear ranging from 30 to 60% was observed.

Using Colloidal Silica in Concrete: Rules for Use in Ready-Mix Trucks

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.

The Impact of Particle Size and Surface Area of Colloidal Silica on Concrete

The Impact of Particle Size and Surface Area of Colloidal Silica on Concrete

Concrete is one of the most widely used construction materials in the world, known for its strength, durability, and versatility. Concrete is a composite material made up of various components such as cement, water, aggregates, and additives. The properties of concrete can be significantly influenced by these individual components, including the use of colloidal silica.

Colloidal silica is a suspension of fine particles in a liquid medium, typically water. It is known for its high surface area and small particle size, making it an ideal additive for concrete production. Colloidal silica can improve the strength, durability, and workability of concrete due to its unique properties.

Particle Size and Concrete

One of the key factors that affect the performance of colloidal silica in concrete is its particle size, ranging from 1 to 100 nanometers. Generally, smaller particles lead to higher surface area and improved properties in concrete. This is because smaller particles can fill the gaps between larger particles, resulting in denser and stronger concrete. Additionally, smaller particles have a higher reactivity with the cementitious materials in concrete, leading to faster and more efficient hydration.

Surface Area and Concrete

When incorporated into concrete mixtures, colloidal silica particles undergo a gel-like transformation, enveloping and uniting with other particles present. Consequently, this engenders a more condensed and tightly knit microstructure within the concrete. The extensive surface area of colloidal silica enables a greater contact area with water molecules contained within the mixture, leading to the heightened efficacy of cement particle hydration. As a result, the hardened concrete benefits from enhanced robustness and durability.

Furthermore, colloidal silica acts as a pozzolan by interacting with calcium hydroxide within the cement, thereby generating additional calcium silicate hydrate (C-S-H) gel. This fortifies the concrete's tenacity and longevity.

The elevated surface area of colloidal silica particles facilitates their adsorption onto other constituents within the mixture, such as aggregates and cement particles. This improves the dispersion of these materials and fosters a more homogenous concoction.

The surface area of colloidal silica plays a pivotal role in its effectiveness within the context of concrete. The greater the surface area, the more reactive sites are available for bonding with other materials in the concrete matrix. Consequently, this yields a denser and more cohesive microstructure, therewith enhancing the strength and durability of the concrete. Moreover, a higher surface area allows for superior dispersion of colloidal silica particles throughout the concrete, reducing the likelihood of cracking and enhancing overall performance.

Conclusion

In conclusion, particle size and surface area are critical factors to consider when using colloidal silica in concrete. Smaller particle sizes and higher surface area can lead to stronger, more durable, and workable concrete. It is essential to carefully select the appropriate type of colloidal silica according to the desired properties and requirements of the concrete mix.

1. "Effect of Particle Size Distribution on Rheological and Mechanical Properties of Colloidal Silica-Based Cement Composites." Cement and Concrete Research, vol. 108, 2018, pp. 131-141.

1. "Influence of colloidal silica surface area on cement hydration." Cement and Concrete Composites, vol. 33, no. 2, 2011, pp. 215-222.

1. "Nanomaterials for Enhancing the Performance of Concrete: A Review." Construction and Building Materials, vol. 125, 2016, pp. 545-554.

Understanding the Difference Between Colloidal Silica, Potassium Silicate and Sodium Silicate

Understanding the Difference Between Colloidal Silica, Potassium Silicate and Sodium Silicate

Silica is a naturally occurring mineral commonly found in sand, rocks, and soil. It is composed of silicon and oxygen atoms and has various industrial applications due to its unique properties. When mixed with water, silica can form colloidal suspensions or solutions that are commonly used in the concrete and construction industries In this article, we will delve into the differences between colloidal silica, potassium silicate, and sodium silicate and how each impacts concrete.

What is Colloidal Silica?

Colloidal silica is a stable dispersion or suspension of ultrafine particles of silicon dioxide (SiO2) in a liquid medium. The particle size of colloidal silica is typically in the range of 1-100 nanometers, making it smaller than traditional silica particles found in sand or rocks. Due to its small size, colloidal silica has a large surface area, providing excellent binding properties. Colloidal silica solutions often appear transparent or slightly opaque and can be either acidic or alkaline.

Colloidal silica particles have a negative surface charge, which makes them repel each other and remain suspended in the liquid medium. This property is known as electrostatic stabilization. Furthermore, colloidal silica has a high affinity for water molecules due to its large surface area, leading it to form strong bonds with surrounding water molecules. These properties make colloidal silica an excellent binder and stabilizer in concrete.

What is Potassium Silicate?

Potassium silicate is a compound composed of potassium oxide (K2O) and silicon dioxide (SiO2). It comes in different forms, including liquids, powders, or granules. Potassium silicate solutions are highly alkaline with pH values ranging from 10-12. Due to its alkalinity, it is often used as a corrosion inhibitor and adhesion promoter in coatings and paints.

When potassium silicate is mixed with water, it forms silicic acid (H4SiO4). This acid dissociates into silicate ions (SiO32-) and potassium ions (K+), which are responsible for the alkaline nature of potassium silicate solutions.

What is Sodium Silicate?

Sodium silicate, also known as water glass or soluble glass, is a compound composed of sodium oxide (Na2O) and silicon dioxide (SiO2). It is available in both liquid and solid forms, with the liquid form being more commonly used in various industries. Sodium silicate solutions have a high alkaline pH ranging from 11-13.

Similar to potassium silicate, when sodium silicate comes into contact with water, it forms silicic acid, which dissociates into sodium and silicate ions. These ions are responsible for the high alkalinity of sodium silicate solutions.

How Does Colloidal Silica Differ from Pottasium Silicate and Sodium Silicate when used in Concrete?

Colloidal silica is a dispersion of ultra-fine amorphous Nano silica particles that are normally grown from ripping and stripping apart potassium and sodium silicates and allowing that silica, that SiO2 to polymerize or to grow on top of each other until it becomes a certain size. Then the growth is stopped and the pure silica is flipped with some type of a cursor on it to create a double layer. This prevents it from sticking to each other when it bounces into other particles or adjacent silica particles. The key thing is a higher purity of silica or a higher content of silica than salt.

Nano silica are larger particles of obscure form of Silica in a given cross sectional area. The potassium, sodium, and lithium silicate is silica or silicate attached to a salt, the carrying agent. Therefore, in potassium, sodium, and lithium silicate dispersions, in a given cross sectional area you're going to have more salt as compared to Colloidal Silica where you have more silica than salt. 

Additionally, most potassium, sodium, and lithium silicates will react faster than a colloidal silica dispersion. This is commonly seen in densifying agents. Colloidal silica provides deeper penetration and greater migration of that product into the concrete surface then seen with silicate versions. This is because normally those silicates will react at the surface, creating a gel and slowing down the migration of that solution into the body of the concrete. Silica is not going to react as fast because it is 100 particles compared to the solutes in solution.

Conclusion

Although colloidal silica, potassium silicate, and sodium silicate have similar chemical compositions, they have distinct properties and applications. Colloidal silica is a stable dispersion of ultrafine particles with excellent binding properties, while potassium silicate and sodium silicate are alkaline compounds used as corrosion inhibitors, adhesion promoters, and binders. By understanding the differences between these elements, concrete providers can choose the most suitable solution for their specific needs.

Colloidal Silica Hydrogels for Retrofitting Marine Base Structures

Colloidal Silica Hydrogels for Retrofitting Marine Base Structures

Marine base structures, such as ports and offshore platforms, are subject to harsh environmental conditions due to constant exposure to saltwater and severe weather. As a result, they are prone to corrosion and damage which can weaken their structural integrity over time. This not only poses a safety risk for those working on these structures but also leads to high maintenance costs and potential downtime for repairs. In this article, we talk about how colloidal silica hydrogels can be used to improve resilience and combat deterioration of concrete used in forming these structures. 

Marine Base Structure Deterioration

Damage to concrete in a marine environment can occur due to physical and chemical attacks. Effects include fatigue, where repeated loadings weaken the concrete by exceeding the strength of the material, and chemical attack, a process that chemically alters the binding matrix or aggregate skeleton of concrete to a weaker and/or greater voluminous version than the original concrete or aggregate skeleton.

Chemical and physical attacks produce cracking and microcracking, increasing the rate of water and salt migration into the concrete. This increase accelerates the potential for ASR, which is defined as a “chemical reaction in either concrete or mortar between hydroxyl reaction, ASR ions (OH-) of the alkalis (sodium and potassium) from hydraulic cement (or other sources), and certain siliceous rocks and minerals, such as opal, chert, microcrystalline quartz, and acidic volcanic glass, present in some aggregates. This reaction and the development of the alkali-silica gel reaction product can, under certain circumstances, lead to abnormal expansion and cracking of the concrete” (FHWA, 2013).

How Colloidal Silica Hydrogels Work

Colloidal Silica Hydrogels are a dispersion of nano sized particles which consume excess water and alkalis that reside in concrete pores and cracks and produces a denser concrete. Concrete is a hardened sponge with channels that allows water to leach through the body of the concrete to the concrete surface while also allowing deleterious chemicals to flow into the concrete. Colloidal Silica Hydrogels are a spray on technology which creates a more homogenous and stable concrete structure that is less prone to excessive degradation from chemical and physical attack. When hydrogels are added, a reaction occurs that chemically binds the concrete pore water solution. In doing so, this converts the pore solution into a bridging technology that spans the crack and pores that would cause further concrete deterioration. Furthermore, this technology in combination with the pore water solution develops into calcium silicate hydrate (“C-S-H”). C-S-H is the backbone of concrete strength and therefore, concrete enhanced with Colloidal Silica Hydrogels is denser and less permeable. This results in the decrease of water and alkalis to the surface as well as the decrease in harmful chemicals that are able to leach from the surface into the body of the concrete.

Advantages of Using Colloidal Silica Hydrogels

Compared to traditional retrofitting materials such as cement or epoxy resins, Colloidal Silica Hydrogels offer several advantages:

• Easy Application: The gel can be applied as a spray on technology with 100 to 300 psi sprayers available at local hardware stores.

• High Penetration: Due to the small size of the particles, Colloidal Silica Hydrogels can penetrate even the tiniest cracks and pores in the structure, ensuring comprehensive reinforcement.

• Strong Bonding: The gel bonds well with both concrete and steel, providing a strong and durable retrofitting solution.

• Chemical Resistance: Colloidal Silica Hydrogels are resistant to chemical corrosion, making them suitable for use in marine environments.

• Improved Longevity: By strengthening the structure from within, these hydrogels can significantly prolong the life of marine base structures.

Conclusion

Colloidal silica hydrogels offer a highly effective and efficient solution for retrofitting marine base structures. With their unique properties and advantages, they have become an increasingly popular choice for enhancing the strength and stability of these vital structures. As technology continues to evolve, we can expect to see further advancements and applications of colloidal silica hydrogels in the marine industry. Using colloidal silica hydrogels is a sustainable option for renovating marine base structures that are exposed to harsh environmental conditions.