Cement, concrete, and mortar are some of the most extensively used materials on our planet — concrete is the second only to water. There is a constant search for fillers and additives to help lower costs and improve the properties of these building materials. One of the most promising is calcium carbonate whisker.
What is Calcium Carbonate Whisker?
Calcium carbonate whisker is an inorganic fiber derivative of calcium carbonate, an extremely common bio-mineral that is found in teeth, bones, eggshells, pearls, and rocks. To our eyes, calcium carbonate whisker looks like a white powdery material, but it is made up of single, short and fiber-shaped crystals of calcium carbonate. This fiber shape gives it a high length/diameter ratio.
Calcium carbonate whisker is described as having a “high tensile strength and strong binding force of adjacent atoms due to the presence of perfect crystalline structure.” Due to this, it is often used as a filler in various materials.
It increases the physical and chemical properties of the material it is added to, including heat resistance, strength, and the modulus of elasticity. In addition to all of this, it comes with a low cost, simple preparation, and is readily available.
Calcium Carbonate Whisker: How It’s Made
There are several main methods of producing Calcium carbonate whisker including carbonation, metathesis reaction, sol gel, urea hydrolysis, and gravity crystallization.
During carbonation, calcium hydroxide slurry – created using limestone – is bubbled with CO2 gas mixed with crystal formation additives like MgCl2 and phosphoric acid. This method is by far the most common because it’s simple and feasible. It is the least energy-intensive method. It’s considered to be an old, trusted method – in 1996 Japanese scientists were using this method to produce CaCO3 whisker.
Both the metathesis reaction method and the sol-gel method are mainly used for small scale production in labs because the reactions are slow. The urea hydrolysis method requires a high temperature and pressure, which equals a higher cost than most of the other methods. Gravity crystallization is the least used of the five methods – the high cost of the equipment drives most people to cheaper methods.
Increased Reinforcement, Serviceability, and Durability
Studies, where calcium carbonate whisker was added to Portland cement, found that the flexural and compressive strength was increased by 33.3% and 12.83%. The researchers found that the calcium carbonate whisker did not make the cement any harder to pour in comparison to cement with different fiber additives.
Studies on calcium carbonate whisker additives in concrete and mortar found similar increases in strength, hardness, durability, and toughness. Authors of a review of calcium carbonate whisker additives studies estimated that those properties were shown to be increased by up to 70% in some studies.
In a study published in the Journal of Materials in Civil Engineering in 2014, calcium carbonate whisker was found to be a great additive for increasing the cracking resistance in cementitious composites. Steel and polyvinyl alcohol fibers were also added.
The authors on the study concluded the “interaction of different fibers and multiscale cracks contributes to enhancing the mechanical properties of cementitious composite, which is also reflected in its deflection hardening performance and multiple cracking behavior.”
They even predicted that the steel fibers and polyvinyl alcohol fibers could be partially replaced by the calcium carbonate whiskers – suggesting an area for huge cost savings.