By Claude Goguen, P.E., LEED AP
In precast concrete, we make big, heavy structures. We tend to think in the macro scale, which is to say we deal in feet and inches or meters and millimeters. But exciting, new technologies are being developed that could affect the performance and durability of your product, and they are based on the study of very small things: nanotechnology.
Nano is a prefix used mainly in the metric system meaning one billionth of a meter. In context, a typical sheet of paper is 100,000 nanometers thick, and the author of this article is 1,900,000,000 nanometers tall! The point is that nano is very small.
Nanotechnology is the manipulation of matter on an atomic and molecular scale. This discipline deals with the production and application of physical, chemical and biological systems at scales ranging from a few nanometers to submicron dimensions. The technology is used across science fields including chemistry, biology, physics, engineering and materials science. The latter is what concerns us, but first, more cool stuff about nanotechnology.
While the science related to nanotechnology is new, nanosized matter has existed on earth as long as life itself. It has been proven that the exceptional mechanical performance of biomaterials, such as bones or mollusk shells, is due to the presence of nanocrystals of calcium compounds.
The framework of nanotechnology was first introduced in 1959 by Nobel Laureate Richard P. Feynman. Tokyo University of Science Professor Norio Taniguchi first coined the term nanotechnology in the early 1970s. It wasn’t until 1981, however, with the development of the Nobel Prize-winning scanning tunneling microscope that could “see” individual atoms, that modern nanotechnology began.
Then in 1989, the first atomic force microscope (AFM) was introduced and is still one of the tools used today for imaging, measuring and manipulating matter at the nano scale.
Further work and research in nanotechnology brought about breakthroughs in areas such as materials and manufacturing, nanoelectonics, medicine and health care, energy, biotechnology, information technology and national security. Construction – and especially the construction materials field – has benefitted and will continue to do so with further developments in nanotechnology.
Nanotechnology and concrete
Researchers are obtaining a better understanding of the complex structure of cement-based materials at nano levels. This may result in a new generation of stronger and more durable concrete with desired behaviors and properties.
Hydration of cement produces a rigid, heterogeneous microstructure. As water is introduced to cement to make a paste, which hardens over time, the main microstructural phases in the hydrated cement paste are:
- Calcium silicate hydrate gel (C-S-H);
- Calcium hydroxide (CH);
- Ettringite (a sulfoaluminate hydrate);
- Unhydrated cement particles; and
- Air voids.
These microstructural phases govern the macroscopic properties of cementitious materials such as strength, ductility, flow and durability. Controlling the macroscopic properties demands a detailed knowledge of the structure of these phases at the smallest size level. Among the various phases, the first one, C-S-H, is the most important product of hydration and accounts for 50 to 70% of the total paste volume. This main binding phase governs the macroscopic properties of the cement paste, but the micro- and nanoscale structure of C-S-H is still not well established. However, University of Leeds professor Ian Richardson discovered from an investigation of the “amorphous” C-S-H gel that at the nanoscale it has a highly ordered structure.
We know that pozzolanic supplementary cementitious materials such as fly ash and silica fume react with the CH in the presence of moisture to form more C-S-H. Researchers have taken this to the nano scale by using a colloidal silica in the concrete matrix to more effectively achieve the same properties. Collodial silica is also being used to control concrete cracking due to alkali silica reactivity (ASR), a chemical reaction between reactive silica in aggregates and alkalis in cement.
Jon Belkowitz, president of Intelligent Concrete LLC and doctoral student of Stevens Institute of Technology, studies chemical reactions within concrete at the nanoscale. His research into the optimal use of colloidal silica is expected to create a new concrete mixture that will result in longer-lasting buildings, roadways, sidewalks, stairs, sewers and dams. “With the advent of nanotechnology, the material properties of concrete, including ASR mitigation, gives engineers and architects the ability to use concrete in applications that were once impossible,” he says.
Belkowitz’s research took a three-tiered approach. “I’m using this new nanotechnology to not only stop ASR from being produced, but I’m also using nano silica to strengthen the hydrated cement matrix of concrete to resist the expansive nature of the ASR gel,” he explains. “I’m also trying to change the properties of the excess water within the concrete so that it can’t react with soluble alkalines in silica to cause ASR gel.”
Nanotechnology has made possible many benefits for precast concrete including:
- Reducing concrete shrinkage
- Reducing permeability
- Increasing durability to physical and chemical attack
- Achieving the same strength with less induced heat
- Higher cement efficiency
- Higher early strength
- Higher tensile strength, ductility and toughness
- Self healing of micro cracks
- Degradation of pollutants and self-cleaning concrete
Nanotechnology is an exciting field of study that has incredible potential for many fields, and precast concrete will undoubtedly continue to benefit from this technology. It will be interesting to see how colossal changes in the concrete industry will take shape at the submicroscopic level.
For more information on this topic, please contact Claude Goguen, NPCA’s director of Sustainability and Technical Education, at (800) 366-7731 or [email protected].
Jon Belkowitz, M Sc, Intelligent Concrete LLC, www.Intelligent-Concrete.com
Ara Jeknavorian, Ph.D., Jeknavorian Consulting Services, www.jeknavorianconsulting.com
National Research Council Canada, www.nrc-cnrc.gc.ca