Building materials such as concrete are created to produce greener, more efficient structures aiming to increase self-cleaning or healing abilities, strength, and durability or optimize thermal insulating properties. Researchers and materials engineers focus on expanding these capabilities with the industry’s future needs in mind.
As a building material, concrete has become the most widely used material in human history since the nineteenth century. Cements, concretes, and gypsum products have been increasing in their complexity and chemical composition ever since. As building around the globe increases and materials development is initiated in one place and finalized in another, materials like concrete are subject to deep scrutiny.
The Global Importance of Concrete in Numbers
Globally, 1.56 billion tons of cement are produced every year.
The United States alone spends 30 billion US-dollars (USD) per year on repair and maintenance of concrete and concrete structures.
China spent 15 billion US-dollars on concrete mixing for its high-speed railway program and the train line between Shanghai and Beijing alone.
Reinventing an Iconic Concrete Structure: The Sixth Street Viaduct
“Concrete cancer” is why officials in the city of Los Angeles were forced to demolish the 3,500-feet-long Sixth Street Viaduct, built in 1932, in the year 2016. ASR (alkali-silica reaction), as it is also called, occurs over time due to high amount of alkali ingredients, causing cracks in the material and snapping the strength of the structure.
Today, the city of Los Angeles is building a new viaduct, called “Ribbon of Light”, which is to become an even more iconic landmark. With ten pairs of smoothly designed, continuous concrete arches of 3060 feet in length and 100 feet in width, the new bridge will tower above the 101 Freeway, 17 railroads, the LA River, and the arts district like no other building before – linking and transforming the urban landscape along the way.
Microscopy solutions for materials research are key to understanding the processing and structure of building materials, analyzing phenomena like “concrete cancer”, helping to improve future materials and, finally, enabling the groundwork for new structures that connect society, just as the “Ribbon of Light” will do.
Microscopy Solutions for Building Materials
What if you could minimize the cracks that are still a major source of reduced durability and financial loss? Apply microscopy techniques to mitigate this problem and move forward with the improvement of properties and performance when developing self-healing concrete.
- Processing: Study hydration of cement with Scanning Electron Microscopy (SEM).
- Structure: Observe and quantify the produced structures, find out how they relate to properties, investigate failure analysis in building materials with the 3D submicron imaging capabilities of X-ray microscopy (XRM).
- Properties and Performance: Investigate or predict how a novel building material, like self-healing concrete, will perform in a real-world application, using SEM.
Analyze building materials like cement, the composition, shape and morphology of its compounds, either dry or in a hydrated state with Scanning Electron Microscopy, which is suited not only to high vacuum experiments but also to environmental conditions.
Environmental Control within Chamber
- Control the sample conditions and therefore the sample humidity by varying the temperature, pressure, and atmospheric gases in the chamber. Determine various hydration states, work at low or extremely low vacuum instead of high vacuum, add water vapor into the chamber, and cool or heat your sample on a dedicated stage.
- Apply pressures of up to 3000 Pa and combine them with wet or dry mode enabling you to image concrete samples in a range of temperatures, pressures, and humidity conditions
- Reveal hydration mechanisms at high resolution using a coolstage
- At the same time, achieve high resolution, high contrast images with minimal sample preparation using detectors especially tailored for these varying conditions delivering crisp images even at higher pressures and lower landing energies.
Secondary and Back-Scattered Electrons
Imagine being able to avoid early-stage cracking in cement-based building materials and save not only 500 M US $ of repair costs, half of them even on site, but also rescue thousands of lives otherwise lost to disasters after building collapses . Using acoustic or micro-computed tomography, you will acquire images with resolutions of several millimeters to possibly a 100 µm. With more high-end micro-CTs, you achieve higher resolutions, yet these experiments can only be carried out with samples of small sizes. Optical or SEM imaging provide you with higher resolutions but force you to destroy the specimen and provide information only in 2D.
Non-destructive 3D Imaging of a Concrete Sample
- Characterize highly varying 3D topologies and crack networks non-destructively.
- Image in 3D at sub-micron resolutions.
- Investigate relatively large sample sizes in situ and quantify fracture evolution during stress and environmental conditions with 3D X-ray microscopy for fast imaging of intact samples.
Sub-micron Imaging to Highlight Cracks and Voids
Benefit from key advantages when investigating the structure of cracks:
- Image emerging hairline fractures and those close to the crack tip with a spatial resolution of 500 nm and a minimum achievable voxel size of 40 nm
- Distinguish different phases within building materials with superior contrast using dedicated detectors to enhance phase contrast and apply a technique that highlights fracture interfaces in implementing propagation phase contrast (see Phase Contrast Tech Note)
- Identify fracture mechanisms in situ and in 4D using dual magnification – optical as well as geometric. Thus, move away from the traditional resolution limitations of projection-based systems.
- Maintain high resolution even at large distances and image samples non-destructively within in situ chambers.
- Undertake measurements of crack network evolution repeatedly under stress and/or environmental, thereby enabling quantification and correlation of cracking within the same sample under varying conditions.
Think of further advancing self-healing concrete like researchers of the Department of Engineering at the University of Cambridge for whom living organisms were a role model. Inspired by their ability to repair themselves to a certain extent after being damaged, the researchers started a project to work with potential minerals (magnesia, bentonite clay, quicklime) used in cement that expand when cracks form. This expansion of the mineral material fills the cracks and bridges them over time. Be inspired by this project when planning your next study.
- Characterize the material’s microstructure and identify the self-healing bridges formed during the healing process. Capture high-definition topographical images using SEM with low acceleration energies
- Identify the composition and mix of self-healing materials based on their structural pattern and formation style, including scaffolding structures, flower-like and other bridging and filling structures produced by different expansive materials during the healing process
Microstructure of Self-Healing Materials
Get in touch with us to find out more about the benefits of ZEISS Microscopy Solutions for your building materials research, book a demo at our customer center, or get a quote. We are looking forward to hearing from you.