This session, sponsored by ACI Committee 236, will explore a diverse range of advanced analytical and characterization techniques for concrete and cementitious materials. Invited experts will discuss advanced methods for measuring chemical and physical composition, including but not limited to diffraction, microscopic imaging, petrography, and spectroscopy. In addition, experts will cover mechanical characterization, thermal and calorimetric analysis, rheological properties, and advanced non-destructive testing methods. Attendees will gain insights into fundamentals, practical applications, and the benefits and limitations of various techniques that contribute to enhanced concrete resilience, durability, sustainability, and overall performance. This session is suitable for researchers, engineers, and practitioners interested in expanding their toolkit of analytical methods for concrete materials.
Learning Objectives:
Laser Diffraction
Presented By: Sriramya Nair
Affiliation: Cornell University
Description: Laser diffraction is a technique in which a volume-based particle-size distribution is inferred by measuring how a dispersed powder scatters a laser beam and inverting the angular pattern (typically with Mie theory). It is typically used to analyze powders such as cements, SCMs, and mineral fillers. It provides information in the ~0.1–1000 µm range, which is critical for dialing in particle size for reactivity, particle packing, and fresh state rheology. Samples are run either dry through air-jet dispersion or wet by dispersing the powder in a non-reactive liquid such as isopropanol or ethanol to avoid hydration; a small dose of dispersant and brief ultrasonication can help break soft agglomerates. During the experiment, obscuration should be kept at moderate levels and appropriate constants should be used. It is typical to report D10/D50/D90 along with the distribution. Care should be taken to check for multimodal peaks and verify repeatability.
Solid-state NMR Spectroscopy
Presented By: Jorgen Skibsted
Affiliation:
Description: Solid-state nuclear magnetic resonance (NMR) probes the electronic environment of nuclear spins (e.g., 1H, 13C, 27Al, 29Si) in powdered solids and is thereby an element specific technique. The electronic structure is measured by chemical shifts relative to an external standard which provide information about the nearest environment of the nucleus. Thus, it detects amorphous and crystalline phases in an equal manner, which has been widely used in studies of less-ordered phases in cementitious systems such as the C-(A)-S-H phase and supplementary cementitious materials such as silica fume, slags, and calcined clays. NMR experiments require 20 – 250 mg of dry, powdered sample and the analysis is non-destructive. The experiments can be time-demanding, depending on the nucleus under investigation, ranging from less than one hour to one day for each spectrum. Solid-state NMR instruments are relatively expensive, and expert knowledge is generally required to maintain the equipment and analyze the results. Sensitivity implies that the technique is most suitable for cement pastes rather than real concrete blends.
How to use Rheology? Just Go with the Flow.
Presented By: Shiho Kawashima
Affiliation: Columbia University
Description: This joint talk will provide an overview of how rheological methods can be used to characterize the flow and deformation response of cement-based materials in the fresh state (before setting) when subjected to shear. Through rheometry, shear is applied to a fresh cement suspension via a controlled torque or rotational velocity, which can then be converted to shear stress and strain rate, respectively. The response of the suspension can be used to obtain fundamental rheological parameters, i.e. yield stress, viscosity, and storage modulus. This talk will discuss different setup geometries, common rheological protocols and flow models, potential artifacts (i.e. wall slip), good practice (i.e. consistent shear history), and how the measured parameters can inform concrete workability for different applications (e.g. concrete pumping, low-carbon formulations).
Using 4D X-ray Micro-CT to Study Cement-based Materials
Presented By: Laura Dalton
Affiliation: Duke University
Description: In this presentation, I will discuss 4D X-ray micro-computed tomography (CT) and the numerous ways my research group is leveraging this robust technique to study changes in cement-based materials as a function of time. X-rays interact strongly with the electron cloud of a material making this technique ideal for studying dense solids such as cement-based materials which have complex micro-structures comprised of hydrated cement, fine and coarse aggregates, supplementary cementitious materials, and air-filled voids. At the Creativ Engineering Laboratory at Duke University, we have the state-of-the-art TESCAN UniTOM XL X-ray Micro-CT scanner designed to balance high temporal (<10 second scans) and high spatial resolution (< 3 µm) with integrated in-situ reactive gas connection and a mechanical loading cell. From self-healing fractures to 3D printing concrete for underwater construction, I will provide a high level overview of ongoing projects in my group and highlight opportunities for future work.
Neutron Imaging
Presented By: Mehdi Khanzadeh Moradllo
Affiliation: Temple University
Description: The durability of concrete in different environments is still a topic of continuing interest due to its scientific complexity and economic impact. This presentation discusses the important role of advanced Neutron imaging techniques in a deeper understanding of the deterioration mechanisms in concrete materials at a microstructural level. Additionally, it highlights how the micro-scale study of concrete materials enables us to manipulate and tailor the microstructure of materials. This opens up tremendous opportunities in developing high-performance and novel concrete materials.
Atom Probe Tomography
Presented By: Gilson Lomboy
Affiliation: Rowan University
Description: Atom probe tomography (APT) is an analytical imaging technique that generates a three-dimensional atom-by-atom image of a specimen, with sub-nanometer spatial resolution. Atoms are field-evaporated from the surface under a high electric field and ionized. By repeating the evaporation-and-detection cycle many millions of times, a specimen volume about 100 nm x 100 nm in cross-section and several hundred nm in length can be analyzed. A three-dimensional atom-by-atom reconstruction is then created on a computer. In the digital 3D reconstruction, quantitative measurements can be performed with computer software, revealing the geometry, topology, and chemical composition of nanoscale features. For the APT tests, a polished portland cement clinker with nanolimestone on its surface was hydrated for 2 and 4 hours. The hydrated portland cement clinker was then imaged with a scanning electron microscope to visually assess the degree of hydration. Tip specimens for APT were then formed by FIB lift-out in a FEI Helios Nanolab, followed by annular ion-beam milling to form APT tips targeted on the nanolimestone/cement clinker interface, so that the nanolimestone is located at the apex of the specimen. The results show the initiation of the nucleation reaction near the nanoparticle.