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.
Neutron Radiography
Presented By: Jason Weiss
Affiliation: Oregon State University
Description: Neutron radiography is a non-destructive imaging technique. Since neutrons are strongly attenuated by hydrogen (¹H), this method is ideal for capturing moisture profiles in cement-based materials with high spatial and temporal resolution. Radiographs are obtained by placing specimens between a collimated neutron beam and a detector that records grayscale images, where pixel intensities correlate with sample thickness and composition. Hardened specimens are conditioned to known internal relative humidities and subjected to controlled fluid ingress or egress experiments. Measurements taken at specific exposure times are compared to oven-dried and fully saturated states to quantify pore saturation. A novel approach combines neutron data with inverse modeling algorithms to estimate liquid permeability and vapor diffusivity, two key parameters to predict the service life and durability of cement-based materials. This coupled approach overcomes the challenge of accurately determining these transport properties.
Neutron Scattering
Presented By: Kai Gong
Affiliation: Rice University
Description: Quasi-elastic neutron scattering (QENS) is a powerful technique for probing the molecular dynamics of hydrogen-bearing species in hydrated and nanostructured materials including cementitious systems. Because hydrogen atoms possess a much larger incoherent neutron-scattering cross section compared with other elements in cement, over 99 % of the QENS signal arise from their motion. This sensitivity enables direct observation of the evolution of distinct H/H2O environments during hydration. By modeling the spectra with Lorentzian functions, the relative fractions of free, bound, and constrained water can be quantified as a function of reaction time, providing a dynamic measure of ongoing chemical transformations. The resulting linewidths yield residence times and apparent diffusivities of hydrogen species, which can be directly compared with molecular dynamics simulations. These insights complement calorimetry and spectroscopy, establishing QENS as a unique tool for elucidating nanoscale water dynamics and reaction mechanisms that govern the formation and durability of cement-based materials.
Micromechanical Testing
Presented By: Luca Sorelli
Affiliation: Université Laval
Description: This presentation introduces advanced micromechanical testing techniques, based on instrumented indentation method, developed to investigate the mechanical and time-dependent behavior of cement paste as the primary binder in concrete. Micro-sized specimens, including prisms (150 × 150 × 300 µm3) and cubes (150 µm), were fabricated and tested under uniaxial compression and splitting tension to determine elastic modulus and strength. Long-term logarithmic creep and recovery were assessed through micro-prism uniaxial creep tests. These techniques also enable direct and rapid investigation of hygro-thermo-mechanical interactions governing mechanical and creep response at the microscale, overcoming the limitations of conventional macroscale testing. Sample preparation involved multiple steps, including precision dicing and polishing, to ensure surface quality and controlled geometry. Data analysis integrated stress-strain and load-displacement evaluation, creep compliance quantification, and capturing the effects of relative humidity and temperature. Together, these techniques provide new insights into the micromechanical and viscoelastic behavior of cement-based materials.
Wired for Insight: Electrical Characterization of Portland Cement Materials
Presented By: Moe Pourghaz
Affiliation: NC State
Description: The electrical properties of concrete have been investigated extensively over the past three decades. Today, the research community possesses a robust understanding of these properties and their physical interpretation. To facilitate broader adoption in practice, recent work has emphasized electrical resistivity measurements, typically performed at a single AC frequency, as a practical means for assessing concrete quality and durability. In this presentation, we will review the historical development of electrical resistivity testing and discuss how resistivity is fundamentally related to transport mechanisms within concrete, such as ion diffusion and moisture movement. We will then explore more advanced electromagnetic methods, including electrical impedance tomography (EIT) and electrical capacitance tomography (ECT), which enable spatial mapping of internal features and material inhomogeneity. These methods provide a more comprehensive view of transport behavior in cement-based materials. Finally, we will examine the advantages and limitations of various measurement approaches and reconstruction techniques. Emphasis will be placed on how these electrical methods can complement traditional durability assessments, providing a more efficient, non-destructive means of characterizing material performance and predicting long-term service behavior.
Demystifying the Practice of Petrography — Divination by Communication with the Stone
Presented By: Karl Peterson
Affiliation: University of Toronto
Description: When questions arise around the performance of hardened concrete, answers are needed. If concrete could speak, perhaps it would reveal its secrets. Of course, during service, concrete may emit at acoustic or infrared wavelengths, but we are not always there to listen, or equipped to see. Instead, in our quest for answers, we are left to other approaches and devices, approaches and devices that include petrography. From the Greek, this combination of pétros (p?t???) and gráfo (???f?) translates to “stone writing” or “stone drawing”. Basically, petrography is the act of studying and communicating about the stone, or in our case, concrete. Traditionally petrographers rely on what they can see in the visible light spectrum, and take advantage of microscopes while they cut, polish, or pluck away. This presentation introduces preparation and analysis techniques frequently employed, and how optical microscopy can complement other analytical techniques.
In-situ TEM: Unraveling Cement Hydration in Real Time
Presented By: Qi Zheng
Affiliation: Stanford University
Description: Cement hydration governs the evolution of microstructure that underpins the strength, durability, and longevity of concrete. Mastering its mechanisms is pivotal for the innovation of low-carbon cementitious materials. Here, we developed a powerful in situ TEM platform that unveils the fundamental mechanisms of cement hydration at nanoscale scale. We directly captured the preferential dissolution of cement grains from the edges and step regions, followed by heterogeneous nucleation and hierarchical growth of calcium silicate hydrates. These dynamic observations uncover how local structural features govern reaction pathways, offering unprecedented insight into the early-stage processes of cement hydration. This work establishes a new paradigm for understanding hydration kinetics and microstructure evolution, enabling the design of next-generation, sustainable cementitious materials.