Nishant Garg

Recent research studies conducted at the Illinois Center for Transportation focused on sustainable applications of quarry-by-products (QB) as pavement foundation materials and demonstrated the superior durability performance of dolomitic aggregate materials exposed to long-term cementitious reaction and repeated freezing and thawing. This study investigated the influence of QB chemical composition on the strength of cement-stabilized samples exposed to freeze–thaw cycles. Dolomitic QB materials from different quarries in Illinois and with different magnesium oxide (MgO) content, and a control limestone sample were chemically characterized by X-ray fluorescence and X-ray diffraction techniques. The QB materials were then stabilized with 3% cement and subjected to a 7-day curing period, followed by freeze–thaw conditioning. Unconfined compressive strength and resonant frequency tests were conducted to examine how the percentage of MgO and dolomitic minerals could alter the strength/stiffness with freeze–thaw cycles. Optical microscopy analysis was also performed to observe the extent of microstructure damage with freezing and thawing. Over the course of the applied freeze–thaw cycles, no notable minerology effect on strength or stiffness characteristics was observed for the short-term curing. Instead, performance was predominantly governed by physical properties, such as the particle size distribution, which played a more significant role after short-term curing. Well-graded QB materials with optimum packing, following Talbot’s equation with a 0.45 exponent, consistently exhibited the highest strength after any freeze–thaw cycle. The next phase of research, focusing on long-term curing, is expected to provide more insights into the chemical and mineralogical effects of QB materials on durability performance.

Ultra-high-performance concrete (UHPC) represents the next generation of concrete, with a strength 3-4 times greater than traditional concrete (100-120 MPa as opposed to 30-40 MPa). However, most of the commercial UHPC mixes are proprietary and expensive. In this project, we document the development of nonproprietary, cost-effective UHPC mixes primarily using locally sourced or pre-qualified materials in Illinois. The research utilizes the modified Anderson and Andreasen packing model to establish a new parameter: “packing factor” that has a significant influence on the design and performance of multi-binder UHPC mixes. Initially, 19 UHPC mixes without fibers are analyzed for their rheological, mechanical, and durability properties, demonstrating promising results. Specifically, we obtain self-flowing capabilities with minimal HRWR usage (<1% by wt.%), a turnover time of 7–10 minutes, and a significant reduction in cement content (47% Type IL and the remaining 53% SCMs by volume) while maintaining superior compressive strengths (~120–150 MPa, 17.2–21.8 ksi @ 28 days). Then, optimal mixes, particularly M18 and M19, are evaluated with fibers, achieving compressive strengths exceeding 150 MPa (21.8 ksi) at 28 days and exhibiting open porosity under 2%, and have shrinkage rates below the target threshold (<800µξ @ 91 days). Finally, effective particle packing resulted in UHPC mixes costs of ~$400/m3 (~$308/yd3) without steel fibers and ~$590/m3 (~$454/yd3) with steel fibers, enabling cost-effective, optimal UHPC for deployment by the Illinois Department of Transportation.

This report investigated pathways to reduce concrete curing time while maintaining mechanical and durability performance. Among several options such as admixtures, supplementary cementitious materials, and low water-to-cement ratio, researchers explored two mix designs in a field demonstration project. For Stage I of the project, a low water-to-cement ratio concrete mixture was used. For Stage II, the use of calcium-silicate-hydrate (C-S-H) based seeds was explored. Concrete laboratory mixtures containing C-S-H seeds X1 and X2 exhibited increased early-age strength and reduced permeability. Based on these findings and the Illinois Department of Transportation acceptance of X2 as a Type S admixture, a field demonstration project was conducted on a box culvert near Armstrong, Illinois. The X2 concrete mix design was compared to a low water-to-cement ratio concrete mix design. Results showed that the X2 mixture with C-S-H seeds consistently demonstrated higher strength than the low water-to-cement concrete mixture, suggesting that seed-based admixtures can provide additional benefits for reducing curing times. The recommended dosage of X2 is 5 fl oz/cwt for optimal performance in reducing cure time.

The tendency of cementitious systems to absorb and transmit liquid through capillary pores is often characterized by initial sorptivity, which is an important indicator of long-term durability. However, sorptivity measurements, which are based on the continuous mass change of specimens exposed to water, are labor-intensive (up to 6 h of continuous measurements). Here, we exploit the fundamental surface-wetting characteristics of cementitious systems to estimate their sorptivity in a rapid fashion, i.e., in a matter of few minutes. In a series of 63 distinct paste systems of varying w/c ratios (0.4–0.8), subject to a range of curing periods (1–7d), we establish strong correlations (adjusted R² ≥ 0.9) between the initial sorptivity (~6 h) and dynamics of drop spreading (contact angle ~0.5 s, drop residence time <10 min). These results elucidate rapid pathways in estimating initial sorptivity and durability of a broad variety of hydrated cementitious matrices.

Carbonation of cementitious systems is an important phenomenon from both durability (rebar corrosion) and greenhouse emissions (CO₂ sequestration) perspectives. Several analytical techniques are well‐established for measuring the kinetics of this dynamic phenomenon, ranging from measuring the pH change to quantifying the calcite content over time. However, the majority of these methods (with the exception of electron imaging) rely on bulk measurements which may miss the fine, microstructural changes that occur during carbonation. In this study, we investigate and evaluate the potential of Raman imaging to follow the spatiotemporal evolution of carbonation in cementitious pastes. By analysing mm‐scale maps (1 mm × 1 mm) at the micron‐scale resolution, we find that nearly ~40% of the sample surface was covered with calcite at the end of a 2‐week carbonation exposure. Simultaneously, the portlandite content declined from ~15% to 5% in the same period, suggesting portlandite consumption for the sake of calcite growth. Finally, the difference between the calcite growth rate and portlandite consumption rate strongly suggests simultaneous carbonation of CSH and ettringite—a finding that is in agreement with recent experimental investigations of carbonation kinetics. Overall, these new results on the spatiotemporal evolution of cementitious microstructure pave the way for utilizing Raman imaging for understanding dynamic phenomena in complex systems.

Cracking is one of the most critical distresses experienced by pavement infrastructure. Both flexible and rigid pavement cracking allow for water intrusion, which can in turn cause freeze–thaw damage and structural issues, causing premature failure. In addition, rigid pavements suffer from corrosion of reinforcing steel, which impedes the ability of the steel to resist deformation of the surface layer. One proposed technology to mitigate such cracking is the engineering of self-healing materials in pavements that can autogenously heal damage at the microscale. However, these technologies are not yet widely implemented, due to various practical issues. The following report provides a comprehensive literature review, preliminary evaluation of self-healing technology in asphalt concrete and Portland cement concrete, and future steps that can be taken to advance these technologies.

Accurate estimation of municipal solid waste (MSW) composition is critical for efficient waste management. In the United States, site-specific and material flow approaches determine the MSW composition at regional and national levels. The material flow-based national estimates are determined by the US EPA; the US EPA’s estimates are known to differ substantially from the aggregated tonnage of MSW managed by waste handling facilities in the United States. However, the material class-specific discrepancies of the US EPA’s material flow approach resulting in these differences are unknown. To find the basis of these discrepancies, we analyze the discarded MSW stream of 27 US states, which roughly accounts for 73 percent of the US population. Our analysis indicates that the material flow-based national estimates are accurate for the food, plastic, and glass material classes. In contrast, we find that the US EPA’s material flow-based predictions underestimate paper waste disposal by at least 15 million tons annually. These differences likely stem from incorrect assumptions of residence time. These results highlight the material class-specific strengths and drawbacks of the US EPA’s material flow-based MSW estimates.

Calcined clays are attracting significant research attention because of their potential to partially replace CO₂‐intensive portland cement. This potential depends largely on their reactivity, especially dissolution under alkaline conditions. Identification and characterization of reactive sites in these amorphous calcined clays has so far not been reported. Here, we investigate kaolinite (1:1 clay) and montmorillonite (2:1 clay) calcined at different temperatures under alkaline conditions (0.1 mol/L NaOH). Solution compositions are determined in batch dissolution experiments, whereas ²⁷Al and ²⁹Si MAS and CP/MAS NMR are used to investigate the structure of the undissolved residues to identify sites that are reactive and undergo preferential dissolution. The highest Si and Al dissolution rates for kaolinite are observed for calcination at 700°C, corresponding to the temperature of optimum reactivity, whereas the rates decrease and become increasingly incongruent at higher temperatures. The Si and Al dissolution rates for optimally calcined kaolinite are 4 and 12 times larger than the corresponding rates for optimally calcined montmorillonite, in accord with the much higher reactivity of calcined kaolinite compared to calcined 2:1 clays. This superior performance of kaolinite is explained by novel ²⁷Al NMR results, which show strong evidence for preferential dissolution of highly reactive pentahedral aluminum sites.

For in situ neutron scattering experiments on cementitious materials, it is of great interest to have access to a robust device which can induce uniaxial load on a given solid sample. Challenges involve selection of materials making up the apparatus that are both weak neutron scatterers and yet adequately strong to induce loads of up to a few kilonewtons on the sample. Here, the design and experimental commissioning of a novel load frame is provided with the intended use as a neutron scattering sample environment enabling time-dependent stress-induced changes to be probed in an engineering material under compression. The frame is a scaled down version of a creep apparatus, which is typically used in the laboratory to measure deformation due to creep in concrete. Components were optimized to enable 22 MPa of compressive stress to be exerted on a 1 cm diameter cement cylinder. To minimize secondary scattering signals from the load frame, careful selection of the metal components was needed. Furthermore, due to the need to maximize the wide angular detector coverage and signal to noise for neutron total scattering measurements, the frame was designed specifically to minimize the size and required number of support posts while matching sample dimensions to the available neutron beam size.

Drying-induced nanoscopic alterations to the local atomic structure of silicate-activated slag and the mitigated effects of nano-ZrO2 are elucidated using in situ X-ray pair distribution function analysis.

Drying-induced nanoscopic alterations to the local atomic structure of silicate-activated slag and the mitigated effects of nano-ZrO2 are elucidated using in situ X-ray pair distribution function analysis.

Usingin situX-ray PDF, we elucidate the crucial role of calcium in the retardation mechanism of zinc oxide.

Usingin situX-ray PDF, we elucidate the crucial role of calcium in the retardation mechanism of zinc oxide.