The broader adoption of raw earth in construction requires overcoming its heterogeneities and high variability, arising from differences in clay mineralogy and texture. These variations control water absorption and, consequently, rheological properties, drying behavior, shrinkage, and mechanical properties, making earth less predictable than cement-based concrete. This unpredictability limits standardization and its use in modern construction. To enable pourable earth, a rapid and robust characterization of fresh properties is essential. This study demonstrates the use of small amplitude oscillatory shear (SAOS) rheology and mini-slump flow tests to characterize clay–water dense suspensions (e.g., pastes) across a wide range of solid volume fractions ( ϕ ). Clay-rich materials, each predominantly composed of kaolinite, illite, and montmorillonite (Ca- and Na-bentonite), their 50:50 blends, and one clay-rich sludge were tested. Distinct rheological trends emerged, reflecting the water adsorption capacity of each material. SAOS and mini-slump flow measurements can be used to distinguish clay-rich materials according to the swelling or non-swelling behavior of their constituent clay minerals. The good agreement between the two methods highlights the mini-slump as a practical, field-compatible tool, while SAOS provides a deeper micro-structural insight into clay pastes (i.e., particle interactions). Together, these approaches offer complementary tools to rapidly classify clays and predict their suitability for earthen construction applications. This paves the way toward optimized, pourable raw earth formulations as a sustainable alternative to high-emission building materials.

The settling of spherical balls in quiescent cement pastes of increasing age is studied. Metallic spheres with radii of 2, 2.5 and 3mm are dropped into the paste and allowed to settle, while their position is tracked using X-ray tomography. The instantaneous velocity of the spheres, calculated from their movement, is observed to be quasi-constant during their fall, and an average is estimated. The results show that the average velocity of the balls decreases logarithmically with paste age until ball stoppage, for all three ball sizes. In parallel, the rheological properties of the cement paste are measured using a rheometer with a vane geometry. The evolution of the paste static yield stress over time is evaluated, and proves to be a reliable predictor for ball stoppage. Finally, thixotropic models of increasing complexity are evaluated. These models consider four forms of structural growth and breakdown parameters, and their ability to capture the ball settling velocity as a function of paste age is compared. This emphasizes the importance of considering paste breakdown in relation to shearing of the paste when the ball passes through it.

The dynamic yield stress associated with the flow cessation of cement pastes is measured using a rheometer equipped with various shear geometries such as vane, helical, sandblasted co-axial cylinders, and serrated parallel plates, as well as with the mini-cone spread test. Discrepancies in yield stress values are observed for cement pastes at various volume fractions, with one to two orders of magnitude difference between vane, helical and mini-cone spread measurements on the one hand, and co-axial cylinder and parallel plate measurements on the other hand. To understand this discrepancy, the flow profile of a cement paste in the parallel-plate geometry is investigated with a high-speed camera, revealing the rapid formation of an un-sheared band near the static bottom plate. The width of this band depends upon the rotational velocity of the top plate, and upon the shear time. Recalculation of shear stress shows that the reduced sheared gap alone cannot explain the low measured yield stress. Further exploration suggests the formation of zones with lower particle content, possibly linked to cement particle sedimentation. Here, we argue that the complex nature of cement pastes, composed of negatively buoyant non-Brownian particles with attractive interactions due to highly charged nano-size hydration products, accounts for their complex rheological behavior.

The integration of construction demolition waste (CDW) as a supplementary cementitious material presents a promising avenue to mitigate the environmental impact of concrete production by reducing clinker content. Notably, in some areas, up to 50

Modeling the shrinkage and creep of concrete is a demanding task due to the large number and high complexity of the parameters that contribute to these two mechanisms. A range of models have been developed to date to predict shrinkage and creep over time. Among them, this study focused on some of the most widely used models, including those developed by the American Association of State Highway and Transportation Officials, the American Concrete Institute, the European Committee for Standardization, the Federation Internationale du Beton, and the Comite Europeen du Beton. This holistic investigation aimed to provide in-depth insights into the input requirements and prediction capabilities of the identified models. For this purpose, using various data sets selected from the NU-ITI database, the performance of each shrinkage and creep model was first assessed, and a calibration approach was then employed to further refine their outputs. The calibration was performed with the objective of adjusting the short- and long-term prediction accuracy, including the rate of shrinkage and creep development over time. The models were evaluated side by side through comparing the outputs of each calibrated model to data from shrinkage and creep experiments. The calibration steps explored in this study were found to improve the performance of the shrinkage and creep prediction models by up to 20%. This helped reduce the possibility to deviate from the expected strains and stresses. The outcome of this detailed study paved the way to properly select and utilize shrinkage and creep models, taking into consideration the key contributing factors for the highest accuracy.

Understanding the mechanisms controlling the early (fresh) and long-term (hardened) hydration of one-part alkali-activated slags (AAS) is key to extend their use as low CO2 substitutes for ordinary Portland cement (OPC). Their "just add water" use makes them easier and less hazardous to manipulate than the more studied two-part ones. This is due to the absence of liquid alkaline activators, which are environmentally and energy demanding. In this work, numerous experimental techniques have been linked to obtain a comprehensive physico-chemical characterization of a one-part AAS activated with Na2CO3 and Ca(OH)(2) powders at several water to solid ratios (w/s). Calorimetry and pH/conductivity measurements describe the functioning of the activators immediately after contact with water. Early reactivity is characterized through in situ X-ray powder diffraction (XRPD) and small amplitude oscillatory shear (SAOS) rheology, which reveal a rapid precipitation of nanometric hydration products (nano-C-A-S-H), which results in a continuous increase in the paste cohesivity until setting. Moreover, SAOS shows that rejuvenating the paste by means of shearing (performed externally to the rheometer in this study) is enough to restore the initial cohesion (i.e., workability) for long time spans until setting occurs. The long-term hydration is characterized by ex situ XRPD on aged AAS pastes, in parallel with mechanical testing on AAS mortar. A correlation can be observed between the amount of nano-C-A-S-H and the increase in compressive strength. Overall, this formulation shows satisfactory fresh and solid properties, demonstrating suitability for low- and normal-strength applications.

The behavior of a suspension of spherical particles in a yield stress, shear thinning, thixotropic fluid is studied under pipe flow at low Reynolds number. Three flow distances, imposed by large amplitude oscillations, are investigated: 25 m, 48 m and 200 m, below and above the development length predicted for a Newtonian suspension of identical bead size and pipe diameter. The base fluid is a cement slurry and the particles are red glass beads, added at 0.3 vol. fraction (phi(0)). The radial distribution of beads over the pipe cross-section is measured after the hardening of the cement and shows a concentration gradient. No clear influence of travel distance is observed. Averaging all results, an increase in bead concentration by 35% above phi(0) (reaching an average 0 = 0.41) is measured in the pipe center region, and a decrease by 20% (reaching an average 0 = 0.24) near the pipe wall. The absence of further densification of beads in the pipe center contrasts with results obtained in Newtonian fluids. This is attributed to the paste increase in yield stress with time at rest, predicted to result in a plug flow zone of increasing radius with time. The radial migration of particles evidenced in this work for a low yield stress cement slurry may contribute to the formation of plugs (zone of high concentration of aggregates) observed at the forefront of concrete during pumping, explaining blockage.

The cracking behaviour of textile-reinforced concrete (TRC) impacts the serviceability and structural integrity of TRC beams. However, textile reinforcement has not yet been standardised and there are numerous available textile reinforcement options. In spite of evidence that the textile properties influence the cracking behaviour of TRC, knowledge of the role of the textile, concrete and geometric parameters on cracking is still limited. This paper investigates a commonly used subset of textile reinforcements, namely epoxy-impregnated textiles with a high yarn count, some of which are prone to induce splitting failure. Through a comprehensive experimental study of 144 uniaxial reinforced concrete tensile tests, the influence of the textile fibre strand geometry and surface finish (plain or sand-coated) on the cracking behaviour was investigated in dependency of the concrete cover thickness. The results show that sand-coating treatment can decrease the transverse crack width to one-third of those observed in analogous plain textile specimens. The geometry of the plain fibre strands, which is affected by the textile fabrication method, also leads to significant differences in the measured crack widths (factor of 2.5). The overall cracking behaviour, however, is decisively influenced by the occurrence of splitting (longitudinal) cracks in the layer of the textile reinforcement, which were observed regardless of the surface treatment for concrete covers thicker than 15 mm. In case of the sand-coated textiles, these splitting cracks initiated immediately after the first main crack and propagated throughout the specimen, which diminished any tension stiffening effect. In the plain textile samples, the cracks led to an excessive spalling of the concrete cover. The results of this study provide a deeper understanding of the cracking behaviour of TRC with epoxy-impregnated textiles and a comprehensive database for further research. This establishes the basis for unified regulations regarding the limit states of TRC structures.

Extremely robust cohesion triggered by calcium silicate hydrate (C-S-H) precipitation during cement hardening makes concrete one of the most commonly used man-made materials. Here, in this proof-of-concept study, we seek an additional nanoscale understanding of early-stage cohesive forces acting between hydrating model tricalcium silicate (C3S) surfaces by combining rheological and surface force measurements. We first used time-resolved small oscillatory rheology measurements (SAOSs) to characterize the early-stage evolution of the cohesive properties of a C3S paste and a C-S-H gel. SAOS revealed the reactive and viscoelastic nature of C3S pastes, in contrast with the nonreactive but still viscoelastic nature of the C-S-H gel, which proves a temporal variation in the cohesion during microstructural physicochemical rearrangements in the C3S paste. We further prepared thin films of C3S by plasma laser deposition (PLD) and demonstrated that these films are suitable for force measurements in the surface force apparatus (SFA). We measured surface forces acting between two thin C3S films exposed to water and subsequent in situ calcium silicate hydrate precipitation. With the SFA and SFA-coupled interferometric measurements, we resolved that C3S surface reprecipitation in water was associated with both increasing film thickness and progressively stronger adhesion (pull-off force). The lasting adhesion developing between the growing surfaces depended on the applied load, pull-off rate, and time in contact. These properties indicated the viscoelastic character of the soft, gel-like reprecipitated layer, pointing to the formation of C-S-H. Our findings confirm the strong cohesive properties of hydrated calcium silicate surfaces that, based on our preliminary SFA measurements, are attributed to sharp changes in the surface microstructure. In contact with water, the brittle and rough C3S surfaces with little contact area weather into soft, gel-like C-S-H nanoparticles with a much larger surface area available for forming direct contacts between interacting surfaces.

Concrete-to-concrete composites have been widely used in a broad range of applications such as buildings, bridges, pavements, dams and tunnels. Numerous studies have been carried out to characterize the structural performance of these composites. This paper presents a state-of-the-art review and key information on the performance of concrete-to-concrete composites. Specifically, design and environmental factors (interface condition, bonding agents, concrete properties, mismatch in overlay and substrate, fibers and admixtures, temperature, humidity) are reviewed and discussed. The test methods developed to determine bond strength under various load combinations are also described. The findings show that a proper selection of overlay and bonding agent composition, interface condition, casting and curing conditions as well as assessment techniques not only result in greater structural performance and durability but also in an optimized material usage and casting cost, leading to a more sustainable approach. Considering the growing application of layered concretes in the recent decade, this review aims at clarifying the parameters that maximize the performance of these composites and at supporting engineers and practitioners in optimizing their composites.

Oscillatory rheology has proved a promising method to measure the nature of interactions between inorganic particles in suspension. In this work, small oscillatory rheology (SAOS) is used to compare the nature of interactions in an ordinary Portland cement (OPC) and a more sustainable alkali-activated binder (AAB). The interstitial solution of the AAB is varied by adding calcium chloride. The linear elastic regime is characterized as a function of volume concentration, in a range for which an attractive gel-like behavior is observed. SAOS measurements show that the nature of interactions in AAB is different from those in OPC and changes with calcium concentration. The influence of calcium over the surface properties of AAB is further proven by the fluidifying effect of polycarboxylether (PCE) when [Ca2+] is increased. The results obtained confirm the relevance of SAOS to qualitatively assess the state of aggregation in cementitious slurries and select candidates for cement substitution.

The high consumption of ordinary Portland cement (OPC) in high-performance concrete (HPC), combined with the growing accumulation of construction and demolition wastes (CDW), raises severe environmental and economic concerns. This study addresses both issues by proposing a novel sustainable binder made of milled recycled HPC (mRHPC). A series of HPC mix designs (R-HPC) was developed replacing OPC by mRHPC (0–100%), and characterized in fresh and hardened states. The residual reactivity of mRHPC was detected using X-ray diffraction, calorimetry, and rheological oscillatory measurements (SAOS). Replacement up to 30% resulted in comparable 28-day compressive and flexural strengths to that of the OPC reference specimen while slightly improving fresh properties. Furthermore, the performance of steel fiber reinforced R-HPC overlays was investigated in repair application, and 30% replacement ratio enhanced the tensile bond strength by a factor of 2.4. The measured improved flow properties and reduced drying shrinkage can explain this remarkable result.

Multi-layer concrete systems have been widely used in bridge decks, rigid pavements, and floors. The restrained drying shrinkage of the overlay is of great concern as it can lead to overlay cracking and/or interfacial debonding. In such constructions, a transverse slope is typically considered to drain off the surface water. Despite advances made in understanding the drying shrinkage of non-sloped concrete-concrete composites, there are still standing questions regarding the overlay cracking, as well as bond failure, in sloped concrete-concrete composites. The current study establishes a high-fidelity computational model validated with experimental tests to evaluate the structural performance of sloped, double-layer overlay systems under drying shrinkage. The simulation scenarios systematically cover the effects of key overlay properties and interface conditions. The numerical analysis results reveal the critical role of overlay thickness and mechanical properties in the time of overlay cracking and interfacial debonding failures. Based on the obtained results, the implementation of a cross slope may delay the failures, depending on the initial thickness. Higher interfacial stiffness also induces stronger restraint against overlay shrinkage strain, leading to a faster overlay cracking.

The effect of casting and curing temperature on concrete-epoxy-concrete interfacial bond strength was evaluated. To cover a wide range of climatic conditions, six different temperature values from 5 to 55 degrees C were considered. The interfacial bond strength of the composites was experimentally assessed using pull-off, wedge splitting and bi-surface shear tests. The individual materials, epoxy and cement paste, were also characterized by means of viscosity, shore D hardness and setting time measurements. Results show that the casting and curing temperature dramatically impacts the mechanical properties of the epoxy bonded concretes. Indeed, increasing temperature from 5 to 55 degrees C leads to a decrease in bond strength up to 65%. The significant drop in setting time of epoxy compared to cement at high temperature, the inferior epoxy mechanical properties, as well as the reduction in epoxy thickness due to material loss in pores and microcracks can explain this decrease.

We evaluate the settling of a suspension in an annular geometry, where the concentric pipes are placed horizontally. The geometry was chosen to mimic cement slurry bleeding (i.e. accumulation of fluid on top of the geometry due to the settling of particles) in horizontal oil and gas wells. We compare the behavior of ideal semi-dilute suspensions, such as polymer beads in oil, with real cement slurries, in cells of similar geometry. Despite the differences between the two systems, our results show striking similarities and explain the presence of weak points at the upper outer diameter, below the internal diameter and at the poles.

Polymers with a finite lifetime are of great interest for oil and gas industry. Thermoplastic elastomers (TPEs) combine the strength of thermoplastics with the flexibility of elastomers, a characteristic also potentially useful in oil and gas applications. We studied the hydrolytic degradation of a TPE of interest at elevated temperatures from both a mechanical and chemical perspective, and have demonstrated that the chemical degradation rates, the change in crystallinity and the storage modulus all follow the pseudo zero order kinetics with respect to varying time at three temperatures. Applying Arrhenius' empirical relationship to the determined rates gives rise to a temperature-dependent model that predicts the degradation behavior of the TPE outside of the experimental temperature range. Our results indicate that hydrolytic degradation leads to an increase of crystallinity (chemicrystallization) and a decrease of tensile strength and strain, and that the increase of crystallinity strongly correlates to the increase of the storage modulus. The polymer eventually deteriorates due to brittleness.

Nearly 70 years old, hydraulic fracturing is a core technique for stimulating hydrocarbon production in a majority of oil and gas reservoirs. Complex fluids are implemented in nearly every step of the fracturing process, most significantly to generate and sustain fractures and transport and distribute proppant particles during and following fluid injection. An extremely wide range of complex fluids are used: naturally occurring polysaccharide and synthetic polymer solutions, aqueous physical and chemical gels, organic gels, micellar surfactant solutions, emulsions, and foams. These fluids are loaded over a wide range of concentrations with particles of varying sizes and aspect ratios and are subjected to extreme mechanical and environmental conditions. We describe the settings of hydraulic fracturing (framed by geology), fracturing mechanics and physics, and the critical role that non-Newtonian fluid dynamics and complex fluids play in the hydraulic fracturing process.

ABSTRACT Swellable elastomers are widely used in oilfield industry for sealing and zonal isolation applications. These materials need to sustain a large amount of external load after swelling. A newly developed reactive hydrogenated nitrile butadiene rubber (HNBR) based elastomer composite with magnesium oxide (MgO) as filler can swell and stiffen when exposed to water, which makes it ideal for oil field applications. However, both the filler hydration and the stiffness evolution inside this composite material are observed to be highly inhomogeneous even for samples on the length scale of millimeters. To understand this coupled diffusion‐hydration process is critical for applications of these materials with larger length scales. In this work, the hydration kinetics and stiffness evolution of the HNBR‐MgO composite are quantitatively studied on microscopic level. The extent of MgO hydration along the thickness of the sample are measured at the different stage of swelling. These results are used to determine the diffusion coefficient of water inside the composite. The diffusivity increases orders of magnitude after the filler hydration. In addition, the modulus change is non‐proportional to the degree of filler hydration as demonstrated by instrumented grid indentation on the hydrated composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133 , 43420.