Low-field 1H Nuclear Magnetic Resonance Research Articles

Effect of M/P ratio, w/c ratio, and additive contents on rheological properties of seawater mixed magnesium phosphate cement system

Rheological properties play a crucial role in determining the grouting effectiveness of magnesium phosphate cement (MPC) slurry. This study aims to investigate the effects of the magnesia-to-phosphate (M/P) ratio, water-to-cement (w/c) ratio, fly ash (FA), and metakaolin (MK) on the rheological properties of seawater-mixed MPC slurries using rheological tests and low-field 1H nuclear magnetic resonance (NMR). Two methods for incorporating FA were explored to modulate the rheological properties of the MPC. The results demonstrated time-dependent viscosity changes with two distinct phases, including a plateau and a subsequent period of sudden change, with the minimum apparent viscosity occurring as hydration progressed. The apparent MPC viscosity was influenced by the MgO-particle content and the theoretical water consumption, with M/P = 3 exhibiting the lowest apparent viscosity within a w/c range of 0.14–0.2. Moreover, the addition of FA increased the minimum apparent viscosity of the MPC slurry. During the pre-hydration stage, using FA as an MPC substitute yielded better rheological properties than using FA as an MgO substitute. The MK increased the apparent MPC viscosity considerably and adversely affected its rheology.

Insight into the early hydration characteristics of Portland cement with hydroxyethyl methyl cellulose highlighted by 1H low-field NMR

1H low-field nuclear magnetic resonance (1H NMR) as a non-destructive test method can effectively capture the water state changes in cement pastes. The water changes can in turn reflect the early hydration characteristics of cement pastes. Hydroxyethyl methyl cellulose (HEMC) with different viscosities affects the hydration characteristics of cement by acting on the water in different states. The following experimental results are obtained by testing hydration of cement pastes with HEMC by using 1H NMR test. Incorporating 0.1–3% HEMC with different viscosities all can effectively control the bleeding water phenomenon. HEMC can absorb a part of the water in the cement pastes. Incorporating 2–3% HEMC significantly delays the enrichment of the gel pores water and interlayer water. When the content of HEMC increases from 0% to 3%, the hydration degree of cement pastes tends to decrease. Besides, HEMC with higher viscosity of 15000–40000 mPa·s obviously delays the hydration process of cement pastes compared to HEMC with lower viscosity of 400 mPa·s.

Discriminating extra virgin olive oils from common edible oils: Comparable performance of PLS-DA models trained on low-field and high-field 1H NMR data.

Olive oil, derived from the olive tree (Olea europaea L.), is used in cooking, cosmetics, and soap production. Due to its high value, some producers adulterate olive oil with cheaper edible oils or fraudulently mislabel oils as olive to increase profitability. Adulterated products can cause allergic reactions in sensitive individuals and can lack compounds which contribute to the perceived health benefits of olive oil, and its corresponding premium price. There is a need for robust methods to rapidly authenticate olive oils. By utilising machine learning models trained on the nuclear magnetic resonance (NMR) spectra of known olive oil and edible oils, samples can be classified as olive and authenticated. While high-field NMRs are commonly used for their superior resolution and sensitivity, they are generally prohibitively expensive to purchase and operate for routine screening purposes. Low-field benchtop NMR presents an affordable alternative. We compared the predictive performance of partial least squares discrimination analysis (PLS-DA) models trained on low-field 60 MHz benchtop proton (1H) NMR and high-field 400 MHz 1H NMR spectra. The data were acquired from a sample set consisting of 49 extra virgin olive oils (EVOOs) and 45 other edible oils. We demonstrate that PLS-DA models trained on low-field NMR spectra are highly predictive when classifying EVOOs from other oils and perform comparably to those trained on high-field spectra. We demonstrated that variance was primarily driven by regions of the spectra arising from olefinic protons and ester protons from unsaturated fatty acids in models derived from data at both field strengths.

Study on activation of fluorogypsum by sodium sulfate and sodium nitrite

Given the issues related to poor hydration activity, long setting time and low early strength of industrial by-product fluorogypsum (FG), the composite modifiers (Na2SO4 and NaNO2) were utilized to enhance its reactivity. The investigation of the mechanism involved the utilization of contemporary analytical methods, including X-ray diffraction (XRD), 1H low-field nuclear magnetic resonance (NMR), and Scanning electron microscope and Energy Dispersive Spectrometer (SEM-EDS). The results demonstrated that the incorporation of modifiers significantly enhanced both the hydration rate and activity of fluorogypsum. The optimum concentration of the composite modifier was found to be 1.5 wt% Na2SO4 and 0.5 wt% NaNO2. The addition of modifiers (1.5 wt% Na2SO4 and 0.5 wt% NaNO2) significantly shortens the setting time of FG paste, reducing it by approximately 500 min compared to the control sample. After 28 days of curing, the flexural strength and compressive strength of the fluorogypsum sample containing modifiers (1.5 wt% Na2SO4 and 0.5 wt% NaNO2) increased by 55.5 % (reaching 4.2 MPa) and 31.5 % (reaching 37.6 MPa), respectively. The modifiers facilitate the transformation from anhydrite (CaSO4, AH) to dihydrate gypsum (CaSO4·2H2O, DH). Both NaNO2 and Na2SO4 alter the growth rates of different crystal axes during DH crystal growth, transforming them into prismatic and needle-shaped DH. The prismatic and needle-shaped DH crystals were arranged in layers, resulting in a compact structure with low hole content and few pores, which led to increased density of the hardened paste and higher strength. The current study provides evidence that the inclusion of composite modifiers greatly improves the activity of FG, making it more efficient in the field of building materials.

A comprehensive review of synthesis kinetics and formation mechanism of geopolymers.

Geopolymers are synthesized by alkali or acid activation of aluminosilicate materials. This paper critically reviews the synthesis kinetics and formation mechanism of geopolymers. A variety of mechanistic tools such as Environmental Scanning Electron Microscopy (ESEM) and in situ Energy Dispersive X-ray diffractometry (EDXRD), in situ Isothermal Conduction Calorimetry (ICC), in situ Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), 1H low-field Nuclear Magnetic Resonance (NMR) and Isothermal Conduction Calorimetry (ISC), and others and phenomenological models such as the John-Mehl-Avrami-Kolmogorov (JMAK) model, modified Jandar model, and exponential and Knudson linear dispersion models were used to study the geopolymerization kinetics and many mechanisms were proposed for the synthesis of geopolymers. The mechanistic tools and phenomenological models provided new insights about geopolymerization kinetics and formation mechanisms but each of the techniques used possesses some limitations. These limitations need to be removed and new methods or techniques must be developed to overcome these challenges and get more detailed information about all types of geopolymers. The formation mechanism consists of three to four stages such as dissolution of raw materials, polymerization of silica and alumina, condensation, and reorganization. The Si/Al ratio above the Si/Al ratio of reactants is more suitable and it increases the rate or degree of reaction and produces a higher compressive strength geopolymer. The Na/Al ratio of 1, water-to-solid (W/S) ratio of 0.30-0.45, a temperature in the range of 30 °C to 85 °C, and a curing time of 24 hours are the best for the synthesis of geopolymers. The growing demand for geopolymers in various fields requires the development of new advanced techniques for further understanding of kinetics and mechanisms for tailoring the properties of geopolymers for specific applications.

Using 1H low-field NMR relaxometry to detect the amounts of Robusta and Arabica varieties in coffee blends

Low-field nuclear magnetic resonance (LF-NMR) is a method of widespread use in food research due to its non-destructive character and the relatively low cost of the instruments, allowing the determination of oil / fat contents and the achievement of images of different types of food materials, among other uses. In this work, 1H LF-NMR relaxometry was used to distinguish the contributions due to Arabica and Robusta coffee varieties present in coffee blends. As the method detects preferentially the NMR signals due to phases with high molecular mobility, which exhibit longer values of the 1H transverse relaxation time (T2), the difference in the oil contents associated with Arabica and Robusta coffee was the key factor responsible for the detection of the contributions due to each variety. The analysis presented in this work showed that the relative hydrogen index is a useful parameter to be used in quantitative analyses of the contents of each coffee variety present in the blends. The results illustrate the high potential of applicability of LF-NMR relaxometry as a screening tool for quality control and adulteration detection of coffee-related products.

Assembly of soy protein-corn starch composite gels by thermal induction: Structure, and properties

The effect of different corn starch (CS) concentrations on the gel formation of soybean isolate protein (SPI) was investigated. Moreover, the texture, rheological properties of the gel were determined, and the spatial structure and interactions of the composite gel system were analyzed. The composite system transitioned from liquid to solid-like with an increase in the CS concentration and did not backflow when inverted for 24 h. With the addition of CS, the gel strength, water holding capacity (WHC), G′, and G′′ increased significantly. The maximum was reached at 10 % starch concentration with gel strength of (228.96 ± 29.86) g and WHC of (98.93 ± 2.02) %. According to low-field 1H nuclear magnetic resonance (LF-NMR) results, CS has a high water absorption capacity, which improved the WHC. The scanning electron microscopy results revealed that composite gels with a high CS concentration had a more dense and small void network structure. According to the results of molecular force interaction, infrared spectroscopy, Raman spectroscopy, and free sulfhydryl group analysis, the added starch promoted the unfolding of SPI molecules, exposure of hydrophobic groups, transformation of free sulfhydryl groups into disulfide bonds, and hydrogen bond formation. Hydrophobic interactions, disulfide bonding, and hydrogen bonding function together to form the SPI–CS composite gel system. The study results provide the basis for applying soy protein and CS gels.

Effect of different expansive agents on the early age structural build-up process of cement paste

CaO-based expansive agent (CEA) and MgO-based expansive agent (MEA) are commonly used expansive agents to control the shrinkage of concrete. Understanding the effect of CEA and MEA on the structural build-up of cement paste is of significance to their application in 3D printing concrete. This study investigates the effect of CEA and MEA on the structural build-up process of cement paste within 120 min. The calorimetric, 1H low-field nuclear magnetic resonance and ion concentration tests were carried out to explore the intrinsic mechanism. The findings suggest that CEA significantly accelerates structural build-up rate by elevating the ionic strength in solution and facilitating cement hydration. The addition of 1%, 3% and 5% CEA increases the 120-min static yield stress of cement paste by 40.6%, 66.8% and 132.9%, respectively. MEA increases the initial static yield stress by decreasing the interparticle distance through its great specific surface area and intensifying interparticle interactions, and the addition of 1%, 3% and 5% MEA increases the initial static yield stress of cement paste by 22.5%, 35.3% and 66.5%, respectively. However, the delaying impact of MEA on hydration offsets its improvement of interparticle interaction, leading to an insignificant impact on the static yield stress evolution. The combination of CEA and MEA takes advantage of their respective benefits in promoting hydration and flocculation, which increases the structural build-up rate while increasing the initial static yield stress of the paste. This study can provide guidance for the rheological controlling of 3D printing concrete containing expansive agent.

In-situ speciation and estimation of iron(II) and iron(III) contents in anisotropic polysaccharide-based hydrogel by 1H low-field nuclear magnetic resonance

This article aims to quantify and differentiate in-situ iron(II) and/or iron(III) in heterogeneous polygalacturonate hydrogels using the 1H‐NMR relaxometry technique. This holds significant importance, for example, in addressing iron-deficiency anemia through the oral administration of iron(II) supplements. The NMR dispersion profiles of the gels exhibited markedly distinct relaxation behaviors corresponding to the different iron oxidation states. At 20 MHz, two primary relaxation mechanisms must be considered: relaxation arising from water molecules confined within the polygalacturonate fiber mesh and paramagnetic relaxation due to iron cations. When iron(III) serves as the cross-linking agent, paramagnetic interaction dominates the relaxation, while with iron(II) as the cross-linker, both mechanisms have to be considered. To distinguish labile from structuring iron, we monitored the evolution of iron concentrations within the gels during successive washes using NMR and atomic absorption spectroscopy. Eventually, a gel containing both iron(II) and iron(III) was analyzed, and successful differentiation between the two cations was achieved. NMR relaxometry demonstrates powerful capabilities in terms of in-situ experiments, rapid results, speciation (iron(II)/iron(III)), and quantification (labile/ bridging iron).

Rheological behavior and early-age reaction kinetics of Portland cement-sulphoaluminate cement blend pastes containing superplasticizer and cellulose ether

The combination of Portland cement (PC) and sulphoaluminate cement (CSA) has the potential to improve the mechanized construction efficiency of cement-based materials, but its rheological behavior still needs to be considered to deeper understand the evolution of workability. Therefore, the blend pastes with different PC-CSA ratio were prepared. To achieve good initial workability, cellulose ether and superplasticizer were added. The shear stress – shear strain rate data of each paste at different resting time was obtained by a rheometer. Herschel-Bulkley (H-B) model was used to imitate the rheological data, and the evolution curve of yield stress with resting time of each sample was achieved. It was found that sample with higher CSA content showed a faster increase in yield stress over time. Furthermore, isothermal calorimetry was conducted to reveal the reaction kinetics of the rheological evolution of the fresh pastes referring to Johnson-Mehl-Avrami-Kolmogorov model. The results showed that CSA accelerated the nucleation and crystallization process of ettringite (AFt), which is contributed to the yield stress. Meanwhile, a novel technique, 1H low-field nuclear magnetic resonance (NMR), was firstly applied to character the early-age reaction process of PC-CSA blend system by monitoring the evaporative water content changes in the pastes. The result was that the relative content of evaporated water in the paste with higher CSA content decreased faster, which is also beneficial for the yield stress. These methods for evaluating reaction kinetics effectively validated the rheological behavior of the slurry, and established a correlation with the rheological parameter, which had not been identified in previous studies.

Distribution and curing kinetics of waterborne epoxy resin in repair system: Characterization and quantification by 1H low-field NMR

Cement-based mortars are commonly modified with Waterborne Epoxy Resin (WER). However, the curing kinetics of WER in mortars has never been quantified up to now. This study proposed using 1H low-field nuclear magnetic resonance (1H LF-NMR) to quantitatively determine the curing kinetics of WER in polymer-cement composite. The distribution and curing of WER in repair systems was also explored using 1H LF-NMR. To avoid the interference of the NMR water signal, heavy water was used to prepare repair mortar. It was found that the curing reaction of WER in a mortar was significantly influenced by the cement hydration. It starts to accelerate when the cement hydration stepped into an acceleration period. Moreover, the 1D spatial NMR signal distribution showed that WER in the repair materials permeated into the substrate with water, which is affected by both the W/C of the repair and the RH of the substrate. The WER was enriched at the interface between the substrate and the repair mortar and exhibited a gradient in the distribution both upwards into the repair mortar and downwards into the substrate.

Effect of diatomite on the reaction kinetics, early-age chemical shrinkage and microstructure of alkali-activated slag cements

Understanding and revealing the relationship between the early-age chemical shrinkage, reaction characteristic and microstructure of alkali-activated slag (AAS) pastes are of importance for the application of this cementitious material. This study investigates the effect of diatomite on the early-age compressive strength and the first 72-h chemical shrinkage of AAS pastes. A novel approach is proposed based on isothermal conduction calorimetry and 1H low-field nuclear magnetic resonance analyses to identify the internal correlation between chemical shrinkage and reaction situation. Results show that the early-age chemical shrinkage is dominated by the reaction process and reaction degree of AAS pastes. The incorporation of diatomite makes a great contribution to the control of chemical shrinkage even though it slightly sacrifices the development of compressive strength. This suggests the controls in the reaction process and chemical shrinkage of AAS pastes can be achieved by incorporating diatomite. The proposed approach can be used to assess chemical shrinkage of AAS, which contributes more to deeper understanding in the early-age volume change of alkali-activated cements.

Research on irrecoverable creep of the hardened cement paste under different relative humidity

Relative humidity (RH) has an important influence on the creep performance of cement-based materials. In this paper, the creep and creep recovery experiments of hardened cement paste (HCP) were carried on under four humidity balance. The low-field 1H nuclear magnetic resonance (NMR) test was performed on the HCP after the creep recovery test to obtain the internal water distribution characteristics of HCP. The creep properties and volume ratio of different micro phases in HCP were acquired by nanoindentation test, backscattered electron (BSE) test, and thermogravimetric (TG) test. Subsequently, the structure features of C–S–H were acquired by the 29Si NMR test and the nitrogen adsorption-desorption test. The results showed that the raise of RH significantly increased the interlayer water content in HCP. The creep properties of C–S–H reduced significantly with the increase of RH. The volume fraction of low-density (LD) C–S–H elevated with raising RH, while the trend of high-density (HD) C–S–H was opposite to the former. When RH increased, the mean chain length of the gel raised, and the gel pores became more numerous, among which the magnitude of change of LD C–S–H pores was more significant.

The investigation of early hydration and pore structure of Portland cements containing waste dolomite powder based on 1H NMR

Waste dolomite powder (WDP) is being actively investigated as the additive of Portland cement (PC) for lowering the energy consumption and carbon emission of PC. In this work, 1H low-field nuclear magnetic resonance (1H NMR) was used to analyze the impacts of WDP on the hydration and pore structure of PC pastes at the early age. Meanwhile, the compressive strengths of blended cements containing 5–20% WDP were also measured. The results show that the T2 average value and evaporable water content of all the pastes decrease dramatically from 0 to 24 h, and the reduction rate slows down after 24 h. Adding 5% WDP can decrease further the T2 average value and evaporable water content attributed to its nucleating and filler effect, resulting in the compacted pore structure and the higher strength. However, adding more than 5% WDP degrades the pore structure and lowers the compressive strength.

Low-field 1H NMR study on geopolymers: The effect of paramagnetic Fe(III)

Geopolymers are inorganic polymers with 3D framework structures having superior mechanical and physical properties. Metakaolin-based geopolymers synthesized using solutions of Fe(III) chloride have been studied ex-situ and in-situ using low-field 1H nuclear magnetic resonance (LF NMR). The results revealed that the introduced Fe(III) could affect the spin relaxation and the pore structure. The effect on spin relaxation was determined by quantifying the relation between surface relaxivities and Fe(III) ion content. The effect on pore size was measured by Mercury Injection Capillary Pressure (MICP), showing a two-stage evolution. The pore size increased slightly before and dramatically after the threshold of 2.0 wt% iron content. We propose herein as possible causes the reaction between hydroxide ions and Fe(III) and the formation of Si(Al)-Fe-oxyhydroxides. During the early (first three days) polymerization of geopolymers the in-situ curves revealed three stages (i.e. dissolution, condensation, and stabilization) which are affected to different degrees by Fe(III).

Determination of soil pore size distribution and water retention curve by internal magnetic field modulation at low field 1H NMR

The determination of the soil pore size distribution, water retention curve, and derived parameters that control important processes in soils, such as water supply for plants; infiltration; water and solute movement in soils; erosion; plant nutrients and contaminants transport, etc, are challenging and the available methods are expensive, time-consuming and prone to bias and errors. The use of 1H Nuclear Magnetic Resonance (NMR) relaxometry to characterise the soil porosity and hydraulic properties through spin-lattice and spin-spin relaxometry results in an ill-posed problem with two correlated unknown quantities: the pore length scales, and surface relaxivity. To overcome this limitation of NMR relaxometry, we propose the use of a method that directly accesses the NMR diffusion modes governed only by the pore size, and therefore, independent of the unknown surface relaxivity. The manuscript describes an unprecedent application in Soil Science of the Decay due to Diffusion in Internal Field (DDIF) method to successfully determine the pore size distribution of undisturbed soil samples, as well as to estimate the water retention curves from the pore size distribution.

New insights into the early-age reaction kinetics of metakaolin geopolymer by 1H low-field NMR and isothermal calorimetry

Early-age reaction kinetics of geopolymers is one of the challenging issues associated to their mechanical performances and durability. In this work, the early-age reaction of metakaolin geopolymer prepared by activators with various silicate moduli was studied. Compared to conventional methods, a novel approach was firstly proposed to evaluate the early-age reaction of geopolymer by using 1H low-field nuclear magnetic resonance (NMR) and isothermal calorimetry. The state and relative quantity of water in geopolymer pastes were detected by NMR during reaction process. While in this timescale, the heat release of pastes was recorded by isothermal calorimetry. A good consistency to the measurement of reaction process between these two testing methods can be observed. Activator with low silicate modulus (i.e., high alkalinity) deepens the reaction degree at the same timescale and the gel pore volume is increased with the alkalinity of activator. This method is useful to monitor the early-age reaction process of geopolymer, which is expected to offer new insights into the early-age reaction kinetics of geopolymer.

Durability of BFRP bars embedded in seawater sea sand coral aggregate concrete in simulated seawater environment: Effects of coral coarse aggregate and cement contents

This study evaluates the influences of coral coarse aggregate (CCA) and cement contents on the durability performance of basalt fiber-reinforced polymer (BFRP) bars embedded in seawater sea sand coral aggregate concrete (SSCC). The evaluation is conducted by characterizing the changes in interlaminar shear strength after accelerated exposure in a simulated seawater environment. Accelerated aging tests were conducted under varying exposure durations (60, 120, and 180 days) and temperatures (25, 40, and 55 °C). The 1H low-field nuclear magnetic resonance, Fourier transform infrared spectroscopy, and scanning electron microscopy analyses were conducted to investigate the deterioration mechanisms of embedded BFRP bars. It was found that SSCC-embedded BFRP bars typically have a lower interlaminar shear strength than that of seawater sea sand concrete (SSC)-embedded BFRP bars subjected to the same immersion conditions. This is mainly attributed to the high porosity of CCA, resulting in higher permeability of SSCC than that of SSC. In addition, increasing cement content enhances the initial amount of OH– in SSCC, expands the pitting area of BFRP bars, and maintains OH– concentration better in the exposure tests, accelerating the interlaminar shear strength deterioration of BFRP bars. Microstructure analysis clearly reveals that the deterioration of embedded BFRP bars is mainly caused by resin hydrolysis, fiber-resin interface debonding, and fiber damage after corrosion. Based on the Arrhenius relationship, accelerated aging test results were utilized to predict the service life of SSCC-embedded BFRP bars under the real service condition. The findings of this study are valuable for the application of BFRP bars reinforced SSCC structures under marine environments and provide some insights into improving the long-term performance of SSCC-embedded BFRP bars, i.e., modifying the CCA to minimize the permeability of SSCC and producing low-alkalinity SSCC.

Insight of rheology, water distribution and in vitro digestive behavior of starch based-emulsion gel: Impact of potato starch concentration

Potato starch-based emulsion gels were fabricated that consisted of whey protein-coated oil droplets dispersed in a gelatinized starch matrix. The impact of potato starch concentration (0–16%) on the rheological properties, water distribution, and in vitro digestive behavior of the emulsion gels was examined. Potato starch-based emulsion gels exhibited shear-thinning and viscoelastic properties. The apparent viscosity increased with progressing starch concentration, and a stronger gel network formed with massive starch. In low-field 1H nuclear magnetic resonance, the transverse relaxation time significantly reduced with progressing starch matrix, indicating a tighter bond between the water molecules with others. The gastrointestinal tract was used to monitor the in vitro digestive behavior of the starch-based emulsion gels in each phase (oral, stomach, and small intestine). Increasing particle size and a reduction charge were found in emulsion gel with potato starch. And the gel network structure remained in emulsion gel with 8–16% potato starch. Overall, a slower rate of initial free fatty acid release was determined in the emulsion system containing starch, and a greater extent of lipid digestion occurred in the hard gel. The results of this study may facilitate the development of starch-based emulsion gels for utilization in foods, cosmetics, and other semi-solid commercial products.

Enhanced survival of fluidized bed-dried microencapsulated Saccharomyces cerevisiae cells in the presence of Hongqu rice distiller's grain peptides

Saccharomyces cerevisiae (strain JH301) cells were micro-encapsulated in microcrystalline cellulose and Hongqu rice distiller's grain peptides (HRP) and subjected to fluidized bed drying. The effect of HRP on the viability of yeast in response to thermal drying was investigated. The moisture-viability profiles showed that HRP reduced the drying rate of yeast cells and increased viability in a concentration-dependent manner. Scanning electron microscopy revealed that HRP protected the morphology of the yeast cells, which presented a normal smooth structure and compact shape after thermal drying. The results of low-field 1H nuclear magnetic resonance and infrared spectroscopy revealed that HRP controls the binding water of yeast powder as opposed to interacting with the membrane surface proteins, further reducing the damage to phospholipids in the cell membrane during drying. Flow cytometry and confocal laser scanning microscopy confirmed that 3% HRP could reduce the proportion of membrane-damaged cells by nearly 19%. After drying, the proportion of unsaturated fatty acids in the cell membrane of JH301-3% HRP was 10.36% higher than that of JH301 in the absence of HRP, achieving increased membrane integrity and higher ATPase activity after rehydration.