Low-field 1H Nuclear Magnetic Resonance Research Articles

Moisture sorption behaviour, microstructural changes and macroscopic deformation of hardened cement pastes during the first three drying–resaturation cycles

Moisture sorption and macroscopic deformation of hardened cement pastes (hcps) were studied in the first three drying–resaturation (D–R) cycles using low–field 1H nuclear magnetic resonance relaxometry. Four types of water (interlayer, gel, interhydrate and capillary) were detected in the hcps. In principle, they were sequentially removed from larger to smaller pores during drying with decreasing relative humidity (RH), resulting in shrinkage of the hcps. Unexpected increases in gel and interlayer water contents as well as greater shrinkage during drying from 100 % to 69 % RH were observed, which is believed to originate from the re–arrangement of C–S–H structure. Because of the C–S–H re–arrangement, irreversible shrinkage was detected during D–R cycles. The drying and irreversible shrinkage in each cycle diminished with the D–R number. A lower water–to–cement ratio and higher curing temperature for hcps are beneficial for reducing drying and irreversible shrinkage.

Three birds with one stone: Sewage sludge deep-drying in 1 hour using secondary aluminum ash to fabricate bricks

Due to the high moisture, strong hydrophilicity, and hard compressibility of sewage sludge (SS), it is difficult to realize the high-efficiency drying. Herein, a novel SS drying technology was developed to quickly and deeply reduce the moisture of SS from 75.6% to 38.5% in 1 h. During the process, secondary aluminum ash (SAA), a solid waste, was added to SS and acted as skeletons to form plenty of channels. Subsequently, NaOH was added and reacted with SAA to produce a lot of heat, resulting in a rapid temperature rise of the system from 20 to 105°C in 60 s. The heat could effectively remove water from these channels, which could be proved by the T1-T2 maps of in-site Low-Field 1H nuclear magnetic resonance. In addition, the extracellular polymeric substances were decomposed by SAA/NaOH successfully, and thus the SS became hydrophobic, favoring the drying. Finally, the dried SS could be used to fabricate unburned bricks. Thus, this work provides a promising method to realize the rapid SS deep drying and high-efficiency utilization of SAA and dried SS.

The Synergistic Effect of Water Reducer and Water-Repellent Admixture on the Properties of Cement-Based Material

Water reducer and water-repellent admixture are very important in improving the workability and durability of cement-based materials. However, the synergistic effect of the two types of admixtures has not been well investigated. In this study, polycarboxylate ether-based superplasticizer (PCE) and octyltriethoxysilane (OTS) were adopted as water reducer and water-repellent admixture, respectively. Their synergistic effect on the fluidity, compressive strength, and water absorption rate of cement-based materials was investigated. Particularly, the pore structure and hydration state of cement paste were analyzed using 1H Low-Field Nuclear Magnetic Resonance (1H LF NMR). The result showed that the fluidity of cement paste containing different dosages of PCE was reduced by 5–10 mm by incorporating 1% OTS, and the compressive strength at the early age of 3 d of mortar containing high PCE dosage of 0.25% decreased up to 15% by using 1% OTS. In contrast, the compressive strength of mortar containing 0.20% PCE was slightly enhanced by the addition of 1% OTS. 1H LF NMR analysis revealed that the combination of PCE and OTS would increase the pore size and total pore volume of cement paste, and more bleeding water would be generated at high PCE dosage. The intensity-weighted T2 values of the main peak (T2¯) implied that both PCE and OTS produced a retardation effect on cement hydration. However, the water absorption rate decreased by 46.6% despite the increase in pore size and total pore volume. The conflict phenomenon powerfully revealed that the internal hydrophobic treatment by OTS has been successfully achieved. Overall, the combination of 0.20% PCE and 1% OTS exerted a positive synergistic effect in improving the compressive strength and water-repelling ability of cement-based materials, which is meaningful for improving their durability and service life.

Machine learning-enabled fatty acid quantification and classification of pork from autochthonous breeds using low-field 1H NMR spectroscopic data

Traditional pig breeds, known for their sustainability and superior meat quality, are experiencing growing consumer preference. The lipid fraction composition of these meats plays a fundamental role in their health benefits and excellent organoleptic properties. Accordingly, accurate characterisation of intramuscular fat is crucial for maintaining quality standards and combating fraudulent practices. This study employs benchtop nuclear magnetic resonance (NMR) spectroscopy to delineate the lipidic profiles of various cuts from two emblematic Spanish autochthonous pig breeds. The implementation of chemometric and machine learning models enabled the classification of pork samples based on cut and breed of origin. Moreover, this investigation pioneers the coupling of benchtop NMR with machine learning models for quantitative purposes, achieving precise quantification of polyunsaturated, monounsaturated and saturated fatty acids in intramuscular fat. This novel approach holds promise for enhancing the traceability and authentication of traditional pig products, fostering consumer confidence and promoting sustainable livestock practices.

Role of oil droplet size on dynamic pore wetting of active carbon and particle-bubble interaction: New inspiration for enhancing the porous mineral floatability

The dynamic pore wetting plays a vital role in the flotation separation process of porous mineral particles, such as low-rank coal, fly ash and chrysocolla, etc. This paper investigated the dynamic pore wetting behavior of active carbon particles in the water-oil emulsion by 1H low-field nuclear magnetic resonance (1H LF-NMR). The influence of oil droplet size on pore wetting process was revealed. The change in the surface properties of particles before and after wetting was analyzed by contact angle and FTIR measurements. The particle-bubble attachment process in the emulsion and pure water was compared. The total pore wetting percentage of active carbon had a first-order kinetic relationship with the wetting time. The emulsion was beneficial to decrease the pore wetting percentage of particles compared with water. And the pore wetting percentage decreased with the decrease of oil droplet size in emulsion. The pores were easily filled by the oil droplet with small size and the hydrophobicity of sample surface was improved, which prevented the subsequent pore wetting by water. As a result, the detachment force of particle-bubble was increased with the help of micro-oil droplets. This work attempts to provide a new inspiration for the study of porous mineral flotation.

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).