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Amphiphilic nanosheets have gained great attractions in diverse applications owing to its unprecedented performances. In this paper, amphiphilic molybdenum disulfide (CTAB-MoS2) nanosheets were pre...

In this study, 1H low-field NMR was used to compare the liquid absorption-release behaviour of superabsorbent polymers (SAPs) in Portland cement (PC) paste, NaOH-activated slag (SH-AAS) paste, and water glass-activated slag (WG-AAS) paste. The liquid absorption of SAPs in the PC paste was lower than that in the SH-AAS paste and the WG-AAS paste. The liquid release was also faster, which was mainly due to the higher Ca2+ concentration in the pore fluid of the PC system. In the AAS system, although the Ca2+ concentration in the pore fluid was low, the Na+ concentration was much higher than that in the PC system due to the activator. The Ca2+ in the PC system is an important factor affecting the swelling of SAPs, while in the AAS system, the swelling limitation of SAPs is the result of the combined effects of Ca2+ and Na+, with Na+ being dominant.

C(-A)-S-H (CaO(-Al2O3)-SiO2-H2O) gel is the main product and source of strength in alkali-activated slag systems. Previous studies on C-A-S-H have focused mostly on the characterization of the structure and composition of the products. In this study, synthetic C-A-S-H particles with a similar composition as gels produced by alkali-activated slag were prepared by a hydrothermal method and were added to the alkali-activated slag systems, and the synthetic can be regarded as a chemical intensifiers of hardening (CIH). The effects of the synthetic C-A-S-H on the hydration process, the early-stage mechanical properties, and the microstructure of the alkali-activated slag were investigated by hydration heat tests, scanning electron microscopy (SEM), mercury intrusion porosimetry tests (MIP), and other methods. The results showed that the synthetic C-A-S-H shortened the setting time, promoted the formation of an acceleration period at an early stage, and increased the hydration heat released during the acceleration period. The synthetic C-A-S-H improved the flexural and compressive strength of the alkali-activated slag to a certain extent and the improvements in the flexural strength were more significant than the improvements in the compressive strength; the flexural strength of the sample with the added 3% synthetic C-A-S-H with 3-d curing increased by 16.25%. Microstructure analysis indicated the synthetic C-A-S-H also reduced the porosity of the alkali-activated slag-hardened paste and optimized the pore size distribution. This study of the early-stage performance provides a new approach and predictions for the late-stage performance and in-depth modification mechanisms of alkali-activated slag systems.

Based on the analytical 1H low-field nuclear magnetic resonance (NMR) technique, we developed a novel method and corresponding model to analyze the hydration degree (αt) of cement in cement paste under different curing conditions. The hydration degree can be calculated quantitatively based on the transverse relaxation time (T2) distributions using NMR measurements. The T2 distributions of the cement paste samples with the water/cement (W/C) ratios of 0.25, 0.35 and 0.45 under standard curing, steam curing at 40 °C and steam curing at 60 °C were obtained. The αt of cement was studied by the hydration heat method and portlandite (CH) quantitative measurements. The results show that the intensity-weighted T2 value of non-surface water peaks ( T 2 ¯ ) has a significant correlation with αt that can be expressed by an exponential equation. In this paper, the derivation of this exponential equation is given, and the effects of W/C ratio and curing condition on its parameters are analyzed.

Compared with the traditional water-based fracturing fluid, the water-based clean fracturing fluid had the advantages of low friction, easy flowback and no residue. A kind of erucic amide propyl betaine (EAPB) was synthesized by using erucic acid and N, N-dimethyl-1,3-propanediamine as raw materials, and a clean fracturing fluid was furtherly constructed by combining EAPB with organic acid. The composition of the fracturing fluid system was determined according to the viscosity change of the system. Meanwhile, the temperature resistance, salt resistance, sand-carrying performance and micelle-breaking properties of the system were studied. The results showed that the optimum molar ratio of EAPB to sodium salicylate (NaSal) in fracturing fluid system was 50:9. The zero-shear viscosity could reach up to 129 Pa·s at 25 ℃. When the shear rate was 170 s−1 and the temperature was 80 ℃, the viscosity could keep above 60 mPa·s after continuous one-hour shearing. Furthermore, it had good sand-carrying and micelle-breaking performance. There was easy flowback and no residue after the micelle-breaking, which did low damage to the formation and achieved the effect of increasing oil and gas production. In addition, the average permeability damage rate of the fracturing fluid to the natural core of the reservoir in the target block was 6.07 %. This showed that the fracturing fluid system had the characteristics of low damage, which could effectively reduce the secondary damage after fracturing and play a certain role in reservoir protection. Therefore, it could be used as a clean fracturing fluid. The research results could provide guidance and reference for the fracturing fluid system in oilfield application.

C-A-S-H (CaO-Al2O3-SiO2-H2O) and N-A-S-H (Na2O-Al2O3-SiO2-H2O) have a wide range of chemical compositions and structures and are difficult to separate from alkali-activated materials. Therefore, it is difficult to analyze their microscopic properties directly. This paper reports research on the synthesis of C-A-S-H and N-A-S-H particles with an average particle size smaller than 300 nm by applying the hydrothermal method. The composition and microstructure of the products with different CaO(Na2O)/SiO2 ratios and curing conditions were characterized using XRD, the RIR method, FTIR, SEM, TEM, and laser particle size analysis. The results showed that the C-A-S-H system products with a low CaO/SiO2 ratio were mainly amorphous C-A-S-H gels. With an increase in the CaO/SiO2 ratio, an excess of Ca(OH)2 was observed at room temperature, while in a high-temperature reaction system, katoite, C4AcH11, and other crystallized products were observed. The katoite content was related to the curing temperature and the content of Ca(OH)2 and it tended to form at a high-temperature and high-calcium environment, and an increase in the temperature renders the C-A-S-H gels more compact. The main products of the N-A-S-H system at room temperature were amorphous N-A-S-H gels and a small amount of sodalite. An increase in the curing temperature promoted the formation of the crystalline products faujasite and zeolite-P. The crystallization products consisted of only zeolite-P in the high-temperature N-A-S-H system and its content were stable above 70%. An increase in the Na2O/SiO2 ratio resulted in more non-bridging oxygen and the TO4 was more isolated in the N-A-S-H structure. The composition and microstructure of the C-A-S-H and N-A-S-H system products synthesized by the hydrothermal method were closely related to the ratio of the raw materials and the curing conditions. The results of this study increase our understanding of the hydration products of alkali-activated materials.

The relatively high shrinkage of the alkali-activated slag (AAS) has restricted its application as a widely-used building material. This research attempts to study the effect of a hydrothermally synthesized C-A-S-H gel, which has a similar composition to that of the main AAS product, on the shrinkage performance of the AAS. The C-A-S-H nano-particles were mixed into AAS mortars in a proportion ranging from 1 wt % to 5 wt % using two different methods, and the drying and autogenous shrinkage ratio of modified AAS mortars were measured at various ages. The effect of C-A-S-H on their microstructures was also characterized. Results obtained indicated that the addition of C-A-S-H gel to AAS mortars had reduced their drying and autogenous shrinkage, with the addition of 3 wt % reaching the maximum reduction. However, the added amount was not directly proportional to the decrease of shrinkage, the proportion of early-stage drying shrinkage of AAS mortars was greater than that of autogenous shrinkage, the dispersion method was slightly better than the dry mixing method in both shrinkage reduction. MIP results suggested that the addition of C-A-S-H gel had reduced the total porosity and the average pore size of AAS mortars, optimized their pore structure distribution, and significantly reduced the volume of mesopores (&lt, 0.05 &micro, m) which resulted in high shrinkage, while the adding method had no significant effect on the pore size distribution of AAS mortars. SEM results showed that the addition of C-A-S-H gel can reduce the crack width of mortars, obtain a dense and uniform matrix structure, increase the density, and effectively suppress both shrinkage deformation of the system, whereas the adding method has no obvious effect on the crack width of the mortar. This research provides a novel approach of the AAS shrinkage reduction and structure refinement, shedding lights on nano-material modification of the AAS.