Mercury Intrusion Porosimeter Research Articles

Study on the performance of alkali-activated phosphorus slag cemented paste backfill material: Effect of activator type and amount

Effective disposal of phosphorus slag (PS) is crucial for ecosystem protection. Herein, this study proposed that Na2SO4 (SS), Na2SiO3 (NS), Na2CO3 (SC) and NaOH (NH) were performed to prepare alkali-activated phosphorus slag cemented paste backfill material (AAPS-PB). The evolution mechanisms of setting time, rheological behavior and mechanical properties at different contents of various activators were systematically investigated. The mineral compositions, bonding structure, micromorphology and pore structure characteristics of AAPS-PB hydration products were further clarified by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) and mercury intrusion porosimeter (MIP). Results indicated that activators were proved to significantly promote the dissolution of PS at appropriate content. NH had stronger alkali activation ability in the early hydration period, whereas NS sufficiently improved the later strength, enhanced the denseness of hydration products and refined the pore structure characteristics. This study expands the avenues for high-value applications of PS.

Results of Hydrogen Reduction of Iron Ore Pellets at Different Temperatures

The application of hydrogen as a reducing agent in existing blast furnaces presents a promising avenue for significantly reducing emissions. The current emphasis on hydrogen reduction may necessitate a review of parameters such as the temperature, chemical composition, porosity, reduction time, and reducing agent. In this study, the impact of varying the temperature of reducing iron ore pellets in hydrogen is focused on. A mercury intrusion porosimeter is used to assess the porosity postreduction. The microstructure of the reduced pellets is analyzed with the help of scanning electron microscopy. Notably, the pore size and overall porosity are higher at higher temperatures. Using an X‐ray diffractometer, it is determined that Fe2O3 is reduced to Fe across all specified temperatures at different reduction times. The maximum degree of reduction is attained at 1000 °C while the minimum degree of reduction is attained at 700 °C. Considering these characteristics, researchers in the field can identify the optimal conditions, develop strategies, and advance technologies that contribute to the production of environmentally friendly steel.

Intensification of flotation separation process of residual carbon from coal gasification fine slag using ultrafine carbon particles conditioning

ABSTRACT Coal gasification fine slag (CGFS) is a high-ash product with high content of residual carbon. Flotation is a common method to separate residual carbon from CGFS. However, conventional flotation is difficult to effectively remove residual carbon due to the intimate interlock between carbon and ash components in CGFS and the developed pore structure of residual carbon. In this work, a separation method was proposed using ultrafine carbon particles during conditioning to achieve the intensification of ash-carbon flotation separation from CGFS. The flotation results showed that employing ultrafine carbon particles conditioning pulp effectively increase the removal rate of unburned carbon by nearly 20%. To investigate the mechanism of the effect of variable contents of ultrafine carbon particles on the decarburization performance of CGFS, the mercury intrusion porosimeter and a self-made laboratory attachment process observation system were used, indicating that the proposed method reduced the cumulative pore volume of CGFS from 1.27 to 1.09, a 15% decrease. During the conditioning process, the ultrafine carbon particles could follow the fluid flow into the residual carbon pores, which prevented the flotation reagent entering the pores. Thus, this avoids waste of flotation reagents and improves flotation performance.

Sustainable binary/ternary blended mortars with recycled water treatment sludge using fly ash or blast slag: Characterization and environmental-economical impacts

Water treatment sludge (WTS) is produced daily and disposed of as hazardous material. It would be advisable to use locally available waste products as supplementary cementitious materials that ensure to be disposed of without harming the environment. As a novelty, this research investigated the potential of using recycled WTS with fly ash (FA) and ground-granulated blast furnace slag (BFS) as ternary blended binders. Thus, it can provide an economical solution and alleviate the adverse environmental effects of excessive production of wastes and cement production. Within this scope, the mortars with 0–30 wt% replacement of cement with modified WTS (MWTS) were produced as binary blend, and also, they were combined with FA/BFS as ternary blended binders. Therefore, optimum utilization of waste products into the mortar in terms of rheological, mechanical, durability, microstructural properties, and environmental-economical aspects was examined. Adding 10% recycled WTS as binary caused higher strengths with lower porosity measured by the mercury intrusion porosimeter test and denser microstructure, as revealed by XRD patterns and SEM results. However, the drawbacks of using recycled WTS, in terms of rheological parameters and environmental-economical aspects, were suppressed by adding FA/BFS with comparable strength values. Specifically, cost, CO2 footprint, and embodied energy were reduced by combining 10% MWTS with FA by 8.87%, 37.88%, and 33.07%, respectively, while 90-day compressive and flexural strength were 5.1% and 5.32% lower. This study developed a feasible solution to use recycled MWTS by obtaining more eco-friendly and cost-effective cement-based materials.Graphical

Medium transmission property of the interfacial transition zone between MK-GGBFS geopolymer mortar and aggregate

In this study, metakaolin (MK)–ground granulated blast furnace slag (GGBFS) was used to prepare geopolymer mortar, and concrete was prepared using prismatic-shaped basalt or aged cement mortar block as coarse aggregate. The pore structure characterization of the mortar, chloride binding capacity of the corresponding paste and the micro dimension of the interfacial transition zone (ITZ) in concrete were analysed by using a mercury intrusion porosimeter, the chloride adsorption equilibrium method and scanning electron microscopy-energy dispersive spectroscopy, respectively. The medium transmission properties of the concrete and corresponding mortar were analysed through a moisture diffusion test, chloride migration test, and chloride natural diffusion test. On this basis, the permeability resistance of the ITZ in geopolymer concrete was studied by manipulating the parameters for the basalt aggregate. The result shows that the geopolymer mortar exhibits higher porosity compared to cement mortar with similar strength, while the most probable pore size is significantly smaller, with more than 80% of the pores showing a pore size of less than 50 nm. The chloride binding mechanism for geopolymer paste primarily involves physical adsorption, and shows a greater binding capacity than cement paste at a chloride ion concentration greater than 1 mol/L. The medium transmission coefficient for geopolymer concrete is found to be 55.1–79.0% of that of cement concrete for the same parameters of the coarse aggregate. The impermeability of geopolymer concrete and its ITZ is found to be always better than that of cement concrete for varying parameters of the coarse aggregate.

Mechanical properties of graphene-mortar at high strain rates

Graphene has been considerably studied as a reinforcing nanomaterial in cementitious composites to improve their mechanical properties under quasi-static loading. However, there is still lack of knowledge in graphene cementitious composites under high strain rate loadings. This paper reports the reinforcing effect of graphene on the mechanical behaviour of mortar at high strain rates. Different graphene contents were incorporated into the mortar to study their effect on the behaviour of mortar quasi-statically and dynamically. Compressive and split tensile strengths were measured under low and high strain rates using a universal testing machine and split-Hopkinson pressure bar (SHPB), respectively. It was found that adding 0.05% and 0.01% of graphene to the mortar enhanced the dynamic compressive and split tensile strengths up to 30% and 9.5% at 175 s-1 and 2–5 s-1 strain rates, respectively. Moreover, to understand the macroscale mechanical behaviour of the graphene mortar, Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometer (EDS) and Mercury Intrusion Porosimeter (MIP) were employed to explore the morphology, porosity and hydration products of graphene mortar. The results indicated that graphene acted to fill the voids as well as to impede the crack path.

Detection and quantification of preferential flow using artificial rainfall with multiple experimental approaches

Preferential flow in the unsaturated zone strongly influences important hydrologic processes, such as infiltration, contaminant transport, and aquifer recharge. Because it entails various combinations of physical processes arising from the interactions of water, air, and solid particles in a porous medium, preferential flow is highly complex. Major research is needed to improve the ability to understand, quantify, model, and predict preferential flow. Toward a solution, a combination of diverse experimental measurements at multiple scales, from laboratory scale to mesoscale, has been implemented to detect and quantify preferential paths in carbonate and karstic unsaturated zones. This involves integration of information from (1) core samples, by means of mercury intrusion porosimeter, evaporation, quasi-steady centrifuge and dewpoint potentiometer laboratory methods, to investigate the effect of pore-size distribution on hydraulic characteristics and the potential activation of preferential flow, (2) field plot experiments with artificial sprinkling, to visualize preferential pathways related to secondary porosity, through use of geophysical measurements, and (3) mesoscale evaluation of field data through episodic master recession modeling of episodic recharge. This study demonstrates that preferential flow processes operate from core scale to two different field scales and impact on the qualitative and quantitative groundwater status, by entailing fast flow with subsequent effects on recharge rate and contaminant mobilizing. The presented results represent a rare example of preferential flow detection and numerical modeling by reducing underestimation of the recharge and contamination risks.

Durability of cementitious mortar: Incorporation of highly dispersed superplasticizer modified graphene oxide in fly ash blended mortar

The present study focuses on the utilization of superplasticizer stabilized graphene oxide (GO) as a reinforcing agent in the fly ash blended cement mortar (30–70 ratio of FA/OPC). GO is moderately stable in water solvent medium while, it agglomerates in the alkaline cement pore solution owing to the interference caused by Mg2+, Na+, Ca2+, and OH− etc. So, here an effort has been made to stabilize the GO via superplasticizer's (PCE-SP) steric effect and has further been used as a reinforcing phase in the cement-fly ash-based mortars. The UV–visible (Agilent Pro) spectrometry was used to measure the degree of stabilization via absorbance values. The increased dispersion of GO due to PCE-SP steric stabilization as compared to without PCE-SP has been monitored by UV–Visible spectroscopy. The results have shown that incorporation of 0.08 % PCE-GO (by weight percentage of blend) amended compressive and split-tensile strength of the mortars by 39.85 % and 48.90 % as compared to control-FA specimen at the curing age of 90 days, respectively. Furthermore, the results achieved were equal or even superior than 100 % cement-based mortar (control-OPC). Micro-structural results showed the acceleration of pozzolanic reactions on the nucleation sites supplied by the PCE-GO's functionalities. Mercury Intrusion Porosimeter studies shows that porosity of fly ash-cement mortar was reduced in comparison to control-FA mortar by 51.5 % after 0.08 % PCE-GO incorporation. The cumulative pore volume also contracted from 0.057 to 0.025 cc/g, depicting densification of C–S–H gel network owing to the synergism acting between FA and PCE-GO in cement-FA matrix. Porosity results are also complying with the enhanced electrical resistivity and reduced water absorption values of mortars. In terms of weight loss and compressive strength gain over various exposure periods, mortars incorporating PCE-GO performed better than control samples in all durability-related aspects. PCE-GO incorporation also resulted in improved acid and sulfate attack resistance, owing to the reduced leaching of calcium ions from hydrated cement-FA matrix. This led to lesser deterioration of PCE-GO incorporated mortars owing to reduced ettringite and gypsum formation, as confirmed by XRD and SEM mapping studies. Overall, the incorporation of PCE-GO in mortars has demonstrated significant enhancements in properties. This development holds great promise for the advancement of the construction and infrastructure sectors. The utilization of high-performance mortars has the potential to enhance the strength, durability, and sustainability of structures, thereby making a valuable contribution to the development of safer and more resilient built environments. Furthermore, the utilization of PCE-GO in an innovative manner has the potential to revolutionize construction methodologies and materials in forthcoming times.

Ultra-low carbon lightweight engineered cementitious composite: Design and material characterization

Lightweight engineered cementitious composites (LWECC) are prized for their exceptional tensile performance, durability, and low self-weight. However, the elevated cement usage in ECC results in a substantial carbon footprint, thus placing significant ecological pressures. This study employed calcium sulfoaluminate-activated supersulfated cement (CSA-SSC) to develop the ultra-low carbon LWECC. The influence of silica fume, lightweight filler, PE fiber contents and water-to-binder ratio on the mechanical characteristics of ULL-ECC were investigated, in terms of density, tensile and compressive properties. The fracture toughness test, single-crack tensile test, mercury intrusion porosimeter (MIP), scanning electronic microscope (SEM) and X-ray diffraction (XRD) analysis were conducted to establish a connection between macro behavior and micro-scale performance. The results reveal ULL-ECC's remarkable tensile behavior, demonstrating a tensile strength of 7.1 MPa and an impressive strain capacity of 12.6%, with compressive strengths ranging from 50.3 MPa to 65.1 MPa. The carbon footprint of ULL-ECC accounts to only 35% of conventional concrete and 22% of traditional ECC. Through the synergistic utilization of eco-friendly FAC, CSA-SSC, and high-strength PE fiber, ULL-ECC not only showcases exceptional mechanical properties but also embodies a substantial improvement in sustainability, coupled with a reduction in self-weight.

Gas permeability of alumina–spinel refractory castables bonded with hydratable magnesium carboxylate

AbstractThe high level of gas permeability can effectively reduce the explosive spalling risk of refractory castables. The hydratable magnesium carboxylate (HMC) is expected to improve the permeability of castables owing to the thermal decomposition of the HMC hydrates. This study compared the gas permeability and explosive spalling resistance of HMC bonded refractory castables (HMCC) with calcium aluminate cement bonded refractory castables (CACC). Thermal decomposition of (Mg3(C6H5O7)2∙11H2O) (hydrates of HMC), drying behavior, and the pores size distribution of castables were investigated. The level of gas permeability of HMCC is higher than that of CACC, which was confirmed by the higher values of Darcian k1 and non‐Darcian k2. The degas temperatures of HMC hydrates (156°C) and HMCC (432°C) are lower than those of CAC hydrates (289°C) and CACC (536°C) at a heating rate of 20°C/min, respectively. The large‐size and more permeable pores in HMCC were obtained according to the mercury intrusion porosimeter (MIP) results, which formed the connected paths for gases (H2O, CO2, C2H4, CO, CH4) released from the castables.

Effect of graphite on the self-sensing properties of cement and alkali-activated fly ash/slag based composite cementitious materials

This study investigated the self-sensing performances of cement and alkali-activated fly ash/slag (AAFS) systems with graphite powders as a conductive filler. Graphite powders must be evenly dispersed through the cement-based and AAFS matrices to obtain an adequate electrical response. The effects of graphite fineness on the fluidity, mechanical, rheological behavior, and cement hydration of cement paste were investigated. The finer graphite was found to have less effect on the mechanical property but seriously damaged the workability. Therefore, this research explored using four surfactants including sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), sodium salt of polynaphthalene sulphonic acid (NNO), and Triton X-100 (TX100) as dispersing agents for fine graphite in cement. The combination of NNO and TX100 was found to be the ideal admixture for improving the fluidity of graphite-containing cementitious materials. Furthermore, cement- and AAFS-based composites were produced with the graphite dispersions, and several tests such as electrical impedance spectroscopy (EIS), energy dispersive X-Ray (EDX) map analysis, mercury intrusion Porosimeter (MIP), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were used to investigate their intrinsic characteristic. The results concluded that AAFS had a better conductivity than cement due to the higher porosity in the range of very small pores (<6 nm) and the higher ion concentration contribution. Finally, the self-sensing behavior of the mortars was investigated under cyclic loading, and the self-sensing mechanism was proposed. The sensing properties of graphite composite mortars under compression load can be attributed to the combination of ionic, contact, and tunneling conduction.

Relationship between fractal characteristics of pore-structure and thermal properties of FA-based AAM under different curing conditions

The microstructure of hardened alkali-activated materials (AAM) plays an essential role in determining the mechanical properties at elevated temperatures, particularly the pore structure. Mercury Intrusion Porosimeter (MIP) was employed to study the fractal characteristics of the pore structure of samples under standard and sealed curing conditions, which includes pore size distribution, shape, surface area, and tortuosity of AAM pastes after exposure to high temperatures. Additionally, the compressive strength of AAMs at elevated temperatures was determined. Comparing the samples under standard curing conditions, sealed curing conditions significantly improved the 28-day compressive strength (43.6 MPa) and residual compressive strength (achieving 60.2% of the 28-day strength) when exposed to 1000 °C. Based on research, the fractal characteristics of pore structures have a significant effect on the thermal properties of samples at high temperatures. Differences in thermal properties may be attributable to resistance caused by pore structures with heterogeneity and complexity, as well as the shape of the pores, which have small pore throats and large pore capacities. Under standard curing conditions, the samples exhibited a pore structure characterized by a reduced neck diameter, larger cavity size, a coarser pore surface, and decreased connectivity. As a result, the 28-day samples under standard curing conditions experienced significantly elevated pore pressure.

Effect of Aluminosilicates' Particle Size Distribution on the Microstructural and Mechanical Properties of Metakaolinite-Based Geopolymers.

The present study focused on investigating the differences in properties between calcined and milled aluminosilicates with different particle size distributions. Two types of clay, i.e., kaolin and kaolinitic claystone, were subjected to calcination at 750 °C, and subsequent milling to obtain different fractions with distinct particle size distributions. These fractions were then combined with a potassium alkaline activator and quartz sand in a 50:50 weight ratio to form a geopolymer composite. The geopolymer binders were then characterized using a mercury intrusion porosimeter (MIP), scanning electron microscopy (SEM), and a rotary rheometer. Mechanical tests were conducted on the geopolymer composites prepared from aluminosilicates with varying particle size distributions. The findings indicated that aluminosilicates with a finer particle size distribution exhibited higher levels of dissolved aluminum (10,000 mg/kg) compared to samples with coarser particle size distributions (1000 mg/kg). Additionally, as the particle size distribution decreased, the dynamic viscosity of the geopolymer binders increased, while the average pore size decreased. Finally, the mechanical properties of the geopolymer composites derived from both tested aluminosilicates demonstrated a decline in performance as the mean particle size increased beyond 10 µm.

Doping Silica Fume Enhances the Mechanical Strength of Slag/Fly Ash Geopolymer Paste under Frost Attack

Benign design of alkali-activated slag/FA geopolymer paste has attracted increasing attention for optimizing its service performance. Therefore, the replacement of fly ash (FA) with 10 wt% silica fume (SF) is investigated by mechanical strength after freeze–thawing cycles and microstructure characterization. The results show that an appropriate dosage (30 wt%) of slag is necessary to prepare heat-free curing alkali-activated slag/FA geopolymer paste with excellent mechanical performance. The SF/slag/FA (SF:slag:FA = 10:30:60, wt%) geopolymer paste exerts an enhanced compressive and flexural strength of 95.2 and 3.2 MPa, respectively. Meanwhile, the doped 10 wt% SF facilitates the propagation of (N, C)-A-S-H chains, rather than the formation of C-S-H gels. It is evidenced by the absent exothermic peak at about 861 °C from the differential scanning calorimetry (DSC) curves. The pores volume and tortuosity also rise for the pore diameter &lt; 20 nm from mercury intrusion porosimeter (MIP) results, corresponding to an improved freezing–thawing resistance with the residual compressive strength of 52.8 MPa and the weight loss of 10.5% after 300 freeze–thawing cycles. It explores a cost-effective and benign facile approach to designing heat-free curing alkali-activated slag/FA geopolymer paste with good freezing–thawing resistance.

Effect of the Chemical Nature of Polyvinyl Alcohol on the Microstructure of Cement Hydration Products

The influence of chemical nature of polyvinyl alcohol (PVA) on the microstructure of cement hydration products was investigated. Thermal analysis, X-ray diffraction, Si29 nuclear magnetic resonance (NMR), and scanning electron microscope were used to explore the microstructure and content of cement hydration products. The pore structure of the matrix was measured by a mercury intrusion porosimeter. Ca(OH)2 in PVA-modified cement composites showed multidirectional growth, and its platelike structure was distorted due to the intersection of different growth orientations. The decomposition temperature of Ca(OH)2 in PVA-modified cement composites was lower than in unmodified cement composites, which was greatly affected by degrees of polymerization of PVA. Besides, the mean chain length of calcium silicate hydrate (C-S-H) gels showed an increasing trend with the increase of degrees of hydrolysis and polymerization of PVA, but it was less than that of unmodified cement composites. The incorporation of PVA increased the porosity, but refined the pore-size distribution of the matrix. PVA film between layered Ca(OH)2 and on the surface of cement hydration products acted as an additional bond and increased the internal cohesion of the matrix.

Mechanical properties and pore structure of 3D printed mortar with recycled powder

This study investigated the hardened mechanical properties of 3D printed mortar (3DPM) with different contents (0–30% by mass of cement) of recycled powder (RP) by anisotropic compressive, splitting tensile and flexural strengths. The pore characteristics tested by X-ray computed tomography and mercury intrusion porosimeter as well as hydration products of 3DPM were analyzed to reveal the influence mechanism of RP on 3DPM. The results showed that the highest compressive strength of the 3D printed specimens was obtained on the loading direction paralleled with the length of printing filament (X direction). When the RP replacement ratio was 20%, the X-direction compressive strength of 3DPM was 24.11% lower than that of cast samples, while the splitting tensile strengths of 3DPM were closed to and the flexural strengths of 3DPM were higher than that of cast samples regardless of the loading directions. This can be attributed to the high fluidity loss rate of 3DPM with RP, leading to the reduction of the surface moisture of interlayer. Besides, more pores at the interlayer and interstrips led to the decrease of mechanical properties. In contrast, the addition of RP had a limited effect on the micro pore structure of the single printed filament without considering the interlayer and interstrip, owing to the secondary hydration and filling effect of RP.

Micro-nano scale pore structure and fractal dimension of ultra-high performance cementitious composites modified with nanofillers

The development of ultra-high performance cementitious composite (UHPCC) represents a significant advancement in the field of concrete science and technology, but insufficient hydration and high autogenous shrinkage relatively increase the pores inside UHPCC, in turn, affecting the macro-performance of UHPCC. This paper, initially, optimized the pore structure of UHPCC using different types and dimensions of nanofillers. Subsequently, the pore structure characteristics of nano-modified UHPCC were investigated by the mercury intrusion porosimeter method and fractal theory. Finally, the fluid permeability of nano-modified UHPCC was estimated by applying the Katz-Thompson equation. Experimental results showed that all incorporated nanofillers can refine the pore structure of UHPCC, but nanofillers with different types and dimensions have various effects on the pore structure of UHPCC. Specifically, CNTs, especially the thin-short one, can significantly reduce the porosity of UHPCC, whereas nanoparticles, especially nano-SiO2, are more conducive to refine the pore size. Among all nanofillers, nano-SiO2 has the most obvious effect on pore structure, reducing the porosity, specific pore volume and most probable pore radius of UHPCC by 31.9%, 35.1% and 40.9%, respectively. Additionally, the pore size distribution of nano-modified UHPCC ranges from 10−1nm–105nm, and the gel pores and fine capillary pores in the range of 3–50 nm account for more than 70% of the total pore content, confirming nanofillers incorporation can effectively weaken pore connectivity and induce pore distribution to concentrate at nanoscale. Fractal results indicated the provision of nanofillers reduces the structural heterogeneity of gel pores and fine capillary pores, and induces homogenization and densification of UHPCC matrix, in turn, decreasing the UHPCC fluid permeability by 15.7%–79.2%.

Chloride penetration resistance of engineered cementitious composite (ECC) subjected to sustained flexural loading

This paper presents a research on the chloride penetration behavior of engineered cementitious composites (ECC) under sustained flexural loads. Three load levels, i.e. 30 %, 60 % and 75 % of the ultimate flexural load were used. Chloride diffusion depth and concentration profile were measured 30, 60 and 150 days after the specimen was exposed to NaCl solution and compared with pre-loaded specimens. Influence of the sustained local bending stress and microcracks were investigated. It shows that under sustained loads, the relationship between the surface chloride content and maximum normal tensile stress can be described using an exponential equation. A binary model was developed to explain the correlation among the chloride ion diffusion coefficient, maximum normal tensile stress and exposure time. Changes of capillary pore structure and phase compositions were measured using mercury intrusion porosimeter and X-ray diffraction, respectively. Unlike mortar, the fiber bridging of ECC helps with limiting crack width and thus the diffusion process, and the measured results were used to explain the observed penetration behavior of ECC. It is believed that the current study provides theoretical foundation for the durable design of the ECC/concrete composite structure.

Laboratory Study on Entire Range Suction Measurement and Microstructure Change of Granite Residual Soil

The shear strength of unsaturated granite residual soil (GRS) will decline rapidly when moisture content increases, because of loss of matric suction in the soil. This can lead to slope instability and embankment collapse during rainfall. Determining the matric suction of GRS accurately at different conditions can improve the accuracy of stability analysis. Generally, matric suction can be characterized as the soil–water characteristic curve (SWCC), and it is closely related to soil microstructure. In this study, the entire range of matric suction was measured using a combination of pressure plate method, filter paper method, and vapor equilibrium method. Microstructure change was investigated based on mercury intrusion porosimeter tests, in which the pore size distribution (PSD) curves of GRS samples with different initial densities and moisture content were measured. The PSDs of samples before and after wetting were also measured and compared to investigate the influence of water intrusion. Test results indicate that the combination of measurement methods can cover the entire matric suction range. The microstructure of GRS with different initial conditions presents a clear bimodal PSD. At the same density, the increase in initial moisture content can increase intra-aggregate pores and decrease inter-aggregate pores. When initial density increases, only the volume of inter-aggregate pores decreases. Wetting can decrease inter-aggregate pores and increase intra-aggregate pores. Finally, the Li model is applied in SWCC fitting for tested samples, the result of which performs well with a high correlation coefficient (R2 &gt; 0.95) and is recommended for GRS analysis.

Long-term performance of ferrite-rich calcium sulfoaluminate cement-based paste under seawater corrosion

Ferrite-rich calcium sulfoaluminate cement (FCSA) is widely used due to its characteristics of short setting time, high early strength, slight expansion and low CO2 emissions. In order to further study the long-term performance of FCSA under seawater environment, this study prepared a quaternary blend based on FCSA clinker, Ordinary Portland cement (OPC), anhydrite and limestone. Meanwhile, artificial seawater solutions were prepared by dissolving granular NaCl, MgSO4 and MgCl2 in deionized water. The long-term performance evolution of physical and mechanical characteristics such as mechanical properties, chloride content, hydration products and micro-structure property were investigated through uniaxial compression test, X-ray diffraction (XRD), thermogravimetric analysis (TG), mercury intrusion porosimeter (MIP) and other test methods by considering different salt concentrations of seawater and corrosion age. The results showed that the mass and expansion rate of corroded specimens increased logarithmically with the corrosion age. The quaternary blend could resist sulfate corrosion by absorbing it in seawater solution and promote the generation of ettringite. In addition, Friedel's salt was mainly generated by ion exchange between chloride and sulfate of monosulfoaluminate. The uniaxial compressive strength of all specimens showed a consistency of increasing first and then decreasing with corrosion age. Meanwhile, the corrosion resistance coefficient K of the specimens varied between 0.95 and 1.30 with the salt concentrations of seawater increasing. According to the mechanical behavior and micro-structure characteristics of the new quaternary blend, it’s indicated that the new cement-based material has adequate ability to resist seawater salt corrosion and has an excellent long-term stable performance.