Zeolite Particles Research Articles

Internal curing mechanism of zeolite pretreated with NaCl under microwave and ultrasonic conditions

Natural zeolite has been used for internal curing to reduce shrinkage of cement-based materials, but the internal curing performance of zeolite needs to be improved. In this study, natural zeolite particles were modified by NaCl solution under conditions of microwave and ultrasonic to improve their internal curing performance. Firstly, the pore structure, chemical bond characteristics, pozzolanic activity, water absorption and water release performance of the modified zeolite were tested. Then, cement paste specimens internally cured with modified zeolite were prepared, the shrinkage, hydration products, and pore structure were tested, and the internal curing mechanism of modified zeolite was discussed. The results show that: (1) Pozzolanic activity of zeolite decreases after NaCl-microwave modification, but increases after NaCl-ultrasonic modification. (2) NaCl modification increases the pore volume and water adsorption of natural zeolite particles. (3) NaCl modified zeolite promotes the formation of ettringite in cement paste, especially for NaCl-microwave modified zeolite. (4) NaCl-microwave modified zeolite has better shrinkage reducing effect and strength improving effect than natural zeolite and NaCl-ultrasonic modified zeolite.

Mass and Heat Transfer of Pressure Swing Adsorption Oxygen Production Process with Small Adsorbent Particles

Rapid-cycle pressure swing adsorption (PSA) with small adsorbents particles is intended to improve mass transfer rate and productivity. However, the mass transfer mechanisms are changed with reduction of particle size during rapid-cycle adsorption process. A heat and mass transfer model of rapid-cycle PSA air separation process employing small LiLSX zeolite particles is developed and experimentally validated to numerically analyze the effects of mass transfer resistances on the characteristics of cyclic adsorption process. Multicomponent Langmuir model and linear driving force model are employed for characterizing the adsorption equilibrium and kinetic. The results of numerical analysis demonstrate that the dominant mass transfer resistance of small adsorbents particles is a combination of film resistance, axial dispersion effect and macropore diffusion resistance. The oxygen purity, recovery and productivity of the product are overestimated by ~2–4% when the effect of axial dispersion on mass transfer is ignored. As particle size decreases, the front of nitrogen-adsorbed concentration and gas temperature become sharp, which effectively improves the performance. However, the adverse effect of axial dispersion on the mass transfer becomes significant at very small particles conditions. It is nearly identical shapes of nitrogen concentration and gas temperature profiles after adsorption and desorption steps. The profiles are pushed forward near the production end with an increase in bed porosities. The optimal oxygen recovery and productivity are achieved with a particle diameter of 0.45 mm and bed porosity of 0.39 during the PSA process.

Fluidisation of Thermochemical Energy Storage Materials: Degradation Assessment

ABSTRACT Composite zeolites impregnated with anhydrous salt particles are promising materials for use in domestic thermochemical energy storage (TCES), however they have limited power output. Fluidization has the potential to increase the mass and heat transfer of TCES systems. In this study, a composite TCES material of LiX zeolite impregnated with MgCl2 salt is produced. This material and a LiX zeolite batch are then fluidized at different gas velocities to study whether degradation of these particles occurs when fluidizing. Images of the particles after fluidizing are analyzed using a validated method utilizing microscope images and specialized software used to study whether fragmentation or abrasion have been induced by fluidization. Composite particles were found to have increased average diameter by 7%−8%, which could be due to imperfect dehydration of these particles after the impregnation process, but also due to observed salt conglomerates present on the surface of some particles. Overall, excess degradation was not found due to fluidization at any gas velocity. No mass loss was measured in any sample after fluidization, and no appreciable fragmentation was observed. The LiX zeolite and composite particles measured 0.6192 mm and 0.6799 mm prior to fluidization and measured 0.6405 mm and 0.7088 mm after fluidization. However, this change is not statistically significant, and it is shown that a change in diameter is unlikely. Despite this, some fines have been produced which were found to have an average diameter of 3.60 μm (σ = 1, ±2.34 μm), and as such present a hazard if inhaled.

Process steam generation from low-grade waste heat in a direct- contact adsorption heat pump based on superhydrophobic surface-modified Zeolite 13X

ABSTRACT Adsorption heat pump (AdHP) is a potential technology to recover and storage low-temperature waste heat. This paper presents an experimental research on direct low-pressure process steam generation from hot water based on superhydrophobic surface-modified zeolite 13X. The measured water contact angle of the modified zeolite is larger than 150°, which restricts free water entering the pores inside the zeolite particles. Cyclic experiments are conducted for performance evaluation. High-temperature steam (205–229°C, 0.1–0.3 MPa) is generated from hot water (72°C) in the AdHP driven by dry air (130°C). The temperature of generated steam is promoted with increasing preset steam pressure, among which the temperature is raised by about 23°C at 0.3 MPa. As the boiling point of water rises simultaneously, the sensible heat demand is increased. Thus, the mass of the steam is accordingly decreased. GTL (gross temperature lift) reaches 130°C. When the preset pressure is increased, COPh (coefficient of performance for heating) and SHP (specific heat power) for direct steam generation are decreased by 36% and 39%, respectively. One feasible option to elevate these two indicators is to increase the inlet water to near boiling water to match the change in the preset pressure. However, the GTL will be decreased based on the option. Balance should be made based on the choice of design for practical application.

Zeolite Integrate with Natural Absorbance to Increase Crop Production

Mesoporous structure of Zeolites particles with higher micropores able to provide higher surface area that able to increase the efficiency of diffusion mechnism as well as cation exchange capacity (CEC). Theuniquness and unreactive properties of zeolites enable to integrate this materials with other potential material to increase the zeolite absorption and CEC performance. Thus, the goal of this work is to study the effect of natural absorbents(chitosan and charcoal) when integrate with zeolite that function as a soil enhancer for the plants growth. Several experiments at different composition of soil, fertilizer, zeolite and absorbance compositions towards water spinach growth, pH and soil humidity were measured. The results of the plant growth show that both natural absorbance materials significantly assist the nutrient uptake either from the soil or fertilizer by showing higher plant growth, pH and humidity values as compared to soil mixedwith fertilizeronly. Integration of these absorbance with zeolite futher increase the capability of nutrient uptake by giving the highest value of plant growth, pH and humidity values. Detail observation also showed that water spinach grew faster in the sample that had fertilizer added to the zeolite with charcoal as compared to chitosanKeywords:Zeolites, natural absorbance, charcoal, chitosan, pH, humidity, plant growth

Multi-scale experimental investigation on the fluidization of Geldart B 13X zeolite particles: A comprehensive dataset for CFD validation

The fluidization of zeolite 13X in a bubbling fluidized bed was experimentally investigated. The objective is to analyze the fluidization behavior of particles in a lab-scale system with a total of 1.5 million particles, enabling accurate characterization of uncertainties. Validation datasets were generated for the fluidization process in a bench-scale rectangular unit. A comprehensive characterization of the particle properties, including size, density, coefficient of friction, coefficient of restitution, and minimum fluidization velocity, is presented using advanced diagnostic tools. Corresponding fluidized bed measurements, such as pressure drop and bed expansion, are reported under three test settings with different flow rates. The tested particles have a Sauter mean diameter of 1,345 μm and a density of 2,054 kg/m3. It is classified in Geldart group B for its vigorous bubbling and good mixing behavior. With increasing the superficial inlet velocity from 0.347 to 0.740 m/s corresponding to 1.41–3.01 Umf, where Umf = 0.2458 m/s is the minimum fluidization velocity, the particles tend to transit from bubbling flow to slug/plug flow regimes. Using high-speed imaging, bubble sizes and velocities in the pseudo-two-dimensional (2D) fluidized bed could be obtained directly. The data acquisition rate is 1200 fps, far above the quantities of interest (QoI) dominant frequency (typically below 10 Hz). The QoI obtained from this study were statistics of interface height, differential pressure, and particle velocities using particle image velocimetry. The results confirm consistency given the use of randomization and repeat in the run order as well as multiple batches of bed material. This experimental dataset can serve as a benchmark for validating numerical models and as a blind study for the multiphase flow modeling community.

Using Natural Zeolite as a Feed Additive in Broilers' Diets for Enhancing Growth Performance, Carcass Characteristics, and Meat Quality Traits.

Using natural zeolites as a food additive in poultry diets offers an intriguing perspective. The objective of this study was to investigate the effects of zeolite addition and particle size on broiler performance, carcass characteristics, meat quality, moisture of excreta and litter, and intestinal measurements during 35 days. A total of 560 1-day-old female Ross-308 broilers were divided into five treatment levels (0, 5, 10, 15, and 20 g zeolite/kg diet) (n = 16 replicates/treatment, n = 8 replicates /particle size of each treatment). Performance was calculated weekly. Carcass characteristics, meat quality, small intestine (SI) measurements, litter pH, and moisture content were determined on day 35. Litter pH, breast redness, cooking loss, chewiness, total weight, and SI length were all affected by zeolite treatments (p < 0.05). Particle size had an impact on the gastric pH and texture analysis. Their interaction had an effect on color redness, litter pH, and cooking loss. Performance was unaffected by either the main or interaction effects. Zeolite as a feed additive may be useful in broiler diets, particularly large particles. The performance and production efficiency factor improved numerically (p > 0.05) with increasing zeolite doses up to 10 g zeolite/kg diet.

Correlation between zeolitic particle size and the low-temperature NOx storage capacity of Pd/ZSM-11 passive NOx adsorber

The effect of zeolitic particle size on the NOx adsorption and desorption was investigated by synthesizing ZSM-11 zeolites with different particle sizes (0.5∼0.8, 1∼2, and 5∼6 μm) for doping Pd as passive NOx adsorbers (PNAs). Several characteristic techniques of XRD, HAADF-STEM, H2-TPR, CO-DRIFT, XPS and NH3-TPD were applied to clarify the essential association of the PNAs performance of Pd/ZSM-11 zeolites with the support zeolite properties and Pd active species. It was found that both the efficient Pd(II) species for assisting NOx adsorption-release and the acid amount (especially the strong acid sites) for facilitating Pd dispersion have positive correlation with the decrease of zeolite particle size. Differently, in addition to the active Pd species, meso-macroporosity properties are another key factors to determine the NOx adsorption ability of PNAs. The meso-macroporosity properties of Pd/Z11-1.5 show a negative correlation with the decrease of zeolite particle size while Pd/Z11-0.7's show the positive correlation with the decrease of zeolite particle size. As a consequence, Pd/Z11-1.5 with higher Pd(II) content but weaker meso-macroporosity properties than Pd/Z11-5.0 shows comparable adsorption capacity to Pd/Z11-5.0, while Pd/Z11-0.7 with both high Pd(II) content and good meso-macroporosity properties not only exhibits the highest NOx storage capacity, but also can release the NOx at the lowest temperature of less than 300 °C, indicating to be a good candidate for purifying NOx at the actual exhaust temperature of diesel vehicles.

In situ biosynthetic BC/zeolite hybrid hemostat for quick clot

AbstractZeolite‐based hemostatic agents are considered as an outstanding material to achieve rapid and definitive hemostasis in pre‐hospital management. However, developing a safer zeolitic hemostat that avoids the potential thrombotic risk caused by tiny zeolite residue in bleeding wounds remains a critical challenge. In this research, we employ an in situ biosynthesis process to fabricate a sandwich‐like structured bacterial cellulose/zeolite (BC/zeolite) hybrid hemostat. Zeolite particles were firmly bonded into the BC membranes with &lt;1% leaching after 24 soaking. This hemostat displays effective hemostatic performance after calcium ion‐exchange process. The BC/zeolite‐Ca hemostat can significantly decrease in vitro blood clotting time from 7.5 ± 0.3 min to 2.2 ± 0.3 min. This work achieves a low‐cost, eco‐friendly, and low‐risk approach through in situ biosynthesis in the preparation of BC‐ and zeolite‐based hybrid for pre‐hospital hemostasis applications.

Influence of co-milling oxide physical properties on the structural changes of natural clinoptilolite zeolites

Zeolites are a family of open-framework aluminosilicate minerals used in many diverse fields, including building materials, agriculture, water treatment, and catalysis. In this study, natural zeolites were mechano-chemically treated by co-milling with corundum and cristobalite. The idea behind the study was that co-milling with high-hardness oxides would cause natural zeolite to undergo more structural distortion, potentially increasing its reactivity and sorption capabilities. Corundum has a density of 3.95 g/cm3 and a hardness of 9, while cristobalite has a density of 2.27 g/cm3 and a hardness of 6-7, according to the Mohs hardness scale. In a planetary ball mill, the zeolites and 20 wt.% of various oxides were co-ground for 30 min. The grinding media used were hardened steel balls with a weight ratio of 20:1 between the balls and the minerals. Raw minerals and milled products were evaluated using X-ray diffraction, Fourier-transform infrared spectroscopy and scanning electron microscopy. It revealed that co-milling with different hardness oxides had a minor effect on the structural distortion of raw zeolite. Crystallite size reduction and amorphization were observed in high hardness oxides rather than in zeolite particles. After milling, the amorphization of natural zeolite milled alone was 30.4%, while no significant amorphization was observed when co-milled with corundum and cristobalite. Preliminary results of Cr(VI) adsorption tests on raw and milled zeolites indicate that co-milling with high-hardness oxides is not the preferred method to enhance the activity of natural zeolite.

Method and apparatus for the production of a zeolite particle composition

Method and apparatus for the production of a zeolite particle composition

Zeolite membrane separators for fire-safe Li-ion batteries – Effects of crystal shape and membrane pore structure

The state-of-the-art lithium-ion batteries (LIB) use carbonate-based liquid electrolytes and polymeric separators which pose safety issues including fire-hazard. The use of fire-retarding salt-concentrated electrolytes can address the safety issues of LIBs, but these electrolytes have high viscosity and low wettability with polymeric separators making it difficult to fabricate high performance LIBs with the electrolytes. Here we report development of zeolite membrane separators with tailored pore structure and surface chemistry for preparation of fire-safe LIBs using salt-concentrated electrolytes. The zeolite membrane separators are made of zeolite particles with a specific zeolite structure, Si/Al ratio, and different particle shapes, coated on cathode by a scalable blade coating method. Intermediate pore, pure silica MFI-type zeolite (silicalite) was selected as the fire-proof material for membrane separators which also offer high wettability for the fire-retarding salt-concentrated electrolyte of lithium bis(fluorosulfonyl)imide (LiFSI) in tri-methyl phosphate solvent (TMP) solvent. Two silicalite membrane separators of similar pore size but different porosity and tortuosity were coated on cathode (LiNi0.5Mn0.3Co0.2O2 or NMC) using plate-shaped silicalite particles of low aspect ratio (LAR) and high aspect ratio (HAR). Both zeolite separators show significantly better wettability for the LiFSI/TMP electrolyte than the commercial polypropylene (PP) separator allowing fabrication of high-performance NMC/LiFSI-TMP/graphite cells with the non-combustible silicalite separator. The new fire-safe zeolite-membrane-based LIBs with the fire-retarding electrolyte exhibit excellent charge and discharge characteristics and cycle performance (similar to the state-of-the-art, but fire-unsafe LIBs with LiPF6-carbonate electrolyte and polymer separator). The membrane separators made of HAR plate-shaped zeolite showing low interparticle porosity and high tortuosity perform better than the membrane made of LAR zeolite particles, due to a more uniform lithium-ion flux from both interparticle pores and intraparticle zeolitic pores at the separator/anode interface.

Fluoride Adsorption from Aqueous Solution by Modified Zeolite-Kinetic and Isotherm Studies.

Fluorine is a very common element in the Earth's crust and is present in the air, food, and in natural waters. It never meets in the free state in nature due to its high reactivity, and it comes in the form of fluorides. Depending on the concentration of fluorine absorbed, it may be beneficial or harmful to human health. Similar to any trace element, fluoride ion is beneficial for the human body at low levels, but as soon as its concentration becomes too high, it is toxic, inducing dental and bone fluorosis. The lowering of fluoride concentrations that exceed the recommended standards in drinking water is practiced in various ways around the world. The adsorption process has been classified as one of the most efficient methods for the removal of fluoride from water as it is environmentally friendly, easy to operate, and cost-effective. The present study deals with fluoride ion adsorption on modified zeolite. There are several influential parameters, such as zeolite particle size, stirring rate, solution pH, initial concentration of fluoride, contact time, and solution temperature. The maximum removal efficiency of the modified zeolite adsorbent was 94% at 5 mg/L fluoride initial concentration, pH 6.3, and 0.5 g modified zeolite mass. The adsorption rate increases accordingly with increases in the stirring rate and pH value and decreases when the initial fluoride concentration is increased. The evaluation was enhanced by the study of adsorption isotherms using the Langmuir and Freundlich models. The Langmuir isotherm corresponds with the experimental results of the fluoride ions adsorption with a correlation value of 0.994. The kinetic analysis results of the fluoride ions adsorption on modified zeolite allowed us to demonstrate that the process primarily follows a pseudo-second-order and then, in the next step, follows a pseudo-first-order model. Thermodynamic parameters were calculated, and the ΔG° value is found to be in the range of -0.266 kJ/mol up to 1.613 kJ/mol amidst an increase in temperature from 298.2 to 331.7 K. The negative values of the free enthalpy ΔG° mean that the adsorption of fluoride ions on the modified zeolite is spontaneous, and the positive value of the enthalpy ∆H° shows that the adsorption process is endothermic. The ∆S° values of entropy indicate the fluoride adsorption randomness characteristics at the zeolite-solution interface.

Influence of 3-aminopropyltriethoxysilane/tetraethylorthosilicate mixture pretreatment on the microstructure and corrosion resistance of zeolite coating

ABSTRACT The influence of silane pretreatment with five different volume ratios (100/0, 75/25, 50/50, 25/75, and 0/100) of 3-aminopropyltriethoxysilane (APTES)/tetraethylorthosilicate (TEOS) on microstructure and corrosion resistance of the hydrothermal synthesized zeolite coatings on the H13 steel substrates was investigated. The surface of the zeolite coatings on the 100/0, 75/25, and 50/50 mixture of the APTES/TEOS pretreated substrates was composed of intergrown rectangular particles. Additionally, pores were observed. A 25/75 mixture of APTES/TEOS pretreatment smoothed the edges and angles of zeolite particles with gel-like materials filled in the pores. In pure TEOS pretreatment, microcracks, and much gel-like materials were observed on the zeolite coating. The electrochemical test revealed that the zeolite coating on a 50/50 mixture of the APTES/TEOS pretreated substrate exhibited the highest corrosion resistance in 3.5 wt-% NaCl solution. This was because a 50/50 mixture of APTES/TEOS pretreatment advantageously promoted development of a dense and thick gel layer, which enhanced the intergrowth of zeolite particles.

Heat generation in a packed bed of zeolite particles using moist air

This work investigated the generation of high-temperature steam by feeding saturated moist air through a steam generation system containing a zeolite 13X packed bed. The use of moist air was a unique aspect, which demonstrated a novel approach to steam generation system design. The issue with the steam generation system in previously existing published research works is that it needs high regeneration energy. In order to solve this issue, it is desirable to employ moist air as the working medium. In order to better understand the physical processes involved, numerical modeling of zeolite energy storage was also performed in addition to the experimental work. As the result, when the temperature of the moist air was raised from 30 to 95 °C, the maximum temperature of the resulting water vapor reached to about 200 °C. The maximum temperature of the water vapor was not greatly affected by the superficial velocity of the moist air between 0.108 and 0.216 mN/s. In the case that the moist air temperature was high, the maximum temperature of water vapor could be predicted based on correlations between the heat balance and adsorption equilibrium, assuming that temperatures of the moist air and zeolite were identical. The numerical technique also included a comparison between Arrhenius and linear driving force models. At higher temperature input moist air, both models resulted the close tendency.

Investigation of the microstructure and corrosion resistance of hydrothermal-synthesized MFI zeolite coating on H13 steel

Three different processes (non-3-aminopropyltriethoxysilane (APTES) pretreatment followed by one-step hydrothermal synthesis, APTES pretreatment followed by one-step hydrothermal synthesis, APTES pretreatment followed by two-step hydrothermal synthesis) were used to synthesize an MFI zeolite coating on mechanically polished H13 steel to improve corrosion resistance. The coatings synthesized by the different processes were remarkably different in terms of zeolite particle size, thickness, density, and corrosion resistance. In the case of the MFI zeolite coating synthesized on non-APTES-pretreated H13 steel, a non-dense gel layer and poorly intergrown zeolite particle layer lowered adhesion strength and corrosion ability, whereas the presence of the APTES film increased the density of the gel layer. Consequently, it showed better adhesion strength, and corrosion resistance with a lower corrosion current density (Icorr) and higher impedance value at 0.01 Hz. The adhesion strength and corrosion resistance of the MFI zeolite coating was further enhanced by two-step hydrothermal synthesis because the gel layer became denser and thicker in the early stages of secondary synthesis. The molten immersion test also indicated that the MFI zeolite coating had a high corrosion resistance in molten aluminum.

Microstructural engineering of zeolite membranes through composite seed layers

MFI membranes were synthesized using composite seeds consisting of zeolite nanocrystals and amorphous silica nanoparticles. The weight compositions of zeolite and silica particles were tuned to 100/0, 75/25, 50/50, and 25/75, respectively, which were then deposited as seed layers on porous alumina support through rubbing. At the seeded growth condition at 135 °C for 24 h, the film thickness of zeolite membranes grown from 4 different seed layers was similar to 3 μm, along with preferential crystal orientation to (h 0 h) direction. The upper parts of the zeolite membrane shared comparable film characteristics independent of seed composition, according to FCOM images of the MFI membranes. On the other hand, the zeolite membrane prepared from a seed layer of 75 wt% zeolite and 25 wt% silica particles had the greatest N2/SF6 gas selectivity of >175 and N2 gas permeance of >3300 GPU. Porosimetry also showed that there are fewer non-zeolite pathways in the zeolite membrane. Such results were attributed to differences in silica loading in the seed layer, where the silica species effectively altered the microstructure of zeolite membranes. The grain size of zeolite membranes increases as silica particle loading increases, reducing the chance of non-zeolitic defects occurring at grain boundaries. The composite seed with a silica loading of 25% was particularly successful because it did not inhibit the intergrowth of zeolite seed crystals while sacrificing slight N2 gas permanence. Thus, adding silica nanoparticles to the seed layer can help reduce non-zeolite defects in MFI membranes, according to this research. Further research is needed to prove that this method can be applied to zeolite membranes with other zeolite frameworks.

Microporous carbon coated zeolite particles for efficient carbon capture from wet flue gas

Carbon capture plays an important role in reducing CO2 emissions, and selective adsorption of CO2 is attracting more and more attention. Consider the fact that the actual flue gas always contains the water molecule which is preferentially adsorbed onto the pore surface of adsorbent, resulting in a significant reduction of CO2 capacity and selectivity. In this contribution, we design and prepare a series of microporous carbon coated commercial zeolite 13X particles (13X@MPC) by pyrolysis of polyvinylidene fluoride (PVDF) where the uniform microporous layer is coated on the surface of zeolite 13X beads. After coated with microporous carbon layer, zeolite 13X turns into hydrophobic from hydrophillic. An optimized sample (13X@MPC(25,550)) displays a high CO2 uptake (76.2 cm3 g−1) similar to 13X (80.5 cm3 g−1) and a low H2O uptake (157.1 cm3 g−1) half to 13X (315.2 cm3 g−1). The ideal CO2/N2 selectivity is predicted as 215 by using the ideal adsorption solution theory. The breakthrough separation experiment further verifies the excellent carbon capture ability of 13X@MPC(25,550) from wet flue gas, where the CO2 capacity (26.5 cm3 g−1) and CO2/N2 selectivity (56.2) are greatly improved to zeolite 13X (6.8 cm3 g−1 and 12.5) under the same condition. The results of this paper can be extended to other water-containing gas separation, such as air separation, natural gas purification, etc.

Hydration kinetics of clinoptilolite zeolite blended ternary cementitious materials with fly ash and metakaolin

The typical characteristics of hydration kinetics for the natural zeolite blended cementitious system may be impacted due to the varied sources and compositions of the zeolite particles. Previous research reported that the substitution of portland cement with natural clinoptilolite zeolite substantially minimized the tricalcium aluminate (C3A) peak heat of hydration apart from the regular matrix of the hydration kinetics, an indication of the potential interaction of zeolite particles in the blended system. Therefore, the present study investigated the suitable reasons for minimizing C3A peak heat of hydration in the blended system replacing the portland cement with clinoptilolite zeolite up to 20% by mass. Similarly, class C fly ash and metakaolin were utilized up to 20% by mass to observe the hydration kinetics of the zeolite blended ternary cementitious system. Additional 5% gypsum replaced the portland cement in the zeolite mixed system to verify the undersulfation. The heat of hydration was observed via isothermal conduction calorimetry. Phase identification of hydration products was done by x-ray diffraction (XRD) analysis at an early age of 3 days. Results revealed that the minimized C3A peak heat of hydration was not due to the undersulfation. Results also revealed that the zeolite blended ternary samples (i.e., cement-zeolite-class C fly ash, and cement-zeolite-metakaolin) obtained a relatively higher C3A peak heat flow and an increased duration for the monosulfate formation compared to the binary (i.e., cement-zeolite) samples. Likely, zeolite particles had a relatively slow chemical dissolution compared to the class C fly ash and metakaolin particles which supplied comparatively reduced amounts of alumina in the system in the early ages. The XRD results indicate the potential formation of a new hydration product (calcium-aluminum–silicate-hydrate), which likely consumed a reasonable amount of aluminate leading to a minimized C3A peak heat of hydration in the clinoptilolite zeolite blended system.

Effect of treated clinoptilolite zeolite on alkali-silica reaction

The reactive aggregates can cause a volumetric expansion in the concrete leading to cracking and spalling due to alkali-silica reaction (ASR). The use of natural zeolite as the supplementary cementitious material can reduce the expansion due to ASR by providing physical space for the ASR gel along with the adsorption of alkalis through the cation exchange. However, the rate of reduction in expansion may sometimes not be satisfactory due to the slow rate of cation exchange along with other factors. Therefore, the present study investigates three different treatment techniques (calcination, milling, and chemical pre-treatment) on clinoptilolite zeolite to obtain an optimal method for reducing the expansion due to ASR. Calcination was done at 400 °C for 3 h to increase the amorphous contents, while milling was done for 3 h to increase the specific surface area of zeolite particles leading to increasing pozzolanic activities. The chemical pre-treatment was accomplished with a 1 M Ca(OH)2 solution to largely remove any existing sodium or potassium ions via cation exchange. To observe the physical expansion due to ASR, mortar bars were prepared with highly reactive cherty sand and up to 20% of both untreated and treated zeolite with the replacement of the portland cement. Results revealed that calcination slightly increased the amorphous contents while milling substantially increased the specific surface area of zeolite particles. The chemical pre-treatment successfully transformed the zeolite into calcium-based clinoptilolite zeolite. Results also revealed that the application of up to 20% untreated, calcined, milled, and chemically treated zeolite reduced the ASR expansion by up to 60%, 40%, 70%, and 42%, respectively, compared to the control sample at 28 days. Overall, among the three different treatment methods, milling was the most effective method to reduce the ASR expansion, while calcined and chemically treated zeolite was less effective than untreated zeolite.