High Curing Temperature Research Articles

Properties of Blended Cement Containing Iron Tailing Powder at Different Curing Temperatures.

The properties of blended cement containing 0%, 20%, and 50% iron tailing powder (ITP) at 20 °C and 60 °C were investigated by determining the hydration heat, microstructure, and compressive strength. The addition of ITP decreases the exothermic rate and cumulative hydration heat of blended cement at 20 °C. The high temperature increases the hydration rate and leads to the hydration heat of blended cement containing 20% ITP higher than that of Portland cement. Increasing the amount of ITP decreases the non-evaporable water content and Ca(OH)2 content as well as compressive strength at both of the two studied temperatures. The addition of ITP coarsens the early-age pore structure but improves the later-age pore structure at 20 °C. The high temperature significantly improves the early-age properties of blended cement containing ITP, but it is detrimental to the later-age properties development. The reaction of ITP is limited even at high temperature. The large ITP particles bond poorly with surrounding hydration products under early high-temperature curing condition. The properties of blended cement containing a large amount of ITP are much poorer at high temperature.

Catalytic Polymerization of Phthalonitrile Resins by Carborane with Enhanced Thermal Oxidation Resistance: Experimental and Molecular Simulation.

Biphenyl phthalonitrile (BPh) resins with good thermal and thermo-oxidative stability demonstrate great application potential in aerospace and national defense industries. However, BPh monomer has a high melting point, poor solubility, slow curing speed and high curing temperature. It is difficult to control the polymerization process to obtain the resins with high performance. Here, a BPh prepolymer (BPh-Q) was prepared by reacting 1,7-bis(hydroxymethyl)-m-carborane (QCB) with BPh monomers. The BPh-Q exhibited much better solubility, faster curing speed and lower curing temperature compared with pure BPh and BPh modified with bisphenol A (BPh-B, a common prepolymer of BPh). Thus, the polymerization process of BPh was greatly accelerated at a low temperature, resulting in a BPh resin with enhanced thermostability and oxidation resistance. The experimental and theoretical models revealed the promotion effect of B-H bond on the curing reaction of phthalonitrile via Markovnikov addition reaction due to the special steric structure of carborane. This study provided an efficient method to obtain low-temperature curing phthalonitrile resins with high thermal and thermo-oxidative resistance, which would be potentially useful for the preparation of high-performance cyanide resin-based composites.

Study on carbonation resistance and micromechanism of shotcrete in high geothermal tunnels

The internal structure of shotcrete is often damaged under variable high-temperature curing conditions. To study the carbonation resistance and microscopic mechanism of shotcrete in high geothermal tunnels, accelerated carbonation tests were performed under different initial curing conditions (40 °C, 60 °C, 80 °C, relative humidity 55%). The results show that with increasing curing temperature, the carbonation rate is faster due to the increase in microcracks and pores in shotcrete caused by variable high-temperature curing. It is speculated that 60 °C is a critical point. When the curing temperature exceeds 60 °C, the carbonation resistance of shotcrete more significantly decreases. A carbonation depth prediction model including curing temperature was established. With increasing carbonation age, the mechanical strength of shotcrete increases, but the splitting tensile strength decreases at a later stage. The carbonation reaction will produce CaCO3-based carbonation products and fill microvoids to make the shotcrete structure denser.

Low Viscosity and High Strength Room Temperature Cured Epoxy Structural Adhesive Based on Different Amine Curing Agents

Low Viscosity and High Strength Room Temperature Cured Epoxy Structural Adhesive Based on Different Amine Curing Agents

Effect of high volume fly ash and curing temperature on delayed ettringite formation

Considering their good performance and environmental friendliness, fly ash based construction materials have great potential as an alternative to ordinary Portland cement. This study investigates the effect of using reactive mineral admixtures such as fly ash as cement replacement on delayed ettringite formation through high volume fly ash mortar cast in the laboratory and exposed to a high curing temperature over a 28-days study period. The delayed ettringite formation (DEF) is seen as a form of internal sulfate attack of cementitious materials, it is a chemical reaction that can cause damage to concrete heated to a temperature above about 70 °C. To achieve the aim of this study, a portion of cement was replaced by class F fly ash with 50% by mass of binder under both standard curing conditions and heat treatment curing conditions. Experiments involved the mechanical strengths and as well as microstructural characteristics.

Preparation and Characterization of High Temperature Resistant Polyimide Films

To prepare high temperature resistant polyimide thin films, we have discussed the synthesis of high-purity diamine precursors in this study. We have prepared polyamide acid solutions first via two-step solution-based polymerization of heat-resisting diamine and dianhydride, and then obtain polyimides after dehydration during a high temperature curing process. The thermal, mechanical and hygroscopic properties of four polyimides thin films were tested and compared.

Experimental Evaluation of the Mechanical Properties of Cement Sheath under High-Temperature Conditions

The sealing integrity of cement sheath in offshore wells is seriously threatened under high-temperature conditions, resulting in gas channeling and other problems. Given the lack of experimental results, in this study relevant samples of a cement slurry sealing section of a typical offshore high-temperature well have been prepared and analyzed. In particular, the mechanical properties have been assessed with a triaxial pressure servo instrument and a high-temperature curing kettle. The density and the Poisson’s ratio of the samples have also been tested. The stress-strain curve has been drawn to obtain the elastic modulus and the compressive strength. The rock brittleness index has been calculated according to the measured elastic modulus and the Poisson’s ratio, together with the brittleness and the compressibility of the cement samples. The test results show that the mechanical properties and bonding strength of the cement samples are optimal at 130°C, medium at 150°C, and poor at 180°C.

Steel slag aggregate concrete filled-in FRP tubes: Volume expansion effect and axial compressive behaviour

Using steel slag as concrete aggregate is an effective, eco-friendly method of steel slag disposal. However, the volume expansion of steel slag aggregates (SSAs) creates premature cracks and reduces the mechanical property and durability of concrete, limiting steel slag aggregate concrete (SSAC) applications. A concrete filled-in fiber-reinforced polymer (FRP) tube (CFFT) is a structural member that exploits the high tensile strength of FRP and the lateral expansion of concrete under compression. FRP tubes can be used for the external confinement of concrete to increase its strength and ductility. In this paper, a steel slag aggregate concrete filled-in FRP tube (SSACFFT) is proposed for steel slag disposal. The physical and mechanical properties of an SSACFFT were investigated experimentally. The volume changes in the SSAC and SSACFFT during high-temperature curing were measured using 3D laser scanning. The results showed that the SSAs in concrete expand and cause cracking/spalling during hydration, which is effectively restrained by the FRP tube. The strength, failure modes and stress–strain relationships of the SSACFFT were investigated via axial compression tests. Finally, the SSACFFT was proposed as a prefabricated structural component called FRP-tube-confined concrete core encased prestressed rebar (FCCC-PR) to capitalize on the volume expansion characteristic of SSAC.

Study on Mechanical Properties of Basalt Fiber Shotcrete in High Geothermal Environment.

With the development of infrastructure, there are growing numbers of high geothermal environments, which, therefore, form a serious threat to tunnel structures. However, research on the changes in mechanical properties of shotcrete under high temperatures and humid environments are insufficient. In this paper, the combination of various temperatures (20 °C/40 °C/60 °C) and 55% relative humidity is used to simulate the effect of environment on the strength and stress–strain curve of basalt fiber reinforced shotcrete. Moreover, a constitutive model of shotcrete considering the effect of fiber content and temperature is established. The results show that the early mechanical properties of BFRS are improved with the increase in curing temperature, while the compressive strength at a later age decreases slightly. The 1-day and 7-day compressive strength of shotcrete at 40 °C and 60 °C increased by 10.5%, 41.1% and 24.1%, 66.8%, respectively. The addition of basalt fiber can reduce the loss of later strength, especially for flexural strength, with a increase rate of 11.9% to 39.5%. In addition, the brittleness of shotcrete increases during high temperature curing, so more transverse cracks are observed in the failure mode, and the peak stress and peak strain decrease. The addition of basalt fiber can improve the ductility and plasticity of shotcrete and increase the peak strain of shotcrete. The constitutive model is in good agreement with the experimental results.

On the early behavior and microstructure of oil well cement paste incorporating with carbon nanotubes cured at a high temperature

With the rapid development of shale gas/oil exploitation, hostile downhole condition asks for more flexible and ductile oil well cement paste (OWCP). This study is devoted to investigating the influence of multi-walled carbon nanotubes (MWCNTs) on the rheological behavior, early mechanical properties and volume stability of OWCP by means of different experimental methodologies. Multiple microstructural techniques are employed to further understand the reinforcing mechanism of MWCNTs on the performances of OWCP. The results show that the optimal dosage of MWCNTs is 0.6wt.‰. The rheological behavior of MWCNTs/OWCP slurry at low shearing rate is improved after the addition of 0.6wt.‰MWCNTs. The mechanical properties and autogenous shrinkage of MWCNTs/OWCP composites are enhanced after the addition of the optimal dosage of MWCNTs, MWCNTs/OWCP composites with addition of 0.6wt.‰MWCNTs exhibit more flexible and ductile than plain OWCP. The additional nucleation sites provided by MWCNTs, the role of bridging effect and pull-out effect by MWCNTs, and the high curing temperature are all responsible for the enhanced mechanical properties of MWCNTs/OWCP composites. Owing to the addition of MWCNTs, the relationship between the compressive strengths of MWCNTs/OWCP composites and gel/space ratios does not exhibit exponential form. However, the addition of MWCNTs does not alter the Avrami-type exponential relationship between the degree of hydration and curing ages, moreover, it does not alter the linear relationship between the mercury intrusion porosity and gel/space ratio.

Electrical resistivity stability of CNT/cement composites after further hydration: A simple evaluation with an accelerated method

A series of simple, short-term experiments were conducted, utilizing an accelerated testing method, to investigate the long-term reliability of the electrical properties of carbon nanotube (CNT)/cement composites after further cement hydration and the corresponding alkali attack on CNTs. The CNTs were exposed to an alkali solution at high temperatures, their chemical structures were evaluated using X-ray photoelectron spectroscopy, and their electrical properties were evaluated via cyclic voltammetry. The hardened CNT/cement composite specimens were cured in high-temperature water and their electrical resistivities were measured. The non-evaporable composite water content was measured to evaluate the increase in hydration degree via high-temperature water curing. The resistance of the CNT networks scarcely changed, even under the strong alkali conditions of the pore solution; the electrical resistivity of the cement composites with well-dispersed CNT networks remained unchanged. The findings indicate that the CNT/cement composites exhibit acceptable electrical stability for practical sensors.

Study of chemical and thermal activations of zeolite-lime blend

The advantages of using zeolites are lower costs and better durability, but it requires longer setting time and slower strength development. Chemical and thermal methods have been developed to overcome these disadvantages and to enhance the reactivity of natural zeolite. This paper addressed through a parametric experimental pozzolanic reactivity, the strength and setting time by varying the cure temperature and the amount and type of chemical activators. To this end, several mixtures of natural zeolite-lime pastes were made with two concentrations of chemical activators including 4% and 8% of NaOH, NaCl, and CaSO4.2H2O. The produced pastes were cured at 20, 40, and 80 °C. The blends were also analyzed by X-ray diffraction and infrared spectroscopy. The results showed that curing at high temperatures accelerated the pozzolanic reactivity and increased the compressive strength. The use of CaSO4.2H2O led to an increase in the consumption of Ca(OH)2 and strength. Adding NaCl improved slightly the compressive strength at high curing temperatures. The addition of 8% NaOH at 40 °C significantly improved reactivity and strength. Setting time was accelerated by adding chemical activators to the blends. The raw zeolite had good pozzolanic activity, but the addition of CaSO4.2H2O enhanced it.

Response surface methodology for multi-objective optimization of fly ash-GGBS based geopolymer mortar

Neat fly ash based geopolymer require high temperature curing to obtain satisfactory properties. In order to improve its workability and mechanical properties under room temperature curing, taking ground granulated blast furnace slag (GGBS) substitution, alkaline solution to binder (S/B) ratio, and Na2SiO3 to NaOH solution ratio (SS/SH) as independent variables and compressive strength, flexural strength, and setting time as response target values, the response surface method (RSM) is used to design the test and establish the regression model. The multi-objective optimization of the comprehensive properties of geopolymer mortar was realized, followed by the verified experiments of the proposed optimized mix. To investigate the microstructure and composition of the hydration products, the optimally proportioned and neat fly ash based specimens were tested by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the quadratic polynomial model was fitted with high accuracy and the GGBS substitution has a significant effect on the setting time and strength of the geopolymer. The compressive and flexural strengths were 80.46 MPa and 11.98 MPa when the slag was mixed at 75%, S/B = 0.45, and SS/SH = 1.5, which was 9% and 14.8% higher than the strength of neat fly ash based geopolymer mortar maintained at high temperature curing. SEM results show that the geopolymer added with GGBS performs a denser microstructure, which confirms the effectiveness of RSM in determining the optimal mix parameters of geopolymer.

Mechanical, microstructure and reaction process of calcium carbide slag-waste red brick powder based alkali-activated materials (CWAAMs)

The paper attends to the utilization and performance improvement of waste red brick powder activated by calcium carbide slag (CCR). Therefore, the improvement of mechanical properties and microstructure of calcium carbide slag-waste red brick powder based alkali-activated materials (CWAAMs) by silica fume, composite activator and curing temperature was explored. Compressive strength tests, reaction process and microstructural analysis were performed including Fourier transform infrared, X-ray diffraction, scanning electron microscope-energy dispersive X-ray spectroscopy and thermogravimetry. The results showed that the compressive strength of CWAAMs increases by 8 times that of CWAAMs without silica fume, resulting from that silica fume increased the stacking speed and yield of C-S-H gel, making the structure of CWAAMs compact. Through the microscopic analysis of the reaction products in the reaction process, it is found that high alkali concentration and high-temperature curing conditions can promote the alkali-activated reaction to proceed faster. Furthermore, the 28d compressive strength of the CWAAMs reached 46.70 MPa curing at 100 °C for 1 d. Because the high concentration of Ca2+ and Na+ ions of the composite activator (CCR and NaOH solution) may produce synergistic effect curing at high temperature, forming massive C-S-H and (C, N)-A-S-H gel to fill the space between the particles, thus forming a more compact paste structure.

Nanostructured and Advanced Designs from Biomass and Mineral Residues: Multifunctional Biopolymer Hydrogels and Hybrid Films Reinforced with Exfoliated Mica Nanosheets.

Transforming potential waste materials into high-value-added sustainable materials with advanced properties is one of the key targets of the emerging green circular economy. Natural mica (muscovite) is abundant in the mining industry, which is commonly regarded as a byproduct and gangue mineral flowing to waste rock and mine tailings. Similarly, chitin is the second-most abundant biomass resource on Earth after cellulose, extracted as a byproduct from the exoskeleton of crustaceans, fungal mycelia, and mushroom wastes. In this study, exfoliated mica nanosheets were individualized using a mechanochemical process and incorporated into regenerated chitin matrix through an alkali dissolution system (KOH/urea) to result in a multifunctional, hybrid hydrogel, and film design. The hydrogels displayed a hierarchical and open nanoporous structure comprising an enhanced, load-bearing double-cross-linked polymeric chitin network strengthened by mica nanosheets possessing high stiffness after high-temperature curing, while the hybrid films (HFs) exhibited favorable UV-shielding properties, optical transparency, and dielectric properties. These hybrid designs derived from industrial residues pave the way toward sustainable applications for many future purposes, such as wearable devices and tissue engineering/drug delivery.

The impact of sulfate- and sulfide-bearing sand on delayed ettringite formation

With the increase of aggregate quarrying to meet the growing need for concrete construction comes a risk associated with new aggregate sources, which may not have uniform compositions and contain potentially harmful substances, such as sulfate and sulfide. To provide insights into the impact of sulfate- and sulfide-bearing sand on susceptibility to delayed ettringite formation (DEF), this study measures the evolution of expansion, acoustic nonlinearity (representing microscale damage), and dynamic elastic modulus of mortars prepared with varying cement compositions and exposed to an early-age high-temperature curing cycle. Samples containing sulfate- and sulfide-bearing sand show substantially higher initial levels of damage, with expansion starting at earlier ages than control samples. Damage in mortars using this sand can be attributed to accelerated decomposition of alkali-feldspar, microcracking due to relative thermal deformation between phases, early release of alkali that increases the amount of sulfate in the pore solution, and release of sulfate ions from aggregates.

Preparation and Characterization of Self-Healing Polyurethane Powder Coating Using Diels-Alder Reaction.

Although powder coating systems offer many environmental, ecological and energy related benefits over liquid based coatings, in the case of uretdione based polyurethane systems, high curing temperature is still an issue. On the other hand, powder coating systems make it possible to reduce the costs and enhance the process of forming complex 3D structures using the deep drawing method by pre-coated metal substrates. During this processing method, there is a probability of micro crack formation in the coated film due to strain impact on the coating layer. A powder coating with self-healing ability is an ultimate solution to face not only this kind of fraction but also any other possible ones (such as defects caused by any impact on film surface during processing, transporting or even service). Here, a single molecule that is prepared via Diels–Alder cycloaddition reaction and retro Diels–Alder cleavage reaction was utilized as a self-healing additive to achieve self-healing ability in the powder coating system that is based on a commercially available uretdione cross-linker and OH-polyester resin. Coatings were prepared through melt mixing of components in a lab mixer, milling, sieving, and then application on the metal substrate through the electrostatic spraying method. To illustrate the role of self-healing additive, various concentrations (4 and 9% wt.) in combination with different curing temperatures (80 °C to 200 °C) were investigated. Both samples containing HA showed self-healing ability at elevated temperature around 120 °C for about 30 min with acceptable roughness and surface properties. Hardness measurement of cured film as well as thermal investigation indicate the chemical reaction of HA in a cross-linked network of cross-linker and resin. In addition, using HA leads to a 40 K drop in curing temperature of the system without using any catalyst. A 2.58% improvement in hardness values at a lower curing temperature and healing time of around 12.5 min at 120 °C to recover 100% of initial scratch (more than 10 cycles) in the sample containing 9% wt. HA was observed.

Direct writing of continuous carbon fibers/epoxy thermoset composites with high-strength and low energy-consumption

Epoxy resin-based thermoset composites are extensively used in industries with billions of dollars in revenue every year. High-rate manufacturing process is highly sought-after to produce complex composite structures with geometric flexibility and low energy-consumption. This work demonstrates printing and in-situ cure of epoxy resin-based thermosets and composites via self-sustaining frontal propagation. Specifically, latent initiator in the resin formulation was tuned from 2 mol% to 0.05 mol% to lower the frontal propagation temperature from ~290 °C to ~240 °C without decreasing the reaction rate. The epoxy resin was soaked into continuous carbon fiber (CF) tows and then printed through a modified direct ink writing system. Synchronization of the printing process and in-situ frontal curing resulted in continuous CF/thermoset composites (c-CFTC). Both single and dual nozzle print-heads were used to print c-CFTC with tunable fiber volume fractions. As-printed specimens exhibited exceptional tensile strength, 1.15 GPa at 48 vol% fibers and 0.42 GPa at 18 vol% fibers in fiber direction and ~35.5 MPa in transverse direction. The energy consumption of the printing process was also calculated, indicating 3.6 billion kilowatt-hours (kWh)/year energy-saving in comparison to conventional manufacturing processes with hours of high-temperature oven curing, equivalent to the energy consumption of 360,000 US families per year (single US family electric consumption: 10,000 kWh/year). The printing speed was 7.5–13.8 cm/min dependent on the fiber fraction, and thus the production rate was estimated to be 400–800 cm3/hour. Such a high-rate and energy-saving approach could revolutionize the c-CFTC industry and aerospace, automobile, and marine industries with environmental and energy sustainability.

Experimental Manufacturing Methods of Glass Fiber Composites Considering Flexural Behaviour

Fiber-reinforced plastic laminates (FRPL) and sandwich composites are outstanding materials due to its mechanical properties (i.e., light weight, low density and high strength to weight ratio). These applications are widely used in the fields of aviation, automotive and construction industries. The superior mechanical properties depend on the properties of reinforcing materials, matrixes and manufacturing processes. This research proposes the comprehensive study of mechanical properties of epoxy resin reinforced by glass fibers under different processes. Glass-fiber sandwich composites were manufactured by the hand lay-up process and cured in different methods (i.e., with and without vacuum bagging). The comparison between curing temperature and pressure is investigated using the vacuum bagging process to determine the mechanical properties under flexural tests. Experimental tests are performed using the universal testing machine (UTM). As a result, it is confirmed that the hand lay-up process affects the flexural stress, deflection and internal force of both fiber-reinforced plastic laminates and sandwich composites. At the high curing temperature, the vacuum bagging method significantly provides the greater flexural stress, deflection and load

High-Density Patterned Array Bonding through Void-Free Divinyl Siloxane Bis-Benzocyclobutene Bonding Process.

Divinylsiloxane-bis-benzocyclobutene (DVS-BCB) has attracted significant attention as an intermediate bonding material, owing to its excellent properties. However, its applications are limited, due to damage to peripheral devices at high curing temperatures and unoptimized compressive pressure. Therefore, it is necessary to explore the compressive pressure condition for DVS-BCB bonding. This study demonstrates an optimization process for void-free DVS-BCB bonding. The process for obtaining void-free DVS-BCB bonding is a vacuum condition of 0.03 Torr, compressive pressure of 0.6 N/mm2, and curing temperature of 250 °C for 1 h. Herein, we define two factors affecting the DVS-BCB bonding quality through the DVS-BCB bonding mechanism. For strong DVS-BCB bonding, void-free and high-density chemical bonds are required. Therefore, we observed the DVS-BCB bonding under various compressive pressure conditions at a relatively low temperature (250 °C). The presence of voids and high-density crosslinking density was examined through near-infrared confocal laser microscopy and Fourier-transform infrared microscopy. We also evaluated the adhesion of the DVS-BCB bonding, using a universal testing machine. The results suggest that the good adhesion with no voids and high crosslinking density was obtained at the compressive pressure condition of 0.6 N/mm2. We believe that the proposed process will be of great significance for applications in semiconductor and device packaging technologies.