Durability Problems Research Articles

Assessment of the efficiency of distinct surface treatments to mitigate ASR-induced development

Over the years, various coating materials have been used to mitigate/rehabilitate concrete once alkali-silica reaction (ASR) takes place. Although promising results are demonstrated, their efficiency is compromised by the progression of ASR and crack formation. Recently, new coatings with higher penetrability and enhanced self-healing properties have shown good performance against distinct durability problems in concrete, yet their behaviour under ASR development is unknown. This research appraises the ability of hydrophilic self-healing coating (CA) mixtures to mitigate concrete deterioration caused by ASR in its initial, moderate and advanced phases. Their efficiency is multi-level assessed, and comparisons with other systems (e.g., silane/siloxane, rigid-coating and lithium-based) are also performed. Results indicate that the surface treatments with CA changed ASR kinetics while not altering the ASR mechanism of deterioration. Finally, qualitative charts are provided to help select different types of surface treatments and the most appropriate “timing” for their application.

Rheology control of cement paste by in-situ polymerization for 3D printing applications

Rheology control is the most critical determinant of success in 3D concrete printing (3DCP), typically achieved through the hydration control of cement. However, this inevitably leads to overdesign of printed concrete featuring a low water-to-binder ratio (w/b), which is incompatible with its non-load bearing purpose and raises a series of environmental and durability problems, such as high carbon footprint and early-age shrinkage. Herein, we propose a novel rheology control strategy via in-situ polymerization, allowing the mix design of printed concrete with a high w/b ratio of 0.6. The proposed approach consists of two stages: 1) introducing monomers as retarders to extend the open time during pumping, and 2) incorporating initiators into the mixture to trigger polymerization, facilitating the structural build-up after deposition by forming polymer bridges between cement particles. We show that the addition of monomers significantly retards yield stress growth, while the following in-situ polymerization engenders a rapid strength development, satisfying the rheological requirements for 3DCP. Mechanistic experiments reveal that the retarding effect results from the complexation of monomers with aqueous species, such as Ca2+ ions, thereby hindering the nucleation of hydrates. As polymerization initiates, the impetus for the structural build-up of the cement pastes first originates from the proliferation of polymer bridges due to the gradual formation and adsorption of polymer, and then relies on the reinforcement of these polymer bridges through the formation of chemical bonds or crosslinks. On top of the environmental benefit, the proposed strategy holds the potential in avoiding admixtures conflict, mitigating early-age shrinkage, and improving mechanical properties. Our strategy opens possibilities for a novel technical route to achieve rheology control of 3DCP, and the discovery in this work will be a landmark for revealing the mechanism of 3DCP via in-situ polymerization.

Multifunctional-structural integrated wood cellulose‑based composite with Magpie’s Nest-shaped enhance flame retardancy and electromagnetic interference shielding

The construction of multifunctional hydrophobic wood with electromagnetic interference shielding effectiveness had attracted great interest, at the same time, the problem of wood flammability must also be solved. In this study, the effectiveness of DOPO-based P and Zn complexes in improving wood flame retardancy and electromagnetic interference shielding effectiveness, and the outstanding contribution of lignocellulose skeleton and multi-interface to shielding effectiveness was demonstrated. DOPO-based P and Zn complexes with “Needle-punched” structure and much functional groups were loaded on the wood surface, and then micro-nano metal Ni particles were deposited. Through the optimization of the wood surface and itself structure, and the construction of a complete conductive network. Wood/ZnP/Ni composites electromagnetic interference shielding effectiveness couold reach 65.04 dB in the X-band. It was worth noting that the lignocellulose skeleton prepared by the top-down method and multi-interface structure increase electromagnetic interference shielding effectiveness by 10.71 % and 33.89 %, respectively. In addition, the synergistic effect of DOPO-based P and Zn complexes and the introduction of PDMS layer improved the flame retardancy (limiting oxygen index was 35.3 %) and hydrophobicity (contact angle was 133.07°), which avoided the wood poor durability problem in use. There was no doubt that it provided a new strategy for the preparation of novel materials with low-cost and extremely excellent electromagnetic interference shielding properties.

The key role of the second material's OER activity on MOR durability enhancement of the Pt alloys

Pt-based precious metal catalysts are generally regarded as the best catalyst materials for direct methanol fuel cells due to their high inherent methanol oxidation (MOR) activity. However, the commercial application of Pt catalyst is still facing with severe durability problem. The CO formed by the incomplete oxidation of methanol will occupy the Pt active site, hindering the further progress of the MOR reaction and causing the rapid attenuation of the activity. In this work, a MOR durability enhancement strategy that relation to the OER performance of the second materials M (M=Ni, Co, Fe and Cu) is reported. The precise electrochemical test results showed that the MOR durability of Pt-M alloy changes with the second material, which is related to the OER activity of M materials. The smaller the overpotential and tafel slopes of the M material, the better the MOR durability. Via M material screening, the Co element with the lowest OER overpotential among M promoted the Pt-Co alloy material with the highest MOR durability, resulting an excellent durability sustain 7000 times CV cycles with just 0.53 A mg−1Pt mass activity loss. According to the current generally accepted OER and MOR reaction mechanism, the association of MOR durability with OER activity is most likely derived from the same reaction step of M-OH formation, which played a key role on both reaction. This relationship between OER overpotential and MOR durability helps to screen the second material from the perspective of OER activity to improve the MOR durability of Pt catalysts, which is of great significance for the development of Pt-based CO-resistant MOR catalysts.

Numerical simulation of strengthening/deterioration and damage development of cementitious materials under sulfate attack environment

Cementitious materials exposed to sulfate environments often suffer from the combined effects of external sulfate attack and dry wet cycling. In order to predict the long-term performance of cement-based materials in sulfur rich environments, this paper aims to establish a numerical model that can reasonably characterize the degradation process of cementitious materials in sulfate environments. Using this model, we can address durability problems common to cementitious materials in real sulphate environments, such as determining the degree of corrosion, predicting the durability life of materials, and calculating the time to failure. The model consists of three parts: transportation, chemical reactions, and material damage. We establish the degradation model for cement-based materials in sulfate environments by considering ion diffusion, water convection, chemical reactions, accumulation of corrosion products, and the development of material strengthening/degradation. Compared with existing sulfate corrosion models, this model not only considers ettringite, but also takes into account the volume changes of gypsum formation, calcium leaching, and salt crystallization precipitation, which can more reasonably simulate the sulfate corrosion process in real environments. The model can reasonably simulate the distribution pattern of ion concentration, hydration products and corrosion products in the cementitious material, and on this basis calculate the porosity of the cementitious material. In order to make the simulation results more applicable to experimental and non-destructive testing results, the model uses easily obtainable relative dynamic elastic modulus to evaluate the degree of material strengthening/degradation and predict the durability life of the material.

Effects of mix composition on the mechanical, physical and durability properties of alkali-activated calcined clay/slag concrete cured under ambient condition

Alkali-activated concrete (AAC), a possible alternative to ordinary Portland cement (OPC), provides increased environmental advantages, notably lower carbon emissions. Likewise, similar to OPC, it faces durability problems under severe environments. This study evaluated the effectiveness and durability of alkali-activated concretes containing low-grade calcined clay and granulated blast furnace slag (GGBFS), using NaOH/KOH as activators and MgO and superabsorbent polymer (SAP) as additives. The study's focus was on their physical-mechanical characteristics and performance under accelerated carbonation and chloride diffusion. Findings showed that calcined clay-GGBFS alkali-activated concretes exhibited a compressive strength range of 41.2–53.3 MPa, positioning them as a viable concrete for many structural usages. Nevertheless, the modified-RCPT (10 V) and NT Build 492 tests showed all concretes falling into the "high chloride penetrability" category, with values exceeding 350 coulombs and 13.5 (×10−12 m2/s) for the non-steady-state migration coefficient (Dnssm). NaOH and sodium silicate led to higher compressive strengths compared to KOH. Furthermore, the chloride migration coefficient of alkali-activated concrete blends ranged from 55.68 to 121.14 (× 10−12 m2/s). The incorporation of 0.6 % SAP decreased compressive strength but improved the non-steady-state migration coefficient (Dnssm). Lastly, MgO-enriched samples showed the lowest water absorption and carbonation depth, attributed to the buffering action of magnesium phases, reducing carbonate formations, as revealed by XRD analysis.

Microstructured Self-Healing Flexible Tactile Sensors Inspired by Bamboo Leaves.

Wearable electronic devices with multifunctions such as flexible, integrated, and self-powered play a crucial role in the fields of health monitoring, motion monitoring, and human-computer interaction. However, their core basic components, flexible pressure sensors, face challenges including poor long-term stability and insufficient real-time sensing accuracy. In order to solve the challenges of long-term, stable, and accurate sensing of the sensor, this paper prepares polydimethylsiloxane (SHPDMS) with intrinsic self-healing property and designs a high-sensitivity self-healing capacitive flexible pressure sensor with dual microstructures (grating microstructured electrodes and microporous dielectric layer) as the substrate based on SHPDMS. Specifically speaking, the self-healing of the sensor under mild conditions was realized by introducing reversible imine bonds with low bonding energy into the polydimethylsiloxane (PDMS) flexible substrate, which solved the problem of the material's long-term service durability. A grating-like microstructure was introduced into the flexible electrode by using a spotted bamboo taro leaf as a template, and a dual microstructure sensor was constructed by combining it with a microporous dielectric layer doped with single-walled carbon nanotubes. This way reduces the elastic modulus of the dielectric layer, improves the dielectric constant of the sensor under loading, and thus significantly improves the sensor's sensitivity and extends the measurement accuracy in a low-stress range. The prepared self-healing flexible sensor achieves a sensitivity of 3.6 kPa-1, a minimum detection limit of 5 Pa, a response recovery time of less than 80 ms, and stability over 5000 cycles, which exceeds most previously reported silicone rubber-based capacitive flexible sensors.

Impact of typical environments in China's western mountainous areas on the durability of railway concrete: a review

PurposeThis study aims to analyze the impact mechanism of typical environments in China's western mountainous areas on the durability of railway concrete and propose measures to improve durability.Design/methodology/approachWith the continuous promotion of infrastructure construction, the focus of China's railway construction has gradually shifted to the western region. The four typical environments of large temperature differences, strong winds and dryness, high cold and low air pressure unique to the western mountainous areas of China have adverse effects on the durability of typical railway structure concrete (bridges, ballastless tracks and tunnels). This study identified the characteristics of four typical environments in the western mountainous areas of China through on-site research. The impact mechanism of the four typical environments on the durability of concrete in different structural parts of railways has been explored through theoretical analysis and experimental research; Finally, a strategy for improving the durability of railway concrete suitable for the western mountainous areas of China was proposed.FindingsThe daily temperature difference in the western mountainous areas of China is more than twice that of the plain region, which will lead to significant temperature deformation and stress in the multi-layered structure of railway ballastless tracks. It will result in cracking. The wind speed in the western plateau region is about 2.5 to 3 times that of the plain region, and the average annual rainfall is only 1/5 of that in the plain region. The drying effect on the surface of casting concrete will significantly accelerate its cracking process, leading to serious durability problems. The environmental temperature in the western mountainous areas of China is generally low, and there are more freeze-thaw cycles, which will increase the risk of freeze-thaw damage to railway concrete. The environmental air pressure in the western plateau region is only 60% of that in the plain region. The moisture inside the concrete is more likely to diffuse into the surrounding environment under the pressure difference, resulting in greater water loss and shrinkage deformation of the concrete in the plateau region. The above four issues will collectively lead to the rapid deterioration of concrete durability in the western plateau region. The corresponding durability improvement suggestions from theoretical research, new technology development and standard system was proposed in this paper.Originality/valueThe research can provide the mechanism of durability degradation of railway concrete in the western mountainous areas of China and corresponding improvement strategies.

Methylene Blue Degradation Using Non-Thermal Plasma

Methylene blue (C16H18ClN3) dye can be decomposed using non-thermal plasma. However, there is a problem in that the maintenance of electrodes and dielectrics is necessary due to the durability and heat generation problems due to the high temperatures. Therefore, in this study, a comparative experiment was performed between the flat DBD plasma module and the diffuser DBD module under the same conditions. For methylene blue decomposition, the characteristic changes in the air flow rate, ozone production rate, energy consumption rate, and decomposition rate were compared. In the experiment, 7 L water was placed in a 15 L reactor, and measurements were performed for approximately 1 h. We performed the same process by setting the initial methylene blue concentration to 143 mg/L. According to the results, the flat DBD module achieved a decomposition rate of 100% in 40 min, an energy yield of 46.7 g/kWh, and an ozone generation amount of 6.5 g/h. The diffuser DBD module achieved a decomposition rate of 90%, an energy production of 24.6 g/kWh, and an ozone generation of 1.97 g/h in 60 min.

Femtosecond Bessel laser beam induced concentric rings on SiC for circular symmetry wide-viewing angle structural color

The laser-induced structural coloring technique holds significant potential for various applications due to its precision, controllability, and versatility across different materials. However, laser-induced structural colors face the problems of durability, homogeneity and indistinguishability, which are not conducive to their application as large-scale identifiable markers. In this paper, an innovative approach has been developed to achieve a circular-symmetric structural color display on durable SiC surfaces by fabricating periodic concentric ring structure arrays using the sidelobe light field of a femtosecond zero-order Bessel beam. The research involved a systematic study of the effects of laser power and pulse number on SiC, along with a detailed analysis of the micro-nanostructures evolving on the SiC surface after laser scanning. Additionally, an examination of the characteristics of circular-symmetric structural color displays and their wide viewing angles in periodic circular structures was conducted. Finally, a comparison was made between the structural color display effects of a concentric ring structure generated by a single pulse and the Laser-Induced Periodic Surface Structures (LIPSS) generated by three pulses. This comparison underscores the potential application of alternating between the high saturation color of the concentric ring structure and the low saturation dark light of the LIPSS for anti-counterfeit coding purposes. The findings of this research present promising opportunities for low-cost mass manufacturing in anti-counterfeit labeling and the advanced processing of photonic devices using SiC.

Chemical resistance in acidic environments of alkali-activated lightweight composites based on secondary raw materials

The durability problems in Portland cement are related to decalcification of C–S–H; alkali-activated composites are proposed as alternative, focusing on acid exposure and resistance. They were prepared from recycled materials, basic oxygen furnace carbonated and desulfurization slags. The standard material is 100% metakaolin geopolymer compared to slag-based alkali-activated materials (AAMs) with and without reinforcement of fibers (basalt, and cellulose), added in 4 wt%. The acidic environments are H2SO4, HCl, and HNO3 N = 2.14 (10, 7.5, and 12.5 wt%, respectively). The chemical resistance is improved by the addition of basalt fibers. The decrease in weight loss is 48% in HNO3 and 47% in HCl for AAM-Bas sample, while for AAM-Cell it is 9% in HCl and 34% in HNO3. The compressive strength of the AAM and AAM-Bas samples remains constant after HCl attack, while this acid attacks cellulose samples, which are stable in HNO3 and have a compressive strength of 10 MPa.

A durable superhydrophobic surface with bud-particle structure prepared by one-step spray method

Superhydrophobic surfaces play an essential role in numerous applications such as anti-fouling, waterproofing, and drag reduction due to their water-repellent. However, for most fabrication methods, there are high requirements for the preparation process and conditions. Meanwhile, the superhydrophobic surfaces generally have the problem of insufficient durability. In this study, a one-step method to fabricate a stable superhydrophobic surface by spraying is proposed. A new bud-particle structure is obtained by modifying micron and nano Aluminium hydroxide(Al(OH)3) particles, which helps the coated surface to demonstrate excellent superhydrophobicity with the water contact angle ∼157.0° and rolling angle ∼2.0°, and it shows great repellency to water droplet impact. Due to the compatibility of Al(OH)3with the pretreatment substrate and the reinforcing effect of nanoparticles, the coating maintained the superhydrophobicity well in the sandpaper wear and the ultrasonic damage test, which reflects the outstanding robustness of the coating.Moreover,benefiting from the control of the wetting state by micronand nanoparticles doping,the coating showed an excellent underwater drag reduction effect in the rheometer experiment, with a drag reduction rate of ∼67.7 %. The one-step spraying method proposed is a simple and convenient way to create the surface with excellent superhydrophobicity and durability, which has great potential applications in improving metal surface oxidation resistance and underwater reducing drag.

SiO2 aerogel modified aggregates: Preparation, heat resistance and improvement mechanism

Modification of natural aggregates using SiO2 aerogel solution can not only radically reduce the rutting disease of asphalt pavement, but also avoid the problems of poor heat-resistant performance, mechanical strength and durability of ordinary heat-resistant aggregates. The effects of SiO2 aerogel solution type, modification method and SiO2 aerogel solution dosage on the thermal resistance and adhesion properties of SiO2 aerogel-modified aggregates (SM-Agg) were explored by orthogonal tests. Based on scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and infrared thermography, the surface micromorphology, elemental composition and dynamic thermal resistance properties of natural aggregate and SM-Agg were analyzed, respectively. The results showed that Both SiO2 aerogel solution type and dosage significantly affect the evaluation indexes and the modification of natural aggregates by soaking method using ZN-S type SiO2 aerogel solution with 15 % of the aggregate mass could obtain SM-Agg with good heat resistance and adhesion properties. The surface of SM-Agg was covered with a “gel layer” containing uniform and densely distributed SiO2 aerogel particles. The temperature of the top surface of the 18.3-mm-thick SM-Agg specimen gradually changed from 2.2°C higher than that of the natural aggregate to about 1.8°C lower than that of the natural aggregate within 60 min of heating at 55°C. The “gel layer” containing SiO2 aerogel particles forms one or more layers of three-dimensional heat-blocking mesh on the aggregate surface, which dramatically reduces the heat transfer area, prolongs the heat transfer path within the specimen, and increases the heat-reflecting capacity of the aggregate surface.

Experimental investigation and numerical simulation of chloride diffusion in rubber concrete under dry-wet cycles

Chloride erosion caused by the dry-wet cycles is one of the most significant factors leading to durability problems in concrete structures. In this paper, the diffusion behavior of chloride in rubber concrete with varying rubber content is studied by experimental investigation and numerical simulation based on setting up artificial dry-wet cycles exposure conditions. The determination of chloride concentration in rubber concrete is achieved through chloride concentration titration, and as a result, the surface chloride concentration and the apparent chloride diffusion coefficient are expressed as a function of time, thus providing a theoretical guide for Comsol Multiphysics to perform numerical simulations. The findings indicate that the chloride diffusion behavior in rubber concrete complies with Fick's second law and that rubber can effectively reduce the diffusion rate of chloride in rubber concrete. Furthermore, the surface chloride concentration and apparent chloride diffusion coefficient are fitted with high accuracy according to the experimental data, which ensures the precision of the numerical simulation. In addition, numerical simulation results indicate that the diffusion of chloride in rubber concrete is impeded by the aggregate, that is, chloride diffusion is faster in areas where the local aggregate volume fraction is small. Also, it is evident that the presence of interfacial transition zone (ITZ) negatively affects the resistance of rubber concrete to chloride diffusion.

DEVELOPMENT OF CONSTRUCTIVE DESIGN OF PICKLING UNITS FOR OPERATION IN HIGHLY AGGRESSIVE HOT SULPHURIC ACID SOLUTIONS

Problem statement. Technological process of metallurgical, pipe-rolling, chemical and other enterprises includes chemical treatment of metal products by pickling in hot (60–80 °C) sulphuric acid solutions with a concentration of 20–22 %. This treatment method is conducted in the pickling departments of enterprises in special containers (pickling units). Pickling solution of the specified concentration and temperature is a highly aggressive environment for all building structures made of traditional materials. Existing pickling units for chemical treatment of metal products do not ensure reliability and durability and are destroyed after 1-2 years of operation. Therefore, ferrous metallurgy enterprises that have pickling departments for chemical treatment of metal structures are classified as enterprises with a highly aggressive environment and their design should be developed with these conditions under consideration. The purpose of the work: Searching for and implementing mechanisms to improve the resistance of polymer concrete in aggressive environments in production. The object of research – is furan resins modified polymer concrete. The subject of the research – investigation of the particularities and improvement of constructive design for pickling baths made of materials based on polymer concrete in an aggressive environment and its implementation in production. Main part. Development of constructive design for technological pickling units made of structural corrosion-resistant material (furan resins modified polymer concrete). Conclusions. Pickling of metal products at ferrous metallurgy enterprises is conducted in highly aggressive hot sulphuric acid solutions of 20–25 % concentration at a temperature of 60–80 °C. Under the conditions of constant exposure to highly aggressive hot sulphuric acid solutions, even protection with chemically resistant materials does not ensure the required reliability and durability. To manufacture such structures, a new structural material is needed that combines chemical resistance with strength and durability. This material is a structurally chemical-resistant polymer concrete based on thermoset furan resins, which have high strength and universal chemical resistance, allowing us to solve the problem of reliability and durability of technological units for chemical treatment of metal structures at ferrous and non-ferrous metallurgy enterprises in a fundamentally new way. New constructive design for pickling units made of reinforced polymer concrete was developed in conjunction with shock-absorbing bars and an improved ventilation system, consisting of individual elements of full factory readiness weighing no more than 5 tonnes, which allows them to be transported and installed in operating pickling workshops using existing mechanisms.

Understanding the deterioration of hydration products in alkali-activated slag/Portland cement exposure to sulfate attack

The deterioration of different phases under sulfate attack is a critical durability problem for cementitious materials. Alkali-activated slag (AAS) is a kind of low carbon footprint cementitious material, whose hydration products are quite different from that of Portland cement (PC). The specific variations in the behavior of different hydration products under sulfate attack in PC and AAS have not been comprehensively explored. In this paper, a combination of BSE and EDS techniques was applied to investigate the change of various hydration products in PC and AAS before and after exposure to sulfate solutions. The results indicate that the unhydrated slag in AAS is more stable than the unhydrated C2S and C3S in PC paste after exposure to deionized water and sulfate solutions, and obvious substitution of Ca by Mg can be found for C2S and C3S after exposure to MgSO4 solution. In PC sample, the Ca/Si reduction of outer product after deterioration in different solutions is less significant than that of inner product, mainly due to the existing of Ca rich phases intermixed in Op. While in AAS, the change of Ca/Si in dark rims in different solutions is consistent with that of C-A-S-H presented in the matrix. After exposure to sulfate solutions, no significant sulfate rich area can be observed for AAS, which should mainly be attributed to the relatively slower formation of gypsum in AAS due to the absence of highly soluble calcium-rich phases like portlandite in PC.

Characteristics analysis of leakage diseases of Beijing underground subway stations based on the field investigation and data statistics

With a continuous increasing of the underground water level of Beijing, many leakage diseases induced by the structural defect have been exposed in the subway tunnels that have been put into operation. The leakage diseases of underground subway stations may severely cause the safety and durability problems of the structure. Moreover, it could affect the passenger experience and seriously threaten the operation safety. Therefore, this paper collected the leakage states of a total of 258 underground subway stations in 16 lines of Beijing by field investigation, which include the number of average leakage points, leakage types and classification, distribution scenes of leakage, the construction methods and operation ages of subway stations and so on. Besides, in order to further investigate the causes of the leakage diseases, three typical cases of Beijing subway stations with severe leakage diseases, which were constructed by different methods, were selected to carry out the statistical analysis of leakage disease. The typical positions of leakage diseases of Beijing subway stations with different construction methods were presented by three-dimensional modelling, and the leakage characteristics of each station were analyzed. Finally, based on the field investigation and data statistics, a data-based Bayesian network leakage prediction model to evaluate the leakage risk of subway stations was constructed. This research can provide an intuitive reference for early warning, monitoring and prevention of leakage diseases of metro subways in operation.

On-farm Evaluation and Selection of Manually Operated Honey Extractor

In the study area, honey is extracted using traditional methods, which leads the product to degradation in nutritional quality and quantity. As a result of this, honey extracted traditionally does not meet international market standards; to minimize this problem several honey extractors are available, but the problem of cost, maintenance place, and durability were the main issues for the farmers. Therefore, the main objective of this research work is to collect and evaluate the performance of available honey extractors and to select a better-performed model. Data like time of extraction (min), mass of honeycomb before and after extraction (kg), and mass of extracted Honey (kg) were collected. Losses (kg), Extraction efficiency (%), and Extraction capacity (kg/hr) were calculated. Simple descriptive statistics were used to analyze data. Accordingly, the mean extraction capacity was 68.28, 62.88, and 56.76 kg/hr, and the mean extraction efficiency was 71.39, 65.83 and 60.31 % for the Imported, Jimma Agricultural Engineering Research Center and Fadis Agricultural Research Center models, respectively. As depicted from the results all extractors have good performance. However, the Jimma Agricultural Engineering Research Center model will be recommended for small-scale holders based on its price, maintenance availability, spare parts, simplicity, and durability.

Low temperature carbonization, smoke suppression and durable flame retardancy of cotton fabric spray-assisted coated by phosphorus nitrogen silicon composite system

To solve the problems of flammability, smoldering, smoking and flame retardant durability of cotton fabric, flame retardant fininshing was executed using spray assisted self-assembly method, and P/N/Si synergistic flame retardant system was constructed by polyethylene imine (PEI), phytic acid (PA) and 3-aminopropyltriethoxysilane (APTES). Cotton cellulose carbonized at low temperature prompting by PA catalytic effect, and this cooperated with PEI thermal decomposition to endow cotton fabric with flame retardancy and smoking suppression by reducing its pyrolysis rate at high temperature and lessening combustible products. Meanwhile APTES as silane coupling agent further improved its flame retardant durability and smoke suppression effect. The synchronous thermal analysis results indicate that cotton fabrics treated by PA/PEI/APTES composite system present significant low-temperature carbonization trend, and their initial decomposition temperatures advance by 46.5℃-75.9℃. Moreover, they form 4.6 %-44.9 % aromatic structure char through dehydration and carbonization reactions during the low-temperature carbonization process, improving their thermal stability at high temperature, and their after-flame and smoldering phenomena disappear. The damaged length of treated fabric with five layers reduces to 5.0 cm, its limiting oxygen index reaches 33.7 %, and it presents excellent flame retardant durability and smoke suppression effect. This low-temperature carbonization mechanism possesses importantly innovative significance for the flame retardant finishing of cotton fabric, and it not only more actively guides the selection of flame retardants to make them match with the material required, but provides a new thinking method for flame retardant material research in the future.

Research Progress on Frost Durability of Rubber Recycled Concrete

Rubber recycled concrete is a new type of green concrete material that partially replaces natural coarse aggregate with recycled aggregate and partially replaces fine aggregate with rubber. Recycled rubber concrete not only improves the problem of poor frost durability of recycled concrete, but also solves the problem of large amounts of waste concrete and rubber difficult to deal with, as well as a series of ecological and environmental problems caused by this. Therefore, it is of great significance to carry out the research on the frost resistance of rubber recycled concrete to promote its application in cold regions. In this paper, based on the current status of domestic and international research on the freeze-thaw damage of rubber recycled concrete, the freeze-thaw damage mechanism of rubber recycled concrete is introduced, and its influencing factors and improvement measures are discussed, so as to provide a favorable basis for the research on the freeze-thaw damage of rubber recycled concrete.