Good Frost Resistance Research Articles

Recycled coarse aggregate from parent concrete with supplementary cementitious materials under freeze-thaw environment: Recyclability, environment and economic evaluation

In order to improve the utilization efficiency of waste concrete in cold regions, this paper studied the properties of parent concrete (PC) and its recycled coarse aggregate (RCA) based on ordinary Portland cement (OPC), fly ash (FA), silica fume (SF), and ground granulated blast-furnace slag (GGBS) combination optimization in freeze-thaw (F-T) environment. The influence of supplementary cementitious materials (SCMs) on the frost resistance of PC was analyzed by compressive strength and relative dynamic elastic modulus. The recyclability potential of RCA was evaluated by the apparent density, water absorption, crushing index and attached mortar content. In addition, the phase composition and microstructure of RCA were analyzed by XRD and SEM, respectively, and the degradation mechanism of PC during F-T process was analyzed. Finally, the environment and economic benefits from cradle to cradle is analyzed. The results showed that PC containing SCMs had good frost resistance. The PC with a binder system of 75 % OPC +15 % FA + 10 % SF had the smallest F-T damage at 0.068, and its RCA quality could be upgraded from Class III to II after mechanical grinding. This combination of cementitious materials reduced harmful pores in concrete and inhibits the development of cracks during F-T cycles. In addition, it had a carbon emission 18 % lower than that of traditional concrete, with cost-effectiveness of 1.054. This research can provide a low-carbon and economic strategy for the preparation and recycling of waste concrete in cold regions.

Dual-stimuli-responsive, anti-freezing, and conductive ionic hydrogels for smart wearable and outdoor UV radiation monitoring devices

Many studies have shown that a certain amount of UV radiation can help the human body synthesize vitamin D. However, prolonged exposure of the skin can cause erythema, inflammation, and skin aging. In recent years, UV monitoring equipment has attracted extensive interest from researchers, and accurate monitoring of UV intensity is a core element of UV monitoring equipment. It is important to display outdoor UV intensity in a simple, convenient, and effective way. However, the development of UV/stress dual-responsive ion-conductive hydrogels with excellent conditioning capabilities for wearable devices remains a major challenge. In this work, we successfully fabricated a gelatin-glycerol-ammonium sulfate (GGS) ionic conductive hydrogel with excellent mechanical properties: high tensile strength of 330 kPa (elongation at break of 225%), high transparency of 90%, good frost resistance (−50 °C), heavy plasticity, and good conductivity. This GGS organic hydrogel has dual responsiveness to UV light and strain. Moreover, the GGS hydrogel has stable electrical signal output in different joint movements, which suggests that it can be used to monitor physiological signals and human movement. Photochromic-GGS hydrogel can achieve reversible color change in response to UV stimulus, and can be used as an outdoor UV intensity indication device. Other than that, the GGS hydrogel also exhibits good re-molding, recyclability, and reusability. Low-cost photochromic-GGS hydrogel's simultaneous stability and environmental friendliness allows GGS hydrogel to be used as a green and sustainable smart material. To the best of our knowledge, these combined features cannot be realized by conventional strategies. Thus, our design strategy for GGS ion-conducting hydrogels promises to be a new generation of "smart" multi-stimuli-responsive hydrogels for visualization of UV-responsive devices, interactive wearables, and visual display devices.

Review on the Role of Rubber on the Performance of Concrete

Due to the rapid development of the vehicle manufacturing industry, the hazards caused by scrap tire rubber have become one of the serious problems faced by people today. Rubber concrete is made of waste rubber into different particle sizes to replace the fine aggregate in ordinary concrete formed by a new type of composite material, for the disposal of waste tires and rubber opened up a new way, so that waste rubber can be reused. Rubber concrete compared to ordinary concrete has Light weight, good elasticity, high toughness, ductility, impact resistance, good damping, good frost resistance, but its strength is reduced. From the perspective of mechanical properties, durability and modification treatment, the article introduces the research progress of its compressive strength, frost resistance, carbonation resistance, modification treatment, etc., which provides a method for rubber concrete to be used in a wider range of practical projects.

Tough conductive cellulose organohydrogels with antifreezing capability, strain-sensitivity and for multi-functional sensors

The mechanical strength of traditional hydrogels is weak, and it is easy to freeze and harden below zero to lose the characteristics and conductivity of hydrogels, which seriously limits the application of hydrogels in sensors. To solve this problem, an organic hydrogel was prepared using a simple method. After testing, this organic hydrogel not only has good frost resistance but also has excellent mechanical properties. Cellulose-based hydrogels have received increasing attention as good materials for preparing flexible, wearable sensors due to their good biocompatibility, flexibility, and excellent mechanical strength. We polymerized 4-carboxy benzaldehyde (FBA) and polyvinyl alcohol (PVA) into gels under acid-catalyzed conditions, imparted freeze resistance to the hydrogels by introducing dimethyl sulfoxide (DMSO) into the hydrogels, and added water-soluble cellulose acetate (WSCA) to the hydrogels to enhance the mechanical properties of the hydrogels. The organic hydrogel prepared by this method is more stable than conventional hydrogel in low-temperature environments, even below − 80゜C can still maintain the soft state and good mechanical flexibility of the hydrogel, of which WSCA can enhance the mechanical properties, and the stress of the hydrogel can reach 0.85 MPa when the WSCA content is 2%, which is 2.5 times that of the hydrogel without WSCA. In addition, the prepared hydrogel also has good electrochemical performance, under the condition of − 80゜C, connected to the circuit, the small bulb can still maintain a weak brightness. Moreover, the sensor composed of hydrogels can distinguish vigorous movement and weak movement of the human body, which provides a new idea for the application of hydrogels on the sensor.

Physical and Mechanical Properties of Expanded Polystyrene (EPS) Particle Lightweight Soil under Freeze-Thaw Cycles.

In seasonally frozen regions, the bearing capacity of soil decreases and gradually deteriorates after undergoing freeze-thaw cycles. To resolve this problem, based on the idea of frost-resistant filling materials, a filling scheme of expanded polystyrene (EPS) particles lightweight soil in cold regions was proposed. Unconfined compressive strength, direct shear, and micro-SEM tests were carried out to study the physical and mechanical properties of EPS particles lightweight soil under freeze-thaw cycles. The results indicate that the EPS particle lightweight soil has good frost resistance and can be used as frost-resistant filling material in cold regions. Under freeze-thaw cycles, EPS particle lightweight soil maintains good integrity; EPS particles can effectively reduce the frost heave rate, mass loss rate, and compressive strength loss rate of lightweight soil. The compressive strength depends on the EPS and cement contents: it decreases with an increase in the EPS content and increases with an increase in the cement content. The strength loss rate decreases with an increase in both. When the content of EPS is larger (more than 2%), the soil cement bound with EPS particles is limited, and the performance of lightweight soil decreases. The shear strength and cohesion decrease with an increase in freeze-thaw cycles and EPS content, and the internal friction angle follows no obvious rule with regard to the increase in freeze-thaw cycles but decreases with an increase in the EPS content. Based on the experimental results, an empirical formula for the compressive strength of EPS particle lightweight soil under freeze-thaw cycles was proposed. This study can provide a reference for the engineering design and application and provide new ideas for resolving freeze-thaw problems in construction engineering in cold regions.

High-Strength, Freeze-Resistant, Recyclable, and Biodegradable Polyvinyl Alcohol/Glycol/Wheat Protein Complex Organohydrogel for Wearable Sensing Devices.

The application of flexible wearable sensing devices based on conductive hydrogels in human motion signal monitoring has been widely studied. However, conventional conductive hydrogels contain a large amount of water, resulting in poor mechanical properties and limiting their application in harsh environments. Here, a simple one-pot method for preparing conductive hydrogels is proposed, that is, polyvinyl alcohol (PVA), wheat protein (WP), and lithium chloride (LiCl) are dissolved in an ethylene glycol (EG)/water binary solvent. The obtained PVA/EG/WP (PEW) conductive organohydrogel has good mechanical properties, and its tensile strength and elongation at break reach 1.19 MPa and 531%, respectively, which can withstand a load of more than 6000 times its own weight without breaking. The binary solvent system composed of EG/water endows the hydrogel with good frost resistance and water retention. PEW organohydrogel as a wearable strain sensor also has good strain sensitivity (GF = 2.36), which can be used to detect the movement and physiological activity signals in different parts of the human body. In addition, PEW organohydrogels exhibit good degradability, reducing the environmental footprint of the flexible sensors after disposal. This research provides a new and viable way to prepare a new generation of environmentally friendly sensors.

Frost Resistance and Shrinkage Characteristics of Soil Stabilized by Carbide Slag and Coal Gangue Powder

With the increase of expressway construction in seasonal frozen soil region, the freeze-thaw problem of subgrade soil has attracted more and more attention. In addition, the comprehensive utilization of industrial solid waste has become an important measure to build a resource-saving and environment-friendly society. In order to improve the frost resistance of subgrade soil and realize the resource utilization of industrial solid waste, carbide slag (CS) and coal gangue powder (CG) were applied to the subgrade soil. The unconfined compressive strength (UCS) test, freeze-thaw cycle test, dry shrinkage test, temperature shrinkage test and scanning electron microscope (SEM) test were carried out on CS-CG stabilized soil with a ratio of CS:CG = 70:30 and dosages of 5%, 10% and 15%. The freeze-thaw cycle degradation model of CS-CG stabilized soil was constructed to show the freeze-thaw deterioration mechanism after the mechanical properties, pore structure, and durability characteristics of the stabilized soil were examined. The results showed that the CS-CG stabilized soil had good frost resistance. After 6 freeze-thaw cycles, the UCS at 7d and 28 d was 2.86 MPa and 3.79 MPa, respectively, which were 22.6% and 35.5% lower than in samples that underwent no freeze-thaw action. The CS-CG stabilized soil had good crack resistance, slightly better dry shrinkage strain than lime stabilized soil, and excellent temperature shrinkage performance. With the increase of CS-CG dosage, the hydration products increased continuously. After freeze-thaw cycles, however, large pores and cracks gradually appeared in the stabilized soil, which led to an increase of porosity and pore diameter, and a decrease of pore abundance. Due to the influence of hydration degree, the porosity change at 7 d was less than that at 28 d. There was a f(n)/f0=βexp−λΔh relationship between UCS residual ratio and porosity variation of the CS-CG stabilized soil, and it had a good correlation. The CS-CG stabilized soil had good frost resistance and shrinkage characteristics, and could replace traditional cementitious materials such as Portland cement (PC) and lime for subgrade soil improvement in regions with seasonal frozen soil. Future research needs to focus on the performance regulation of CS-CG stabilized soil, which can make it more widely used.

Comparison between the Influence of Finely Ground Phosphorous Slag and Fly Ash on Frost Resistance, Pore Structures and Fractal Features of Hydraulic Concrete

Hydraulic concrete in cold regions is necessary for good frost resistance. The utilization of finely ground PS (FGPS) in the construction of hydropower projects could solve the pollution issue and the fly ash shortage problem. In this work, the influence of FGPS and fly ash on frost resistance, pore structure and fractal features of hydraulic concretes was investigated and compared. The main results are: (1) The inclusion of 15–45% FGPS reduced the compressive strength of plain cement concretes by about 21–52%, 7–23% and 0.4–8.2% at 3, 28 and 180 days, respectively. (2) The inclusion of FGPS less than 30% contributed to the enhancement of 180-day frost resistance. At the same dosage level, the FGPS concrete presented larger compressive strengths and better frost resistance than fly ash concrete at 28 and 180 days. (3) At 3 days, both the addition of FGPS and fly ash coarsened the pore structures. FGPS has a much stronger pore refinement effect than fly ash at 28 and 180 days. The correlation between frost resistance of hydraulic concrete and pore structure is weak. (4) At 28 days, the incorporation of FGPS and fly ash weakened the air void structure of hydraulic concrete. At 180 days, the presence of FGPS and fly ash was beneficial for refining the air void structure. The optimal dosage for FGPS and fly ash in terms of 180-day air void refinement was 30% and 15%, respectively. The frost resistance of hydraulic concretes is closely correlated with the air void structure. (5) The pore surface fractal dimension (Ds) could characterize and evaluate the pore structure of hydraulic concretes, but it was poorly correlated with the frost resistance.

Study on Evolution Law of Pore Structure and Frost Resistance of High-Performance Activated Cement-Based Composites in Severe Cold Area

In order to explore the frost resistance of high-performance activated cement-based composites(HACC), The freeze-thaw cycle test of HACC with different water-binder ratio and basalt fiber content was carried out, the mass loss rate, relative dynamic elastic modulus and related pore structure parameters of different freeze-thaw cycles were measured, and the influence of different factors on the frost resistance of HACC was studied, and the variation law of pore structure parameters with freeze-thaw cycles was explored. The results show that the mass loss rate of high performance cement-based composites has a small range, the maximum is less than 1% during failure, and the relative dynamic modulus changes significantly, which is the main indicator to evaluate the freeze-thaw failure of HACC; The frost resistance of HACC decreased gradually with the increase of the water-binder ratio, and showed a change rule of first increasing and then decreasing with the increase of basalt fiber content; HACC have good frost resistance when the air content is 3% ~ 4%. The bubble chord length is directly related to the freeze-thaw deterioration characteristics of HACC, and the bubble chord length reflects the frost resistance of HACC to some extent.

Experimental Study and Microscopic Analysis on Frost Resistance of Iron Ore Tailings Recycled Aggregate Concrete

Freeze-thaw harm is the major factor that reduces the durability of hydraulic concrete buildings at high altitudes and in cold regions. To solve the durability problem of hydraulic buildings in alpine regions, the study prepared sixteen groups of concrete specimens with different replacement ratios of iron ore tailings and recycled aggregate were prepared, and indoor deterioration accelerated tests were designed. Nuclear magnetic resonance (NMR) technology was used to analyze the pore distribution in the structure, and macro indicators of concrete mass loss rate and relative dynamic elastic modulus (RDEM), were selected. Combined with SEM, images, the frost resistance of iron ore tailings sand (IOT), with Recycled aggregate concrete (RAC), was explored. The final analysis shows that when only RCA is replaced, the frost resistance of RAC decreases with the increase of the RCA replacement rate. When only replacing IOT, the frost resistance of IOT concrete with a replacement rate of 50% is better than that of other replacement rates. In addition to ordinary concrete, the combination of 30% iron ore tailings and 30% recycled aggregate concrete (RAC3-IOT3) has good frost resistance. The mass loss of the RAC3-IOT3, specimen increased by 0.09% compared with ordinary concrete. From the microscopic level, with the addition of the dosage of RCA, the number of macropores (0.05∼1 μm) and microcracks (>1 μm) in concrete increased. After replacing the appropriate amount of iron ore tailings, the pore space structure of RAC was improved, and some harmful pores spaces were transformed into harmless pores. However, the combination of excess IOT, and RCA, does not improve the interface transition zone of RCA. From the micromorphology, with an increasing dosage of RCA, the bonding force between cementitious material and sand aggregate weakens and there are more pores. The combination of excess IOT, and RCA, does not improve the interface transition zone of RCA but will accelerate the spalling of surface mortar because of its small fineness. All things considered, RAC3-IOT3 is the most suitable concrete for high altitude and cold areas.

Hydrophobically/oleophilically guarded powder metallurgical structures and liquid impregnation for ice mitigation

Icing hazards often pose operational and safety challenges. Various surface and coating approaches have been attempted for ice mitigation purposes, but the durability remains an outstanding issue. Inspired by traditional powder metallurgy and slippery icephobic surfaces, a new strategy for slippery liquid-impregnated porous metallic structure (LIPMS) with gradient porosity was proposed in this study for ice mitigation, by directly impregnating selected liquids into sintered porous copper components with hydrophobic/oleophilic guarding consideration. The results indicated that robust LIPMS with desired porosity were obtained, significantly delaying the icing of surface water droplets, providing good frost resistance in a high humid environment, and demonstrating ultra-low ice adhesion strength (less than 1 kPa). It was confirmed that the hydrophobic/oleophilic guarding design significantly improved icephobic durability, attributing to its role in repelling external water and maintaining internal slippery liquid. To offer a comprehensive understanding of icephobic mechanisms and the potentials of LIPMSs, a concept of ice initiation position was also proposed and theoretically discussed. The pivotal factor of icephobic LIPMS is to maintain the icing initiation position at the unfrozen liquid–liquid interface or inside the homogeneous liquid, thus inhibiting icing and facilitating the ice removal.

Bond properties of basalt fiber reinforced polymer (BFRP) bars in recycled aggregate thermal insulation concrete under freeze–thaw cycles

In this study, recycled aggregate thermal insulation concrete (RATIC) with good frost resistance and basalt fiber reinforced ploymer (BFRP) bars were used to overcome the corrosion of recycled aggregate concrete (RAC). First, the influence of recycled coarse aggregate (RCA) and glazed hollow beads (GHBs) on the basic mechanical properties of concrete under freeze–thaw (FT) cycles was studied. Second, through FT cycle tests, the freeze–thaw resistance of four kinds of concrete (normal concrete, RAC, GHB thermal insulation concrete, and RATIC) was determined and the apparent morphology, mass loss rate, relative dynamic elastic modulus, and durability coefficient were obtained and analyzed. Finally, the bond performance between BFRP bars and four kinds of concrete under different FT cycles was investigated by center pull-out tests. The effects of RCA and GHBs on the failure mode, ultimate bond strength, peak slip, and bond slip curve of concrete were analyzed. The research results show that RCA has adverse effects on the mechanical properties, freeze–thaw resistance, and bond properties of RAC. The reasonable addition of GHB can compensate for the adverse effects of RCA and significantly improve the freeze–thaw resistance of concrete. GHB can also improve the bond properties between BFRP bars and RAC under freeze–thaw cycles. The combined use of BFRP bars and recycled aggregate thermal insulation concrete is an important way to effectively solve the problem of steel bar corrosion in structural engineering in severely cold areas.

Stretchable, self-adhesive, conductive, anti-freezing sodium polyacrylate-based composite hydrogels for wearable flexible strain sensors

The vigorous development of flexible sensors, wearable electronic devices, and human-computer interaction techniques has promoted the construction of flexible, stretchable, and conductive hydrogels. However, due to the lack of self-adhesion and environmental adaptability, these hydrogels still face huge challenges in accurately and stably monitoring human motions as flexible sensors. In this paper, a multifunctional hydrogel of poly(sodium polyacrylate-dopamine based methylacrylamide)/polyvinyl alcohol (i.e., P(AAS-DAAM)/PVA) with the properties of stretchable, self-adhesive, conductive, and anti-freezing was synthetized by introducing methacrylic acid modified dopamine into sodium polyacrylate crosslinked network, and combine with a physical cross-linked network of the polyvinyl alcohol. The hydrogel exhibits excellent stretchability (>1000%), the higher conductivity (0.038 ± 0.003 S·cm−1), good frost resistance (−30°C) and excellent adhesion (419.3 ± 5.95 N/m) and remarkable biocompatibility (relative cell viability up to 132 ± 2.63%). The results indicate that P(AAS-DAAM)/PVA hydrogel can be used as a flexible sensor. Moreover, P(AAS-DAAM)/PVA-based strain sensor not only can stably and repeatedly monitor the changes of different strains (50% ~ 200%) with high sensitivity (GF = 1.65), but also stable and accurate monitoring capabilities for large joint bending (fingers, wrists, elbows, knees) or small physical (swallowing, speaking) activities. This hydrogel preparation strategy strongly promotes the development of new multifunctional hydrogels and hydrogel-based flexible sensors and other equipment to a new step.

Influence of iron tailing powder on properties of concrete with fly ash

The influences of iron tailing powder (ITP) on slump, compressive strength, drying shrinkage, carbonation resistance, chloride permeability, frost resistance and sulfate attack of concrete with fly ash were investigated. The incorporation of ITP enhances cohesiveness of concrete with small loss of slump. Partial replacement of fly ash with ITP increases early-age compressive strength but decreases later-age compressive strength of concrete. Increasing ITP content has little effect on early-age drying shrinkage but decreases total shrinkage within 180 days. The carbonation resistance is improved and the good frost resistance of concrete is obtained by adding ITP. The chloride permeability grade of concrete cannot be affected when the proportion of ITP replacing fly ash does not exceed 50%. The best resistance to sulfate attack is obtained when 50% fly ash is replaced by ITP. Decreasing water/binder ratio is advantageous to improving mechanical properties and durability of concrete containing fly ash and ITP.

Evaluation of Freeze-Thaw Durability of Silica Fume Concrete with Spraying Inorganic Coating Using Ultrasonic Testing

To study the antifreezing durability of internal coating silicon fume concrete with different external coatings, fast freeze-thaw (FT) cycle testing was performed for three types of external coatings applied to the internal coatings of silicon fume concrete. Using ultrasonic testing and compressive strength tests, we analysed the relationships between the ultrasonic pulse velocity and the mechanical and physical properties of concrete under freeze-thaw action. The results show that the compressive strength and pulse velocity of the studied concrete changed little before the first 100 FT cycles but varied significantly after being subjected to 100 FT cycles and diminished linearly with increasing FT cycles. The dynamic elastic parameters of the concrete were inferred using pulse velocity calculations, and the dependence on FT cycles was very similar to that of ultrasonic pulse velocity. The concrete strength was strongly and positively correlated with ultrasonic pulse velocity. The linear regression model of between ultrasonic pulse velocity, kinetic coefficient, and compressive strength of concrete was also established. The damage incurred to the external coating material (XT-HPA + XT-SS and XT-HPS) was small, and the good performance of the concrete with the added inorganic coating after freeze-thaw cycles indicates good frost resistance.

Synthesis and Characterization of Epoxidized Silkworm Pupae Oil and Its Application as Polyvinyl Chloride.

More and more industries demand environmental friendliness. Silkworm pupae oil (SPO), extracted from the desilked silkworm pupae, can serve as a promising substrate alternative to use in plasticization. This study aimed to prepare epoxidized silkworm pupae oil (ESPO) and investigate their effects on the thermal stability and plasticization of polyvinyl chloride (PVC) films. A chemo-enzymatic method of ESPO was developed in the presence of Lipase SMG1-F278N and H2O2 in natural deep eutectic solvents (DESs). Lipase SMG1-F278N could initiate the epoxidation reaction effectively at room temperature with a negligible loss of activities 10 batches. A maximum oxirane value of 6.94% was obtained. The formation of oxirane ring in ESPO was confirmed by FTIR and 13C NMR spectra. Moreover, ESPO showed a better thermal stability and lower freezing point than epoxidized soybean oil (ESO). It was demonstrated that ESPO had a good frost resistance. In addition, ESPO showed a significantly improved plasticizing effect on flexible polyvinyl chloride (PVC). Compared with ESO, ESPO could increase the tensile elongation at break effectively. A significantly lower migration rate of plasticizer was observed in PVC plasticized with ESPO.

Novel chemically cross-linked chitosan-cellulose based ionogel with self-healability, high ionic conductivity, and high thermo-mechanical stability

Developing flexible electrochemical devices with high-performance electrolytes by using natural renewable polymer is of great significance for meeting green and sustainable energy requirements. Here, a new type of chemically cross-linked ionogel based on natural chitosan and cellulose with good self-healability has been designed by a two-step method in ionic liquid. The rheological and dynamic mechanical analysis tests revealed that the as-prepared ionogel exhibited excellent thermo-mechanical stability even when the temperature was as high as 150 °C. Furthermore, the obtained ionogels showed good frost resistance, and still could maintain excellent flexibility even when the temperature was as low as − 20 °C. More importantly, the ionogel showed superior room temperature ionic conductivity (up to 2.1 mS/cm) and retained high electrical performance over a temperature range from − 50 to 120 °C. Additionally, the ionogel was used as electrolyte for preparing flexible supercapacitors and showed good performance under high temperature and harsh mechanical conditions. Such an ionogel, based on natural polymers with robust mechanical properties, high ionic conductivity, self-healability, and wide working temperature range, could be very useful for next-generation sustainable electrochemical devices.

EPOXY-CONTAINING ADDUCTS OF ROSIN ASLIGHT- AND THERMOSTABILIZERS FOR PVC

The thermo- and light-stabilizing activity of glycidyloxycarbonyl- and glycidyloxymethylsubstituted derivatives of the sulphur-containing rosin in the compositions on the basis of plasticized polyvinyl chloride were studied. It found that the proposed epoxy-derivative adducts of rosin possess thermal stability allowing them to withstand the processing temperature of polyvinyl chloride compositions. The developments showed that the proposed stabilizers can protect the polymer matrix against light radiation. It revealed that the film samples prepared with the help of the proposed stabilizers showed the high thermal stability, impact resistance, good frost resistance and mechanical strength.

Stress on Steel-concrete Composite Truss Joints Research Status and Application Overview

Based on the comprehensive analysis of various stress research schemes for steel-concrete composite truss joints, the current research status of steel-concrete composite truss joints and epoxy resin concrete at home and abroad are systematically elaborated. The existing problems in the current composite truss joints are analyzed, and possible solutions are proposed. At present, the research on epoxy resin concrete has been very extensive. Epoxy resin concrete has high strength, good toughness, high impact strength, good chemical corrosion resistance, wear resistance, water resistance, frost resistance, tensile resistance and compressive resistance, which make it widely used in engineering. The problem of using epoxy resin concrete instead of ordinary concrete in steel-concrete composite truss is put forward, analyzed and discussed.

Experimental Determination of Frost Resistance of Autoclaved Aerated Concrete at Different Levels of Moisture Saturation

The ability of porous building materials to stand up to moisture phase changes induced by alternating environment is described mostly by means of their frost resistance. However, the test conditions defined by relevant standards might not capture the real situation on building site in various locations. In particular, the prescribed full water saturation of analyzed specimens during the whole time of a freeze/thaw experiment presents an ultimate case only but certainly not an everyday reality. Even the materials of surface layers are mostly exposed to such severe conditions just for a limited period of time. In this paper, the experimental analysis of frost resistance of three different types of autoclaved aerated concrete (AAC) is performed in an extended way, including not only the standard testing but also the investigation of dry- and partially saturated samples. A complementary computational analysis of an AAC building envelope in Central European climate is presented as well, in order to illustrate the likely hygric conditions in the wall. Experimental results show that according to the standard test the loss of compressive strength, as well as the loss of mass after 25 cycles, is acceptable for all studied samples but after 50 cycles only the material with the compressive strength of 4 MPa performs satisfactorily. On the other hand, the tests with initially dried or partially saturated samples indicate a good frost resistance of all studied materials for both 25 and 50 cycles.