Relative Dynamic Elastic Modulus Research Articles

Damage characteristics and constitutive model of concrete under uniaxial compression after Freeze-Thaw damage

In order to study the uniaxial compressive damage characteristics and stress–strain behavior of concrete with different degrees of freeze–thaw (F-T) damage, and then effectively evaluate the mechanical properties of concrete under different F-T damage degree. The rapid F–T cycle test was performed on different groups of concrete specimens, and an F–T damage evolution equation was established according to the change law of the relative dynamic elastic modulus. Uniaxial compression tests were performed on specimens with different F–T cycles, and damage evolution during compression was studied using an acoustic emission (AE) system. Finally, the AE characteristic parameters were used to establish a uniaxial compression constitutive model of concrete considering F–T damage. The results showed that the degree of F–T damage increased as the F–T cycles increased. During the concrete compression failure, the AE amplitude showed a more obvious and rapid rising trend when it was close to the critical state point. The proportion of low-amplitude AE events (≤50 dB) gradually decreased, whereas that of medium- and high-amplitude events exhibited a corresponding upward trend. These results indicate that the concrete after F–T damage exhibited more brittle characteristics during the compression failure process. The damage constitutive model established in this study can accurately reflect the damage evolution law of concrete during the entire process of uniaxial compression after F–T cycles. Moreover, the model was sufficiently consistent with test data, providing a reference for the design and safe operation of concrete structures in cold regions.

Performance evaluation and lifetime prediction of steel slag coarse aggregate concrete under sulfate attack

The durability of steel slag coarse aggregate concrete limits the application of steel slag in construction engineering. This study carried out the erosion test, material mechanics test, and microscopic test of steel slag coarse aggregate concrete under the action of different mass fractions of sulfate solution to investigate the effect law and mechanism of steel slag coarse aggregate on sulfate erosion resistance of concrete. The deterioration laws of performance indexes such as compressive strength, mass change, and relative dynamic elastic modulus of steel slag coarse aggregate concrete under sulfate erosion were investigated. X-ray diffraction (XRD) and Scanning electron microscope (SEM) were used to examine the erosion products and microstructure changes of samples before and after sulfate erosion, and the GM (1, 1) model of grey theory was used to forecast the service life of steel slag coarse aggregate concrete under various conditions. The results demonstrate that utilizing steel slag instead of coarse aggregate to prepare concrete may significantly alleviate the damage caused by the attack of sulfate solutions. And in 15% sulfate erosion environment, the maximum compressive strength increase rate of 20.7% was obtained when the steel slag substitution rate was 60%. Microscopic study reveals that the active components (such as dicalcium silicate (C2S) and tricalcium silicate (C3S)) in steel slag can promote the production of hydrated calcium silicate gel in concrete, improving the strength and durability of the material. To a certain extent, the addition of steel slag can improve the sulfate resistance of concrete. The prediction results of the GM (1, 1) model show that the service lifetime of concrete with 60% steel slag coarse aggregate substitution rate under sulfate solution erosion is better than that of the other three groups, and the predicted results are compatible with the experimental results.

Evaluation of molybdenum tailings as replacement for fine aggregate in concrete: Mechanical, corrosion resistance, and pore microstructural characteristics

This study explored the feasibility of molybdenum tailings (MTs) as an alternative to natural river sand for concrete production. Firstly, the compressive (fcu) and splitting tensile strengths (fsts) of molybdenum tailings concrete (MTs-C) and the relationship between the two were evaluated. Then, the corrosion resistance of MTs-C was investigated. This includes fcu loss, relative dynamic elastic modulus (RDEM) loss, and mass loss. Subsequently, the pore distribution under the sulfate freeze–thaw (F-T) cycle was tested by nuclear magnetic resonance (NMR). Besides, the pore evolution characteristics were visualized and quantified using industrial computed tomography (CT) techniques. Finally, the corrosion products were identified by X-ray diffraction (XRD). The results showed that the mechanical properties of concrete with 60% MTs only decreased by less than 10%. In the sulfate F-T environment, the corrosion resistance of MTs-C decreases as the replacement ratio of MTs increases, and it decreases significantly when the replacement ratio exceeds 60%. The porosity of MTs-C was the first to decrease and then increase with the F-T cycle, while the proportion of large pores gradually increased. Based on industrial CT scanning, it was further verified that the evolution of small pores to large pores is the main degradation mechanism of sulfate F-T cycles for the pore structure of MTs-C. Taking into account the mechanical properties, durability, and pore evolution, it was determined that 60% MTs replacement of natural sand for concrete production would be feasible.

Effect of multi-walled carbon nanotube on reactive powder concrete (RPC) performance in sulfate dry-wet cycling environment

Sulfate erosion is one of the most harmful chemical corrosions, which can cause the durability problem of a cement-based material. Multi-walled Carbon nanotubes (MWCNTs) are nanomaterials that can be utilized as an additive for cement-based material. However, the research on the durability of MWCNTs modified cement-based material under sulfate dry-wet cycles is rare. The purpose of this research is to understand the effect of MWCNTs on the mechanical and microstructure properties of reactive powder concrete (RPC) during dry-wet cycles with a high concentration of sulfate. The sulfate accelerated erosion phenomenon of RPC with or without carbon nanotubes were discovered. In this research, the degradation rule of RPC subjected to sulfate erosion was investigated from several directions including compressive strength changes, mass loss, and variation of relative dynamic elastic modulus (RDEM). Moreover, the microstructure and phase composition of RPC were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Inner pores and porosity were tested by X-ray computed tomography (CT) images. The results show that with the addition of MWCNTs, RPC showed better sulfate resistance and the type of sulfate is related to the property of corroded RPC. MWCNTs not only fill the pores and cracks within the samples, but also form bridges between cracks, which strengthens the resistance to sulfate attacks. In addition, the MgSO4 solution caused more expansion damage to RPC compared with the Na2SO4 solution in this research.

Study on the frost resistance durability of recycled aggregate concrete under an extreme cold environment

Recycled aggregate concrete (RAC), as a way to reuse waste concrete, is good for solving environmental and resource problems. In this paper, the frost resistance durability of RAC under an extreme cold environment was studied, RAC specimens with different replacement rates were designed, and then the indexes of the specimens, such as mass loss rate, were calculated and compared. It was found that with the progress of the freeze-thaw cycle, the higher the replacement rate of recycled concrete aggregate (RCA) was, the worse the frost resistance durability was. The mass loss rate of RAC-3 (100% RCA replacement rate) was 5.56%, the strength loss rate was 40.86%, and the relative dynamic elastic modulus was 61.89%, all of which were significantly lower than that of RAC-0. The experimental results verify that the excessively large replacement rate of RCA is not conducive to the frost resistance durability of concrete. The replacement rate of RCA needs to be paid attention to when used in an extremely cold environment.

Study of the Durability Damage of Ultrahigh Toughness Fiber Concrete Based on Grayscale Prediction and the Weibull Model

The purpose of this research is to investigate the durability damage law for ultrahigh toughness cementitious composites (UHTCCs) under freeze–thaw environments and impact resistance. In this study, UHTCCs with fiber length-to-diameter ratios of 5/30, 8/30, 12/20, 12/30 and 12/48 were tested for impact resistance and freeze–thaw cycles. The freeze–thaw cycle process and impact resistance process for UHTCC are comprehensively analyzed and evaluated in terms of mass loss, compressive strength loss, relative dynamic elastic modulus loss and impact resistance number. The freeze–thaw damage prediction model for the relative dynamic elastic modulus of the UHTCC is established based on the regularity of the measured data for the relative dynamic elastic modulus of UHTCC and also on the GM(1,1) power model. The accuracy and reliability of the GM(1,1) power model is analyzed using the relative error, absolute correlation degree, mean variance and probability of small errors. According to the evolution law of the impact resistance number of the UHTCC, the impact damage prediction model for UHTCC is established based on the Weibull distribution model, and the accuracy of the model is analyzed by using the decision coefficient R2. The results show that UHTCC has high durability performance, and the durability performance of UHTCC at a length-diameter ratio of 12/48 is optimal. The freeze–thaw damage evolution model and impact damage evolution model established in this research are sufficiently realistic, the average relative error of the GM(1,1) power model is less than 5%, and the coefficient of determination R2 of the Weibull distribution model is greater than 0.93, which effectively reflects the damage development process for concrete under freeze–thaw and impact environment with high fitting accuracy.

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.

Life Prediction of Iron Ore Tailings Concrete under Freeze-Thaw Cycle Based on Weibull Distribution

It is urgent to improve the comprehensive utilization rate of tailings, especially to solve the problem of fine iron ore tailings treatment and the shortage of natural sand, so iron ore tailings concrete with different replace rates was prepared in this paper. At the same time, in order to further popularize the wide application of iron tailings concrete, it is of great significance to study the frost resistance and life prediction of it in cold regions. Thereby, a series of experimental research on iron ore tailings concrete under freezing-thawing cycles was carried out to analyze the attenuation law of quality, compressive strength, and relative dynamic elastic modulus after different freezing-thawing cycles. In this paper, the relative dynamic elastic modulus was used to define the damage factor, and the freezing-thawing damage model of iron ore tailings concrete was established based on Weibull distribution. Here, the specific function form of two-parameter Weibull distribution of iron ore tailings concrete under freezing-thawing cycle was proposed, and the model was used to predict life of it. The results showed that, compared with the replacement rates of 20%, 60%, and 80%, the iron ore tailings with 40% replacement rate had the best improvement effect on the frost resistance of concrete and can delay the attenuation of the compressive strength of concrete. This model can not only predict the durability life of iron ore tailings concrete under freezing-thawing conditions, but also provide theoretical reference for the application of iron ore tailings concrete in cold areas.

Effect of carbonation curing on durability of cement mortar incorporating carbonated fly ash subjected to Freeze-Thaw and sulfate attack

High-calcium fly ash (HFA) is available in large quantity produced by coal-based electrical power plants. Up to now, the utilization of HFA in construction materials is limited. In this research, carbonation treatment of HFA in association with carbonation curing was applied for stabilization of hazardous residues and CO2 sequestration. The improvement on durability of carbonation-cured cement mortar incorporating carbonated HFA against coupled freeze–thaw and sulfate attack was investigated. The results show that the synergy of carbonation treatment and carbonation curing mitigated the deterioration of relative dynamic elastic modulus and compressive strength caused by coupling action of freeze–thaw and sulfate attack. The collaborative carbonation treatment and carbonation curing can also reduce the content of expansile free-CaO, as well as the components that would expand under sulfate attack conditions, such as CH and aluminates. On the other side, the results of MIP show that carbonation curing improved the pore structure and decreased the permeability of cement mortars specimens.

Effect of Graphene Oxide and Fly Ash on Frost Resistance of the Steel Fiber Reinforced Concrete

The addition of graphene oxide (GO) and fly ash (FA) to SFRC (steel fiber reinforced concrete) increases frost resistance. Based on the analysis of the amelioration of GO on the frost resistance of SFRC, the improvement mechanism and the effects of GO and FA on the durability of SFRC were studied in depth. The test blocks’ compressive strength, relative dynamic modulus of elasticity, and mass-loss rate were tested through experiments. The pore distribution and morphological characteristics of concrete were captured by industrial CT scanning technology. The effects of GO and FA on the pore distribution and morphology of the SFRC are discussed. The results show that the compressive strength of GO-SFRC(graphene oxide and steel fiber reinforced concrete)with GO proportion of 0.03% is 28.20% higher than that of ordinary SFRC without freezing and thawing; after 100 freeze-thaw cycles, the compressive strength of the G0.03S25 increased by 31.70% compared with the compressive strength of the G0.00S25, and pore shape of G0.03S25 presents a spherical shape and an elliptical spherical shape; based on the data analysis of the strength loss, relative dynamic elastic modulus loss and mass-loss rate, it is considered that the properties of ordinary SFRC are the worst under freezing and thawing; as FA admixture increases, the porosity decreases; with FA of 30% and GO of 0.03%, the GO-FA-SFRC has the best frost resistance, as well as most of the pores are closed which resemble spheres and ellipsoids.

Selecting Environment-Friendly Mineral Admixtures to Improve the Durability of Shotcrete under Sulfate Attack

The main purpose of this study was to explore the deterioration of shotcrete with different liquid accelerators and mineral admixtures under sulfate attack. By measuring the mass loss, compressive strength, and relative dynamic elastic modulus of shotcrete with liquid accelerators and mineral admixtures, the regularity of sulfate resistance of shotcrete was obtained. In addition, visual observation of surface macro-morphology of shotcrete was conducted. Compared with shotcrete with 4.0% AR and 7.0% AS, it was found that the overall surface condition of shotcrete with mineral admixtures was better in the presence of 7.0% AF. Meanwhile, the result of MIP analysis showed that adding 7.0% AF or 10% silica fume was more conducive to shotcrete compactness. Furthermore, the crystal composition and micromorphology of hydration products were analyzed by XRD, TG, and SEM. It was found that the addition of mineral admixtures could improve the sulfate resistance of shotcrete to varying degrees in the presence of different liquid accelerators.

Deterioration mechanism of coal gangue concrete under the coupling action of bending load and freeze–thaw

Coal gangue, as a solid waste produced in the process of coal mining, has caused great harm to the environment and society. It is the most practical means to make concrete as coarse aggregate. In practical engineering, concrete materials are often subjected to the combined action of external load and environmental factors. Simply considering the freeze–thaw effect cannot reflect the deterioration characteristics of coal gangue concrete, so that the popularization and application of coal gangue cannot be realized. Based on this, through bending load and freeze–thaw coupling test (stress level 0, 0.2, 0.4, 0.6, 0.8), the mass loss rate, relative dynamic elastic modulus, damage layer thickness, and compressive strength of coal gangue concrete with a replacement rate of 40% were analyzed. The degradation characteristics of pore structure and interface transition zone of coal gangue concrete were studied by nuclear magnetic resonance test and microhardness test. The effects of different stress levels on pore size distribution, pore grade ratio, pore fluid characteristics, and interface zone characteristics were analyzed. The results show that the larger the bending stress ratio is, the faster the degradation of compressive strength and relative dynamic elastic modulus of coal gangue concrete is, the faster the thickness of damage layer increases, the larger the proportion of large pores in the specimen is, and the pore connectivity is enhanced. In addition, the interface area between coal gangue aggregate and mortar is the weak position of coal gangue concrete, and its thickness and microhardness are widened and decreased with the increase of stress level. The deterioration of the interface area makes the specimen close to failure.

Experimental Study on the Salt Freezing Durability of Multi-Walled Carbon Nanotube Ultra-High-Performance Concrete.

Ultra-high-performance concrete (UHPC) is a new type of high-performance cement-based composite. It is widely used in important buildings, bridges, national defense construction, etc. because of its excellent mechanical properties and durability. Freeze thaw and salt erosion damage are one of the main causes of concrete structure failure. The use of UHPC prepared with multi-walled carbon nanotubes (MWCNTs) is an effective method to enhance the durability of concrete structures in complex environments. In this work, the optimal mix proportion based on mechanical properties was obtained by changing the content of MWCNTs and water binder ratio to prepare MWCNTs UHPC. Then, based on the changes in the compressive strength, mass loss rate, and relative dynamic modulus of elasticity (RDME), the damage degree of concrete under different salt erosion during 1500 freeze-thaw (FT) cycles was analyzed. The changes in the micro pore structure were characterized by scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The test results showed that the optimum mix proportion at the water binder ratio was 0.19 and 0.1% MWCNTs. At this time, the compressive strength was 34.1% higher and the flexural strength was 13.6% higher than when the MWCNTs content was 0. After 1500 salt freezing cycles, the appearance and mass loss of MWCNTs-UHPC prepared according to the best ratio changed little, and the maximum mass loss was 3.18%. The higher the mass fraction of the erosion solution is, the lower the compressive strength and RDME of concrete after FT cycles. The SEM test showed that cracks appeared in the internal structure and gradually increased due to salt freezing damage. However, the microstructure of the concrete was still relatively dense after 1500 salt freezing cycles. The NMR test showed that the salt freezing cycle has a significant influence on the change in the small pores, and the larger the mass fraction of the erosion solution, the smaller the change in the proportion of pores. After 1500 salt freezing cycles, the samples did not fail, which shows that MWCNTs UHPC with a design service life of 150 years has good salt freezing resistance under the coupling effect of salt corrosion and the FT cycle.

Experimental study on sulfate resistance of shotcrete with different liquid accelerators

The shotcrete used as the initial lining of tunnel was easily damaged by sulfate attack in groundwater environment. The purpose of this study was mainly to explore the deterioration and mechanism of shotcrete mixed with different liquid accelerators under the conditions of semi-immersion and dry-wet cycles sulfate attack. Through comparative analysis of the test results of mass loss, compressive strength, relative dynamic elastic modulus and surface morphology of shotcrete specimens, it was obtained that different liquid accelerators had obvious differences in the performance of shotcrete deterioration. Among them, the shotcrete with 5.0% AR (alkaline liquid accelerator based on sodium aluminate) was the most severely degraded, while the shotcrete with 8.0% AS (alkali-free accelerator based on aluminum sulfate) had the strongest resistance to sulfate attack. In addition, combined with XRD, TG and SEM to analyze the corrosion products on the surface of shotcrete, it was found that the sulfate attack of shotcrete with 5.0% AR might be mainly gypsum and ettringite corrosion, but the deterioration of shotcrete with 8.0% AF (alkali-free accelerator based on fluoroaluminate) and AS was basically caused by little ettringite corrosion.

The role of aggregate and cement paste in the deterioration of the transitional interface zone of pervious concrete during freeze-thaw cycles

Improving the performance of the cement matrix is an effective method to enhance the freeze-thaw (F-T) damage resistance of pervious concrete. However, the interfacial transition zone (ITZ) is the weakest component. The purpose of this paper is to evaluate the effect of ITZ on the deterioration of pervious concrete under F-T circumstances. The evolution of the compressive strength of samples under water and salt F-T conditions was obtained by uniaxial compression tests. Additionally, the development of the ultrasonic velocities and the relative dynamic modulus of elasticity were examined. Changes in the microstructure and the pore structure were also continuously monitored. The results demonstrate that as the number of F-T cycles rises, compressive strength and dynamic elastic modulus diminish, and the deterioration of samples in 3% NaCl solution is more severe than that in water. Within 100 F-T cycles, cement paste samples with the identical w/c as pervious concrete showed no discernible strength deterioration, and detrimental porosity did not alter considerably. Scanning electron microscopy (SEM) results showed that the performance difference between aggregate and ITZ and the expansion stress lead to debonding at the interface of aggregate and cement, which is the primary culprit for the worsening of pervious concrete under F-T conditions. This work serves as a reference for the deterioration mechanism and durability enhancement of pervious concrete under F-T circumstances.

Prediction of the frost resistance of high-performance concrete based on RF-REF: A hybrid prediction approach

Infrastructure projects in extremely cold areas have high requirements regarding the frost resistance of concrete. To more efficiently design concrete mix proportions in engineering applications to meet the requirements of frost resistance (in terms of the relative dynamic modulus of elasticity after freezing and thawing cycles), an intelligent framework based on the random forest (RF) algorithm is developed to predict the frost resistance of concrete. First, orthogonal tests and engineering data are used to obtain a dataset of raw material mix proportions for concrete and the corresponding frost resistance index values. Second, the RF and recursive feature elimination (RFE) are combined to eliminate coupling factors and noise and determine the optimal factor index system for the concrete mix proportion considering the corresponding influence on frost resistance, and the RF is used to establish a regression prediction function between the concrete mix proportion and frost resistance. Finally, the State Key Project of the Songtong Expressway in Jilin Province is used as a case study to verify the feasibility of the proposed method in a cold region, and the results show that (1) RF-RFE can effectively screen important indicators. After screening, the characteristic parameters are the water binder ratio, cement dosage, coarse aggregate dosage, fine aggregate dosage, compound superplasticizer amount and fly ash dosage. (2) The frost resistance of concrete can be accurately predicted by the RF model. The root mean square error (RMSE) of the test set is 0.077, and the goodness of fit (R2) is 0.9578. The proposed framework can be used to effectively predict the frost resistance of concrete to improve its durability, thus providing a good foundation for the optimization of the concrete mix design in practical engineering and excellent economic benefits and application prospects.

Improving the freeze-thaw resistance of mortar by a combined use of superabsorbent polymer and air entraining agent

Air entraining agent (AEA) is often used to improve the freeze-thaw (F-T) resistance of concrete, but with the deterioration of compressive strength. In this paper, the combination of AEA and superabsorbent polymer (SAP) was used to improve the F-T resistance of mortar without sacrificing its compressive strength. The mass loss and relative dynamic elastic modulus were measured after the rapid F-T cycles test. Meanwhile, the change in the pore structure of mortar was observed. Results showed that the air entraining effect of AEA was better than that of SAP, and the effect of the mixture of SAP and AEA on the compressive strength of mortar was nonlinear. Compared to mortar containing 0.2 wt‰ AEA alone, the combination of 0.05 wt‰ AEA and 0.2 wt% SAP can improve the compressive strength of mortar by around 10% with comparable F-T resistance. The mechanisms behind the phenomenon were unveiled based on the quantitative analysis of the air void characteristics of mortar. Furthermore, the combination use of AEA and SAP increases the air content and porosity of mortar, and the addition of SAP leads to redistribution of air void, the pores with a diameter larger than 200 μm increase, and those with a diameter less than 100 μm reduce.

Performance degradation and damage model of rice husk ash concrete under dry-wet cycles of sulfate environment.

Rice husk ash concrete (RHAC) is a new type of concrete that has been rapidly gaining acceptance in recent years. In this paper, the improvement effect of rice husk ash (RHA) on the sulfate erosion performance of concrete was confirmed. The ratio of rice husk ash concrete (RHAC) was optimized and compared with ordinary concrete (OC). The performance degradation of 9%RHAC (rice husk ash at 9% by weight of cement) and OC within 135 times erosion dry-wet cycles solution with Na2SO4 at 5% by weight of solution were studied, including the change of apparent phenomena, compressive strength, tensile strength, effective porosity, and dynamic elastic modulus. The microstructure changes of samples before and after sulfate dry-wet cycle were observed by using a scanning electron microscope (SEM). The results show that with the increase of sulfate dry-wet cycle times, the concrete specimen gradually peels off and expands in volume. The compressive strength and tensile strength increase first and then drop sharply, the effective porosity decreases first and then increases, and the relative dynamic elastic modulus increases and then decreases. The reason is that the ettringite and gypsum are formed by the reaction of sulfate intrusion and hydration products under wetting treatment. After drying treatment, ettringite and free water combine to form sodium sulfate. In the early of circulation, ettringite, gypsum, and sodium sulfate fill the internal pores of the concrete and improve the density. As the number of sulfate dry-wet cycles increases, expansion products accumulate, causing structural expansion damage and deterioration of mechanical performance. However, the hydrated calcium silicate hydrate gel was produced by mixing rice husk ash with concrete to improve the material strength and corrosion resistance. The deterioration degree of the 9%RHAC is better than that of OC at all stages. Finally, the damage constitutive models were established, and the accuracy is higher compared with the measured value.

Study on the mechanical properties and frost resistance of multiple modified concrete

To study the effects of graphene oxide (GO), fly ash, and steel fiber on the mechanical properties and durability of concrete, the mechanical properties, frost resistance, and internal pore structure of modified concrete are investigated by compression tests, freeze–thaw cycle tests, and industrial computed tomography (CT) tests. The test results show that the compressive strength of concrete with GO is better than that of mixed concrete, concrete mixed with only steel fiber, and ordinary concrete. Further, it is strongest at all ages when the GO content is 0.03%; the compressive strength of mixed concrete with 30% of fly ash is generally better than that with 15% and 45% of fly ash. In general, the frost resistance of concrete with only GO is better than that of ordinary concrete. With the increase in fly ash content, the internal porosity of concrete decreases, and its compressive strength increases accordingly; as GO increases, the porosity decreases and then increases, with the lowest porosity and the highest compressive strength of concrete at 0.03% of GO. With an increase in porosity, the mass loss and relative dynamic elastic modulus of concrete increase after 100 freeze–thaw cycles, which indicates that porosity directly affects the frost resistance of concrete.

Relationship Between Microscopic Pore Structure and Strength of Cement-Based Materials with Low Water-Binder Ratio Under Sulfate Attack Environment

In this paper, the mass loss test, relative dynamic elasticity modulus test, compressive strength test, thermogravimetric analysis (TGA-DTG), and mercury intrusion porosimetry (MIP) were used to study the performance of cement-based materials with low water-binder ratio after sulfate attack, and the influence of microsilica dosage and erosion period on the performance was also investigated. The results indicate that the microsilica mixed can improve the macro-properties of cement-based material with low water-binder ratio after sulfate attack, and as the microsilica dosage is increased, the improvement effect tends to decrease after an increase, while the microsilica dosage is 15%, all performance indexes are the best. This study also demonstrates that the microsilica dosage could affect the mass percent and pore structure distribution of the hydration products of cement-based materials with low water-binder ratio after sulfate attack, and different pore structure distribution may have impact on compressive strength of cement-based materials. Besides, we established relation models for the influence of capillary pores’ and gel pores’ proportion on the compressive strength of cement-based material after sulfate attack, and concluded that there was no interaction between the impacts of two pore types on compressive strength.