Microcracks In Concrete Research Articles

Microbes: A Remedy for Micro Cracks of Concrete

Crack formation is a very common phenomenon in concrete structures, which allows the entry of water and different type of chemicals into the concrete through the cracks and decreases their durability, strength and, which also affect the reinforcement when it comes in contact with water, CO2 and other chemicals. For repairing the cracks developed in the concrete, it requires regular maintenance and special type of treatment which will be very expansive. To overcome this problem autonomous self-healing mechanism is introduced in the concrete cracks which helps to repair the cracks by producing calcium carbonate crystals that fills the micro cracks and pores in the concrete. During the present investigation Bacillus megaterium is identified for alkaline environment based on their survival.

Effect of flowing water on the ettringite-induced healing of concrete cracks by electrodeposition: Experiments and molecular dynamics simulations

The electrodeposition method (EDM) has been regarded as a new technique for healing concrete microcracks in recent years due to its advantages of excellent remediation in aqueous environments. However, a flowing water environment may influence the effectiveness of the EDM. Therefore, in this paper, the effect of flowing water on the synthesis of ettringite by the EDM to heal concrete cracks was investigated through experiments and molecular dynamics simulations. The experiment results showed that the impermeability coefficient of concrete decreased from 6.41 to 5.36 and 5.18 as the flow rate increased from 0 to 1 m/d and 3 m/d after 7d. The healing products on the surface developed from a cotton-like floc structure to a gel-like morphology. At the microscopic level, with the increase in flow rate, the ettringite changed from the disordered distribution of reticulation to the orderly growth of clusters in the form of long rods. Meanwhile, the phase compositions of healing products transformed from ettringite to gypsum and calcium carbonate. In addition, combined with the molecular dynamics simulations by LAMMPS, the increase in flow rate changed the crystal characteristics of the synthesized ettringite, both the decrease in length-to-diameter ratio and crystallinity, as well as the increase in specific surface area, d-spacing, and crystallite size.

Multisource ultrasound-excited thermography for detecting concrete microcracks in hydraulic structures

ABSTRACT Hydraulic concrete structures often suffer from cracking that could lead to engineering accidents. Thus, it is important to identify emerging concrete cracks so that the premonitory danger of the components can be comprehensively evaluated, and the disaster management level can be advanced to the initial stage of the hazard. This study investigated the use of ultrasound-excited thermography to detect surface microcracks in concrete engineering components. A detection system and method for the synergistic excitation of multiple excitation sources were developed, and self-adaptive pressure-loading sleeves containing back shafts made of glass fibre-reinforced nylon were developed to exert pressure on the transducers. Eighteen groups of in-situ experiments were conducted on important parts of the key component using a combination of 28-kHz and 40-kHz-transducers with a power of 100 W. The results demonstrate that ultrasound-excited thermography with the synergistic excitation of multiple excitation sources can be applied to detect surface cracks in approximately semi-infinite reinforced concrete members in-situ. The radius of the current investigation of cracks stimulated by one 100-W transducer pressed by the self-adaptive sleeve in reinforced concrete members is as far as 300 mm. The minimum widths of the detected cracks are 0.03 mm.

Experimental Study on Fracture Toughness of Shale Based on Three-Point Bending Semi-Circular Disk Samples

A large number of construction practice projects have found that there are many joints and microcracks in rock, concrete, and other structures, which cause the complexity of rock mechanical properties and are the main cause of geological or engineering disasters such as earthquakes, landslides, and rock bursts. To establish a rock fracture toughness evaluation method and understand the distribution range of fracture toughness of Longmaxi Formation shale, this study prepared three-point bending semi-circular disk shale samples of Longmaxi Formation with different crack inclination angles. The dimensionless fracture parameters of the samples, including the dimensionless stress intensity factors of type I, type II, and T-stress, were calibrated using the finite element method. Then, the peak load of the samples was tested using quasi-static loading, and the load–displacement curve characteristics of Longmaxi Formation shale and the variation in fracture toughness with crack inclination angle were analyzed. The study concluded that the specimens exhibited significant brittle failure characteristics and that the stress intensity factor is not the sole parameter controlling crack propagation in rock materials. With an increase in crack inclination angle, the prefabricated crack propagation gradually transitions from being dominated by type I fracture to type II fracture, and the T-stress changes from negative to positive, gradually increasing its influence on the fracture. An excessively large relative crack length increases the error in fracture toughness test results. Therefore, this paper suggests that the relative crack length a/R should be between 0.2 and 0.6. The fracture load distribution range of shale samples with different crack angles is 3.27 kN to 10.92 kN. As the crack inclination angle increases, the maximum load that the semi-circular disk shale samples can bear gradually increases. The pure type I fracture toughness of Longmaxi Formation shale is 1.13–1.38 MPa·m1/2, the pure type II fracture toughness is 0.55–0.62 MPa·m1/2, and the T-stress variation range of shale samples with different inclination angles is −0.49–9.48 MPa.

The Applicat ion of Super Absorbent Polymer in Self-Healing Morta r: The Effect on Mechanical Properties

Super Absorbent Polymer (SAP) were used in various application, including in mortar production. The ability of SAP to absorb a high amount of water made this material become a promising water reservoir in the mortar that can later mitigate micro-cracks in concrete. Besides SAP, a nutrient must be embedded into self-healing mortar to support metabolism in bacteria-based self-healing mortar. However, adding SAP and nutrient was reported to decrease the mechanical properties of the resulting self-healing mortar. Thus, in this research, the modification in the mix design of mortar containing SAP and nutrient were observed. The water to cement ratio was decreased up to 0.3. The amount of SAP and entrained water added is based on its swelling capacity. The swelling capacity of SAP, the workability of fresh mortar, and the compressive strength of mortar were examined. The results show that the swelling capacity of SAP was affected by the pH and the presence of calcium ions in the solution. The higher the pH and the calcium ion in the solution, the lower SAP’s swelling capacity. Applying the modified mortar mix design containing SAP and nutrient proofed to mitigate the reduction in workability and compressive strength of the resulting self-healing mortar.

Analysis of the structural behavior of reinforced concrete components with acoustic emission analysis

The use of non-destructive testing methods can provide insights into processes within the interiors of structures. Acoustic emission testing is one of the non-destructive testing methods that allows the detection of material damage during its occurrence. When structures, such as concrete components, fail under load, elastic waves are generated, propagating within the component. These signals can be detected by acoustic emission sensors placed on the surface of the component, enabling the tracking of the material's condition and the location of failure. This paper summarizes recent applications of acoustic emission measurements on large-scale laboratory specimens made of reinforced concrete. The first example describes measurements during a tensile fatigue test on a large- scale reinforced concrete specimen to investigate the fatigue behaviour of an embedded concrete dowel. The second example involves measurements during a dynamic three-point bending test to examine the fatigue behaviour of a prestressed concrete railway sleeper. The third example describes a full-scale test conducted on a flat slab concrete test specimen with dimensions of 2.8 m × 2.8 m. The objective of these investigations is the development and optimization of new components to enhance punching shear resistance and provide an economical solution. To detect microcracking during loading acoustic emission measurement has been carried out using broadband sensors with a measurement frequency of up to 200 kHz which were especially developed for the detection of microcracks in concrete. For the three-dimensional location of the acoustic emission events, 16 of these acoustic emission sensors were attached to the surface of the specimens. Most of the events were in the centre of the sample in the punching area. These events form a circular structure with a diameter of approximately 1m. A visual inspection of the sample after the experiment shows that macroscopic cracks have formed in this area, which extend up to the surface of the sample.

Recognition of concrete microcrack images under fluorescent excitation based on attention mechanism deep recurrent neural networks

This study aims to recognize fluorescent excitation images of microcracks in concrete components through the adoption of an Attention Mechanism-based Deep Recurrent Neural Network (RNN) model, thereby enhancing the accuracy and efficiency of crack detection. Considering the significance of concrete crack detection and the limitations in efficiency and accuracy of existing methods, this paper proposes an innovative image processing technique that combines fluorescent excitation methods with deep learning models to achieve earlier and more accurate identification of concrete microcracks. C30 concrete specimens were prepared experimentally and treated with fluorescent solution spray. Fluorescent images of cracks under UV light excitation were collected and processed using a segmented attention mechanism deep RNN model. Various performance evaluation metrics, including mean Intersection over Union (mIoU), mean Image Intersection over Union (miIoU), mean Image Dice Coefficient (miDice), and F1 score, were employed to comprehensively assess the model's performance. The results demonstrate that the proposed model achieved significant effectiveness in concrete crack image recognition, showing higher mIoU, miIoU, miDice, and F1 scores compared to other representative deep learning models, thus proving its advantages in recognition accuracy and efficiency. Particularly, by introducing the segmented attention mechanism, the model could capture microcrack features more effectively, significantly improving the accuracy of crack identification. This method not only provides a new technical approach for the early detection of concrete cracks but also lays the foundation for further development of efficient and accurate crack detection technologies to accommodate more complex engineering application scenarios.

Experimental study on aerial detection of concrete microcracks based on fluorescent selective excitation

ABSTRACT In order to solve the problem of detecting and finding microcracks on concrete structures, a method on aerial detection of concrete microcracks based on fluorescence selective excitation was proposed in this study. Concentration brightness relationship curves for fluorescent solutions were plotted based on experimental analysis results. Specialised fluorescent aqueous solutions for concrete microcrack detection were identified as excitation reagents by integrating with the fluorescence development patterns of each solution. Concrete specimens containing authentic microcracks were prepared, and fluorescence selective excitation detection tests for concrete microcracks were conducted. The morphology of microcrack development under fluorescent labelling was scrutinised, and the intervals of opening widths for the examined cracks were quantified. The findings demonstrate that concrete microcracks draw surrounding fluorescent solutions into the cracks through capillary adsorption. Under UV radiation, microcracks manifest dark bands in relation to the fluorescence attachment area due to the loss of fluorescent solution around them. This band elucidates the location and morphology of the marked crack, amplifying its visual representation. Furthermore, the fluorescence selective excitation UV detection method proves effective in identifying concrete microcracks with a width as small as 0.02 mm. The improved UAV equipment was used to carry out the aerial detection experiment on the actual concrete structure.

Parametric Study on Mechanical Properties of Basalt Fiber-Reinforced Pea Gravel Concrete

Basalt fiber-reinforced pea gravel concrete (BFRPGC) has remarkable potential for use as the retrofitting covers for masonry walls. However, a quantitative understanding of the mechanical properties of the BFRPGC material is still a perceived gap in the current literature. In this study, the role of basalt fibers in pea gravel concrete was evaluated by a comprehensive experimental investigation involving compressive strength tests and splitting tensile tests. Fiber length and volume fraction were selected as the key parameters. Two fiber lengths of 6 mm and 12 mm were considered, while the volume fraction corresponding to each of the fiber lengths was increased from 0.3% to 0.8%, with a step of 0.1%. The measured strengths were not simply proportional to the fiber volume fraction. The reason behind this phenomenon, i.e., the coupling effect of the bridging role of basalt fibers on concrete microcracks and the fiber agglomeration in concrete, was analyzed. The best performance of the BFRPGC material was achieved by incorporating 12-millimeter-length fibers with a volume fraction of 0.4%. Compared to that of the reference pea gravel concrete, a significant increase of up to 44.5% in compressive strength was recorded in this case. Furthermore, the failure mechanism of basalt fibers in pea gravel concrete was disclosed via the scanning electron microscope observations. In addition, the uniaxial compressive stress–strain model of the BFRPGC material was established.

Effect E. coli Bacteria Concentration as Self Healing on Compressive Strength and Hydrophobic Properties on Micro Cracks of Concrete

Buildings are facilities created by humans to support various human activities. Potential damage to old buildings, such as the appearance of cracks in building concrete. Self-healing is carried out by bacteria to repair micro cracks that occur in concrete by deposition of CaCO3. Bacteria-based preservatives consist of bacterial spores and organic compounds that are incorporated into the concrete structure. This research aims to determine the effect of variations in the concentration of E. coli bacteria on compressive strength and contact angle. Based on the results of the research data, two research results can be stated. First, the concentration of bacteria affects the compressive strength of the concrete and the maximum compressive strength occurs on day 14. Second, the concentration of bacteria affects the contact angle of the concrete so that it can be said that the concrete is hydrophobic. As for the XRD characterization, intensity data (I), diffraction angle ( ) were analyzed using High Score Plus. FTIR characterization was carried out in the range 4000 cm-1-500 cm-1. SEM characterization to see the morphology of the concrete with a magnification of 2500 times. SEM can also show E. coli bacteria in concrete

Macro-micro crack and damage evolution characteristics of concrete: After the action of acidic drying-saturation cycle

Repeated saturation and drying of acidic mine water have a major influence on the mechanical properties and stability monitoring of artificial dams (concrete walls) in underground reservoirs. A uniaxial compression acoustic emission (AE) monitoring test was conducted to quantify the evolution characteristics of micro cracks in concrete. In addition, the evolution characteristics of macro cracks during sample failure were quantitatively analyzed by fractal dimension theory and Image-Pro. Finally, the damage constitutive model was established and the damage evolution law was studied. The results of the study showed that the percentage of micro shear cracks in dry samples exhibited a decreasing and then increasing trend during the loading stage before the uniaxial compressive strength (UCS). However, after the acidic drying-saturation cycle (ADSC), this percentage of concrete showed an increasing trend. As the number of drying-saturation cycles increases or the pH decreases, the fractal dimension, total length, and area of the macro cracks also increase. The damage constitutive model, based on ADSC and loading conditions, works well. After the ADSC, the concrete sample will have three damage stages. Additionally, the strain at entry into each stage increases. Expansion and shrinkage of hydration products and chemical damage due to ion exchange are the mechanisms that change the mechanical properties and the macro-micro crack evolution pattern of concrete after ADSC.

Coupling pressure of an ultrasonic transducer excitation under the action of a loading device

ABSTRACT Ultrasonic thermal excitation can be regulated by coupling pressure conditions that indirectly influence the excitation effect. This study evaluated the effects of coupling pressure conditions on concrete microcracks detection through ultrasonic thermal excitation testing. Concrete microcracks were subjected to coupling tests, and two coupling pressure conditions were applied to the stimulation. A finite element simulation model was used to quantify the coupling pressure excitation, and the differences in temperature rises due to the coupling pressure conditions were analyzed. The study indicates the addition fluctuations in coupling pressure under the direct loading excitation could be neglected; while the coupling pressure increases by about 53% under the aluminum alloy sleeve loading excitation, and the fluctuation increases with the initial coupling pressure. The excitation effects of the tests are influenced by the coupling pressure condition, which will be weak if the perturbation of coupling pressure is great and changes drastically. Analysis suggests the drastically varying coupling pressure leads to substantial changes in the transducer’s equivalent resistance and the output efficiency of the piezoelectric transducer decreases. It emphasizes the importance of controlling the perturbation of coupling pressure and provides research ideas to enhance the detection efficiency.

Increased Concrete Strength with the Addition of Hyacinth Natural Fibers

Concrete is a brittle and fragile construction material so it needs to be increased in strength. This study aims to increase the strength of concrete by adding natural fibers of water hyacinth to the concrete mixture. Hyacinth fibers are cut by 3-5 cm and added with variations of 0%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5% of the volume of concrete. Cylindrical specimens 15 cm in diameter and 30 cm in height were tested for compressive strength and tensile strength at the age of 28 days. The test results showed that the addition of hyacinth fiber up to 0.5% increased the compressive strength of concrete up to 17.6% and tensile strength up to 71.4% compared to normal concrete without fiber. The increase in strength is due to hyacinth fibers being able to withstand micro-cracks in concrete. The more fiber added, the more microcracks are able to be prevented thereby increasing the strength of concrete. In conclusion, the natural fiber of hyacinth effectively increases the strength of concrete both in compressive and tensile capacity.

Cyanobacteria as an eco-friendly bioresource for EPS production with crack healing capacity in concrete

Cyanobacteria, alike microalgae, are photosynthetic microorganisms found in different environmental conditions. These photosynthetic bacteria are also considered promising solutions for cracking problem in concretes. These photosynthetic organisms precipitate CaCO3 crystals in concrete microcracks and pores, thus sealing the cracks and increasing the strength gain of the concrete blocks. Cyanobacteria Lyngbya sp., Phormidium sp., and microalgae Chlorella vulgaris were studied initially. Lyngbya sp., Phormidium sp., and Chlorella vulgaris have the additional property of secreting the exopolysaccharide (EPS). EPSs are an important class of biopolymers with great ecological importance. Because of their high charge density and capacity to act as mineralization nucleation sites, cyanobacterial exopolysaccharides are currently receiving more attention. Using the three strains stated above, this study investigates the impact of physiochemical factors on biomass concentration and exopolysaccharide synthesis and creates mathematical models. Using Central Composite Design (CCD), it is possible to study the interactions between the many parameters, including nitrate concentration, starting media pH, light intensity, and temperature. The biochemical characteristics of the leftover biomass are assessed after exopolysaccharide extraction, and because of its high carbohydrate and fat content, it can be used to produce biofuel. The study of checking the microbial crack healing capacity and strength gain of the concrete using these three cyanobacterial strains is being studied. Based on the outcome, the best species was chosen. Further microstructural analyses, such as X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to support the calcium carbonate precipitation.

Characterization of ureolytic based bio concrete

One of the oldest and most popular building materials in the world is concrete., mostly because it is inexpensive, readily available, has a long lifespan, and can withstand harsh weather conditions. But as concrete is brittle tends to fail in cracks more. The consequence of micro-cracks in concrete is many such as corrosion, faster degradation of the structure, reduced load-carrying capacity, etc. As it is impossible to avoid these cracks due to their behavior, many new techniques have been explored to repair them. But with a sustainability perspective, it is important to proceed such that it can benefit the environment. Therefore, the aim of the present work focuses on sustainability solutions for crack repair and strength enhancement. One such mechanism is Calcium carbonate precipitation from the bacteria to fill the cracks. CaCO3 has been observed to blend with concrete easily and enhance its properties. Among different pathways available, the use of ureolytic bacteria such as the Bacillus family to obtain CaCO3 by degrading urea is more effective and economical. The current study used culturing of a new type of Bacillus pseudofirmus and Bacillus cohnii bacteria to investigate the stress behaviour and resilience of concrete. A large number of samples were cast to investigate various strength properties such as compressive, flexural, split tensile strength, water absorption, and SEM analysis. According to the results of the tests, there was a 36.36% growth in compressive stress for 106 cell concentrations after 56 days. Similarly, there was a noticeable growth in split tensile and flexural stress. SEM images, finally, confirmed the occurrence of CaCO3 in the mix. The outcome of this study can assist researchers and the construction industry to look into the different possibilities to enhance the properties of concrete.

Experimental study on nonlinear ultrasonic characterization of concrete during crack propagation

Damage and failure of concrete structures are essentially caused by crack initialization and expansion. Conventional ultrasonic tests cannot detect changes in the micro-cracks in concrete. Second harmonic generation (SHG) is effective at characterizing the micro-damage. However, research on the influence of micro-cracks on the nonlinear parameter β is still insufficient. Three cubic concrete specimens 150 mm × 150 mm× 150 mm were fabricated, and the design and average compressive strength were 30 MPa and 39.24 MPa, respectively. Before compressive loading, the integrity of concrete specimens was verified using scanning electron microscopy. The load rate is set to 0.6 kN/s during the test. A simultaneous test system for stress σ, strain ε, and nonlinear parameter β was designed, and the regularity of the nonlinear parameter β during compressive loading was investigated. The nonlinear parameter β increases significantly at the beginning of the compressive load. As the load continues to increase, the nonlinear parameter β decreases rapidly and then fluctuates during the subsequent loading. Furthermore, attenuation was also analyzed in this experiment based on the head-wave amplitudes. At the beginning of the compressive loading, the attenuation is weak as no obvious damage exist in concrete. The non-linear parameter β is less affected by the attenuation when the integrity of the concrete specimens is good. When the cracks expand and penetrate, strong attenuation can be observed at the fundamental and second harmonic waves. The results of the experiment have considerable importance with respect to the method of SHG for micro- and macro-scale damage in concrete.

A resource-efficient and portable nanotechnology-enabled disinfection system: Performance studies and a novel strategy to recycle spent material

The paper describes developing a point-of-use disinfection system consisting of a film-forming nanocomposite packed in a nylon sachet. The composite film consists of silver nanoparticles embedded in a matrix containing chitosan, reduced graphene oxide, and tannic acid. The long-term ability of the portable sachet bag to release silver ions and disinfect surface and groundwater is demonstrated. The sachet bag's disinfection potential is demonstrated by taking Escherichia coli MTCC 443 as the model microorganism. The system produced a complete and consistent 3 log10 reduction of E. coli over multiple cycles of use. The paper also describes a green recycling approach to utilise spent composite film and prevent AgNPs from entering the waste stream. The spent nanocomposite film is transformed into a concrete micro-crack sealant through a soft chemical route. The sealant's ability to plug micro-cracks in concrete is demonstrated, and the mechanism of sealant interaction with concrete is proposed. The sealant can fill cracks and solidify in an alkaline environment. The concrete cube specimens repaired with sealant showed enhanced compressive strength compared to the residual concrete cube specimens. The possible leaching of residual silver from the sealant in concrete is investigated via toxicity characteristic leaching procedure analysis. The study demonstrates that silver leaching is negligible (< 0.05 mg/L) and well below the permissible limit of 5 mg/L.

Effect of types of curing environments on the self-healing capacity of mortars incorporating crystalline admixture

The presence of microcracks can lead to a reduction in the durability of concrete structures. In recent years, crystalline admixture has been used to repair microcracks in concrete. In this study, the effect of different amounts of crystalline admixture on the performance of mortar was firstly determined. In order to reveal the purpose of this study, a mortar with 4% crystalline admixture has been healed under three types curing environments (standard curing, water immersion, and saturated calcium hydroxide solution). The self-healing effect of the specimens was characterized macroscopically by water absorption tests and visualized crack images after repair. The type of crack filler was determined by microscopic analysis experiments XRD and SEM-EDX. The experimental results show that, firstly, the self-healing effect of mortar with crystalline admixture is limited by standard curing environments. Secondly, water immersion environment plays a weak role in promoting crack healing of mortars without crystalline admixture, and the addition of crystalline admixture leads to self-healing of the mortar due to a large amount of production of hydrated calcium silicate. Finally, the saturated calcium hydroxide solution has a beneficial effect on the self-healing of cracks in mortars without crystalline admixture due to the precipitation of calcium hydroxide from the healing solution. After the addition of crystalline admixture to the mortar, calcium ions and water promote the generation of calcium silicate hydrate, and the precipitation of calcium hydroxide acts together to fill the crack, resulting in the crack being completely healed.

Colloidal Nanosilica Treatments for Sealing Cracks in Mortar.

Presence of microcracks in concrete can diminish the service life of a structure. The injection of materials for filling the crack is proposed for facing this problem. The traditional materials used for sealing cracks present some drawbacks, such as the difficulties of inorganic materials for flowing to all the depth of the crack and the lack of compatibility with the cementitious matrix in the case of organic materials. In this work, the injection of colloidal nanosilica dispersed in water is proposed for filling microcracks in mortars. The effect of the injection procedure on the sealing performance of the colloidal nanosilica has been assessed. The ability of colloidal nanosilica for penetrating through the crack and its posterior gelification-solidification inside the crack after a curing period have been confirmed. The microscopic analysis of a cross-section of the crack indicates that the sealing ability of the nanosilica seems to be not only due to the filling of the crack but also to chemical interactions with the cementitious phases of the surrounding crack sides.

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 (&gt;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.