This paper examines the feasibility of applying inorganic thermal-insulating concrete in high geothermal roadways in underground coal mines. This innovative material is based on a mixture of ceramsite, glazed hollow beads, cement, and natural sand, enhanced with varying degrees of basalt fibers. Fibers were used as a partial substitute in the mixture, in the following volumes: 0% (reference specimen), 5%, 10%, 15%, and 20%. Their compressive strength, permeability resistance, and thermal conductivity were studied. A high content of fibers tends to entangle into clumps during mixing, resulting in a significant reduction in the mechanical properties of compressive strength. The appropriate amount of fiber content can improve impermeability, and the permeability height of 5% fiber concrete was reduced by 22.5%. Experiments on thermal behavior showed that an increase of basalt fibers leads to a significant reduction in thermal conductivity. For concrete containing 20% fiber, the thermal conductivity for the reference specimen (0%) in the wet state was reduced from 0.385 W/(m∙°C) to 0.098 W/(m∙°C). There was a slight increase in thermal conductivity when the temperature increased from 30 °C to 60 °C. Despite the reduced mechanical strength, the resulting concrete is well-suited for use in the insulation of underground roadways, as numerical simulations showed that insulating concrete with optimal fiber content (15%) can reduce the average temperature of the wind flow in a high ground temperature roadway of 100 m in length in a mine by 0.3 °C. The final cost-benefit analysis showed that insulating concrete has more economic benefits and broad development prospects when applied to high geothermal roadway cooling projects. China is rich in coal resources. With the gradual development of the national economy and changes in society, the industrialization process is accelerating, and the demand for coal resources is increasing. Relevant research studies have shown that many coal mines have carried out high-intensity mining for a long time to meet the rapid economic development, resulting in fewer and fewer coal resources in shallow areas near the surface. With these changes, together with improvements in the mechanization level of mining, coal mines have gradually progressed to deep mining .When mining deep resources, the problem of thermal damage caused by high geothermal heat is often encountered. The effects of high temperatures on the roadway within a mine, such as a deteriorating construction environment, a reduction in labor productivity, threats to the health and safety of workers ,3, and aThermal insulation materials are widely developed in various contemporary construction industries because of their low costs, good insulation effects, and easy methods of preparation ,7,8. In Ceramsite is made, at high temperatures, of muddy shale, clay, gangue, and fly ash. It is characterized by low density, low water absorption, high closed porosity, high strength, and internal pores filled with gas, which can be used as a barrier for heat transfer and for good thermal insulation . Adding Basalt fiber is a pollution-free “green industrial material” for the 21st century. It has excellent mechanical and thermal properties, stable chemical properties, and compatibility . Adding Basalt is a natural inorganic fiber that has no harmful effects on humans or the environment during its production and application. It is abundant in most parts of the world and is cheap to mine and process. Basalt does not require additives in the production process, which provides it with an additional advantage in terms of cost. In addition, basalt fibers have very low thermal conductivity (0.032 W/(m∙°C)). Therefore, basalt-fiber thermal-insulated concrete is an ideal candidate for supporting high geothermal roadways in mines, with excellent potential for improving building insulation and reducing the cooling costs of coal mines. Most researchers studying the mechanical properties of basalt-fiber concrete use very low percentages of fiber reinforcement (1% to 5%), and the compressive strength, splitting tensile strength, and flexural strength of concrete can be significantly improved ,18,19. ICurrently, numerical simulations are widely used to study the heat transfer between rock and wind flow in mining roadways. Zhou et al.  developeWe focused on the potential use of basalt fibers as reinforcing additives in thermal-insulating concrete. Basalt fibers were used as partial substitutes in concrete mixtures at different volume levels: 0% (reference specimen), 5%, 10%, 15%, and 20%. The average length of the fibers that were used was approximately 10 mm. An experimental test procedure was used to study the properties of the hardened specimens, including their apparent density, compressive strength, permeability, and thermal conductivity in the dry and wet states. Then, Fluent numerical-simulation software was applied to analyze the cooling effect after spraying insulating concrete on the surface of a high-temperature mine tunnel in Shandong, China. Finally, the cost-effectiveness of the thermal-insulating concrete was analyzed. The innovative material reduced energy consumption in mines by slowing down rock exotherms, within the broader context of low carbon and environmental protection. At the same time, the simulations provided an essential guide for selecting cooling measures for high geothermal mines.3; the compressive strengths of 3 d and 28 d are 28.9 MPa and 52.3 MPa, respectively. We used river sand of 2.78 fineness modulus, with density of 2.63 g/cm3, Llevel II, and bulk density of 1.50 g/cm3. The ceramsite particle size was ~0.8 mm to 1.5 mm with loose bulk density of 600 kg/m3, numerical tube pressure of 3.5 MPa, water absorption of 7%, thermal conductivity of 0.039 W/(m·°C), and porosity of 25%. The particle sizes of the glazed hollow beads were ~0.5 mm to 1.0 mm, with bulk density of 80 kg/m3, thermal conductivity of 0.027 W/(m·°C), a closed-cell rate of 96%, and water absorption of 8%. The basalt fiber was 10 mm in length, with a diameter of 15 μm, density of 2.65 g/cm3, tensile strength of ~3300 MPa to 4500 MPa, and ultimate elongation of ~2.4% to 3.0% [We used 42.5 ordinary Portland cement with a density of 3.10 g/cm to 3.0% . The expThe core of the preparation of thermal-insulation concrete is basalt fiber, as an additive to improve the performance of shotcrete. Therefore, the ratio-design method should consider not only the ratio of ordinary shotcrete, but also the compatibility of basalt fiber with concrete. Due to the high ground stress, high ground temperature, and high-karst water pressure in deep mines, the concrete shot on a roadway’s surface needs to have strong mechanical strength, thermal-insulation properties, and impermeability. These factors ultimately make the ratio of insulated concrete different from that of ordinary shotcrete. The proportion of concrete that is suitable for high geothermal roadways was selected, especially to meet the thermal-insulation requirements ,24. CombMixing is a very complex process in the preparation of thermal-insulation concrete. The purpose of mixing is not only to achieve a homogeneous mixing of the materials, but also to consider the homogeneous dispersion of the fibers in the cement matrix. Before making the mortar, the ceramsite and the glazed hollow beads were soaked in water for 3 h to achieve better bonding with the cement. Then, the dry fiber, cement, and sand were mixed thoroughly in a standardized mortar mixer. The moistened ceramsite, glazed hollow beads, and water were gradually added to the mixer until a homogeneous mixture was obtained. The concrete was loaded into the mold and fully compacted on a vibrating table. After the specimens were stripped, they were placed in a curing chamber at 20 ± 2 °C and 98% relative humidity. The process of specimen fabrication is shown in The performance tests of the hardened specimens included the apparent dry density, determined by geometric measurements and weighing. According to “Standard for test method of mechanical properties on ordinary concrete”, the compressive strength of the specimens was measured using an AGX-250 electronic universal testing machine. This tester has a maximum load capacity of 2000 kN and a constant rate of 1 mm/min , using a3 for concrete without fibers to 1304 kg/m3 for concrete with 20% fibers, a reduction of approximately 18% in dry density. In order to have a fresh cement mortar with good compatibility, the fiber concrete required more water than the reference specimen, resulting in a highly porous matrix during the drying process. In addition, many tiny pores were created around the fibers, reducing the insulating concrete’s density [ density . The firIn order to resist the strain on the surrounding rock, a completed roadway of an underground coal mine development needs to be shotcrete in full section, especially a roadway dug in the coal seam. It is also necessary to install an anchor net before the shotcrete. The concrete in a roadway is a compressed element and its strength is essential to ensure the safe use of the roadway. The compressive strength of shotcrete can only be put to use after it meets the standard requirements. Therefore, the effect of fiber incorporation on the compressive strength of concrete is worth exploring. Concrete specimens were prepared with four different volume contents of fibers  and compared with concrete without fibers (0%) to study the effect of fiber content on concrete strength.Three sets of concrete specimens of each fiber content were prepared and tested for compressive strength after 28 days of curing, and the average compressive strength values are shown in According to Asim et al. , the fibWhen the mining depth is more than 800 m, the karst water pressure will be greater than 3 MPa. At the same time, the native fissures in the surrounding rock of the roadway gradually develop under the influence of mining coal, forming seepage channels that result in high-temperature fissure water entering the extraction space and more severe heat damage in the mine. The seepage resistance of concrete is closely related to the underground thermal environment, so seepage resistance is an essential index for evaluating thermal-insulation concrete. In this paper, the hydrostatic pressure method was used to analyze the seepage resistance of concrete.Two sets of concrete specimens with four fiber volume contents were prepared, along with two sets of reference specimens (0%), which were tested for permeability after 28 days of curing. The average values of permeability heights are shown in 2 and Al2O3. The SiO2 content reaches 45% to 60% and has a composition similar to that of silicate cement. Although the surface of basalt fiber is smooth, it has a natural compatibility with cement [h cement . As seenOur research aimed to prepare shotcrete materials with good thermal-insulation properties to effectively slow down the heat dissipation from the surrounding rock. Thermal conductivity is a physical quantity that reflects the ability of a material to transfer heat, and the thermal-insulation properties of shotcrete are quantified using thermal conductivity. Underground coal mines are dark and humid; the relative humidity of the air is above 80% all year round, and the high ground temperature of the surrounding rock is generally ~30 °C to 60 °C. The tests were conducted in conjunction with actual downhole conditions. The thermal conductivity was measured in the wet state on the third day of curing, and in the dehydrated state. The thermal conductivity was also measured at temperatures of 30 °C, 40 °C, 50 °C, and 60 °C when the specimen was wet. Three sets of concrete specimens were prepared for each fiber content. The average of the three values was taken as the thermal conductivity for that fiber content.The thermal conductivity of concrete with different fiber contents was generally smaller in the dry state than in the wet state, with the most enormous difference in the reference specimen, with a 24.6% difference in thermal-insulation properties. This can be explained by the high-water content of wet concrete. At normal temperature and normal pressure, the thermal conductivity of liquid water is approximately 22 times higher than that of air. The dry air in the pores is replaced by moist air and water, and the diffusion of water vapor and the movement of water molecules play a major role in heat transfer . TherefoThe relationship between the thermal conductivity and the temperature of the concrete specimens in the wet condition is shown in The correlation matrix method (RMA) is a comprehensive system evaluation method that is often used in system-engineering systems, which mainly use matrices to represent the quantitative relationships among evaluation indicators. The key to the correlation-matrix-system evaluation method is to use the pair-by-pair comparison method to determine each evaluation index’s weights and scales and to obtain the final system evaluation value by weighting. We used the correlation-matrix method to comprehensively evaluate concrete with different fiber contents and select the best basalt-fiber content.We determined a scheme for adding four kinds of fiber content to concrete: 5%, 10%, 15%, and 20%. The four evaluation indicators were apparent density, compressive strength, impermeability, and thermal insulation. The results of the evaluation are shown in iV is the comprehensive evaluation value, n is the number of evaluation programs, m is the number of evaluation indicators.According to the weights of the system-evaluation indices, combined with the evaluation scale and the scoring results, the comprehensive evaluation values of different fiber contents were obtained using the calculation method of the correlation matrix, which as follows.n = 4 and m = 4 in the calculation; the correlation matrix was constructed as shown in According to the established systematic-evaluation system, The ANSYS Fluent numerical simulation software was used to simulate the spraying of plain concrete and insulating concrete on the roadway surface. Previous studies generally treated the surrounding rock as zero thickness and set the rock wall temperature as a constant, using either temperature-boundary conditions or convective-heat-transfer-coefficient-boundary conditions ,36. HoweIn this study, a section of a high-temperature mine in Shandong Province, China, at a depth of 1150 m below ground with a concentrated flat roadway, was used as the object of the study. The roadway was located in the rock at the bottom of the coal seam and had a service life of ~5 to 7 years. The CFD method was used to study the heat transfer between the surrounding rock–air flow. Specific geometric parameters were measured practically, and a full-size 3D geometric model of the three-centered archway was established by applying Rhino 6.0 software, as shown in The quality of the delineated mesh determined the accuracy of the simulation solution results. The model was meshed using Fluent’s Meshing software, and contained 6,339,966 elements and 1,396,927 nodes. Skewness and orthogonality are the two principal quality measures in ANSYS meshing. Skewness determines how close a face or cell is to the ideal state. In the higher-quality meshes, a skewness average of 0.21 and an orthogonality quality average of 0.78 generated a high-quality mesh.Among the commonly used turbulence models, the tunnel airflow temperature calculated by the k-ε model is closest to the actual situation and provides the best results for the simulation of airflow temperature ,39. In tContinuity equation:3), P is the static pressure (Pa), U is the velocity vector (m/s), Momentum equation:E is total energy (J), jh is the formation enthalpy of species j (J/kg), jJ is the diffusion flux of species j (kg/(m2∙s)), qS includes the heat of the chemical reaction and any other volumetric heat sources (J).Conservation of energy is described as follows:k, and its rate of dissipation, ε, were obtained from the following transport equations:kG represents the generation of turbulence kinetic energy due to the mean velocity gradients, μ the dynamic viscosity of the fluid (Pa∙s), 1εC and 2εC are model constants, kσ and εσ are the turbulent Prandtl numbers corresponding to the k equation and the ε equation, respectively, and tμ is turbulent viscosity (Pa∙s).The turbulence kinetic energy, (1)The incompressible ideal gas law was applied to define the fluid density.(2)The heat loss caused by the work done by the viscous force of the fluid was ignored.(3)The airflow was fully developed and turbulent.(4)The turbulent viscosity was isotropic, and the turbulent viscosity coefficient could be considered a scalar.(5)The thermal continuity involving stationary and no-slip conditions was applied to the outer surface of the heading and between the inner surface of the airway and the air.(6)The rock surrounding the roadway was isotropic, homogeneous, and fissure-free.(7)The wall of the roadway and its internal surrounding rock were dry.(8)There was no internal heat source in the alleyway.(9)The constant temperature, regarded as the virgin rock temperature, was applied to the far-field boundary condition.The main assumptions commonly used for coupled rock–airflow heat-ransfer models are the following :(1)The iAccording to the actual coal mine site, the heat source in the roadway was mainly the surrounding rock. Heat sources such as ventilation equipment, pumps, lighting facilities, and operators generated little scattered heat, so they were neglected. The velocity of the airflow inlet was 2.5 m/s, and the temperature was 296.15 K; the outlet used a pressure outlet. According to the geological data for the coal mine, the temperature of the surrounding rock remained constant beyond 30 m. The rock temperature at 30 m was 323.15 K. Therefore, the fixed temperature (323.15 K) boundary condition was applied to the far-field boundary of the surrounding rock. The coupled boundary conditions were applied by creating cross interfaces between the surrounding rock and the outside of the support layer and between the roadway surface and the air, so that fluid heat transfer and solid heat transfer were coupled. The primary rock type of the surrounding rock was siltstone. An 0.2 m thick concrete support layer was sprayed on the roadway surface to reinforce the roadway. These materials were considered to be isotropic and homogeneous. The settings of the boundary condition parameters in the simulation are shown in X-axis. The closer to the wall, the faster the temperature rose, and the temperature rose significantly in the radial direction of the roadway. In the flow layer, the wind flow temperature was almost unchanged and remained around the inlet temperature (288.65 K). The surrounding-rock temperature was higher than the wind-flow temperature. The wind flow was constantly washing the wall of the roadway. The heat exchange was via convection heat transfer between solid and fluid, with high heat exchange efficiency. However, the heat transfer between the wind streams was thermal convection with low heat-transfer efficiency, resulting in a slight temperature gradient in the flow layer and insignificant heat transfer in the axial direction of the roadway.In general, the thermal conductivity of insulated concrete is much smaller than that of ordinary concrete. The wind flow is less affected by the heat dissipation of the surrounding rock, which can make more cold volume transfer to the mining face and play a cooling role.When there was a temperature difference between the roadway wind flow and the heat source deep in the surrounding rock, ignoring the heat transfer between the gas and liquid phases inside the rock, the heat transfer process was as shown in Under plain-concrete support, the average temperature difference between the two walls was 1.9 K, while with under-insulated concrete support, the average temperature difference between the two walls was 15.1 K. This showed that insulated concrete can effectively keep heat out of the roadway.X-axis, the heat transfer between the surrounding rock and the airflow was gradually reduced. The average value of the convective-heat-transfer coefficient was 7.02 W/(m2·°C), and the maximum value was 7.47 W/(m2·°C) in the area of intense heat transfer under plain-concrete support, which was approximately 30 m. The area of intense heat transfer under the support of insulating concrete, approximately 25 m, had an average convective heat transfer coefficient of 6.01 W/(m2·°C) and a maximum value of 6.42 W/(m2·°C). The convective-heat-transfer intensity between ordinary concrete with larger thermal conductivity and wind flow was more significant, and more heat was emitted from the surrounding rock.The airflow flows out of the section of the concentrated flat lane and enters the air cooler of the mining work surface. If the airflow temperature is low, the cooling power of the air cooler can be reduced, saving energy. The raw-rock temperature of the mine studied in this paper was more than 45 °C. The heat damage was severe, especially in summer, and mechanical cooling was required throughout the year. We believe that cost-benefit analysis plays an essential role in cooling design and construction when selecting cooling methods and determining the cost and benefit of the entire cooling project. Therefore, the integrated costs of jetted insulated concrete must be analyzed.The formula shows that the integrated costs include material costs, construction, and management costs, and maintenance management costs . CompareThe ratio used for thermal-insulating concrete was ceramsite and glazed-hollow-bead composite concrete material with 15% basalt fiber, and the spraying thickness was 0.2 m. According to the market survey, the raw materials and costs needed per square meter of thermal insulating concrete and plain concrete are shown in The material cost per square meter of insulating concrete is USD 4.584, while the material cost per square meter of plain concrete is USD 1.104. The increase in cost per square meter of the alleyway is approximately USD 3.57.2·°C)), 2).The Newtonian cooling equation is often used to determine the heat load of development .(9)Q=α. The average temperature of the wall of the insulated concrete roadway was 294.5 K, and the convective-heat-transfer coefficient was 6.01 W/(m2∙°C). The wind-flow temperature was 288.62 K. The electricity price in the industrial sector was 0.105 kW∙h/$; the refrigeration efficiency of the mechanical refrigeration cooling system was 85%; and the motor efficiency of the compressor was 89%. The cost of mechanical cooling for 5 years was USD 329.54 per square meter of the roadway under plain concrete support, and USD 212.96 per square meter of under-insulated concrete support. According to the coal mine information and the related technical personnel, the maintenance and management cost per square meter of insulating concrete will increase by about USD 30.5 in 5 years, so the cost saving by spraying insulating concrete on the roadway wall can be USD 82.51 in 5 years, which is an excellent economic measure and suitable for promotion.This simulated section of the centralized flat lane has a long service life, and the cost-effectiveness of spraying insulated concrete on the roadway’s surface was considered for 5 years. The average temperature of the wall of the plain concrete roadway was simulated to be 296.4 K, and the convective-heat-transfer coefficient was 7.02 W/ The physical property indices of basalt -iber-insulated concrete were derived by testing the apparent density, compressive strength, permeability, and thermal conductivity. The apparent density of the dried specimens containing 20% fiber was reduced by about 18%, compared with the reference specimens. Evaluating the compressive strength of fiber-insulated concrete highlighted the detrimental effects of high-fiber content. The compressive strengths were lower than those of the reference specimen (0%), from 36.7 MPa to 17.4 MPa. However, the compressive strengths of the fiber concrete for all fiber contents, except for the 20% fiber content, met the standard. The appropriate amount of fiber content can improve the impermeability of concrete to a certain extent. The impermeability of concrete with 5% and 10% fiber content increased by 22.5% and 4.2%, respectively. The thermal conductivity of insulating concrete containing 20% fiber in the wet state was reduced to 0.098 W/(m∙°C), and the thermal insulation performance was increased by approximately 74.5%. Although the thermal conductivity of insulated concrete showed an increasing trend with increasing temperature, the increase was minimal. Finally, the optimum fiber content in concrete was analyzed by the correlation matrix method, with the 15% fiber content showing the best overall performance.(2) The thermal insulation performance and insulation mechanism of basalt-fiber concrete were investigated by numerical simulation. The wall temperatures and convective heat transfer coefficients were much lower in shotcrete-insulated concrete roadways, compared with plain concrete roadways, while the surrounding rock temperatures were higher. The insulation of concrete can effectively slow down the heat dissipation rate from the surrounding rock and improve the utilization of the cold volume in the wind flow. Compared with plain concrete, the average airflow temperature at the exit of a 100 m long tunnel supported by insulated concrete decreased by 0.3 K.(3) The reduction of heat dissipation per square meter of surrounding rock after spraying basalt-fiber-insulated concrete, and the electricity cost savings, were calculated by Newton’s law of cooling, which verified the good economic benefits of insulated concrete.Basalt-fiber-insulated concrete is a promising application. Further studies on the size, orientation, and distribution of basalt fibers in concrete are needed to further improve the thermal and mechanical properties of concrete.


DNA resection—the nucleolytic processing of broken DNA ends—is the first step of homologous recombination. Resection is catalyzed by the resectosome, a multienzyme complex that includes bloom syndrome helicase (BLM), DNA2 or exonuclease 1 nucleases, and additional DNA-binding proteins. Although the molecular players have been known for over a decade, how the individual proteins work together to regulate DNA resection remains unknown. Using single-molecule imaging, we characterized the roles of the MRE11–RAD50–NBS1 complex (MRN) and topoisomerase IIIa (TOP3A)–RMI1/2 during long-range DNA resection. BLM partners with TOP3A–RMI1/2 to form the BTRR (BLM–TOP3A–RMI1/2) complex (or BLM dissolvasome). We determined that TOP3A–RMI1/2 aids BLM in initiating DNA unwinding, and along with MRN, stimulates DNA2-mediated resection. Furthermore, we found that MRN promotes the association between BTRR and DNA and synchronizes BLM and DNA2 translocation to prevent BLM from pausing during resection. Together, this work provides direct observation of how MRN and DNA2 harness the BTRR complex to resect DNA efficiently and how TOP3A–RMI1/2 regulates the helicase activity of BLM to promote efficient DNA repair. A) (Homologous recombination (HR) is one of two major eukaryotic dsDNA break (DSB) repair pathways. HR uses the intact sister chromatid during the S/G2 phase to promote error-free repair of DSBs , 2. HR iFig. 1A) , 10. TheA) , 16, 17.Saccharomyces cerevisiae, the Sgs1 helicase (BLM homolog) and Dna2 nuclease/helicase interact with Mre11–Rad50–Xrs2  and Top3–Rmi1 for efficient DNA resection (via an incompletely understood nuclease-independent mechanism (S. cerevisiae Top3–Rmi1 are TOP3A (a type 1A topoisomerase) and the heterodimer RMI1–RMI2 (yeast do not encode an RMI2 homolog). These proteins interact with BLM to form the BTRR (BLM–TOP3A–RMI1/2) complex   , 38, 39.lvasome) , 42, 43.lvasome) , 45. In lvasome) , 47. Tholocation .Here, we use single-molecule fluorescence imaging to decipher the functions of individual resectosome components during DNA resection. Both MRN and TOP3A–RMI1/2 help BLM to initiate DNA unwinding. MRN and TOP3A–RMI1/2 also stimulate DNA2-mediated resection. Finally, MRN synchronizes the translocation speeds of BLM and DNA2 to prevent BLM pausing. We reveal that MRN and TOP3A–RMI1/2 are regulatory resectosome components that initiate DNA resection and synchronize the individual motors during kilobase-long DNA processing.A). TOP3A–RMI1/2 was then mixed with BLM to assemble the BTRR resectosome and labeled with fluorescent anti-FLAG antibodies (targeting RMI2 as described previously). Biotinylated MRN was conjugated with streptavidin quantum dots (QDs) that emit in spectrally distinct channels (A and B). We have previously shown that fluorescently labeled MRN retains its biochemical activities, including diffusion along nucleosomal DNA and nucleolytic removal of Ku from DNA ends  . As expected, MRN and BTRR in complex with DNA2 and EXO1 bound the free DNA ends and resected the DNA in the presence of 1 nM RPA (C). The MRN–BTRR–DNA2 complex resected DNA for 18 ± 6 kb  with a velocity of 18 ± 11 bp s−1. Omitting either TOP3A–RMI1/2 or MRN decreased BLM–DNA2 velocity for approximately two-fold  and decreased processivity by 1.4-fold  , suggesting that MRN and TOP3A–RMI1/2 selectively regulate DNA2-mediated resection  (A and B). Furthermore, a helicase-deficient (hd) DNA2(K654R) mutant decreased resection processivity and velocity . Omitting TOP3A–RMI1/2 and MRN abrogated the negative effects of DNA2(K654R) on resection processivity and velocity  (A and B). We repeated the resection experiments with an hd BLM(K695A) mutant on both 5′-overhang and 3′-overhang DNA substrates but did not see long-distance motor activity beyond our ∼500 bp resolution (C). This indicates that the helicase activity of BLM provides a 5′-flap for DNA2. In addition, BLM prevents the initiation of long-range helicase activity by DNA2, even with a 12-nt 5′-overhang. These results are consistent with our previous study that showed that hd BLM also blocks nuclease-dead DNA2 from unwinding DNA  , A and B n = 42) , A and Bsolution C. This iin vitro (C and D). We saw a more modest 65% of TOP3A–RMI1/2 complexes (n = 22/34) colocalizing with DNA2. DNA2 did not translocate beyond our spatial resolution of ∼500 bp with MRN and TOP3A–RMI1/2 (together or independently) in the presence of RPA. Previous studies showed that suppression of the nuclease activity of DNA2 stimulates processive helicase activity on DNA substrates containing a 5′-flap in the presence of RPA (−1 (n = 23 molecules)  antibody directed to an N-terminal HA epitope, as we described previously (A). We recently showed that RPA aids BLM in initiating helicase activity from 3′-ssDNA overhangs (B). TOP3A was sufficient to recapitulate most of this stimulation , whereas adding RMI1/2 alone slightly decreased the number of translocating BLM molecules . Finally, adding RPA did not further stimulate the number of translocating BTRR complexes . Surprisingly, although TOP3A–RMI1/2 initiated more BLM helicases, it also decreased the velocity of BLM approximately two-fold  and slightly reduced processivity ∼1.2-fold (14 ± 8 kb) . BLM–TOP3A had a similar velocity and processivity as the BTRR complex (n = 83). However, the processivity of BLM–RMI1/2 was further reduced approximately two-fold compared with the BTRR complex . Adding RPA did not change BTRR velocity but slightly decreased the average processivity . We conclude that TOP3A–RMI1/2 helps to initiate DNA unwinding but reduces the velocity and processivity of BLM.Next, we investigated how TOP3A–RMI1/2 regulates BLM helicase. BLM was fluorescently labeled eviously . TOP3A–Reviously A. We recverhangs . When RPverhangs B. TOP3A A). In the presence of 1 nM RPA, ∼90% (n = 131/145) of MRN–BTRR resectosomes initiated DNA unwinding . MRN also retained BLM molecules on the DNA . In the presence of MRN, fewer than 30% of the BLM molecules dissociated from the DNA (n = 131). This resulted in a 1.3-fold increase in processivity  but a ∼1.4-fold decrease in MRN–BTRR helicase velocity  (D and E).Having established that TOP3A–RMI1/2 helps initiate DNA unwinding, we tested whether MRN further stimulates the BTRR complex. MRN is important for BLM recruitment to DSB and has been shown to stimulate unwinding activity , 60, 61.Fig. 4B–E). MR was sufficient to initiate the helicase activity of BLM but decreased processivity. MRE11 alone did not stimulate BLM initiation, suggesting the RAD50 subunit is critical for regulating the activity of BLM. To test whether the ATPase of MRN is also required to stimulate BLM, we repeated helicase experiments with the ATPase-deficient MR(S1202R)N . MRN and BLM may also interact indirectly via RPA and/or TRR N , 63. Intwith BLM A. MRN and/or TRR . We concF). The yeast homolog of BLM, Sgs1, and Dna2 also show approximately two-fold difference in unwinding rates (F and G). The change in resection velocity after the pause was heterogeneous and did not correlate with the prepause velocity (E). Adding MRN suppressed these pauses . MRN also suppresses pauses with the minimal MRN–BLM–DNA2 assembly . MR and MRE11 did not stimulate resection and suppress pausing (G–I). Interestingly, MR(S1202R)N decreased processivity, velocity, and could not suppress pausing (G–I). Thus, the ATP-dependent activities of MRN, along with BLM and DNA2, are also required to promote efficient DNA resection, possibly by stimulating the engagement of BLM with the ss/ds junction. We also tested whether pausing was sequence or GC content specific. The GC content of λ-DNA is greater on the cosL side than on the cosR side of our DNA substrate (B). Therefore, we assayed resection from the GC-rich (cosL) end or GC-poor (cosR) ends. The pausing frequency was similar on both substrates, suggesting that pausing is not strongly sequence or GC content dependent but instead may be caused by the accumulation of ssDNA (C and D). We conclude that MRN coordinates BLM and DNA2 to stimulate efficient DNA resection.The unwinding rate of DNA2 is approximately three-fold slower than that of BLM in the presence of RPA F. The yeng rates . This ding rates , F and Gvelocity E. Adding pausing , G–I. In pausing , G–I. Thubstrate B. Therefof ssDNA , C and DDNA resection is catalyzed by either the EXO1 or DNA2 nucleases. Although EXO1 may be the predominant resection nuclease in human cells , 67, 68,A). We propose that these physical interactions with BLM increase the processivity of BLM and suppress pausing by anchoring BLM to the ss/ds DNA junction. Similarly, the TRR complex also binds free DNA ends and interacts with BLM  , 77, 78.B motors . The molThe underlying reason for pausing by BTRR–DNA2 is unknown, but it is unlikely to depend on a χ-like DNA sequence as sequence-dependent resection regulation has not been observed in yeast and human resectosomes. We conjecture that BTRR may unwind DNA in front of DNA2, leading to a growing ssDNA loop that ultimately pauses the entire complex. In this model, MRN prevents the accumulation of such ssDNA loops by synchronizing BLM and DNA2 helicase velocities. In support of this hypothesis, a recent single-molecule study showed that BLM retains contact with ssDNA as it unwinds dsDNA . AdditioMRE11 and BLM colocalize early at DNA breaks immediately following damage in cells . This isE. coli using a pET expression vector (Oligonucleotides were purchased from IDT. Human RPA (pIF47) was purified from n vector , 80, 81.n vector , 52, 82.n vector . Wildtypn vector , 82.6 (pIF527) was expressed in Sf21 insect cells infected using the Bac-to-Bac expression system (Life Tech)  resin  in batch and eluted with an imidazole gradient containing 50 mM Tris–HCl (pH 7.5), 500 mM NaCl, 10% glycerol, 2 mM β-mercaptoethanol, and 10 to 250 mM imidazole. BLM fractions were then loaded on a 1 ml HiTrap Heparin  and eluted with a gradient from buffer B  to buffer C . BLM was further purified using a Superose 6 in buffer D .For single-molecule fluorescent imaging, 3xHA-BLM-Hisfe Tech) . Cells w6-TOP3A and RMI1-His6/FLAG-RMI2 were kindly provided by Patrick Sung and Jim Daley. The TOP3A plasmid was transformed into Rosetta (DE3) pLysS cells and grown in LB media and induced with 0.2 mM IPTG for 18 h at 16 °C. Cells were pelleted and resuspended in buffer E  supplemented with 0.01% Igepal and 1 mM PMSF. The cells were sonicated, and the soluble material was clarified by centrifugation at 35,000 RCF for 45 min. The supernatant was added to Ni–NTA in batch, washed with buffer A supplemented with 20 mM imidazole, and eluted with buffer F  supplemented with 250 mM imidazole. TOP3A was further purified using a 1 ml HiTrap SP  with a gradient from buffer G  to buffer H  and dialyzed overnight at 4 °C in buffer I .pRSF-Duet plasmids containing His6/FLAG-RMI2 plasmid was transformed into Rosetta (DE3) pLysS cells and grown in LB media and induced with 0.2 mM IPTG for 18 h at 16 °C. The cells were sonicated, centrifuged, and purified by Ni–NTA resin similar to TOP3A. RMI1/2 elution from Ni–NTA purification was diluted to 50 mM KCl with buffer J , loaded on a 5 ml HiTrap Q XL , and eluted with a gradient with buffers G and H. RMI1/2 was further purified using a Superdex 200 Increase  in buffer I. The TOP3A–RMI1/2 complex was assembled by incubating purified TOP3A and RMI1/2 (1:3 ratio) followed by purification using a Superdex 200 Increase in buffer I.The RMI1-HisAll single-molecule data were collected on a Nikon Ti-E microscope in a prism-total internal reflection fluorescence configuration equipped with a prior H117 motorized stage. Flow cells were loaded into a custom-designed stage insert incorporating a chip mount, fluidic interface, and heating element . All expDNA substrates for single-molecule studies contained a 78 nt 3′-overhang or 12 nt 5′-overhang. These were prepared by annealing oligonucleotides IF007 and LM003 (3′-overhang ligated to cosR site), IF006 and LM024 (3' overhang ligated to cosL site), or IF007 only (5′-overhang)  28)..28).2, and 1 mM ATP), we typically observe intermittent fluorescent emission (blinking), which is an intrinsic property of single QDs . XY drift was then subtracted from all resectosome complexes during postprocessing. For each frame, the point spread function of DNA-bound proteins was fit to a 2D Gaussian to obtain  coordinates with subpixel resolution. We ensured that resectosome components were DNA bound by briefly stopping buffer flow at the beginning of each experiment. Stopping buffer flow recoils the DNA and all associated proteins to the diffusion barrier, providing a useful control that these are not surface-tethered particles. Only DNA-bound particles were included in all subsequent analyses. We did not attempt to analyze the trajectories of particles that moved less than 1 kb, which is approaching the resolution of the DNA curtain assay under the buffer flows used here (∼500 bp).The image stacks collected from the EMCCD cameras were exported as full-resolution TIFF stacks. To correct for XY-stage sample drift, a stationary particle on the flow cell surface was picked, and its position was tracked by fitting the point-spread function to a 2D-Gaussian using a custom-written ImageJ script . For individual moving particles, the processivity was determined by measuring the distance traveled along DNA, and velocity was determined by fitting the time-dependent position along DNA to a line. To determine DNA binding lifetimes, we measured the time each molecule was bound to DNA. The survival probabilities were fit to a single exponential decay in MATLAB. Particles from at least two flow cells were pooled for the final analysis. Statistical significance was determined 2, and 1 mM ATP) to 200 μl and injected into the flow cell. FLAG-TOP3A–RMI1/2 (80 nM) or FLAG-DNA2 (40 nM) were labeled with QDs preincubated with a mouse anti-FLAG antibody (Sigma–Aldrich) on ice for 10 min prior to injection. In addition, biotin–MRN (2 nM) was labeled via streptavidin QDs. Saturating biotin was added to the protein–QD conjugates to bind free streptavidin sites prior to injection.3xHA-BLM (40 nM) were conjugated to QDs preincubated with a rabbit anti-HA antibody (ICL Lab) on ice for 10 min in 20 μl. Next, BLM was incubated with the anti-HA QDs at a ratio of 1:2 for an additional 10 min on ice, diluted with imaging buffer  where the positions of individual molecules on DNA were determined by fitting the point spread function to a 2D Gaussian. Trajectories were used to calculate the velocity and processivity for BLM and DNA resection complexes. Statistical details of experiments can be found in the For https://github.com/finkelsteinlab/single-particle-tracking-scripts.All custom MATLAB and FIJI scripts are available at ilya@finkelsteinlab.org).Further information and requests for resources and reagents should be directed to and will be fulfilled by the Lead Contact, Ilya Finkelstein (This article contains The authors declare that they have no conflicts of interest with the contents of this article.


The creation of sustainable composites reinforced with natural fibers has recently drawn the interest of both industrial and academics. Basalt fiber (BF) stands out as the most intriguing among the natural fibers that may be utilized as reinforcement due to their characteristics. Numerous academics have conducted many tests on the strength, durability, temperature, and microstructure characteristics of concrete reinforced with BF and have found promising results. However, because the information is dispersed, readers find it problematic to assess the advantages of BF reinforced concrete, which limits its applications. Therefore, a condensed study that provides the reader with an easy route and summarizes all pertinent information is needed. The purpose of this paper (Part II) is to undertake a compressive assessment of basalt fiber reinforced concrete’s durability features. The results show that adding BF significantly increased concrete durability. The review also identifies a research deficiency that must be addressed before BF is used in practice. In recent years, there have been increased demands for strength and durability features due to the construction of large-scale infrastructure in several challenging service settings ,2,3,4. CSince ancient times, many parts of the world have been using fibers in construction materials. The motivation for this effort was to boost the tensile strain of the concrete’s “perceived” delicate properties. In the 20th century, this technique was employed to produce fiber-reinforced concrete, which has grown in popularity and apply in construction sector due to its improved strength. The components of concrete are reinforced with a variety of fibers, including biological and inorganic fibers. The surface of the fibers, length, elastic modulus, and the material from which they are made all perform a role in determining the type of fibers used in concrete to increase tensile strength. Additionally, it is uncertain to what degree these fibers affect the functionality of concrete . Metalli2 is the primary component and Al2O3 is the second, as indicated in BFs are made from genuine basalt ore using hot melting and wire drawing techniques at high temperatures . When thThe kind, quality, and production method of the raw materials, as well as the qualities of the finished product, all influence the base cost of BFs. The chemical and mechanical qualities are influenced by the composition of the raw materials, much like the price. Variations in composition and element concentration result in variations in thermal and chemical stability as well as favorable strength and basic qualities. Generally, the production of this type of fiber is comparable to that of glass fiber (GF), but it uses less energy and does not include any additives, making it less expensive than GF or carbon fiber (CF). Basalt rock from volcanic eruptions is used as the raw material to make BF, which is then molten in a kiln at 1450–1500 °C. The heated substance is then driven through a platinum/rhodium crucible bushing to produce fibers. Constant spinning is a technique that may provide reinforcing material in the form of continuous fibers or chopped fibers for use in the manufacture of textiles and has a lot of potential users in composite materials. Along with being simple to handle using standard procedures, it also has significant cost advantages . The advA new class of inorganic fiber called BF has several benefits, including strength, stability, insulation, corrosion resistance, simple production, cheap cost, and high compatibility . The insEvery year, significant economic losses and security risks are brought on by steel corrosion in concrete buildings. In salty conditions, chloride damage is a virulent reason for steel corrosion . Accordi2 mixture for three months [According to the findings, self-compacting concrete is less practical when BFs are added. The physical qualities of concrete might be greatly improved, but BF decreased the flow properties . The impe months .Many scholars work on strength properties, durability aspects, thermal properties, and microstructure analyses of BFs-reinforced concrete and stated an encouraging response. However, information is dispersed, and readers cannot simply judge the benefits of BFs-reinforced concrete, which restricts its uses. Therefore, a compressive study is required that summarizes all relevant information and provides an easy path for the reader. Although a compressive review was conducted by other scholars , some duAdditionally, BF creates a network structure that boosts the matrix’s internal binding force and prevents cement paste from flowing or segregating. Therefore, the presence of BF causes concrete’s flowability to decrease , making It can be concluded that the density of concrete decreased with the addition of BF. However, with the substitution of cementitious materials such as fly ash, a slightly decreased in density was observed up to 0.45% addition of BF, further addition of BF (0.6%) results in considerably decreased density.Hazardous chemicals like chloride and sulphate ions may penetrate construction materials via water infiltration. Diffusion and capillary action are the two major methods of transporting chloride and sulphate ions through the material, although transformation by itself is a very sluggish procedure. Consequently, particularly close to the unsaturated concrete surface, capillary action could be the primary transport pathway. Understanding how concrete transports moisture is crucial for determining its service life and enhancing its value as a construction material .The total water absorption over 6 h and 8 days, respectively, was used to calculate the initial and secondary sorptivity. Concrete must have both compressive strength and long-term durability. The density of concrete has an impact on its long-lasting qualities. Compact (dense) concrete has more load carrying capacity and has fewer voids and pores. Concrete with fewer voids is less porous to liquid chemicals and water. As a result, this kind of concrete will last longer, and less WA or other harmful chemicals will penetrate.A study  shows thGlass fibers (GF) had a far better effect on water absorption (WA) than polypropylene fibers. Adding 1.35 percent GF decreased the sample WA from 3.49 percent to 1.99 percent, with a maximum reduction of 43.1 percent, when the water/binder ratio was 0.30. The highest decline of 10.6 percent in water absorption (WA) was achieved by incorporating 0.45 percent PPF, which decreased it from 3.49 to 3.12 percent .The statistics on water absorption show that increasing the fiber content somewhat improves the WA as associated to reference SCC. Nevertheless, the water absorption values of all fiber-reinforced SCC were within 2% of one another. Concrete has less water penetration because of a more compact pore structure as a consequence of the GF’s tight bond with cement particles. The endurance of the concrete is increased by the introduction of GF . It was The defects generated by BF, such as fractures and pores surrounding fiber in the matrix, are responsible for the charge rise . ParticuThe total charge transmitted through BF reinforced with 30% fly ash (FA) falls by 7.4 percent to BF without fly ash. Fly ash (FA) and silica fume (SF) both drop by 20.3 percent and 50.7 percent after 56 days. This finding suggests that the charge of BF-reinforced concrete is reduced when mineral admixtures are added, particularly when fly ash and silica are combined together. The pozzolanic activity and pore-filling properties of SCM are responsible for this alteration . AdditioAccording to Thomas et al. , ternaryShrinkage is seen in the early hours after casting, however, it may be prevented by improving the blend mix and proper curing. Carbon dioxide and solidified cement paste combine to induce carbonation shrinkage .According to the experimental findings, depending on the fiber content, using BFs greatly reduced concrete shrinkage and increased efficiency. The concrete shrinks by 0.716 mm/m, which is 25% less than the control sample, when the fiber content is utilized at 0.5 percent. The shrinkage will be reduced by 56.9% and 91.6 percent, respectively, associated with the reference, with the fiber content raised to 1.5 and 1.75 percent. When fibers are added to concrete mixtures, shrinkage in concrete is improved. A reduction in the amount of moisture in the concrete and shrinkage of the concrete will occur along with the hydration of the cement. However, the fiber will play a role as a bridge to transport stress throughout the concrete in the presence of micro-sized BF, considerably decreasing shrinkage. A study also reported that carbon nanotubes delay the propagation of micro-cracks and strengthen the interfacial transition zone . HoweverThe research looked at the effects of steel and BF on the concrete’s dry shrinkage characteristics. Since the fibers will prevent the cementitious matrix from shrinking, shrinkage values should, in theory, decrease as fiber volume is raised. As the concrete has more water available to be utilized in the cement hydration process, enabling the concrete to not shrink for a longer length of time, the boost in the w/c percentage would result in a drop in shrinkage strain. With an increase in fiber content, shrinkage strain values reduced consistently across all fiber samples. Additionally, as compared to the same percentages of BFs, the usage of steel fibers revealed a much reduced shrinkage strain .According to research fiber concrete had less shrinkage deformations than plain concrete without fibers, suggesting that it was more stable. By strengthening the bond among the fibers and mix, which facilitates the limiting of shrinkage during the drying activity, fibers may help reduce the amount of shrinkage in concrete .Another study’s  investigThe possibility of electrical charge transport through the composite is made clear by the material feature known as specific electrical resistivity. It often relies on the chemical makeup of the cementitious material, the kind and form of the pores, and the composition of the pore solution . An esseThe samples with the biggest improvements were sample (w/c = 0.35) with 0.30 percent BFs and an increase in chloride ion penetration resistance of 61 percent, and sample (w/c = 0.45) with 0.45 percent BF and an increase in chloride ion penetration resistance of 47 percent. Due to the rise in the w/c ratio, sample (w/c = 0.35) results are higher than sample (w/c = 0.45) values, as predicted, and at 0.30 percent fiber offers the greatest improvement. Using steel fibers improved the resistance to chloride ion infiltration. This is because steel fibers interact with one another, increasing their susceptibility to assaults from chloride. The steel fiber reinforcement shows a 48.45 percent decline or a 0.50 percent decrease (w/c = 0.45) in chloride ion penetrability resistance.3 of fiber. There is no linear relationship between fiber content and electrical resistivity; when an additional 30 kg/m3 of fibers were added, the loss of electrical resistivity was only around 30%. Contrarily, it was evident that conductivity almost linearly correlated with fiber concentration [According to research, adding fibers to concrete increased its electrical conductivity or decreased its electrical resistance. Particularly small fiber doses had a significant influence on the electrical resistivity that was measured, but larger fiber dosages made the changes less noticeable. The electrical resistance of the unreinforced concrete was split in half, from roughly 50 to 25 Ωm, with the addition of 30 kg/mntration . It can The compressive capacity is intimately connected with its porosity, the smaller the perviousness, the denser the composition, the greater the compressive capacity and the critical pore size and pore size distribution are directly correlated with the permeability and durability of concrete.The expansion tension brought on by sulphate crystallization and the tensile stress brought on by freezing pressure and capillary osmotic pressure enhanced the perviousness . After 2The pore structure system in concrete is interconnected and dispersed at random. The critical pore diameter, which may indicate the connectedness of pores, is the maximum pore diameter that can link the bigger pores. The physical meaning is that pores cannot be linked to one another if the pore thickness is bigger than the critical aperture. The better the critical pore size, the more durable and impermeable the cement concrete pore arrangement.The critical pore size of the concrete rose progressively for each group as the cycle continued. The critical pore diameters for additions of 0, 0.01, 0.02, and 0.03 percent of BF were, respectively, 205.5, 133.3, 115.4, and 165.6 nm after 20 cycles. Concrete’s permeability resistance diminishes with an increase in critical pore size, making it less stable in service when subjected to a single cycle of salt, freezing, drying, and wetting. Each major cycle of control concrete saw a steady rise in growth rate. After 10 cycles, the growth rates of the concrete in the 0.01 and 0.02 percent BF groups greatly rose, but those in the 0.03 percent BF group notably increased after 5 cycles. It has been revealed that while BF has the impact of strengthening and crack resistance, the optimal performance still requires the synergistic action of SCM and the proper quantity of BF. The required pore width for concrete’s durability and impermeability is reliable with its macroscopic performance index in each cycle. It can be concluded that pore diameter decreased considerably with the addition of BF due to the crack prevention of BF. However, at a higher dose of BF (0.3%), the results increased in pore diameter value due to a lack of flowability, which increased compaction efforts, leading to more voids.The total chloride concentration of concrete after the addition of BF is shown in The pressure differential between the interior and exterior of the aggregate enables the prewetted water to be released when the moisture content of the concrete lowers due to continual hydration. Chloride ions from the inside of the aggregate with the water enter the concrete matrix as the internal curing process is accomplished. The internal curing action is most noticeable, the chloride ion concentration is maximum, and the pore structure is optimum in the 0.05 percent of BF-based concrete. A decreased total chloride ion concentration is the consequence of the internal curing action of concrete being less effective because of the greater BF content.The free chloride ion concentration of BF reinforced concrete reduces during the first stages of hydration as shown in The network structure created by BF additionally strengthens the matrix’s internal binding force and prevents cement paste from flowing or segregating. As a result, the existence of BF reduces the flowability of concrete , making The challenge of excessive alkalinity from the adjacent material is a major problem when the fiber reinforced concrete components are buried in the concrete using the near-surface mounting technique. As concrete is alkaline, the alkali resistance of BF used in concrete is crucial. The research findings on BF’s alkali resistance are contradictory. According to research, BF has strong alkali resistance at both low and high temperatures . Similar2 content. No such reaction product was seen in the CF, and the projected volume decrease after 28 days of immersion was less than 20%. The strength fluctuated in relation to the duration of immersion. Over 28 days, the capacity of the glass and BF decreased by more than 80%. After the CF had been submerged for 28 days, a strength drop of roughly 13 percent was recorded.The SEM images of the fibers after dipping at different mediums are shown in According to the research , BF is mAssessments of the tensile capacity of various fibers after 66 days of exposure are displayed in Basalt fibers (BFs) may help to enhance the pore size distribution of concrete. Concrete durability properties are therefore significantly increased by BF, which may minimize fractures and stop water or hazardous ions from infiltrating concrete. In this analysis, the effects of BFs on the durability assets of concrete are summarized. The detailed conclusions are given below.The apparent density and ultra-sonic pulse velocity exhibit a decreasing trend with increasing BF volume content.Shrinkage declined with the addition of BF. It is owing to the crack’s prevention and higher elastic modulus of BF.Surface resistivity boosted with BF up to 0.3%. However, beyond the accumulation of BF, the results declined in surface resistivity due to a lack of flowability.The rapid chloride ions penetrability of concrete increased with the addition of BFs due to a weak fiber-matrix interfacial transition zone (fiber-ITZ) with extreme permeability. However, the addition of mineral admixture decreased the rapid chloride ions penetration up to some extent due to pozzolanic and micro fill-up cavities. Though data are fewer, and additional details analyses are necessary.The freezing and thawing resistance of concrete was boosted with the addition of BF. The highest resistance was detected at a 0.02% addition of BF. However, further addition of BF resulted in a decrease in freezing and thawing resistance due to a lack of flowability.BFs show comparable resistance to water, salt, and alkaline corrosion, but weaker resilience to acid corrosion than GFs and CFs. However, the statement is not clear, as some studies conclude that the BF is more corrosion resistant than carbon and GFs.Overall, less knowledge is accessible on the durability characteristics of BFs-reinforced concrete. Furthermore, some studies claim improvements in durability assets of concrete reinforced with BF, while other findings claimed decreased durability properties of concrete reinforced with BF. Thus, the review suggests a detailed study on the durability aspects of BFs-reinforced concrete. Additionally, no information is available on the creep properties of BFs-reinforced concrete. Finally, the review also suggests a detailed study on the corrosion resistance of BF by adjusting the matrix and the coupling agent to enhance the corrosion endurance of BF-reinforced concrete.


Structural deterioration during fire leads to significanteconomiclosses, severe injuries, and deaths. Research to accurately estimatethe impact of fire on structural security and performance, and toidentify ways to reduce it, has been increasing recently with capitalinvestments in the building and infrastructure sectors. This researchaims to establish a reliable algorithm for simulating the behaviorof reinforced concrete (RC) beams under thermal and structural loads.The proposed algorithm is based on the combination of thermal andstructural analyses using the sequential link technique. These analysesuse material characteristics such as conductivity, specific heat,stress–strain relationship, and thermal expansion to capturethermal and structural responses during the heating phases accordingto Eurocode 1 and Eurocode 2 using the finite element method. Beammodels in the study, which have been exposed to the ISO-834 fire curve,were designed to exhibit flexural failure. Nonlinear numerical analysisresults have mostly coincided with the previous studies regardingthe residual load-bearing capacity. Depending on the outcomes of theprevious experimental studies, an RC member’s structural strengthincreases when the internal temperature is between 150 and 250 °Cand degradation starts after 300 °C. This outcome has been supportedby the previous numerical and experimental studies, propounding theaccuracy of preferred modeling and analysis approaches. As the essentialdistinctness of the research, the effects of elevated temperatureson the bonding behavior between concrete and rebar were consideredfor numerical analyses. However, concrete resistance to fire shouldbe considered at the design stages, as its strength deteriorates whenexposed to high temperatures.2 Althoughconcrete and steel are non-flammable materials, it has been recordedthat concrete has a loss of strength at high temperatures.6Structural deteriorationis seen during many fire events everyyear. It is known that such events lead to severe injuries, deaths,and significant economic loss. Among the factors affecting the amountof damage and losses caused by fires, type of structures and fireresistance and durability of the materials are essential. Concretehas the advantage of being resistant to fire, as it is a non-flammablematerial with low thermal conductivity.Laboratory experiments aiming to evaluate fire resistanceare expensive,time-consuming, and there are limitations to test different parameters.Using numerical models to evaluate the structural fire resistanceof reinforced concrete (RC) members is an alternative to the experiments.Numerical models enable researchers to take various parameters intoaccount accurately and cost-effectively. This study presents a three-dimensional(3D) finite element (FE) model accurately estimating the thermal andmechanical behavior of reinforced concrete beams exposed to fire.This finite element analysis approach highly considers modeling thebonding behavior between reinforcement bars and concrete, a featurerarely considered in previous numerical studies. It showed that theinclusion of rebar-concrete bonding (adherence) yields more accurateresults regarding the behavior of RC members exposed to fire.This study is based on establishing a modeling approach to provideideas and information about the residual strength of RC members, whichare intended to be re-used after a fire. Numerical outcomes presentedin the research demonstrate that finite element analysis of RC memberscan be used directly in performance-based fire safety design and parametricstudies aiming to develop simple design rules.It has been intendedto achieve a reliable algorithm to simulatereinforced concrete beams under both mechanical and fire loads inthis study. The proposed approach was modeled by ANSYS software for3D analysis of RC members under high temperatures, and their thermaland structural analyses were performed. Most numerical analysis softwaresuch as ANSYS uses the sequential combination technique or the directlink technique to interconnect two types of analyses. The sequentialcombination technique is based on the concept of running each typeof analysis separately and applying the results of the first analysisas initial conditions for the second one. On the other hand, the directconnection technique has been used as a single combined analysis forthermal and structural analyses with the activated degrees of freedomat each node.27 stated that thetemperature in steel rebars is the most critical factor affectingthe strength of beams, while examining the bending effect of RC beamsin case of being exposed to ASTM E119 standard fire. In their studieson RC members, Kumar and Kumar8 and Chenet al.9 showed that the increased load-carryingcapacity decreases due to the increased exposure time to fire. Ahmadet al.10 and Sharma et al.11 found that the strength of concrete decreases with increasingtemperature, and 600 °C is the critical temperature for seriousdeterioration in concrete.Ellingwoodand Lin19 Yağan20 stated that the main reasonfor the carrying capacity decrease of the beam elements is the damageon the concrete and the decrease in the clamping of the concrete reinforcementdue to this damage. Khan et al.21 reportedthat bond strength decreases up to 44%, starting from 300 °C.Exposure of RC members to high temperaturescauses significantlosses on the mechanical and physical properties of concrete and steelreinforcements and also their bonding performance. Deterioration ofbonding features in a fire can significantly affect the load capacityof concrete members. For this reason, the bonding behavior of RC structuresshould be considered for structural fire engineering design. Today,general information is available about the material deteriorationof concrete and rebars at high temperatures. However, research onthe effect of bonding between concrete and rebars at elevated temperaturesis still limited. Experimental studies on bonding have been conductedin the literature.22 observed seriouseffects on the tensile properties of bare steel bars after 600 °C,which were exposed to high-temperature effects in the range of 23–800°C. By examining the effect of high temperatures on adherence,it was stated that the bond strength gradually decreases with theincrease in temperature.13Özkal et al.24 However, fire tests are costlyand require too much time. Advanced analytical methods are generallybased on the finite element method (FEM).25 FEM has been regarded as the most common tool for performing advancedfire-resistant analysis, and necessity of structural performance investigationunder fire is significantly required.27 As a resultof the studies on the numerical analysis of RC structures under hightemperatures, it has been supported that both the thermal and mechanicalbehavior of the structures can be reliably feasible.40In order to improve fire design provisions, studies investigatingthe structural behavior of RC members exposed to fire have attractedattention for the last four decades through fire tests and advancedanalytical methods.25 and Terro41 developed a finite element analysis approach detailing the thermaland mechanical properties of concrete and steel. It has been observedthat numerical analysis including thermal and structural modelingis able to coincide with the experimental results to evaluate theperformance of RC structural elements during exposure to fire.33 Jawdhari et al.42 developed a transientthermal-mechanical finite element technique by using ANSYS, whichincludes two separate but related time-domain simulations of heattransfer on a nonlinear structure. Ozbolt et al.33 numerically simulated the behavior of RC. The initial strengthof the beams decreased with the increase of the fire exposure time.They also stated in addition to predicting the general response ofbeams, the model could be an effective tool to numerically investigatea few phenomena that are difficult to observe experimentally. Kodurand Agraval43 developed an approach toassess the capacity of RC beams exposed to fire and applied this approachwith a detailed numerical model developed in ABAQUS software. It showedthat finite element analysis gives more realistic strength resultsthan predicted from the simplified cross-sectional analysis. By usingthe FEM with ANSYS software, Kada et al.35 showed that fire failure of beams would be caused by the web characteristicsof the beams in most cases. A detailed three-dimensional temporarythermal finite element analysis was performed by Musmar et al.36 to examine the performance of RC beams exposedto fire. The RC beam was exposed to ASTM E11944 standard fire on the lower and side surfaces under a time-boundtemporary temperature load, while a constant load was applied on theupper surface. Verification of the finite element model is comparedwith the experimental results performed for similar RC beams underthe same conditions. Ryu et al.37 exposedthe ISO-83445 standard fire curve to differentRC beams with different loads. After the experimental stage, numericalanalysis was performed with the ABAQUS software. Results showed thatthe higher the load level, the higher the temperature distributions.The temperature distributions can be explained by the crack propagationcaused by loading. Failure of the beams developed as the fire temperatureincreased. Trong et al.38 investigatedthe effects of fire on temperature distribution in the concrete structureusing the finite element method by ANSYS software. Based on the lawof temperature distribution, it was stated that it is possible todetermine the variation of mechanical properties such as elastic modulus,strength, strain, and so forth. Elshorbagy and Abdel-Mooty39 investigated the effect of fire parameters oncompressive strength of concrete, concrete cover, and lateral stiffnessof the beam with detailed numerical finite element models using theANSYS program and supported their findings with experimental observations.To predict the behavior of three-dimensional RC members infire,Lie46 Sincenumerical models are insufficient to interpret the effects of bondingproperties between concrete and rebars at high temperatures, mostnumerical models developed to predict the fire behavior of RC structuresare based on the assumption of fully bonded contact.47 More research has been required to accurately estimatethe impact of fire on structural safety and performance and to identifyways to reduce this impact. Therefore, the primary purpose of thisresearch is to develop robust numerical models for predicting theadherence between concrete and reinforcement under fire conditionsand finding a reliable method to simulate the thermal–structuralanalysis of RC members and evaluate critical parameters affectingthe performance of RC structures during exposure to fire loads.Previous studies on structural fire behavior provide essentialinformation about parameters affecting the bonding performance athigh temperatures and form a solid basis for developing numericalmodels for interlocking bonds.48 studied to simulatethe adherence between concrete and rebars. However, studies51 simulating the bond-shear relationship under hightemperatures are limited. Huang47 adoptedthe CEB-FIP52 (1991) adherence model atambient temperature and considered the deterioration of bond strengthat high temperatures using the experimental results generated by Bazantand Kaplan.53 Huang’s model47 was a significant step forward on evaluatingbonding properties in a fire. Hemmaty et al.54 considered a nonlinear bond-shear law based on experimental studiesbetween concrete and rebars. They stated that material models couldalso be used for modeling the bond-shear relationship , and they suggestedthe actual modeling with COMBIN39 spring elements. As a result, thecrack results obtained from four different material models definedfor the spring element in ANSYS were compared with the cracks in thesamples applied with the tensile test and it was stated that concrete-rebarbonding could be modeled realistically by using appropriate bond-shearlaws.Currently, a limited number of numerical models are available toconsider bonding behavior at high temperatures. Several researcherssuch as Bolmsvik et al.355 software. Two types ofanalysis are needed to model the beam exposed to mechanical and thermalloads. First, thermal analysis is required to calculate temperaturesacross the beam at any time step. Through this analysis, the fireload was applied in the form of thermal load in addition to the structuralloads in the structural analysis. There are two options to conducttwo different analyses together. The first option is to apply theresult of one analysis as the initial boundary condition for the otheranalysis, where each analysis type is performed separately. The secondoption is performing both analyses simultaneously.Finite elementmodels of the RC beams were developed using ANSYS(Release 18.2)56 As the temperatures from thermal analysis form the inputfor structural analysis, thermal analysis is to be carried out first,followed by structural analysis.57The thermalRC element (SOLID70) used in this study does not havethe feature of cracking, which prevents observing the cracks in concrete.Additionally, since the steel rebar (LINK180) in a structural analysishas no thermal equivalent, it is not possible to directly performboth analyses simultaneously. For all these reasons, the sequentiallycombined thermo-mechanical analysis was preferred.Step 1Define the beam model for structuralanalysis.Step 2Evaluationof the beam’sfinal capacity at room temperatureStep 3Define the beam for thermal analysiswithout deformationStep 4Thermal analysis solution.Step5Structurally changing the analysisand thermal type and defining the structural model.Step 6Adding the thermal analysis results.Step 7If there is a collapsein the beamstrength; evaluation of fire resistance, if there is no collapse formation;evaluation of residual strength by applying mechanical loads.The thermal–structural analysis steps in the ANSYS programare shown below3.13.1.1SOLID70 was usedto model the behavior of the concrete in heat transfer problems dueto its heat conduction feature. It has eight nodes with one degreeof temperature freedom in each node. LINK33 was used to model longitudinaland transverse reinforcements as it can transmit heat between twopoints. LINK33 is a uniaxial element with one degree of freedom ateach node. Both elements can be used in 3D time-independent or 3Dtime-dependent thermal analysis.58 At the same time, different properties can beassigned to the spring element in tension and pressure, and both torsionand longitudinal elongation in 1-, 2-, and 3-dimensional problemscould be operated. Uniaxial tensile-pressure characteristic of theelement has three degrees of freedom at all joints for the longitudinalextension option. At the same time, these nodes can freely extendin x, y, and z axes.59Bond shift modeling was consideredin the study to achieve more realistic results in numerical modeling.As the standard approach in structural analysis of RC members, 100%bonding (adherence) is assumed between concrete and rebar. However,this is not possible in actual conditions due to human errors, concretecasting, weather conditions, and so forth. Hence, the COMBIN39 nonlinearspring element was preferred at the coinciding nodes of the concreteand rebars. It is a one-directional spring element that nonlinearforce–deformation relations can be defined. COMBIN39 is definedby a nonlinear force–displacement curve and two nodes.3.1.2x, y, and z axes). The most substantial properties of this element are the processingof nonlinear material properties. LINK180 is a three-dimensional sparelement that can be used in uniaxial tension and pressure conditions,which was used to model rebars in concrete. The element has plasticdeformation capacity, two nodes, and three translational degrees offreedom at each node . In addition, it is suitable for plasticity, stretching,rotation, and extinction.SOLID65 wasused for modeling concrete because it has plastic deformation, tensileand crushing capabilities in three directions. The element has eightnodes and each node has three translational degrees of freedom  weredefined by calculating from Eurocode 161 with three basic thermal properties . Thermal material propertiesof the steel rebars are shown in The thermal model of the rebars was modeled usingthe LINK33 element,and this element was defined by calculating from Eurocode 23.2.261 and Eurocode 3.62 The secondpart demonstrates the plastic region of the curve by defining themultivariate kinematic stiffening values for stress and strain. Thisprocess is defined for each temperature range since concrete and steelbehave differently at various temperatures. Material properties areshown in Stress–strainrelationship is generally defined in two parts for concrete and steelrebars. The first part demonstrates the elastic region of the curveby defining the linear isotropic values of the modulus of elasticityin terms of temperature, as explained in Eurocode 23.362 provide guidelines for verifying thermal analysisresults for RC members exposed to the standard ISO-83445 fire curve on one side and all sides. For theimproved ANSYS finite element model, film coefficients in surfaceelements used to apply heat loads in terms of convection were acceptedas αc = 25 W m2 °C–1 for surfaces exposed to fire and αc = 9 W m2 °C–1 forsurfaces not exposed to fire.39 In thisstudy, following the selection of the time-dependent analysis typeand initial boundary conditions for the room temperature of 20 °C,fire load is applied to the three surfaces of the beam as shown in Eurocoderegulations60 and Eurocode261 according to g is the gas temperature in the fire compartment (°C); t is the time in minutes; “20” correspondsto the initial temperature (T0) and if T0 ≠ 20 °C, it can be changed toanother value.To simulate the time-dependent temperature alterationin the beamwith the fire phase, a temperature–time curve should be definedas a function. The temperature–time curve that was used inthis study is shown in After performing thermal analysis, the analysistype is switchedto structural, and SOLID70 and LINK33 elements are converted to SOLID65and LINK180. The fire load applied to three beam surfaces by selectingthe time-dependent resolution type is shown in 63 Two differentnumerical analyses with thermal and structural loads were performedfor each of them, and similar results and heat profiles were obtained.While creating the numerical model for thermaland structural analyses,the validation study was initially performed considering experimentalresearch of Kodur et al.Beams were modeled considering the standard strength concrete.The beam dimensions are 2.5 m long, 0.250 m wide, and its total depthequals 0.4 m. The beam has two tensile rebars with 12 mm diameterand two compression reinforcements with 12 mm diameter. Stirrups with8 mm diameter were placed with 0.15 m spacing. The yield strengthof steel is 500 MPa, and the total load given to the beam is vertically150 kN. The beam geometry, reinforcement spacing, and cross-sectionaldetails are presented in 3.445 temperature–time curve, and thermal/structuralresponses of both beams were evaluated. As soon as the ambient targettemperature is achieved for the periods specified in the ISO-834 firecurve, the load-bearing capacities of the beams are determined. Twelvedifferent ambient temperatures were determined, starting with roomtemperature. The point that makes this study unique is that the ISO-834fire curve of the ambient temperature allows each temperature to beexamined precisely, although the high temperature is reached in ashort time. Thermal results were calculated according to the temperaturevariance over time at each node.Within thisresearch, a finite element model of an RC beam was designed to exhibitflexural failure by considering the bonding (adherence) behavior.Finite element modeling of the concrete and rebars has been performedby applying a four-point loading. The beam was subjected to the ISO-834Concrete elements have a meshsize of approximately 2.5 cm. Steel elements of longitudinal and transverserebars were placed, leaving a 2.5 cm concrete cover. Concrete meshis shown in y and z directions using CP (Couple) command. It was forced tomake equal displacements in these directions under lateral loads.In the x direction, nodes were intended to displaceaccording to the bond stress-rebar slippage curve given for COMBIN39,and nodes were modeled independently from each other. Concrete-steelbond models of Lowes,64 Eligehausen etal.65 and Murcia-Delso et al.66 are the most basic and widely used approaches.As previously stated for bond modeling, ANSYS assumes100% adhesionbetween concrete (SOLID65) and rebars (LINK180). Since this assumptionis not practically possible, the COMBIN39 spring element was preferredfor bond modeling. Nodes of the concrete and rebar elements were modeledseparately, coinciding with each other. An illustration of the appliedtechnique at the coincident nodes is shown in 3 Diederichs and Schneider,12 Morley and Royles,13 Haddad et al.,16 Özkal et al.,22 Huang,47 Pothisiriand Panedpojaman,49 Raouffard and Nishiyama,67 Matsudo and Nishida,68 Wang,69 Haddad and Shannis,70 Khalaf et al.,71 andTariq and Bhargava.72Bond stress–rebar slippage models at differenttemperaturesare required for thermal analysis. Some of those have been suggestedby Hertz,In terms ofperforming a validation study, a bond stress–rebarslippage model was created by averaging and idealizing the suggestionsfrom these previous studies for the different temperature levels asshown in 4It is knownthat in a reinforced concrete structure exposed tofire, the ambient temperature and its own temperature cannot be thesame. Since the thermal conductivity coefficient of the concrete isrelatively low, concrete transmits the heat more slowly. After thethermal analysis was carried out on RC beams, the maximum temperaturevalues reached through the beam at different ambient temperaturesare shown in 7 Bamonteand Monte,73 and Gao et al.,50 supported the mentioned change in the temperaturedistribution regarding inner and outer sections of the concrete.Because the ISO834 fire curve reaches the target temperatureina very short time and thermal conductivity coefficient of the concreteis relatively low, even the outer surfaces of the beam could not reachthe ambient temperature. The fact that the heat cannot reach the interiorof the concrete in such a short time is clearly seen from the heatdistributions of the beams exposed to different temperatures 12. Altho45 fire and target temperatureswere achieved. Following the thermal and structural analyses, load–deflectionand moment–curvature histories of the beams were obtained andare presented in Structural loads were applied on the beams, whichwere exposedto ISO-83474When the load–deflection and moment–curvaturehistoriesare examined 13 and 1475 Savva et al.,76 andAydın et al.77 indicated that theconcrete compressive strength increases with increasing temperaturebetween 100 and 300 °C. On the other hand, Yamazaki et al.78 came across an increase in the compressive strengthof concrete at around 200 °C, and after that, rapid decreaseswere observed in strength with the increase in temperature. Xiao andKönig79 stated that when the compressivestrength of the concrete is increased from room temperature to 400°C, they observed a small decrease, and then, a slight increaseand a very significant decrease in strength when the temperature reached400 °C. They stated that only 20% of the initial strength couldbe preserved at 800 °C. Rashid et al.80 stated that there is no significant change regarding the concretecharacteristics up to 150 °C, and when the temperature risesabove 150 °C, it starts to lose strength. As a result of thestudy by El-Hawary and Hamoush,5 an increasein the bond strength of the samples, which were heated at 100 °Cfor a short time, was determined. This increase was explained as shrinkagedue to the evaporation of water in the concrete and providing a betterinterlocking, but they stated that it was due to the decrease in adherencewith the increase in temperature and heating time at later temperatures.Bingöl and Gül17 also statedthat the bond strength of the concrete increases until 150 °C.The increase for the general structural performance of B8–B9beams (700–800 °C), in which the concrete achieves the150–250 °C temperature range, is supported by previousstudies. To explain also the structural performance increment after700 °C and sequential decrease after 900 °C, outcomes ofsome previous studies could be beneficial. Handoo et al.,81Concrete is a non-combustible material and is more resistant tofire than other construction materials. However, the compressive,tensile, and bending strength values of the concrete decrease dueto elevated temperature. In addition, it is stated in different studiesthat there may be no deterioration in concrete characteristics upto 200 °C, and even a slight increase in strength. These strengthincreases are explained by the energy generated by the effect of temperaturethat causes the unhydrated cement grains to complete their hydration.In addition, it should be considered that sample properties and testconditions are important parameters in determining the behavior ofthe concrete after high temperatures, and there may be differencesbetween the outcomes.The criticalambient temperature for the beam was found to be approximately900 °C considering the B10 beam, which achieved more than 300°C at the inner region and 600 °C at the outer regions and36% of the beam strength was lost at this level. Despite the reasonabledecrease in load-bearing capacity and initial stiffness, B10 and B11beams lost 98 and 99.4% of their energy dissipation capacities. Furthermore,the B12 beam (1100 °C) with an internal temperature of nearly600 °C received excessive damage. The mentioned outcomes aresupported by When the internal temperatureof the beams was between 150 and250 °C, they had the maximum load-bearing capacities with anincrement of nearly 10% as explained in detail. Furthermore, a comparisonof energy dissipation capacity and ductility 15 and 16545 fire curve. Furthermore,an algorithm has been developed by combining nonlinear finite elementanalysis with thermal analysis. The finite element method makes iteasier for researchers to study various structural problems and achievea solution in a shorter time compared to experimental investigation.Within the scope of thisstudy, reinforced concrete (RC) beamswere designed to exhibit failure by forming flexural cracks, takinginto account the different fire durations and temperatures based onthe ISO-834It has been observed that the fire effect increases the load-bearingcapacity of the RC beams up to a specific temperature and then decreasesthat rapidly as the ambient temperature increases. This boundary levelis 100 °C for the internal temperature. Therefore, it can beasserted that steel rebars do not have a significant role in heattransmission depending on the volumetric ratio compared to concrete.Hence, the rebar temperature could be considered equal to the concretetemperature at the depth where the reinforcement is located.The heat profile of the concrete was examined in two ways by takingcross sections from the outer and inner regions. A rapid temperatureincrease was observed on the outer regions of the beam that was exposedto heating directly. However, heat distribution at the interior regionscould not rise above 250 °C until the ambient temperature was900 °C. The main cause is the sudden increase in temperaturein a very short time regarding the ISO-834 fire curve. The environmentreaching high temperatures in a very short time caused the concreteto not lose its load-bearing capacity for a while due to the slowheat transmission. Exposure time to elevated temperatures draws moreattention to the apparent importance of exposure time to heating indetermining the residual strength of RC members, rather than ambienttemperature.The numerical modeling approach in this researchis compatiblewith the results of the previous studies. As shown in the numericalsimulation of the reinforced concrete beams, it is clear that theinternal surface temperature reached by the beam is more determinantof the bearing capacity than the ambient temperature. At the sametime, it was observed that concrete compressive strength and correspondinglythe concrete-rebar bonding performance increased when the internaltemperature was between 150 and 250 °C and structural deteriorationstarted to occur when it exceeded 300 °C. Therefore, such modelscan be further used to design and optimize fire protection systemsto achieve cost-effective solutions.