Concrete strength and factors affecting its development during early concrete curing are important research topics. Avoiding uncertain incidents during construction and in service life of structures requires an appropriate monitoring system. Therefore, numerous techniques are used to monitor the health of a structure. This paper presents a nondestructive testing technique for monitoring the strength development of concrete at early curing ages. Dispersed carbon nanotubes (CNTs) were used with cementitious materials and piezoelectric (PZT) material, a PZT ceramic, owing to their properties of intra electromechanical effects and sensitivity to measure the electromechanical impedance (EMI) signatures and relevant properties related to concrete strength, such as the elastic modulus, displacement, acceleration, strength, and loading effects. Concrete compressive strength, hydration temperature, mixture ratio, and variation in data obtained from the impedance signatures using fuzzy logic were utilized in the comparative result prediction method for concrete strength. These results were calculated using a fuzzy logic-based model considering the maturity method, universal testing machine (UTM) data, and analyzed EMI data. In the study, for data acquisition, a hybrid PZT–CNT sensor and a temperature sensor (Smart Rock) were embedded in the concrete to obtain the hydration temperature history to utilize the concrete maturity method and provide data on the EMI signatures. The dynamic changes in the medium caused during the phase in the concrete strengthening process were analyzed to predict the strength development process of concrete at early curing ages. Because different parameters are considered while calculating the concrete strength, which is related to its mechanical properties, the proposed novel method considers that changes in the boundary condition occurring in the concrete paste modify the resonant frequency response of the structure. Thus, relating and analyzing this feature can help predict the concrete strength. A comprehensive comparison of the results calculated using the proposed module, maturity method, and cylindrical specimens tested using the UTM proved that it is a cost-effective and fast technique to estimate concrete strength to ensure a safe construction of reinforced cement concrete infrastructures. To improve the construction quality and provide a safe environment for the construction of infrastructure, numerous techniques have been developed to monitor the health of a structure. To conduct such monitoring during construction and the service life of infrastructures, the tests must be advantageous and of high accuracy. Several in situ tests have been conducted on concrete structures ,9,10,11.CNTs are a focus in global research because of their excellent properties of electrical network formation and piezoresistivity. Since Iijima introduced CNTs in 1991 , they haCementitious materials are quasi-brittle and present electrical and thermal insulation features. Thus, their sensitivity is affected by the addition of nanofibers, which inverts the cementitious matrices, thereby modifying the properties of the concrete. The signal processing pathway is shown in Research and development in the field of structural health monitoring has generated significant interest in nanosized fibers, such as CNTs, for modifying the properties of concrete. The metallic property of piezoresistivity of CNTs enables them to detect the changes in the stress/strain in a specimen. Furthermore, CNTs can simultaneously act as reinforcement elements for improving the toughness of concrete. This study demonstrates that the sensitivity of CNTs to strain is enhanced when PZT pitches are added, which can be optimized by the remarkable maintenance of the intra-mechanical and electrical properties of PZT materials and CNTs. For such materials, the stress variations are correlated to the variations in their properties, such as impedance and electrical resistance. These specimens actuate to generate vibrations and actuation in a concrete structure and, subsequently, act as a sensor to detect the vibrations and waves for the detection of the dynamic response of the host structure.The fabrication process of the proposed smart hybrid PZT–CNT materials involved two steps.2O3) and a sulfate-resistant material (4 wt.%) were used. For the good growth of CNTs, Al2O3, SiO2, and MgO are effective mixing materials; therefore, they were employed as is done typically. To ensure cost effectiveness and a low decomposition temperature, acetylene was used as the main source of carbon. According to Kim, the dispersion of CNTs can be enhanced by minimizing the water content, which increases the collision probability between particles of silica fume and the agglomerated CNTs in the matrix of a CNT–cement composite. Some details about dispersion of CNT partials in the prepared paste are given in The first step was the synthesis of the CNT specimens, which was conducted using a simple process following the American Society for Testing and Materials (ASTM) C 305. A standard Hobart mixer was used for the preparation of the paste. As the cementitious materials, Portland cements containing various concentrations of iron oxide particles  represents the electric charge density’s tensor of displacement.In Equation (1), From Hook’s law,Combining Equations (1) and (2) yieldsS is the strain, T is the stress, and Here, The data of the sensor directly depend on the parameters related to the concrete strength, such as the stiffness, curing time, temperature, modules of elasticity, hydration temperature, and humidity. Therefore, for different mixtures, the conditions were varied, and the water–cement ratio was changed while keeping the concrete type constant. To obtain the design strength, appropriate curing of the specimen and maintenance of the water–cement ratio are required. For this purpose, Abrams’ equation can be considered.Here, Concrete strength decreases with increasing water and air contents, whereas it increases with the addition of cement paste. The temperature and humidity directly affect the concrete strength at the early curing ages after the concrete paste is poured. A long curing time with appropriate moisture results in a high strength for a concrete mixture at a specified water–cement ratio. The American Concrete Institute Committee 209 (2008) recommends the following strength relationship for a concrete containing normal Portland cement, which has a high moisture content and is cured well :(5)fcmt t days and In Equation (5), t days and s is a cement-type dependent coefficient, i.e., for quick-strength cement, cement with normal hardening, and cement with slow hardening, its values are 0.20, 0.25, and 0.38, respectively [Here, ectively . For a cectively .Addition of CNTs to the cementitious material increases the heat and mechanical response effects in the paste. The dynamic response obtained from the electromechanical and ultrasonic waves yields the boundary changes in the material, from which the phase variations of the concrete paste at early curing ages can be estimated. A noise-free data procurement procedure is introduced to extract the features for the prediction of the concrete compressive strength. The concrete strength estimation technique uses algorithms based on fuzzy logic for the extraction of the feature variation in the host structure.The transducer was polarized for the measurement of the features from the signal processing of the EMI. To detect the effects, pattern changes in concrete, signal processing, and dynamic responses of the structure, we used PZT–CNT sensors  to intensify the sensibility of the transducer. As discussed earlier, the PZT material can generate a signal to actuate a specimen and measure the propagated response signal based on piezoelectricity, whereas CNTs can respond to the stresses developed by the PZT actuators in the specimen. An example of the energy interconversion is presented in To estimate the concrete compressive strength, we have used the sensor data collected from the early pouring time till the 28th day of curing. We used the EMI as a function of the curing parameter and the calculated cross-correlations (1-CC) among the data. As the curing time progresses in the initial sitting time, the concrete paste phase changes with the increasing stiffness of the material. The dynamic change responses of the structure were monitored by the hybrid PZT–CNT sensor, and the EMI data depended on the changes in the frequency and time. A fuzzy logic-based module was used to analyze and simplify the data precisely with a time factor and yield the EMI in the signals of the structure, which were further used to predict the compressive strength. The algorithm of the fuzzy logic-based module was implemented in MATLAB by employing several parameters and quantifying rules to categorize and simulate the data for strength evaluation. The properties of the specimens were continuously measured in 30 min intervals by the hybrid PZT–CNT sensors, using a signal digitizer computer setup. The EMI was measured as a function of the curing time. The data acquisition process is presented in The hybrid PZT–CNT sensors were designed for the measurement of ordinary concrete strength. Two types of concrete mixtures were prepared for the experiment, whose details are provided in For data acquisition, the experimental setup was arranged before casting the concrete. The experiment was conducted at the room temperature of 23 °C because of the use of ordinary Portland cement concrete. Two types of concrete mixtures, with designed compressive strengths of 18 MPa and 20 MPa, respectively, were prepared. For the data acquisition, 25 cylindrical specimens of each type of concrete mixture were casted, into which the sensors were embedded, and the remaining specimens were cured for the compressive strength test by a destructive method using a Servo-Hydraulic universal testing machine (UTM) . For monitoring, the hydration temperature history of each concrete mixture specimen was measured using Smart Rock™ sensors. Each concrete mixture was tested for compressive strength using its cylindrical core, which was cured on days 1, 3, 7, 14, 21, and 28 after casting.After casting the concrete in the formwork, the experimental setup was attached to the concrete specimens, and the data measurement process was started immediately. The responses of the signals propagating in the concrete paste depend on the hydration process. According to Mirmiran , the resThe strength phase change in the concrete with the curing time is shown in Regarding the features of the impedance data change, Giurgiutiu and Rogers conducted a promising study in which they used the EMI technique for structural health monitoring (SHM) in terms of damage detection. This procedure was also used by Kim. The impedance in the concrete media can be expressed as ,53(7)ZcHere, Because the hybrid PZT–CNT sensors are embedded in the concrete specimens, the voltage applied by the sensors will generate vibrations in the concrete structures. Therefore, the dynamic change responses of the concrete specimens can be expressed as the mechanical impedance response of the PZT–CNT sensors. Thus, the data previously measured by the sensors are the effective EMI of the host structure. The sensor data can be expressed as follows:Here, In this study, the EMI signature attenuation of the structures was investigated to predict the concrete strength with the change in the amplitude of the admittance. Using the EMI data and Equation (9), the 1-CC for the specimens were calculated. The 1-CC index further provides the information required for determining the dynamic change of the propagated signals.Re(z0) is the impedance real part at the baseline and Re(iz) is the impedance real part at the i-th interval for each point of measurement.Here, In this study, as the fuzzy logic tool has been used as the artificial intelligence (AI) data selection method, the model was prepared for obtaining noise free data from the data measured by sensors. As defined in recent studies of fuzzy logic theory, which relates various sets of objects having unsharp boundaries, for that selection, which depends upon the degree. For this study, keeping the result clear of high concentrated data, where the results vary with minor increase or decrease, we have implemented the fuzzy logic-based algorithm considering the perimeters of temperature, maturity, and curing age during the concrete curing period. The procedure of fuzzy logic was placed as depicted in In the process of defining the maturity of the concrete and estimating the compressive strength, the hydration temperature history is used to predict the concrete strength using an NDT technique. It yields the features related to the hydration temperature history of concrete for calculating the concrete compressive strength. During construction using the concrete specimens, various techniques can be used to monitor the parameters of time and hydration temperature . To dilut is S; the initial sitting time is t0; and the limiting strength of concrete is k [Here, the strength at time ate of k . The picThe datum temperature value affects the value of the maturity index and, for different types of concrete, the datum temperatures are different, depending on the properties of the concrete type. According to the Nurse–Saul theory, the maturity can be expressed asM is the maturity function. This technique was applied experimentally, considering some parameters, to verify the strength data references. The temperature history of the hydration temperature shown in Here, The temperature history reveals that the temperatures of concrete mixture type 1 are higher than those of concrete mixture type 2. This shows that the difference is a result of the concrete mixture type because concrete mixture type 1 has higher strength than concrete mixture type 2. The results in When the maturity method is used, the strengths of concrete mixture type 1 on the 28th day measured by sensors 1 and 2 are 19.88 MPa and 19.2 MPa, respectively. Similarly, the strengths of concrete mixture type 2 on the 28th day measured by sensors 1, 2, and 3 are 15.88 MPa, 14.78 MPa, and 16.22 MPa, respectively. The results for concrete mixture types 1 and 2 are compared in The proposed model was applied to the data for the embedded sensors of concrete mixture types 1 and 2. Concrete mixture types 1 and 2 were monitored by two and three hybrid PZT–CNT sensors embedded in the specimens, respectively. Similarly, temperature sensors were also embedded in the concrete specimens to measure their hydration temperatures. The various parameters related to the concrete properties that were considered for estimating the concrete strength are listed in Following data acquisition from the sensors, strength estimation was conducted based on the maturity method procedure using the data measured by the temperature sensors. The results estimated for concrete mixture type 1 on day 14 revealed that, for specimens 1 and 2, the strength gains were 15.55 MPa and 16.02 MPa, respectively, which are approximately 80% of 28th day strength of concrete mixture type 1. This trend is observed because the hydration temperature of concrete mixture type 1 is higher than that of concrete mixture type 2.For concrete mixture type 2, the results show lower strengths than those for concrete mixture type 1. The figures show that, on day 1, the predicted strengths are 2.96 MPa, 3.25 MPa, and 3.8 MPa for sensors 1, 2, and 3, respectively. These values are higher than 2.3 MPa, which is the strength obtained by the UTM test. For concrete mixture type 2, the strength is gained rapidly in the earlier ages; in 72 h, it reaches 6.5 MPa. For comparison, the estimated strengths of specimens 1 and 2 of concrete mixture type 1 are 18.78 MPa and 19.35 MPa, respectively, which are very similar to the strength gain obtained from the UTM test (19.1 MPa). Thus, the predicted results for concrete mixture type 1 are similar to its actual results. A comparison of the results for sensor 1 and 2 for concrete mixture type 1 is presented in On the 7th day, the estimated value by sensor 1 and the UTM result for concrete mixture type 2 are 9.54 MPa and 10 MPa, respectively. The strength estimation curve shows a similar pattern over the remaining days at strength pointed intervals. Therefore, The present study overcomes the limitations of concrete compressive strength development in the early curing days by analyzing and modifying various test methodologies for strength estimation. Smart materials, such as PZT material, CNTs, and some other alloys and materials, have excellent electromechanical properties; therefore, they can be used as sensors and actuators for different objectives in NDT.The results of the study clarify the sensing effect enhancement of CNTs used as smart sensors by incorporating PZT materials, which exhibit excellent electrical and mechanical properties in a composite with cement and silica fume. In addition, at a high dispersion rate, the sensitivity of the CNTs increases, which clarifies their use as sensors.From the results of the study, it can be concluded that the curing age time and the EMI signatures are the vital parameters in the measurement of structural dynamic responses, which can yield accurate prediction results for the designed concrete strength of a structure.Regarding the maturity method, to calculate the maturity index, the datum temperature is important for each type of concrete and under every environmental condition. Therefore, it should be defined for each concrete mixture type. Here, we observed a rapid strength development at a high temperature.The results of the study validate that the proposed technique can assist in SHM in massive industrial multi-step projects by expediting the process and ensuring structural safety. Moreover, the proposed method can be further integrated with other techniques, such as remote monitoring system, artificial intelligence technology, and so on, that may be structurally well-equipped for construction systems.


The classical continuum mechanics theory cannot sufficiently describe the effect of pebbles on projectile, which leads to a large calculation error. In this paper, an orthogonal curvilinear coordinate system is constructed, which effectively describes and perfects the normal cavity expansion theory. A couple stress theory based on the normal cavity expansion is proposed in which not only the tangential movements but also the rotations of the concrete medium are considered. According to the high-speed impact of pebble concrete, combined with dynamic equations and the FE simulation, the theoretical and simulation results of pebble particles scale on warhead resistance are compared. It is shown that, the larger the scale of pebble particles, the stronger the effect of rotation on the resistant force applied on the warhead. In earlier research on the penetration resistance characteristics of concrete target, several explorations were carried out on many aspects, such as penetration depth and projectile mass loss, and research results such as semi-empirical formulas and projectile mass loss characterization models accumulated. However, most of these studies are based on macroscopic models of concrete material. With further research of penetrating concrete, the FE simulation of the 3D meso-scale model has gradually assisted new technologies, such as mapping technology and deep learning ,2. In reFor the research of projectiles penetrating against concrete targets, the classic analytical method is based on the cavity expansion theory, including the cylindrical expansion theory and the spherical cavity expansion theory ,12,13,14In order to analyze the penetration of the concrete media containing pebbles effectively, this paper proposes the continuum mechanics theory of the couple stress ,20,21,22To facilitate analysis, an orthogonal curvilinear coordinate system The gradient operator vector is represented asThe components of substantive derivative of velocity The curl of velocity From this, the angular velocity can be obtainedThe divergency of velocity Stress can be represented by a second-order tensor A, and the divergence of stress is a vector. Its three components can be represented by the formula When only considering the rotation with the material, it belongs to the couple stress theory, which belongs to the category of modern continuous medium mechanics. According to the couple stress theory, for the adiabatic process, the basic equations of the medium in the response region during dynamic deformation include mass conservation equation, momentum conservation equation and angular momentum conservation equation, which can be written asFor the high-speed impact, the medium response region is continuously expanding. Such an expansion represents the propagation of shock waves. There is a shock wave front between the response region and the free region. The shock wave front is a discontinuity surface. The stress To establish the couple stress model of continuum mechanics based on the normal cavity expansion, the following assumptions are made: (1) the shock expansion wave expands in the normal direction of warhead surface at the wave velocity In this paper, the rotation is mainly caused by antisymmetric stress, so the effects of body force, the body couple stress and the couple stress can be ignored. Then, the basic equations of mass conservation equation, momentum conservation equation and angular momentum conservation equation can be rewritten as the following:The medium in the response region has two boundaries, one is the boundary –(22) can be simplified as follows:By the state equation of the ultimate density, substituting Substituting the relationship The total pressure of the warhead surface along the axial direction of the projectile isThat isor When the projectile penetrates vertically into the concrete target containing stone particles, considering the projectile to be rigid, the dynamic equation is written byThat isBy means of the couple stress model, the calculation is carried out on the deceleration and velocity of a conical nose projectile as shown in For a projectile with conical nose as shown in Equation (55) can be obtained from Equations (53) and (54) and the condition This paper focuses on the mechanical characteristics of high-speed impact. Therefore, in this section, when the projectile velocity is in the high-speed zon Based on the dynamic equations of the projectile in This paper uses random ellipsoid to simulate the aggregate. According to LV , on the According to the hypothesis proposed in this paper, the projectile is regarded as a rigid body, so MAT_RIGID is adopted for the projectile. Through the theoretical simulation and experiments, it is found that when considering the meso-scale model of concrete, the model parameters of MAT_JOHNSON_HOLMQUIST_CONCRETE provided by Holmquist cannot effectively simulate the actual situation of concrete ,8,9. TheIt should be noted that in the FE simulation, the rotation movement of pebbles cannot be intuitively expressed. In the FE simulation, by extracting the displacement of any four points (point A–point D) on the pebble aggregate, it is found that the displacement curves of the four points are different, as shown in The simulation results still focus on the variation of deceleration and velocity with time. The dotted lines in It can be seen from For most concrete targets, there are several pebbles to strengthen the structures. The method is proposed in this paper for analyzing the effects of pebbles on the resistant forces of targets on the projectile. Firstly, an orthogonal curvilinear coordinate system is constructed, which effectively describes and perfects the normal cavity expansion theory. Then, based on this theory, a couple stress model is proposed using the basic equations and discontinuity theory of continuum mechanics. The model describes the effects of the translational and rotational motion of pebble aggregates on the resistant force applied on the warhead during the penetration. The theoretical analysis is verified by the simulation of the 3D meso-scale model. Numerical calculations and simulation results show that, with the increasing of the pebble scales, the peak values of deceleration will increase. This means that the larger the scale of stone particles, the stronger the effect of movement of the pebble on the resistant force is applied on the warhead.


Understanding the pattern of antibiotic prescriptions in a country may inform monitoring and stewardship activities, which are crucial in the fight against antibiotic resistance. We aimed to determine the prevalence and describe the pattern of antibiotic prescriptions among National Health Insurance Fund (NHIF) insured patients receiving treatment at health facilities in Ilala Municipality, Dar es Salaam, Tanzania.a cross-sectional analysis of claim forms of NHIF insured patients. A data extraction form was used to capture data for September, 2019 submitted to the Ilala NHIF offices.among 993 insured patients  a total of 357  received an antibiotic prescription. Of the 357 patients who received an antibiotic prescription, 71(19.9%) received more than one antibiotic prescription. The most common antibiotic prescribed was amoxicillin/clavulanate (17.1%) followed by amoxicillin (16.5%) whereas the most commonly prescribed antibiotic class was the penicillins (51.3%) followed by the nitroimidazoles (14.0%). Among patients who received more than one antibiotic, the most commonly co-prescribed antibiotics were Ampicillin/Cloxacillin plus Metronidazole (11.4%) followed by Amoxicillin plus Metronidazole (7.1%). According to 2019 WHO Access, Watch, Reserve (AWaRe) Classification of antibiotics, 60.8% of patients received the access antibiotics, 33.3% received the watch antibiotics whereas 17.4% of patients received antibiotics that were not recommended. No patient received an antibiotic from the reserve group.the prevalence of antibiotic prescriptions in Tanzania is high and some antibiotics not recommended by the WHO are still prescribed. We recommend revision of the current Tanzania treatment guideline on antibiotics to reflect WHO recommendations, and further research to address local factors influencing antibiotic prescriptions is warranted. Discovery of antibiotics has revolutionized medicine in terms of clinical outcomes of various infectious diseases which prior to that were untreatable and deadly ,2. MoreoAntibiotic prescription rate from healthcare settings is increasing in many countries and in fact, sometimes antibiotics are over prescribed ,7. DespiThe access group include antibiotics that are active against commonly encountered susceptible pathogens while also showing lower resistant potential than antibiotics in other groups. The World Health Organization (WHO) specifies a country-level target of at least 60% of antibiotics consumed should be from the Access group. Watch group include antibiotics classes that have higher resistance potential and includes most of the highest priority agents among the critically important antimicrobials for human medicine and/or antibiotics that are at relatively high risk of selection of bacterial resistance. The Reserve group, treated as ‘´last resort´´ option, include antibiotics that should be reserved for treatment of confirmed or suspected infections due to multi-drug-resistant organisms . StudiesStudy setting and population: the study was conducted in 73 NHIF-accredited health-care facilities in Ilala Municipality in Dar es Salaam, Tanzania. Ilala is the most populous municipality in Dar es Salaam, the commercial hub of Tanzania. The population in Ilala municipality was projected to be about 1.6M people in 2017 [2 [ in 2017 . The mun 2017 [2 . This stStudy design, sample size and sampling procedures: the study was a cross-sectional analysis of the NHIF claim forms that were filled from Ilala Municipality health-care facilities. The minimum sample size was estimated using the formula by Kirkwood and Sterne [d Sterne . Assumind Sterne  and ε isData collection methods: a data extraction form was used to capture data from the NHIF database. Specifically, the original yellow claim forms 2A & B which health-care facilities submit to NHIF headquarters were the data source. These NHIF claim forms included the health provider in/outpatient claim form and the health provider surgery claim form. Only the accessible claim forms or data sets were used as our data source, as we appreciated that it was difficult to access unprocessed forms.Data management and statistical analysis: during and immediately after data collection, all data extraction forms were checked for completeness and omissions. Secondary reviews of the claim forms were warranted to ensure the correctness of data. Homogeneous subgroups were clustered together and then the data was coded to simplify the analysis. Coded data was then entered and analyzed in IBM SPSS Statistics Version 23 software. A summary of frequency and proportions of categorical variables was obtained using descriptive statistics whereas that of numerical variables was obtained from measures of central tendency and dispersion. Analyzed data was presented in text, tables, and charts.Ethical consideration: the proposal for this study was reviewed and approved by the MUHAS Institutional Ethics Review Board (IRB). Permission to use the NHIF database was sought from the Director of NHIF and was granted. Data collection did not start until these approvals had been obtained. Confidentiality was maintained as no personal identifiers were collected by our data capture tool.A total of 1100 claim forms were reviewed and 107 were omitted from analysis due to either incomplete data or with non-prescriber status. Analysis was performed on 993 claim forms. The sampled claim forms were from a total of 73 NHIF-accredited health facilities of which 37 (50.7%) were dispensaries, 14 (19.2%) were health centers, 13 (17.8%) were National Referral Hospitals including level three clinics run by super-specialists, 3 (4.1%) were from Regional Hospitals including level two clinics run by specialists and 6 (8.2%) were from District Hospitals including level one clinics run by medical officers. The final analyzed sample is as shown in the flow chart . The majAntibiotic prescription prevalence and pattern: among patients who received a medication prescription, 46.4%  contained one or more antibiotic medication. Furthermore, 92.2% of the antibiotics prescribed were in agreement with current Tanzania standard treatment guideline recommendation with respect to health facility level (2017 TZ STG/NEMLIT). The most common antibiotic name prescribed was amoxicillin/clavulanate (17.1%) followed by amoxicillin (16.5%) whereas the most commonly prescribed antibiotic class was the penicillins (51.3%) followed by the nitroimidazoles (14.0%) ( (14.0%) . Nearly  (14.0%) . No patiIn this cross-sectional analysis of insured patients attending health facilities in an urban setting, we aimed to determine the prevalence and describe the pattern of antibiotic prescriptions. The prevalence of an antibiotic prescription was high (46.4%). The most common antibiotic name prescribed was amoxicillin/clavulanate whereas the most common antibiotic class prescribed was the penicillins. The most commonly co-prescribed antibiotics were ampicillin/cloxacillin plus metronidazole whereas, as per WHO AWaRe classification, the most commonly prescribed antibiotics were from the Access group.We found that antibiotic prescriptions are highly prevalent (46.4%) with 19.6% of the patients receiving more than one antibiotic. This finding is above the ideal antibiotic prescription rate of 30.0%, therefore, indicating over prescription ,21. A prThe observation that amoxicillin/clavulanate was the most commonly prescribed antibiotic, and penicillins were the most common antibiotic class is consistent with previous studies ,22-25. TOur data show that the Access group of antibiotics is the most commonly prescribed antibiotics among insured patients in Tanzania. However, the level at which these antibiotics are prescribed is still low (60.8%), just above the WHO country-level recommendation of 60.0% . The finThis study has some limitations. Firstly, there is lack of generalizability of the study findings due to the involvement of one municipality and among insured patients only. However, this may reflect a similar or worse trend in other areas of the country and among uninsured patients. Secondly, we could not control for seasonal bias in antibiotic prescription prevalence and pattern as we used retrospective data over one-month period.This study has highlighted that, among insured patients, the prevalence of antibiotic prescriptions is high and antibiotics of fixed-dose combinations which are not recommended by the WHO are still prescribed. We recommend, the standard treatment guidelines currently in use should be revised to reflect the current WHO recommendation especially on removing the antibiotics which are not recommended and further research to address local factors that may influence an antibiotic prescription is warranted.Antibiotics are over prescribed globally;Antibiotics over prescription may lead to drug resistance;Understanding the prevalence and pattern of antibiotic prescriptions may inform public health interventions in combating increased antibiotic use.Antibiotic prescription among insured patients in Tanzania is high;Access antibiotics prescribed met the WHO country level recommendation;WHO un-recommended antibiotics are still prescribed among insured patients in Tanzania.


The results obtained, compared with the relevant legislation, have proved that the inclusion of glass powder in a high percentage of substitution and with a granulometry of 20 µm in the manufacture of deactivated concretes is feasible for exterior pavements.Glass is a material that can be reused, except for a small part that, due to its residual characteristics, cannot be reused and becomes a nonbiodegradable waste to accumulate in landfills. The chemical composition and pozzolanic properties of waste glass are encouraging for the use of these wastes in the cement and concrete industries and for providing technically and environmentally viable solutions. In this study, we propose the production of deactivated concretes with a high content of glass powder in the binder. The substitution percentage of glass powder for cement used in this work was between 70% and 80%. Consistency, air content, bulk density, workability, compression strength, and permeability tests were performed. Regarding compressive strength, the results obtained at 90 days for percentages of cement substitution by glass powder of 70 and 80%, respectively, were 14.2 and 8.6. The chemical analysis of leachates showed concentrations of Fe, Cu, V, Ni, and Mo, in mg L Currently, the industrial sector generates large quantities of waste, part of which is recycled and the other part of which is deposited in landfills, causing environmental impacts . These wThe sustainability of the civil engineering sector is crucial to drive society toward a circular economy, and to make this possible, the application of the waste hierarchy principle   is a pri2) into the atmosphere. Globally, the cement industry contributes 7% of the CO2 generated [Concrete is by far the most widely used material in civil engineering. It is estimated that around 10 billion tons of this material are produced worldwide each year, which involves the use of nonrenewable natural resources, a significant demand for energy, as well as the emission of greenhouse gases . For exaThe traditional use of concrete is to build load-bearing structures due to its mechanical properties, durability, and workability. In recent times, the general commitment to sustainability has prompted a search for new concretes that can improve their properties in terms of environmental protection and aesthetic performance.Numerous studies have shown the good performance of mortars and concretes made from different waste materials, especially waste glass ,9,10.The final glass wastes from packaging, demolition of buildings, the automotive industry, sanitary containers, and the ceramic industry that are not reusable by the glass industry can be recovered as raw material for the manufacture, after a process of fine grinding and mixing with nonpolluting reagents, of hydraulic binders .Despite all benefits indicated, in the use of glass powder as a binder in the manufacture of concrete, it should be considered that these materials might contain potentially harmful substances such as heavy metals and trace elements, which can contaminate surface water that are often sources of drinking water supply ,13,14. IStudies on the pozzolanic activity of waste glass carried out by Shao et al.  showed tHongjian et al.  studied The range of pavements includes deactivated concrete, exposed aggregate, and washed concrete. This is a type of paving that is easy to install on site. The aggregates are visible on the surface in a concrete screed. This type of pavement, in addition to its mechanical function, can have an infinite number of finishes. This makes possible to obtain greater slip resistance and to improve the aesthetic component of concrete, until now considered by many as something gray and smooth . DeactivIn this article, we propose the use of glass powder as a high percentage cement substitute in the manufacture of deactivated concrete to be used as pavement in outdoor areas, studying its mechanical characteristics and leaching to verify that it does not cause a negative environmental impact on soils.Aggregates, essentially siliceous and nonreactive, are used. They are sand with a grain size <4 mm, gravel 4–12 mm, and gravel 12–20 mm. 3, a specific surface area of 4440 cm2/g, and a greenish gray color. The particle size of cement CEM I 52.5 R in volume fraction for particle diameter lower than 8 µm was 41.5% and for particle diameter lower than 96 µm was 99.7%.The cement used was a commercial Portland cement CEM I 52.5 R . This cement has a density of 3.12 g/cm2 (19%), Al2O3 (5.5%), FeO3 (2.65%), SO3 (2%), MgO (2%), Na2O (0.15%), K2O (0.7%).Chemical composition of CEM I 52.5 R cement was as follows: CaO (65%), SiOGlass powderThe material used is the last fraction of glass that cannot be reused by the glass industry. This residue is ground with a bar mill until a grain size of 21 µm is obtained. The size was based on the results of the analysis in the COULTER LS 100 Q laser particle sizer . Based on the results of the analysis in the particle sizer, the accumulated particle size curve was obtained, which shows the different particle size distribution as can be observed in 2, 11.85% Na2O, 11.19% CaO, 2.38% Al2O3, 1.60% Fe2O3, 1.60% MgO, 0.60% K2O, 0.10% MnO, 0.08% TiO2, and 0.05% P2O5, with 0.90% volatile LF (loss of the fire).The chemical composition of glass powder was 72.00% SiO50 glass powder of 21 μm was used . Two series of specimens, each of which had 15 units , were maTo study the compressive strengths of the manufactured concretes, they were introduced into 10 × 30 cylindrical test tubes. Once compacted and after 24 h, they were removed from the mold and placed in a humid curing chamber at a temperature of 20 °C. The curing time ranged between 28 and 90 days. After these curing times, they were broken following the UNE 83-304-84 standard [Consistency testIt was carried out according to the UNE-EN12350-2  consiste2.Air contentThe air content of ready-mixed concrete was determined according to UNE-EN 12350-7  by press3.Apparent densityThe procedure followed for the calculation of densities and porosities is based on UNE-EN 1015-6 .4.WorkabilityWorkability was measured using the procedure described in UNE-EN 12350-5 .5.Permeability testPermeability tests were performed according to UNE-EN 12390-8 . The pur3 through a 0.7 μm glass filter. They were later analyzed using atomic absorption spectrometry (FAAS) and inductively coupled plasma mass spectrometry (ICP-MS).In order to analyze the leached elements, a vacuum filtration was conducted. The filtrations were collected in successive fractions of ±20 cmWith the formulations shown in In order to make the aggregate visible on the surface of the plates, two methods were used. The first one consisted of deactivating the surface setting process by applying a deactivating product during the hours after the concrete has been placed. This chemical product was then removed by water jetting to expose the aggregate surface grains. The final appearance depends on the type and the amount of deactivator used, and the time of application before rinsing. In this case, a surface deactivator used for concrete floors with exposed aggregates similar to the one indicated by the Pieri VBA 2002 trademark . The appThe second one was a mechanical method consisting of passing a broom over the concrete surface during the hours following its placement, in order to drag a thin layer of mortar or grout, thus revealing the aggregate grains on the surface. This method allowed the work to be finished immediately after sweeping. The final appearance varied according to the intensity of the sweeping . The broThe percentage of glass powder substitution by cement was based on the study carried out by García del Toro et al. , who repResults obtained for consistency, air content, apparent density, and workability tests are shown in 3 compared to 2.54 g/cm3 for glass powder. As for workability, it can be observed that as the percentage of glass powder in the mix increases, the concrete becomes more workable, a fact that is also related to the lower density of glass powder compared to cement.From According to consistency tests (Abrams cone slump), these concretes can be qualified as suitable for pavements. It can also be observed that the water content of these concretes is somewhat lower than that of conventional concretes in order to obtain a drier concrete. The air content is higher due to the presence of ground glass. The presence of air is convenient for this product since it facilitates its workability. On the other hand, it causes a decrease in compressive strength in the short term.The results of the compressive strength tests of the concrete with 70% and 80% substitution of cement by glass powder are shown in As previously observed , for conIn a previous work , a preliRegarding leaching characteristics, the elements analyzed in the leachate samples were as follows: Si, Na, K, Al, Ca, Li, B, Mg, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Yb, Lu, Hf, Ta, Tl, Pb, Th, and U.The results below are the average of the results obtained by the two detection methods used: atomic absorption spectrometry (FAAS) and inductively coupled plasma mass spectrometry (ICP-MS).Most of the elements showed no relevant concentrations in the first hours of the test, reaching not detectable concentrations at the end of the test. For the rest of elements, in order to study their concentration in the leachates and their variation over time, they were divided into two groups. We took potentially contaminating elements b, which The potentially hazardous elements—molybdenum, chromium, copper, vanadium, nickel, iron, boron, and aluminum—were all found in the glass composition. The elements iron, copper, vanadium, nickel, and molybdenum showed concentrations of 1.57, 1.38, 0.85, 0.95, and 0.44 ppm, respectively, after five hours of the test, with a decreasing tendency until they stabilized after 20 h. At 72 h, their concentrations remained below the quantification limits of the analytical techniques used.F test and it was found that there were no significant differences between them. At this regard, the hypothesis statement was as follows:For the rest of the elements, and in order to verify that the results obtained in this work were in agreement with those obtained in a preliminary study by Mas et al. , a hypotAs previously mentioned, the hypothesis contrast was performed for the elements whose concentrations at 72 h remained above the quantification limits of the analytical techniques used.t used to test the hypothesis.t test result obtained with the experimental data for each and every one of the elements analyzed was lower than the tabulated data for a Student’s t distribution with ν degrees of freedom and a 95% confidence level, it was accepted that there were no significant differences for the means of the data obtained for each of the elements analyzed.Since the Student’s Of all the elements, sodium (Na) was the one released in the greatest quantity; its concentration in the filtered water was around 5350 ppm in the first 5 h of the test. Sodium and potassium, especially sodium, mainly from glass, were released in significant quantities, but this does not pose a danger to the environment, since they were not released in sufficient quantity to cause changes in the electrical conductivity of the soil. Calcium does not constitute an environmental hazard; since it is a nontoxic element and at the concentration level determined, it would not cause soil pH modifications. The presence of chromium and boron during the first hours of the test in the filtrate water was relevant. However, these elements tended to disappear at the end of the test, probably because they got into the cementitious matrix.In the present work, the use of glass powder as a high percentage cement substitute in the manufacture of deactivated concrete to be used as pavement in outdoor areas was examined. Deactivated concrete slabs manufactured with a high percentage of glass dust in the binder represent an ecofriendly alternative that is in line with the circular economy, which is currently imposed as a principle in civil engineering.The experimental results indicated that it is feasible to produce mortar with fine glass powder and that floors made of deactivated concrete with a glass powder binder base are highly stable against atmospheric and mechanical agents. These characteristics give them a long-life cycle and low maintenance. Exposed aggregate finishes are rough, nonslip, and resistant to wear and tear and the action of atmospheric agents. Its application would be suitable for pedestrian areas such as park streets and outdoor traffic areas in need of a durable pavement, as well as accesses to garages, terraces and patios, swimming pool areas, and roads with light traffic.Regarding leachates, alkaline elements, especially sodium, were released in significant quantities, although not in quantities sufficient to cause changes in the electrical conductivity of the soil, so they do not pose an environmental hazard, similar to calcium, which is a nontoxic element and, at the concentration level determined, would not cause a soil pH modification. The considerable presence of chromium and boron, potentially contaminating elements, in the filtrate water during the first hours of the test is remarkable. These elements tended to disappear at the end of the process, since they were incorporated into the cement matrix; therefore, they do not cause environmental contamination. Finally, the rest of the elements detected were found at trace levels in the filtered water, so due to their scarcity, they cannot constitute a danger to the natural environment according to the legislation in force.


At present, the research on the high temperature degradation of concrete usually focuses on only the degradation of concrete itself without considering the effect of the plastering layer. It is necessary to take into account the influence of the plastering layer on the high temperature degradation of concrete. With an increase in the water/cement ratio, the explosion of concrete disappeared. Although increasing the water/cement ratio can alleviate the cracking of concrete due to lower pressure, it leads to a decrease in the mechanical properties of concrete after heating. It is proved that besides the water/cement ratio, the apparent phenomena and mechanical properties of concrete at high temperature can be affected by the plastering layer. The plastering layer can relieve the high temperature cracking of concrete, and even inhibit the high temperature explosion of concrete with 0.30 water/cement ratio. By means of an XRD test, scanning electron microscope test and thermogravimetric analysis, it is found that the plastering layer can promote the rehydration of unhydrated cement particles of 0.30 water/cement ratio concrete at high temperature and then promote the mechanical properties of concrete at 400 °C. However, the plastering layer accelerated the thermal decomposition of C-S-H gel of concrete with a water/cement ratio of 0.40 at high temperature, and finally accelerate the decline of mechanical property of concrete. To conclude, the low water/cement ratio and plastering layer can delay the deterioration of concrete at high temperature. As a stable and reliable building material, concrete is widely used in various infrastructure construction facilities. The service life of concrete can theoretically reach a century under normal service conditions, but concrete can deteriorate rapidly in some extremely harsh environments, such as fire conditions. The Fire and Rescue Bureau of the Ministry of Emergency Management, PRC reported 252,000 fires across China in 2020, resulting in 1183 deaths, 775 injuries and 4.09 billion yuan in direct property losses [3) of concrete decompose, resulting in a decline of concrete strength [The reasons for concrete degradation at high temperature are as follows: high temperature vapor pressure, temperature stress, difference in thermal expansion coefficient between aggregate and paste and thermal decomposition of hydration products ,4,5,6,7,strength ,9,10. CoThe main causes of concrete cracking and explosion are too-low water/cement ratio  with a plaster layer under high temperature by combining a scale structure test and finite element software. Hodhod indicated that traditional cement coating can delay the temperature rise of the RC column, and that traditional mortar coating can increase the residual load capacity of the RC column after 30 min at 650 °C . Andrii The ultimate load capacity and fire resistance of concrete components under fire are determined by the mechanical properties of concrete at high temperature. Du pointed out that the ultimate limit state in fire for the concrete slab under bending moment and compressive force was decided by the mechanical property of concrete . Allam rIn the past studies, researchers generally calculated the fire resistance and moment/axial capacity of concrete members at high temperatures by means of the mechanical strength reduction factor of the reinforcement and concrete. However, the mechanical properties of concrete do not necessarily decrease monotonously with the temperature increase (≤400 °C), and the fundamental mechanisms of concrete mechanical properties under high temperatures are affected by many factors such as water/cement ratio and plaster layer due to the rehydration of cement particles. Simply using the reduction factor cannot adequately calculate the mechanical properties of concrete at high temperatures, which may lead to errors in subsequent calculation and modeling.Hence, it is necessary to study concrete damage mechanisms under the action of plaster layer, water/cement ratio and high temperature coupling. This paper analyzed the concrete degradation mechanisms of concrete under the coupling effect of water/cement ratio, plastering layer and high temperature by measuring the residual mass of concrete, ultrasonic pulse velocity, compressive strength, XRD diffractograms, SEM images and Thermogravimetric analysis.3, and each sample was poured in the mold at one time and placed on the vibration table to vibrate evenly. After the specimen was placed at room temperature for 24 h, the mold was removed, and the concrete specimens were soaked in a water tank for 28 d curing. For easy identification, each plastered concrete mixture was assigned a label in the format of water/cement ratio—mortar plastered layer thickness—room temperature/heating temperature. The concrete mixtures are shown in To study the mechanism of the coupling effect of plastering layer and water/cement ratio on heat degradation, a total of 30 groups of concrete specimens with different mortar plaster thickness and different water/cement ratio heated to different temperatures were produced. The paste volume and fine-to-aggregate ratio of all concrete mixtures was set at 0.40 and 0.45, respectively. The water/cement ratio varied from 0.30 to 0.40 with a difference of 0.05. According to the general practice of concrete production, a water reducing agent was added into each concrete mixture to make the workability meet the requirements. Water reducing agent was added to each mixture bit by bit until the mixture had a slump of 100 ± 20 mm. Concrete specimens were prepared according to the standard for evaluation of concrete compressive strength  and for the uniaxial compressive strength test. The size of the concrete sample was 100 × 100 × 100 mmMortar for plastering was designed in accordance with the Specification for mix proportion design of masonry mortar . The mixture of mortar is shown in Their residual mass ratios, ultrasonic pulse velocities and various compressive strengths after heating were measured. In order to reveal the reasons of concrete degradation at different high temperatures, XRD diffractograms, scanning electron microscopy (SEM) images and thermogravimetric results of the concrete specimens were analyzed.The OPC was of type CEM I 42.5R obtained from China Resources Cement Co., LTD. Foshan natural river sand with maximum diameter of 1.3 mm was used as fine aggregate, basalt with particle size of 5–30 mm was used as coarse aggregate. The water-reducing agent supplied from Shaanxi Qinfen building materials Co., Ltd. . The chemical compositions of the OPC were obtained through X-ray diffraction method as displayed in The concrete was poured into the slump barrel three times. After each filling, the rammer was used to hit the barrel wall 25 times to tamp it. The slump barrel was filled with concrete and the surface concrete was leveled. The slump bucket was pulled and the slump was calculated by subtracting the height of the peak of the concrete behind the collapse from the height of the bucket (300 mm).An integrated resistance furnace oven produced by Shanghai Zheti Machinery Manufacturing Co., Ltd.  was used for heating test. The rated power of the resistance furnace oven was 12 kW and the rated temperature was 1050 °C. After curing, the specimens were placed in a resistance furnace oven and kept at a constant temperature for 2 h after the furnace oven was heated up to the target temperature  at a rate of 10 °C /min. Then the resistance furnace oven was turned off and the specimens were taken out. After the specimens were cooled to room temperature, cracks in the concrete specimens were observed. The remaining mass ratios of the concrete specimens were calculated by weighing the mass. Follow-up tests were carried out after the specimens were left standing at room temperature for 7 days.Zbl-u510 non-metallic ultrasonic detector was used in the ultrasonic pulse velocity test. Technical specification for detecting strength of concrete by ultrasonic-rebound combined method  was adopted in the test.A concrete compressive strength test was carried out according to Standard for evaluation of concrete compressive strength , and the loading rate was 0.8 MPa/s.After the concrete compressive strength test was completed, some fragments in the core of the concrete specimens were taken out for subsequent analysis. In order to stop the hydration reaction of concrete fragments, we soaked the concrete fragments with anhydrous ethanol for 3 days. After soaking, the concrete fragments were placed in a drying oven to dry (heating temperature was 40 °C) to constant weight, and ground through a 75 μm sieve. The analysis conditions were 10°~60°, 40 kV and 40 mA. The XRD test was performed with a Rigaku X-ray powder diffractometer ULTIMA IV .The treatment process of mortar fragments was the same as that in The treatment process of mortar fragments was the same as that in Concrete slump results are shown in the second column of The appearance of concrete in each group after the heating test is shown in In addition, the test photos also show that in addition to temperature, water/cement ratio and the plastering layer influenced the deterioration of concrete appearance. Under the condition of no plastering layer, the lower the water/cement ratio of concrete was, the easier it was for it to explode. The concrete with a water/cement ratio of 0.35 and 0.40 only cracked and spalled after heating. Kodur pointed out that the explosion and spalling of HSC is due to the low water/cement ratio . Hence, The test photos also show that the plastering layer can effectively alleviate the appearance deterioration of concrete, and this phenomenon was more obvious with the decrease of the water/cement ratio. The plastering layer had no obvious effect on the appearance deterioration of concrete with a 0.40 water/cement ratio at high temperatures. When the water/cement ratio dropped to 0.35, the cracking degree of concrete with a plastering layer was lower than that of concrete without a plastering layer. When the water/cement ratio dropped to 0.30, the plastering layer reduced the cracking degree and inhibited the explosion of concrete. This is because the plastering layer can slow the rate of concrete heating, resulting in a decrease in temperature gradient and vapor pressure ,18,19,20The ratio of residual mass of concrete of each group is shown in At the same time, the data in Theoretically, the lower the water/cement ratio is, the denser the concrete is, and the less the free water is, which leads to the increase of the residual mass ratio of concrete after heating. However, in this test, the residual mass ratio of concrete at different temperatures increased first and then decreased with the increase of water/cement ratio. When the water/cement ratio dropped to 0.30, the residual mass ratio of concrete decreased, which was obviously in contradiction with the theory. When the water/cement ratio dropped to a certain extent, the concrete was more likely to crack and explode at high temperatures. When the water/cement ratio dropped to 0.30, concrete exploded at 400 °C, while concrete with 0.35 and 0.40 water/cement ratio had no obvious explosion  With the decrease of water/cement ratio, the number of unhydrated cement particles of concrete increased , and higIn addition, it can be seen from In order to further analyze the influence of temperature, water/cement ratio and plastering layer on the hydration products of concrete, XRD tests were conducted on all specimens with a water/cement ratio of 0.30 and 0.40. The specific test results are shown in Because quartz has good high temperature resistance, the peak intensity of Quartz is very stable at high temperatures. High temperatures can promote the continuous hydration of unhydrated cement particles to generate CH. When the temperature exceeded 400 °C, CH rapidly decomposed . Therefo2SiO4 in an SEM figure of mortar heated at 800 °C [2SiO4 in an SEM figure of mortar heated at 900 °C, and pointed out that beta-Ca2SiO4 was the product of thermal decomposition of C-S-H gel at high temperature [2SiO4 produced by the thermal decomposition of C-S-H gel, which is consistent with the XRD results. This explains why concrete basically loses its compressive strength after 800 °C.At room temperature, with the increase of water/cement ratio, the microstructure of concrete became sparser and a large amount of ettringite was generated. Hydration products of concrete with different water/cement ratios decomposed to different degrees at high temperatures: Ettringite disappeared at 200 °C. With the temperature rise, C-S-H gel and CH decomposed seriously at 600 °C. Moghadam found beta-Cat 800 °C . Aydin operature . TherefoBy comparing Although the previous ultrasonic pulse velocity test results and XRD test results show that the plastering layer changed the crack development behavior and hydration product decomposition behavior of concrete at high temperatures, this was not clearly reflected in the SEM figure, which may be the result of the error caused by the selection of points in the test.In order to quantify the effects of temperature, water/cement ratio and plastering layer on the contents of C-S-H gel of concrete, thermogravimetric tests were carried out in this study. The C-S-H gel amount of the sample were calculated according to Equation (1) , C-S-H gd 400 °C ).(2)C−SThe calculation results of C-S-H gel ratio are shown in Temperature is an important factor leading to the deterioration of concrete, as high temperatures will bring high-temperature vapor pressure, thermal stress and thermal decomposition of the hydration products and other adverse factors ,4,5,6,7,Although the compressive strength of concrete increased with the decrease of the water/cement ratio at all temperatures, the concrete with a low water/cement ratio (0.30) was too dense, which led to the agglomeration of water vapor and easily led to explosion.The test results show that the factors that changed the high temperature resistance of concrete were not only the water/cement ratio but also the plastering layer, and whether the plastering layer improved the high-temperature resistance of concrete depended on the water/cement ratio of concrete. For concrete with a high water/cement ratio, most cement was hydrated during the 28 days curing ,31, so tThere were two main functions of the plastering layer in the heating test: reducing the rate of rise and drop of the temperature of internal concrete ,18,19,20Analysis of the thermogravimetric tests results also proved that concrete with a water/cement ratio of 0.30 at high temperatures can continue to hydrate unhydrated cement particles to generate more C-S-H gel, as the plastering layer slows the escape of water vapor, resulting in a slower rate of compressive strength decline of concrete (and even compressive strength grew at 400 °C). In addition, the plastering layer can completely inhibit the cracking of 0.30 water/cement ratio concrete at high temperatures, because the plastering layer can delay the heating rate of internal concrete and thus delay the damage of high temperature vapor pressure and thermal stress on concrete.Generally speaking, concrete will deteriorate with the rise of temperature, which leads to the decline of compressive strength. At the same time, the test results also show that the compressive strength of concrete after heating is affected by the water/cement ratio and the plastering layer. Therefore, the influence of the water/cement ratio and plastering layer on concrete compressive strength after heating should be considered when calculating the fire resistance limit and residual load capacity of concrete members, and the compressive strength of heated concrete should not be calculated directly by a reduction factor.(1)Reducing the water/cement ratio can improve the strength of concrete at any temperature, but too low water/cement ratio can easily cause high temperature cracking, and ultimately lead to the decline of high temperature resistance of concrete. Under the condition of no plastering layer, all concrete with a water/cement ratio of 0.3 or 0.35 cannot be tested for compressive strength by spalling and explosion at 800 °C. Concrete with a water/cement ratio of 0.4 can still be tested for compressive strength despite obvious cracking.(2)After exposure to a high temperature (400 °C), the compressive strength of 0.30–0–400 °C was 4.48% higher than 0.30–0–200 °C, and the compressive strength of 0.30–20–400 °C was 7.38% higher than 0.30–20–200 °C. The increase of compressive strength can be attributed to the hydration of unhydrated cement particles of concrete and the Van der Waals force.(3)A plastering layer can accelerate or decelerate the damage of concrete at high temperatures, which depends on the water/cement ratio of concrete. A plaster layer at a high temperature can inhibit water vapor’s escape to promote the hydration of unhydrated cement in concrete with a low water/cement ratio (0.3) to delay the loss of the compressive strength of concrete. However due to the high hydration rate of concrete with a high water/cement ratio (0.4) the plaster layer cannot delay the loss of the compressive strength of concrete at high temperatures and can even exacerbate the loss of the compressive strength of concrete. Therefore, the plastering layer can increase the compressive strength of concrete with a 0.3 water/cement ratio by 11.35–15.02% between 200 °C and 800 °C and increase the compressive strength of concrete with a 0.35 water/cement ratio by 3.95–43.33% between 200 °C and 800 °C. However, the plastering layer decreases the compressive strength of concrete with 0.4 water/cement ratio between 200–600 °C, and increases the compressive strength by 33.40% at 800 °C.(4)The compressive strength of concrete after heating is affected by the water/cement ratio and plastering layer, so the influence of the water cement/ratio and plastering layer should be considered when calculating the fire resistance limit and residual load capacity of concrete members under fire, and the reduction factor should not be directly used to calculate the strength of concrete  after heating.Through analyzing the appearance of concrete after exposure to high temperatures, ultrasonic pulse velocity, compressive strength and hydration products, the main conclusions are as follows:


This, coupled with an increase in the advocacy for environmental sustainability, has led to the development of various innovative solutions and supplementary cementitious materials. These aims to substantially reduce the overall volume of cement required in concrete and to meet the consistently increasing demand for concrete, which is projected to increase as a result of rapid construction and infrastructural development trends. Palm oil fuel ash (POFA), an industrial byproduct that is a result of the incineration of palm oil wastes due to electrical generation in power plants has unique properties, as it is a very reactive materials with robust pozzolanic tendencies, and which exhibits adequate micro-filling capabilities. In this study, a review on the material sources, affecting factors, and durability characteristics of POFA are carefully appraised. Moreover, in this study, a review of correlated literature with a broad spectrum of insights into the likely utilization of POFA-based eco-friendly concrete composites as a green material for the present construction of modern buildings is presented.Rapid global infrastructural developments and advanced material science, amongst other factors, have escalated the demand for concrete. Cement, which is an integral part of concrete, binds the various individual solid materials to form a cohesive mass. Its production to a large extent emits many tons of greenhouse gases, with nearly 10% of global carbon (IV) oxide (CO The intmissions . Apparenmissions ,8. If thmissions .2), trepel (85–89%), volcanic tuff (9–23%), and diatomite (82–87%). Technogenic SCMs include silica fume (over 90%), metakaolin (53–54%), rice husk ash (90–99%), fly ash (60–70%), ash and slag mix (50–60%), granulated blast furnace slag (28–38%), and red mud (3–50%) [The use of supplementary cementitious materials (SCMs) has continued to gain increased attention ,12,13,14 (3–50%) ,19,20,21Palm oil fuel ash (POFA) has been deemed a potential alternative from agricultural waste  on the mechanical and durability properties of eco-friendly concrete composites.POFA is a by-product from the palm oil industry, which is achieved through the incineration of sufficient amounts of waste materials, such as the husk, fiber, and shell of palm oil plants  shown i. BurningPOFA, as an SCM, has a high carbon content, loss on ignition (LOI), and enormous particle size, making it inactive. Compared with normal POFA, ultrafine POFA (UPOFA) has better properties after extensive grinding . This ca3 [Enhancing concrete properties is the main reason that POFA is applied in concrete manufacturing . For exa3 . The 10–3 , and it 3 . It was 3 . As show3 ,68 utili2O3 and SiO2 with Ca(OH)2, hence increasing the sulfate resistance and reducing Ca(OH)2 content [Durability is another concern for concrete structures, as materials gradually erode, reducing the serviceability period of infrastructure. Therefore, introducing FA and POFA into concrete have been investigated for durability and corrosion resistance . Regardi content .Demonstrating the benefits of waste utilization from the oil palm industry in concrete production should be promoted for related agencies for further implementation . It is cThe interest in introducing SCMs into conventional concrete has increased the desire to produce better chemical and physical characteristics ,72. The Agro-based waste materials, such as rice husk ash (RHA), FA, and POFA as pozzolanic materials or SCM in concrete matrix have been studied . By imprAnother use of POFA is in producing self-compacting concrete for application in a narrow area of industry where compaction cannot be done , for ins2/kg may be obtained from different treatments, which include acidic or alkaline pretreatments, calcination temperature, and others [2/g specific surface area was able to be achieved, and only 10.5% of the ash was found to be retained in a 45-µm sieve [Fineness is deemed as one of the most notable characteristics of POFA. The rate of hydration and the nature of pozzolanic materials rely on the fineness of POFA particles, where a higher degree of fineness increases the compressive strength of concrete ,87. Grind others . Khalid d others . It was µm sieve .2 [2, from 69.02% to 59.17% [2, MgO, and SO3 [Higher degree of fineness can be obtained and a higher packing effect of POFA cement the is found when the paste increases with more fineness. A pozzolanic reaction between 12 to 23% with average particle sizes but lower than that of cement at a characteristic concrete age was achieved ,45. The 2 . The rea2 ,90. Furt and SO3 ,92,93,942 was also observed in several low strength samples at 7 days. In general, 20% cement replacement in HSC with POFA showed the highest compression strength value and the lowest permeable porosity [In terms of microstructure property, as discussed before, additional C–S–H bonding resulted in a more dense concrete microstructure and also improved the interfacial bond, which improved the strength, transport characteristics, and durability of concrete ,96 as a porosity .Generally, ground POFA is smaller than unground POFA in term of particle size. Ground POFA has angular and irregular shapes (crushed particles) and unground has a spherical shape with pores . Ground Durability denotes the resistance of concrete to decay and disintegration. One of the main characteristics that influences durability is permeability, which can increase the rate of capillary absorption (RoCA) and the resistance of concrete to potentially deleterious materials. By ensuring a full compaction of admixtures and adequate curing, POFA concrete is sufficiently able to withstand environmental effects. The permeability, RoCA, and resistance to aggressive environment and other external attacks of POFA are described in subsequent subsections.Permeability describes the rate of infiltration of a liquid (water) and other aggressive particles into the POFA concrete and originates carbonation, chloride-ion attack, and corrosion ,108. Redw1 = weight of saturated specimen.w2 = weight of oven-dry specimen.Water absorption (WA) is usually calculated using Equation (1).pK = coefficient of water permeability (m/s).d = depth of water penetration into concrete (m).v = porosity of concrete.h = hydraulic head of water (m).ρ = water density (1000 kg/m3).t = time under pressure (s).m = gain in weigh (g).A = area of sample (mm2).The water permeability coefficient of POFA concrete can be calculated using Equation (2).A = dried-weight (g).B = saturated-weight (g).Vol = sample volume (cm3).wρ = water density at 21°C (kg/cm3).Void content,K = coefficient of water permeability, (mm/s).tubeA and A are the areas of the tube and sample, (mm2).L = sample length, (mm).t = time needed for water to drop from level h1 to level h2, (s).Numerous researchers have previously applied the falling-head experiment to obtain the water permeability coefficient of concrete The rate of capillary absorption  is relatPR = CPR, (m/(v.hr)).CU = absolute value of the used voltage, (V).t = time of test (h).dX = penetration depths, (m).Corrosion is one of the main problems in RCs utilized in infrastructure; for instance, harbor and offshore constructions, bridges, and pavement . Chlorid4 and 5% Na2SO4 for 182 days. Thanks to active interactions, CaSO4 depositions cause a decrease in MgSO4 with an upsurge in ground slag, resulting in a reduction of strength and weight of the samples, contrary to what occurs in samples exposed to Na2SO4 [4 compared to Na2SO4. The addition of GGBS and metakaolin (10% to 15%) to POFA admixtures can also increase the RSA of concrete and significantly reduce its alkali–silica reactivity, as shown in the following equations [The choice of materials and the proportioning of concrete in susceptible zones should be precisely determined to withstand external attack ,132,133.o Na2SO4 . This fiquations .Acid-based reaction:Siloxane bridge attack and silica disintegration:Sulfate attack reduces concrete durability by altering the natural chemical composition of the adhesive and the mechanical characteristics of the concrete . The hydThe hydrated calcium aluminate + sulfate ion or the calcium-hydroxide compositions of water + mechanical cement paste = gypsum are expressed (III and IV) as: 3A and Ca(OH)2 are condensed in a solidified concrete, hence decreasing the fabrication of ettringite and gypsum re-crystallization.It is also shown that the addition of finer POFA diminishes the overall content of calcium hydroxide and the expansion scale of the concrete bars, but it also promotes as plaster, contributing to a decrease in holes among the hydration products and aggregates, tending to produce a heavier concrete ,75,92. M2 was low due to the small amount of lime content [2. Reports indicated that the most susceptible element of hydrated cement is Ca(OH)2, when acid can still attack the C–S–H gel [Concrete is known to be very alkaline in nature and extremely susceptible to acid attack ,132. Aci content . The ext–S–H gel . Concret–S–H gel . Studies–S–H gel ,142. It –S–H gel . In geneThe alkali–silica reaction (ASR) is more generally recognized as a cancer of concrete, and is a bulge activation that arises with age in concrete with extremely alkaline-paste and volatile amorphous silica that presents in various popular aggregates with a specified adequate moistness . ASR is 2 to shape calcium carbonates [2 in the atmosphere and are transformed into calcium carbonate [2, indicating that the pH of fresh concrete paste has a minimum of 12.5 [2 of mixtures. This carbonation activation possibly decreases the pH value to less than 9 in the pore solution [2 is re-ingested from the air during the carbonation process of concrete [2 in the mass of concrete, and hence could contribute to an improvement in carbonation of mortar [The carbonation of concrete, among other factors, is one of the primary reasons while reinforcement bars corrode . It is arbonates . Carbonaarbonate . The pas of 12.5 . Carbon solution . It was solution ,75. The solution . A certaconcrete ,152. Invf mortar ,153. Thif mortar ,155,156.f mortar . This wif mortar .α = 0.7 to 1.0) in a small-frequency zone of 40 to 150 Hz [α < 0.1 at a frequency of 100 Hz to 2000 Hz [α > 0.5 in these zones [α) is computed as:R = reflection coefficient.j = wave number.d1 and d2 = distances between the sample surface and the far and close active microphones, accordingly.P = sound pressure ratio at the dual active microphone rooms.The AIR of POFA concrete can be evaluated according to ASTM C 423 . Thin foo 150 Hz , as a reo 150 Hz . Howevero 150 Hz ,149,157.o 150 Hz . The inc 2000 Hz . GFC alsse zones . Using sse zones . Any addThermal conductivity is an important property that can improve the energy efficiency and environmental sustainability of modern buildings . Thermal2 in the POFA mortar [2 emissions than OPC [Construction materials with advanced properties, such as superior fire resistance ASTM E 2748), have recently been in demand . As the A mortar ,166. HowA mortar ,167,168.48, have than OPC . As statthan OPC , geopolythan OPC . Several2) is generated for every ton of clinker production [2 gas emissions. Cement manufacturing was predicted to have increased by 100% from 2008 to 2020 [2 gas emissions contributor worldwide [In industrial sectors, cement consumes 12–15% of the allocated energy , which eoduction . This pr to 2020 . Referri to 2020 . Moreove to 2020  with 1.5 to 2020  and it horldwide .2 generation will damage the atmosphere [2 emissions [There are several environmental issues, and global warming is one of them, which is partially induced by industrial and agricultural solid waste materials . A previmosphere ,177,178.mosphere  or in thmosphere . The higmosphere . By utilmissions .2 gas emissions by 5 to 8% of the level generated by cement production [As there is an increasing demand for energy resources and new renewable resources are urgently needed; non-renewable resources from petrochemicals and natural gases should be consumed less, as they may contribute to global warming . POFA cooduction . The untoduction . It has oduction . Other toduction .Concrete matrix formed from biomass products should cause less environmental damage compared to traditional chemical materials. POFA, as cement replacement in concrete, may lead to better solid waste management . As POFA2, silica fume, nano-clay, and nano fly ash, in addition to carbon nano-tubes [2 [Nanotechnology, a current trend, has found applications in various industries  and has no-tubes ,186. Nanno-tubes ,71 by reno-tubes . POFA istubes [2 . A more tubes [2 . Severaltubes [2 ,41,176 atubes [2 ,97,155, tubes [2 .Nano particles can be used to represent the ground POFA in order to increase reactivity with other constituents and enhance concrete properties ,155; 7.43S dissolution [2 in terms of the properties of mortar paste and concrete mixtures. Nano silica in POFA concrete also showed a positive influence on concrete shrinkage beyond the microstructure [Spherical particles of nano silica, sized 1–50 mm, can enhance fresh and hardened concrete properties . In termsolution . In termsolution . As POFAsolution . The fastructure . In gene2, methane, CO, etc.) emissions in the air while reducing the overall cost of cement usage. Considering the fresh and hardened characteristics of POFA their use for making concrete is pivotal. Based on this review, the fineness of POFA is an important property in concrete; however, the great fineness of POFA enhances its capability for micro-filing and PA, thereby leading to enhanced concrete mechanical characteristics and durability properties. POFA-based composites presented a similar and, from time to time, superior performance than normal concrete in withstanding carbonation, sulfate resistance, as well as acid attack. Further investigation is suggested to determine the overall influences of POFA on various characteristics of concrete, in addition to durability properties, and therefore inspire the inclusion of POFA in producing concrete. These are highly imperative for continued incorporation of POFA in self-compacting concretes (SCC). POFA has been used as a potential binder (as a PCR) up to a particular substitution level of OPC in which is safe from any negative influence on the strength or/and durability of concrete. In conclusion of this review study and to address the favorable influences of POFA on some concrete properties and durability problems, which make POFA an alternative PCR in concrete, several research investigations are recommended for the future:-To investigate the effects of POFA on the slump loss, plastic shrinkage and the air content of concrete while examining the influences of POFA on rheological characteristics, such as plastic viscosity and yield stress of concrete;-To examine the effect of POFA on the bond, tensile, fatigue, impact, shear, and flexural strengths of concrete; and to study the feasibility of using POFA concrete in resisting aggressive environments;-Determination of the effects of POFA on the autogenous, creep, water absorption, drying shrinkage, thermal resistivity, oxygen penetration, as well as diffusion of aggressive ions in concrete;-Evaluating the durability performance of POFA concrete with regards to de-icing, salt-scaling, freeze and thaw, abrasion, and corrosion resistance.The majority of preceding research has concentrated on the specific characteristics of POFA concrete, for instance its high compressive strength and PA, rather than on the morphological micro-structure characteristics. This research also ignored some components, for instance artificial and natural fibers, as well as alkaline activator solutions, and how they affect the strength of POFA concrete matrix. For example, a binder paste that contains a small amount of carbon nano-fiber reveals great stability and sensitivity in POFA concrete. The subsequent conclusions can be noted on the basis of the observations from this study review regarding POFA in mortar/concrete. The inclusion of POFA as a PCR in concrete mixes will ameliorate the challenges due to agro-based waste disposal and subsequent environmental issues, reduce the ecological vulnerabilities assumed by ordinary Portland cement plants, and reduce to a considerable extent the greenhouse gases (COGeneral investigations into the properties of high fineness POFA with the aim of enhancing the micro-structure, which can result in a dense extremely impervious concrete matrix is highly recommended; in particular to investigate the performance of POFA materials incorporated in ultra-high-strength and self-compacting concretes while enhancing their mechanical and durability properties using fibers.


The results show that GSA-GBR performs higher prediction performance (R2GSA-GBR = 0.958) and stronger robustness (RMSEGSA-GBR = 0.202) than the other five types of algorithms employed to predict the healing performance of autogenous healing concrete. Therefore, reliable prediction accuracy of the healing performance and efficient assistance on the design of autogenous healing concrete can be achieved.Cracks typically develop in concrete due to shrinkage, loading actions, and weather conditions; and may occur anytime in its life span. Autogenous healing concrete is a type of self-healing concrete that can automatically heal cracks based on physical or chemical reactions in concrete matrix. It is imperative to investigate the healing performance that autogenous healing concrete possesses, to assess the extent of the cracking and to predict the extent of healing. In the research of self-healing concrete, testing the healing performance of concrete in a laboratory is costly, and a mass of instances may be needed to explore reliable concrete design. This study is thus the world’s first to establish six types of machine learning algorithms, which are capable of predicting the healing performance (HP) of self-healing concrete. These algorithms involve an artificial neural network (ANN), a k-nearest neighbours (kNN), a gradient boosting regression (GBR), a decision tree regression (DTR), a support vector regression (SVR) and a random forest (RF). Parameters of these algorithms are tuned utilising grid search algorithm (GSA) and genetic algorithm (GA). The prediction performance indicated by coefficient of determination (R Concrete is a commonly used material for construction and aesthetic purposes. It is estimated that about three tons of concrete are used per person per year, with that amount doubled when other materials are added for construction . ConcretThe extent of corrosion was investigated that manifests different cracking widths in the reinforced concrete. Corrosion was observed on the rebars of test specimens with varying crack thicknesses. It was found that corrosion did occur in the reinforcement of samples with 400 µM crack girths. No corrosion was detected in concrete attaining a maximum crack width of 100 µM, even after 365 days have elapsed from the commencement of the trials . PaintinConcrete has been found to have self-healing capacities that seal microcracks depending on various testing conditions and concrete mix proportions . Self-he2 reacts with calcium ions (white precipitation), exhibited in The mechanisms of autogenous healing concrete can be concluded as follows, shown in A combination of  contact , triggerThe hydration of previously un-hydrated cement particles present in the mixture aids in sealing the small cracks. Continuous hydration autogenous healing utilises the reaction between the cement and the water, producing a gel that swells and blocks the narrow pathway paved by fissures, thus reducing the flow rate within the sample ,16. The ASR generally has destructive repercussions. The internal effect of the interaction between alkali, found in sand or gravel used in the mixture, and cement produces an expansive gel that swells within the member ,18. BuilIncorporating mineral additions with cementitious materials is an effective method of improving HP of self-healing concrete, and the most commonly employed minerals are fly ash, blast furnace slag and silica fume ,20. The Crystalline admixtures are commercial types of healing materials whose ingredients are confidential. According to open literature, sulphur trioxide and sodium oxide are revealed as constituents of crystalline admixtures ,22. The Superabsorbent polymers (SAP) are white powder or scale-like ranging from mi-cros to millimetres. The healing steps of concrete with SAP can be concluded as follows. Firstly, the water inside SAP is released into concrete matrix to promote further hydration of cementitious materials. As a result, C-S-H, which is able to heal cracks, can be formed during the further hydration of cementitious materials. Secondly, SAP particles can expand to seal cracks when water penetrates concrete through cracks ,24,25,26Concrete containing fibre has been paid more attention to because of its excellent ability to crack resistance. The healing mechanisms of concrete with fibre can be drawn as follows. Firstly, fibre can effectively limit the crack width of concrete matrix under varying conditions and offer the bridging force to enhance the healing ability of concrete with fibre. Secondly, fibre can be the cores of precipitations to stimulate the formation of healing products. The results of published articles related to fibre healing concrete demonstrated that various types of fibre, different geometry including diameter, length and tensile strength of fibre exhibited a significant influence on the healing performance of concrete ,28.Healing methods involving external interference, namely agent-based healing concrete, were investigated. According to the research on agent-based healing concrete, calcium carbonate for healing cracks was induced by applying bacteria, such as ureolytic bacteria, aerobic bacteria and nitrifying bacteria, and their nutrients onto the test specimen. The general mechanism of agent-based healing concrete can be attributed to the following steps. Firstly, capsules containing healing agents are incorporated into the mixture and spread throughout the cast concrete samples. Secondly, when cracks are formed, the damage would cause the aforementioned capsules to release the entrained substances within them, thus healing the cracks ,30,31.However, better healing performance of agent-based healing concrete is mentioned. Up to 970 µM wide of cracks were reported to be healed by employing agent-based healing concrete . Two maiMachine learning (ML) has been broadly utilised to solve regression, clustering and classification problems according to the information dug out from massive data sets. The reason why ML has the ability to figure out these problems can be attributed to ML being able to obtain new knowledge by means of learning from existing information imitating human learning behaviour. To date, two studies attempted to predict HP of self-healing concrete. One study carried out by Ramadan and Nehdi was involved in predicting HP of intrinsic healing concrete employing ANN whose parameters were optimised by GA . In a st2 and RMSE. Finally, sensitive analysis on the optimal ML model is conducted.In this paper, 16 influencing factors are utilised for the first time to predict HP of autogenous healing concrete. Firstly, 1417 experimental data sets in total of autogenous healing concrete are collected from eight open literature. Then, 16 variables are set as the inputs, and the healing performance of autogenous healing concrete is recognised as the sole output. Subsequently, unprecedented six ML algorithms are employed to build various ML models, and two types of hyperparameters optimisation methods are applied to tune the parameters of each ML algorithm. After that, the prediction performance and the prediction accuracy of each ML model are demonstrated and then compared using RIn this study, 1417 experimental data sets related to HP of autogenous healing concrete are collected from eight open literature published from 2000 to 2020 shown in Yn is the normalised data, y represents the data before normalisation, and miny and maxy are the minimum and maximum data before normalisation.It is essential to normalise data for improving the working efficiency and the prediction performance of machine learning models. Therefore, the data are normalised between  before inputting data into machine learning models by employing Equation (10) .(10)Yn=2 = 0.9185) for predicting the compressive strength of concrete with recycled aggregate. Furthermore, DTR and GBR models were employed to predict the mechanical properties of hydraulic concrete. The results showed that GBR models demonstrated better prediction performance than DTR models. The R2 of GBR models for predicting the compressive strength, ultimate tensile strain, elastic modulus, dry shrinkage rate and splitting tensile strength were 0.951, 0.858, 0.934, 0.922 and 0.929 respectively.In this section, six ML algorithms are introduced from articles related to concrete properties prediction to predict HP of autogenous healing concrete. Therefore, ANN, kNN, DTR, SVM are classified as the single ML algorithms. GBR and RF are recognised as ensemble ML algorithms by employing bagging or boosting strategy to improve the prediction performance and overcome the overfitting problem. Detailed information of these algorithms can be accessed in other open literature ,46,47,48GA is a probabilistic searching algorithm and an intelligence solution inspired by biological evolution processes. Each individual of a population in GA is called a chromosome. A certain proportion of chromosome among a population is selected as the next generation to continuously iterate until the global optimal chromosome is found in accordance with the fitness degree of each chromosome ,50.The searching scope and length are confirmed, and then, the searching grid is generated.The node in the searching grid with the highest accuracy and the lowest coefficient penalty calculated by K-fold validation is defined as the node which can output the best parameter value.GSA is an optimisation method to analyse all possible cases in the constraint range. The processes to conduct GSA can be concluded as follows ,52:The Characteristics of GA and GSA are summarised in 2 calculated by Equation (12) has also been noted to evaluate the prediction performance of ML models. Its output ranges from zero to one, one indicating a perfect model [RMSE shown in Equation (11) is elected as the governing factor in determining the accuracy of the predictive models as it calculates the square root of the error between the predicted and observed values for all the values. The lower the RMSE, the better the fit and the more accurate the predictions . R2 calcct model .(11)RMS2 and RMSE value shown in 2 value and the lowest RMSE value is recognised as the best ML model for predicting HP of autogenous healing concrete. What can be clearly seen in 2 (0.958) and lower RMSE (0.202) than other types of ML algorithms. As is shown in 2 and RMSE values of the GA-GBR model are 0.955 and 0.210, respectively which are similar to those of GSA-GBR. The R2 and RMSE of GSA-RF and GA-RF are  and  accordingly, which indicate a slight low prediction performance and prediction accuracy than those of GSA-GBR and GA-GBR. In addition, GSA-DTR, GA-DTR, GSA-ANN, GA-ANN, GSA-kNN and GA-kNN models demonstrate fluctuation of R2 and RMSE values around  which are , , , ,  and , respectively. What is striking in 2 and RMSE of GSA-SVR and GA-SVR. The R2 and RMSE values of GSA-SVR and GA-SVR are  and  accordingly. GA performs the better optimisation ability than GSA to enhance the prediction performance of SVR in this paper. To sum up, GSA-GBR is defined as the optimal algorithm to explain the relationship between 16 variables and HP of autogenous healing concrete.The prediction performance and the prediction accuracy of six machine algorithms with two hyperparameters optimisation methods are indicated by RAdditional display of the predicted HP against the individual experimental samples for the GSA-GBR model is exhibited in Sensitive analysis is a type of uncertainty analysis employed to explain the results of ML according to the analysis of the impact of changed inputs on the outputs. It is significant for sensitive analysis to explore the relationship between the changes in the number of inputs and the output . In this2 and RMSE of GBR models 1–11. The R2 value of GBR models 11 and 12 increases from 0.672 to 0.704, while a decline of the RMSE from 0.573 to 0.528 is exhibited between GBR model 11 and GBR model 12. Subsequently, the R2 value of GBR13 rises moderately from 0.704 to 0.783. At the same time, a lesser decline of RMSE from 0.528 to 0.481 of GBR13 is demonstrated. Finally, what stands out is the rapid growth of R2 value of GBR14, which soars from 0.783 to 0.958. Meanwhile, the RMSE of GBR14 plummets from 0.481 to 0.202. In summary, CW, CD and TH have higher influence on HP of autogenous healing concrete, which means that they are the most significant inputs that should be paid more attention to in ML models to achieve higher prediction performance. Therefore, TH is the input which has the highest impact on HP of autogenous healing concrete.This study is the world’s first to predict HP of autogenous healing concrete employing ML models using six kinds of advanced algorithms. ML models are employed to explain the relationship between 16 inputs and HP. Meanwhile, GSA and GA hyperparameter tuning methods are utilised to optimise the parameters of the ML models.2 and RMSE values of ML models, obvious findings to emerge from this paper can be concluded as follows.With regards to the R2 value and the RMSE value  of GSA-GBR model. On the basis of the R2 value and the RMSE value, it can be attributed that the GSA-GBR ML model has an excellent ability for predicting HP of autogenous healing concrete using the 16 inputs.This paper identifies that the GSA-GBR ML model has the best performance to predict HP of autogenous healing concrete, as indicated by the R2 and the RMSE values of other ML models with five types of algorithms  optimised by two kinds of hyperparameter tuning methods (GA and GSA) are compared with that of GSA-GBR. The results reveal that GSA has a better optimisation ability than GA on ML models based on DTR.The RThe results of the sensitive analysis indicate that CW, CD and TH demonstrate stronger correlation of HP prediction of autogenous healing concrete than other inputs. Most importantly, CW, CD and TH have higher impact on HP prediction of autogenous healing concrete than healing materials characteristics.With respect to the future work, the healing performance of agent-based healing concrete can be investigated employing the latest and promising machine learning algorithms.