Method for evaluating reaction durability of alkali active aggregate of concrete structure

Abstract

The invention belongs to the technical field of civil engineering and building materials, particularly relates to a concrete structure alkali active aggregate reaction durability evaluation method, and aims to solve the problems that the existing in-service concrete structure AAR durability evaluation is lagged, the period is long, and the existing in-service concrete structure AAR durability evaluation is disjointed from the actual service state. According to the method, an aggregate sample in a service state is obtained from a concrete structure, the aggregate sample is pretreated and prepared into a standard test piece, accelerated soaking, high-precision expansion rate measurement and kinetic analysis are performed, and the durability and service risk of the sample are comprehensively evaluated based on multiple parameters. According to the method disclosed by the invention, fine control is carried out on the acquisition, pretreatment and test piece re-preparation processes of the aggregate sample, particularly, the service state characteristics of the aggregate are reserved to the greatest extent in the aggregate separation process, and secondary damage or activation on the active surface of the aggregate is avoided; the early-stage and accurate judgment of the in-service aggregate reaction potential and the future durability prediction can be realized, the evaluation early-warning capability is improved, and a scientific basis is provided for maintenance decision making.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering and building materials technology, and specifically relates to a method for evaluating the reactive durability of alkali-reactive aggregates in concrete structures. Background Technology

[0002] Concrete, as one of the most widely used structural materials in contemporary infrastructure construction, is crucial for ensuring the safe, stable operation and service life of various engineering structures. Among the many types of defects that can lead to the deterioration of concrete structures, alkali-reactive aggregate reaction has become a major durability issue of widespread concern in the engineering community worldwide due to its insidious nature, gradual progression, and irreversible destructiveness once it occurs. The essence of this reaction lies in the complex chemical reaction between the highly alkaline pore solution inside the concrete and certain reactive silica or carbonate mineral components in the aggregate, generating a colloidal product that can absorb moisture and expand. This expansion effect accumulates slowly and continuously within the concrete, eventually forming enormous internal stress, leading to a series of deterioration phenomena such as cracking, a significant decrease in strength and stiffness, and even loss of load-bearing capacity. This seriously threatens the safety, reliability, and expected service life of critical infrastructure such as bridges, dams, and nuclear power plants. Therefore, developing efficient, accurate, and forward-looking methods for evaluating the reactive durability of alkali-reactive aggregates is of immeasurable engineering practical significance and economic value for the safety assessment of in-service structures, the formulation of preventive maintenance strategies, and the optimal allocation of resources.

[0003] Furthermore, the fundamental flaws of rapid laboratory tests on raw aggregates are particularly prominent when assessing in-service structures. These tests target unused raw aggregates, whose physicochemical properties, surface microstructure, and interfacial characteristics with cement paste differ significantly from aged aggregates that have served in concrete structures for many years, experiencing complex environmental erosion, load-bearing effects, and prolonged immersion in alkaline solutions. In-service aggregates may have had their surface-active components partially consumed or passivated due to prolonged immersion in highly alkaline pore solutions, or more active surfaces exposed due to microcracks; even the pore structure of the surrounding cement paste matrix and the migration pathways of alkali ions may have changed. These factors profoundly affect the actual reactivity of the aggregates and their expansion behavior within the concrete. Therefore, simply applying the reactivity test results of raw aggregates directly to evaluate the future reactivity potential of aggregates already in service in in-service structures lacks sufficient scientific basis and is highly susceptible to misjudgment of the actual reaction process, leading to underestimation or overestimation of the durability risks of in-service structures. This results in a lack of reliable scientific basis for the development of preventative maintenance and precise intervention measures. The underlying reason lies in the fact that existing technologies have not yet established a system for processing and evaluating aggregate samples that can effectively overcome the limitations of on-site sampling and obtain representative aggregate samples from in-service concrete structures that can truly reflect their reaction potential under service conditions in a laboratory environment. This disconnect between on-site and laboratory testing leads to two core technological contradictions: first, it is impossible to achieve early and sensitive assessment of potential alkali-aggregate reactivity before damage manifests; second, it is impossible to scientifically and accurately connect and predict accelerated testing results from the laboratory with the actual reaction environment of in-service aggregates in existing structures and their future durability evolution.

[0004] The aforementioned deep-seated contradictions highlight the severe challenges currently faced by technology in evaluating the reactive durability of alkali-reactive aggregates in concrete structures. Therefore, establishing a comprehensive evaluation method that overcomes the inherent shortcomings of traditional methods, such as lag, long cycles, and the disconnect between laboratory testing and actual service conditions, to efficiently obtain representative aggregates from in-service structures, accurately simulate their real reaction environment and durability evolution in the laboratory, and then scientifically predict their future performance, has become a key challenge and an urgent technical problem for those skilled in the art. Summary of the Invention To achieve the above objectives, this application provides the following technical solution: According to a first aspect of the present invention, the present invention claims protection for a method for evaluating the reactive durability of alkali-reactive aggregates in concrete structures, comprising the following steps: S1: Obtain multiple representative aggregate samples in service condition from the concrete structure to be evaluated. The acquisition process is carried out by directional core drilling and a layered strategy is adopted to obtain aggregate samples from different depths and locations of the concrete structure. S2: The obtained aggregate samples are subjected to fine pretreatment and mixed with standard cement to prepare standard specimens for accelerated testing; S3: The standard specimen is placed in a precisely controlled alkaline solution for accelerated immersion treatment; S4: Within a predetermined time interval, perform high-precision expansion rate measurement on the standard specimen being immersed, and perform expansion kinetic analysis; S5: Based on the expansion rate measurement data, expansion kinetic parameters and microstructure analysis results, the alkali-reactive aggregate reaction durability of the concrete structure is comprehensively evaluated, and service risk is predicted. S6: Generate a durability evaluation report, which includes all measurement data, analysis results, evaluation conclusions, and specific maintenance recommendations.

[0005] Furthermore, in step S1, the directional core drilling sampling operation is carried out using a low-speed, water-cooled drilling machine equipped with a diamond drill bit, which reduces thermal damage, mechanical damage or the induction of new microcracks to the aggregate sample during the sampling process. The drilling machine is equipped with an online cooling system, which continuously injects clean cooling water into the drill bit and the hole wall at a preset flow rate through a circulating water pump to ensure that the temperature in the drilling area is kept constant below 25°C. The stratification strategy includes obtaining surface layer aggregate samples from a depth range of 0mm to 30mm below the structural surface, obtaining near-surface layer aggregate samples from a depth range of 30mm to 100mm below the structural surface, and obtaining core layer aggregate samples from the middle or core area of ​​the structure. The sampling points are pre-planned based on the size, geometry, load distribution, and observed deterioration phenomena of the structure. The sampling locations also include sampling near areas where obvious cracks or expansion deformation have been observed, and comparative sampling in areas where no obvious deterioration has been observed.

[0006] Furthermore, in step S2, the refined preprocessing includes the following sub-steps: S21: Cut the obtained aggregate sample into aggregate blocks and clean the aggregate blocks using a low-impact ultrasonic cleaning device. After cleaning, rinse the aggregate blocks repeatedly with deionized water until the rinsing water is neutral and there are no visible suspended matter. S22: The cleaned aggregate blocks are placed in a vacuum oven for drying. The drying process lasts for 48 to 72 hours, or until the mass change of the aggregate blocks between two consecutive weighings with a 24-hour interval is less than 0.1% and a constant weight is reached. S23: The dried aggregate blocks that have reached a constant weight are subjected to primary crushing by a low-stress roller crusher. The roller crusher achieves a crushing method mainly based on shearing and compression by precisely controlling the gap between the rollers. The crushed aggregate blocks are then subjected to fine mechanical vibration screening using a standard sieve based on the selected particle size range. S24: After crushing and screening, a small number of samples are randomly selected from the aggregates in each particle size range. The surface morphology, microcrack distribution, adhesion of alkali silica gel products, and chemical element composition of the aggregate particles are characterized by scanning electron microscopy combined with energy dispersive spectroscopy. The characterization aims to record the microscopic service characteristics of the aggregates. S25: The aggregate with a particle size within the preset range obtained by sieving in step S23 is mixed with standard cement in a predetermined mass ratio. The mass ratio of the aggregate to cement and the water-cement ratio are determined according to the relevant standard mortar specimen preparation requirements. The mixing water is an alkaline solution of sodium hydroxide or potassium hydroxide dissolved in advance, so that the total alkali content of the mortar reaches a specific level. S26: Pour the uniformly mixed mortar mixture into a standard prism mold of a preset size in two layers. Each layer of mortar is vibrated and compacted by a standard vibrating table. Two standard measuring heads for length measurement are pre-installed inside the mold. The compacted specimen, together with the mold, is placed in a standard curing room for preliminary curing. After that, the specimen is demolded and continues to be cured under the same temperature and humidity conditions.

[0007] Furthermore, step S3 also includes: S31: The alkaline solution is a sodium hydroxide solution, which is prepared by dissolving analytical grade NaOH in high-purity deionized water. The volume of the immersion solution should ensure that each specimen is immersed in a solution at least three times its own volume. S32: Place the container containing the soaking solution and standard test pieces in a high-precision constant temperature water bath, and equip it with a temperature monitoring probe to record the solution temperature in real time. The container should be sealed with a lid to reduce water evaporation and carbon dioxide absorption.

[0008] Furthermore, step S4 also includes: S41: Before the standard specimens begin immersion treatment, use a digital dilatometer with a preset micron resolution to measure the initial length L0 between the probes at both ends of each standard specimen; S42: During the soaking process, standard specimens are periodically removed from the constant temperature water bath at preset time intervals. The removal operation involves wiping the surface of the specimen with a damp cloth and measuring its current length Lt using the same dilatometer. The measurement time points are adjusted according to the dynamic changes in the dilatation rate. S43: For each measurement time point, calculate the expansion rate of the standard specimen according to the formula expansion rate % (9Lt-L0 / L0×100), and use professional data analysis software to plot the curve of the expansion rate of each specimen changing with time. The curve should include error bars. S44: Perform nonlinear regression analysis on the plotted expansion rate-time curve, and fit it using a three-parameter Logistic function model or an Avrami equation model. Extract key dynamic parameters from the fitting results, including the induction period t_ind, the maximum expansion rate R_max, and the final expansion potential. S45: During the soaking process, a portion of the specimens are randomly selected from the parallel specimens periodically for destructive testing. The testing includes using X-ray diffraction to analyze the crystal phase composition of the newly generated reaction products in the specimens, using scanning electron microscopy to observe the development of microcracks in the interface area between aggregate and cement paste, the morphology and distribution of alkali-silica gel products, and using energy-dispersive X-ray spectroscopy to perform micro-area analysis of the elemental composition of the reaction products.

[0009] Furthermore, step S5 also includes: S51: Based on the service environment, importance level, and design life requirements of the concrete structure, a multi-level expansion rate threshold system shall be established. The level classification shall be modified in conjunction with the induction period and the maximum expansion rate. S52: Construct a comprehensive durability index DI, which is a weighted function of multiple parameters including expansion rate, induction period, maximum expansion rate and micro-damage degree. The weights are determined by expert experience, historical data, principal component analysis or analytic hierarchy process. S53: Based on the calculated comprehensive durability index, the concrete structure to be evaluated is classified into different service risk levels, and the classification of the levels should be directly linked to subsequent maintenance decisions. S54: Based on the obtained expansion dynamics parameters and the established degradation model, combined with the actual environmental factors and historical degradation data of the structure, establish or calibrate the Remaining Service Life (RSL) prediction model. The prediction model infers the probability or time of the in-service concrete structure reaching the preset damage threshold in a specific time period in the future based on the accelerated test results. S55: Quantify the uncertainty of durability evaluation and remaining service life prediction results, and conduct sensitivity analysis by analyzing the impact of input parameter fluctuations on the final results.

[0010] Furthermore, in step S6, the recommendations for generating and maintaining the durability evaluation report include the following: S61: Project overview, including detailed information on the concrete structure to be evaluated, sampling location map, sampling depth and quantity; S62: Description of aggregate sample pretreatment and specimen preparation process, with detailed records of all key parameters in step S2; S63: Expansion rate measurement data and kinetic curves, listing the expansion rate measurement data of each specimen at different time points, and attaching a curve of expansion rate changing with time, the curves are labeled with kinetic parameters such as induction period, maximum expansion rate and final expansion potential; S64: Microstructure analysis results, including SEM images, EDS spectra and XRD spectra, and detailed interpretation of the results. Based on the comprehensive durability evaluation results, the conclusion of the alkali-reactive aggregate reaction durability level assessment of the concrete structure to be evaluated is given. S65: Remaining service life prediction, providing the expected remaining service life of the structure under current service conditions or the probability of reaching a preset damage level, and proposing specific and actionable preventive maintenance, monitoring strategies or intervention measures. S66: Generate uncertainty analysis results, including quantitative information on the uncertainty of the evaluation results and prediction models.

[0011] This invention belongs to the field of civil engineering and building materials technology, specifically relating to a method for evaluating the alkali-reactive aggregate (AAR) reaction durability of concrete structures. It aims to address the problems of existing AAR durability evaluation methods for in-service concrete structures, such as delays, long cycles, and disconnection from actual service conditions. This invention obtains aggregate samples from concrete structures in service condition, pre-treats them, and then prepares them into standard specimens. These specimens are then subjected to accelerated immersion, high-precision expansion rate measurement, and kinetic analysis. Based on a multi-parameter comprehensive evaluation, the durability and service risk are assessed. This invention provides refined control over the acquisition, pre-treatment, and specimen preparation processes of aggregate samples. In particular, it maximizes the preservation of the service condition characteristics of the aggregates during aggregate separation, avoiding secondary damage or activation of the active surfaces of the aggregates. This enables early and accurate judgment of the reaction potential of in-service aggregates and prediction of future durability, improving evaluation and early warning capabilities and providing a scientific basis for maintenance decisions. Attached Figure Description

[0012] Figure 1 The flowchart is a process diagram of a method for evaluating the reactive durability of alkali-reactive aggregates in concrete structures, for which protection is sought in this invention. Figure 2 This is a second workflow diagram of a method for evaluating the reactive durability of alkali-reactive aggregates in concrete structures, which is claimed in this invention. Figure 3 This is a third workflow diagram of a method for evaluating the reactive durability of alkali-reactive aggregates in concrete structures, for which this invention is claimed. Figure 4 The fourth workflow diagram is for a method for evaluating the reactive durability of alkali-reactive aggregates in concrete structures, which is claimed in this invention. Figure 5 The fifth flowchart is for a method for evaluating the reactive durability of alkali-reactive aggregates in concrete structures, for which this invention is claimed. Detailed Implementation

[0013] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0014] The terms "first," "second," and "third" in this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of those features. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationships and movements between components in a specific orientation (as shown in the figures). If the specific orientation changes, the directional indications also change accordingly. Furthermore, the terms "including" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0015] References to embodiments herein mean that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0016] For a long time, engineers have relied primarily on several traditional methods to evaluate the hazards and development trends of alkali-reactive aggregate reaction in existing concrete structures. One common strategy involves core sampling of the structure, followed by laboratory testing of the core samples to assess a range of macroscopic mechanical properties and durability indicators. For example, by measuring changes in mechanical parameters such as compressive strength, tensile strength, and elastic modulus of the core samples, or by combining visual observation and metallographic analysis, the distribution of microcracks and the formation of aggregate reaction products within the core samples can be evaluated, thereby indirectly inferring the extent of alkali-aggregate reaction and its impact on the macroscopic performance of the structure. Another traditional method focuses on long-term natural exposure observation of the structure. This method typically includes periodically visually inspecting surface cracks, measuring crack width and length changes over time, recording macroscopic deformation of the structure, and conducting empirical assessments in conjunction with changes in temperature and humidity in the service environment. Furthermore, during the selection of concrete raw materials, rapid aggregate testing methods are frequently used in laboratories. These methods aim to assess the potential alkali reactivity of new aggregates within a short timeframe by simulating accelerated reaction conditions, thereby providing a basis for material selection in concrete mix design. These traditional methods provided preliminary judgment criteria for engineering practice under specific historical contexts. For example, macroscopic performance testing can intuitively reflect the current degree of structural damage, while long-term observation provides information on the macroscopic performance of the structure under actual service conditions. Rapid laboratory testing, on the other hand, provided an early warning mechanism for the selection of aggregates in fresh concrete, thus addressing some of the localized technical problems encountered at the time.

[0017] However, with the increasing service life of engineering structures and the increasingly stringent requirements of modern engineering management for the efficiency, accuracy, and predictive ability of structural durability assessments, the aforementioned traditional evaluation methods are gradually revealing their inherent limitations in addressing complex challenges, particularly in the early prediction and accurate assessment of potential alkali-aggregate reaction hazards in in-service structures. Specifically, the method relying on core sampling of the structural entity and macroscopic performance testing is limited by the fact that the measured macroscopic performance degradation usually results from significant damage already occurring within the structure after the alkali-aggregate reaction has progressed to a certain stage. This means that the method is essentially a delayed diagnosis, unable to provide timely and sensitive judgments in the early stages of the reaction or during the potentially active period of the reaction, thus often missing the best opportunity for early intervention and preventive maintenance. Furthermore, core sampling itself causes localized damage to the existing structure, and the core samples often only represent the average condition of a local area, making it difficult to comprehensively and accurately reflect the complex reaction state of the entire structure. Correspondingly, while long-term natural exposure observation methods can obtain data on structural degradation in real-world environments, their assessment period is excessively long, typically requiring several years or even decades to observe a clear degradation trend. This is severely inconsistent with the timeliness requirements of modern engineering decision-making. This method lacks a quantitative and standardized assessment process, relies heavily on the observer's subjective experience, and its results are easily affected by a combination of environmental factors. It is difficult to accurately isolate the pure contribution of alkali-aggregate reaction, leading to significant uncertainty in the assessment results.

[0018] According to the first embodiment of the present invention, referring to Figure 1 This invention seeks to protect a method for evaluating the reactive durability of alkali-reactive aggregates in concrete structures, comprising the following steps: S1: Obtain multiple representative aggregate samples in service condition from the concrete structure to be evaluated. The acquisition process is carried out by directional core drilling and a layered strategy is adopted to obtain aggregate samples from different depths and locations of the concrete structure. S2: The obtained aggregate samples are subjected to fine pretreatment and mixed with standard cement to prepare standard specimens for accelerated testing; S3: The standard specimen is placed in a precisely controlled alkaline solution for accelerated immersion treatment; S4: Within a predetermined time interval, perform high-precision expansion rate measurement on the standard specimen being immersed, and perform expansion kinetic analysis; S5: Based on the expansion rate measurement data, expansion kinetic parameters and microstructure analysis results, the alkali-reactive aggregate reaction durability of the concrete structure is comprehensively evaluated, and service risk is predicted. S6: Generate a durability evaluation report, which includes all measurement data, analysis results, evaluation conclusions, and specific maintenance recommendations.

[0019] In this embodiment, it further includes: In S1, representative aggregate samples in service condition were systematically obtained from the concrete structure to be evaluated. Sampling was performed using directional core drilling with a low-speed drilling machine equipped with a diamond drill bit. This drilling machine was equipped with a water-cooling system, which continuously injected clean cooling water at a constant flow rate into the contact area between the drill bit and the concrete during drilling, ensuring the operating interface temperature remained below 25 degrees Celsius. A stratified sampling strategy was adopted. Based on the structural geometry, load distribution characteristics, and existing signs of degradation, surface samples were collected at a depth of 0-30 mm, near-surface samples at a depth of 30-100 mm, and internal samples were collected in the core area of ​​the structure. Sampling points were arranged to cover areas adjacent to cracked or expanded deformation areas, while seemingly intact areas were selected as control sampling points.

[0020] In S2, standard specimens were prepared after refined pretreatment of the obtained aggregate samples. The pretreatment process included: cutting the core samples into aggregate blocks of specified dimensions, cleaning the surface using a low-intensity ultrasonic cleaner, and then repeatedly rinsing with deionized water until the effluent was neutral and free of suspended particles. The cleaned aggregate blocks were transferred to a vacuum drying oven for 48-72 hours of drying, until the mass change was less than 0.1% for 24 consecutive hours, which was considered constant weight. The dried samples were then subjected to primary crushing using a roller crusher with adjustable gaps, followed by mechanical vibration sieving through a standard sieve group to obtain aggregates of the target particle size. Representative samples were randomly selected from each particle size group, and the particle surface morphology, microcrack distribution, and elemental composition were characterized using a scanning electron microscope combined with an energy dispersive spectroscopy (EDS) system. Finally, the sieved aggregates were mixed with standard cement in a predetermined ratio, using a solution containing alkali ions as mixing water. The mixture was then layered into a prism mold equipped with a measuring probe according to the standard mortar specimen preparation procedure. After vibration compaction, the mixture was cured in the mold, and after demolding, it was cured under standard conditions.

[0021] In S3, the molded specimens are placed in a strictly controlled alkaline environment to accelerate the reaction. The immersion solution is an alkaline solution prepared with analytical grade sodium hydroxide and high-purity deionized water, and the solution volume is ensured to be more than three times the volume of the specimen. The container holding the specimen and solution is placed in a high-precision constant temperature water bath, and a temperature monitoring probe is installed in the bath to record the solution temperature changes in real time. The container opening is sealed to prevent water evaporation and carbon dioxide dissolution.

[0022] In S4, specimen deformation is periodically measured and reaction kinetics are analyzed during the accelerated reaction process. Before immersion, the initial length between the two probes is measured using a micrometer-precision digital dilatometer. Specimens are removed from the immersion environment according to a preset time sequence, and the length measurement is repeated after wiping the surface with a damp cloth. The expansion rate at each time point is calculated based on the measurement data, and an expansion rate-time curve including the error range is plotted. A nonlinear fitting method is used to analyze the curve to obtain kinetic parameters such as the reaction induction period and maximum expansion rate. Simultaneously, samples are extracted from parallel specimens for destructive testing. The phase composition of the reaction products is analyzed by X-ray diffraction, and the evolution of the interface microstructure is observed using electron microscopy.

[0023] S5 performs a systematic evaluation and risk prediction of structural durability based on test data. A multi-level expansion rate threshold system is established according to the structural service environment, importance level, and design service life, with threshold adjustments made based on reaction kinetic parameters. A comprehensive durability index model is constructed, integrating multiple parameters such as expansion rate, induction period, expansion rate, and micro-damage, with weighting coefficients determined through professional analysis methods. The structure is classified into different risk levels based on the durability index, establishing a correspondence with maintenance strategies. Based on reaction kinetic parameters and actual environmental conditions, a remaining service life prediction model is established to quantify the probability of the structure reaching a specific damage state in the future. Uncertainty analysis is performed on the evaluation results to examine the impact of key parameter fluctuations on the prediction conclusions.

[0024] S6 requires the preparation of a durability evaluation report containing complete technical elements. The report should include: a project overview and sampling plan description, detailing structural information, sampling location distribution, and sample quantity; a complete description of the sample processing and specimen preparation process, listing all key process parameters; expansion test data and kinetic curves, clearly labeling characteristic parameters; microscopic analysis results, including raw data such as electron microscope images and energy dispersive spectroscopy (EDS) spectra, and their interpretation; durability level determination conclusions and basis; remaining service life prediction results; specific maintenance recommendations based on the evaluation conclusions; and an explanation of uncertainty analysis.

[0025] According to an embodiment of the present invention, the alkali-reactive aggregate reaction durability evaluation of concrete piers of an in-service highway bridge is conducted. This highway bridge is located in a temperate monsoon climate zone and requires the application of de-icing salt in winter. Piers P3 and P7 were evaluated. The evaluation team first collected the structural design drawings, construction records, and annual inspection reports, and conducted a preliminary on-site investigation, meticulously recording the morphology, width, distribution pattern of cracks, and any visible expansion deformation. Based on this information, a comprehensive core sampling plan was developed.

[0026] Furthermore, in step S1, the directional core drilling sampling operation is carried out using a low-speed, water-cooled drilling machine equipped with a diamond drill bit, which reduces thermal damage, mechanical damage or the induction of new microcracks to the aggregate sample during the sampling process. The drilling machine is equipped with an online cooling system, which continuously injects clean cooling water into the drill bit and the hole wall at a preset flow rate through a circulating water pump to ensure that the temperature in the drilling area is kept constant below 25°C. The stratification strategy includes obtaining surface layer aggregate samples from a depth range of 0mm to 30mm below the structural surface, obtaining near-surface layer aggregate samples from a depth range of 30mm to 100mm below the structural surface, and obtaining core layer aggregate samples from the middle or core area of ​​the structure. The sampling points are pre-planned based on the size, geometry, load distribution, and observed deterioration phenomena of the structure. The sampling locations also include sampling near areas where obvious cracks or expansion deformation have been observed, and comparative sampling in areas where no obvious deterioration has been observed.

[0027] In this embodiment, before sampling, the hydraulic drilling machine and its diamond thin-walled core drill bit were inspected and calibrated. The speed control system was adjusted to ensure stable operation within the predetermined low speed range. The circulating water pump and pipeline of the online cooling system were thoroughly cleaned to ensure the cleanliness of the cooling water.

[0028] Sampling procedure: On the selected piers P3 with obvious cracks and P7 with an intact appearance, the operators strictly followed the plan for positioning. Drilling began with a smaller pressure initially, gradually increasing to normal drilling pressure once the drill bit stabilized. Throughout the process, cooling water was continuously and evenly injected into the borehole center, with the flow rate adjusted to ensure immediate removal of drill cuttings and maintain the borehole temperature well below room temperature. After drilling to a certain depth, the drill bit was slowly raised to remove debris from the core slot, ensuring the core sample was retrieved intact.

[0029] For the stratified sampling, three core samples were drilled from the dense crack area of ​​the P3 pier column for the surface layer sample. Each core sample was drilled to a predetermined depth, and obvious traces of environmental erosion were visible on the surface of the core samples at this depth.

[0030] For near-surface layer samples, drilling continued at the same borehole location after replacing the extension rod to obtain core samples within the predetermined depth range. These core samples exhibit a relatively uniform appearance, but may still be affected by humidity gradients.

[0031] For the core layer samples, two full-length core samples were drilled at the center of the P7 pier column. The obtained core samples were of uniform texture and had no visible cracks.

[0032] Each concrete core sample taken out is immediately uniquely identified with a waterproof label, indicating the pier number, sampling date, sampling location, and orientation. The core sample is then wrapped in moistened gauze, placed in a special core sample box, and transported to the laboratory to avoid vibration and drying during transportation.

[0033] Furthermore, referring to Figure 2 In step S2, the refined preprocessing includes the following sub-steps: S21: Cut the obtained aggregate sample into aggregate blocks and clean the aggregate blocks using a low-impact ultrasonic cleaning device. After cleaning, rinse the aggregate blocks repeatedly with deionized water until the rinsing water is neutral and there are no visible suspended matter. S22: The cleaned aggregate blocks are placed in a vacuum oven for drying. The drying process lasts for 48 to 72 hours, or until the mass change of the aggregate blocks between two consecutive weighings with a 24-hour interval is less than 0.1% and a constant weight is reached. S23: The dried aggregate blocks that have reached a constant weight are subjected to primary crushing by a low-stress roller crusher. The roller crusher achieves a crushing method mainly based on shearing and compression by precisely controlling the gap between the rollers. The crushed aggregate blocks are then subjected to fine mechanical vibration screening using a standard sieve based on the selected particle size range. S24: After crushing and screening, a small number of samples are randomly selected from the aggregates in each particle size range. The surface morphology, microcrack distribution, adhesion of alkali silica gel products, and chemical element composition of the aggregate particles are characterized by scanning electron microscopy combined with energy dispersive spectroscopy. The characterization aims to record the microscopic service characteristics of the aggregates. S25: The aggregate with a particle size within the preset range obtained by sieving in step S23 is mixed with standard cement in a predetermined mass ratio. The mass ratio of the aggregate to cement and the water-cement ratio are determined according to the relevant standard mortar specimen preparation requirements. The mixing water is an alkaline solution of sodium hydroxide or potassium hydroxide dissolved in advance, so that the total alkali content of the mortar reaches a specific level. S26: Pour the uniformly mixed mortar mixture into a standard prism mold of a preset size in two layers. Each layer of mortar is vibrated and compacted by a standard vibrating table. Two standard measuring heads for length measurement are pre-installed inside the mold. The compacted specimen, together with the mold, is placed in a standard curing room for preliminary curing. After that, the specimen is demolded and continues to be cured under the same temperature and humidity conditions.

[0034] In this embodiment, a water-cooled rock cutter is used in a laboratory to carefully cut along the axial direction of the concrete core sample. The goal is to separate appropriately sized blocks containing intact original aggregate, while minimizing direct contact and damage to the aggregate particles by the cutting blade. The cut aggregate blocks are placed in an ultrasonic cleaning tank with sufficient deionized water, and the cleaning program is run. After cleaning, each aggregate block is placed in a beaker and repeatedly rinsed with deionized water until the rinse water is visually clear and pH paper is used to confirm that the rinse water is neutral.

[0035] Place the washed aggregate blocks evenly on the tray of the vacuum drying oven, ensuring sufficient gaps between the blocks to facilitate moisture evaporation. Set the drying temperature and vacuum level, and start the program. During the drying process, close the vacuum approximately every 24 hours, remove the sample, and cool it to room temperature inside the desiccator. Weigh the sample using a precision electronic balance and record the weight. Repeat this process until the mass change stabilizes within a very small range, confirming constant weight.

[0036] Adjust the gap between the two rollers of the roller crusher to be slightly less than the upper limit of the target aggregate particle size. Slowly and evenly feed the dry aggregate blocks into the crusher feed inlet. Collect the crushed material and pour it onto the top layer of a set of standard sieves stacked from top to bottom according to aperture size. Cover the sieve and fix it on a mechanical vibrating screen. Set the vibration time and start the vibrating screen. After screening, carefully collect the aggregate particles remaining on the sieves within the target particle size range, combine them into a sample group, and remove any flat or needle-shaped particles mixed in.

[0037] Dozens of representative aggregate particles were randomly selected from each sample group corresponding to different piers and layers. These particles were adhered to the sample stage and sputter-coated with gold to increase conductivity. They were then placed in the sample chamber of a scanning electron microscope. The particle surface was systematically observed at different magnifications.

[0038] Key areas of focus include: the presence of a smooth, dry, cracked gel-like coating; the width, length, and orientation of the original microcracks; and whether reaction products fill the cracks. Select a typical region, activate the energy dispersive spectroscopy (EDS) probe, and perform point or area scanning analysis to obtain the elemental composition spectrum of that region, paying particular attention to the relative contents of elements such as silicon, calcium, sodium, potassium, and oxygen.

[0039] According to standard requirements, accurately calculate and weigh the specified mass of treated aggregate and reference cement. Simultaneously, based on the target total alkali content, accurately calculate the required mass of sodium hydroxide, dissolve it in a measured amount of high-purity deionized water, and prepare an alkaline solution for mixing. Pour the aggregate and cement into a forced-mixing pot, dry-mix until uniform, then slowly add the alkaline solution and wet-mix for a sufficient time until a mortar mixture with uniform color and consistent workability is obtained.

[0040] The well-mixed mortar was poured into a standard triple-prism mold pre-installed with probes in two layers. After each layer was poured, the mold was fixed on a standard vibrating table and vibrated for a specified time to ensure that the mortar was fully compacted and that slurry surface was visible. Excess mortar was scraped off and the surface was smoothed. The molded specimen, along with the mold, was transferred to a constant temperature and humidity standard curing chamber and covered with plastic film to prevent excessive moisture evaporation. When the specimen strength was sufficient to resist demolding damage, the mold bolts were carefully loosened and the specimen was removed. The demolded specimen was immediately transferred to a curing tank filled with saturated lime water, or continued to be cured on a wet sieve cloth in the standard curing chamber until the specified test age.

[0041] Furthermore, step S3 also includes: S31: The alkaline solution is a sodium hydroxide solution, which is prepared by dissolving analytical grade NaOH in high-purity deionized water. The volume of the immersion solution should ensure that each specimen is immersed in a solution at least three times its own volume. S32: Place the container containing the soaking solution and standard test pieces in a high-precision constant temperature water bath, and equip it with a temperature monitoring probe to record the solution temperature in real time. The container should be sealed with a lid to reduce water evaporation and carbon dioxide absorption.

[0042] In this embodiment, analytical grade sodium hydroxide granules and high-purity deionized water are used to prepare a sodium hydroxide solution of a predetermined concentration in an alkali-resistant container. A magnetic stirrer is used to assist dissolution during the solution preparation process, and the solution is allowed to stand and cool to room temperature. A plastic sealed container with good chemical stability is selected as the soaking container. Based on the volume and number of test specimens, the solution volume injected into each container is calculated and ensured to be well more than three times the total volume of the test specimens.

[0043] Remove the standard specimens from the curing environment after curing is complete. Gently wipe the surface with a damp cloth and quickly place them vertically into a sealed container filled with alkaline solution. Use an inert material, such as a plastic grid, to line the container to prevent direct contact between the specimens and the bottom wall. Cover the container, ensuring the sealing ring is correctly positioned and tightened. Then, completely immerse the sealed container in the heating medium of a high-precision constant-temperature water bath. Set the target temperature of the water bath and start the circulation and temperature control system. Insert the sensing part of a calibrated precision temperature probe into a pre-reserved control container containing the same alkaline solution but without the specimens. This allows for real-time monitoring and recording of the true temperature in the core area of ​​the solution, ensuring it remains within a very narrow fluctuation range of the target temperature.

[0044] Furthermore, referring to Figure 3 Step S4 further includes: S41: Before the standard specimens begin immersion treatment, use a digital dilatometer with a preset micron resolution to measure the initial length L0 between the probes at both ends of each standard specimen; S42: During the soaking process, standard specimens are periodically removed from the constant temperature water bath at preset time intervals. The removal operation involves wiping the surface of the specimen with a damp cloth and measuring its current length Lt using the same dilatometer. The measurement time points are adjusted according to the dynamic changes in the dilatation rate. S43: For each measurement time point, calculate the expansion rate of the standard specimen according to the formula expansion rate % (9Lt-L0 / L0×100), and use professional data analysis software to plot the curve of the expansion rate of each specimen changing with time. The curve should include error bars. S44: Perform nonlinear regression analysis on the plotted expansion rate-time curve, and fit it using a three-parameter Logistic function model or an Avrami equation model. Extract key dynamic parameters from the fitting results, including the induction period t_ind, the maximum expansion rate R_max, and the final expansion potential. S45: During the soaking process, a portion of the specimens are randomly selected from the parallel specimens periodically for destructive testing. The testing includes using X-ray diffraction to analyze the crystal phase composition of the newly generated reaction products in the specimens, using scanning electron microscopy to observe the development of microcracks in the interface area between aggregate and cement paste, the morphology and distribution of alkali-silica gel products, and using energy-dispersive X-ray spectroscopy to perform micro-area analysis of the elemental composition of the reaction products.

[0045] In this embodiment, before the specimen begins immersion, it is removed from the curing environment, wiped clean with a damp cloth, and then stably placed on a calibrated digital length comparator stand under standard laboratory atmospheric conditions. The specimen position is adjusted so that the spherical tips of the probes at both ends make good contact with the measuring contacts of the length comparator. After the instrument reading stabilizes, the initial length value is recorded. Each specimen is measured several times, and the average value is taken as its initial length.

[0046] Measurements were performed strictly according to the pre-established schedule. At the designated time point, the entire sealed container was removed from the constant-temperature water bath. The lid was carefully opened, and the specimen was removed using plastic tweezers. Immediately, any residual solution on the surface was gently wiped away with a damp, soft cloth. Then, under the same conditions as the initial length measurement, the current length was quickly measured. After measurement, the specimen was immediately returned to its original container, ensuring complete immersion, and then resealed and placed back into the water bath. Based on the recorded current and initial lengths, the expansion rate at that time point was calculated.

[0047] All specimens and expansion rate data at all time points were compiled into a table and entered into professional data processing software. A scatter plot was drawn with time on the horizontal axis and expansion rate on the vertical axis. A preset mathematical model was selected to perform nonlinear regression fitting on the data. Through iterative calculations, the fitted curve was optimized to best approximate the measured data points. From the successfully fitted model, key kinetic parameters were extracted: for example, the induction period can be defined by the horizontal axis corresponding to the inflection point of the curve or the time when the expansion rate reaches a certain small threshold; the maximum expansion rate is the maximum value of the first derivative of the fitted curve; and the final expansion potential is the asymptotic value corresponding to when the curve tends to flatten.

[0048] At pre-set critical time points, a specified number of specimens are randomly selected from parallel prepared spare specimens, and their immersion is terminated. These specimens are then broken, and representative internal fragments are selected. Some fragments are ground into fine powder for X-ray diffraction analysis to identify the phase composition; other fragments are used to prepare samples for scanning electron microscopy (SEM): after vacuum impregnation and curing with epoxy resin, they are polished to a smooth surface, lightly etched, and carbonized. The microstructure of the aggregate-slurry interface transition zone is then observed under an SEM, particularly the origin and propagation path of microcracks, as well as the morphology and distribution of reaction products. The chemical composition of the observed characteristic areas is analyzed using energy dispersive spectroscopy (EDS).

[0049] Furthermore, referring to Figure 4 Step S5 further includes: S51: Based on the service environment, importance level, and design life requirements of the concrete structure, a multi-level expansion rate threshold system shall be established. The level classification shall be modified in conjunction with the induction period and the maximum expansion rate. S52: Construct a comprehensive durability index DI, which is a weighted function of multiple parameters including expansion rate, induction period, maximum expansion rate and micro-damage degree. The weights are determined by expert experience, historical data, principal component analysis or analytic hierarchy process. S53: Based on the calculated comprehensive durability index, the concrete structure to be evaluated is classified into different service risk levels, and the classification of the levels should be directly linked to subsequent maintenance decisions. S54: Based on the obtained expansion dynamics parameters and the established degradation model, combined with the actual environmental factors and historical degradation data of the structure, establish or calibrate the Remaining Service Life (RSL) prediction model. The prediction model infers the probability or time of the in-service concrete structure reaching the preset damage threshold in a specific time period in the future based on the accelerated test results. S55: Quantify the uncertainty of durability evaluation and remaining service life prediction results, and conduct sensitivity analysis by analyzing the impact of input parameter fluctuations on the final results.

[0050] In this embodiment, taking into account the importance of the bridge, its environment, and the design reference period, and referring to relevant domestic and international standards and literature, a multi-level expansion rate evaluation threshold was set.

[0051] For example, an inflation rate below a certain value is defined as safe, between two values ​​as a warning, and above a certain value as an action. Furthermore, this threshold system is dynamically adjusted based on the length of the induction period and the rate of maximum inflation. For instance, in cases with an extremely short induction period and an extremely rapid inflation rate, even if the final inflation rate does not reach the highest action threshold, the risk level may still be upgraded.

[0052] A comprehensive durability index calculation model was constructed. This model uses representative expansion rate, induction period, and maximum expansion rate obtained from accelerated expansion tests, as well as the degree of microcrack development and the amount of gel products as semi-quantitatively assessed in microscopic analysis, as input parameters. An appropriate weight was assigned to each parameter using a combination of expert experience and the analytic hierarchy process (AHP). The comprehensive durability index value corresponding to each sample group was calculated. Based on the range of index values, the durability status of each region of the structure was clearly divided into different levels, such as Level I (low risk), Level II (medium risk), and Level III (high risk).

[0053] Based on kinetic parameters obtained under accelerated laboratory conditions, particularly the relationship between reaction rate and temperature, and combined with meteorological data from the past few decades for the bridge's location, such as monthly average temperature, humidity, and number of rainy days, an equivalent model of the degree of reaction is established. This model links the actual environmental conditions on-site with the accelerated laboratory conditions. Through model calculations, the approximate time required for the structural concrete to reach the preset critical expansion damage level under natural conditions, i.e., the remaining service life, is estimated; the prediction results are usually given in the form of a time range or probability distribution.

[0054] The process clearly identifies potential uncertainties in the entire evaluation process, such as material variability, sampling representativeness, testing equipment errors, measurement reading deviations, mathematical model fitting errors, and environmental data uncertainties. Appropriate mathematical methods are used to quantify these uncertainties and assess their cumulative impact on the comprehensive durability index and remaining service life prediction results. Simultaneously, sensitivity analysis is conducted to examine the impact of fluctuations in key input parameters within a reasonable range on the final prediction results, thereby identifying the most sensitive parameters.

[0055] Furthermore, referring to Figure 5 In step S6, the recommendations for generating and maintaining the durability evaluation report include the following: S61: Project overview, including detailed information on the concrete structure to be evaluated, sampling location map, sampling depth and quantity; S62: Description of aggregate sample pretreatment and specimen preparation process, with detailed records of all key parameters in step S2; S63: Expansion rate measurement data and kinetic curves, listing the expansion rate measurement data of each specimen at different time points, and attaching a curve of expansion rate changing with time, the curves are labeled with kinetic parameters such as induction period, maximum expansion rate and final expansion potential; S64: Microstructure analysis results, including SEM images, EDS spectra and XRD spectra, and detailed interpretation of the results. Based on the comprehensive durability evaluation results, the conclusion of the alkali-reactive aggregate reaction durability level assessment of the concrete structure to be evaluated is given. S65: Remaining service life prediction, providing the expected remaining service life of the structure under current service conditions or the probability of reaching a preset damage level, and proposing specific and actionable preventive maintenance, monitoring strategies or intervention measures. S66: Generate uncertainty analysis results, including quantitative information on the uncertainty of the evaluation results and prediction models.

[0056] In this embodiment, the report begins with a detailed description of the project background, including the bridge name, location, construction year, main structural form, and the reason for this evaluation. It includes a clear map of the pier locations, a diagram of the distribution of defects, and a detailed map of the core sampling locations, clearly marking the number of each sampling point and the corresponding stratum information.

[0057] Using a combination of text and tables, the entire preparation process from concrete core samples to standard mortar specimens is systematically described. Detailed information on key equipment and materials is recorded, such as drilling rig model, cutting machine model, cement brand and grade, and chemical reagent purity, as well as all critical process parameters, such as ultrasonic cleaning power and time, drying temperature and time, crusher roller gap, sieving time, bone binder ratio, water-binder ratio, alkali solution concentration, and curing conditions.

[0058] List the raw expansion rate data of all specimens at each measurement time point in a clearly structured table. Plot the expansion rate-time curves containing all specimen data, using different line types and colors to distinguish different groups of specimens. Clearly indicate the values ​​of each key kinetic parameter obtained through fitting in the figure or in the notes.

[0059] The report includes selected representative scanning electron microscope (SEM) images, energy dispersive spectroscopy (EDS) spectra, and X-ray diffraction (XRD) patterns, with detailed interpretations of each image and spectrum, explaining the microstructural features and chemical information they reflect. Based on the synthesis of all macroscopic expansion data and microscopic analysis results, qualitative and quantitative evaluations of the alkali-aggregate reactivity and damage state of the P3 and P7 piers and concrete layers are presented, and their final risk levels are clearly defined.

[0060] Clearly state the predicted remaining service life, including the predicted life range and confidence level for core and damaged areas. Based on the risk level and predicted life, provide highly actionable, tiered maintenance and management recommendations. For example: for Level I areas, it is recommended to include them in routine inspections and re-inspect them every few years; for Level II areas, it is recommended to add surface waterproofing treatment and shorten the deformation monitoring cycle to once a year; for Level III areas, it is recommended to conduct a detailed structural load-bearing capacity assessment immediately and develop a medium- to long-term reinforcement or replacement plan.

[0061] In a separate chapter or appendix of the report, present the key findings of the uncertainty and sensitivity analyses. Explain the confidence range of the evaluation conclusions and predicted lifetimes, and identify the key factors affecting the accuracy of the predictions, providing decision-makers with a comprehensive understanding of the risks.

[0062] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between apparatuses or units, and may be electrical, mechanical, or other forms.

[0063] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated units described above can be implemented in hardware or as software functional units. The above are merely embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made based on the description and drawings of this application, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

[0064] The specific embodiments of the invention have been described in detail above, but they are only examples, and this application is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications or substitutions to the invention are also within the scope of this application. Therefore, all equivalent changes, modifications, and improvements made without departing from the spirit and principles of this application should be covered within the scope of this application.

Claims

1. A method for evaluating the alkali-reactivity of aggregates in concrete structures, characterized by, Includes the following steps: S1: Obtain multiple representative aggregate samples in service condition from the concrete structure to be evaluated. The acquisition process is carried out by directional core drilling and a layered strategy is adopted to obtain aggregate samples from different depths and locations of the concrete structure. S2: The obtained aggregate samples are subjected to fine pretreatment and mixed with standard cement to prepare standard specimens for accelerated testing; S3: The standard specimen is placed in a precisely controlled alkaline solution for accelerated immersion treatment; S4: Within a predetermined time interval, perform high-precision expansion rate measurement on the standard specimen being immersed, and perform expansion kinetic analysis; S5: Based on the expansion rate measurement data, expansion kinetic parameters and microstructure analysis results, the alkali-reactive aggregate reaction durability of the concrete structure is comprehensively evaluated, and service risk is predicted. S6: Generate a durability evaluation report, which includes all measurement data, analysis results, evaluation conclusions, and specific maintenance recommendations.

2. The evaluation method according to claim 1, characterized in that, In step S1, the directional core drilling sampling operation is carried out using a low-speed, water-cooled drilling machine equipped with a diamond drill bit, which reduces thermal damage, mechanical damage or the induction of new microcracks to the aggregate sample during the sampling process. The drilling machine is equipped with an online cooling system, which continuously injects clean cooling water into the drill bit and the hole wall at a preset flow rate through a circulating water pump to ensure that the temperature in the drilling area is kept constant below 25°C. The stratification strategy includes obtaining surface layer aggregate samples from a depth range of 0mm to 30mm below the structural surface, obtaining near-surface layer aggregate samples from a depth range of 30mm to 100mm below the structural surface, and obtaining core layer aggregate samples from the middle or core area of ​​the structure. The sampling points are pre-planned based on the size, geometry, load distribution, and observed deterioration phenomena of the structure. The sampling locations also include sampling near areas where obvious cracks or expansion deformation have been observed, and comparative sampling in areas where no obvious deterioration has been observed.

3. The evaluation method according to claim 1, characterized by, In step S2, the refined preprocessing includes the following sub-steps: S21: Cut the obtained aggregate sample into aggregate blocks and clean the aggregate blocks using a low-impact ultrasonic cleaning device. After cleaning, rinse the aggregate blocks repeatedly with deionized water until the rinsing water is neutral and there are no visible suspended matter. S22: The cleaned aggregate blocks are placed in a vacuum oven for drying. The drying process lasts for 48 to 72 hours, or until the mass change of the aggregate blocks between two consecutive weighings with a 24-hour interval is less than 0.1% and a constant weight is reached. S23: The dried aggregate blocks that have reached a constant weight are subjected to primary crushing by a low-stress roller crusher. The roller crusher achieves a crushing method based on shearing and compression by precisely controlling the gap between the rollers. The crushed aggregate blocks are then subjected to fine mechanical vibration screening using a standard sieve based on the selected particle size range. S24: After crushing and screening, a small number of samples are randomly selected from the aggregates in each particle size range. The surface morphology, microcrack distribution, adhesion of alkali silica gel products, and chemical element composition of the aggregate particles are characterized by scanning electron microscopy combined with energy dispersive spectroscopy. The characterization aims to record the microscopic service characteristics of the aggregates. S25: The aggregate with a particle size within the preset range obtained by sieving in step S23 is mixed with standard cement in a predetermined mass ratio. The mass ratio of the aggregate to cement and the water-cement ratio are determined according to the relevant standard mortar specimen preparation requirements. The mixing water is an alkaline solution of sodium hydroxide or potassium hydroxide dissolved in advance, so that the total alkali content of the mortar reaches a specific level. S26: Pour the uniformly mixed mortar mixture into a standard prism mold of a preset size in two layers. Each layer of mortar is vibrated and compacted by a standard vibrating table. Two standard measuring heads for length measurement are pre-installed inside the mold. The compacted specimen, together with the mold, is placed in a standard curing room for preliminary curing. After that, the specimen is demolded and continues to be cured under the same temperature and humidity conditions.

4. The evaluation method according to claim 1, characterized by Step S3 further includes: S31: The alkaline solution is a sodium hydroxide solution, which is prepared by dissolving analytical grade NaOH in high-purity deionized water. The volume of the immersion solution should ensure that each specimen is immersed in a solution at least three times its own volume. S32: Place the container containing the soaking solution and standard test pieces in a high-precision constant temperature water bath, and equip it with a temperature monitoring probe to record the solution temperature in real time. The container should be sealed with a lid to reduce water evaporation and carbon dioxide absorption.

5. The method for evaluating the alkali reactivity of concrete structural aggregate according to claim 1, characterized by, Step S4 further includes: S41: Before the standard specimens begin immersion treatment, use a digital dilatometer with a preset micron resolution to measure the initial length L0 between the probes at both ends of each standard specimen; S42: During the soaking process, standard specimens are periodically removed from the constant temperature water bath at preset time intervals. The removal operation involves wiping the surface of the specimen with a damp cloth and measuring its current length Lt using the same dilatometer. The measurement time points are adjusted according to the dynamic changes in the dilatation rate. S43: For each measurement time point, calculate the expansion rate of the standard specimen according to the formula expansion rate % (9Lt-L0 / L0×100), and use professional data analysis software to plot the curve of the expansion rate of each specimen changing with time. The curve should include error bars. S44: Perform nonlinear regression analysis on the plotted expansion rate-time curve, and fit it using a three-parameter Logistic function model or an Avrami equation model. Extract key dynamic parameters from the fitting results, including the induction period t_ind, the maximum expansion rate R_max, and the final expansion potential. S45: During the soaking process, a portion of the specimens are randomly selected from the parallel specimens periodically for destructive testing. The testing includes using X-ray diffraction to analyze the crystal phase composition of the newly generated reaction products in the specimens, using scanning electron microscopy to observe the development of microcracks in the interface area between aggregate and cement paste, the morphology and distribution of alkali-silica gel products, and using energy-dispersive X-ray spectroscopy to perform micro-area analysis of the elemental composition of the reaction products.

6. The evaluation method according to claim 1, characterized by Step S5 further includes: S51: Based on the service environment, importance level, and design life requirements of the concrete structure, a multi-level expansion rate threshold system shall be established. The level classification shall be modified in conjunction with the induction period and the maximum expansion rate. S52: Construct a comprehensive durability index DI, which is a weighted function of multiple parameters including expansion rate, induction period, maximum expansion rate and micro-damage degree. The weights are determined by expert experience, historical data, principal component analysis or analytic hierarchy process. S53: Based on the calculated comprehensive durability index, the concrete structure to be evaluated is classified into different service risk levels, and the classification of the levels should be directly linked to subsequent maintenance decisions. S54: Based on the obtained expansion dynamics parameters and the established degradation model, combined with the actual environmental factors of the structure and historical degradation data, establish or calibrate the Remaining Service Life (RSL) prediction model. The prediction model infers the probability or time of the in-service concrete structure reaching the preset damage threshold in a specific time period in the future based on the accelerated test results. S55: Quantify the uncertainty of durability evaluation and remaining service life prediction results, and conduct sensitivity analysis by analyzing the impact of input parameter fluctuations on the final results.

7. The evaluation method according to claim 1, characterized by, In step S6, the recommendations for generating and maintaining the durability evaluation report include the following: S61: Project overview, including detailed information on the concrete structure to be evaluated, sampling location map, sampling depth and quantity; S62: Description of aggregate sample pretreatment and specimen preparation process, with detailed records of all key parameters in step S2; S63: Expansion rate measurement data and kinetic curves, listing the expansion rate measurement data of each specimen at different time points, and attaching a curve of expansion rate changing with time. The curve is labeled with kinetic parameters such as induction period, maximum expansion rate and final expansion potential. S64: Microstructure analysis results, including SEM images, EDS spectra and XRD spectra, and detailed interpretation of the results. Based on the comprehensive durability evaluation results, the conclusion of the alkali-reactive aggregate reaction durability level assessment of the concrete structure to be evaluated is given. S65: Remaining service life prediction, providing the expected remaining service life of the structure under current service conditions or the probability of reaching a preset damage level, and proposing specific and actionable preventive maintenance, monitoring strategies or intervention measures. S66: Generate uncertainty analysis results, including quantitative information on the uncertainty of the evaluation results and prediction models.

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