A method for rapid identification of application risks of active sulphide aggregates

Abstract

This invention relates to the field of building material testing and concrete durability evaluation technology, and particularly to a rapid identification method for the application risk of reactive sulfide aggregates. The method includes: molding mortar from a control group and an experimental group into molds with pre-embedded probes at both ends for later use; the control group mortar consists of water, cement, and standard quartz sand, while the experimental group mortar is prepared by replacing the standard quartz sand in the control group with an equal volume of the aggregate to be tested; subjecting the cured specimens to multiple rounds of wet-dry cycles for accelerated corrosion; calculating the expansion rate of the specimens and the increase in expansion rate of the experimental group relative to the control group after each wet-dry cycle to determine whether the aggregate to be tested is a reactive sulfide aggregate with application risk; and significantly increasing the oxidation reaction rate of iron sulfide minerals and enhancing the expansion response by constructing an accelerated test system coupled with a sodium hypochlorite oxidation environment and wet-dry cycle conditions, thereby identifying the presence of reactive sulfide minerals in the aggregate in a shorter time.

Description

Technical Field

[0001] This invention relates to the field of building material testing and concrete durability evaluation technology, and in particular to a rapid identification method for the application risks of reactive sulfide aggregates. Background Technology

[0002] When natural rocks or mine tailings are processed into concrete aggregates, they may contain a certain amount of iron sulfide minerals, such as pyrite (FeS2), marcasite (FeS2), and pyrrhotite (Fe). 1-x When these minerals undergo oxidation reactions in concrete, they generate sulfates and trigger a series of chemical reactions, leading to expansion, cracking, and even structural damage in the concrete. Several such incidents have occurred in my country. Therefore, identifying whether aggregates contain reactive sulfide minerals before application is crucial for ensuring the durability of concrete structures.

[0003] One current detection method relies on sophisticated scientific instruments to analyze the parent rock. However, this method is relatively inefficient for detecting active sulfides dispersed and embedded in the ore as associated minerals, and the results are affected by sampling and cannot reflect the safety of these minerals as aggregates in concrete. Another detection method involves long-term oxidation exposure tests under different temperature and humidity conditions to determine the application risk of unstable sulfide minerals in the aggregate. However, this method has a long testing cycle, typically taking six months to several years to observe obvious reactions, resulting in low detection efficiency and failing to meet the needs of rapid screening in engineering projects.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the general background of this disclosure and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] This invention provides a rapid identification method for the application risks of reactive sulfide aggregates. By constructing an accelerated test system coupled with sodium hypochlorite oxidation environment and dry-wet cycle conditions, the oxidation reaction rate of iron sulfide minerals is significantly improved and the expansion response is enhanced, thereby identifying the presence of reactive sulfide minerals in aggregates in a short time and effectively solving the problems in the background technology.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A rapid identification method for the application risks of reactive sulfide aggregates, the method comprising: S1 involves molding the mortar from the control group and the experimental group into molds with pre-embedded probes at both ends, and then curing them to the specified age for later use. The control group mortar consists of water, cement, and standard quartz sand, while the experimental group mortar uses the same volume of the aggregate to be tested as the standard quartz sand in the control group. More specifically, the specimen dimensions are 25mm × 25mm × 280mm. This step, by setting the aggregate type as the only variable in the control and experimental groups, eliminates the interference of non-experimental variables such as cement type, water-cement ratio, and curing conditions on the test results. The standardized specimen molding and curing with pre-embedded probes provide a unified and homogeneous specimen benchmark for the expansion rate test, ensuring the comparability and repeatability of the test data between groups. It is important to note that at least three parallel specimens are prepared for both the control and experimental groups. S2 subjected the cured specimens to multiple rounds of wet-dry cycles to accelerate corrosion. Each round of wet-dry cycles consisted of drying, sealed immersion in NaClO solution, rinsing with clean water, high-temperature curing, and air drying. The wet-dry cycles in this step constructed an accelerated reaction system synergistically combining a strong oxidizing environment with alternating wet and dry conditions. The strong oxidizing environment of NaClO significantly accelerated the oxidation rate of active sulfide minerals in the aggregate, while the alternating wet and dry conditions promoted the penetration of the oxidant solution into the pores of the mortar through capillary action, accelerating the migration and accumulation of oxidation products, amplifying the expansion response, significantly shortening the detection cycle, and improving detection sensitivity. During the experiment, the NaClO solution was kept sealed throughout to avoid contact with CO2 in the air, and a fresh NaClO solution was replaced weekly to maintain a stable effective concentration of the oxidant. After each wet-dry cycle, S3 performs length tests on specimens from both the control and experimental groups, calculating the expansion rate of the specimens and the increase in expansion rate of the experimental group relative to the control group. This step, through standardized length testing after each wet-dry cycle and quantitative calculation of expansion rate and its increase, enables continuous tracking of specimen volume deformation. Using length change as an intuitive and precisely quantifiable indicator, it characterizes the mortar expansion effect caused by the oxidation reaction of active sulfides, providing quantitative data support for subsequent aggregate application risk assessment. S4 determines whether the aggregate under test is an active sulfide aggregate with application risks based on the expansion rate and the increase in expansion rate after a preset number of dry and wet cycles. It should be noted that the length change of the control group specimen should be continuously monitored throughout the test. The control group specimen should be in a shrinking state or fluctuating shrinkage state to determine the validity of the test process. If the control group shows continuous expansion, it indicates that the test process is abnormal and the test needs to be repeated.

[0007] This invention constructs an accelerated reaction system that combines a strong oxidizing environment of sodium hypochlorite with dry-wet cycles, making the oxidative expansion of sulfides easier to detect and significantly shortening the detection cycle for the application risks of reactive sulfide aggregates. At the same time, relying on a single-variable control test system and a dual-index quantitative judgment of expansion rate, it effectively eliminates the interference of non-aggregate factors and improves the accuracy of risk identification.

[0008] Furthermore, the ratio of the control group was: water: cement: standard quartz sand = 0.60:1:2.25.

[0009] Furthermore, the total cycle time for a single dry-wet cycle is 48±2 hours, and the specific method is as follows: S21 After curing, the specimen is dried at 80±5℃ for 12±2h. This step can fully remove the free water in the pores inside the specimen, forming a continuous and interconnected capillary network, providing a smooth channel for the penetration of NaClO solution. At the same time, this gentle drying process can prevent the specimen from cracking due to sudden changes in temperature and humidity, activate the active sulfide mineral sites on the surface of the aggregate, and remove free water inside the specimen to avoid diluting the NaClO solution during subsequent soaking, thus ensuring the effective concentration of the NaClO solution remains stable. S22 involves completely immersing the dried specimens in a 5-7 wt% NaClO solution with a pH of 12.5 ± 0.1 in a sealed environment for 12 ± 2 hours. This step utilizes the strong oxidizing properties of NaClO to directly oxidize active sulfide minerals such as pyrite and pyrrhotite in the aggregate, rapidly generating sulfate products that can induce expansion, thus accelerating the sulfide reaction process and significantly shortening the testing cycle. Furthermore, the alkaline environment of 12.5 ± 0.1 simulates the highly alkaline pore solution environment inside concrete, ensuring the test results closely match the actual application state of the aggregate, while effectively maintaining the chemical stability of NaClO and preventing its decomposition and failure. The sealed immersion method isolates CO2 from the air, preventing a decrease in solution pH and loss of oxidant. The 12 ± 2 hour immersion time ensures that the oxidant solution fully penetrates the pores inside the mortar, fully contacting the active sulfides at all points in the aggregate, ensuring a uniform and complete oxidation reaction. S23 After removing the specimen and rinsing it with clean water to remove any residual NaClO solution, the specimen is placed in a steam curing chamber at 80±5℃ for 12±2 hours. This step first removes the residual NaClO solution from the specimen surface by rinsing with clean water to avoid localized over-reaction caused by residual oxidant and to eliminate uneven reactions between the specimen and its interior. Then, the high-temperature curing in the 80±5℃ steam curing chamber for 12±2 hours accelerates the reaction process between the sulfate generated by oxidation and the cement hydration products, promotes the rapid formation and crystallization of expansive products such as ettringite and gypsum, and quickly converts the chemical effect of sulfide oxidation into accurately measurable specimen volume expansion deformation, effectively amplifying the expansion response signal. At the same time, the constant temperature curing environment ensures the stability of the cement matrix hydration process, avoids interference from fluctuations in the matrix's own strength and volume deformation on the test results, and ensures the authenticity of the expansion data. S24 Remove the specimen and place it in a fume hood to air dry for 4±0.5h. Test it while it is cooled. After the test, put the specimen back into the oven at the same time on the first drying day to complete one dry-wet cycle. This step, through air drying, allows the moisture inside the specimen to evaporate evenly and reach a stable humidity state, avoiding interference with the length test results caused by volume deformation due to differences in moisture content.

[0010] Preferably, the NaClO solution content is 6 wt%.

[0011] Preferably, the specific steps for testing under cooling conditions are as follows: after the specimen has undergone a specified number of wet and dry cycles, the specimen to be tested is placed in an environment of 20±2℃ and relative humidity of not less than 50% for 2 hours in advance. Under saturated surface dry conditions, an expansion test is performed using a comparator with a measurement range of 280mm~300mm and an accuracy of 0.01mm. Each specimen was tested at least twice, and the average of the two readings with a difference within the instrument's accuracy range was taken as the length measurement value.

[0012] Furthermore, the aggregate to be tested did not contain reactive silica or steel slag; More specifically, the active silica in the aggregate will react with potassium hydroxide and sodium hydroxide produced by cement hydration to form an alkali-silicic acid reaction, generating water-absorbing and expanding alkali-silicic acid gel, which will also cause the mortar specimen to expand and deform, causing confusion with the expansion effect caused by the oxidation of active sulfides. The iron phase and reducing components in steel slag react with NaClO, rapidly consuming the available chlorine in the solution. This causes a sharp drop in NaClO concentration, making it impossible to maintain a stable strong oxidizing environment and significantly reducing the efficiency of accelerated oxidation of active sulfides.

[0013] Furthermore, in S1, the probe is made of stainless steel; in S2, before each soaking in NaClO solution, Vaseline is evenly applied to the surface of the probe, and the surface of the probe is wiped clean before the length test. More specifically, the stainless steel probe has excellent structural rigidity and corrosion resistance, and can maintain dimensional stability in multiple cycles of strong oxidizing environment. NaClO solution is a strong oxidizing solution, and long-term contact will cause the metal probe to rust and deform, leading to detection errors. Applying Vaseline before each soaking can form a dense isolation layer on the probe surface, effectively preventing direct contact between the strong oxidizing solution of NaClO and the probe. Wiping the probe surface clean before length testing can eliminate the influence of the Vaseline coating on the length detection results.

[0014] Furthermore, the formula for calculating the expansion ratio is: ; in, The expansion rate of the specimen was measured after t cycles of wet and dry drying. The length of the specimen after t wet-dry cycles; The initial length of the specimen; This refers to the exposed length of a single-ended probe. The above formula uses the initial length of the specimen after standard curing as the deformation benchmark, and the absolute difference between the measured length after t wet-dry cycles and the initial length to characterize the total deformation of the specimen. At the same time, by subtracting the total length of the pre-embedded probes at both ends from the benchmark length, the interference of the probe size on the calculation of the effective deformation length of the specimen is eliminated, and the calculation benchmark is locked as the effective length of the mortar specimen body. Finally, the true volume expansion rate caused by the oxidation reaction of active sulfides after t wet-dry cycles is quantified in the form of a relative percentage, which conforms to the industry general standard for testing the expansion performance of cement-based materials.

[0015] Furthermore, the formula for calculating the increase in the expansion rate is as follows: ; in, This represents the increase in the expansion rate. The expansion rate of the mortar specimens in the experimental group; The expansion rate of the mortar specimens in the control group is shown below. More specifically, cement-based materials themselves undergo drying shrinkage and temperature-induced deformation during the hydration process, and some cement may even exhibit slight self-expansion. These deformations are superimposed on the total expansion rate of the specimen, making it impossible to distinguish whether the expansion deformation is caused by the reactive sulfide aggregate or by the deformation of the cement matrix itself. This invention, by calculating the relative value based on the expansion rate of the control group, can effectively remove the influence of basic deformation caused by non-aggregate factors such as the hydration deformation of the cement-based material itself and fluctuations in environmental temperature and humidity, highlighting the true expansion effect caused only by the aggregate under test.

[0016] Furthermore, in step S4, the preset cycle period is 15 dry and wet cycle periods; if the expansion rate of the specimen tends to level off within 15 cycles, the expansion rate under this stable state is recorded as the result; if the specimen does not show a tendency to stop expanding within 15 cycles, the expansion rate measured in the 15th cycle is used as the result. More specifically, the 15 dry-wet cycle cycles match the progress of the oxidation reaction of active sulfides in this accelerated reaction system. This ensures sufficient reaction time to fully manifest the expansion effect of active sulfides in the aggregate, and also perfectly matches the purpose of rapid identification in this invention, avoiding unnecessary extension of the test cycle. Compared with traditional long-term exposure tests of six months to several years, the detection efficiency is improved by tens of times. The above result value rules eliminate the controversy of result value when the expansion has not entered the stable stage, ensure the consistency and standardization of the judgment results of different batches of tests, and avoid the difference in judgment results caused by different value points.

[0017] Furthermore, step S3 also includes an accuracy check of the expansion rate measurement value. The check rules are as follows: when the average expansion rate of the three parallel specimens is ≤0.05%, the difference between the measurement value of a single specimen and the average value should be less than 0.01%, which can strictly control the detection error under low expansion level and avoid misjudgment under critical conditions; when the average value is >0.05%, the difference between the measurement value of a single specimen and the average value should be less than 20% of the average value, taking into account the test flexibility under medium and high expansion levels; when the expansion rate of the three parallel specimens is >0.10%, there is no accuracy requirement, which is suitable for the significant expansion deformation of highly reactive aggregates; when the above accuracy requirements are not met, the measurement value with the smallest expansion rate is discarded, and the average value of the remaining two specimens is taken as the expansion rate measurement value for that cycle number.

[0018] Furthermore, if the expansion rate of the experimental group specimens increases by more than 100% and the expansion rate is greater than 0.03%, they are judged as high-risk aggregates.

[0019] An expansion rate greater than 0.03% is an absolute threshold derived from the actual impact of aggregate expansion on concrete structures: only when the expansion reaches this value can microcracks be generated inside the concrete, affecting the structural integrity. It is the direct basis for judging whether aggregate expansion has the ability to cause substantial damage. An increase in expansion rate of >100% is a relative threshold designed based on the expansion trend of reactive aggregates: the expansion of reactive sulfide aggregates will continue to intensify and will not decay on its own, while normal inert aggregates will only show occasional slight deformation with a very small increase in deformation. Using this index can effectively distinguish between continuously deteriorating reactive expansion and occasional slight stable deformation, and eliminate numerical fluctuations caused by inactive factors. By combining the two indicators, we can accurately identify reactive sulfide risk aggregates that have both sufficient destructive power and a continuously deteriorating trend, thereby maximizing the accuracy of risk assessment.

[0020] Furthermore, the aggregate gradation to be tested is as follows: 8-10% for particle size of 5-2.5mm, 22-27% for particle size of 2.5-1.25mm, 22-27% for particle size of 1.25mm-630μm, 22-27% for particle size of 630-315μm, and 12-17% for particle size of 315-160μm. More specifically, the aforementioned continuous gradation can stabilize the specific surface area, particle interlocking state, and expansion constraint conditions of aggregates, avoiding differences in oxidant penetration rate and reactive sulfide reaction degree caused by fluctuations in particle size distribution. This ensures the uniformity and stability of oxidation reaction and expansion deformation, enabling standardized horizontal comparability of test results for aggregates from different batches and sources. Furthermore, this gradation is compatible with the gradation range of commonly used fine aggregates in engineering, and the test results can truly reflect the application risks of aggregates in actual concrete engineering, thus improving the engineering applicability of this method.

[0021] Furthermore, step S0, which determines whether the aggregate is a hazardous aggregate, is included before step S1. S01 checks the source and application history of aggregates; aggregates without safe application records and originating from iron tailings or areas surrounding sulfur mines are entered into S02. S02 Inspect the appearance of the aggregate. For abnormal aggregates with metallic luster particles or oxide rust stains, proceed directly to step S04. For aggregates without abnormalities, proceed to step S03. S03 tests the total sulfur content of aggregates. Aggregates with a total sulfur content ≥0.1% are included in S04, while those with a total sulfur content below 0.1% are considered non-risk aggregates. S04 involves mineral phase analysis of the aggregates. Aggregates containing active sulfides such as pyrrhotite, pyrite, or marcasite are moved to step S1. Aggregates not containing these active sulfides are classified as non-active sulfur risk aggregates.

[0022] More specifically, the specific method for step S0 is as follows: S01: Initial risk screening is conducted through source investigation and on-site testing. First, the source of aggregates is understood through geological background, with a focus on whether they are from iron tailings or quarries near sulfur mining areas. Historical data is used for extensive screening. Aggregates with a history of application in concrete that meet the conditions are directly treated as non-risk aggregates; otherwise, proceed to S02. The safe application history must meet the following conditions simultaneously: previously used as concrete aggregate, used as a major aggregate, building service history > 10 years, and good long-term durability. S02: For aggregates lacking historical data, observe the metallic luster and rust stains of hand specimens; for abnormal aggregates identified as having a risk of iron phase oxidation, proceed directly to S04 to improve screening efficiency; otherwise, proceed to S03 in sequence. S03: Chemical indicators are determined through high sulfur screening; total sulfur content can be detected by analytical methods such as XRF, chemical titration, infrared analysis or ICP; aggregates with a total sulfur content of less than 0.1% are treated as non-risk aggregates, and any other aggregates with a sulfur content of ≥0.1% are entered into S04. S04: Determine the presence of pyrrhotite through mineral phase identification; If the rust is determined by XRD to be introduced by other iron phase minerals, directly proceed to step S1 if XRD determines that pyrrhotite, pyrite or marcasite is present and there is a risk of sulfur activity. For samples that proceed through the normal screening process, the laboratory personnel can determine the level of active mineral content and choose either XRD or a combination of petrographic analysis and BSE / EDS. For samples with high levels of active sulfur, XRD can be used to specifically search for characteristic peaks of pyrrhotite. For samples that may have low levels of pyrrhotite, a combination of petrographic analysis and BSE / EDS can be directly used. If the sample is confirmed to have potential active sulfur risk through optical section examination and elemental distribution verification in BSE / EDS, it will proceed to S1. If the initial judgment is incorrect or considering the detection limit of XRD for trace components, a combination of petrographic analysis and BSE can be performed after XRD testing.

[0023] The technical solution of this invention can achieve the following technical effects: By constructing an accelerated reaction system that combines a strong oxidizing environment of sodium hypochlorite with dry-wet cycles, the oxidative expansion of sulfides is more easily detected, significantly shortening the detection cycle for the application risks of reactive sulfide aggregates. At the same time, relying on a single-variable control test system and quantitative judgment based on the dual indicators of expansion rate, the interference of non-aggregate factors is effectively eliminated, improving the accuracy of risk identification. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of a single-cycle dry-wet cycle; Figure 2 This is a schematic diagram of the specimen expansion testing device; Figure 3 This is a flowchart illustrating step S0. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0028] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Example 1:

[0029] This embodiment provides a rapid identification method for the application risks of reactive sulfide aggregates, and the specific steps are as follows: 1. Experimental raw materials and instruments like Figure 3 As shown, pre-screening of aggregates to be tested S01 Source Investigation: This aggregate is prepared from copper mine tailings and has no history of long-term safe application in concrete engineering. The source is located in a high-risk area with pyrite mineral occurrence and will proceed to the subsequent screening stage. S02 Visual inspection: If obvious metallic mineral particles are visible in the hand specimen, proceed directly to the S04 phase identification stage; S04 Phase Identification: The total sulfur content was determined to be 3.6% by ICP and characteristic peaks of pyrite and pyrrhotite were detected by XRD, confirming the presence of active sulfides, and the sample preparation process proceeded to S1.

[0030] 1.1 Raw material specifications: Cement: P.O42.5 grade ordinary Portland cement, specific surface area 350 m² 2 / kg, initial setting time 156min, final setting time 238min, 28d compressive strength 46.8MPa, no admixtures added; Quartz standard sand: High-purity quartz sand purified by sieving, with a silica content ≥98.5%, pre-tested and confirmed to be free of active sulfides and active silica, and an apparent density of 2.65 g / cm³. 3The particle size distribution is completely consistent with the aggregate to be tested: 10% of the particles are 5.00~2.50mm, 25% are 2.50~1.25mm, 25% are 1.25mm~630μm, 25% are 630~315μm, and 15% are 315~160μm.

[0031] Aggregate to be tested: Preliminary testing using the mortar bar rapid method in GB / T14684-2022 "Construction Sand" showed that it contained no active silica and was free of steel slag; the aggregate particle size distribution was the same as that of standard quartz sand, and the apparent density was 2.70 g / cm³. 3 ; NaClO solution: Prepared with analytical grade sodium hypochlorite reagent and deionized water, with a fixed mass fraction of 6 wt%. The pH of the solution is adjusted to 12.5 using analytical grade sodium hydroxide. The solution is replaced with a fresh solution once a week. Stainless steel probe: Made of 304 austenitic stainless steel, with a single-end embedded length of 5mm, an exposed length of 5mm, a diameter of 6mm, a polished surface free of rust, and a dimensional deviation of ≤0.01mm; Test water: Deionized water, conforming to the Class III water standard of GB / T6682-2008 "Specifications and Test Methods for Water Used in Analytical Laboratories", with a conductivity ≤0.5mS / m; Auxiliary materials: pharmaceutical-grade petroleum jelly, nitrile protective gloves.

[0032] 1.2 Instruments and Equipment Cement mortar test mold: 25mm×25mm×280mm prism steel mold, with pre-drilled positioning holes for measuring heads at the center of both ends of the test mold; Standard curing chamber: Temperature control range 0~50℃, temperature control accuracy ±0.5℃; Humidity control range 30%~98%, humidity control accuracy ±3%; Electric heating forced-air drying oven: Temperature control range: room temperature to 200℃, temperature control accuracy: ±2℃; Constant temperature and humidity steam curing chamber: Temperature control range: room temperature to 100℃, temperature control accuracy: ±2℃, relative humidity control range: ≥90%; Length comparator: measuring range 280mm~300mm, scale division 0.01mm, indication error ≤0.005mm, conforming to GB / T14684-2022 standard requirements; Fume hood: face velocity 0.3~0.8m / s, all-steel corrosion-resistant material; Ultrasonic cleaning machine: used for rinsing the surface of test pieces, power 100W.

[0033] 2. Specimen preparation 2.1 Mortar mix proportion The control group mortar had a fixed mix ratio of water:cement:quartz standard sand = 0.60:1:2.25, and the amount of materials used in a single specimen was: 450.0g of cement, 270.0g of deionized water, and 1012.5g of quartz standard sand. Experimental mortar: The same volume of the aggregate to be tested was used to replace all the standard quartz sand in the control group. After conversion according to apparent density, the amount of materials used in a single group of specimens was: 450.0g cement, 270.0g deionized water, and 1031.6g copper tailings aggregate.

[0034] 2.2 Specimen Molding and Curing 2.21 The stainless steel probe is fixed in the positioning holes at both ends of the test mold in advance to ensure that the coaxiality deviation of the probe is ≤0.1mm; 2.22 Use a cement mortar mixer and mix the mortar according to the procedure specified in GB / T17671-2021 standard. Mix at low speed for 30 seconds, add all aggregates within the second 30 seconds, mix at high speed for 30 seconds, stop mixing for 90 seconds, and then mix at high speed for 60 seconds. 2.23 The mixed mortar was poured into the mold in two layers. Each layer was tamped evenly 20 times with a tamping rod. The mold was then vibrated on a vibrating table for 60 seconds until the surface was covered with mortar. The surface was then leveled and the specimen number and test direction were marked. Figure 2 ; 2.24 After molding, the specimens were placed in an environment with a temperature of 20±2℃ and a relative humidity of ≥95% for 24 hours before demolding. Immediately after demolding, they were placed in a standard curing chamber and cured for 28 days at a temperature of 20±2℃ and a relative humidity of >95%. During the curing period, the specimens were prevented from contacting each other or being bumped.

[0035] 3. Accelerated oxidation test After the specimens were cured for 28 days, their initial length was measured. Subsequently, 15 cycles of wet-dry accelerated oxidation tests were conducted, with each cycle lasting a fixed total of 48 hours. Figure 1 The steps for each cycle are fixed as follows: 3.1 Drying process: Place the specimen in an electric heating drying oven at 80℃ and dry at a constant temperature for 12 hours; 3.2 Sealed Immersion Process: After drying, take out the test piece and apply Vaseline evenly to the exposed part of the probe to form an anti-corrosion isolation layer; immediately immerse the test piece completely in a 6wt% NaClO solution with pH=12.5, seal the container and immerse it in the dark for 12 hours. During the immersion process, the container must be sealed to avoid contact with air. 3.3 Rinsing with clean water: After soaking, take out the specimen and rinse it with deionized water 3 times, 1 minute each time, to thoroughly remove the residual NaClO solution on the surface of the specimen. Before testing, wipe the petroleum jelly off the surface of the probe with lint-free paper. 3.4 High-temperature curing procedure: After rinsing, immediately place the specimens into a constant temperature and humidity steam curing chamber at 80℃ and relative humidity ≥90% for 12 hours. 3.5 Drying and Testing Procedures: After curing, remove the specimens and place them in a fume hood at 20±2℃ for 4 hours. Then, place them in a constant temperature and humidity environment at 20±2℃ and relative humidity ≥50% for 2 hours. After the specimens reach saturated surface dryness, use a length comparator to test the specimen length. After the test is completed, at the same time on the first drying day, put the specimens back into the electric heating drying oven and start the next cycle.

[0036] Throughout the experiment, the NaClO solution was replaced with a fresh one every week to maintain a stable effective concentration of the oxidant. Nitrile gloves were worn during all operations, and the specimens were handled with care to avoid impact damage.

[0037] 4. Performance Testing and Data Processing 4.1 Initial length test: When the specimens were cured to 28 days, they were placed in an environment with a temperature of 20±2℃ and a relative humidity of ≥50% for 2 hours. The initial length L0 of the specimens was measured using a length comparator. Each specimen was tested twice, and the average of the two readings with a difference of ≤0.01mm was taken as the initial length measurement value. 4.2 Cycle Length Test: After each dry-wet cycle, wipe the Vaseline off the probe surface and test the specimen length L using the same method. t The length of each cycle was recorded; three parallel specimens were set up for both the control group and the experimental group, and the average value of the three parallel specimens was used as the expansion rate measurement value for that number of cycles. 4.3 Calculation of Expansion Rate: The expansion rate of the specimen is calculated using the following formula: ; in, L represents the expansion rate of the specimen after t wet-dry cycles. t L0 represents the measured length of the specimen after t cycles, in mm; L0 represents the initial length of the specimen, in mm. In this embodiment... Use 5mm; calculate the result to an accuracy of 0.01%; 4.4 Accuracy Verification: The validity of the data shall be verified according to the following rules: When the average expansion rate of the three parallel specimens is ≤0.05%, the difference between the measured value of a single specimen and the average value shall be <0.01%; when the average value is >0.05%, the difference between the measured value of a single specimen and the average value shall be <20% of the average value; when the expansion rate of the three specimens is >0.10%, there is no accuracy requirement; if the requirements are not met, the measured value with the smallest expansion rate shall be discarded, and the average value of the remaining two specimens shall be taken as the measured value. 4.5 Calculate the increase in the specimen's expansion rate using the following formula: ; in, This represents the increase in the expansion rate. The expansion rate of the mortar specimens in the experimental group; The expansion rate of the mortar specimens in the control group is when When the measured value is 0.00%, the increase in expansion rate is no longer calculated, and the value is directly... As The measured value; the calculation result is accurate to 0.1%.

[0038] 5. Test Results and Judgment 5.1 The expansion rates of the three parallel specimens in the control group after 15 wet-dry cycles were -0.011%, -0.013%, and -0.012%, respectively, with an average value of -0.012%, which meets the accuracy verification requirements. The specimens in the control group were in a state of contraction throughout the process, which meets the requirements for the validity verification of the test process. The expansion rate of the experimental specimens continued to increase with the number of cycles, and the expansion trend tended to level off after the 12th cycle. The measured expansion rate values ​​for each key cycle are shown in Table 1. Table 1. Measurement values ​​of expansion rate at each key cycle. Calculations showed that the expansion rate of the experimental group specimens increased by 683.3% after 15 cycles, which met the judgment threshold. 5.2 Furthermore, the expansion rate of the experimental group specimens after 15 wet-dry cycles was 0.07%, which is greater than the judgment threshold of 0.03%. Therefore, it is determined that the mechanical fine aggregate prepared from this batch of copper mine tailings is an active sulfide aggregate with application risks and cannot be directly used in concrete engineering.

[0039] Example 1: The aggregate to be tested was confirmed by existing petrographic analysis, X-ray diffraction detection and long-term oxidation exposure test to contain active sulfide minerals such as pyrite and pyrrhotite. It will expand and crack after long-term service, which is consistent with the result of the present invention to identify it as a risky aggregate. Example 2:

[0040] This embodiment provides a rapid identification method for the application risks of reactive sulfide aggregates. Except for the differences specifically mentioned, the raw material specifications, instruments and equipment, specimen molding and curing methods, accelerated oxidation test procedures, performance testing and data processing methods used in this embodiment are the same as those in Embodiment 1.

[0041] Compared with Example 1, this example differs in that: the aggregate to be tested is a limestone fine aggregate for a certain construction project. It was pre-tested using the rapid mortar bar method in GB / T14684-2022 "Construction Sand" to confirm the absence of reactive silica and the absence of steel slag. Preliminary inspection revealed rust bands on the aggregate surface, and ICP testing showed a total sulfur content of 0.77%. XRD analysis detected characteristic peaks of pyrite. The aggregate particle size distribution was completely consistent with the quartz standard sand in Example 1, with an apparent density of 2.68 g / cm³. 3 .

[0042] The experimental group mortar used the above-mentioned limestone fine aggregate to replace all the quartz standard sand in the control group by volume. After conversion according to apparent density, the amount of materials used in a single group of specimens was: 450.0g cement, 270.0g deionized water, and 1024.0g limestone aggregate to be tested.

[0043] The expansion rates of the three parallel specimens in the control group after 15 wet-dry cycles were -0.010%, -0.012%, and -0.011%, respectively, with an average value of -0.011%, which met the accuracy verification requirements. The specimens were in a contraction state throughout the test, indicating that the test process was valid. The expansion rate of the experimental group specimens steadily increased with the number of cycles, and exceeded the risk assessment threshold after 15 cycles. The measured expansion rate values ​​for each critical cycle are shown in Table 2. Table 2. Measurement values ​​of expansion rate at each key cycle. Calculations showed that the expansion rate of the experimental group specimens increased by 390.9% after 15 cycles. The expansion rate of the experimental group specimens after 15 wet-dry cycles was 0.032%, which is greater than the judgment threshold of 0.03%, and the increase in expansion rate is greater than 100%. Therefore, this batch of limestone machine-made fine aggregate is determined to be an active sulfide aggregate with application risks and cannot be directly used in concrete engineering.

[0044] Example 2: The aggregate to be tested was tested using the existing technical method in Example 1, which confirmed that the pyrite-containing active sulfide minerals would have the risk of expansion and cracking after long-term service, which is consistent with the results of the present invention that identified it as a risky aggregate. Example 3:

[0045] This embodiment provides a rapid identification method for the application risks of reactive sulfide aggregates. Except for the differences specifically mentioned, the raw material specifications, instruments and equipment, specimen molding and curing methods, accelerated oxidation test procedures, performance testing and data processing methods used in this embodiment are the same as those in Embodiment 1.

[0046] Compared with Example 1, this example differs in that: the aggregate to be tested is amphibole-based fine aggregate for a certain construction project. It was pre-tested using the rapid mortar bar method in GB / T14684-2022 "Construction Sand" to confirm the absence of reactive silica and the absence of steel slag. Preliminary inspection revealed no obvious metallic luster, oxidation, or rust on the hand sample. XRF testing showed a total sulfur content of 0.14%, and trace amounts of pyrrhotite mineral particles were observed using a petrographic microscope. The aggregate particle size distribution is completely consistent with the quartz standard sand in Example 1, with an apparent density of 2.69 g / cm³. 3 .

[0047] The experimental group mortar used the above-mentioned amphibole-based fine aggregate to replace all the standard quartz sand in the control group by volume. After conversion according to apparent density, the amount of materials used in a single group of specimens was: 450.0g cement, 270.0g deionized water, and 1027.9g amphibole aggregate to be tested.

[0048] The expansion rates of the three parallel specimens in the control group after 15 wet-dry cycles were -0.011%, -0.013%, and -0.012%, respectively, with an average value of -0.012%, which met the accuracy verification requirements. The specimens were in a contraction state throughout the test, indicating that the test process was valid. The expansion rate of the experimental group specimens increased only slightly and steadily with the number of cycles, without any abnormal rapid expansion trend throughout the process. After 15 cycles, the risk assessment threshold was not exceeded. The measured expansion rate values ​​for each key cycle are shown in Table 3. Table 3. Measurement values ​​of expansion rate at each key cycle. Calculations showed that the expansion rate of the experimental group specimens increased by 225% after 15 cycles. The expansion rate of the experimental group specimens after 15 wet-dry cycles was 0.015%, which is less than the judgment threshold of 0.03%. Therefore, it is determined that this batch of amphibole-based fine aggregate is a non-reactive sulfide aggregate without application risk and can be used normally in concrete engineering.

[0049] In Example 3, the aggregate to be tested was tested using the existing technical method in Example 1. Although trace amounts of pyrrhotite were detected, the content was so low as to be insufficient to cause destructive expansion. No abnormal expansion was observed during long-term service, which is consistent with the result of the present invention that the aggregate is a risk-free aggregate.

[0050] Although this application has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made thereto without departing from the spirit and scope of this application. Accordingly, this specification and drawings are merely exemplary illustrations of the application as defined herein, and are to be considered as covering any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Thus, if such modifications and modifications fall within the scope of this application and its equivalents, this application intends to include such modifications and modifications.

Claims

1. A rapid identification method for the application risks of reactive sulfide aggregates, characterized in that, The method includes: S1 The mortar of the control group and the experimental group are respectively molded into test molds with pre-embedded probes at both ends, and then cured to the specified age for use; wherein, the mortar of the control group includes water, cement and quartz standard sand, and the mortar of the experimental group is prepared by replacing the quartz standard sand in the control group with the same volume of the aggregate to be tested; S2 accelerates corrosion by subjecting the cured specimens to multiple rounds of dry-wet cycles. Each round of the dry-wet cycle consists of drying, closed immersion in NaClO solution, rinsing with clean water, high-temperature curing, and ventilation drying. S3 After each round of the dry-wet cycle is completed, the length of the specimens in the control group and the experimental group is measured, and the expansion rate of the specimens and the increase in expansion rate of the experimental group relative to the control group are calculated. S4 determines whether the aggregate to be tested is an active sulfide aggregate with application risks based on the expansion rate and the increase in expansion rate after a preset number of dry and wet cycles.

2. The rapid identification method for application risks of reactive sulfide aggregates according to claim 1, characterized in that, The total cycle of a single dry-wet cycle is 48±2 hours, and the specific method is as follows: S21 The cured specimens were dried at 80±5℃ for 12±2h; S22 The dried specimen is completely immersed in a 5-7 wt% NaClO solution with a pH of 12.5±0.1 and soaked in a sealed container for 12±2 hours; S23 Remove the specimen, wash away the residual NaClO solution on the surface with clean water, and then continue to place the specimen in a steam curing box at 80±5℃ for 12±2h. S24 Remove the specimen and place it in a fume hood to air dry for 4±0.5h. Test it while it is cooled. After the test is completed, put the specimen back into the oven at the same time on the first drying day. This completes one wet-dry cycle.

3. The rapid identification method for application risks of reactive sulfide aggregates according to claim 1, characterized in that, The aggregate to be tested does not contain reactive silica or steel slag.

4. The rapid identification method for application risks of reactive sulfide aggregates according to claim 1, characterized in that, In S1, the probe is made of stainless steel; in S2, before each soaking in NaClO solution, Vaseline is evenly applied to the surface of the probe, and the surface of the probe is wiped clean before the length test.

5. The rapid identification method for application risks of reactive sulfide aggregates according to claim 1, characterized in that, The formula for calculating the expansion ratio is: ； in, The expansion rate of the specimen was measured after t cycles of wet and dry drying. The length of the specimen after t wet-dry cycles; The initial length of the specimen; This refers to the exposed length of a single-ended probe.

6. The rapid identification method for application risks of reactive sulfide aggregates according to claim 5, characterized in that, The formula for calculating the increase in the expansion rate is as follows: ； in, This represents the increase in the expansion rate. The expansion rate of the mortar specimens in the experimental group; The expansion rate is the same as that of the control group mortar specimens.

7. The rapid identification method for application risks of reactive sulfide aggregates according to claim 1, characterized in that, In step S4, the preset cycle period is 15 dry and wet cycle periods; if the expansion rate of the specimen tends to level off within 15 cycles, the expansion rate under this stable state is recorded as the result; if the specimen does not show a tendency to stop expanding within 15 cycles, the expansion rate measured in the 15th cycle is used as the result.

8. The rapid identification method for application risks of reactive sulfide aggregates according to claim 1, characterized in that, Step S3 also includes an accuracy check of the expansion rate measurement value. The check rules are as follows: when the average expansion rate of the three parallel specimens is ≤0.05%, the difference between the measurement value of a single specimen and the average value should be less than 0.01%; when the average value is >0.05%, the difference between the measurement value of a single specimen and the average value should be less than 20% of the average value; when the expansion rate of the three parallel specimens is >0.10%, there is no accuracy requirement; when the above accuracy requirements are not met, the measurement value with the smallest expansion rate is discarded, and the average value of the remaining two specimens is taken as the expansion rate measurement value for that number of cycles.

9. The rapid identification method for application risks of reactive sulfide aggregates according to claim 6, characterized in that, If the expansion rate of the test specimens in the experimental group increases by more than 100% and the expansion rate is greater than 0.03%, they are judged to be high-risk aggregates.

10. The rapid identification method for application risks of reactive sulfide aggregates according to claim 1, characterized in that, Before step S1, there is also a step S0 to determine whether the aggregate is a risk aggregate, including: S01 checks the source and application history of aggregates; aggregates without safe application records and originating from iron tailings or areas surrounding sulfur mines are entered into S02. S02 Inspect the appearance of the aggregate. For abnormal aggregates with metallic luster particles or oxide rust stains, proceed directly to step S04. For aggregates without abnormalities, proceed to step S03. S03 tests the total sulfur content of aggregates. Aggregates with a total sulfur content ≥0.1% are included in S04, while those with a total sulfur content below 0.1% are considered non-risk aggregates. S04 involves mineral phase analysis of the aggregates. Aggregates containing active sulfides such as pyrrhotite, pyrite, or marcasite are moved to step S1. Aggregates not containing these active sulfides are classified as non-active sulfur risk aggregates.

Images