Rapid detection method for alkali-reactive aggregate

Abstract

The present invention discloses a rapid alkali-reactive aggregate detection method. Siliceous rock aggregate samples are first screened and processed into thin rock slices for use on a microscope hot stage. The slices are then slowly heated on the hot stage. If cracks occur, indicating a phase transition, the sample is alkali-reactive siliceous aggregate. By heating the sample under normal pressure, a phase transition of inactive silica is initiated, altering the original volume of the mineral and causing the inactive silica to fracture within the slice. This method establishes a rapid siliceous alkali-reactive aggregate detection method, shortening the alkali-reactive aggregate detection cycle.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete detection for building materials, and particularly relates to a rapid detection method for alkali-reactive aggregate. Background Art

[0002] Alkali-aggregate reaction (AAR) occurs when alkali in hardened concrete chemically reacts with active minerals in the aggregate, causing the concrete to expand, crack, and even fail. Considered a "cancer" of concrete, AAR has a long incubation period and, once it occurs, is incurable and difficult to remediate. AAR is one of the main causes of reduced concrete durability, as it not only significantly reduces the strength of concrete structures but also, due to the appearance of cracks, exacerbates corrosion from ambient water and other media, as well as freeze-thaw cycles, significantly shortening the service life of concrete buildings. Therefore, testing the alkali activity of aggregates is crucial for selecting concrete aggregates and improving concrete performance.

[0003] Currently, the alkali reactivity of aggregates is generally tested domestically and internationally using traditional petrographic methods, such as the rock column method, the mortar bar method, and the concrete prism method. The traditional petrographic method, for example, has the advantage of being able to quickly and directly determine the active components in the aggregate. Aggregates without potentially active components can be directly determined to be free of alkali-aggregate reaction hazards. The petrographic analysis results play a key role in guiding the selection of subsequent testing methods and have long been the preferred test method for testing aggregate alkali reactivity. However, the petrographic method has the disadvantage of requiring the tester to possess a solid foundation in rock and mineral microscopy and extensive testing experience, making it difficult for beginners and prone to misjudgment. Other testing methods, such as the mortar bar method and the concrete prism method, are time-consuming and can only evaluate highly active, rapidly expanding aggregates, but are not suitable for slower-expanding aggregates, resulting in potential misjudgments. Therefore, a rapid, simple, and reliable testing method is urgently needed. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for rapid detection of alkali-reactive aggregate, which solves the problem of long detection period of alkali-reactive aggregate in the prior art.

[0005] The technical solution adopted by the present invention is a method for rapid detection of alkali activity of concrete aggregate, which is specifically implemented according to the following steps:

[0006] Step 1: Processing the aggregate sample;

[0007] Step 2: Use a microscope hot stage to heat and observe.

[0008] The present invention is also characterized in that:

[0009] Aggregate samples of siliceous rocks were screened out, and the siliceous samples were made into rock slices specially used for microscope hot stage.

[0010] The thickness of the rock slices specially used for the microscope hot stage is 0.04mm.

[0011] The rock slices were slowly heated at a heating rate of 20°C / min, and the temperature of the hot plate was raised to 400°C±5 to determine whether there was a mineral phase change.

[0012] The criterion for determining whether a mineral phase change exists is that if the minerals in the rock thin section are broken, a mineral phase change exists.

[0013] The beneficial effects of the present invention are:

[0014] A rapid detection method for alkali-reactive aggregate is provided. A microscope hot stage is used to heat a thin slice of aggregate to 400°C. The internal cracks of the slice are observed to determine whether the aggregate is active. The method does not require the tester to have a solid foundation in rock and mineral microscopy and rich testing experience, nor does it require the use of other instruments. This method saves testing costs, simplifies the testing method, and shortens the testing time. DETAILED DESCRIPTION

[0015] The present invention will be described in detail below using specific embodiments.

[0016] A method for rapid detection of alkali-reactive aggregates, which uses a microscope hot stage fusion method to achieve rapid detection of alkali-reactive aggregates, specifically includes the following steps:

[0017] (1) Aggregate sample processing: According to my country's GB / T14685 "Pebbles and Crushed Stones for Construction", GB / T14684 "Sand for Construction", JTG E42 "Test Procedures for Aggregates in Highway Engineering", and other standards, siliceous rock aggregate samples can be screened out and the siliceous samples can be made into 0.04 mm thick rock slices specially used for microscope hot stage;

[0018] (2) Observation under a polarizing microscope at room temperature: Place a thin slice of siliceous rock on the stage of a microscope, place a cover glass on it, adjust the objective lens and eyepiece of the polarizing microscope, and observe the phenomenon under the microscope from small to large magnification of the objective lens. You only need to take pictures to record whether the mineral is broken;

[0019] (3) Microscope hot stage heating: Slowly heat the rock slice on the microscope hot stage to 400℃±5 for 20 minutes. The phase transition temperature of active silica (chalcedony, low-temperature cristobalite, and tridymite) in the alkali-active aggregate is lower than that of inactive silica. The phase transition temperature of inactive silica at normal pressure is 573℃, and the phase transition temperature of active silica is significantly lower than 400℃. Therefore, the hot stage temperature is raised to 400℃±5. If there is a mineral phase change, there are alkali-active components in the aggregate. If a mineral phase change occurs, the phenomenon under the microscope needs to be photographed and recorded.

[0020] (4) Determine the alkali activity of minerals: The phase change of SiO2 is a physical phenomenon. The phase change process causes a significant change in the volume of the mineral. Therefore, to determine whether a mineral has undergone a phase change, it is only necessary to observe whether the mineral in the rock slice is broken. If it is broken, there is a phase change, which means it is an alkali-active siliceous aggregate.

[0021] The present invention promotes the phase change of inactive silica by heating under normal pressure, thereby changing the original volume of the mineral and causing the inactive silica to break in the rock slice, thereby establishing a rapid detection method for siliceous alkali-reactive aggregate, thereby shortening the detection cycle of alkali-reactive aggregate and serving capital construction projects more quickly, efficiently and economically.

[0022] Example 1

[0023] The aggregate component that undergoes the alkali-silica reaction is reactive silicon dioxide (SiO2), which is widely found in various rocks, such as opal, obsidian, flint, perlite, mylonite, diatomite, rhyolite, and andesite. Therefore, the inventors collected flint, obsidian, and granite as representative samples, cut them into specialized rock slices, and conducted temperature-elevated tests at atmospheric pressure according to relevant standards and design plans to test the alkali activity of the aggregates.

[0024] Table 1 Cracking characteristics of aggregate slices under different temperature conditions

[0025] rock type 100℃ 200℃ 300℃ 400℃ 500℃ flint Unruptured Unruptured rupture - - obsidian Unruptured rupture - - - granite Unruptured Unruptured Unruptured Unruptured Unruptured

[0026] The results show that the flint and obsidian samples have already cracked before 400℃, so they are alkali-reactive aggregates, while the granite sample has not cracked at 500℃, so it is an inactive aggregate.

[0027] Example 2

[0028] The aggregate component that undergoes the alkali-silica reaction is reactive silicon dioxide (SiO2), which is widely found in a variety of rocks, such as opal, obsidian, flint, perlite, mylonite, diatomaceous earth, rhyolite, andesite, and diorite. Therefore, the inventors collected representative samples of opal, rhyolite, and diorite, cut them into specialized rock slices, and conducted temperature-elevated tests at atmospheric pressure according to relevant standards and design plans to test the alkali activity of the aggregate.

[0029] Table 2 Cracking characteristics of aggregate slices under different temperature conditions

[0030] rock type 100℃ 200℃ 300℃ 400℃ 500℃ opal Unruptured rupture - - - rhyolite Unruptured Unruptured rupture - - diorite Unruptured Unruptured Unruptured Unruptured Unruptured

[0031] The results show that opal and rhyolite samples have already cracked before 400℃, so they are alkali-reactive aggregates, while diorite samples have not cracked at 500℃, so they are inactive aggregates.

[0032] Example 3

[0033] The aggregate component that undergoes the alkali-silica reaction is reactive silicon dioxide (SiO2), which is widely present in various rocks, such as opal, obsidian, flint, rhyolite, and andesite. Therefore, the inventors collected flint, obsidian, and granite as representative samples, cut them into specialized rock slices, and conducted temperature-elevated tests at atmospheric pressure according to relevant standards and design plans to test the alkali activity of the aggregate.

[0034] Table 3 Cracking characteristics of aggregate slices under different temperature conditions

[0035]

[0036]

[0037] The results show that the perlite, diatomite and mylonite samples have already cracked before 400℃, so they are alkali-reactive aggregates. The gabbro sample has not cracked at 500℃, so it is an inactive aggregate.

[0038] Compared with the traditional petrographic method, this method greatly reduces the difficulty of identifying the alkali activity of siliceous rock aggregates, simplifies the identification procedure of aggregate alkali activity, and reduces the testing costs of construction projects.

[0039] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A rapid detection method for alkali-reactive aggregate, characterized in that: Please follow the steps below to implement: Step 1: According to my country's GB / T14685 "Pebbles and Crushed Stones for Construction", GB / T14684 "Sand for Construction", and JTG E42 "Test Procedures for Aggregates in Highway Engineering", siliceous rock aggregate samples were selected and the siliceous samples were made into 0.04 mm thick rock slices specially used for microscope hot stages; Step 2: Place the siliceous rock slice on the microscope stage, put a cover glass on it, adjust the polarizing microscope objective lens and eyepiece, and observe the phenomenon under the microscope from small to large magnification of the objective lens, and take pictures to record whether the mineral is broken; Step 3: Slowly heat the rock slice on a microscope hot stage at a heating rate of 20°C / min to raise the hot stage temperature to 400±5°C to determine whether there is a mineral phase change; The criterion for mineral phase change is that if the minerals in the rock thin section are broken, then there is mineral phase change, that is, it is alkali-reactive siliceous aggregate.

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