Simple and convenient device for improving accuracy of sandstone aggregate alkali activity experiment

Abstract

The utility model provides a simple and convenient device for improving the accuracy of a sandstone aggregate alkali activity experiment. The simple and convenient device comprises an outer curing barrel, an inner curing barrel, a partition plate and a plurality of test piece boxes, the outer maintenance barrel and the inner maintenance barrel are both made of corrosion-resistant and high-temperature-resistant materials, the inner maintenance barrel is arranged in the outer maintenance barrel, a maintenance water storage cavity is formed between the outer maintenance barrel and the inner maintenance barrel, and barrel covers are arranged on the tops of the outer maintenance barrel and the inner maintenance barrel respectively; the interior of the inner curing cylinder is divided into at least two independent chambers by partition plates, the chambers are used for placing the test piece boxes, and the inner curing cylinder is further used for containing an alkaline solution; the liquid level of the curing water in the curing water storage cavity is higher than the liquid level of the alkaline solution in the inner curing barrel; the test piece boxes are put into different bins in groups, and the test piece boxes are mortar rod molds. The device solves the problems of gravity interference and temperature difference interference.

Description

Technical Field

[0001] This utility model relates to the field of energy-saving control, specifically to a simple device for improving the accuracy of alkali activity tests on sand and gravel aggregates. Background Technology

[0002] In current testing and inspection methods for aggregate quality in water conservancy, highway, and municipal construction projects, the rapid mortar bar method is recommended for testing the alkali reactivity of aggregates. Examples include Section 3.38 of SLT353-2020 "Test Procedures for Hydraulic Concrete" (Rapid Method for Alkali Reactivity Testing of Aggregates) and Section 6.20 of JGJ52-2020 "Test Methods for Quality and Inspection of Sand and Stone for Ordinary Concrete" (Rapid Method for Alkali Reactivity Testing of Sand). These methods involve artificially preparing mortar bars or concrete prism specimens from the aggregate, immersing them in a saturated alkaline solution at 80°C, allowing the active substances in the aggregate to fully react with the alkali ions and expand. A length profiler is then used to accurately measure the growth of the specimen after a certain age, thus determining whether the aggregate is alkali-reactive. Due to its intuitiveness, simplicity, and reliability, this method has become one of the routine testing indicators on construction sites.

[0003] However, this method overlooks an important detail in practice: the influence of gravity on the experimental results. According to the experimental specifications, after the specimens are prepared, they should be placed in groups of three, upright in a specimen box filled with an alkaline solution. The specimen box is then sealed and placed upright in a curing chamber filled with water. The temperature of the water in the curing chamber is kept under controlled conditions. After a period of time, the specimens are removed and their deformation is measured to draw experimental conclusions.

[0004] This device appears to be ingeniously designed, but it has the following drawbacks in actual operation.

[0005] The first experimental specimen was always kept vertical. The question arises whether axial compressive deformation would occur. This is especially true for freshly demolded specimens, which, standing vertically in the specimen box, sometimes experience axial compressive deformation due to their own weight exceeding the experimental error value. Therefore, it is necessary to consider how to avoid this.

[0006] Secondly, during the 16-day storage period, the specimens may tilt at any time due to various reasons. This could cause the elongated specimens to bend radially under gravity. If readings are taken at this time, the axial length will inevitably become smaller and smaller. Furthermore, once bending occurs, it could lead to a misjudgment as to whether it is related to the alkali-aggregate reaction, resulting in an incorrect conclusion.

[0007] The third test specimen box has a limited volume. When a specimen is removed for reading, the alkaline solution level immediately drops, exposing the upper parts of the other specimens to air. The significant temperature difference between air and the 80°C alkaline solution causes immediate thermal shrinkage deformation of the upper parts of the specimens. Once the first specimen has been read, readings of these already deformed specimens will yield inconsistent results. Therefore, these factors drastically reduce the accuracy of the experiment, potentially leading to erroneous conclusions.

[0008] Therefore, the experimental setup needs to be appropriately modified to reduce interference with the experimental process. Utility Model Content

[0009] The purpose of this invention is to address the shortcomings of existing technologies by providing a simple device that improves the accuracy of alkali activity tests on sand and gravel aggregates by solving the problems of gravity interference and temperature difference interference.

[0010] To achieve the above objectives, the technical solution adopted by this utility model is: a simple device for improving the accuracy of alkali activity test of sand and gravel aggregates, including an outer curing cylinder, an inner curing cylinder, a partition, and several test specimen boxes;

[0011] Both the outer curing cylinder and the inner curing cylinder are made of corrosion-resistant and high-temperature-resistant materials. The inner curing cylinder is set inside the outer curing cylinder, and a curing water storage cavity is formed between the outer curing cylinder and the inner curing cylinder. The top of the outer curing cylinder and the inner curing cylinder are respectively provided with cylinder caps.

[0012] The interior of the inner curing cylinder is divided into at least two independent compartments by a partition. The compartments are used to place the specimen box, and the inner curing cylinder is also used to hold an alkaline solution.

[0013] The curing water level in the curing water storage cavity is set higher than the alkaline solution level in the inner curing cylinder.

[0014] The test specimen boxes are grouped and placed in different compartments, and the test specimen boxes are mortar rod molds.

[0015] Preferably, the test specimen box is placed horizontally in the compartment.

[0016] Preferably, both the outer curing cylinder and the inner curing cylinder are containers with a length dimension greater than their height dimension.

[0017] Preferably, the outer curing cylinder and the inner curing cylinder are made of polypropylene, polyethylene or stainless steel.

[0018] Preferably, the temperature of the maintenance water in the maintenance water storage cavity is 80±2 degrees Celsius.

[0019] Preferably, the top opening height of the inner curing cylinder is lower than the top opening height of the outer curing cylinder, and the water level in the curing water storage cavity is lower than and close to the top opening height of the inner curing cylinder.

[0020] Preferably, at least three test specimen boxes are placed flat and side by side in each compartment.

[0021] Preferably, the bottom end of the inner curing cylinder is supported and fixed to the bottom end of the outer curing cylinder by a pad block.

[0022] Preferably, one end of the specimen box is provided with a probe insertion hole.

[0023] Preferably, a probe is installed in the probe insertion hole, and the embedded end of the probe is flat.

[0024] This utility model has substantial features and progress compared to the prior art. Specifically, this utility model has the following advantages:

[0025] This application designs an outer curing cylinder and an inner curing cylinder. The inner curing cylinder is used to hold the alkaline solution and the specimen box for alkaline activity testing. The outer curing cylinder is filled with curing water, and the overall temperature of the inner curing cylinder is controlled within a small range by controlling the temperature of the curing water. At the same time, the length-to-width ratio of the inner and outer curing cylinders is improved, and the traditional method of placing the specimen box vertically is changed to placing it horizontally. On the one hand, the amount of compression deformation caused by gravity in the vertical direction is reduced after the specimen box is horizontally placed. On the other hand, when one specimen box is removed for measurement, even if the liquid level of the alkaline solution inside drops, other specimen boxes will not be partially exposed above the liquid surface. Therefore, through comprehensive consideration and new design, this scheme solves the problem that the specimen testing is easily affected by gravity and temperature changes in the traditional scheme, making the testing process more scientific and the conclusions more consistent. Attached Figure Description

[0026] Figure 1 This is a side view of a simple device for improving the accuracy of alkali activity tests on sand and gravel aggregates according to this utility model.

[0027] Figure 2 This is a top view of a simple device for improving the accuracy of alkali activity tests on sand and gravel aggregates, as described in this utility model.

[0028] In the diagram: 1. Outer curing cylinder; 2. Inner curing cylinder; 3. Divider; 4. Specimen box; 5. Curing water; 6. Alkaline solution; 7. Pad; 8. Probe insertion hole. Detailed Implementation

[0029] The technical solution of this utility model will be further described in detail below through specific embodiments.

[0030] like Figure 1 and Figure 2 As shown, a simple device for improving the accuracy of alkali-activity tests on sand and gravel aggregates includes an outer curing cylinder 1, an inner curing cylinder 2, a partition 3, and several specimen boxes 4.

[0031] Both the outer curing cylinder 1 and the inner curing cylinder 2 are made of corrosion-resistant and high-temperature-resistant materials, such as polypropylene, polyethylene, or stainless steel. The inner curing cylinder 2 is located inside the outer curing cylinder 1, forming a curing water storage cavity between the outer curing cylinder 1 and the inner curing cylinder 2 for storing curing water 5. The temperature of the curing water is usually controlled at 80±2 degrees Celsius. The tops of the outer curing cylinder 1 and the inner curing cylinder 2 are respectively provided with cylinder caps (not shown in the figure). The top opening height of the inner curing cylinder 2 is lower than the top opening height of the outer curing cylinder 1. The water level in the curing water storage cavity is lower than and close to the top opening height of the inner curing cylinder 2, so that the liquid level of the curing water 5 in the curing water storage cavity is higher than the liquid level of the alkaline solution 6 in the inner curing cylinder 2.

[0032] The interior of the inner curing cylinder 2 is divided into at least two independent compartments by a partition 3. The compartments are used to place the specimen box 4, and the inner curing cylinder is also used to hold an alkaline solution 6.

[0033] The specimen boxes 4 are grouped and placed in different chambers. The specimen box 4 is a mortar rod mold. The specimen boxes are placed horizontally in the chamber. Due to their long length, both the outer curing cylinder 1 and the inner curing cylinder 2 are containers with a length dimension greater than their height dimension.

[0034] Specifically, in this embodiment, at least three specimen boxes 4 are placed flat and side by side in each compartment. In this embodiment, the bottom end of the inner curing cylinder 2 is supported and fixed to the bottom end of the outer curing cylinder 1 by a pad 7.

[0035] To detect the aggregate temperature, a probe insertion hole 8 is provided at one end of the specimen box 4. A probe is installed in the probe insertion hole, and the embedded end of the probe is set to be flat. The flat design can effectively prevent the probe from rotating based on the mortar rod.

[0036] Based on the process of testing the alkali reactivity of aggregates in section 3.38 of the industry standard SLT353-2020 "Test Procedures for Hydraulic Concrete", the application process of the improved method is explained:

[0037] 3.38 Aggregate Alkali Activity Test (Mortar Rod Rapid Method)

[0038] 3.38.1 This test is used to measure the length change of mortar specimens in an alkaline solution at 80℃, and to assess whether the aggregate has potential alkali-silica reactivity. It is suitable for aggregates with slow alkali-silica reactions or those that only expand in the later stages.

[0039] 3.38.2 Instruments, equipment, reagents, and protective equipment should include the following:

[0040] 1. The instruments and equipment should include the following:

[0041] 1) The test sieve shall comply with the provisions of Section 3.1.

[0042] 2) Balance: The scale division value is not greater than 0.1g.

[0043] 3) The mortar mixer used for testing shall comply with the provisions of JG / T3033.

[0044] 4) Mortar rod mold and probe: The mold (i.e., specimen box 4 in this embodiment) should be made of steel, with a cavity size of 25mm × 25mm × 280mm. Probe insertion holes are located in the center of both end plates of the mold to fix the probe. The probe should be made of stainless metal, with a diameter of 6mm and a length of 25mm. The portion of the probe embedded in the specimen should be flattened to facilitate anchoring it in the mortar specimen and prevent slippage or rotation.

[0045] 5) The curing cylinder consists of an inner curing cylinder 2 and an outer curing cylinder 1: both are made of alkali-resistant and high-temperature-resistant (80℃) polypropylene, polyethylene, or stainless steel, and should not leak. Each has a sealed cap. A partition 3 divides them into two independent compartments. Each independent compartment can hold three mortar rod specimens (with specimen boxes) horizontally. The interior is filled with alkaline solution and has a sealed cap to prevent external moisture from entering. The outer curing cylinder 1 can completely fill the inner curing cylinder 2 and is filled with curing water at 80±2 degrees Celsius; it also has a sealed cap.

[0046] 6) Alkali aggregate test oven: A laboratory oven with a temperature controllable at (80±2)℃ and a certain strength, capable of housing the entire inner and outer curing cylinders.

[0047] 7) Length comparator: Effective measuring distance 280~320mm, graduation value not greater than 0.001mm, and should be equipped with a measuring rod with a length within the effective measuring distance range, and should comply with the provisions of SL137. Length measuring instruments such as outside micrometers may also be used.

[0048] 8) Auxiliary tools: trowel, iron spoon, measuring cylinder, hardwood tamping stick (14mm x 13mm cross section, 150mm long), etc.

[0049] 2. Reagent: 1 mol / L NaOH solution, prepared by dissolving (40±1) g of sodium hydroxide (chemically pure) in 1 L of distilled water, with a concentration of 0.99 ~ 1.01 mol / L.

[0050] 3. Protective equipment: acid and alkali resistant aprons, sleeves, gloves, rubber shoes, and face shields, etc.

[0051] 38.3 The test procedures shall be carried out in accordance with the following provisions:

[0052] The raw materials and mix proportions of mortar shall be implemented in accordance with the following provisions:

[0053] 1) The cement should be silicate cement or reference cement. The autoclaving expansion rate of the cement should be less than 0.20% when tested using the method specified in GB / T750. The alkali content of the cement should be 0.9% ± 0.1% (calculated as Na2O, i.e., Na2O + 0.658K2O). When the alkali content of the cement is low, NaOH can be added to adjust it.

[0054] 2) Preparation of fine aggregate samples. Take an appropriate amount of representative fine aggregate, sieve it according to the method in Section 3.1, and then prepare samples according to the mass specified in Table 3.38.3. The prepared samples should be washed, dried, and stored in a sealed container for later use.

[0055] 3) If the coarse aggregate is a single-mineral rock, it can be sampled, crushed, and prepared into fine aggregate samples according to the aforementioned method; if it contains multiple mineral rocks, active and inactive rocks can be selected based on the petrographic identification results, and fine aggregate samples can be prepared separately for each group. Alternatively, the samples can be sorted and prepared according to particle size, and then mixed according to the actual proportion of the coarse aggregate to prepare fine aggregate samples.

[0056] 4) Mortar mix proportions. The mass ratio of cement to fine aggregate in the mortar is 1:2.25, and the water-cement ratio is 0.47. A set of 3 specimens is prepared using mortar rod molds, requiring a total of 400g of cement, 900g of fine aggregate sample, and 188g of water.

[0057] 2. The specimen preparation shall be carried out according to the following steps:

[0058] 1) 24 hours before molding, place all materials (cement, fine aggregate sample, mixing water) in a constant temperature room at (20±2)℃.

[0059] 2) Before molding, check the assembly of the trial mold and the application of the release agent. Measure the length of the probe and install it. The trial mold should be assembled tightly to ensure water tightness; the release agent should be applied evenly; the gap between the probe and the hole should be sealed with grease; the probes on both sides should be coaxial and firmly installed, and should not loosen during the molding process.

[0060] 3) When preparing mortar, first pour the cement and fine aggregate sample into the mixing pot and start the mixer. After mixing for 5 seconds, slowly add water, completing the addition in 30 seconds. Mix for 3 minutes from the start of the machine and then stop. Scrape off the mortar adhering to the blades and remove the mixing pot.

[0061] 4) Fill the mold with mortar in two layers, tamping each layer 20 times with a tamping rod (ensuring the area around the test head is filled completely). After tamping, scrape off the excess mortar with a trowel and smooth the surface. After the specimen has been molded for 4 hours, smooth the surface again and number it.

[0062] 3. The curing and length measurement of the specimens shall be carried out according to the following steps.

[0063] 1) After the specimen is molded, place it together with the mold in a curing chamber or standard curing room with a temperature of (20±2)℃ and a relative humidity of 95% or higher. After curing for (24±2)h, demold it and immediately measure the initial length of the specimen in a constant temperature chamber of (20±2)℃ using a length comparator (as a reference value for the baseline length). Before each measurement, the length of the measuring rod should be measured first to calibrate the measured value.

[0064] 2) After measurement, completely immerse the specimen in a sealed inner curing cylinder filled with tap water, and place it in an outer curing cylinder filled with tap water. Put them together in an oven at a temperature maintained at (80±2)℃ for 24 hours. Each independent compartment in the inner curing cylinder should contain the same group of specimens, and specimens with different material components should be placed separately.

[0065] 3) Open the inner curing cylinder lid, quickly remove the specimen from the cylinder, wipe the surface of the specimen and the probes at both ends dry with a towel, and measure the reference length (L0) of the specimen as soon as possible; the reading at this point is zero. The measurement should be completed within (10±5) seconds after the specimen is removed from the solution. Simultaneously record the temperature of the alkaline solution. The temperature should be strictly controlled at 80±2℃ during measurement.

[0066] 4) After measuring a set of specimens, immediately place them into the inner curing cylinder containing 1 mol / L NaOH solution. The specimens should be completely immersed horizontally in the solution. Seal the inner curing cylinder lid, and place the inner curing cylinder into the outer curing cylinder. The water level in the outer curing cylinder should be roughly level with that in the inner curing cylinder. Then place them together in an oven at a temperature of (80±2)℃.

[0067] 5) Subsequently, the specimens were taken out and their length (Lt) was measured after soaking in alkaline solution for 3 days, 7 days, and 14 days.

[0068] The long-term age should be measured from the time the specimen is immersed in the alkaline solution, and should be accurate to 1 hour.

[0069] 6) During each measurement, the appearance of the specimen should be carefully observed. If there are cracks, bends, etc., they should be recorded and the testing of that group of specimens should be stopped.

[0070] 3.38.4 The processing of test results shall be carried out in accordance with the following provisions:

[0071] 1. The specimen length change rate is calculated according to formula (3.38.4):

[0072] In the formula, t represents the rate of change in specimen length after immersion in alkaline solution for t days (positive values ​​indicate expansion, negative values ​​indicate shrinkage);

[0073] Lt — Length of the specimen after soaking in alkaline solution for t days, in mm

[0074] L0—Reference length of the specimen, mm

[0075] L – Length of the probe, mm.

[0076] 2. The average value of the three specimens was taken as the length change rate at a certain age (rounded to 0.01%).

[0077] 3. The evaluation of results shall be carried out in accordance with the following provisions:

[0078] 1) If the expansion rate of the mortar bar specimen after 14 days is less than 0.10%, it is determined to be an inactive aggregate.

[0079] 2) If the expansion rate of the mortar bar specimen after 14 days is greater than 0.20%, or if the expansion rate is not greater than 0.20% but there are cracks, bending or other phenomena, it is judged to be an active aggregate with potential hazards of alkali-silica reaction.

[0080] 3) For mortar bar specimens with an expansion rate of 0.10% to 0.20% after 14 days, the evaluation of this aggregate should be based on a comprehensive assessment, including on-site records, petrographic analysis, other auxiliary tests, and the expansion rate after 28 days of specimen testing.

[0081] 4) If necessary, the test shall be conducted in accordance with the method in Section 3.39, and the results of the concrete prism test shall be used as the final evaluation.

[0082] This device has been successfully tested and verified in the Thana Lake Hydropower Project in Nepal, achieving good results. The following two test tables illustrate this.

[0083] At the beginning of the experiment, the tests were conducted strictly according to the American standards ASTM C1260 and ASTM C1567 (the American test procedures are completely equivalent to the Chinese SLT353-2020 "Test Procedure for Hydraulic Concrete" 3.38 Aggregate Alkali Reactivity Test (Mortar Bar Rapid Method)). The test results, as shown in Table 1, indicate that most specimens exhibited varying degrees of bending deformation and warping, with intra-group errors exceeding 15%. According to the experimental procedures, the data should be discarded. The analysis suggests that the influence of gravity and drastic temperature differences on the test results was the primary cause. Furthermore, the readings within each group gradually decreased, indicating that the later readings were affected by air temperature for a longer period, resulting in more significant specimen shrinkage.

[0084]

[0085] Table 1. Experimental results using traditional methods

[0086] After discussion, an improved experimental setup was adopted, and the same materials were used to conduct the experiment again. The results are shown in Table 2. It can be seen that the data exhibits a very clear regularity, the intra-group error has completely disappeared, and the specimens no longer exhibit bending deformation. For the specimen without fly ash, the test value exceeded the standard value by 0.1%, indicating a potential alkali-aggregate reaction hazard. After adding 20% ​​fly ash, the test value was less than the standard value by 0.1%. This shows that the alkali-aggregate expansion performance was significantly controlled after adding fly ash. This conclusion is consistent with all domestic and international engineering specifications, and the conclusion that adding fly ash can effectively inhibit alkali-aggregate reaction damage is further verified by the experimental data.

[0087]

[0088] Table 2. Test results of the new scheme

[0089] After the device was put into operation, it was tested and verified, confirming the reliability of the conclusions. It completely eliminated the influence of temperature differences and gravity on experimental accuracy, making the results more precise and scientific. The obtained experimental data are accurate, reliable, and highly predictable, and have been widely recognized.

[0090] Finally, it should be noted that: the preferred embodiments of this patent have been described in detail above, but this patent is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this patent.

Claims

1. A simple device for improving the accuracy of alkali-reactivity tests on sand and gravel aggregates, characterized in that: It includes an outer curing tube, an inner curing tube, a partition, and several specimen boxes; Both the outer curing cylinder and the inner curing cylinder are made of corrosion-resistant and high-temperature-resistant materials. The inner curing cylinder is set inside the outer curing cylinder, and a curing water storage cavity is formed between the outer curing cylinder and the inner curing cylinder. The top of the outer curing cylinder and the inner curing cylinder are respectively provided with cylinder caps. The interior of the inner curing cylinder is divided into at least two independent compartments by a partition. The compartments are used to place the specimen box, and the inner curing cylinder is also used to hold an alkaline solution. The curing water level in the curing water storage cavity is set higher than the alkaline solution level in the inner curing cylinder. The test specimen boxes are grouped and placed in different compartments, and the test specimen boxes are mortar rod molds.

2. The simple device for improving the accuracy of alkali activity tests of sand and gravel aggregates according to claim 1, characterized in that: The specimen boxes are placed horizontally in the chamber.

3. The simple device for improving the accuracy of alkali reactivity tests of sand and gravel aggregates according to claim 1, characterized in that: Both the outer curing cylinder and the inner curing cylinder are containers whose length dimension is greater than their height dimension.

4. The simple device for improving the accuracy of alkali reactivity tests of sand and gravel aggregates according to claim 1, characterized in that: The outer curing cylinder and the inner curing cylinder are made of polypropylene, polyethylene or stainless steel.

5. The simple device for improving the accuracy of alkali reactivity tests of sand and gravel aggregates according to claim 1, characterized in that: The temperature of the maintenance water in the maintenance water storage cavity is 80±2 degrees Celsius.

6. The simple device for improving the accuracy of alkali reactivity tests of sand and gravel aggregates according to claim 1, characterized in that: The top opening height of the inner curing cylinder is lower than the top opening height of the outer curing cylinder, and the water level in the curing water storage cavity is lower than and close to the top opening height of the inner curing cylinder.

7. The simple device for improving the accuracy of alkali reactivity tests of sand and gravel aggregates according to claim 1, characterized in that: At least three test specimen boxes are placed flat and side by side in each compartment.

8. The simple device for improving the accuracy of alkali reactivity tests of sand and gravel aggregates according to claim 1, characterized in that: The bottom end of the inner curing cylinder is fixed to the bottom end of the outer curing cylinder by a pad block.

9. The simple device for improving the accuracy of alkali reactivity tests of sand and gravel aggregates according to claim 1, characterized in that: One end of the specimen box is provided with a probe insertion hole.

10. The simple apparatus for improving the accuracy of alkali reactivity tests of sand and gravel aggregates according to claim 9, characterized in that: A probe is installed in the probe insertion hole, and the embedded end of the probe is flat.

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