Method for measuring saturated surface dry water absorption rate of regenerated fine aggregate
By combining centrifugation and temperature-controlled evaporation methods with the slump cone method, the problem of determining the saturated surface dry water absorption rate of recycled fine aggregates was solved, enabling quantitative assessment and accurate judgment of standard conditions, simplifying the operation process and reducing errors.
Patent Information
- Application Number
- CN202610086424.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-22
- Publication Date
- 2026-02-24
AI Technical Summary
Existing technologies lack effective methods to determine the saturated surface-dry water absorption rate of recycled fine aggregates, resulting in large human errors, complex and time-consuming operations, making it difficult to accurately determine the saturated surface-dry standard state of recycled fine aggregates.
Centrifugation was used to remove free water from the surface of recycled fine aggregates. The water evaporation rate was controlled by temperature-controlled evaporation. The slump state of the recycled fine aggregates was tested by the slump cone method, and a moisture content curve was plotted to quantitatively assess the saturated surface dry water absorption rate.
It enables quantitative assessment of the saturated surface-dry state of recycled fine aggregates, reduces human error, saves testing time, reduces the labor intensity of test personnel, and is applicable to the testing of natural fine aggregates and manufactured sand.
Smart Images
Figure CN121558561A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of building material testing technology, specifically a method for determining the saturated surface-dry water absorption rate of recycled fine aggregates. Background Technology
[0002] Recycled fine aggregate particles often have micropores, cracks, or are covered with microparticles smaller than 0.075 mm on their surface. These micropores, cracks, or microparticles easily absorb water. When using recycled fine aggregate as concrete fine aggregate, the impact of its water absorption on the mix proportions of recycled concrete needs to be considered. A common method is to first determine the saturated surface-dry water absorption rate of the recycled fine aggregate, and then calculate the additional water absorption based on this rate. The additional water absorption added during the design of the recycled concrete mix proportions is not included in the water-cement ratio. Therefore, determining the saturated surface-dry water absorption rate of recycled fine aggregate is crucial for the mix proportion design of recycled fine aggregate concrete. However, there is currently no standardized method for measuring the saturated surface-dry water absorption rate of recycled fine aggregate. The slump cone method is an internationally accepted standard method for determining the saturated surface-dry water absorption rate of fine aggregates. The "Test Procedures for Aggregates in Highway Engineering" (JTG 3432-2024) details the method and process for determining the saturated surface-dry water absorption rate of fine aggregates using the slump cone method (T 0330-2024). This method involves transferring the water-saturated fine aggregate into a metal pan, spreading it evenly, and then using a handheld blower to slowly move above the aggregate particles, uniformly blowing warm air onto the surface while continuously stirring to ensure even evaporation of free water from the aggregate surface until it reaches a saturated surface-dry state. The specification also uses images of the fine aggregate's slump state to define the standard for judging the saturated surface-dry state: for natural sand, the standard state is considered to be "the upper part of the aggregate forming approximately 2 / 3 of a cone, i.e., approximately 1 / 3 collapsed." Figure 1 Medium (d) state; for manufactured sand and stone chips, the standard state should be "when the first collapse occurs after the test mold is removed", see [reference]. Figure 1 Medium (c) to (d) states. For fully washed 0.075mm manufactured sand and stone chips, their slump shape is no longer affected by the 0.075mm content, but is still somewhat affected by their angularity. Their slump state is close to that of natural sand, and the overall state is between... Figure 1 In states (c) to (d), no such occurrence will occur. Figure 1 The state is between (a) and (c). According to GB / T 14684, "Construction Sand", for natural sand... Figure 1 In the middle (d) state, the manufactured sand is Figure 1(b) Medium condition. The standards for determining the saturated surface-dry slump standard state of manufactured sand are inconsistent between the regulations and GB / T 14684. Determining the saturated surface-dry standard state in the slump cone test is crucial to ensuring the accuracy of the test, but it is very difficult to determine the saturated surface-dry standard state of manufactured sand and stone chips. There is currently no corresponding standard for the saturated surface-dry standard state of recycled fine aggregates.
[0003] As the procedure indicates, the angularity and fine powder content of fine aggregates significantly influence the determination of the saturated surface-dry standard state in the slump test. According to the inventors' previous research, for recycled fine aggregates, gradation and surface porosity or cracks also greatly affect the determination of the saturated surface-dry standard state. Furthermore, the method described in the procedure, using a handheld blower to uniformly evaporate free water from the surface of the fine aggregates, is difficult to operate during the test. It is hard to guarantee uniform evaporation of free water from the surface of the fine aggregates, and the distance between the blower and the surface of the fine aggregates is greatly affected by the operator's actions. This makes it difficult to quantify and uniformly measure the airflow, velocity, and temperature received by the surface of the fine aggregates, thus failing to guarantee uniform evaporation of free water from different parts of the shallow pan. Moreover, finer particles in the fine aggregates are easily blown out of the shallow pan during the blowing process. In addition, the long testing time increases the workload of the testing personnel. Summary of the Invention
[0004] This invention overcomes the shortcomings of the prior art and proposes a method for determining the saturated surface-dry water absorption rate of recycled fine aggregates. This method overcomes the defects of the existing methods, enabling the transformation from qualitative assessment to quantitative assessment of the saturated surface-dry state of recycled fine aggregates, reducing human error, saving testing time, and also reducing the labor intensity of test personnel.
[0005] This invention is achieved through the following technical solution: A method for determining the saturated surface-dry water absorption rate of recycled fine aggregate includes the following steps: First, a portion of the surface free water on the water-saturated recycled fine aggregate particles was removed by centrifugation, and the moisture content of the recycled fine aggregate after centrifugation was measured. Next, the heating time and heating temperature were set, and then the surface free water evaporation rate of the recycled fine aggregate after centrifugation was controlled by temperature-controlled evaporation method, and the moisture content of the recycled fine aggregate during the temperature-controlled evaporation process was measured. Then, the slump state and cone height of the recycled fine aggregate after the temperature-controlled evaporation method were tested by the slump cone method; the temperature-controlled evaporation method and the slump cone method were repeated until the cone height of the recycled fine aggregate tended to be relatively stable. Finally, a curve of time versus moisture content for removing surface free water from recycled fine aggregate was plotted. The starting point where the curve slowly declines and then rapidly declines is identified as the first inflection point, and the inflection point appearing in the rapid decline segment is identified as the second inflection point. The moisture content corresponding to the second inflection point is the saturated surface dry water absorption rate of the recycled fine aggregate.
[0006] Furthermore, the centrifugation method involves first thoroughly washing away the micro-powder in the recycled fine aggregate, and then repeatedly dewatering the recycled fine aggregate using a centrifuge; the micro-powder has a particle size of less than 0.075 mm.
[0007] Furthermore, the method for thoroughly washing away the micro-powder is as follows: place the recycled fine aggregate into a container, add water to submerge the recycled fine aggregate in the water, let it stand, and then use a stirring rod to thoroughly stir the recycled fine aggregate so that the micro-powder on the recycled fine aggregate is completely detached and suspended in the water to form a turbid liquid. After stirring, slowly pour the turbid liquid onto a 0.075mm standard square hole sieve, and use water rinsing to wash away the micro-powder with a particle size smaller than 0.075mm on the 0.075mm standard square hole sieve. Then, add the remaining recycled fine aggregate particles on the 0.075mm standard square hole sieve into the container; repeat rinsing the recycled fine aggregate in the container several times until the rinse water is visually clear.
[0008] Furthermore, the centrifuge includes a shell, a rotating drum, a motor, a control device, and a base; the shell is connected above the base, the motor is located inside the base, the rotating drum is located inside the shell, and the drive shaft of the motor is connected to the bottom of the rotating drum; the rotating drum includes an inner drum and an outer drum, the wall of the outer drum is parallel to the inner wall of the shell and maintains a gap, the inner drum contracts towards the center, and a "V"-shaped annular cavity is formed between the inner drum and the outer drum, and the walls of the inner drum and the outer drum are provided with sieve holes; the annular cavity is used to fix the filter screen, and the filter screen is used to place the regenerated fine aggregate that needs to be dewatered.
[0009] Furthermore, the temperature-controlled evaporation method involves placing the centrifuged recycled fine aggregate into a forced-air drying oven to evaporate the free water in the recycled fine aggregate particles.
[0010] Furthermore, the temperature of the forced-air drying oven is set to 40-50℃, and the wind speed is 0.5-1.0 m / s.
[0011] Furthermore, the slump cone method involves loosely loading the cooled recycled fine aggregate into a saturated surface-dry mold at once, gently tamping the surface of the recycled fine aggregate particles multiple times with a tamping rod, then vertically lifting the saturated surface-dry mold, observing the slump state of the recycled fine aggregate while simultaneously taking images of a typical slump cone state and measuring the cone height of the recycled fine aggregate.
[0012] Furthermore, after the height of the recycled fine aggregate cone tends to be relatively stable, the recycled fine aggregate is dried to constant weight at 105℃±5℃, and then the slump state of the recycled fine aggregate is tested by the slump cone method and the height of the slump cone is measured.
[0013] The beneficial effects of this invention compared to the prior art are as follows: Based on previous research, this invention, considering the degree of free water between and on the surface of loose recycled fine aggregate particles after saturation, as well as the tightness of the bond between the bound water on the particle surface and the recycled fine aggregate particles, first uses centrifugation to remove free water between particles and on some particle surfaces. Then, a temperature-controlled evaporation method is used to remove free water from the particle surfaces in stages, achieving quantitative control of the saturated surface-dry standard state of the recycled fine aggregate. Simultaneously, the slump state of the recycled fine aggregate during the removal of free water from the particle surfaces is tested using the slump cone method. Comparison with existing testing methods demonstrates the rationality and practicality of this invention. This invention can effectively determine the saturated surface-dry standard state of recycled fine aggregate and the corresponding saturated surface-dry water absorption rate; this invention is also applicable to the testing of the saturated surface-dry water absorption rate of fine particles such as natural fine aggregate and manufactured sand. Attached Figure Description
[0014] Figure 1 Schematic diagram of different slump standard states of fine aggregate (referencing T0330-2024 in JTG 3432-2024); Figure 2 The graph shows the time versus moisture content for removing surface free water from the sample. Figure 3 The slump cone state and cone height of recycled fine aggregate in its initial and dried states; Figure 4 The first inflection point, the second inflection point, and the final slump cone state and cone height of the recycled fine aggregate using the temperature-controlled evaporation method; Figure 5 This is a schematic diagram of a centrifuge. In the diagram: 1-outer shell; 2-rotating drum; 3-motor; 4-outlet; 5-control device; 6-top cover; 7-base; 21-inner cylinder; 22-outer cylinder; 23-cavity; 8-drive shaft; 9-partition plate. Detailed Implementation
[0015] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.
[0016] This embodiment proposes a method for determining the saturated surface-dry water absorption rate of recycled fine aggregates, which specifically includes the following steps: Step 1: Preparation of experimental equipment: 1.1 Check the centrifuge wiring connections and operating status, and ensure the centrifuge is in normal working condition with a voltage of 220V and a speed of 630 rpm; See Figure 5 The centrifuge includes a shell 1, a rotating drum 2, a motor 3, a control device 5, a base 7, and a partition 9. The partition 9 is located on top of the base 7 and divides the vertical space inside the centrifuge into upper and lower spaces. The upper space is surrounded by the shell 1, and the lower space is surrounded by the base 7. The partition 9 protrudes upward in the middle and is connected to the shell 1 on all sides. A top cover 6 is connected to the top of the shell 1. The motor 3 is located inside the base 7, and the rotating drum 2 is located inside the outer shell 1. The drive shaft 8 of the motor 3 passes through the central hole of the partition 9 and is connected to the bottom of the rotating drum 2. The rotating drum 2 can rotate under the drive of the motor 3. The rotating drum 2 includes an inner drum 21 and an outer drum 22. The wall of the outer drum 22 is parallel to the inner wall of the outer shell 1 and maintains a sufficient gap. The inner drum 21 contracts towards the central axis, so a "V"-shaped annular cavity 23 is formed between the inner drum 21 and the outer drum 22. The included angle of the "V" shape is 15°±5°. The annular cavity 23 is used to fix a 200-mesh steel filter screen, and the steel filter screen is used to place the recycled fine aggregate that needs to be dewatered. The control device 5 is connected to the outer shell 1 to control the speed of the motor 3. The water outlet 4 is located on the side of the outer shell 1, above the plane connecting the partition 9 and the outer shell 1, and is used to discharge the surface free water removed from the recycled fine aggregate. The outer cylinder 22 has an inner diameter of Φ300mm, a height of 400mm, and a wall thickness of 1mm. The inner cylinder 21 and the outer cylinder 22 have sieve-like round holes with a diameter not exceeding 3mm. The steel filter screen has a funnel-shaped structure, with the inner diameter of the inner ring at the wider end of the funnel being the inner diameter of the larger end. The inner diameter of the larger end of the steel filter screen is Φ170mm, and the height of the steel filter screen is 400mm. The steel filter screen has several water outlet holes with a mesh size of 200 mesh. 1.2. Start the electric heating forced air drying oven. Set the temperature of the electric heating forced air drying oven to 50℃ and control the wind speed within the range of 0.5-1.0m / s. 1.3 Preparation of saturated surface-dry test mold: The saturated surface-dry test mold is a metal slump cone with an upper diameter of 40mm, a lower diameter of 90mm, and a height of 75mm, with a wall thickness of 6mm. Metal tamping rod: tamping end diameter 25mm, mass 346g; 1.4 Test sieves: Standard square-hole sieves with apertures of 4.75 mm and 0.075 mm.
[0017] The second step is to determine the saturated surface-dry water absorption rate of the recycled fine aggregate: 2.1 Collect recycled fine aggregate, air dry it, crush it with a crusher, and then screen it with 0.075mm and 4.75mm standard square hole sieves to remove particles with a diameter greater than 4.75mm and less than 0.075mm, and prepare recycled fine aggregate samples (hereinafter referred to as samples). 2.2 Take one prepared sample and place it in a water-filled container. The sample mass is 2300g. Add water until it is 150mm above the sample. Let it stand for a certain period of time, then stir the sample thoroughly with a stirring rod to ensure that the micro-powder completely detaches from the particle surface of the sample and suspends in the water to form a turbid liquid. Immediately after stirring, slowly pour the turbid liquid onto a 0.075mm standard square-hole sieve, taking care not to pour out coarser particles and damage the sieve surface. Use water rinsing to remove micro-powder smaller than 0.075mm from the 0.075mm standard square-hole sieve. Add the remaining particles from the 0.075mm square-hole sieve to the container. 2.3 Add water to the container again and repeat step 2.2 to rinse the recycled fine aggregate in the container several times until the rinse water is visually clear; 2.4. Spread the cleaned sample evenly on the bottom of a shallow metal dish, add water, and make sure the water level is at least 20 mm above the top of the sample. Soak for at least 24 h ± 0.5 h, and keep the ambient temperature at 23 ℃ ± 2 ℃. 2.5. Securely fix the 0.075mm standard square-hole sieve on the support. Place a water collection container at the bottom of the support. Then, thoroughly stir the sample soaked in step 2.4 with a stirring rod. If there is turbidity after stirring, slowly pour the turbid liquid onto the 0.075mm standard square-hole sieve. Rinse several times with water to remove the micro-powder smaller than 0.075mm from the 0.075mm standard square-hole sieve. Add the remaining particles from the 0.075mm standard square-hole sieve into the container. When pouring, avoid pouring out the coarser particles in the sample located at the bottom of the metal pan, which may damage the sieve surface. 2.6. Divide the sample in the shallow metal dish into two equal portions using a bisection method. Place each portion of the sample into a 200-mesh steel filter screen. Tie the openings of the two steel filter screens containing the sample tightly, place them symmetrically in the centrifuge chamber 23, and fix them in place. Set the dehydration time to 1 minute using the control device 5, start the centrifuge, and drain the surface free water from the sample through the outlet 4. After stopping the centrifuge, remove the steel filter screens and take samples from both screens to determine the moisture content of the recycled fine aggregate sample. Take the average moisture content of the recycled fine aggregate sample from the two steel filter screens as the moisture content of the recycled fine aggregate, denoted as . ω 01 =15.28%; 2.7 After sampling, the steel filter screen was symmetrically placed back into the centrifuge chamber 23 and fixed. Step 2.6 was repeated for dewatering. The centrifuge dewatering time was set sequentially to 1 min, 2 min, and 2 min. After each dewatering, samples were taken from the steel filter screen to determine the moisture content of the recycled fine aggregate, recorded as follows: ω 0j j=2,3,4 (i.e.) ω 02 The cumulative dehydration time was 2 minutes. ω 03The cumulative dehydration time was 4 minutes. ω 04 The cumulative dewatering time was 6 minutes, and a total of 4 measurements were taken. The moisture content of the recycled fine aggregate after each dewatering is shown in Table 1. 2.8 After centrifugation, the sample was poured from two steel filter screens into a shallow metal dish and combined. The residual recycled fine aggregate particles on the steel filter screens were brushed off into the shallow metal dish. The recycled fine aggregate collected in the shallow metal dish was stirred evenly and divided into two equal portions using the dichotomy method. One portion was taken out and placed in a sealed metal box for storage at 23℃±2℃, and numbered N2. The remaining sample in the shallow metal dish was numbered N1 (N1 and N2 are two parallel samples). 2.9. Spread sample N1 evenly on the bottom of a shallow metal dish, place it in a 50℃ forced-air drying oven to evaporate moisture for 10 minutes, then remove the metal dish, thoroughly stir the sample, cool it to room temperature, and take a sample to determine the moisture content of the recycled fine aggregate, recording it as follows. ω 1-1 The moisture content ω of the recycled fine aggregate tested in this experiment was... 1-1 =12.17%; 2.10. Loosely load the cooled sample N1 into the saturated surface-dry mold in one go. Gently tamp the sample N1 particles evenly 25 times with a tamping rod, ensuring the tamping rod is no more than 5 mm from the sample N1 surface, allowing it to fall freely under its own weight. After tamping, smooth the mold opening. If, after the first tamping, the surface drop of the recycled fine aggregate in the mold is significantly lower than the mold opening height, add recycled fine aggregate appropriately above the mold opening, and then continue to gently tamp the surface of the recycled fine aggregate evenly. Slowly and vertically lift the saturated surface-dry mold, observe the collapse state of the recycled fine aggregate, and simultaneously photograph a typical collapse cone image. Measure the cone height of the recycled fine aggregate, which is recorded as h. 1-1 ; The first evaporation time in the forced-air drying oven is 10 minutes (corresponding to...) Figure 2 The horizontal axis is 16 min, which is the sum of the cumulative centrifugation time of 6 min in step 2.7 and the evaporation time of 10 min in the forced-air drying oven. The cone height of the regenerated fine aggregate is measured as h. 1-1 =7.5cm, the image of the slump cone state of the recycled fine aggregate is as follows Figure 3 (a) The cone remains intact and has not collapsed; 2.11. Repeat steps 2.9-2.10: Spread sample N1 evenly back onto the bottom of a shallow metal dish, place it in a forced-air drying oven to evaporate moisture, with each evaporation time being 3 minutes. Repeat the test 9 times consecutively, and record the corresponding moisture content of the recycled fine aggregate as follows: ω 1-m The cone height is recorded for each collapse test. h 1-m , mImages of typical collapsed cone states were taken sequentially at numbers 2, 3, ..., 10. (See attached image) Figure 4 (a) ~ (c); until the height of the cone of sample N1 tends to be relatively stable, then dry sample N1 to constant weight; Specifically, the slump state and cone height of recycled fine aggregate were tested using the slump cone method, as shown in Table 2. Typical images of the slump state of recycled fine aggregate were also captured. Figure 4 (a)~(c). After sample N1 was dried to constant weight, the cone height h1 = 4.0 cm was measured using a slump cone. The images of the slump state of sample N1 are shown in [images]. Figure 3 (b) The cone completely collapsed; 2.12. Plot the curve of time for removing free water from the sample surface versus moisture content (see...). Figure 2 The time axis is a logarithm with base 2, and the ordinate is a linear axis. The overall curve is a parabola, with the first inflection point marking the transition from a slow to a rapid descent. Figure 2 In section A1, the curve shows a clear inflection point in the rapid descent phase, designated as the second inflection point B1. The moisture content corresponding to this second inflection point B1 is taken as the saturated surface dry water absorption rate. The saturated surface dry water absorption rate of sample N1 is... ω 1-m =8.99%, cone height is 5.1cm. Figure 2 The test results of the collapse cone state and cone height corresponding to the first inflection point A1 and the second inflection point B1 of the intermediate sample N1 are shown in the figure. Figure 4 (a) and (b); 2.13. Take sample N2 and repeat steps 2.9 to 2.12. The moisture content of sample N2 in each step is recorded as follows: ω 2-m The cone height of the collapse tube test at each step is recorded as follows: h 2-m The value of m is the same as before. See the images of a typical collapsed cone state. Figure 4 (d)~(f). The moisture content test results of sample N2 are shown in Table 2. The time versus moisture content curves are plotted. Figure 2 .Depend on Figure 2 It can be seen that the time and moisture content curves of sample N2 and sample N1 have good overlap, thus verifying the reliability of the test results; in Figure 2 The test results of the collapse cone state and cone height corresponding to the first inflection point A2 and the second inflection point B2 of the intermediate sample N2 are shown in the figure. Figure 4 (d) and (e), the saturated surface dry water absorption rate corresponding to the second inflection point B2 is ω 2-m =9.05%, cone height is 4.9cm; after the sample N2 is dried to constant weight, the cone height h2=4.0cm is measured by the slump cone method.
[0018] Table 1. Moisture content of recycled fine aggregate (centrifugal method)
[0019] Table 2. Moisture content and slump cone height of recycled fine aggregate (temperature-controlled evaporation method)
[0020] The third step is to compare and verify the test results. 3.1. The cone height of recycled fine aggregate was measured using the slump cone method. Typical images of the slump state and cone height of recycled fine aggregate were taken, and the time versus moisture content curves were compared. Figure 2 It can be seen that the collapse state image characteristics of the recycled fine aggregate corresponding to the first inflection points A1 and A2 of samples N1 and N2 are as follows: Figure 4 (a) and (d) both correspond to a cone height of 7.5 cm, with one side or perimeter of the cone collapsing, illustrating a different slump standard state compared to fine aggregate. Figure 1 (b) is consistent with the standard slump condition of manufactured sand in "Construction Sand" (GB / T 14684); 3.2 Figure 2 The image characteristics of the slump state of the recycled fine aggregate corresponding to the second inflection points B1 and B2 of samples N1 and N2 are as follows: Figure 4 (b) and (e) show obvious collapse with pointed tops, which differs from the standard slump state of fine aggregate. Figure 1 (d) is consistent. At the same time, the corresponding cone heights are 5.1cm and 4.9cm, respectively. Taking the average value as 5.0cm, the average cone collapse height is 2.5cm, which is 1 / 3 of the initial cone height of 7.5cm. This is consistent with the standard state of natural sand collapse described in JTG 3432-2024, that is, "the upper part of the aggregate center becomes about 2 / 3 of a cone, that is, about 1 / 3 collapses" is the standard state. 3.3 Figure 4 Images (c) and (f) are the final collapse cylinder test images of samples N1 and N2 using the temperature-controlled evaporation method. The cone heights of samples N1 and N2 are 4.2 cm and 4.3 cm, respectively. Figure 3 (b) Basically the same, the only difference being that the cone height is reduced to 4cm, and the slump standard state diagram is different from that of fine aggregate. Figure 1 (d) Matches.
[0021] 3.4. Using a combination of qualitative and quantitative methods, the saturated surface-dry slump standard state of recycled fine aggregate was comprehensively judged according to the following three criteria: (1) When the recycled fine aggregate was loaded into the slump cone, the particles slightly stuck to the scoop or did not stick to the scoop; (2) When the slump cone mold was removed, obvious slump occurred, and a peak appeared; (3) The slump height was about 1 / 3 of the mold height. It can be seen that the state corresponding to the second inflection point simultaneously meets the above three criteria. Figure 1 (c) The moisture content corresponding to the second inflection point is the saturated surface dry water absorption rate of the recycled fine aggregate.
[0022] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the present invention, and all of these should be considered to fall within the scope of patent protection determined by the submitted claims.
Claims
1. A method for determining the saturated surface-dry water absorption rate of recycled fine aggregate, characterized in that, Includes the following steps: First, a portion of the surface free water on the water-saturated recycled fine aggregate particles was removed by centrifugation, and the moisture content of the recycled fine aggregate after centrifugation was measured. Next, the heating time and heating temperature were set, and then the surface free water evaporation rate of the recycled fine aggregate after centrifugation was controlled by temperature-controlled evaporation method, and the moisture content of the recycled fine aggregate during the temperature-controlled evaporation process was measured. Then, the slump state and cone height of the recycled fine aggregate after the temperature-controlled evaporation method were tested by the slump cone method; the temperature-controlled evaporation method and the slump cone method were repeated until the cone height of the recycled fine aggregate tended to be relatively stable. Finally, a curve of time versus moisture content for removing surface free water from recycled fine aggregate was plotted. The starting point where the curve slowly declines and then rapidly declines is identified as the first inflection point, and the inflection point appearing in the rapid decline segment is identified as the second inflection point. The moisture content corresponding to the second inflection point is the saturated surface dry water absorption rate of the recycled fine aggregate.
2. The method for determining the saturated surface-dry water absorption rate of recycled fine aggregate according to claim 1, characterized in that, The centrifugation method involves first thoroughly washing away the micro-powder in the recycled fine aggregate, and then repeatedly dewatering the recycled fine aggregate using a centrifuge; the micro-powder has a particle size of less than 0.075 mm.
3. The method for determining the saturated surface-dry water absorption rate of recycled fine aggregate according to claim 2, characterized in that, The method for thoroughly removing micro-powder is as follows: Place the recycled fine aggregate in a container, add water to submerge the recycled fine aggregate, let it stand, and then stir the recycled fine aggregate thoroughly with a stirring rod to completely remove the micro-powder from the recycled fine aggregate and suspend it in the water to form a turbid liquid. After stirring, slowly pour the turbid liquid onto a 0.075mm standard square hole sieve and use water rinsing to remove micro-powder particles smaller than 0.075mm from the 0.075mm standard square hole sieve. Then, add the remaining recycled fine aggregate particles on the 0.075mm standard square hole sieve into the container. Repeat rinsing the recycled fine aggregate in the container several times until the rinse water is visually clear.
4. The method for determining the saturated surface-dry water absorption rate of recycled fine aggregate according to claim 2, characterized in that, The centrifuge includes a shell (1), a rotating drum (2), a motor (3), a control device (5), and a base (7); the shell (1) is connected above the base (7), the motor (3) is located inside the base (7), the rotating drum (2) is located inside the shell (1), and the drive shaft (8) of the motor (3) is connected to the bottom of the rotating drum (2); the rotating drum (2) includes an inner cylinder (21) and an outer cylinder (22), the wall of the outer cylinder (22) is parallel to the inner wall of the shell (1) and maintains a gap, the inner cylinder (21) shrinks towards the center, and a "V"-shaped annular cavity (23) is formed between the inner cylinder (21) and the outer cylinder (22), and the inner cylinder (21) and the outer cylinder (22) are provided with sieve holes; the annular cavity (23) is used to fix the filter screen, and the filter screen is used to place the regenerated fine aggregate that needs to be dewatered.
5. The method for determining the saturated surface-dry water absorption rate of recycled fine aggregate according to claim 1, characterized in that, The temperature-controlled evaporation method involves placing the centrifuged recycled fine aggregate into a forced-air drying oven to evaporate the free water on the surface of the recycled fine aggregate particles.
6. The method for determining the saturated surface-dry water absorption rate of recycled fine aggregate according to claim 5, characterized in that, The temperature of the forced-air drying oven is set to 40-50℃, and the wind speed is 0.5-1.0 m / s.
7. The method for determining the saturated surface-dry water absorption rate of recycled fine aggregate according to claim 1, characterized in that, The slump cone method involves loosely loading the cooled recycled fine aggregate into a saturated surface-dry mold at once, gently tamping the surface of the recycled fine aggregate particles multiple times with a tamping rod, then vertically lifting the saturated surface-dry mold to observe the slump state of the recycled fine aggregate while simultaneously taking images of a typical slump cone and measuring the cone height of the recycled fine aggregate.
8. The method for determining the saturated surface-dry water absorption rate of recycled fine aggregate according to claim 1, characterized in that, After the height of the recycled fine aggregate cone tends to be relatively stable, the recycled fine aggregate is dried to constant weight at 105℃±5℃, and then the slump state of the recycled fine aggregate is tested by the slump cone method and the height of the slump cone is measured.