Foam light soil pore structure test method based on ultrasonic characteristics
By monitoring the wave velocity change rate of the pore structure of foamed lightweight soil using ultrasonic features, the problem of real-time non-destructive monitoring in existing technologies has been solved, enabling accurate determination of pore structure stability and construction guidance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANDONG UNIV
- Filing Date
- 2026-04-02
- Publication Date
- 2026-07-10
Smart Images
Figure CN121955200B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of foamed lightweight soil testing technology, specifically relating to a method for testing the pore structure of foamed lightweight soil based on ultrasonic characteristics. Background Technology
[0002] Foamed lightweight soil is a commonly used lightweight filling material in civil engineering. Pore structure is the core indicator that determines its performance. The evolution of pore structure is closely coupled with the hydration process. Real-time monitoring of pore structure changes is crucial for determining whether the pore structure is stable and guiding subsequent construction.
[0003] Current pore structure detection methods primarily rely on offline techniques. Some of these methods require sampling and processing outside of actual working conditions, resulting in a lag in response to changes in pore structure. This makes continuous monitoring of the same sample throughout its entire lifecycle impossible, and hinders the accurate capture of key nodes in pore structure evolution. Therefore, a non-destructive, real-time testing method is urgently needed. This method monitors changes in ultrasonic characteristics during the hydration process to accurately determine the stability of the pore structure and its framework, thereby providing scientific guidance for subsequent construction operations. Summary of the Invention
[0004] To address the shortcomings of existing technologies, this invention provides a method for testing the pore structure of lightweight foam soil based on ultrasonic characteristics.
[0005] The main technical problems solved by this invention include: how to monitor the stability of the pore structure of foamed lightweight soil in real time under non-destructive conditions, and how to improve the monitoring efficiency and accuracy of the stability of the pore structure of foamed lightweight soil.
[0006] The technical solution of the present invention is as follows:
[0007] This invention provides a method for testing the pore structure of lightweight foam soil based on ultrasonic characteristics, comprising the following steps:
[0008] S1. Prepare a mold, install a transmitting probe and a receiving probe at the center of opposite side walls of the mold, connect the transmitting probe and the receiving probe to the ultrasonic pulse detector, set the transmitting voltage and sampling frequency, and adjust the system gain.
[0009] S2. Use vernier calipers to measure the straight-line distance between the radiating surfaces of the transmitting probe and the receiving probe, and record it as the ultrasonic propagation distance L.
[0010] S3. Fill the mold with freshly mixed foamed lightweight soil. Take the moment when the slurry is completely poured into the mold as zero point t0. Trigger the transmitting probe to emit ultrasonic pulses at fixed time intervals. Simultaneously record the transmission time T(t1) when the transmitting probe emits a pulse signal and the arrival time T(t2) when the receiving probe detects the pulse signal. Calculate the propagation time difference of ultrasonic waves in the foamed lightweight soil medium and calculate the ultrasonic wave velocity.
[0011] S4. Perform numerical differentiation on the ultrasonic wave velocity data to calculate the relative rate of change of wave velocity over time, i.e., the amount of wave velocity increase per unit time.
[0012] S5. Real-time monitoring of relative wave velocity change rate And compare it with the stability threshold, when The value remains below the stability threshold for an extended period of time. When the time is right, it is determined that the evolution of the pore structure of the foamed lightweight soil has ended, the pore structure has become stable, and the pore structure test of the foamed lightweight soil is completed.
[0013] According to a preferred embodiment of the present invention, in step S1, the mold has dimensions of 100mm × 100mm × 100mm and is made of polyvinyl chloride (PVC) to effectively reduce noise reflection of ultrasonic waves on the inner wall of the mold and improve the accuracy of the first wave reading.
[0014] According to a preferred embodiment of the present invention, in step S1, the specific process of installing the transmitting probe and the receiving probe at the center positions of the opposite side walls of the mold is as follows: a probe mounting hole is reserved at the center position of the opposite side walls of the mold, an ultrasonic coupling agent is evenly applied to the radiating surface of the transmitting probe and the receiving probe, and then the transmitting probe and the receiving probe are tightly installed in the probe mounting hole on the side walls of the mold, and the radiating surface of the transmitting probe and the receiving probe are flush with the inner wall of the mold.
[0015] Preferably, the ultrasonic coupling agent is an industrial-grade ultrasonic coupling agent or petroleum jelly.
[0016] According to a preferred embodiment of the present invention, in step S1, the transmitting voltage of the ultrasonic pulse detector is set to 400V-800V and the sampling frequency is set to 5MHz-15MHz;
[0017] Preferably, the transmitting voltage of the ultrasonic pulse detector is set to 600V and the sampling frequency is set to 10MHz.
[0018] In this invention, because the lightweight foam soil contains a large number of air bubbles, it greatly scatters and attenuates sound waves. The high transmission voltage of 600V ensures that the ultrasonic waves have enough energy to penetrate the medium. The 10MHz sampling frequency determines the time resolution (0.1µs). The higher the frequency, the more accurate the capture of the arrival time.
[0019] According to a preferred embodiment of the present invention, in step S1, both the transmitting probe and the receiving probe are piezoelectric ceramic ultrasonic transducers, and the center frequency of the piezoelectric ceramic ultrasonic transducers is 50-100kHz; preferably, the center frequency of the piezoelectric ceramic ultrasonic transducers is 50kHz.
[0020] The center frequency of this invention is below 50kHz, which results in stronger ultrasonic penetration but decreased resolution; the center frequency is above 100kHz, which results in higher resolution but a sharp increase in attenuation in bubbles.
[0021] According to a preferred embodiment of the present invention, the specific method for filling the mold with freshly mixed foamed lightweight soil in step S3 is as follows: inject the freshly mixed foamed lightweight soil into the mold until it is completely filled, shake the mold to remove large air bubbles introduced during the pouring process, smooth the surface of the slurry with a scraper, and cover it with plastic wrap to prevent moisture evaporation.
[0022] According to a preferred embodiment of the present invention, in step S3, the fixed time interval is 1-3 minutes.
[0023] According to a preferred embodiment of the present invention, in step S3, the propagation time difference is T(t2) - T(t1); the formula for calculating the ultrasonic wave velocity is: .
[0024] According to a preferred embodiment of the present invention, in step S4, The calculation formula is:
[0025] ;
[0026] Wherein, V(t) i-1 ): at time t i-1 The corresponding ultrasonic wave velocity; V(t) i+1 ): at time t i+1 The corresponding ultrasonic wave velocity.
[0027] The technical features and beneficial effects of this invention are as follows:
[0028] 1. The method of this invention abandons the traditional method that relies on experience-based judgment and innovatively introduces "relative change rate of ultrasonic wave velocity" as the core criterion. By monitoring whether the wave velocity growth rate is lower than a set threshold, the stability of the pore structure is transformed into a quantifiable mathematical index, thereby achieving a scientific and accurate determination of the stability state of the foam lightweight soil pore structure and avoiding the risks and waste caused by premature or delayed demolding.
[0029] 2. The method of this invention employs a penetration-type test with a pre-installed probe within the mold, eliminating the need for sample cutting and avoiding the defects of traditional offline testing, such as sample damage and data feedback lag. This method ensures that the test conditions are completely consistent with actual working conditions, significantly improving the authenticity and representativeness of the monitoring data.
[0030] 3. The method of this invention achieves high-frequency continuous data acquisition throughout the entire process from the fluid state of freshly mixed slurry to the hardened solid state, overcoming the limitation of existing technologies that can only acquire discrete time-point data. It can completely capture every key node and dynamic characteristic of pore structure evolution, providing complete data support for revealing the microscopic mechanism of materials and optimizing construction processes. Attached Figure Description
[0031] Figure 1 The ultrasonic wave velocity evolution curves of lightweight foamed soil with different foam content provided in Example 1 of the present invention are shown; wherein, Figure 1 In the middle (a), the ultrasonic wave velocity evolution curve of lightweight soil with 30% foam content is shown. Figure 1 (b) shows the ultrasonic wave velocity evolution curve of lightweight soil with 40% foam content. Figure 1 (c) shows the ultrasonic wave velocity evolution curve of lightweight soil with 50% foam content. Figure 1 The curve in (d) shows the evolution of ultrasonic wave velocity of lightweight soil with 60% foam content. Detailed Implementation
[0032] The present invention will be further described below with reference to embodiments, but is not limited thereto. The described embodiments are some embodiments of the present invention. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0033] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Unless otherwise specified in the embodiments of the present invention, all techniques existing in the art can be used.
[0034] Example 1
[0035] A method for testing the pore structure of lightweight foam soil based on ultrasonic characteristics includes the following steps:
[0036] S1. Prepare a PVC mold with smooth inner walls (geometric dimensions 100mm×100mm×100mm), and pre-drill sensor mounting holes at the center of opposite side walls of the mold. Select a pair of piezoelectric ceramic ultrasonic transducers with a center frequency of 50kHz, as the transmitting and receiving probes respectively. Apply industrial-grade ultrasonic coupling agent evenly to the radiating surfaces of the transmitting and receiving probes. Securely install the probes, coated with coupling agent, into the pre-drilled holes on both sides of the mold, ensuring the probe surfaces are flush with or tightly adhered to the inner wall of the mold to guarantee good acoustic coupling. Connect the probes to an ultrasonic pulse detector, set the transmitting voltage (600V) and sampling frequency (10MHz), and adjust the system gain.
[0037] S2. Use a high-precision vernier caliper to measure the straight-line distance between the end faces of the transmitting probe and the receiving probe, and record it as the ultrasonic propagation distance L (unit: mm).
[0038] S3. Slowly pour the freshly mixed foamed lightweight soil into the mold until the slurry completely submerges the probe and fills the mold. Vibrate the mold to remove large air bubbles introduced during pouring, smooth the surface of the slurry with a scraper, and cover with plastic wrap to prevent moisture evaporation.
[0039] Taking the moment the slurry is completely poured into the mold as zero point t0, the automated acquisition program is started, and the sampling time interval is set (once per minute). The instrument automatically drives the transmitting probe to excite ultrasonic pulses at the set intervals, and the system synchronously records the transmission time T(t1) of the pulse signal and the arrival time T(t2) when the receiving probe detects the signal. The propagation time difference T(t2)-T(t1) of the ultrasonic wave in the foamed lightweight soil medium is calculated, combined with L measured in step five, and according to the formula... Calculate the ultrasonic wave velocity at that moment.
[0040] S4. Perform numerical differentiation on the ultrasonic wave velocity data and calculate the relative rate of change of wave velocity over time. That is, the amount of wave speed increase per unit time; The calculation formula is:
[0041] ;
[0042] Wherein, V(t) i-1 ): at time t i-1 The corresponding ultrasonic wave velocity; V(t) i+1 ): at time t i+1 The corresponding ultrasonic wave velocity.
[0043] S5. Real-time monitoring of relative wave velocity change rate and with stability threshold Comparison, stability threshold For 5 m / s / h, when The value remains below the stability threshold for an extended period of time. When the time is right, it is determined that the evolution of the pore structure of the foamed lightweight soil has ended, the pore structure has become stable, and the pore structure test of the foamed lightweight soil is completed.
[0044] In this embodiment, the raw materials used for foamed lightweight soil include: reference cement, deionized water, and animal protein foaming liquid. The foaming liquid is prepared by mixing foaming agent and deionized water at a ratio of 1:49. The water-cement ratio (mass of deionized water + foam / mass of cement) is fixed at 0.5. A total of 4 groups of foamed lightweight soil are prepared. The formulation of the four groups of foamed lightweight soil is shown in Table 1.
[0045] Table 1. Mix proportions of four groups of foamed lightweight soil
[0046]
[0047] In this embodiment, the preparation method of freshly mixed foamed lightweight soil includes the following steps:
[0048] Step 1: Select silicate cement (PI 42.5) and deionized water that meet the experimental requirements, and weigh them strictly according to the preset water-cement ratio of 0.5.
[0049] Step 2: According to GB / T 1346-2011, put the weighed reference cement into the mixing pot.
[0050] Step 3: Start the mixer program and slowly add the measured deionized water. First, mix at low speed for 120 seconds, stop for 15 seconds, and then mix at high speed for 120 seconds.
[0051] Step 4: Observe the state of the slurry after mixing, confirm that the slurry has achieved rheological uniformity, and that there is no particle agglomeration or clumping observed by the naked eye, thus obtaining a stable cement paste.
[0052] Step 5: Mix and dilute the foaming agent stock solution with water in the specified ratio (1:49) to prepare the foaming liquid.
[0053] Step 6: Start the compressed air physical foaming machine, introduce the foaming liquid into the equipment, and adjust the air pressure valve and liquid suction valve to the working state.
[0054] Step 7: After the foaming machine has stabilized, take a foam sample, immediately measure its wet density and observe its stability until the foam wet density meets the preset range.
[0055] Step 8: Based on the mix design of the foamed lightweight soil, accurately weigh the required mass of standard foam.
[0056] Step 9: Add the weighed foam to the cement paste prepared in Step 4.
[0057] Step 10: Gently stir the gas-liquid-solid three-phase mixture using a low-speed stirring mode until the foam group is evenly dispersed in the slurry to obtain freshly mixed foamed lightweight soil.
[0058] In this embodiment, the ultrasonic wave velocity evolution curves of lightweight foamed soil with different foam content are shown in the figure. Figure 1 .
[0059] Depend on Figure 1The results showed that when the hydration of the 30% foam-content lightweight soil reached 78 minutes, the relative change rate of wave velocity was consistently below 5 m / s / h for the first time, indicating that the pore structure of this group of samples had reached a stable state. The 40% foam-content lightweight soil met the stability threshold criteria at 95 minutes, confirming that the pore structure had reached a stable state. The 50% foam-content lightweight soil met the criteria at 108 minutes, confirming that the pore structure had reached stability. The 60% foam-content lightweight soil showed that the wave velocity growth tended to stagnate and met the threshold requirements at 122 minutes, initially indicating that the pore structure evolution was stable.
[0060] In summary, the ultrasonic-based method for testing the pore structure of foamed lightweight soil of the present invention can accurately determine the pore structure stability of lightweight soil with different foam content, and accurately provide the pore structure stability time node, proving the effectiveness and accuracy of the method in real-time monitoring and state determination of the pore structure of foamed lightweight soil.
Claims
1. A method for testing the pore structure of lightweight foam soil based on ultrasonic characteristics, characterized in that, Includes the following steps: S1. Prepare a mold and reserve probe mounting holes at the center of the opposite side walls of the mold. Apply ultrasonic coupling agent evenly to the radiating surfaces of the transmitting and receiving probes. Then, tightly install the transmitting and receiving probes into the probe mounting holes on the side walls of the mold. The radiating surfaces of the transmitting and receiving probes are flush with the inner wall of the mold. Connect the transmitting and receiving probes to the ultrasonic pulse detector and set the transmitting voltage and sampling frequency. Adjust the system gain. S2. Use vernier calipers to measure the straight-line distance between the radiating surfaces of the transmitting probe and the receiving probe, and record it as the ultrasonic propagation distance L. S3. Fill the mold with freshly mixed foamed lightweight soil. Take the moment when the slurry is completely poured into the mold as zero point t0. Trigger the transmitting probe to emit ultrasonic pulses at fixed time intervals. Simultaneously record the transmission time T(t1) when the transmitting probe emits the pulse signal and the arrival time T(t2) when the receiving probe detects the pulse signal. Calculate the propagation time difference of ultrasonic waves in the foamed lightweight soil medium and calculate the ultrasonic wave velocity. S4. Perform numerical differentiation on the ultrasonic wave velocity data and calculate the relative rate of change of wave velocity over time. That is, the amount of wave speed increase per unit time; The calculation formula is: ； Wherein, V(t) i-1 ): at time t i-1 The corresponding ultrasonic wave velocity; V(t) i+1 ): at time t i+1 The corresponding ultrasonic wave velocity; S5. Real-time monitoring of relative wave velocity change rate and with stability threshold When a comparison is performed, The value remains below the stability threshold for an extended period of time. When the time is right, it is determined that the evolution of the pore structure of the foamed lightweight soil has ended, the pore structure has become stable, and the pore structure test of the foamed lightweight soil is completed.
2. The method for testing the pore structure of lightweight foam soil based on ultrasonic characteristics according to claim 1, characterized in that, In step S1, the mold has dimensions of 100mm×100mm×100mm and is made of polyvinyl chloride.
3. The method for testing the pore structure of lightweight foam soil based on ultrasonic characteristics according to claim 1, characterized in that, The ultrasonic coupling agent is an industrial-grade ultrasonic coupling agent or petroleum jelly.
4. The method for testing the pore structure of lightweight foam soil based on ultrasonic characteristics according to claim 1, characterized in that, In step S1, the transmission voltage of the ultrasonic pulse detector is set to 400V-800V, and the sampling frequency is set to 5MHz-15MHz.
5. The method for testing the pore structure of lightweight foam soil based on ultrasonic characteristics according to claim 1, characterized in that, In step S1, both the transmitting probe and the receiving probe are piezoelectric ceramic ultrasonic transducers, and the center frequency of the piezoelectric ceramic ultrasonic transducers is 50-100kHz.
6. The method for testing the pore structure of lightweight foam soil based on ultrasonic characteristics according to claim 1, characterized in that, In step S3, the specific method for filling the mold with fresh foamed lightweight soil is as follows: inject the fresh foamed lightweight soil into the mold until it is completely filled, shake the mold to remove large air bubbles introduced during the pouring process, smooth the surface of the slurry with a scraper, and cover it with plastic wrap to prevent moisture evaporation.
7. The method for testing the pore structure of lightweight foam soil based on ultrasonic characteristics according to claim 1, characterized in that, In step S3, the fixed time interval is 1-3 minutes.
8. The method for testing the pore structure of lightweight foam soil based on ultrasonic characteristics according to claim 1, characterized in that, In step S3, the propagation time difference is T(t2) - T(t1); the formula for calculating the ultrasonic wave velocity is... .