A method of determining the pore size distribution of a cementitious material

Abstract

The present application relates to a method for determining the pore size distribution of cement-based materials, comprising the following steps: a dry cement-based material sample is loaded into a mercury porosimeter sample tube and vacuumized; low pressure is applied until the sample is completely surrounded by mercury; cyclic pressurization and depressurization is applied, the total volume of mercury exiting each throat and the total volume of residual mercury in each ink-bottle pore is measured, and the volume of each throat and the volume of each ink-bottle pore adjacent to the throat are calculated; finally, the volume of each ink-bottle pore is redistributed into the volume of pores of different diameters using volume distribution theory and iterative algorithm; the method can reliably describe the volume distribution of pores of different sizes in cement-based materials.

Description

Technical Field

[0001] This invention relates to the field of material microstructure testing technology, and in particular to a method for determining the pore size distribution of cement-based materials. Background Technology

[0002] The pore characteristics of cement-based materials are a key factor affecting their mechanical properties and durability. Cement-based materials contain a wide variety of pores of different sizes and shapes. When studying the impact of pore characteristics on the permeability of harmful ions, it is necessary to distinguish between throat pores (smaller in size) and ink bottle pores (larger in size). The permeability of harmful ions mainly depends on the interconnected throat pores, while being less affected by ink bottle pores. On the other hand, the mechanical properties of cement-based materials are significantly affected by the larger ink bottle pores. Considering the connectivity of throat pores and ink bottle pores, and the differences in location and size among different ink bottle pores, the size and distribution of pores directly affect not only the mechanical properties of cement-based materials but also the transport rate of harmful ions or gases within them, thus affecting the durability of the cement-based materials. High-strength, long-life concrete has become a trend in modern concrete development, and accurately determining the characteristics and size distribution of pores is of great significance for the design and application of (ultra)high-performance cement-based materials.

[0003] In cement-based materials, ink bottle pores can account for 40-80% of the total pore volume. However, traditional mercury intrusion porosimetry suffers from a severe "ink bottle" effect, failing to measure ink bottle pores and only characterizing smaller throat pores. Based on the Washburn equation, when the applied pressure reaches a value corresponding to the throat pore diameter, the throat pore is filled with mercury, and the ink bottle pores connected to the throat pore are also filled with mercury. This leads to the erroneous inclusion of the ink bottle pore volume into the throat pore volume, failing to obtain the ink bottle pore volume distribution and resulting in an overestimation of throat pore volume. Therefore, a reliable method for characterizing the pore characteristics and size distribution of cement-based materials has significant theoretical and practical value. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for determining the pore size distribution of cement-based materials, which is beneficial for accurately characterizing throat pores and ink bottle pores, thereby determining the pore size and volume distribution of cement-based materials.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for determining the pore size distribution of cement-based materials, comprising the following steps:

[0006] Step 1) Place the dried cement-based material specimen in the sample tube of the fully automatic mercury porosimeter for vacuum treatment;

[0007] Step 2) Low-pressure operation increases the pressure from 0 to the initial pressure P0 until the specimen is tightly surrounded by mercury;

[0008] Step 3) High-pressure operation: Increase the pressure from P0 to P1, so that the first throat orifice and the first ink bottle orifice with a diameter of d1 are filled with mercury. The volume of mercury pressed into the specimen is denoted as . The volume of the first laryngeal foramen. Let P1 be the volume of the first ink bottle orifice; then the pressure is reduced from P1 to the initial pressure P0, causing the mercury in the first throat orifice to exit the specimen, and the volume of the mercury remaining in the specimen is... The volume of the first ink bottle orifice

[0009] Step 4) k is successively taken as 2, 3, ..., n, where n is the number of mercury intrusion-removal cycles. Repeat the following steps: high pressure operation increases from the initial pressure P0 to P k Such that the diameters are d1, d2, ..., d k The first to the kth throat holes and the first to the kth ink bottle holes are filled with mercury, and the corresponding mercury volume pressed into the specimen is denoted as . Then the pressure is changed from P k The pressure was reduced to the initial pressure P0, causing the mercury in the first to the kth throat holes to exit the specimen, thus obtaining the total volume of residual mercury in the first to the kth ink bottle holes. in Let K be the volume of the k-th ink bottle orifice; thus, the cumulative volume of mercury injected can be obtained. and cumulative ink bottle orifice volume

[0010] Step 5) Based on the results obtained in steps 3)-4), the diameters of the cement-based material specimens are d1, d2, ..., d. i ,...,d n The volume distribution of the throat orifice and its adjacent ink bottle orifice is as follows:

[0011] When k=1, the volume of the first ink bottle orifice Volume of the first laryngeal orifice

[0012] When n≥k≥2, the volume of the k-th ink bottle hole Volume of the k-th larynx

[0013] Step 6) Based on the results obtained in Step 5), considering the influence of threshold porosity and most probable porosity on pore connectivity, the measured ink bottle pore volume is... 2≤k≤n, and the diameters of the specimens d1, d2, ..., d are gradually allocated and included using an iterative algorithm. n The pore volume, wherein the threshold pore size is the diameter d. p The p-th throat opening; the most probable pore is of diameter d. qThe qth larynx; V k,n The diameter calculated in the nth iteration is d. k pore volume;

[0014] Step 7) Based on the results obtained from the iterative calculation in step n of step 6, the pore size distribution in the cement-based material specimen is expressed as:

[0015] The pore volume with diameter d1 is V1 = V 1,n ;

[0016] Diameter d k pore volume V k =V k,m (k = 2, 3, ..., n-1);

[0017] Diameter d n pore volume V k =V n,n .

[0018] In a preferred embodiment, step 6) specifically includes:

[0019] Step 1: Set the pore diameter d1 as the initial value of the iterative algorithm, that is, the diameter d1 of the first throat hole is the maximum pore size of the specimen, and redistribute the volume of the first ink bottle hole into the pore volume with diameter d1.

[0020]

[0021] Step 2: Redistribute the volume of the second ink bottle orifice into the pore volume with diameter d1;

[0022]

[0023]

[0024] Step k: Similar to the algorithm in step 2, redistribute the volume of the k-th ink bottle orifice;

[0025] ①When d k ≥d q The volume of the k-th ink bottle orifice is gradually redistributed according to the volume ratio and included in the diameters d1, d2, ..., d. k-1 pore volume;

[0026]

[0027]

[0028] ②When d k <d q The volume of the k-th ink bottle orifice is gradually redistributed according to the volume ratio and included in the diameter d. p ,dq+1 ,...,d k-1 pore volume;

[0029] Step n: Redistribute the volume of the nth ink bottle orifice according to the volume ratio and include it in the diameter d. q ,d p+1 ,...,d n-1 pore volume;

[0030]

[0031]

[0032] In a preferred embodiment, considering the influence of threshold porosity and most probable porosity on pore connectivity, and taking into account the continuity of pore size, the pressure is gradually increased from an initial value P0 to P1, P2, ..., P n And each time the pressure is increased to P k Then, k = 1, 2, ..., n, the pressure is reduced to the initial pressure P0, so that all the mercury in the first throat hole to the kth throat hole is expelled, while the first ink bottle hole to the kth ink bottle hole is completely filled with mercury.

[0033] In a preferred embodiment, volume distribution theory and iterative algorithms are used to determine the volume of each ink bottle orifice. The redistribution includes diameters d1, d2, ..., d k-1 pore volume.

[0034] In a preferred embodiment, the volumetric size of the cement-based material specimen is 0.8–1.2 cm. 3 .

[0035] Compared with the prior art, the present invention has the following beneficial effects: The present invention considers the continuity of pore size and the distribution of gel pores, and also considers the connectivity between large capillaries and small capillaries, wherein the large capillaries refer to those with a size greater than d. p Pores, small capillaries refer to pores with a size smaller than d p The volume distribution of pores in different throats and ink bottle pores can be more accurately determined by utilizing the volume difference between high-pressure mercury injection and low-pressure mercury removal in a cyclic process, without needing to know the contact angle between the material and mercury. Furthermore, by utilizing the theory of porous media volume distribution and iterative algorithms, the volume distribution of pores of different sizes can be calculated, providing a scientific basis for studying the pore characteristics, mechanical properties and durability of cement-based materials. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the pore structure of the cement-based material in an embodiment of the present invention.

[0037] Figure 2This is a schematic diagram of the cyclic high-pressure mercury injection and low-pressure mercury removal in an embodiment of the present invention.

[0038] Figure 3 The threshold pore size d obtained by conventional mercury intrusion porosimetry in this embodiment of the invention is... p and the most probable diameter d q .

[0039] Figure 4 This is a pore size distribution diagram of the cement-based material in an embodiment of the present invention.

[0040] In the diagram, 1-first throat hole, 2-second throat hole, 3-i-1th throat hole, 4-ith throat hole, 5-first ink bottle hole, 6-second ink bottle hole, 7-i-1th ink bottle hole, 8-ith ink bottle hole, 9-mercury injection direction. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0042] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0043] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0044] This embodiment provides a method for determining the pore volume distribution of a cement-based ink bottle, including the following steps:

[0045] 1) Place the dried cement-based material specimen in the sample tube of the fully automatic mercury porosimeter for vacuum treatment;

[0046] 2) Low-pressure operation increases the pressure from 0 to the initial pressure P0 until the specimen is tightly surrounded by mercury;

[0047] 3) High-pressure operation increases the pressure from P0 to P1, causing the first throat (volume) with diameter d1 to... ) and the first ink bottle hole (volume) The sample is filled with mercury, and the volume of mercury pressed into the sample is recorded as . The pressure was then reduced from P1 to the initial pressure P0, causing the mercury in the first throat to exit the specimen. The volume of mercury remaining in the specimen was... The volume of the first ink bottle orifice

[0048] 4) k is successively taken as 2, 3, ..., n, where n is the number of mercury intrusion-removal cycles. Repeat the following steps: high-pressure operation increases from the initial pressure P0 to P k Such that the diameters are d1, d2, ..., d k The first to the kth throat holes and the first to the kth ink bottle holes are filled with mercury, and the corresponding mercury volume pressed into the specimen is denoted as . Then the pressure is changed from P k The pressure was reduced to the initial pressure P0, causing the mercury in the first to the kth throat holes to exit the specimen, thus obtaining the total volume of residual mercury in the first to the kth ink bottle holes. in Let K be the volume of the k-th ink bottle orifice; thus, the cumulative volume of mercury injected can be obtained. and cumulative ink bottle orifice volume

[0049] 5) Based on the results obtained in steps 3-4, the diameters of the cement-based material specimens are d1, d2, ..., d i ,...,d n The volume distribution of the throat orifice and its adjacent ink bottle orifice is as follows:

[0050] When k=1, the volume of the first ink bottle orifice Volume of the first laryngeal orifice

[0051] When n≥k≥2, the volume of the k-th ink bottle hole Volume of the k-th larynx

[0052] 6) Based on the results obtained in step 5, consider the threshold porosity (the p-th throat, with diameter d). p ) and most probable pores (the qth throat pore, diameter d) p The effect of pore connectivity on the measured pore volume of the ink bottle. (2≤k≤n) The diameters d1, d2, ..., d in the specimen are gradually allocated and counted using an iterative algorithm. n pore volume, V k,n The diameter calculated in the nth iteration is d. k pore volume.

[0053] Step 1: Set the pore diameter d1 as the initial value of the iterative algorithm, that is, the diameter d1 of the first throat hole is the maximum pore size of the specimen, and redistribute the volume of the first ink bottle hole into the pore volume with diameter d1.

[0054]

[0055] Step 2: Redistribute the volume of the second ink bottle orifice into the pore volume with diameter d1.

[0056]

[0057]

[0058] Step k: Similar to step 2, redistribute the volume of the k-th ink bottle orifice.

[0059] ①When d k ≥d q The volume of the k-th ink bottle orifice is gradually redistributed according to the volume ratio and included in the diameters d1, d2, ..., d. k-1 pore volume.

[0060]

[0061]

[0062] ②When d k <d q The volume of the k-th ink bottle orifice is gradually redistributed according to the volume ratio and included in the diameter d. p ,d q+1 ,...,d k-1 pore volume.

[0063] Step n: Redistribute the volume of the nth ink bottle orifice according to the volume ratio and include it in the diameter d. p ,d p+1 ,...,d n-1 pore volume.

[0064]

[0065]

[0066] 7) Based on the results obtained from the iterative calculation in step n of step 6, the pore size distribution in the cement-based material specimen is expressed as:

[0067] The pore volume with diameter d1 is V1 = V 1,n

[0068] Diameter d k pore volume V k =V k,n (k = 2, 3, ..., n-1)

[0069] Diameter d n pore volume V k =Vn,n

[0070] In this embodiment, the pressure applied during high-pressure operation ranges from P1 to P... n The pressure is continuously increased to fill the corresponding throat and ink bottle orifice with mercury; when the pressure increases to P... i (i = 1, 2, ..., n), and then reduce the pressure to the initial value P0 to allow all mercury in the throats to exit. The volume distribution of the throats and ink bottles can be accurately calculated based on the volume difference between mercury injection and mercury withdrawal, without requiring contact angle data between the cement-based material and mercury. This is a more reliable and convenient method for characterizing the "ink bottle" effect.

[0071] In this embodiment, the volumetric dimensions of the cement-based material specimen are 0.8–1.2 cm. 3 It can be a cubic or cylindrical specimen block.

[0072] Mercury intrusion porosimetry involves injecting mercury into the porous system of a vacuum-sealed specimen under applied pressure. Because mercury is non-wetting of cement-based materials, it will not spontaneously flow into solid pores without pressure. See also Figure 1 and Figure 2 When an external force is present, mercury is forced into the pores under a given pressure. The greater the external force, the smaller the pores that mercury can be forced into. Based on the Washburn equation, the volume of the pores of the corresponding diameter can be obtained by measuring the amount of mercury injected at each pressure. Two common assumptions are used in mercury intrusion spectroscopy: first, the irregular pore shape is assumed to be cylindrical; second, for a given pressure, the injected mercury can simultaneously contact pores of different diameters (including throats and ink bottle holes). Since mercury in the throats exits during decompression, while mercury in the ink bottle holes remains, the volume of different throats and their corresponding ink bottle holes can be calculated step-by-step by using the relationship between the volume of mercury injected during each pressurization and the volume of mercury expelled during decompression. Then, based on volume distribution theory and iterative algorithms, the volume distribution of pores of different sizes in the specimen is calculated; the volume of ink bottle holes per unit volume (ml) of the specimen is used as the unit of measurement, i.e., ml / ml.

[0073] This example uses a size of 1.0cm. 3 Ordinary silicate cement paste specimens with a water-cement ratio of 0.4 and a curing time of 28 days were used. The cement paste specimens were dried using a freeze-drying method; this method involved immersing the specimens in liquid nitrogen at -196℃ for 5 minutes, followed by placing them in a freeze dryer until the daily mass loss of the specimens did not exceed 0.01%; the temperature and pressure of the freeze dryer were -24℃ and 0.1 Pa, respectively. In this example, the maximum pressure applied by the mercury porosimeter was 210 MPa, and n = 19 was used. The volume distribution of the ink bottle pores of the cement paste was determined according to the following steps:

[0074] 1) As Figure 1 After drying, the cement-based material specimens shown were placed into the sample tube of a mercury porosimeter for vacuum treatment.

[0075] 2) Increase the pressure of the mercury porosimeter from 0 to the initial pressure of 0.15 MPa for low-pressure operation until the cement-based material specimen is completely surrounded by mercury.

[0076] 3) Increase the pressure from 0.15 MPa to P1, filling the first throat (diameter d1) and the first ink bottle orifice with mercury; decrease the pressure from P1 to 0.15 MPa, causing the mercury in the first throat to exit, and obtain the volume of residual mercury in the first ink bottle orifice.

[0077] 4) k is successively taken as 2, 3, ..., 19, and the following steps are repeated: the pressure is increased from 0.15 MPa to P. k The specific values ​​are shown in Table 1, such that the diameters of the first laryngeal orifice to the kth laryngeal orifice (d1, d2, ..., dk) are respectively... k The total volume of mercury injected is obtained by filling the first ink bottle hole to the kth ink bottle hole with mercury. Then change the pressure from P k The pressure was reduced to 0.15 MPa, causing mercury to exit from the first to the kth pore, thus obtaining the total volume of residual mercury from the first to the kth ink bottle pores. That is, by cyclically increasing the pressure and returning to low pressure, the total volume of mercury injected each time is obtained. The total volume of mercury residue in the ink bottle hole (k = 2, 3, ..., 19). The process is as follows: Figure 2 As shown.

[0078] 5) Based on the results obtained in steps 3-4, the diameters of the cement-based material specimens are d1, d2, ..., d i ,...,d n The volume distribution of the throat orifice and its adjacent ink bottle orifice is as follows:

[0079] When k = 1, the pore volume with diameter d1 is Set d1 as the maximum pore size and ignore the "ink bottle" effect.

[0080] When n≥k≥2, the volume of the k-th ink bottle hole Volume of the k-th larynx

[0081] 6) The threshold pore diameter d of the specimen was measured using the traditional mercury intrusion porosimetry method. p and the most probable pore diameter d q The corresponding wavelengths are 91.1nm and 42.6nm, respectively. See [link / reference]. Figure 3As shown. Pore diameter greater than or equal to the threshold d p The capillaries exist in the spaces not filled by cement hydration product particles, and their diameter is less than d. p Capillary pores exist within the cement hydration product particle packing system; the inner diameter of the specimen is greater than the most probable pore size d. q All the pores cannot form interconnected channels, while those with a diameter greater than or equal to d q+1 All the pores can form interconnected channels, d q+1 <d q ; diameter less than d q Pores with diameters greater than d p The pores are not directly connected.

[0082] 7) Based on the results obtained in steps 5-6, the diameters of the cement-based materials are d1, d2, ..., d i ,...,d 19 The volume distribution of the pores is as follows:

[0083] ①When d k ≥d q The volume of the k-th ink bottle orifice is gradually redistributed according to the volume ratio and included in the diameters d1, d2, ..., d. k-1 pore volume.

[0084]

[0085]

[0086] ②When d k <d q The volume of the k-th ink bottle orifice is gradually redistributed according to the volume ratio and included in the diameter d. p ,d p+1 ,...,d k-1 pore volume.

[0087]

[0088]

[0089] 8) Based on the results obtained from the last iteration in step n of step 7, the pore size distribution in the cement-based material specimen is expressed as:

[0090] The pore volume with diameter d1 is V1 = V 1,n

[0091] Diameter d k pore volume V k =V k,m (k = 2, 3, ..., n-1)

[0092] Diameter dn pore volume V k =V n,n

[0093] Thus, the diameters d1, d2, ..., d in the cement-based material specimens are obtained. 19 The pore volume distribution is shown in the figure. Figure 4 .

[0094] Table 1

[0095]

[0096] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent changes and modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, in accordance with the scope of the patent application of the present invention, shall be covered by the present invention.

Claims

1. A method for determining the pore size distribution of cement-based materials, characterized in that, Includes the following steps: Step 1) Place the dried cement-based material specimen in the sample tube of the fully automatic mercury porosimeter for vacuum treatment; Step 2) Low-pressure operation increases the pressure from 0 to the initial pressure. , until the specimen is tightly surrounded by mercury; Step 3) High-pressure operation will increase the pressure from Increase to , so that the diameter is The first throat orifice and the first ink bottle orifice were filled with mercury, and the volume of mercury pressed into the specimen was denoted as . , , The volume of the first laryngeal foramen. The volume of the first ink bottle orifice; then the pressure is transferred from... Reduce to initial pressure This causes the mercury in the first throat orifice to exit the specimen, and the volume of mercury remaining in the specimen... The volume of the first ink bottle orifice ; Step 4) k is successively set to 2, 3, …, n, where n is the number of mercury intrusion-removal cycles. Repeat the following steps: High-pressure operation starts from the initial pressure. Increase to So that the diameters are respectively , , …, The first to the kth throat holes and the first to the kth ink bottle holes are filled with mercury, and the corresponding mercury volume pressed into the specimen is denoted as . Then the pressure is transferred from Reduce to initial pressure This allows the mercury in the first to the kth throat orifice to exit the specimen, yielding the total volume of residual mercury in the first to the kth ink bottle orifice. ,in , Let K be the volume of the k-th ink bottle orifice; thus, the cumulative volume of mercury injected can be obtained. , , …, and cumulative ink bottle orifice volume , , …, ; Step 5) Based on the results obtained in steps 3)-4), the diameter of the cement-based material specimen is... , , ..., , ..., The volume distribution of the throat orifice and its adjacent ink bottle orifice is as follows: when At that time, the volume of the first ink bottle hole Volume of the first laryngeal foramen ; when At that time, the volume of the k-th ink bottle orifice The volume of the kth laryngeal foramen ; Step 6) Based on the results obtained in Step 5), considering the influence of threshold porosity and most probable porosity on pore connectivity, the measured ink bottle pore volume is... 2 ≤ k ≤ n, and the diameter of the specimen is gradually allocated and included in the calculation through an iterative algorithm. , ,..., The pore volume, wherein the threshold pore size is the diameter The p-th throat opening; the most probable pore is the diameter The qth laryngeal foramen; The diameter calculated in the nth iteration is pore volume; Step 7) Based on the results obtained from the iterative calculation in step n of step 6, the pore size distribution in the cement-based material specimen is expressed as: Diameter pore volume = ; Diameter pore volume = (k = 2, 3, …, n-1); Diameter pore volume = ; Step 6) specifically includes: Step 1: Set the pore diameter The initial value for the iterative algorithm is the diameter of the first throat opening. To determine the maximum porosity of the specimen, the volume of the first ink bottle orifice is redistributed and included in the diameter. pore volume; ； Step 2: Redistribute the volume of the second ink bottle orifice into the diameter. pore volume; ； ； Step k: Similar to the algorithm in step 2, redistribute the volume of the k-th ink bottle orifice; when ≥ The volume of the k-th ink bottle orifice is gradually redistributed according to the volume ratio and included in the diameter. , , ..., pore volume; (1 ≤ i < k) ; ； when < The volume of the k-th ink bottle orifice is gradually redistributed according to the volume ratio and included in the diameter. , , ..., pore volume; Step n: Redistribute the volume of the nth ink bottle orifice according to the volume ratio and include it in the diameter. , , ..., pore volume; (p ≤ k < n); 。 2. The method for determining the pore size distribution of cement-based materials according to claim 1, characterized in that, Considering the influence of threshold porosity and most probable porosity on pore connectivity, and taking into account the continuity of pore size, the pressure is increased from the initial value. Gradually increase to , , …, And each time the pressure is increased to Then, for k = 1, 2, …, n, the pressure is reduced to the initial pressure. This causes all the mercury in the first to the kth larynx to exit, while the first to the kth ink bottle holes are completely filled with mercury.

3. The method for determining the pore size distribution of cement-based materials according to claim 1, characterized in that, Using volume distribution theory and iterative algorithms, the volume of each ink bottle orifice is determined. The diameter is redistributed. , , ..., pore volume.

4. The method for determining the pore size distribution of cement-based materials according to claim 1, characterized in that, The volumetric dimensions of the cement-based material specimens ranged from 0.8 to 1.2 cm. 3 .

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