Method for improving quality of sand mortar produced by steam curing machine and application

Abstract

The invention belongs to the technical field of machine-made sand aggregate quality control, and particularly provides a method for improving the quality of steam-curing machine-made sand mortar and application. The method comprises the following steps: measuring the stacking density of machine-made sand in a natural state and a tight loading state, calculating the void ratio of aggregate, and evaluating the compactness; representing the morphology of the machine-made sand particles by adopting a digital image technology, and extracting morphological characteristics of the machine-made sand particles; based on the maximum bulk density theory, grading evaluation parameters are introduced; and considering the influence of the difference of the screening residues on the strength of the cement mortar, supplementing the particle size of the machine-made sand according to an evaluation result, and optimizing the proportion of the components to prepare the mortar. Precise particle size supplementation is carried out through the maximum bulk density theory, a highly dense machine-made sand skeleton structure is constructed, mortar has good working performance, the mortar strength under the steam curing condition is remarkably improved, the problem that the anti-permeability performance is reduced due to harmful holes in steam curing cement mortar is solved, the anti-permeability performance of the mortar is enhanced, and the anti-permeability performance of the mortar is improved. Therefore, the quality of steam-cured mortar is comprehensively improved.

Description

Technical Field

[0001] This invention relates to the field of manufactured sand aggregate quality control technology, and in particular to a method and application for improving the quality of steam-cured manufactured sand mortar. Background Technology

[0002] Fine aggregates are composed of particles of different sizes in specific proportions and are generally used as a transitional material between cementitious materials and coarse aggregates. In a general sense, the characteristics of fine aggregates are manifested as fineness modulus, apparent density, bulk density, and porosity, while the gradation reflects the distribution of particles of different sizes. There are certain correlations among the above-mentioned characteristics.

[0003] In practical engineering, river sand and manufactured sand are widely used fine aggregates. Besides differences in particle size and morphology, these two types of sand also differ significantly in their sieve bottom material; river sand sieve bottom material contains more mud and powder, while manufactured sand sieve bottom material contains more stone powder. In summary, the main factors influencing the properties of fine aggregates based on the composition of these two commonly used sand types include particle morphology, particle size distribution, parent rock type, stone powder content, mud content, and methylene blue value.

[0004] In existing technologies, the control indicators for fine aggregate characteristics are concentrated on the latter four categories of factors. For manufactured sand, quality control mainly focuses on stone powder content and MB value, while for river sand, the focus is primarily on mud content. This neglects two important factors: particle morphology and particle size distribution. Meanwhile, the evaluation and control of manufactured sand gradation primarily uses the cumulative sieve residue percentage. However, numerous studies have shown that using the cumulative sieve residue percentage to determine the particle size distribution of manufactured sand may be insufficient, leading to an inability to fully reflect particle distribution characteristics, distinguish gradation types, or ignore the influence of intermediate particles. Currently, there is no comprehensive evaluation system. Furthermore, research on river sand and manufactured sand largely focuses on the performance of the concrete they produce, with little in-depth research on the characteristics of the raw materials themselves. Therefore, how to improve the quality of manufactured sand mortar is a worthy research topic for researchers. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned shortcomings of existing technologies by providing a method and application for improving the quality of steam-cured manufactured sand mortar. This method utilizes gradation evaluation parameters. S 2 The gradation characteristics of manufactured sand are comprehensively evaluated by combining the sieve residue curve of the separator, which improves the quality of the prepared manufactured sand mortar and makes it better suited for concrete preparation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The first objective of this invention is to provide a method for improving the quality of steam-cured manufactured sand mortar, comprising the following steps: Prepare manufactured sand that meets the standards for construction sand, determine the bulk density of manufactured sand in its natural and compacted states, calculate the aggregate porosity, and assess the degree of compaction. Digital image technology was used to characterize the morphology of manufactured sand particles and extract their morphological features. Based on the maximum packing density theory, gradation evaluation parameters are introduced. Quantitatively evaluate the degree of deviation between the mechanical sand aggregate and the ideal optimal gradation curve; Based on the evaluation results, the particle size of the manufactured sand was adjusted, the component ratio was optimized, and mortar was prepared.

[0007] Furthermore, the process of extracting the morphological features of manufactured sand particles involves importing the acquired image into Adobe Photoshop software, erasing overlapping particles, retaining the original RGB data of the image for binarization, and then importing the processed binarized image into Image-Pro Plus to extract parameters, including primary parameters and secondary parameters calculated from the primary parameters.

[0008] Furthermore, the first parameter includes aspect ratio, longitudinal-to-horizontal ratio, inner diameter ratio, and roundness; the second parameter includes edge angle, roughness, flatness, and overall profile coefficient.

[0009] Furthermore, the aspect ratio is the ratio of the major and minor axes of the equivalent ellipse of the measured object, with a value ranging from 1.1 to 1.7; the longitudinal aspect ratio is the ratio of the height to the width of the smallest rectangle of the measured object, with a value ranging from 0.3 to 2.0; the inner diameter ratio is the ratio of the radius of the largest circumcircle to the smallest incircle of the particle, with a value ranging from 1.5 to 2.1; and the roundness is the similarity between the shape of the measured object and an ideal circle, with a value ranging from 1.0 to 1.3.

[0010] Further, the angularity is the ratio of the perimeter of the smallest circumscribed polygon to the perimeter of the equivalent area ellipse, with a value range of 1.01 to 1.35; the roughness is the square of the ratio of the particle's projected perimeter to the perimeter of the outer polygon, with a value range of 1.01 to 1.05; the flatness is the ratio of the longest dimension to the second longest dimension of the aggregate's projected area, with a value range of 1.25 to 1.45; and the overall profile coefficient is the ratio of the circumference of the equivalent area circle to the perimeter of the aggregate's profile, with a value range of 0.90 to 0.97.

[0011] Furthermore, the Thabo formula was used to evaluate the gradation of manufactured sand aggregate to obtain the rationally optimal gradation curve. The Thabo formula is as follows:

[0012] In the formula, P i For an aperture of d i The sieve throughput, %; d idenoted as aggregate size (mm); D represents the maximum aggregate size (mm); n represents the experimental index. i This refers to the sieve aperture size.

[0013] Furthermore, gradation evaluation parameters The calculation formula is as follows:

[0014] In the formula, σ represents the deviation between the actual aggregate gradation and the Thabo continuous gradation curve. i For the sampling group, the intermediate pairing should be i Cumulative sieve residue rate at sieve aperture size, %; τ i For the continuous pairing of the Thai wave, i Cumulative sieve residue rate at sieve aperture size, % i The sieve aperture size is 4.75~0 mm.

[0015] Furthermore, using gradation evaluation parameters The gradation characteristics of manufactured sand were comprehensively evaluated using the sieve residue curve and the partial sieve residue curve. The content of coarse particle characteristic size was controlled between 48% and 52%, while the content of other particle sizes was controlled between 14% and 16%. These parameters were used to evaluate porosity and gradation. Fit the curve and adjust the gradation based on the fitting results.

[0016] Adjacent particle size combinations are referred to as characteristic particle size groups and are used as the main gradation characteristic index for analysis. In the sieve residue, the content of particles in two adjacent particle size groups is significantly higher than that of other particle sizes. Particles with adjacent particle sizes of 2.36 mm and 1.18 mm are classified as coarse particles; particles with particle sizes of 1.18 mm and 0.60 mm are classified as medium-coarse particles; particles with particle sizes of 0.6 mm and 0.30 mm are classified as medium-fine particles; and particles with particle sizes of 0.30 mm and 0.15 mm are classified as fine particles. A second objective of this invention is to provide the application of the above-described method for improving the quality of steam-cured manufactured sand mortar in the preparation of cement mortar.

[0017] Furthermore, the cement mortar is prepared in a high temperature and high humidity environment, with the high temperature being in the range of 45℃ to 60℃ and the high humidity being a humidity of not less than 95%.

[0018] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention provides a method for improving the quality of steam-cured manufactured sand mortar. The method includes determining the bulk density of manufactured sand in its natural and compacted states, calculating the aggregate porosity, and evaluating the degree of compaction; using digital image technology to characterize the particle morphology of manufactured sand and extracting particle morphology features; introducing gradation evaluation parameters based on the maximum bulk density theory; considering the influence of the difference in sieve residue on the strength of cement mortar, supplementing the particle size of manufactured sand according to the evaluation results, optimizing the component ratio, and preparing mortar. By introducing the maximum bulk density theory for precise particle size supplementation, a highly compact manufactured sand skeleton structure is constructed, resulting in mortar with better workability.

[0019] (2) Improve the strength of steam-cured cement mortar while ensuring its workability; (3) Overcome the problem of reduced impermeability caused by harmful pores inside steam-cured cement mortar, enhance the impermeability of steam-cured cement mortar, and thus comprehensively improve the quality of steam-cured mortar.

[0020] (4) It is conducive to the development and application of steam curing technology. Attached Figure Description

[0021] Figure 1 The sieve residue curve for N0 fractionation; Figure 2 This is the cumulative sieve residue curve for N0; Figure 3 The sieve residue curve for M0 fractionation; Figure 4 The cumulative sieve residue curve for M0; Figure 5 The sieve residue curve for MA1 fractionation; Figure 6 The cumulative sieve residue curve for MA1; Figure 7 The sieve residue curve for MA2 fractionation; Figure 8 The cumulative sieve residue curve for MA2; Figure 9 The sieve residue curve for MA3 fractionation; Figure 10 The cumulative sieve residue curve for MA3; Figure 11 The sieve residue curve for MA4 fractionation; Figure 12 The cumulative sieve residue curve for MA4; Figure 13 The sieve residue curve for MB1 fractionation; Figure 14 The cumulative sieve residue curve for MB1; Figure 15 MB2 sieve residue curve; Figure 16The cumulative sieve residue curve for MB2; Figure 17 The sieve residue curve for MB3 fractionation; Figure 18 The cumulative sieve residue curve for MB3; Figure 19 The sieve residue curve for MB4 fractionation; Figure 20 The cumulative sieve residue curve for MB4; Figure 21 The relationship between fineness modulus and particle size content of group S1; Figure 22 The relationship between fineness modulus and particle size content of group S2; Figure 23 The relationship between fineness modulus and particle size content of group S3; Figure 24 The relationship between fineness modulus and particle size content of group S4; Figure 25 The apparent density of fine aggregate; Figure 26 The effect of characteristic particle size group on apparent density; Figure 27 The bulk density and porosity of fine aggregates; Figure 28 This is a diagram illustrating the filling of fine particles; Figure 29 The influence of characteristic particle size group on porosity; Figure 30 The maximum density curve; Figure 31 S is the gradation evaluation parameter 2 Fitting curve with porosity; Figure 32 A comparison chart of flowability test values ​​for different test groups; Figure 33 The diagram shows the compressive strength of the positive test group under steam curing. Figure 34 This is a diagram showing the compressive strength of the reverse control group under steam curing. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0023] In this invention, steam-cured manufactured sand mortar refers to a mortar product that uses manufactured sand as fine aggregate to replace natural sand in factory prefabrication. After batching, mixing, and molding, it is cured by steam (at normal pressure or high pressure) to achieve rapid hardening. It is commonly used in prefabricated components such as wall panels, blocks, and bridge grouting in industrialized construction.

[0024] Example 1 This embodiment provides a method for improving the quality of steam-cured machine-made sand mortar.

[0025] (1) Particle size distribution According to the requirements for fine aggregates in "Construction Sand" (GB / T 14684-2022), and considering the actual conditions of the raw materials on site, four test groups, MA1 to MA4, were prepared. The gradation characteristics of the test groups are that the particle content of adjacent particle sizes is significantly higher than that of other particle sizes; among them, each adjacent particle size group is referred to as the "characteristic particle size group". To make the gradation grouping more complete, gradation combinations MB1 to MB4, which are complementary to MA1 to MA4 in terms of gradation characteristics, were set up in reverse. In addition, commonly used raw river sand and manufactured sand were also considered in the test groups, numbered N0 and M0 respectively. The gradation status of the raw material groups and the test groups with gradation reset is shown in Table 1. The cumulative sieve residue curves and individual sieve residue curves of different test groups are shown in Table 1. Figures 1 to 20 As shown.

[0026] Table 1. Particle size distribution of each experimental group

[0027] Depend on Figures 1 to 20The gradation curve series and summary table data show that the cumulative sieve residue curves of river sand, manufactured sand, and the gradation resetting test group all fall within the Zone II gradation range of the "Construction Sand" (GB / T 14684-2022) standard. Analysis of the data from groups N0 and M0 indicates that different particle types have a certain degree of influence on the fine aggregate gradation. From the individual sieve residue curves, river sand exhibits a more uniform particle size distribution, with a more reasonable content of large-sized particles and bottom particles, with the main particle sizes ranging from 16% to 20%. Manufactured sand raw materials mainly consist of particles in the 1.18 mm to 0.60 mm size range, with both particle sizes exceeding 20%, and the bottom particle content is significantly higher than that of river sand (10.5% for river sand raw materials and 16.5% for manufactured sand raw materials). Meanwhile, the cumulative sieve residue of group M0 on a 0.30 mm sieve is consistently higher than that of group N0. Therefore, without considering the type of parent rock, the gradation composition of fine aggregates produced by different production methods varies to some extent. This may be because the long-term effects of water flow impact, corrosion, and mutual collision make the particle size distribution of river sand relatively uniform across different zones, and the long-term water flow scouring also easily carries away a large number of small particles with low mass and low adhesion from the bottom of the screen. Manufactured sand is mostly produced by instantaneous impact crushing. However, due to the high density and few internal defects of the parent rock material, it is more brittle. When subjected to instantaneous impact, stress concentration often occurs in the small defect areas inside the material, resulting in breakage points. The high brittleness causes the stress to be released rapidly in a single direction, and cracks cannot develop uniformly. Therefore, a phenomenon of "more at both ends and less in the middle" occurs, with more large-sized particles and more bottom particles.

[0028] Observation of the particle size distribution of MA1, MA2, MA3, and MA4 in the positive test groups shows that, regardless of whether it is the manufactured sand raw material or the gradation replacement group, the particle content at the 4.75 mm size is 0, which complies with the relevant provisions of "Construction Sand" (GB / T 14684-2022). For the other sieve sizes, it can be seen that the particle size content of every two adjacent particles in the positive test groups is roughly the same, and significantly higher than the particle content of other sizes. For example, the particle sizes of group MA1 are concentrated at 2.36 mm (25% content) and 1.18 mm (25%); group MA2 is concentrated at 1.18 mm (25% content) and 0.60 mm (25% content); group MA3 is concentrated at 0.60 mm (25% content) and 0.30 mm (25% content); and group MA4 is concentrated at 0.30 mm (25% content) and 0.15 mm (24% content). These adjacent particle size combinations are referred to as the "characteristic particle size groups" and are used as the main gradation characteristic indicators for analysis, as shown in Table 2. The content of other particle sizes is controlled within a small range of 14% to 16%, and the content of bottom material is controlled at 6%.

[0029] In the reverse control group, the particle size distribution was completely opposite to that of the forward experimental group. The sieve residue curves for MB1, MB2, MB3, and MB4 show that all four groups exhibited a lack of specific particle sizes. Specifically, the content of particles of other sizes ranged from 22% to 26%, while the content of 2.36 mm and 1.18 mm particles in MB1 was only 10%, in MB2 the content of 1.18 mm and 0.60 mm particles was also only 10%, in MB3 the content of 0.60 mm and 0.30 mm particles was also 10%, and in MB4 the content of 0.30 mm and 0.15 mm particles was still only 10%. Regarding the distribution of adjacent particle sizes, unlike the "particle size concentration" in the forward experimental group, the reverse control group showed "particle size deficiency." Therefore, these four groups were used as the control group for the forward experimental group to conduct a comparative experiment and observe the corresponding experimental phenomena. It is worth noting that the distribution of sieve bottom material content in the reverse control group was basically similar to that in the forward experimental group, all controlled below 10%.

[0030] Table 2. Characteristic Particle Size Combinations

[0031] (2) Fineness modulus The fineness modulus of different experimental groups was calculated using the following formula: (2-1) In the formula, M x : Fineness modulus of sand; A1, A2, A3, A4, A5, and A6: These represent the cumulative percentage of residue on 4.75mm, 2.36mm, 1.18mm, 0.60mm, 0.30mm, and 0.15mm sieves, respectively. The results are shown in Table 3.

[0032] Table 3. Fineness modulus of each experimental group

[0033] To analyze the influence of different characteristic particle size groups on the fineness modulus of fine aggregates, the particle size contents of S1, S2, S3, and S4 in the forward experimental group and the reverse control group were linearly fitted with their corresponding fineness moduli. The results are as follows: Figures 21 to 24 As shown in the figure. From the correlation, we can see that R... 2 The closer the correlation is to 1, the better the correlation between the two quantities. Therefore, the contents of characteristic particle size groups S1 and S4 have a good positive correlation with the fineness modulus of fine aggregates. Specifically, analyzing the correlation data, the fit between characteristic particle size group S1 and the fineness modulus is R1. 2The fineness modulus of S1 group is 0.88, while that of S2 group is 0.328, and that of S3 and S4 are 0.450 and 0.793, respectively. The fitting effect of group S1 on the fineness modulus is significantly better than that of the other three groups. The reasons for this are twofold: firstly, the increase in fine particle content makes the overall aggregate particles significantly finer, thus reducing the fineness modulus; secondly, in the fineness modulus calculation formula (Equation 2-1), the coarse particle content has a large weight, making the fineness modulus more sensitive to the coarse particle content. Since the content of 4.75mm particles in manufactured sand is basically 0, the content of characteristic particle size group S1 is consistent with the cumulative sieve residue value of 1.18mm. Therefore, the fineness modulus of different manufactured sands can be roughly distinguished to a certain extent by the content of characteristic particle size group S1 (or the cumulative sieve residue of 1.18mm).

[0034] (3) Apparent density Apparent density tests were conducted on each experimental group, and the results are as follows: Figure 25 As shown.

[0035] It can be seen that the apparent density of river sand is 2609 kg / m³. 3 This value is lower than the apparent density of most manufactured sand test groups. This is mainly because the raw material of manufactured sand is rock, and the density of rock is greater than that of river sand; while the apparent density of manufactured sand raw material is 2809 kg / m³. 3 The apparent density of the MB2 group is 7.6% higher than that of river sand; the apparent density of the MB2 group is 2811 kg / m³. 3 The apparent density of this material is 7.7% higher than that of river sand. These results indicate that even fine aggregates with similar fineness moduli can exhibit significant differences in apparent density due to variations in particle type and gradation.

[0036] The measured data from the positive and negative control groups show that the apparent density of fine aggregates is generally negatively correlated with the fineness modulus. For example, the apparent density of group MA1 is 2611 kg / m³. 3 The apparent density of group MB4 was 3.8%, 4.8%, and 9.7% lower than that of groups MA2, MA3, and MA4, respectively; the apparent density of group MB4 was 2580 kg / m³. 3The apparent density of the fine aggregate was 5.3%, 8.2%, and 3.7% lower than that of groups MB3, MB2, and MB1, respectively. Analysis shows that an increase in coarse particle content significantly reduces the apparent density of fine aggregate, while an increase in fine or medium-fine particle content increases it. This is because medium-fine or fine particles effectively fill the packing voids in the fine aggregate, thus increasing the overall apparent density. However, a high content of fine particles also reduces the apparent density. This is because excessive fine aggregate replacing medium-coarse particles not only degrades the gradation but also reduces the overall quality of the fine aggregate. Therefore, for manufactured sand, the fineness modulus reflects its apparent density within a certain range, and there exists an optimal fineness modulus (i.e., optimal gradation) that maximizes the apparent density of the manufactured sand. Within the range of fineness modulus variation, the apparent density of manufactured sand first increases and then decreases with increasing fineness modulus.

[0037] To analyze the impact of different characteristic particle size groups on apparent density, the differences between the "particle size concentration" and "particle size loss" test values ​​in the experimental groups were calculated, and the percentage of these differences was determined. Since the gradation distributions within the forward experimental group and the reverse control group are largely complementary, this percentage of differences is used to represent the impact of different characteristic particle size groups on apparent density when particle size is concentrated. Figure 26 As shown, increasing the content of characteristic particle size groups S1, S2, and S3 all have a negative effect on the apparent density of fine aggregates, while increasing the content of characteristic particle size group S4 has a significant effect on improving the apparent density, which is closely related to the filling effect of fine particles. Excluding the deterioration of the gradation of group MB1, it can be seen that the change in the content of characteristic particle size group S2 has a relatively low impact on the overall apparent density of fine aggregates.

[0038] (4) Bulk density and porosity The bulk density and porosity of each test group are as follows: Figure 27 As shown.

[0039] It can be seen that the loose bulk density and the compacted bulk density of river sand are 1571 kg / m³. 3 and 1674kg / m 3 The loose bulk density and compacted bulk density of the manufactured sand raw material are 1624 kg / m³. 3 and 1823kg / m 3 The density of manufactured sand is 3.4% and 12.3% higher than that of river sand, respectively. This data indicates that the density of manufactured sand is higher than that of river sand. This may be because the density of the parent rock of manufactured sand is greater than that of river sand, or it may be because the cumulative bulk percentage of manufactured sand raw material at 0.3 mm is always higher than that of river sand. In the graded replacement group, the bulk density of manufactured sand ranges from 1692 kg / m³. 3 ~1801kg / m 3 and 1835kg / m 3 ~1972kg / m 3The maximum values ​​were 6.4% and 7.4% higher than the minimum values, respectively, with slight variations in the range of variation. The impact of gradation on bulk density was limited. Test results showed that manufactured sand generally had a higher bulk density than river sand. The relationship between gradation and bulk density was similar to that between apparent density and fineness modulus; that is, a reasonable content of fine particles in the fine aggregate positively affects bulk density, but excessive fine particles lead to poor gradation and are more likely to form more voids in the packing space. Figure 28 As shown.

[0040] Regarding porosity, the porosity of river sand was 39.7%, while the porosity of the manufactured sand gradation reset group ranged from 34.8% to 37.3%, which was 6.0% to 12.3% lower than that of river sand, and the porosity of the manufactured sand raw material was as high as 42.2%. The lowest porosity in the manufactured sand group appeared in groups MB3 and MB4, both at 34.8%, while the highest porosity appeared in group MA3 at 37.3%, which was 7.2% higher than the minimum, with a relatively small fluctuation range. In the forward test groups, the porosities of groups MA1, MA2, MA3, and MA4 were 35.2%, 36.6%, 36.8%, and 37.2%, respectively; while the porosity of the reverse control group ranged from 34.8% to 37.3%. Both the forward and reverse control groups showed a trend of increasing porosity with decreasing fineness, indicating excessive filling of fine particles. Combined with the characteristics of the gradation setting, it can be seen that "particle size concentration" or "particle size deficiency" is not conducive to subsequent gradation optimization. The test data above shows that when the gradation is similar or close, the effect of gradation on porosity is relatively small. However, excessively poor gradation can significantly increase the porosity of fine aggregates (such as group M0). Furthermore, although the porosity of river sand is lower than that of manufactured sand raw materials, it is still higher than that of the other manufactured sand test groups. This indicates that gradation has a greater effect on improving the porosity of fine aggregates than particle type. Therefore, poorly graded sand should be given serious attention.

[0041] Figure 29 The influence of characteristic particle size groups on porosity was demonstrated. The evaluation method involved analyzing the porosity difference percentage between two gradation groups (e.g., MA1 and MB1) where the characteristic particle size groups were significantly "concentrated" or "absent," based on the gradation characteristics of the forward test group and the reverse control group. This analysis illustrated the degree to which the content of the characteristic particle size group affected the improvement (or deterioration) of porosity. As shown in the figure, the influence of characteristic particle size group S2 on the porosity of the manufactured sand was significantly lower than that of the other characteristic particle size groups, with its percentage essentially approaching zero. The porosity reduction rates of characteristic particle size groups S1, S3, and S4 were 5.4%, 5.7%, and 6.5%, respectively, all indicating a relatively low level of influence on the porosity of the manufactured sand.

[0042] (5) Morphological characteristics of fine aggregates The two-dimensional image analysis method in the direct method is relatively easy to meet in terms of experimental cost and requirements, the research method is relatively mature, and it can directly display the morphology of sand particles. Many studies based on two-dimensional graphics usually obtain the basic parameters of sand particle morphology (aspect ratio, aspect ratio, inner diameter ratio, roundness, etc.) directly from the image projection surface, as well as the particle morphology parameters (edge ​​angle, roughness, flatness, overall profile coefficient, etc.) derived from the basic parameters.

[0043] After acquiring particle morphology images of river sand and manufactured sand, the images were processed as follows: First, the original images were binarized using Photoshop, and then thresholding and parameter extraction were performed in Image Pro Plus software. Taking the processing of river sand particles as an example, as follows... Figures 30-32 As shown.

[0044] The morphological parameters of manufactured sand particles are mainly divided into two categories: primary parameters and secondary parameters. Primary parameters include aspect ratio, longitudinal-to-transverse ratio, inner diameter ratio, and roundness, while secondary parameters are calculated from primary parameters using equations (5-1), (5-2), (5-3), and (5-4). (5-1) In the formula, L For edge angle, P c , P E These are the perimeter of the smallest circumscribed polygon of the particle and the perimeter of the equivalent area ellipse, respectively. (5-2) In the formula, r For roughness, P Let the projected perimeter of the particle be . Pc The perimeter of the polygon surrounding the particle; (5-3) In the formula, e For flatness, L and B are the longest and second longest dimensions measured on the particle plane, i.e., length and width, respectively; (5-4) In the formula, α The overall profile coefficient is given by D, where D is the equivalent circle diameter of the aggregate. P The perimeter of the aggregate.

[0045] According to the data statistics from the IPP software, the results are shown in Table 4.

[0046] The aspect ratio of particles primarily reflects the degree of difference between their longitudinal and perpendicular axes. Statistical results show that the aspect ratio of fine aggregates is mostly between 1.0 and 1.9, indicating a certain degree of directionality in both river sand and manufactured sand, a characteristic inherent to aggregates. Specifically, the average aspect ratio of river sand particles is 1.30, while that of manufactured sand particles is 1.44, 10.8% higher. A very small portion of manufactured sand particles also exhibits "flaky particles" with aspect ratios of 2.0 to 3.0. This may be due to the difference in manufacturing processes between the two types of sand. Manufactured sand is subjected to several unidirectional instantaneous crushing impacts during molding, resulting in unevenly propagated cracks. In contrast, river sand, under long-term natural environmental influences and water erosion, receives roughly the same cumulative effect in all directions, resulting in mostly rounded particles with a lower difference between their longitudinal and perpendicular axes.

[0047] Table 4. Primary Parameters

[0048] In another morphological index reflecting differences along the length and vertical directions, the aspect ratio characterizes the ratio of the width to the height of the smallest bounding rectangle of aggregate particles. The aspect ratios of both river sand and manufactured sand range from 0.3 to 2.0, a relatively large range; however, the average aspect ratio of river sand particles is 1.06, while that of manufactured sand particles is 1.13, 6.6% higher than that of river sand. Due to the large data range, the calculated standard deviation for the patterns is 1.26 for river sand and 2.05 for manufactured sand. These results, from another perspective, indicate the existence of aggregate particle orientation issues and, to some extent, explain that the uniformity of morphological distribution in river sand is higher than that in manufactured sand.

[0049] The inner diameter ratio of particles mainly reflects the anisotropy of particle shape. Statistical results show that the basic distribution range of the inner diameter ratio for both types of particles is 1.14 to 2.20. The distribution ranges of the inner diameter ratios of river sand and manufactured sand largely overlap, but the average inner diameter ratio of river sand particles is 1.57, while that of manufactured sand is 1.81, which is 15.3% higher than that of river sand. This indicates that the directionality of river sand particles is weaker than that of manufactured sand, which may be due to the fact that river sand particles are more rounded and smoother than manufactured sand particles.

[0050] Roundness reflects the degree to which particles resemble a circle; the closer the roundness value is to 1, the closer the particles are to a circle. The average roundness value of river sand particles is 1.05, while that of manufactured sand particles is 1.18, 12.4% higher than that of river sand, showing a significant difference. This is because river sand is subjected to long-term scouring, transportation, and corrosion by water flow, causing all its edges and corners to participate in the stress. Under long-term interaction, it tends to form a more rounded shape to adapt to external forces.

[0051] Edge angle is mainly used to indicate the number and protrusion of the surface edges of particles. The results show that the average edge angle of river sand is 1.016, while that of manufactured sand is 1.031, slightly higher than that of river sand. This indicates that manufactured sand particles exhibit more angularity. Regarding roughness, the average roughness of river sand aggregate is 1.012, while that of manufactured sand particles is 1.047, significantly higher than that of river sand, demonstrating that manufactured sand particles have a higher degree of roughness than river sand particles.

[0052] The most significant indicator for comparison is flatness, which reflects the degree of difference in the radial and vertical directions. Specifically, the flatness of river sand particles is 1.29, while that of manufactured sand is 1.43, 10.9% higher. However, in reality, manufactured sand particles also contain a small number of non-negligible "needle-shaped" and "flaky" particles, which increases the average flatness of the particle cluster.

[0053] The overall profile coefficient is evaluated in a similar way to the roundness index, 0 < α <1, when α When the value approaches 1, the aggregate particles tend to be round; the greater the protruding edges and roughness of the particles, the larger the particle perimeter, which will cause... α The value decreases. The average overall profile coefficient of both types of aggregates is above 0.9, but the average value of river sand is 0.963, while that of manufactured sand is 0.919.

[0054] The statistical results of the secondary parameters again show that both types of sand have their own characteristics in terms of particle morphology. Both river sand and manufactured sand show a certain degree of directionality; however, compared with river sand, manufactured sand exhibits more angularity, roughness, and inhomogeneity. Overall, the morphological characteristics of river sand are superior to those of manufactured sand.

[0055] Table 5 summarizes the morphological characteristics and packing void ratios of river sand and manufactured sand. The table shows a strong correlation between the morphological characteristics and packing void ratios of both raw river sand and manufactured sand, indicating that the morphological advantages of particles can improve the internal condition of particle aggregates to a certain extent. However, the packing void ratios of the gradation-replaced groups are all lower than those of the raw river sand, suggesting that the influence of gradation on packing void ratio cannot be ignored. In practical engineering applications, the influence of indicators such as void ratio and roughness must be considered, and the evaluation indicators should be optimized and adjusted accordingly to obtain more significant quantitative analysis results.

[0056] Table 5. Secondary parameters and packing porosity of river sand and manufactured sand

[0057] (6) Gradation evaluation based on maximum packing density theory The Typographic formula was used to evaluate the gradation of the experimental group, and the formula is as follows.

[0058] (6-1) In the formula, P i Aperture is d i The throughput of a sieve of mm, % d i : Particle size of each grade of material, mm; D: Maximum particle size of mineral aggregate, mm; n: Test index.

[0059] The gradation evaluation was carried out using the particle size content at n=0.5 as the optimal gradation curve. The allowable variation range of the reasonable gradation of n is 0.3~0.7.

[0060] Maximum density curve and test group pass rate curve as follows Figure 30 As shown, group MA1 has a higher content of coarse particles, with a characteristic particle size group of S1, and its throughput curve is basically located near the Taylor gradation curve. As the characteristic particle size group shifts further down the spectrum, the content of fine particles in the aggregate increases, and the throughput curves of groups MA2, MA3, and MA4 gradually shift towards the upper limit of the Thaler curve, eventually exceeding the optimal curve range. Compared with the upper and lower limits of the Thaler curve, the slope of the curves in the middle of the four positive test groups gradually increases, and the unevenness of the curves also intensifies; more fine particles result in a steeper curve slope.

[0061] Compared with the upper and lower limits of the Taybo curve, the slope of the four positive test groups gradually increased in the middle of the curve, and the unevenness of the curve also intensified. Moreover, the higher the content of fine particles, the greater the slope of the curve.

[0062] In the reverse control groups MB1-MB4, groups MB4 and MB3 were both distributed within the upper and middle ranges of the Thabo curve, with only a significant difference in the slope of the middle segment. However, groups MB1 and MB2 showed a clear trend of variation above the upper limit of the Thabo curve. Regarding the gradation, the characteristic particle size groups for groups MB1 and MB2 were S1 and S2, respectively, with significantly higher fine particle content in these two groups compared to the other two. Therefore, it can be concluded from another perspective that an increased fine particle content will adversely affect a reasonable gradation. Considering the specific characteristics of the particle size groups, it is necessary to reasonably control the content of fine particles below 0.60 mm in practical engineering.

[0063] To more quantitatively evaluate the degree of deviation between different experimental groups and the rational optimal gradation curve, gradation evaluation parameters are defined. S 2 The calculation is shown in Equation 6-2 below.

[0064] (6-2) In the formula, S 2This represents the deviation between the experimental gradation and the Fuller gradation curve; σ i For experimental pairing i Cumulative sieve residue rate at sieve aperture size, % τ i For Fuller-level pairing i Cumulative sieve residue rate at sieve aperture size, % i The sieve aperture size is 4.75~0 mm.

[0065] The cumulative sieve residue of the forward test group and the reverse control group were compared with the maximum density curve, and the sum of the squares of the distribution deviations of the two was used for characterization. (This is repeated for each sand grain group.) S 2 The relevant physical properties are shown in Table 6.

[0066] Table 6. Gradation Evaluation Parameters

[0067] As shown in the table, the porosity of manufactured sand in both the forward and reverse control groups generally decreases with increasing fineness modulus. However, the patterns observed in the two groups cannot be effectively unified. Therefore, using only the fineness modulus and gradation range cannot comprehensively reflect the particle size distribution and packing state of manufactured sand. S 2 However, it shows a good correlation with porosity, and the fitting curves of the two are as follows: Figure 31 It can be seen that, S 2 The smaller the particle size, the lower the porosity of the manufactured sand. At this point, the gradation curve of the manufactured sand is closer to the maximum density curve, and the sand particles of different sizes fill the interior step by step to form a relatively dense accumulation.

[0068] In summary, using S 2 The evaluation of the gradation characteristics of manufactured sand by combining the gradation and screening residue has good rationality and accuracy; however, the fineness modulus and gradation range can only reflect the coarseness of manufactured sand and cannot reasonably characterize the unique gradation distribution characteristics of manufactured sand.

[0069] Example 2 The workability of steam-cured mortar is compared with that of different aggregate particle size groups. Table 7 shows the workability of different test groups and the fluidity is as follows. Figure 32 As shown.

[0070] Table 7. Fulfillment of different experimental groups.

[0071]

[0072] from Figure 32As can be seen, different characteristic particle size groups have varying degrees of influence on mortar flowability. The difference in mortar flowability between the characteristic particle size groups, from smallest to largest, is as follows: S1 group (58mm), S2 group (20mm), S3 group (-17.5mm), and S4 group (-33mm). Among the four characteristic particle size groups, the particle size concentration phenomenon in groups S1 and S2 shows a positive correlation with the flowability difference, while the particle size concentration phenomenon in groups S3 and S4 shows a negative correlation with the flowability difference. This indicates that increasing the particle size combination of groups S1 and S2 can improve the workability of the mortar, while the particle size combination of groups S3 and S4 will worsen the workability of the mortar. From a particle size perspective, the particle content at both ends plays a crucial role in the workability of mortar. Furthermore, manufactured sand often exhibits a "more at both ends, less in the middle" situation during production. Therefore, the content of coarse and fine particles must be carefully considered in gradation design. It is worth noting that although the impact of intermediate-sized particles on workability is relatively small, improper matching of particles with a common particle size (0.6mm) between groups S2 and S3 can turn a favorable effect of gradation on particle size into a negative one. From a certain perspective, variations in the content of intermediate particle size within a certain range will not lead to a severe deterioration in mortar workability.

[0073] The effect of particle size distribution on the compressive strength of steam-cured mortar According to the mortar steam curing scheme, the compressive strength of the manufactured sand mortar specimens was tested at 2d (after steam curing), 3d, 7d, 14d, and 28d after steam curing. The test results are as follows: Figure 33 and Figure 34 As shown, It is easy to see that the strength difference between the MA1 group and the MB4 group is the lowest in the forward test group and the reverse control group, at 1.5% and 0.8% respectively, indicating that excessive coarse particle content impairs the steam curing effect; while the maximum values ​​in the forward test group and the reverse control group are the MA4 group and the MB2 group, respectively, both at 11.3%, indicating that an increase in fine particle content will enhance the steam curing effect of the mortar.

[0074] Based on the analysis of characteristic particle size groups, the difference percentages between groups MA2 and MB2 are similar, both at 1.5%. However, the differences in intensity difference percentages between groups MA1 and MB1, MA3 and MB3, and MA4 and MB4 are significantly higher than 1.5%. These data indicate that the "concentration" or "absence" of characteristic particle size groups S1, S3, and S4 will significantly affect the steam curing effect. Essentially, this difference is determined by the ratio of coarse to fine particles. In contrast, the "concentration" or "absence" of characteristic particle size group S2 did not cause serious fluctuations in the steam curing effect, and the steam curing effect remained at a relatively high value.

[0075] Excessive fine particle content can cause a severe loss of mortar strength in the later stages, which is the opposite of the effect of fine particle content on the early strength of mortar. At the same time, characteristic particle size group S2 has a more significant effect on improving the compressive strength of mortar, while characteristic particle size group S3 has a lower effect on improving the strength of mortar.

[0076] After the strength development stabilized, taking the 28-day strength as an example, the influence of fineness on compressive strength under different curing methods was analyzed. Under steam curing, the compressive strength from largest to smallest was MA2 group > MA1 group > MA3 group > MA4 group. MB4 group (55.8 MPa) > MB3 group (52.7 MPa) > MB2 group (51.4 MPa) > MB1 group (49.5 MPa). It can be seen that the variation law of mortar compressive strength with fineness is basically consistent under both curing methods. Numerically, the forward test group shows that the mortar compressive strength first increases and then decreases with increasing fineness, while the reverse control group shows that the mortar compressive strength increases with increasing fineness. Due to the influence of gradation, the strength difference in the reverse control group is relatively small.

[0077] Therefore, considering the development trends of fineness and compressive strength, it should be that when the cumulative sieve residue percentage changes in a similar trend, the mortar compressive strength first increases and then decreases with the increase of fineness.

[0078] In summary, the particle size distribution of manufactured sand has a significant impact on the compressive strength of mortar. A higher content of fine particles can improve the steam curing effect, but excessive fine particle content is also very detrimental to the development of later strength. At the same time, while increasing the content of coarse particles can improve the later strength of mortar, there is also a limit to this.

[0079] Based on the above data and results analysis, the restrictions on particle size distribution of manufactured sand in the "Construction Sand" standard (GB / T 14684-2011) are insufficient. Controlling only the cumulative sieve residue and fineness of manufactured sand is incomplete, as the differences in individual sieve residues have a significant impact on the strength of cement mortar. Considering key indicators such as early strength, later strength, and steam curing effect, it is recommended to focus on the content of medium and coarse particles represented by the characteristic particle size group S2. The excessive incorporation of large amounts of coarse or fine particles should be avoided as much as possible to prevent adverse effects on the overall performance of the mortar.

[0080] The effect of gradation on the capillary water absorption properties of steam-cured mortar The influence of aggregate gradation on the capillary water absorption performance of mortar was investigated using groups MA2, MA4, MB1, and MB3. The fineness, from largest to smallest, was MB3 > MA2 > MA4 > MB1, spanning from 3.0 to 2.4. Group MA2 showed the highest 28-day strength among all gradation groups, while groups MA4 and MB1 showed the lowest 28-day strength values. The test results are shown in Table 8 below. Table 8. Capillary water absorption coefficient S of graded groups (g / (cm³)) 2 min 0.5 ))

[0081] Under 3-day steam curing conditions, the minimum capillary water absorption coefficient within the gradation group was 0.020 (MA2 group) and the maximum was 0.059 (MB3 group). Under 28-day steam curing conditions, the minimum capillary water absorption coefficient within the gradation group was 0.009 (MA2 group) and the maximum was 0.026 (MB3 group). This indicates that the gradation condition is a very important factor affecting the capillary water absorption performance of cement mortar.

[0082] For any points not covered above, existing technologies shall apply.

[0083] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the quality of steam-cured manufactured sand mortar, characterized in that, Includes the following steps: Prepare manufactured sand that meets the standards for construction sand, determine the bulk density of manufactured sand in its natural and compacted states, calculate the aggregate porosity, and assess the degree of compaction. Digital image technology was used to characterize the morphology of manufactured sand particles and extract their morphological features. Based on the maximum packing density theory, gradation evaluation parameters are introduced. Quantitatively evaluate the degree of deviation between the mechanical sand aggregate and the ideal optimal gradation curve; Based on the evaluation results, the particle size of the manufactured sand was adjusted, the component ratio was optimized, and mortar was prepared.

2. The method according to claim 1, characterized in that, The process of extracting the morphological features of manufactured sand particles is as follows: the acquired image is imported into Adobe Photoshop software, overlapping particles are erased, the original RGB data of the image is retained and binarized, and the binarized image is imported into Image-Pro Plus to extract parameters, including primary parameters and secondary parameters calculated from the primary parameters.

3. The method according to claim 2, characterized in that, The first parameter includes aspect ratio, longitudinal-to-horizontal ratio, inner diameter ratio, and roundness; the second parameter includes edge angle, roughness, flatness, and overall profile coefficient.

4. The method according to claim 3, characterized in that, The aspect ratio is the ratio of the major and minor axes of the equivalent ellipse of the measured object, with a value ranging from 1.1 to 1.7; the longitudinal aspect ratio is the ratio of the height to the width of the smallest rectangle of the measured object, with a value ranging from 0.3 to 2.0; the inner diameter ratio is the ratio of the radius of the largest circumcircle to the smallest incircle of the particle, with a value ranging from 1.5 to 2.1; and the roundness is the similarity between the shape of the measured object and an ideal circle, with a value ranging from 1.0 to 1.

3.

5. The method according to claim 3, characterized in that, The angularity is the ratio of the perimeter of the smallest circumscribed polygon to the perimeter of the equivalent area ellipse, with a value range of 1.01 to 1.35; the roughness is the square of the ratio of the particle's projected perimeter to the perimeter of the outer polygon, with a value range of 1.01 to 1.05; the flatness is the ratio of the longest dimension to the second longest dimension of the aggregate's projected area, with a value range of 1.25 to 1.45; the overall profile coefficient is the ratio of the circumference of the equivalent area circle to the perimeter of the aggregate's profile, with a value range of 0.90 to 0.

97.

6. The method according to claim 1, characterized in that, The optimal gradation curve for manufactured sand aggregate was obtained by using the Thabo formula for gradation evaluation. The Thabo formula is as follows: In the formula, P i For an aperture of d i The sieve throughput, %; d i denoted as aggregate size (mm); D represents the maximum aggregate size (mm); n represents the experimental index. i This refers to the sieve aperture size.

7. The method according to claim 6, characterized in that, Gradation evaluation parameters The calculation formula is as follows: In the formula, σ represents the deviation between the actual aggregate gradation and the Thabo continuous gradation curve. i For the sampling group, the intermediate pairing should be i Cumulative sieve residue rate at sieve aperture size, %; τ i For the continuous pairing of the Thai wave, i Cumulative sieve residue rate at sieve aperture size, % i The sieve aperture size is 4.75~0 mm.

8. The method according to claim 1, characterized in that, Using gradation evaluation parameters The gradation characteristics of manufactured sand were comprehensively evaluated using the sieve residue curve and the partial sieve residue curve. The content of coarse particle characteristic size was controlled between 48% and 52%, while the content of other particle sizes was controlled between 14% and 16%. These parameters were used to evaluate porosity and gradation. Fit the curve and adjust the gradation based on the fitting results.

9. The method for improving the quality of steam-cured manufactured sand mortar as described in any one of claims 1-8 is applied in the preparation of cement mortar.

10. The application according to claim 9, characterized in that, The cement mortar is prepared in a high temperature and high humidity environment, with the high temperature ranging from 45°C to 60°C and the high humidity being no less than 95%.

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