A machine-made sand concrete containing stone powder and a corresponding mix proportion design method

Abstract

The application relates to the field of concrete design, and particularly discloses a stone powder-containing machine-made sand concrete and a corresponding mix proportion design method. The method comprises the following steps: calculating the dosages of coarse aggregate, fine aggregate and cementitious material of the concrete, adopting a rapid screening mode for the stone powder-containing machine-made sand fine aggregate, measuring the stone powder content of the machine-made sand fine aggregate and adding all the stone powder content into the cementitious material, and replacing part of cement and fly ash and mineral powder to form a cementitious system, wherein 10%-20% of the cement dosage is replaced by cement, and the remaining part is replaced by fly ash and mineral powder; the strength influence coefficient under the specific replacement proportion of the stone powder to the cement is calculated by using a formula gamma Lf =-3.16x2-0.048x+1, the mortar strength of the cementitious system is calculated according to the strength influence coefficient, the water dosage meeting the strength requirement is adjusted and determined, and finally the dosages of all components of the concrete are determined. In the application, the stone powder in the stone powder-containing machine-made sand is used as a cementitious component, efficient resource utilization of the machine-made sand with high stone powder content is realized, the dosages of cement and fly ash are reduced, and the problem of long-term low carbon of the concrete is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of concrete, more particularly, it relates to a stone powder-containing machine-made sand concrete and a corresponding mix proportion design method. BACKGROUND

[0002] In recent years, machine-made sand has been used as the main sand source for concrete. A certain amount of stone powder is inevitably produced in the production process of machine-made sand. When the traditional mix proportion design method is used, the stone powder in the machine-made sand is considered as part of the fine aggregate, which leads to a calculated sand rate greater than the actual sand rate, and the gradation of each component of the concrete is unreasonable. In order to meet the requirements of the workability of the concrete, the total amount of cement or cementitious material is usually increased to improve the workability, which leads to a larger amount of cement or cementitious material in the concrete, which is not conducive to low-carbon environmental protection and is also not conducive to the volume stability of the concrete, resulting in a still severe problem of cracks.

[0003] Machine-made sand, as an important building aggregate, is a rock particle with a particle size of less than 4.75 mm, which is made by mechanical crushing, screening and shaping of parent rock. A large amount of stone powder (usually particles with a particle size of less than 75 μm) is inevitably produced in the production process, especially under the dry production process, the content of stone powder in machine-made sand often exceeds 10%, and even can be as high as 20% or more. The current standard "Standard for Quality and Test Methods of Sand and Stone for Ordinary Concrete" (JGJ52) strictly stipulates that the content of stone powder in machine-made sand for C25 and below strength grade concrete shall not be greater than 10%, and for C30-C55 strength grade concrete, the content of stone powder shall not be greater than 7%. The above provisions are considered by taking the stone powder in machine-made sand as fine aggregate. How to break the contradiction between the existing provisions and the machine-made sand with high stone powder content and the specification, and to realize the reasonable utilization of machine-made sand with stone powder according to the existing technical specification for the mix proportion design and production of concrete is the technical background of the present application.

[0004] At present, the general treatment method for stone powder in machine-made sand in the industry has a fundamental defect, mainly reflected in the following two aspects:

[0005] One is to classify stone powder as "inert mineral admixture": According to the standards such as "Technical Specification for Application of Limestone Powder in Concrete" (JGJ / T 318), the stone powder with a standard active index is often regarded as inert mineral admixture. This method ignores the potential chemical cementitious activity of stone powder and does not calculate its contribution in the cementitious material system. The stone powder that should be included in the cementitious material system is included in other components, so that the calculated sand rate is greater than the actual sand rate, leading to unreasonable gradation of each component of the concrete, and the calculated water-binder ratio is greater than the actual water-binder ratio, resulting in reduced workability of the concrete. In order to meet the workability requirements under the premise of ensuring strength, it is necessary to increase the water consumption (actual slurry under a certain water-binder ratio), resulting in an increase in cement consumption or cementitious material consumption, poor carbon reduction of concrete, an increase in slurry-bone ratio, poor volume stability of concrete, and easy cracking, which seriously affects the durability.

[0006] Two is to forcibly wash away the stone powder as "useless waste": A more conservative and common approach is to flush the machine-made sand at additional cost, water and energy in order to meet the upper limit requirement of stone powder content in the current standard, and discharge the valuable stone powder as "waste mud". This not only causes significant resource waste, but also brings serious environmental burden (such as silt accumulation, water pollution) and economic cost (treatment cost and sand loss).

[0007] Therefore, it is an urgent need to develop a method that can scientifically quantify the cementitious performance of stone powder and guide the precise design and production of machine-made sand concrete with high stone powder content, in order to promote the resource utilization and technology development of the industry. SUMMARY

[0008] To solve the above problems, the present application provides a machine-made sand concrete containing stone powder and a corresponding mix proportion design method.

[0009] The design idea of the present application is as follows: The idea and method of the present application include: calculating the amounts of coarse and fine aggregates and cementitious materials of the concrete, using a rapid screening method for the fine aggregate machine-made sand containing stone powder, determining the stone powder content and counting all the cementitious materials, and replacing part of the cement and fly ash and mineral powder to form a new cementitious system, wherein 10%-20% of the cement is replaced by cement, and the remaining part is replaced by fly ash and mineral powder; using the formula γ Lf =-3.16x²-0.048x+1 to calculate the strength influence coefficient under the specific replacement ratio of cement by stone powder, and calculate the mortar strength of the cementitious system accordingly; adjust the water consumption to meet the strength requirements, and finally determine the amount of each component of the concrete.

[0010] The technical scheme adopted by the present application is as follows:

[0011] In a first aspect, the present application provides a mix proportion design method for machine-made sand concrete containing stone powder, which comprises:

[0012] (1) According to the provisions of the "ordinary concrete mix design regulations" JGJ55, the total mass of coarse aggregate and fine aggregate of the reference concrete, the amount of cementitious material, and the amount of cement, fly ash and slag are determined by absolute volume method;

[0013] (2) The machine-made sand containing stone powder is used as fine aggregate, the content of stone powder in the fine aggregate is determined by sieving, and the stone powder is used to replace part of the cement and / or fly ash and slag in the mix design to form a cementitious system composed of cement, fly ash, slag and stone powder in a specific proportion;

[0014] The stone powder replacement principle is as follows:

[0015] The stone powder in the machine-made sand is used to replace 10%-20% of the amount of cement;

[0016] If there is still stone powder left, the remaining stone powder is used to replace fly ash and slag;

[0017] (3) According to the strength influence coefficient of each component material, the mortar strength of the new cementitious system is calculated, wherein the strength influence coefficient of the stone powder replacing cement is γ Lf The formula is as follows:

[0018] γ Lf = -3.16x 2 - 0.048x + 1 Formula (I)

[0019] In the formula, x is the mass percentage (%) of stone powder replacing cement;

[0020] (4) The water-binder ratio required for concrete preparation strength calculation is calculated: if the water-binder ratio meets the strength requirement, the corresponding water consumption is determined; if it does not meet the requirement, the amount of cementitious material is adjusted, and the calculation is iterated until the water-binder ratio meets the strength requirement;

[0021] (5) The amount of each component per unit volume of concrete is finally determined.

[0022] Further, the machine-made sand containing stone powder described above is derived from common diabase, basalt, dolomite and limestone.

[0023] Further, in the step (2) above, when the stone powder replaces cement in different proportions, the ratio of the strength of the obtained concrete to the strength of the reference concrete meets the following rules:

[0024] When the proportion of stone powder replacing cement is 10% of the theoretical cement amount, the ratio of the strength of the obtained concrete to the strength of the reference concrete is 89.0%-98.0%;

[0025] When the proportion of stone powder replacing cement is 15% of the theoretical cement amount, the ratio of the strength of the obtained concrete to the strength of the reference concrete is 84.5%-96.4%;

[0026] When the proportion of stone powder replacing cement is 20% of the theoretical cement amount, the ratio of the strength of the obtained concrete to the strength of the reference concrete is 80.88%-89.82%.

[0027] Further, in the step (3), on the basis of calculating the strength influence coefficient γ Lf according to the formula, the range of the strength influence coefficient value corresponding to the 95% confidence interval of the stone powder replacement ratio is further introduced.

[0028] Further, in the step (3),

[0029] When the stone powder replacement ratio is 10% of the theoretical cement amount, the 95% confidence interval of the strength influence coefficient γ Lf is 0.912-0.979;

[0030] When the stone powder replacement ratio is 15% of the theoretical cement amount, the 95% confidence interval of the strength influence coefficient γ Lf is 0.848-0.964;

[0031] When the stone powder replacement ratio is 20% of the theoretical cement amount, the 95% confidence interval of the strength influence coefficient γ Lf is 0.805-0.866.

[0032] Further, in the step of determining the specific value of the strength influence coefficient γ Lf , the following steps are further included:

[0033] The stone powder is subjected to negative pressure screening method to determine the mass proportion of the sieve residue of particles above 45 μm;

[0034] If the mass proportion of the sieve residue is less than 10%, the upper limit value of the corresponding confidence interval is taken as γ Lf ;

[0035] If the mass proportion of the sieve residue is 10%-20%, the calculated value according to the formula (I) is taken as γ Lf ;

[0036] If the mass proportion of the sieve residue is greater than 20%, the lower limit value of the corresponding confidence interval is taken as γ Lf .

[0037] Further, in the step (2), the stone powder used to replace fly ash and slag in equal amount has a strength influence coefficient which is the same as that of the replaced fly ash and slag, and the value of the strength influence coefficient is determined according to the provisions of the Design Regulation for Mix Proportion of Ordinary Concrete JGJ 55.

[0038] In a second aspect, the application provides a stone powder-containing machine-made sand concrete prepared according to the above mix proportion design method, which comprises the following components:

[0039] cement, fly ash, slag, water;

[0040] coarse aggregate, stone powder-containing machine-made sand fine aggregate;

[0041] The stone powder in the machine-made sand is part of the cementitious material, which, together with the cement, fly ash and slag, forms a composite cementitious system.

[0042] Further, the stone powder is produced in the process of producing common diabase, basalt, dolomite or limestone machine-made sand and has a particle size of less than 75 μm.

[0043] Further, the 28-day compressive strength of the concrete is not less than 80% of the strength of the reference concrete without stone powder under the same conditions.

[0044] In summary, the application has the following beneficial effects:

[0045] The application first confirms through systematic material analysis (laser particle size analyzer, XRD, mortar test, mercury intrusion analysis) that the stone powder of different rock machine-made sand is not an "inert material", but has a clear cementitious material property. Based on this, the application breaks through the traditional cognition of simply classifying it as "inert admixture" or "waste" in the current standard, and creates a new theory and method of including stone powder as an independent cementitious component in the mix proportion design.

[0046] The application takes the stone powder in the stone powder-containing machine-made sand as a cementitious component and provides a mix proportion calculation process and control parameters, realizing the scientization and precision of the mix proportion design:

[0047] - a clear stone powder replacement rule (preferably replacing 10% to 20% of cement, and the remaining part replacing fly ash and / or slag) is established, and the influence coefficient of the excess stone powder is innovatively linked to the replaced materials (cement, fly ash, slag), solving the core technical problem that machine-made sand with high stone powder content cannot be used for high-performance concrete preparation;

[0048] - a quantitative design method based on the strength influence coefficient is proposed, and the formula γ Lf= -3.16x² - 0.048x+ 1 and the corresponding 95% confidence interval, which can accurately quantify the contribution of stone powder to the strength of concrete;

[0049] The strength influence coefficient based on the particle size (45 μm residue) of stone powder is introduced, which makes the design results more reliable and more in line with the actual situation.

[0050] The application realizes efficient resource utilization of high stone powder content manufactured sand, reduces the amount of cement and fly ash, and solves the problem of long-term low carbon of concrete. The workability, strength and durability of the prepared concrete can be effectively controlled and guaranteed through precise design, and the 28-day compressive strength can reach more than 80% of that of the reference concrete, with stable and reliable performance. The limitation of stone powder content in the current standard is broken, so that high stone powder content manufactured sand can be safely applied to concrete projects with C30 and above strength grade, greatly expanding the resource range and application scenarios of high-quality manufactured sand. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 Figure 1 is a field diagram of the concrete shrinkage test in Test Example 1.

[0052] Figure 2 Figure 2 is a field diagram of the concrete slab cracking test in Test Example 1.

[0053] Figure 3 Figure 3 is a situation diagram of the concrete slab cracking test in Test Example 1.

[0054] Figure 4 Figure 4 is a 7d shrinkage situation diagram of the concrete in Test Example 1.

[0055] Figure 5 Figure 5 is a particle size size analysis diagram of different rock stone powders in Test Example 2: A is a differential distribution curve, and B is an integral distribution curve.

[0056] Figure 6 Figure 6 is an XRD analysis of different rock stone powder mineral components in Test Example 2: A is the XRD diagram of CA (diabase), HC-S1 (dolomite), HC-S2 (limestone), and QH (limestone); B is the XRD diagram of LT-S1 (basalt), LT-S2 (dolomite), LT-S3 (limestone), and SY (limestone).

[0057] Figure 7 Figure 7 is a mortar strength analysis diagram of 8 kinds of stone powder with different replacement ratios in Test Example 3: A is the 3d mortar strength; B is the 7d mortar strength; C is the 28d mortar strength.

[0058] Figure 8The pore size distribution curves of the 8 kinds of stone powder under different replacement ratios in Test Example Three: A is 10% cement replacement ratio; B is 20% cement replacement ratio; C is 30% cement replacement ratio.

[0059] Figure 9 The porosity of the cement-based material under different replacement ratios in Test Example Three.

[0060] Figure 10 The normal distribution graph under different stone powder replacement ratios in Test Example Four: A is 10% cement replacement ratio; B is 15% cement replacement ratio; C is 20% cement replacement ratio.

[0061] Figure 11 The concrete strength influence coefficient curve in Test Example Four.

[0062] Figure 12 The concrete strength influence coefficient curve (95% confidence interval) in Test Example Four. DETAILED DESCRIPTION

[0063] The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. The specific conditions not noted in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer, and the reagents or instruments not noted by the manufacturer are all conventional products that can be purchased on the market.

[0064] The specific embodiments of the present application will be described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0065] EMBODIMENT

[0066] The present embodiment provides a method for designing the mixing proportion of stone powder-containing machine-made sand concrete, which aims to prepare C50 concrete. The method for designing the mixing proportion comprises the following steps:

[0067] (1) According to the provisions of the “Mixing Proportion Design Regulation for Ordinary Concrete” JGJ55, the total mass of the coarse aggregate and the fine aggregate of the reference concrete, the amount of cementitious material, and the amounts of cement, fly ash and mineral powder in the cementitious material are determined by using the absolute volume method, as shown in Table 1:

[0068] Table 1. Theoretical calculation amount of each component of C50 concrete (unit: kg / m 3 )

[0069]

[0070] (2) Select the machine-made sand (derived from diabase) containing stone powder as fine aggregate, fast screening, determine the stone powder content in fine aggregate (710 kg / m 3 ) is 60.9 kg / m 3 ; The stone powder is screened by negative pressure screening method, and the mass fraction of particles above 45 μm is 11.3%.

[0071] (3) The stone powder is used as part of the gel material, which replaces cement, fly ash and mineral powder by 10%, 20% and 11% respectively, and the total amount of fine aggregate is adjusted slightly, and the results are shown in Table 2:

[0072] Table 2. The amount of each component after replacement (unit kg / m 3 )

[0073]

[0074] According to the strength influence coefficient of each component material, the mortar strength of the gel system is calculated, wherein:

[0075] - The strength influence coefficient γ Lf of the stone powder replacing cement is calculated as follows:

[0076] γ Lf = -3.16x 2 - 0.048x + 1 = 0.9636

[0077] In order to reduce the influence of particle size and chemical composition of stone powder on the strength of concrete, when the replacement ratio of stone powder is 10% of the theoretical cement amount, the 95% confidence interval of the strength influence coefficient γ Lf is 0.912-0.979; After negative pressure screening method is performed on the stone powder, the mass fraction of particles above 45 μm is 11.3%, so the calculated value 0.9636 is taken as the final γ Lf ;

[0078] - The strength influence coefficient of the stone powder replacing fly ash is determined according to the provisions of “Ordinary Concrete Mix Design Regulations” JGJ55;

[0079] - The strength influence coefficient of the stone powder replacing mineral powder is determined according to the provisions of “Ordinary Concrete Mix Design Regulations” JGJ55.

[0080] (5) Calculate the water-cement ratio according to the strength of the prepared concrete, determine the corresponding water consumption, and finally determine the amount of each component per unit volume of concrete, as shown in Table 3. The concrete prepared according to the mix ratio is numbered YH-C50.

[0081] Table 3. Mix design of C50 concrete (unit kg / m3 )

[0082]

[0083] The comparative example provides a C50 concrete prepared according to a conventional method of mix proportion design, which considers the stone powder in the stone powder machine-made sand as part of the fine aggregate, and the specific proportion is shown in Table 4, and the number is JZ-C50.

[0084] Test Example One

[0085] Performance tests are conducted on the C50 concrete provided by the examples and comparative examples

[0086] 1. Comparative analysis of components:

[0087] Table 4. Comparative analysis of C50 concrete mix proportion design (unit kg / m 3 )

[0088]

[0089] According to the method of Example 1 of the present application, the stone powder should be all counted into the water-binder ratio calculation, the cement dosage in the single concrete is reduced by 30 kg, the total amount of cementitious materials is reduced by 60 kg, and the paste-aggregate ratio is reduced from the original 0.58 to 0.49.

[0090] 2. Experimental method:

[0091] - NELD-ES731 type series non-contact concrete shrinkage and deformation tester is used to test the early self-shrinkage of concrete, as shown in Figure 1 ;

[0092] - The concrete slab restrained cracking test is carried out according to the Standard Test Methods for Long-term Performance and Durability of Ordinary Concrete (GB / T50082), as shown in Figure 2 .

[0093] 3. Experimental results

[0094] (1) The compressive strength values at different ages are shown in Table 5.

[0095] Table 5. Compressive strength values (MPa) of C50 concrete mix proportion design

[0096]

[0097] The 3d age slab surface cracking of JZ-C50 and YH-C50 two groups of concrete is tracked and observed, and the results are shown in Figure 3 , it is found that the JZ group slab surface appears 2 cracks, the widest part of the crack can reach 0.2 mm, and the YH group surface does not find any visible cracks.

[0098] (2) The results of the concrete shrinkage test are as follows Figure 4 As shown.

[0099] Depend on Figure 4 It can be seen that the shrinkage curves of both JZ-C50 and YH-C50 show a trend of slight expansion followed by shrinkage. Moreover, the shrinkage value increases rapidly in the first 40 hours, and then gradually slows down. When the test time is 40 hours, the shrinkage value of YH-C50 accounts for about 73% of the shrinkage value of JZ-C50. The volume stability of YH-C50 concrete is significantly better than that of JZ-C50 concrete designed using the traditional technical route.

[0100] Experimental Example 2

[0101] This experiment investigated the cementitious properties of stone powder in silty manufactured sand from different rocks.

[0102] 1. Test method:

[0103] (1) Experimental raw materials:

[0104] Stone powder was derived from eight groups of manufactured sand commonly used in engineering, numbered CA (diabase), LT-S1 (basalt), LT-S2 (dolomite), LT-S3 (limestone), SY (limestone), QH (limestone), HC-S1 (dolomite), and HC-S2 (limestone). The manufactured sand was sieved according to the national standard "Sand for Construction" (GB / T14684-2022), and particles smaller than 0.075mm were used as stone powder for research. PO 42.5 / 42.5 ordinary Portland cement was used, fly ash was Grade II fly ash produced by Datang Shenglong Power Plant, mineral powder was S95 grade mineral powder produced by Lizhilin Company, and the sand was ISO standard sand.

[0105] (2) Experimental design

[0106] The influence of stone powder as a cementitious material on concrete strength was investigated according to the "Test Method for Strength of Cement Mortar (ISO Method)" (GB / T 17671-2021). A fly ash substitution test with the same proportion was conducted as a control in the experimental design. To eliminate the influence of factors other than stone powder on the pore structure of cement-based materials, mercury intrusion porosimetry (MIP) specimens were prepared using cement paste with the same water-cement ratio as the mortar. Based on the mortar strength test results and mercury intrusion porosimetry porosity analysis, a reasonable range of stone powder substitution ratios was obtained. Concrete strength tests were conducted at common water-cement ratios of 0.3 and 0.5 with different stone powder dosages, in accordance with the national standard "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019).

[0107] To eliminate the influence of other factors on the strength, the test raw materials were selected with uniform technical parameters, including stone, fly ash, and slag, except for different batches of cement. Since the cement was of different batches, the final strength index was represented by the comparison rate with the benchmark strength value of the control group.

[0108] (3) Mortar and concrete mix proportions

[0109] The mortar test and concrete mix proportions are shown in Tables 6 and 7.

[0110] Table 6. Mortar test mix proportions

[0111]

[0112] Table 7. Concrete mix proportion design

[0113]

[0114] 2. Results and analysis

[0115] 2.1 Particle size analysis

[0116] The particle size of 8 representative stone powders was analyzed by a laser particle size analyzer, and the particle size curve is shown in Figure 5 .

[0117] According to the above test results, the particle size evaluation value D(n) of stone powder and other cementitious materials and the cumulative proportion of different particle sizes were established, as shown in Tables 8 and 9.

[0118] Table 8. Particle size evaluation value of powder (µm)

[0119]

[0120] Table 9. Cumulative proportion of different particle sizes of powder (%)

[0121]

[0122] Based on the above analysis, different machine-made sand stone powders have certain differences in particle size distribution due to different production processes, but the particle size distribution of different rock stone powders is between that of slag and fly ash, indicating that stone powder has the properties of replacing part of cement, fly ash, and slag in terms of particle size distribution.

[0123] According to the "central core hypothesis" model, stone powder can be used as the second level of particle size ≥10 μm sub-central core, and the cement paste is the sub-medium. The cumulative distribution value of all stone powder 45 μm is less than the cumulative value of cement 45 μm, which exactly makes up for the current cement due to the over-fine, resulting in the loss of particle size between 0.075mm~0.045mm, especially the relatively coarse particles such as LT-S1, LT-S2, etc. Therefore, from the size effect, different stone powders meet the properties of "cementitious materials", which can effectively fill the particle size grading loss of the filler below 0.075mm in the concrete component, and better perfect the particle size grading of cementitious materials and optimize the filling effect. Therefore, the appropriate amount of stone powder, cement, fly ash, and slag are combined to form a "stone powder-cement-slag-fly ash" combined cementitious material system, which has better overall particle size grading and better concrete performance.

[0124] 2.2 Chemical composition of different stone powders

[0125] According to the XRD analysis results of different stone powders Figure 6 , different rock stone powders are mainly composed of CaCO3, and the chemical composition of different stone powders is shown in Table 10:

[0126] Table 10. Mineral composition of different stone powders

[0127]

[0128] As can be seen, the common rock stone powder is mainly composed of CaCO3, and the content of Ca(Mg)CO3 and SiO2 has a certain range of variation, but the main chemical composition of CaCO3, Ca(Mg)CO3 and SiO2 has potential hydration activity. In the case of meeting the specific surface area greater than 350m 2 / kg and the existence of alkali or sulfate, it has certain ability to generate hydrated calcium silicate C-S-H.

[0129] 2.3 Specific surface area

[0130] The specific surface area test method and steps of the stone powder refer to the standard "Cement Specific Surface Area Test Method Blaine Method" (GB / T8074-2008), and the results are shown in Table 11.

[0131] Table 11. Specific surface area values (m 2 / kg) of different stone powders

[0132]

[0133] According to the fineness test results, the specific surface area of common machine-made sand stone powder is close to 350m 2 / kg, which makes the stone powder itself have certain activity excitation physical conditions.

[0134] In summary, analysis of the particle size distribution, chemical composition, and fineness of stone powder shows that common stone powder has similar cementitious material properties to other cementitious materials and can be used as a cementitious material to replace part of the cement.

[0135] Experimental Example 3

[0136] This experimental example examines the mortar strength and mercury intrusion porosimetry results under different proportions of stone powder substitution.

[0137] The experimental method for this example is described in Example 2.

[0138] 3.1 Mortar strength

[0139] The strengths of mortar specimens at 3d, 7d, and 28d under different stone powder substitution ratios of 0%, 10%, 20%, 30%, and 40% are as follows: Figure 7 As shown.

[0140] As can be seen from the 3D strength measurement ( Figure 7 A) The average strength of the specimens with a 10% replacement ratio is about 10% to 15% higher than the baseline strength of the same age without stone powder; the average strength of the specimens with a 20% replacement ratio is slightly lower than the baseline strength of the specimens without stone powder, by about 5%; the average strength of the specimens with 30% and 40% replacement ratios is even lower than the baseline strength of the specimens without stone powder, by about 0% to 30%; the 3-day strength of the specimens with stone powder varies depending on the type of stone powder in each different dosage range. The 3-day strength of the stone powder mortar specimens with the same replacement ratio as fly ash shows a greater decrease, indicating that the contribution of stone powder to the strength of concrete at 3 days is much greater than that of fly ash.

[0141] The strength was determined by the 7-day strength test. Figure 7 (B) The average strength of concrete with a 10% replacement ratio was about 10% higher than the baseline strength of concrete without stone powder at the same age; the average strength of concrete with a 20% replacement ratio was further reduced, by about 15% to 25%; the average strength of concrete with 30% and 40% replacement ratios was even more significantly reduced than the baseline strength of concrete without stone powder, by about 25% to 45%; the strength of the stone powder-containing test blocks at 7 days varied depending on the type of stone powder within each different dosage range. The strength of the fly ash-containing test blocks at 7 days with the corresponding replacement ratio was close to the lower limit of the strength range of mortar with stone powder at the same age, indicating that the contribution of stone powder to the strength of concrete at 7 days was greater than that of fly ash.

[0142] The strength was determined by the 28-day strength test. Figure 7C), the average value of the strength of the 10% replacement ratio is slightly reduced by about 5% compared with the reference strength value without stone powder at the same age; the average value of the strength of the 20% replacement ratio is further reduced by about 10% to 15% compared with the reference strength value without stone powder; the average value of the strength of the 30% and 40% replacement ratios is more greatly reduced by about 30% to 45% compared with the reference strength value without stone powder; the strength of the 28d test block of each different replacement ratio interval is different due to the different types of stone powder. The 28d mortar strength value of the fly ash corresponding to the same replacement ratio is close to the average value of the mortar strength of each interval with stone powder at the same age, which indicates that the average contribution of different stone powders to the strength of concrete at 28d is consistent with that of fly ash.

[0143] In combination with the foregoing Figure 5 It can be seen that the particle size of stone powder is an important factor affecting the upper and lower limits of each interval. The particle size of stone powder is relatively small compared with cement or fly ash. At 10% and 20% replacement ratios, the 3d and 7d strengths are basically in the upper limit range of each interval, but at 30% and 40% replacement ratios, the 3d and 7d strengths are not significantly affected by the particle size fineness. At 10% and 20% replacement ratios, the particle size distribution fineness has a greater impact on the 28d test block strength, but at 30% and 40% replacement ratios, the 28d strength is not significantly affected by the particle size fineness. Secondly, for stone powders that meet a certain fineness, chemical composition is another important factor affecting the upper and lower limits of each interval.

[0144] 3.2 Mercury intrusion test analysis

[0145] The 28d paste test block pore size distribution and porosity results of fly ash, mineral powder and different rock mechanism sand stone powders in engineering under the same replacement ratio of 0%, 10%, 20%, 30% replacement of cement are shown in Figure 8 .

[0146] Under the conditions of 10%, 20% and 30% replacement ratios, the pore size differential distribution curves of the paste test blocks of different stone powders are higher than the differential distribution curves of the reference test blocks without stone powder, which indicates that the pores in the cement-based paste material containing stone powder are greatly increased, resulting in a reduction in the strength of the concrete. Therefore, there is an upper limit value for the content of stone powder to ensure the quality of the concrete.

[0147] From Figure 9It can be seen that the average porosity of all cement pastes containing stone powder in the interval section under the replacement ratios of 10%, 20%, and 30% is 19.86%, 19.89%, and 21.73%, respectively. Therefore, compared with the average porosity under the replacement ratio of 10%~20%, the average porosity under the replacement ratio of 20%~30% is larger, and the porosity of each stone powder in the interval section of 30% replacement ratio is larger. Considering the strong correlation between the strength of concrete and porosity, it can be considered that when the replacement ratio of stone powder is greater than 20%, it is not conducive to the development of strength, which also conforms to the rule that the strength of mortar test block under the replacement ratio of 30% and 40% stone powder decreases more than the reference strength.

[0148] The sand usage in the common concrete mix proportion is between 800kg / m 3 ~1000kg / m 3 The national standard "Sand for Building" (GB / T14684-2022) stipulates that the stone powder content in machine-made sand should not exceed 15%, so the maximum content of stone powder in single concrete is between 120kg / m 3 ~150kg / m 3 Considering stone powder as cementitious material, the optimal replacement ratio of stone powder in machine-made sand that meets the strength and workability is between 8%~22% of the cement mass.

[0149] Combining the strength of mortar under different replacement ratios and mechanism analysis, the stone powder in different rock machine-made sand in engineering can be considered as cementitious material. Therefore, the content of stone powder in machine-made sand should be considered in the design of concrete mix proportion, and the cement dosage should be deducted by "the optimal replacement ratio of cement". Replacing 10%~20% of cement can meet the strength, workability, and other properties of concrete. If the content of stone powder in machine-made sand exceeds the above range, the excess part can be considered to replace part of fly ash or mineral powder.

[0150] Test Example Four

[0151] This test example investigates the influence coefficient of different stone powders on the strength of concrete under different replacement ratios

[0152] 4.1 Parameter Analysis

[0153] According to the common 9 groups of stone powder, each group is replaced with cement according to the replacement ratio of 10%, 15%, and 20%, respectively, to obtain the strength value of concrete.

[0154] Combining the strength data of 10%, 15%, and 20% mortar test and the strength data of concrete, 24 data in each group under the replacement ratio of 10% and 20% are taken as random samples, and 16 data in each group under the replacement ratio of 15% are taken as random samples. According to the replacement ratio of different stone powders, the respective probability density distribution graph can be obtained (Fig. Figure 10 ).

[0155] The normal distribution of different stone powder replacement ratios has two parameters: mean and standard deviation. The mean parameter represents the average level of concrete strength under the same stone powder replacement ratio, while the standard deviation parameter represents the homogeneity of concrete strength under the same stone powder replacement ratio. The better the homogeneity, the smaller the standard deviation, and the curve exhibits a "tall and thin" distribution, meaning that all values ​​are concentrated around the mean, and the dispersion is smaller. Figure 10 It can be seen that the distribution of the histogram of the ratio of the test strength to the reference strength of stone powder under each substitution ratio is well fitted with the probability distribution curve. It can be considered that the distribution of the ratio of the test strength to the reference strength of stone powder under each substitution ratio conforms to the normal distribution curve.

[0156] 4.2 Normal Distribution Model Analysis

[0157] The concrete strengths under different replacement ratios of 10%, 15%, and 20% stone powder were obtained and the normal model was verified. The corresponding average value, standard deviation, and quantile at the 95% probability were calculated based on the data, as shown in Table 12.

[0158] Table 12. Parameter values ​​of the normal distribution model

[0159]

[0160] Experimental data analysis shows that when the stone powder replacement ratio is 10%, the ratio of concrete strength to the benchmark strength is 89.0%~98.0%; when the stone powder replacement ratio is 15%, the ratio of concrete strength to the benchmark strength is 84.5%~96.4%; and when the stone powder replacement ratio is 20%, the ratio of concrete strength to the benchmark strength is 80.88%~89.82%.

[0161] 4.3 Strength Influence Coefficient

[0162] The strength influence coefficient of stone powder is obtained by normalizing the strength test results of concrete of different strength grades under different substitution ratios, resulting in a strength influence coefficient curve. Figure 11 As the proportion of stone powder replacement increases, the overall compressive strength of concrete shows a decreasing trend. Regression analysis of the data yields the expression (I) for the strength influence coefficient under different stone powder replacement proportions:

[0163] γ Lf = -3.16x 2 - 0.048x + 1 Equation (I)

[0164] In the formula, x is the mass percentage (%) of stone powder replacing cement;

[0165] The formula can provide quantitative reference for the influence of different replacement ratios of stone powder on the strength of concrete. According to the strength influence coefficient expression (I), the strength influence coefficients of stone powder under the replacement ratios of 10%, 15% and 20% are obtained, and the results are shown in Table 13.

[0166] Table 13. Strength influence coefficients of stone powder under different dosages

[0167]

[0168] Considering the influence of the particle size and chemical composition of stone powder on the strength, the 95% confidence interval strength influence coefficient values corresponding to the dosages of 10%, 15% and 20% of stone powder are calculated and an envelope diagram is made (Fig. 4.3), Figure 12 The calculation results of the strength influence coefficient confidence interval are shown in Table 14.

[0169] Table 14. Strength influence coefficients of stone powder under different dosages

[0170]

[0171] 4.4 Upper and lower limit determination and influence

[0172] According to the results in Table 14, the strength influence coefficient value intervals under the replacement ratios of 10%, 15% and 20% of stone powder are formed, as shown in Table 15.

[0173] Table 15. Strength influence coefficients of stone powder under different dosages

[0174]

[0175] Because the activity of stone powder needs to reach 350 m 2 / kg and above and there is alkali or sulfate, it has the ability to generate hydrated calcium silicate C-S-H, so according to the results of the mortar test, under the premise of a certain replacement ratio, the influence of stone powder on the strength of cement-based materials mainly depends on the particle size or fineness of stone powder, so whether it is calcareous or siliceous stone powder, the determination of the upper and lower limits of the 28d strength influence coefficient is mainly based on the particle size of stone powder. The fineness analysis of different stone powders can refer to the negative pressure screening method in the standard “Cement Fineness Test Method - Sieving Method” (GB / T 1345-2005), and the stone powder residue data are shown in Table 16.

[0176] Table 16. Mass percentage of 45 μm and above sieve residue (%)

[0177]

[0178] The size of the mass percentage of particles above 45 μm in the sieve residue obtained by negative pressure screening can be used to determine the upper and lower limit values. When it is less than 10%, the upper limit value of the stone powder influence coefficient calculated according to the strength influence coefficient formula in this paper can be taken; when it is between 10-20%, the calculated value of formula (I) can be directly taken as the stone powder influence coefficient; when it is greater than 20%, the lower limit value of the stone powder influence coefficient obtained according to the formula can be taken.

[0179] 4.5 Verification of strength influence coefficient expression

[0180] Randomly select five kinds of stone powder of different rock types and different batches from the same manufacturer, randomly select two common C30 and C50 mix proportions, maintain the consistency of the selected mix proportion materials, and randomly conduct 28d concrete strength test according to 10%, 15% and 20% replacement ratio, compare and analyze the calculated value and experimental value of formula (I), and the results are shown in Table 17.

[0181] Table 17. Evaluation and analysis of influence coefficient

[0182]

[0183] As can be seen from the table, the ratio of the calculated value to the test value fluctuates around 1.0, the calculation result is in good agreement with the test result, the mean and standard deviation of the ratio of the calculated value to the test value are 1.03 and 0.12 respectively, which shows that the strength influence coefficient expression based on regression analysis has good prediction accuracy and applicability, and can be used to calculate the influence of 10%-20% stone powder content on the strength of concrete.

[0184] This specific embodiment is only an explanation of the present application, and is not a limitation of the present application. Those skilled in the art can make modifications to the present embodiment without creative contribution after reading the present specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A method for designing the mix proportion of manufactured sand concrete containing stone powder, characterized in that, It includes: (1) According to the provisions of the "Specification for Mix Proportion Design of Ordinary Concrete" JGJ55, the total mass of coarse and fine aggregates and the amount of cementitious materials in the reference concrete are calculated and determined by the absolute volume method, and the amount of cement, fly ash and mineral powder in the cementitious materials are determined respectively. (2) Using manufactured sand containing stone powder as fine aggregate, the stone powder content in the fine aggregate is determined by sieving, and stone powder is used to replace part of cement and / or fly ash and mineral powder in the mix proportion calculation to form a new type of cementitious system composed of cement, fly ash, mineral powder and stone powder in a specific proportion. The principle of stone powder substitution is as follows: stone powder in manufactured sand is used to replace 10%-20% of the cement dosage; if there is any stone powder left over, the remaining stone powder is used to replace fly ash and mineral powder. (3) calculating the mortar strength of the new cementitious system in accordance with the strength influence coefficient of each component material, wherein the strength influence coefficient γ of the stone powder replacing cement Lf is calculated as follows: gamma Lf = -3.16x 2 -0.048x + 1 Equation (I) In the formula, x is the mass percentage (%) of stone powder replacing cement; (4) Calculate the required water-cement ratio based on the concrete mix strength: If the water-cement ratio meets the strength requirements, determine the corresponding water consumption; if not, readjust the amount of cementitious material and iterate until the water-cement ratio meets the strength requirements. (5) Determine the final dosage of each component in the unit volume of concrete; In the step (3), in order to further take the influence of the particle size and chemical composition of the stone powder on the strength of the concrete into the calculation system, on the basis of calculating the strength influence coefficient γ Lf according to the formula I, the strength influence coefficient value range corresponding to the 95% confidence interval of the stone powder replacement ratio is also introduced. When the replacement ratio of stone powder is 10% of the theoretical cement consumption, the strength influence coefficient γ Lf of the 95% confidence interval is 0.912-0.979; When the replacement ratio of stone powder is 15% of the theoretical cement consumption, the strength influence coefficient γ Lf of the 95% confidence interval is 0.848-0.964; When the replacement ratio of stone powder is 20% of the theoretical cement consumption, the strength influence coefficient γ Lf of the 95% confidence interval is 0.805-0.866; The determination of the specific value of the intensity influence coefficient γLf also includes the following steps: The stone powder was subjected to negative pressure sieving to determine the proportion of sieve residue of particles larger than 45μm. If the mass percentage of the sieve residue is less than 10%, the upper limit value of the corresponding confidence interval is taken as γ Lf ; If the percentage of the sieve residue is 10%-20%, then the value calculated according to formula (I) is taken as γ. Lf ; If the percentage of the sieve residue is greater than 20%, then the lower limit of the corresponding confidence interval is taken as γ. Lf .

2. The method for designing the mix proportion of manufactured sand concrete containing stone powder according to claim 1, characterized in that, The manufactured sand containing stone powder is derived from common diabase, basalt, dolomite, and limestone.

3. The mix design method for manufactured sand concrete containing stone powder according to claim 1, characterized in that, In step (2), when stone powder replaces cement in different proportions, the ratio of the strength of the resulting concrete to the strength of the reference concrete follows the following rule: When the proportion of stone powder replacing cement is 10% of the theoretical cement content, the strength of the resulting concrete is 89.0%-98.0% of the strength of the reference concrete. When the proportion of stone powder replacing cement is 15% of the theoretical cement content, the strength of the resulting concrete is 84.5%-96.4% of the strength of the reference concrete; when the proportion of stone powder replacing cement is 20% of the theoretical cement content, the strength of the resulting concrete is 80.88%-89.82% of the strength of the reference concrete.

4. The mix design method for manufactured sand concrete containing stone powder according to claim 1, characterized in that, In step (2), the strength influence coefficient of the stone powder used to replace fly ash and mineral powder in equal amounts is the strength influence coefficient corresponding to the replaced fly ash and mineral powder. The value of the strength influence coefficient is determined in accordance with the provisions of the "Specification for Mix Proportion Design of Ordinary Concrete" JGJ 55.

5. A type of manufactured sand concrete containing stone powder, prepared according to the mix design method of any one of claims 1-4, characterized in that, It includes the following components: cement, fly ash, mineral powder, and water; Coarse aggregate and manufactured sand fine aggregate containing stone powder; wherein, the stone powder in the manufactured sand is part of the cementitious material, which together with cement, fly ash and mineral powder constitutes a composite cementitious system.

6. The stone powder-containing manufactured sand concrete according to claim 5, characterized in that, The stone powder is derived from powder with a particle size of less than 75μm produced during the production of manufactured sand from common diabase, basalt, dolomite, or limestone.

7. The stone powder-containing manufactured sand concrete according to claim 5, characterized in that, The 28-day compressive strength of the concrete shall not be less than 80% of the strength of the benchmark concrete without stone powder under the same conditions.

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