Special silicon sand for cement strength detection

Abstract

This invention discloses a special silica sand for cement strength testing, belonging to the technical field of standard materials for cement performance testing. It is suitable for non-ISO method cement mortar strength testing, requiring no additional components and made solely from natural siliceous mineral particles through physical processing. This silica sand achieves uniform performance through precise control of chemical composition, continuous three-gradation particle design, physical properties, and stability indicators, relying on a fully physical preparation process, thus avoiding the defects of existing technologies and the limitations of ISO standards. Through quantitative indicators and dedicated testing methods, it optimizes particle sphericity, surface roughness, and packing characteristics, improving the interfacial bonding force with cement paste and the density of the mortar. This invention solves the problems of large testing deviations, poor adaptability, and unstable performance of existing silica sand, making it suitable for testing various grades of cement, significantly improving the accuracy and repeatability of test results, facilitating industrial production and control, and showing broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of standard materials for cement performance testing, specifically a special silica sand for cement strength testing. It is suitable for non-ISO method cement mortar flexural and compressive strength testing scenarios, and can accurately match the strength testing requirements of different grades of cement, improving the stability and repeatability of test results. Background Technology

[0002] Cement strength is a core indicator for evaluating cement quality grade, and the accuracy of its test results directly determines the application range and safety of cement products. In the cement strength testing process, silica sand, as a key aggregate in mortar preparation, has a significant impact on the mortar's setting and hardening process and strength performance due to its chemical composition, particle size distribution, and physical properties.

[0003] In existing technologies, silica sand used for cement strength testing often suffers from the following drawbacks: some silica sands are designed using the composition and gradation of ISO standard sand, which limits their applicability and makes them susceptible to revisions of international standards; non-ISO standard silica sands generally exhibit large fluctuations in chemical composition. Issues such as insufficient purity and poor particle size distribution continuity lead to significant deviations in test results for the same cement sample under different batches of silica sand, failing to meet the requirements for high-precision testing. Furthermore, existing silica sands have not been optimized for the physical properties of cement hydration reactions; parameters such as particle sphericity and surface roughness are unreasonable, affecting the interfacial bonding strength and thus interfering with the accuracy of strength testing. In addition, current technologies lack quantitative indicators and control methods for the compatibility of silica sand properties with cement strength testing, making it difficult to achieve a precise match between silica sand properties and testing requirements.

[0004] Therefore, developing a special silica sand that circumvents ISO standards, has stable performance parameters, is precisely compatible with cement testing, and has clear quantitative control indicators is key to solving the current problem of insufficient accuracy in cement strength testing. Summary of the Invention

[0005] The purpose of this invention is to provide a special silica sand for cement strength testing, which circumvents the design of ISO standards. By precisely controlling the chemical composition, particle size distribution, physical properties and stability indicators of the silica sand, it solves the problems of large testing deviation, poor adaptability and unstable performance of existing silica sand, and achieves high precision and high repeatability of cement strength testing results. Moreover, it does not require the addition of any additional components, but only relies on the performance optimization of the silica sand itself to meet the testing requirements.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a special silica sand for cement strength testing, wherein the silica sand contains no additional additives and is made solely from natural siliceous mineral particles through physical processing. The mass fraction is strictly controlled at ≥99.2%, the total mass fraction of impurities is ≤0.8%, and the mass fraction of each impurity component is further precisely limited to [specific values ​​to be filled in]. ≤0.15%, ≤0.30%, ≤0.12%, ≤0.08%, + ≤0.10%, loss on ignition ≤0.05%, and no other unmentioned impurities. Chemical quantitative analysis was used to sample and test the composition at at least three points for each batch of silica sand to ensure chemical stability. The formula for calculating the composition fluctuation coefficient is as follows (1): = (Maximum mass fraction of this component in the same batch of silica sand - minimum mass fraction of this component) / Average mass fraction of this component × 100%, and the fluctuation coefficient of each component. With a content of ≤0.5%, and through strict component control and fluctuation management, the composition design system of ISO standard sand is completely bypassed, making it suitable for non-ISO method cement strength testing. This effectively avoids interference from impurities and compositional fluctuations on the cement hydration reaction, ensuring the consistency of chemical composition in each batch of silica sand. This provides a stable material basis for cement strength testing, significantly reduces test result deviations caused by differences in silica sand composition, and improves the reliability of test data.

[0007] Furthermore, a continuous three-gradation particle design is adopted, with the particle size range strictly limited to 0.15-1.18 mm. No particles larger than 1.18 mm or smaller than 0.15 mm are present. The particle size range and corresponding mass fraction percentage of each gradation are precisely controlled as follows: fine gradation (0.15-0.30 mm) 32%-35%, medium gradation (0.30-0.60 mm) 40%-43%, and coarse gradation (0.60-1.18 mm) 22%-25%. The sum of the mass fractions of the three gradations is strictly equal to 100%, with no deviation in gradation ratio. Equation (2) is adopted. Calculate the gradation uniformity coefficient, where The particle size when the cumulative mass fraction reaches 60%. The particle size when the cumulative mass fraction reaches 10% is the particle size in this invention. Strictly controlled within the range of 1.8-2.2, each grade of particle size is precisely screened and mixed using a standard sieve grading method to ensure continuous, uniform gradation without any discontinuities. This continuous and uniform three-gradation design optimizes the silica sand packing structure, reduces internal voids in the mortar, and allows the cement paste to fully fill the gaps between particles. This avoids the uneven mortar structure caused by gradation dispersion in existing technologies, improves the overall density of the mortar, ensures that cement strength test results accurately reflect the cement's inherent properties, and enhances the repeatability of test data from different batches.

[0008] Furthermore, the sphericity of silica sand particles ≥0.82, the image analysis method was used for determination. Specifically, at least 500 random particles in each batch of silica sand were projected using a high-definition image acquisition device. Particles that were broken or had excessively sharp edges were excluded. The sphericity of each individual particle was calculated and the average value was taken as the final test result. The formula for calculating sphericity is shown in formula (3): Where A is the projected area of ​​the particle. This refers to the projected perimeter of the particles. By precisely controlling the sphericity parameter, the porosity during mortar preparation can be reduced, improving the density of the mortar structure. It also avoids insufficient interfacial bonding between silica sand and cement paste caused by excessive sphericity, accurately matching the interfacial requirements of cement hydration and ensuring a stable bond between silica sand and cement paste. Reasonable sphericity balances mortar porosity and interfacial bonding force, avoiding stress concentration within the mortar due to irregular particle morphology, reducing the randomness of specimen fracture during testing, and further improving the accuracy and stability of cement strength testing results.

[0009] Furthermore, the surface roughness of silica sand particles The roughness is controlled within the range of 0.8-1.2 μm, and is measured using a laser roughness meter. The measurement range covers different areas such as the top, sides, and bottom of the silica sand particles. At least three test points are selected for each particle, and at least 30 particles are selected for testing from each batch of silica sand. The average value of all test points is taken as the final result. This roughness range is precisely calculated to ensure that the silica sand particles form a good mechanical interlock and interfacial bond with the cement paste. This avoids the problems of weak bonding and easy peeling caused by insufficient roughness, while preventing the problems of stress concentration and easy cracking of the specimen caused by excessive roughness. It ensures that the mortar strength can truly reflect the performance of the cement itself during the test, without being affected by the surface condition of the silica sand. Precise surface roughness control provides a guarantee for the interfacial bonding between silica sand and cement paste, making the overall strength of the mortar more stable, reducing the test deviation caused by interfacial bonding problems, adapting to the hydration characteristics of different grades of cement, and broadening the application range of silica sand.

[0010] Furthermore, the true density of silica sand The density should be controlled between 2.64-2.66 g / cm³, representing the natural bulk density. =1.65-1.72 g / cm³, tapped bulk density =1.80-1.88 g / cm³, the true density was determined using the volumetric flask method, and the bulk density was determined using a standard volumetric container. Formula (4) was used. Calculate the natural packing porosity. =34%-38%, using formula (5) Calculate the vibratory compaction porosity. =29%~32%. By precisely controlling the bulk density and porosity parameters, a reasonable and stable space is provided for the cement paste filling, ensuring that the mortar forms a uniform and dense structure after setting and hardening. This avoids the problem of low mortar strength due to excessive porosity or insufficient filling of the cement paste due to insufficient porosity, thus improving the repeatability of strength test results. Stable bulk density and porosity ensure that the preparation state of each batch of mortar is consistent, reducing test fluctuations caused by differences in material packing states, providing a uniform material environment for cement strength testing, and further improving the comparability of test data.

[0011] Furthermore, the moisture content of the silica sand is ≤0.1%. The drying and weighing method is used for determination. During the determination, 500g of silica sand sample is accurately selected, spread evenly in a drying tray, and dried at 105±5℃ for 2h. After being taken out, it is placed in a desiccator to cool to room temperature and then weighed. The formula for calculating the moisture content is shown in formula (6): ,in For the quality of silica sand before drying, To ensure the quality of the dried silica sand, at least two parallel tests were conducted on each batch of samples, and the average value was taken as the final moisture content. Strict control of the moisture content effectively avoids interference from additional moisture in the silica sand on the water-cement ratio of the cement mortar, ensuring accurate and controllable water-cement ratio during testing. This avoids the problems of abnormal cement hydration rate and excessive deviation in mortar strength caused by moisture content fluctuations in existing technologies. Extremely low and stable moisture content ensures the accuracy of cement mortar preparation parameters, allowing the cement hydration reaction to proceed according to the preset state, reducing testing errors caused by moisture interference, and ensuring that the test results truly reflect the strength performance of the cement.

[0012] Furthermore, the abrasion rate of the silica sand is ≤0.25%, measured using a Los Angeles abrasion tester. During the test, 1000g of silica sand sample is placed in the tester cylinder, and a specified number of steel balls are added. After completing the abrasion test according to the set rotation speed and abrasion time, particles smaller than 0.15mm are removed by sieving through a standard sieve. The ratio of the sample mass difference before and after abrasion to the initial mass is calculated as the abrasion rate. Simultaneously, the particle size distribution of each grade of particles after abrasion is detected to ensure that the particle size change rate after abrasion is ≤0.3%. By strictly controlling the abrasion rate and particle size change rate, the particle morphology and gradation of the silica sand remain stable during the testing process, preventing secondary impurities from being generated due to stirring, compaction, or other operations. This avoids impurity contamination of the mortar system and ensures the accuracy of the test results. Excellent abrasion resistance allows the silica sand to maintain its original properties throughout the testing process, avoiding the impact of particle breakage and gradation changes on the mortar structure and strength. This ensures that each test is based on stable silica sand performance, improving the reliability and repeatability of the test data.

[0013] The preparation process of this silica sand includes six steps in sequence: screening of silica raw materials, crushing, grading and screening, purification, drying, and performance calibration. Only silica raw material screening is performed. The raw materials are natural silica with a mass fraction ≥99.5%, excluding those with excessive impurities. The crushing stage employs a multi-stage crushing process to avoid excessive particle crushing and the generation of fine dust. The grading and screening stage uses precise grading equipment to ensure that the particle size and proportion of each grade meet the standards. The purification step uses a physical purification method, employing a combination of scrubbing, gravity separation, and magnetic separation to remove surface-adhered impurities, high-density impurities, and ferromagnetic impurities from the raw materials. No chemical purification reagents are used throughout the process to avoid interference from residual chemicals in the test results. The drying step uses a segmented drying process: first drying at 80±5℃ for 1 hour to remove surface moisture, then raising the temperature to 105±5℃ for 1 hour to remove internal moisture, ensuring that the moisture content meets the standards and that the particle morphology does not change. In the performance calibration stage, each batch of silica sand undergoes full-index testing; unqualified products are prohibited from leaving the factory. The all-physical preparation process avoids chemical contamination, segmented drying and precise grading ensure stable silica sand performance, and multi-step quality control enables industrial-scale mass production with high performance consistency across batches, meeting the material requirements for large-scale cement testing.

[0014] Furthermore, this silica sand is suitable for strength testing of cement mortars using non-ISO methods. It is widely applicable to the strength testing of general-purpose Portland cements of grades 42.5, 52.5, and 62.5, as well as special cements used in fields such as roads and nuclear power. During the mortar preparation process, the mass ratio of silica sand to cement is strictly controlled at 2.5:1, and the water-cement ratio is precisely set between 0.44 and 0.48 according to the cement type. For general-purpose Portland cement, the water-cement ratio is 0.46, while for special cement, the water-cement ratio is adjusted within a range according to its hydration characteristics. When mixing silica sand with cement and water, a dedicated mixing equipment is used, with the mixing time controlled at 120-180 seconds. This includes 30 seconds of low-speed mixing followed by 90-150 seconds of high-speed mixing, with a mixing speed of 300±20 r / min. This ensures that the silica sand and cement paste are fully and uniformly mixed without particle agglomeration, fully leveraging its testing compatibility advantages. Its advantages lie in its compatibility with various types of cement testing. It can complete the strength testing of different grades and types of cement without changing the silica sand, simplifying the testing process, unifying the testing material standards, and the precise mortar preparation parameters can be perfectly matched with the performance of silica sand, further improving the accuracy of the test results.

[0015] Furthermore, each batch of silica sand undergoes comprehensive performance testing before leaving the factory. The testing strictly covers chemical composition, particle size distribution, sphericity, surface roughness, bulk density, moisture content, and abrasion rate. All indicators must meet the limits specified in claims 1-7, with no indicators exceeding the limits. After passing the tests, the sand is packaged in double-layer sealed moisture-proof packaging: an inner waterproof and breathable membrane and an outer wear-resistant woven bag. The packaging specifications are 25kg / bag and 1355g smaller packages for easy storage and retrieval. The silica sand storage environment must meet the requirements of a temperature of 5-35℃ and a relative humidity of ≤60%, avoiding direct sunlight and humid environments. The shelf life is 12 months. Regular sampling inspections are conducted during storage to ensure the silica sand's performance remains stable, without moisture absorption, clumping, or compositional changes. It can be used directly for testing without additional treatment before use. The comprehensive factory testing and sealed storage design ensure stable silica sand performance from production to use, eliminating the need for additional pretreatment steps, saving testing preparation time. Standardized packaging facilitates management and batch use, meeting the needs of laboratory and industrial testing scenarios.

[0016] This invention provides a special silica sand for cement strength testing, which has the following beneficial effects: 1. Completely bypassing ISO standard design, it forms a dedicated silica sand system for cement strength testing through precise quantification of chemical composition, particle size distribution, physical properties and stability indicators, solving the problems of poor compatibility and large testing deviation of existing silica sand. All parameters are different from existing technologies and have no overlap. 2. No additional ingredients are required. The performance of silica sand is optimized solely through its own properties. Physical purification and grading processes ensure stable performance, avoiding interference from chemical additives on test results and reducing preparation costs. 3. Provides complete quantitative formulas and testing methods, clarifies the control range and calculation method of each indicator, facilitates industrial production and quality control, ensures high consistency of silica sand performance in each batch, long shelf life, and convenient storage and transportation. 4. It is compatible with non-ISO method strength testing of various grades of cement, improving the accuracy and repeatability of test results, providing reliable material support for cement quality evaluation, and has broad application prospects. Attached Figure Description

[0017] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the preparation process of silica sand for cement strength testing according to the present invention. Figure 2 This is a flowchart of the full performance testing process for the special silica sand of this invention; Figure 3 This is a flowchart illustrating the application of the special silica sand for cement strength testing in this invention. Detailed Implementation

[0019] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses consistent with some aspects of this disclosure as detailed in the appended claims.

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] How to use: Pre-use verification of silica sand: Before use, it is necessary to verify whether the silica sand meets the composition requirements to ensure... The mass fraction is ≥99.2%, the total mass fraction of impurities is ≤0.8%, the fluctuation coefficient of each component is ≤0.5%, and there are no additional impurities mixed in. At the same time, it is confirmed that the silica sand packaging is intact, meets the sealing standard of claim 10, the storage environment meets the requirements of temperature 5-35℃, relative humidity ≤60%, shelf life is within 12 months, there is no moisture absorption or clumping, and it can be used without additional pretreatment.

[0022] Silica sand gradation confirmation: According to the gradation standard, the silica sand is confirmed to be a continuous three-gradation of 0.15-1.18mm, with the proportions of fine, medium, and coarse gradations conforming to the ranges of 32%-35%, 40%-43%, and 22%-25%, respectively. The gradation uniformity coefficient is [not specified]. Between 1.8 and 2.2, there are no particles with a diameter exceeding the specified range, ensuring a uniform packing structure.

[0023] Physical property verification: Rapidly verify the physical properties of silica sand, including sphericity ≥ 0.82 and surface roughness. Between 0.8 and 1.2 μm, the natural bulk density is 1.65-1.72 g / cm³, the vibrated bulk density is 1.80-1.88 g / cm³, and the packing porosity is within the corresponding range, ensuring compatibility with cement paste.

[0024] Moisture content and abrasion rate inspection: The moisture content was checked by drying and weighing to ensure it was ≤0.1% to avoid interfering with the water-cement ratio; the abrasion rate of the silica sand was confirmed to be ≤0.25%, the particle shape was stable, there was no breakage or change in gradation due to transportation or storage, and no secondary impurities were generated.

[0025] Mortar preparation ratio control: The ratio is determined according to the type of cement. The mass ratio of silica sand to cement is fixed at 2.5:1. The water-cement ratio of general silicate cement is 0.46, and the water-cement ratio of special cement is adjusted within the range of 0.44-0.48. The non-ISO method testing requirements are strictly followed.

[0026] Mixing operation specifications: Use dedicated mixing equipment and control according to parameters. First, mix at low speed for 30 seconds, then mix at high speed for 90-150 seconds, with a total mixing time of 120-180 seconds and a mixing speed of 300±20 r / min. This ensures that the silica sand is fully mixed with cement and water, without particle agglomeration, and gives full play to the interfacial bonding advantages of silica sand.

[0027] Specimen preparation and curing: The well-mixed mortar is poured into the mold. During compaction, the stable packing properties of the silica sand are utilized to ensure the specimen is dense and uniform, avoiding internal stress concentration. Curing is performed according to non-ISO methods to ensure a stable curing environment and fully demonstrate the inherent strength properties of the cement.

[0028] Post-test silica sand treatment: Any silica sand remaining after a single test must be sealed and placed in the specified environment according to storage standards to prevent moisture absorption and deterioration. It can be used for parallel tests of the same type of cement, but the moisture content and particle morphology must be checked again to ensure that the indicators still meet the requirements.

[0029] Batch usage control: When using in batches, the performance calibration report of each batch of silica sand must be checked to ensure that the preparation process is compliant and all indicators meet the standards. The packaging specifications are uniformly 25kg / bag and small package of 1355g to facilitate accurate measurement of usage. At the same time, usage records should be kept to ensure traceability of testing.

[0030] This method fully conforms to the indicators of each claim, avoiding the problems of poor compatibility of silica sand and non-standard operation in the prior art. The process is simple and conforms to the actual testing scenario. It does not require complex data calculation. The testing advantages of special silica sand can be brought into play simply by verifying the indicators and standardizing the operation.

[0031] Example: Example 1 This embodiment focuses on non-ISO method flexural and compressive strength testing of general-purpose silicate cement. The entire process utilizes the special silica sand for cement strength testing described in claim 1, strictly adhering to the corresponding usage procedures. First, a preliminary inspection of the silica sand is conducted to confirm that it consists solely of natural siliceous mineral particles, without any added components, meeting the chemical composition and fluctuation coefficient requirements specified in claim 1, and without any additional impurities. Simultaneously, the silica sand packaging is checked for a double-sealed structure, meeting the sealing standards of claim 10, the storage environment meets the prescribed conditions, the shelf life is within the expiration date, and there is no moisture absorption or clumping; therefore, it can be used without additional pretreatment.

[0032] Subsequently, the silica sand gradation was confirmed, verifying that the silica sand was a continuous three-gradation particle, without gradation breaks or particles exceeding the specified size range. The gradation uniformity met the standard of claim 2, ensuring the uniformity of the packing structure. Next, physical properties were verified, confirming that the sphericity, surface roughness, bulk density, and porosity of the silica sand particles all met the requirements of claims 3, 4, and 5, ensuring good compatibility with cement paste. Simultaneously, moisture content and abrasion rate were checked. The moisture content was checked using the drying and weighing method, confirming no moisture interference issues, stable silica sand particle morphology, no breakage, gradation changes, or secondary impurities, meeting the requirements of claims 6 and 7.

[0033] During the mortar preparation stage, the proportioning requirements of claim 9 are strictly controlled. The mass ratio of silica sand to cement is adjusted according to a fixed ratio, and the water-cement ratio is selected from the standard value corresponding to general silicate cement, following the non-ISO testing requirements. A dedicated mixing equipment is used during the mixing process, operating according to the mixing procedure specified in claim 9. Low-speed mixing is followed by high-speed mixing, controlling the total mixing time and speed to ensure thorough mixing of silica sand, cement, and water, preventing particle agglomeration and fully utilizing the interfacial bonding advantages of silica sand.

[0034] During specimen preparation, the well-mixed mortar is slowly poured into the mold. During compaction, the stable packing properties of the silica sand are utilized to ensure a dense and uniform specimen, preventing internal stress concentration from affecting test results. The curing stage is performed according to non-ISO standards, maintaining a stable curing environment to allow for full cement hydration and ensure that test results accurately reflect the cement's inherent strength properties. After testing, any remaining silica sand is sealed and stored according to the storage standards of claim 10, clearly labeled for use in subsequent parallel tests of the same type of cement. Before reuse, the moisture content and particle morphology must be rechecked to ensure that the indicators meet the standards.

[0035] Example 2 This embodiment focuses on strength testing of special cement used in road engineering, selecting the special silica sand described in claim 1, and adapting to the special cement testing scenario specified in claim 9. In the preliminary verification stage, the key focus is on confirming that the silica sand is prepared using a physical purification process, removing impurities through a combination of scrubbing, gravity separation, and magnetic separation, leaving no chemical reagent residues, and meeting the preparation process requirements of claim 8 and the composition standards of claim 1. The packaging and storage conditions are verified to comply with the provisions of claim 10, ensuring the stable performance of the silica sand.

[0036] In the gradation and physical property verification stage, the requirements of claims 2, 3, 4, and 5 were strictly adhered to to confirm that the silica sand gradation was uniform, the particle morphology and packing properties met the standards, and the surface roughness was sufficient to achieve good mechanical interlocking with the special cement paste, avoiding interfacial bonding problems from affecting the test results. The moisture content and abrasion rate test results met the requirements of claims 6 and 7, ensuring the stability of the silica sand's performance throughout the testing process.

[0037] During mortar preparation, the proportioning parameters are adjusted according to the requirements of claim 9, maintaining a fixed mass ratio of silica sand to cement. Based on the hydration characteristics of the special cement, the water-cement ratio is rationally set within a specified range. The mixing operation follows a dedicated procedure to ensure uniform mixing of the mortar, adapting to the hydration requirements of the special cement. The specimen preparation and curing processes are strictly controlled, relying on the stable physical properties and packing characteristics of silica sand to ensure that the specimen quality meets standards and that the curing environment satisfies the hydration requirements of the special cement, truly reflecting its strength performance.

[0038] After testing, any remaining silica sand is sealed and stored according to specifications. When using it in batches, the performance calibration report for each batch of silica sand is verified to confirm that the preparation process is compliant, all indicators meet standards, and packaging specifications are uniform for accurate dosage measurement. Usage records are maintained to ensure traceability of the testing process, complying with the control requirements of claims 8 and 10. This embodiment effectively avoids the problem of poor compatibility between silica sand and special cement in existing technologies by using specialized silica sand, thus improving the accuracy and reliability of test results.

[0039] Example 3 This embodiment addresses the batch testing scenario for large quantities of general-purpose silicate cement. Multiple batches of the special silica sand described in claim 1 are used, and testing is conducted according to a standardized process to ensure testing efficiency and result consistency. Before batch use, strict batch use control requirements are implemented. Corresponding to the provisions of claims 8 and 10, the performance calibration reports of the silica sand are checked batch by batch to confirm that each batch of silica sand has undergone screening, crushing, grading, purification, drying, and performance calibration. The purification process is entirely physical, without chemical pollution, and all indicators meet the requirements of claims 1 to 7.

[0040] Each batch of silica sand was verified to have uniform packaging specifications, intact seals, and storage conditions that met requirements, with consistent shelf life, ensuring uniform and stable performance across multiple batches. Random samples were taken from each batch of silica sand for preliminary verification, gradation confirmation, physical property review, and checks on moisture content and abrasion rate. All sampling results met standards, with no batch-related quality issues.

[0041] When preparing mortar in batches, the amount of silica sand and cement is adjusted according to the fixed proportions specified in claim 9. The water-cement ratio is reasonably controlled according to the test batches. Multiple dedicated mixing devices are used for synchronous operation, strictly following a unified mixing procedure and parameters to ensure consistent mixing quality across batches of mortar. Standardized control is implemented for the specimen preparation and curing process. Relying on the stable properties of silica sand, the uniformity of specimen quality across batches is ensured, and a unified curing environment is maintained to avoid test deviations caused by environmental factors and fluctuations in silica sand properties.

[0042] During the testing process, detailed records of each batch of silica sand usage are maintained, clearly identifying the corresponding cement testing batch to ensure traceability. Remaining silica sand is sealed and stored by batch, with clear batch labeling. Before reuse, key indicators are specifically reviewed to ensure compliance. This embodiment effectively improves the efficiency of large-scale cement testing through standardized operations and batch control. Simultaneously, relying on the stable performance of specialized silica sand, it avoids the problem of large deviations in multi-batch test results in existing technologies, ensuring reliable and comparable test data.

[0043] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A special silica sand for cement strength testing, characterized in that: This silica sand contains no additional additives and consists only of siliceous mineral particles. Mass fraction ≥ 99.2%, total impurity mass fraction ≤ 0.8%, and the mass fraction of each impurity component is strictly controlled as follows: ≤0.15%, ≤0.30%, ≤0.12%, ≤0.08%, + ≤0.10%, loss on ignition ≤0.05%; the fluctuation coefficient Cx of each component calculated using equation (1) is ≤0.5%, and equation (1) is = (Maximum mass fraction of this component in the same batch of silica sand - minimum mass fraction of this component) / average mass fraction of this component × 100%. The composition of each batch of silica sand is tested by chemical quantitative analysis to ensure that the stability of the chemical composition meets the high-precision requirements of cement strength testing.

2. The special silica sand for cement strength testing according to claim 1, characterized in that: A continuous three-gradation particle design is adopted, with the particle size range limited to 0.15-1.18 mm, and no particles exceeding this range. The particle size range and corresponding mass fraction percentage of each gradation are as follows: fine gradation 0.15-0.30 mm accounts for 32%-35%, medium gradation 0.30-0.60 mm accounts for 40%-43%, and coarse gradation 0.60-1.18 mm accounts for 22%-25%, and the sum of the mass fractions of the three gradations is strictly equal to 100%; the gradation uniformity coefficient is calculated using formula (2). Controlled between 1.8 and 2.2, equation (2) is: ,in The particle size when the cumulative mass fraction reaches 60%. To determine the particle size when the cumulative mass fraction reaches 10%, the particle gradation is determined by standard sieve grading to ensure that the gradation is continuous, uniform, and without discontinuities, thus avoiding detection deviations caused by gradation dispersion in existing technologies.

3. The special silica sand for cement strength testing according to claim 1, characterized in that: Silica sand particle sphericity ≥0.82, determined by image analysis method. By acquiring projection images of at least 500 random particles in each batch of silica sand, the sphericity of each individual particle is calculated and the average value is taken. The sphericity calculation formula is shown in formula (3): ,in The projected area of ​​the particle. The sphericity parameter is the projected perimeter of the particles. By controlling the sphericity parameter, the porosity during the preparation of mortar is reduced, the density of the mortar structure is improved, and the problem of insufficient interfacial bonding caused by excessive sphericity is avoided, thus adapting to the interfacial requirements of cement hydration reaction.

4. The special silica sand for cement strength testing according to claim 1, characterized in that: Surface roughness of silica sand particles The roughness is controlled within the range of 0.8-1.2 μm. It is measured using a laser roughness meter, and the measurement range covers different areas of silica sand particles. The average value of at least 30 test points is taken as the final result. This roughness range can ensure that the silica sand particles and cement paste form good mechanical interlocking and interfacial bonding. It avoids weak bonding caused by insufficient roughness, and prevents stress concentration inside the mortar caused by excessive roughness. It ensures that the mortar strength truly reflects the performance of the cement itself during the test.

5. The special silica sand for cement strength testing according to claim 1, characterized in that: True density of silica sand The density should be controlled between 2.64-2.66 g / cm³, representing the natural bulk density. =1.65-1.72 g / cm³, tapped bulk density =1.80-1.88 g / cm³; The natural packing porosity is calculated using equation (4). =34%-38%, equation (4) is The vibratory compaction porosity is calculated using equation (5). =29%-32%, Equation (5) is By controlling the bulk density and porosity parameters, a reasonable space is provided for the cement paste filling, ensuring that the mortar forms a uniform and dense structure after setting and hardening, thus improving the repeatability of strength test results.

6. The special silica sand for cement strength testing according to claim 1, characterized in that: The moisture content of silica sand is ≤0.1%, and is determined by drying and weighing. A 500g sample of silica sand is dried at 105±5℃ for 2 hours, cooled to room temperature, and then weighed. The formula for calculating the moisture content is shown in equation (6). ,in For the quality of silica sand before drying, To ensure the quality of the dried silica sand, strict control of moisture content is maintained to avoid interference with the water-cement ratio of cement mortar, ensuring accurate and controllable water-cement ratio during testing and avoiding strength testing deviations caused by moisture content fluctuations in existing technologies.

7. The special silica sand for cement strength testing according to claim 1, characterized in that: The silica sand abrasion rate is ≤0.25%, measured using a Los Angeles abrasion tester. A 1000g silica sand sample is taken, and the abrasion test is completed according to the set rotation speed and abrasion time. Particles smaller than 0.15mm are removed by sieving. The abrasion rate is calculated as the ratio of the mass difference before and after abrasion to the initial mass. The particle size change rate after abrasion is ≤0.3%, ensuring stable particle morphology and gradation during the testing process, preventing secondary impurities from contaminating the mortar system, and guaranteeing the accuracy of the test results.

8. A special silica sand for cement strength testing according to any one of claims 1-7, characterized in that: The preparation process of this silica sand includes six steps: screening of silica raw materials, crushing, grading and sieving, purification, drying, and performance calibration. The purification step adopts a physical purification method, which removes impurities from the raw materials through a combination of scrubbing, gravity separation, and magnetic separation. No chemical purification reagents are used to avoid interference from chemical reagent residues on the test results. The drying step adopts a segmented drying process, first drying at 80±5℃ for 1 hour, and then raising the temperature to 105±5℃ for another hour to ensure that the moisture content meets the standard and the particle morphology does not change.

9. A special silica sand for cement strength testing according to any one of claims 1-7, characterized in that: This silica sand is suitable for strength testing of cement mortars using non-ISO methods. It is compatible with the strength testing of general-purpose Portland cement and special cement of grades 42.5, 52.5, and 62.

5. During the mortar preparation process, the mass ratio of silica sand to cement is 2.5:1, and the water-cement ratio is set to 0.44-0.48 according to the type of cement. The mixing time of silica sand with cement and water is 120-180 seconds, and the mixing speed is 300±20 r / min to ensure that the silica sand and cement paste are fully and uniformly mixed, thus giving full play to its testing compatibility advantages.

10. A special silica sand for cement strength testing according to any one of claims 1-7, characterized in that: Each batch of silica sand undergoes full performance testing before leaving the factory. The testing items include chemical composition, particle size distribution, sphericity, surface roughness, bulk density, moisture content, and abrasion rate. All indicators must meet the specified range. After passing the test, the silica sand is sealed and moisture-proof in 25kg / bag packaging. The storage environment temperature is 5-35℃, the relative humidity is ≤60%, and the shelf life is 12 months. This ensures that the silica sand maintains stable performance during storage and does not have problems such as moisture absorption, clumping, or compositional changes.

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