Quality evaluation method of silica fume

Abstract

To provide a method for evaluating quality of silica fume easily and with high accuracy, without producing mortar or the like.SOLUTION: A method comprises: a dispersion step for mixing silica fume being an evaluation object and a dispersion liquid, for obtaining a first fluid dispersion in which at least partially, the silica fume exists in a form of an aggregate; an energy supply step for supplying to the first fluid dispersion, energy for dispersing the aggregate of the silica fume in the first fluid dispersion as single particles, for obtaining a second fluid dispersion; a second grain size distribution measurement step for obtaining second data related to a grain size distribution of the silica fume included in the second fluid dispersion; and an evaluation step for evaluating quality of the silica fume being an evaluation object, using data related to the silica fume being an evaluation object and the second data related to the grain size distribution.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the quality of silica fume. [Background technology]

[0002] In ultra-high strength concrete, it is effective to use silica fume as a cement admixture to obtain a desired fluidity. Silica fume is almost perfectly spherical, with a particle size of submicron. Therefore, using silica fume as a cement admixture can improve filling properties (microfiller effect) and reduce friction when cement particles come into contact with each other (ball bearing effect), thereby improving the fluidity of concrete and other materials.

[0003] On the other hand, silica fume is an industrial by-product, and its quality is known to vary depending on the raw materials and production method. As a method for evaluating the quality of silica fume, Patent Document 1 describes a method for determining the quality of silica fume for concrete, which is characterized by applying an external force to silica fume in water and measuring changes in the particle size distribution of the silica fume or changes in parameters related to the particle size distribution before and after the application of the external force or depending on the duration of the external force. Patent Document 2 also describes a method for evaluating silica fume, which comprises dispersing 1 g of silica fume in 100 g of water, measuring the particle size distribution of the obtained silica fume dispersion, and determining whether A is the 50% cumulative particle size of the silica fume obtained by measuring the particle size distribution of the obtained silica fume dispersion, and applying ultrasonic waves at a frequency selected from 15 kHz to 50 kHz for 540 seconds to the obtained silica fume dispersion, and determining B is the 50% cumulative particle size of the silica fume obtained by measuring the particle size distribution of the obtained silica fume dispersion. [A / B]≦5.0 Formula (I) 1.0μm≦B≦2.0μm Formula (II) [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-35676 [Patent Document 2] Japanese Patent Application Publication No. 2019-45195 Summary of the Invention [Problem to be solved by the invention]

[0005] One method for evaluating the quality of silica fume (e.g., the effect on the fluidity of cement compositions obtained when silica fume is used as a cement admixture) is to directly evaluate the quality of silica fume by actually preparing mortar using silica fume as a cement admixture and conducting a flow test. Such methods have the following problems: (i) they involve human factors; (ii) they evaluate the quality of mortar containing silica fume, rather than silica fume alone, so the compatibility of the silica fume with the cement and admixtures in the mortar affects the quality; and (iii) they require the preparation of multiple samples and require the adjustment of cement dispersants such as high-range air-entraining water-reducing agents, which is labor-intensive. On the other hand, indexes for evaluating the quality of silica fume include the particle size distribution and BET specific surface area of ​​silica fume. However, because silica fume has an ultrafine particle size of submicron order, aggregation of primary particles occurs easily, making it difficult to accurately measure the particle size distribution of primary particles. Furthermore, although a certain degree of correlation has been confirmed between the BET specific surface area of ​​silica fume and the fluidity of cement compositions using said silica fume as a cement admixture, there are cases where the correlation deviates, making a logical interpretation difficult. An object of the present invention is to provide a method for easily and accurately evaluating the quality of silica fume without actually producing mortar or the like. [Means for solving the problem]

[0006] As a result of extensive research into solving the above problems, the present inventors have found that the above objects can be achieved by a method comprising the steps of mixing silica fume to be evaluated with a dispersion liquid to obtain a first dispersion, supplying energy to the first dispersion to obtain a second dispersion, obtaining second data relating to the particle size distribution of the silica fume contained in the second dispersion, and evaluating the quality of the silica fume to be evaluated using the data relating to the silica fume to be evaluated and the second data, and have completed the present invention. That is, the present invention provides the following [1] to [9]. [1] A method for evaluating the quality of silica fume, comprising: a dispersion step of mixing silica fume to be evaluated with a dispersing liquid to obtain a first dispersion in which the silica fume is at least partially present in the form of aggregates; an energy supply step of supplying energy to the first dispersion to disperse the silica fume aggregates in the first dispersion into single particles to obtain a second dispersion; a second particle size distribution measurement step of obtaining second data on the particle size distribution of the silica fume contained in the second dispersion; and an evaluation step of evaluating the quality of the silica fume to be evaluated using the data on the silica fume to be evaluated and the second data on the particle size distribution.

[0007] [2] The quality evaluation method for silica fume according to [1] above, wherein the data on the silica fume to be evaluated is the average primary particle diameter of the silica fume to be evaluated, calculated using the following formula (1): Average primary particle size (μm) of the silica fume to be evaluated above = 6 / (BET specific surface area (m 2 / g) × true density of silica fume to be evaluated above (g / m 3 ) ···(1) [3] The method for evaluating the quality of silica fume according to [2] above, wherein the second data on the particle size distribution is the 50% area cumulative particle size of the silica fume contained in the second dispersion, and the quality of the silica fume to be evaluated is at least one of the fluidity of a cement composition containing the silica fume and the mixing efficiency of the cement composition. [4] The method for evaluating the quality of silica fume according to the above item [3], wherein in the evaluation step, the numerical value of the cohesion degree of silica fume contained in the second dispersion calculated using the following formula (2) is used to evaluate the fluidity of a cement composition containing the silica fume as the quality of the silica fume to be evaluated. Degree of aggregation of silica fume contained in the second dispersion liquid = 50% area cumulative particle size (μm) of silica fume contained in the second dispersion liquid / average primary particle size (μm) of silica fume to be evaluated (2)

[0008] [5] The method for evaluating the quality of silica fume according to [3] above, further comprising, between the dispersing step and the energy supplying step, a first particle size distribution measuring step of obtaining first data relating to the particle size distribution of silica fume contained in the first dispersion, wherein the first data relating to the particle size distribution is the 50% area cumulative particle size of the silica fume contained in the first dispersion, and wherein the evaluation step uses the numerical values ​​of the degree of aggregation of the silica fume contained in the first dispersion calculated using the following formula (3), the degree of aggregation of the silica fume contained in the second dispersion calculated using the following formula (4), and the degree of dispersibility calculated using the following formula (5) to evaluate the mixing efficiency of a cement composition containing the silica fume as the quality of the silica fume to be evaluated. Degree of aggregation of silica fume contained in the first dispersion liquid = 50% area cumulative particle size (μm) of silica fume contained in the first dispersion liquid / average primary particle size (μm) of silica fume to be evaluated (3) Degree of aggregation of silica fume contained in the second dispersion liquid = 50% area cumulative particle size (μm) of silica fume contained in the second dispersion liquid / average primary particle size (μm) of silica fume to be evaluated (4) Dispersion degree (1 / kJ)=|log 10 (Degree of aggregation of silica fume contained in the second dispersion)-log 10 (Degree of aggregation of silica fume contained in the first dispersion)| / Amount of energy supplied (kJ)= (5)

[0009] [6] The method for evaluating the quality of silica fume according to any one of [1] to [5] above, wherein the energy is ultrasonic. [7] The method for evaluating the quality of silica fume according to [6], wherein the amount of energy supplied in the energy supplying step is 5 kJ or more. [8] The method for evaluating the quality of silica fume according to any one of [1] to [7] above, wherein the dispersion liquid is an aqueous solution of sodium hexametaphosphate. [9] The method for evaluating the quality of silica fume according to any one of [1] to [8], wherein a laser diffraction particle size distribution analyzer is used in the second particle size distribution measurement step. [Effects of the Invention]

[0010] According to the method for evaluating the quality of silica fume of the present invention, the quality of silica fume can be evaluated easily and with high accuracy without actually producing mortar or the like. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 10 is a diagram showing the relationship between the amount of energy supply and the degree of cohesion. [Figure 2] FIG. 1 is a graph showing the relationship between dispersity and fluidization time. [Figure 3] FIG. 10 is a diagram illustrating the relationship between the degree of cohesion and the flow value. DETAILED DESCRIPTION OF THE INVENTION

[0012] The method for evaluating the quality of silica fume of the present invention includes: (A) a dispersion step of mixing silica fume to be evaluated with a dispersing liquid to obtain a first dispersion in which the silica fume is at least partially present in the form of aggregates; (B) an energy supply step of supplying energy to the first dispersion for dispersing the silica fume aggregates in the first dispersion as single particles to obtain a second dispersion; (C) a second particle size distribution measurement step of obtaining second data regarding the particle size distribution of the silica fume contained in the second dispersion; and (D) an evaluation step of evaluating the quality of the silica fume to be evaluated using the data regarding the silica fume to be evaluated and the second data regarding the particle size distribution. Each step will be explained in detail below.

[0013] [(A) Dispersion process] Step (A) (dispersion step) is a step of mixing the silica fume to be evaluated with a dispersing liquid to obtain a first dispersion in which the silica fume is at least partially present in the form of aggregates. The dispersion liquid is not particularly limited as long as it is a liquid capable of dispersing silica fume, and examples thereof include an aqueous solution of sodium hexametaphosphate, an aqueous solution of sodium pyrophosphate, an aqueous solution of trisodium phosphate, cyclohexane, hexane, heptane, benzene, bromobenzene, methyl acetate, acetone, water, and ethanol. Among these, an aqueous solution of sodium hexametaphosphate is preferred from the viewpoint of being able to uniformly disperse silica fume and to evaluate the quality of silica fume with higher accuracy. The amount of silica fume relative to the dispersion liquid is an amount such that the concentration index (Diffraction Volume) of the first dispersion liquid measured using a Microtrac measurement device is preferably 0.001 to 0.1, more preferably 0.002 to 0.05. The content of silica fume in the dispersion is preferably 10 to 1000 ppm, more preferably 50 to 500 ppm (mass basis). The method for mixing silica fume and the dispersion liquid is not particularly limited, and silica fume may be added to the dispersion liquid in the container and mixed, or silica fume and the dispersion liquid may be simultaneously poured into the container and mixed. Since the particle size of the primary particles of silica fume is on the order of submicron, in the first dispersion, at least a portion of the primary particles constituting the silica fume (an aggregate of silica fume consisting of a plurality of particles) are present in the form of aggregates formed by agglomeration of a plurality of the above primary particles. In this specification, the term "silica fume" includes both a single particle (single particle) and an aggregate of multiple particles.

[0014] [(E) First particle size distribution measurement step] Step (E) (first particle size distribution measurement step) is a step optionally provided between the dispersing step and the energy supplying step (described later), and is a step for obtaining first data on the particle size distribution of silica fume contained in the first dispersion. An example of the first data regarding the particle size distribution of silica fume is the 50% area cumulative particle size of the silica fume contained in the first dispersion, measured using a laser diffraction particle size distribution measuring device, etc. The first data may be one type of data or two or more types of data. Here, the "50% area cumulative particle size" refers to the particle size at 50% of the area cumulative distribution obtained by measuring the particle size of silica fume particles using a laser diffraction particle size distribution analyzer and accumulating the particle sizes from smallest to largest based on the measured particle size. The particle size of silica fume particles measured in step (E) and step (C) described later is the particle size of a single particle when silica fume exists in the dispersion in the form of a single particle, or is the particle size of an aggregate when silica fume exists in the dispersion in the form of an aggregate formed by agglomeration of a plurality of silica fume primary particles. Furthermore, the single particle includes a primary particle and a secondary particle formed by agglomerating or sintering the primary particle.

[0015] [(B) Energy supply process] Step (B) (energy supply step) is a step of supplying energy to the first dispersion obtained in the dispersion step to disperse the silica fume aggregates in the first dispersion as single particles, thereby obtaining a second dispersion (a dispersion in which the silica fume aggregates in the first dispersion are dispersed as single particles). The energy is not particularly limited as long as it is energy that can break down aggregates of silica fume in the dispersion liquid and disperse them as single particles, and examples thereof include ultrasonic waves and shear force. Among these, ultrasonic waves are preferred from the viewpoint of easily breaking down aggregates of silica fume and dispersing them as single particles. When ultrasonic waves are supplied to the dispersion as energy, the amount of energy supplied is preferably 5 kJ or more, more preferably 10 kJ or more, even more preferably 15 kJ or more, even more preferably 20 kJ or more, and particularly preferably 25 kJ or more. If the amount supplied is 5 kJ or more, regardless of the type of silica fume, silica fume agglomerates are sufficiently disintegrated and dispersed as single particles, allowing more accurate measurement of data on the particle size distribution of silica fume (for example, 50% area cumulative particle size of silica fume). Furthermore, from the viewpoint of preventing waste of energy costs due to the continued supply of energy even when the disintegration of silica fume agglomerates has reached a plateau, the amount of energy supplied is preferably 40 kJ or less, more preferably 35 kJ or less, even more preferably 30 kJ or less, and particularly preferably 28 kJ or less.

[0016] Furthermore, from the viewpoint of evaluating the quality of silica fume with higher accuracy, the amount of energy supply may be determined depending on the type of quality of silica fume to be evaluated. Specifically, when the fluidity of a cement composition containing silica fume is evaluated using the numerical value of the cohesion degree of silica fume contained in the second dispersion (described in detail later), the amount of energy supplied is preferably 15 to 40 kJ, more preferably 20 to 30 kJ. By setting the amount of energy supplied within the above numerical range, the fluidity can be evaluated with higher accuracy. Furthermore, when evaluating the mixing efficiency of a cement composition containing silica fume using the numerical value of the degree of dispersion (described in detail later), the amount of energy supplied is preferably 5 to 15 kJ, more preferably 6 to 10 kJ. By keeping the amount of energy supplied within the above numerical range, the mixing efficiency can be evaluated with higher accuracy.

[0017] The ultrasonic output is preferably 10 to 500 W, more preferably 30 to 300 W, even more preferably 50 to 250 W, even more preferably 80 to 200 W, and particularly preferably 120 to 180 W. If the output is 10 W or more, silica fume agglomerates can be sufficiently disintegrated and dispersed as single particles in a shorter time. If the output is 500 W or less, the cost of the device for supplying ultrasonic waves can be further reduced. The ultrasonic supply time is preferably 20 to 1,000 seconds, more preferably 40 to 600 seconds, even more preferably 60 to 300 seconds, even more preferably 90 to 240 seconds, and particularly preferably 150 to 200 seconds. If the supply time is 20 seconds or longer, the silica fume aggregates can be more effectively broken down and dispersed as single particles. If the supply time is 1,000 seconds or shorter, the quality of the silica fume can be evaluated in a shorter time. Examples of a method for supplying shear force as energy include a method of stirring the dispersion using a stirring means, and a method of imparting a flow velocity to the first dispersion using a wet circulator or the like.

[0018] [(C) Second particle size distribution measurement step] Step (C) (second particle size distribution measurement step) is a step of obtaining second data on the particle size distribution of silica fume contained in the second dispersion obtained in the energy supply step. An example of the second data regarding the particle size distribution of silica fume is the 50% area cumulative particle size of the silica fume contained in the second dispersion, measured using a laser diffraction particle size distribution analyzer, etc. The second data may be one type of data or two or more types of data.

[0019] [(D) Evaluation process] Step (D) (evaluation step) is a step of evaluating the quality of the silica fume to be evaluated using data on the silica fume to be evaluated and second data on particle size distribution. In addition, the quality of the silica fume to be evaluated can also be evaluated using data on the silica fume to be evaluated, second data on particle size distribution, and a numerical value calculated using a specific formula as an index. Data on the silica fume to be evaluated include the average primary particle size of the silica fume. The average primary particle size can be calculated using the following formula (6). Average primary particle size (μm) of the silica fume to be evaluated = 6 / (BET specific surface area (m 2 / g) × true density of silica fume to be evaluated (g / m 3 ) ···(6) By evaluating the quality of silica fume using the above average primary particle diameter, it is possible to evaluate and determine whether the effect on the physical properties of a cement composition containing silica fume is due to the large size of the individual silica fume particles themselves, or due to the fact that although the individual silica fume particles are small, they have become integrated into a single particle through aggregation, coagulation, or the like. In step (D), the quality of silica fume (powdered silica fume) to be evaluated includes the fluidity of a cement composition containing the silica fume, the mixing efficiency of the cement composition, etc. The quality to be evaluated in step (D) may be one type or two or more types.

[0020] An example of a specific method for evaluating the quality of silica fume to be evaluated in step (D) will be described below. (i) Method for evaluating the fluidity of cement compositions containing silica fume The fluidity of the cement composition containing silica fume can be evaluated using the numerical value of the degree of aggregation of the silica fume contained in the second dispersion, calculated using the following formula (7). Degree of aggregation of silica fume contained in the second dispersion = 50% area cumulative particle size (μm) of silica fume contained in the second dispersion / average primary particle size (μm) of silica fume to be evaluated (7) The degree of cohesion of the silica fume contained in the second dispersion and the fluidity have a negative correlation, and the lower the degree of cohesion, the more excellent the fluidity of the cement composition, and the higher the degree of cohesion, the more inferior the fluidity of the cement composition. For example, with regard to fluidity, a degree of cohesion of 4.2 or more may be evaluated as "extremely poor (mortar flow value of 240 mm or less)," a degree of cohesion of 3.5 or more and less than 4.2 may be evaluated as "poor (mortar flow value of more than 240 mm and less than 260 mm)," a degree of cohesion of 2.8 or more and less than 3.5 may be evaluated as "good (mortar flow value of 260 mm or more and less than 280 mm)," and a degree of cohesion of less than 2.8 may be evaluated as "very good (mortar flow value of more than 280 mm)."

[0021] (ii) Methods for assessing the mixing efficiency of cement compositions containing silica fume The mixing efficiency of a cement composition containing silica fume can be evaluated using the average primary particle size of the silica fume to be evaluated, the 50% area cumulative particle size of the silica fume contained in the first dispersion, and the 50% area cumulative particle size of the silica fume contained in the second dispersion, as well as the dispersibility calculated using the following formula (8): Dispersion degree (1 / kJ)=|log 10 (Degree of aggregation of silica fume contained in the second dispersion)-log 10 (Degree of aggregation of silica fume contained in the first dispersion)| / Amount of energy supplied (kJ)= (8)

[0022] In formula (8), the degree of aggregation of silica fume contained in the first dispersion can be calculated using the following formula (9). Degree of aggregation of silica fume contained in the first dispersion = 50% area cumulative particle size (μm) of silica fume contained in the first dispersion / average primary particle size (μm) of silica fume to be evaluated (9) The degree of aggregation of silica fume contained in the second dispersion can be calculated using the above-mentioned formula (7).

[0023] The numerical value of the degree of dispersion and mixing efficiency have a positive correlation, and the higher the degree of dispersion, the better the mixing efficiency of the cement composition, and the lower the degree of dispersion, the worse the mixing efficiency of the cement composition. For example, with regard to mixing efficiency, a degree of dispersion of 0.08 or less may be evaluated as "extremely poor (fluidization time of 600 seconds or more)", a degree of dispersion of more than 0.08 and less than 0.10 may be evaluated as "poor (fluidization time of 500 seconds or more and less than 600 seconds)", a degree of dispersion of more than 0.10 and less than 0.14 may be evaluated as "good (fluidization time of 400 seconds or more and less than 500 seconds)", and a degree of dispersion of more than 0.14 may be evaluated as "very good (fluidization time of less than 400 seconds)". In addition, excellent mixing efficiency means that the fluidization time (the time required for the cement composition to attain a predetermined fluidity) when mixing the cement composition is shorter, and poor mixing efficiency means that the fluidization time when mixing the cement composition is longer.

[0024] In step (D), a threshold value may be determined in advance, and the quality of the silica fume to be evaluated may be evaluated based on the threshold value. For example, the threshold value of the cohesion degree of the silica fume contained in the second dispersion may be set to a value (e.g., 3.5) arbitrarily selected from a range of values ​​from 1.5 to 5.5, and the numerical value of the cohesion degree of the silica fume contained in the second dispersion may be compared with the predetermined threshold value. If the numerical value of the cohesion degree of the silica fume contained in the second dispersion is less than the threshold value, the silica fume to be evaluated may be evaluated as one that imparts excellent fluidity to the resulting cement composition when used as a cement admixture, and if the numerical value of the cohesion degree of the silica fume contained in the second dispersion is equal to or greater than the threshold value, the silica fume may be evaluated as one that imparts poor fluidity to the resulting cement composition.

[0025] Alternatively, the threshold value of the degree of dispersion may be set to a value (for example, 0.10) arbitrarily selected from a range of 0.05 to 0.40, and the value of the degree of dispersion may be compared with the predetermined threshold value. If the value of the degree of dispersion exceeds the threshold value, the silica fume to be evaluated is evaluated as one that, when used as a cement admixture, makes the resulting cement composition have excellent mixing efficiency; if the degree of dispersion is equal to or less than the threshold value, the silica fume is evaluated as one that makes the resulting cement composition have poor mixing efficiency. The terms "below threshold," "above threshold," "exceed threshold," and "below threshold" are used for convenience to divide into two categories based on specific values, and therefore can be replaced with the terms "below threshold," "above threshold," "above threshold," and "below threshold," respectively.

[0026] In addition, the quality of one or more types of silica fume to be evaluated may be evaluated, and then based on the evaluation results, it may be determined whether or not the silica fume should be selected as a material for a cement composition having the desired quality. For example, in step (D), if the numerical value of the cohesion degree of the silica fume contained in the second dispersion is less than the threshold value, the silica fume being evaluated may be selected as a material for the cement composition, and if the numerical value of the cohesion degree of the silica fume contained in the second dispersion is equal to or greater than the threshold value, it may be determined that the silica fume is not selected as a material for the cement composition. [Example]

[0027] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. [Materials used] (1) Silica fume A to D: Details are shown in Table 1. (2) Cement: Ordinary Portland cement, manufactured by Taiheiyo Cement Corporation (3) Fine aggregate: crushed sand (4) High-performance AE water reducer; polycarboxylic acid ether compound (5) Antifoaming agent: polyalkylene glycol derivative (6) Water; tap water

[0028] [Table 1]

[0029] [Example 1] A first dispersion was prepared by mixing silica fume and an aqueous solution of sodium hexametaphosphate for each of silica fume A to D. The concentration index (Diffraction Volume) of the first dispersion was 0.005 to 0.0074. The 50% area cumulative particle size of the silica fume contained in the obtained first dispersion was measured using a laser diffraction particle size distribution measuring device (manufactured by Microtrack Bell, product name "MT3300EX II"). The aggregation degree A of the silica fume contained in the first dispersion was calculated using the 50% area cumulative particle size of the silica fume contained in the first dispersion and the above-mentioned formula (9). Next, ultrasonic waves were supplied (applied) to the first dispersion at an output of 40 W for 3 minutes (energy supply amount: 7.2 kJ) to obtain a second dispersion, and then the 50% area cumulative particle size of the silica fume contained in the second dispersion was measured using a laser diffraction particle size distribution analyzer. Using the 50% area cumulative particle size of the silica fume contained in the second dispersion and the above-mentioned formula (7), the aggregation degree B-1 of the silica fume contained in the second dispersion (aggregation degree when the energy supply amount is 7.2 kJ) was calculated.

[0030] Similarly, a first dispersion was prepared for each of silica fume A to D. Then, ultrasonic waves were applied to the first dispersion at an output of 150 W for 3 minutes (energy supply amount: 27.0 kJ) to obtain a second dispersion. The 50% area cumulative particle size of the silica fume contained in the second dispersion was then measured using a laser diffraction particle size distribution analyzer. Using the 50% area cumulative particle size of the silica fume contained in the second dispersion and the above-mentioned formula (7), the aggregation degree B-2 of the silica fume contained in the second dispersion (aggregation degree when the energy supply amount is 27.0 kJ) was calculated. The relationship between the amount of energy supplied and the degree of cohesion is shown in Figure 1. From Figure 1, it can be inferred that as the amount of energy supplied increases, the degree of cohesion converges. In addition, for each of the silica fume A to D, the dispersibility B-1 was calculated using the aggregation degree A of the silica fume contained in the first dispersion, the aggregation degree B-1 of the silica fume contained in the second dispersion, and the above-mentioned formula (8). Similarly, the dispersibility B-2 was calculated using the aggregation degree A of the silica fume contained in the first dispersion, the aggregation degree B-2 of the silica fume contained in the second dispersion, and the above-mentioned formula (8).

[0031] The dispersion B-1 value was used to evaluate the mixing efficiency of silica fume. Specifically, a dispersion of 0.08 or less was rated as "×: extremely poor," a dispersion of more than 0.08 but less than 0.10 was rated as "△: poor," a dispersion of more than 0.10 but less than 0.14 was rated as "〇: good," and a dispersion of more than 0.14 was rated as "◎: very good." The fluidity of silica fume was evaluated using the numerical value of the cohesion B-2. Specifically, a cohesion of 4.2 or more was evaluated as "×: extremely poor," a cohesion of 3.5 or more but less than 4.2 was evaluated as "△: poor," a cohesion of 2.8 or more but less than 3.5 was evaluated as "◯: good," and a cohesion of less than 2.8 was evaluated as "◎: very good."

[0032] Silica fume premixed cement A was prepared by mixing ordinary Portland cement with silica fume A. Silica fume premixed cements B to D were also prepared in the same manner, except that silica fume B to D were mixed in place of silica fume A. Mortar compositions A to D containing silica fume premixed cements A to D were then prepared. The water / binder ratio of the mortar composition was 0.15. The materials were prepared by adding silica fume premix cement, which was made by thoroughly mixing cement and silica fume in advance, and fine aggregate to a mixer and dry mixing for 1 minute, after which water and a high-performance air-entraining water-reducing agent were added and mixed for 300 seconds. When preparing the mortar composition, the fluidization time of the mortar composition was also measured. The relationship between the degree of dispersion B-1 and fluidization time is shown in Figure 2. The mortar flow values ​​of the obtained mortar compositions A to D were measured as the spread of flow at 180 seconds in a flow test without dropping, with reference to "JIS R 5201:2015 (Physical Testing Methods for Cement)". The relationship between the cohesion degree B-2 and the mortar flow value is shown in Figure 3. The results are shown in Tables 2 and 3.

[0033] [Table 2]

[0034] [Table 3]

[0035] From Table 3 and Figure 2, it can be seen that the greater the dispersion of silica fume, the shorter the fluidization time of the cement composition using said silica fume, and the cement composition using said silica fume has excellent mixing efficiency. This shows that the mixing efficiency of silica fume can be evaluated using the numerical value of dispersion. Furthermore, from Table 3 and Figure 3, when the degree of aggregation of silica fume is small, the flow value of the cement composition is large, and the cement composition using the above silica fume has excellent fluidity. From this, it is understood that the fluidity of silica fume can be evaluated using the numerical value of the degree of aggregation of silica fume contained in the second dispersion.

Claims

1. a dispersion step of mixing the silica fume to be evaluated with a dispersing liquid to obtain a first dispersion in which the silica fume is at least partially present in the form of aggregates; an energy supply step of supplying energy to the first dispersion to disperse the silica fume aggregates in the first dispersion into single particles, thereby obtaining a second dispersion; a second particle size distribution measuring step for obtaining second data relating to the particle size distribution of silica fume contained in the second dispersion; an evaluation step of evaluating the quality of the silica fume to be evaluated using data on the silica fume to be evaluated and second data on the particle size distribution; A method for evaluating the quality of silica fume, comprising:

2. 2. The method for evaluating the quality of silica fume according to claim 1, wherein the data on the silica fume to be evaluated is the average primary particle diameter of the silica fume to be evaluated, calculated using the following formula (1): Average primary particle size (μm) of the silica fume to be evaluated above = 6 / (BET specific surface area (m ２ / g) × the true density (g / m) of the silica fume to be evaluated ３ ) ... (1)

3. the second data on particle size distribution is a 50% area cumulative particle size of the silica fume contained in the second dispersion, 3. The method for evaluating the quality of silica fume according to claim 2, wherein the quality of the silica fume to be evaluated is at least one of the fluidity of a cement composition containing the silica fume and the mixing efficiency of the cement composition.

4. 4. The method for evaluating the quality of silica fume according to claim 3, wherein in the evaluation step, the fluidity of a cement composition containing said silica fume is evaluated as the quality of the silica fume to be evaluated using a numerical value of the degree of aggregation of the silica fume contained in the second dispersion calculated using the following formula (2): Degree of aggregation of silica fume contained in the second dispersion=50% area cumulative particle size (μm) of silica fume contained in the second dispersion / average primary particle size (μm) of silica fume to be evaluated (2)

5. a first particle size distribution measuring step for obtaining first data relating to the particle size distribution of silica fume contained in the first dispersion, between the dispersing step and the energy supplying step; the first data relating to the particle size distribution is a 50% area cumulative particle size of the silica fume contained in the first dispersion, 4. The method for evaluating the quality of silica fume according to claim 3, wherein in the evaluation step, the mixing efficiency of the cement composition containing said silica fume is evaluated as the quality of the silica fume to be evaluated using the degree of aggregation of silica fume contained in said first dispersion calculated using the following formula (3), the degree of aggregation of silica fume contained in said second dispersion calculated using the following formula (4), and the numerical value of the dispersibility calculated using the following formula (5). Degree of aggregation of silica fume contained in the first dispersion=50% area cumulative particle size (μm) of silica fume contained in the first dispersion / average primary particle size (μm) of silica fume to be evaluated (3) Degree of aggregation of silica fume contained in the second dispersion=50% area cumulative particle size (μm) of silica fume contained in the second dispersion / average primary particle size (μm) of silica fume to be evaluated (4) Dispersity (1 / kJ) = |log １０ (Degree of aggregation of silica fume contained in the second dispersion) -log １０ (Degree of aggregation of silica fume contained in the first dispersion) | / Amount of energy supplied (kJ)= (5)

6. 3. The method for evaluating the quality of silica fume according to claim 1 or 2, wherein the energy is ultrasonic.

7. 7. The method for evaluating the quality of silica fume according to claim 6, wherein the amount of energy supplied in the energy supplying step is 5 kJ or more.

8. 2. The method for evaluating the quality of silica fume according to claim 1, wherein the dispersion liquid is an aqueous solution of sodium hexametaphosphate.

9. 3. The method for evaluating the quality of silica fume according to claim 1, wherein a laser diffraction particle size distribution measuring device is used in the second particle size distribution measuring step.

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