Cement composition, and method for estimating the strength development of a cement composition

Abstract

To provide a cement composition containing a cementitious hardened body and having an excellent strength development property.SOLUTION: A mass ratio of a cementitious hardened body to cement is 1 mass% or more and 25 mass% or less. A value of [(B / A)×(molecular weight of calcium oxide / molecular weight of calcium carbonate)×{(100-D) / (100-C)}] is 0.40 or more, or / and a silica gel content of the cementitious hardened body is 3.0 mass% or more, where an amount of calcium oxide contained in the cement used to produce the cementitious hardened body is A [mass%], an amount of calcium carbonate in the cementitious hardened body is B [mass%], an ignition loss of the cementitious hardened body is C [%], an ignition loss of the cement used to produce the cementitious hardened body is D [%].SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a cement composition and a method for estimating the strength development property of a cement composition.

Background Art

[0002] As described in Patent Document 1 below, a technique for producing recycled aggregates from heat-treated concrete waste by performing a rubbing treatment on the heat-treated concrete waste is known. In the process of this rubbing treatment, powdery cement hardened bodies are generated as by-products from the concrete waste. In order to effectively utilize this cement hardened body, Patent Document 2 below proposes a cement composition containing Portland cement and a cement hardened body.

[0003] By the way, regarding the relationship between the composition of this cement hardened body and the strength development property of the cement composition produced using this cement hardened body, sufficient research has not yet been conducted. Currently, whether the compressive strength of mortar or concrete produced using such a cement composition reaches the desired level is unknown until the compressive strength of the mortar or concrete is actually measured.

[0004] And when the measured compressive strength is below the desired level, the produced cement composition, or the mortar or concrete produced using that cement composition, has to be discarded, so the time and cost required for their production are wasted. With such a risk, there is a possibility that the effective utilization of the powdery cement hardened body, which is a by-product of the rubbing treatment, may not progress sufficiently.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] Therefore, the inventors conducted research on the relationship between the composition of a hardened cement body and the strength development of a cement composition containing this hardened cement body. As a result, they found that there is a positive correlation between a predetermined index indicating the composition of a hardened cement body and the strength development of a cement composition containing this hardened cement body. The present invention is based on this finding and aims to provide a cement composition containing a hardened cement body that has high strength development. The present invention also aims to provide a method for estimating the strength development of a cement composition containing a hardened cement body. [Means for solving the problem]

[0007] The cement composition according to the present invention comprises cement and a cementite. As the cement, for example, Portland cement as specified in JIS R 5210 or a blended cement can be used. As the Portland cement, for example, ordinary Portland cement, rapid-hardening Portland cement, moderate-heat Portland cement, or low-heat Portland cement can be used. As the blended cement, for example, blast furnace cement as specified in JIS R 5211 or fly ash cement as specified in JIS R 5213 can be used.

[0008] The mass ratio of the cementified body to the cement is set to 1% by mass or more and 25% by mass or less. When the amount of calcium oxide contained in the cement used to manufacture the cementified body is A [by mass%], the amount of calcium carbonate in the cementified body is B [by mass%], the loss on ignition of the cementified body is C [%], and the loss on ignition of the cement used to manufacture the cementified body is D [%], the value of [(B / A) × (molecular weight of calcium oxide / molecular weight of calcium carbonate) × {(100-D) / (100-C)}] is set to 0.40 or more, or / or the silica gel content of the cementified body is set to 3.0% by mass or more.

[0009] The method according to the present invention estimates the strength development of a cement composition comprising cement and a cementite. Specifically, this method estimates the compressive strength of a cement mixture produced by mixing cement, a cementite, and water, based on the following index. This index is defined as the value of [(B / A) × (molecular weight of calcium oxide / molecular weight of calcium carbonate) × {(100-D) / (100-C)}], where A [mass%] is the amount of calcium oxide contained in the cement used to produce the cementite, B [mass%] is the amount of calcium carbonate in the cementite, C [%] is the loss on ignition of the cementite, and D [%] is the loss on ignition of the cement used to produce the cementite. [Effects of the Invention]

[0010] The cement composition according to the present invention can enhance the strength development of a cement composition including a hardened cement body. The method according to the present invention can estimate the strength development of a cement composition including a hardened cement body. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is an explanatory diagram illustrating the procedure for estimating the compressive strength of a cement mixture according to one embodiment of the present invention. [Modes for carrying out the invention]

[0012] First, a cement composition according to one embodiment of the present invention will be described. This cement composition includes cement and a hardened cement body. Here, the cement included in this cement composition and the cement used in the manufacture of the hardened cement body include, for example, Portland cement as specified in "JIS R 5210:2009" (one example being ordinary Portland cement). The hardened cement body refers to a hardened cement mixture produced by mixing cement and water. Examples of cement mixtures include cement paste, mortar, or concrete.

[0013] The fineness of the hardened cement is preferably equal to or greater than that of the cement contained in the cement composition according to this embodiment. Specifically, the Blaine specific surface area of ​​the hardened cement is 2500 cm². 2 It is preferable that the concentration is 1 / g or more, and the maximum particle size of the hardened cement is 300 μm or less.

[0014] In the cement composition according to this embodiment, the mass ratio of the hardened cement to the cement is 1% by mass or more and 25% by mass or less (preferably 1% by mass or more and 20% by mass or less). This cement composition satisfies at least one of the following conditions 1 or 2.

[0015] Condition 1: The degree of carbonation of the hardened cement is set to 0.40 or higher. The degree of carbonation of the hardened cement is the value of [(B / A) × (molecular weight of calcium oxide / molecular weight of calcium carbonate) × {(100-D) / (100-C)}], where A [mass%] is the amount of calcium oxide contained in the cement used to manufacture the hardened cement, B [mass%] is the amount of calcium carbonate in the hardened cement, C [%] is the loss on ignition of the hardened cement, and D [%] is the loss on ignition of the cement used to manufacture the hardened cement. Condition 2: The silica gel content of the hardened cement is 3.0% by mass or more.

[0016] The specific range for the degree of carbonation of the hardened cement is, for example, 0.40 to 0.85. Furthermore, the specific range for the silica gel content of the hardened cement is, for example, 3.0% by mass to 9.0% by mass.

[0017] An example of a method for producing the cement composition according to this embodiment is described below. First, in the process of producing recycled aggregate from concrete waste (see, for example, Patent Document 1), powdered cementite generated from concrete waste is recovered. Next, the recovered cementite is mixed with water in a mass of 2 to 20 times the mass of the cementite. Furthermore, carbon dioxide gas (for example, carbon dioxide concentration of 20%) is supplied to the resulting water containing the cementite for a period of 120 to 480 minutes (preferably 240 to 480 minutes). Here, the amount of carbon dioxide gas supplied is adjusted, for example, to a flow rate of 16 mL / min per 1 g of cementite mass.

[0018] Next, a method for estimating the compressive strength of a cement mixture according to one embodiment of the present invention will be described. As shown in Figure 1, this method comprises a calculation step S1 and an estimation step S2.

[0019] In calculation step S1, the degree of carbonation of the hardened cement is calculated. Here, the degree of carbonation of the hardened cement is the value of [(B / A) × (molecular weight of calcium oxide / molecular weight of calcium carbonate) × {(100-D) / (100-C)}], where A [mass%] is the amount of calcium oxide contained in the cement used to manufacture the hardened cement, B [mass%] is the amount of calcium carbonate in the hardened cement, C [%] is the loss on ignition of the hardened cement, and D [%] is the loss on ignition of the cement used to manufacture the hardened cement.

[0020] In calculation step S1, the above variables A to D are obtained, for example, as follows: A: Before using cement in the production of a cement hardened body, in accordance with JIS A 5204 "Method of Chemical Analysis of Cement by Fluorescent X - Ray", obtain the mass ratio of calcium oxide contained in this cement by fluorescent X - ray analysis. B: Obtain the mass of calcium carbonate contained in the cement hardened body by TG - DTA (simultaneous thermogravimetry and differential thermal analysis). Further, multiply this mass ratio of calcium carbonate by the molecular weight ratio of calcium oxide to calcium carbonate. C: By TG - DTA for obtaining the above B, also obtain the loss on ignition of the cement hardened body. D: Before using cement in the production of a cement hardened body, obtain the loss on ignition of this cement based on JIS R 5202:2015 "Method of Chemical Analysis of Cement".

[0021] In the estimation step S2, estimate the compressive strength of a cement mixture produced by kneading the cement hardened body, cement, and water targeted in the calculation step S1. In this specification, the compressive strength is, for example, the compressive strength of a cement mixture at an age of 7 days or more, and is measured in accordance with JIS R 5201 "Physical Testing Methods of Cement". There is a positive correlation between the carbonation degree of the cement hardened body and the compressive strength of the cement mixture. Therefore, in the estimation step S2, estimate the compressive strength of the cement mixture based on the carbonation degree (index) of the cement hardened body.

[0022] Specifically, in the estimation step S2, for example, the following estimations can be made. Compare the carbonation degrees of two types of cement hardened bodies, and estimate that the compressive strength of a cement mixture containing a cement hardened body with a higher carbonation degree is higher than the compressive strength of a cement mixture containing a cement hardened body with a lower carbonation degree. Alternatively, set a reference value (for example, 0.40) for the carbonation degree of the cement hardened body, estimate that the compressive strength of a cement mixture containing a cement hardened body with a carbonation degree equal to or higher than this reference value is high, and estimate that the compressive strength of a cement mixture containing a cement hardened body with a carbonation degree less than this reference value is low.

[0023] If the compressive strength of the cement mixture containing the hardened cement is estimated to be high in estimation step S2, then mixing the hardened cement with cement and water after the estimation step S2 can increase the compressive strength of the resulting cement mixture (at 7 and 28 days of age).

[0024] Next, referring to Table 1 below, we will describe test examples A1 to A9 concerning means of increasing the degree of carbonation of cementite. The purpose of test examples A1 to A9 is to clarify the relationship between the means of supplying carbon dioxide to the cementite and the degree of carbonation of the cementite supplied with carbon dioxide by this means.

[0025] [Table 1]

[0026] (Preparation process: Preparation of cemented body) This preparation process was carried out prior to the above-mentioned test examples A1 to A9. Specifically, a cement paste was prepared by mixing 100 parts by mass of ordinary Portland cement with 30 parts by mass of water. Next, this cement paste was cured for 28 days in an environment of 60% humidity and 20°C. Furthermore, a powdered cement paste (particle size 300 μm or less) was prepared by crushing the resulting hardened cement.

[0027] (Summary of Exam Examples A1-A9) In Test Example A1, the degree of carbonation of the cementite prepared in the above preparation step was calculated. In Test Examples A2 to A9, carbon dioxide was supplied to the cementite prepared in the above preparation step by various means, and the degree of carbonation of the resulting cementite was calculated.

[0028] (Specific procedures for test examples A1-A9) In Test Example A1, a portion of the hardened cement body prepared in the preparation step was taken. The mass of calcium carbonate contained in the taken hardened cement body and the loss on ignition of this hardened cement body were measured using TG-DTA (thermogravimetric and differential thermal analysis). The measurement range was the time period during which the temperature of the hardened cement body was raised from 500°C to 800°C. Using this data, the degree of carbonation of the hardened cement body was calculated. TG-DTA was performed immediately after the preparation of the hardened cement body in the preparation step.

[0029] In Test Example A2, the means of supplying carbon dioxide was left indoors (contact with carbon dioxide in the air). Specifically, in Test Example A2, a portion of the hardened cement prepared in the preparation process was taken, and the taken hardened cement was left indoors (humidity 55%, temperature 20°C) for 42 weeks before TG-DTA was performed. However, during this 42-week period, in order to maintain a water ratio of 0.2 in the hardened cement, distilled water was periodically sprayed onto the hardened cement and the cement was stirred. Other aspects were the same as in Test Example A1.

[0030] In Test Example A3, carbon dioxide gas was supplied from the air as the means of supplying carbon dioxide. Specifically, in Test Example A3, a portion of the hardened cement body prepared in the preparation step was taken, and carbon dioxide gas (CO2 content: 20%, N2 content: 80%) was supplied to the taken hardened cement body for 480 minutes before TG-DTA was performed. The amount of carbon dioxide gas supplied was adjusted to a flow rate of 4 L / min for 250 g of hardened cement body. Other aspects were the same as in Test Example A1.

[0031] In Test Examples A4 to A9, carbon dioxide gas was supplied underwater as the means of supplying carbon dioxide. Specifically, in Test Examples A4 to A9, a portion of the hardened cement produced in the preparation step was taken, the taken hardened cement and a predetermined amount of water were placed in a container, and the carbon dioxide gas was supplied to the resulting hardened cement in water for a predetermined time. After that, the hardened cement was removed from the water and left in a drying oven at 110°C for 24 hours. Subsequently, TG-DTA was performed on the hardened cement removed from the drying oven. The amount of carbon dioxide gas supplied was the same as in Test Example A3. Other aspects were the same as in Test Example A1.

[0032] (Conditions and results for test examples A1-A9) Table 1 shows the conditions and results for test examples A1 to A9. In the "Water Ratio (-)" column in Table 1, the mass ratio of water to the hardened cement placed in the container is shown for each of test examples A4 to A9. In the "Carbon Dioxide Supply Time" column in Table 1, the time the hardened cement was left at room temperature is shown for test example A2, and the time the carbon dioxide gas was supplied to the hardened cement is shown for each of test examples A3 to A9. In the "Carbonation Degree (-)" column in Table 1, the carbonation degree (-) of the hardened cement calculated for test examples A1 to A9 is shown.

[0033] (Consideration) In Table 1, comparing test examples A3-A5 and A9, where the carbon dioxide gas supply time was 480 minutes, test example A5, with a water ratio of 2, and test example A9, with a water ratio of 20, showed a higher degree of carbonation in the hardened cement compared to test example A3, where no water was supplied to the hardened cement, and test example A4, with a water ratio of 1.

[0034] In Table 1, comparing test examples A6 to A9, where the water ratio is 20, test examples A7 to A9, where the carbon dioxide gas supply time is 240 minutes or more, show a higher degree of carbonation in the hardened cement compared to test example A6, where the carbon dioxide gas supply time is less than 240 minutes.

[0035] In other words, to increase the degree of carbonation of the hardened cement, it is preferable to supply water to the hardened cement in an amount between 2 and 20 times the mass of the hardened cement, and further supply carbon dioxide gas to the hardened cement in the resulting water for a period of 240 to 480 minutes.

[0036] Next, with reference to Table 2 below, test examples B1 to B9 of cement compositions according to one embodiment of the present invention will be described. The purpose of test examples B1 to B9 is to clarify the relationship between the silica gel content and degree of carbonation of the hardened cement contained in the cement composition and the strength development of this cement composition.

[0037] [Table 2]

[0038] (Overview of Exam Examples B1-B9) In Test Examples B1 to B9, cementitious bodies with various silica gel content and carbonation levels were mixed with ordinary Portland cement at various mixing ratios, and the compressive strength (at 3, 7, and 28 days of age) of the mortar produced from the resulting cement composition was measured.

[0039] (Specific procedures for test examples B1-B9) 1. Measurement of silica gel content In Test Examples B1 to B3, a portion of the hardened cement body removed from the drying oven in Test Example A9 was taken, and the silica gel contained in the taken hardened cement body was eluted with methanol salicylate, hydrochloric acid, and potassium hydroxide. The silica gel content of the resulting liquid was measured by ICP emission spectrometry (RF power: 1KW, measurement wavelength: 251.611nm). Furthermore, the silica gel content of the hardened cement body was calculated based on these measurements.

[0040] 2. Measurement of compressive strength Furthermore, in test examples B1 to B3, a portion of the hardened cement removed from the drying oven in test example A9 was taken, and the taken hardened cement was mixed with ordinary Portland cement in a predetermined ratio. In addition, mortar (cement mixture) was molded from the resulting mixture (cement composition) in accordance with JIS R 5201:2015 "Physical Test Methods for Cement," and the compressive strength of the mortar (strength development of the cement composition) was measured at 3 days, 7 days, and 28 days of age.

[0041] In Test Examples B4 to B6, a portion of the hardened cement sample from Test Example A2, which had been left indoors, was taken, and the silica gel content and compressive strength were measured using the collected hardened cement sample. Other aspects were the same as in Test Examples B1 to B3.

[0042] In Test Examples B7 to B9, a portion of the hardened cement prepared in the preparation step was taken, and the silica gel content and compressive strength were measured using the taken hardened cement. Other aspects were the same as in Test Examples B1 to B3.

[0043] (Conditions and results for test examples B1-B9) Table 2 shows the conditions and results for test examples B1 to B9. The "Silica Gel Content (%)" column in Table 2 shows the silica gel content of the hardened cement measured in test examples B1 to B9. The "Mixing Ratio (%)" column in Table 2 shows the mass ratio of the hardened cement to ordinary Portland cement in test examples B1 to B9. The "Compressive Strength (N / mm²)" column in Table 2 shows the compressive strength (N / mm²). 2 The section ")" shows the compressive strength of the mortar at 3 days, 7 days, and 28 days of age in test examples B1 to B9.

[0044] (Consideration) In Table 2, comparing test examples B1, B4, and B7, where the cementitious body mixing ratio is 5%, test examples B1 and B4, where the silica gel content of the cementitious body is 3.0% or higher and the carbonation degree of the cementitious body is 0.40 or higher, show higher compressive strength of the mortar (at 7 and 28 days) than test example B7, where the silica gel content of the cementitious body is less than 3.0% and the carbonation degree of the cementitious body is less than 0.40. Furthermore, a similar trend is observed when comparing test examples B2, B5, and B8, where the cementitious body mixing ratio is 10%, or when comparing test examples B3, B6, and B9, where the cementitious body mixing ratio is 20%.

[0045] In other words, in a cement composition containing cement (for example, ordinary Portland cement) and a cementite, wherein the mass ratio of the cementite to the cement is 1% by mass or more and 25% by mass or less (preferably 1% by mass or more and 20% by mass or less), the strength development of the cement composition can be enhanced if the degree of carbonation of the cementite is 0.40 or higher, or if the silica gel content of the cementite is 3.0% by mass or higher.

[0046] In Table 2, comparing test examples B1, B4, and B7, where the cementitious body mixing ratio is 5%, the compressive strength of the mortar (at 7 and 28 days of age) increases as the degree of carbonation of the cementitious body increases. Furthermore, a similar trend is observed when comparing test examples B2, B5, and B8, where the cementitious body mixing ratio is 10%, or when comparing test examples B3, B6, and B9, where the cementitious body mixing ratio is 20%.

[0047] In other words, by calculating the degree of carbonation of the hardened cement, it is possible to estimate the compressive strength (at 7 and 28 days old) of the mortar (cement mixture) based on the carbonation degree, without actually manufacturing mortar (cement mixture) using this hardened cement and waiting for 7 or 28 days. For example, it can be estimated that the compressive strength (at 28 days old) of mortar manufactured using a hardened cement with a carbonation degree of 0.50 will be higher than that of mortar manufactured using a hardened cement with a carbonation degree of 0.30.

Claims

1. A cement composition comprising cement and a cementite, wherein the mass ratio of the cementite to the cement is 1% by mass or more and 25% by mass or less, When the amount of calcium oxide contained in the cement used to manufacture the cementified body is A [mass%], the amount of calcium carbonate in the cementified body is B [mass%], the loss on ignition of the cementified body is C [%], and the loss on ignition of the cement used to manufacture the cementified body is D [%], the value of [(B / A) × (molecular weight of calcium oxide / molecular weight of calcium carbonate) × {(100 - D) / (100 - C)}] is 0.40 or more and 0.85 or less, or / and, A cement composition characterized in that the silica gel content of the hardened cement is 3.0% by mass or more and 9.0% by mass or less.

2. A method for estimating the compressive strength of a cement mixture produced by mixing cement, cementite, and water, based on the following indicators: A method for estimating the compressive strength of a cement mixture, characterized in that the index is the value of [(B / A) × (molecular weight of calcium oxide / molecular weight of calcium carbonate) × {(100 - D) / (100 - C)}], where A [mass%] is the amount of calcium oxide contained in the cement used to manufacture the cement hardened body, B [mass%] is the amount of calcium carbonate in the cement hardened body, C [%] is the loss on ignition of the cement hardened body, and D [%] is the loss on ignition of the cement used to manufacture the cement hardened body.

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