Method for measuring amount of carbon dioxide

Abstract

To provide a method for measuring the amount of carbon dioxide, capable of easily and accurately measuring the amount of carbon dioxide contained in concrete.SOLUTION: In the method for measuring the amount of carbon dioxide in concrete, the amount of carbon dioxide in drilling powder obtained by forming a drilling hole in the concrete is measured by a measuring means.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the amount of carbon dioxide. [Background technology]

[0002] The quantitative determination of carbon dioxide contained in concrete is an important technique for quantitative evaluation of concrete neutralization and evaluation of carbon dioxide fixation materials. Generally, thermal decomposition or acid dissolution is used to easily extract carbon dioxide from the target sample during the analytical process.

[0003] However, due to the need to shorten extraction times and limitations on the sample size of analytical equipment, it is necessary to break down the sample into smaller pieces by crushing, etc. On the other hand, there is a concern that the sample itself may come into contact with carbon dioxide in the atmosphere during sample size adjustment, resulting in a quantified value that differs from the sample's original amount of carbon dioxide.

[0004] For example, Patent Document 1 describes a method for measuring the CO2 absorption of a specimen made of hardened mortar from the mass loss within a specified temperature range using simultaneous differential thermal analysis and thermogravimetry (TG-DTA). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6305874 Summary of the Invention [Problem to be solved by the invention]

[0006] However, Patent Document 1 is directed to hardened mortar, not concrete. In other words, to measure the amount of carbon dioxide contained in concrete, it is necessary to collect a sample from the concrete on-site. Depending on the collection method, the sample to be analyzed may be in contact with the atmosphere for a long time during the subsequent process of transportation, adjustment in a laboratory, and analysis, making it difficult to easily measure the amount of carbon dioxide accurately.

[0007] In view of the above, an object of the present invention is to provide a highly reproducible measurement method for measuring the amount of carbon dioxide contained in concrete simply and with high accuracy. [Means for solving the problem]

[0008] In view of the above problems, the present inventors have conducted extensive research and have come up with the following invention, which has been found to solve the above problems.

[0009] [1] A method for measuring the amount of carbon dioxide in concrete, comprising drilling holes in the concrete and measuring the amount of carbon dioxide in the drilled powder obtained by drilling holes in the concrete using a measuring means. [2] A method for measuring the amount of carbon dioxide described in [1], in which the drilling powder is stored in a storage body with low oxygen permeability immediately after being obtained. [3] The method for measuring the amount of carbon dioxide according to [1] or [2], wherein the means for forming the hole is a drill. [4] The method for measuring the amount of carbon dioxide according to any one of [1] to [3], wherein the measuring means is either TG-DTA or a coulometer. [5] The method for measuring the amount of carbon dioxide according to any one of [1] to [4], wherein the diameter of the drilled holes is 0.75 times or more the maximum dimension of the coarse aggregate in the concrete. [6] The method for measuring the amount of carbon dioxide according to any one of [1] to [5], wherein the length of the drilled hole is at least twice the maximum dimension of the coarse aggregate in the concrete. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for measuring the amount of carbon dioxide fixed in concrete simply and more accurately. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, one embodiment of the present invention (the present embodiment) will be described in detail. The carbon dioxide contained in concrete in this embodiment refers to carbon dioxide contained in the hardened cement body and aggregate in the concrete, and includes carbon dioxide originally present in the materials constituting the concrete before mixing, carbon dioxide fixed due to effects such as carbonation during use, and carbon dioxide present in the calcium carbonate constituting the hardened cement body and forms other than calcium carbonate. Examples of forms other than calcium carbonate include amorphous calcium silicate hydrate (CSH) and limestone aggregate.

[0012] The method for measuring the amount of carbon dioxide in this embodiment measures the amount of carbon dioxide in concrete, and involves drilling holes in the concrete and measuring the amount of carbon dioxide in the drilling powder obtained by drilling holes in the concrete using a measuring means.

[0013] In most conventional sample preparation methods, cylindrical coring samples with diameters of 30mm, 50mm, 100mm, etc. are first collected on-site. To set up the coring machine, anchor holes must be drilled in advance, and the heavy coring machine must be anchored to the target structure before coring can begin. This requires a lot of labor to transport and set up the equipment.

[0014] The coring sample is then transported to the laboratory and crushed using a jaw crusher or mortar to a particle size suitable for analysis, and used as a sample for measurement. The coring sample is then brought back to the laboratory and cut and crushed, but because the coring sample comes into contact with the atmosphere during sample preparation, carbon dioxide in the atmosphere can bind to the sample, resulting in the analyzed value being different from the carbon dioxide actually contained in the sample.

[0015] In contrast, this embodiment uses drilled powder from a drill or the like, for example, by using a hand hammer drill or the like, eliminating the need to set up equipment and enabling on-site labor savings. Furthermore, because the sample is pulverized simultaneously with sampling, the sample preparation process can be omitted, further reducing the impact of carbon dioxide that increases during preparation due to reaction with atmospheric carbon dioxide. In other words, this embodiment enables accurate measurement of carbon dioxide levels, while also reducing labor, allowing for simplified measurement.

[0016] Examples of means for performing the above-mentioned drilling process include a drill such as a hammer drill, a breaker that uses impact, etc. A drill is preferable from the viewpoint of reducing the labor required for the work and obtaining powder in a state suitable for measurement. Furthermore, by providing a guide with a hole for contacting the blade of the hammer drill with the object to be measured, scattering of drilling powder and the inclusion of foreign matter other than drilling powder can be prevented.

[0017] The drilling powder is preferably stored in a container with low oxygen permeability immediately after it is obtained. Examples of containers with low oxygen permeability include bags or boxes made of plastics such as nylon or metals such as aluminum.

[0018] The composition of hardened concrete is mainly classified as cement paste, fine aggregate (sand: mainly 5 mm or less), and coarse aggregate (gravel: mainly 5 mm or more). The part that can be treated as a relatively uniform material is the mortar portion, which is made up of cement paste and fine aggregate. In other words, compared to hardened mortar, concrete contains coarse aggregate, so if the cutting edge diameter of a drill such as a hammer drill is small, the resulting drilling powder may not be treated as a uniform sample. Therefore, from the perspective of obtaining uniform drilling powder, more accurate carbon dioxide measurement is possible by appropriately adjusting the relationship between the drilling diameter and the maximum dimension of the coarse aggregate, and between the drilling length and the maximum dimension of the coarse aggregate.

[0019] The above will be explained in more detail. First, coarse aggregate does not fix carbon dioxide. Therefore, if there is more coarse aggregate than necessary in the drilling target, the carbon dioxide will be underestimated. On the other hand, if there is no coarse aggregate, the carbon dioxide will be overestimated.

[0020] It is preferable that the drilled portion be in a state close to the mix ratio of concrete, and it is preferable to avoid the presence of coarse aggregate in the drilled hole having a large effect on the measurement results. Therefore, in order to reduce the effect of the presence of coarse aggregate on the measurement results, it is preferable to perform a probabilistic evaluation using the drilled hole diameter and drilled hole length as factors.

[0021] The inventors have 3 Considering a concrete block, we divided it into elements (masses) with a side length of D, and considered the probability p that coarse aggregate exists in one mass, and derived the following formula. Formula) p=n / N=αG / (ρD 3 ) / (1 / D) 3 =αG / ρ n:1m 3 Number of coarse aggregates of particle size D (mm) per N: Number of elements in the mass block (1 / D is the cube of the number of equal parts of the mass block divided by D) 3 becomes) α: Residual rate (%) calculated from the passing percentage of the sieve nominal size D ρ: Density of coarse aggregate (kg / m3 ) G: Unit amount of coarse aggregate (kg / m 3 )

[0022] In other words, D, which was set as the particle size, is eliminated, and the existence probability p can be organized using the unit amount of coarse aggregate, density, and sieve retention rate. For example, if G is 1000 kg / m 3 , ρ: 2500 kg / m 3 If the particle size is 15mm in 50%, then 0.5 x 1000 ÷ 2500 = 20%, meaning that there is a 1 / 5 probability that it will exist in one square.

[0023] When the probability that coarse aggregate exists in a square is P, if there are n squares in the depth direction, the combination of squares in which coarse aggregate does not exist is (1 / P-1) n Also, all combinations can be expressed as (1 / P) n Therefore, when the drilling length is n, the probability q that there is no coarse aggregate within the drilling range is (1 / P-1) n ÷(1 / P) n =(1-P) n This becomes:

[0024] Here, we considered the aggregate particle size of JIS A 5308:2019 (ready-mixed concrete) as a representative example of the particle size distribution of coarse aggregate, and examined the probability that coarse aggregate with a maximum dimension of 25 mm would be present in a drilled hole in terms of the relationship between drilling diameter and drilling length.We found that the larger the drilling diameter, the higher the probability that coarse aggregate would not be present, and that when the drilling diameter is approximately the same as the maximum dimension of the coarse aggregate, the probability that coarse aggregate would not be present is as high as 80%, even if the drilling length is approximately 10 times the drilling diameter.

[0025] Next, the probability p of coarse aggregate being present in one square was calculated, and random numbers were generated by computer. The coefficient of variation was calculated from the standard deviation and average value obtained from 1,000 data sets. The calculation factors were drilling diameter and drilling length, and calculations were performed for a total of 140 levels. It was found that when the drilling diameter was small, the coefficient of variation increased, resulting in greater dispersion in the measured values. Furthermore, the longer the drilling length, the smaller the coefficient of variation tended to become. Increasing the drilling length increases the number of squares, which can be said to have the same effect as increasing the test quantity N. It was found that the most desirable case is when the drilling diameter is approximately the same as the maximum dimension of the coarse aggregate, and the drilling length is approximately 2 to 4 times the drilling diameter.

[0026] From the above, the diameter of the drilled holes is preferably 0.75 times or more the maximum dimension of the coarse aggregate in the concrete, and taking into account the drilling time, it is more preferably 1 to 5 times, and even more preferably 1 to 3 times.

[0027] Furthermore, the length of the drilled hole is preferably at least twice the maximum dimension of the coarse aggregate in the concrete, more preferably 2 to 10 times, and even more preferably 2 to 8 times, taking into account the drilling time.

[0028] The components constituting the concrete according to this embodiment include components constituting general concrete. Examples of cement include various Portland cements such as ordinary, early-strength, extra-early-strength, low-heat, and moderate-heat cements, various blended cements obtained by mixing these cements with blast furnace slag, fly ash, or silica, filler cements obtained by mixing limestone powder, slowly cooled blast furnace slag powder, and the like, and environmentally friendly cements (ecocements) produced using municipal waste incineration ash and sewage sludge incineration ash as raw materials.

[0029] The aggregate is not particularly limited, but one with low water absorption and high aggregate strength is preferred. Examples of fine aggregate include river sand, mountain sand, sea sand, lime sand, and silica sand. Examples of coarse aggregate include river gravel, mountain gravel, lime gravel, crushed sand, crushed stone, and artificial aggregate (such as slag aggregate). These can be used alone or in combination of two or more. The maximum size of the aggregate is 25 mm or 20 mm.

[0030] In the case of aggregates that use lime sand or lime gravel, the amount of carbon dioxide contained in these aggregates can also be measured.

[0031] In concrete that uses lime sand or lime gravel as aggregate, if the concrete surface is in contact with the atmosphere containing carbon dioxide, carbon dioxide will be neutralized from the surface that comes into contact with the atmosphere, resulting in the fixation of carbon dioxide. To determine the amount of fixed carbon dioxide, it is necessary to measure the amount of carbon dioxide before fixation, but in such cases, samples can be taken from two locations: one where carbonation has not progressed and one where carbonation has progressed, and the amount of carbon dioxide fixed in the concrete itself can be determined from the difference between the two.

[0032] Other examples include admixtures such as silica fume, rice husk ash, fly ash, natural pozzolan, limestone fine powder, zeolite, expansive agents, colorants, crushed stone powder, polymer emulsions, air-entraining agents, water-reducing agents, organic fibers, inorganic fibers, steel fibers, high-performance water-reducing agents, high-performance air-entraining water-reducing agents, shrinkage-reducing agents, dust-reducing agents, thickeners, waterproofing agents, rust inhibitors, cold-resistance promoters, foaming agents, and air-forming agents.

[0033] The measurement means for measuring the amount of carbon dioxide in the drilling powder is preferably either TG-DTA or a coulometer.

[0034] TG-DTA (simultaneous thermogravimetric analysis with differential thermal analysis) is a method for simultaneously measuring the change in weight (mass) of a sample and the temperature difference between the sample and a reference material while changing the temperature of the sample and reference material according to a program.

[0035] The measurement temperature range when measuring the carbon dioxide content by TG-DTA is preferably 500 to 900°C, and more preferably 600 to 800°C.

[0036] The temperature rise rate is preferably 5 to 15°C / min, more preferably 8 to 12°C / min, from the viewpoints of the temperature of thermal change, the magnitude of the endothermic or exothermic peak, the sharpness of the peak, and the time required for measurement.

[0037] Coulometry (coulometric titration) is a method in which a measurement sample is acidified, the carbon dioxide gas generated is introduced into an absorption liquid, the amount of carbon is measured from the amount of electricity required to maintain a constant transmittance of the absorption liquid, and this measurement is converted into the amount of carbon dioxide to determine the carbon dioxide content.

[0038] To make the measurement sample acidic, it is preferable to add perchloric acid with a perchloric acid concentration of 10 to 14%, more preferably 11 to 13%, to the measurement sample. With this concentration of perchloric acid, carbonates in the cementitious material can be sufficiently dissolved and carbon dioxide gas can be generated.

[0039] In both TG-DTA and coulometer, the particle size of the measurement sample is preferably 200 μm or less, more preferably 50 to 150 μm, from the viewpoint of workability. The particle size can be measured using a sieve.

[0040] Of the measurement means TG-DTA and coulometer, it is preferable to use a coulometer, since it can measure and quantify carbon dioxide that exists in forms other than calcium carbonate.

[0041] The method for measuring the amount of carbon dioxide according to this embodiment is not particularly limited, but is particularly effective when investigating the degree of neutral deterioration occurring in reinforced concrete structures. [Example]

[0042] <Materials used> Cement: Ordinary Portland cement (commercially available) Fine aggregate: River sand from the Himekawa River system, 5mm below Coarse aggregate: River gravel from the Himekawa River system, maximum size 20mm Water: Tap water

[0043] <Manufacturing reinforced concrete specimens and measuring carbon dioxide content> A reinforced concrete specimen measuring 1m x 1m x 0.3m was prepared. The concrete mix had a cement content of 300kg / m 3 The water-cement ratio was 55% and the s / a ratio was 48%. The mixed concrete had a slump of 15±2.5cm and an air content of 4.5±1.5%. The reinforced concrete specimens were left outdoors for 90 days.

[0044] [Experiment No. 1] The reinforced concrete specimens were crushed using a chisel and hammer to obtain powder. The carbon dioxide content was measured three times using this powder with a coulometer. The powder contained many large particles of 1 mm or larger.

[0045] [Experiments No. 2-9] Reinforced concrete specimens were drilled using a hand hammer drill to obtain drilled powder. By changing the diameter and length of the drill, the drilled diameter and length were changed as shown in Table 1. The amount of carbon dioxide was measured three times using the obtained drilled powder using a coulometer.

[0046] [CO2 content measurement using a coulometer] Using a coulometer (UIC CM5017), powders placed in a dedicated flask, perchloric acid (concentration: 12%) was added to 40 mg of each drilling powder, and the mixture was stirred with a stirrer. The generated CO2 gas was introduced into the absorption solution, and the amount of carbon was measured from the amount of electricity required to maintain the transmittance of the absorption solution at a constant level. 3 Carbon dioxide content of concrete per unit area (kg / m 3The results are shown in Table 1. From the measured values, the difference between the maximum and minimum values ​​was calculated, and the ratio of this difference to the average value was calculated to evaluate the variation.

[0047] [Table 1] [Industrial Applicability]

[0048] The present invention can be widely used in the fields of civil engineering and construction to measure the amount of carbon dioxide in various types of concrete.

Claims

1. A method for measuring the amount of carbon dioxide in concrete, comprising: A method for measuring the amount of carbon dioxide, which comprises drilling holes in the concrete and measuring the amount of carbon dioxide in the drilled powder obtained by drilling holes in the concrete using a measuring means.

2. 2. A method for measuring the amount of carbon dioxide as described in claim 1, wherein the drilling powder is stored in a storage body having low oxygen permeability immediately after being obtained.

3. 2. The method for measuring the amount of carbon dioxide according to claim 1, wherein the means for forming the hole is a drill.

4. 2. The method for measuring the amount of carbon dioxide according to claim 1, wherein the measuring means is either a TG-DTA or a coulometer.

5. 2. The method for measuring the amount of carbon dioxide according to claim 1, wherein the diameter of the drilled holes is 0.75 times or more the maximum dimension of the coarse aggregate in the concrete.

6. 2. The method for measuring the amount of carbon dioxide according to claim 1, wherein the length of the drilled hole is at least twice the maximum dimension of the coarse aggregate in the concrete.

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