Method for estimating water immersion expansion ratio of slag, steel slag for roads and reinforced roadbed material and method for manufacturing same

Abstract

To propose a simple and accurate method for estimating the water immersion expansion ratio of slag, a reinforced roadbed material that does not cause reverse fault type failure, and its manufacturing method.SOLUTION: There is provided a method for estimating the water immersion expansion ratio of steel slag for road building, in which the water immersion expansion test of the slag is performed to obtain a water immersion expansion ratio of the slag at a predetermined measurement temperature and measurement time, and the water immersion expansion ratio can be obtained in a predetermined estimated time when the water immersion expansion test of the slag is performed at a predetermined estimated temperature, and reinforced roadbed material made of a mixture of cement and slag is composed of materials whose estimated water immersion expansion ratio (%) of slag is lower than the strain rate (%) that brings about compressive failure of reinforced roadbed material in a compression test of reinforced roadbed material after cement curing.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for estimating the water immersion expansion ratio of steel slag, such as steelmaking slag, which is a by-product of steelworks and is used in road base materials, as well as to steel slag for roads, and further to reinforced road base materials using steel slag and methods for producing the same. [Background technology]

[0002] Materials used for the base of an asphalt pavement are selected taking into consideration the stability and durability of the base. Materials used for base courses are specified in the common civil engineering specifications and pavement recycling handbook of each prefecture, and are required to meet various characteristics such as modified CBR.

[0003] It is well known that steel slag, such as steel slag, which is generated as a by-product of steelworks, is one of the materials for roadbed materials. In steel slag, some lime from the refining process remains unreacted. When this lime expands in volume by hydrating with water, it expands. For this reason, JIS A 5015:2018 stipulates that roadbed materials using steel slag should be aged to stabilize their expansion. In addition, the water immersion expansion ratio (expansion characteristics) of steel slag is measured by the water immersion expansion test method for steel slag for roads described in JIS A 5015:2018 Appendix B. The water immersion expansion test is performed by compacting steel slag into a mold. Then, the slag is kept in 80°C hot water for 6 hours and then allowed to cool. This operation is repeated once a day for 10 days, and the water immersion expansion ratio (%) is calculated from the expansion amount measured by a dial gauge.

[0004] The technology disclosed in Patent Document 1 calculates an estimated time based on the magnification of the water immersion expansion rate per unit temperature, the measured temperature, and the estimated temperature from the water immersion expansion curves of multiple steelmaking slags expanded at different temperatures, and determines the expansion characteristics based on a gradient consisting of the estimated time and the logarithmically transformed water immersion expansion ratio.

[0005] In addition, when steel slag is used as a roadbed material, it is common to perform pretreatment such as aging beforehand, and then add cement to the pretreated steel slag to form a stabilized mixture. Meanwhile, reinforced roadbed materials containing steel slag are required to not cause reverse fault type failure due to the expansion of steel slag, in addition to the desired strength, filling property, compaction property, etc. For this reason, excessive pretreatment has been performed by uniformly setting a large safety factor. It has not yet been clarified to what extent the expansion of steel slag needs to be suppressed to avoid reverse fault type failure. Note that the reverse fault type failure referred to here refers to a phenomenon in which a horizontal compressive force acts on the roadbed due to the expansion of steel slag after the roadbed material solidifies, causing a fault in the roadbed, and the roadbed on one side of the fault rises above the roadbed on the other side, causing the roadbed to rise near the fault.

[0006] As prior art related to roadbed materials, for example, Patent Documents 2 and 3 propose a method for estimating future strength development from unconsolidated soil cement. Patent Document 4 proposes a method for estimating compressive strength at a specified age according to the construction conditions at the soil cement construction site. Furthermore, Patent Document 5 proposes a method for evaluating the filling property, compaction property, etc. of concrete from the viewpoint of management and rationalization of the construction site. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2018-025461 A [Patent Document 2] JP 2018-135696 A [Patent Document 3] JP 2014-111879 A [Patent Document 4] JP 2015-059325 A [Patent Document 5] JP 2017-223490 A Summary of the Invention [Problem to be solved by the invention]

[0008] As in Patent Document 1, in order to determine the magnification of the water immersion expansion rate per unit temperature, it was necessary to carry out water immersion expansion tests in advance at various temperatures for each type of steelmaking slag, which was a very heavy burden.

[0009] Patent Documents 2 to 5 do not mention the avoidance of reverse fault rupture caused by expansion of roadbed materials after solidification.

[0010] The present invention aims to solve the above problems, propose a method for estimating the water immersion expansion ratio of slag that can easily and accurately estimate the water immersion expansion ratio at an estimated temperature and estimated time, provide steel slag suitable for roads, and propose a reinforced roadbed material and a manufacturing method thereof that do not cause reverse fault-type failure due to slag expansion. [Means for solving the problem]

[0011] The means for solving the above problems are as follows. [1] A method for estimating the water immersion expansion ratio of steel slag for road use, comprising: conducting a water immersion expansion test of the slag to obtain the water immersion expansion ratio of the slag at a specified measurement temperature and measurement time; and estimating that the water immersion expansion ratio will be obtained in a specified estimated time when a water immersion expansion test of the slag is conducted at a specified estimated temperature. [2] A method for estimating the water immersion expansion ratio of slag as described in claim 1, wherein the estimated time t of the water immersion expansion test of the slag is estimated using the following equation (1).

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[0012] According to the method for estimating the water-immersion expansion ratio of slag of the present invention, the water-immersion expansion ratio estimation formula is expressed as a function including the measured expansion rate, measurement time, measured temperature, and estimated temperature of the water-immersion expansion test as variables, and the water-immersion expansion ratio that satisfies this function is calculated. This makes it possible to accurately estimate the water-immersion expansion ratio at the estimated temperature and estimated time. It also makes it possible to estimate the water-immersion expansion ratio when the estimated time is shortened and extended. Using this water-immersion expansion ratio estimation method, steel slag with a predetermined water-immersion expansion performance can be selected for road use.

[0013] According to the reinforced roadbed material and its manufacturing method of the present invention, the strain rate (%) that leads to compressive failure of the reinforced roadbed material after cement curing is assumed to be due to the expansion of slag, and this strain rate (%) is compared with the estimated water immersion expansion ratio (%) of the steelmaking slag. By making the estimated water immersion expansion ratio (%) lower than the strain rate (%), it is possible to suppress the expansion of the slag and thereby avoid reverse fault failure of the reinforced roadbed material. [Brief description of the drawings]

[0014] [Figure 1] 1 is a graph showing the relationship between the amount of cement added and the strain rate at the time of compressive failure. [Diagram 2] 1 is a graph showing the relationship between the reduction rate and the strain rate at the time of compressive failure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [Method for estimating the water immersion expansion ratio of slag] The method for estimating the water immersion expansion ratio of slag according to the first embodiment of the present invention expresses the water immersion expansion ratio estimation formula as a function including the measured expansion rate, measurement time, measured temperature, estimated temperature, and estimated time of the water immersion expansion test as variables, and calculates the time that satisfies this function.

[0016] In this embodiment, the steel slag constituting the slag roadbed material for roads is not particularly limited as long as it is slag generated in a steelworks. For example, various types of slag can be exemplified, such as pretreatment slag generated in the hot metal pretreatment process (desiliconization, dephosphorization, desulfurization), converter slag (decarburization slag) generated in the decarburization process in a converter, electric furnace slag generated in the process in an electric furnace, secondary refining slag generated in the secondary refining process, and ingot slag generated in the casting process. These can be treated alone or in a mixture of two or more types.

[0017] The variables of the function shown in the (1) formula of the following formula 2 are the measured expansion speed (ν 0 ), measured temperature (T 0 ), measurement time (t 0 ), estimated temperature (T), and estimated time (t). In the water immersion expansion test method for steel slag for road use described in JIS A 5015:2018 Appendix B, a test is conducted for 10 days, but in this embodiment, this can be shortened or extended as desired. The test temperature is also 80°C, but it may be changed as desired for testing. In the above JIS test, the sample is kept in 80°C hot water for 6 hours and then allowed to cool. This operation is repeated once a day for 10 days, but the temperature may be kept continuously.

[0018]

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[0019] In the above formula (1), ν is the estimated expansion rate in the water immersion expansion test, but the measured expansion rate (ν 0 ) may be used, with units of % / day. Estimated temperature (T) and measured temperature (T 0 ) is the test temperature for the water immersion expansion test, and is in the range of 273K≦T≦373K under atmospheric pressure where water exists as a liquid. However, this is the temperature range where water exists as a liquid under pressure. V is the water immersion expansion ratio (%).

[0020] Here, the estimated expansion rate (ν) in the water immersion expansion test is calculated by dividing the measured expansion rate (ν 0) and estimate the estimated time (t) at the estimated temperature (T) that will be equal to the measured water immersion expansion ratio (V). By transforming equation (1), we obtain the following equation (1') in Equation 3.

[0021]

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[0022] The measurement temperature for the water immersion expansion test (T 0 Since the temperature may fluctuate during the test, the test temperature of the water immersion expansion test is continuously measured, and the cumulative temperature is divided by the test time and averaged. 0 In this way, in order to estimate the water immersion expansion ratio at the desired estimated temperature (T) and estimated time (t), a water immersion expansion test of the slag is performed at a predetermined measurement temperature and a predetermined measurement time to measure the water immersion expansion ratio.

[0023] The above slag was subjected to water immersion expansion tests at various temperatures and times. 0 )[K], measurement time (t 0 ) [days]. Also, the measured pressure (P 0 ) [MPa]. Using the above relational expression, the estimated time (t) [days] for the water immersion expansion test of slag that would result in the same estimated water immersion expansion ratio (Ve) [%] as the measured water immersion expansion ratio (V) [%] at the estimated temperature (T) [K] for each test was estimated using the above formula (1') and listed. The actual water immersion expansion ratio (Va) obtained as a result of the water immersion expansion test of the same slag using the estimated temperature (T) and estimated time (t) is also listed. The obtained results were statistically processed, and conditions where the error between the estimated water immersion expansion ratio (Ve) and the actual water immersion expansion ratio (Va) was within 3σ (standard deviation) were judged with the symbol ○, and other conditions were judged with the symbol ×.

[0024] [Table 1]

[0025] Measurement temperature (T 0In Test Nos. 1 to 24, where the temperature range was set so that water exists as a liquid, the estimated water immersion expansion ratio (Ve) and the actual water immersion expansion ratio (Va) were in good agreement. 0 ) In tests No. 25 to 33, which were performed in a temperature range where water does not exist as a liquid at atmospheric pressure, there was a large error between the estimated water immersion expansion ratio (Ve) and the actual water immersion expansion ratio (Va).

[0026] [Steel slag for roads] In the case of the steel slag for road use according to the second embodiment of the present invention, when the water immersion expansion ratio V of the slag is estimated at room temperature (293K) for an estimated time t of 10 years (3652 days) using the method for estimating the water immersion expansion ratio of the slag according to the first embodiment, the water immersion expansion ratio V must be 3.5% or less. By satisfying this condition, it is possible to obtain an effect of preventing the roadbed material from heaving. If the water immersion expansion ratio V exceeds 3.5%, there is a risk of heaving occurring in the roadbed material. For example, when the measurement temperature (T 0 ) and measurement time (t 0 ) and measuring the water immersion expansion ratio V, it is possible to estimate the water immersion expansion ratio V at room temperature (293 K) when the estimated time t is 3652 days.

[0027] [Reinforced roadbed material] The third embodiment of the present invention is a method for evaluating reinforced roadbed material by comparing the water immersion expansion ratio (%) of the slag estimated using the method for estimating the water immersion expansion ratio of the slag in the first embodiment with the strain rate (%) at which the reinforced roadbed material will be crushed in a compression test of the reinforced roadbed material after cement curing. If the estimated water immersion expansion ratio (%) at room temperature (293K) and an estimated time t of 10 years (3652 days) is lower than the strain rate (%) at which the reinforced roadbed material will be crushed, it can be determined that it is possible to avoid the occurrence of reverse fault type fracture caused by the expansion of the material after solidification. This is based on the novel finding that it is possible to set the amount of cement to be added that will not cause reverse fault type fracture in the future.

[0028] Figure 1 shows the relationship between the strain rate (%) at the time of compressive failure and the amount of cement added (mass%) of several specimens with a diameter of 100 mm and a height / diameter ratio of 1.27, which were made by adding 1.0-5.0 mass% of cement to steel slag adjusted to a grain size of 0-40 mm, mixing, compacting (the water content was adjusted to a water content sufficient for cement to solidify for 28 days), and sealing and curing. Table 2 shows the amount of cement added (mass%) of each specimen, the strain rate (%) at the time of compressive failure of each specimen, the estimated water immersion expansion ratio (%) of steel slag, and the results of the investigation into applicability. Here, the estimated water immersion expansion ratio was estimated at room temperature (293K), normal pressure (atmospheric pressure), and an estimated time t of 10 years (3652 days).

[0029] In this investigation, the particle size distribution of the steelmaking slag was measured according to JIS A 1102:2014, and the relative particle size was created using the measured particle size, and the particle size was adjusted so that there would be no particle size difference between the specimens (the maximum particle size of the slag was adjusted to 1 / 4 or less of the diameter of the specimen). The mixture was tamped according to E011 and F007 of the test manual, and the rolling speed in the compression test was set to 0.2 mm / min. The strain rate (%) at the time of compression failure was obtained by creating a load-strain curve from the compression test results and converting the strain at the maximum load in the load-strain curve into a strain rate. The estimated water immersion expansion ratio (%) of the steelmaking slag was estimated from the water immersion expansion test at a specified measurement temperature and for a specified measurement time shown in the first embodiment. Applicability was indicated by a circle when the estimated water immersion expansion ratio (%) of the steelmaking slag was lower than the strain rate (%) at the time of compressive failure, a double circle when the difference between the strain rate (%) and the estimated water immersion expansion ratio (%) was 0.2% or more, and an × when the estimated water immersion expansion ratio (%) was higher than the strain rate (%) at the time of compressive failure.

[0030] [Table 2]

[0031] In Table 2, Test Nos. 1 to 3 are cases where the amount of cement added was 1.5 mass%. Test Nos. 4 to 6 are cases where the amount of cement added was 3.5 mass%. Test No. 7 is a case where the amount of cement added was 5.0 mass%. As is clear from Table 2, the estimated water immersion expansion ratio (%) of all of the invention examples is lower than the strain rate (%) at the time of compressive failure. Therefore, the results showed that the method is applicable. In contrast, the estimated water immersion expansion ratio (%) of all of Test Nos. 8 to 11 exceeded the strain rate (%) at the time of compressive failure, making them inapplicable.

[0032] In this embodiment, the reduction rate in the compression test is preferably 0.1 to 1% / min. The reason for this is that it is believed that the stress that occurs when the steelmaking slag expands under restraint can be intentionally generated. To achieve this, it is essential to make the reduction rate as small as possible while avoiding any influence on the strain rate (%) that leads to compressive failure. The results shown in FIG. 2 were obtained from a preliminary test.

[0033] In this embodiment, the reinforced roadbed material is manufactured by performing a compression test on the reinforced roadbed material after cement curing to determine the strain rate at which the reinforced roadbed material will fail under compression, and also determining the estimated water swelling ratio of the slag. The estimated water swelling ratio of the slag is compared with the strain rate at which the roadbed material will fail under compression, and cement is added and mixed with the slag under conditions where the estimated water swelling ratio is lower than the strain rate. To this end, it is preferable to use slag whose particle size is adjusted to the range of 0 to 40 mm, and the amount of cement added is preferably determined in the range of 1 to 5 mass% according to the required roadbed bearing capacity. The slag and cement are mixed by adjusting the humidity of the slag the day before compaction and mixing it with the cement immediately before compaction. It is also preferable that the sealed curing be performed under conditions of a temperature of 20°C and a humidity of 98%. [Industrial Applicability]

[0034] According to the method for estimating the water immersion expansion ratio of slag of the present invention, the water immersion expansion ratio at the estimated temperature and estimated time can be easily estimated with high accuracy. By estimating with this method, it is possible to provide steel slag with a water immersion expansion ratio suitable for road use. According to the reinforced roadbed material and the manufacturing method thereof of the present invention, it is possible to provide a reinforced roadbed material that does not cause reverse fault type failure and a manufacturing method thereof.

Claims

1. A method for estimating the water immersion expansion ratio of a steel slag for road use, comprising: conducting a water immersion expansion test of the slag to obtain a water immersion expansion ratio of the slag at a predetermined measurement temperature and measurement time; and estimating that the water immersion expansion ratio will be obtained in a predetermined estimated time when the water immersion expansion test of the slag is conducted at a predetermined estimated temperature, A method for estimating the water immersion expansion ratio of a slag, comprising estimating an estimated time t of the water immersion expansion test of the slag using the following formula (1). [0010] where V is the water immersion expansion ratio (%), ν is the estimated expansion rate (% / day), t is the estimated time (days), ν 0 is the measured expansion rate (% / day); t 0 is the measurement time (days); e is Napier's constant (-), T is the estimated temperature (K), T 0 is the measurement temperature (K).

2. The method for estimating the water immersion expansion ratio of slag according to claim 1, wherein the water immersion expansion test of the slag is carried out at an atmospheric pressure of 0.1 to 0.3 MPa and at a measurement temperature selected from a temperature range in which water exists as a liquid.

3. A steel slag for roads, the water immersion expansion ratio of which is 3.5% or less when estimated at room temperature (293 K) and for an estimated time t of 3652 days using the method for estimating the water immersion expansion ratio of slag described in claim 1.

4. A reinforced roadbed material consisting of a mixture of cement and slag, The reinforced roadbed material is characterized in that the water immersion expansion ratio (%) of the slag at room temperature (293 K) and at an estimated time t of 3652 days, estimated using the method for estimating the water immersion expansion ratio of slag described in claim 1, is lower than the strain rate (%) that leads to compressive failure of the reinforced roadbed material in a compression test of the reinforced roadbed material after cement curing.

5. A compression test is carried out on a reinforced roadbed material made of a mixture of cement and slag after cement curing to determine the strain rate (%) at which the reinforced roadbed material is subjected to compression failure. A method for manufacturing reinforced roadbed material, comprising: estimating the water immersion expansion ratio (%) of the slag at room temperature (293 K) and when the estimated time t is 3652 days using the method for estimating the water immersion expansion ratio of slag as described in claim 1; comparing the water immersion expansion ratio of the slag with the strain rate at which the reinforced roadbed material will undergo compressive failure; and adding cement and mixing it with the slag under conditions where the water immersion expansion ratio is lower than the strain rate.

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