JP7639787B2 - Method for estimating water immersion expansion ratio of slag, steel slag for roads and reinforced roadbed material and method for manufacturing same - Google Patents

Description

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, and to steel slag for roads, as well as reinforced road base materials using steel slag and methods for manufacturing the same.

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.

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 may remain unreacted. When hydrated with water, the lime expands in volume. For this reason, JIS A 5015:2018 stipulates that roadbed materials using steel slag must be aged to stabilize the 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 the 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.

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 the gradient consisting of the estimated time and the logarithmically transformed water immersion expansion ratio.

When steel slag is used as a roadbed material, it is common to pre-treat it by aging or other methods, and then add cement to the pre-treated steel slag to make a stabilized mixture. However, reinforced roadbed materials containing steel slag are required to have the desired strength, filling properties, compaction properties, and other properties, as well as to avoid reverse fault type failures caused by the expansion of steel slag. For this reason, in the past, excessive pre-treatment was performed by setting a large safety factor across the board. It has not yet been clarified to what extent the expansion of steel slag needs to be suppressed in order to avoid reverse fault type failures. 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.

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 the compressive strength of soil cement at a specified age depending on the construction conditions at the construction site. Furthermore, Patent Document 5 proposes a method for evaluating the filling property, compaction property, etc. of concrete from the perspective of construction site management and rationalization.

JP 2018-025461 A JP 2018-135696 A JP 2014-111879 A JP 2015-059325 A JP 2017-223490 A

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

Patent documents 2 to 5 do not mention how to avoid reverse fault rupture caused by expansion of roadbed materials after solidification.

The present invention aims to solve the above problems, propose a method for estimating the water immersion expansion ratio of slag that easily and accurately estimates 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 its manufacturing method that do not cause reverse fault-type failures caused by slag expansion.

ここで、Ｖは水浸膨張比（％）、
νは推定膨張速度（％／日）、
ｔは推定時間（日）、
ν_０は測定膨張速度（％／日）、
ｔ_０は測定時間（日）、
ｅはネイピア数（－）、
Ｔは推定温度（Ｋ）、
Ｔ_０は測定温度（Ｋ）である。
［３］前記スラグの水浸膨張試験を０．１～０．３ＭＰａの雰囲気圧力で、かつ、水が液体として存在する温度範囲から選んだ前記測定温度で実施する、［１］または［２］に記載のスラグの水浸膨張比推定方法。
［４］
［１］または［２］に記載のスラグの水浸膨張比推定方法を用いて、常温（２９３Ｋ）における前記推定時間ｔが３６５２日における水浸膨張比を推定したとき、前記水浸膨張比が３．５％以下である、道路用鉄鋼スラグ。
［５］セメントとスラグとの混合物からなる強化路盤材であって、
該強化路盤材は、［１］または［２］に記載のスラグの水浸膨張比推定方法を用いて推定した前記スラグの水浸膨張比（％）が、セメント養生後における強化路盤材の圧縮試験における該強化路盤材の圧縮破壊に至る歪み率（％）よりも下回るものであることを特徴とする強化路盤材。
［６］
セメントとスラグとの混合物からなり、セメント養生後の強化路盤材に対して圧縮試験を行って該強化路盤材の圧縮破壊に至る歪み率（％）を求めるとともに、
［１］または［２］に記載のスラグの水浸膨張比推定方法を用いて前記スラグの水浸膨張比（％）を推定し、該スラグの水浸膨張比と該強化路盤材の圧縮破壊に至る歪み率とを比較し、該水浸膨張比が、該歪み率よりも下回る条件下でセメントを添加してスラグと混合する、強化路盤材の製造方法。 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 at 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).

where V is the water immersion expansion ratio (%),
ν is the estimated expansion rate (%/day),
t is the estimated time (days),
v _is the measured expansion rate (%/day);
_t0 is the measurement time (day);
e is Napier's constant (-),
T is the estimated temperature (K),
_T0 is the measurement temperature (K).
[3] The method for estimating the water immersion expansion ratio of a slag according to [1] or [2], 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.
[4]
A steel slag for roads, the water immersion expansion ratio of which is 3.5% or less when the water immersion expansion ratio is estimated at room temperature (293 K) for an estimated time t of 3652 days using the method for estimating the water immersion expansion ratio of slag described in [1] or [2].
[5] 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 estimated using the method for estimating the water immersion expansion ratio of slag described in [1] or [2] 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.
[6]
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 a reinforced roadbed material, comprising: estimating the water immersion expansion ratio (%) of the slag using the method for estimating the water immersion expansion ratio of the slag described in [1] or [2]; comparing the water immersion expansion ratio of the slag with the strain rate at which the reinforced roadbed material will be compressed and broken; and adding cement and mixing it with the slag under conditions where the water immersion expansion ratio is lower than the strain rate.

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 that includes 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 the specified water immersion expansion performance can be selected for road use.

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 considered to be due to the expansion of the 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 avoid the resulting reverse fault failure of the reinforced roadbed material.

1 is a graph showing the relationship between the amount of cement added and the strain rate at the time of compressive failure. 1 is a graph showing the relationship between reduction rate and strain rate at the time of compressive failure.

[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.

In this embodiment, the steel slag that constitutes the slag roadbed material for roads is not particularly limited as long as it is slag generated in a steelworks. Examples of slag include 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 electric furnace process, 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.

The variables of the function shown in the following formula (1) include the measured expansion rate (ν ₀ ), the measured temperature (T 0 ), the measured time (t ₀ ), the estimated temperature ( _T ), and the estimated time (t) of the water immersion expansion test of the target slag roadbed material. In the water immersion expansion test method for steel slag for roads described in JIS A 5015:2018 Appendix B, the test is performed for 10 days, but in this embodiment, the test temperature can be shortened or extended as desired. In addition, the test temperature is 80°C, but it may be changed as desired for testing. In the above JIS test, the material 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.

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 also be used, and the unit is %/day. The estimated temperature (T) and the measured temperature (T ₀ ) are the test temperatures in the water immersion expansion test, and are in the range of 273 K≦T≦373 K under atmospheric pressure at which water exists as a liquid. However, this is the temperature range in which water exists as a liquid under pressure. V is the water immersion expansion ratio (%).

Here, the estimated expansion rate (ν) in the water immersion expansion test is set equal to the measured expansion rate (ν ₀ ), and the estimated time (t) at the estimated temperature (T) at which the estimated expansion rate becomes equal to the measured water immersion expansion ratio (V) is estimated. By modifying equation (1), the following equation (1′) of Equation 3 is obtained.

Since the measurement temperature (T ₀ ) of the water immersion expansion test may vary during the test, the test temperature of the water immersion expansion test may be continuously measured, and the integrated temperature may be divided by the test time, and the average may be used as the actual value of the measurement temperature (T ₀ ). In this way, in order to estimate the water immersion expansion ratio at the desired estimated temperature (T) and estimated time (t), the water immersion expansion test of the slag is performed at a predetermined measurement temperature and a predetermined measurement time, and the water immersion expansion ratio is measured.

The above slag was subjected to water immersion expansion tests at various measurement temperatures and measurement times. Table 1 shows the measurement temperature (T ₀ ) [K] and the measurement time (t ₀ ) [days]. The measurement pressure (P ₀ ) [MPa] is also shown. Using the above relational expression, the estimated time (t) [days] of the water immersion expansion test of the slag that would give the same estimated water immersion expansion ratio (Ve) [%] as the measured water immersion expansion ratio (V) [%] at the estimated temperature (T) [K] was estimated by the above formula (1') for each test and listed. The actual water immersion expansion ratio (Va) obtained as a result of performing 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 in which 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 ×.

In Test Nos. 1 to 24, in which the measurement temperature (T ₀ ) was set to a temperature range in which water exists as a liquid, the estimated water immersion expansion ratio (Ve) and the actual water immersion expansion ratio (Va) were in good agreement. In Test Nos. 25 to 33, in which the measurement temperature (T ₀ ) was set to a temperature range in which water does not exist as a liquid at atmospheric pressure, the error between the estimated water immersion expansion ratio (Ve) and the actual water immersion expansion ratio (Va) was large.

[Iron and steel slag for roads]
In the steel slag for road use as the second embodiment of the present invention, when the water immersion expansion ratio V at room temperature (293 K) is estimated using the method for estimating the water immersion expansion ratio of the slag according to the first embodiment, the water immersion expansion ratio V at the estimated time t of 10 years (3652 days) must be 3.5% or less. By satisfying this condition, it is possible to obtain an effect of preventing the roadbed material from being bulged. If the water immersion expansion ratio V exceeds 3.5%, there is a risk of the roadbed material being bulged. For example, the water immersion expansion ratio V at room temperature (293 K) when the estimated time t is 3652 days can be estimated by performing a water immersion expansion test of the slag at one measurement temperature (T ₀ ) and measurement time (t ₀ ) selected from Test Nos. 22 to 24 in Table 1 and measuring the water immersion expansion ratio V.

[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 water immersion expansion ratio estimation method of 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.

Figure 1 shows the relationship between the strain rate (%) at 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 to 5.0 mass% cement to steel slag adjusted to a grain size of 0 to 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 (%) of each specimen at compressive failure, the estimated water immersion expansion ratio (%) of steel slag, and the results of an investigation into applicability. Here, the estimated water immersion expansion ratio was estimated at room temperature (293 K), normal pressure (atmospheric pressure), and an estimated time t of 10 years (3652 days).

In this investigation, the particle size distribution of the steel 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 was no difference in particle size between each specimen (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 compression speed in the compression test was set to 0.2 mm/min. The strain rate (%) at the time of compression failure was calculated by creating a load-strain curve from the compression test results and converting the strain at the maximum load on the load-strain curve into a strain rate. The estimated water immersion expansion ratio (%) of the steel slag was estimated from the water immersion expansion test at the specified measurement temperature and for the specified measurement time shown in the first embodiment. Applicability was indicated by a circle if 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 if the difference between the strain rate (%) and the estimated water immersion expansion ratio (%) was 0.2% or more, and an × if the estimated water immersion expansion ratio (%) was higher than the strain rate (%) at the time of compressive failure.

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.

In this embodiment, it is preferable to carry out the compression test at a reduction rate of 0.1 to 1%/min. The reason for this is that it is believed that the stress that occurs when the steelmaking slag expands in a restrained state can be intentionally generated. To achieve this, it is essential to make the reduction rate as small as possible while avoiding any effect on the strain rate (%) that leads to compressive failure. The results shown in Figure 2 were obtained from preliminary tests.

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 by 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 achieve this, it is preferable to use slag with a particle size 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 to seal and cure the slag at a temperature of 20°C and a humidity of 98%.

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 (5)

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) .

where V is the water immersion expansion ratio (%),
ν is the estimated expansion rate (%/day),
t is the estimated time (days),
v _is the measured expansion rate (%/day);
t0 _is the measurement time (days),
e is Napier's constant (-),
T is the estimated temperature (K),
T0 is the measurement temperature (K) _. 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. 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. 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. 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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