Soil-based paving materials

Abstract

To provide a high-strengthened and high-durability soil-based paving material excellent in scenery while considering environment.SOLUTION: There is provided a soil-based paving material obtained by mixing and kneading at least soil, a solidification material, and water, and as the solidification material, magnesium oxide and magnesium chloride, and monocalcium phosphate are added, and cement-based solidification material is not added.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a highly durable earth-based paving material that can solidify earth-based materials with a solidifying agent and is environmentally friendly.

Background Art

[0002] Conventionally, there has been earth-based paving that solidifies earth-based materials such as natural sand and has excellent landscape properties due to a color that harmonizes with nature. For example, Patent Document 1 discloses an invention of earth-based paving in which natural sand or pottery shells are solidified with a cement-based solidifying agent. In addition, asphalt-based and resin-based solidifying agents have been variously studied and used to improve the functions and durability of earth-based paving.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, conventional earth-based paving has problems such as the occurrence of cracks due to aging deterioration and wear. In addition, in order to increase the strength to handle roadways, a large amount of solidifying agent was used, which increased the environmental load and made the earth-based paving look whitish, damaging the color. It had various problems.

[0005] Therefore, an object of the present invention is to provide an earth-based paving material that is excellent in landscape properties, has high strength and high durability, while taking environmental considerations.

Means for Solving the Problems

[0006] The invention relating to (1) is a soil-based paving material in which at least soil, a solidifying agent, and water are mixed, characterized in that magnesium oxide, magnesium chloride, and monocalcium phosphate are added as the solidifying agent, and no cement-based solidifying agent is added.

[0007] The invention relating to (2) is the soil-based paving material described in (1) above, further comprising fine aggregate and / or coarse aggregate.

[0008] The invention relating to (3) is the soil-based paving material described in (1) or (2) above, wherein the amount of monocalcium phosphate added is 3% by weight or more of the amount of magnesium oxide added.

[0009] The invention relating to (4) is the soil-based paving material described in (1) or (2) above, wherein the amount of monocalcium phosphate added is 3 to 7% by weight of the amount of magnesium oxide added. [Effects of the Invention]

[0010] According to the present invention, since magnesium oxide, magnesium chloride, and monocalcium phosphate are added as solidifying agents without the addition of cement-based solidifying agents, it is possible to manufacture soil-based paving materials that do not emit hexavalent chromium, have excellent aesthetic appeal, and possess high strength and durability. [Brief explanation of the drawing]

[0011] [Figure 1] This is a comparison table of strengths and other properties based on the mixing ratio of magnesium oxide and magnesium chloride. [Figure 2] The proportions of magnesium oxide and magnesium chloride in the embodiments of the present invention are shown, where (a) is the proportion for wet soil and (b) is the proportion for dry soil. [Figure 3] This is a comparison table of the curing speeds of monocalcium phosphate and other additives. [Figure 4] This is a comparison table of the strength of monocalcium phosphate and other additives. [Figure 5]This is a comparison table of the length change rates of monocalcium phosphate and other additives. [Figure 6] This is a comparative table evaluating the length change rates of monocalcium phosphate and other additives. [Figure 7] This is a comparison table showing the individual evaluations and overall assessments of monocalcium phosphate and other additives. [Figure 8] This is a formulation table for the examples of the present invention. [Figure 9] This table shows the bending strength in the embodiments of the present invention. [Modes for carrying out the invention]

[0012] The soil-based paving material in an embodiment of the present invention will be described below with reference to the drawings.

[0013] The soil-based paving material in this embodiment is a soil-based paving material in which at least soil as the base material, a solidifying agent, and water are mixed together. Masado soil is used as the soil, and magnesium oxide (MgO), magnesium chloride (MgCl2), and monocalcium phosphate are added as solidifying agents. Therefore, the soil-based paving material in this embodiment does not contain cement-based solidifying agents and does not leach hexavalent chromium, which has adverse effects on the environment.

[0014] In determining the amount of magnesium oxide and magnesium chloride to be added as solidifying agents, test specimens were prepared and verified using multiple formulations, as shown in Figure 1. For the strength tests of the test specimens, they were cured in air at 20°C for 6 days, and then immersed in water for 1 day before being tested. Furthermore, the amount of water added to each formulation was set to achieve approximately the same fluidity.

[0015] (Regarding the amount of magnesium oxide to be added) Looking at the relationship between the addition amounts of magnesium oxide and magnesium chloride and the amount of added water shown in Fig. 1, when the addition amount of magnesium oxide is the same, it can be seen that by increasing the addition amount of magnesium chloride, the amount of added water required to achieve almost the same fluidity can be reduced. Also, it can be seen that the uniaxial compressive strength is improved accordingly.

[0016] On the other hand, when using powdered magnesium chloride basically, there is no particular problem. However, when using flaky magnesium chloride, if its addition amount exceeds 0.15 times the mass ratio to the wet soil, it takes more time to dissolve compared to powdered magnesium chloride. Therefore, when the flakes are completely dissolved, a sudden change in fluidity occurs in the soil paving material, and it becomes clear that it is difficult to adjust the fluidity.

[0017] Also, when the addition amounts of magnesium chloride are 0.03 times and 0.05 times the mass ratio to the wet soil, no increase in strength can be expected due to the addition of the magnesium chloride. Therefore, the addition amount of magnesium chloride is preferably in the range more than 0.05 times and less than 0.15 times the mass ratio to the wet soil.

[0018] (Regarding the addition amount of magnesium oxide) Subsequently, regarding the addition amount of magnesium oxide, within the above-mentioned suitable addition amount range of magnesium chloride (in the verification experiment, it was set to 0.1 times the mass ratio to the wet soil), specimens (30 cm × 30 cm × 5 cm) were prepared at three levels of 0.1 times, 0.15 times, and 0.2 times the mass ratio of magnesium oxide to the wet soil, and an exposure test was conducted.

[0019] When checking the condition of the specimens after 1 month of exposure, it was found that the occurrence of warping and cracking became more prominent as the addition amount of magnesium oxide increased. As a result of additional investigation, it was found that the greater the addition amount of magnesium oxide, the greater the expansion.

[0020] Furthermore, in formulations where the amount of magnesium chloride added was 1x and 1.5x the mass ratio of magnesium oxide, significant expansion was observed at 1.5x, and cracks appeared on the surface of the specimens after 3 days of water immersion curing. In addition, the strength after 7 days of air curing increased with the amount of magnesium oxide added, but when the amount of magnesium oxide added was 0.2x the mass ratio of the wet soil, the strength continued to decrease with the passage of water immersion days, and after 14 days of water immersion, the strength decreased to about 10%. In formulations where the amount of magnesium oxide added was 0.05x and 0.1x the mass ratio of the wet soil, the strength continued to decrease until about 3 days of water immersion, after which there was no significant change, and after 14 days of water immersion, the strength decreased to about 50-60%.

[0021] The above verification results revealed that adding too much magnesium oxide causes expansion during water immersion, leading to a decrease in strength. Therefore, it is preferable to add magnesium oxide in an amount equivalent to that of magnesium chloride.

[0022] Figure 2 shows an example of a mixture in which the amount of magnesium oxide and magnesium chloride added is 0.1 times the mass ratio of the base material, based on the verification results of the amount of magnesium oxide and magnesium chloride added as described above. Specifically, Figure 2(a) shows the amount of magnesium chloride and magnesium oxide added and the amount of water added to wet soil, and Figure 2(b) shows the amount of magnesium chloride and magnesium oxide added and the amount of water added to dry soil.

[0023] (Regarding the application of monocalcium phosphate) As mentioned above, the most distinctive feature of the embodiments of this invention is the addition of monocalcium phosphate as a solidifying agent. When only magnesium chloride and magnesium oxide were added as solidifying agents, demolding was possible the next day even if the amount of water added changed. Figure 3 shows the verification results regarding the hardening speed of soil-based paving materials when monocalcium phosphate and other phosphate compounds were used as additives.

[0024] Verification results show that when superphosphate is added, demolding is possible the next day when the addition is at a mass ratio of 20% to magnesium oxide, but the soil-based paving material becomes hard, making the placement work extremely difficult. Furthermore, when 30% and 50% superphosphate are added, demolding becomes possible only two days after placement.

[0025] When sodium dihydrogen phosphate and monocalcium phosphate are added, demolding becomes impossible the next day at a mass ratio of 10% relative to magnesium oxide, but demolding is possible the next day at addition levels of 3% and 5%. In both cases, hardening tends to slow down as the amount added increases, and this delay in hardening can be a factor in delaying the opening of soil-based pavements to traffic.

[0026] Next, Figure 4 shows the verification results evaluating the water resistance of soil-based pavement materials with each additive. Since the water resistance of soil-based pavement materials is closely related to their strength, test specimens of soil-based pavement were prepared and strength tests were conducted. Specifically, the flexural strength after 7 days of air curing at 20°C, the flexural strength after 7 days of air curing followed by 3 days of water immersion, and the flexural strength after 7 days of air curing followed by 14 days of water immersion were measured. In Figure 4, a "○" is indicated for test specimens that exceeded the flexural strength of specimens without additives (solidifying agents consisting only of magnesium oxide and magnesium chloride).

[0027] The verification results show that the additives that exceeded the strength and residual strength ratio of specimens without additives (solidifying agents consisting only of magnesium oxide and magnesium chloride) after 3 and 14 days of water immersion are, as shown in the figure, superphosphate and sodium dihydrogen phosphate at 5-10% and monocalcium phosphate at 3-10%.

[0028] Furthermore, the only cases where the strength increase rate was greater than that of the case without additives from 3 to 14 days after water immersion were when monocalcium phosphate was added at 5-10% and dicalcium phosphate at 5%. Moreover, when comparing monocalcium phosphate and dicalcium phosphate, monocalcium phosphate showed higher strength and residual strength ratio even at the same amount added. In other words, from the viewpoint of water resistance of soil-based paving materials, it is preferable to add monocalcium phosphate, and it is even more preferable when the amount added is 5-10% (relative to Mg 0%).

[0029] Next, we investigated the effect of each additive on expansion. When no additives were used (solidifying agents consisted only of magnesium oxide and magnesium chloride), the amount of expansion increased with increasing water content, and when the water content exceeded a predetermined level, cracks appeared on the surface of the specimen on the second day of water immersion curing.

[0030] Figure 5 shows the results of an investigation into the rate of change in length over time with immersion in water for monocalcium phosphate, dicalcium phosphate, and tricalcium phosphate, while Figure 6 summarizes the evaluation results regarding expansion. As shown in the figures, when tricalcium phosphate is added, greater expansion occurs than when no additive is added, and cracks appear on the surface of the specimen after one day of water curing. For the other additives, the amount of expansion was smaller than when no additive was added, but for superphosphate, the amount of expansion tended to increase with the passage of water immersion days. Furthermore, with sodium dihydrogen phosphate, a tendency towards shrinkage was observed at an addition amount of 5%. In addition, with monocalcium phosphate, the expansion tended to be suppressed as the amount added increased.

[0031] Furthermore, as shown in Figure 5, in calcium salts of phosphate, the amount of expansion tends to increase with increasing calcium content. This may be due to volume expansion caused by the hydration reaction of calcium ions, which is thought to have led to a significant decrease in strength in tricalcium phosphate.

[0032] As described above, the results of the evaluation of each additive regarding the effects of hardening speed, water resistance (strength), and expansion are summarized in Figure 7. As shown in the figure, monocalcium phosphate can be suitably used as an additive. As mentioned above, when dicalcium phosphate is added, the strength is relatively high, but the amount of expansion is large, making it unsuitable as an additive for soil-based paving materials.

[0033] Furthermore, regarding the range of monocalcium phosphate addition, an increase in flexural strength and residual strength during water immersion is observed when the addition amount is 3% or more by mass relative to magnesium oxide, an increase in strength is observed between 3 and 14 days of water immersion when the addition amount is 5% or more, and the expansion is suppressed and the decrease in strength is suppressed as the addition amount increases, and the curing time is delayed as the addition amount increases, with demolding possible the next day when 7% was added during specimen preparation. Considering these points, it is preferable to add 3% (relative to Mg 0%) or more monocalcium phosphate, and more preferably 3 to 7% (relative to Mg 0%).

[0034] Next, we will explain the amount of water added. Based on the strength test results from 7 days of air curing + 3 days of water immersion, the water-solidifying agent ratio that can satisfy a flexural strength of 3 MPa (corresponding to the strength required for paving material of concrete roads that can withstand the passage of maintenance vehicles) was 0.64. Furthermore, the water-solidifying agent ratio that can satisfy a flexural strength of 5 MPa (corresponding to the strength required for paving material of concrete roads that can withstand the passage of heavy vehicles) was 0.42. In other words, it is preferable to use the amount of solidifying agent and the amount of water added to satisfy the above-mentioned water-solidifying agent ratio according to the required strength.

[0035] Furthermore, by adding crushed stone, gravel, or sand to the base material of soil-based paving materials, in addition to soils containing a large amount of fine-grained material that easily retains water, such as decomposed granite, it is possible to obtain fluidity that allows for construction with a small amount of added water. This makes it possible to reduce the water-solidifying agent ratio and obtain high-strength soil-based paving materials.

[0036] Next, Figure 8 shows five soil-based paving material mixes, A to E, in this embodiment, and Figure 9 shows the results of strength tests for these mixes A to E. In all cases, it is possible to ensure good water resistance (strength) and quality. Furthermore, in this invention, since high-strength soil-based paving materials can be manufactured without using cement-based solidifying agents, there is no emission of hexavalent chromium, and the environmental burden can be greatly reduced.

[0037] For example, if 30% of the base material of soil-based paving material is replaced with yellow chart (Figure 8, No. E), as shown in the figure, both magnesium oxide and magnesium chloride can achieve a bending strength of 5 MPa (equivalent to paving material for roads that can be used by large vehicles) at a mass ratio of 0.11 times the base material. Although not shown in the figure, both magnesium oxide and magnesium chloride can also achieve a bending strength of 3 MPa (equivalent to paving material for roads that can be used by maintenance vehicles) at a mass ratio of 0.08 times the base material.

[0038] Furthermore, the more solidifying agent is added, the closer the surface of the soil-based pavement becomes to concrete in terms of whiteness. Therefore, if you want to retain the texture of soil, it is preferable to limit the amount of solidifying agent (magnesium oxide and magnesium chloride) added to 0.08 times the mass ratio of the base material.

[0039] (others) Although one embodiment of the present invention has been described above, when constructing a pavement using the soil-based paving material of the present invention, it can be handled in the same way as concrete. For example, instead of compaction as with ordinary soil-based pavements, it is possible to finish the surface with a trowel using a vibrating machine or the like. This makes it possible to construct even in narrow spaces without using roller-type construction machinery. In addition, shot blasting and polishing finishes on the pavement surface, which were not possible with ordinary soil-based pavements, are also possible.

[0040] Although embodiments of the present invention have been described above with reference to the drawings, the specific configurations are not limited to these embodiments. The scope of the present invention is indicated by the claims rather than the above-described embodiments, and all modifications within the meaning and scope of equivalence to the claims are included. Furthermore, the specific materials, dimensions, shapes, etc., described in the above embodiments can be modified to the extent that they solve the problems of the present invention.

Claims

1. A soil-based paving material in which at least soil, a solidifying agent, and water are mixed together, Magnesium oxide, magnesium chloride, and monocalcium phosphate are added as the solidifying agent. The amount of monocalcium phosphate added is 3% by weight or more of the amount of magnesium oxide added. No cement-based solidifying agent is added. A soil-based paving material characterized by the following features.

2. Furthermore, fine aggregate and / or coarse aggregate are mixed together. The soil-based paving material according to claim 1.

3. The amount of monocalcium phosphate added is 3 to 7% by weight of the amount of magnesium oxide added. The soil-based paving material according to claim 1 or 2.

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