Modified phosphogypsum semi-rigid base material for highways in seasonal frozen soil areas and preparation method thereof

Abstract

The application discloses a modified phosphogypsum semi-rigid base material for highways in seasonal frozen soil areas and a preparation method thereof, which is prepared from phosphogypsum, lime cement and proper water, wherein, based on the phosphogypsum, the lime content is 1-10%, the cement content is 1-10%, the lime content is equal to 100%*the weight of the lime / the weight of the phosphogypsum, and the cement content is equal to 100%*the weight of the cement / the weight of the phosphogypsum. The modified phosphogypsum semi-rigid base material formed after modification has good frost resistance, and the UCS value is reduced less after freeze-thaw cycles.

Description

Technical Field

[0001] This invention relates to the field of construction, and in particular to a modified phosphogypsum semi-rigid base material for highways in seasonally frozen soil areas and its preparation method. Background Technology

[0002] In highway construction projects, base courses are classified into flexible base courses, semi-rigid base courses, and rigid base courses, with rigid base courses being the commonly known concrete base courses. Among these three types, the mechanical properties are ranked as follows: concrete base course > semi-rigid base course > flexible base course; in terms of cost, the ranking is: concrete base course > flexible base course > semi-rigid base course. Semi-rigid base courses, being the lowest-cost type, offer better mechanical properties than flexible base courses and have become a research hotspot in pavement construction in recent years.

[0003] Fly ash is a fine ash collected from the flue gas after coal combustion. It is a major solid waste discharged from coal-fired power plants. In recent years, fly ash has been successfully used as a raw material in concrete and semi-rigid base courses, saving a lot of cement, fine aggregate and water. However, with the surge in the use of fly ash in industrial construction, its originally low price has gradually increased. Finding a low-cost raw material to replace fly ash has become a hot topic in the construction industry.

[0004] Phosphogypsum is a solid waste residue produced during the treatment of phosphate rock with sulfuric acid in the production of phosphoric acid. It is known that phosphogypsum is used to produce cement retarder. However, phosphogypsum itself has the following defects as a semi-rigid base layer: its unconfined compressive strength is less than 2 MPa after 28 days of curing, and its mass change rate is large before and after freeze-thaw cycles.

[0005] The above background information is provided to facilitate understanding of the present invention and is not intended to be publicly known technology disclosed to the general public prior to the application of this invention. Summary of the Invention

[0006] To address the aforementioned shortcomings, this invention provides a modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas. By modifying the phosphogypsum, the resulting modified phosphogypsum semi-rigid base course exhibits good frost resistance and a relatively small reduction in UCS value after freeze-thaw cycles.

[0007] The technical solution is: a modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas, which is made of phosphogypsum, lime cement and appropriate amount of water. The phosphogypsum is the base, the lime content is 1-10%, the cement content is 1-10%, the lime content = 100% * lime weight / phosphogypsum weight, and the cement content = 100% * cement weight / phosphogypsum weight.

[0008] Furthermore, the lime content is 2.5-6.5%, and the cement content is 2.5-6.5%.

[0009] Furthermore, the lime content is 4.5%, and the cement content is 4.5%.

[0010] Furthermore, the lime content is 6.5%, and the cement content is 6.5%.

[0011] On the one hand, the present invention also provides a method for preparing a modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas.

[0012] The technical solution is: a method for preparing a modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas, comprising the following steps:

[0013] S1, take phosphogypsum, lime, and cement. Based on phosphogypsum, the lime content is 1-10%, the cement content is 1-10%, the lime content = 100% * lime weight / phosphogypsum weight, and the cement content = 100% * cement weight / phosphogypsum weight.

[0014] S2, mix phosphogypsum and lime for 1-2 minutes, then add some water and stir for 2-3 minutes before soaking for 6 hours;

[0015] S3, after impregnation, add cement and mix for 1-2 minutes, then add the remaining water and mix for 2-3 minutes to form a modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas.

[0016] On the one hand, the present invention also provides a highway in seasonally frozen land areas.

[0017] The technical solution is: a seasonally frozen soil area highway, which includes the aforementioned modified phosphogypsum semi-rigid base course for seasonally frozen soil areas highways.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] This invention modifies phosphogypsum, resulting in a modified phosphogypsum semi-rigid base layer with excellent frost resistance and minimal UCS value reduction after freeze-thaw cycles. In seasonally frozen soil areas without a surface layer, the base layer using the modified phosphogypsum semi-rigid base layer as filler still exhibits good load-bearing capacity, and the base layer surface does not experience significant frost heave or frost heave, thus not affecting traffic safety. This expands the utilization scope of phosphogypsum, an industrial waste, and increases its comprehensive utilization. Attached Figure Description

[0020] Figure 1 This is the X-ray diffraction pattern of phosphogypsum, the raw material of this invention.

[0021] Figure 2 This is a schematic diagram of the 7-day unconfined compressive strength and 28-day unconfined compressive strength of the present invention. Detailed Implementation

[0022] The present invention will be further described below.

[0023] In this invention, unless otherwise specified, % refers to mass percentage.

[0024] In the examples below, the basic physical properties of phosphogypsum are shown in Table 1, and the X-ray diffraction is as follows: Figure 1 The main component of phosphogypsum is CaSO4·2H2O.

[0025] Table 1

[0026]

[0027] In the following examples, the modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas was prepared by the following method:

[0028] S1, made from phosphogypsum, lime, and cement.

[0029] S2, Preparation of modified phosphogypsum: Mix phosphogypsum and lime for 1-2 minutes, then add water and mix for 2-3 minutes, followed by soaking for 6 hours. The amount of water added should be sufficient to soak the phosphogypsum and lime. After soaking, add cement and mix for 1-2 minutes, then add water and mix for 2-3 minutes. The water addition requirement is the same as the existing concrete water addition requirement; this invention does not specify any special requirements. The total water addition is based on phosphogypsum, and the water addition / phosphogypsum ratio is 0.15-0.25.

[0030] S3, when cured at 20℃±2℃ and above 95% humidity, forms a modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas.

[0031] Examples 1-15

[0032] In Examples 1-15, the modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas is prepared by the preceding steps S1-S3. The amount of phosphogypsum, lime, and cement added is based on phosphogypsum: 100% * weight of lime / weight of phosphogypsum = lime content, 100% * weight of cement / weight of phosphogypsum = cement content. Examples 1-5 are Group B experiments, Examples 6-10 are Group C experiments, and Examples 11-15 are Group D experiments. The amount of phosphogypsum, lime, and cement added and the curing period are shown in Table 2 below.

[0033] Table 2

[0034]

[0035] The modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas prepared in Examples 1-15 can be tested for unconfined compressive strength (standard) directly, or after soaking in water for one day, the unconfined compressive strength can be tested (saturated water), or after freeze-thaw cycles, the unconfined compressive strength can be tested (freeze-thaw, 5 cycles). The treatment conditions and unconfined compressive strength test results are shown in Table 3 below.

[0036] Table 3

[0037]

[0038] Plot the 7-day unconfined compressive strength / 28-day unconfined compressive strength of each group in Table 3 on the ordinate. The results are as follows: Figure 2 .

[0039] The modified phosphogypsum semi-rigid base courses for highways in seasonally frozen soil areas of Examples 5, 10, and 15 were weighed before and after freeze-thaw cycles, and the results are shown in Table 4 below.

[0040] Table 4

[0041] Example Weight before freeze-thaw / g Freeze-thaw mass / g Quality change rate Wn (%) Example 5 186.3 182.2 2.236 Example 10 183.7 182.1 0.898 Example 15 183.2 182.5 0.398

[0042] The testing method standard mentioned in Tables 3 and 4 above is JTG E51-2009 (Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering).

[0043] The activated phosphogypsum of this invention meets the UCS requirements of lime-stabilized soil for the base and subbase of highways and expressways in terms of unconfined compressive strength before and after freeze-thaw cycles, as specified in the "Technical Specifications for Construction of Highway Pavement Base Course" (JTGT F20-2015). It maintains good strength and quality before and after freeze-thaw cycles and still has strong load-bearing capacity.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas, characterized in that, It is made of phosphogypsum, lime, cement and appropriate amount of water. The lime content is 2.5-6.5% and the cement content is 2.5-6.5% based on phosphogypsum. The lime content = 100% * lime weight / phosphogypsum weight, and the cement content = 100% * cement weight / phosphogypsum weight.

2. The modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas according to claim 1, characterized in that, The lime content is 4.5%, and the cement content is 4.5%.

3. The modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas according to claim 1, characterized in that, The lime content is 6.5%, and the cement content is 6.5%.

4. A method for preparing a modified phosphogypsum semi-rigid base course for highways in seasonally frozen soil areas as described in any one of claims 1-3, characterized in that, Includes the following steps: S1, take phosphogypsum, lime, and cement. Based on phosphogypsum, the lime content is 2.5-6.5%, the cement content is 2.5-6.5%, the lime content = 100% * lime weight / phosphogypsum weight, and the cement content = 100% * cement weight / phosphogypsum weight. S2, mix phosphogypsum and lime for 1-2 minutes, then add some water and stir for 2-3 minutes before soaking for 6 hours; S3, after soaking, add cement and mix for 1-2 minutes, then add the remaining water and mix for 2-3 minutes.

5. A highway in a seasonally frozen land area, characterized in that, The seasonally frozen soil road includes the modified phosphogypsum semi-rigid base course for seasonally frozen soil roads as described in any one of claims 1-3.

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