Phosphogypsum-based concrete admixture as well as preparation method and application thereof

Abstract

The invention relates to the technical field of road engineering, and discloses a phosphogypsum-based concrete admixture as well as a preparation method and application thereof. The concrete admixture is prepared from 12-15 parts of modified phosphogypsum, 1-3 parts of limestone and 2-5 parts of silica; through synergistic treatment of chemical modification and high-temperature activation, the adverse effect of harmful impurities in the phosphogypsum is thoroughly eliminated, and the activity of the phosphogypsum is remarkably improved. The obtained product has excellent performance, can safely and efficiently replace mineral slag and other admixtures in concrete, realizes high-added-value resource utilization of phosphogypsum, and has both environmental protection and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of road engineering technology, and in particular to a phosphogypsum-based concrete admixture, its preparation method, and its application. Background Technology

[0002] Phosphogypsum is a large-scale industrial solid waste generated during the wet-process phosphoric acid production process. Its main component is calcium sulfate dihydrate (CaSO4·2H2O). Large stockpiles of phosphogypsum not only occupy land, but also pose a threat to the ecological environment due to the presence of harmful impurities such as soluble phosphorus and fluorine, as well as its strong acidity. Its resource utilization is a major challenge in the industry.

[0003] In the concrete industry, active admixtures such as slag and fly ash are widely used to improve concrete performance and reduce cement usage, thereby saving costs and resources. However, high-quality mineral powder resources are becoming increasingly scarce. If phosphogypsum could be used to prepare concrete admixtures with comparable performance, it would have significant environmental and economic value.

[0004] However, directly using phosphogypsum as a concrete admixture presents serious problems: First, the soluble phosphorus and fluorine it contains severely delay cement hydration, leading to excessively long concrete setting time or even failure to set; second, phosphogypsum crystals are large, have low activity, and lack the pozzolanic effect, thus failing to contribute to strength; third, its acidic environment may corrode reinforcing steel. Therefore, developing a technology that can completely "detoxify" and efficiently activate phosphogypsum to meet the requirements for concrete admixtures is a pressing problem to be solved in this field. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a concrete admixture based on phosphogypsum, its preparation method and application, which can safely and efficiently replace slag in concrete.

[0006] The solution of the present invention is: A phosphogypsum-based concrete admixture is made from the following raw materials in parts by weight: 12-15 parts of modified phosphogypsum; 1-3 parts limestone; 2-5 parts silica; The modified phosphogypsum is obtained by mixing and aging phosphogypsum and quicklime in a mass ratio of 18-20:0.5-1.5.

[0007] As a preferred technical solution, the mass ratio of the modified phosphogypsum, limestone and silica is 13:1:3.

[0008] As a preferred technical solution, the fineness of the concrete admixture is not less than 325 mesh (i.e., the residue on a 45μm square hole sieve is not more than 15%).

[0009] As a preferred technical solution, the modified phosphogypsum is obtained by mixing and aging water-washed phosphogypsum with a water content of 16-22% and quicklime in a mass ratio of 19:1.

[0010] This invention also discloses a method for preparing a phosphogypsum-based concrete admixture, comprising the following steps: S1. To prepare modified phosphogypsum, mix phosphogypsum, quicklime and curing agent at a mass ratio of 18-20:0.5-1.5 and stir for 8-10 minutes, then age for 24 hours to obtain modified phosphogypsum. S2. High-temperature activation: The modified phosphogypsum obtained in step S1 and the curing agent are placed in a rotary kiln and dried at 400-600℃ for 25-35 minutes; the mass ratio of modified phosphogypsum to curing agent is 18-20:1. S3. Composite grinding: Mix 12-15 parts by weight of the thermally activated modified phosphogypsum, 1-3 parts by weight of limestone, and 2-5 parts by weight of silica obtained in step S2, and grind them together to a fineness of not less than 325 mesh to obtain the concrete admixture.

[0011] As a preferred technical solution, in step S2, the product is dried at 500°C for 30 minutes.

[0012] As a preferred technical solution, after step S2 and before step S3, a step of pre-grinding the thermally activated modified phosphogypsum using a vertical mill is also included.

[0013] The present invention also discloses the application of a phosphogypsum-based concrete admixture as an admixture in concrete preparation.

[0014] As a preferred technical solution, the application is to replace slag in concrete.

[0015] Compared with the prior art, the advantages of the present invention are: Deep "detoxification" and efficient activation: This invention adopts a two-step core process of "chemical modification + high temperature activation".

[0016] Chemical modification: By neutralizing the acidity of phosphogypsum with quicklime and by complexing, encapsulating or transforming soluble phosphorus, fluorine and other harmful impurities with a special curing agent, the adverse effects of these impurities on cement hydration are fundamentally eliminated.

[0017] High-temperature activation: At 500℃, phosphogypsum is partially dehydrated to produce anhydrous gypsum (CaSO4). At the same time, the crystal structure changes, the internal energy increases, the activity is significantly enhanced, and it has the ability to participate in hydration reactions.

[0018] Synergistic formulation design: The innovative 13:1:3 ratio enables thermally activated phosphogypsum (providing sulfates and calcium), limestone (micro-aggregate effect and catalytic action), and silica (providing siliceous components and possessing potential pozzolanic activity) to produce a synergistic effect after ultrafine grinding, together forming a high-performance composite admixture system.

[0019] Excellent performance and strong substitutability: The prepared admixture has high activity and can effectively replace slag. When replaced in equal amounts, it has no adverse effect on the workability, mechanical properties and durability of concrete, and may even improve them.

[0020] Low cost and significant environmental benefits: Using bulk solid waste phosphogypsum as the main raw material, it realizes "turning waste into treasure", significantly reduces the production cost of concrete, and solves the environmental problems caused by phosphogypsum stockpiling. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0022] Figure 1 The compaction curves of the modified phosphogypsum mixtures with different proportions in Example 5 are shown. Figure 2 This is a bar graph showing the increase of unconfined compressive strength (UCS') of Example 5 with the curing age; Figure 3 This is a diagram showing the state of the dedicated transport road in the Jinning Kunyang Second Street Industrial Park before construction, as described in Example 5. Figure 4 This is a diagram showing the post-construction state of the dedicated transportation highway in the Kunyang Second Street Industrial Park of Jinning, as described in Example 5. Detailed Implementation

[0023] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0024] Example 1: S1. Take 190 kg of water-washed phosphogypsum with a moisture content of 20% and 10 kg of quicklime, mix them in a spiral mixer for 9 minutes, and age for 24 hours to obtain modified phosphogypsum.

[0025] S2. Place the above modified phosphogypsum and 10 kg of GH73LV16 type curing agent (purchased from Kunming Liluli Technology Co., Ltd.) in a rotary kiln and calcine at 450°C for 30 minutes to obtain thermally activated phosphogypsum.

[0026] S3. Weigh the thermally activated phosphogypsum, limestone, and silica in a mass ratio of 13:1:3, totaling 170 kg, and grind them together in a ball mill until they pass through a 325-mesh sieve with a residue of <12%, thus obtaining the phosphogypsum-based concrete admixture.

[0027] Example 2: The steps are the same as in Example 1, except that the calcination temperature in step S2 is 500°C and the calcination time is 33 minutes.

[0028] Example 3: S1. Preparation of modified phosphogypsum: Phosphogypsum and quicklime are mixed and stirred at a mass ratio of 18:1 for 8 minutes, and then aged for 24 hours to obtain modified phosphogypsum.

[0029] S2. High-temperature activation: The modified phosphogypsum obtained in step S1 and the curing agent are placed in a rotary kiln at a mass ratio of 18:1 and dried at 480℃ for 25 minutes.

[0030] S3. Composite grinding: Mix 13 parts by weight of thermally activated modified phosphogypsum, 2 parts by weight of limestone and 4 parts by weight of silica obtained in step S2, and grind them together to a fineness of not less than 325 mesh to obtain the concrete admixture.

[0031] The process includes a step of pre-grinding the thermally activated modified phosphogypsum using a vertical mill after step S2 and before step S3.

[0032] Example 4: S1. Preparation of modified phosphogypsum: Phosphogypsum and quicklime are mixed and stirred at a mass ratio of 18:1 for 10 minutes, and then aged for 24 hours to obtain modified phosphogypsum.

[0033] S2. High-temperature activation: The modified phosphogypsum obtained in step S1 and the curing agent are placed in a rotary kiln at a mass ratio of 18:1 and dried at 500℃ for 35 minutes.

[0034] S3. Composite grinding: Mix 13 parts by weight of thermally activated modified phosphogypsum, 1 part by weight of limestone and 3 parts by weight of silica obtained in step S2, and grind them together to a fineness of not less than 325 mesh to obtain the concrete admixture.

[0035] The process includes a step of pre-grinding the thermally activated modified phosphogypsum using a vertical mill after step S2 and before step S3.

[0036] Example 5: Road Engineering Verification Test This embodiment verifies the excellent mechanical properties and water stability of phosphogypsum modified by the method of this invention through geotechnical tests in road engineering, which provides cross-domain performance endorsement for its use as a core raw material for concrete admixtures.

[0037] (1) Raw materials and modification: Raw material phosphogypsum: This phosphogypsum is derived from industrial waste from Kunyang Second Street. It is dark gray in color and turns grayish-white after air drying. Its particle size is mainly between 0.05 and 0.35 mm, exhibiting a normal distribution, and it belongs to the silt category. The initial pH value is 3.5–4.1, and the moisture content is as high as 32%. Its main chemical composition is shown in Table 1.

[0038] Table 1 Modification method: The method of the present invention is to mix the above phosphogypsum and quicklime at a mass ratio of 19:1 and age them for 24 hours to obtain modified phosphogypsum; High temperature activation: The obtained modified phosphogypsum and curing agent are placed in a rotary kiln at a mass ratio of 19:1 and dried at 500℃ for 35 minutes to obtain thermally activated modified phosphogypsum.

[0039] The thermally activated modified phosphogypsum, limestone and silica are mixed according to the mass ratio in Table 2 and ground together to a fineness of not less than 325 mesh to obtain the concrete admixture.

[0040] Table 2 (2) Performance verification: Concrete admixtures and cement are mixed in a certain proportion, and water is added (see Table 3 for details). Specimens are prepared and tested to evaluate their engineering performance.

[0041] Table 3 Compaction test: Conducted according to JTGE51-2009 standard. Test results show that the optimum moisture content of the modified phosphogypsum mixture is approximately 14.91% on average, and the maximum dry density is approximately 1.61 g / cm³ on average. 3 .

[0042] Unconfined compressive strength test: The average unconfined compressive strength (UCS') of specimen P after 6 days of standard curing and 1 day of saturated water curing is ≥2.3 MPa. The strength increases significantly with the curing age.

[0043] Water stability: The optimized mix design of specimen P maintained structural integrity after immersion for 24 hours. Among them, the specimens with combined cement and P2O5GH73LV16 series curing agent showed particularly outstanding water stability coefficient (K value).

[0044] California load-bearing ratio test: The CBR value of the modified phosphogypsum specimen P increased significantly with increasing compaction degree (90%, 95%, 98%). At 98% compaction degree, the specimen exhibited a high CBR value and low expansion (maximum expansion of only 0.60 mm), meeting the requirements for heavy-duty road base courses.

[0045] (3) Conclusion: This embodiment demonstrates that the phosphogypsum modified by the core method of this invention possesses high strength, high water stability, and excellent load-bearing capacity. This fundamentally guarantees the activity and reliability of concrete admixtures prepared using it as a raw material.

[0046] To verify the engineering applicability of the above conclusions, we used the thermally activated modified phosphogypsum prepared by the above method as a base material in the reconstruction and expansion project of the dedicated transportation highway in the Jinning Kunyang Second Street Industrial Park. This road sees approximately 500 vehicles passing daily, including heavy-duty vehicles with a maximum load exceeding 100 tons. After more than six months of actual traffic testing, the road base (referring to the part constructed using a mixture of the modified phosphogypsum of this invention, limestone, and silica in a 13:1:3 mass ratio to replace concrete admixtures) exhibited excellent stability and load-bearing capacity. The road surface was smooth, without cracks, subsidence, or other defects, fully meeting the stringent requirements of heavy-duty traffic.

[0047] This successful engineering application not only confirms the accuracy of the indoor tests, but also demonstrates, from the perspective of large-scale field application, that the modified phosphogypsum and its derivative concrete admixtures provided by this invention possess excellent engineering performance and reliability.

[0048] Comparative example: Untreated raw phosphogypsum was directly mixed with limestone and silica in a mass ratio of 13:1:3 and ground to a fineness of not less than 325 mesh as a control sample.

[0049] Performance Testing: The activity index of Examples 1, 2, and the comparative sample was tested according to GB / T18046-2017 standard. The results showed that the activity index of Example 1 reached 75% at 7 days and 95% at 28 days, meeting the requirements for S95 grade slag powder. However, the comparative sample had an extremely low activity index due to the incomplete removal of harmful impurities, leading to abnormal cement paste setting. When the admixture obtained in Example 1 was added to cement at a 30% replacement rate to prepare concrete, its workability was good, and its 28-day compressive strength was comparable to the benchmark group (using S95 slag powder).

[0050] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A phosphogypsum-based concrete admixture, characterized in that, The concrete admixture is prepared from the following raw materials by weight: Modified phosphogypsum 12-15 parts; Limestone 1-3 parts; Silica 2-5 parts; The modified phosphogypsum is obtained by mixing and stirring phosphogypsum and quicklime in a mass ratio of 18-20:0.5-1.5 and then aging.

2. A phosphogypsum based concrete admixture as claimed in claim 1, wherein: The mass ratio of the modified phosphogypsum, limestone and silica is 13:1:

3.

3. A phosphogypsum based concrete admixture as claimed in claim 1, wherein: The fineness of the concrete admixture is not less than 325 mesh.

4. A phosphogypsum based concrete admixture as claimed in claim 1, wherein: The modified phosphogypsum is obtained by mixing and stirring washed phosphogypsum with a water content of 16-22% and quicklime in a mass ratio of 19:1 and then aging.

5. A method of manufacturing a phosphogypsum based concrete admixture according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: S1, preparing modified phosphogypsum, mixing and stirring phosphogypsum, quicklime and a solidifying agent in a mass ratio of 18-20:0.5-1.5 for 8-10 min, and then aging for 24 h to obtain modified phosphogypsum; S2, high-temperature activation, placing the modified phosphogypsum obtained in step S1 and the solidifying agent in a rotary kiln, drying at 400-600℃ for 25-35 min; the mass ratio of the modified phosphogypsum and the solidifying agent is 18-20:1; S3, composite grinding, mixing and grinding 12-15 parts by weight of the heat-activated modified phosphogypsum obtained in step S2, 1-3 parts by weight of limestone and 2-5 parts by weight of silica to a fineness of not less than 325 mesh to obtain the concrete admixture.

6. A method of manufacturing phosphogypsum based concrete admixture as claimed in claim 5 wherein: In the S2 step, drying is performed at 500℃ for 30 min.

7. A method of manufacturing phosphogypsum based concrete admixture as claimed in claim 5 wherein: After step S2 and before step S3, a step of pre-grinding the heat-activated modified phosphogypsum using a vertical mill is further included.

8. Use of the phosphogypsum-based concrete admixture according to any one of claims 1 to 4 as an admixture in the preparation of concrete.

9. Use according to claim 8, wherein the compound is ###0002### The use is to replace slag in concrete.

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