Cement stabilized red sandstone base material with compensating shrinkage performance and preparation method thereof

Abstract

The present application relates to a kind of red sandstone as aggregate, cement, calcined phosphogypsum, slag and cement stable red sandstone base material of stable base dry shrinkage of cement, including aggregate and inorganic binder, the aggregate includes and only includes graded red sandstone, the inorganic binder includes cement, calcined phosphogypsum, mixture of slag and calcium carbide slag, wherein, the mass fraction of each component is aggregate 94 parts, inorganic binder 6 parts;Inorganic binder, cement accounts for 3.3-3.72 parts, slag accounts for 1.8 parts;Calcined phosphogypsum and calcium carbide slag account for 0.48-0.9 parts, wherein the weight ratio of calcium carbide slag and calcined phosphogypsum is (0.6-2):1.The material of the present application is compensated for dry shrinkage, used as pavement base, can eliminate pavement dry shrinkage, improve the durability of road base.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a cement stabilized red sandstone base material and a base test piece with calcined phosphogypsum, slag, carbide slag and cement, and belongs to the technical field of road building materials. BACKGROUND

[0002] Sandstone, as a kind of sedimentary rock, has a very high content on the ground. However, due to the lack of understanding of the type of rock deposition, sandstone has been rarely used as a supplementary resource material of natural aggregate. And there have been a lot of related researches on cement stabilized macadam, but the research on using soft sandstone as aggregate is relatively less.

[0003] In the highway construction of most areas, a large amount of red sandstone spoil will be produced in tunnel excavation, roadbed excavation, slope treatment, etc. However, due to the dry-wet cycle of red sandstone in the natural environment, especially when it meets water, it is prone to mudification and expansion. Therefore, red sandstone cannot be directly used as a road material, resulting in the storage of red sandstone spoil and occupying a large amount of land resources.

[0004] The invention disclosed in Publication No. CN 116484569 A discloses a cement phosphogypsum stabilized base anti-cracking mix proportion design method based on the integration of results and materials. Cement and phosphogypsum are used as inorganic binding materials, and reasonable design and utilization are carried out for the rational utilization of solid waste phosphogypsum, and the defects of existing cement stabilized base fatigue cracking are effectively solved. However, this invention still uses natural high-quality aggregate. As we all know, with the rapid development of highway traffic, natural high-quality aggregate is becoming increasingly scarce. In addition, the large amount of replacement of phosphogypsum for cement leads to a significant reduction in strength.

[0005] Publication No. CN 115893966 A discloses a cement stabilized phosphogypsum stabilized macadam material for road base and its preparation method and use, which aims to use water, cement, coarse aggregate, phosphogypsum and modifier (metakaolin and calcium oxide) as inorganic binding material. The results show that it meets the requirements of the cement stabilized material of the Chinese highway asphalt pavement design specification. However, this invention does not involve the replacement of aggregate and the study of durability (dry shrinkage).

[0006] Publication No. CN 115893966 A provides a cement stabilized phosphogypsum bottom ash macadam for road base and its preparation method, which uses modified phosphogypsum, waste incineration fine bottom ash, sodium hydroxide solution and fly ash as inorganic binder to stabilize the macadam base, which can broaden the utilization of waste incineration bottom ash and phosphogypsum. However, the composition of the raw materials obtained by incineration varies greatly depending on the different garbage classification in different regions, and it is not universally applicable. SUMMARY

[0007] The present application aims at the lack of natural high-quality aggregate and the road deterioration caused by the dry shrinkage of cement stabilized base, and provides a new low-carbon cement stabilized red sandstone composite base pavement structure taking red sandstone as aggregate and cement, calcined phosphogypsum, carbide slag and slag as binder. While ensuring the mechanical properties of gel materials, the durability problem caused by dry shrinkage is solved, the demand for natural high-quality aggregate is reduced, the transportation cost is reduced, and the carbon dioxide emission in the preparation process is reduced.

[0008] The present application proposes a method for compensating the dry shrinkage of cement stabilized base by using a large amount of calcined phosphogypsum and slag as aggregate, aiming to solve the problems of large accumulation, low utilization rate and environmental pollution of solid waste red sandstone, phosphogypsum and slag, broaden the use of natural soft rock in road base, solve the road deterioration problem caused by the dry shrinkage of cement stabilized base, and in addition, reduce the transportation cost and expand the large-scale optimization and utilization of solid waste.

[0009] To solve the problems of insufficient strength, more dry cracks and poor durability of red sandstone, the present application ingeniously utilizes the synergistic effect between calcium sulfate in phosphogypsum and aluminum in cement and slag, i.e. a large amount of ettringite is generated by reaction, thereby compensating the dry shrinkage of cement and red sandstone and the reduced strength after dilution of cement, and solving the weakness of insufficient strength of red sandstone in cement stabilized base.

[0010] At the same time, the phosphogypsum is ball milled into fine powder and calcined at 500-900 DEG C for 30-90 min, and the impurities in the phosphogypsum are eliminated by calcination to affect the early hydration reaction.

[0011] In addition, the high alkaline performance of carbide slag can well neutralize the acidity of phosphogypsum and balance the inhibition effect on the early hydration of cement; red sandstone is a siliceous acidic aggregate, and the addition of carbide slag can well improve the interface transition zone between red sandstone aggregate and cementitious material.

[0012] Based on the scheme of the present application, red sandstone can be used as road aggregate, which can greatly reduce the transportation cost, carbon dioxide emission and solve the problem of lack of natural high-quality aggregate. The local mountain soil is taken as road material, which reduces the construction cost and has significant economic and social significance in improving resource efficiency and protecting ecological environment.

[0013] To achieve the above object, the technical scheme provided by the present application is as follows:

[0014] A cement stabilized red sandstone base material, comprising aggregate and inorganic binder, the aggregate comprising and only comprising graded red sandstone, the inorganic binder comprising cement, calcined phosphogypsum, carbide slag and slag mixture, wherein the mass fraction of each component is 94 parts of aggregate and 6 parts of inorganic binder.

[0015] In the inorganic binder, the cement accounts for 3.3-3.72 parts, and the slag accounts for 1.8 parts; the calcined phosphogypsum and the carbide slag together account for 0.48-0.9 parts, wherein the weight ratio of the carbide slag to the calcined phosphogypsum is (0.6-2):1.

[0016] Preferably, the mass fraction of each component is: 94 parts of aggregate, 3.6 parts of cement, 1.8 parts of slag, 0.3 parts of calcined phosphogypsum, and 0.3 parts of carbide slag.

[0017] Preferably, water is further included, and the amount of water is calculated according to the optimum water content obtained from the aggregate compaction experiment, wherein 80-90% of the amount of water is used for the dampening of the aggregate, and the remaining amount of water is used for mixing.

[0018] Preferably, the crushing value of the graded red sandstone is ≤26%, and the graded gravel is selected in four grades in terms of mass percentage: 15-17% of gravel with a nominal particle size of 16-26.5 mm, 27-29% of gravel with a nominal particle size of 9.5-16 mm, 31-33% of gravel with a nominal particle size of 2.36-9.5 mm, and 23-25% of gravel with a nominal particle size of less than 2.36 mm.

[0019] Preferably, the particle size range of the cement is 12-23.5 μm, and the particle size range of the mineral blended calcined phosphogypsum, carbide slag and slag is 5-20 μm.

[0020] Preferably, the calcined phosphogypsum is obtained by grinding phosphogypsum at a speed of 500 rpm for 10 min, repeatedly for about 20 times, and reaching below 20 μm, and calcining at 500-900 ℃ for 30-90 min, wherein the content of CaSO4 in the phosphogypsum is 35-65%, the content of SiO2 is 5-15%, and the content of P2O5 is 1-5%.

[0021] Preferably, the slag has a CaO content of 20%-50%, a SiO2 content of 10-30%, and an Al2O3 content of 5-20%, and the slag is ground by a ball mill at a speed of 500 rpm for 10 min, repeatedly for about 20 times, and reaches below 20 μm.

[0022] Preferably, the carbide slag is ground by a ball mill at a speed of 500 rpm for 30-60 min, and reaches below 20 μm, and the content of calcium hydroxide in the carbide slag is 40%-70%.

[0023] Preferably, the content of tricalcium silicate in the cement is 30-60%, and the content of dicalcium silicate is 10-30%.

[0024] The preparation method of any one of the foregoing cement-stabilized red sandstone base materials comprises the following steps:

[0025] (1) red sandstone aggregate is weighed according to the percentage of each grade of mixture;

[0026] (2) cement, calcined phosphogypsum, carbide slag and slag are weighed according to the mass fraction;

[0027] (3) 90-80% of the water added amount calculated according to the optimum water content obtained from the compaction experiment is mixed and stirred uniformly with the red sandstone aggregate, and the mixture is soaked for 2 hours;

[0028] (4) the remaining water is mixed and stirred uniformly with the soaked red sandstone aggregate, cement, calcined phosphogypsum and slag, and then the mixture is pressed in a press machine at a compaction degree of 98% and a loading rate of 1 mm / min until the upper and lower pressing columns are pressed into the test mold, and the pressure is maintained for 2 minutes; the test piece is demolded 2-6 hours after molding, thereby obtaining the cement-stabilized red sandstone base material.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] A large amount of calcium sulfate in the phosphogypsum can react with aluminum in the cement and slag to generate a large amount of ettringite, thereby achieving the effects of compensating for dry shrinkage and filling voids to improve strength. The addition of carbide slag can well neutralize the acidity of the phosphogypsum, and a large amount of active calcium oxide in the carbide slag can react with the slag to accelerate the pozzolanic reaction of the slag. The dry shrinkage performance of the material is compensated, and when used as a pavement base, the dry shrinkage of the pavement can be eliminated, the degradation of the road base caused by dry shrinkage can be solved, and the durability of the road base can be improved.

[0031] Further based on the above effects, the cement content in the stabilized base material made of the material of the present application is reduced, the hydration heat can be reduced, cracking caused by the temperature difference between the inside and outside of the mass concrete can be avoided, and carbon emissions can be reduced.

[0032] Still further, the natural soft rock red sandstone can be completely used to replace high-quality natural aggregate, local materials can be well obtained, the cost can be reduced, the problem of insufficient high-quality aggregate can be solved, and the performance requirements of multiple highway grades can be met. The red sandstone is widely distributed in the country, and can well solve the problem of inconsistent regional raw materials. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The gradation distribution range diagram is referred to the specification (JTG E42-2005).

[0034] Figure 2XRD pattern of cement, phosphogypsum and slag raw materials.

[0035] Figure 3 Bar chart of unconfined compressive strength of comparative examples 1-3 and examples 1-3 at 7 days of curing.

[0036] Figure 4 Dry shrinkage curve of comparative examples 1-3 and examples 1-3 at 56 days of curing. DETAILED DESCRIPTION

[0037] The application will be further described in conjunction with the examples, but the application is not limited by the examples.

[0038] The red sandstone aggregate is usually large rock after blasting or mechanical cutting. They can have irregular shape and edge, and vary in size. The cement, calcined phosphogypsum, carbide slag and slag are inorganic binding materials. The mixture of the aggregate and the inorganic binding materials is referred to as red sandstone aggregate. In this example, the red sandstone aggregate is used as the aggregate, and the cement, calcined phosphogypsum, carbide slag and slag are used as the inorganic binding materials to prepare the cement stabilized red sandstone base.

[0039] The cement stabilized red sandstone base prepared by the cement, calcined phosphogypsum, carbide slag and slag as the inorganic binding materials has the advantages of low carbon emission, easy availability of materials, short transportation distance, good durability and low cost, compared with the ordinary cement stabilized base. The phosphogypsum, carbide slag and slag are used to replace the cement, which provides a solution for the large-scale optimization of industrial solid waste, and further reduces carbon emission.

[0040] The large amount of calcium sulfate in the phosphogypsum can well react with the aluminum in the cement and slag to generate a large amount of ettringite, which can well supplement the dry shrinkage of the cement and red sandstone. The addition of the carbide slag can well neutralize the acidity of the phosphogypsum, and the large amount of active calcium oxide in the carbide slag can react with the slag to accelerate the pozzolanic reaction of the slag. After the incorporation of the supplementary cementitious materials (SCMs) under the appropriate mix design, the durability of the material can be improved without compromising the mechanical properties, and the degradation and cracking problems of the road base caused by dry shrinkage can be solved. Secondly, the incorporation of the supplementary cementitious materials can effectively reduce the use of cement clinker and reduce carbon dioxide emission.

[0041] The red sandstone is rich in storage and widely distributed throughout the country, which can supply road construction throughout the country and greatly reduce the transportation distance.

[0042] The red sandstone aggregate is manually sieved according to the 4-grade grading, and each grade is selected according to the mass percentage after sieving. The selection refers to the specification "Highway Engineering Aggregate Test Method" (JTG E42-2005), which is shown in Figure 1The crushed stone with a nominal particle size of 16-26.5 mm is 15-17%, the crushed stone with a nominal particle size of 9.5-16 mm is 27-29%, the crushed stone with a nominal particle size of (2.36-9.5 mm) is 31-33%, and the crushed stone with a nominal particle size of (0-2.36 mm) is 23-25%, as shown in Table 1 in detail.

[0043] Table 1. Aggregate mix ratio (%)

[0044] aggregate 0-2.36 2.36-9.5 9.5-16 16.26.5 red sandstone 24.0 32.0 28.0 16.0

[0045] Cu-Kα radiation is used The raw material composition is analyzed by XRD. The current and working voltage are 30 mA and 40 kV, respectively. The sample is scanned from 5° to 80° (2-theta) with an increment of 0.013°, and the cumulative time of each step is 8.67 seconds. The test results are shown in Figure 2 The specific components are shown in Table 2:

[0046] Table 2. Chemical composition of cement, phosphogypsum and slag

[0047] ％ Al2O3 Fe2O3 MgO SiO2 CaO TiO2 SO3 K2O P2O5 cement 6.10 3.36 1.95 19.6 62.2 1.34 3.92 - 0.196 phosphogypsum 0.5002 0.1677 0.0788 8.997 37.78 0.094 51.31 0.1717 0.8022 slag 15.044 0.367 8.639 27.981 42.167 1.374 2.768 0.381 0.0151 carbide slag 1.11 0.71 0.129 2.23 95.0 - 0.527 - 0.0254

[0048] In the present application, the phosphogypsum is ground by a ball mill at a speed of 500 rpm for 10 min, repeated for about 20 times, to below 20 μm, and calcined at 500-900 ℃ for 30-90 min, to eliminate the influence of phosphorus element on the early hydration reaction.

[0049] The slag is ground by a ball mill at a speed of 500 rpm for 10 min, repeated for about 20 times, to below 20 μm. The carbide slag is ground by a ball mill at a speed of 500 rpm for 30-60 min, and reaches below 20 μm.

[0050] In the aggregate of the present application, water is additionally added to prepare the base test piece. The amount of water added is calculated based on the optimum water content of the aggregate measured by the compaction experiment. The compaction experiment of the cement stabilized base is carried out according to the Chinese standard (JTG E51-2009) by using an iron hammer with a mass of 4.5 kg and a diameter of 5.0 cm, hammering in three layers, 98 times per layer, and according to the method C. The maximum dry density and the optimum water content of each aggregate are calculated by the quadratic polynomial fitting method according to the test results. The optimum water content and the maximum dry density are mainly used to calculate the required amount of water added according to the calculation formula and the mass of the aggregate and the inorganic binder according to the standard (JTG E51-2009) T 0843-2009, and to achieve the purpose of controlling the compaction degree. The water content and dry density data of each example and the comparative example can also be controlled to be close, to increase the comparability.

[0051] In the present application, the adding amount of each aggregate and inorganic binder is calculated by the maximum dry density and optimum moisture content of the mixture obtained by the compaction experiment, and the calculation formula is as follows:

[0052] The standard mass of a single test piece: m0=v x p max (1+ω opt ) x g

[0053] Considering the mass loss in the test piece forming process, the mass of each test piece in the actual operation process can be increased by 0-2%, that is: m'0=m0 x (1+delta)

[0054] The total mass of dry materials (including dry soil and inorganic binder) of each test piece: m1=m'0 / (1+alpha)

[0055] The mass of inorganic binder in each test piece: m2=m1 x alpha / (1+alpha) by external mixing method

[0056] The mass of inorganic binder in each test piece: m2=m1 x alpha by internal mixing method

[0057] The mass of dry soil in each test piece: m3=m1-m2

[0058] The water added in each test piece: m w =(m2+m3) x omega opt

[0059] Check: m'0=m2+m3+m w

[0060] Formula: v-the volume of the test piece (cm 3 );

[0061] omega opt -the optimum moisture content of the mixture (%);

[0062] p max -the maximum dry density of the mixture (g / cm 3 );

[0063] gamma-the compaction degree standard of the mixture (%);

[0064] m0, m'0-the mass of the mixture (g);

[0065] Accordingly, the water added to the aggregate is calculated according to the optimum moisture content obtained by the compaction experiment.

[0066] In the examples and comparative examples of the present application, the preparation method of the cement stabilized base is as follows:

[0067] The test piece preparation was performed according to the Chinese standard (JTG E51-2009) T 0843-2009 Inorganic Bonding Stable Material Test Piece Preparation Method, and the size of the test piece was 150 mm x 150 mm.

[0068] First, the red sandstone aggregate was prepared by weighing according to the four-grade gradation; then, the cement, calcined phosphogypsum, carbide slag, slag and red sandstone powder were weighed according to the mass fraction; the red sandstone aggregate was mixed and stirred uniformly according to the water amount of 80-90% of the optimum water content calculated by the compaction experiment, and was soaked for 2-4 hours;

[0069] The remaining water, the soaked aggregate, the cement, the calcined phosphogypsum, the carbide slag, the slag and the red sandstone powder were mixed and stirred uniformly, and were pressed by using a press machine at a compaction degree of 98% and a loading rate of 1 mm / min until the upper and lower pressing columns were pressed into the test mold, and the pressure was maintained for more than 2 min; the test piece was demolded 2-6 h after the test piece was formed, so that the base test piece was prepared. The test piece was immediately placed in a plastic bag after weighing, and was covered with a wet towel, and was moved to a standard temperature and humidity environment for curing.

[0070] Correlation of each example and comparative example

[0071] Examples 1-3 were used as preferred examples of the present application, and comparative examples 1-3 were used for comparison to illustrate the performance advantages of the embodiments of the present application. For clarity, the mass ratio of each component in the aggregate and inorganic binder in each example and comparative example is shown in Table 3, and the maximum dry density and the optimum water content obtained by the compaction experiment are shown in Table 3.

[0072] Table 3. Maximum dry density and optimum water content of each aggregate using red sandstone or granite as aggregate.

[0073]

[0074] The inorganic binder was added by the internal mixing method, and the raw material composition of the examples is shown in Table 4.

[0075] Table 5. Raw material composition of the examples.

[0076]

[0077] For clarity, the raw material composition of each of the above comparative examples is shown in Table 5.

[0078] Table 5. Raw material composition of the comparative examples.

[0079]

[0080] Comparative Example 1

[0081] The raw materials of Comparative Example 1 included red sandstone aggregate 5810.51 g and cement 370.88 g.

[0082] In addition to water, the raw materials of Comparative Example 1 only use red sandstone aggregate and cement in a mass ratio of about 94:6. The red sandstone aggregate and cement used in Comparative Example 1 and the following examples and comparative examples are the four-grade red sandstone aggregate described above, and the cement used is ordinary Portland cement, with the specific composition being that the content of tricalcium silicate is 30-60%, and the content of dicalcium silicate is 15-30%.

[0083] The weight of the cement in Comparative Example 1 will be referred to as the reference weight of the cement in the following examples and comparative examples. That is, 6 / 94 of the red sandstone aggregate is taken as the reference weight of the cement.

[0084] Comparative Example 2

[0085] Comparative Example 2 is different from Comparative Example 1 in that 10% of the reference weight of the cement is further replaced by calcined phosphogypsum and carbide slag, that is, 10% of the reference weight of the cement is replaced by 5% of the reference weight of calcined phosphogypsum and 5% of the reference weight of carbide slag, under the premise that the aggregate and inorganic binding material ratio remains unchanged (the mass ratio is about 94:6).

[0086] Comparative Example 3

[0087] Comparative Example 3 is different from Comparative Example 1 in that 30% of the reference weight of the cement is replaced by slag, that is, 30% of the reference weight of the cement is replaced by slag.

[0088] Example 1

[0089] The raw materials of Example 1 include red sandstone aggregate 5768.58g, cement 228.29g, calcined phosphogypsum 18.41g, carbide slag 11.05g, and slag 110.46g.

[0090] Example 1 is different from Comparative Example 1 in that the amount of cement is reduced, 38% of the reference weight of the cement is replaced by 30% of the reference weight of slag, 5% of the reference weight of calcined phosphogypsum, and 3% of the reference weight of carbide slag, under the premise that the aggregate and inorganic binding material ratio remains unchanged (the mass ratio is about 94:6).

[0091] Example 2

[0092] Example 2 is different from Comparative Example 1 in that the amount of cement is further reduced, 40% of the reference weight of the cement is replaced by 30% of the reference weight of slag, 5% of the reference weight of calcined phosphogypsum, and 5% of the reference weight of carbide slag, under the premise that the aggregate and inorganic binding material ratio remains unchanged (the mass ratio is about 94:6), and the weight ratio of carbide slag to calcined phosphogypsum reaches 1:1.

[0093] Example 3

[0094] Example 3 is different from Comparative Example 1 in that the cement dosage is further reduced, 45% of the reference weight of cement is replaced by 30% of the reference weight of slag, 5% of the reference weight of calcined phosphogypsum, and 10% of the reference weight of carbide slag, and the weight ratio of carbide slag to calcined phosphogypsum reaches 2:1, while the aggregate and inorganic binding material ratio remains unchanged (the mass ratio is about 94:6).

[0095] The compressive strength test is carried out according to the Chinese standard (JTG E51-2009) T 0805-1994 unconfined compressive strength test, the test size is diameter x height = 150 x 150 mm, the test piece is soaked for one day before the unconfined compressive strength test, and the test piece soaked for one day is taken out of the water before the test, and the water on the surface of the test piece is absorbed with a soft cloth. During the experiment, the loading rate of the pressure machine is kept at 1 mm / min, and the maximum pressure at the time of failure is recorded. The test results of the compressive strength of Examples 1-3 and Comparative Examples 1-3 at 7 days, 28 days and 56 days are shown in Table 6, and the corresponding comparison changes are visually displayed in the form of bar charts. Figure 3

[0096] Table 6. Compressive strength of Examples 1-3 and Comparative Examples 1-3 at 7 days, 28 days and 56 days.

[0097] compressive strength (MPa) 7 days 28 days 56 days Example 1 5.25 7.10 8.15 Example 2 6.03 7.39 9.06 Example 3 5.52 6.97 7.86 Comparative Example 1 6.23 7.78 8.88 Comparative Example 2 5.67 7.75 8.34 Comparative Example 3 5.86 7.59 8.98

[0098] Table 7. Standard (JTG / F20-2015) 7-day unconfined compressive strength R of cement stabilized materials d (MPa)

[0099]

[0100] As can be seen from Table 6, the unconfined compressive strength of Example 2 of the present application at seven days is higher than that of Comparative Examples 2-3, which shows that the addition of calcined phosphogypsum and carbide slag is beneficial to the development of strength, mainly because the high alkalinity of carbide slag well balances the acidity of calcined phosphogypsum, thereby eliminating the inhibition of phosphogypsum on the early hydration of cement. The calcium hydroxide generated by the reaction of a large amount of calcium oxide in carbide slag with water can generate hydration product C-S-H through pozzolanic reaction with slag in the early hydration stage, and there is a mutual synergistic effect between calcium sulfate in calcined phosphogypsum and aluminum phases in cement and slag, which can generate a large amount of ettringite to fill the voids to achieve the effect of improving the strength, and inhibit the shrinkage.

[0101] ​The compressive strength at 56 days is higher than that of Comparative Examples 1-3, indicating that the calcium hydroxide generated by cement hydration continues to react with the slag to generate more hydration products C-S-H, and the calcium sulfate in the calcined phosphogypsum continues to react with the aluminum phase in the cement and slag to generate a large amount of ettringite to fill the voids. In addition, due to the siliceous weakly acidic aggregate of red sandstone, the high alkalinity of the carbide slag well improves the weak problem of the interface transition zone of the siliceous weakly acidic aggregate of red sandstone.

[0102] As can be seen from Examples 1-3 and Comparative Example 1, the strength of Examples 1-3 is slightly lower than that of Comparative Example 1 at 7 days of hydration, which is mainly because the dilution effect of a large amount of calcined phosphogypsum on the cement leads to a decrease in early hydration reaction. However, at 56 days, the strength of Example 2 is slightly higher than that of Comparative Example 1, mainly due to the pozzolanic reaction of the slag and the reaction of the calcined phosphogypsum with the aluminum phase in the cement and slag to generate more ettringite. However, the strength still meets the requirement of the standard for unconfined compressive strength.

[0103] From Figure 4 As can be seen from the drying shrinkage curve, the drying shrinkage of Examples 1-3 is significantly lower than that of Comparative Examples 1-3, especially in the later hydration period. The drying shrinkage of Comparative Example 1 is the largest, and the drying shrinkage of Example 2 is the smallest, indicating that Example 2 has the best performance. This is mainly because the reaction of calcined phosphogypsum with the aluminum phase in the cement and slag generates more ettringite, which inhibits the drying shrinkage strain. In addition, the carbide slag can well improve the interface transition zone of red sandstone, and the generated hydration products wrap the surface of the red sandstone aggregate, inhibiting the loss of water in the red sandstone aggregate, thereby inhibiting shrinkage.

[0104] In addition, as can be seen from the 56-day drying shrinkage rate data, the 56-day drying shrinkage of Examples 1-2 is 81.9%, 74.21% and 78.73% of that of Comparative Example, respectively.

[0105] The improvement of the compressive strength of each age of the embodiments 1-3 of the present application shows that the optimization of the addition amount and mixing ratio of the calcined phosphogypsum and the slag can realize the improvement of the compressive strength, and can well play the effect of inhibiting the dry shrinkage. It is found through research that the reason is a comprehensive result of many aspects: first, the addition of the carbide slag can balance the acidity of the calcined phosphogypsum, alleviate the inhibition of the calcined phosphogypsum on the early hydration of the cement, and the active calcium oxide in the carbide slag can generate calcium hydroxide by reacting with water, which can generate more C-S-H by the pozzolanic reaction with the slag in the early hydration; second, the addition of the calcined phosphogypsum and the slag provides a large number of nucleation sites for the hydration of the cement, and promotes the early hydration of the cement. Third, the large amount of replacement of the cement by the calcined phosphogypsum and the slag ensures that the cement can be fully hydrated, and will not cause the hydration of the product to be wrapped to cause hydration to supplement, fourth, the mutual coordination of the calcium sulfate in the phosphogypsum and the aluminum phase in the cement and the slag generates a large amount of ettringite to compensate for the strength reduction caused by the dilution of the cement, and to compensate for the dry shrinkage of the cement and the red sandstone aggregate, and to enhance the durability, to meet the requirement of the specification on the unconfined compressive strength. In the later hydration, the pozzolanic property of the slag can also well react with the calcium hydroxide to generate hydrated calcium silicate and hydrated silico-aluminate, thereby improving the strength.

[0106] Finally, the addition of the carbide slag improves the interface transition zone between the red sandstone aggregate and the inorganic binder, and the generated more hydration products can better fill and wrap the red sandstone aggregate, inhibit the moisture release of the red sandstone in the later hydration, and achieve the purpose of inhibiting the shrinkage of the aggregate.

[0107] Compared with the prior art, the present application has the following beneficial effects:

[0108] The cement stabilized base layer using the red sandstone as the aggregate and the calcined phosphogypsum, the slag, the carbide slag and the cement as the inorganic binder can completely replace the natural high-quality aggregate with the red sandstone, can well solve the problem of the shortage of the natural high-quality aggregate and the difficulty in handling the large amount of excavation of the red sandstone, realizes the on-site material taking, and greatly reduces the transportation cost.

[0109] The cement in the inorganic binder is partially replaced, the replacement of the mineral admixture is 5-50% on the premise of guaranteeing not to damage the mechanical properties, and the replacement of the cement can be used to adjust the strength of the cementitious material and reduce the dry shrinkage of the cement stabilized base layer.

[0110] Especially, the large amount of phosphogypsum, carbide slag and slag partially replace the cement, which can well solve the environmental problem of the accumulation of industrial solid waste, greatly reduce the amount of cement, and well reduce the carbon dioxide emission.

[0111] The present application ingeniously utilizes the large amount of calcium oxide and high alkalinity of carbide slag to improve the pozzolanic reaction of slag and balance the acidity of phosphogypsum to reduce the inhibition of early hydration; the calcium sulfate in phosphogypsum reacts with aluminum in cement and slag to generate a large amount of ettringite to fill the voids and inhibit the drying shrinkage of cement and red sandstone, thereby improving the durability of the road base.

[0112] In the description of the present specification, the embodiments refer to the specific features, structures, materials or characteristics described in combination with the embodiments or examples, which are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms is not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. Furthermore, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0113] Although the embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and cannot be construed as limiting the present application, and those skilled in the art can modify, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A cement-stabilized red sandstone base material for compensating for drying shrinkage, comprising aggregate and inorganic binder, characterized in that, The aggregate includes, but is limited to, graded red sandstone. The inorganic binder includes a mixture of cement, calcined phosphogypsum, carbide slag and slag, wherein the mass fraction of each component is 94 parts aggregate and 6 parts inorganic binder. Among them, cement accounts for 3.3-3.72 parts and slag accounts for 1.8 parts in the inorganic binder; calcined phosphogypsum and carbide slag together account for 0.48-0.9 parts, of which the weight ratio of carbide slag to calcined phosphogypsum is (0.6-2):1; The crushing value of the graded red sandstone is ≤26%. The graded red sandstone is selected by mass percentage and divided into four grades: 15-17% for crushed stone with a nominal particle size of 16-26.5 mm, 27-29% for crushed stone with a nominal particle size of 9.5-16 mm, 31-33% for crushed stone with a nominal particle size of 2.36-9.5 mm, and 23-25% for crushed stone with a nominal particle size of less than 2.36 mm. The calcined phosphogypsum is obtained by grinding phosphogypsum at 500 rpm for 10 min, repeating this process 20 times until the phosphogypsum reaches a particle size of less than 20 μm, and then calcining it at 500-900℃ for 30-90 min.

2. The cement-stabilized red sandstone base material according to claim 1, characterized in that: The mass fractions of each component are as follows: Aggregate, 94 parts; Cement, 3.6 parts; Slag, 1.8 parts; Calcined phosphogypsum, 0.3 parts; Carbide slag, 0.3 parts.

3. The cement-stabilized red sandstone base material according to claim 1, characterized in that: It also includes water, the amount of which is calculated based on the optimal moisture content obtained from the aggregate compaction test. 80-90% of the water is used for the curing of the aggregate, and the remaining water is used for mixing.

4. The cement-stabilized red sandstone base material according to claim 1, characterized in that, The cement has a particle size range of 12-23.5 μm, and the calcined phosphogypsum, carbide slag, and mineral slag have a particle size range of 5-20 μm.

5. The cement-stabilized red sandstone base material according to claim 1, characterized in that: The phosphogypsum contains 35-65% CaSO4, 5-15% SiO2, and 1-5% P2O5.

6. The cement-stabilized red sandstone base material according to claim 1, characterized in that, The slag contains 20%-50% CaO, 10-30% SiO2, and 5-20% Al2O3. The slag is ground in a ball mill at 500 rpm for 10 minutes, repeated 20 times, until it reaches a particle size of less than 20 μm.

7. The cement-stabilized red sandstone base material according to claim 1, characterized in that: The carbide slag is ground in a ball mill at 500 rpm for 30-60 minutes to a depth of less than 20 μm, and the calcium hydroxide content in the carbide slag is 40%-70%.

8. The cement-stabilized red sandstone base material according to claim 1, characterized in that, The cement contains 30-60% tricalcium silicate and 10-30% dicalcium silicate.

9. The preparation method of the cement-stabilized red sandstone base material according to any one of claims 1-8 comprises the following steps: (1) Weigh the red sandstone aggregate according to the mixing percentage of each grade; (2) Weigh out cement, calcined phosphogypsum, carbide slag and mineral slag by weight; (3) Mix 80-90% of the water added to the red sandstone aggregate based on the optimum moisture content obtained from the compaction test, stir evenly, and let it sit for 2 hours; (4) Mix the remaining water with the soaked red sandstone aggregate, cement, calcined phosphogypsum, carbide slag and slag evenly. Then, use a press to press the mixture at a compaction degree of 98% and a loading rate of 1 mm / min until the upper and lower pressure columns are pressed into the mold. Maintain the pressure for 2 minutes. Demold the specimen 2-6 hours after it is formed to obtain cement-stabilized red sandstone base material.

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