Retarded cement for roadbed and preparation method thereof

Abstract

The invention relates to the technical field of cement production, and particularly provides retarded cement for a roadbed and a preparation method of the retarded cement. Raw materials of the coal cinder cement comprise 45-55 parts of cement clinker, 5-10 parts of coal cinder micro powder, 25-30 parts of fly ash and 3-5 parts of a composite delayed coagulation activator, the composite delayed coagulation activator comprises an alkaline excitation component and a delayed coagulation component, the specific surface area of the coal cinder micro powder is larger than or equal to 400 m < 2 > / kg, the content of free calcium oxide in the coal cinder micro powder is larger than or equal to 6%, and the content of magnesium oxide in the coal cinder micro powder is smaller than or equal to 5%. According to the retarded cement disclosed by the invention, the coal cinder micro powder with a high doping amount is utilized and has a synergistic effect with the sodium silicate-lithium carbonate composite exciting agent, so that the early strength and the later strength are remarkably improved on the premise of ensuring that the final setting time does not exceed 8 hours.

Description

Technical Field

[0001] The present invention relates to the technical field of cement production, and particularly relates to a retarding cement for roadbeds and a preparation method thereof. Background Art

[0002] With the global emphasis on environmental protection and sustainable development, low-carbon cement technology has gradually become an important development direction in the cement industry. As a special cement material, roadbed cement not only needs to meet the requirements of high strength and durability, but also should pay attention to the carbon emission problem in the production process. By using industrial waste and optimizing the composition of activators, the carbon emission of roadbed cement can be significantly reduced, while its strength and construction performance can be improved, thus realizing the low-carbon and green development of roadbed cement.

[0003] In road engineering construction, retarding cement is a key material for roadbed construction, and it needs to meet the requirements such as controllable setting time, qualified early strength, and excellent durability. However, there are still significant defects in the formula and production process of retarding cement in the existing technology.

[0004] Traditional retarding cement mostly relies on gypsum-based retarders or single organic retarders. Such retarders are prone to failure in high-temperature and dry environments, resulting in the final setting time being difficult to reach more than 6 hours, and unable to meet the requirements of large-area construction. In addition, the addition method of retarders is mostly late physical mixing, which has problems such as uneven mixing and poor control accuracy of the dosage, and is prone to cause fluctuations in setting time or a decrease in strength. For example, some processes use alternating laying of clinker layers and sugar layers to improve the dispersibility of retarders, but it requires high-temperature melting of sugar, with complex processes and high energy consumption.

[0005] Therefore, it is urgent to develop a technical solution for retarding cement for roadbeds with excellent retarding effect. Summary of the Invention

[0006] In view of this, the present invention proposes a retarding cement for roadbeds, and the retarding effect is improved through the compound optimization of retarders.

[0007] The technical solution of the present invention is realized as follows: The present invention provides a retarding cement for roadbeds, including the following components in parts by mass:

[0008] 45 - 55 parts of cement clinker

[0009] 5 - 10 parts of pulverized coal slag

[0010] 25 - 30 parts of fly ash

[0011] 3 - 5 parts of compound retarding activator

[0012] Wherein, the compound retarding activator includes an alkaline activation component and a retarding component, and the specific surface area of the pulverized coal slag ≥ 400m 2 / kg, the free calcium oxide content of the coal gangue powder is ≥6%, and the magnesium oxide content is ≤5%.

[0013] In the above embodiments, the coal gangue powder is pre-calcined at a temperature of 800°C for 2 hours. If the requirements of free calcium oxide content ≥6% and magnesium oxide content ≤5% cannot be met after calcination, the calcination time can be appropriately extended, and / or calcium oxide can be added, and / or an appropriate amount of silicate can be added before calcination to remove magnesium oxide.

[0014] In the above embodiments, the highly active free calcium oxide (f-CaO) in the coal gangue is rapidly released in the initial stage of hydration, reacts with water to form Ca(OH)2, provides an alkaline environment and accelerates the dissolution of slag and fly ash, improving the early strength; the alkaline components activate the latent activity of fly ash and slag, and the retarding components inhibit the early hydration of C3A minerals by adsorbing on the surface of cement particles, prolonging the setting time; the microspheres of fly ash optimize the particle size distribution, reducing the water demand. At the same time, its active SiO2 and Al2O3 react with Ca(OH)2 to form C-S-H gel, supplementing the later strength.

[0015] In some embodiments, the composite retarding activator is compounded from sodium silicate and lithium carbonate in a mass ratio of (5-7):1.

[0016] In the above embodiments, the modulus of the sodium silicate is 1.2-1.5, which provides an alkaline environment, dissolves the Si-O and Al-O bonds in the fly ash glass body, and releases active silicate aluminates; the Li + ions are adsorbed on the surface of C3A, delaying the formation of ettringite (AFt), and the final setting time is extended to 6-8 hours; when the sodium silicate is excessive, the alkalinity is too strong, resulting in too fast setting, and when the lithium carbonate is excessive, the hydration is overly inhibited. The ratio of (3-5):1 balances the excitation and retarding effects.

[0017] In some embodiments, it further includes 15-20 parts of blast furnace slag powder, and the mass ratio of the coal gangue powder to the blast furnace slag powder is 1:(2-3). The specific surface area of the blast furnace slag powder is ≥600m 2 / kg.

[0018] In the above embodiments, f-CaO (≥8%) in the coal gangue provides early alkalinity, and the highly active CaO-SiO2-Al2O3 glass body in the slag (specific surface area ≥600m 2 / kg) supplements the later hydration. The two cooperate to form a dense C-S-H gel; a specific surface area ≥600m 2 / kg increases the reaction interface and accelerates the secondary hydration reaction.

[0019] In some embodiments, it further includes 0.2-0.4 parts of nano-silica, and the particle size of the nano-silica is 20-50nm.

[0020] In the above embodiments, the nano-particles fill the nano-scale pores of the cement matrix, reduce the capillary connectivity, and inhibit the water evaporation path; the surface silanol groups (-Si-OH) react with Ca 2+ to form C-S-H gel, enhancing the interfacial transition zone.

[0021] In some embodiments, the loss on ignition of the fly ash is ≤5%, and the water demand is ≤95%.

[0022] In the above embodiments, when the loss on ignition of the fly ash is ≤5%, the unburned carbon's interference with hydration can be reduced, and the decrease in fluidity caused by the adsorption of admixtures can be avoided; when the water demand ratio is ≤95%, the spherical particles reduce the frictional resistance and improve the fluidity of the slurry.

[0023] For the retarding cement for subgrade in the above embodiments, its initial setting time is ≥5 h, the final setting time is ≤8 h, the 3-day compressive strength is ≥24 MPa, the 28-day compressive strength is ≥50 MPa, the dry shrinkage rate is ≤0.025%, and the abrasion resistance is ≤1.8 g / cm 3 .

[0024] The second aspect of the present invention also provides a preparation method for the above retarding cement for subgrade, including the following steps:

[0025] Step 1: Mix the cement clinker, coal slag fine powder and fly ash and grind them to a specific surface area of ≥600 m 2 / kg;

[0026] Step 2: Dissolve the composite retarding activator in water and spray it into the mixture obtained in Step 1, and stir evenly;

[0027] Step 3: Homogenize the mixture obtained in Step 2 for 4 - 6 h to obtain the product.

[0028] Mix and grind to ≥600 m 2 / kg: The high specific surface area increases the reaction active sites and accelerates hydration; when the activator is added by spraying, the liquid activator uniformly coats the particle surface, avoiding too high local concentration.

[0029] In some embodiments, Step 1 further includes:

[0030] The first stage: Mix the cement clinker, coal slag fine powder and fly ash and grind them to a specific surface area of 500 - 600 m 2 / kg;

[0031] The second stage: Adjust the grinding pressure to 0.8 - 1.2 MPa and grind to a specific surface area of ≥600 m 2 / kg, and the temperature during the grinding process does not exceed 70°C.

[0032] The rough grinding in the first stage reduces the hardness of the coal slag and decreases the energy consumption; the high-pressure fine grinding in the second stage optimizes the grading and enhances the activity of the fly ash; the mold temperature not exceeding 70°C prevents the thermal decomposition and invalidation of sodium silicate and lithium carbonate.

[0033] In some embodiments, in step two, the water consumption for dissolution is 2 - 3 times the mass of the composite setting retarder activator.

[0034] The water consumption of 2 - 3 times ensures the complete dissolution of the activator, avoiding the local setting retardation failure caused by undissolved particles. The excessive water will evaporate during the subsequent homogenization process and does not affect the water-cement ratio.

[0035] In some embodiments, in step one, it further includes adding 15 - 20 parts of ground granulated blast-furnace slag, and the specific surface area of the ground granulated blast-furnace slag ≥ 600 m 2 / kg.

[0036] Addition of ground granulated blast-furnace slag: It forms a "CaO - SiO2" complementary system with the coal slag, and the active SiO2 in the slag reacts with the f-CaO in the coal slag to generate more C-S-H gels; high fineness slag (≥ 600 m 2 / kg): Shortens the hydration induction period and accelerates the strength development.

[0037] In some embodiments, in step two, after adding the composite setting retarder activator, it further includes adding nano-silica into the mixture containing the composite setting retarder activator by ultrasonic dispersion and continuing to stir for 10 - 15 min.

[0038] In some embodiments, the ultrasonic dispersion power is 500 - 800 W and the dispersion time is 10 - 15 min.

[0039] The present invention has the following beneficial effects compared with the prior art:

[0040] Through the high-ratio utilization of ground granulated blast-furnace slag and the synergistic effect of the sodium silicate-lithium carbonate composite activator, the present invention significantly improves the early strength and late strength on the premise that the final setting time does not exceed 8 hours. Combining the gradient grinding process and the modification of nano-silica, it further reduces the dry shrinkage rate and wear resistance. Meanwhile, the utilization rate of waste residue ≥ 50%, and the grinding energy consumption ≤ 35 kWh / t. This solution overcomes the problem that it is difficult to balance the setting retardation, strength and durability of traditional setting retarder cement, and has the advantages of high efficiency, environmental protection and economy, and is applicable to the subgrade engineering in high-temperature and dry environments. Specific embodiments

[0041] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the embodiments of the present invention belong. If the definitions stated in this part are contrary to or inconsistent with the definitions stated in the patents, patent applications, published patent applications, and other publications incorporated herein by reference, the definitions listed in this part shall prevail over the definitions incorporated herein by reference.

[0043] Unless otherwise specified, the methods used in the following examples are all conventional methods. The materials, reagents, and instruments used, unless otherwise specified, are all conventional materials, reagents, and instruments in the art, and those skilled in the art can obtain them through commercial channels.

[0044] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper limit preferred values and lower limit preferred values, it should be understood that all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value are specifically disclosed, regardless of whether the ranges are separately disclosed. For example, when the range "1 to 5" is disclosed, the described range should be interpreted as including the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range. In the specification and claims of this application, range limitations can be combined and / or interchanged, and if not otherwise stated, these ranges include all sub-ranges contained therein.

[0045] In the following examples, the coal slag fine powder has been pre-calcined at 800 °C for 2 h.

[0046] Example 1

[0047] This example provides an improved basic formula using a composite retarder activator.

[0048] Components:

[0049] Cement clinker: 50 kg (P·O 42.5 grade, specific surface area 350 m 2 / kg)

[0050] Coal slag fine powder: 8 kg (free CaO content 7%, specific surface area 450 m2 / kg, with a magnesia content of 4% and a particle size ≤ 45 μm)

[0051] Fly ash: 28 kg (Class I ash, loss on ignition 4%, water demand ratio 93%, residue on 45 μm sieve ≤ 12%)

[0052] Composite retarder activator: 4 kg, including sodium silicate: lithium carbonate with a mass ratio of 6:1 (sodium silicate modulus 1.3, lithium carbonate purity ≥ 99%)

[0053] Preparation process:

[0054] Pre-grinding coal slag: The coal slag fine powder is ground alone to a specific surface area of 450 m 2 / kg;

[0055] Mixed grinding: After mixing the coal slag fine powder, clinker, and fly ash, it is ground in two stages (the first stage to 500 m 2 / kg, the second stage adjusts the grinding pressure to 1.0 MPa, and the final specific surface area is 600 m 2 / kg, temperature ≤ 70°C);

[0056] Activator addition: The activator is dissolved in water (the dosage is 3 times the mass of the activator), sprayed into the mixture, and stirred for 15 minutes;

[0057] Homogenization curing: Homogenize for 5 hours and cure under standard conditions (20 ± 2°C, humidity ≥ 95%).

[0058] Example 2

[0059] In this example, based on Example 1, 18 kg of blast furnace slag fine powder is added.

[0060] Example 3

[0061] In this example, based on Example 1, 0.2 kg of nano-SiO2 (average particle size 30 nm) is added.

[0062] Example 4

[0063] In this example, based on Example 1, 18 kg of blast furnace slag fine powder and 0.2 kg of nano-SiO2 (average particle size 30 nm) are added simultaneously.

[0064] Example 5

[0065] In this example, based on Example 2, the raw material of coal slag fine powder is adjusted to 5 kg, and the raw material of blast furnace slag fine powder is 15 kg (coal slag fine powder: blast furnace slag fine powder = 1:3).

[0066] Example 6

[0067] Based on Example 2, in this example, the raw material of coal slag micro - powder is adjusted to 10 kg, and the raw material of blast furnace slag micro - powder is 20 kg (coal slag micro - powder: blast furnace slag micro - powder = 1:2).

[0068] Example 7

[0069] Based on Example 3, in this example, the raw material of nano - SiO2 is adjusted to 0.1 kg (particle size 50 nm).

[0070] Example 8

[0071] Based on Example 3, in this example, the raw material of nano - SiO2 is adjusted to 0.3 kg (particle size 20 nm).

[0072] Example 9

[0073] Based on Example 1, in this example, the mass ratio of sodium silicate to lithium carbonate is adjusted to 5:1.

[0074] Example 10

[0075] Based on Example 1, in this example, the mass ratio of sodium silicate to lithium carbonate is adjusted to 7:1.

[0076] Comparative Example 1

[0077] Based on Example 1, in this comparative example, the composite retarder activator is replaced with 5 kg of desulfurized gypsum.

[0078] Comparative Example 2

[0079] Based on Example 1, in this comparative example, it is ground to 600 m 2 / kg at one time, and the grinding temperature is 90 °C.

[0080] Comparative Example 3

[0081] Based on Example 2, in this comparative example, the raw material of coal slag micro - powder is adjusted to 8 kg, and the raw material of blast furnace slag micro - powder is 8 kg (coal slag micro - powder: blast furnace slag micro - powder = 1:1).

[0082] Comparative Example 4

[0083] Based on Example 5, in this comparative example, the raw material of coal slag micro - powder is adjusted to 5 kg, and the raw material of blast furnace slag micro - powder is 20 kg (coal slag micro - powder: blast furnace slag micro - powder = 1:4).

[0084] Comparative Example 5

[0085] Based on Example 3, in this comparative example, the raw material of nano - SiO2 with a larger particle size is kept at 0.2 kg (particle size 80 nm).

[0086] Comparative Example 6

[0087] On the basis of Example 9, the mass ratio of sodium silicate to lithium carbonate in this comparative example was adjusted to 2:1, the amount of sodium silicate used was 2.7 kg, and the amount of lithium carbonate used was 1.3 kg.

[0088] Comparative Example 7

[0089] On the basis of Example 1, the raw material of coal cinder fine powder was removed in this comparative example.

[0090] Comparative Example 8

[0091] On the basis of Example 1, lithium carbonate was replaced with an equal mass of sodium silicate in this comparative example.

[0092] Comparative Example 9

[0093] On the basis of Example 1, sodium silicate was replaced with an equal mass of lithium carbonate in this comparative example.

[0094] Examples 1 - 10

[0095] Refer to the formula in the following table, mix cement clinker, coal cinder fine powder, fly ash and blast furnace slag fine powder (if any), and grind to a specific surface area of 550 m 2 / kg; then adjust the grinding pressure to 1.0 MPa and continue grinding to a specific surface area of 650 m 2 / kg. Then, dissolve the composite retarder activator in 3 times the amount of water, spray it into the mixed powder material, stir for 15 min, then add nano-silica (if any) to the mixture by ultrasonic dispersion, stir for 10 min with 600 W ultrasonic dispersion, and then mix and homogenize for 5 h, cure at 20 ± 2 °C and humidity ≥ 95%.

[0096]

[0097] Comparative Examples 1 - 6

[0098] Refer to the formula in the following table, and the preparation method is the same as that of the example

[0099]

[0100] The specific surface area of the coal cinder fine powder used in the above examples and comparative examples was 450 m 2 / kg, the free CaO content was 9%; the fly ash was grade I ash, its loss on ignition was 4%, the water demand ratio was 93%, and the residue on 45 μm sieve was ≤ 12%; the modulus of sodium silicate was 1.3, and the specific surface area of blast furnace slag fine powder was 620 m 2 / kg, and the activity index was 95%.

[0101] The initial setting time, final setting time, 3-day strength, 28-day strength, dry shrinkage rate and abrasion resistance of the cement prepared in the above examples and comparative examples were tested respectively. The results are shown in the following table:

[0102]

[0103]

[0104] From the comparison between Example 1 and Comparative Example 1 above, it can be seen that for traditional gypsum retarders, the final setting time is only 4.2 h, which cannot meet the construction requirements. After the composite retarder activator of the present application is adopted, the initial setting time reaches 5.5 h and the final setting time reaches 7.2 h, meeting the construction requirements. For Comparative Example 7, after eliminating the ground granulated blast furnace slag powder, although its final setting time also meets the requirements, its strength decreases significantly.

[0105] After the further improvement scheme of using slag and nano-silica in Example 4, the strength and dry shrinkage rate performance are greatly improved. Although Comparative Example 5 also uses nano-silica, due to its particle size not being within the preferred range, its wear resistance decreases significantly, being inferior to Example 3.

[0106] Although Comparative Example 3 also uses a compound system of steel slag and slag, due to its ratio not being within the preferred range, its 28-day strength of 48 MPa is significantly lower than 56 MPa of Example 2.

[0107] Compared with Example 1, all performances of Comparative Example 2 using one-time grinding treatment are significantly reduced. Moreover, the grinding energy consumption of Comparative Example 2 reaches 45 kWh / t, while that of Example 1 is only 34 kWh / t. It can be seen that the gradient grinding process can also greatly reduce energy consumption and has good economic applicability.

[0108] Comparative Example 8 uses sodium silicate to accelerate hydration in an alkaline environment, and its initial setting time is only 4.2 h, far lower than 5.5 h of Example 1. However, the 3-day strength decreases by 17%, indicating that a single activator cannot balance retardation and strength.

[0109] Comparative Example 9 uses lithium carbonate, and its final setting time is extended to 10.2 h, far exceeding the construction requirements. Moreover, the 3-day strength drops sharply by 30%, indicating that a single retarder severely inhibits activity.

[0110] For the composite retarder activator scheme adopted in Example 1, sodium silicate provides an alkaline environment to activate the activity of slag and fly ash, dissolves the fly ash glass body, and releases active SiO2 and Al2O3, but using it alone causes too fast setting; in lithium carbonate, Li + adsorbs on the surface of C3A, delays the formation of ettringite, and precisely inhibits the early hydration of C3A, but using it alone excessively delays the reaction. The combined use under its preferred ratio balances activation and retardation.

[0111] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A retarder cement for subgrade, characterized in that, Comprising the following components in parts by mass: 45 - 55 parts of cement clinker 5 - 10 parts of coal cinder fine powder 25 - 30 parts of fly ash 3 - 5 parts of composite retarder activator Among them, the composite retarding activator includes an alkaline activation component and a retarding component, and the specific surface area of the pulverized fuel ash is ≥400 m 2 / kg, the free calcium oxide content of the pulverized fuel ash is ≥6%, and the magnesium oxide content is ≤5%.

2. The retarding cement for subgrade according to claim 1, wherein, The composite retarder activator is compounded from sodium silicate and lithium carbonate in a mass ratio of (5 - 7):

1.

3. The retarder cement for subgrade according to claim 1, characterized in that, It also includes 15 - 20 parts of ground granulated blast furnace slag, and the mass ratio of pulverized coal ash to ground granulated blast furnace slag is 1:(2 - 3). The specific surface area of the ground granulated blast furnace slag is ≥600 m 2 / kg.

4. The retarder cement for subgrade according to claim 1, characterized in that, It further includes 0.2 - 0.4 part of nano-silica, and the particle size of the nano-silica is 20 - 50 nm.

5. The retarding cement for subgrade according to claim 1, characterized in that, The loss on ignition of the fly ash is ≤5%, and the water demand is ≤95%.

6. The retarding cement for roadbed according to claim 3 or 4, characterized in that, Its initial setting time ≥ 5h, final setting time ≤ 8h, 3-day compressive strength ≥ 24MPa, 28-day compressive strength ≥ 50MPa, dry shrinkage rate ≤ 0.025%, abrasion resistance ≤ 1.8g / cm 3 .

7. The preparation method of the retarding cement for subgrade according to claim 1, characterized in that, Including the following steps: Step 1. Mix cement clinker, pulverized coal slag and fly ash and grind them to a specific surface area of ≥ 600 m 2 / kg; Step 2: Dissolve the composite retarder activator in water and spray it into the mixture obtained in Step 1, and stir evenly. Step 3: Homogenize the mixture obtained in Step 2 for 4 - 6 h to obtain the product.

8. The preparation method of the retarding cement for subgrade according to claim 7, characterized in that, Step 1 further includes: First stage: Mix the cement clinker, pulverized coal slag and fly ash and grind them to a specific surface area of 500 - 600 m 2 / kg; Second stage: Adjust the grinding pressure to 0.8 - 1.2 MPa, grind until the specific surface area ≥ 600 m 2 / kg, and the temperature during the grinding process does not exceed 70 °C.

9. The preparation method of the retarding cement for subgrade according to claim 7, characterized in that In Step 2, the water consumption for dissolution is 2 - 3 times the mass of the composite retarder activator.

10. The preparation method of the retarding cement for subgrade according to claim 7, characterized in that, In Step 1, it also includes adding 15 - 20 parts of blast furnace slag powder, and the specific surface area of the blast furnace slag powder ≥ 600 m 2 / kg.

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