A retarded cement for roadbed and its preparation method
By using composite retarder activators and gradient grinding processes, the composition and process of retarded cement were optimized, solving the problem of insufficient final setting time of retarded cement under high temperature conditions. This resulted in improved early and late strength, making it suitable for roadbed engineering.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-06
- Publication Date
- 2026-03-13
AI Technical Summary
Existing retarded cement is prone to failure in high-temperature and dry environments, and its final setting time is difficult to reach more than 6 hours. It also suffers from uneven mixing and poor dosage control, which cannot meet the needs of large-scale construction.
A composite retarder activator, consisting of sodium silicate and lithium carbonate, combined with coal slag powder and blast furnace slag powder, is used to generate CSH gel through gradient grinding and nano-silica modification. This gel provides early strength and extends setting time.
It significantly improves the final setting time and early strength of retarded cement, reduces drying shrinkage and wear resistance, and is suitable for roadbed engineering in high-temperature and dry environments, combining high efficiency, environmental protection and economy.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of cement production technology, and in particular to a retarded cement for roadbeds and its preparation method. Background Technology
[0002] With increasing global emphasis on environmental protection and sustainable development, low-carbon cement technology has gradually become an important development direction for the cement industry. As a special type of cement material, roadbed cement not only needs to meet the requirements of high strength and durability, but also requires attention to carbon emissions during its production process. By utilizing industrial waste and optimizing the composition of activators, the carbon emissions of roadbed cement can be significantly reduced, while simultaneously improving its strength and workability, thereby achieving the low-carbon and green transformation of roadbed cement.
[0003] In road construction, retarded cement is a key material for subgrade construction, requiring it to meet requirements such as controllable setting time, early strength attainment, and excellent durability. However, the formulation and production process of retarded cement in existing technologies still have significant shortcomings.
[0004] Traditional retarded cement often relies on gypsum-based retarders or single organic retarders. These retarders are prone to failure in high-temperature, dry environments, making it difficult to achieve a final setting time of more than 6 hours, which cannot meet the needs of large-scale construction. Furthermore, the addition of retarders is mostly done through later-stage physical mixing, which can lead to uneven mixing and poor dosage control, easily causing fluctuations in setting time or a decrease in strength. For example, some processes use alternating layers of clinker and sugar to improve retarder dispersibility, but this requires high-temperature melting of the sugar, making the process complex and energy-intensive.
[0005] Therefore, there is an urgent need to develop a technical solution for retarded cement used in roadbeds with excellent retarding effect. Summary of the Invention
[0006] In view of this, the present invention proposes a retarding cement for roadbeds, which improves the retarding effect through the optimization of the compounding of retarder.
[0007] The technical solution of this invention is implemented as follows: This invention provides a retarding cement for roadbeds, comprising the following components in parts by weight:
[0008] 45-55 parts cement clinker
[0009] 5-10 parts of coal slag powder
[0010] 25-30 parts fly ash
[0011] 3-5 parts of compound retarder activator
[0012] The composite retarder and activator comprises an alkaline activating component and a retarding component, and the specific surface area of the coal slag powder is ≥400 m². 2 / kg, the free calcium oxide content of coal slag powder is ≥6%, and the magnesium oxide content is ≤5%.
[0013] In the above embodiments, the coal slag 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 the 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, highly active free calcium oxide (f-CaO) in the slag is rapidly released in the early stage of hydration, reacting with water to generate Ca(OH)2, providing an alkaline environment and accelerating the dissolution of slag and fly ash, thus improving early strength; the alkaline component activates the potential activity of fly ash and slag, and the retarding component inhibits the early hydration of C3A minerals by adsorbing on the surface of cement particles, thus prolonging the setting time; the fly ash microspheres optimize the particle size distribution, reducing water demand, while their active SiO2 and Al2O3 react with Ca(OH)2 to generate CSH gel, supplementing later strength.
[0015] In some embodiments, the composite retarder activator is prepared by compounding sodium silicate and lithium carbonate in a mass ratio of (5-7):1.
[0016] In the above embodiments, the sodium silicate has a modulus of 1.2-1.5, which provides an alkaline environment to dissolve the Si-O and Al-O bonds in the fly ash glass, releasing active aluminosilicates; the Li in lithium carbonate... + Ions adsorbed on the C3A surface delay the formation of ettringite (AFt) and extend the final setting time to 6-8 hours; excessive sodium silicate leads to excessive alkalinity and excessively fast setting, while excessive lithium carbonate excessively inhibits hydration. The ratio of (3-5):1 balances the activation and retarding effects.
[0017] In some embodiments, the mixture also includes 15-20 parts of blast furnace slag powder, with a mass ratio of coal slag powder to blast furnace slag powder of 1:(2-3), and the specific surface area of the blast furnace slag powder is ≥600m². 2 / kg.
[0018] In the above embodiments, f-CaO (≥8%) in the slag provides early alkalinity, and the highly active CaO-SiO2-Al2O3 glass in the slag (specific surface area ≥600m²) 2 / kg) replenishes the hydration in the later stages, and the two work synergistically to form a dense CSH gel; specific surface area ≥600m² 2 / kg increases the reaction interface and accelerates the secondary hydration reaction.
[0019] In some embodiments, 0.2-0.4 parts of nano-silica are also included, wherein the nano-silica has a particle size of 20-50 nm.
[0020] In the above embodiments, nanoparticles fill the nanoscale pores of the cement matrix, reducing capillary connectivity and inhibiting moisture evaporation pathways; surface silanol groups (-Si-OH) and Ca 2+ The reaction generates CSH gel, which enhances the interfacial transition zone.
[0021] In some embodiments, the loss on ignition of the fly ash is ≤5%, and the water requirement is ≤95%.
[0022] In the above embodiments, a fly ash loss on ignition of ≤5% can reduce the interference of unburned carbon on hydration and avoid adsorption of additives leading to decreased fluidity; when the water demand ratio is ≤95%, spherical particles reduce frictional resistance and improve slurry fluidity.
[0023] The retarded cement for roadbeds described above has an initial setting time ≥ 5 hours, a final setting time ≤ 8 hours, a 3-day compressive strength ≥ 24 MPa, a 28-day compressive strength ≥ 50 MPa, a drying shrinkage rate ≤ 0.025%, and an abrasion resistance ≤ 1.8 g / cm³. 3 .
[0024] A second aspect of the present invention also provides a method for preparing the above-mentioned retarding cement for roadbeds, comprising the following steps:
[0025] Step 1: Mix cement clinker, coal slag powder, and fly ash, then grind them to a specific surface area ≥ 600 m². 2 / kg;
[0026] Step 2: Dissolve the composite retarder and activator in water and spray it into the mixture obtained in Step 1, then stir until homogeneous;
[0027] Step 3: Homogenize the mixture obtained in Step 2 for 4-6 hours to obtain the final product.
[0028] Mix and grind to ≥600m 2 / kg: High specific surface area increases reactive sites and accelerates hydration; when the activator is added by spraying, the liquid activator evenly coats the particle surface, avoiding excessively high local concentrations.
[0029] In some implementations, step one further includes:
[0030] Phase 1: Mix cement clinker, coal slag powder, and fly ash, then grind them to a specific surface area of 500-600 m². 2 / kg;
[0031] Second stage: Adjust the grinding pressure to 0.8-1.2 MPa, and grind until the specific surface area is ≥600 m². 2 / kg, and the grinding process temperature does not exceed 70℃.
[0032] The first stage of coarse grinding reduces the hardness of coal slag and reduces energy consumption; the second stage of high-pressure fine grinding optimizes the gradation and improves the activity of fly ash; the parting temperature does not exceed 70℃ to prevent the thermal decomposition and failure of sodium silicate and lithium carbonate.
[0033] In some implementations, in step two, the amount of water used for dissolving is 2-3 times the mass of the composite retarder activator.
[0034] Use 2-3 times the amount of water to ensure the activator is completely dissolved, and avoid undissolved particles causing localized retarding failure. Excess water will evaporate during the subsequent homogenization process and will not affect the water-cement ratio.
[0035] In some embodiments, step one further includes adding 15-20 parts of blast furnace slag powder, wherein the specific surface area of the blast furnace slag powder is ≥600m². 2 / kg.
[0036] Adding slag micronized powder: Forms a complementary "CaO-SiO2" system with coal slag; the active SiO2 in the slag reacts with f-CaO in the coal slag to generate more CSH gel; high-fineness slag (≥600 μm) 2 / kg): Shortens the hydration induction period and accelerates intensity development.
[0037] In some embodiments, after adding the composite retarder activator in step two, the process further includes adding nano-silica to the mixture containing the composite retarder activator by ultrasonic dispersion, and continuing to stir for 10-15 minutes.
[0038] In some implementations, the ultrasonic dispersion power is 500-800W and the dispersion time is 10-15min.
[0039] The present invention has the following advantages over the prior art:
[0040] This invention utilizes a high dosage of coal slag powder and the synergistic effect of a sodium silicate-lithium carbonate composite activator to significantly improve early and late strength while ensuring a final setting time of no more than 8 hours. Combined with gradient grinding technology and nano-silica modification, it further reduces drying shrinkage and abrasion resistance, while achieving a waste residue utilization rate of ≥50% and grinding energy consumption of ≤35kWh / t. This solution overcomes the challenge of balancing retarding, strength, and durability in traditional retarded cement, offering high efficiency, environmental friendliness, and economy, and is suitable for roadbed engineering in high-temperature and dry environments. Detailed Implementation
[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this invention pertain. If any definition stated in this section is contrary to or otherwise inconsistent with a definition stated in a patent, patent application, published patent application, or other publication incorporated herein by reference, the definitions listed here shall prevail over those incorporated herein by reference.
[0043] Unless otherwise specified, the methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials, reagents, and instruments used are conventional materials, reagents, and instruments in the art, and can be obtained commercially by those skilled in the art.
[0044] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. In this specification and claims, range definitions may be combined and / or interchanged, unless otherwise stated, these ranges include all subranges contained therein.
[0045] In the following examples, the coal slag powder was pre-calcined at 800℃ for 2 hours.
[0046] Example 1
[0047] This embodiment provides a basic improved formulation using a composite retarder and activator.
[0048] Components:
[0049] Cement clinker: 50kg (P·O 42.5 grade, specific surface area 350m²) 2 / kg)
[0050] Coal slag powder: 8 kg (free CaO content 7%, specific surface area 450 m²)2 / kg, magnesium oxide content 4%, particle size ≤45μm)
[0051] Fly ash: 28 kg (Grade I ash, loss on ignition 4%, water requirement ratio 93%, residue on 45μm sieve ≤12%)
[0052] Composite retarder activator: 4 kg, including sodium silicate:lithium carbonate in a mass ratio of 6:1 (sodium silicate modulus 1.3, lithium carbonate purity ≥99%).
[0053] Preparation process:
[0054] Pre-ground coal slag: Coal slag powder is separately ground to a specific surface area of 450 m². 2 / kg;
[0055] Mixed grinding: After mixing coal slag powder, clinker, and fly ash, the mixture is ground in two stages (the first stage up to 500m). 2 / kg, the second stage of grinding pressure was adjusted to 1.0MPa, and the final specific surface area was 600m². 2 / kg, temperature ≤70℃);
[0056] Activator addition: Dissolve the activator in water (the amount should be 3 times the mass of the activator), spray it into the mixture, and stir for 15 minutes;
[0057] Homogenization and curing: Homogenize for 5 hours, then standard curing (20±2℃, humidity ≥95%).
[0058] Example 2
[0059] This embodiment adds 18 kg of blast furnace slag powder to the existing embodiment 1.
[0060] Example 3
[0061] This embodiment is based on Example 1, but with the addition of 0.2 kg of nano-SiO2 (average particle size of 30 nm).
[0062] Example 4
[0063] This embodiment, based on embodiment 1, adds 18 kg of blast furnace slag powder and 0.2 kg of nano-SiO2 (average particle size of 30 nm).
[0064] Example 5
[0065] This embodiment is based on embodiment 2, but the raw material of coal slag powder is adjusted to 5 kg and the raw material of blast furnace slag powder is 15 kg (coal slag powder: blast furnace slag powder = 1:3).
[0066] Example 6
[0067] This embodiment is based on embodiment 2, but the raw material of coal slag powder is adjusted to 10 kg and the raw material of blast furnace slag powder is 20 kg (coal slag powder: blast furnace slag powder = 1:2).
[0068] Example 7
[0069] This embodiment is based on Example 3, but the amount of nano-SiO2 raw material is adjusted to 0.1 kg (particle size 50 nm).
[0070] Example 8
[0071] This embodiment is based on Example 3, but the amount of nano-SiO2 raw material is adjusted to 0.3 kg (particle size 20 nm).
[0072] Example 9
[0073] This embodiment is based on Example 1, but the mass ratio of sodium silicate to lithium carbonate is adjusted to 5:1.
[0074] Example 10
[0075] This embodiment is based on Example 1, but the mass ratio of sodium silicate to lithium carbonate is adjusted to 7:1.
[0076] Comparative Example 1
[0077] This comparative example is based on Example 1, but the composite retarder activator is replaced with 5 kg of desulfurized gypsum.
[0078] Comparative Example 2
[0079] This comparative example, based on Example 1, uses a one-time grinding process to 600 mg / L. 2 / kg, grinding temperature 90℃.
[0080] Comparative Example 3
[0081] This comparative example is based on Example 2, with the coal slag powder raw material adjusted to 8 kg and the blast furnace slag powder raw material to 8 kg (coal slag powder: blast furnace slag powder = 1:1).
[0082] Comparative Example 4
[0083] This comparative example is based on Example 5, with the coal slag powder raw material adjusted to 5 kg and the blast furnace slag powder raw material to 20 kg (coal slag powder: blast furnace slag powder = 1:4).
[0084] Comparative Example 5
[0085] This comparative example is based on Example 3, but uses nano-SiO2 raw material with a larger particle size to maintain 0.2 kg (particle size 80 nm).
[0086] Comparative Example 6
[0087] This comparative example is based on Example 9, but the mass ratio of sodium silicate to lithium carbonate is adjusted to 2:1, the amount of sodium silicate is 2.7 kg, and the amount of lithium carbonate is 1.3 kg.
[0088] Comparative Example 7
[0089] This comparative example is based on Example 1, but with the coal slag powder raw material removed.
[0090] Comparative Example 8
[0091] This comparative example is based on Example 1, but with lithium carbonate replaced by an equal mass of sodium silicate.
[0092] Comparative Example 9
[0093] This comparative example is based on Example 1, except that sodium silicate is replaced with an equal mass of lithium carbonate.
[0094] Examples 1-10
[0095] Referring to the formula in the table below, mix cement clinker, coal slag powder, fly ash, and blast furnace slag powder (if any), and then grind them to a specific surface area of 550 m². 2 / kg; then adjust the grinding pressure to 1.0MPa and continue grinding until the specific surface area is 650 m². 2 / kg Then, dissolve the composite retarder activator in 3 times the amount of water, spray it into the mixed powder, stir for 15 minutes, then add nano silica (if any) into the mixture by ultrasonic dispersion, ultrasonically disperse and stir for 10 minutes at 600W, then mix and homogenize for 5 hours, and cure at 20±2℃ and humidity ≥95%.
[0096]
[0097] Comparative Examples 1-6
[0098] Referring to the formulation in the table below, the preparation method is the same as in the examples.
[0099]
[0100] The specific surface area of the coal slag powder used in the above embodiments and comparative examples is 450 m². 2 / kg, free CaO content is 9%; fly ash is Grade I ash, with a loss on ignition of 4%, water requirement ratio of 93%, and 45μm sieve residue ≤12%; sodium silicate modulus is 1.3, and blast furnace slag powder specific surface area is 620m². 2 / kg, activity index 95%.
[0101] The cements prepared in the above embodiments and comparative examples were tested for initial setting time, final setting time, 3-day strength, 28-day strength, drying shrinkage, and abrasion resistance. The results are shown in the table below:
[0102]
[0103] A comparison of Example 1 and Comparative Example 1 shows that the traditional gypsum retarder has a final setting time of only 4.2 hours, which cannot meet the construction requirements. However, the composite retarder activator used in this application achieves an initial setting time of 5.5 hours and a final setting time of 7.2 hours, meeting the construction requirements. While Comparative Example 7, by omitting the coal ash powder, also meets the requirements for final setting time, its strength is significantly reduced.
[0104] Example 4, with its further improved scheme using slag and nano-silica, showed a significant improvement in strength and shrinkage rate. Comparative Example 5, although also using nano-silica, suffered a significant decrease in wear resistance due to its particle size being outside the preferred range, making it inferior to Example 3.
[0105] Although Comparative Example 3 also used a compound system of steel slag and slag, its 28-day strength of 48 MPa was significantly lower than that of Example 2 of 56 MPa because its ratio was not within the preferred range.
[0106] Compared to Example 1, Comparative Example 2, which uses a single-stage grinding process, shows a significant reduction in various performance characteristics. Furthermore, the grinding energy consumption of Comparative Example 2 reached 45 kWh / t, while Example 1 only consumed 34 kWh / t. This demonstrates that the gradient grinding process can further reduce energy consumption and exhibits good economic applicability.
[0107] Comparative Example 8 used sodium silicate, which accelerated hydration in an alkaline environment. The initial setting time was only 4.2 hours, much lower than the 5.5 hours of Example 1. However, the strength decreased by 17% after 3 days, indicating that a single activator could not balance retarding and strength.
[0108] Comparative Example 9 used lithium carbonate, and its final setting time was extended to 10.2 hours, far exceeding the construction requirements. Moreover, its strength dropped by 30% after 3 days, indicating that a single retarder severely inhibited its activity.
[0109] Example 1 uses a composite retarder / activator scheme. Sodium silicate provides an alkaline environment to activate the slag and fly ash, dissolves the fly ash glass, and releases active SiO2 and Al2O3. However, its use alone leads to excessively rapid coagulation. In lithium carbonate, Li... + Adsorbed on the surface of C3A, it delays the formation of ettringite and precisely inhibits the early hydration of C3A, but its use alone can excessively delay the reaction. The optimal ratio of its combined use balances activation and retardation.
[0110] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A set retarding cement for embankments, characterized by, The cement clinker 45-55 parts Coal ash 25-30 parts Composite retarder activator 3-5 parts Blast furnace slag powder 15-20 parts Nano-silica 0.2-0.4 parts The preparation method of the subgrade retarder cement comprises: Step one, The composite retarder accelerator is compounded by sodium silicate and lithium carbonate with a mass ratio of (5-7) : 1, the specific surface area of the coal cinder micro-powder is greater than or equal to 400 m 2 / kg, the free calcium oxide content of the coal cinder micro-powder is 6-7%, the magnesium oxide content is less than or equal to 5%, the mass ratio of the coal cinder micro-powder to the blast furnace slag micro-powder is 1: (2-3), the specific surface area of the blast furnace slag micro-powder is greater than or equal to 600 m 2 / kg, and the particle size of the nano-silicon dioxide is 20-50 nm.
2. The method according to claim 1, wherein the step of determining the at least one parameter comprises: determining the at least one parameter based on a comparison of the at least one parameter with a plurality of parameters stored in a memory of the device.
3. The method according to claim 1 or 2, wherein the step of determining the at least one parameter comprises: determining the at least one parameter based on a comparison of the at least one parameter with a plurality of parameters stored in a memory of the device.
4. The method according to any one of claims 1 to 3, wherein the step of determining the at least one parameter comprises: determining the at least one parameter Step two, after dissolving the composite retarder activator in water, it is sprayed into the mixture obtained in step one, stirred uniformly, and the nano-silica is dispersed by ultrasonic and added into the mixture containing the composite retarder activator, and then stirred for 10-15 min; Step three, the obtained mixture is homogenized for 4-6 h, and the subgrade retarder cement is obtained. First stage: cement clinker, coal cinder micro-powder, fly ash and blast furnace slag micro-powder are mixed and ground to specific surface area of 500-550 m 2 / kg; Second stage: adjust the grinding pressure to 0.8-1.2 MPa, grind to specific surface area ≥600 m 2 / kg, the temperature of the grinding process does not exceed 70℃; The loss on ignition of the fly ash is ≤5%, and the water requirement is ≤95%. The preparation method comprises the following steps:
2. The set retarding cement for embankment according to claim 1, wherein Step one, 3. The set retarding cement for embankment according to claim 1, wherein The initial setting time thereof 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 drying shrinkage is ≤ 0.025%, and the abrasion resistance is ≤ 1.8 g / cm 3 .
4. The method of producing a set retarding cement for embankment according to claim 1, characterized by, Step two, after dissolving the composite retarder activator in water, it is sprayed into the mixture obtained in step one, stirred uniformly, and the nano-silica is dispersed by ultrasonic and added into the mixture containing the composite retarder activator, and then stirred for 10-15 min; Step three, the obtained mixture is homogenized for 4-6 h, and the subgrade retarder cement is obtained. First stage: cement clinker, coal cinder micro-powder, fly ash and blast furnace slag micro-powder are mixed and ground to specific surface area of 500-550 m 2 / kg; Second stage: adjust the grinding pressure to 0.8-1.2 MPa, grind to specific surface area ≥600 m 2 / kg, the grinding process temperature is not more than 70℃; In step two, the amount of water for dissolving is 2-3 times the mass of the composite retarder activator. 5. The method of producing a setting-retarded cement for embankments according to Claim 4, characterized by,