High crack-resistant cement fly ash stabilized base course materials and their applications

Abstract

This invention discloses a high-crack-resistant cement-fly ash stabilized base course material, belonging to the field of road engineering technology. The material comprises the following components by mass percentage: 2.0-3.0% cement, 16-20% fly ash, and the balance being stabilized aggregate. The cement is an external admixture, the fly ash is an internal admixture, and the gradation of the stabilized aggregate conforms to the specifications of CF-A-2L or CF-A-2S in JTG / T F20-2015. This invention, by adopting a "low cement, high fly ash" mix design, controls the 7-day unconfined compressive strength within a reasonable range of 3.5-4.5 MPa, effectively avoiding the problem of regular transverse cracks in the base course caused by excessively high early strength. Simultaneously, the high fly ash content ensures the continuous growth of the material's later strength, with its 21-day unconfined compressive strength remaining stable above 6 MPa. Its overall performance is superior to the mix ratios recommended by current standards. This invention is particularly suitable for highway base course construction in arid regions with large temperature differences, such as Xinjiang.

Description

Technical Field

[0001] This invention belongs to the field of road engineering technology, specifically relating to a high crack-resistant cement fly ash stabilized base course material and its application. Background Technology

[0002] Cement-fly ash stabilized crushed stone (hereinafter referred to as "cement-fly ash stabilized material") is a commonly used semi-rigid material for highway pavement base courses. Article 4.5.7 of the current industry standard JTG / T F20-2015, "Technical Specifications for Construction of Highway Pavement Base Courses," specifies the mix proportions for cement-fly ash stabilized materials. For example, when used in the base courses of expressways and Class I highways, it is recommended that the total dosage (mass percentage) of cement and fly ash should be 12%, and should not exceed 18%; the total mass of the stabilized material (aggregate) should be no less than 85%, and the recommended mix proportions for CF-A-2L and CF-A-2S grades are given.

[0003] In practical engineering, especially in arid regions like Xinjiang Uygur Autonomous Region with high evaporation rates and significant diurnal temperature variations, strictly adhering to the upper limit of the aforementioned specifications (e.g., using 4% cement + 10% fly ash, total dosage 14%) in mix design can easily lead to an unconfined compressive strength exceeding the minimum requirement (e.g., 4 MPa) or even reaching over 8 MPa after 7 days. However, this often results in excessively rapid and high early strength growth in the base course. This causes significant drying and temperature shrinkage stresses, resulting in regular transverse through-cracks appearing in the base course after the curing period, with crack spacing often around 5-6 meters. These cracks easily reflect onto the asphalt surface layer, affecting pavement smoothness, integrity, and service life.

[0004] Therefore, how to effectively control early shrinkage cracks while meeting the strength requirements of the base layer is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the main objective of this invention is to provide a high-crack-resistant cement fly ash stabilized base course material and its application.

[0006] The objective of this invention is achieved through the following technical solution: A high crack-resistant cement-fly ash stabilized base course material comprises the following components by mass percentage: 2.0-3.0% cement, 16-20% fly ash, and the balance being stabilized aggregate; wherein the cement is an external admixture, the fly ash is an internal admixture, and the gradation of the stabilized aggregate conforms to the requirements of CF-A-2L or CF-A-2S in JTG / T F20-2015.

[0007] In some specific embodiments, the components include, by weight percentage, 2.5% cement, 18% fly ash, and the balance being stabilized aggregate.

[0008] In some specific embodiments, the components include, by weight percentage, 2.0% cement, 20% fly ash, and the balance being stabilized aggregate.

[0009] In some specific embodiments, the components include, by weight percentage, 3.0% cement, 16% fly ash, and the balance being stabilized aggregate.

[0010] In some specific embodiments, the nominal maximum particle size of the stabilized aggregate is no greater than 26.5 mm, and the target gradation greater than 1 mm conforms to the provisions of CF-A-2L or CF-A-2S in JTG / T F20-2015 "Technical Specifications for Construction of Highway Pavement Base".

[0011] As part of the same inventive concept, this invention also provides the application of the high crack resistance cement fly ash stabilized base course material in the construction of highway pavement base courses in arid and semi-arid regions.

[0012] Compared with the prior art, the present invention has at least the following advantages: The high crack-resistant cement fly ash stabilized base course material provided by this invention has the following characteristics: 1) Effectively suppresses early cracks: By significantly reducing the cement dosage (from the conventional 4% to 2.0%~3.0%), while greatly increasing the fly ash dosage (from the conventional 10% to 16%~20%), the hydration reaction rate and strength growth level of the base layer within 7 days are effectively controlled; the 7-day unconfined compressive strength is controlled within a reasonable range of 3.5 MPa~4.5 MPa, avoiding excessive shrinkage stress caused by excessively high early strength, thereby fundamentally reducing the generation of through transverse cracks; 2) Ensure and optimize later performance: High doses of fly ash continue to exert pozzolanic effect and micro-aggregate filling effect in the later stages (14 days, 21 days and above), resulting in a steady increase in the later strength of the material (≥5MPa at 14 days, ≥6MPa at 21 days) and exceeding the specification requirements; the cementing and gap-filling effect of fly ash makes the bond between aggregates more compact, improving the long-term stability and durability of the material; 3) Breaking through the limitations of the standard and adapting to regional characteristics: Based on the special climatic conditions of arid regions (dryness and large temperature difference), this invention has broken through the mechanical limitations of the current standard on total dosage and gradation through a large number of experiments. It has been found and verified that in arid areas, the "low cement, high fly ash" ratio strategy has a significant advantage in balancing crack resistance and strength development compared with the medium dosage ratio recommended by the standard.

[0013] 4) Economic and environmental protection: Fly ash is an industrial waste. This invention improves its utilization rate, reduces cement consumption, conforms to the concept of green building materials and sustainable development, and also helps to reduce material costs. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0015] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range.

[0016] The materials, methods, and embodiments described herein are exemplary and should not be construed as limiting unless otherwise stated.

[0017] Example 1 This embodiment provides a high crack-resistant cement-fly ash stabilized base course material, which includes the following steps: A trial was conducted in the reconstruction and expansion project of the S240 highway from Zhundong Dajing Service Area to Qitai in Xinjiang Uygur Autonomous Region.

[0018] The design mix proportion is: 2.5% external cement and 18% internal fly ash. The target gradation of the stabilized aggregate is CF-A-2L. The mixing, spreading, rolling and curing processes are strictly carried out in accordance with the requirements of JTG / T F20-2015.

[0019] This application conducts performance testing on the high crack-resistant cement fly ash stabilized base course material prepared in this embodiment, and the results are as follows: 7-day unconfined compressive strength: approximately 4.0 MPa; 14-day unconfined compressive strength: approximately 5.2 MPa; 21-day unconfined compressive strength: approximately 6.1 MPa; Crack resistance observation: After the curing period, the surface of the base layer of the test section was flat and there were no regular transverse through cracks every 5-6 meters as seen in the comparative example. Only a small number of fine shrinkage cracks were present.

[0020] Example 2 This embodiment provides a high crack-resistant cement-fly ash stabilized base course material, which includes the following steps: A trial was conducted in the reconstruction and expansion project of the S240 highway from Zhundong Dajing Service Area to Qitai in Xinjiang Uygur Autonomous Region.

[0021] The design mix proportion is: 2.0% external cement and 20% internal fly ash. The target gradation of the stabilized aggregate is CF-A-2L. The mixing, paving, compaction and curing processes are strictly carried out in accordance with the requirements of JTG / T F20-2015.

[0022] This application conducts performance testing on the high crack-resistant cement fly ash stabilized base course material prepared in this embodiment, and the results are as follows: 7-day unconfined compressive strength: approximately 3.5 MPa; 14-day unconfined compressive strength: approximately 4.3 MPa; 21-day unconfined compressive strength: approximately 4.8 MPa; Crack resistance: Early cracking is effectively controlled, and the later strength meets the strength requirements of the base material as specified in the code.

[0023] Example 3 This embodiment provides a high crack-resistant cement-fly ash stabilized base course material, which includes the following steps: A trial was conducted in the reconstruction and expansion project of the S240 highway from Zhundong Dajing Service Area to Qitai in Xinjiang Uygur Autonomous Region.

[0024] The design mix proportion is: 3.0% external cement and 16% internal fly ash. The target gradation of the stabilized aggregate is CF-A-2L. The mixing, paving, compaction and curing processes are strictly carried out in accordance with the requirements of JTG / T F20-2015.

[0025] This application conducts performance testing on the high crack-resistant cement fly ash stabilized base course material prepared in this embodiment, and the results are as follows: 7-day unconfined compressive strength: approximately 4.5 MPa; 14-day unconfined compressive strength: approximately 5.5 MPa; 21-day unconfined compressive strength: approximately 6.5 MPa; Crack resistance: The crack resistance performance is better than the traditional 4% cement + 10% fly ash ratio, and the early cracks are significantly reduced.

[0026] Comparative Example 1 This comparative example provides a high crack-resistant cement-fly ash stabilized base course material, which includes the following steps: A trial was conducted in the reconstruction and expansion project of the S240 highway from Zhundong Dajing Service Area to Qitai in Xinjiang Uygur Autonomous Region.

[0027] The design mix proportion is: 4.0% external cement and 10% internal fly ash. The target gradation of the stabilized aggregate is CF-A-2L. The mixing, paving, compaction and curing processes are strictly carried out in accordance with the requirements of JTG / T F20-2015.

[0028] This application conducted performance testing on the high crack-resistant cement fly ash stabilized base course material prepared in this comparative example, and the results are as follows: 7-day unconfined compressive strength: ≥8.0 MPa.

[0029] Crack resistance observation: After the curing period, an obvious transverse through crack appeared on average every 5-6 meters in the base layer.

[0030] In summary, the "low cement, high fly ash" mix design provided by this invention (especially the preferred mix of 2.5% cement + 18% fly ash) can greatly improve the crack resistance of materials under the arid climate conditions of Xinjiang Uygur Autonomous Region, while ensuring the strength of the base layer (especially the later strength). The overall road performance is better than the traditional mix design that strictly follows the upper limit of the specification.

[0031] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A high crack-resistant cement-fly ash stabilized base course material, characterized in that, The product comprises the following components by mass percentage: 2.0-3.0% cement, 16-20% fly ash, and the balance being stabilized aggregate; wherein the cement is an external admixture, the fly ash is an internal admixture, and the gradation of the stabilized aggregate conforms to the requirements of CF-A-2L or CF-A-2S in JTG / T F20-2015.

2. The high crack-resistant cement-fly ash stabilized base course material according to claim 1, characterized in that, It comprises the following components by weight percentage: 2.5% cement, 18% fly ash, and the balance being stabilized aggregate.

3. The high crack-resistant cement-fly ash stabilized base course material according to claim 1, characterized in that, It comprises the following components by weight percentage: 2.0% cement, 20% fly ash, and the balance being stabilized aggregate.

4. The high crack-resistant cement-fly ash stabilized base course material according to claim 1, characterized in that, It comprises the following components by weight percentage: 3.0% cement, 16% fly ash, and the balance being stabilized aggregate.

5. The high crack-resistant cement-fly ash stabilized base course material according to claim 1, characterized in that, The nominal maximum particle size of the stabilized aggregate is no more than 26.5 mm, and the target gradation with a particle size greater than 1 mm conforms to the provisions of CF-A-2L or CF-A-2S in JTG / T F20-2015 "Technical Specifications for Construction of Highway Pavement Base".

6. The application of a high crack-resistant cement fly ash stabilized base course material according to any one of claims 1-5 in the construction of highway pavement base courses in arid and semi-arid regions.