Method for improving construction quality of cement stabilized macadam base

Abstract

The invention discloses a method for improving the construction quality of a cement stabilized macadam base. The method comprises the following steps: controlling the quality of materials; designing a mix proportion; mixing the mixture; transporting and paving the mixture; compacting the mixture; and curing the cement stabilized macadam. The construction method has the advantages that the construction quality improvement control key points and the process steps of the cement stabilized macadam base are clarified; the compressive strength and the breaking strength of the cement stabilized macadam base are improved, and the cement stabilized macadam base can bear large vehicle loads; the stability of the cement stabilized macadam base is improved, under the condition that the temperature and the humidity change, the volume change is small, and cracks and deformation are not prone to being generated; the durability, the anti-scouring performance and the anti-abrasion performance of the cement stabilized macadam base are improved, and good using performance can be kept for a long time; the one-time construction qualification rate can be effectively improved, the cement stabilized macadam construction quality and the overall construction quality are improved, repairing or reworking of a base layer can be avoided to the maximum extent, and reliable base layer guarantee is provided for subsequent procedures.

Description

Technical Field

[0001] The present application belongs to the field of road construction technology, and specifically relates to a method for improving the construction quality of cement-stabilized gravel base, which is applied to the construction and quality improvement of cement-stabilized gravel base of municipal roads. Background Art

[0002] With the booming development of infrastructure construction, cement-stabilized gravel has become a popular base material for high-grade highways due to its excellent strength, stiffness, and road performance. However, numerous issues arise during actual construction, such as insufficient compaction, shrinkage cracks, and loose surfaces. These quality issues seriously impact the service life of municipal roads. Currently, traditional cement-stabilized gravel base construction techniques remain unable to fully address the quality issues faced in water-stabilized construction of municipal roads. Summary of the Invention

[0003] The purpose of this application is to provide a method for improving the construction quality of cement-stabilized gravel base by clarifying the key process control points of the precise mixing and stirring of cement, graded gravel, stone chips and water, and then paving and rolling it to finally form a semi-rigid structural layer with stable quality, thereby effectively improving the mechanical properties, integrity, stability, durability and bonding ability of the municipal road water-stabilizing layer with the surface layer, thereby achieving an improvement in the (quality) of the municipal road water-stabilizing layer.

[0004] The purpose of this application is achieved through the following technical solutions:

[0005] A method for improving the construction quality of a cement-stabilized gravel base comprises the following steps:

[0006] Step S01, material quality control: Materials include cement, coarse aggregate, fine aggregate, and mixing and curing water. The quality of the materials is controlled to ensure the quality of subsequent construction;

[0007] Step S02, mix ratio design: design the mix ratio of aggregate proportion and gradation, cement dosage, optimal moisture content and maximum dry density to ensure the quality of subsequent construction;

[0008] Step S03, mixing the mixture;

[0009] Step S04, transportation and paving of the mixture;

[0010] Step S05, compacting the mixture;

[0011] Step S06, curing of cement-stabilized gravel.

[0012] Furthermore, in step S01, the cement selected is ordinary Portland cement, slag Portland cement or pozzolanic Portland cement, and the strength grade must reach 32.5 or 42.5; the initial setting time of the cement is not less than 3 hours, and the final setting time is controlled between 6 and 10 hours; after the cement is brought into the tank, it is left to stand for at least 7 days and put into use after the cement stability is qualified.

[0013] Furthermore, in the step S01, the coarse aggregate is selected with a maximum particle size of less than 31.5 mm, and is divided into four different specifications of 19-31.5 mm, 9.5-19 mm, 4.75-9.5 mm and 0-4.75 mm for on-site preparation according to the particle size; the coarse aggregate is selected from hard, clean and impurity-free limestone, basalt or diabase; the fine aggregate is non-weathered and free of impurities, and includes graded fine aggregate, and the sand equivalent of the fine aggregate is not less than 50%.

[0014] Furthermore, in step S02, in the proportion and gradation of aggregates, for the base and subbase of second-level and above highways, the graded crushed stone and gravel used must be a mixture of at least four materials of different specifications; the plasticity index of the fine aggregate in the graded crushed stone or gravel shall not exceed 12. If this requirement is not met, lime, non-plastic sand or stone chips shall be added for adjustment; representative samples are selected from the material yard for screening, and then the optimal blending ratio of each grade of aggregate is determined by trial and error or graphical method; when graded crushed stone is used as the base, the nominal maximum particle size for expressways and first-level highways shall not exceed 26.5 mm, and for second-level and below highways, it shall not exceed 31.5 mm.

[0015] Furthermore, in step S02, the cement dosage used in actual construction is increased by 0.5% to 1% based on the laboratory determination to ensure the quality of the cement-stabilized base, but at the same time does not exceed the limit of 6%.

[0016] Furthermore, in the step S02, the water content during actual mixing is 0.5% to 1% higher than the optimal water content; in the case of high temperature or long-distance transportation, the water content during actual mixing is 1% to 1.5% higher than the optimal water content.

[0017] Furthermore, in step S03, vibration stirring is used during the mixing process of cement-stabilized gravel. Vibration is applied during mixing to put the cement particles in a trembling state, thereby breaking up the cohesive cement clumps and promoting the uniform distribution of cement particles. Each silo and cement electronic scale must be calibrated by a qualified testing unit before use, and a dynamic load test must be performed. Before opening the market, the moisture content of coarse and fine aggregates is tested, and the construction mix ratio of the day is calculated accordingly to control the water consumption during the mixing process. The sign that the mixing of cement-stabilized gravel is completed is that the color of the mixture is uniform, the coarse and fine aggregates are evenly distributed, and the moisture content is moderate. Sampling and analysis are carried out regularly during the production process to check the uniformity of gradation and moisture content, and the cement dosage is measured by EDTA titration, and adjusted according to the analysis results.

[0018] Furthermore, in step S04, the transport vehicle must meet the progress requirements of mixing, discharging and paving, and leave a margin; the mixture on the vehicle is covered, and if the mixture cannot be transported to the construction site and completed paving and compaction within the initial setting time of the cement, it must be discarded; before paving, the construction is carefully laid out, and the line is hung according to the loose paving coefficient determined by the test section to ensure the thickness of the cement stable base layer; the surface of the lower bearing layer is kept flat, solid and clean, and the lower bearing layer is sprinkled with water before construction; the base layer construction adopts multiple pavers for full-width paving , ensure that the specifications and models of the pavers are consistent, and the front and rear spacing is controlled within the range of 5 to 10 meters. When paving, the speed of the paver is set to 1 to 1.5 meters per minute; the front and rear pavers should maintain an overlap of 50 to 100 mm, and the middle seam should be manually trimmed. During the paving process, the paver maintains a continuous, uniform and uninterrupted paving state; set up special personnel in front and behind the paver to eliminate the segregation of coarse and fine aggregates, remove coarse material pockets, and fill them with freshly mixed materials to ensure the stability and uniformity of the mix ratio.

[0019] Furthermore, in step S05, the mixture is kept moist during the rolling process, and is first rolled with a light two-wheel roller following the paver, and then continued with a heavy vibratory roller to ensure that the rolling of the mixed cement mixture is completed within 2 hours and the required density is achieved; the speed of the first and second roller rolling is controlled at 1.5-1.7 km / h, and then increased to 1.8-2.2 km / h, and the overlapping width during rolling is kept at 1 / 2 of the wheel width; if "spring", "looseness" or "peeling" occurs during the rolling process, the mixture is immediately turned over for remixing or other treatment measures are taken; the base layer construction adopts a layered method, and the compaction thickness of each layer is controlled within the range of 18-20 cm.

[0020] Furthermore, in the step S06, after the subbase and base of the cement-stabilized crushed stone are rolled and the compaction inspection is passed, curing is immediately carried out; during curing, moistened linen or permeable non-woven geotextile is covered on the top surface of the compacted base, and the covering is ensured for 2 to 3 hours; thereafter, a sprinkler truck is used to sprinkle water to keep the base moist during the curing period; after the curing period, the covering should be completely removed, and the construction of the next structural layer should be started immediately to avoid cracking problems caused by shrinkage.

[0021] Beneficial effects of this application:

[0022] 1. Clarified the key control points and process steps for improving the construction quality of cement-stabilized gravel base.

[0023] 2. The compressive strength and flexural strength of the cement-stabilized gravel base layer have been improved, making it able to withstand larger vehicle loads.

[0024] 3. The stability of the cement-stabilized gravel base is improved. When the temperature and humidity change, its volume changes little and it is not easy to crack and deform.

[0025] 4. It improves the durability, anti-scouring and anti-wear properties of the cement-stabilized gravel base, and can maintain good performance for a long time.

[0026] 5. It can effectively improve the first-time construction qualification rate, improve the construction quality of cement-stabilized gravel and the overall construction quality, and can avoid the repair or rework of the base layer to the greatest extent, providing a reliable base layer guarantee for subsequent processes.

[0027] The aforementioned main solution of this application and its further options can be freely combined to form multiple solutions, all of which are solutions that can be adopted and protected by this application; and in this application, (non-conflicting options) can also be freely combined with each other and with other options. After understanding the solution of this application, those skilled in the art will understand that there are many combinations based on existing technology and common knowledge, all of which are technical solutions to be protected by this application, and they are not exhaustive here. DETAILED DESCRIPTION

[0028] The following non-limiting examples illustrate the present application.

[0029] Example 1

[0030] A method for improving the construction quality of a cement-stabilized gravel base comprises the following steps: Step S01, material quality control: the materials include cement, coarse aggregate, fine aggregate, and mixing and curing water, and the quality of the materials is controlled to ensure the subsequent construction quality.

[0031] Cement is the key binder for cement-stabilized gravel. Use ordinary Portland cement, slag Portland cement, or pozzolanic cement, with a strength grade of 32.5 or 42.5. Avoid using fast-setting cement, early-strength cement, or cement that has deteriorated due to moisture. This ensures sufficient time for mixing, transporting, spreading, and compacting the cement-stabilized gravel, and that it reaches the desired strength.

[0032] The initial setting time of cement should be no less than 3 hours, and the final setting time should be controlled between 6 and 10 hours to ensure that the material has sufficient time for construction. After the cement is brought to the site and placed in the tank, it should be left to stand for at least 7 days before it is put into use after the cement meets the stability requirements.

[0033] Coarse aggregate is selected with a maximum particle size of 31.5mm or less. Four different sizes are prepared on-site: 19-31.5mm, 9.5-19mm, 4.75-9.5mm, and 0-4.75mm. Coarse aggregate is hard, clean, and free of impurities, including limestone, basalt, or diabase.

[0034] To ensure the quality of coarse aggregate, various indicators must be strictly controlled. These indicators include the crushing value of the stone, the content of needle-like particles, the dust content below 0.075mm, and the soft stone content. These indicators must all meet the requirements of relevant specifications.

[0035] The fine aggregate shall be free of weathering and impurities and shall include graded fine aggregate to ensure its quality. The sand equivalent of the fine aggregate shall not be less than 50%.

[0036] The water used for mixing and curing shall be drinking water that complies with the "National Drinking Water Quality Standard" GB 5749-2022, and shall be used for mixing and curing of base and sub-base materials.

[0037] Step S02, mix ratio design: design the mix ratio of aggregate proportion and gradation, cement dosage, optimal moisture content and maximum dry density to ensure the quality of subsequent construction.

[0038] For the aggregate proportions and gradations of Grade II and higher highway base and subbase, the graded crushed stone and gravel used must be a mixture of at least four different material specifications. The plasticity index of the fine aggregate in the graded crushed stone or gravel must not exceed 12. If this requirement is not met, lime, non-plastic sand, or stone chips should be added to adjust the plasticity.

[0039] Select representative samples from the material yard for screening, then determine the optimal blending ratio for each grade of aggregate using a trial and error method (such as the normal equation method) or a graphical method. When graded crushed stone is used as the base layer, the nominal maximum particle size for expressways and first-class highways should not exceed 26.5mm, while for second-class highways and below, it should not exceed 31.5mm.

[0040] To account for various losses during construction, the actual cement dosage used in construction is increased by 0.5% to 1% from the laboratory-determined amount to ensure the quality of the cement-stabilized base layer, while at the same time not exceeding the 6% limit. Insufficient cement dosage cannot guarantee the construction quality of the cement-stabilized gravel base layer, while excessive dosage is not only uneconomical but may also lead to an increase and widening of cracks in the base layer, which in turn may cause reflective cracks in the surface layer.

[0041] During construction, the moisture content needs to be flexibly adjusted based on factors such as weather and transportation distance to ensure the mix is in optimal condition during compaction. The actual moisture content during mixing should be 0.5% to 1% higher than the optimal moisture content. In high-temperature or long-distance transportation, the actual moisture content during mixing should be 1% to 1.5% higher than the optimal moisture content to compensate for the natural loss of moisture during transportation, paving, and compaction.

[0042] Excessive water content will lead to insufficient compaction of the base layer, affecting the shrinkage of the mixture and increasing the risk of shrinkage cracks. On the other hand, if the water content is too low, the mixture will be difficult to roll and form, which will also affect the compaction and strength of the base layer.

[0043] Maximum dry density directly impacts two key quality technical indicators: seven-day unconfined compressive strength and on-site compaction. At the construction site, the ratio of the actual dry density of the mixture to the indoor standard maximum dry density constitutes the compaction of the cement-stabilized gravel base. Therefore, maximum dry density is not only a core quality control parameter in cement-stabilized graded gravel construction, but also directly affects the degree of base compaction, a crucial criterion for measuring the inherent quality of the base. If the base compaction does not meet the standard, its compressive resistance will be insufficient, which may eventually lead to cracking in the base, which in turn may cause cracks in the asphalt pavement, seriously affecting the performance of the pavement.

[0044] Step S03: mixing the mixture.

[0045] The use of vibration mixing is crucial in the mixing process of cement-stabilized gravel. Vibration mixing, applied during mixing, causes the cement particles to vibrate, breaking up any agglomerates and promoting even distribution of the cement particles. Compared to conventional static mixing, vibration mixing optimizes the microstructure of cement-stabilized gravel, improving its appearance, porosity, and pore structure, thereby enhancing its durability and mechanical properties.

[0046] To ensure accurate measurement, all silos and electronic cement scales must be calibrated by a qualified testing agency before use and undergo dynamic load testing. Before the start of the mixing process, the moisture content of coarse and fine aggregates is tested and used to calculate the day's construction mix ratio to control water usage during the mixing process.

[0047] The hallmark of a completed cement-stabilized crushed stone mix is a uniform color, even distribution of coarse and fine aggregates, and an appropriate moisture content. To ensure the quality of the mix, samples are regularly taken and analyzed during production to check the uniformity of gradation and moisture content. Cement dosage is measured using EDTA titration and adjusted based on the results.

[0048] Step S04: transportation and paving of the mixture.

[0049] Transport vehicles must meet the mixing, discharging, and paving schedule requirements, with a margin. To minimize moisture loss, the mixture on the vehicle is covered. If the mixture cannot be transported to the construction site and paved and compacted within the initial setting time of the cement, it must be discarded.

[0050] Before paving, carefully stake out the concrete and use the loose paving coefficient determined on the test section to ensure the thickness of the cement-stabilized base. The sub-base surface should be kept flat, solid, and clean, and should be moistened with water before construction.

[0051] The base layer is constructed using multiple pavers, ensuring that the specifications and models of the pavers are consistent and that the spacing between them is controlled within 5 to 10 meters. During paving, the paver speed is set at 1 to 1.5 meters per minute, and the two pavers should overlap by 50 to 100 millimeters. The center seam is manually trimmed, and the pavers maintain a continuous, uniform, and uninterrupted paving process.

[0052] Minimize the number of times the paver hopper is opened and closed. Dedicated personnel should be posted before and after the paver to eliminate segregation of coarse and fine aggregates, remove pockets of coarse aggregate, and fill them with fresh mix to ensure a stable and uniform mix ratio.

[0053] Step S05: compacting the mixture.

[0054] The mixture should be kept moist during compaction. If the water evaporates too quickly, a small amount of water should be sprayed on it. A light two-wheel roller should be used first, following the paver, followed by a heavy vibratory roller. Ensure that the cement mixture is compacted within 2 hours and reaches the required density.

[0055] The speed of the roller should be controlled at 1.5-1.7 km / h during the first and second passes, then increased to 1.8-2.2 km / h, and the overlap width should be kept at 1 / 2 of the wheel width. If "springing", "loosening" or "skinning" occurs during the rolling process, the mixture should be immediately turned over and remixed or other treatment measures should be taken.

[0056] The base layer should be constructed in layers. The maximum compacted thickness of each layer should not exceed 20 cm, and the minimum should not be less than 16 cm. The preferred compacted thickness of each layer should be controlled within the range of 18 to 20 cm. When rolling, follow the principle of "light first, heavy later, slow first, fast later." Minimize the time interval between mixing, paving, and rolling. The mixture should be rolled to the required degree of compaction, and there should be no obvious wheel marks on the surface.

[0057] Step S06, curing of cement-stabilized gravel.

[0058] After the cement-stabilized crushed stone subbase and base have been rolled and the compaction inspection has passed, curing should be carried out immediately. During curing, moistened linen or permeable non-woven geotextile should be covered on the top surface of the rolled base for 2-3 hours. Afterwards, water should be sprayed with water to keep the base moist during the curing period.

[0059] After the curing period, the covering should be completely removed and the construction of the next structural layer should be started immediately to avoid cracking due to shrinkage.

[0060] The aforementioned basic examples and their further selected examples can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and claimed for protection in this application. In this application, each selected example can be arbitrarily combined with any other basic examples and selected examples.

[0061] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for improving the construction quality of cement-stabilized gravel base, characterized in that: The process includes the following steps: Step S01, material quality control: the materials include cement, coarse aggregate, fine aggregate, and mixing and curing water, and the quality of the materials is controlled to ensure the quality of subsequent construction; Step S02, mix ratio design: design the mix ratio of aggregate proportion and gradation, cement dosage, optimal moisture content and maximum dry density to ensure the quality of subsequent construction; Step S03, mixing the mixture; Step S04, transportation and paving of the mixture; Step S05, compacting the mixture; Step S06, curing of cement-stabilized gravel.

2. The method for improving the construction quality of cement-stabilized crushed stone base according to claim 1, characterized in that: In step S01, the cement used is ordinary Portland cement, slag Portland cement or pozzolanic Portland cement, and the strength grade must reach 32.5 or 42.5; the initial setting time of the cement is not less than 3 hours, and the final setting time is controlled between 6 and 10 hours; after the cement is brought into the tank, it is left to stand for at least 7 days and put into use after the cement stability meets the requirements.

3. The method for improving the construction quality of cement-stabilized crushed stone base according to claim 1 or 2, characterized in that: In step S01, the coarse aggregate is selected with a maximum particle size of less than 31.5 mm, and is prepared on site in four different specifications according to the particle size: 19-31.5 mm, 9.5-19 mm, 4.75-9.5 mm, and 0-4.75 mm; the coarse aggregate is selected from hard, clean, and impurity-free limestone, basalt, or diabase; the fine aggregate is non-weathered and free of impurities, and includes graded fine aggregate, and the sand equivalent of the fine aggregate is not less than 50%.

4. The method for improving the construction quality of cement-stabilized crushed stone base according to claim 1, characterized in that: In step S02, the proportion and gradation of aggregates are such that for the base and subbase of second-level and above highways, the graded crushed stone and gravel used must be a mixture of at least four different specifications of materials; the plasticity index of the fine aggregate in the graded crushed stone or gravel must not exceed 12. If this requirement is not met, lime, non-plastic sand, or stone chips are added for adjustment; representative samples are selected from the material yard for screening, and then the optimal blending ratio of each grade of aggregate is determined by trial and error or graphical method; when the graded crushed stone is used as the base, the nominal maximum particle size for expressways and first-level highways shall not exceed 26.5 mm, and for second-level and below highways, it shall not exceed 31.5 mm.

5. The method for improving the construction quality of cement-stabilized crushed stone base according to claim 1, characterized in that: In the step S02, the cement dosage used in actual construction is increased by 0.5% to 1% based on the laboratory determination to ensure the quality of the cement-stabilized base, but at the same time does not exceed the limit of 6%.

6. The method for improving the construction quality of cement-stabilized crushed stone base according to claim 1 or 5, characterized in that: In the step S02, the water content during actual mixing is 0.5% to 1% higher than the optimum water content; in the case of high temperature or long-distance transportation, the water content during actual mixing is 1% to 1.5% higher than the optimum water content.

7. The method for improving the construction quality of cement-stabilized gravel base according to claim 1, characterized in that: In step S03, the cement-stabilized gravel is mixed using vibration. Vibration is applied during mixing to tremble the cement particles, thereby breaking up any agglomerated cement clumps and promoting uniform distribution of the cement particles. Each silo and cement electronic scale must be calibrated by a qualified testing organization before use and must undergo a dynamic load test. Before the start of the market, the moisture content of the coarse and fine aggregates is tested and the mix ratio for the day is calculated accordingly to control the water consumption during the mixing process. The sign that the mixing of cement-stabilized gravel is complete is that the mixture has uniform color, even distribution of coarse and fine aggregates, and moderate moisture content. During the production process, samples are taken and analyzed regularly to check the uniformity of gradation and moisture content, and the cement dosage is measured by EDTA titration method, and adjustments are made based on the analysis results.

8. The method for improving the construction quality of cement-stabilized crushed stone base according to claim 1, characterized in that: In the step S04, the transport vehicle must meet the progress requirements of mixing, discharging and paving, and leave a margin; the mixture on the vehicle is covered, and if the mixture cannot be transported to the construction site and completed paving and compaction within the initial setting time of the cement, it must be discarded; before paving, the construction is carefully laid out, and the line is hung according to the loose paving coefficient determined by the test section to ensure the thickness of the cement stable base layer; the surface of the lower bearing layer is kept flat, solid and clean, and the lower bearing layer is sprinkled with water before construction; the base layer construction adopts multiple pavers for full-width paving to ensure Ensure that the specifications and models of the pavers are consistent, and the front and rear spacing is controlled within the range of 5 to 10 meters. When paving, the speed of the paver is set to 1 to 1.5 meters per minute; the front and rear pavers should maintain an overlap of 50 to 100 mm, and the middle seam should be manually trimmed. During the paving process, the paver maintains a continuous, uniform and uninterrupted paving state; set up special personnel in front and behind the paver to eliminate the segregation of coarse and fine aggregates, remove coarse material pockets, and fill them with freshly mixed materials to ensure the stability and uniformity of the mix ratio.

9. The method for improving the construction quality of cement-stabilized crushed stone base according to claim 1, characterized in that: In step S05, the mixture is kept moist during the rolling process. A light two-wheel roller is first used to follow the paver for rolling, and then a heavy vibratory roller is used to continue rolling, ensuring that the cement mixture is rolled within 2 hours and reaches the required density. The speed of the first and second roller rolling is controlled at 1.5-1.7 km / h, and then increased to 1.8-2.2 km / h, and the overlapping width during rolling is kept at 1 / 2 of the wheel width. If "spring", "looseness" or "peeling" occurs during the rolling process, the mixture is immediately turned over for remixing or other treatment measures are taken. The base layer construction adopts a layered method, and the compaction thickness of each layer is controlled within the range of 18-20 cm.

10. The method for improving the construction quality of cement-stabilized crushed stone base according to claim 1, characterized in that: In step S06, after the subbase and base of the cement-stabilized crushed stone are rolled and the compaction inspection is passed, curing is immediately carried out; during curing, moistened linen or permeable non-woven geotextile is covered on the top surface of the rolled base, and the covering is ensured for 2 to 3 hours; thereafter, a sprinkler truck is used to sprinkle water to keep the base moist during the curing period; after the curing period, the covering should be completely removed, and the construction of the next structural layer should be started immediately to avoid cracking problems caused by shrinkage.