Lime fly ash soil is a kind of pavement structure layer composed of three inorganic materials, lime, fly ash and soil, which are mixed evenly by special machinery in a certain proportion with water, and then spread and rolled. Its specific name depends on the soil used. Lime fly ash and gravel are called lime fly ash gravel soil, lime fly ash and gravel are called lime fly ash gravel soil, lime fly ash soil and fine grained soil are called lime fly ash soil, and lime fly ash and industrial waste residue are called lime fly ash. The construction quality control of lime-fly ash stabilized soil is the key to ensure the engineering quality. Only by scientifically organizing the construction can we make a high-quality lime-fly ash stabilized soil structure. Otherwise, there will be common diseases such as spring, peeling and cracking. Therefore, the construction of lime-fly ash stabilized soil should be strictly controlled.

1, raw material control

Strictly control the quality of raw materials and do not use unqualified materials. In the selection of materials, we should compare quality and economy, and strive for economy on the premise of meeting the quality requirements.

Lime: In order to meet the technical requirements of lime above Grade III, the digested lime shall be used, and the lime shall be fed in batches without affecting the construction progress, and it shall not be stored too much; Try to shorten the stacking time. If it is stored for a long time, it should be stamped and sealed for safekeeping.

Fly ash: In the construction of lime-fly ash soil, under the excitation of lime, fly ash has a chronic consolidation effect, which makes the later strength increase more. Therefore, fine fly ash with large specific surface area and low combustion moisture content should be selected, and it should not contain lumps, humus or other impurities, in which the total content of SiO2, AL2O3 and Fe2O3 is not less than 70%, the loss on ignition is not more than 10%, and the specific surface area is more than 2500 cm2/g (or 90% passes through 0.3mm sieve holes and 70% passes through 0.075). The moisture content of wet fly ash should not exceed 35%, and the fly ash stacked in the site should be covered to avoid dust or rain erosion. Keep it moist during transportation and cover it with tarpaulin to prevent pollution caused by powder flying.

Soil: cohesive soil (loam) with plasticity index of 12-20 should be used. The maximum particle size of clods in soil should not be greater than 15 mm, and soil with organic matter content >: 10% should not be used. The maximum particle size of gravel and gravel particles in soil shall not exceed 37.5 mm In actual construction, more tests and comparisons should be made in combination with local soil conditions, and optimization should be made in consideration of project cost.

Water: All drinking water will do. If there are suspicious water sources, entrust relevant departments to detect and identify them.

2, the construction process

2. 1 Determination of construction parameters

Before the construction of high-grade highway, a test section should be selected first, and the following contents should be determined through the construction of the test section:

Calculate the amount of soil used. According to the formula 1- 1, calculate the loose laying thickness of soil. According to the width and calculated thickness of the stabilized soil and the tonnage of the vehicles used, the paving area of each vehicle soil is calculated.

Formula 1- 1:

H=ρ0Ph( 1+ω)K/ρ

H- loose laying thickness of raw materials;

ρ 0-the maximum dry density of the mixture;

P- the ratio of dry mass of raw materials to dry mass of mixture;

ω-water content of raw materials;

ρ-wet bulk density of raw materials;

H- mixture compaction thickness;

K- compactness of mixtures.

Calculate the amount of fly ash (white ash). Calculate the thickness of fly ash (lime) according to the formula 1- 1, and calculate the paving area of fly ash (lime) per vehicle according to its loose wet density and width and vehicle tonnage.

Determine the best aggregate mix ratio and loose paving coefficient

Determine the reasonable working length and paving thickness;

Determine the supporting conditions of construction machinery;

Determine the construction operation coefficient, aggregate water content and compaction degree of paving and rolling machinery.

2.2 Road Mixing Method Construction Technology

Construction technology of lime-fly ash stabilized soil.

2.2. 1 Prepare the lower bearing layer.

The surface of the lower bearing layer of lime-fly ash stabilized soil should be smooth and dense, and the elevation, width and cross slope should meet the design requirements, without loose materials and weak sites.

2.2.2 survey lofting

Restore the center line pile, and set indicator piles outside the edges on both sides to mark the loose laying elevation and design elevation of the edge of lime-fly ash stabilized soil layer.

Material preparation

Preparation of fly ash, such as wet fly ash, should be transported to the site a few days before use to filter water. Dry fly ash should be properly transported by water or by closed vehicles before shipment to avoid ashing. When stacking, fly ash must contain enough water (water content 15%-20%) to prevent flying, especially in dry and windy seasons, the surface of the pile body should be kept wet or covered.

pave a road

When loading the car, assign a special person to command at the scene. According to the principle of feeding sequence and uniform arrangement, the vehicles are respectively commanded to be unloaded in blocks, and paved with graders or bulldozers in time. The insufficient part will be filled, and more will be pushed away. The feeding sequence of lime fly ash soil is soil, fly ash and hydrated lime, and the feeding sequence of lime fly ash, hydrated lime and lime fly ash. Transportation and laying shall be carried out in accordance with the layered method in the process flow chart. After the first material is spread evenly, first use bulldozer to discharge pressure 1-2 times, and then transport and spread the second material; A third material is also laid on the second material layer.

Mixing and sprinkling water

The road mixing method is carried out after three layers of materials are paved. Two kinds of mixing machines are used in the construction site, one is the stabilized soil mixer, and the other is the tractor disc harrow with plough and notch. It is best to mix the fine materials first for the second ash. The principle of mixing is dry mixing first, then sprinkling water to the optimum water content and wet mixing. When mixing with a blender, dry mix 1-2 times first, and then wet mix 2-3 times. When using the tractor, dry mix it for 2-3 times, and then wet mix it for 5-6 times. The mixing depth should reach the bottom of the stable layer. It is forbidden to leave a plain soil interlayer at the bottom of the mixed layer, and the surface of the lower bearing layer is slightly damaged by about 1cm, which should not be too much to facilitate the combination of the upper and lower layers. Check the water content in time during mixing. If the water content is insufficient, spray water evenly on the dry-mixed mixture with a spray nozzle. Considering air drying and evaporation, control the water content of the mixture to be equal to or slightly greater than the optimal water content (about 1%). In the process of mixing, it is necessary to check the mixing depth in time to make the whole depth mix evenly. For mixed materials, air drying is considered, and the water content of mixed materials is controlled to be equal to or slightly greater than the optimal water content (about 65438 0%) under evaporation air drying and evaporation conditions. In the process of mixing, it is necessary to check the mixing depth in time to make the whole depth mix evenly. Sprinklers and bends should be more than 2 meters beyond the mixing section to prevent local water from being too large. The mixture shall be of the same color, free of gray stripes, blocks and "painted faces", and the water content shall be appropriate. When mixing, attention should be paid to prevent the leakage of interlayer and joint.

Plastic operation

After the mixture is stirred evenly, it will be leveled and shaped with a grader. During leveling, thin layer subsidy should be avoided, leveling should be adopted as far as possible, and the elevation and cross slope should be checked and controlled with stay wires. After the initial molding, check the loose laying thickness of the mixture, and make up or reduce the material if necessary. The loose laying coefficient is determined by the test section. Then use a grader, tractor or tire roller to quickly roll it to expose the potential unevenness, and then repeat the above steps.

roll

After leveling meets the requirements, it shall be compacted and shaped immediately. Rolling should follow the principle of static pressure stabilization first, then vibration pressure, and then static pressure to the specified degree of compaction.

(1) According to the road width, wheel width and wheel pitch of the road roller, the rolling scheme shall be made, the rolling times of each part shall be the same as far as possible, and the two sides of the road surface shall be pressed for 2-3 times more.

(2) After molding, when the water content of the mixture is (+1%-+2%) of the optimal water content, it shall be immediately rolled with a light roller and a roller with a capacity of 18t or above. Straight lines and curved lines without superelevation shall be rolled from the shoulders on both sides to the center of the road; Set the ultra-high curve segment and roll it from the inner shoulder to the outer shoulder. Generally, it needs to be rolled 6-8 times. The rolling speed of the roller should be 1.5- 1.7km/h in the first two passes, and 2.0-2.5km/h in the future.

(3) It is forbidden for the roller to turn around or suddenly brake on the completed or rolling road section to ensure that the surface of the stable soil layer is not damaged.

(4) In the process of rolling, the surface of stabilized soil should always be moist. If the water evaporates too fast, a small amount of water should be added in time, but it is forbidden to sprinkle water to crush it.

⑤ In the process of rolling, if there are "spring", looseness, peeling, etc., it should be turned over in time to mix again (adding proper amount of cement) or treated by other methods to meet the quality requirements.

⑥ Before the end of rolling, level it again with a grader to make it longitudinal and comfortable, and the road arch and superelevation meet the design requirements. The final leveling should be carefully carried out, and the local higher part must be scraped off and the road cleared; For local low-lying areas, no repair will be carried out.

2.2.8 Treatment of Joints and Turning Points

The joints of two working sections should overlap. After the last stage of mixed molding, leave 5-8m without rolling; During the latter stage of construction, the uncompacted part of the former stage should be mixed with some quicklime again and rolled together with the latter stage.

maintain

The strength of lime-fly ash soil depends largely on the humidity and curing temperature of the structural layer. The curing process has an important influence on the strength growth of lime-fly ash soil, preventing early cracking and plate formation, but it is often ignored. Therefore, it is necessary to do a good job of moisturizing and curing. Moisturizing and keeping in good health shall not be less than 7d. Maintenance should be carried out in time, and maintenance should be started immediately after the compaction degree is qualified through inspection.

(1) When the lime-fly ash stabilized soil subbase is constructed in layers, when it is rolled by a heavy vibratory roller, the lime-fly ash stabilized soil in the lower layer shall be rolled, and then the lime-fly ash stabilized soil in the upper layer shall be paved after 7 days of curing. Before laying the upper stabilized soil, the lower surface should always be wet. When laying the upper stabilized soil, it is advisable to sprinkle a small amount of water on the lower surface. Before laying subbase, subbase shall be cured for 7d.

(2) After each section of rolling is completed and passed the compaction inspection, curing shall be started immediately.

(3) Keep in good health with sprinklers. The number of sprinklers per day should depend on the climate. During the whole curing period, the surface of the stabilized soil layer should always be moist.

(4) During the maintenance of lime-fly ash stabilized soil layer without covering measures, except sprinkling water, traffic should be closed. In the lime-fly ash stabilized soil layer with covering measures, when traffic cannot be closed, heavy vehicles should be restricted, and the speed of other vehicles should not exceed 30 km/h. 。

3. Conclusion

Lime-fly ash soil is widely used in highway construction because of its high strength in the later stage, good diffusion stress, dense whole formed by physical and chemical reactions inside, good water stability and frost resistance, waste utilization and environmental protection. Therefore, it is very important to control all aspects of lime-fly ash soil construction to improve the quality of highway engineering.