Cement stabilized macadam is generally suitable for base or subbase, and its thickness is generally 15 ~ 22 cm. In order to ensure its quality and standardize the construction process, the technical disclosure of cement stabilized macadam construction is specially formulated. This technical disclosure is only a supplement to the chapter "Cement Stabilized Soil" in JTJ034-2000 "Technical Specification for Highway Pavement Base Construction", the technical specifications in drawings and tenders, and the annex to the contract, so all units are requested to jointly implement it.
1.0 material
1. 1 Materials such as cement, gravel and sand used for roads must be approved by the supervision engineer. Unauthorized entry and use are not allowed.
1.2 cement: the final setting time is long (preferably more than 6 hours), so 325# slag and ordinary portland cement should be adopted. It is strictly prohibited to use quick-hardening cement, early-strength cement and cement deteriorated by moisture. The choice of cement brand should consider its quality stability, production quantity and transportation distance. Cement should have a certificate of approval before entering the site every time, and the setting time and label of cement should be sampled every 200T t.
1.3 crushed stone: it is required that the crushing value should not exceed 30% and the maximum particle size should not be greater than 30mm. The particle composition of crushed stone shall meet the requirements of 2# gradation in 2.2. 1.6 in JTJ034-93. For the convenience of construction, coarse aggregate of 10-30 mm, medium aggregate of 5- 10 mm and fine aggregate of 0-5 mm should be used. The crushing value of coarse aggregate, the screening of various granular materials (mainly to check the particle grading deviation of feed), the plasticity index of fine soil below 0.5mm and the particle content below 0.075mm should meet the requirements in JTJ034-93. After the above materials enter the site, two samples shall be inspected every 2000m3.
1.4 water: the drinking water of people or livestock can be used for the construction of cement macadam.
2.0 Composition Design of Mixture
2. 1 Composition design principle: ① powder content should not be too much; (2) on the premise of strength, the minimum cement dosage should be adopted, but not less than 4.0%; (3) improve the aggregate gradation, and reduce the cement dosage to no more than 6%.
2.2 The dosage of cement can be prepared in five ways: 4%, 4.5%, 5%, 5.5% and 6%.
2.3 Make 9 samples for each dose (minimum quantity).
2.4 The specimen must be kept moist at the specified temperature (20 2℃) for 6 days, and the unconfined compressive strength test shall be conducted after soaking 1 day, and the average value and deviation coefficient of the test results shall be calculated, and whether RX( 1- 1.645Cv) is greater than Rd (the design strength of this project is 3.5MPa). The design dose should be the minimum dose to meet the strength and should not exceed 6%.
2.5 According to the designed dosage, do experiments on the influence of delay time on the strength of mixture, and determine the delay time to be controlled through experiments.
2.6 The amount of cement actually used in the construction site increased by 0.5% compared with the designed amount.
3.0 Quality control standard of cement stabilized macadam.
3. 1 Specific detection technical indicators: (see the figure below)
3.2 After the rolling of each operation section is completed, the indicators shall be tested immediately, and the information in the industry shall be collated and submitted to the supervision and inspection (within 24 hours), and the strength indicators shall be submitted for inspection separately. Supervisors should go to the site to conduct spot checks in time, and notify them in time when problems are found.
3.3 Each subdivisional work shall be graded according to the Standard for Quality Inspection and Evaluation of Highway Engineering in Hebei Province and the Measures for Quality Supervision, Inspection and Evaluation of Highway Engineering in Hebei Province. Engineering scores must be above 97. Those who fail to meet this requirement are not allowed to complete.
4.0 Key points of construction technology
4. See JTJ034-93 Technical Specification for Construction of Highway Pavement Base 2.5-2.7 for the construction technology of1cement macadam.
4.2 Sub-base detection and soil-raising mold
4.2. 1 Before paving the cement stabilized macadam base, the subbase must be comprehensively inspected, including plane position, elevation, cross slope, width (strength and thickness have been inspected) and surface cleaning. If it fails to meet the requirements, reasonable measures should be taken to deal with it (especially the thickness is insufficient), especially the loose and peeling materials at the grass-roots level should be thoroughly removed, and no weak interlayer should be left. Sprinkle water on the subbase before paving the subbase to keep the surface moist (without water).
The specified value of each inspection item or the allowable deviation inspection method requires the qualified rate of indicators.
1. The extreme degree of compaction is 98% and 94%, with 2 places per lane every 200m. According to mathematical statistics, 100%
2. Flatness (mm) 83m ruler 100ft100 m 95%.
3. Width (cm)≥ 1200 feet, around every 200m 100%.
4. The longitudinal elevation (mm) is 5,-10 level, and 85% of every 200m 4 section (left, middle and right elevation) (including unqualified points within 10 mm-20mm).
5. The transverse gradient (%) is 0.3, with 95% in 4 sections every 200m.
6. The representative value of thickness is-10mm-20mm, and the extreme value of 100% is calculated by mathematical statistics.
7. The strength (MPa) is greater than the design 1 group (9 specimens) per 2000m2. According to mathematical statistics, it is 100%.
8. Cement dosage is 0.5% ~ 2%, 6 samples 100% per 2000m2/group.
9. The first few sets of sloping must be done within the specified range, and then it should be done at a time according to 2000 square meters 100%.
10. The delay time shall not exceed the specified time.
4.2.2 Before paving cement stabilized macadam, the soil on both sides must be ploughed. The width of soil model is wider than the design width 10-20 cm, and the height of soil model is the same as that of water-stabilized virtual paving. The soil must be cut vertically with a stay wire, and the soil should have a certain density, generally around 80%. The specific data depends on the test section.
4.3 The person in charge of cement macadam site (foreman, operator and quality inspector) shall be a person with strong ambition, skilled business and strong management ability. The person in charge of the construction site should always keep an eye on the construction site and must not leave temporarily.
4.4 Selection of benchmarks
4.4. 1 Before lofting, the surveyors of the joint management department and the technicians of the internal supervision section shall disclose the control points and leveling points, control the measured data must be the data approved by the supervisor, and sample the measured lofting data.
4.4.2 Choose φ (2-3 mm) steel wire as the baseline.
4.4.3 The tensioning length should be 100-200m, and both ends should be tensioned at the same time with tightener, so as to avoid deflection caused by steel wire looseness, and the tensioning force should be 1KN.
4.4.4 Steel bars shall be brazed with φ16-18 round steel with relatively high rigidity, and equipped with a fixing frame. It is best to use threads for the fixing frame, which is convenient for disassembly and elevation adjustment; Generally, the rebar spacing is 5- 10m (straight line segment is not more than 10m, curve segment is not more than 5m). Drill pipes should be placed at a distance of 30cm-40cm from the laying width.
4.4.5 Use steel wire to control the internal and external elevation, and the elevation error shall be controlled between-2mm and 5mm.
4.4.6 Steel bars must be buried firmly, and there will be special personnel to take care of them during the whole operation. Do not touch the steel wire, and recover immediately if any abnormality is found.
4.4.7 Surveyors should pay close attention to the construction site and regularly check the steel wire elevation.
4.5 Mixing of cement stabilized macadam.
4.5. 1 Selection of mixing equipment
Mixing equipment with good performance and high mixing quality should be selected. This equipment is equipped with an electronic dosage device (which belongs to the weight ratio control of material ratio). The quantity and type of mixing equipment must meet the requirements of paving and construction progress on the construction site and be reported to the supervision engineer for approval.
4.5.2 Quality control of graded macadam aggregate
This project adopts the construction method of mixing materials with different specifications to form mixture. Before mixing, it should be adjusted repeatedly to meet the grading requirements. At the same time, the first few plates should be screened before mixing every day. If there is any problem, it should be adjusted in time. All-day mixture shall be sampled according to the paving area and detection frequency (2000m2 each time) required by the specification.
4.5.3 Cement dosage control
Considering the influence of construction dispersion, the amount of cement used in construction increased by 0.5% compared with the design value. During the mixing process, observe the color of the mixed mixture at any time to prevent the cement from blocking and not flowing. Sample the cement dosage according to the specified frequency, and calculate whether the total cement dosage meets the requirements according to the quantity of cement and aggregate used in each shift.
4.5.4 Water content control
Water content is an important control index of cement stabilized graded macadam, which must be strictly controlled. In the hot summer construction, considering the evaporation of water in the process of mixing, transportation and paving, the water consumption can be increased when mixing, and the increased water value should be compared with the water content of paving and rolling when mixing and discharging, so as to make up for the loss. According to the construction experience, before 9: 00 a.m. and after 5: 00 p.m. in summer, the water ratio increases by about 0.5%- 1%, and between 9: 00 a.m. and 5: 00 p.m., the water ratio can increase by 0.8%- 1.5%. During the rainy season construction, due to the influence of rain, there is a certain amount of water in the aggregate. Therefore, before mixing every day, the water content of aggregate should be determined, and the water addition should be controlled according to the optimal water content MINUS the water content of aggregate. In other seasons, the increase or small increase is not considered, and the increase is controlled within 0.5%.
4.5.5 Prevent crushed stone aggregate and materials larger than 3cm from entering the mixer.
The hopper of the domestic stabilized soil mixer is small, and the hopper spacing is close, and the phenomenon of crossing the hopper often occurs when feeding, which leads to inaccurate classification. Therefore, the hoppers should be separated by baffles. 1-3cm stones often contain stones above 3cm. In order to avoid entering the mixer, a layer of 3cm grid was added at the outlet. Materials smaller than 3cm leaked from the grid into the conveyor belt, and those larger than 3cm were promptly eliminated on the screen.
4.6 Transportation of Cement Stabilized Graded Macadam
4.6. 1 In order to save the time of reversing and paving cement stabilized macadam, dump trucks with the size of 15T or more are adopted, and the vehicle condition is better. The number of dumpers depends on the distance.
4.6.2 Before going to work every day, the vehicles should be inspected to eliminate faults, so as to prevent the vehicles from dumping after loading and waste caused by solidification of cement stabilized macadam mixture. It is also necessary to consider the length of transportation distance and weather conditions to decide whether to cover it with tarpaulin.
4.6.3 During loading, the position must be constantly moved, so that the mixture flowing out of the mixing building will not segregate.
4.6.4 When issuing materials, the issuing list should be filled in carefully, including car number, mixer discharging time, tonnage and cement varieties used. When transported to the paving site by the driver, it shall be inspected and checked by the receiving personnel, and the delay time from mixing to rolling of the mixture shall be strictly controlled within 3 hours. Otherwise, the whole vehicle materials will be scrapped.
4.6.5 When the dump truck unloads the mixture into the hopper of the paver, it is forbidden to hit the paver.
4.7 Paving of Cement Stabilized Graded Macadam
Paver selection:
1. ABG paver full-face paver is preferred, or two pavers of the same model can be used for paving at the same time, that is, the two pavers are 5-8 meters apart, and the mixture can be spread forward synchronously.
2. The tamping frequency of paver should be adjusted according to paving speed, thickness, width and other factors, so that the compactness before rolling can reach more than 80%.
3. Adjust the screw feeder to the best state, so that the height of the mixture in the screw feeder will bury 2/3 of the diameter of the screw, so as to avoid segregation and large materials at the bottom. In general, the distance between the flange of the screw and the surface of the subbase is 15 ~ 17 cm.
4.7.2 Before the paver is in place, the lower bearing layer must be cleaned and watered to keep it moist, and the transverse joints must be watered with mud.
4.7.3 After the mixture is transported to the site, it shall be spread evenly according to the loose thickness immediately. Before paving, the mixture (about 50-60 cm wide) separated at the spreading joints on both sides should be removed. When paving, if there is segregation (especially on both sides of the edge), it should be repaired manually, and at the same time pay attention to the water content, and feedback it to the mixing station in time for appropriate adjustment.
4.7.4 When the paving length is 3-6m, the elevation and cross slope of the paving surface shall be detected immediately. If it does not meet the design requirements, the height and cross slope of the screed should be adjusted appropriately, and then paving should be carried out until it is qualified. During normal construction, every time the paver advances10m, the inspectors should check the elevation and cross slope of the paver. And record the virtual paving thickness. Mud and large-grained stones on the road surface should be picked out manually.
4.7.5 To keep the speed of the paver constant during paving, the production capacity of the mixing station should be matched with the paving speed to avoid unnecessary downtime, and the paving speed should be 1.0-3.0m/min. In addition, it is necessary to ensure that the vibration frequency of the rammer or rammer plate of the paver is uniform, and these data can be summarized through the test section. Once you get reliable data, you should use it constantly and don't adjust it at will.
4.7. When the paver spreads the mixture, for some reason, it is absolutely necessary to set the transverse joints at the end of the working cycle of 2 hours or a day, and the paver should leave the end of the mixture.
4.7.7 The treatment method of transverse joints is to draw the compacted ends with satisfactory elevation and smoothness into a transverse (vertical to the center of the road) vertical downward section, and all end mixtures that do not meet the compactness elevation and smoothness shall be carved out from the roots.
4.8 Rolling of Cement Stabilized Macadam
4.8. 1 roller selection: it is recommended to adopt two large-tonnage vibratory rollers (such as YZ 18) and one three-wheeled smooth rubber roller.
4.8.2 Rolling sequence: firstly, use a vibratory roller without vibration, stabilize the pressure for 1-2 times, then vibrate for 3-4 times, then use a three-wheel smooth roller (18T or more) to roll 1-2 times, and finally use a rubber-tyred roller (as above) to roll 1-2 times.
4.8.3 Rolling speed: In the stable stage, the rolling speed should be controlled at 65438 0.5 km/h.. The speed of compaction complex should be controlled at 2KM/H, the walking speed at steady stage should be controlled at 2.5 km/h, and the starting and braking should be slow and slow to prevent sudden starting and braking.
4.8.4 Scroll mode:
When rolling, the principle of "outside first, then inside" should be followed, and the outside rolling must be pressed on the soil model above 10CM. It should be indented longitudinally (at least staggered by one meter) and cannot be pressed together on a line. The roller should run on the compacted road surface and return three meters before reaching the pressure stabilizing place. Staggered half shafts and rolling joints should be horizontally staggered into a 45-degree step shape; Before and after voltage stabilization and micro-vibration, it is one meter wrong, micro-vibration and revitalization are half wrong, and glossy surface and revitalization are one meter wrong. Both sides of water-stabilized macadam should be compacted 2-3 times more; It is forbidden for the roller to "turn around" and suddenly brake on the completed or rolling section, and it is also forbidden to stop on the uncompacted section.
4.8.5 Treatment of transverse hard joints:
Sprinkle water on the transverse hard joints before starting work every day. Before rolling, hard joints must be treated first. Transverse hard joints must be pressed horizontally to ensure flatness. The lateral pressure of hard joints must also be divided into stable pressure and microseismic. There should be a difference of half a meter before and after voltage stabilization and microseismic.
4.8.6 flatness control:
In order to ensure the smoothness of asphalt concrete surface, the smoothness of cement stabilized macadam base must be controlled within 0.8cm, and the unqualified places shall be handled in time when rolling (designated persons shall be responsible).
4.9 Maintenance of Cement Stabilized Macadam
Designate a person to be responsible for health care, supervise the sprinkler to spray water regularly, and keep the water stable surface moist, regardless of the frequency and water consumption. In addition, when spraying water, pay attention to the uniformity, especially the upper edge. After five days of curing, you can spray primer oil or seal oil, otherwise you should keep curing until the primer oil is sprayed.
5.0 Relevant requirements
5. 1 In the process of paving and rolling, full-time quality inspectors will inspect the shift, give timely feedback on the elevation, cross slope, flatness and thickness, and handle the problems in time when found.
5.2 Testing, Prosecution and Construction Guidance
Main indicators of water-stabilized macadam detection: aggregate crushing value, silt content, initial setting and final setting time of cement, cement dosage, composition and gradation of construction aggregate, construction water content, molding compactness, unconfined compressive strength and other indicators. Testers should follow the shift, detect by frequency, give feedback in time and adjust in time.
5.3 For the project signed by the supervision engineer, the construction unit shall timely apply for phased appraisal of water-stabilized macadam. (Generally within 7 days after completion) The Municipal Bureau of Quality Supervision Station will conduct a detailed inspection on the water-stabilized macadam (elevation, transverse slope, flatness, width and appearance, etc.). ). Loose drilling and indicators that do not meet the quality objectives will be handled or reworked.
6.0 Quality Management Point
6. 1 The construction unit should be equipped with skilled foreman and technicians with high political quality to be responsible for the mixing, paving and testing process, and carry out the responsibilities, formulate the responsibility system of rewards and punishments, strictly reward and punish, check and handle in time, resolutely rework the cement stabilized macadam that fails to meet the quality standards, and investigate the responsibilities of those responsible.
6.2 Quality Management Point
The quality management point shall be responsible by a special person, implement the responsibility system, and formulate the reward and punishment system and inspection system. The specific management points are as follows:
(1), raw material test: ① cement ② crushed stone aggregate.
(2) Deviation control of mineral aggregate gradation during construction.
(3) Deviation control of cement dosage in construction.
(4), mixing station and yard management.
(5) Uniformity control of water-stable aggregate in factory mixing.
(6) Strength test of cement stabilized macadam.
(7), road cleaning control (including making soil model or supporting the square wood).
(8), the centerline plane deviation control.
(9) Daily inspection and maintenance of all kinds of machinery used, especially key machinery such as mixing station, generator, paver and roller.
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