Cement stabilized macadam has good mechanical properties, high strength, good water stability and good road performance, and is suitable for the base of heavy traffic and heavy load roads. However, the construction of cement stabilized macadam is a comprehensive process, and there are often diseases such as spring, looseness, inability to take out core samples and cracks on the surface, which affect the construction quality. Now the author puts forward some common problems and preventive measures of cement stabilized macadam according to his own experience.
1 crack
Cement-stabilized macadam cracks are tiny cracks on the surface of cement-stabilized macadam base mixture after cement curing and drainage, and then extend to the deep and lateral, running through the whole base. The crack width is about 1cm~3cm, which can reach 4cm~5cm seriously. The appearance of cracks will lead to the overall stress state of the upper base plate to a certain extent. If the cracks develop further, it will cause reflection cracks, which will lead to cracks or broken slabs on the pavement.
The author analyzes the causes of cracks in water-stable layer: 1) The water content of cement-stabilized macadam mixture is much higher than the optimum water content, and the drying shrinkage strain of cement-stabilized macadam base increases with the increase of water content of mixture; 2) Selection of cement varieties; 3) Too much cement and poor gradation; 4) The maintenance of cement stabilized macadam is not timely and standardized; 5) Reasons for temperature difference.
Precautionary measures: 1) Pay attention to the selection of raw materials, ensure good gradation, and reduce the dosage of cement on the premise of meeting the design strength; 2) Selection of cement: Different types of cement have different dry shrinkage, ordinary portland cement has little dry shrinkage, followed by pozzolanic portland cement and slag cement. Therefore, selecting suitable cement can reduce shrinkage cracks to some extent; 3) control the dosage of fine aggregate, and the particle content of fine aggregate < < 0.075mm should be less than 5% ~ 7% as far as possible; 4) Control the water content, and control the water content in strict accordance with the design of cement stabilized macadam mixture ratio to make it close to the optimal water content and reduce man-made cracks caused by improper water consumption; 5) Reasonable selection of construction time. It is best to choose the construction time before the high temperature season in summer, such as the high temperature season in summer, and try to construct in the morning or evening; 6) Strengthen maintenance, because the drying shrinkage damage occurs in the early stage, so timely covering with geotextile, sack or film for good maintenance can prevent hydration and excessive evaporation of water in the mixture of cement stabilized macadam layer from causing surface drying shrinkage cracks. If construction conditions permit, paving asphalt pavement in time is a good way to reduce dry shrinkage cracks; 7) Adding fly ash (10%~20% of aggregate weight) to the crushed stone base of water-stable layer can delay the setting of water-stable layer mixture, increase its freezing capacity and improve its deformation performance.
2 A complete core sample cannot be taken.
According to the requirements of technical specifications, a complete drill piece should be taken out of the cement stabilized macadam layer at the age of 7d~ 10d, but the actual situation is that a complete core sample cannot be taken out because some sections are loose. The reasons are as follows: 1) Low cement dosage leads to poor cementation between aggregates and fails to achieve strength; 2) If the curing is not carried out completely according to the specification requirements, it shall be carried out immediately after each section of rolling is completed according to the specification requirements and passes the compaction inspection. Wet sand curing is adopted, and the thickness of sand layer is 7cm~ 10cm. Asphalt emulsion can also be used for health preservation. When this condition is not available, sprinklers can also be used for health preservation. The curing period should not be less than 7 days; 3) The raw material gradation of cement stabilized macadam layer is not good; 4) The water content is not suitable, so that the cement can not be completely hydrated and hydrolyzed in the mixture, and the stabilizing effect of cement on macadam can not be exerted, which affects the strength of cement stabilized macadam; 5) If the cement is not selected properly, ordinary portland cement, slag portland cement and pozzolanic portland cement can be used to stabilize the macadam, but the initial setting time should be more than 3 hours and the final setting time should be longer (preferably more than 6 hours). It is not advisable to use quick-hardening cement, early-strength cement and cement deteriorated due to moisture; 6) Uneven mixing, insufficient compaction under the optimum water content, and too long construction rolling time destroy the gelation of hardened cement and reduce the strength.
Precautions: 1) In terms of raw materials, each batch of cement can only be used after inspection; Gravel shall meet the grading requirements, and the maximum material diameter shall not exceed 31.5 mm. Unqualified materials are strictly prohibited from entering the site. 2) Improve the mixing process to avoid segregation as far as possible, and the construction personnel should strengthen the control of the cement agent, and improve and handle the problems in time when found; 3) Before construction, the shaking measuring instruments should be sent to the measurement and quality inspection center for verification to ensure weighing ... >>
Question 2: How is the water-stable layer constructed? Construction method of water-stable layer:
1, according to the mixture ratio, transport all kinds of graded materials to the site, pile them up in proportion, mix them evenly with large trucks, and pay attention to the graded moisture content of cement and stone, and adjust them at any time to ensure the uniform mixing of materials.
2. Pave immediately after mixing, compact with 12t roller, and manually assist in trimming, and roll for not less than three times. The construction of the stable layer of each layer should be properly watered and maintained.
3, after the completion of the rolling and compaction degree inspection, should be timely health, water conservation period should not be less than 7 days. During the maintenance of cement macadam base, large trucks can't crush it, so as not to crush the subgrade.
Extension of knowledge points:
The water-stable layer is a graded cement macadam layer, which should be mixed at the specific construction site during construction.
Question 3: Construction method of road water-stable layer 5. Pavement base construction includes road mixing method and factory mixing method. Now, in order to ensure the construction quality, the factory mixing method is generally required.
Pay attention to the construction time: the road mixing method is controlled within 6h; The factory mixing method is controlled within 3h;
Pay attention to the construction temperature; Pay attention to the compacted layer and so on.
You'd better read the relevant chapters in Technical Specification for Pavement Base Construction carefully, which contains detailed answers.
Question 4: What information do you need to do for municipal road construction and construction to the water-stable layer? Test records of soil layer, grid and geotextile construction, elevation and section.
Question 5: The construction mixture ratio of water-stabilized layer is 5 points. Here, the mixture ratio of cement stabilized macadam layer per cubic meter is as follows
Cement: p.o42.5 dosage: 107kg.
Stone powder: General dosage: 1050kg.
Gravel: 5-3 1.5 continuous grading dosage: 1087kg.
Water: 63 kg
Stirring time: 50 seconds
Dump trucks have short transportation distance.
The above is for reference only. Please try it first.
Question 6: What are the problems that the supervisor should control in the construction of water-stable layer? Matters needing attention in the construction of kneeling water-stable layer are as follows:
1, mixture ratio of cement stabilized layer, silt content, sand and gravel gradation.
2, layered rolling control elevation (including unreinforced elevation and molding elevation).
3. Tonnage and rolling times of vibratory roller (generally 8 times).
4. The top floor needs to pay attention to flatness.
5. Pay attention to wet water maintenance of straw bags.
The above are some experiences in my practical work, I hope to help you!
Question 7: What are the specific construction procedures and precautions for paving water stability, and where do you need mechanical equipment? Basic acceptance-measuring and setting out-spreading by paver-rolling-testing-maintenance. Note: the construction time (including mixing) shall not exceed the initial setting time of cement, and the rolling shall be timely and formed at one time. The Matsuura coefficient needs to be determined. During curing, no heavy vehicles are allowed to roll. Pay attention to maintenance. Equipment: paver, 18T vibratory roller, 18~2 1T three-wheel roller, sprinkler, etc.
The above is the method of stabilizing macadam with commercial cement. If it is self-mixing, it is another matter.
Question 8: Can the road water-stable layer be constructed in winter? What protective measures should be taken? Generally, it is not suitable for construction below 5 degrees. Construction should be carried out in accordance with the relevant provisions of winter construction. It mainly affects the setting of cement. Mainly take warm measures to prevent freezing.
Question 9: What quality, mixture ratio, mixing, paving, compaction and maintenance should be paid attention to in the construction supervision of cement stabilized macadam base?
Question 10: What is the hydrosphere 100? Explain in detail, what is the general thickness and what are the construction technical requirements? How to organize construction? 10 cement stabilized macadam is also called cement stabilized macadam grading, which can be called cement or cement stabilized macadam graded macadam. The so-called polymerization is the combination of gravel (or gravel), sand and powder (sometimes clay can appear), and the mixture of gravel (or gravel) and sand mineral aggregate, which is called aggregate. Usually refers to the mixture of controlled aggregate graded macadam or clay graded macadam. At present, cement-stabilized macadam at the grass-roots level is mixed with cement and water, and the compaction material meets the strength requirements, which is called cement-stabilized macadam with a grade of 20mm, and sand powder with the largest particle size is appropriately mixed. Factors affecting cement quality 2.2 affect polymerization stability.
① Particle strength (compressive strength of cement stabilized macadam aggregate) and matching strength grade;
② Cement properties and cement delay time stabilize the strength and compactness of crushed stone;
(3) Hygienic conditions and temperature.
2.3 Construction of Cement Stabilized Macadam
(1) mechanical equipment should use forced mixer or other mixing machinery, equipment performance should meet the requirements of paving and compaction. Two JS50 forced mixers are used for mechanical stirring of textile road.
(2) structurally, strictly control the water content and cement dosage of cement stabilized macadam, and record the weight ratio of each board in detail, and timely calibrate the deviation of electronic scales to achieve accurate matching.
(3) Due to the evaporation of the textile road in summer, considering the weather conditions, transportation distance, time and moisture caused by pavement hardening, the water consumption during mixing is appropriately increased; In order to ensure water-stable pavement materials, 10 dump trucks are transported to the site to ensure water-stable materials to meet the requirements of optimal water content during compaction and paving.
2.4 cement stabilized macadam paving
(1) Cement stabilized macadam shall be paved with paver.
② The loose laying thickness should be based on the designed and realized dry density. The compaction coefficient is determined by pressure test and loose laying thickness, and the loose laying coefficient is 1.35.
(3) For the old road reconstruction project, the next sequence of low-lying water accumulation should be taken in advance. It is expected that after formal construction, the leveling layer will be stabilized (it can be repaired by sections), so as to better grasp the design elevation and flatness control of the water-stable layer.
④ The concentration of coarse aggregate should prevent paving from forming "bird's nest" or "belt". When using "bird's nest" or "belt", it should be separated from water-stable materials in time to fill the gap between homogeneous materials with fresh water stability on the surface of mechanical paving, so it is not enough to spread by manual hanging.
2.5 cement stabilized macadam
Integer Integer ① When paving manually, the paving should have sharp sides and a preliminary arch plate or cable integer; while
BR/>； (2) The mechanical paver shall be shaped by grader; After ...
(3) When paving, it should be carried out immediately on the rapidly rolled initial flat pavement to expose potential violations. For the lower teeth, the rake should be applied locally to the tooth surface, the depth is more than 5cm, and a new combination should be found and mixed smoothly. Then, check whether coarse aggregate, "bird's nest" and "strip" exist, and eradicate the filling according to the above method.
2.6 water-stable aggregate rolling
① According to different lanes, rollers and wide wheel tracks, with the development of rolling works, all parts should be compacted as many times as possible, and the pressure on both sides of the pavement should be two to three times greater.
(2) After operation, when the water content of water-stable material is the best (+1%+2%), the full width of a smooth rolled structure layer should be compacted immediately. For sections without superelevation straight line and plane curve, rolling from shoulder to both sides of road center should overlap. The width of rear wheel 1/2 must be more than two coal seams, and the full width of pressing surface smoothness 1 times, 2 times. Smooth rollers should be compacted after being reused by heavy rollers. Generally, it needs to be rolled for 6 to 8 times, and the rolling speed of the roller is 2 times. It is more appropriate to use 1.5 km/h and 1.7 km/h at first, and 2.0 km/h and 2.5 km/h should be adopted in the future.
③ It is forbidden to turn around or roll the brakes for the completed or pushed parts, and ensure that the surface with stable water level is not damaged.
④ During the rolling process, the surface of cement stabilized layer should always be moist. If the water evaporates too fast, it should be replenished in time, but there should be no leakage and flood rolling.
⑤ In the process of rolling, if the "spring" appears loose and peeling, it should be re-opened in time (cement addition) or adopt other methods to meet the quality requirements.
⑥ Before mixing, the formed cement stabilized layer should be initially set, and the cement should be rolled within the required density range. The delay time of rolling is determined by the test, and there is no obvious wheel track.
⑦ Before the end of rolling, use the last grader again to make the longitudinal flatness, road arch and elevation meet the design requirements. The last level should be handled carefully ... >>