The cement pavement construction of this project is planned to be completed within 50 days, and the total amount of the project is 36 18 cubic meters.

The construction procedure is: (1) Select the mixing site; (2) Material preparation and mixture ratio adjustment; (3) measuring and setting out; (4) basic inspection and transformation; (5) shuttering and installation of steel bars (tie rods and dowel bars); (6) mixing concrete; (7) transport concrete; (8) laying concrete; (9) Vibrating concrete; (10) Dredging and leveling; (1 1) laying filter cloth and air cushion film suction pad; (12) vacuum treatment; (13) mechanical screeding; (14) mechanical finishing; (15) surface roughening; (16) mechanical sawing; (17) form removal; (18) caulking; (19) maintenance; (20) open traffic.

A, the construction preparation work

The preparation work before construction includes the selection of concrete mixing site, material preparation and quality inspection, inspection and adjustment of mixture ratio, inspection and renovation of base course, etc.

(A) the choice of concrete mixing site

According to the length of the construction route and the means of transportation used, concrete can be mixed at one place, or several places along the route can be selected to migrate with the progress of the project. The selection of mixing station should first consider the shortest transportation distance of transporting mixture. At the same time, the mixing station should be close to the water source and power supply. In addition, the mixing station should have enough area to pile up sand and gravel and build a cement warehouse.

(2) Material preparation and performance inspection

According to the construction progress plan, various materials (including cement, sand, stone and necessary additives) are prepared in batches before construction, and the selected sand and stone are inspected and adjusted in actual use to detect mud content, gradation, harmful substance content and firmness; The strength, acicular particle content and wear of the stone should also be sampled. If the silt content exceeds the allowable value, it should be washed or sieved 1 ~ 2 days in advance until it meets the requirements. If other items do not meet the requirements, other materials should be used first or effective remedial measures should be taken.

In addition to the factory quality report, the prepared cement should be inspected batch by batch for fineness, setting time, stability and 3d, 7d and 28d strength. In order to save time, the rapid determination method of 2h autoclaving can be used for determination and calculation. It is forbidden to use cement caked by moisture. In addition, newly produced cement should be stored for at least one week before use. Admixtures should be tested according to their performance indicators, and whether they are applicable should be determined through tests.

(3) Inspection and adjustment of mixture ratio

Before concrete construction, it is necessary to check whether the design mixture ratio is appropriate. If it is not suitable, it should be adjusted in time.

(1) Check and adjust the workability. According to the design mixture ratio, sample for trial mixing, determine its workability (or slump), and pass the trial paving site inspection when necessary.

(2) Strength inspection. According to the mixture ratio meeting the workability requirements, the flexural-tensile and compressive specimens of concrete are molded, and the strength is measured after 28 days of curing, or calculated after 4 hours of autoclaving. When the strength is low, measures such as increasing cement grade and reducing water-cement ratio can be adopted to improve aggregate gradation.

In addition to the above inspection, you can also choose different water consumption, different water-cement ratio, different sand ratio or different aggregate gradation to prepare the mixture, and choose an economical and reasonable scheme through comparison. The water content of sand and gravel in the construction site often changes, so it must be measured step by step and its actual dosage should be adjusted.

(4) basic inspection and renovation

1. Basic inspection

Check whether the width, bulging and elevation, surface smoothness, thickness and compactness of the base meet the specification requirements. If there is any discrepancy, it should be repaired. In engineering practice, it is required that after the completion of the grass-roots unit, the maintenance should be strengthened, the driving should be controlled, and there should be no car slot. If there is any damage, it should be repaired with the same material before pouring the concrete slab, and it is forbidden to fill it with loose granular materials. Semi-rigid base Pay attention to the decoration time, decoration is difficult and labor-consuming. For the widened part, the strength of the old and new parts should be consistent. Paving concrete pavement on old gravel road or asphalt pavement, if the old pavement is potholed and loose, and the transverse slope or width of road arch does not meet the requirements, it should be renovated, adjusted and compacted in advance.

2. Measurement and lofting

Measuring and setting out is an important work in cement concrete pavement construction. First of all, according to the design drawings, set out the center line and side line, and set up pile positions such as expansion joints, contraction joints, starting and ending points of curves and turning points of longitudinal slopes. At the same time, according to put away the center line and sideline, the concrete block line of the construction drawings shall be checked on site. It is required to keep a distance of at least 1cm from the edge line of manhole covers and other public works, otherwise the position of blocking line should be moved. In order to ensure the reasonable division of concrete blocks in the inner and outer lanes of curved sections, the transverse block line must be vertical to the road center line. Measuring lofting must be checked frequently. Including in the process of pouring concrete, we should be diligent in measurement, inspection and error correction.

Step 3 Install the template

After the grassroots inspection is qualified, the template can be installed. The formwork shall be steel formwork, with a length of 3 ~ 4m, and the joints shall be firmly assembled and easily disassembled. The height of formwork shall be the same as the thickness of concrete slab. On both sides of the template, iron brazing is driven into the base for fixing. The top surface of formwork shall be flush with the top surface of concrete slab and shall meet the design elevation. The bottom surface of formwork should be close to the top surface of grass-roots level, and local low-lying places (gaps) should be paved with cement slurry in advance and fully compacted. When there is no steel mold, you can also use a wooden mold, but the thickness should be above 5cm.

After the formwork is installed, the height difference between the joint of the formwork and the inside of the formwork should be checked to see if there is dislocation and inequality. Formwork with height difference greater than 3mm or uneven dislocation shall be dismantled and reinstalled. If correct, evenly coat a thin layer of oil or asphalt on the inside for demoulding.

Second, the concrete mixing and transportation

(1) concrete mixing

Concrete must be mixed mechanically. The mixing station should reasonably arrange the mixing machine and the stacking place of materials such as sand, gravel and cement. Strive to improve the productivity of the mixer. The capacity of the mixer should be configured according to the engineering quantity and construction progress. At the same time, the construction site should have spare mixers and generator sets.

The feeding system of ready-mixed concrete should adopt automatic metering equipment equipped with electronic scales as far as possible. When there are difficulties, at least the weighing method of adding a weighbridge to the aggregate box should be adopted, and the volume measuring method is difficult to meet the requirements of accurate measurement and should be stopped. When using automatic metering equipment, before mixing every day, it should be carried out in accordance with the requirements of concrete mixture ratio. After the dosage of cement, water and various aggregates is accurately adjusted (especially the water content of sand and gravel should be determined according to the weather change to adjust the actual dosage during mixing), it is input into the automatic metering control memory and verified by trial mixing before formal mixing production. The measurement accuracy is: water and cement:1%; Coarse and fine aggregate: 3%. Admixtures should be measured separately with an accuracy of 2%. Check the accuracy of material ratio at least twice per shift, and check the slump of mixture twice every half day.

The correct charging sequence of the mixer is: sand, cement, crushed (gravel) stone or crushed (gravel) stone, cement and sand. After feeding, add water while stirring. The mixing time should be determined according to the performance of the mixer and the workability of the mixture. The shortest mixing time of concrete mixture shall be the continuous mixing time from the mixing and expansion of all materials to the beginning of discharging, which shall comply with the provisions in the table below. The longest mixing time shall not exceed three times of the shortest time.

Minimum mixing time of concrete mixture

Capacity speed of mixer (rpm) mixing time (s)

Low fluidity concrete and hard concrete

Freestyle 400l18105120.

800 l 14 165 2 10

Mandatory 375L38 90 100

1500 l 20 180 240

(2) Concrete transportation

In order to ensure the workability of concrete, evaporation water loss and hydration water loss (referring to the hydration reaction of cement after mixing, which reduces its fluidity) and concrete segregation caused by bumps and vibrations during transportation should be considered. To reduce the influence of these factors, the key is to shorten the transportation time and take appropriate measures to prevent water loss (such as covering its surface with curtains or other appropriate methods) and segregation.

Concrete mixture can be transported by dump trucks. When the transportation distance is far, it is advisable to use a mixer truck for transportation. After the concrete mixture is discharged from the mixer, it will be sent to the paving site for paving, vibrating and mixing, until the longest allowable pouring time is completed, which is determined by the laboratory according to the initial setting time of cement and construction temperature, and shall comply with the provisions in the table below. If the time exceeds the limit, or when paving roads in summer, retarder should be used.

In the process of loading concrete mixture, it is not allowed to leak slurry to prevent segregation. The height of discharging when paving shall not exceed 1.5cm. When there is obvious segregation, it shall be re-mixed when paving. Cars used for transportation must be cleaned with water after work every day.

The maximum allowable time from the concrete mixer to the completion of pouring.

Maximum allowable time of construction temperature (℃) (h)

5~ 1 2 20~30 1

10~20 1.5 30~35 0.75

Third, paving and vibrating.

(1) Pave the road

Before laying concrete, the spacing, height, lubrication, support stability, smoothness and wettability of the base, and the location of steel bars and dowel bar devices should be comprehensively checked.

After the concrete mixture truck arrives at the paving site, it is generally poured directly into the road groove where the side formwork is installed, and it is repaired evenly by manpower. If segregation is found, it should be stirred with a shovel.

When the thickness of concrete slab is not more than 24cm, it can be paved at one time. When it is more than 24cm, it should be paved twice, and the thickness of the lower layer is 3/5 of the total thickness. Considering the influence of compaction, a certain height should be reserved for the loose material thickness of paving. According to the test, the specific value is generally about 10% of the design thickness.

When paving with a shovel, the method of "shovel" should be adopted, and throwing and harrowing are strictly prohibited to prevent segregation. When paving near the formwork, tamp it several times with a spade to tamp the mortar and avoid honeycomb.

(2) placing steel bars

1. Place the steel mesh.

Don't trample when placing the steel mesh. First, lay a layer of concrete mixture at the bottom, and the paving height should be pre-added with a certain sinking height according to the design position of steel mesh. After the steel mesh is installed in place, continue pouring concrete. If double-layer steel mesh is placed, for the plate with a thickness of less than 25cm, the upper and lower layers of steel mesh can be tied into a skeleton with vertical bars in advance and put in place at one time. When the thickness is greater than 25cm, the upper and lower layers of steel mesh should be laid twice.

2. Place corner and edge reinforcement

When placing corner reinforcement, a layer of concrete mixture should be laid at the corner where the reinforcement is placed. The paving height should be pre-loaded with a certain degree of settlement than the design position of reinforcement. After the angle spacer is in place, flatten it with concrete mixture.

When placing the edge reinforcement, first spread a layer of concrete mixture along the edge, and compact it to the height set by the reinforcement, then place the edge reinforcement, and flatten the bent parts at both ends with concrete mixture.

(3) Vibration

Paved concrete mixture shall be vibrated uniformly with flat vibrator and plug-in vibrator immediately. The effective depth of flat vibrator is generally about 22cm. When vacuum dehydration process is not used, 2.2kw flat vibrator should be used; When the vacuum dehydration process is used, a flat vibrator with lower power can be used. Plug-in vibrators are mainly used in the corners of vibrating panels, near manholes and water inlets, and where steel bars are installed. In construction, vibrators with frequency greater than 6000 times/minute should be used first.

When the concrete mixture is vibrated, firstly, the internal vibrator and other flat vibrators shall be used for external use at the edges and corners of the formwork (if the panel thickness is greater than 22cm, the internal vibrator shall be used for full-sequence vibration once), and the same position shall be no less than 20s. The moving distance of the internal vibrator should not be greater than 65438+ 0.5 times of its half-length, and the distance between the internal vibrator and the template should not be greater than 0.5 times of its radius of action, and collision between the template and the steel bar should be avoided. When paving and vibrating the upper concrete mixture twice, the internal vibrator should be inserted into the lower concrete mixture by 5cm, and the vibrating of the upper concrete mixture must be completed before the initial setting of the lower concrete mixture. Secondly, fully vibrate with a flat vibrator. Vibrating should overlap 10 ~ 20 cm. When vibrating at the same position, when the water cement ratio is less than 0.45, the vibrating time should not be less than 30 s; When the water-cement ratio is greater than 0.45, it should not be less than 15s, subject to no more bubbles and cement slurry.

After the concrete is fully vibrated, it will be further dragged and vibrated with a vibrating rod for preliminary leveling. The vibrating beam is pulled back and forth for 2 ~ 3 times, so that the surface is submerged and bubbles are driven away. The moving speed of the vibrating beam should be slow and uniform, and the forward speed should be 1.2 ~ 1.5m/min. For uneven places, fill them in by hand. When filling, use finely mixed virgin pulp, and it is forbidden to fill with pure mortar. When the vibrating beam travels, it is not allowed to stop over. The traction rope should not be too short to reduce the inclination of the bottom of the vibrating beam. The bottom of the vibrating beam should be kept straight. When the bending exceeds 2mm, it should be checked or replaced. When off work or not in use, it should be cleaned and placed in a flat place (if necessary, the vibrating beam should be put down to correct its straightness), and it should not be exposed to the sun or caught in the rain.

Finally, it is further rolled and kneaded with a flat roller, so that the surface is further slurried and evenly mixed. Roller structure is generally straight, straight through 75 ~ 100 mm seamless steel pipe. End plates are welded at both ends of the steel pipe, and bearings are embedded in the plates. Two elbow push-pull positioning pins are welded at both ends of the steel pipe, and the push-pull rod passes through the extended traction shaft. Its structure is shown in Figure 8-3. This structure can promote the slurry by rolling and pushing, and drive the slurry to keep a mortar layer of about 5 ~ 6 mm evenly on the surface, which is beneficial to sealing and surface making. When there is an arch, the arch forming plate should be used for leveling.

If it is found that there is still a big height difference between the concrete surface and the arch slab, it should be filled in again and rolled and leveled again. Finally, hang up the line to check the flatness. If it is found that it does not meet the requirements, it should be further processed and scraped until the flatness meets the requirements.

Fourthly, vacuum dehydration.

Vacuum dewatering technology is a mechanical water absorption method of concrete, which was listed as one of the four new technologies in concrete construction abroad in the 1970s. At present, this technology has been widely used in concrete construction in China. Because the vacuum suction process uses the pressure and dehydration of vacuum negative pressure, the compactness of concrete is improved and the water-cement ratio is reduced, thus improving the physical and mechanical properties of concrete. It is an effective measure to solve the contradiction between workability and strength of concrete, reduce cement consumption, save engineering investment, shorten maintenance time and open traffic before pulling. At the same time, because the moisture content of the mixture after vacuum dehydration is reduced, the shrinkage during curing is greatly reduced, which effectively prevents the plastic cracking of concrete during construction and prolongs the service life of pavement.

(1) supporting machines and tools

In the construction of vacuum concrete pavement, four main processes are usually carried out in blocks, namely pouring and paving, vibration leveling, vacuum treatment, mechanical finishing and texturing (embossing). Each process cycle is about 25min, and each shift can complete about 18 pieces, and the total operation time of each piece is about 100min.

Take the pavement with a width of 3.5 m and a length of 100 ~ 120m as an example. Each pavement is 3.5m×5m×24cm * * 20 ~ 40 pieces, with a total concrete volume of 420~500m3. The required supporting machinery is:

3 sets of 400L concrete mixers (including 1 set for standby)

10 manual small dumper (used for mixing and feeding)

1t electric dump truck 10 (including 2 spare cars)

3 built-in vibrators (3 spare club heads)

3 flat vibrators (standby 1)

2 sets of 3.75m vibrating beams

2 sewing machines

2 special vacuum pumps

4 air cushion film suction cups (3.5m× 5m).

1 set of vacuum concrete mold test.

3 polishing machines (including 1 spare machine)

Wool making machine (cotton gin) 1 set

(2) Vacuum dehydration process

The main working procedures of vacuum dehydration process are as follows.

1. Check the pump pad.

Before dehydration, open the water tank cover of the vacuum pump unit, inject fresh water into the vacuum chamber and water collection chamber to make the water level equal to or slightly higher than the nozzle in the box, adjust the tightness of the buckle, cover the box cover tightly, block the water inlet with a 3 ~ 4 mm thick rubber plate, and check the no-load vacuum degree of the pump. The pressure gauge of the pump should be greater than 650 ~ 700 mm Hg. Then check the connecting hose, suction pad surface, adhesive joint and pipe joint. If any damage, air leakage or blockage is found, it should be repaired or replaced quickly. In addition, it is necessary to check whether the adhesives, maintenance supplies and common maintenance tools are complete.

Step 2 lay suction cups

V88 new absorbent pad is recommended, and nylon pad cloth can be omitted. And it sucks evenly. Secondly, you can use V82 absorbent pad, which does not need plastic net, but only needs nylon gasket, and absorbs water evenly.

When V88 or plastic net suction pad is recommended, nylon cloth should be laid first. It is required that the cloth surface should be flat, with few wrinkles, and it can be folded if it is too long. Nylon cloth should be slightly smaller than the board surface by 6 ~ 8 cm (that is, the width of sealing tape), and air cushion film should be slightly smaller than the board surface by small 8 ~ 10 cm. When it is placed, use a small brush to gently sweep and press along the sealing edge, while pumping and pressing, and start the machine to dehydrate to ensure the sealing effect. If a nylon net suction pad is used, mesh sheets should be laid, and the periphery should be aligned with nylon cloth, with each mesh sheet overlapping by 2 ~ 3 cm. Finally, lay the suction cover and connect the bucket.

3. Turn on the pump for dehydration.

Start the pump for dehydration, and generally control the vacuum gauge to gradually increase to 400 ~ 500 mm Hg within 65438 0 minutes. The maximum value should not be greater than 650~700mmHg. If the required vacuum degree is reached within the specified time (3 minutes), the air leakage should be found immediately and remedied. If you use a sealant tape, you can generally add a little water to wet the sealing edge, and then gently sweep the pressure. If it still doesn't work, measures such as maintenance or replacement should be taken. In the process of vacuum treatment, the vacuum degree, dehydration time and amount should be carefully recorded, and the water flow in the air cushion film should be observed at any time. If the local water movement is not smooth, the adjacent sealing edges can be temporarily lifted at intervals to infiltrate a small amount of air and promote the water movement on the concrete surface. When dehydration reaches the specified time (dehydration time is generally 1 ~ 1.5 times the thickness (cm) in min) or a specified amount of water has been removed (dehydration rate is generally 12% ~ 15%), the position around the suction pad should be slightly raised/kloc-.

Before continuing vacuum dehydration, roll up the suction pad and move it to the next working face. The position of each suction pad should overlap the previous one by 20cm to prevent leakage and uneven distribution of water content.

4. Preventive measures

Vacuum dehydration should pay attention to the following items:

(1) The operating depth of vacuum dehydration shall not exceed 30cm, and the water cement ratio of the mixture shall not be greater than 0.55;

(2) When purchasing filter cloth and suction pad, the appropriate size should be selected according to the size of concrete pavement slab. Too large or too small will affect the dehydration effect;

(3) Vacuum operators must walk on the self-made "working bridge" and are not allowed to walk on the suction pad at will. It is not allowed to wear shoes with nails on hard soles, and it is best to wear rubber shoes or sports shoes for operation;

(4) When dewatering, it is necessary to make a good record of dewatering, grasp the dewatering time and uniformity, and prevent the concrete from appearing "spring layer" and cracks.

(5) When storing or moving the suction pad, avoid contact with sharp hard objects. Hold the pole in your hand when rolling up or laying the suction pad. So as not to damage the sucker.

(6) After the construction of each shift is completed, the suction pad should be cleaned, and the deposits in the vacuum pump box should be cleaned to discharge the water.

Verb (abbreviation of verb) surface renovation and anti-skid treatment

(1) surface renovation

1. Vacuum concrete panel renovation

When vacuum technology is used, mechanical polishing, fine polishing and texturing should be carried out after dehydration.

(1) mechanical polishing, rough polishing with a disc polisher or vibrating with a vibrating beam once, can play the role of homogenization, rough finishing and surface densification. It can smooth the unevenness left after vacuum dehydration, close the directional capillary holes after vacuum dehydration, eliminate the surface pores through extrusion grinding, increase the surface compactness, improve the uneven distribution of residual water and slurry on the surface, and reduce uneven shrinkage. Practice has proved that thickening is the key to determine the roughness and smoothness of the road surface, so it is necessary to check with a 3m straightedge. After inspection, the method of grinding at high places and filling pulp (virgin pulp) at low places is used for grinding and leveling, and the flatness is not greater than 1cm by vertical and horizontal detection with a 3cm ruler. It should be noted that the effects of polishing machines in different directions are slightly different. It is easy to ensure the longitudinal flatness when driving along the road, but the longitudinal flatness effect is slightly worse when crossing the road.

(2) Fine wiping. Dressing is the key process of pavement smoothness. In order to create conditions for fine plastering, after coarse plastering, the concrete surface can be scraped by rubbing with wood or sawing with a small bar (or rolling pin) wrapped with iron sheet, while rubbing horizontally and scraping vertically. In order to avoid template unevenness or template seam dislocation affecting flatness, longitudinal leveling should be carried out after horizontal leveling (leveling rod is parallel to template), and a 3cm ruler should be attached for inspection. Be sure to clean the template before scraping. After scraping, you can gently press the two sides and the middle three places near the pulp surface with a 3cm ruler. There is no indentation or imprint in the low recess, and the imprint in the high part is deep. Therefore, we should make up the fine level. Every time you wipe it, you should check it with a 3m ruler, and check it repeatedly until the flatness meets the requirements. Fine plastering should use virgin pulp, mortar should not be mixed, and sprinkling water or cement powder is prohibited, otherwise it will not only easily cause bleeding, prolong the interval of hair pulling, but also cause uneven shrinkage due to uneven water-cement ratio. When the temperature is high, surface cracks will appear, and the surface will fall off after the pavement is formed and opened to traffic.

(3) Texturing. Fuzzing is to maintain the smoothness of the pavement and improve the anti-skid performance of the pavement, but it also has a certain impact on the smoothness of the pavement. Generally, embossing (or grooving) and napping (or grooving) are used to make wool, but these two methods have their own advantages and disadvantages. Embossing has the function of downward compaction, which can enhance the wear resistance of pavement. If properly mastered, the texture is flat and even (the depth is generally 0.6 ~ 1.0 mm), which is more beautiful. However, it is difficult to grasp the uniformity of texture depth, because it is not only related to embossing time, but also related to the uniformity of vacuum dehydration of concrete. Around the suction pad, especially at the sealing belt, the embossing time is longer because of the small vacuum distribution and less dehydration, while the embossing time is shorter because of the large vacuum and more dehydration in the middle of the suction pad, which leads to the contradiction of embossing time. The solution to this problem is to take the time when the surrounding concrete is suitable for embossing as the standard. In the area with high strength such as the center of the plate, it is solved by loading on the embossing machine. When the concrete is not dehydrated enough and its strength is low, embossing should be avoided, otherwise it is easy to form uneven bulges on the road between two adjacent embossing machines. Brush coating is easy to make the surface loose and damage, affecting the compactness of the surface in the range of 1 ~ 2mm, which is not conducive to the wear resistance of the pavement, but will improve the smoothness. The flatness of embossed pavement is generally not as good as that of brushed pavement.

2. Renovation of ordinary concrete panels

When vacuum dehydration process is not used, large pieces of wood plastering should be used for multiple plastering until there is no bleeding on the surface. See the table below for the interval of water absorption plastering.

Interval time of water absorption and plastering for ordinary concrete pavement slab

Cement variety construction temperature (℃) interval time (minutes) cement variety construction temperature (℃) interval time (minutes)

common

through

water

Ni 0 35 ~ 45 ore

dregs

water

Mud 0 55 ~ 70

10 30~35 10 40~55

20 15~25 20 25~40

30 10~ 15 30 15~25

Note: The interval of water absorption plastering is not only related to the construction temperature, but also affected by sunshine, wind power, cement dosage and other factors, and the actual operation needs to be determined according to the current situation.

When finishing, it should overlap the last trace by half at a time. Low-lying parts of the board surface should be filled with concrete, and the flatness should be checked with a 3m ruler.

After plastering, the concrete surface can be transversely textured (grooved) with a nylon wire brush (or grooving device).

VI. Joint construction

Joint is the weak link of concrete pavement, and the quality of joint construction is not high, which will cause all kinds of damage to the slab and affect the driving comfort. Therefore, joint construction should be especially careful.

(1) longitudinal joint

During the construction of small machines and tools, the construction shall be carried out at one time according to the width of a lane (3.75~4.5m), and the longitudinal construction joints are generally in the form of flat joints and tie rods or tongue-and-groove joints and tie rods. However, in special parts such as crossings, the width of the concrete slab poured at one time may be greater than 4.5m, so it is necessary to set longitudinal contraction joints (false joints). Longitudinal false seam generally should also set the pull rod.

Longitudinal tie rods shall be made of threaded steel bars and set in the middle of the plate thickness. And should avoid release agent (such as asphalt, etc. ) on the tie rod.

There are three ways to set the longitudinal construction joint tie rod. The first is to set holes in the formwork, and put the tie rod into the holes before pouring concrete after the formwork is erected. The disadvantage of this method is that it is difficult to remove the mold. The second is to bend the tie rod at a right angle, tie half of the formwork with iron wire after the formwork is erected, and pour the other half into concrete. After form removal, bend the tie rod exposed to the concrete pouring side. The third way is to use a tie rod with bolts, half of which is fixed on the base with brackets, and the other half is connected with half of the tie rod buried in the poured concrete after formwork removal by bolt joints.

In the construction of longitudinal contraction (false) joint, the tie rod should be fixed on the base with a portal in advance, or put in with a tie rod placing machine during construction. Cut the joint on the top surface of the prosthetic joint with a slit cutter. The width of the joint is 3 ~ 8 mm and the depth is 1/4 ~ 1/5, so that the concrete can crack down from this joint regularly when it shrinks, and irregular cracks can be prevented due to insufficient joint depth.

(2) Transverse joint

1. Shrink joint

The transverse shrinkage joint can be slit after concrete is solidified (the compressive strength of crushed stone concrete reaches 6.2 ~ 12.0 MPa, and the compressive strength of crushed stone concrete reaches 9.0 ~ 12.0 MPa) or pressed when concrete is paved. The construction method of joint pressing method is: when the concrete mixture is used as the surface layer, the joint should be pressed immediately with a vibrating joint pressing knife. When the pressure reaches the specified depth, the caulking knife should be raised, and the slot should be leveled with virgin pulp. It is forbidden to mix pulp separately. Then put in iron or wood strips, and then level the joints. After concrete mixture oozes water before initial setting, rounded corners shall be taken out to form joints. Because cutting seam can get better quality shrinkage seam than pressing seam, this method should be used as far as possible. Especially for high-grade highways, slit method must be adopted. The construction technology is as follows:

(1) Before sewing, check the power supply, water supply and debugging of the sewing machine set, and the blade of the sewing machine should be in the machine body.

The center line forms a 90-degree angle and should be in the same straight line with the cutting line.

(2) Before starting longitudinal cutting, adjust the feed depth of the blade and adjust the cutting direction of the blade at any time during cutting. When the seam cutting stops, turn off the knob switch, lift the blade to the concrete surface and stop running.

(3) When slotting, the cooling water pressure of the blade should not be lower than 0.2Mpa, and at the same time, the kerf water should be prevented from infiltrating into the base and soil foundation.

(4) When the concrete strength reaches 25% ~ 30% of the design strength, it can be cut. When the temperature changes suddenly, the time for cutting seams should be advanced appropriately, or a seam should be cut first every 20 ~ 40m to prevent irregular cracks caused by temperature stress. Never cut a seam twice.