Precast concrete blocks used for highway emergency

parking lane pavement engineering practice

Wang Huoming 1 Nie Xin1 Zhou Gang1 Cai Congbing 2 Xiong Shiyin 3

（1 China Merchants Chongqing communications research and Design Institute Company Limited Chong Qing 400067; 2 Yunnan Luqiao Limited by Share

Ltd Kun Ming 650200; 3 Mo Si Expressway Development Co Pu 'er 665100）

Abstract：

Prefabricated concrete pavement is composed of a single precast block assembled as a special pavement structure according to certain rules， is widely used in city sidewalks, parks and scenic pavement. Due to there are a large number of seams on the surface，it have a certain influence on driving comfort and safety, restricting the precast block pavement used in highway. This paper based on the engineering practice that the precast block pavement is used in expressway emergency parking lane, introducing the Material requirements 、Construction technology、internal drainage design 、Test situation and so on in construction process。. Finally, according to entity project implementation giving the opinions and suggestions.to solve problems occurred in construction process.

Keywords: Pavement engineering Precast block pavement Expressway Emergency parking lane Engineering practice

1 Outline

Precast concrete pavement has many advantages such as construction flexible， strong adaptability to deformation, easy coloring, easy to repair and reusable ,so it is widely used in City Road, airport apron and part of road in the United States, Britain, Australia, Japan and South Africa [1,2]. As a result of many joints, coupled with the construction quality is uneven, it is difficult to guarantee the smoothness of pavement, limiting its used in road especially highway. In China, precast block pavement is mainly applied to the city sidewalks, parks, scenic areas and the non motorized vehicle lane at present.

In recent years, with the improvement of technology, and the economic and environmental pressure increasing year by year, people began to study that using block pavement in parking areas in highway, such as emergency parking lane, a service area and viewing platform. The author had favour to participate in such a job and success to paved two-way 600concrete block pavement in emergency parking lane from simao to mohei in Yunnan. This article mainly aims at introducing construction process and completion quality testing and other aspects in the emergency parking lane.

2 The Profiles Of Test Road

In March 2011, paving a long about 500m concrete prefabricated block test road in emergency parking strip in left images ( k55+371.5 ~ k56+026.5) left and right images ( k55+381.5~ k56+026.5) Yunnan maosi expressway. Test road pavement is made of precast block surface layer, sand cushion, seal, permeable layer, the base and subbase, the specific of pavement structure scheme : 16cm precast block surface layer + 2cm sand cushion + 38cm cement stabilized macadam. Block size:29cm * 19cm * 16cm ( length * width * height ), block using CIS paving.

In addition to the original design drainage system of pavement, pavement drainage increases partial drainage system of the precast block surface layer, excavating 30cm wide vertical drainage ditch close to the roadway, laterally on each20m set deep 6cm, width 30cm blind ditch, ditch uses permeable concrete to pave.

3 Test Road Construction

3.1 subgrade preparation

According to the design document, after roadbed is completed, the degree of compaction of top surface on heavy compaction standard shall not be less than 96%, the detection representative deflection value shall not exceed 160(0.01mm ) in adverse seasons, using the axle load 100KN standard car to test deflection, testing frequency is each piece of each10m is two, detection section shall be staggered, if the deflection value is too large, doing roadbed partial treatment, before the acceptance of qualified , construction of road subbase and base.can not begin.

3.2 basic construction

Before basic construction, cleaning soils and water in the surface, and watering the working surface wet. Cement stabilized macadam mixture by mixing center station ( mixing ) construction, by two sets of paver echelon to operate paving, which can avoid the longitudinal seam. the mixing section of trial pavement, paving, compacting, each procedure is according to the current pavement base construction technology .

3.3 drainage facilities construction

after the acceptance of qualified basic，it is time to begin block pavement structural drainage system construction. In the test section of pavement structural drainage system is made of longitudinal and transverse void concrete rubble blind ditch. Close to the roadway，excavating 30cm wide vertical drainage ditch, laterally on each 20m excavating the depth 6cm, width 30cm blind ditch, longitudinal slope of ditch bottom is not less than 3%, filling materials of vertical drainage ditch are pervious concrete, filling materials of transverse drainage ditch is single particle size pervious macadam. The construction process of drainage facilities: groove,

leveling the groove bottom, mix design of pervious concrete, mixing, pouring, molding, curing.

①groove：after the acceptance of qualified basic，In close proximity to the lane position，cutting out a wide 30cm,6cm deep trench, after the cutting using picks to break cutting section, there are still rough which should be manual excavated during construction, as shown in figure 1.

Fig 1 dugging blind ditch on the base top surface Fig 2 void concrete blind ditch after construction

②When then bottom is flatted and trench is formed, then the bottom will be uneven, using 75cement mortar to level the ditch, cement mortar also can prevent the infiltration of water into the basic, setting a not less than 3% drainage gradient on ditch bottom is useful to water discharge

③To irrigate, mold the permeable concrete: pouring the mixed permeable concrete to the excavated groove, when artificial bed is paved，using plate compactor to compact, covering plastic film to preserve, because the permeable concrete is hard , so every half day watering a time, figure 2 is void concrete blind ditch after construction

3.4 Sand cushion construction

Sand cushion is between the base layer and precast block and can absorp and buffer pavement impact load and transfer the load to the primary, besides bedding sand has leveling and drainage effect, the thickness is 2~ 5cm. Precast block road has higher demand on bedding sand, at the initial stage of use permanent deformation accumulation, mostly produced in the sand cushion, which is an important factor effect block pavement. Sand cushion shall hard, clean, no decency, no impurities, and has appropriate particle size distribution, its quality should accord with the regulations in Table1 and table 2's requirements.

Table 1 quality requirements of precast block bedded sand

Project Unit Quality Requirements Test Method

Apparent relative density — Not less than 2.50 T0328

sturdiness （the part >0.3mm） % No more than 12 T0340

Sand content % Not less than 65 T0334

the passing rate is smaller than 0.075mm by washing method

% No more than 3 T0333

Table 2 the bedded sand gradation range

Sieve size（mm） 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075

The percentage through quality

（%） 100 90~100 70~90 40~80 20~60 7~30 0~15 0~5

The clean degree of sand, natural sand is shown by the percentage which t is less than0.075mm content, the chips and the mechanism is shown by sand equivalent (for 0~4.75mm ). The cushion can be selected in the sand, coarse sand or stone chips, fineness modulus should be 2.5~3.0, prohibiting weathered, softted, mud or impurity content material is used in sand cushion.

In order to prevent the sand plugging pervious concrete, before sand cushion paved, in pervious concrete surface is covered with two layers of nonwoven geotextiles geosynthetics. The construction method of sand cushion is scraper, control sand layer smoothness, let the layer of sand uniform thickness. The construction process is shown in figure 3.

Fig 3 the cushion sand construction paving block Figure 4 precast concrete block construction

3.5 precast concrete block construction

Cement concrete prefabricated block indicators should meet the" concrete brick road" ( JCT446-2000) requirements, the using test road precast concrete blocks adopt centralized prefabrication, the size is 30cm ×20cm ×16cm, mixture ratio design in accordance with the relevant provisions of national standards for calculation and test, the compressive strength of 28d as the standard test, strength of more than 30MPa, the measuring error of block size is not more than2mm, meet the requirements of project construction guide. Precast block uses artificial backward method for paving, paving process uses 3M ruler and a hanging cross line method for the control of pavement smoothness, block paving as shown in figure 4.

3.6 joint sand construction

Block pavement joint sealing material is mainly used to fill the gaps between blocks, interlock block pavement, strengthen the integrity, and to protect the block edge angle, to prevent surface water from infiltration. Caulking sand adopt natural sand or mechanism sand with good gradation, cleanness, hardness. Caulking fineness modulus of sand is 1.6~3.0, the maximum particle size is less than 5.0mm, mud content in control is less than 5%, water content is less than 3%., gradation shall satisfy the requirements in table 3.

Table 3 filling sand gradation range

Sieve size（mm） 4.75 2.36 1.18 0.6 0.3 0.15 0.075

Quality through percentage（%）

100 90~100 75~95 60~90 30~60 15~30 5~10

After the precast concrete block paving, then sweep caulking sand, there are two kinds of construction methods, one is that swept sand into the reserved joint artificially ,the other is watering sealing sand into seams, but the latter one is applied to the more humid regions, this paper uses artificial sand swept into the seam in the construction process, as shown in figure 5.

Fig 5 caulking sand construction Figure 6 block pavement compaction

3.7 roller compaction and filling sand

After the caulking sand is constructed, should be compacted by more than 12t vibratory roller or tyre roller, this paper use tire roller on the block pavement the construction is shown in figure 6. In the rolling process, fill surface sand on leaked seam area, to ensure that the compacted caulking full, smooth, dense.

After the construction, inspect on the block pavement,the block pavement surface should be smooth, compact, neat lines, block without loosening, shaking phenomena, and no pollution, hollowing, tilting, off angle and road brick fracture etc.. Take timely treatment on the existence situation that local block is loosed joint sand is not full.

4 Test Road Test Results

After the completion of the test section construction, in accordance with the interlocking type pavement brick pavement construction and acceptance rules "(CJJ E60-1998) and the related request of the project construction technical guidelines, to detect the flatness, deflection, and permeable of precast block road surface.

4.1 smoothness

The determination methods of cement concrete precast block road surface roughness,using of 3 m straightedge rule method, every 200 m in the 2 x 10 feet. Test results, see table 4.

Table 4 test road roughness detection results ( mm )

3M ruler method detection project

Point position Design requirements 1 2 3 4 5 6 7 8 9 10

Transverse（mm） 3 3 5 4 2 4 3 4 3 4 ≤5(mm)

Longitudinal（mm） 4 5 4 4 5 5 3 4 5 3

From the test results, test road flatness control is better, can meet the requirements of detection value guide. Among them, the lateral1points is close to the upper limit value,4close to the upper limit value of longitudinal.

4.2 road surface deflection

Concrete block pavement detection method, using the Backman beam determination of pavement subgrade rebound deflection experiment method, specific requirement according to the relevant provisions of the " code for field measurement of highway subgrade pavement". To have the completed construction of the concrete block pavement deflection value detection, detection results in Table 5, the detection process is shown in figure 7.

Table 5 rebound deflection testing results (0.01mm )

Project Point position Test road

Requirement 1 2 3 4 5 6 7 8 9 10

The left picture

40 34 18 8 18 16 28 24 32 24

≤100 The right picture

32 8 14 46 44 24 48 18 14 20

Fig 7 test road deflection testing Fig 8test road permeability coefficient test

4.3 seepage coefficient

At present, there is no requirements and test method for precast concrete block pavement seepage coefficient in domestic and foreign countries ,the road test uses the asphalt pavement seepage coefficient tester to test block pavement seam permeability coefficient according to the research results of this project. Test results see table 6, test process is shown as in figure 8.

Table 6 block pavement seepage coefficient test results

Pile Permeability coefficient(ml/min)

The left pictureK55＋385 175

The left pictureK55＋550 205

The left pictureK55＋840 165

The right pictureK55＋450 185

The right pictureK55＋640 190

The right pictureK55＋900 215

From the test result, in different position the seepage coefficient of the seams has some differences. Among them, the left water seepage coefficient was between 205ml / min and 165ml / min; the right water seepage coefficient was between 215ml / min and 185ml / min; in the whole testing section joint seepage coefficients is in the range of165 ~ 215ml / min. Permeability coefficient of the test road and the seam permeability coefficient of indoor loop has lots of differences, the differences have very big relations with this test road construction technology.

4.4 comfort

Due to the existence of a large number of joints on the block pavement road surface, it can cause certain effect on road comfort, when at high speed driving the vehicle vibration is obvious, there will be noise and certain safe hidden trouble. In order to test block pavement traffic comfort, task group has the rich experience drivers to drive at different speeds through the block pavement test road, then test driving noise and vehicle vibration, the results is in table 7.

Table 7 block pavement ride comfort test results

Driving speed（km/h） Running noise(dB) Comfort

20 48.1 Well, slight vibration, noise is not obvious

40 56.5 In general, obvious vibration, low noise;

60 68.4 Poor, vibration, noise is obviously;

80 77.8 Very poor, vibration is stronger, larger noise;

100 84.6 Range, vibration sense is very strong, a lot of noise;

From the test results, when the vehicle speed is in 20km / h,48.1dB running noise, drivers feel a slight vibration, comfort is passable; when the vehicle speed is in 40km / h, noise rise to 56.5dB, people have obvious vibration feeling, comfort decreases obviously; when the driving speed can reach 60km / h, noise rise to68.4dB , people have stronger vibration feeling , they need to hold the car handle to be secured, not very comfortable; when the vehicle speed is up to 80km / h, the car has the obvious noise, vibration, people must hold the car handle, the driver need to grip the steering wheel, or the direction will have deflection. When the speed is up to100km / h, people can feel the direction of the car of apparent instability, general driver will be very difficult to grasp the steering wheel, there is a

big hidden driving safety trouble, people should be very careful.

The main source of the block pavement traffic noise is vehicle vibration, due to more road surface seam , the vehicle (especially high speed driving)has significant vibration, thus makes noise increase. Having a good control of the seam width and pavement smoothness, can greatly reduce the vibration in the driving process of the vehicle, thereby reducing noise. Recent foreign studies have revealed that, with large interstices permeable brick can significantly reduce the noise in driving on precast block pavement.

Block pavement noise in driving and the driving speed relationship is shown in figure 9, will comfort was numerical, if good, general, poor, very poor, very very poor were given comfort score:80,70,50,30,10, we can get the prefabricated block pavement ride comfort and driving speed relationship, see figure 10.

Fig 9 the relationship between traffic noise and speed Fig 10 the relationship between driving comfort and speed

From Figure 9 and figure 10 shows that, with the increase of vehicle speed, traffic noise was significantly increased, driving comfort dramatically deteriorated. Especially when the vehicle speed exceeds 60km / h, the traffic noise and comfort are difficult to accept, and there is a certain security risk. Therefore, when on the precast block road, the speed should not exceed 60km / h, the results the research group get and the results obtained in front is consistent.

5 Problems And Suggestions

From the test road paving process, expose the issue of the following sides, which should be paid attention in the next block pavement constructiont:

(1) block must be designed in accordance with the size requirement of prefabricated, otherwise it will cause great influence to construction quality, especially the joint width is difficult to control. Secondly, block in the process of handling should be paid attention of light-light, avoid knocking off angles.

(2) prefabricated block pavement roughness has a very big impact on bedding sand thickness and final block pavement roughness. Because the smoothness of

base is not good, then cause the uneven thickness of sand, then influence the pavement smoothness.

(3) using backward paving method during the construction, construction personnel should stampede on the completed construction of the sand cushion, so it will impact the flatness and thickness of the sand cushion, when serious it can make void at the bottom of the precast block, not well contact with the pad sand, has disadvantage on block stability. It is recommended that in precast construction using a forward paving method, namely the construction personnel stand on a good paved block pavement for construction, avoid the occurrence of the above.

(4) the original design scheme of test road drainage is a horizontal stone blind ditch, process of construction by single particle size gravel paving blind ditch, in the latter part of the process of rolling stone will produce bigger deformation, lead block sinking, it is difficult to guarantee the smoothness of asphalt pavement. Later all problems can be solved using porous concrete. In addition, the filter layer (such as labor cloth ) must be set between the porous concrete drainage layer and the layer of sand, otherwise, the sand is easy to drain into the drainage layer, clogging interstices, on one hand impact the road of drainage, on the other side will make bedding sand erosion, leading to block sinking.

(5) the original design of the test road caulking material is the fine sand, after the process of construction, using the pure fine sand, hard to make dense. Especially when the joint is wide and large, using fine sand filling is hard to make dense. After switching to cement and sand (1:4), adding20% cement, joints dense. From the test road using situation, using cement + fine sand (1:4) as a preformed block pavement joint sealing material is feasible, adding cement not only make the joints dense, also can reduce the juncture of water seepage and the loss of the joint sand.

Reference

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Author brief introduction:

1, Wang Huoming, male, birth date:1982 October,

Origin: Hubei Huanggang, degree:postgraduate, Title: engineer,

working unit: China Merchants Chongqing communications research and Design Institute Company Limited;

address: area of Chongqing City South Bank University Avenue 33, Chongqing communications research and design institute road,

zip code: 400067 Tel: 13594351997 email: wanghuoming@cmhk.com