# Maintenance and repair of motorways Chapter 3 Investigation and assessment of road surface condition - 2

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 Experimental methods: 2.1. Experimental methods to evaluate pavement texture 2.1.1. Method ʺSandingʺ according to TCVN 8866-2011:  Roughness of road surface at each test location (hi), in millimeters, to the nearest 2 decimal places, according to the following formula: 40  V hi    d 2  The roughness of the pavement is considered to be uniform, calculated by the following formula: n hi Htb = i 1 n Advantages: Simple, uncomplicated equipment Cons: Low productivity, The results depend on the operator's manipulation, which is difficult to do on less rough pavement.

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2.1.2. MTM (Mini Texture Meter) Surface Removal Device:  Sample laser beam is projected on the face to prevent the multi-beams received from the surface. i-sensitivity, on the scale has been determined to be about a small distance from one side to a calculated "control" of the road. such a wide range of products.  The MTM ® is tested by hand by a mini device with a laser power of about 500Hz ®Tested by the computer This machine gives us an average value of flaking. 10 m moving distance with small average child support for a total of 50m ®· is perfected.  To correct the maximum number of MTMs with the least amount of time compared to the “Rough cut” experiment. Furthermore, the MTM has been extensively tested for the use of thunderstorms.

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2.2. Experiment to determine adhesion coefficient: 2.2.1. Method of measuring braking distance:  When the wheel is fully braked, measure and determine the speed V1 and V2 at 2 points where the wheel slips, measure the distance x and use the principle of conservation of work. h2 factor 2 the average frictional resistance fd over that distance can be determined. fd  V1 V2 2 g . x  This measurement method has the disadvantage that when measuring it affects traffic on the road and is not safe. 2.2.2. Traction trailer wheel braking method:  A trailer fitted with a standard wheel is towed by a trailer; run the trailer at a certain speed and brake the trailer wheels, and then measure the force Fb required to move the trailer when its wheels are fully engaged. Divide Fb by the load h.Effective on the wheel P will find the coefficient of friction coefficient fb: fb b P

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2.2.3. Method of using trailers with skewed wheels:  Trailers fitted with two experimental wheels. The ground of the tire is off at an angle. Water injection is in the air. = 7.50 ~ 200 relative to the vehicle's direction of motion. When the vehicle is moving forward, the test wheel will follow the vehicle to slide forward, on the wheel will be applied a lateral force FL. For a variable displacement angle, different lateral forces will be measured and a maximum lateral force value will be obtained. Coefficient of frictional resistanceFc in the lateral direction fL: fL  LP 15 PP This measurement does not require wheel brakes, when measured does not affect traffic on the road, and can be measured continuously, the speed is quite fast. Glue filter

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2.2.4. Method “British pendulum tester”:  A pendulum with mass P = 1500  30 g, the bottom surface is fitted with a standard rubber slide (6.35 x 25.4 x size). 76.2 mm) falls from a specified height H = 411  5 mm and slides on a wet road surface with a constant slide length L = 125  2 mm, after which the pendulum will swing up to a height H. G Depending on the different surface roughness, the energy loss of the pendulum A is also different, leading to a change in the height Q of the splash h. A measuring needle is attached to determine the swing height h of the pendulum. The reading of the gauge needle on the graduation table is denoted by the SRT (Skid Resistance Tester) index. The test is to determine the sliding resistance corresponding to the condition of the vehicle driving M on a wet road with a speed of 50 Km/

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2.3. Intemational Friction Index (IFI). IFI is the standard measure in testing and assessing the quality of pavement slip resistance. IFI is a composite coefficient related to pavement roughness structure, pavement slip resistance and test speed. IFI allows to adjust the slip resistance measurement by different devices to the same general index. The IFI(F60, Sp) index consists of 2 components: + F60: Friction Number - Friction Number is the value of slip resistance of the wheel braking hard at a speed of 60 km/h. F60 = A + B FRSeS 60 + CTX + Sp: calculated from rough texture depthS P average macroscopic road surface: Sp (km/h) = a + b TX Quality assessment The amount of road surface through the IFI index is as follows: + Corresponding to each road level, there will be the required slip resistance value and the specific operating vehicle speed value, or in other words, have the required F60* and Sp* values, i.e. the required IFI* (F60*, Sp*) index. + Measure and determine the actual IFI value (F60, Sp) of the road segment. Compare the actual IFI (F60, Sp) and the required IFI* (F60*, Sp*) to assess the existing capacity of the IFI path and propose solutions if insufficient.

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Keeping the load at Benkenman's location in line with the requirement Transmitting from the province to Benkenman Named with FWD

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 Use Benkenman according to TCVN 8866-2011:

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3.4. Assessment of load carrying capacity of pavement structure 1.1. Preparation: - Measuring point. - Prepare to measure the ring. - Prepare the measuring vehicle. 1.2. Measuring the road surface circumference along the route: - Let the measuring vehicle enter the measuring position; installation boom; - The write stability loop takes the initial reading at the next displacement n0. - Drive the measuring vehicle forward until the rear axle of the measuring vehicle is at least 5m from the measuring point; When the circularity is stable, record the last reading at the next displacement nS. - Elasticity of the road surface at the measuring point: Li = n0 - ns The reason for the measurement point, the humidification conditions, the condition of the road surface at the measurement point must be recorded. Do not measure at too bad points. It is not recommended to measure laps at times when the pavement temperature is higher than 400C. Measure pavement temperature: approximately every 1 hour during lap measurement along the route. The measurement of the pavement temperature only requires actual

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1.3. Processing of roundness measurement results: To calculate the position before the ith test: L iTT = Kq. Km .Kt . Li Li - Elasticity of pavement measured at position i, mm. Kq - Load correction factor of the measured results according to the parameters of the rear axle of the car measured in terms of the results of the standard car rear axle. Km - Elasticity correction factor for the most unfavorable season of the year. KT - Elasticity correction factor at the measured temperature to the roundness at temperature tt. 1.4. Determine the characteristic elastic ring and the characteristic elastic modulus for each test track: Value of the characteristic elastic ring of each test track: L ˜T = LTB + K. LTB - Elasticity mean regression of the test segment, mm.  - Mean square deviation of the test segment. K - Guaranteed probability coefficient, taken depending on the road class. The characteristic elastic modulus of each test road segment: p .

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* Use rigid plate according to TCVN 8861-2011: See TC  FWD test (22TCN 335-06): 2.1. Content of the experiment: A load mass (Q) falls from a height (H) onto a pressure plate (D), through the shock absorber causing a definite impulse to act on the pavement. The deformation (circle) of the pavement at the center of the presser plate and at the positions at a specified distance from the plate will be recorded by the revolution sensor heads. Measured data such as: impulse acting on the road surface, pressure acting on the road surface, and the road surface roundness determine the strength of the pavement structure. The FWD device is installed on a trailer and is towed by a light truck during travel and measurement. The control of the measurement process and data collection is automated through specialized software.

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2.2. Main parts of measuring equipment: 2.2.1. Impulse generator: Q, H load block. Time of impact on the road surface (0.02 - 0.06 seconds). 2.2.2. Press plate: The plate transmits the effect of the load to the road surface with a diameter of 30cm. The pressing plate is made of alloy, the bottom of the plate is glued with a thin layer of rubber. There is a hole in the center of the press plate to place the sensor. 2.2.3. Ring measuring sensors: The usual number of ring probes is 7 probes, a minimum of 5 probes. There is a measuring probe placed at the center of the press plate, the other probes are at a distance from the center in the order: 30, 60, 90, 120, 150, 180 mm.). a2 D3 E ⎤ 2 P ⎟ M r When measuring the circularity to determine the elastic modulus of the roadbed, the distance r from the measuring sensor the loop adjacent to the last ring sensor to the center of the plate must satisfy the following conditions: r ≥ 0.7ae This distance r is empirical, taken from 0.9m to 1.2m. Hey

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2.2.4. Force sensor: The magnitude of the impulse depends not only on the weight of the falling ball, the height of the fall, but also on other factors (friction between the weight and the guide bar, the contact between slabs and pavement.). The load cell is capable of measuring the maximum value of impulse acting on the pavement at each drop of the load. 2.2.5. System for recording, storing and processing data: Data such as the magnitude of the load (impulse) applied, the pressure exerted on the pavement, the measured value of the pavement's roundness, etc., are obtained by the software. dedicated record to computer. Other supporting information such as air temperature, road surface temperature, distance between measurement locations, measurement position history are saved by software or recorded in a manual.

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2.3. Preparation: 2.3.1. About the measuring device: FWD dynamic measuring device: according to the attached user manual. Other laboratory instruments: thermometer, water or glycerin, hammer, chisel. Tools to ensure traffic safety: flags, signs, flashing lights. 2.3.2. Measuring point: Density of measuring points: Divide into homogeneous segments: Measure representative segment (500-1000m): measure 20 points. If it is not possible to divide homogeneous sections: - For projects making investment reports and management and exploitation of motorways: the measurement density is from 5 to 10 measuring points/1 km. - For investment projects (basic design and technical design): measure evenly throughout the route with a density of 20 measuring points/1km. Selecting the position of measuring points: the measuring points are usually arranged in the trail

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2.4. Measure the lap along the route: Drag the FWD device to the position to measure the lap. Equipment installation. Measure the roundness: - Step 1: bring the load block to the specified height and drop the falling load block on the press plate to transmit an impulse to the road surface. The head of the force sensor, the ring sensor will determine the impulse, the roundness of the road surface. Attention should be paid to adjusting the drop height or weight of the weight so that the impact force on the road surface is 40kN. - Step 2: repeat B.1. Compare the results of the ring measurement at the center of the pressure plate between the two measurements. If two lap measurements differ by less than 5% th?~ end of measurement. Use the measurement results in the 2nd time as a basis for calculation. - Step 3: if B.2 does not satisfy th?~, B.1 must be repeated until the roundness of two consecutive measurements does not differ by more than 5%. Use last measurement. - Step 4: if the measurement is repeated as steps 1 to 5 but still not successful, it is necessary to perform the following tasks: + Re-check the experimental equipment system; + Consider the contact status between the pressure plate, the ring gauges and the md; + Move the device to a new location 1~2m away from the old position and measure again.

Date published: 09/07/2022
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