Method for detecting compaction and shear strength characteristics of asphalt mixture during construction compaction

Abstract

The present invention discloses a method for detecting compaction and shear strength characteristics of an asphalt mixture during construction compaction. The method mainly includes the following steps: using a device for detecting compaction and shear strength characteristics of the asphalt mixture; pressing a test claw into the asphalt mixture during construction; rotating the test claw slowly and uniformly to measure an internal temperature and a shear characteristic of the mixture during paving and subsequent compaction; calculating a corresponding compaction detection index based on the shear characteristic; and monitoring and guiding the construction quality and construction process accordingly based on the real-time detection index. The present invention measures the compaction detection index of the asphalt mixture during compaction simply, quickly and accurately. The present invention uses the compaction detection index together with a degree of compaction for dual control of asphalt pavement compaction.

Claims

1. A method for detecting compaction and shear strength characteristics of an asphalt mixture during construction compaction, comprising the following steps: step 1: the asphalt mixture is paved on site; after the asphalt mixture is compacted by a compactor, a detection device is moved to a selected detection point; step 2: a claw-shaped blade on an output end of a test claw is pressed into the asphalt mixture with a certain degree of compaction through a lift switch; step 3: a power switch of an electric motor is turned on; the electric motor drives the test claw to rotate slowly and uniformly; a temperature T (° C.) and a torque M (N.Math.m) on a display are recorded; step 4: the torque M obtained in step 3 is used to calculate a shear strength and a shear stiffness of the asphalt mixture: $F=G\gamma =\frac{M\rho }{I_p}G=\frac{F}{\gamma }=\frac{M\rho }{\gamma I_p}$ wherein, F is the shear strength, G is the shear stiffness, γ is a shear strain, ρ is a radius, and I.sub.p is a polar moment of inertia; and step 5: the shear strength and the shear stiffness obtained in step 4 are used to calculate a compaction detection index K/K.sub.min of the asphalt mixture, wherein K is defined as an inverse of the shear stiffness, $K=\frac{1}{G},$ and K.sub.min is a minimum value of K of the asphalt mixture under a corresponding degree of compaction.

2. The method for detecting compaction and shear strength characteristics of an asphalt mixture during construction compaction according to claim 1, wherein in step 3, the rotation speed is 5°/min to 10°/min.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a structural diagram of a detection device for a method for detecting compaction and shear strength characteristics of an asphalt mixture during construction compaction according to the present invention.

(2) FIG. 2 is a structural diagram of a test claw.

(3) FIG. 3 is a diagram showing the use of a device for detecting compaction and shear strength characteristics of an asphalt mixture on a construction site.

(4) Reference numerals: 1. fixed frame; 2. display; 3. control panel; 31. power switch; 32. speed regulator; 4. test claw; 5. electric motor; 6. lift switch; 7. torque sensor; 8. temperature sensor; 9. claw blade; and 10. universal wheel.

DETAILED DESCRIPTION

(5) To make the technical means, creative features, purpose of use and effects of the present invention comprehensible, the present invention is further described blow with reference to the specific implementations.

(6) Referring to FIG. 1 and FIG. 2, the present invention provides a device for detecting compaction and shear strength characteristics of an asphalt mixture during construction compaction. The device includes a fixed frame 1 and a detection system. A universal wheel 10 is arranged at the bottom of the fixed frame 1 to facilitate a free movement for on-site construction detection. The detection system includes a display 2, a control panel 3, a test claw 4, an electric motor 5 for driving the test claw 4 to rotate, a lift switch 6 for controlling a vertical movement of the test claw 4, a torque sensor 7 and a temperature sensor 8. The control panel 3 includes a power switch 31 for controlling the electric motor 5 and a speed regulator 32 for controlling a rotation speed of the test claw 4. An output end of the electric motor 5 is connected to an input end of the torque sensor 7, and an output end of the torque sensor 7 is connected to an input end of the test claw 4. An output end of the test claw 4 is provided with a claw-shaped blade 9. There are 6 claws of the claw-shaped blade 9. The bottom of the claw-shaped blade is a conical tip, which is convenient for pressing into the asphalt mixture with a certain degree of compaction. The claw-shaped blade is provided therein with the temperature sensor 8.

(7) As shown in FIG. 3, a specific process is as follows:

(8) step 1: surface, intermediate and base courses of the asphalt mixture are paved separately on site; after the base course is compacted by a compactor, the detection device is moved to a selected detection point, and the universal wheel is fixed;

(9) step 2: the claw-shaped blade on the output end of the test claw is pressed into the asphalt mixture with a certain degree of compaction through a lift switch;

(10) step 3: the power switch of the electric motor is turned on; the electric motor drives a stirring shaft to rotate slowly and uniformly with a speed freely selected between 5°/min and 10°/min; a temperature T (° C.) and a torque M (N.Math.m) on the display are recorded;

(11) step 4: the torque M obtained in step 3 is used to calculate a shear strength and a shear stiffness of the asphalt mixture:

(12) $F=G\gamma =\frac{M\rho }{I_p}G=\frac{F}{\gamma }=\frac{M\rho }{\gamma I_p}$

(13) where, F is the shear strength, G is the shear stiffness, γ is a shear strain, ρ is a radius, and I.sub.p is a polar moment of inertia; and

(14) step 5: the shear strength and the shear stiffness obtained in step 4 are used to calculate a compaction detection index K/K.sub.min of the asphalt mixture, where K is defined as an inverse of the shear stiffness,

(15) $K=\frac{1}{G},$
and K.sub.min is a minimum value of K when the asphalt mixture is correspondingly compacted; the compaction detection index K/K.sub.min obtained in real time is compared with a standard interval of K/K.sub.min in Standard Table 1 to determine the compaction status of the asphalt mixture, so as to adjust and control the construction process and construction quality in time; when a value of K/K.sub.min is greater than a right end value of the standard interval, a section is under-compacted and supplementary compaction construction should be implemented in time; when the value of K/K.sub.min is smaller than a left end value of the standard interval, the section is over-compacted, and a remedial measure for over-compaction should be taken in time; when the value of K/K.sub.min is within the range of the standard interval, the compaction of the base course is completed and steps 1-5 may be repeated to construct the intermediate and surface courses.

(16) The corresponding values of the compaction detection index K/K.sub.min and the degree of compaction in Table 1 are standard values obtained by using the detection device and method of the present invention to repeatedly test the design asphalt mixture (AC-13C asphalt mixture herein) and acquire and calibrate the data in a design stage. It should be noted that the values in the standard table may vary with different design asphalt mixtures in actual engineering, but the detection device and method used are essentially unchanged. The degree of compaction is a ratio of a density of the asphalt mixture to a maximum theoretical density thereof. For a test method, refer to JTG F40-2017 “Technical Specifications for Construction of Highway Asphalt Pavement”.

(17) TABLE-US-00001 TABLE 1 Standard table of compaction detection index K/K.sub.min and degree of compaction for dual control Degree of compaction 0.8 0.82 0.84 0.86 0.88 0.9 0.92 0.94 0.96 0.98 K/K.sub.min Left end 0.8 0.82 0.84 0.85 0.86 0.87 0.88 0.88 0.9 0.9 value Right end 2.2 2.0 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.2 value

Embodiment 1

(18) In this embodiment, for example, an AC-13C asphalt mixture in a surface course is under a post-paving state. Three compactors are used to compact a section with a compaction method as shown in Table 2.

(19) TABLE-US-00002 TABLE 2 Compaction method of section Compaction Primary Secondary Final step compaction compaction compaction Type of Steel drum Vibratory Steel drum compactor compactor compactor compactor Compaction speed 3 4 5 (km/h) Compaction times 2 2 3

(20) A compactor follows a paver to perform primary compaction. After static compaction by a steel drum compactor, a nuclear-free density gage is used to measure a degree of compaction of the asphalt mixture. Compaction and shear strength characteristics detection device is used to measure a real-time compaction detection index K/K.sub.min and an internal temperature T of the mixture. An electric motor drives a stirring shaft to rotate slowly and uniformly. A rotation speed is freely selected from 5°/min to 10°/min. The detection indexes of the compaction status are shown in Table 3.

(21) TABLE-US-00003 TABLE 3 Detection indexes of primary compaction status of section Internal temperature Degree of Stake No. of mixture °/C. compaction /% K/K.sub.min K2 + 060 127.1 82 1.96 K2 + 080 129.9 86 1.24 K2 + 100 126.2 84 1.27

(22) The purpose of the primary compaction is to level and stabilize the mixture, while creating a condition for secondary compaction. After the primary compaction is completed, the degree of compaction of the mixture reaches more than 80%, and the primary compaction temperature is maintained at 110-130° C., which is a normal construction temperature. The degree of compaction and the compaction and shear strength characteristics index K/K.sub.min are compared with a standard value in Table 1. The degree of compaction is greater than a design degree of compaction (80%), and the compaction detection index K/K.sub.min of the asphalt mixture in each section is in the range of a standard interval. The degree of compaction and the compaction detection index both are acceptable, indicating that the primary compaction of the mixture is in good status and a next stage of construction may be implemented.

(23) The secondary compaction follows the primary compaction. The secondary compaction is a key step for the compaction, stabilization and formation of the mixture. After the secondary compaction is completed with a vibratory compactor, the compaction performance of the asphalt mixture is detected the same as that in the primary compaction step. The detection indexes of the compaction status are shown in Table 4.

(24) TABLE-US-00004 TABLE 4 Detection indexes of secondary compaction status of section Internal temperature Degree of Stake No. of mixture °/C. compaction /% K/K.sub.min K2 + 060 108.2 97 1.02 K2 + 080 110.6 95 1.24 K2 + 100 90.4 86 1.84

(25) For section K2+060, the internal temperature of the mixture is 108.2° C.; the degree of compaction and the compaction and shear strength characteristics index of the mixture are consistent with those in Table 1. This indicates that the compaction of the mixture is in good status and a next stage of construction may be implemented.

(26) For section K2+080, the temperature of the mixture is 110.6° C. The degree of compaction under this temperature meets a design requirement. The detection index K/K.sub.min of the mixture is 1.24, which is greater than a normal value of 1.20 under a corresponding degree of compaction (95%). This indicates that the internal mechanical property of the mixture is not up to standard, and the compaction of the mixture is unqualified. The following methods may be used to improve the mechanical property of the mixture:

(27) 1. replace the vibratory compactor with a tire compactor to knead the mixture to reduce the friction between particles and allow a small particle to enter a gap between large particles; and

(28) 2. slow down the compaction of the vibratory compactor and increase the contact time between the compactor and the mixture; or adopt a high-frequency large-amplitude method to generate a large excitation force.

(29) For section K2+100, the degree of compaction after the secondary compaction is too small. The detection index K/K.sub.min of the mixture is 1.84, which is greater than a normal value of 1.70 under a corresponding degree of compaction (86%), indicating that the compaction of the section is not qualified. The internal temperature of the mixture is 90.4° C., which is lower than a normal secondary compaction temperature (95-115° C.). Therefore, remedial construction cannot be performed. In this case, if compaction is continued, it will cause insufficient compaction of the section, and it will easily cause problems such as rutting and peeling in long-term use. Therefore, it is recommended that the section be scrapped and repaved.