| Semi-rigid bases possess many advantages such as high strength,good integrity,and low cost.Semi-rigid bases are used in the vast majority of high-grade asphalt pavements in China.Roads usually experience overload,and road damage gradually deteriorates and affects the normal operation of roads.At present,road damage is usually to be detected by ground penetrating radar(GPR).The GPR can easily detect voids of road bases which are large size of damage,but very difficultly detect slight damage of road bases.In general,the damage is affected adversely by the moisture condition of road bases.If the moisture condition can be detected,the damage of road bases can be evaluated.The damage of materials can be detected by acoustic emission in advantage,which is passive nondestructive examination.Accordingly,the acoustic emission technology is used in our study on the moisture condition of semi-rigid bases.1.In order to find the acoustic emission criterion of uniaxial compressive failure process of Semi rigid base of dense skeleton type,the acoustic emission(AE)test of semi-rigid base specimens subjected to uniaxial compression was carried out by TYE mechanical testing machine and acoustic emission system.AE counts,cumulative energy of AE signal waveform data and the b-value of AE amplitude analysis was discussed in detail in this paper.The results indicated that the AE parameters can reflect the failure process of Semi rigid base of dense skeleton type.AE results have shown three distinct stages of AE activity.The failure process mainly experienced three stages that was divided by AE parameters into initial stage of development(early period of loading),stable growth stage(middle period of loading),unstable stage(end period of compression).The knees of curve of AE parameters are 25% and 85% of ultimate load.The variation of the b-value,which changes systematically with the different stages of failure process,can not only indicate the stress of specimens but also be precursors to failure of specimens.In general terms,if the b-value is greater than 3.5,the specimens are indicated to be in the initial stage of development.And when the b-value keeps be stable value between 1 to 2,it is indicated to be in the stable growth stage.If the b-value seems to fluctuate and increase,it is indicated to be in unstable stage.The AE parameters,which be saved by different test methods of position offering for layout of sensors,have shown that the test methods of sensors disposed at the waist of specimens are more optimized.2.Water stayed in semi-rigid base is a primary role that causes road diseases.It is important to detect moisture content of road basic layer for assessing level of road diseases.The main detection method for moisture content of road basic layer is oven drying that have to drilling core sample in the road,which will damage roads.Acoustic emission(AE)detection is a typical non-destructive method.AE testing of semi-rigid base specimens,who included three types of moisture,subjected to bend was performed by a mechanical testing machine and AE system to find the AE criterion of moisture content in semi-rigid bases.Results indicated that velocity of AE wave,which propagated in semi-rigid bases samples cured for ninth days in a curing box,was approximately 1650 m/s,and unsuitable moisture affected AE wave velocity of semi-rigid bases.Attenuation of AE signal in semi-rigid bases increased with moisture content increased.Cumulative AE energy generated by broken specimens decreased with moisture content of semi-rigid bases increased.Cracking stress reduced because of high or low moisture content.The frequency bands of AE signal generated by specimens during the cracking stage were at 8-40 kHz and 80-120 kHz,and low-frequency component decreased with unsuitable moisture content.3.Investigation on the effect of water on the specimens,which is a sort of semi-rigid base with different moisture content,is performed by applying acoustic emission(AE).The theories of AE rate and crack classification by AE have been introduced into the AE test of the semi-rigid base.The AE signals are analyzed by utilizing the AE rate theory,and the result proposes that the moisture content could be deemed as a type of damage and should be considered as an evaluating indicator in the damage detection of the semi-rigid base.But the AE rate theory is not suitable for the dried semi-rigid base in the damage detection.Meanwhile,by utilizing the theory of crack classification,the mechanization that how water affect the compressive performance of the semi-rigid base is analyzed.The results reveal that the water weakens the cement strength of the semi-rigid base by the softening,and moreover,the friction among the aggregate by the lubrication;the effect of the lubrication is more notable than the softening. |
PDF Full Text Request