# Study on the Effect of Vibrating Process on the Compactness of Slipform Concrete
## 1 Introduction  
Cement concrete is widely used in airport road surfaces because of its high strength, high stiffness, good integrity, and high economy [1; 2; 3]. As the volume of cement concrete roadway projects increases every year, the inefficiency and cost of manual construction also increase, causing the trend of intelligent roadway construction to become more evident. Roadway slipform concrete construction [4] is becoming an inevitable trend in the future [5]; however, the performance requirements of roadway slipform concrete are more stringent to match [6]. Vibrating is the key link to ensure the performance of concrete [7; 8]. However, the actual slipform concrete paving process mainly relies on the payers to set the vibrating parameters and paving speed according to their experience. The lack of scientific guidance can cause the concrete to be prone to under- or over-vibration. Therefore, improving the quality of slipform concrete paving is important. Scholars have concluded that freshly mixed concrete has a certain degree of stability under the combined effect of plastic viscosity and yield stress when lightly vibrated or left to stand. With the increase in vibration strength, the plastic viscosity contributes much more to its stability than the yield stress and has a critical role [9]. Scholars have also theoretically analyzed the interrelationship between shear rate and shear stress, and put forward the intrinsic theoretical equations of freshly mixed concrete [10]. Concrete is denser under the high-frequency vibration process, which reduces the defects on the surface of aggregate mortar, and has an improved effect on bending tensile strength and fatigue strength [11]. When the vibrating rod is working, the internal liquefaction region appears near the vibrating rod due to the shear effect, and liquefaction in the peripheral area is mainly due to the action of compressed waves propagating, which is defined as the radius of vibration action [9]. The greater the frequency or acceleration of vibration, the greaterthe radius of the corresponding vibration action, and the better the effect of liquefaction on concrete [12; 13; 14]. The vibration energy of the concrete in the forward direction of the vibrating rod will increase first and then decrease [15]. Based on the principle of concrete vibration densification, [PERSON] et al. observed the densification corresponding to the state of vibration by varying the admixture and sand rate of freshly mixed concrete and found that the vibration densification was higher as the admixture and sand rate increased [16]. [PERSON] proposed the Box-Test method to evaluate the workability of slipform concrete after high-frequency vibration [17]. For slipform concrete, its construction performance has a close relationship with the concrete mix ratio [18; 19; 20], but also with the vibration frequency, radius of action, and amplitude of the vibrating rod. This discovery has an important role in guiding the improvement of the smoothness of slipform concrete and the prevention of caving in the actual construction process [21]. Internal air bubbles will directly affect the concrete's compactness. After mixing an appropriate amount of air-entraining agent in slipform concrete, a large number of tiny bubbles can promote vibration liquefaction, reduce the resistance of paving construction, and improve its overall performance [22]. [PERSON] et al. analyzed the relationship between the frequency of vibration, vibration time, and bubble discharge through the test and concluded that the ideal vibration time of the vibrating rod is 25 s and the vibration spacing should not be greater than 160 mm [23]. The air content inside the concrete will be significantly reduced under high-frequency vibration, and proper vibration can improve the bubble structure of concrete, while over-vibration will lead to a bubble structure with a tendency to deteriorate [24].