Preliminary Study on Assessing Delaminated Cracks in Cement Asphalt Mortar Layer of High-Speed Rail Track Using Traditional and Normalized Impact–Echo Methods

The severe deterioration of a cement asphalt (CA) mortar layer may lead to the movement of the upper concrete slab and impair the safety of the speedy train. In this study, a test specimen simulating the structure of high-speed rail track slabs was embedded with delaminated cracks in various lateral sizes inside the CA mortar layer. Impact–echo tests (IE) were performed above the flawed and flawless locations. In present study, the IE method is chosen to assess defects in the CA mortar layer. Both traditional IE and normalized IE are used for data interpolation. The normalized IE are the simulated transfer function of the original IE response. The peak amplitudes in the normalized amplitude spectrum and the peak frequency in the traditional amplitude spectrum for the top concrete overlay were used to develop simple indicators for identifying the integrity of the CA mortar layer. The index was based on the difference of the experimental peak amplitude and frequency of the ones calculated from previously developed formulas for plates without substrates. As a result, the technique does not require an experimental baseline for the crack assessment. A field test and analysis procedure for evaluating high-speed rail slab systems are proposed.

Effects of Temperature on Fluidity and Early Expansion Characteristics of Cement Asphalt Mortar

In order to solve the problems of the sudden loss of fluidity and low expansion rate of CAM I (cement asphalt mortar type I) in a construction site with high environmental temperature, this paper studies the effect of temperature on the fluidity, expansion ratio and pH value of CAM I. The mechanism of action was analyzed by IR (infrared spectrometry), SEM (scanning electron microscopy) and other test methods. The results showed that a high temperature accelerates aluminate formation in cement paste. Aluminate adsorbs emulsifiers leading to demulsification of emulsified asphalt, and wrapped on the surface of cement particles, this causes CAM I to lose its fluidity rapidly. The aluminum powder gasification reaction is inhibited, resulting in an abnormal change in the expansion ratio. Based on findings, the application of an appropriate amount of superplasticizers can effectively improve the workability and expansion characteristics of CAM I at a high temperature.

Temperature Sensitivity of Mechanical Properties of Cement Asphalt Mortar with Nanoparticles

Cement asphalt mortar (CAM) in high-speed lines is subjected to varying environmental conditions, which lead to the deterioration of CAM. The nanoparticles of nano-SiO2 and nano-TiO2 are added to improve the performance of CAM, and the temperature sensitivity of CAM with nanoparticles is primarily studied in this paper. The flexural strength and compressive strength of CAM with and without nano-SiO2 and nano-TiO2 were measured and compared to study the effect of nanoparticles on the performance of CAM subjected to different temperatures. Temperature sensitivity factors of flexural and compressive strength based on Arrhenius model were proposed to evaluate the temperature dependence of CAM by nanoparticles. Furthermore, the microstructure of hardened CAM was studied using scan electronic microscope (SEM) to investigate the mechanism of temperature sensitivity of CAM with and without nanoparticles. The results indicated that the flexural and compressive strength of CAM with and without nanoparticles decreased with the increasing temperature; however, the decreasing rate of strength with temperature was different in CAM with and without nanoparticles. The reduction in the decreasing rate of strength was obtained by using nano-SiO2 rather than nano-TiO2 in CAM. Based on the SEM results, the free asphalt was seen to be greatly reduced in the CAM with nano-SiO2, suggesting a positive effect of nano-SiO2 on the mitigation of temperature sensitivity of CAM.