Xie Youjun

Some factors affecting early compressive strength of steam-curing concrete with ultrafine fly ash

Abstract Hardening process and strength gaining rate of concrete under room temperature curing conditions are slow with respect to the production rate of concrete plants in response to demand. In order to reach a desired strength level for concrete in a short time, heat treatment is widely used. When fly ash is included in concrete and the raw materials were selected, the factors affecting early compressive strength are water–binder ratio, fly ash content, etc. In this context, heat-treatment parameters, which are commonly adopted by most plants in China, were determined, and some factors affecting early compressive strength of steam-curing ultrafine fly ash (UFA) concrete were studied. The experimental results indicated that the content of UFA and water–binder ratio are main factors influencing the early compressive strength; the other factors have influence, too. Concrete containing ultrafine fly ash composite (UFAC) and ground blast furnace slag (GBFS) can give a desired early compressive strength.

Basic scientific issues on dynamic performance evolution of the high-speed railway infrastructure and its service safety

The development of Chinese high-speed railway has entered the new stage of long-term safe and stable operations from the stage of large-scale constructions. How to scientifically maintain the large-scale operating lines, with the aim of holding a high operation quality of the high-speed railway characterized with a high safety, a high stability, and a high reliability during its long-term operation, is a key research task currently faced by China. Based on the summary and analysis of construction characteristics and operation environments of Chinese high-speed railway infrastructures, this paper proposes three key scientific issues on dynamic performance evolution of the high-speed railway infrastructure and its service safety. They include dynamic performance evolution of the critical materials and structures of the high-speed railway infrastructures subjected to repeated train and environment loads, the mapping relationship between the cumulative deformation of the high-speed railway infrastructures and the rail surface geometry, and the interaction and evolution mechanism between the infrastructure deteriorations and dynamic performances of the coupled high-speed train-infrastructure system. Then this paper reviews the current research status and the latest progress on the above three scientific issues, and points out the developing trends and the fundamental research works that need to be focused on and strengthened in the future.

Dynamic mechanical properties of CRTS II type CA mortar for high-speed railway based on SHPB test

Dynamic mechanical properties of CRTS II type cement and asphalt mortar (CA mortar) for high-speed railway was studied by split Hopkinson pressure bar (SHPB), and the corresponding dynamic constitutive model was established in present paper. The experimental results show that the peak strength of CA mortar increases gradually with the increasing of strain-rate. However, the increasing rate of peak strength of CA mortar deceases with the further increasing of strain-rate. The increasing rate of peak strength is 52.28% for the strain-rate ranging from 44.17 s-1 to 54.79 s-1 and 7.5% for the strain-rate from 54.79 s-1 up to 108.47 s-1, respectively. The dynamic Youngs modulus of CA mortar increases by 3~25 times of initial value in this investigated strain-rate. The larger the strain rate is, the more serious the cracking is when CA mortar specimen damaged. The specific energy absorption of CA mortar increases with the increase of strain rate. The fitting curves of the established dynamic constitutive model agree well the experimental curves.