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ABSTRACT The precast structures prepared by steam-cured concrete have been increasingly used in order to speed up the construction of China's High-Speed Rail and passenger dedicated lines in recent years. [...]

ABSTRACT As one of the core components, high quality self-compacting concrete filling layer is of great importance to the long-term safe service of CRTS III type slab ballastless track. The [...]

ABSTRACT Steam curing is commonly used to produce the prefabricated elements to meet the requirement of the high early strength. However, this curing regime was proved to lead to the [...]

ABSTRACT Magnesium phosphate cement (MPC) was proved to be a cementitious material for preparing porous materials with high early-stage strength under standard curing condition. However, the poor water resistance of [...]

ABSTRACT The main goal of our work was to study mechanism of interfacial adhesion between basalt fiber and asphalt. Solution of silane coupling agent (2.5 wt%, KH-550) was used to [...]

ABSTRACT The earth-based construction with unique advantages in raw material origin, energy conservation and environment protection has attracted growing attention recently. In South China, raw soils which have been used [...]

ABSTRACT The influence of mineral admixtures and curing conditions on the permeability of concrete with high volume mineral admixtures is investigated. Fly ash and ground granulated blast furnace slag (GGBFS) [...]

ABSTRACT The earth-based construction with unique advantages of wide raw material origin, energy conservation and environment protection has attracted growing attention recently. Although the mechanical properties can be improved by [...]

ABSTRACT Bugholes are surface voids that result from the migration of entrapped air to the fresh concrete-formwork interface. The influencing factors, such as mix proportions and construction technology, on surface [...]

ABSTRACT Based on the relations between slump flow (SF), coarse aggregate average diameter ([d.sub.av,i]) and volume of coarse aggregate ([V.sub.g,i]) used in self-compacting concrete (SCC), it was found that the [...]

ABSTRACT In order to mitigate the thermal damage of steam curing process at elevated temperature on microstructure of concrete and thus prepare high quality steam-cured concrete, the effects of type [...]

ABSTRACT Rheological behaviors are the essential workability characteristics of fresh concrete. Generally speaking, paste volume in self-compacting concrete (SCC) are no less than 340 L/[m.sup.3]. Therefore, rheology of paste could [...]

ABSTRACT Sealed-space-filling self-compacting concrete (SSFSCC) is used in China Rail Track System (CRTS) III ballastless slab track of high-speed rail, which has been originally developed in China recently. In this [...]

ABSTRACT The present paper focuses on understanding the relationship between the mixing proportion parameters of self-compacting concrete (SCC) and its environmental impact and thus developing more greener SCC. Three simple [...]

ABSTRACT In order to find a new test method to investigate the relationship between the compositions and fluidity of the cement and emulsified asphalt mortar (CA mortar), the conductivity and [...]

Addressing the scarcity of research on the residual expansion deformation of steam-cured concrete and its underlying factors, this study introduces a testing apparatus to characterize the internal stress in fresh concrete during the thermal treatment. It explores the impact of water-to-cement ratio (w/c) and paste-to-aggregate ratio (p/a) on internal stress and elucidates the developmental patterns of internal stress in concrete throughout the thermal treatment phase. The key findings are as follows: (i) During the thermal treatment, the internal stress in concrete under constraint is predominantly compressive, exhibiting a rapid increase in the heating stage, followed by a gradual decline in the constant temperature treatment stage, and a continued decrease with a decelerating trend during the cooling stage. (ii) Both w/cand p/csignificantly influence internal stress in concrete, and this stress can be enhanced by reducing the initial free water content and augmenting the initial structural strength of the concrete. This paper serves as a valuable foundation and reference for further investigations into the residual expansion deformation of steam-cured concrete.

Filling layer self-compacting concrete (FLSCC) is a key construction material in China Rail Track System (CRTS) III slab ballastless track and its resistance to impact loading is of great importance to the service security of high-speed train. In this paper, the dynamic mechanical characteristics of FLSCC under impact loading were investigated with a split Hopkinson pressure bar (SHPB) at strain rates ranging from 101s−1to 102s−1. Results show that the compressive strength, peak strain, elastic modulus and toughness ratio of FLSCC all increase with strain rate. The increase factors of compressive strength (DIFc) and strain (DIFɛ) of FLSCC increase linearly with decimal logarithm of strain rate. The elastic modulus (Ed) and toughness ratio (TR) increase linearly with strain rate. Self-compacting concrete (SCC) shows greater strain rate effect than normal concrete (NC). However, FLSCC presents lower strain rate effect but better toughness performance than normal SCC. The incorporation of large content of SP and VMA provides FLSCC with higher porosity, which makes it possess excellent dynamic mechanical performance.

The electrical resistivity is an important property for the structure concrete of metro track. In this work, the effect of dynamic flexural load on the electrical resistivity of concrete was investigated. Results show that the electrical resistivity of concrete first rapidly decreased and then slowly decreased with loading cycles; The higher the stress level and loading frequency, the greater the attenuation of concrete resistivity, the maximum value reached 33%. Acoustic emission test showed that the electrical resistivity is related to the damage of concrete. According to the theory of concrete fatigue damage, a new model was proposed to characterize the relationship between the dynamic damage of concrete and the electrical resistivity, R2> 0.98. This work provides insight into development of the theory of electrical conductivity in concrete, and novel strategy for the dynamic damage monitoring of concrete.

•Premature deterioration mechanism of steam-cured concrete track slab was investigated.•Steam-cured heat damage (SCHD) makes track slab concrete surface layer loose, porous and more micro cracks.•3.Long-time dynamic load and moist environment acting on track slab enlarges micro cracks and results in water penetration into concrete easily.•Ingression of water into concrete causes the formation of alkali-silica gel and delayed ettringite.

In the tunnels of the Cheng-Kun Railway in China, concrete failure can usually be observed from the effect of sulfates. A field investigation was conducted to analyze the concrete damage mechanism by means of XRD, IC, AAS and EPMA. The results showed that (1) large amounts of Na2SO4were generated on the surface layer of the concrete lining, causing concrete detachment layer by layer; (2) the concrete lining in contact with air had been neutralized to more than 50mm in depth, and the cement hydration products had been converted into CaCO3; (3) ettringite and gypsum, the products of chemical sulfate attack, were also detected in the neutralized concrete lining. This analysis of a field case concluded that Na2SO4crystallization caused the detachment of the surface layer of the concrete lining, and the chemical sulfate attack occurred in the inner part of the concrete lining.

CA mortar, as a filling layer, has been widely used in slab ballastless track. Since the creep deformation directly determines the track regularity and the train ride comfort, we investigated the effect of various stress levels on CA mortar creep. Results showed that the creep strain of CA mortar increased by 10 times when the stress level increased from 10%σpto 40%σp. Furthermore, it was first discovered that creep of CA mortar was attributed to the organic–inorganic interface slip and the propagation of microcracks. This work proposed a new CA mortar creep model based on the micro-meso structure characteristics, and its accuracy of prediction was much higher than previous models, R2> 0.93.

The dynamic mechanical property of concrete is one of the key parameters, which greatly influences durability of infrastructures subjected to continuous heavy loading, such as girder and track slab of high-speed railway foundation structure. This paper reports serials of experiments designed to investigate the deterioration of dynamic mechanical properties of different concretes under fatigue loading condition. Four parameters including relative dynamic elastic modulus (RDEM), relative dynamic shear modulus (RDSM), relative compressive strength (RCS) and water absorption (WA) of concrete were evaluated to assess the dynamic properties and microstructures of concretes. Results show that the fatigue stress levels and fatigue cycle durations significantly influence the dynamic mechanical properties of concrete including dynamic elastic modulus and dynamic shear modulus. Addition of proper mineral admixture can improve the dynamic mechanical characteristics of concrete and increase its resistance against the fatigue loading effect. Keeping the amount of mineral admixture in concrete constant, its dynamic mechanical property with fly ash is lower than that with fly ash and silica fume. The water absorption in concrete, which is an indirect parameter reflecting capillary porosity, increases evidently after bearing fatigue-loading. There is a close correlation between the deterioration of dynamic mechanical property and the increasing of water absorption of concrete. This indicates that the damage of microstructure of concrete subjected to fatigue loading is the indispensable reason for the decay of its dynamic mechanical performance.

Steam-cured concrete is widely used to manufacture prefabricated units of high-speed railway foundation structure such as girder and track slab. The dynamic mechanical property of steam-cured concrete is one of the key properties affecting service performance of high-speed railway foundation structure. In the present paper, serial macro/micro-experiments were carried out to investigate the dynamic elastic modulus, shear modulus, damping ratio, and microstructure of steam-cured concrete. The relationships between compositions, curing regime, microstructure, and dynamic properties of steam-cured concrete as well as the corresponding mechanisms were discussed. The results indicate that steam-cured concrete in early age has a larger dynamic elastic modulus and shear modulus as well as a smaller damping ratio compared with standard-cured concrete. On the contrary, at a later age a slightly smaller dynamic elastic modulus and a larger damping ratio of steam-cured concrete are observed. Addition of mineral admixture results in a bit lower dynamic elastic modulus and damping ratio of concrete than that of the control specimen without mineral admixtures. The achievements can provide some fundamental suggestions for materials parameters selection during structural design of steam-cured concrete precast element.

To clarify the volume deformation characteristics and residual expansion deformation formation mechanism of steam-cured concrete, the content of free water and air of fresh concrete before heating, and the hydration kinetics and mechanical characteristics evolution of concrete during the steam curing process were obtained by experiment and fitting. The residual expansion strain calculation model of steam-cured concrete was proposed and its accuracy was verified by a non-contact test. Results showed that: (i) the volume deformation characteristics of steam-cured concrete could be divided into two stages: rapid expansion in heating stage, then rapid shrinkage in constant temperature treating period and gentle shrinkage in cooling period; besides, an irrecoverable residual deformation was gained at the end of cooling period; (ii) the tested peak value of residual expansion strain of steam-cured concrete appeared at 0.5–1 h later than the fitting value, and the final tested residual expansion strain is lower than the fitting value; (iii) the higher the initial free water content and the lower the initial structural strength, the greater the final residual expansion deformation of steam-cured concrete. This paper aims to reveal the mechanism of residual expansion deformation and propose a method of restraining the deformation of high-speed railway steam-cured concrete. This paper could provide technical support for the production of steam-cured concrete prefabricated components and predict the residual expansion deformation.

Steam-cured concrete with high early strength has been widely applied in high-speed railway. However, heat damage caused by the steam curing process brings adverse effects on the pore structure and durability of steam-cured concrete. It has been found that phase change materials (PCMs) help improve the durability of cement-based materials. Therefore, the influences of two PCMs on the strength, water absorption, and microstructure of steam-cured mortar are discussed in this study. Two PCMs used include pure paraffin and a composite phase change material composed of porous diatomite and paraffin (D/P). The results show that the addition of appropriate PCMs does not significantly reduce the strength of steam-cured mortar. The addition of a small amount of PCMs shows little influence on the pore structure of steam-cured mortar but effective in improving the water-penetration resistance. This is partially attributed to the improvement of hydrophobic characteristics in the pores, resulting from the adhesion of hydrophobic PCMs on the pores during the steam curing. Compared with specimens containing pure paraffin, the pore structure of specimens containing D/P is refined, resulting in higher compressive strength. This may be due to the uniform distribution of small particles D/P in the specimen and the pozzolanic reaction of diatomite in D/P. The use of suitable phase change materials will be helpful to improve the durability of steam-cured concrete.