The picture shows an HSR ballastless track concrete track bed slab constructed with high-performance concrete.
Concrete is the cornerstone for ensuring the century-long durability of HSRs, which are the major strategic projects in China. China's HSRs were built in very cold areas, plateaus, subtropical coastal areas and areas with strong wind, drought and large temperature difference. Under the action of high-speed train's high-frequency dynamic load and multiple environment factors, the traditional railway concrete is disadvantageous in short fatigue life, large shrinkage and creep, and poor durability, which is difficult to meet the HSR project's construction goal of "less maintenance and no repair". In order to ensure the safe service of HSRs, HSR concrete should have high performance characteristics of "stable dynamic mechanical properties", "maintained physical geometry" and "reliable long-term durability". After nearly 20 years of theoretical and technical innovation, the theory of high-performance concrete has been developed, which has removed the bottleneck of concrete preparation technology for new HSR structures, established a technical standard system for concrete quality assurance, and formed a complete technology of HSR high-performance concrete. Main innovations are as follows:
1. A new method for microstructure optimization design of HSR high-performance concrete has been proposed, and the theory of concrete high-performance has been developed. The deterioration mechanism of concrete performance under dynamic load – environmental effects was revealed, and "calculation model of synergistic effect of multi-component cementitious system", "calculation model of slurry-aggregate interface structural parameters considering aggregate morphology characteristics" and "calculation model of cement stone micro-defect self-healing effect evaluation" were established. A microstructure optimization design method of high-performance concrete based on slurry compactness, interface transition zone strengthening and micro-defect self-healing was proposed, which lays a theoretical foundation for regulating dynamic mechanical properties, physical geometry and long-term durability of HSR concrete under service conditions.
2. New technologies for regulating the performance of HSR concrete and a series of high-performance concrete matching the new HSR structures have been developed. A new method to regulate and control the strength development of high performance concrete by applying the cement stepped hydration mechanism has been proposed, and the high-early-strength anti-fatigue concrete for track slabs/sleepers has been developed (anti-fatigue more than 4 million times), which solved the problem that the anti-fatigue performance of high-early-strength concrete decreases when the track slabs/sleepers are rapidly produced on a large scale. A new method of improving creep performance of prestressed steam cured concrete with mineral admixtures has been proposed, and low creep concrete for precast box girder has been developed (creep coefficient is 40% lower than that of ordinary concrete), which provides technical support for solving the problem of easy over-limit of creep camber of precast box girder and breaks through the forbidden zone of using mineral admixtures in railway prestressed concrete. The internal curing agent to regulate and control the humidity and deformation of concrete and the low-shrinkage high-crack-resistance concrete for cast-in-situ track bed slabs have been developed (which has reduced the cracks on the track bed slabs by more than 80%), breaking through the technical bottleneck in the construction of long continuous stripped ballastless track.
3. Innovations have been made on precise control technology for HSR concrete construction performance, and the technical standard system for HSR concrete quality assurance has been established. A concrete mix proportion dynamic control system based on real-time monitoring of raw material performance was developed, a durability-oriented rapid test method for key parameters of fresh concrete was innovated, characteristic indexes for ensuring the construction quality of HSR concrete were put forward, and a technical standard system for concrete materials, design, construction and acceptance was established to ensure the construction quality of HSR high-performance concrete in different regions, changing climates and multiple environments.
The complete technology has been applied to all HSR projects in China. Over more than 10 years' operation shows that HSR high-performance concrete is technically advanced, environmental-friendly, and excellent in service performance. It won the second prize of National Prize for Progress in Science and Technology 2019.