Zhigang Zhu

Ballastless track slabs are subjected to complex restraint conditions and operational environments, making deformation-induced cracking a critical factor affecting durability and service performance. Conventional cracking resistance evaluations generally rely on individual parameters, which cannot adequately describe the relationship between cracking driving forces and resistance capacity under restrained conditions. This study proposes a cracking resistance evaluation and mixture optimization framework for ballastless track slabs. A cracking resistance index (CRI) was developed based on the competition between deformation-induced stress demand and flexural cracking resistance by integrating shrinkage deformation, elastic modulus, and flexural strength. The proposed CRI is intended as a comparative index for quantitatively assessing the relative cracking resistance among different concrete mixtures. The effects of key mixture parameters, including water-to-binder ratio, sand ratio, binder content, air-entraining agent dosage, and internal curing admixture dosage, on fresh properties, mechanical performance, shrinkage behavior, and CRI were systematically investigated. The results indicated that the water-to-binder ratio, air-entraining agent dosage, and internal curing admixture dosage were the dominant factors affecting CRI. In particular, internal curing reduced shrinkage deformation and consequently decreased the CRI, which may be attributed to improved internal moisture conditions. Based on the Box–Behnken design method, a response surface model (RSM) was established to optimize mixture proportions with the objective of minimizing CRI while satisfying the mechanical requirements for C40 ballastless track slab concrete. A preliminary experimental verification using three replicate specimens prepared with the optimized mixture showed good consistency between the RSM-predicted and measured CRI values, with a relative error of 3.81%. The proposed framework provides a quantitative approach for cracking resistance-oriented mixture optimization of concrete used in ballastless track slab.

The construction industry has been a significant contributor to global carbon emissions. Fortunately, it is well known that precast concrete structures possess the benefit of reducing carbon emission, of which the beam–column joint plays a crucial role in resisting severe loads. Nowadays, the cast-in-place joint is mostly adopted for beam–column joint The authors declare no conflict of interests of precast concrete structures, and the building industrialization degree is insufficient. In light of this, a novel precast concrete beam–column joint using the mortise–tenon (MT) connection is proposed inspired by traditional timber structures, and the contrastive analysis of mechanical behaviors of this joint and the same-sized cast-in-place joint is conducted by the finite element method. The results indicate that the proposed MT joint has a better mechanical behavior by comparing with the corresponding cast-in-place joint as the beam–column joint. Meanwhile, the MT connection mode has the characteristics of standardized construction, in line with the concept of sustainable development, which can greatly save the construction period. This research demonstrates the feasibility of MT joints in traditional timber structures as beam–column joints in precast concrete structures, and the application of MT joints may be promoted if the size and shape of that are further optimized. Furthermore, this in turn helps research and innovation of precast building construction technology and promotes the sustainable development of the construction industry in the direction of energy conservation and environmental protection.