Abstract

Concrete structures are widely used in modern constructions including energy storage system such as all concrete liquefied natural gas (ACLNG) storage tanks. In ACLNG tanks, concrete structure is exposed to cryogenic temperatures and freeze-thaw (FT) cycles. Cryogenic temperatures and FT cycles are recognized to influence the mechanical characteristics of concrete. To ensure safety of the critical energy infrastructure, it is crucial to explore the concrete structural response under the combined cryogenic FT cycles and accidental impact loading. This study aims to numerically examine the damage caused by impact loading on reinforced concrete panels after exposure to cryogenic FT cycles. A plasticity based continuous surface cap model was adopted to simulate concrete. The material modulus, uniaxial and triaxial strength surface as well as damage parameters were updated to incorporate the effect of cryogenic FT cycles. A numerical model was established to forecast the impact resistance of the reinforced concrete panels after various cryogenic FT cycles. Through the numerical simulation, it was evident that FT cycles exerted detrimental effects on the impact resistance of reinforced concrete panels. With an escalation in the number of FT cycles, there was a pronounced increase in the size of the crater formed on the top surface, accompanied by a corresponding rise in the penetration depth of the panel. The results of this research offer insights into the impact resistance of reinforced concrete structures following cryogenic FT cycles. Such insights are vital for the design and maintenance of critical structures like liquefied natural gas (LNG) storage tanks and other cryogenic facilities.

Introduction

Reinforced concrete structures play a vital role in various engineering applications, providing strength, durability, and resilience. However, when subjected to extreme environmental conditions, like cryogenic freeze-thaw (FT) cycles, the structural safety of concrete elements can be remarkably affected. Moreover, of specific concern is the accidental impact resistance of reinforced concrete structures while enduring the challenges posed by cryogenic FT cycles. The demand for efficient and reliable energy storage systems, particularly All Concrete LNG (ACLNG) storage tank, has been rapidly increasing in recent years [1], [2]. Liquid natural gas storage tanks commonly maintain a storage temperature of approximately − ۱۶۵ °C, therefore, concrete is under ultra-low temperature condition. These storage tanks are subjected to both cryogenic temperatures, FT cycles and potential impact loading scenarios, rendering it crucial to assess their structural response and safety under such conditions.

Numerous researchers have investigated the concrete’s mechanical properties at low and super-low temperatures to facilitate the scientific, rational, and cost-effective design of structures while ensuring their performance and safety in extreme cold environments [3], [4], [5], [6], [7]. Van de Veen [8] had a comprehensive review on the properties of concrete such as the compressive strength, tensile strength, modulus of elasticity at low and cryogenic temperature and after FT cycles. It revealed that the mechanical properties of concrete could be affected by the type of aggregate, cooling condition, water to cement ratio (w/c) and moisture content (MC). It is commonly reported that the strength of concrete was improved at low or super-low temperatures [1], [8], [9], [10]. This improvement can be attributed to several factors. Firstly, as water within the concrete freezes at lower temperatures, it crystallizes into a solid reticulated pattern that imparts prestress to the concrete. This prestressing phenomenon contributes to an enhancement in the compressive strength due to the existence of multiaxial stress [6]. Moreover, the complete filling of capillary pores with ice helps eliminate stress concentrations within the concrete and inhibits the formation of microcracks at low temperatures. For a more comprehensive understanding of the reinforcement impacts of low temperatures on concrete, researchers have employed micro-scale models to explore the formation of ice within concrete pores and subsequent cracks [11], [12].

Conclusions

The impact resistance of reinforced NSC panels after FT cycles was investigated using a refined finite element model. The CSCM model was adopted and modified to incorporate various parameters such as shear modulus (G), bulk modulus (K), uniaxial and triaxial compression surface, as well as damage parameters. The subsequent conclusions can be drawn:
• After FT cycles, the elastic modulus, splitting tensile, and compressive strength as well as fracture energy of concrete decrease. As the number of FT cycles increases, the performance of concrete also continuously decreases.

• The modified CSCM model effectively captures the impact behaviour of reinforced concrete panels after FT cycles, considering various mechanical parameters.

• The predictive capability of the numerical model was validated through experimental verification, demonstrating its reliability in assessing the impact resistance of reinforced concrete structures.

• FT cycles were observed to adversely affect the impact resistance of the concrete structures. As the number of FT cycles increased, there was an observable escalation in the dimensions of craters formed on the surface as well as an increase in the penetration depth of the panels. These trends collectively suggested a decline in the impact resistance of the panels with the progression of FT cycles.