Journal of Cold Regions Engineering

Abstract

This study analyzed the mechanical properties of reinforced concrete flexural and axial-tension members at low temperatures ranging from 273.15 to 108.15 K based on experimental and theoretical analyses. Special test chambers were used to separately apply mechanical forces and low temperatures to the test members. The steel strain caused by the mechanical and thermal restraint forces was obtained using the self-compensation test method. The effects of low temperatures on the tensile and flexural stiffness behaviors of reinforced concrete beams, as well as the internal forces generated because of the different linear expansion coefficients of concrete and steel at low temperatures, were analyzed. Analytical models were developed to predict the restraint stress corresponding to different temperatures. The accuracy of the analytical models was verified using the test results. The results show that the deformation stiffness of both flexural and axial-tension members increases linearly with decreasing temperature. The difference between the thermal deformation of concrete and steel bars becomes more considerable as the temperature decreases, resulting in nonnegligible restraint stress in the steel bars. The study can provide a basis for the design of structures in service at low and ultralow temperatures, such as liquefied natural gas storage tank structures.

Practical Applications

Liquefied natural gas (LNG) is primarily composed of methane. After extraction from gas fields, it goes through a purification process; thereafter, it is subjected to a series of ultralow-temperature liquefaction steps and transported through specialized LNG carriers. LNG has extensive applications in various aspects of daily life, including energy supply, transportation, industrial use, and power generation. Compared with traditional fuels, LNG offers higher efficiency and environmental benefits. Nonetheless, optimizing the design of LNG storage facilities presents several technical challenges. Presently, reinforced concrete is the predominant material used in the construction of LNG storage facilities. To fully exploit the advantages of concrete structures in ultralow-temperature environments and reduce construction costs, comprehensive studies on the performance of concrete under such extreme conditions are crucial. This study is of immense scientific value and offers promising prospects for practical applications.

Recently, numerous studies have highlighted that the climate worldwide is changing rapidly due to increased greenhouse gas (GHG) emissions. The average ambient temperatures across Canada are rising approximately twice as fast as the rest of the world. The projected change in climate may increase the air and surface temperature indices, thus affecting the duration of spring load restrictions (SLRs) on roads, which may potentially impact the trucking industry and economy. Therefore, the best practices must be adjusted when identifying the optimal SLR periods that consider climate change. In Ontario, Canada, the SLR periods are imposed based on subsurface temperature data that is obtained from the road weather information system (RWIS) and spring load adjustment (SLA) stations in conjunction with visual observations. In this study, different methods of determining SLR periods were investigated. Then, new models were developed to correlate the surface cumulative thawing index (CTI) and thawing depth (TD) of a site. These models were developed utilizing atmospheric, surface, and subsurface data that was collected from different SLA and RWIS weather stations at various locations across Ontario, Canada. Finally, the developed models were utilized to predict the SLR periods for future scenarios using data from different global circulation models (GCM) and representative concentration pathways (RCPs). This study concludes that the SLR periods are expected to shrink across Ontario, Canada, by 2100. The results of this study might help different road authorities and trucking agencies maximize the life of the road structure and minimize the economic hardships that are faced during SLR periods.

Abstract

This paper attempts to evaluate the change in the behavior of the acoustic waves associated with flexure cracks developed in rubberized concretes in a subfreezing environment. Seven normal and rubberized concrete mixtures were developed with different compositions. Prism samples from each mixture were tested at two temperatures (25°C and −20°C) under a four-point monotonic flexure test while being monitored via two attached acoustic emission (AE) sensors to collect the emitted AEs till failure. The AE signal characteristics such as signal amplitudes, number of hits, and cumulative signal strength (CSS) were collected and used for three AE parameter-based analyses: b-value, intensity, and rise time–amplitude (RA) analysis. Analyzing the acoustic activity revealed micro- and macrocracks nucleation, which were found to be associated with a noticeable spike in CSS, historic index [H(t)], severity (S_r) values, and a significant dip in the b-values. In addition, cold temperature was found to increase the micro- and macrocracking onset load and time regardless of mixture composition. Besides, mixtures with a lower C/F, less crumb rubber (CR) content, and/or smaller rubber particle size witnessed higher micro- and macrocrack load and time thresholds. Noticeably, the AE signal attenuation effect caused by the high CR content (up to 30%) at 25°C was significantly relieved when samples were tested at −20°C. Three charts were developed to classify the cracking level based on the values of the intensity analysis parameters [H(t) and S] and RA analysis.

Practical Applications

Infrastructure failures can cause severe economic losses and fatalities, but luckily they can be avoided through regular inspections with the aid of nondestructive testing and subsequent repairs. Aging structures need more inspections to detect potential deficiencies, whereas newly constructed ones can safely undergo fewer inspections and preserve resources. Data from nondestructive testing programs can optimize inspection schedules. When it comes to hard-to-reach structures in extreme weather, acoustic emission (AE) has the potential to be a more suitable nondestructive testing technique over other conventional methods. Some concerns were raised regarding the effectiveness of the AE technique for applications involving novel construction materials such as rubberized concrete, because rubber particles have noticeable acoustic absorption capacities that may affect the parameters of the AE waves and impact the posttesting analysis. Another concern was the influence of cold temperature on the AE wave characteristics due to the change in concrete microstructure at low temperatures. This study aimed at addressing these concerns by utilizing AE analysis to highlight the onset of micro- or macrocracks in rubberized concrete mixtures exposed to cold temperatures. Three user-friendly charts are presented that can advise on inspection decisions based on whether deterioration has reached a certain level.

Owing to the scarcity of land resources, the rational development and use of frozen soil resources and solutions to frozen soil disasters are essential. In this study, an indoor one-dimensional soil column simulation test was conducted under unidirectional freezing conditions. The temperature, water content, and conductivity of the sand were monitored using a time-domain reflectometer (TDR), and a mathematical model to analyze the relationships among solute concentration, temperature, and conductivity was established, to convert the conductivity into soil solute concentration. Then, the sodium chloride solute redistribution in soil under different soil densities (1.23 and 1.40 g/cm³), initial water contents (10% and 13%), freezing temperatures (−20°C and −35°C), and salt concentrations (0.2 and 0.3 mol/L) was analyzed. The results show that solute concentration and temperature are the two factors that affect conductivity. The relationship between conductivity and solute concentration can be used to quantitatively analyze the solute changes in soil. The soil density, initial water content, freezing temperature, and solute concentration affect solute migration under unidirectional freezing conditions. The solute migration efficiency decreases with increasing soil density and initial water content and increases with decreasing freezing temperature and increasing solute concentration. In this study, the aim was to further understand the mechanism through which solute migration occurs in frozen soil, to provide theoretical support for the rational exploitation and use of resources, the prevention and control of soil pollution, and the promotion of agricultural development in cold regions. These results provide theoretical support for soil water and salt simulations, pollution control, and agricultural development in cold regions.