Winter Construction Research Articles

Protection and Heat Insulation Performance Comparison using Insulation Formwork in Winter

Concrete pouring in winter is critical to both concrete manufacturers and end users owing to the possibility of concrete damage due to cold weather. In this context, various methods have been used to prevent frost damage to concrete in winter, including adjusting the concrete mix using a chemical admixture and heat-curing with tents. Of these methods, the insulated-gang-form approach does not require concrete-mix adjustment via a chemical-admixture addition. Furthermore, its positive effect on the initial quality of concrete during concrete construction in winter has previously been confirmed. In this study, the power consumption of the conventional gang form was compared with that of the insulated gang form to evaluate the efficiency of the two protection methods. A thermal vision camera was used to examine the surface heat loss of the gang forms after concrete pouring. The insulated gang form significantly outperformed the conventional one through its significantly reduced power consumption and reduced surface heat loss. These findings can contribute to the standardization of insulated gang form application to concrete protection in cold-weather conditions.

Effect of shrinkage-mitigating additive and curing condition on flexural and fracture behavior of ultra-high-performance concrete (UHPC) unnotched beam

The study aims to examine how the flexural and fracture behavior of UHPC is impacted when shrinkage is mitigated by adding shrinkage-mitigating additives. Furthermore, due to the consistent use of UHPC for structural repair and reinforcement throughout the year, including emergency construction in winter, it is necessary to carry out construction operations in winter conditions. Thus, this study adopts the natural cold curing condition of UHPC specimens to mimic real-world outdoor construction settings, while also using the standard curing condition as a comparison. The bending test was performed on three different types of UHPC materials: material 1 without a shrinkage-reducing agent (SRA) or expansive agent (EA), material 2 with 1 % SRA, and material 3 with 1 % SRA and 7.5 % EA. Fracture and flexural behavior of UHPC beams were studied, and Spearman's correlation between shrinkage and flexural/fracture toughness was evaluated. The study revealed that adding SRA/EA decreased the mean flexural tensile strength of specimens cured in standard conditions. Additionally, specimens cured in natural conditions showed less flexural tensile strength when SRA/EA was added. Furthermore, when compared to material 1, the addition of SRA and EA greatly reduced the fracture energy of UHPC, resulting in reductions of 21.9 % and 26.6 %, respectively, for materials 2 and 3. The fracture toughness showed a modest correlation with the shrinkage behavior, and the fracture energy exhibited a high association with the shrinkage behavior. The research findings can provide references for UHPC applications in natural winter conditions when the material contains shrinkage-mitigating additives.

Electric Resistance and Curing Temperature Development of Carbon Fiber-Reinforced Conductive Concrete: A Comparative Study.

The development of electric resistance is a key factor affecting the performance of conductive concrete, especially the electrical-thermal performance. In this work, the effects of different influencing factors (including the water-to-binder ratio, coarse aggregate content and carbon fiber (CF) content) on the electric resistance of conductive concrete were systematically investigated. At the same time, ohmic heating (OH) curing was applied to fabricate CF-reinforced conductive concrete (CFRCC) under a negative temperature environment at -20 °C. The effects of different factors on the electrothermal properties (curing temperature and conductive stability) of the samples were studied. The mechanical strengths of the CFRCC cured by different curing conditions were also tested, and the feasibility of OH curing for preparing CFRCC in a negative-temperature environment was verified at various electric powers. This work aims to give new insights into the effects of multiple factors on the performance of CFRCC for improved concrete construction in winter.

Effects of Lime Powder on the Properties of Portland Cement-Sulphoaluminate Cement Composite System at Low Temperature.

In order to reduce the risk of early freezing damage to cement-based materials in winter construction, lime powder was used to improve the properties of the Portland cement-sulphoaluminate cement (PC-CSA) composite system at low temperatures. In this study, the effects of lime powder dosage on the properties of a PC-CSA blended system with two proportions (PC:CSA = 9:1 and 7:3) at -10 °C were investigated, and the mechanisms of improvement were revealed. The results showed that the compressive strength of the PC-CSA composite system was effectively improved, and the setting time was shortened by the addition of lime powder. Lime powder could effectively act as an early heating source in the PC-CSA composite system, as the maximum temperature of samples exposed to sub-zero temperatures was increased and the time before dropping to 0 °C was prolonged by the addition of lime powder. The extra CH generated by the hydration of lime powder provided an added hydration path for C4A3S¯, which accelerated the formation of AFt at each stage. Frozen water as well as the early frost damage were effectively decreased by lime powder because of the faster consumption of free water at an early stage. The modification of the hydration products also contributed to the denseness of the microstructure.

Long-term performance of magnesium phosphate cement concrete prepared in the winter

Previous studies have established the strength development of magnesium ammonium phosphate cement (MAPC) concrete and magnesium potassium phosphate cement (MKPC) concrete at sub-zero temperatures. However, the long-term performance of these magnesium phosphate cement (MPC) concrete, prepared at low temperatures and exposed to complex environmental effects of cold regions, remains underexplored. This study monitored the mechanical properties and durability of MAPC concrete at different ages for 520 d, which fully demonstrated the feasibility of MAPC concrete for winter construction in cold regions. At the age of 520 d, MAPC concrete had a compressive strength of over 65 MPa and excellent resistance to chloride ion penetration with a measured charge of 129.1 C, and could endure more than 250 rapid freeze-thaw cycles. In contrast, MKPC concrete exhibited significant disadvantages in terms of freeze-thaw resistance during natural freeze-thaw cycles. No expansive substances or damage were found in MKPC concrete that was prepared at low temperatures and subsequently experienced temperature increases along with accelerated hydration. The relatively poor freeze-thaw resistance of MKPC concrete could be attributed to a combination of factors including larger capillary size and volume, reduced air content, greater air-void spacing factor, wider and weaker interface zone between cement mortar and coarse aggregate.

Temperature rising and anti-freezing performance of gravel-clay mixed with PCM applying infrared radiation during winter construction

Freeze–thaw cycles could easily cause the structural damage and mechanic performance deterioration of clay. In order to prevent the freeze–thaw cycles problem in the core-wall zone of the high core-wall rock-fill dam in cold regions, gravel-clay mixed with phase change material (GC-PCM) can be used as damming material and present a certain level of anti-freezing performance during winter construction. However, GC-PCM construction work area is still likely to run a risk of freezing under the severe cold and strong wind weather. In order to solve the freezing problem of GC-PCM, this study developed an infrared radiant heating device without interfering with the original construction procedure and conducted an indoor test to investigate the temperature rising performance of GC-PCM after receiving infrared radiation. Also, a numerical simulation method was proposed for the temperature rising and anti-freezing performance of the GC-PCM construction work area and the effects of different factors (including radiant pass, moving speed of infrared device and wind speed) on the anti-freezing performance were analysed subsequently. Main results show that: (1) the effectiveness of proposed numerical simulation method is validated by the indoor test; (2) after receiving 8-pass infrared radiation, the GC-PCM construction work area at 4 % PCM content remains unfrozen in 24 hours under the typical weather in December; and (3) instead of increasing radiant passes, reducing the moving speed of infrared device can better improve the anti-freezing performance of GC-PCM. This study validates the feasibility of applying infrared radiant heating method on GC-PCM, providing a potential technical means for gravel-clay anti-freezing during winter construction.

Temperature field analysis and prediction of winter construction warm shed method based on hot air heating

The warm shed method is commonly employed in concrete construction during winter as an effective technique. This study aims to investigate the impact of different sizes and heating methods on the temperature inside the shed and the concrete through scale model testing. The hot air heating method is simulated using finite element software, and a prediction model is developed. The findings reveal an inverse relationship between the size of the warm shed and its heat preservation effect. When utilizing hot air, both the maximum temperature inside the warm shed and at the center of the concrete increase by 15.5 °C and 25.2 °C respectively compared to when employing a point heat source, resulting in earlier stabilization times of 390 min and 1000 min respectively, as well as a more uniform temperature distribution across all parts. Based on finite element simulation results, an optimal wind speed μ is proposed along with a corresponding prediction model.

Optimizing anti-freezing agent on the properties of Portland cement-calcium sulphoaluminate cement system based on Taguchi-GRA method

The investigate of novel cementitious system suitable for negative temperature concreting was the key way to solve the high energy consumption of traditional winter construction. In this study, the matching effects of anti-freezing agents (CaCl2, NaNO2 and Li2CO3) on the Portland cement-calcium sulphoaluminate cement blended system (PC-CSA system) based on Taguchi-Grey Relational Analysis (Taguchi-GRA method) were studied. The setting time, compressive strength and freezing point were tested, and the hydration products, pore structure and morphology were also analyzed to reveal the mechanism. The results showed that CaCl2 was the main parameter influencing the initial and final setting time. Whether at the early stage of continuous negative temperature curing, or from negative to positive temperature curing, CaCl2 had a dominant influence on the compressive strength of PC-CSA system, which promoted the increase of the early hydration products, resulting in the rapid formation of a network structure. At the later stage of continuous negative temperature curing, the influential parameter changed to NaNO2. The basic condition for hydration was provided due to the lowering of the freezing point of the liquid phase by NaNO2. The presence of Li2CO3 enhanced the promoting effect of CaCl2 on early strength. The optimal parameter combination for PC-CSA system was 1.0 % CaCl2, 2.0 % NaNO2 and 0.4 % Li2CO3 based on Taguchi-GRA method.

Exploring the influence of sodium nitrite on the early-age freeze resistance of low-carbon sulphoaluminate cement (SAC)

Despite offering higher early strength and faster hydration rates, low-carbon sulphoaluminate cement (SAC) remains vulnerable to adverse cold weather conditions during winter construction. This study proposes the utilization of sodium nitrite (SN) as an antifreeze admixture to enhance the mechanical properties of SAC paste under sub-zero temperatures (−5 °C and −10 °C). The influences of SN on the hydration kinetics, phase assemblage, freezing point, microstructural evolutions and mechanical properties of SAC paste under sub-zero temperature are comprehensively investigated. It turns out that the mechanical properties of SAC paste at low temperatures (−5 °C and −10 °C) can be significantly improved by incorporating SN. Low-temperature differential scanning calorimetry (LT-DSC) results showed that the freezing point of SAC paste is sharply decreased from −1.1 °C to −11.6 °C owing to the elevated effect of SN on the ion concentration within pore solution. Moreover, X-ray diffraction (XRD) and thermogravimetric (TG) analysis are conducted to confirm the increase in the hydration degree of SAC paste with SN under sub-zero temperatures. Furthermore, mercury intrusion porosimetry (MIP) results demonstrate the role of SN on the refining pore of SAC paste. In conclusion, this work proposes a new way and optimal control of dosage for enhancing the mechanical properties of SAC cement at low temperatures.

Feasibility of winter construction for prefabricated subway station: Waterproof performance analysis of composite cross-section gasket treated by low temperature

The construction of prefabricated subway stations in northeastern China necessitates a focused investigation into the behavior of composite cross-section gaskets with ethylene propylene diene monomer (EPDM) and water swelling rubber (WSR) under low-temperature conditions. This research conducted experimental and numerical studies to analyze the mechanical and waterproof properties of WSR-EPDM gaskets treated at low temperatures. The mechanical properties were evaluated through hardness and compression tests at various treatment temperatures. Additionally, the study examined the impact of treatment temperature and loading rate on the load-deformation relationship. Then, finite element (FE) models were developed and validated based on mechanical experimental results of the gasket-in-groove system under various low-temperature conditions. Subsequently, the nonlinear FE model was used to analyze the effects of joint offset and opening angle on assembly load and waterproof performance. The results demonstrated a direct correlation between the treatment temperature and the Shore hardness and assembly load of the WSR-EPDM gasket. Lower treatment temperatures led to higher hardness and assembly load. Notably, at temperatures below −10 °C, the loading rate had a more pronounced effect on the assembly load. Furthermore, the assembly load initially decreased and then increased with an increase in joint offset, while it consistently decreased with a larger opening angle. Additionally, as the treatment temperature decreased, the average contact pressure during operation also decreased. The influences of joint offset and opening angle were negligible when the treatment temperature was below −20 °C. However, the coupling influence of offset or opening angle and treatment temperature on the waterproofness is evident for a treatment temperature between 0 ∼ −15 °C. In summary, this study serves as a useful reference for evaluating the waterproof properties of these gaskets in low-temperature environments.

Effects of nano-silica modification on early age hydration process in winter construction of tunnel engineering

Fast hardening and high early strength are crucial factors for concrete used in tunnel construction in cold regions. The incorporation of nano-silicate has been found to be an effective method for improving the properties of cement-based materials at an early age. Thus, the objective of this paper is to investigate the nano-modification effects of different nano-silica contents on the hydration process, mechanical properties, and hydration products of cement cured in a low-temperature environment. The effects of various nano-silica concentrations, including 1%, 2%, 3%, and a high dose of 6%, on the properties of the concrete were investigated. According to the test results, the optimal quantity of nano-silica plays a crucial role in determining the properties of concrete. The effects of nano-silica on the hydration of C3A were found to dominate the cement hydration process at an early age. The incorporation of nano-silica led to a significant improvement in the dissolution rate of anhydrite and the reaction rate of the C3A renewal, which may be responsible for the gain in early strength of concrete. However, an excessive amount of nano-silica could negatively affect the hydration process of the alite and C3A, as evidenced by the total heat generated during the silica and aluminate reactions. The XRD patterns further confirmed these results.

The role of admixed CaO in a sulphoaluminate cement system under winter environments

Sulfoaluminate cement (CSA) is a low-carbon binder and can be regarded as an ideal cementitious material for winter construction and repair projects. However, the admixed CaO on the performance of CSA and its mechanism is still unclear, as well as the investigations and applications of CSA in negative temperature environments are very limited. Therefore, the impact of CaO on the setting time, compressive strength, cooling curve, and microscopic properties of CSA composite are systematically investigated. The experimental results reveal that the admixed CaO can significantly improve the compressive strength of CSA composite at negative temperatures (e.g., −5 °C, −10 °C, and −20 °C), and the admixed 2% CaO is the most effective in enhancing the compressive strength of CSA paste. At the beginning of hydration, CaO-modified CSA paste shows a significant exothermic peak, thus the freezing process of the liquid phase is retarded and the CSA can sustain hydration at −20 °C. Remarkably, the admixed 2% CaO can reduce the freezing point of the liquid phase of CSA paste to −7.2 °C, accordingly, decreasing the amount of freezable water and the risk of frost damage.

Prediction of concrete strength considering thermal damage using a modified strength-maturity model

The maturity method is widely used to estimate early-age concrete strength. However, the traditional maturity models exhibit limited predictive capability for late concrete strength under thermal curing conditions due to the influence of the “crossover effect”. This study developed a curing scheme for Standard Portland cement concrete in the absence of supplementary cementitious materials at temperatures ranging from 5 °C to 50 °C and analyzed the temperature variations inside thermally cured concrete specimens. The findings reveal that an increase in curing temperature and time between 30 °C and 50 °C and 8 and 72 h respectively led to an increase in the early strength and a decrease in the late strength of concrete, due to the “crossover effect”. Additionally, a linear relationship was found between curing temperature and the late strength reduction coefficient. Utilizing this relationship, a modified maturity model that considers the “crossover effect” was proposed, improving the accuracy of predicting concrete strength under thermal curing conditions (with a prediction error of less than 10%). The research outcomes are of significant guiding significance for winter construction by ensuring the quality of concrete, reducing construction accidents, and improving construction efficiency.

Rheological concerns arising from the use of anti-freezing additives in cement mortar with/without SP and AEA for low-temperature construction

This paper aims to provide insights into the coupled influence of typical anti-freezing agents (AFAs) and cold environment on rheological performance of cement mortar with/without different superplasticizer (SP) and air-entraining agent (AEA) components. Fresh mixtures were prepared with chemical admixtures singly or in groups (AFA; AFA/SP; AFA/SP/AEA) for the continuous measurement of their time-dependent rheological behavior at variable temperatures (24 °C; 0 °C; −5 °C; −10 °C). Hydration kinetics, pore solution and air-void system were systematically evaluated to provide evidences supporting for the variations in rheological parameters. It was found that the yield stress of mixture decreased and the plastic viscosity increased with the temperature falling from 24 °C to 0 °C, while both the yield stress and the plastic viscosity increased rapidly with the temperature falling from 0 °C to −10 °C. Temperature could affect the rheological parameters development by changing the interaction of SP with ions. For the SP-plasticized mixtures under low temperature, the dosage of calcium nitrite (CN) as AFA should be carefully restricted. For the air-entrained mixtures, the incorporation of CN enhanced the shear stress in the high shear rate region, while the incorporation of ethylene glycol (EG) showed a converse behavior. The results will provide theoretical supports for the manufacture and the early-age properties control of flowable concrete during winter construction.

Effects of urea on carbonation properties and microstructure of cementitious materials

Urea has been utilized in concrete technology to reduce the temperature cracking and promote winter construction property. In this work, the influence of urea on cement hydration and carbonization resistance of cement-based materials was studied through carbonation depth experiment, isothermal conduction calorimetry, XRD, BET and water vapor sorption. It is indicated that the reduction of rate in the hydration acceleration period can be attributed to the increasing pH and lower supersaturation when urea is added to the cement mixture. In addition,the existing of NH4+in pore solution andpH profile results in the decrease of decalcified C-S-Hdeterioration rate,which prolongs carbonation duration to asimilar depth. This study provides a new admixture way to improve the durability of cement-based materials to prolongthe life of reinforced concrete.

Numerical simulation of the anti-freezing performance of a phase change clay core-wall with loose covering

Clay core-wall of rockfill dam may endure short-term freezing or freeze–thaw cycles owing to negative temperature conditions during winter construction in cold regions, resulting in the degradation of the clay compaction, frost swelling, and cracking performance. The most commonly used insulation cover measures interfere with the continuous construction of clay core-walls, which may shorten the effective time available for construction and delay the dam construction progress. To address this problem, we proposed using the upper layer of the loose-covering clay and the latent heat of phase change materials (PCMs) to control the core-wall temperature. We implemented a numerical model for simulating the anti-freezing performance of the PCM mixed clay (PCM-clay) with loose covering. First, a heat transfer model was established using the finite element software COMSOL, and the effectiveness of the model was verified by comparing it with indoor temperature control test results. Subsequently, numerical models including different construction conditions were established, and the temperature control effect was analyzed under different loose-covering thicknesses, initial soil temperatures, and PCM contents. The results showed that at the design ambient temperature and a 2% PCM content, an effective construction time availability of two consecutive days was maintained under a 20-cm-thick loose covering. In contrast, under the same temperature conditions, but for a 4% PCM content, the effective construction time available under a 5-cm-thick loose covering was 43.1 h. Thus, the use of PCM-clay combined with the upper layer loose covering for temperature control proved feasible and effective. Additionally, by increasing the thickness of the loose covering and the initial temperature of the PCM-clay, the PCM content can be reduced. This provides a theoretical basis and a potential technical solution to maximize the time available for construction and accelerate the construction progress of core-wall rockfill dams.

Temperature variation and distribution in underground sidewall: On-site monitoring and finite simulation

Sidewall is the main structure with the highest crack risk in underground engineering, and temperature deformation is an essential factor leading to cracking. Quantitative study on temperature variation and temperature gradient is the basis of temperature deformation research. However, there are few related research reports. This paper aims to quantitatively study the effect of thickness, demolding time, and construction season on the sidewall's temperature variation and temperature gradient. Sensors were installed on-site to collect temperature data, and a finite element model of the sidewall was established to analyze the temperature change process. The temperature variation and distribution under different conditions were analyzed by changing the simulation parameters. Results show that heat is mainly lost in the thickness direction and temperature gradient variations from outside to inside. After demolding, sidewall's surface temperature gradient will suddenly increase, and the cracking risk will be the highest. Sidewall's surface temperature gradient is the largest during construction in winter. Simultaneously, mitigation measures were put forward to reduce the risk of temperature deformation and cracking. The research results can provide a reference value for engineering practice.

Temperature Control for Mass Concrete Construction of Wentang Bridge 5# Pier Pile Cap in Winter Construction

In order to ensure the construction quality of mass concrete structures in winter, and avoid and prevent harmful temperature cracks of mass concrete, a calculation method of temperature field of hydration heat in winter based on finite element method is proposed in this paper. First, the three-dimensional finite element model of the temperature field of hydration heat is established; Then, the temperature variation of winter hydration heat temperature field of Wentang Bridge is calculated through experiments. The results show that the maximum measured temperature of the core point is 44.2 °C, and the corresponding calculated temperature is 53.7 °C. The maximum internal and external temperature difference measured is 24.7 °C, and the corresponding calculated temperature is 22.4°C. The research results prove that the calculation model can better simulate the concrete hydration process.

Frost Mitigation Techniques for Tunnels in Cold Regions: The State of the Art and Perspectives

Tunnels located in cold regions are vulnerable to frost damage resulting from the special atmosphere, which directly threatens the safety of the tunnel structure and operation. Frost problems of tunnels in cold regions have not been fundamentally resolved. This paper reviews design theory and the frost mitigation techniques currently used in the design, construction and maintenance of cold region tunnels. The depths of freezing and thawing and frost heaving force are the key indexes of design theory. Insulation is the main design technology used to prevent frost heaving and thawing, and the active heating technology has also been applied in practice. In construction, reducing the heat of hydration and blasting by specific winter construction techniques can prevent tunnel freeze–thaw damages. In operation, the restoration of drainage systems, the reinforcement of structures and the reinstallation of freezing-prevention systems are effective measures to treat frost problems. Finally, some constructive suggestions and opinions are put forward to improve the service performance of tunnels.

Approximate analytical method for calculating the heating process of concrete structures in heating formwork

The use of electric heating of concrete during construction in winter makes it possible to create an optimal thermal regime in which the hardening process takes place, and to obtain a structure of the required quality. When developing a system for automatic control of the heating process, it is necessary to determine the law of regulating the power of heaters. This article presents a method for calculating the thermal heating regime of concrete structures in heating formwork, the essence of which is to reduce the boundary value problem of thermal conductivity to a system of equivalent integral equations. To solve this problem, a theoretical study was carried out, a theoretical study of the heat transfer process in concrete structures heated during winter concreting was carried out, and a mathematical description of this process was presented in the form of a system of differential equations. After the transformations of the above system of equations and the application of the Green function of the second kind to it for the plate and rod, an approximate solution of the equivalent equation was obtained. As a result of the application of the asymptotic method to the solution of the integral equation, an analytical solution of the problem under consideration is obtained. The resulting solution makes it possible to determine the temperature fields on the concrete surface, as well as the value of the specific heat flux from electric heaters. In order to automate the process of performing the thermal calculation of heating concrete structures with the help of heating forms, a program for calculating temperature fields in heating forms has been developed based on the solution obtained, which makes it possible to effectively solve the tasks of monitoring and controlling the concrete hardening process. The developed program makes it possible to calculate temperature fields not only at constant heater power, but also when it changes with the help of regulators. The presented method of thermal calculation with a hardware and software complex for regulating the power of electric heaters allows solving a fairly wide range of tasks related to maintaining a constant temperature field.