Winter Construction Research Articles

Nano-modification effect on the pore characteristics and the water multiscale transport properties of concrete in winter construction of tunnel engineering

Seepage has become the dominant damage that affected tunnel stability. Although drainage and the waterproofing system are frequently employed in seepage tunnels, the poor performance of shotcrete is still an inducement for the waterproofing system failure. Further, the frost damage caused by seepage becomes more pronounced when tunnel construction locates in cold region environments. Therefore, the objective of the study is to explore the nano-modification effects on the water multiscale transport behaviors of concrete in winter construction environments. Firstly, the pore characteristics of the hydrated cement were experimentally determined by the mercury intrusion porosimetry (MIP) test. The meso-structures of concrete were obtained via the X-ray computed tomography (CT) test. Secondly, the fractal analysis was conducted to derive the permeability of the hydrated cement based on the capillary model with the interaction of solid and fluid molecules considered. Then, the permeability distribution of concrete was calculated by combining test results at the micro-scale and that at the meso-scale. Finally, the unified multiscale simulations based on the generalized Lattice Boltzmann method (GLBM) were conducted to obtain the permeability of all groups. The water transport process of concrete on the meso-scale was simulated by considering the influence of micro-structures. The permeability tests were conducted to verify the simulation results. Results indicated that the addition of nano-materials can markedly increase the complexity of the pore structure and decrease the porosity, thereby enhancing the impermeability of concrete.

Effect of Alkali Cation on Performance of Alkali-Activated Slag Mortar in Cold Environments

Alkali-activated slag (AAS) is a promising cementing material for winter construction due to its continuous hydration at sub-zero temperature. In order to obtain a higher mechanical strength of AAS mortar in winter construction, the most efficient alkali activator should be selected. Potassium silicate and sodium silicate as alkaline activators of AAS mortar possess a high strength and hydration rate at ordinary temperature. Potassium silicate and sodium silicate as alkali activators showed different properties because of different alkali cations, so the effect of alkali cation on the performance of AAS mortar was studied at sub-zero temperature. The mechanical properties of potassium-silicate-activated AAS (K-AAS) mortar and sodium-silicate-activated AAS (N-AAS) mortar were thoroughly compared at the ambient temperatures of −10 °C, 0 °C, and 20 °C. The compressive and flexural strength of K-AAS mortar was increased by 130.4% and 72.3% at the age of 1 day and increased by 49% and 33.7% at the age of 28 days at the ambient temperature of −10 °C compared with N-AAS mortar. In order to reveal the mechanism behind the influence of different alkali cations on the mechanical properties of AAS mortar, the hydration heat, hydration products, and pore structures of AAS were characterized. The hydration heat exhibited that the rate of heat release and the cumulative heat release of K-AAS are higher than N-AAS, indicating the higher reaction degree of K-AAS. DTG/TG and ATR-FTIR spectra showed that K-AAS generated more gel product C(-A)-S-H compared with N-AAS at the same curing temperature. The MIP results exhibited that the porosity of K-AAS was lower than N-AAS. Finally, the mechanism explanation of the effect of alkali cation on the performance of AAS mortar was proposed. To sum up, potassium silicate should be selected as an alkali activator of AAS in winter construction.

Evaluation of common defects of grouted sleeve connectors

Grouted sleeve connectors have been widely used in vertical connections of prefabricated reinforced concrete structures. However, the quality of grouted sleeve connections are likely affected by adverse factors during winter construction such as grouting operation error, adverse environmental change, and management negligence. Some defects in winter construction are difficult to check including insufficient strength of grouting material, insufficient anchorage length of connecting reinforcement bars and adverse impact of low-temperature grouting. Although research has been carried out on the connection performance of grouted sleeves with defects, few are on the comprehensive evaluation of the connection performance of grouted sleeves with different defects caused in winter construction. In this paper, 25 groups (75 sleeves) of semi-grouted sleeve connectors with various defects are designed and manufactured. The effects of insufficient anchorage (i.e. insufficient length of reinforcement bar extending into the sleeve), insufficient strength of grouting materials and low-temperature grouting on the tensile properties of semi-grouted sleeve connectors are experimentally studied. On the basis of the test, finite element analysis is performed on extended defect conditions to comprehensively evaluate the safety control indicators. This research provides reference for the safety evaluation of grouted sleeve connections for prefabricated structures.

The Influence of Alkali-Free Shotcrete Accelerators on Early Age Hydration and Property Development within Cement Systems.

Fluoride-containing alkali-free setting accelerators are a common type of admixture used in tunnel shotcrete but few studies in the literature focus on the effect of their fluoride compounds on the setting and hardening properties of accelerated cement paste under low environment temperatures. Tunnel shotcrete in cold regions or winter construction periods would be obviously influenced by low environment temperatures, especially for its fast setting and quick support applications. The objective of this work is to evaluate the early age hydration behavior of different accelerated cement pastes under 20 °C and 5 °C environment temperatures. In this study, setting time measurement, early age strength development, hydration ion leaching concentration, isothermal calorimetry, X-ray diffraction, and ESEM were performed on cement systems prepared with a non-fluoride alkali-free accelerator (aluminum sulfate solution with over 60% solid content) and a designed fluoride-containing alkali-free setting accelerator (aluminum sulfate and fluoride compound). The results showed that the fluorides obtained in alkali-free accelerators promote C3S dissolution and massive ettringite needles together with monosulfoaluminate (AFm) hydrate formation, thus leading to a quicker setting effect and low sensitivity to low environment temperatures than in non- fluoride groups. However, the rate of mechanical strength development of cement pastes hydrated within 24 h was decreased obviously when fluorine-containing alkali-free accelerator was used. This phenomenon is mainly related to the crystallization of thin-plate shape calcium fluoride (CaF2) formations and promoted conversion of ettringite to monosulfoaluminate hydrate in the accelerating period, thus weakening the denseness of C-S-H gel and inhibiting alite further hydration.

Numerical simulation on anti-freezing performance of PCM-Clay in core wall during winter construction

The clay directly incorporated with phase change material (PCM-Clay) can prevent core-wall surface from freezing thanks to the latent heat, which is potential to extend the freezing hysteresis time of earth-rock dams in cold regions. The indoor thermal test requires time and effort to prepare different PCM-Clay samples with a tedious procedure to control temperature and fails to completely imitate the actual conditions during the core wall construction process. It is also a challenge to get the utmost out of the latent heat of PCM while prevent the PCM-Clay from freezing. Aiming to solve the above-mentioned problems, this paper proposed a numerical method for simulating the anti-freezing performance of PCM-Clay considering the actual condition of core-wall construction unit during winter construction according to a verified numerical model of indoor thermal test. Based on the proposed method, the temperature profiles of different PCM-Clays in core wall were simulated under the compulsory suspension weather required in specification and extreme weather from local meteorological record, respectively. Results show that: (1) the model efficiencies of temperature for PCM-Clay at different paraffin contents in numerical simulation reach 0.92 and above; (2) 8% PCM-Clay is able to prevent the core wall from freezing under the compulsory suspension weather and extend a freezing hysteresis time of 4.0 h under the extreme weather; (3) freezing hysteresis time of core-wall PCM-Clay decreases with the wind speed under compulsory suspension weather. This paper overcomes the defect of indoor thermal test where the actual environment for core-wall winter construction cannot be completely reproduced and temperature profiles of PCM-Clay at different paraffin contents in core-wall construction unit are analysed, providing a basis for the utilization of PCM-Clay to prevent core wall from freezing during winter construction.

Economic strategies for low-temperature transportation of asphalt pavement: a comparative analysis of temperature variations

ABSTRACT Highway construction strategies impact the early damage of asphalt pavement and its sustainability. The pavement quality is directly influenced by the temperature segregation of the mixture during transportation, which has rarely been investigated. Low-temperature transportation strategies for highway pavement are proposed by assessing the temperature variations in the mixture through field tests. The extreme condition of winter construction is considered, and the effects of insulation materials are considered in laboratory and field tests. A 3D Multiphysics Coupling Finite Element model is developed in COMSOL to analyse the heat transfer mechanism. The vehicle speed, thermal conductivity and ambient temperatures are considered in this parametric study. The economic efficiency of intelligent transportation is improved by optimising the effective area and the thickness of insulation materials. This study aims to propose economic strategies to avoid the temperature segregation of pavement materials and to explore more environmentally friendly insulation measures for low-temperature highway constructions.

Enhancing the hardened properties of blended cement paste cured at 0 °C by using alkali-treated ground granulated blast furnace slag

The use of high-volume ground granulated blast furnace slag (GGBFS) in cement-based materials significantly reduces CO2 emissions. Nevertheless, low curing temperatures are barriers to using environmentally friendly materials in winter construction works. This is mainly attributed to slow GGBFS's reactivity and blends' strength development due to the low alkalinity offered by the slow hydration rate of Portland cement (PC) at low temperatures. In this study, sodium hydroxide was employed to produce dry reactive pre-alkali-activated GGBFS (A-GGBFS), with an intention to increase the system's alkalinity and reactivity. The blended cement paste was prepared with 50% PC replacement with untreated and treated GGBFS, and cured constantly at 0 °C for 28 days. The A-GGBFS accelerated the hydration rate and enhanced the precipitation of hydration products. By adding an optimal NaOH content during the pre-alkali-activation process, the 3 and 28 days compressive strengths of paste increased by 41% and 37%, respectively, gaining a comparable 28 days compressive strength to that measured in a 100% PC-based binder. The microstructural assessments are consistent with compressive strength measurements.

Assessment of mechanical performance and ice content of concrete at low temperature using impact-echo method

• The application of impact-echo method was extended to frozen concrete. • The influence of various factors on wave velocity and strength are analyzed. • Wave velocity-strength correlations of frozen concrete were obtained. • A method for evaluating on-site concrete strength in winter was stablished. • A semi-empirical model for assessing ice content by wave velocity was proposed. Ice formation and its volume expansion are important causes of concrete damage in winter construction. This paper presented a non-destructive method to evaluate the strength and ice content of concrete in winter using the impact-echo method. The longitudinal wave velocity obtained by the impact-echo method was the main monitoring indicator. Firstly, the variation of wave velocity and strength of concrete under positive temperature curing and freezing conditions was studied. The influences of pre-curing time, water to cement ratio and exposure temperature on concrete were analyzed. The differences in the strength-wave velocity relationships between frozen and unfrozen concrete are revealed. Further, a quantitative method for evaluating on-site concrete strength in winter by the impact-echo method was established. Secondly, a semi-empirical approach was proposed for calculating ice content based on wave velocity. This model provides a non-destructive way to study the freezing behavior of concrete, which is helpful for further understanding the freezing damage mechanism of concrete in the field.

Study on Thermal Insulation Measures for Construction of Reinforcement Sleeve Grouting Connection in Winter

In this paper, the feasibility of winter construction of steel sleeve grouting connection is studied, and two technical schemes of thermal insulation measures for winter construction are provided. This paper mainly introduces the experimental research work of sleeve grouting by simulating winter construction, including test scheme, test operation flow, test equipment and test data collection and analysis. It is concluded that the thermal insulation measures of prefabricated wall panel covering electric heating blanket, XPS insulation board and sleeve outer wall winding electric companion heat preservation are feasible. Finally, according to the actual project case to verify the feasibility of thermal insulation measures, so that the project can progress smoothly, for similar projects in winter construction to provide reference and reference.

Engineering Method for Calculating the Process of Heating Concrete Structures in Heating Formworks

Issues related to the technology of winter concreting are very relevant. The organization of heating the erected monolithic enclosing structures with minimal thermal or electrical energy consumption is undoubted of scientific and practical interest. The use of electric heating of concrete during construction in winter allows one to create an optimal thermal regime. The hardening process takes place and obtains a structure of the required quality. When developing an automatic control system for the heating process, it is necessary to determine the law for regulating the power of the heaters. This article presents a methodology for calculating the thermal regime of heating concrete structures in heating formwork. The essence is to reduce the boundary value problem of thermal conductivity to a system of equivalent integral equations. A theoretical study of the heat transfer process in concrete structures heated during winter concreting was carried out. A mathematical description of this process was presented in a system of differential equations. After transformations of the above system of equations and applying Green's function of the second kind for the plate and the rod, an approximate solution of the equivalent equation was obtained. As a result of applying the asymptotic method to the integral equation, an analytical solution of the problem under consideration is obtained. The solution obtained makes it possible to determine the temperature fields on the concrete surface and the value of the specific heat flux from electric heaters. A program for calculating temperature fields in heating formworks has been developed. This program effectively solves the problems of monitoring and controlling the concrete hardening process to automate the thermal calculation of heating concrete structures with the help of heating formworks, based on the solution obtained. The developed program makes it possible to calculate the temperature fields at a constant power of the heaters and when it is changed with the help of regulators. The presented method of thermal calculation with a hardware-software complex for controlling the power of electric heaters allows solving a relatively wide range of problems associated with maintaining a constant temperature field.

Geosynthetic-reinforced embankment in cold regions: observations and numerical simulations

An embankment underlain by permafrost foundation was reinforced with wicking woven geotextiles at its side slopes to reduce slope displacements when the fill material that was compacted at frozen condition thaws during subsequent spring and summer seasons following winter construction. The embankment fill and permafrost foundation were instrumented with thermistor strings to monitor soil temperatures as well as ShapeAccelArrays installed at the mid-slope of the embankment to measure displacements. A numerical model was developed in a commercially-available finite element software to simulate the thermal and mechanical behaviour of this embankment and further understand the benefit of using woven geotextiles in cold regions. A sequentially-coupled approach was used where temperature-dependent mechanical properties were invoked based on a heat transfer analysis. Four years of monitored results from the reinforced embankment were used to calibrate the numerical model. An adjacent section of the embankment without the geotextiles was also modelled and results show a significant reduction in slope displacements. The monitored performance and the model results presented will improve the design guidelines for embankments in cold regions using geotextiles.

Research and Discussion on Technical Points of Concrete Construction in Winter of Water Conservancy Project

Research and Discussion on Technical Points of Concrete Construction in Winter of Water Conservancy Project

Организационно-технологические мероприятия по экономии ресурсов и энергосбережению в процессе проектирования и строительства в зимний период

This article considers the problems of obtaining construction products in winter, along with complex technological processes, in the light of scientific achievements and analysis of influencing factors when solving thermophysical problems, as well as evaluating the results on production indicators, especially those related to economics. The accumulated domestic and foreign experience reflects years of intensive work carried out by scientists and engineers, which continues to this day. In Eastern Siberia and neighbouring regions characterised by a prolonged winter period, construction works are carried out all year round. Special attention should be paid to planning construction activities in winter and developing working documentation in view of the seasonality of work. The material and technical resources of the construction contractor should be taken into account, mainly the feasibility of the operational plans for construction and installation activities and the financing schedule. The paper includes examples of winter construction demonstrating the existing limitations, in particular the increased energy consumption. Some recommendations are given aimed at improving the quality of project documentation.

Experimental and Numerical Investigation of Temperature Development of Ohmic Heating Cured Nonmass Concrete under Subzero Temperature

In this paper, carbon fiber/carbon nanofiber strengthening nonmass concrete slab was designed, and ohmic heating (OH) curing was used to promote the strength formation of the slab under −20°C. COMSOL multiphysical field coupling program has been used to simulate the heating process of nonmass concrete slabs under different conditions. COMSOL analysis results showed that the optimal loading power density of OH cured sample under −20°C was 1000 W/m2∼1200 W/m2. Moreover, numerical analysis results were experimentally validated by the multipoint temperature measurement method. Furthermore, the mechanical properties showed that the compressive strength of the sample cured by 2 days OH curing at −20°C reached up to 48.2 MPa. SEM analysis exhibited that OH curing could improve the interfacial transition zone (ITZ) between the fiber and the matrix, leading to a denser microstructure. This study proved that COMSOL program could provide good theoretical guidance for OH cured nonmass cement concrete under subzero temperature. This work establishes an accurate guideline for electric power supplementation, laying a solid foundation of winter construction with high efficiency and low energy consumption.

Calculation of the temperature fields spread at subzero temperature in a monolithic beam

Monolithic construction in winter is faced with problems of concrete strength gain at subzero ambient temperatures. In order to ensure the necessary temperature conditions for hardening and hardening of concrete, various methods of heating structures are used. The relevance of this article is due to the climatic conditions of construction in most of the Russian territory and lack of a unified calculation method. The existing calculation methods are either easy to use, but give approximate answers, or exact solutions, but cumbersome and inconvenient in daily use. This paper presents group analysis method of differential equations used to predict temperature regimes for concreted structures. Solving the nonlinear differential equation of thermal conductivity by group analysis made it possible to derive, using nonlinear submodels, simple and convenient for practical application calculation formulas for modeling the temperature fields of heated structures. Experimental verification of the two proposed solutions of the nonlinear equation was carried out on the basis of the monolithic girder model, subjected to heat treatment at different powers.

Standortoptimierung ÖBB Kraftwerk Spullersee – Bauen zwischen Naturjuwel und alpinen Extremen

AbstractThe construction site is located close to the Spullersee, one of the most impressive mountainsides in the Alps, and is part of the ÖBB Spullersee power station, which is used to generate green 16.7 Hz traction current. The Spullersee, a formerly natural mountain lake, is located over 1800 m a.s.l.in the municipality of Dalaas in Vorarlberg. After almost a century of generating electricity, essential parts of the plant have reached the end of service life, resulted in essential facility renewals as well as numerous operational optimizations in the last two years. In a first construction phase, a new access tunnel to the existing apparatus chamber had to be excavated before seasonal winter closure of the access road. For the winter construction phase, thousands of tons of building materials were stored on the construction site in order to replace the old system parts in the area of the lake‐side apparatus chamber after the Spullersee had been completely emptied. Due to high‐alpine location of the site in one of the snowiest regions in Austria, not just working in winter was challenging, but also access. In winter the site was achieved only by using a small cable car and a narrow footpath through the almost two‐kilometer‐long pipe tunnel. This was not everyone's cup of tea.

Seismic Behaviour of Steel Staggered Truss in Building

In this study staggered-truss system (STS) is studied for structural steel framing for the multi-story and high-rise buildings. The staggered-truss systems (STS) consists of a series of story-high trusses spanning the total width between two rows of external columns and arranged in a staggered pattern on adjacent column lines. The system is known to be appropriate for use in residential buildings such as apartments, dormitory and hotels. The columns are located only on the external faces of the building. The large clear span and open areas can be created. The interaction of the floors, trusses, and columns makes the structure perform as a single unit, there by taking maximum advantage of the strength and rigidity of all the components simultaneously. Each component performs its particular function, totally dependent upon the others for its performance. These column free areas can be utilized for ballrooms, concourses and other large areas. The one added benefit of the staggered-truss framing system is that it is highly efficient for resistance to the lateral loading caused by wind and earthquake. The stiffness of the STS provides the desired drift control for wind and earthquake loadings. The staggered-truss framing system is one of the quickest available methods to use during winter construction. The floor system not only carries the direct vertical loads. In addition, It has to act as a diaphragm to transfer the horizontal shear forces between stories through truss diagonals. Because of this double use concept this system results in a lighter structure and provides more column-free space than a conventional beam-column framed structure.

Enhancing the mechanical and durability properties of subzero-cured one-part alkali-activated blast furnace slag mortar by using submicron metallurgical residue as an additive

Cold weather (<0 °C) is known for its detrimental impacts on concrete, and thus expensive and energy-consuming heating and insulation systems are used in cold-weather concreting to prevent frost damage. Supplementary cementitious materials are not recommended for use in cold-weather concreting because they slow down the setting time of concrete. In this study, one-part alkali-activated slag (AAS) was presented as an alternative environment-friendly binder for winter construction. The impacts of iron-containing submicron metallurgical residue on the reactivity, hardened properties, and durability of subzero-cured one-part AAS pastes and mortars were comprehensively studied. The incorporation of submicron particles (SMPs) enhanced the reactivity of AAS pastes by increasing the amount of precipitated hydrate phases and developing supplemental hydration products like calcium ferrosilicate hydrate. The positive effects of SMPs were highlighted via the denser microstructure, higher ultrasonic pulse velocity, increased compressive strength, and better durability properties of the AAS mortars. These improvements were attributed to the nucleation and filling behaviors of the added SMPs. On the contrary, decreased subzero curing temperature hindered the reaction progress, which adversely affected the hardened and durability properties of the mortars and limited the SMPs efficiency. With additional above-zero curing, higher compressive strength and lower water absorption and permeable porosity were measured in the AAS mortar cured initially at −5 °C compared to that cured at +20 °C.

Comparative Analysis on the Micropore and Microstructure Characteristics of Concrete under Insulated Formwork.

During concrete construction in winter, the concrete performance is generally improved by adding a chemical admixture or providing protection using tents and hot-air blowers. However, long-term strength or safety accidents may occur due to the installation and removal of the tents. This study considered insulated gang forms to improve formwork methods. In this regard, the microstructure and micropore characteristics of concrete were investigated experimentally to examine the insulated gang form effect on the physical and mechanical properties of concrete. The micropore characteristics were investigated through scanning electron microscopy. The results confirm that applying insulated gangs improves workability and safety without adding chemical admixture. Moreover, the application of insulated gang forms reduces the use of tents and hot-air blowers. Therefore, insulated gangs provide excellent initial quality to the concrete.

Potential Applications of Phase Change Materials to Extend the Winter Construction Time of Earth-Rock Dam in Cold Regions

AbstractDuring earth-rock dam construction, temperature control to reduce the freeze–thaw impact on core-wall clay in cold regions is difficult. To address this challenge, this research developed a...