Evaluation of prestress losses in prestressed concrete specimens subjected to freeze–thaw cycles

Prestressed concrete structures are considered to be reliable and durable. However, their long-term performance when subjected to frost attack is still unclear. In this work, experiments were carried out to evaluate the prestress losses in post-tensioned prestressed concrete specimens subjected to freeze–thaw cycles (FTCs). Two cases were considered: in one case, a series of specimens were prepared and tested in a freeze–thaw chamber; in the second case, the same series of specimens were tested in an indoor environment (outside the chamber). The difference between the prestress losses of the specimens inside the freeze–thaw chamber and those outside the chamber equalled the prestress losses due to FTCs. When using mathematical models to predict the prestress losses due to the FTCs, it was found that they were relatively small when the concrete was slightly damaged. However, they increased rapidly when the FTCs were repeated. The eccentricity of the prestress wires led to larger prestress losses when subjected to FTCs. Moreover, the same cross section and eccentricity resulted in similar prestress losses due to the FTCs, and the relatively high-strength concrete could withstand more FTCs.     

Evolution of mechanical behaviours of an expansive soil during drying-wetting,freeze–thaw,and drying-wetting-freeze–thaw cycles

This paper investigates the volumetric, microstructural, and shear behaviours of an expansive soil during multiple drying-wetting (DW), freeze–thaw (FT), and drying-wetting-freeze–thaw (DWFT) cycles. Specimens compacted at natural moisture content and dry density were subjected to 1, 4, 6, and 10 DW, FT, or DWFT cycles. Volumetric changes were recorded during the treatments and mercury intrusion porosimetry, and scanning electron microscope tests were conducted to observe the soil’s microstructure before and after treatments. As compacted specimens and specimens after different numbers of DW, FT, and DWFT cycles were saturated and sheared under consolidated undrained condition to determine their undrained elastic modulus (E_u), shear strength (q_u), total cohesion (c), and friction angle (?). Experimental results show that DW, FT, and DWFT cycles mainly influence the soil’s macropores with diameters between 5 and 250 μm. Macropores collapse during DW cycles, which lead to collapse in the soil’s global volume. Cracks develop during FT cycles and result in slight swelling in the soil’s volume. These two effects offset during DWFT cycles and cause an intermediate volumetric behaviour. The E_u, q_u, c, and ? decline during DW, FT, and DWFT cycles, and the reduction was most significant during DWFT cycles. They reach an equilibrium after approximately 6 cycles of treatment. A simple normalized model was developed to describe the stress–strain curves considering the influence of DW, FT, and DWFT cycles. Good agreements were achieved between the model predictions and measurements for all stress–strain curves obtained in this study.

     

Flexural behaviour of reinforced concrete beams under freeze–thaw cycles and sustained load

This paper presents an experimental investigation on the flexural behaviour of reinforced concrete beams under the combined effects of freeze–thaw cycling and sustained loading. Thirteen beams (2000 × 250 × 150 mm) were fabricated and tested. Test parameters included four numbers of freeze–thaw cycles (20, 40, 60 and 80) and three levels of sustained load (0, 20 and 50% of the ultimate load of the control beam). After exposure, the beams were tested at room temperature under four point bending up to failure. The flexural behaviour was evaluated by studying the load-deflection curve, the ultimate load capacity, the ductility, the crack pattern and crack width and the evolution of the neutral axis depth. It was found that freeze–thaw cycles and sustained loading had significant effects on the flexural performance of reinforced concrete beams.     

Correction to: Shear properties and pore structure characteristics of soil–rock mixture under freeze–thaw cycles

Bulletin of Engineering Geology and the Environment - A Correction to this paper has been published: https://doi.org/10.1007/s10064-021-02169-7     

Shear properties and pore structure characteristics of soil–rock mixture under freeze–thaw cycles

Bulletin of Engineering Geology and the Environment - Soil–rock mixtures (S-RMs) are widely distributed in the shallow surfaces of cold regions that experience frequent freeze–thaw...     

Coupled effects of chemical environments and freeze–thaw cycles on damage characteristics of red sandstone

To study the influence of freeze–thaw cycles under complex chemical environments on the red sandstone, nuclear magnetic resonance (NMR) technology was used to analyze the damage evolution law of red sandstone. The freeze–thaw cycles were carried out on four groups of samples soaked in sulfuric acid solution, sodium hydroxide solution, sodium chloride solution and pure water, respectively. Further, NMR tests were performed on the samples and the porosity change of samples, T₂ distribution and nuclear magnetic resonance images were analyzed. Results show that: (1) chemical environments have significant effects on the freezing-thawing damage, and the porosity increases linearly with increasing number of freeze–thaw cycles. (2) Under the frost-heaving force and ionic reactions, the T₂ spectrum will successively shift towards the left and then to the right with increasing number of freeze–thaw cycles. Micropores will constantly appear, and small pores will dynamically expand into macropores. (3) With increasing number of freeze–thaw cycles, the areas of light spots in NMR images will increase gradually, which means that the damage degree is aggravated with continuous development of internal pores. (4) The samples soaked in sodium hydroxide solution and sodium chloride solution are damaged more seriously than those soaked in sulfuric acid solution and pure water. By analyzing and comparing the NMR characteristics of rock under the coupled effects of chemical environments and freeze–thaw cycles, more reliable test data will be available to study the damage mechanism of rock.     

Analysis of the effect of freeze–thaw cycles on the degradation of mechanical parameters and slope stability

Bulletin of Engineering Geology and the Environment - The changes that occur to the physicomechanical features of rocks during freeze–thaw cycles are crucial to research on the stability of...     

Experimental and numerical investigation on the deterioration mechanism for grouted rock bolts subjected to freeze–thaw cycles

Bulletin of Engineering Geology and the Environment - Development of durable anchorage systems for slope support in high-cold and high-altitude areas has been becoming a global research hotspot....     

Structural damage and shear performance degradation of fiber–lime–soil under freeze–thaw cycling

The freeze–thaw cycling damages the soil structure, and the shear performance of soil are degraded. A series of tests on lime–soil(L–S) and fiber–lime–soil(F–L–S), including freeze–thaw test, the triaxial compression test, nuclear magnetic resonance (NMR) test and scanning electron microscope (SEM) test, were completed. The test results showed that fiber reinforcement changed the stress–strain behavior and failure pattern of soil. The cohesion and internal friction angle of soil gradually decreased with the increase of freeze–thaw cycles (F–T cycles). The pore radius and porosity of soil increased, while the micro pore volume decreased, and the small pore volume, medium pore volume and large pore volume increased, and the large pore volume had a little variation after 10 F–T cycles. The number of pores of F–L–S was less than L–S, demonstrating that the addition of fiber helped to reduce the pore volume. The interweaved fibers limited the development and the connection of cracks. By means of the spatial restraint effect of fiber on the soil and the friction action between fiber and soil, the shear performances and freeze–thaw durability of F–L–S better were than that of L–S.     

Effect of chemical erosion and freeze–thaw cycling on the physical and mechanical characteristics of granites

Bulletin of Engineering Geology and the Environment - Rocks in nature are very often subjected to weathering processes. The physical and mechanical properties of granites exposed to chemical...     

Effect of freeze–thaw and thermal shock weathering on the physical and mechanical properties of an andesite stone

Natural stones are exposed to physical weathering due to freeze–thaw (F–T) and thermal shock (TS) when they are used as pavement, cladding and masonry material. In this study, the deterioration of andesite was investigated by determining the physical and mechanical properties of andesite samples after each 10 cycles of F–T and TS up to 50 cycles. It was found that the P-wave velocity, Schmidt hardness and compressive strength decrease to different extents with F–T and TS while porosity and water absorption increase with F–T cycles but decrease with TS cycles. The results showed that F–T has a more destructive effect on the studied material than TS, although abrasion loss measurements suggest that the effect on the surface of the material is greater with TS. An exponential model is proposed to predict the variation of material properties with F–T and TS cycles.     

Mechanical behavior and decay model of the sandstone in Urumqi under coupling of freeze–thaw and dynamic loading

Bulletin of Engineering Geology and the Environment - In cold regions, recurrent freeze–thaw action and loading conditions are important factors affecting the long-term durability of natural...     

Detecting freeze–thaw damage degradation of sandstone with initial damage using NMR technology

Bulletin of Engineering Geology and the Environment - The nuclear magnetic resonance (NMR) technique was used to study freeze–thaw damage degradation of sandstone with initial damage. The...     

The effect of freezing–thawing (F–T) cycles on the radiation shielding properties of concretes

The variation of linear attenuation coefficients μ$\mu$ (cm⁻¹) with the freezing–thawing (F–T) cycles has been investigated for concretes, in which different materials were used as an aggregate. For this purposes, six different concrete blocks have been produced in various ratios of water/cement (w/c) utilizing different materials as aggregates. Then, linear attenuation coefficients were measured for five different F–T cycles. It was noticed that the linear attenuation coefficients decreased with F–T cycles for all concrete types and also different effect observed for different w/c ratio and different aggregate.     

Response of steel beam–columns exposed to fire

Steel beams when exposed to fire develop significant restraint forces and often behave as beam–columns. The response of such restrained steel beams under fire depends on many factors including fire scenario, load level, degree of restraint at the supports, and high-temperature properties of steel. A set of numerical studies, using finite element computer program ANSYS, is carried out to study the fire response of steel beam–columns under realistic fire, load and restraint scenarios. The finite element model is validated against experimental data, and the importance of high-temperature creep on the fire response of steel beam–columns is illustrated. The validated model is used to carry out a set of parametric studies. Results from the parametric studies indicate that fire scenario, load level, degree of end-restraint and high-temperature creep have significant influence on the behavior of beams under fire conditions. The type of fire scenario plays a critical role in determining the fire response of the laterally-unrestrained steel beam within a space subframe. Increased load level leads to higher catenary forces resulting in lower fire resistance. Rotational restraint enhances the fire resistance of a laterally-unrestrained steel beam, while the axial restraint has detrimental effect on fire resistance.     

Comparative effects of cement,coal dust and fly‐ash on H. Abelmoschus

Three types of dusts, i.e. cement, coal and fly‐ash were applied daily at the rate of two grams per square metre per day to 15 days old plants for a period of one month. Visible foliar symptom, photosynthetic pigment content and dry weight were taken as parameters. Small chlorotic spots and marginal chlorosis appeared in leaves sprayed with cement and coal dust respectively. Cement dust was more toxic to chlorophylls than coal dust, while a slight increase was noted in case of fly‐ash. Carotenoids were relatively unaffected by dust pollution.