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Compressive and Tensile Strength of Nano-clay Stabilised Soil Subjected to Repeated Freeze–Thaw Cycles

Roustaei Mahya, Sabetraftar Mahdi, Taherabadi Ehsan, Bayat Meysam

Studia Geotechnica et Mechanica

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2023

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Vol. 45, nr 3

221--230

EN

Improvement of the mechanical properties of clayey soils by additional elements to enhance the strength under numerous freezing and thawing cycles has been considered as a serious concern for engineering applications in cold regions. The objective of the current study is to investigate the effect of nano-clay as a stabiliser on the mechanical properties of clay. To this end, the clay specimens were prepared by adding various percentages of nano-clay ranging from 0.5% to 3% by dry weight of soil and were experimentally tested under the uniaxial compression and tensile splitting tests under different curing times (0, 7 and 28 days) after experiencing various freeze–thaw cycles ranging from 0 to 11. It can be concluded from the results that nano-clay particles may be used as a stabiliser in geotechnical applications to improve soil property. The results indicate that the optimum moisture content (OMC) of specimens increases and the maximum dry density (MDD) decreases with the increasing nano-clay content. The specimens containing about 1% nano-clay recorded maximum values of unconfined compressive strength (UCS) as well as tensile strength. For example, the addition 1% nano-clay increased the UCS and tensile values of clay specimens under the curing time of 28 days by 34% and 247%, respectively. In addition, the long-term durability of specimens against freeze–thaw cycles increases further with the addition of nano-clay content ranging from 2% to 3%.

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The durability of concrete subject to mechanical load coupled with freeze–thaw cycles: a review

Xu Yanqun, Ye Hansong, Yuan Qiang, Shi Caijun, Gao Yun, Fu Qiang

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 1

art. no. e47, 2022

EN

In cold regions, concrete structures are often subject to the coupled effect of mechanical loading with freeze–thaw (F–T) cycles, which results in a reduced service life. In this paper, the state of the art and challenges regarding the durability of concrete subjected to mechanical loading coupled with F–T cycles are reviewed in depth. The experimental setups used to simulate the coupled effect of mechanical loading with F–T cycles were summarized first, including the shapes of the specimens, operation methods, advantages, and limitations. Subsequently, relevant research methods such as numerical simulation methods and damage characterization methods were presented. Afterward, special attention was dedicated to the mechanism elaboration and performance improvement of the concrete subject to the coupled effect. Finally, some thoughts on potential directions for future work were discussed.

3

The effect of freeze-thaw cycles on flexural behaviour of FRP-reinforced ECC beams

Wang Yi, Wang Guan, Guan Zhongwei, Ashour Ashraf, Ge Wenjie, Zhang Pu, Lu Weigang, Cao Dafu

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 3

265--288

EN

This paper presents experimental and theoretical investigations on the flexural utilised of FRP (fibre-reinforced polymer) rebar-reinforced ECC (engineered cementitious composite) beams subjected to freeze–thaw cycles. Eight FRP-reinforced specimens after subjected to 0, 50, 100 and 150 cycles of freeze–thaw were tested to failure under flexural loading. Experimental results show that the moment capacity decreases with the increase of freeze–thaw cycles regardless of the material used, but the decreasing rate of the reinforced ECC specimen is lower than that of the conventional reinforced concrete specimen. The bearing capacity, deflection and crack width of the reinforced ECC specimens under quasi-permanent combination of moments are 1.13 ~ 1.21, 0.66 ~ 0.90 and 0.71 times of those of the conventional reinforced concrete specimens, respectively. Due to the excellent tensile and durability performance of ECC materials, bearing capacity, stiffness and crack resistance of FRP-reinforced ECC beams are enhanced compared with their conventional counterparts, particularly with more freeze–thaw cycles. Based on the formulae from ACI 440 and GB 50608, taking into account of the contribution of ECC material and balanced reinforcement ratio, the simplified formulae are developed to estimate the moment capacity and stiffness of the FRP-reinforced ECC beams. The results predicted on the moment capacity and deflection are in good agreement with the corresponding experimental measurements.

4

The Effect of Environmental Stressors on Respiration Activity of Afforested Mine Soils

Pudełko A., Sroka K.

Geomatics and Environmental Engineering

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2017

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Vol. 11, no. 4

97--110

PL

Funkcje gleb silnie zależą od aktywności mikroorganizmów i ich zdolności do przeciwstawiania się różnym stresom środowiskowym. Celem pracy było porównanie wpływu dwóch często występujących czynników stresowych – cykli susza-wilgoć i mrożenie-rozmrażanie – na respirację gleb industrioziemnych i gleb naturalnych. Próbki gleby (n = 18) zostały pobrane na zrekultywowanych terenach kopalni piasku w Szczakowej oraz w lasach naturalnych w jej sąsiedztwie. W próbkach oznaczono zawartość materii organicznej, tempo respiracji, pH i przewodność elektrolityczną. Badane próbki z gleb industroziemnych i naturalnych miały podobne uziarnienie i zostały sklasyfikowane jako piaski gliniaste. Gleby naturalne zawierały znacznie więcej OM [%] niż gleby industrioziemne, natomiast obie rozpatrywane kategorie gleb nie róż- niły się znacząco pod względem pH. Ponadto nie zaobserwowano istotnych różnic w zawartości materii organicznej, pH i uziarnienia gleb w próbkach pobranych pod różnymi drzewostanami (sosna, brzoza, modrzew). Gleby industroziemne wykazywały znacznie niższe początkowe wartości respiracji (1,34 μg C-CO2 g−1 24 h−1 ) niż gleby naturalne (3,13 μg C-CO2 g−1 24 h−1 ). Pięciocyklowy proces mrożenia-rozmrażania zredukował skumulowane wartości wydzielania CO2 zarówno w industrozimenych, jak i naturalnych glebach o odpowiednio 17,8% i 6,7%. Ponadto reakcja na wskaźnik respiracji w cyklu susza-wilgoć różniła się znacząco w przypadku gleb industroziemnych i naturalnych: w glebach naturalnych wszystkie cykle suszenia-nawadniania zwiększały wartość respiracji, przy czym wzrost ten był bardziej widoczny w ostatnich dwóch cyklach. Podsumowując, można stwierdzić, że okresy suszy w lecie i mrożenia-rozmrażania jesienią oraz wiosną mogą wywierać bardziej negatywny wpływ na leśne ekosystemy na ternach zrekultywowanych niż na obszarach występowania naturalnych drzewostanów.

EN

The functioning of soils strongly depends on the activity of the soil microbial communities and their ability to withstand different environmental stresses. The aim of this work is to compare the effect of two frequently occurring stressors (drought-rewet and freeze-thaw cycles) on the basal respiration rate of mine and natural soils. Soil samples (n = 18) were delivered from the Szczakowa open-cast sand quarry in Poland. The samples were measured for organic matter (OM) content, basal respiration, pH levels, and electric conductivity. The studied mine and natural soils had a similar texture and were classified as loamy sands. The natural soils contained significantly more OM than the mine soils but did not differ in terms of pH. There were no significant differences in the OM content, pH, and texture of the soils under the studied tree species (Pine, Birch, Larch). Mine soils exhibited significantly lower initial respiration rate (RESP value) than the natural soils (1.34 μg C-CO2 g−1 24 h−1 vs. 3.13 μg C-CO2 g−1 24 h−1 ). Five freeze-thaw cycles reduced cumulative CO2 evolution both in both the mine and the natural soils by 17.8% and 6.7%, respectively. Moreover, the reaction of the respiration rate to dry-rewet cycles differed distinctly between the mine and natural soils. In the natural soils, all dry-rewet cycles increased the respiration rate, wherein the increase was much more pronounced in the last two cycles. We conclude that periods of drought in the summer and freeze-thaw events in the autumn and spring may have a stronger negative effect on the functioning of forest ecosystems in the reclaimed lands than in natural stands.

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Effects of freezing and freeze-thaw cycles on soil microbial biomass and nutrient dynamics under different snow gradients in an alpine meadow (tibetan plateau)

Liu L., Wu Y., Wu N., Luo P., Xu J., Mao Y., Zhang L.

Polish Journal of Ecology

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2010

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Vol. 58, nr 4

717-728

EN

In alpine zones, cold season processes, particularly those associated with snow accumulation and ablation, have a central role in ecosystem functioning. However, we know very little about soil carbon and nitrogen processes under the snowpack in these ecosystems, including the Tibetan Plateau. We conducted an experiment comparing three snow regimes (11 m x 1 m plots) of different snow depths and durations at an altitude of 4,100 m in the Minshan Range on the eastern Tibetan Plateau. The three snow regimes included a shallow and short duration snowpack (SS; depth <10 cm), a moderate snow depth and medium duration snowpack (MS; depth <20 cm), as well as a deep and long duration snowpack (DS; depth > 30 cm). This study explores the effects of different snow conditions on soil temperature, and further describes the sequence and timing of dissolved nutrients and microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) in soils under different snow regimes during the autumn-winter transition (i.e. November 7, 2008 - March 7, 2009). Three successive phases of temperature change were distinguished: I - initial decline - soil temperatures dropped steadily from 4[degrees]C to about 0[degrees]C at the same rate for all three snow regimes; II - moderate freezing - soil temperatures fluctuated between 0[degrees]C and -7[degrees]C under all three snow regimes; III - multiple freeze-thaw cycles took place in the SS and MS regimes, but permanent freezing occurred in the DS regime. Under moderate freezing, we found that soil temperature fluctuation was an essential factor for the transformation of soil C and N. Our results indicate that larger temperature fluctuations correlate with a greater increase in dissolved organic nitrogen (DON) content. Dissolved organic carbon (DOC) content increased markedly only under the most drastic temperature fluctuations. In contrast, MBC content increased significantly only when soil temperatures were relatively steady. Under the permanent freezing, only a large number of freeze-thaw cycles caused a significant decline of NO[^][3] -N and DOC concentrations. DON content declined markedly under permanent freezing and multiple freeze-thaw cycles. However, MBC content declined significantly only under permanent freezing. Ultimately, multiple freeze-thaw cycles resulted in the export of dissolved nutrients (organic and inorganic nitrogen) from the alpine ecosystem which had previously accumulated in the moderate freezing phase of the soil.