Effect of Silica Fume and Polyvinyl Alcohol Fiber on Mechanical Properties and Frost Resistance of Concrete

To improve the mechanical properties and frost resistance of concrete, silica fume, and polyvinyl alcohol fiber compounded in concrete. The mechanical and frost resistance of concrete were comprehensively analyzed and evaluated for strength change, mass loss, and relative dynamic elastic modulus change by compressive strength test, flexural strength test, and rapid freeze-thaw test. The results showed that with the incorporation of silica fume and polyvinyl alcohol fiber, the compressive and flexural strengths of concrete were improved, and the decrease in mass loss rate and relative dynamic elastic modulus of concrete after freeze-thaw cycles were significantly reduced, which indicated that the compounding of silica fume and polyvinyl alcohol fiber improved the frost resistance of concrete. When the content of silica fume was 10% and the volume content of polyvinyl alcohol fiber was 1%, the comprehensive mechanical performance and frost resistance of concrete is the best. The compressive strength increased by 26.6% and flexural strength increased by 29.17% compared to ordinary concrete. Based on the test data, to study the macroscopic damage evolution of concrete compound silica fume and polyvinyl alcohol fiber under repeated freeze-thaw conditions. The Weibull distribution probability model and GM (1, 1) model were established. The average relative errors between the predicted and actual data of the two models are small and very close. It is shown that both models can reflect well the development of concrete damage under a freeze-thaw environment. This provides an important reference value and theoretical basis for the durability evaluation and life prediction of compound silica fume and polyvinyl alcohol fiber concrete in cold regions.

Influence of Steel Fiber on Durability Performance of Concrete under Freeze-Thaw Cycles

To verify the steel fiber effect on durability properties of the concrete in cold regions, four types of steel fiber reinforced concrete were prepared, and the fiber dosage were 0, 20 kg, 40 kg, and 60 kg, respectively. The rapid freeze-thaw test was adopted to evaluate the frost resistance durability, and the evaluation indexes of the mass loss and the residual dynamic modulus of elasticity (RDME) the samples were compared, respectively. The frost damage of the matrix regarding the different freeze-thaw cycles (FTCs) was evaluated using the Weibull distribution. The capillary water absorption (CWA) experiments were also conducted corresponding to different freeze-thaw cycles (FTCs). The results revealed that the mass loss was not an effective index for frost damage evaluation of macro-steel fiber reinforced concrete. The FTCs corresponding to the loss of RDME to 60% were enhanced noticeably with the increase of fiber content. The relationship between the frost damage and the FTCs can be evaluated using the Weibull distribution. Compared with the PC, the frost resistance grade of the reinforced concrete with fiber dosage of 60 kg/m3 increased by 125%. After the frost action, the CWA capacity of concrete improved significantly, while, under the same FTCs, the CWA of the matrix decreased with the increment of macro-steel fiber dosage. The steel fiber showed a strong positive influence on enhancing the durability performance of concrete in cold region.

State evaluation of some Hydrangea macrophylla (Thunb.) varieties after winter hardiness in the agrometeorological conditions of central Russia

Hydrangea macrophylla (Thunb.) Ser. is one of the most popular ornamental crops, used in landscape design. This article represents the study of the variety resistance of species and influence their of climatic change. In that sense the effective technology of plant shelter for the winter hardiness can be considered as a successful important factor for the promotion of this crop in northern area. Wherefore we consider in a comparative analysis of H. macrophylla varieties Forever & Ever Blue and Peppermint, which we carried out after winter hardiness in the conditions of central Russia. The most reliable and proven way to shelter for winter of hydrangea is the shelter of lutrasil, which contributed to an increase in the viability of shoots and the amount awakened buds, and also provided the better growth of shoots during the month. The highest percentage of overwintered shoots (77,8%), the amount of vegetative and generative buds (19,3±1,3 сm и 9,6±0,7 сm., respectively) and the total growth of shoots in spring (10,2 cm) were characteristic for variety Forever & Ever Blue for using lutrasil as a shelter. Keywords: HYDRANGEA MACROPHYLLA, VARIETIES, WINTER HARDINESS, FROST RESISTANCE, VIABILITY, SHELTER

Winter resistance and frost resistance of representatives of the genus Cotinus Mill. in the conditions of the Right Bank Forest Steppe of Ukraine

Aim. The goal is to assess the winter and frost resistance of plants of representatives of the genus Cotinus Mill. from the collection of the National Dendrological Park "Sofiyivka" of the National Academy of Sciences of Ukraine and the Botanical Garden named after Academician Alexander Fomin of the Taras Shevchenko National University of Kyiv. Methods. The frost resistance of plants was investigated in the laboratory of plant physiology of the Institute of Horticulture of the National Academy of Sciences of Ukraine, by the method of direct freezing of shoots during the period of forced dormancy of plants. The intensity of damage (browning) of tissues on transverse sections of shoots was assessed using a six-point scale by M. A. Solov'eva (1982). The objects of study were plants C. obovatus Raf., C. coggygria Scop., C. coggygria 'Royal Purple', C. coggygria 'Purpurea'. Winter hardiness was assessed visually on an eight-point scale by S. Ia. Sokolov, (1957). Results. According to estimates of the general freezing of plants in the winter period of 2014–2020, minor injuries were found in all representatives of the genus Cotinus, which were estimated at 1–2 points. The results of experimental studies of plant frost resistance showed that in most variants of the experiment, the tissues of the upper internode and buds froze more. The tissues of the medial part of the shoot turned out to be the most resistant to freezing. According to the results of artificial freeze testing of cut shoots of C. coggygria and C. coggygria 'Royal Purple", sampled in the period of forced dormancy of plants, insignificant tissue damage was revealed at freezing temperature of –25 °С and –30 °С (0.63–1.70), only at temperature of –35 °C, the score of bark damage was 2.3–2.5 points. Conclusions. The low temperatures of the winter period of the study area cannot be considered as limiting abiotic factors that limit the widespread use of the studied representatives of the genus Cotinus in landscape construction. The high potential of frost and winter hardiness of the studied taxa gives grounds to test them in the more northern regions of the Right Bank Forest-Steppe of Ukraine to create garden and park compositions, because due to high decorative flowering and specific crown shape they have an attractive appearance in both group and solitary plantations.

The effect of weather conditions in southern Russia on the frost resistance of apricot generative buds

One of the reasons limiting the apricot expansion in the world is the short period of winter dormancy in the plants and the rapid development of generative buds in the spring. Apricot flower buds often die even after small spring return frosts that limit the commercial culture of this fruit crop. The aim of this investigation was to study collection-breeding plantations and select frost-resistant genotypes that have promise for commercial and breeding use. To solve this problem, the frost resistance of generative buds in 50 apricot cultivars and the breeding forms of various origins were studied by freezing treatments of the branches in a climatic chamber. The Czech cultivar ‘Leala’ was selected due to its best frost resistance. In late winter 2020–2021, six cultivars and breeding forms, which kept 41.8 to 65.9% of the generative buds alive, were identified. These genotypes are characterised by a slow development that prevents any negative freezing temperature effects. Thus, the results of the study confirmed the dependence of the adaptation mechanisms in apricot plants on the rates of their morphogenesis and abiotic factor pressures.

Investigation of the Freezing—Thawing Effect on the Slip Resistance of Natural Stones

The effect of freeze–thaw cycling on the slip resistance of dimension stones was investigated. Slip and frost resistance of limestones, granites and marbles were determined via pendulum tester in dry and wet conditions and controlled freeze–thaw cycles, respectively. Unpolished surfaces under dry conditions (mainly granites and marbles) were positively affected by freezing-thawing. In wet surfaces no significant change was observed. Polished surfaces were not affected even after 100 freeze–thaw cycles. Electron microscopy showed increased wear, hence roughness, of unpolished surfaces after freezing–thawing; homogeneity of polished surfaces prevented slip resistance from being significantly affected.

Study on Mechanical and Frost Resistance Properties of Slag and Macadam Stabilized with Cement and Fly Ash

China is a large country in terms of coal production and consumption. The fly ash and slag produced by thermal power plants pose a great threat to the environment. To reduce the adverse effects of fly ash and slag on the environment, a mixture of slag and macadam stabilized with cement and fly ash was prepared as pavement base material. Compaction tests, unconfined compressive strength tests, splitting strength tests, frost resistance tests, and ultrasonic tests were performed on the mixture. The results show that with an increase in slag replacement rate, the unconfined compressive strength and splitting strength decreased. However, the adverse influence of the slag replacement rate on unconfined compressive strength and splitting strength of specimens gradually weakened with increasing curing time. The frost resistance of the mixture first increased and then decreased with an increase in the slag replacement rate. When cement content was 5% and the slag replacement rate was 50%, the frost resistance of the mixture was the best. Regression analysis of the ultrasonic test showed that the ultrasonic test can effectively characterize the strength of the mixture and the internal damage degree under freeze–thaw cycles. In conclusion, the slag replacement rate of the mixture is recommended to be ~50%, which has preferable mechanical and frost resistance performance.