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CIVIL ENGINEERING AND ARCHITECTURE
STUDY OF CHANGES IN THE STRENGTH AND DEFORMATION PROPERTIES OF CONCRETE IN A DRY HOT CLIMATE
Bakhodir Rizaev
Assistant professor of Namangan Engineering Construction Institute, Republic of Uzbekistan, Namangan E-mail: Rizayev1952 @gmail.com
Adkhamjon Mamadaliyev
PhD of Namangan Engineering Construction Institute, Republic of Uzbekistan, Namangan E-mail: [email protected]
Muzaffar Mukhitdinov
Senior teacher
of Namangan Engineering Construction Institute, Republic of Uzbekistan, Namangan
Mukhtasar Mukhtoraliyeva
Assistant
at Namangan engineering construction institute Republic of Uzbekistan, Namangan E-mail: mailto:[email protected]
ИССЛЕДОВАНИЕ ИЗМЕНЕНИЯ ПРОЧНОСТНЫХ И ДЕФОРМАЦИОННЫХ СВОЙСТВ БЕТОНА В УСЛОВИЯХ СУХОГО ЖАРКОГО КЛИМАТА
Ризаев Баходир Шамситдинович
доцент,
Наманганский инженерно-строительный института Республика Узбекистан, г. Наманган
Мамадалиев Адхамжон Тухтамирзаевич
PhD
Наманганский инженерно-строительный института Республика Узбекистан, г. Наманган
Мухитдинов Музаффар Бахтиёрович
ст. преподаватель, Наманганский инженерно-строительный института Республика Узбекистан, г. Наманган
Мухторалиева Мухтасар Акрамжон цизи
преподаватель,
Наманганский инженерно-строительный института Республика Узбекистан, г. Наманган
Библиографическое описание: STUDY OF CHANGES IN THE STRENGTH AND DEFORMATION PROPERTIES OF CONCRETE IN A DRY HOT CLIMATE // Universum: технические науки : электрон. научн. журн. Rizaev B.S. [и др.]. 2022. 4(97). URL: https://7universum.com/ru/tech/archive/item/13443
AUNiVERSUM:
№ 4 (97)_♦ ♦ - -¿-■i-i-ir.:.- ■:>: I _апрель. 2022 г.
ABSTRACT
The article provides the experimental value of experimental studies, showing the kinetics of changes in the strength and deformative characteristics of concrete in time under short-term loading. concrete in dry and hot climates. The change in the strength of concrete in a dry hot climate is the result of the influence of cyclical daily and seasonal changes in temperature and humidity of the environment.
АННОТАЦИЯ
В статье приводится экспериментальные значение экспериментальных исследований, показывающие кинетику изменения прочностных и деформативных характеристик бетона во времени при кратковременном нагружении бетона в условиях сухого и жаркого климата. Изменение прочности бетона в условиях сухого жаркого климата является результатом влияния циклических суточных и сезонных изменений температуры и влажности среды.
Keywords: shrinkage, creep, stresses, deformation, humidity, temperature, temperature expansion, wet storage, solar radiation, moisture loss of concrete, seasonal change, normal conditions
Ключевые слова: прочность на сжатие, призменная прочность, напряжения, деформация, влажность, температура, нормальное условие, температурное расширение, влажное хранение, солнечная радиация, влажностный градиент , сезонное изменение.
The compressive and tensile strength, hardening of concrete in a dry hot climate lead to a change in its strength. Compared with a similar characteristic obtained for hardening concrete under normal temperature and humidity conditions. These changes are mainly associated with the physical and chemical processes occurring in the hardening concrete in time, which determines the regularity of the manifestation of strength characteris-tics[1, 2, 3,4,5,6,7,8].The combined variable effect of temperature, solar radiation and low relative humidity leads to a change in strength. In this case, the noted changes depend on the age of the concrete. To establish the nature of the change in the strength of concrete over time, the results of testing samples hardening in the open air under the influence of solar radiation and protected from solar radiation in the workshop after 7 days of wet storage of concrete in wet sawdust were analyzed. The samples were made in July, when the air temperature was 350 C and the humidity was 20%. Table 1 shows the results of experimental studies showing the kinetics of changes in the strength and deformation characteristics of concrete over time under short-term loading [9,10,11,12,13].
A comparative analysis of the data given in Table 1 shows that at the age of 28 days, concrete hardened in the open air under solar radiation reveals a shortage of cubic and prism strength within 5-10% in relation to concrete hardened in the workshop and protected from solar radiation. The decrease in the values of these indicators, in all likelihood, is associated with the destructive processes occurring in concrete during its hardening in natural conditions of a dry hot climate[14,15,16,17].
At an early age of concrete in a dry hot climate at elevated temperatures, a more intensive increase in the strength of concrete occurs than under normal conditions. During the year, the increase in strength during storage in the open air under the influence of solar radiation reached 8%, in the workshop 11% of the strength of concrete in 28 days (Table 1). At the same time, from the data in the table, one can also notice the absence of a significant increase in the strength of concrete in the latest terms of hardening in natural conditions of a dry hot climate.
Terms hardening
Concrete age /day/
R MPa/%
£bc X 10"
Influenced by solar radiation
28
60
180
360
16.6
17.5
17.6 106"
18.6 108
14.4
ТпгГ
0.86
14.9
TÖ3
1.8
0.85
15.1
1.76
0.84
1.78 0^8
15.3 Tnfi"
0.85
1.31 100
20400 ПП
20600 mä
21000 102
24600 100
125
128 To?
133
Töü
136 108
In the shadow
in room
t= 25...35^ w= 65...70 ■c
28
60
180
360
19.8
20.9 105
21.4
22.1 123"
17.5
ЛЖ
0.8
18.1 105
2.03
Tññ"
0.86
108
18.8 ML
0.87
19.0 108
All.
0.86
123
118
Tön
128 ToT
123
ML
126 TÖ6
Table 1.
The strength of concrete in 28 days
The increase in the prism strength of concrete exposed to solar radiation was less intense than the increase in the prism strength of concrete in the workshop and amounted to 6% per year, respectively. The prismatic strength of concrete during the year of being in a dry hot climate under the influence of solar radiation increased to a lesser extent than the cubic strength. Of practical interest are the results of determining the coefficient of prism strength Kvs. So, for example, according to SNiP 2.03.01-96, the Kvs value is assumed to be the same for light and heavy concretes and must be at least 0.72.
The obtained data on the coefficients of prism strength Kvs presented in Table 1 indicate some influence of hardening conditions. A decrease in the average value
of Kvs to 8% was established during concrete hardening under the influence of solar radiation[18,19,20].
As follows from Fig. 1, the experimental data on the coefficient of prism strength of specimens in a dry hot climate in natural conditions do not coincide with the experimental points for concrete under normal conditions. The tensile strength of concrete exposed to solar radiation is less than the tensile strength of concrete in the workshop. This can be explained by an increase in air temperature and a decrease in its relative humidity. Tensile strength at the age of 28 and 360 days when stored outdoors under the influence of solar radiation, respectively, is lower by 12% and 14% than the tensile strength of concrete located in the workshop.
— under solar radiation. — in a dry hot climate in in room Figure 1. Coefficient ofprismatic strength of concrete in a dry hot climate
The significant difference between the tensile strength of concrete hardened in a dry hot climate and under normal conditions is the result of stresses from temperature and humidity gradients, leading to stress in concrete. The change in the strength of concrete in a dry hot climate is the result of the influence of cyclic daily and seasonal changes in temperature and humidity.
If the increase in the strength of concrete over time under normal hardening conditions is not intermittent and increasing, this is not observed here due to the influence of the external environment, which gives some features to the ongoing physical and chemical processes in the structure of concrete. In a dry hot climate, in addition to temperature, low relative humidity affects concrete. This causes a change in the hygrometric state of the concrete. Transported by the action of solar radiation, the strength changes to a greater extent than for concrete protected from direct sunlight.
Figure 2 shows the experimental values of the strength and compression of concrete under the influence of solar radiation /3/ and in the workshop /4/ The regularity of the increase in the strength of heavy concrete under normal conditions of a logarithmic dependence is also shown,
(1)
Where ^ г - aged concrete strength 1
strength of concrete at the age of 28 days.
T- age of concrete, days.
The estimate of the increase in the strength of concrete according to formula (1) was derived based on the analysis of extensive experimental data obtained for concretes of various strengths, hardening under normal conditions.
Experimental data obtained in work /6/ in relation to concrete hardening under normal conditions also correspond to the established theoretical regularity according to (1).
However, in dry hot climates, the compressive strength is less than in normal conditions. The greater the impact of dry hot climates on concrete, the greater the divergence of concrete strength values compared to normal storage.
____
• Ш ---—^^
г
7 t4 26 80 180 »0
Figure 2. The nature of the change in the strength of concrete over time during hardening under normal conditions and in a dry hot climate
1 and 2 - according to the logarithmic dependence for concrete with a strength of 20 and 15 MPa under normal conditions;
3- under the influence of solar radiation (dark dots);
4- in a dry hot climate in the workshop (light dots) The strength of concrete also depends on the time of
year of manufacture.
Thus, under natural conditions, the strength of concrete is significantly affected by the season of its preparation, the degree of completion of the hydration process, and the hygrometric state of concrete at the time of application of the load.
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