CC BY
16
SRSTI 67.15.35
Brzhanov Rashit Temerzhanovich
Candidate of Technical Sciences, Associate Professor,
Academician of the International Academy of Informatization,
Caspian State University of Technology and Engineering named after S. Esenov,
Aktau, 130000, Republic of Kazakhstan,
e-mail: brzhanov@mail.ru
THE STUDY OF THE DURATION OF THE SET OF
winter concrete critical strength
This paper assesses the technological features of winter concreting. In order to predict the cooling time to the set of critical strength, the following are taken into consideration: surfacing module, initial and final temperature of concrete, specific heat capacity of concrete, outdoor temperature, type of concrete formwork. The additional costs of thermal insulation of concrete are considered by taking into account its heat release, thermal conductivity of heat of various formwork.
Keywords: winter concreting, concrete cooling time, critical strength, winter concreting methods.
INTRODUCTION
The urgency of the problem is the need to increase the durability of materials and products, formed of multicomponent chemical compounds. Concrete and reinforced concrete, in fact, are the products of chemical transformation of dry, loose components into the hard stone, after a large number of interactions with each other in the presence of water. In what way the reaction will go between the concrete components and whether it goes, depends, among other things, on external influences.
Particularly it refers to the construction of buildings from solid concrete. This technology improves the efficiency of construction, there is an opportunity of diversity architectural expression and volume planned solutions.
MAIN PART
However, these and other advantages of the concrete is not completely implemented, since the peculiarity of interaction patterns are not sufficiently investigated, constituting of these systems based on deformability, durability of characteristics. The properties of materials are caused by temperature, humidity impacts, and also the interaction time of hydration products with each other and with the environment. This provision is particularly important for the majority of regions of Russia and Kazakhstan, where the winter period lasts for more than 6 months a year. Moreover, a substantial impact on the qualitative and quantitative indicators of these patterns exert all sorts of additives and technological products (ash, slag) [1-5].
For winter concreting a variety of technological methods are used, which can be divided into two major groups - heating methods and no heating methods. The main parameters of choice of winter concreting production technology are the massiveness of
concreted structures; critical strength of concrete; presence of a developed infrastructure for ensuring the construction of energy resources and equipment. The module of surface characterizes the massiveness of construction and equal to the ratio of the cooling surface structure F, m2 to its volume V, m3.
Table 1 - Selection of the most economical method for standing of concrete at winter concreting
Type of construction Minimal air temperature, ° C, until The method of concreting
Massive concrete and reinforced concrete foundations, blocks and slabs with Mn * £ 3 -15 thermos
-20 an accelerated thermos
Foundations under the construction of buildings and equipment, massive walls, etc. with Mn =3 - 6 -15 thermos, an accelerated thermos
Columns, beams, purlins, elements of frame structures, piled grillages, walls, overlaps with Mn = 6 - 10 -15 an accelerated thermos, an accelerated thermos with electro warming or electrical heating
Economically the most expedient is the method of «thermos» (table 1). During the application of any method of winter concreting is necessary to provide so-called critical strength, i.e., the strength by the complete freezing time of the concrete. In practice, standing the construction by the method of thermos is more often necessary to determine the cooling time of the concrete, as well as the amount collected during this strength time. Depending upon the specific conditions of production work, this task can be solved by the calculation method of B. G. Skramtaev or by the method of V. S. Lukyanov. Besides these methods, there are different methods for calculating of cooling concrete and reinforced concrete structures - analytical, divisional integration, approximate solutions, analogies (hydraulic and electric), experimental.
The simplest and sufficiently reliable for practical purposes is the calculation method of B. G. Skramtaev with changes in the calculation formula brought by S. A. Mironov. By this method the cooling of the construction is calculated by the formula
T = n •v(tb. n - tb. .) + EC
Ê • Î, (tber - tv ) ' (1)
where t - positivity of concrete cooling, hour;
c - specific heat capacity of concrete kJ / (kg. °C);
Y - volume weight of concrete kg / m3;
tb.n. - the initial temperature of the concrete mix before laying into the construction °C;
tb.k. - the final temperature of concrete, to which the continuance of the concrete cooling is calculated, °C;
E - heat generation of 1 kg cement during the cooling time, KJ;
C - cement consumption for 1m3 of concrete, kg;
K - the heat transfer coefficient of formwork, W / (m2. °C);
Mn - the module of a surface cooling construction, m-1;
tb.sr. - the average value of the concrete temperature during the cooling time, °С;
tb. - the external air temperature, °С.
Accelerated thermos extends the area of thermos application, due to introduction of antifreeze additives into the concrete. Such concrete, having accumulated the critical strength in the cold, after thawing and hardening (28 days) under normal conditions acquires the strength not less than 100 % of the grade. In order to conduct the calculation time of cooling the concrete, the following data is needed: the size of construction, type and grade of concrete, consumption and activity of cement, the external air temperature, wind speed, steel consumption to 1m3 of concrete, the initial temperature of concrete, formwork material. The sequence of calculation.
Determine the volume of concrete in the construction
V= h В (2)
Complete surface of cooling the construction
F=2(hB+ BL+ hL) (3)
where h, B, L - is subsequently the thickness, width, length of concreted structure.
The module of surface structure
M.-I
11 V
(4)
The initial temperature of the concrete considering the armature heating
(5)
where C1 and C - is a specific heat of concrete and fittings (kJ / kg) P1 - is a consumption of fittings kg / m3.
From the tables and handbooks [6] the average temperature of concrete hardening is defined (K.cp) which can achieve the required strength at specified time (t). For this specific material and formwork construction its coefficient of heat transfer is calculated by the formula
(6)
The application range of this formula
W >0 625
C-t,
A specific heat flux through the formwork
(7)
g = K(tbn - tv) (8)
For the selected type of formwork, the temperature at its outer surface is specified
(9)
The value topH must satisfy the requirement:
tH -t'
ш 011 X100% < ±5%
(10)
Determine the average temperature of formwork heating at the beginning of cooling:
t' +t"
Calculate the heat, consumed for formwork heating
(11)
Q™ = (C-tIÊciF1ôi71
ivl
(12)
where C.,F., g. - is a specific heat capacity, area, thickness and volume weight of form-work
We specify the temperature of concrete to the beginning of cooling taking into account heat losses on the heating of the fittings and formwork. The coefficient value of formwork heat transport
(13)
If this calculation does not confirm the necessary heat protection of formwork, it is necessary to enter additional thermal insulation of formwork and re-count the heat transfer coefficient [7]. Considering that, with rising temperature the thermal conductivity of the materials change, according to the empirical formula of O. V. Vlasov the thermal conductivity material of formwork A,t is calculated by the formula:
X = X (1 + 0,0025t p)
t ov 7 on /
(14)
where Ào - coefficient of thermal conductivity of formwork material at 0° C topr - heating temperature of formwork materials.
The thickness of thermal protection of formwork is determined by the formula
(15)
which à., À - coefficient of thermal conductivity, according to insulation and components of formwork materials at tonr
The specific heat flux is specified through the formwork
q1 - K'Oi,,, - tv)
(16)
The final temperature of outer surface of formwork is specified
(17)
We specify the percentage of error given by the t1 and rated temperature of to on the outer surface of formwork
(18)
Determine the concrete temperature at the end of a specified period of cooling
(19)
heck the continuation of concrete cooling to t
'bn
(20)
CONCLUSIONS
In the given formula the heat from exotherm of cement is not considered, because it is already considered during the calculation of the average temperature of concrete hardening, as well as the calculation of the heat transfer coefficient of formwork [8].
OK
d
By these formulas the cooling time of concreted structures for specific climatic and other conditions can be calculated, and also diagrams of cooling for these conditions can be constructed, necessary thermal insulation of formwork can be select [9, 10].
REFERENCES
1 Brzhanov, R. T. Problems of selecting the methods of winter concreting. Messenger of PGU - № 2. - 2009. - P. 14-33.
2 Корниенко, П. В., Тугумбаев, Д. А., Ахметова, У. Е., Атконова, А. П. Системный подход при проектировании бетона с требуемыми свойствами в железобетонных конструкциях // Наука и техника Казахстана - 2018. - № 2 - С. 45-55.
3 Васильев, А. А., Кирюшина, В. И. Прогнозирование времени критического коррозионного повреждения стальной арматуры в бетонах различных классов по прочности на сжатие // В сборнике : «European Research» - Сборник статей XXI Международной научно-практической конференции : в 2 ч. - 2019. - С. 195-198.
4 Агибаева, А. Ж., Аманжолов, А., Ларичкин В. В. Разработка оптимального состава бетонных смесей на основе шламаглиноземного производства // Наука и техника Казахстана - 2018. - № 3 - С. 64-70.
5 Dudar, I., Kovalenko, A. Review methods and winter concreting hold concrete mix medium under negative temperature // Сучасш технологи, матерiали i конструкци в будiвництвi. - 2013. - № 2 (15). - С. 29-32.
6 Bagheri-Zadeh, S. H. et al. Field study of concrete maturity methodology in cold weather // Journal of Construction Engineering and Management. - 2007. -Т. 133. - №. 11. - С. 827-835.
7 Giancoli, D. C., Giancoli, D. C. Physics for scientists and engineers with modern physics. - Upper Saddle River, NJ : Prentice hall, 2000. - Т. 130215171.
8 Yang, K. H., Mun, J. S., Cho, M. S. Effect of curing temperature histories on the compressive strength development of high-strength concrete //Advances in Materials Science and Engineering. - 2015. - Т. 2015.
9 Brzhanov, R. T., Pikus, G. A., Traykova, M. Methods of increasing the initial strength of winter concrete // IOP Conference Series : Materials Science and Engineering. - IOP Publishing, 2018. - Т. 451. - №. 1. - С. 012083.
10 Бржанов, Р. Т. Особенности зимнего бетонирования // В сборнике : «Особенности современного этапа развития естественных и технических наук» -Сборник научных трудов по материалам Международной научно-практической конференции. в 2-х частях. - Под общей редакцией Е. П. Ткачевой. - 2018. - С. 39-42.
Material received on 02.03.20.
Бржанов Рашит Темержанулы
т^.к., доцент, Хальщаральщ а^параттандыру академиясыныц академии, Ш. Есенова атындаFы Каспий мемлекетлк технологиялар жэне инжиниринг университет^
Актау к., 130000, Казахстан Республикасы, e-mail: brzhanov@mail.ru Материал баспаFа 02.03.20 TYCTi.
Кыскы бетонныц сыни бер1кт1г1ц алуынын мерз1м1ц зерттеу
Бул мацалада цысцы бетонныц технологиялъщ ерекшелiктерi царастырылады. Бетон сыни бержтжке жеткенге дейт салцындату уацытын болжау ушт келеалер ecKeprnedi: бетонныц модулi, бетонныц бастапцы жэне соцгы температурасы, бетонныц нацты жылуыг, сыртцы температура, бетонды вцдеу тyрi. Бетонныц жылу оцшаулауыныц цосымша шыгындары оныц жылуды шыгаруын, эр тyрлi тштдердщ жылу вттзгшт^т ескере отырып царастырылады.
Кiлттi свздер: цысцы бетондау, бетонныц салцындату уацыты, сыни бержтш, цысцы бетондау эдiстерi.
Бржанов Рашит Темержанович
к.т.н., доцент, академик Международной академии информатизации,
т/» и и U U
Каспийский государственный университет технологий
и инжиниринга имени Ш. Есенова,
г. Актау, 130000, Республика Казахстан,
е-mail: brzhanov@mail.ru
Материал поступил в редакцию 02.03.20.
Изучение продолжительности набора зимнего бетона критической прочности
В данной статье рассматриваются технологические особенности зимнего бетонирования. Для прогнозирования времени остывания до набора бетоном критической прочности принимаются во внимание: модуль поверхности, начальная и конечная температура бетона, удельная теплоёмкость бетона, температуру наружного воздуха, тип опалубки бетона. Рассмотрены дополнительные расходы на теплоизоляцию бетона с учётом его тепловыделений, теплопроводимость тепла различных опалубок.
Ключевые слова: зимнее бетонирование, время охлаждения бетона, критическая прочность, методы зимнего бетонирования.
