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12T. 2 №11. 2022
Texnik fanlar / Technical sciences / Технические науки
International journal of theoretical and practical research
Scientific Journal
QR-Article
Volume: 2 30.11.2022
Year: 2022 Issue: 11 Published: http://alferganus.uz
Citation:
Amirov, T.J. (2022). Designations of the design age of road cement concrete. SJ International journal of theoretical and practical research, 2 (11), 7-11.
Amirov, T.J. (2022). Designations of the design age of road cement concrete. Nazariy va amaliy tadqiqotlar xalqaro jurnali, 2 (11), 7-11.
Doi:
https://dx.doi.org/10.5281/zenodo.7388644
Amirov, Tursoat Jumaevich
PhD., Docent, Tashkent State Transport University
E-mail: tursoat. amirov@mail. ru
UDC 625.84
DESIGNATIONS OF THE DESIGN AGE OF ROAD CEMENT CONCRETE
Abstract. This article presents the results of experimental studies to determine the estimated age of road concrete. In addition, the influence of the estimated age of the concrete pavement on the strength characteristics was studied.
Keywords: Cement-concrete pavement, Portland cement, design age of concrete, mineralogical composition, coefficient of strength increase, alite, belite, normalized strength, day, flexural strength.
Амиров, Турсоат Жумаевич
канд. техн. наук, доцент, Ташкентский государственный транспортный университет
НАЗНАЧЕНИЯ ПРОЕКТНОГО ВОЗРАСТА ДОРОЖНОГО
ЦЕМЕНТОБЕТОНА
Аннотация. В данной статье представлены результаты экспериментальных исследований по определению расчетного возраста дорожного бетона. Кроме того, изучалось влияние расчетного возраста бетонной покрытии на прочностные показатели.
Ключевые слова: Цементобетонное покрытие, портландцемент, проектный возраст бетона, минералогический состав, коэффициент нарастания прочности,
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License type supported CC: Attribution 4.0 International (CC BY 4.0)
ISSN 2181-2357
I INTERNATIONAL JOURNAL OF THEORETICAL AND PRACTICAL
RESEARCH _,
ISJIF 2022:5.962
алит, белит, нормируемый прочность, сутки, предел прочности при изгибе.
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Amirov, Tursoat Jumaevich
Texnika fanlari nomzodi, dotsent, Toshkent Davlat transport Universiteti
YO'LBOP SEMETBETONNING LOYIXA YOSHINI BELGILASH
Annotatsiya. Ushbu maqolada yo'lbop betonning loyihaviy yoshini belgilash bo'yicha eksperement tadqiqotlar natijalari keltirilgan. Bundan tashqari, beton qoplamasi loyihaviy yoshining mustahkamlik ko'rsatkichlariga ta'siri o'rganilgan. Kalit so'zlar: Sementbeton qoplama, portlandtsement, betonning loyihaviy yoshi, minerologik tarkib, mustahkamlikning oshish koeffitsienti, alit, belit, me'yorlangan mustahkamlik, sutka, egilishdagi cho'zilishga mustahkamlik
Introduction
It should be noted that there is a common, but not entirely correct "concept" about the design age of concrete: that it is 28 days.
The requirements [1] determine that the technical requirements for concrete must be met at the design age, which is indicated in the design documentation and assigned in accordance with the design standards, depending on the conditions of concrete hardening, methods of erection and the timing of the actual manufacture of these structures and products. Only in this case, when the design age is not indicated in the working drawings, the normalized concrete strength indicators must be provided at the age of 28 days. At the same time, it should be borne in mind that it is very important to assign the design age of concrete for reasons of technical and economic feasibility, depending on the actual terms of loading the structure, structure and putting them into operation.
The need for rational appointment of the design age of concrete is especially relevant in road construction due to the fact that, according to [2], the strength of concrete of cement-concrete pavements is assigned not lower than the Btb4.0 (B30) class, and to ensure that the standard strength at the age of 28 days is obtained, it is necessary to use cements of the grade not lower than M500.
At the same time, in accordance with [3], in the case of using cement grade M400, the design age is set not to be 28 days, but 90-180 days.
Methods
The impossibility of ensuring normalized strengths, especially the tensile strength of concrete in bending Btb4.0 at the age of 28 days using sulfate-resistant Portland cement without additives SSPTs 400-D0, is confirmed by the practice of building a cement concrete pavement on the A-380 highway "Guzar-Bukhara-Nukus-Beyneu" by the companies "GP PAPENBURG BAUGESELLSCHAFT mBH" (Germany) and "POSCO Engineering" (Republic of Korea), at the site "Reconstruction of the A-373 Tashkent-Osh highway on the section 116-190 km of the Kamchik pass" by EVROSCON OJSC (Azerbaijan), PU Alliance Capital (Denmark) and others.
Considering that the construction of the road is carried out for a relatively long
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time, and the time of stripping and loading is not such an urgent problem, the expediency of setting the design age of road concrete 90-180 days becomes indisputable.
According to numerous studies for concretes based on Portland cements, a significant increase in strength and especially water resistance (the intensity of which gradually decreases with time) takes place up to the age of 180 days.
In the future, the positive effect of concrete age on its properties becomes less noticeable. At the same time, it is important to take into account that the intensity of concrete strength growth over time depends on a number of factors: the type and quality of cement, aggregates, concrete composition, water-cement ratio, type and type of additives, hardening conditions, etc.
The increase in the strength of concrete on Portland cements to a large extent depends on the mineralogical composition of the cement.
Studies conducted at different times proved that concretes based on cements with a high content of alite (C3S) quickly gain strength in the early stages of hardening (up to 28 days), with further hardening, the increase in the strength of concretes on these cements is relatively slow.
The increase in the strength of concretes on cements with a high content of belite (C2S) in the initial periods of hardening is much less intensive. However, the increase in strength in the late periods of hardening is much higher than that of concretes based on high-alite cements.
According to the standards, sulfate-resistant cements belonging to the class of belite should have the following mineralogical composition: C3S-alite no more than 50%, aluminate C3A no more than 5%, the sum of C3A and C4AF no more than 22%.
Results
According to the results of testing the mineralogical composition of cement by JSC "Kizilkumcement" in the laboratory of the company "GP PAPENBURG BAUGESELLSCHAFT mBH" and using for the construction of the above objects, it was established: C3S-34.1%, C2S-41.2%, C3A -2.5%, C3A +C4AF=15.8%.
Thus, when calculating changes in the strength of concrete over time, it is necessary to take into account the mineralogical composition of cement, and the generalized quantitative indicators of strength growth used in practice should be taken into account depending on the type of cement.
According to [4], the data on the increase in the strength of concrete on various cements are given during hardening under normal conditions (Table 1):
Table 1
The coefficients of increase in the strength of concrete on various cements
Type of cement Strength factor of concrete aged
7 days 28 days 90 days 180 days
Alite Portland cements 0,65-0,75 1,00 1,10-1,25 1,30-1,40
Ordinary Portland 0,60-0,70 1,00 1,15-1,35 1,30-1,50
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cements
Belite Portland cements 0,55-0,65 1,00 1,30-1,40 1,45-1,60
is:
According to other researchers [5], the generalized coefficient of strength increase
7 days 28 days 90 days 180 days
0,42-0,75 1,00 1,12-1,52 1,22-1,70
The top layer of the driveway should work mainly on the bend. When M400 cement was used as a binder in cement concrete, this resulted in a change in the design age of the concrete from flexural strength. Therefore, we determined the design age of flexural tensile strength of concrete designed based on local materials (Figure 1).
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6/j
«
S
H «
6 5 4
J3 3
2 1
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5 8
4 73 73 5 3 5, 6
3,8 4,
2 8
28 56 90 120
Age of the concrete sample, days
180
Figure 1. Dependence of the design age of the flexural tensile strength of cement concrete
According to the results of the laboratory test for the construction of cement-beton coating of the automobile road A-380 "Guzar-Bukhara-Nukus-Beyneu" company "GP PAPENBURG BAUGESELLSCHAFT mBH" the coefficient of growth of concrete strength at 90 days of age was 1.18-1.70.
Conclusion
Due to the variety of factors influencing the increase in the strength of concrete over time, it is very difficult to accurately predict and quantify the increase in strength.
However, the use of the coefficient of strength increase is a necessity, because due to the increase in the design age of road concrete to 90 and 180 days, there are problems associated with a delay in the acceptance of the volume of concrete work performed and
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In this situation, conditional acceptance of concrete work is possible according to the conclusion of the laboratory using the coefficient of strength increase, partially (5075%) or completely.
At the same time, the accepted volumes of concrete work in terms of the coefficient of strength increase should be considered conditional, and the actual strength of concrete should be determined without fail at the design age (90 or 180 days) with testing according to the standard method.
References:
1. GOST 26633-2015 "Heavy and fine-grained concrete. Specifications".
2. ShNK 2.05.02-07 "Roads".
3. ShNK 5.01.23-08 "Typical consumption rates of cement for the preparation of prefabricated and monolithic concrete products and structures."
4. Adilkhodjaev A.I., Amirov T.J. On the issue of assigning the design age of road concrete. "Resource-saving technologies in railway transport". Scientific works of the republican scientific and technical conference with the participation of foreign scientists. TashIIT. -Tashkent. -2018. Issue 13. c.34-36.
5. Tursoat Amirov, Xojiakmal Aripov, Bobomurod Qurbonov, Matchon Tuxtayev, Sukhrob Rakhmatov. Designing the composition of road concrete with chemical additives. International Scientific Conference "Construction Mechanics, Hydraulics and Water Resources Engineering" (CONMECHYDRO - 2021) E3S Web Conf. Volume 264, 2021. https://doi.org/10.1051/e3sconf/202126402049
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