CC BY
0DETERMINATION OF THE TIME OF CUTTING SEAMS ON FRESHLY LAID MONOLITHIC CEMENT CONCRETE
PAVEMENTS
Abstract. This article determines the time for cutting joints in freshly laid cement concrete pavements depending on air temperature and concrete strength based on test and observation results.
Keywords: deformation, compression joint, expansion joint, chips, cracks, chamfer, concrete, reinforcement, construction, strength, weld cutter, concrete slab.
The specific natural and climatic conditions of the regions of our republic, the properties of concrete mixtures prepared on the basis of local building materials, the automation of construction technology and the quality of the work being performed, and the correct organization of the time of cutting seams in newly laid cement concrete pavements affect the long-term durability of cement concrete pavements.
As a result of not being able to correctly choose the time of cutting the seams in cement concrete pavements, dents, fractures, and abrasions are formed on the edges of the seams, which deteriorates the quality and causes various inconveniences to the driver of the vehicle, leading to an increase in transportation costs [1].
For this purpose, 228-315 km (87 km) of the reconstructed section of the A-380 Guzar-Bukhara-Nukus-Beynov highway was selected as the object of study (Figure 1).
As part of the project, China Railway 20 Bureau Group Corporation of the Republic of China brought modern machinery and high-precision measuring instruments and test equipment to ensure the quality of construction work at this facility.
Execution of consulting services on quality control at the construction site is carried out by Dohwa Engineering Co. of the Republic of South Korea. Ltd. specialists.
Amirov T.J.
Tashkent State Transport University https://doi.org/10.5281/zenodo.11395301
Figure 1. Location of the research object
Construction of a 25-cm-thick, B30 (Btb4.0) strength cement concrete coating is planned for the facility. Figure 2 shows an example scheme of a monolithic cement concrete pavement.
Top view
-r -
Typical Spacing: 3.7-6.1 m (12-20ft)
Direction of travel
Longitudinal Joint
Tie 9ar
1 Trar Side view i i J îvetse Joint <T , 7 Dowel \ 1 i
1
Base/Subbase
Subgrade
Figure 2. Typical layout of jointed plain concrete pavements
The experience of operating cement concrete pavements shows that over time steps of several millimeters can appear as a result of elevations between slabs. The formation of bumps worsens the longitudinal smoothness of the carriageway, increases resistance to movement, reduces the ease of movement of vehicles, causes vertical vibration of vehicles, and increases the load on the carriageway [2].
Therefore, in order to eliminate the appearance of steps between the adjacent plates and to smoothly transfer the compressive force partially from one plate to the other, usually the plates should be connected with steel rods installed along the seams [3].
Figure 3. Dowelled Joint vs undowelled Joint
Timely cutting of deformation seams, compliance with the geometric dimensions of seam cracks, quality of edges, filling of seams with sealing materials and the filling process ensure the long service life of cement concrete roads.
The formation of defects and distortions in cement concrete coatings mainly starts from the seams. One of the causes of defects in seams is that the seam cutting time is not adjusted to the
weather temperature. As a result of not being able to choose the time of cutting the seam correctly, the formation of various defects near the joint groove is shown in Fig. 4. Such cases reduce the quality of the weld edges.
Figure 4. Disruption of joint edges According to the results of the inspection and testing, the dependence of the time of cutting the seam on the cement concrete coating in different seasons of the year was studied, and it was found that the choice is the most effective and at the level of demand when the strength of 8-10 MPa is reached. The relationship between seam cutting time and concrete placement weather temperature is shown in Figure 5.
35 30
i.
г 25
y = -1.0149x + 34.588 R2 = 0.9798
eg 20
5 15
10
о и
S 5 H
0
5 10 15 20 25 30
Air temperature at the time of concrete pavement, °С
35
Figure 5. The graph of the dependence of the joint cutting time on weather conditions
0
Compression joints should be cut in 2 stages. At the first stage, it is recommended to cut 1/3 of the coating thickness and 4 mm wide (as shown in Figure 6) when the compressive strength of concrete is 8-10 Mpa [4].
Figure 6. A view of the compression joint after it was cut in step 1.
The second cut is made in hardened concrete. In this case, the cutting depth is 40 mm, and it is recommended to cut the width to 8 mm. The joint edges are chamfered with a 3mm chamfer to prevent vehicle breakage and damage to vehicle wheels. Faska is opened by a package of disks. Another factor affecting the quality of joints is the expansion of concrete slabs due to changes in air temperature and the intensity of solar radiation.
Concrete cast in the winter will expand at first during the early stages because of heat of hydration, after which it will contract (thermal and hydraulic shrinkage). The net result is contraction. Concrete cast in the summer will expand first and it will contract afterward. The net result is expansion, because the magnitude of contraction is lower than the magnitude of expansion (Figure 7).
1
Ik CL u] C+> - = ;z: o z < Q- X LU 1— LLJ S
J L o \ i- X >- y X LU < \ zi X z \ Time
1 r <~> WINTER TIME E ---- SUMMER TIME
f LJ 1 F
Exp = expansion Con = contraction
Figure 7. Concrete Expansion and Contraction
The opening AL for the distance L between two consecutive seams in cement concrete pavement is calculated by the following formula [5]:
AL = R • L • (aAT+e) (1)
Here: AL-joint opening width, mm
R-base restriction coefficient (for bases reinforced with cement - 0.65, for non-reinforced bases 0.8);
L- the distance between 2 successive seams, i.e. the length of the plate; «-coefficient of heat board of concrete ( ^£/°C);
AT- maximum temperature range (usually the temperature of concrete at the time of laying, minus the average daily minimum temperature, in °C in January;
^-hydraulic shrinkage of concrete [28].
Through the values of (1) at air temperatures at which concrete can be laid, we can see how much concrete expands at what temperature:
AL = 0.65 * 5000(12 * 10-6 * 10 + 0.0006) = 2.34 mm AL = 0.65 * 5000(12 * 10-6 * 15 + 0.0006) = 2.535mm AL = 0.65 * 5000(12 * 10-6 * 20 + 0.0006) = 2.73 mm AL = 0.65 * 5000(12 * 10-6 * 25 + 0.0006) = 2.92 mm AL = 0.65 * 5000(12 * 10-6 * 30 + 0.0006) = 3.12 mm AL = 0.65 * 5000(12 * 10-6 * 35 + 0.0006) = 3.315 mm AL = 0.65 * 5000(12 * 10-6 * 40 + 0.0006) = 3.51 mm
Figure 8. The expansion of concrete depending on the air temperature at the time of placing
the concrete mixture
Judging from the obtained graph, the maximum temperature at which the concrete slabs can be laid has reached an expansion of 3.51 mm at 30 0C, in this case, no expansion joints or construction of 1 expansion joint during the shift recommend
In conclusion, the selection and cutting of seams in newly laid cement concrete pavements depending on the weather temperature has a high impact not only on the quality of the seam, but also on the service life of the cement concrete pavement. High-quality cut seams prevent the increase in transport costs, improve the smoothness of the pavement and do not make drivers feel uncomfortable.
REFERENCES
1. Amirov T.J. Construction of cement concrete pavements of highways and airfields. Study guide - T.: "SANO STANDART". 2017 - 256 p.
2. A.G.Yunusov, T.J.Amirov, B.A.Khalikov, A.A.Normukhammadov. problems of ensuring fluidity in the construction of cement concrete pavements. Scientific and technical journal of architectural and construction problems. Samgasi. - Samarkand-2020. #2 (Part 1). 73-75 p.
3. MQN 44-08 "Instructions for the design of concrete road surfaces".
4. Amirov T.J, Nurillayev Sh.G. Determining the time of cutting seams on newly laid cement concrete road surfaces. Collection of the international scientific and practical conference on "Training of international experts in the field of transport". TDTrU. Tashkent April 21-22, 2022. Pages 466-471.
5. Mikael Di Tomasso et al. Practical guidance on the technology of cement concrete roads. Tashkent: "Bactria press", 2021 - 148 p.
6. 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
