# Optimization of the Temperature and Thermo-Stressed State of a Concrete Dam Constructed from Particularly Lean Roller-Compacted Concrete

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

^{3}, and the main drawback was considered to be the high risk of transverse cracking. This factor had a key influence on the selection of a low-cement mix, which was laid without expansion joints and compacted by rollers [1,2,3,4,5,6,7,8,9,10,11,12]. The idea of using low-cement concrete in gravity dam construction was proposed in 1960 as part of the discussion of the International Committee on Large Dams. In 1961 the first application of the technology took place on the cofferdam of the Shihmen dam on the island of Taiwan, where a central core was made of low-cement concrete. In 1970, a full-size test section was erected at Tims Ford Dam in the USA, and as early as 1983, the Willow Creek Dam was built in 5.5 months (52 m high, dam body concrete volume—333,000 m

^{3}).

^{3}of concrete body), the maximum concrete work intensity was 12,250 m

^{3}/day, and the construction period was 12 months (Figure 1). The high intensity of the concrete works due to layer-by-layer mixture placing, the absence of formwork and dismantling, the reduction in labor costs to 0.15 man-days/m

^{3}(Upper Stillwater Dam), and the associated reduction in overhead costs enabled more than 828 dams of this type to be realized, including gravity, arch, and buttressed dams as of 2019. Statistics on the cost per cubic meter of low-cement concrete poured as a function of construction volume in the USA are shown in Figure 2.

^{3}) in 1976 confirmed the possibility of the application of roller-compacted concrete in the construction of dams, the first of which, including the Shimazhiva dam (dam body volume—317,000 m

^{3}), was constructed in 1980. One of the largest low-cement concrete dams in the world is located in Japan. This is the Tamagawa dam (1987), which is 100 m high, and the volume of in situ roller-compacted concrete is 1,150,000 m

^{3}[3,13].

^{3}). This was followed by Bukhtarminskaya HPP on the Irtysh river in Kazakhstan with 90 m height and 450 m length (the volume of laid low-cement concrete—587 thousand m

^{3}), Bureyskaya HPP on the Bureya river with 139 m height and 810 m length on ridge (volume of laid low-cement concrete—587 thousand m

^{3}), and also separate constructions or experimental plots at Kurpskay, Kureysky, Sayano-Shushensky HPPs. The Kapanda hydroelectric dam in Angola and the Son La hydroelectric dam in Vietnam was built in accordance with the designs developed by the Hydroproject Institute (Moscow, Russia).

^{3}of in situ concrete), and the 121 m high dam (1.1 million m

^{3}of low-cement concrete placed).

## 2. Materials and Techniques

#### 2.1. Methodology for Determining the Temperature Regime

#### 2.2. Methodology for Determining the Thermo-Stressed State

## 3. The Setting and Results of the Research

#### 3.1. Consideration of Solar Radiation Effects

#### 3.2. Analysis of the Impact of Existing Factors Using the Methodology of a Factor Experiment

^{n}, where the number of factors considered was n = 4. The total number of experiments needed for such a plan is N = 2

^{4}= 16. The response function as a regression equation for this experiment is as follows [30] (8):

- ${X}_{1}$—consumption of cement in the mixture (varies from 70 kg/m
^{3}to 150 kg/m^{3}). - ${X}_{2}$—thickness of the low-cement concrete layer to be placed (0.5 m to 1.5 m).
- ${X}_{3}$—heat release of cement (from 339 kJ/kg (moderate) to 387.7 kJ/kg (elevated).
- ${X}_{4}$—laying temperature of low-cement concrete (+10 °C to +30 °C).

^{4}was considered) for the selected factors were performed for the following options:

- (1)
- Depending on the month when the construction work started: May or October with the corresponding ambient temperatures (according to the schedule, Figure 6).
- (2)
- (3)
- The responses chosen were: the absolute maximum temperature in the concrete mass (°C), maximum temperatures at characteristic points 2, 8, 14, 20, 26 in the center of the mass (°C), the maximum temperature gradient between the point in the center of the mass and the point on the pressure face (°C/m), the maximum value of the main tensile stress at characteristic points 2, 8, 14, 20, 26 in the center of the massif (MPa), the maximum value of equivalent plastic deformations at characteristic points 2, 8, 14, 20, 26 in the center of the massif (%). A diagram of the point locations is shown in Figure 7. All temperature calculations for all variants were carried out using the Ansys software package.

**Option 1. Beginning of concreting in May excluding solar radiation.**

**Option 2. Beginning of concreting in October excluding solar radiation.**

**Option 3. Beginning of concreting in May taking into account solar radiation.**

**Option 4. Beginning of concreting in October taking into account solar radiation.**

- All of the selected factors had a sufficiently strong influence on the values of the maximum temperature at the selected points. The cement consumption (factor ${\mathrm{X}}_{1}$), the thickness of the concrete layer to be placed (${\mathrm{X}}_{2}$), and the temperature of the concrete mix (${\mathrm{X}}_{4}$) had the greatest impact. Increasing cement consumption from 70 kg/m
^{3}to 150 kg/m^{3}led to a significant (on average by 9.31 °C per fixing point) temperature increase in all points of the massif, reaching maximum values in the case of the concreting that started in May at point 2 (the temperature at the point with 70 kg/m^{3}cement content was 45.18 °C, with 150 kg/m^{3}—54.42 °C). - The degree and operator of the influence of the factor ${x}_{2}$ (the thickness of the concrete layer to be paved) depended on the placement area, the seasonality of the paving operation, and the solar radiation. When solar radiation was not taken into account and concreting started in May in massive areas of the dam, the temperature of the concrete mass decreased as the thickness of the layer of concrete that began to be placed increased (the regression equation coefficients with the clause ${\mathrm{X}}_{2}$ are negative). However, for this option, the picture changed in the area at the crest of the dam, where the opposite was obtained: as the layer thickness increased the temperature rose as well. When concreting started in October, the picture was reversed: in the lower massive part of the dam, an increase in layer thickness led to a rise in temperature, while in the area near the crest, the opposite was true.
- For options with solar radiation in most areas of the dam, with an increasing layer thickness, there was a decrease in the mass temperature due to lower solar heating in thicker layers. The exception is the area near the base (point 2) for the option with the start of construction in low air temperatures during the autumn-winter period of the year. Paving in thin layers involved the intensive cooling of the concrete with cold air.
- For the climatic conditions considered, a consideration of solar radiation made a significant contribution to the increase in temperature warming of the structure during its construction (the temperature inside the concrete mass increases by 8.46 °C to 16.14 °C (Figure 8), depending on the fixing point.

^{3}, a layer thickness of 0.5 m, increased heat generation, the initial temperature of the concrete mixture +10 °C, and the start of work in May. The most favorable temperature regime was obtained under the following conditions: cement consumption of 70 kg/m

^{3}, a layer thickness of 1.5 m, moderate heat dissipation, the initial temperature of concrete mixture +10 °C, and the start of work in October.

_{ref.}), where T

_{ref.}was the initial temperature of the concrete mix.

**1. The tensile stress fracture assessment.**

**2. Assessment of fracture formation by plastic deformation.**

^{3}in the most favorable design case, the limit of deformation is 0.6%. For a cement consumption of 150 kg/m

^{3}in the least favorable design case, the limit deformation is 0.85%.

**3. Cost-effectiveness assessment.**

## 4. Findings

- The conducted research indicates the necessity of considering the influence of solar radiation on warming up the massive gravity dam made of low-cement concrete in the climate conditions of Pskem HPP in the Republic of Uzbekistan and similar ones. The methodology for accounting for the influence of solar radiation with respect to cloud cover makes it possible to predict the temperature and radiation regime of a massive gravity dam, taking into account field and satellite observations and determining the amount of absorbed solar energy and the associated heating of the concrete mass with respect to seasonality and the topography surrounding the construction site.
- The optimization of the temperature regime of the structure, carried out on the basis of the experimental planning theory with a numerical solution in the ANSYS software package, allowed the contribution of each to be evaluated in the internal and external environmental factors to the thermal stress state of the dam in the climate conditions of the construction area in the Republic of Uzbekistan.
- The created prediction model of the thermo-stressed state made it possible to estimate the values of absolute maximum temperature in the concrete mass; the maximum temperature at characteristic points; the maximum temperature gradient between a point in the mass center; and a point on the pressure face; values of the maximum main tensile stresses and plastic deformations. This enabled a comprehensive analysis to be carried out and the best design option to be selected.
- Regression equations have been derived from the results of the calculations to determine the values of the required indicators at any of the points under consideration. The equations can be applied to any solid, low-cement concrete dam with a minimum footprint of 40 m in all climate conditions.
- Based on the results of this work, a construction optimization algorithm was proposed for use in the engineering and justification of design solutions for low-cement concrete gravity dams.
- Recommendations and prospects for further development of the topic. Laboratory research on the determination of the optimum composition of the concrete mixture, a more detailed consideration of the influence of concrete strength growth in time and its influence on the state of the structure, a more detailed study of the thermal properties of different types of foundations and the general improvement of calculation models and methods are advisable. In addition, a promising direction is the study of cracking processes in massive structures made of low-cement concrete and the search for the new refinement of existing criteria for its assessment.

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

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**Figure 4.**Map of direct solar radiation intensity, kW/m

^{2}in the area of the Pskem HPP (under construction).

**Figure 5.**Graph of changes in angular altitude $({h}_{0}$) and the azimuth of the sun, where: 1—local time in the construction area (time zone Tashkent, Uzbekistan, UTC+05:00); 2—movement of the sun at the summer solstice 21.07. 2021; 3—true solar time; 4—sun movement at the spring/autumn equinox; 5—sun movement at the winter solstice 21.12.2021; 6—zone of active solar exposure; 7—shading caused by surrounding terrain; 8—contour of the surrounding terrain at the construction site.

**Figure 6.**Graph of changes in concrete surface temperature, taking into account the ambient temperature: (

**a**) Without the influence of solar radiation; (

**b**) Taking into account the influence of solar radiation.

**Figure 7.**Location of fixed points for the values of the set responses across the cross section of the dam.

**Figure 8.**Example of calculating the maximum temperature in a concrete mass: (

**a**) Calculation taking into account solar radiation; (

**b**) Calculation excluding solar radiation.

**Figure 9.**Calculation results for maximum temperature in concrete mass: (

**a**) The least favorable calculation case; (

**b**) The most favorable calculation case.

**Figure 10.**Results of the determination of plastic deformation in a concrete mass: (

**a**) The least favorable calculation case; (

**b**) The most favorable calculation case.

**Figure 13.**Results of calculating the maximum temperature in the concrete mass in the least favorable calculation case: (

**a**) Calculation excluding the effect of the reservoir; (

**b**) Calculations considering the effect of the reservoir.

**Figure 14.**Results of calculation of tensile stresses ${\sigma}_{y}$ in the concrete mass at the time of completion of construction: (

**a**) The most favorable calculation case; (

**b**) The least favorable calculation case.

**Figure 15.**Results of calculation of plastic deformation in concrete mass at the time of completion of construction with: (

**a**) The most favorable design case; (

**b**) The least favorable calculation case.

**Figure 16.**The main maximum stresses in the dam: (

**a**) Stresses when calculating with regard to temperature factors; (

**b**) Stresses when calculating excluding temperature factors.

Features | I | II | III | IV | V | VI | VII | VIII | IX | X | XI | XII | Av. an. |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|

Monthly average air temp., °C | −4.0 | −2.0 | 3.0 | 11.0 | 16.0 | 21.0 | 24.0 | 24.0 | 19.0 | 11.0 | 4.0 | −1.1 | 9.5 |

№. of the Calculation Case | Natural Values of Variation Factors and Construction Conditions | |||||
---|---|---|---|---|---|---|

Cement Consumption, ${\mathit{x}}_{1}$, kg/m^{3} | Thickness of a Layer, ${\mathit{x}}_{2}$, m | Heat Dissipation ${\mathit{x}}_{3},$$\mathbf{kJ}/\mathbf{kg}\left({\mathit{Q}}_{\mathit{m}\mathit{a}\mathit{x}}\right)$ | Laying Temperature, ${\mathit{x}}_{4}$, °C | Month of the Work Start | Consideration of Solar Radiation | |

6 | 70 | 1.5 | 339 | 10 | October | Yes |

25 | 150 | 0.5 | 387.7 | 10 | May | Yes |

Indicator Name | Option with an Earth Dam with a Loamy Core | Option with Low-Cement Concrete Dam with a Liner on the Upstream Face |
---|---|---|

Volume of dam body material, m^{3} | 36,945,000 | 6,925,170 |

Present value of 1 m^{3} of dam body material including all possible costs over the whole construction period, US dollars | 27.25 | 85.00 |

Total cost of erecting the dam, US dollars | 1,006,765,470 | 588,639,450 |

Construction time, years | 12 | 7 |

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**MDPI and ACS Style**

Aniskin, N.A.; Shaytanov, A.M. Optimization of the Temperature and Thermo-Stressed State of a Concrete Dam Constructed from Particularly Lean Roller-Compacted Concrete. *Buildings* **2023**, *13*, 914.
https://doi.org/10.3390/buildings13040914

**AMA Style**

Aniskin NA, Shaytanov AM. Optimization of the Temperature and Thermo-Stressed State of a Concrete Dam Constructed from Particularly Lean Roller-Compacted Concrete. *Buildings*. 2023; 13(4):914.
https://doi.org/10.3390/buildings13040914

**Chicago/Turabian Style**

Aniskin, Nikolai Alekseevich, and Alexey Mikhailovich Shaytanov. 2023. "Optimization of the Temperature and Thermo-Stressed State of a Concrete Dam Constructed from Particularly Lean Roller-Compacted Concrete" *Buildings* 13, no. 4: 914.
https://doi.org/10.3390/buildings13040914