What is the significance of adiabatic temperature in concrete

A computer-controlled cell is designed to measure the adiabatic temperature rise in concrete with initial concrete temperature at 20, 30, or 40 C. Slag replacement up to 70 percent by mass of total cementitious binder content was studied. Other parameters studied include water-binder ratio ranging from 0. The results of the adiabatic temperature rise in concrete show that an increase in slag replacement reduces the temperature rise. The effect of higher fineness or higher total cementitious binder content leads to higher temperature rise.

However, the influence of placing temperature on the temperature rise indicates a lower rise at higher placing temperature. It is also noted that at higher placing temperature, slag replacement greater than 55 percent by mass tends to reduce temperature rise to a greater extent than at lower replacement levels.

The development of the heat of hydration with time of the concrete mixes under adiabatic condition is expressed in equation form. ACI Materials Journal. The main findings of the study are as follows: 1 Both the adiabatic temperature rise rate and the final adiabatic temperature rise of RFC are negatively correlated with the rock-fill ratio.

The results of the present study indicate that dam construction with RFC can simplify the measures of temperature control and crack prevention, improve the construction efficiency, and reduce the cost of dam construction.

Rock-fill concrete RFC is a new type of concrete developed from self-compacting concrete SCC and makes full use of its advantages, such as high fluidity, segregation resistance, and filling-ability.

It also breaks through the limitations of traditional construction technology, in which SCC filling rock-filled voids solely depends on self-gravity, not by forced vibration to form a mass concrete with integrity, high density, and enhanced strength [ 1 — 4 ]. In comparison with conventional mass concrete, RFC possesses the following engineering and economic advantages [ 5 — 7 ]: 1 The high fluidity and cohesive force of SCC ensures the high density and strength of RFC.

RFC was first proposed and applied for national patent by Prof. Jin Feng and Prof. An Xuehui from Tsinghua University in [ 8 ].

In , RFC successfully entered the List of Circular Economy Technology, Technology and Equipment encouraged by China National Development and Reform Commission and received a wide application in the field of water conservancy and hydropower engineering thereafter [ 9 ].

RFC has created remarkable economic, social, and environmental benefits with its obvious technical advantages and has been utilized in the construction of Baoquan pumped storage power station in Henan Province, Changkeng third-level reservoir reconstruction in Zhongshan of Guangdong Province, the back-filling of the caisson group Xiang Jiaba hydropower station of the Jinsha River in Sichuan Province, and the hydro-junction cofferdam at the mountain pass of Buerjin.

With the wider application of RFC within the domain of water conservancy and hydropower engineering, a greater importance has been attached to the effect of heat released by cement hydration on the endurance and stability of an RFC structure [ 10 ]. An adiabatic temperature rise serves as an important thermal indicator affecting the temperature stress and crack resistance of the concrete structure.

Hence, it is imperative to study the adiabatic temperature rise property in order to quantify the temperature stress of RFC and evaluate the effect of temperature cracks on RFC. In recent years, a large number of researchers have conducted theoretical and numerical simulation studies on the property of adiabatic temperature rise.

Zhu Bofang [ 13 ] derived the adiabatic temperature rise expression for concrete, considering the influence of temperature, and discussed the inversion method of the adiabatic temperature rise of concrete according to the measured engineering temperature.

Lim C. Yao Wu et al. Wang Licheng et al. Mai Ge et al. Evsukoff A. However, the above-mentioned studies only dealt with the mesoscopic simulation of the adiabatic temperature rise performance of concrete from both theoretical and numerical simulations. Owing to the imperfect aggregate generation algorithm and complex grid partitioning algorithm, the mesoscopic simulation of the adiabatic temperature rise of concrete in an actual application has yet to be adequately expounded.

As a new type of mass concrete, RFC is developing rapidly. Due to the existence of a large amount of rock-fill, the thermal properties of RFC such as hydration temperature rise must vary from that of conventional mass concrete.

The temperature stress characteristics of using RFC to build dams are currently unclear, and important questions still remain: whether temperature control measures are needed and what measures should be taken. This is followed by the regression analysis of the test data in order to derive the calculation model of the adiabatic temperature rise of RFC, while considering the rock-fill ratio. The results provide greater insight and reference for the design and construction of similar practical projects.

The hydration heat of cement is an important factor affecting the temperature stress of concrete, and the thermal parameter used in the actual temperature field calculation is the adiabatic temperature rise of concrete. There are two methods for measuring the adiabatic temperature rise of concrete [ 11 ].

However, it is known that there are considerable differences between the concrete adiabatic temperature rise obtained by the indirect method and the value directly measured through the concrete adiabatic temperature rise test.

Therefore, if possible, the adiabatic temperature rise test of concrete should be carried out. The design principle is shown in Figure 1. The main technical indicators are as follows. Thus, an adiabatic closed space is provided to the concrete specimen to ensure the adiabatic temperature rise of the whole test process. The double-layered temperature controlled device can effectively solve the effect on the whole system and the hysteresis on the tracking heating device caused by constantly changing external temperature.

In general, the specification requires a constant temperature for the test equipment; an outer heating temperature control installation can effectively shield the interference of the external environment, which results in a higher accuracy of the test results.

As a result, an investigation into the adiabatic temperature rise characteristics of SCC is required to study the adiabatic temperature rise of RFC. In the present study, the SCC, with design strength of C20, is employed, with the mix proportion shown in Table 1 , which is referred to as the actual mix proportion of RFC gravity dam that follows.

The slump of the SCC should be determined prior to putting it in the measuring instrument for the adiabatic temperature rise, in order to ensure design fluidity. According to the mix proportions shown in Table 1 , self-compacting concrete is mixed and tested in accordance with SL Test Regulations for Hydraulic Concrete.

The adiabatic temperature rise of SCC reaches ca. After the 10th day of testing, the center temperature of the SCC specimen remains constant, and the interior maximum temperature rise of the specimen is Figure 2 shows the adiabatic temperature rise curve of the SCC.

It is known that the relationship between the adiabatic temperature rise and concrete age represented by the composite exponents is more consistent with the experimental data [ 11 ].

Therefore, the relationship between adiabatic temperature rise and age of SCC is expressed as follows:.

In the engineering field, RFC with varying rock-fill ratios is generally prepared according to actual demands. The adiabatic temperature rise characteristics of RFC with different rock-fill ratios differ due to the various amounts of SCC. In order to investigate the effect of rock-fill ratio on the adiabatic temperature rise of RFC, it is necessary to carry out a test with varying rock-fill ratios, which is expressed in volumetric ratios.

According to SL Test Regulations for Hydraulic Concrete , the container size of the measuring instrument for the adiabatic temperature rise should be not less than three times the maximum aggregate diameter.

Due to container size limitations, the original size test cannot be conducted directly. Previous studies [ 6 ] have shown that the particle size of RFC exerts no direct effect on the adiabatic temperature rise.

On this basis, the adiabatic temperature rise test of small-diameter RFC can be conducted by scaling the actual rock-fill diameter in proportion according to the barrel size. From a macroscopic point of view, the adiabatic temperature rise is a thermal parameter caused by the thermal behavior of concrete hydration. Therefore, the adiabatic temperature rise test of a small-diameter RFC can completely replace the original size of RFC adiabatic temperature rise test. The mix proportions are shown in Table 2.

The results of the adiabatic temperature rise test show that the final adiabatic temperature rise for RFC decreases with increasing rock-fill ratio. That is, the final adiabatic temperature rise of RFC is negatively correlated with its rock-fill ratio. According to the data, the adiabatic temperature rise rate of RFC decreases with an increase in rock-fill ratio. We found that the higher the ratio of rock-fill, the lower the final adiabatic temperature rise and rate of RFC.

The reason is that all the hydration heat of RFC originates from cement, the rock itself does not generate heat, and part of the heat generated by the cement hydration reaction should gradually heat the rock-fill. Therefore, the adiabatic temperature rise of SCC far exceeds that of RFC, and the RFC is conducive to reduce the actual hydration heat temperature rise of mass concrete structures.

There are many factors affecting adiabatic temperature rise of RFC. For general RFC, when analyzing the conventional temperature problem, the nonuniformity effect of rock-fill on temperature and temperature stress field can be neglected. Microscopically, the adiabatic temperature rise of RFC can be obtained through the thermal parameters of rock-fill and SCC by weighted average according to each part [ 5 ]. Supposing the final adiabatic temperature rise of SCC is , then the final adiabatic temperature rise of the RFC is as follows:.

Incorporating formula 7 into formula 6 is as follows. According to the composite exponential fitting results of the adiabatic temperature rise of SCC and RFC, substituted with the three sets of data, which are in the first three columns of Table 4 , into formula 9 and by calculating the arithmetic average, we obtain.

Regression analysis was carried out to determine the relevant interim parameters in accordance with the composite exponential fitting results of the adiabatic temperature rise of SCC and RFC, which is in the fourth column of Table 4.

The calculation model is then derived for the adiabatic temperature rise of RFC to allow for further comparison between the test and theoretical calculation values, as shown in Table 4. The results indicate that the deviation between the test and calculated value is less than 0. Therefore, this can provide a theoretical basis for the prediction of the adiabatic temperature rise of RFC with different rock-fill ratios.

Table 5 shows the statistical data of the monthly mean temperature at the dam site. After the reservoir storage, water temperature can be calculated according to the following formula [ 11 ]:. Construction work was suspended during the winter period from October 17th, , to April 10th, Concrete pouring recommenced on April 11th, The concrete pouring reached the overflow crest on August 10th, , and the dam crest on August 25th, In the overflow section of the dam, the normal concrete C25W6F with the second gradation is adopted for cushion, C20W10F for upstream and downstream anti-seepage slab, and C40W6F for the overflow face.

The thermodynamic parameters of the materials are shown in Table 7. As seen in Figure 5 , the finite element model takes the left dam heel as its coordinate origin, the direction of water flow is Y-axis forward, the direction of the vertical flow and pointing to the right bank is X-axis forward, and the dam height is Z-axis forward.

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