Experimental and Numerical Studies of Controlling

applied sciences Article

Experimental and Numerical Studies of Controlling Thermal Cracks in Mass Concrete Foundation by Circulating Water Wenchao Liu 1 , Wanlin Cao 1, *, Huiqing Yan 2 , Tianxiang Ye 2 and Wang Jia 3 1 2 3

*

College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100124, China; [email protected] China Railway Airport Construction Group Co., Beijing 100093, China; [email protected] (H.Y.); [email protected] (T.Y.) Beijing Jialong Group Co., Beijing 100125, China; [email protected] Correspondence: [email protected]; Tel.: +86-10-6739-2819

Academic Editor: Andrea Paglietti Received: 26 January 2016; Accepted: 13 April 2016; Published: 20 April 2016

Abstract: This paper summarizes an engineering experience of solving the problem of thermal cracking in mass concrete by using a large project, Zhongguancun No.1 (Beijing, China), as an example. A new method is presented for controlling temperature cracks in the mass concrete of a foundation. The method involves controlled cycles of water circulating between the surface of mass concrete foundation and the atmospheric environment. The temperature gradient between the surface and the core of the mass concrete is controlled at a relatively stable state. Water collected from the well-points used for dewatering and from rainfall is used as the source for circulating water. Mass concrete of a foundation slab is experimentally investigated through field temperature monitoring. Numerical analyses are performed by developing a finite element model of the foundation with and without water circulation. The calculation parameters are proposed based on the experiment, and finite element analysis software MIDAS/CIVIL is used to calculate the 3D temperature field of the mass concrete during the entire process of heat of hydration. The numerical results are in good agreement with the measured results. The proposed method provides an alternative practical basis for preventing thermal cracks in mass concrete. Keywords: circulating water; mass concrete; 3D temperature field; temperature monitoring; simulation

1. Introduction With the continuous development of high-rise buildings, the height of buildings is constantly increasing, thus posing increasing challenges to the foundation of buildings. Generally, a deeper foundation can provide a better safety factor for the whole building [1]. Thus, in the future, the depth of the building foundation can be predicted to increase. However, increased foundation depth can cause several problems. One such problem is associated with the construction of mass concrete, which is receiving growing research interest [2–6]. In particular, heat of hydration is a major problem of mass concrete. When the internal temperature of concrete exceeds a certain limit, it will produce large thermal stress, which will lead to internal premature cracks in concrete [7–9]. Such cracks are known as thermal cracks in construction. The main principle of controlling the thermal cracks in a construction is either to reduce the production of heat of hydration or to dissipate the heat so as not to accumulate it inside concrete. At present, the three main methods for controlling construction temperature cracks include: (i) installing a pre-buried cooling water pipe, (ii) covering with a thermal insulation material, and

Appl. Sci. 2016, 6, 110; doi:10.3390/app6040110

www.mdpi.com/journal/applsci

Appl. Sci. 2016, 6, 110

2 of 18

(iii) adding a new material (PCM- Phase Change Material) in concrete. Seo et al. [10] developed a vertical pipe cooling method and tested it in a wall-type mass concrete specimen to validate the method. The experimental result showed that the temperature of the concrete specimen with the vertical pipe cooling system was 8–14 ˝ C lower than that of the control specimen without the vertical pipe cooling system. Some construction measures [11,12] have adopted thermal insulation material to cover mass concrete in order to control thermal cracks in mass concrete. Some other studies [13–15] have investigated the use of phase change materials (PCM) to limit the rise in temperature of mass concrete. For the pre-buried cooling water pipe method, concrete should be embedded with a large number of pipelines; the process is complex and costly. If the treatment measure for the permanently buried steel pipe is not enough, it will lead to internal defects within a concrete structure. For the method of covering with a thermal insulation material, the materials used are not environmentally friendly, and are also unsuitable for the high strength mass concrete that requires a relatively larger cement content. The new materials (PCM materials), because of their relatively immature technology and high cost, are not widely used. In the meantime, a new technology of circulating water to control the thermal cracking in mass concrete foundation has emerged [16–18]. The circulating water comes from well points used for dewatering and from rainfall. Water is stored in a thermostat tank and the initial temperature of the water is adjusted to a specified temperature. Water with an appropriate temperature is brought into the temperature drop pool lying above the foundation slab. The temperature difference between the surface and the interior (core) of mass concrete is finally achieved by changing the temperature and the depth of water in the thermostat tank and varying the temperature in the drop pool. In this paper, an experimental study (temperature monitoring) is performed by utilizing the new technology of circulating water in a mass concrete foundation in the construction of “A” and “D” areas of the project—Zhongguancun No. 1 in China (the project has four working areas which are named A, B, C and D). The variation in the internal temperature field of mass concrete is analyzed by using the finite element software MIDAS/CIVIL to simulate the 3D temperature field. The proposed method provides an alternative practical basis for preventing thermal cracks in mass concrete. 2. General Description of Project Zhongguancun No. 1 (A and D areas) is located in Yongfeng industrial base, Beijing, China, with a total construction area of 232320 m2 . Building structure type of A and D area is core tube structure as shown in Figure 1a. The underground part of A and D areas has three floors. The foundation concrete is standard mass concrete. Construction features are as follows: (1) (2) (3)

Large area: Each block in the area is more than 3000 m2 . Thick slab: The thickness of concrete slab is 1.8–2.2 m, and the local set puddle is up to 5.0 m. (i) Ambient temperature of the construction site was relatively higher with the temperature as high as 38.5 ˝ C. Maximum temperature of steel surface was about 55 ˝ C; (ii) the amount of each pour of concrete was 5600–6000 m3 . Concrete was C35 (P8) grade and was low-permeability type. Based on these data, the temperature inside the mass concrete would increase due to heat of hydration and could reach 65–75 ˝ C.

Appl. Sci. 2016, 6, 110

3 of 18

(a)

(b)

Figure 1. The project site of Zhongguancun. (a) Plan sketch of “A” and “D” areas; (b) Site operation of “A” area.

3. Experimental Technique 3.1. Test Object The object of this experiment was the foundation slab of the three basement floors at A1-A9/H-Q axis in the “A” area, as shown in Figure 1b. The concrete slab size was 48 m (width), 48.6 m (length), 1.8 m (depth) and the total volume of concrete was 4199 m3 . The ambient daily average temperature during the construction was 32.5 ˝ C and the maximum temperature was 38.5 ˝ C. The grade of mass concrete was C35, and vibrators were used for compaction. The cement strength grade was P.0 42.5, the water to cement ratio was 0.42, and the sand ratio (the quantity of sand/the total mass of sand and stone) was 43%. The concrete mix design is detailed in Table 1. Table 1. Mix design of concrete (kg/m3 ). Component

Cement

Water

Medium Sand

Crushed Pebble

Admixture

Fly Ash

Content

280

170

774

1026

8

120

3.2. Technical Scheme 3.2.1. Control Principle The temperature control system comprised of circulating water for mass concrete foundation. The system was composed of circulating water pipeline, thermostat tank, cooling tank, dewatering wells and other apparatus, as shown in Figure 2a,b. The circulating water that came from well-points dewatering and rainfall was collected and used during the concrete curing process. Water was conveyed to the thermostat tank and an initial water temperature of 16–18 ˝ C was adjusted by hot swapping (for approximately 24 h) in the natural environment (the ambient mean temperature was 32.5 ˝ C based on the on-site temperature monitoring). Figure 3 shows the temperature of water in the thermostat tank during 24 h of water circulation. The water which had a temperature of 25–28 ˝ C was brought into the cooling pool that was positioned right above the foundation slab. The temperature difference between the water and the surface of the mass concrete was controlled to be no more than 20 ˝ C. The temperature of the water in the cooling pool increased because of the heat exchanged with the mass concrete. After it reached the interval time (4 h, 6 h, 8 h), water in the pool was replaced with new water, and the same cycle repeated. Monitoring of the water temperature in the cooling pool showed that the water temperature could reach about 35–38 ˝ C during the first cycle of water circulation. As new cycles continued, the maximum temperature of the water in the cooling pool declined. The circulation process was customized based on the construction regime and a detailed

Appl. Sci. 2016, 6, 110

4 of 18

explanation about Appl. Sci. 2016, 6, 110 the regime is presented in Section 3.2.2. Finally, the desired temperature difference 4 of 18 between the surface and the interior of the base slab was maintained by varying the depth of water in difference between the surface and the interior of the base slab was maintained by thetemperature cooling pool. varying the depth of water in the cooling pool. Natural ground Direction of water flow

Direction of water flow

Municipal drainage ditch

Aqueduct Cooling pool

Dewatering well

Foundation slab Thermostat tank

(a)

(b) Figure 2. 2. Temperature circulatingwater waterininaathick thickfoundation foundation construction. Figure Temperaturecontrol controlsystem systemcomprising comprising of circulating construction. Sketch mapofofthe theconstruction; construction;(b) (b)Storing Storing arrangement arrangement for (a)(a) Sketch map forcirculating circulatingwater waterofofthe thefoundation. foundation.

Figure3.3.Temperature Temperatureof ofthe thewater water in in the the thermostat Figure thermostattank tankduring during2424hhofofcirculation. circulation.

3.2.2. ConstructionRegime Regime 3.2.2. Construction Four thermostat tanks were built during the project. The thermostat tank (600 mm wide and Four thermostat tanks were built during the project. The thermostat tank (600 mm wide 850 mm deep) was built 0.8 m away from the foundation slab. Cement mortar (the ratio of and 850 mm deep) was built 0.8 m away from the foundation slab. Cement mortar (the ratio cement/mortar was 1:2.5) was used for waterproofing. Each thermostat tank was equipped with a of cement/mortar was 1:2.5) was used for waterproofing. Each thermostat tank was equipped 5.5 kW submersible pump, the caliber was 65 mm, the flow was 36 m3/h, and the lift was 27 m. Circulating water was provided by the dewatering well system as its secondary utilization and the

Appl. Sci. 2016, 6, 110

5 of 18

with a 5.5 kW submersible pump, the caliber was 65 mm, the flow was 36 m3 /h, and the lift was 27 m. Circulating water was provided by the dewatering well system as its secondary utilization and the aqueduct DG-150 (the internal diameter is 150 mm) was used for conveying water to the foundation slab. After pouring the mass concrete, the foundation slab was frequently cured by sprinkler and was covered with plastic sheets. Double layer bags were used to cover the sides of mass concrete for providing moisture. The cooling pool was built around the slab when the foundation was finished. For the thickness of the mass concrete less than 2 m, the cooling pool was 120 mm wide and 240 mm high. For the thickness of the mass concrete greater than 2 m, the cooling pool was 240 mm wide and 350 mm high. Cement mortar (the ratio of cement:mortar was 1:2) was used for waterproofing. Past experience and real time data showed that the temperature inside the mass concrete increased slowly at the first day after pouring the mass concrete; increased rapidly at the second day to reach the maximum value at the third day; and decreased thereafter. Therefore, curing was done by sprinkling water for the first day (0–24 h). Thereafter, water was circulated every four hours for the second and third days (24 h–72 h) to maintain a ponding depth of 240 mm. For the fourth day (72–96 h), water was supplied every six hours, and the ponding depth was 200 mm. For the fifth and sixth days (96–144 h), water was supplied every eight hours and the ponding depth was reduced to 150 mm. After the seventh day (144–168 h), the ponding depth was reduced by 20 mm for each day until the 14th day by when the circulating water was removed, as shown in Table 2. The convection coefficient as calculated in section 4.3 was obtained based on this construction regime. Table 2. Construction regime of circulating water. Time/day

1

2

3

4

5

6

7

Interval time/h Water depth

sprinkling water -

circulating water 4 240






Time/day

8

9

10

11

12

13

14







removing water 8 0

Measures

Measures Interval time/h Water depth

3.3. Monitoring the Temperature of Mass Concrete The base slab was a rectangular symmetric structure. Thus, only one quarter of the foundation concrete was chosen as the test object for temperature monitoring. Fifteen temperature measurement points were arranged, as illustrated in the layout of the sensors shown in Figure 4a. In the figure, A1, A2, and A3 are located at the edge of the foundation; C1, C2 and C3 are located at the center of the foundation; and E1, E2 and E3 are located at the corner of the foundation. Similarly, sensor points B (labeled as B1, B2 and B3) are located between the A and C points along the longitudinal direction; sensor points D (labeled as D1, D2 and D3) are located between the C and E points along the diagonal direction. An integrated temperature logging device (No.AD592) (Analog Devices: Norwood, MA, USA) was used for monitoring the temperature from all 15 sensors. The measurement range of the device is ´30 ~ 150 ˝ C and the error is less than ˘0.3 ˝ C. Since each sensor was given a unique ID number, data acquisition and recording was conveniently performed by the device. Another instrument (No. JDC-2) (Beijng Building Construction Research Institute: Beijing, China) was used as an electronic thermometer for monitoring the temperature of the circulating water. The instrument was powered by a battery and was convenient for measuring temperature at a desired location, as shown in Figure 4b. As shown in Figure 4c, the measuring points A1, B1, C1, D1, and E1 were located at the top 50 mm of the foundation as suggested by the reference [19]; the measuring

Appl. Sci. 2016, 6, 110

6 of 18

points A2, B2, C2, D2, and E2 were located in the middle 900 mm; and the measuring points A3, B3, C3, D3, and 6,E3110were located at the bottom 50 mm of the foundation. Appl. Sci. 2016, 6 of 18

4860

4800

C1(C2)(C3)

D1(D2)(D3) B1(B2)(B3)

A1(A2)(A3)

E1(E2)(E3)

(b)

50

(a)

Top surface A1(B1)(C1) D1 E1

2

Foundation center A2(B2)(C2) D2 E2

3

Bottom surface A3(B3)(C3) D3 E3

50

850

1800

850

1

(c) Figure 4. Monitoring the temperature of the foundation slab. (a) Layout of sensors of the plan; (b) Figure 4. Monitoring the temperature of the foundation slab. (a) Layout of sensors of the plan; (b) Temperature reading instrument; (c) Layout of sensors along the depth. The unit is mm. Temperature reading instrument; (c) Layout of sensors along the depth. The unit is mm.

3.4. Test Results and Data Analysis 3.4. Test Results and Data Analysis 3.4.1.Analysis Analysisofofthe thechange Change Temperature across Different Test Points (1) inin temperature across different test points In order order to to facilitate facilitate the the analysis, analysis, the the temperature temperaturedata dataof ofall all the the test test points points were were collected collected and and In plotted for 254 h. The time points were 0 h, 39 h, 44 h, 48 h, 63 h, 71, 93, 110 h, 118, 135, 160 h, 182 h, plotted h. The time points were 0 h, 39 h, 44 h, 48 h, 63 h, 71, 93, 110 h, 118, 135, 160 h, 190 h, 212 h, 233 h, and 254 h. The test points A, B, C, D and E are analyzed in detail below. 182 190 212 233 h, and 254 h. The test points A, B, C, D and E are analyzed in detail below. As can can be be seen seen from from Figure Figure 5, 5, itit takes takes about about 44–72 44–72 hh for for all all the the test test points points to to attain attain the the peak peak As ˝ C was attained at test point C2. After temperature. The maximum temperature of approximately 74 temperature. The maximum temperature of approximately °C was attained at test point C2. After attaining the the peak peak temperature, temperature, the the rate rate of of drop drop in in temperature temperature was was the the greatest greatest for for the the corner corner test test attaining point E1, E1, located located at at the the top 50 mm of the foundation. On On the the other other hand, hand, the the temperature temperature of of test test point points A3-E3, which located at the bottom 50 mm of the foundation, was relatively stable. Test points points which located at the bottom 50 mm of the foundation, was relatively stable. Test A2-E2,A2-E2, which which were located in the in mid of theof concrete slab, had effecteffect of theofheat points were located thedepth mid depth the concrete slab,pronounced had pronounced the ˝ C/d, of hydration as illustrated by their high temperatures. The cooling rate was no more than 2.0 heat of hydration as illustrated by their high temperatures. The cooling rate was no more than which met the requirements of the standard GB50496-2009 [20]. 2.0 °C/d, which met the requirements of the standard GB50496-2009 [20].

Appl. Sci. 2016, 6, 110 Sci. 2016, 6, 110 Appl.Appl. Sci. 2016, 6, 110

7 of 18 7 of7 18 of 18

Appl. Sci. 2016, 6, 110

7 of 18

Figure 5. Temperaturecurves curves of of hydration hydration (A-E points). Figure 5. Temperature (A-Etest test points). Figure 5. Temperature curves of hydration (A-E test points). (2) Analysis of the variation in temperature among the test points at the same depth range

3.4.2. Analysis of the Variation in Temperature among the Test Points at the Same Depth Range (2) Analysis ofsame the variation in temperature among the test atpoints). the same depth Figure 5. Temperature curves of hydration (A-E test For the depth range, the trend in temperature forpoints all measuring points was range basically the For theThe same depth range, thegreatest trend for in temperature measuring basically same. temperature was the the test points for thatall were located at points a depth was of 900 mm; it the the same depth range,inthe trend in temperature forpoints all measuring points basically the (2) For Analysis of the variation temperature among the test at the same depthwas range same.was Theabout temperature the greatest fortest thepoints test points that were located at a depthsurface of 900 mm; 70 °C. Thewas temperature of the at 50 mm depth under the foundation same. The temperature was the greatest for the test points that were located at a depth of 900 mm; it ˝ C. The For the same depth trend intest temperature all measuring points was basically it wasdropped about 70faster of theDue points at for 50preservation mm depth under the foundation surface thantemperature atrange, otherthe points. to the heat effect of the ground, the was about 70 °C. The temperature of the test points at 50 mm depth under the foundation surface same. The temperature the which greatest forthe the test50points that were located at aground, depth ofthe 900temperature mm; at it temperature of the testwas points above mm from theeffect bottom was maintained dropped faster than at other points. Duewere to heat preservation ofsurface the dropped faster than attemperature other points. Due to the atheat preservation effect of the ground, the was about 70 °C. The of the test points 50 mm depth under the foundation surface 50–55 °C, as shown in Figure 6. of the test points which were above 50 mm from the bottom surface was maintained at 50–55 ˝ C, as temperature of the test points which were above 50 mm from the bottom surface was maintained dropped faster than at other points. Due to the heat preservation effect of the ground, the at shown 6. in Figure 6. 50–55in °C,Figure as shown temperature of the test points which were above 50 mm from the bottom surface was maintained at 50–55 °C, as shown in Figure 6.

(a)

(b)

(c)

Figure (a) 6. Temperature curves at the same depth. (b)(a) 50 mm below the top surface; (b) 900(c)mm depth (a) (b) (c) of foundation; (c) 50 mm above the bottom surface.

Figure 6. Temperature curves at the same depth. (a) 50 mm below the top surface; (b) 900 mm depth of Figure 6. Temperature curves in at the same depth. (a) 50 mmdepths below along the topa surface; 900 mm depth (3) Analysis of temperature at different vertical (b) plane foundation; 50the mmvariation above the bottom surface. 6. (c) Temperature thebottom same depth. (a) 50 mm below the top surface; (b) 900 mm depth ofFigure foundation; (c) 50 mmcurves aboveatthe surface. of Taking foundation; 50 mm aboveas the bottom surface. A, B,(c)and C points examples, the temperature data of points at different depths along 3.4.3. Analysis of thewere Variation in Temperature at 7. Different Depths along a Vertical Plane a vertical plane plotted as shown in Figure (3) Analysis of the variation in temperature at different depths along a vertical plane (3) Analysis of the variation in temperature at different depths along a vertical plane

Taking A, B, and C points as examples, the temperature data of points at different depths along a Taking A, B, and C points as examples, the temperature data of points at different depths along Takingwere A, B,plotted and C points as examples, the7.temperature data of points at different depths along vertical plane as shown in Figure a vertical plane were plotted as shown in Figure 7. a vertical plane were plotted as shown in Figure 7.

(a)

(a)(a)

(b)

(b) (b)

(c)

(c)(c)

Figure 7. Temperature curves in the same plane position. (a) Position of A points; (b) Position of B points; (c) Position of C points.

Appl. Sci. 2016, 6, 110

8 of 18

Figure curves in the same plane position. (a) Position of A points; (b) Position of B8 of 18 Appl. Sci. 2016,7.6,Temperature 110 points; (c) Position of C points.

Along a vertical plane, the temperature of the measuring points was markedly different with depth. Because Because of of aa good good convection convection effect, effect, the the test test points points that that were located located on the surface had the temperature. Due Due to to the the heat preservation preservation effect, the temperature temperature of the bottom surface was lowest temperature. The central central concrete concrete was was in a typical scenario of heat of hydration in higher than at the top surface. The mass concrete; thus, the temperature here was the highest. (4) ofof foundation at at thethe core andand at the surface 3.4.4.Comparative Comparativeanalysis Analysisononthe thetemperature Temperature Foundation Core at the Surface By By calculating calculating the the temperature temperature difference difference between between the the concrete concrete surface surface and and the the concrete concrete core core (D-value) for the testing points, the actual temperature difference for each test point was obtained (D-value) for the testing points, the actual temperature difference for each test point was obtained ˝ C. As and and compared compared with with the the standard standard temperature temperature difference difference of of 25 25 °C. As can can be be seen seen from from Figure Figure 8, 8, the the ˝ C, maximum temperaturedifference differencebetween between foundation the foundation surface maximum temperature thethe foundation corecore and and the foundation surface was 25was 25 the total temperature difference the requirements of GB50496-2009 (3.0.4 of and°C, theand total temperature difference met the met requirements of GB50496-2009 (3.0.4 Terms of Terms Code for Code for construction of mass concrete). The maximum temperature difference occurred mostly in construction of mass concrete). The maximum temperature difference occurred mostly in the morning, the morning, which due temperature to the lowestoftemperature of the surface inThe thetemperature morning. The which was due to thewas lowest the base surface in base the morning. of temperature of the base surface was greatly influenced by the surrounding environment; hence, the the base surface was greatly influenced by the surrounding environment; hence, the temperature temperature difference wasduring fluctuating during the process. construction process. difference was fluctuating the construction

Figure 8. 8. D-value D-value between between the the foundation foundation center center and and the the foundation foundation surface. surface. Figure

3.4.5.Comparative Comparative Analysis the Temperature of the Foundation and the (5) analysis of of the temperature of the Surface foundation surface and the Surrounding Environment surrounding environment By calculating the temperature difference between concrete surface and the environment By calculating the temperature difference between concrete surface and the environment (D-value #) for the testing point, the actual temperature difference for each test point was obtained and (D-value #) for the testing point, the actual temperature difference for each test point was obtained compared with the standard temperature difference of 20 ˝ C [20]. As can be seen from Figure 9, the and compared with the standard temperature difference of 20 °C [20]. As can be seen from Figure 9, maximum temperature difference between the foundation surface and the surrounding environment the maximum temperature difference between the foundation surface and the surrounding was 21 ˝ C. The temperature difference basically met the requirements of the standard value. environment was 21 °C. The temperature difference basically met the requirements of the standard value.

Appl. Sci. 2016, 2016, 6, 6, 110 110 Appl. Sci.

of 18 18 99 of

Figure 9. 9. D-value D-value between between the the concrete concrete surface surface and and the the surrounding surrounding environment. Figure environment.

4. TheoreticalCalculation Calculationand andAnalysis Analysis 4. Theoretical 4.1. Thermodynamic Principle The concrete structure was assumed continuous and homogeneous. Considering an infinitesimal The concrete structure was assumed continuous and homogeneous. Considering an volume within the concrete structure, the net heat (calorie) inflows in the volume along the x, y and z infinitesimal volume within the concrete structure, the net heat (calorie) inflows in the volume directions are given as: along the x, y and z directions are given as: B2 T pq x ´ q x`dx dydzq “ λ∂ 2T 2 dxdydz (1) (qx − qx + dx dydz ) = λ Bx2 dxdydz (1) ∂x2 B T pqy ´ qy`dy dxdzq “ λ 2 2 dxdydz (2) ∂By T (q y − q y + dy dxdz ) = λ 2 dxdydz (2) ∂y2 B T (3) pqz ´ qz`dz dxdyq “ λ 2 dxdydz 2 ∂Bz T − qz +unit dxdydz (qz per ) = λ per (3) dz dxdy Suppose that the heat produced volume ∂z 2 unit time is Q. The heat emitted by an infinitesimal volume during a unit time is Qdxdydz. During the time dτ, the heat absorbed by the Supposevolume that theis heat infinitesimal cρ BBTτ produced dτ dxdydz.per unit volume per unit time is Q. The heat emitted by an . During time dτby , the absorbed byheat the infinitesimal during a unitprinciple, time is Qdxdydz Based onvolume the thermal balance the sum of the heatthe produced theheat interior and the ∂T inflow is equal to the total absorbed heat as: infinitesimal volume is c ρ dτ dxdydz . τ ∂ „ ˆ 2 ˙  B T B 2 Tprinciple, B 2 T the sum of the heat produced BT Based on the thermal by the interior and the λ balance ` ` ` Q dxdydzdτ “ cρ dτdxdydz (4) 2 2 2 Bτ Bx By Bz heat inflow is equal to the total absorbed heat as:

Simplifying Equation  (4), ∂ 2 T ∂ 2 T ∂ 2T λ  2 + 2 + 2   ∂x λ∂yˆ B 2 T∂z ` Simplifying Equation (4), cρ Bx2

  ∂T dτ dxdydz  + Q  dxdydzdτ = c ρ ∂τ 2  2 ˙ B T B T Q BT ` 2 ` “ cρ Bτ By2 Bz

(4) (5)

 ∂ 2Tof temperature Due to the heat of hydration, the under adiabatic temperature ∂ 2T ∂ 2T  rise ∂T λ rate Q of concrete + 2 + 2 + = (5)  2 condition is given as, ∂y ∂z  c ρ ∂ τ c ρ  ∂x Bθ Q Wq “ “ (6) Due to the heat of hydration, the Bτ rate cρ of temperature rise of concrete under adiabatic cρ temperature condition is given as, Hence, Equation (5) could be revised as, ∂θ Q Wq ˆ ˙ (6) λ B 2 T B 2 T= B 2=T Bθ BT ∂ τ c c ρ ρ` ` ` “ (7) 2 2 2 cρ Bx Bτ Bτ By Bz Hence, Equation (5) could be revised as,

Appl. Sci. 2016, 6, 110

10 of 18

In Equations (6) and (7), θ is the adiabatic temperature rise of concrete, W is the cement content of concrete (kg/m3 ), q is the heat source intensity (heat released by a unit volume of cement at a unit time), c is the specific heat of concrete, ρ is the density of concrete, λ is the thermal conductivity and T is the transient temperature of concrete. 4.2. Calculation Parameters According to the weight percentage of each component of concrete, the thermal conductivity λ and the specific heat capacity c of the concrete were estimated. The heat transfer coefficient and specific heat capacity of different materials were obtained based on the literature [21], and were used to calculate λ and c by using Equations (8) and (9). Finally, the thermal conductivity and specific heat of concrete were obtained by considering the adjustment coefficient: λ “ p280 ˆ 4.593 ` 774 ˆ 11.099 ` 1026 ˆ 10.467 ` 170 ˆ 2.160q{2250 “ 9.33kJ{pm ¨ h ¨ ˝ Cq

(8)

c “ 1.05 ˆ p280 ˆ 0.536 ` 774 ˆ 0.745 ` 1026 ˆ 0.708 ` 170 ˆ 4.187q{2250 “ 1.01kJ{pkg ¨ ˝ Cq

(9)

According to the concrete mix design, the concrete adiabatic temperature rise θ can be calculated by Equation (10) as: θ“

QpW ` kFq 375 ˆ p280 ` 0.25 ˆ 120q “ “ 47.9 ˝ C cρ 1.01 ˆ 2401

(10)

In Equation (10), ρ is taken as 2401 kg/m3 ; F is the amount of active admixture in concrete; Q is the heat of hydration of cement taken as 375 kJ/kg [22]; k is the blending material reduction coefficient, taken as 0.25 for fly ash [22]. 4.3. Finite Element Model The simulation of the 3D temperature field for the entire process of heat of hydration in the mass concrete foundation was performed by using the three-dimensional finite element software MIDAS/Civil (version 8.0.5). The factors such as the convection condition, the ambient temperature, and the boundary condition of the actual construction process were considered appropriately. 4.3.1. Parameter Definition The main parameters included elastic modulus, specific heat, and thermal conductivity. As shown in Table 3, two material models were defined as the foundation and the ground (the strength grade of concrete is C35). Table 3. Material properties. Parameter

Specific Heat c kJ{ pkg ¨ ˝ Cq

Thermal Conductivity λ kJ{ pm ¨ h ¨ ˝ Cq

Poisson’s Ratio

Foundation Ground

1.01 0.84

9.33 7.12

0.2 0.2

4.3.2. Building Model Since the foundation is rectangular, only one quarter was modeled and analyzed [23]. In order to describe the heat transfer from the foundation to the ground, the ground was modeled as a structure with a certain specific heat and heat conductivity. Eight-node brick elements were used. The model of foundation concrete was divided into 7670 nodes and 6372 elements. As shown in Figure 10, number 1 represents 50 mm below the top surface, number 2 represents the foundation center 900 mm, and number 3 represents the 50 mm above the bottom surface of the foundation.

Appl. Sci. 2016, 6, 110

11 of 18

Figure 10, number 1 represents 50 mm below the top surface, number 2 represents the foundation Appl. Sci. 2016, 6, 110 11 of 18 center 900 mm, and number 3 represents the 50 mm above the bottom surface of the foundation.

1/4foundation. foundation. Figure 10. Model of 1/4

4.4. 4.4. Defining Defining Boundary Boundary Conditions Conditions The single process. process. The The numerical numerical analysis analysis considered considered the entire construction as aa single The initial initial temperature was set set to to 25 25˝°C. Theenvironmental environmentaltemperature temperaturewas wasdefined definedasasa temperature (casting temperature) was C. The aconstant constantwith witha avalue valueofof32.5 32.5˝ C. °C. Two differentconvection convection coefficient functions set considered for the convection Two different coefficient functions were were set considered for the convection conditions conditions of the top and surface the lateral surface the mass concrete foundation. of the top surface andsurface the lateral of the massofconcrete foundation. (1) transfer coefficient function for for thethe topTop surface 4.4.1.Convective Convectiveheat Heat Transfer Coefficient Function Surface The The convective convective heat heat transfer transfer coefficient coefficient is is defined defined as as the the heat heat transfer transfer capability capability of of an an interface interface between a fluid and a solid surface. The unit of the convective heat transfer coefficient between a fluid and a solid surface. The unit of the convective heat transfer coefficient is is ` 22 ˘ ˝ kJ （ / m • h • ℃） in this paper. In order to simplify the circulation process of water, a layer of water kJ{ m ¨ h ¨ C in this paper. In order to simplify the circulation process of water, a layer of water was layer. Based on the [22], [22], if a concrete surface has a was considered consideredas asa athermal thermalinsulation insulation layer. Based on literature the literature if a concrete surface thermal insulation layer,layer, the heat transfer coefficient of of thethe thermal has a thermal insulation the heat transfer coefficient thermalinsulation insulationlayer layercan can be be considered same as the convective heat transfer coefficient. According to the time and depth considered same as the convective heat transfer coefficient. According to the time and depth of of water water circulation circulation during during the the construction construction process, process, the the convective convective heat heat transfer transfer coefficient coefficient during during the the water water storing storing process process was was calculated calculated by by using using Equations Equations (11) (11) and and (12) (12) as as shown shown below. below. At At the the same same time, the corresponding enhancement coefficient [22] was considered according to the interval time, the corresponding enhancement coefficient [22] was considered according to the intervaltime. time. The convective heat heattransfer transfer coefficient of the top surface the foundation each was The convective coefficient of the top surface of theof foundation at each at step wasstep obtained obtained through an interpolation. A curve was fitted as a function of the top surface temperature through an interpolation. A curve was fitted as a function of the top surface temperature as shown in as shown Figure 11.in Figure 11. β =23.9 + 14.5ν β “ 23.9 ` 14.5ν 1 11 βs = 1 = ř /λ ） βs “ “ / β )+` （h i {λ i q ph RRS (1p1{βq S

i

(11) (11) (12) (12)

i

In Equation (11), ν is the wind speed of air. In Equation (12), βs is the convective heat In Equation (11), ν is the wind speed of air. In Equation (12), βs is the convective heat transfer R s isthermal the total thermal of resistance of the transfer coefficient of surface the top of surface of the foundation; coefficient of the top the foundation; Rs is the total resistance the circulating β is theheat convective transfer of and the air and can be circulating layer; water layer;water β is the convective transfer heat coefficient of coefficient the air layer canlayer be calculated by Equation (11); water; of andcirculating λi is the thermal circulating water; conductivity and λi is of the thermal calculated by hEquation (11);of hcirculating i is the depth i is the depth water at different depths. conductivity of circulating water at different depths.

Appl. Sci. 2016, 6, 110 Appl. Sci. Sci. 2016, 2016, 6, 6, 110 110 Appl.

12 of 18 12 of of 18 18 12

Figure 11. Convection coefficient coefficient curve of top surface. Figure 11. 11. Convection coefficient curve curve of of top top surface. surface. Figure

4.4.2. Convectiveheat Heattransfer Transfer Coefficient Function Side Surface (2) Convective Convective heat transfer coefficient function forfor thethe side surface (2) coefficient function for the side surface Due to the of the heat transfer Due to to the the relatively relatively smaller smaller influence influence of of the the foundation foundation sides, sides, the the convective convective heat heat transfer transfer Due relatively smaller influence the foundation sides, convective coefficient function sides can be taken as a constant. Thus, Equation (11) was directly used coefficient for the sides can be taken as a constant. Thus, Equation (11) was directly used to coefficient function for the sides can be taken as a constant. Thus, Equation (11) was directly used to to calculate the convective heat transfer coefficient of the foundation sides that were with a calculate the convective heat transfer coefficient of the foundation sides that were covered calculate the convective heat transfer coefficient of the foundation sides that were ` 2 covered ˘ with aa ˝C . 2 thermal insulating material. The convective heat transfer coefficient was 25.9kJ{ m ¨ h ¨ 25.9kJ kJ（ /m m2 ••hh••℃） ℃）.. thermal insulating insulating material. material. The The convective convective heat heat transfer transfer coefficient coefficient was was 25.9 /（ thermal In the process of establishing the model, the temperature of the side surfaces, the bottom surface In the the process process of of establishing establishing the the model, model, the the temperature temperature of of the the side side surfaces, surfaces, the the bottom bottom In and the top surface of the ground (not including the part between the foundation and the ground) surface and the top surface of the ground (not including the part between the foundation and the surface and the top surface of the ground (not including the part between the foundation and the were set constant at a temperature of 25 ˝ C [22]. ground) were set constant at a temperature of 25 °C [22]. ground) were set constant at a temperature of 25 °C [22]. ´ −ααt t TTT“==Kp1 K(1 (1´ K −−ee−αt ))q

(13) (13) (13)

Equation (13) (13)was wastaken takenasas as the heat source function. where is the the reaction reaction rate of the the thethe heat source function. where α is the rate of the concrete, αα reaction Equation (13) was taken heat source function. where is rate of concrete, which was taken as 0.78 [24] and the adiabatic adiabaticThe temperature. The functiontowas was which waswhich takenwas as 0.78 [24]as and T is[24] theand adiabatic function was assigned the TT isistemperature. concrete, taken 0.78 the temperature. The function assigned to the corresponding units as shown in Figure 12. The maximum adiabatic temperature corresponding as shown units in Figure 12. The adiabatic temperature rise K of mass assigned to the units corresponding as shown in maximum Figure 12. The maximum adiabatic temperature K was of mass mass concrete was calculated by Equation Equation (10) and and was˝obtained obtained as 47.9 47.9 °C. It It should should be rise K concrete calculated bywas Equation (10) and was obtained as 47.9 C. It should be emphasized that of concrete calculated by (10) was as °C. be rise emphasized that the heat generated by the concrete can be calculated by Equations (10) and (13), the heat generated by the concrete can be calculated by Equations (10) and (13), and the calculation emphasized that the heat generated by the concrete can be calculated by Equations (10) and (13), and the theare calculation results arethe in agreement agreementcalorimetry with the the adiabatic adiabatic calorimetry test results results [21]. [21]. results in agreement with adiabatic test results [21]. and calculation results are in with calorimetry test

Figure 12. 12. Boundary Boundary conditions conditions for for the the foundation foundation slab. slab. Figure Boundary conditions

4.5. Analysis of of the Calculation Calculation Results 4.5. 4.5. Analysis Analysis of the the Calculation Results Results 4.5.1. Analysis Analysis of of Temperature Temperature Contours Contours 4.5.1. Analysis The temperature temperature contours contours corresponding corresponding to to different different test test times times were were generated generated by by the the finite finite The temperature contours corresponding to different test times generated element software. software. The The contours contours at at 39 39 h, h, 71 71 h, h, and and 254 254 hh were weretaken takenas asexamples examplesfor fordetailed detailedanalysis, analysis, element for detailed analysis, as shown in Figure 13a–c. as shown in Figure 13a–c.

Appl. Sci. 2016, 6, 110

13 of 18

Appl. Sci. 2016, 6, 110

13 of 18

(a)

(b)

(c) Figure 13. 13. Temperature Temperature contour contour map map corresponding to different times. (a) 39 h; (b) 71 h; (c) 254 h. Figure

Appl. Sci. 2016, 6, 110

14 of 18

Appl. Sci. 2016, 6, 110

14 of 18 At 39 h, the maximum temperature reached 66 ˝ C at the core of the foundation, 55 ˝ C at the top ˝ surface of foundation, and 50 C at the bottom surface of the foundation. The temperature rise of At 39 h, the maximum temperature reached 66 °C at the core of the foundation, 55 °C at the top the ground in contact with the foundation was relatively slower, and the temperature of the concrete surface of foundation, and 50 °C at the bottom surface of the foundation. The temperature rise of located at the boundary was relatively lower, especially at the corners. The convection effect of the the ground in contact with the foundation was relatively slower, and the temperature of the boundary was so thewas temperature dissipated concrete concrete located at thebetter, boundary relatively was lower, especiallyquickly. at the corners. The convection ˝ At of 71the h, the temperature reached 71 C the center of the and 55 ˝ C at the bottom effect boundary concrete was better, soat the temperature wasfoundation dissipated quickly. ˝ C. and theAttop The temperature ground in connect with the foundation 71 surfaces. h, the temperature reached of 71 the °C at the center of the foundation and 55 °C was at the43bottom ˝ C at the core of the foundation and 38 ˝ C at the top the temperature dropped to 55 andAt the254 toph,surfaces. The temperature of the ground in connect with the foundation was 43 °C. surface, the temperature of °C theatsurrounding environment. On the other hand, Atwhich 254 h,has the reached temperature dropped to 55 the core of the foundation and 38 °C at the topthe ˝ C owing to temperature of the bottom surface of the foundation dropped slowly and remained at 47 surface, which has reached the temperature of the surrounding environment. On the other hand, the thermal insulation effect of the ground. the temperature of the bottom surface of the foundation dropped slowly and remained at 47 °C owing to the thermal insulation effect of the ground. 4.5.2. Comparison between Experimental Results and Finite Element Analysis Results 4.5.2. Comparison between Experimental Results and Finite Element Analysis Results The numerical and the experimental results of the temperature of the test points (A1, B3, C2) were The and numerical andas the experimental compared analyzed shown in Figureresults 14a–c.of the temperature of the test points (A1, B3, C2) were compared and analyzed as shown in Figure 14a–c.

(a)

(b)

(c)

Figure 14. Comparison of temperature from the experiment and the finite element analysis. (a) A1 test Figure 14. Comparison of temperature from the experiment and the finite element analysis. (a) A1 point; (b) B3 test point; (c) C2 test point. test point; (b) B3 test point; (c) C2 test point.

The analysisfitted fittedwell wellwith withthe theexperimental experimental temperature curve. Thetemperature temperaturecurve curve from from the the analysis temperature curve. The trend of overall temperature variation was consistent, and the calculation error was within 15%. The trend of overall temperature variation was consistent, and the calculation error was within 15%. InIn order toto further analyze order further analyzethe theerror errorbetween betweenthe thecalculated calculatedresults resultsand andthe theexperimental experimentalresults, results,all allthe calculation results were subtracted from test results at test point, as shown in Table 4. the calculation results were subtracted from test results at test point, as shown in Table 4. Table betweencalculation calculationresults resultsand andtest test results. Table4.4. The The difference difference between results. Time Time

A1 A1 A2 A3 B1 A3 B2 B3 B1 C1 B2 C2 C3 B3 D1 D2 C1 D3 C2 E1 E2 C3 E3 A2

00

39 39

33 ´2 2 23 ´2 32 3 −2 ´2 2 2 3 ´2 3 2 −23 ´2 2 2

6.1 6.1 ´1.7 −1.7 6.5 8.4 6.5 8.4 ´1.1 8.4 8.4 8.4 5.7 ´0.1 −1.1 2 5.5 8.4 ´0.5 5.7 4.5 1.8 −0.1 6.5

−2

44 44

4.1 4.1 ´0.2 4.9 2.4 4.9 3.3 ´2.7 2.4 8.7 3.3 5.3 5.2 −2.7 7.8 ´1.7 8.7 1.7 5.3 ´3.4 ´3.3 5.2 6.2 −0.2

48 48

5.9 5.9 ´1.6 ´0.4 4.6 −0.4 ´1.6 ´6.8 4.6 9.1 −1.6 ´1.4 ´1.8 −6.8 8.3 ´3.5 9.1 ´4.7 −1.4 ´1.4 3.3 −1.8 5.1 −1.6

63 63

4.6 4.6 ´2.4 ´2.1 ´1.1 −2.1 3.7 ´1.2 −1.1 6.9 3.7 ´2.6 5.4 −1.2 5.7 ´5.6 6.9 0.4 −2.6 1.2 ´2.8 5.4 5.6 −2.4

71 71

93 93

110 110

118 118

135 135

160 160

182 182

190 190

212 212

233 233

254 254

ME ME

2.1 2.1 ´2.2 ´0.8 ´0.6 −0.8 4 ´0.2 −0.6 3.3 4 ´2.9 5.7 −0.2 5.1 2.8 3.3 3.9 −2.9 ´3.2 ´0.8 5.7 6.2

´0.3 −0.3

44 6.2 ´3.2 0.9 −3.2 0.5 3.2 0.9 ´0.1 0.5 1.6 6.1 3.2 1.2 4.6 −0.1 0.8 1.6 ´1.8 2.6 6.1 4.6

´4.5 −4.5

´3.7 −3.7

´0.7 −0.7

´0.1 −0.1

´3.4 −3.4

´3.1 −3.1

´2.6 ´1.2 0.5 −1.2 ´1.1 1.8 0.5 ´4.5 −1.1 ´2.2 2.9 1.8 ´1.6 ´4.2 −4.5 2.8 −2.2 ´4.5 ´6.8 2.9 0.6

3.3 ´0.4 3.7 −0.4 2 3.72 ´1.3 26.2 4 2 1.2 6.2 −1.3 0.4 6.2 ´0.3 0 4 ´1.2

3.3 ´0.2 0.7 −0.2 ´1.4 2.7 0.7 ´1.3 −1.4 5.3 2.7 2.7 2.1 1.3 −1.3 0.6 5.3 ´5.2 0 2.7 ´0.8

´0.2 ´5.3 ´0.1 −5.3 ´2.9 1.7 −0.1 ´2.1 −2.9 ´3 ´0.2 1.7 ´1.6 ´5.3. −2.1 ´2.2 −3 ´3.2 ´6.4 −0.2 ´0.6

´1.6 −1.6 ´4.3 −4.3 ´5.8 0.6 −5.8 ´2.9 0.8 0.6 0.6 −2.9 ´3 4.2 0.8 ´1.2 ´5.4 0.6 ´0.7 −3 ´0.9 ´5.3 4.2 ´2.3

00 3.1 ´6.2 ´0.4 −6.2 ´0.5 ´0.2 −0.4 ´0.4 −0.5 1.4 3.1 −0.2 3.6 ´0.9 −0.4 ´0.5 1.4 0.6 ´1 3.1 1.2

6.1 6.1

´1.8 2.4 3.2 2.4 ´0.8 2.3 3.2 ´0.7 −0.8 ´0.8 7.1 2.3 1.3 ´1.8 −0.7 5.1 −0.8 ´3.3 ´5.2 7.1 0.3

−2.2

´0.9 ´0.3 1.5 −0.3 0.1 0.5 1.5 ´2.5 0.1 ´2.2 1.3 0.5 4.1 ´2.5 −2.5 2.2 −2.2 ´2.7 ´0.1 1.3 7.1 −0.9

6.2

´0.4 2.1 ´3.8 2.1 4.2 4.3 −3.8 ´3.2 4.2 1.6 4.2 4.3 4.6 3.5 −3.2 ´5.1 1.6 ´3.2 1.6 4.2 3.2 −0.4

−1.8

−2.6

3.3

3.3

−0.2

3.1

6.2 6.5 8.4 6.5 8.4 ´6.8 8.4 9.1 8.4 6.2 7.1 −6.8 8.3 ´5.4 9.1 ´5.1 6.2 ´5.2 ´6.8 7.1 7.1

AE AE

0.78 0.78 ´0.28 ´0.50 1.47 −0.50 0.81 0.57 1.47 1.09 0.81 0.44 3.23 0.57 2.85 0.56 1.09 0.39 0.44 ´1.68 ´1.73 3.23 2.73

6.2

−0.28

D1

3

2

7.8

8.3

5.7

5.1

4.1

1.2

4.6

1.3

−1.6

1.2

2.1

−1.6

−1.2

3.6

8.3

2.85

D2

−2

5.5

−1.7

−3.5

−5.6

2.8

−2.5

4.6

3.5

−1.8

−4.2

6.2

1.3

−5.3.

−5.4

−0.9

−5.4

0.56

E2

−2

1.8

−3.3

3.3

−2.8

−0.8

−0.1

2.6

1.6

−5.2

−6.8

0

0

−6.4

−5.3

−1

−6.8

−1.73

E3

2

6.5

6.2

5.1

5.6

6.2

7.1

4.6

3.2

0.3

0.6

−1.2

−0.8

−0.6

−2.3

1.2

7.1

2.73

The average error at each test point is small with the maximum value of only 3.23 ˝ C. D3 2 −0.5 1.7 −4.7 0.4 3.9 2.2 0.8 −5.1 5.1 2.8 0.4 0.6 −2.2 −0.7 −0.5 −5.1 0.39 The simulated temperature curves are consistent with the experimental curves, and the calculated E1 3 4.5 −3.4 −1.4 1.2 −3.2 −2.7 −1.8 −3.2 −3.3 −4.5 −0.3 −5.2 −3.2 −0.9 0.6 −5.2 −1.68 results are in good agreement with the measured results.

Appl. Sci. 2016, 6, 110

15 of 18

Appl. Sci.The 2016,average 6, 110 error at each test point is small with the maximum value of only 3.23 °C. 15 of 18

The simulated temperature curves are consistent with the experimental curves, and the calculated results are in good agreement with the measured results. 5. Analysis of the Effectiveness of the Circulating Water 5. Analysis of the Effectiveness of the Circulating Water 5.1. The Thermal Simulation without Considering the Circulating Water 5.1.In The Thermal Simulation without Considering the Circulating order to further understand the characteristics of theWater water circulation technology, a thermal simulation was conducted for a reference case without considering the circulating water. All the In order to further understand the characteristics of the water circulation technology, a thermal parameters were kept the same as in Section 4.2 except for the convective heat transfer coefficient simulation was conducted for a reference case without considering the circulating water. All the function of the topkept surface. Theasconvective heat transfer coefficient function for the top surface parameters were the same in Section 4.2 except ` 2 for ˝the˘ convective heat transfer coefficient was revised set surface. at a constant value of heat 25.9kJ{ m ¨coefficient h ¨ C (taken sameforasthe fortop thesurface side surface). function of and the top The convective transfer function was 2 The results from thea thermal without thesame circulating water compared kJ （ / m considering • h •℃） (taken revised and set at constant simulation value of 25.9 as for the sideare surface). The in Figure 15from with the results the thermal simulation performed in Sectionwater 4.5 with consideration results thermalfrom simulation without considering the circulating arethe compared in ofFigure the circulating The symbol in A1# insimulation Figure 15 isperformed used to refer the simulation 15 withwater. the results from “#” theasthermal in to Section 4.5 withwithout the consideration the circulating symbol “#” as in A1# in Figurerefers 15 is to used refer to the considering theof circulating waterwater. while The the notation without the symbol theto simulation with simulation without consideringwater. the circulating water while the notation without the symbol refers consideration of the circulating to the simulation with consideration of the circulating water.

(a)

(b)

(c)

Figure Comparing the the results with with the thermal simulation withoutwithout considering the circulating Figure15.15. Comparing results the thermal simulation considering the water. (a) A1water. test point; B3point; test point; test point. circulating (a) A1(b) test (b) B3(c) testC2 point; (c) C2 test point.

Asshown showninin Figure results FEM while the temperature As Figure 15a15a forfor thethe testtest results FEM A1 A1 andand FEMFEM A1#,A1#, while the temperature curves curves overlapped during the first 0–35 h, the two curves were widely different after 35 h. For the overlapped during the first 0–35 h, the two curves were widely different after 35 h. For the simulation simulation without considering the circulating water, the temperature was set at 55 °C. At 254 h, the ˝ without considering the circulating water, the temperature was set at 55 C. At 254 h, the temperature temperature of the FEM A1# was greater than that of the FEM A1 by approximately 10 °C. of the FEM A1# was greater than that of the FEM A1 by approximately 10 ˝ C. This clearly indicates This clearly indicates that the cooling rate was significantly slower for the case without water that the cooling rate was significantly slower for the case without water circulation. Consequently, circulation. Consequently, the temperature difference between the foundation surface and the the temperature difference between the foundation surface and the ambient temperature exceeded ambient temperature exceeded the safe limit of 20 °C, and thus became vulnerable to induce cracks the safe limit of 20 ˝ C, and thus became vulnerable to induce cracks on the surface of the mass on the surface of the mass concrete foundation. concrete foundation. As shown in Figure 15b for the test results FEM B3 and FEM B3#, the two temperature curves As shown in Figure 15b for the test results FEM B3 and FEM B3#, the two temperature curves overlapped. This was because the temperature of the bottom surface of the foundation was not overlapped. This was the temperature of the bottom the foundation wasshown not affected affected despite thebecause availability of the circulating water surface on the ofupper surface. As in despite the availability of the circulating water on the upper surface. As shown in Figure 15c,were for the Figure 15c, for the test results FEM C2 and FEM C2#, the trends of the temperature rise test resultsduring FEM C2 andh.FEM of the temperature risewas werehigher identical identical 0–30 AfterC2#, 30 h,the thetrends temperature of the FEM C2# thanduring that of 0–30 the h. After theapproximately temperature 5of°C. theThis FEM C2# was higher than of the FEM C2 by FEM30 C2h,by was because the heat of that the concrete surface wasapproximately exchanged ˝ C. This was because the heat of the concrete surface was exchanged quickly by the circulating 5 quickly by the circulating water in the case of FEM C2, and hence, the heat of the central concrete water in the case of FEM C2,upper and hence, the which heat ofhad the central concrete flowed effectivelyThis to the flowed effectively to the concrete a relatively lower temperature. upper concrete which had a relatively temperature. demonstrates effectiveness of the demonstrates the effectiveness of the lower circulating water in This providing cooling the effect to the middle part, in addition to providing the upper part, of the masstoconcrete foundation. circulating water in cooling effect the middle part, in addition to the upper part, of the mass concrete foundation. 5.2. The Effect of Circulating Water in Practical Engineering Problems 5.2. The Effect of Circulating Water in Practical Engineering Problems By using the new technology in the Zhongguancun No.1 project, the thermal cracking problem, theBy main quality control problem associated with mass concrete, of approximately m3 (Aproblem, area using the new technology in the Zhongguancun No.1 project, the thermal25198 cracking

the main quality control problem associated with mass concrete, of approximately 25198 m3 (A area 13198 m3 and D area 12000 m3 ) of mass concrete was solved successfully. Compared to the pre- buried pipe cooling method, due to the reduction of the pipe laying and the associated work, the construction

Appl. Sci. 2016, 6, 110 Appl. Sci. 2016, 6, 110

16 of 18 16 of 18

13198 m3 and D area 12000 m3) of mass concrete was solved successfully. Compared to the preburied could pipe cooling method, due to theThe reduction of the laying and associated work, the period be shortened by one-third. abandoned wellpipe dewatering andthe rainwater can be utilized construction period shortened The abandoned well dewatering as the source of coolingcould water,be thus serving asby an one-third. environmentally-friendly solution. At the end ofand the rainwater can be utilized as the source of cooling water, thus serving as an concrete construction, there were no cracks on the surface of the concrete slab, as confirmed repeatedly environmentally-friendly solution. At theindicators end of theofconcrete there were no crackswas on by the competent authorities. The quality the massconstruction, concrete foundation engineering theasurface ofthe thestandard concreteof slab, as Wall confirmed repeatedly byDB11/T) the competent The quality on par with Great Cup [25] (1074-2014 and theauthorities. finished surface was as indicators of the16. mass concrete foundation engineering was on a par with the standard of Great shown in Figure Wall Cup [25] (1074-2014 DB11/T) and the finished surface was as shown in Figure 16.

Figure mass concrete concrete foundation foundation slab. slab. Figure 16. 16. Crack-free Crack-free surface surface of of the the mass

6. Conclusions Conclusions

The following followingconclusions conclusionscan canbebe drawn from research on controlling thermal in drawn from thethe research on controlling thermal crackscracks in mass mass concrete foundation structures by circulating concrete foundation structures by circulating water:water: (1) A new method for controlling the thermal cracking cracking of mass concrete concrete was was developed. developed. methodisisbased basedononthe the structural characteristics of the foundation (A1-A9/H-Q The The method structural characteristics of the foundation slab slab (A1-A9/H-Q axis).axis). The heat heat of hydration was monitored by employing temperature at different Theshowed results of hydration was monitored by employing temperature sensorssensors at different depths. depths. The results showed that the temperature difference theand surface and of thethe core of the mass slab concrete that the temperature difference between between the surface the core mass concrete couldslab be ˝ could be effectively controlled within 25the °C. same At thetime, samesince time,the since the cooling of mass concrete effectively controlled within 25 C. At cooling rate ofrate mass concrete was was reduced, the material strength of concrete was fully utilized. reduced, the material strength of concrete was fully utilized. (2) For the the surface surface of ofthe thefoundation, foundation,aaconvective convectiveheat heattransfer transfercoefficient coefficient function can used function can bebe used to to simulate the variation the depth the interval time of the circulating in the simulate the variation in theindepth and theand interval time of the circulating water in thewater construction construction process. The calculation by the finite are element analysis are with in good process. The calculation results obtainedresults by the obtained finite element analysis in good agreement the agreement with the field test results. field test results. (3) Because of the good convection effect at the surface of the foundation slab, the cooling rate was relatively faster. However, due to the "heat preservation effect" of the ground, the temperature drop rate at the bottom surface of the concrete foundation was slow. For the ideal heat of hydration was the the greatest greatest at at the the core core of of the the mass mass concrete. concrete. effect, the rate of rise in temperature was (4) In order to illustrate the effectiveness of the circulating water, the thermal simulation results for the case with circulating water were compared with the thermal simulation results for a reference withoutcirculating circulatingwater. water.The The comparison showed the circulating has acooling good case without comparison showed that that the circulating water water has a good cooling effect on the upper and middle parts of the mass concrete foundation, and has little effect effect on the upper and middle parts of the mass concrete foundation, and has little effect on the on the bottom of theconcrete. mass concrete. bottom part of part the mass Acknowledgments: The authors would like to acknowledge the financial support from the topics of National Acknowledgments: The authors would like to acknowledge the financial support from the topics of National Science and andTechnology TechnologyProgram Program (Grant NO. 2015BAL03B01), the National Nature Science Foundation of Science (Grant NO. 2015BAL03B01), the National Nature Science Foundation of China China (Grant NO.51308011) and the Natural Foundation of Beijing, NO. 8144040). (Grant NO. 51308011) and the Natural ScienceScience Foundation of Beijing, China China (Grant(Grant NO. 8144040). Author Contributions: Wenchao Liu performed the experiments and and analyzed analyzed the the data, data, and and wrote wrote the the paper. paper. Wanlin Tianxiang Ye, Ye, Huiqing Huiqing Yan Yan and Wanlin Cao Cao proposed proposed the the topic topic of of this this study study and and designed designed the the experiments. experiments. Tianxiang and Wang Jia participated in the manuscript preparation. Wang Jia participated in the manuscript preparation.

Appl. Sci. 2016, 6, 110

17 of 18

Conflicts of Interest: The authors declare that there is no conflict of interests regarding the publication of this paper.

Abbreviations The following abbreviations are used in this manuscript: PCM D-vaule D-vaule # ME AE

Phase change material The temperature difference between concrete surface and concrete center The temperature difference between concrete surface and the environment Maximum error Average error

References 1. 2. 3. 4. 5.

6.

7.

8. 9. 10. 11.

12. 13. 14. 15. 16.

Code for Design of Building Foundation; GB 50007–2011; Standard Press of China: Beijing, China, 2011. Bobko, C.R.; Zadeh, V.Z.; Seracino, R. Improved Schmidt Method for Predicting Temperature Development in Mass Concrete. ACI Mater. J. 2015, 112, 579–586. [CrossRef] Da Silva, W.R.L.; Smilauer, V.; Stemberk, P. Upscaling semi-adiabatic measurements for simulating temperature evolution of mass concrete structures. Mater. Struct. 2015, 48, 1031–1041. [CrossRef] Lee, M.H.; Khil, B.S.; Yun, H.D. Influence of cement type on heat of hydration and temperature rise of the mass concrete. Indian J. Eng. Mater. Sci. 2014, 21, 536–524. Schindler, A.K.; Keith, K.P. Behavior of high-volume fly ash concrete in mass concrete applications. In Proceedings of the 1st International Conference on Construction Materials and Structures, Johannesburg, South Africa, 24–26 November 2014; pp. 268–275. Lee, M.H.; Chae, Y.S.; Khil, B.S. Influence of Casting Temperature on the Heat of Hydration in Mass Concrete Foundation with Ternary Cements. In Proceedings of the 2nd International Conference on Sustainable Energy and Environmental Engineering (ICSEEE), Shenzhen, China, 28–29 December 2013; pp. 478–481. Heap, M.J.; Lavallée, Y.; Laumann, A. The influence of thermal-stressing (up to 1000 ˝ C) on the physical, mechanical, and chemical properties of siliceous-aggregate, high-strength concrete. Constr. Build. Mater. 2013, 42, 248–265. [CrossRef] Conceicao, J.; Faria, R.; Azenha, M. Early-age behaviour of the concrete surrounding a turbine spiral case: Monitoring and thermo-mechanical modelling. Eng. Sturct. 2014, 81, 327–340. [CrossRef] Nagy, A. Thermally induced softening and cracking in concrete with minimal reinforcement. Mater. Struct. 1997, 30, 527–532. [CrossRef] Seo, T.-S.; Kim, S.-S.; Lim, C.-K. Experimental Study on Hydration Heat Control of Mass Concrete by Vertical Pipe Cooling Method. J. Asian Archit. Build. Eng. 2015, 14, 657–662. [CrossRef] Zhu, J.; Zhang, Y.B.; Du, X.F. Study on Mass Concrete Construction Technology of Raft Foundation in Yantai Ocean Development Center. In Proceedings of the 4th International Conference on Structures and Building Materials (ICSBM), Guangzhou, China, 28–29 March 2014; pp. 1421–1425. Hou, Y.N. On the control and measures to deal with crack in mass concrete. Master’s Theses, Shandong University, Shandong, China, April 2007. (In Chinese) Qian, C.X.; Gao, G.B.; He, Z.H. Feasibility Research of Using Phase Change Materials to Reduce the Inner Temperature Rise of Mass Concrete. J. WuHan Univ. Technol.-Mater. Sci. Ed. 2015, 30, 989–994. [CrossRef] Kim, Y.-R.; Khil, B.-S.; Jang, S.-J. Effect of barium-based phase change material (PCM) to control the heat of hydration on the mechanical properties of mass concrete. Thermochim. Acta 2015, 613, 100–107. [CrossRef] Choi, W.-C.; Khil, B.-S.; Chae, Y.-S. Feasibility of Using Phase Change Materials to Control the Heat of Hydration in Massive Concrete Structures. Sci. World J. 2014, 2014. [CrossRef] [PubMed] Ye, T.X.; Yan, H.Q.; Sun, M.H. Patent Search and Analysis of SIPO, A system for controlling cracks of mass concrete foundation by circulating water, China, ZL201420816500.8. Available online: http://www.pss-system.gov.cn/sipopublicsearch/search/searchHomeIndex.shtml (accessed on 17 June 2015). (In Chinese)

Appl. Sci. 2016, 6, 110

17.

18.

19. 20. 21. 22. 23. 24. 25.

18 of 18

Sun, M.H.; Jia, W.; Cao, W.L. Patent Search and Analysis of SIPO, A cooling tank for controlling cracks of mass concrete by circulating water, China ZL201420816495.0. Available online: http://www.pss-system.gov.cn/sipopublicsearch/search/searchHomeIndex.shtml (accessed on 17 June 2015). (In Chinese) Ye, T.X.; Yan, H.Q.; Sun, M.H. Patent Search and Analysis of SIPO, A cooling system for controlling cracks of mass concrete by circulating water, China, ZL201420816497.X. Available online: http://www.pss-system.gov.cn/sipopublicsearch/search/searchHomeIndex.shtml (accessed on 17 June 2015). (In Chinese) Gong, J.; Li, H.W. Crack Control of Mass Concrete Construction. Constr. Technol. 2012, 41, 28–32. (In Chinese) Code for Construction of Mass Concrete; GB50496–2009; Standard Press of China: Beijing, China, 2009. Zhu, B.F. Temperature Stress and Temperature Control of Mass Concrete; China Electric Power Pres: Beijing, China, 1999. Ge, J.Y. Guide for Use of Midas Civil Bridge Engineering Software; People's Communications Press: Beijing, China, 2013. Lu, E.X. Analysis and controlling of hydration hear temperature in mass concrete pile cap. Master’s Theses, Hunan University, Hunan, China, 2007. (In Chinese) Ma, K.S.; Tang, J.X. 3D finite element analysis of the transient temperature field of mass concrete. Henan Build. Mater. 2001, 3, 36–37. (In Chinese) The Specification of Building structure-Quality Evaluation for the Great Wall Cup; 1074–2014 DB11/T; Standards Press of Beijing: Beijing, China, 2014. © 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).