Evaluation of behavior and cracking potential of early-age cementitious systems using uniaxial restraint tests: A review

Construction and Building Materials 231 (2020) 117146

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Review

Evaluation of behavior and cracking potential of early-age cementitious systems using uniaxial restraint tests: A review Jianda Xin a,b, Guoxin Zhang a,b,⇑, Yi Liu a,b, Zhenhong Wang a,b, Zhe Wu a,b a State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, A-1 Fuxing Road, Beijing 100038, PR China b Department of Structures and Materials, China Institute of Water Resources and Hydropower Research, A-1 Fuxing Road, Beijing 100038, PR China

h i g h l i g h t s
Application of uniaxial restraint test for cementitious systems is reviewed.
Newly developed uniaxial restraint test methods are discussed.
Insight into the current application rationalities is addressed.
Suggestions are made for standardization of TSTM.

a r t i c l e

i n f o

Article history: Received 4 May 2019 Received in revised form 2 August 2019 Accepted 3 October 2019

Keywords: Uniaxial restraint test Rigid cracking frame Temperature stress test machine Restraint degree Cracking potential

a b s t r a c t This paper provides a state-of-the-art review of uniaxial restraint tests for evaluation of behavior and cracking potential of early-age cementitious systems in the last five decades. Histories of design concept and improvement of uniaxial restraint tests (longitudinal-passive and longitudinal-active test) have been introduced. Particularly, analytical methods of restraint degree and restrained stress, sensitivity analysis of uniaxial restraint test parameter, as well as cracking potential evaluation with respect to their application rationalities are addressed, which are extended contents compared with the last review in early 2000s. Finally, challenges and perspectives of uniaxial restraint tests for evaluation of behavior and cracking potential of cementitious systems are given for future improvement. Ó 2019 Elsevier Ltd. All rights reserved.

Contents 1. 2.

3.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Longitudinal-passive test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Longitudinal-passive test with external restraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1. Rigid cracking frame with temperature controlling mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.2. Rigid cracking frame with environmental chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Longitudinal-passive test with internal restraint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Evaluation of restraint degree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. Evaluation of restrained stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1. Rigid cracking frame with temperature controlling mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2. Rigid cracking frame with environmental chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Longitudinal-active test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Uniaxial restraint test machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Temperature stress test machine (TSTM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1. 1st-gen TSTM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 2 3 3 3 4 4 4 4 4 5 5 5 5

⇑ Corresponding author at: State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, A-1 Fuxing Road, Beijing 100038, PR China. E-mail address: [email protected] (G. Zhang). https://doi.org/10.1016/j.conbuildmat.2019.117146 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved.

2

J. Xin et al. / Construction and Building Materials 231 (2020) 117146

4.

5.

6.

7.

3.2.2. 2nd-gen TSTM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2.3. Comparison of existing TSTMs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Data analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Material properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1.1. Cracking stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1.2. Elastic modulus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1.3. Tensile strain capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1.4. Creep/relaxation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.1.5. CTE and autogenous deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.2. Cracking potential analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.2.1. The second-zero-stress temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.2.2. Cracking temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.2.3. Restrained stress-to-tensile strength ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.2.4. Integrated criterion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.2.5. Cracking age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Sensitivity analysis of uniaxial restraint test parameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5.1. Comparison of different restraint degree calculation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5.2. Influence of threshold value on restrained stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 5.3. Influence of displacement controlling method on true restraint degree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.4. Influence of load controlling method on elastic deformation deduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Challenges and perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1. Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1.1. Selection of threshold value. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1.2. Rationality of creep deduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1.3. Displacement measuring method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1.4. Restraint degree definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1.5. Specimen dimension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.1.6. Selection of cracking potential evaluation criterion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.2. Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Declaration of Competing Interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1. Introduction Considerable volume deformation can be generated after concrete casting: the drying shrinkage due to the water loss, the autogenous and thermal deformation due to the cementitious material hydration, as well as the carbonation shrinkage, etc. Once these deformations are restrained, the restrained stress is generated inside of the cementitious system and the crack will occur when the restrained stress exceeds tensile strength, resulting in jeopardy of durability and safety of concrete structures [1–3]. Under the restraint condition, the autogenous deformation of cementitious system with a low w/b and the thermal deformation of massive concrete with a relatively high w/b are crucial precipitating factors for cracking, which have drawn much attentions from researchers to the cracking potential evaluation of cementitious system and development of reliable test machines in the laboratory [2]. The application of uniaxial restraint test can be traced back to 1970s [1]. Researchers from Germany developed a rigid cracking frame (RCF) to investigate the thermal stress and cracking susceptibility of concrete under a pseudo-adiabatic temperature history, which solved defects of ring test, such as the limited aggregate size, the unclear stress condition, and the uncontrolled temperature history. In 1994, this method was recommended by RILEM for estimation of cracking potential of concrete [2]. With the increasing demand of restraint test, improvements of uniaxial restraint tests have been made. New functions, such as the variable restraint degree (0–100%), the temperature controlling mold, and the closed loop restraining system of uniaxial restraint test machine, have greatly boosted the application of uniaxial restraint tests and enriched the research field of cracking potential

evaluation of cementitious system in the laboratory, especially with respect to the tensile behavior at early ages. Table 1 presents references regarding the uniaxial restraint test since 1973. Key parameters of uniaxial restraint test machines are given and identified for comparison. Previous reviews regarding the uniaxial restraint test were mainly published in 2003 [2,3], however, remarkable developments of RCF and temperature stress test machine (TSTM) have been made since then, along with numerous analytical methods. It is then necessary to give a summary on these significant advancements and modifications. The aim of this paper is to clarify the status of uniaxial restraint test and prompt the standardization of design concept and experimental procedure, as well as the popularization of uniaxial restraint test. This paper consists of five main sections: longitudinal-passive test (Section 2), longitudinal-active test (Section 3), data analysis (Section 4), sensitivity analysis of uniaxial restraint test parameter (Section 5), as well as challenges and perspectives (Section 6). 2. Longitudinal-passive test Longitudinal-passive test refers to the test of restrained stress acquirement and cracking potential evaluation by uniaxially restraining the deformation of cementitious material. Rigid cracking frame is the most widely used restraint body in the longitudinal-passive test machines, which can provide a timedependent external restraint for the restrained cementitious system. Meanwhile, some researchers also developed internal restraint tests (mostly with embedded reinforcements) to investigate the restrained stress of cementitious system. Furthermore, the temperature controlling system also can be

3

J. Xin et al. / Construction and Building Materials 231 (2020) 117146 Table 1 Characteristics of uniaxial restraint test in the references. Type of device Passive

[4–36]

Active

[37–111]

<150  150

[5–22,25,26,28,30,32–36,42–47, 49,50,59,60,70–72,74,79–83, 85–91,93,101–111]

<1500

[5,7,8,10,20,21,36–53,55–57,61,62, 70–72,74,77–83,87–89,93,99, 101–103,107–111]

No

[4,6,9,11,15–17,22–27,29–35, 37–41,48,51–57,61,62,64,74, 76–78,90–92,94–99]

Displacement measuring method Strain gauge [4–16,18–22,24–31,33–36,74,77,78]

LVDT

[17,32,37–73,75,76,79–111]

Load measuring method Strain deduction [4–14,16,18–22,24–26,28–34,36,74]

Load cell

[15,17,37–73,75–111]

Material Concrete

[4–22,24–63,65–111]

Mortar

[23,64]

[5,7,8,10–14,16,18–22,24–26,28, 32–33,35–38,40–50,56,58–73,75, 77–91,93,99–101,103–111]

Drying

[4,6,9,15,17,23,27,29–31,34,39, 40,51–55,57,74,76,92,94–98,102]

Relative humidity measurement Yes [32]

No

[4–31,33–111]

Year of publication 1973–1999

2000–2009

[4,17–22,27,29,36,37,39,42,48,50–52, 57–60,62–65,73,75,77–78,84,86, 90–92,94–101,107,108]

Cross-section area/mm2 <100  100 [4,23,24,27,29–31,37–41,48,51–58, 61–69,73,75,76,84,92,94–100] Length of specimen/mm <1000 [4,6,9,11–19,22–35,54,58–60,63–69, 73,75–76,84–86,90–92,94– 98,100,104–106] Temperature controlling system Yes [5,7,8,10,12–14,18–21,28,36,42–50, 58–60,63,65–73,75,79–89,93, 100–111]

Seal condition Sealed

[23,25,38,40,41,54–56,61]

>150  150

[77,78]

VWSG

[74]

Others

[61,104]

2010-present

[5–16,24,26,28,30–35, 43–47,49,53,66–72,74, 76,79–83,85,87–89,93, 102–106,109–111]

Note: VWSG: Vibrating wire strain gauge.

added to longitudinal-passive test machines to simulate arbitrary temperature boundaries and thermal cracking potential can then be evaluated. 2.1. Longitudinal-passive test with external restraint 2.1.1. Rigid cracking frame with temperature controlling mold The cross-section area of specimen in the RCF can exceed 100  100 mm in case of demand of large aggregate size [5–22,2 5,26,28,30,32–36]. The ends of specimen are dove-tail type, which can help to guarantee the effectiveness of restraint from RCF (shown in Fig. 1). A thin plastic sheet is placed between the molds and specimen in order to prevent the water loss and friction. Thermal insulating materials are placed near the molds, so the heat due to the hydration process is kept inside of the specimen. Factors, such as the autogenous deformation, the drying deformation and the thermal deformation can be together/separately investigated

Fig. 1. Rigid cracking frame [2].

for cracking potential evaluation of cementitious system. The cracking potential of cementitious system under an isothermal condition is considered to be a function of autogenous shrinkage, while the cracking potential of cementitious system under a changing temperature history is considered to be a function of autogenous shrinkage and thermal deformation [14]. Based on the principle of deformation compatibility and force equilibrium, the restrained stress of cementitious system can be obtained according to the measured strain data collected by strain gauges glued on the restraint bar or the mounted load cell. Hence, quantitative analysis on cracking parameters (e.g. cracking temperature [12,25], cracking age [27], cracking stress [21,29]), and material properties (e.g. viscoelastic behavior [13– 16,30,31], stress-independent deformation [13,16], tensile strain capacity [27,29]) can be fulfilled. The magnitude of shrinkage deformation is one of important factors on cracking occurrence, however, once the stiffness of RCF and specimen are determined, the restraint provided by RCF maybe not high enough to induce concrete cracking, especially for large cross-section area of specimen [24]. For that case, temperature controlling molds can be considered as an effective procedure to further lower the temperature of cementitious material until cracking [12,13,20,21]. Usually, the molds are hollow and filled with circulating liquids, which can be transferred to molds by a pump. The accurate computer-controlled temperature of liquid is also helpful for achievements of arbitrary temperature boundaries.

2.1.2. Rigid cracking frame with environmental chamber Temperature controlling molds are usually placed on all surfaces of specimen and the rest part of machine is kept at a constant

4

J. Xin et al. / Construction and Building Materials 231 (2020) 117146

temperature. On the other hand, some researchers put RCF in an environmental chamber to simulate the temperature history of cementitious material after casting [11,16,17,22,26]. Compared with RCF with temperature controlling molds, parallel tests can be simultaneously conducted under the same temperature history. It should be noted that due to the thermal deformation of RCF, collected strain or load data has to be corrected before subsequent calculation of restrained stress and cracking potential evaluation. Another advantage of this temperature controlling mode is to simulate the restrained stress induced by the restraint from the foundation/adjoining structures (i.e. external restraint) and the self-induced stress induced by the thermal gradient due to the thick cross-section (i.e. internal restraint). Kim et al. [17] developed a thermal stress device with different coefficients of thermal expansion (CTE) of restraint frame. During the temperature rise-cooling history of cementitious material, the tensile stress was firstly generated, followed by the compressive stress when the CTE of restraint frame is larger than that of cementitious material. This phenomenon can be explained by the fact that the cementitious material is stretched during the temperature rise stage and compressed during the temperature cooling stage due to the larger deformation of restraint frame; similarly, the compressive stress was firstly generated, followed by the tensile stress when the CTE of restraint frame is smaller than that of cementitious material.

cR ¼

As E s Ac Ec;eff þ As Es

where Ec;eff is calculated as

ð2Þ Ec , ð1þuÞ

and u is the creep coefficient of

cementitious material. Clearly, due to the smaller value of Ec;eff , the restraint degree calculated using Eq. (2) is higher than that calculated using Eq. (1). The second expression way of restraint degree is based on the restrained deformation and free deformation, as shown in Eq. (3) [32,79,89,101]

cR ¼

eres efree

ð3Þ

where eres is the restrained deformation of specimen, and efree is the free deformation of specimen. The third expression way of restraint degree is based on the actual restrained stress and theoretical restrained stress under the full restraint condition, as shown in Eq. (4) [70]

R

cR ¼

R

Rðt; t 0 Þ  de0 ðtÞ  t Rðt; t0 Þ  deðtÞ rð t Þ R ¼ t rfix ðtÞ Rðt; t 0 Þ  de0 ðtÞ t

ð4Þ

where Rðt; t0 Þ is the relaxation modulus of cementitious material;

e0 ðtÞ is the free deformation, and eðtÞ is the actual deformation of cementitious material.

2.2. Longitudinal-passive test with internal restraint 2.4. Evaluation of restrained stress Internal restraint is usually implemented by embedding reinforcements into the cementitious material (shown in Fig. 2), the restrained stress due to the deformation restraint can then be obtained [29–34]. Furthermore, the effect of reinforcement configuration on the restrained stress can also be evaluated, however, the restraint degree provided by reinforcements was much lower than that provided by the restraint frame, and can reach approximately 40% with a reinforcement ratio of 1.57% [32].

2.4.1. Rigid cracking frame with temperature controlling mold Based on the principle of deformation compatibility and force equilibrium, the restrained stress of cementitious material can be evaluated with the measured rigid cracking frame strain es , as shown in Eq. (5)

rc ¼

es Es As Ac

ð5Þ

2.3. Evaluation of restraint degree The restraint degree cR can be expressed in three ways. The first expression way of restraint degree is based on the stiffness of restraint frame and cementitious material, as shown in Eq. (1) [13,21,30,36]

cR ¼

As E s Ac Ec þ As Es

ð1Þ

where As and Ac are the cross-section area of restraint frame and cementitious material, respectively; Es and Ec are the elastic modulus of restraint frame and cementitious material, respectively. It should be noted that the value of Ec in Eq. (1) was consider as the measured time-dependent elastic modulus in some references [13,21,36], while others indicated an ‘‘effective” modulus Ec;eff incorporating the relaxation behavior of cementitious material was more appropriate, as shown in Eq. (2) [30].

2.4.2. Rigid cracking frame with environmental chamber When RCF is placed in the environmental chamber, the measured strain or load has to be corrected due to the thermal deformation of sensors and rigid cracking frame. For the machine with the load cell, the actual restrained stress takes the following expression [17]

rc ¼

F s  F com Ac

ð6Þ

where F com is a compensation force of load cell induced by the temperature variation. For the machine with glued strain gauges, the actual restrained stress is [26]

rc ¼

ðes  DT s  as ÞEs As Ac

Fig. 2. Internal restraint by embedded reinforcements [33].

ð7Þ

J. Xin et al. / Construction and Building Materials 231 (2020) 117146

where DT s is the temperature variation of restraint frame, as is the CTE of restraint frame. 3. Longitudinal-active test Due to the increasing stiffness of cementitious material with hydration process, the restraint degree provided by the uniaxial restraint machine introduced in Section 2 was no longer 100% and gradually decreased to 75% at late ages [25]. Therefore, longitudinal-active tests have been developed to fulfil 100% restraint condition. This function is achieved by adding a special instrument on the end of movable grip, while the other end is fixed [37–111]. When the deformation of specimen reaches a threshold value, the step motor or servo motor will be activated to push/pull the specimen to the original position, which has overcome the deficiencies of longitudinal-passive test machines, such as the limited cross-section area and corresponding weak restraint. The threshold value can be determined based on the variation of test results influenced by the accuracy of displacement sensor, the sensitivity of feedback system and the machining precision of machine [58]. For example, the evolution of tangent elastic modulus can be determined based on the incremental stress and threshold value during each cycle. In this sense, a small variation is desirable.

5

Furthermore, variable restraint degrees also can be achieved based on the selected restraint degree along with deformation data, and fulfilled via the displacement controlling system of machine [68,89,101]. In case of thermal stress analysis, the temperature controlling system also has been added to the longitudinal-active test machine for evaluation of thermal cracking potential [2,42–47,49–50, 58–60,63,65–73,75–91,93,100–111]. Fig. 3 presents numbers of published references in different years. It is shown that due to the advanced design concept, studies regarding the cracking potential evaluation using longitudinalactive tests have made greater growth than those using longitudinal-passive tests.

3.1. Uniaxial restraint test machine A vertical uniaxial restraint test machine with 100% restraint function was developed in 1976 and the details of machine can be found in ref. [2]. An air pressing equipment was mounted on the free end of machine. Changes of specimen were monitored by the gauge and constant length was guaranteed by manually adjusting the position of the grip. Bloom and Bentur [40] reported a horizontal uniaxial restraint test machine, which was an improvement as the restrained stress of early-age hardening cementitious material can be obtained and a parallel free specimen was added for separation of deformations during the loading stage. In general, the total deformation of restrained specimen consists of free deformation, elastic deformation and creep deformation. The accumulated deformation of restrained specimen can be considered as the elastic deformation, so the creep deformation is the only unknown parameter and can be determined based on the free deformation measured on the parallel free specimen.

3.2. Temperature stress test machine (TSTM)

Fig. 3. Number of published references in different years.

3.2.1. 1st-gen TSTM In 1985, the first temperature stress test machine was developed to study the restrained stress due to the hydration heat [2], as shown in Fig. 4. With the temperature controlling molds, any temperature boundary of restrained specimen can be achieved.

1-Specimen; 2-Adjustable cross-head; 3-Fixed cross-head; 4-Step motor; 5-Load cell; 6aMeasurement of cross-head movements; 6b-Length measurement with carbon fiber bars; 7Formwork with heating/cooling system; 8-PC for controlling and recording; 9-Cryostat for cooling/heating of the formwork. Fig. 4. Principle sketch of TSTM [2]. 1-Specimen; 2-Adjustable cross-head; 3-Fixed cross-head; 4-Step motor; 5-Load cell; 6a-Measurement of cross-head movements; 6bLength measurement with carbon fiber bars; 7-Formwork with heating/cooling system; 8-PC for controlling and recording; 9-Cryostat for cooling/heating of the formwork.

6

J. Xin et al. / Construction and Building Materials 231 (2020) 117146

As soon as the deformation of restrained specimen reaches the threshold value, an additional force provided by the motor will be applied on the specimen to return the specimen to the original position, then 100% restraint is fulfilled as the total deformation of restrained specimen is zero. 3.2.2. 2nd-gen TSTM In 1994, a closed loop restraining system of TSTM with two specimens (one free specimen and one restrained specimen) was developed by Kovler based on the design concept of Bloom and Bentur (shown in Fig. 5) [55], and the application of automatic controlling system has greatly improved the accuracy of TSTM. This concept was later used by numerous scientific research institutions for developments of similar machines [44,58,59,63,74,79,85,89,91,101,109]. 3.2.3. Comparison of existing TSTMs Usually, TSTM consists of four main systems: the temperature controlling system, the displacement measuring system, the load controlling system and the displacement controlling system. Based on the available TSTM design parameters from existing references, the differences of TSTM design details have been introduced herein. 3.2.3.1. Temperature controlling system. Most TSTMs are equipped with temperature controlling molds, as shown in Fig. 6. The molds are hollow and filled with circulating liquids, which can be rapidly heated/cooled. The temperature histories of molds, restrained specimen and free specimen are accurately controlled (as shown in Fig. 7). Temperature boundaries of all surfaces of specimen are simultaneously maintained to avoid the thermal gradient. Recently, a TSTM developed in Tsinghua University was manufac-

Fig. 5. Schematic description of the closed loop instrumented restraining system [55].

Fig. 6. TSTM with temperature controlling molds [89].

Fig. 7. Temperature history of TSTM.

tured with an environmental chamber and the temperature controlling molds were removed, however, delicate designs have to be done to compensate the effect of temperature variation on deformations of TSTM parts. The main concept is that the deformation of longitudinal steel shaft is designed to be equal to the total deformation of other components, such as fix heads, movable heads, snap joints, etc. So, the effect of thermal deformation of TSTM on restrained specimen can be ignored [44]. 3.2.3.2. Displacement measuring system. Most TSTMs adopt a direct displacement measuring method, i.e. linear variable differential transformer (LVDT) deforms simultaneously with the specimen using embedded rods. LVDT is usually mounted on a horizontally placed rod made with low CTE materials, such as invar and quartz, etc [68,89]. LVDT can either be on top [44,70,89,98] or side [68,85,90] of machine due to different designs. Locating parts are fixed after concrete casting to keep embedded rods and the connected horizontally placed rod still until the final setting age is reached. Then, the locating parts are removed and LVDT can simultaneously measure the deformation of specimen. Furthermore, the small deformation of horizontally placed rod due to the temperature variation also has to be deducted from measured data [68,77,89]. For some TSTMs, the LVDT was mounted on the movable grip [40,99]. Altoubat and Lange [96] reported that the restrained stress based on this indirect displacement measuring method was lower and the cracking potential of cementitious material was underestimated. Refs. [77,104–106] also reported that the deformation of restrained specimen can be measured through strain gauges glued on embedded reinforcements based on the perfect bonding, which is more convenient compared with the direct displacement measuring method using LVDT. 3.2.3.3. Load controlling system. Most TSTMs have the motor on the end of movable grip, and the load can be transfer to the restrained specimen through the grip [58,59,70,79,86,89]. Meanwhile, the restrained stress can be measured by the load cell mounted on the connecting shaft between the motor and movable grip. Refs. [74,77] also reported that the load can be transferred to the restrained specimen through embedded reinforcements and the shape of specimen was designed to be prismatic. There are two load controlling methods: the first one is to keep the stress of restrained specimen constant during each cycle [95] (Fig. 8(a)); the second one is that the motor is only activated when the deformation of restrained specimen reaches the threshold, so a stress increment Dri due to the restraint provided by the rigid frame occurs during each cycle [75] (Fig. 8(b)).

7

J. Xin et al. / Construction and Building Materials 231 (2020) 117146

Fig. 10. Displacement control of restrained specimen using Eq. (9) [68].

Table 2 Threshold values in TSTM tests.

Fig. 8. Different load controlling methods.

3.2.3.4. Displacement controlling system. For the 100% restraint, the total deformation of restrained specimen is zero, which is easy to fulfil. For the partial restraint, there are currently two controlling methods. The first method was introduced in ref. [101]. The residual deformation of restrained specimen with a certain restraint degree was controlled based on the known free deformation (i.e. measured deformation data from free specimen) and can be express as

e ¼ efree ð1  cR Þ

ð8Þ

Based on Eq. (8), the residual deformation of restrained specimen can be accurately controlled by the computer, as shown in Fig. 9. The second method was introduced in ref. [68] (Fig. 10). The residual deformation of restrained specimen with a certain restraint degree was controlled based on the deformation of restrained specimen (i.e. deformation of free specimen is unavailable) and can be express as

e¼

X


eð1  cR Þ

ð9Þ

where De is the threshold value of restrained specimen. It can be concluded that since De consists of free deformation and creep deformation, the actual residual deformation controlled

Threshold value/le

References

0.2 0.4 0.5 0.6 0.67 1.3 1.5 2 3 3.7 4 5 6.7 8 8.57 10

[58,75] [84] [103,107,108] [58,75] [88,93,109] [47,79–81,83] [111] [44,49,58,75,82,89,101,110] [111] [104–106] [51–53 ,57,64] [37,38,41,48,50,55,56,61,99] [45,70–72] [42,57,76,85,86,92,94–98] [66–69] [54,62]

Note: [51–53]: the threshold value varied between 4 and 8 le.

by Eq. (9) is smaller than that controlled by Eq. (8), resulting in a relatively higher restraint degree. Furthermore, the selection of threshold value is inconsistent. Table 2 presents different threshold values of TSTM tests. The threshold value varies between 0.2 and 10 le, and a threshold value higher than 1 le seems more popular. Actually, the true 100% restraint means that no deformation occurs and existing test methods are considered to be pseudo. For the larger threshold value, due to the increasing elastic modulus, the stress increment of each cycle becomes larger, which may lead to divergent results compared with the test results with the smaller threshold value. On the other hand, the selection of smaller threshold value also requires a high-level machining and accurate controlling system of TSTM, or the larger scatter is adverse for the effective data analysis [58]. Therefore, the selection of threshold value should depend on the balance of data accuracy and available manufacturing technique. 4. Data analysis

Fig. 9. Displacement control of restrained specimen using Eq. (8) [101].

By means of uniaxial restraint tests, material properties and cracking potential of cementitious material can be obtained simultaneously, which have simplified experiment procedures and enriched application ranges of test results.

8

J. Xin et al. / Construction and Building Materials 231 (2020) 117146

4.1. Material properties 4.1.1. Cracking stress Cracking stress is related to the stress when the concrete cracks during the test, which is an index of axial tensile strength of cementitious material under the long-term loading. Many researchers reported the relationship between the cracking stress and axial tensile strength/splitting tensile strength measured on standard specimens of mechanical property test. Fig. 11 presents the ratios of cracking stress to axial tensile strength/splitting tensile strength from existing references. SP in the legends of Fig. 11 is the abbreviation of splitting tensile strength. It can be seen that, except for refs. [47,49] and [110], this value is generally in a range of 0.6–0.8. The possible explanations are as follows [36,58,68]: (1) the loading rate of mechanical property test is faster than that of TSTM test, which is beneficial for prevention of microcrack propagation; (2) the size effect of TSTM test gives a larger scatter of tensile strength; (3) particularly, ref. [58] reported that this value was attributed to the asymmetry effect of TSTM, which can be proved by the fact that the axial tensile strength of cementitious materials under the short-term loading on TSTM was still lower than that obtained from mechanical property test. 4.1.2. Elastic modulus The elastic modulus of cementitious material can be determined by the stress increment and displacement increment during each cycle [68]. Theoretically, this tangent modulus is more appropriate for calculation of restrained stress, however, due to the accuracy limitation of TSTM on measuring and controlling system, the scatter of calculated elastic modulus might be unsatisfactory [58]. It is recommended in ref. [77] that the elastic modulus would better be obtained by partial unload/reload cycles with a large deformation, which can overcome the insignificant noise in the feedback signal.

4.1.3. Tensile strain capacity Based on the analytical method developed by Kovler, as shown in Fig. 12 [55], the cumulative strain of restrained specimen in each cycle can be considered as the elastic strain and the final value at cracking age represents the tensile strain capacity of cementitious material. Other researchers used the restrained stress and tangent modulus to calculate elastic strain of cementitious material [77,89].

Fig. 12. Analytical method of deformation deduction recommended by Kovler [55].

4.1.4. Creep/relaxation Compared with the classic compressive creep machine, the tensile creep of early-age cementitious material can be easily obtained by TSTM, and factors, such as the temperature variation, the drying condition and the stress level, can be simultaneously considered [68,75,84]. It is worth mentioning that by means of the analytical method recommend by Kovler [55], a series of creep parameters can be obtained and used for subsequent analyses. The specific creep can be expressed as [56,57,61,62,77,79,82,83, 86,99,101,109]

C ðt Þ ¼

ecr ðtÞ rð t Þ

ð10Þ

A creep-to-free deformation ratio K ðt Þ is adopted to evaluate the relaxation behavior of cementitious material [61,79,83,89,95, 97,98,101,109]

K ðt Þ ¼

ecr ðtÞ efr ðtÞ

ð11Þ

4.1.5. CTE and autogenous deformation It is well known that temperature has a great effect on the evolution of autogenous deformation, so the separation of thermal and autogenous deformation also has been done on the free specimen of TSTM. Several methods have been recommended to determine early-age CTE and autogenous deformation [68,77,80,90]. 4.2. Cracking potential analysis Quantitative cracking potential analysis for the cementitious material with different test conditions (e.g. the temperature variation, the drying condition, the restraint condition) is the most important function of TSTM. In this section, different cracking potential evaluation criteria are summarized. 4.2.1. The second-zero-stress temperature The second-zero-stress temperature is related to the temperature when the compressive stress induced in the cementitious material is eliminated. Many references reported that the second-zero-stress temperature affected the early-age cracking potential of cementitious material, the higher the second-zerostress temperature, the higher the cracking potential [12,25].

Fig. 11. Relationship between the threshold value and ratio of cracking stress to tensile strength.

4.2.2. Cracking temperature Cracking temperature is related to the temperature when the concrete cracks. This index is recommended by RILEM that a lower

9

J. Xin et al. / Construction and Building Materials 231 (2020) 117146

cracking temperature indicates a lower potential of cracking [2,12,25]. 4.2.3. Restrained stress-to-tensile strength ratio This ratio is calculated based on the restrained stress rðt Þ measured in the restraint test and tensile strength f ðt Þ measured from mechanical property test, and adopted by researchers to evaluate the cracking potential of cementitious material [21,28,36,61,68,99]

I ðt Þ ¼

rð t Þ

ð12Þ

f ðt Þ

The smaller the ratio, the lower the cracking potential. Particularly, this value also reflects the time-dependent cracking potential of cementitious material, which is beneficial for the real-time cracking potential evaluation. 4.2.4. Integrated criterion This criterion is based on the net time of cracking and the rate of tensile stress at the time of cracking, which is a modification of criterion recommend by ref. [112].

I ðt Þ ¼

S t cr

ð13Þ

where t cr is the net time between the second-zero-stress age and cracking age; S is the tensile stress rate at the time of cracking. The smaller the ratio, the lower the cracking potential. This method has been adopted for cracking potential evaluation by some researchers [79,81–83]. 4.2.5. Cracking age Cracking age is related to the age of concrete cracking. This index is mainly used for cracking potential evaluation of cementitious material without the temperature variation [27]. The later the cracking age, the lower the cracking potential. 5. Sensitivity analysis of uniaxial restraint test parameter 5.1. Comparison of different restraint degree calculation methods As a matter of fact, Eqs. (2) and (3) are equivalent when the creep behavior is involved. Fig. 13 shows the strain evolution of concrete under the restraint condition (temperature cooling stage). The dotted lines represent the original position of concrete, while the solid lines represent the actual position of concrete. Assuming that the actual strain of restraint frame is es , then the elastic strain of concrete ee can be calculated based on the principle of deformation compatibility and force equilibrium

ee ¼

es Es As

ð14Þ

E c Ac

If no creep strain occurred during the loading period, then the restraint degree provided by the restraint frame can be expressed using Eq. (3) as

cR ¼

ee

e þ es e

Fig. 13. Strain of concrete under the restraint condition.

Substituting Eq. (14) into Eq. (15), one can obtain the restraint degree expressed by Eq. (1). In reality, the creep deformation occurs when the concrete experiences the long-term loading. If the creep effect is considered, then Eq. (15) should be rewritten as

cR ¼

ee þ ecr e þ ecr þ es

ð16Þ

e

Assuming that the creep coefficient u is calculated as eee , Eq. (16) then can be rewritten as cr

cR ¼

As Es Ac Ec =ð1 þ uÞ þ As Es

ð17Þ

That is to say, when calculating the restraint degree of restrained cementitious materials under the long-term loading, Eqs. (2) and (17) are equivalent to Eq. (3). Particularly, if the restraint degree is constant, substituting Eq. (3) into Eq. (4), one can obtain that the restraint degree expressed by the stress and deformation are equivalent. However, Eq. (4) is less adopted due to its complex on calculation of restrained stress. Fig. 14 shows the calculated restraint degrees using Eqs. (1), (2) and (4) based on the measured data from uniaxial restraint tests in ref. [22], which different cross-section areas of restraint frame were used for simulation of varying restraint degree tests. Calculation of restraint degree using Eq. (3) is ignored due to the lack of deformation data. As expected, due to the effect of creep, the calculated restraint degrees using Eq. (1) are globally lower than those using Eq. (2) for the metal plate thickness of 10 and 40 mm. Meanwhile, the calculated restraint degrees using Eq. (4) are similar with those using Eq. (2).

5.2. Influence of threshold value on restrained stress It can be seen from Table 2 that there exist several threshold values for parameter setting of TSTM. In order to quantitatively evaluate the influence of threshold value e0 for the restraint stress measurement, a one-dimensional numerical analysis using Matlab software is conducted and the stress calculation flow chart is shown in Fig. 15. Once the deformation of concrete reaches the threshold value, a stress increment is applied to pull/push the concrete to the original position and these loading times are controlled by the coupling effect of free and creep deformation. The cumulative stress is then the restrained stress obtained from TSTM. For the numerical analysis process, the CTE of concrete is 105 le/°C; the elastic modulus of concrete equals 38  (1  exp(0.4  (t)0.34)) GPa and t is the concrete age (in days); the cooling rate of concrete k is set to be 0.1 °C/h; the initial calculation age of concrete restrained stress is 80 h. A specific creep [113] (Eq. (18)) is adopted and creep parameters are given in Table 3.

ð15Þ

Fig. 14. Calculation of restraint degree using different methods.

10

J. Xin et al. / Construction and Building Materials 231 (2020) 117146

Fig. 16. Restrained stress evolutions with different threshold values.

Fig. 15. Flow chart of stress calculation. Fig. 17. Influence of threshold value on restrained stress. Table 3 Parameters of specific creep.

5.3. Influence of displacement controlling method on true restraint degree

parameter

f i (104)

g i (104)

pi

ri

i=1 i=2

0.1045 0.2360

0.9614 0.4012

0.7 0.7

0.3 0.005

As mentioned in Section 3, the restrained deformation of each cycle using Eq. (9) is

  Deres ¼ c0R Defree  Decreep

ð19Þ

where De is the creep deformation of concrete of each cycle, and c0R is the nominal restraint degree. creep

The first term (i = 1) represents the recoverable creep at an early age and the second term (i = 2) represents the recoverable creep at a late age.

C ðt; sÞ ¼

2 X

ðf i þ g i s

pi

  Þ 1  eri ðtsÞ

ð18Þ

Then the restraint degree calculated by Eq. (3) takes the following expression

cR ¼

i¼1

where s is the loading age. Fig. 16 shows the restrained stress evolutions with different threshold values. As expected, the amount of stress increment step is strongly associated with the threshold value. For the restrained stress evolution with the larger threshold value, the interval time between two cycles becomes longer. It is interesting to observe from Fig. 16 that the final restrained stress with the largest threshold value of 7 le is the highest. Fig. 17 shows the restrained stress difference trends with different threshold values. The larger the threshold value, the higher the restrained stress. Meanwhile, the stress differences g ðg ¼ ½rðe0 ¼ 2; 4; 7leÞ  rðe0 ¼ 1leÞ=rðe0 ¼ 1leÞÞ become smaller with the larger threshold value. These phenomena can be explained by the fact that due to the increasing elastic modulus, the stress increment with the larger threshold value is higher, especially at an early age with a rapid elastic modulus evolution. Hence, theoretically, the restraint test using TSTM with the smaller threshold value leads to more accurate results as the condition of restrained specimen is closer to the true ‘‘full restraint” status (i.e. no deformation occurs).

   Defree  1  c0R Defree  Decreep Defree

ð20Þ

Assuming that DK ¼ Decreep =Defree , then Eq. (20) can be rewritten as





cR ¼ c0R þ 1  c0R DK

ð21Þ

The calculated restraint degree using Eq. (21) is obtained and depicted in Fig. 18 (the value of DK is from ref. [92] and

Fig. 18. Influence of displacement controlling method on restraint degree.

J. Xin et al. / Construction and Building Materials 231 (2020) 117146

11

c0R ¼ 0:5). Due to the creep effect, the true restraint degree provided by Eq. (9) is higher than the preset c0R of 0.5, leading to a con-

6. Challenges and perspectives

servative cracking resistance capability of concrete.

6.1. Challenges

5.4. Influence of load controlling method on elastic deformation deduction

6.1.1. Selection of threshold value It can be seen from Table 2 that there is no consensus on the selection of threshold value. The sensitivity analysis of effect of threshold value on restrained stress shown in Section 5.2 implies that the threshold value should be as small as possible to fulfil the true full restraint condition. On the other hand, experimental results in ref. [58] showed that the threshold value had a great influence on the determination of incremental elastic modulus, which indicated the scatter of incremental stress of each cycle, as well as the cumulative restrained stress. Hence, the theoretical restrained stress analysis result and TSTM mechanical technology limitation should be simultaneously considered for the acquirement of accurate experimental data.

During each deformation cycle of TSTM, if the load of restrained specimen is not constant, then the elastic strain increment for the ith cycle can be expressed based on Eq. (14)

Dee ðt i Þ ¼

es ðti ÞEs As

ð22Þ

Ec ðt i ÞAc

Then, the elastic strain after n cycles can be obtained

ee ¼

n X i¼1

e e ðt i Þ ¼

n Es As X es ðti Þ Ac i¼1 Ec ðt i Þ

ð23Þ

Assuming that the deformation of specimen (restraint frame) is equal to the threshold value e0 and the elastic modulus of concrete keeps constant, then the elastic strain is

ee ¼

n Es As X EA es ðti Þ ¼ ne0 s s Ec Ac i ¼ 1 E c Ac

ð24Þ

Bearing in mind that ne0 is the cumulative strain eecumulative recommended by Kovler [55], then the true elastic strain of restrained specimen is



eetrue ¼ ee þ eecumulative ¼ 1 þ If

Es As Ec Ac

E s As E c Ac



eecumulative

ð25Þ

¼ X, then the true (corrected) elastic strain is

eetrue ¼ ð1 þ XÞeecumulative

ð26Þ

Fig. 19 presents a comparison of elastic strain of restrained specimen calculated using Eq. (26) and the method in ref. [55]. Due to the relatively high stiffness of TSTM, considerable elastic strain can be generated during each deformation cycle and these deformations have to be subtracted from the total free deformation to calculate creep capability of concrete; otherwise, the creep capability will be greatly overestimated using the elastic strain calculation method recommended in ref. [55].

Fig. 19. Influence of restraint frame stiffness on elastic strain of restrained specimen.

6.1.2. Rationality of creep deduction As mentioned in Section 5.4, the frequency of specimen reaching the threshold deformation is strongly related to the stiffness of uniaxial restraint test machine. Theoretically, the cumulative strain of restrained specimen becomes smaller with the higher stiffness of uniaxial restraint test machine, resulting in a larger creep deformation provided that the free deformation remains same for different tests. Therefore, the creep behaviors of cementitious material obtained from different TSTMs cannot be directly compared. There are two possible solutions: the first one is to keep the stress of restrained specimen constant during each cycle, only the creep deformation occurs in this stage and the effect of stiffness can be ignored (double-feedback system) [95]; the second one is to additionally record the stress increment Dri of each cycle and the incremental elastic deformation can be determined (single-feedback system). Those additional elastic deformations need to be added in the cumulative elastic strain (as shown in Fig. 19), and the creep deformation is correspondingly corrected [110]. 6.1.3. Displacement measuring method As discussed in the above sections, the direct displacement measuring method is beneficial for the acquirement of accurate restrained stress, however, the specific details of displacement measuring system of TSTMs are different, such as the material of embedded rod, the location of LVDT, and the age of locating part removal, etc. The CTE of embedded rod should be as small as possible to eliminate the effect of thermal deformation on the displacement measuring system. The LVDTs mounted on two sides of specimen help to measure the eccentricity of axial loading with the uniaxial restraint test machine. This method might be more reasonable compared with some tests with only one LVDT mounted on the top of specimen. The removal age of locating part can be determined based on the final setting test, which can guarantee the bond between the embedded rods and specimen. Inappropriate removal age of locating part may lead to inaccurate specimen deformation measurements and loadings. The influence of these factors on measurement accuracy of restrained stress needs further explorations, especially for studies regarding thermal stress and cracking potential evaluation. 6.1.4. Restraint degree definition It is mentioned in Section 5.3 that due to different restraint degree definitions, the measured restrained stresses of different TSTMs are not same, leading to various cracking potential evaluations. Especially for the partial restraint test, it is necessary to fur-

12

J. Xin et al. / Construction and Building Materials 231 (2020) 117146

ther confirm the appropriate restraint degree definition. To the authors’ knowledge, the method using Eq. (3) for the partial restraint control in TSTM is more reasonable compared with that using Eq. (9) because Eq. (3) accords with the definition of restraint degree and corresponding test data from different tests can be directly compared. On the other hand, the stiffness of concrete after casting is changing and the restraint provided by the foundation or adjoining structures is not constant, however, the uniaxial restraint test with a constant restraint degree is more popular, implying that the cracking potential of cementitious material obtained in the laboratory might be inconsistent with that under the real environmental condition. 6.1.5. Specimen dimension For the prismatic specimen of uniaxial restraint test [74,77], the stress distribution along the axial direction is uniform and the crack occurs at the weakest section of specimen. For the more common dove-tail type specimen, the stress concentration at ends of specimen is a key factor, which has a great influence on the determination of true cracking stress and cracking potential evaluation. The rational crack position of specimen (usually in the range of central linear part of specimen) should be firstly verified to guarantee the accuracy of test and design details of RCF are available for reference [2]. 6.1.6. Selection of cracking potential evaluation criterion There are currently several cracking potential evaluation criteria adopted by researchers conducting uniaxial restraint tests, however, systematic studies on rigorous physical meanings and derivation procedures of these criteria are still lacking. Furthermore, the inherent relation of these criteria is also worth exploring.

(4) The uniaxial restraint test using the longitudinal-passive machine is still promising, however, the thermal stress deduction methods using RCF should be carefully differentiated as the deformation measured in RCF with temperature variation is coupled with the ineffective thermal deformation. (5) The effect of threshold value on restrained stress cannot be ignored and theoretical analysis results show that the restrained stress obtained from TSTM increases with the larger threshold value. (6) The stiffness of restraint frame should be considered for the deformation deduction of restrained specimen when the single-feedback system of TSTM is available, or the elastic strain of restrained specimen will be greatly underestimated. (7) The control of partial restraint only based on the deformation of restrained specimen leads to a higher restraint degree and more conservative cracking resistance capability compared with that based on the deformation of restrained and free specimen. (8) Based on the review of uniaxial restraint tests and sensitivity analysis of TSTM parameters, it is suggested that the standardization of TSTM regarding design concepts and details is beneficial for the normalization of measured data and broader utilization of cracking potential evaluation.

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

6.2. Perspectives Acknowledgements Although the design concepts and details of different TSTMs are not identical, the advantages of using TSTM on cracking potential evaluation of cementitious material are noticeable. Early-age material properties obtained from TSTM test are essential for the numerical simulation of stress field of concrete structure, especially for the massive concrete structure which cannot be experimentally tested at a full-scale level. On the other hand, it is meaningful that the optimization of cementitious material can now depend on the reliable experimental data, which are coupled with multiple factors that do exist in the stage of construction. 7. Conclusions In this paper, a state-of-the-art review of uniaxial restraint tests for behavior and cracking potential evaluation of cementitious material has been presented. The following conclusions can be drawn: (1) The invention of temperature controlling system has prompted the cracking potential evaluation of cementitious material using uniaxial restraint tests. (2) The analytical method for the creep deformation deduction based on the closed loop restraining system with two parallel specimens has improved the utilization efficiency of measured data. (3) The direct displacement measuring method and temperature controlling mold of TSTM are suitable for the accurate restrained stress measurement and cracking potential evaluation.

The authors would like to acknowledge the support provided by the National Key R&D Program of China, China (Grant No. 2018YFC0406703), the National Natural Science Foundation of China, China (Grant No. 51779277), the Special Scientific Fund sponsored by IWHR for Department of Structures and Materials, China (Grant Nos. SS0145B612017, SS0145B712017), the Special Scientific Research Project of the State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin of IWHR, China (Grant No. SS0112B102016), and the Special Scientific Research Project of the China Institute of Water Resources and Hydropower Research, China (Grant No. SS0145B392016). Support provided by China Three Gorges Corporation research project (Grant No. WDD/0428) is also gratefully acknowledged. References [1] R. Springenschmid, Untersuchungen uber die Ursache von Querrissen im jungen Beton, Beton und Stahlbetonbau 68 (9) (1973) 221–226. [2] R. Spingenschmid, Prevention of Thermal Cracking in Concrete at Early Ages, E&FN Spon, London, 1998. [3] A. Bentur, K. Kovler, Evaluation of early age cracking characteristics in cementitious systems, Mater. Struct. 36 (3) (2003) 183–190. [4] E.I. Yang, S.T. Yi, H.J. Lee, Mechanical characteristics of axially restrained concrete specimens at early ages, J. Mater. Civ. Eng. 16 (1) (2004) 35–44. [5] B.E. Byard, A.K. Schindler, R.W. Barnes, Early-age cracking tendency and ultimate degree of hydration of internally cured concrete, J. Mater. Civ. Eng. 24 (8) (2011) 1025–1033. [6] T. Seo, M. Lee, C. Choi, et al., Properties of drying shrinkage cracking of concrete containing fly ash as partial replacement of fine aggregate, Mag. Concr. Res. 62 (6) (2010) 427–433. [7] B.E. Byard, A.K. Schindler, Modeling early-age stress development of restrained concrete, Mater. Struct. 48 (1–2) (2015) 435–450.

J. Xin et al. / Construction and Building Materials 231 (2020) 117146 [8] S. Slatnick, K.A. Riding, K.J. Folliard, et al., Evaluation of autogenous deformation of concrete at early ages, ACI Mater. J. 108 (1) (2011) 21–28. [9] K.H. Younis, Restrained Shrinkage Behaviour of Concrete with Recycled Materials PhD thesis, University of Sheffield, Sheffield, 2014. [10] B.E. Byard, A.K. Schindler, R.W. Barnes, Cracking tendency of lightweight aggregate bridge deck concrete, ACI Mater. J. 111 (2) (2014) 179–187. [11] S.L. Cha, Y. Lee, G.H. An, et al., Prediction of thermal stress in concrete structures with various restraints using thermal stress device, Comput. Concr. 17 (2) (2016) 173–188. [12] A. Markandeya, N. Shanahan, D.M. Gunatilake, et al., Influence of slag composition on cracking potential of slag-Portland cement concrete, Constr. Build. Mater. 164 (2018) 820–829. [13] A. Williams, A. Markandeya, Y. Stetsko, et al., Cracking potential and temperature sensitivity of metakaolin concrete, Constr. Build. Mater. 120 (2016) 172–180. [14] B. Byard, Early-Age Behavior of Lightweight Aggregate Concrete PhD thesis, Auburn University, Auburn, 2011. [15] H. Kagimoto, Y. Yasuda, M. Kawamura, ASR expansion, expansive pressure and cracking in concrete prisms under various degrees of restraint, Cem. Concr. Res. 59 (2014) 1–15. [16] I. Chu, Y. Lee, M.N. Amin, et al., Application of a thermal stress device for the prediction of stresses due to hydration heat in mass concrete structure, Constr. Build. Mater. 45 (2013) 192–198. [17] J.H.J. Kim, S.E. Jeon, J.K. Kim, Development of new device for measuring thermal stresses, Cem. Concr. Res. 32 (10) (2002) 1645–1651. [18] J. Whigham, Evaluation of Restraint Stresses and Cracking in Early-Age Concrete with the Rigid Cracking Frame Master thesis, Auburn University, Auburn, 2005. [19] J. Meadows, Early-Age Cracking of Mass Concrete Structures Master thesis, Auburn University, Auburn, 2007. [20] K.A. Riding, Early Age Concrete Thermal Stress Measurement and Modeling PhD thesis, University of Texas, Austin, 2007. [21] K.A. Riding, J.L. Poole, A.K. Schindler, et al., Quantification of effects of fly ash type on concrete early-age cracking, ACI Mater. J. 105 (2) (2008) 149–155. [22] M.N. Amin, J.S. Kim, Y. Lee, et al., Simulation of the thermal stress in mass concrete using a thermal stress measuring device, Cem. Concr. Res. 39 (3) (2009) 154–164. [23] N. Banthia, M. Azzabi, M. Pigeon, Restrained shrinkage cracking in fibrereinforced cementitious composites, Mater. Struct. 26 (7) (1993) 405–413. [24] N.B. Tiburzi, T. Drimalas, K.J. Folliard, Evaluation of precast bridge girder cracking: The role of volume change, Cem. Concr. Res. 101 (2017) 55–67. [25] R. Breitenbücher, Investigation of thermal cracking with the cracking-frame, Mater. Struct. 23 (3) (1990) 172–177. [26] S.L. Cha, S.S. Jin, G.H. An, et al., A prediction approach of concrete properties at early ages by using a thermal stress device, Constr. Build. Mater. 178 (2018) 120–134. [27] S. Tongaroonsri, S. Tangtermsirikul, Effect of mineral admixtures and curing periods on shrinkage and cracking age under restrained condition, Constr. Build. Mater. 23 (2) (2009) 1050–1056. [28] T. Meagher, N. Shanahan, D. Buidens, et al., Effects of chloride and chloridefree accelerators combined with typical admixtures on the early-age cracking risk of concrete repair slabs, Constr. Build. Mater. 94 (2015) 270–279. [29] C. Freidin, Effect of aggregate on shrinkage crack resistance of steam cured concrete, Mag. Concr. Res. 53 (2) (2001) 85–89. [30] I. Khan, T. Xu, A. Castel, et al., Early-age tensile creep and shrinkage induced cracking in internally restrained concrete members, Mag. Concr. Res. (2018) 1–13. [31] I. Khan, A. Castel, R.I. Gilbert, Effects of fly ash on early-age properties and cracking of concrete, ACI Mater. J. 114 (4) (2017) 673–681. [32] L. Huang, J. Hua, M. Kang, et al., Influence of reinforcement configuration on the shrinkage and cracking potential of high-performance concrete, Constr. Build. Mater. 140 (2017) 20–30. [33] V. Semianiuk, V. Tur, M.F. Herrador, Early age strains and self-stresses of expansive concrete members under uniaxial restraint conditions, Constr. Build. Mater. 131 (2017) 39–49. [34] Y. Thiebaut, S. Multon, A. Sellier, et al., Effects of stress on concrete expansion due to delayed ettringite formation, Constr. Build. Mater. 183 (2018) 626– 641. [35] Y. Takahashi, K. Shibata, M. Maruno, et al., Uniaxial restraint tests under highstress conditions and a chemo-hygral model for ASR Expansion, in: Proceedings of the 10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete Structures, 2015, pp. 1061–1065. [36] K.A. Riding, J.L. Poole, A.K. Schindler, et al., Effects of construction time and coarse aggregate on bridge deck cracking, ACI Mater. J. 106 (5) (2009) 448– 454. [37] A. Bentur, S. Igarashi, K. Kovler, Prevention of autogenous shrinkage in highstrength concrete by internal curing using wet lightweight aggregates, Cem. Concr. Res. 31 (11) (2001) 1587–1591. [38] S. Igarashi, M. Kawamura, T. Morishita, Features of characteristic microstructure and their effects on restrained autogenous shrinkage behavior in high strength concretes at early ages, Proc. JSCE 704 (55) (2002) 173–186. [39] A. Bentur, N.S. Berke, M.P. Dallaire, et al., Crack mitigation effects of shrinkage reducing admixtures, ACI SP 204 (2001) 155–170.

13

[40] R. Bloom, A. Bentur, Free and restrained shrinkage of normal and highstrength concretes, ACI Mater. J. 92 (2) (1995) 211–217. [41] K. Kovler, Interdependence of creep and shrinkage for concrete under tension, J. Mater. Civ. Eng. 7 (2) (1995) 96–101. [42] S.G. Park, T. Noguchi, M.H. Kim, A study on the creep and autogenous shrinkage of high performance concrete with expansive additive and shrinkage reducing admixtures at early age, Int. J. Concr. Struct. Mater. 18 (2E) (2006) 73–77. [43] C. Miao, J. Liu, F. Guo, et al., Shrinkage and cracking behavior of high performance concrete containing a MgO-CaO composed expansive agent, in: International RILEM Conference on Use of Superabsorbent Polymers and Other New Additives in Concrete, RILEM Publications SARL, 2010, pp. 179– 191. [44] H. Zhu, Q. Li, Y. Hu, Self-developed testing system for determining the temperature behavior of concrete, Materials 10 (4) (2017) 1–18. [45] C. Boulay, S. Staquet, B. Delsaute, et al., How to monitor the modulus of elasticity of concrete, automatically since the earliest age?, Mater Struct. 47 (1–2) (2014) 141–155. [46] X. Chen, H. Yang, S. Zhou, et al., Sensitive evaluation on early cracking tendency of concrete with inclusion of light-burnt MgO, J. Wuhan Univ. Technol.-Mater. Sci. Ed. 26 (5) (2011) 1018–1022. [47] D. Shen, X. Liu, Q. Li, et al., Early-age behavior and cracking resistance of highstrength concrete reinforced with Dramix 3D steel fiber, Constr. Build. Mater. 196 (2019) 307–316. [48] M. Xinwei, N. Changren, R.D. Hooton, Mechanical analysis of concrete specimen under restrained condition, J. Wuhan Univ. Technol.-Mater. Sci. Ed. 20 (3) (2005) 91–94. [49] D. Shen, W. Wang, J. Liu, et al., Influence of Barchip fiber on early-age cracking potential of high performance concrete under restrained condition, Constr. Build. Mater. 187 (2018) 118–130. [50] H. Ba, A. Su, X. Gao, et al., Cracking tendency of restrained concrete at early ages, J. Wuhan Univ. Technol.-Mater. Sci. Ed. 23 (2) (2008) 263–267. [51] T. Aly, J.G. Sanjayan, Shrinkage cracking properties of slag concretes with oneday curing, Mag. Concr. Res. 60 (1) (2008) 41–48. [52] T. Aly, J.G. Sanjayan, Factors contributing to early age shrinkage cracking of slag concretes subjected to 7-days moist curing, Mater. Struct. 41 (4) (2008) 633–642. [53] T. Aly, J.G. Sanjayan, Shrinkage-cracking behavior of OPC-fiber concrete at early-age, Mater. Struct. 43 (6) (2010) 755–764. [54] J.J. Brooks, X. Jiang, The influence of chemical admixtures on restrained drying shrinkage of concrete, ACI SP 173 (1997) 249–266. [55] K. Kovler, Testing system for determining the mechanical behaviour of early age concrete under restrained and free uniaxial shrinkage, Mater. Struct. 27 (6) (1994) 324–330. [56] K. Kolver, S. Igarashi, A. Bentur, Tensile creep behavior of high strength concretes at early ages, Mater. Struct. 32 (5) (1999) 383–387. [57] M. Pigeon, G. Toma, A. Delagrave, et al., Equipment for the analysis of the behaviour of concrete under restrained shrinkage at early ages, Mag. Concr. Res. 52 (4) (2000) 297–302. [58] Ø. Bjøntegaard, E.J. Sellevold, The temperature-stress testing machine (TSTM): capabilities and limitations, First International Rilem Symposium on Advances in Concrete through Science and Engineering, 2004. [59] I. Pane, W. Hansen, Early age creep and stress relaxation of concrete containing blended cements, Mater. Struct. 35 (2) (2002) 92–96. [60] I. Pane, W. Hansen, Predictions and verifications of early-age stress development in hydrating blended cement concrete, Cem. Concr. Res. 38 (11) (2008) 1315–1324. [61] S. Igarashi, A. Bentur, K. Kovler, Stresses and creep relaxation induced in restrained autogenous shrinkage of high-strength pastes and concretes, Adv. Cem. Res. 11 (4) (1999) 169–177. [62] S. Igarashi, M. Kawamura, Effects of microstructure on restrained autogenous shrinkage behavior in high strength concretes at early ages, Mater. Struct. 35 (2) (2002) 80–84. [63] A. Kamen, E. Denarié, H. Sadouki, et al., UHPFRC tensile creep at early age, Mater. Struct. 42 (1) (2009) 113–122. [64] A. Schwartzentruber, M. Philippe, G. Marchese, Effect of PVA, glass and metallic fibers, and of an expansive admixture on the cracking tendency of ultrahigh strength mortar, Cem. Concr. Compos. 26 (5) (2004) 573–580. [65] A. Kamen, E. Denarié, H. Sadouki, et al., Thermo-mechanical response of UHPFRC at early age—experimental study and numerical simulation, Cem. Concr. Res. 38 (6) (2008) 822–831. [66] A.E. Klausen, T. Kanstad, Ø. Bjøntegaard, et al., The effect of realistic curing temperature on the strength and E-modulus of concrete, Mater. Struct. 51 (6) (2018) 168. [67] A.E. Klausen, T. Kanstad, Ø. Bjøntegaard, Updated temperature-stress testing machine (TSTM): introductory tests, calculations, verification, and Investigation of variable fly ash content, in: Proceedings of CONCREEP 10, Vienna, 2015, pp. 724–732. [68] A.B.E. Klausen, Early Age Crack Assessment of Concrete Structures Experimental Investigation of Decisive Parameters PhD thesis, Norwegian University of Science and Technology, Trondheim, 2016. [69] A.E. Klausen, T. Kanstad, Ø. Bjøntegaard, et al., Comparison of tensile and compressive creep of fly ash concretes in the hardening phase, Cem. Concr. Res. 95 (2017) 188–194.

14

J. Xin et al. / Construction and Building Materials 231 (2020) 117146

[70] A. Darquennes, S. Staquet, B. Espion, Behaviour of slag cement concrete under restraint conditions, Eur. J. Environ. Civ. Eng. 15 (5) (2011) 787–798. [71] A. Darquennes, S. Staquet, M.P. Delplancke-Ogletree, et al., Effect of autogenous deformation on the cracking risk of slag cement concretes, Cem. Concr. Compos. 33 (3) (2011) 368–379. [72] S. Staquet, B. Delsaute, A. Darquennes, et al., Design of a revisited TSTM system for testing concrete since setting time under free and restraint conditions, in: Proceedings of the Concrack3—RILEM-JCI International Workshop on Crack Control of Mass Concrete and Related Issues Concerning Early-Age of Concrete Structures, Paris, France, 2012, pp. 15–16. [73] D. Bosniak, Self-Induced Cracking Problems in Hardening Concrete Structure PhD thesis, Norwegian University of Science and Technology, Trondheim, 2000. [74] R. Faria, L. Leitão, L. Teixeira, et al., A structural experimental technique to characterize the viscoelastic behavior of concrete under restrained deformations, Strain 53 (1) (2017) e12216. [75] D. Atrushi, Tensile and Compressive Creep of Early Age Concrete Testing and Modelling PhD thesis, Norwegian University of Science and Technology, Trondheim, 2003. [76] M. D’Ambrosia, Early Age Creep and Shrinkage of Emerging Concrete Materials PhD thesis, University of Illinois at Urbana-Champaign, Urbana, Illinois, 2012. [77] D. Cusson, T. Hoogeveen, An experimental approach for the analysis of earlyage behaviour of high-performance concrete structures under restrained shrinkage, Cem. Concr. Res. 37 (2) (2007) 200–209. [78] D. Cusson, T. Hoogeveen, Internal curing of high-performance concrete with pre-soaked fine lightweight aggregate for prevention of autogenous shrinkage cracking, Cem. Concr. Res. 38 (6) (2008) 757–765. [79] D. Shen, J. Jiang, Y. Jiao, et al., Early-age tensile creep and cracking potential of concrete internally cured with pre-wetted lightweight aggregate, Constr. Build. Mater. 135 (2017) 420–429. [80] D. Shen, J. Jiang, J. Shen, et al., Influence of curing temperature on autogenous shrinkage and cracking resistance of high-performance concrete at an early age, Constr. Build. Mater. 103 (2016) 67–76. [81] D. Shen, J. Jiang, J. Shen, et al., Influence of prewetted lightweight aggregates on the behavior and cracking potential of internally cured concrete at an early age, Constr. Build. Mater. 99 (2015) 260–271. [82] D. Shen, J. Jiang, M. Zhang, et al., Tensile creep and cracking potential of high performance concrete internally cured with super absorbent polymers at early age, Constr. Build. Mater. 165 (2018) 451–461. [83] D. Shen, J. Jiang, W. Wang, et al., Tensile creep and cracking resistance of concrete with different water-to-cement ratios at early age, Constr. Build. Mater. 146 (2017) 410–418. [84] G. Ji, Cracking Risk of Concrete Structures in the Hardening Phase: Experiments, Material Modeling and Finite Element Analysis PhD thesis, Norwegian University of Science and Technology, Trondheim, 2008. [85] H. Choi, M. Lim, H. Choi, et al., Modelling of creep of concrete mixed with expansive additives, Mag. Concr. Res. 67 (7) (2015) 335–348. [86] I. Maruyama, S.G. Park, T. Noguchi, Properties of high performance concrete in early age under quasi-complete restraint condition, Proc. Jpn. Concr. Inst. 25 (1) (2003) 485–490. [87] J. Carette, S. Staquet, Monitoring the setting process of mortars by ultrasonic P and S-wave transmission velocity measurement: mortar vs concrete, Constr. Build. Mater. 110 (2016) 32–41. [88] J. Xin, S. Lin, N. Shi, et al., Effect of reinforcement on early-age concrete temperature stress: preliminary experimental investigation and analytical simulation, Adv. Mater. Sci. Eng. 2015 (2015) 1–9. [89] J. Xin, G. Zhang, Y. Liu, et al., Effect of temperature history and restraint degree on cracking behavior of early-age concrete, Constr. Build. Mater. 192 (2018) 381–390. [90] M. Sule, Effect of Reinforcement on Early-Age Cracking in High Strength Concrete PhD thesis, Delft University of Technology, Delft, 2003.

[91] M. Sule, K. Van Breugel, The effect of reinforcement on early-age cracking due to autogenous shrinkage and thermal effects, Cem. Concr. Compos. 26 (5) (2004) 581–587. [92] M.D. D’Ambrosia, S. Altoubat, C. Park, et al., Early-age tensile creep and shrinkage of concrete with shrinkage reducing admixtures, in: Proceeding of the Sixth International Conference on Creep, Shrinkage, and Durability Mechanics of Concrete and Other QuasiBrittle Materials, 2001, pp. 645–651. [93] N. Shi, J. Ouyang, R. Zhang, et al., Experimental study on early-age crack of mass concrete under the controlled temperature history, Adv. Mater. Sci. Eng. 2014 (2014) 1–10. [94] S.A. Altoubat, D.A. Lange, The Pickett effect at early age and experiment separating its mechanisms in tension, Mater. Struct. 35 (4) (2002) 211–218. [95] S.A. Altoubat, D.A. Lange, Creep, shrinkage, and cracking of restrained concrete at early age, ACI Mater. J. 98 (4) (2001) 323–331. [96] S.A. Altoubat, D.A. Lange, Grip-specimen interaction in uniaxial restrained test, ACI SP 206 (2002) 189–204. [97] S.A. Altoubat, D.A. Lange, Tensile basic creep: measurements and behavior at early age, ACI Mater. J. 98 (5) (2001) 386–393. [98] S.A. Altoubat, Early Age Stresses and Creep-Shrinkage Interaction of Restrained Concrete PhD thesis, University of Illinois at Urbana-Champaign, Urbana, Illinois, 2000. [99] S. Igarashi, A. Bentur, K. Kovler, Autogenous shrinkage and induced restraining stresses in high-strength concretes, Cem. Concr. Res. 30 (11) (2000) 1701–1707. [100] T.A. Hammer, K.T. Fosså, Ø. Bjøntegaard, Cracking tendency of HSC: Tensile strength and self generated stress in the period of setting and early hardening, Mater. Struct. 40 (3) (2007) 319–324. [101] Z. Tao, Q. Weizu, Tensile creep due to restraining stresses in high-strength concrete at early ages, Cem. Concr. Res. 36 (3) (2006) 584–591. [102] T. Mizobuchi, K. Ishizeki, T. Sagawa, et al., Study on the influence of minor constituents in blast furnace slag rich cement on the thermal and mechanical properties of concrete, J. Adv. Concr. Technol. 17 (1) (2019) 46–61. [103] X.F. Wang, C. Fang, W.Q. Kuang, et al., Experimental study on early cracking sensitivity of lightweight aggregate concrete, Constr. Build. Mater. 136 (2017) 173–183. [104] Y. Wei, W. Hansen, Early-age strain–stress relationship and cracking behavior of slag cement mixtures subject to constant uniaxial restraint, Constr. Build. Mater. 49 (2013) 635–642. [105] Y. Wei, S. Liang, W. Guo, et al., Stress prediction in very early-age concrete subject to restraint under varying temperature histories, Cem. Concr. Compos. 83 (2017) 45–56. [106] Y. Wei, W. Hansen, Tensile creep behavior of concrete subject to constant restraint at very early ages, J. Mater. Civ. Eng. 25 (9) (2012) 1277–1284. [107] Z.H. Lin, Quantitative Evaluation of the Effectiveness of Expansive Concrete as a Countermeasure for Thermal Cracking and the Development of its Practical Application PhD thesis, University of Tokyo, Tokyo, 2006. [108] Z. Lin, T. Kishi, S. Lim, Experimental evaluation of early-age creep by a temperature-stress testing machine, in: The 3rd ACF International Conference-ACF/VCA, 2008, pp. 812–820. [109] Z. Zhao, K. Wang, D.A. Lange, et al., Creep and thermal cracking of ultra-high volume fly ash mass concrete at early age, Cem. Concr. Compos. 99 (2019) 191–202. [110] H. Zhu, Q. Li, Y. Hu, et al., Double feedback control method for determining early-age restrained creep of concrete using a temperature stress testing machine, Materials 11 (7) (2018) 1079. [111] L. Liu, J. Ouyang, F. Li, et al., Research on the crack risk of early-age concrete under the temperature stress test machine, Materials 11 (10) (2018) 1822. [112] K. Kovler, A. Bentur, Cracking sensitivity of normal-and high-strength concretes, ACI Mater. J. 106 (6) (2009) 537–542. [113] B.F. Zhu, Thermal Stresses and Temperature Control of Mass Concrete, Butterworth-Heinemann, Oxford, 2013.