- Email: [email protected]
Early-age performance investigations of magnesium phosphate cement by using fiber Bragg grating
Construction and Building Materials 120 (2016) 147–149
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Technical note
Early-age performance investigations of magnesium phosphate cement by using fiber Bragg grating Huafu Pei a,⇑, Qing Yang a, Zongjin Li b a b
Department of Geotechnical Engineering, Faculty of Infrastructure, Dalian University of Technology, State Key Lab of Coastal and Offshore Engineering, Dalian 116024, China Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
a r t i c l e
i n f o
Article history: Received 8 December 2015 Received in revised form 5 May 2016 Accepted 12 May 2016
Keywords: Magnesium phosphate cement Early-age shrinkage Fiber Bragg grating
a b s t r a c t Recently, fiber Bragg gratings (FBGs), as a novel and robust sensor, has already been successfully applied to measure the internal early age shrinkage and the temperature changes in ordinary Portland cement. Currently, magnesium phosphate cement is becoming a popular material for structure repair and reinforcement as its fast setting properties. In this paper, the basic material is actually magnesium phosphate cement (MPC) mortar, with big difference from ordinary Portland cement. In spite of the existing discrepancy in the sample preparation, the fundamental sensing principles are same for OPC and MPC. After several sets of experiments we have been able to reach some initial inferences of physical properties of the composites from the patterns of changes of the strain during the solidification. Ó 2016 Published by Elsevier Ltd.
1. Introduction Practically, shrinkage strains measurement of specimen in the first twelve hours right after mixing is quite hard because of the fact that only after reaching a minimum strength can the strain be attached. Hence, most shrinkage strain measurements started from the time when the molds were casted with specimens and technical norms for determining such quantities are based on a certain age for starting the shrinkage measurement. Our work presented here was to learn more about early age shrinkage of mortar by using the fiber Bragg gratings (FBGs). Nowadays, this technique hasn’t been put forward as a new shrinkage testing method due to its complicated preparations and relatively high costs for buying those fragile FBG sensors, we hope our experiments can help conquer some obstacles in the research of concrete. 1.1. Working principle of fiber Bragg grating Since 1978, Hill et al. [1] have fabricated the first fiber Bragg grating (FBG) with a laser beam. Nowadays, FBGs are widely applied in structural health monitoring and sensor development. For Bragg grating in a typical single mode silica optical fiber, the linear relationship between wavelength shift DkB , strain De, and temperature DT can be expressed by
⇑ Corresponding author. E-mail address: [email protected] (H. Pei). http://dx.doi.org/10.1016/j.conbuildmat.2016.05.089 0950-0618/Ó 2016 Published by Elsevier Ltd.
DkB ¼ ce De þ cT DT kB
ð1Þ
where ce and cT are the calibration coefficients for strain and temperature, respectively [2]. 1.2. Previous studies on the early age shrinkage measurement As is well known, early age properties are big issues for concrete structures especially for large-scale concrete structures such as dams, shearing wall, and nuclear reactor [9]. To study the early age shrinkage in cementitious materials, researchers focused on the measurement of early age shrinkage by using different sensing technology [11,10]. Loukili et al. [12] initiated a new approach to monitor autogenous shrinkage of mortar at an early age considering temperature history. A new type of device was proposed and developed to measure the shrinkage at different temperatures. However, the thermocouple is prone to be disturbed by the resistor.
2. Experiments In every set of experiments, we use two fiber Bragg gratings sensors to measure the strain change and the temperature change separately. As well known, force and temperature changes resulted from the shrinkage of mortar can influence the length of the FBGs sensors, causes the changes of distances between those gratings caved on the fiber sensors, so that they reflect light of a different wavelength. Thus, by analyzing the change of wavelength of the reflected light, we are able to know the strain and temperature change in the specimen.
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H. Pei et al. / Construction and Building Materials 120 (2016) 147–149
2.1. Experiment setup
2.5. Strain measurement
The very first step of the experiment is making the most important but also most fragile fiber sensors [7,8,5,6,4,3]. Actually what we did is simply connecting a fiber with gratings on it to a fiber that can be connected to the interrogator which is linked to the computer to collect data. Though sounds simple, it’s not that easy. As the fibers are fragile, we need to be very careful during the process. Firstly, we cut off a length of the protection cover to expose a length of the fiber. Then we use the high precision cleaver to cut one end of both the main fiber and the fiber with gratings on it to ensure that the connecting planes are flat. After that we put both fibers on the single fiber fusion splicer to fuse them together. Finally, to protect the junction, we cover it with a protective jacket. Then we can see a peak appear on the screen of the computer, which means that we successfully connect the two fiber and the preparation of the FBGs sensor is now done.
We take the other FBG sensor and insert it into the other thin copper tube. This time what we need to do is different from the previous one that we use to measure the temperature change. After inserting the sensor we slowly pull the copper cube from the bottom to make sure that the fiber sensor is embedded in the mortar. Of course this sensor will be affected not only by the shrinkage strain but also the temperature unavoidably. However, we can still analyze the strain as we can know how the temperature change influences the fiber sensor from the other sensor.
2.2. Get the mould prepared In this experiment, we use a cylindrical hollow stainless-steel case which contains four parts: the top, the bottom and the two semi-circle side walls, as our mould. What we did here is merely putting two layers inside the mould, one cling wrap layer and one silver paper layer. There are two purposes for this step. The first is that during the shrinkage of the specimen, there must be friction between the mortar and the inside surface of the mould. Putting these two layer can help significantly reduce the friction to ensure more precise and persuasive data. Secondly, these two layers can prevent the sticky mortar from sticking to the mould, so that the mould can be reused again. Also, we need to insert two thin copper cubes in the mould as the tunnels in advance for inserting the FBGs sensors in later step.
2.3. Specimen preparation There are totally 2 sets of experiments, in each set there are two experiments. The compositions of specimens in different experiments of the same set are basically the same but proportion of water differs in each set. In the first set of experiment, masses for MgO, KDP, Na2B4O7-10H2O and sand are accordingly 1550 g, 668 g, 168 g, 2120 g. For water, the masses are 901.2 g and 1351.8 g respectively in two experiments, corresponding to the water-solid ratios 0.2 and 0.3 accordingly. And for the second set, we replace KPP with NPP and set the two water-solid ratios to be 0.2 and 0.25, corresponding to 901.2 g and 1126.5 g of water. After weighing all these compositions, we then pour all of them except water into the pot of the mixer. Turn on the mixer and wait for 3–5 min before we pore the water into the pot and wait for another 3–5 min. Then we need to cast the mixed specimen into the prepared die as soon as possible or the specimen will solidify quickly (Fig. 1).
2.4. Temperature measurement One FBG sensor was inserted in the thin copper tube that we put in the die in advance, adjust the height, and leave the copper cube in the specimen (Fig. 1). As is well known, copper is good conductor of heat. Also with the protection of copper, this FBG sensor won’t be affected by the shrinkage of mortar, so that it shows the temperature change of the mortar only, which will allow us to minimize the influence of temperature while analyzing the influence of strain.
3. Experimental results and discussion As mentioned above, there are two sets of experiments. In one set of experiments we used KDP as one of the components of mortar, while in the other set we use NDP instead. Also, in each set of experiments we set two different water-solid ratios. So it’s not difficult to see that KDP/NDP and the water-solid ratio are the two independent factor in our experiments. When we consider this factor, we need to fix the water-solid ratio. As mentioned above, the water-solid ratios in the first set of experiment are 0.2 and 0.3. Thus, let’s pick the experiments in each set whose water-solid ratios are 0.2 and 0.3 for comparison. Here are the two figures (see Figs. 2 and 3). Actually, data here are not the direct data from the sensors. Instead, they are the result of calculations that involve the two sets of data of temperature change and the strain so that they are eliminated from the influence of temperature and show the strain only. Comparing two figures above, it’s easy to figure out the differences. There is an obvious peak appearing approximately 2 h after casting in the first figure while the curve in the second figure is quite smooth. This may indicate that KDP can probably help accelerate the shrinkage during the solidification process. Also, there is an increase of strain in the figure, which means that the specimen containing KDP experienced an expanding period during the solidification. The same situation didn’t appear in the second figure, so we may infer that the specimen containing NDP kept shrinking before reaching a steady stage. Both curves tend to be level over a long period of time. When considering the second factor, similarly we need to apply control variables method. Here we only analyze the first set of experiments where we use KDP. The two figures are as followed (Figs. 4 and 5). The differences are also quite obvious. We can see that it takes longer time for the curve in the second figure (about 2 h) to reach the lowest point than the curve in the first figure (about 1.5 h). Thus, we can infer that the larger the water-solid ratio, the longer the shrinking period will last. Also, the curve in the first figure has a trend of increasing before reach a steady stage while the second curve tend to decrease before becoming steady.
0
0
200
400
600
800
1000
-200
Micro strain
-400 -600 -800 -1000 -1200 -1400 -1600 -1800
Elapsed time (minute) Fig. 1. Simultaneous measurement of thermal strain and temperature.
Fig. 2. NDP, water-solid ratio: 0.2.
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H. Pei et al. / Construction and Building Materials 120 (2016) 147–149
0
0
200
400
600
800
1000
1200
-200
4. Conclusions Based on the analysis above, we can have the following conclusions.
-400
Micro strain
149
-600
a) Mortar containing KDP will shrink remarkably and rapidly soon after casting while mortar containing NDP mere shrink gradually. b) Mortar containing KDP will experience a period of expanding right after the rapid shrinkage while mortar containing NDP will keep shrinking until reaching a steady stage. c) For mortar containing the same materials (KDP or NDP), the larger the water-solid ratio is, the longer it will take for the mortar to reach a steady stage.
-800 -1000 -1200 -1400 -1600
Elapsed time (minute) Fig. 3. NDP, water-solid ratio: 0.3.
Acknowledgement 200
0
1000
2000
3000
4000
5000
6000
Micro strain
0 -200
References
-400 -600 -800 -1000
Elapsed time (minute) Fig. 4. KDP, water-solid ratio: 0.2.
0
0
100
200
300
400
-50
Micro strain
-100 -150 -200 -250 -300 -350 -400 -450
The financial support from National Natural Science Foundation of China under No. 51408148, Dalian University of Technology under No. DUT16RC(3)029 and China Ministry of Science and Technology under 2015CB655104 are greatly acknowledged.
Elasped time (minute) Fig. 5. KDP, water-solid ratio: 0.3.
500
600
[1] K.O. Hill, F. Fujii, D.C. Johnson, B.S. Kawasaki, Photosensitivity on optical fiber waveguides: application to reflection filter fabrication, Appl. Phys. Lett. 32 (10) (1978) 647–649. [2] A. Othonos, K. Kalli, Fiber Bragg Gratings: Fundamentals and Applications in Telecommunications and Sensing, Artech House, London, 1999. [3] H.F. Pei, Z.J. Li, B. Zhang, H.Y. Ma, Multipoint measurement of early age shrinkage in low w/c ratio mortars by using fiber Bragg gratings, Mater. Lett. 131 (2014) 370–372. [4] D. Luo, Z. Ismail, Ibrahim. Zainah, Added advantages in using a fiber Bragg grating sensor in the determination of early age setting time for cement pastes, Measurement 46 (10) (2013) 4313–4320. [5] Y.W. Yun, Y. Jang, Research on early age deformation of high performance concrete by fiber Bragg grating sensor, KSCE J. Civ. Eng. 12 (5) (2008) 323–328. [6] Y.W. Yun, Y. Jang, W.W. Wang, Early-age autogenous shrinkage of highperformance concrete columns by embedded Fiber Bragg-Grating sensor. Research Paper Structural Engineering, KSCE J. Civ. Eng. 16 (6) (2012) 967–973. [7] A.C.L. Wong, P. Childs, W. Terry, N. Gowripalan, G.D. Peng, Experimental investigation of drying shrinkage and creep of concrete using fibre-optic sensors, Adv. Struct. Eng. 10 (3) (2007) 219–228. [8] A.C.L. Wong, P.A. Childs, R. Berndt, T. Macken, G.D. Peng, N. Gowripalan, Simultaneous measurement of shrinkage and temperature of reactive powder concrete at early-age using fibre Bragg grating sensors, Cement Concr. Compos. 29 (6) (2007) 490–497. [9] D.P. Bentza, M.R. Geikerb, K.K. Hansenb, Shrinkage-reducing admixtures and early-age desiccation in cement pastes and mortars, Cem. Concr. Res. 31 (2001) 1075–1085. [10] E. Holt, M. Leivo, Cracking risks associated with early age shrinkage, Cement Concr. Compos. 26 (2004) 521–530. [11] D.P. Bentz, A review of early-age properties of cement-based materials, Cem. Concr. Res. 38 (2008) 196–204. [12] A. Loukili, D. Chopin, A. Khelidj, J.Y. Le Touzo, A new approach to determine autogenous shrinkage of mortar at an early age considering temperature history, Cem. Concr. Res. 30 (2000) 915–922.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Technical note
Early-age performance investigations of magnesium phosphate cement by using fiber Bragg grating Huafu Pei a,⇑, Qing Yang a, Zongjin Li b a b
Department of Geotechnical Engineering, Faculty of Infrastructure, Dalian University of Technology, State Key Lab of Coastal and Offshore Engineering, Dalian 116024, China Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
a r t i c l e
i n f o
Article history: Received 8 December 2015 Received in revised form 5 May 2016 Accepted 12 May 2016
Keywords: Magnesium phosphate cement Early-age shrinkage Fiber Bragg grating
a b s t r a c t Recently, fiber Bragg gratings (FBGs), as a novel and robust sensor, has already been successfully applied to measure the internal early age shrinkage and the temperature changes in ordinary Portland cement. Currently, magnesium phosphate cement is becoming a popular material for structure repair and reinforcement as its fast setting properties. In this paper, the basic material is actually magnesium phosphate cement (MPC) mortar, with big difference from ordinary Portland cement. In spite of the existing discrepancy in the sample preparation, the fundamental sensing principles are same for OPC and MPC. After several sets of experiments we have been able to reach some initial inferences of physical properties of the composites from the patterns of changes of the strain during the solidification. Ó 2016 Published by Elsevier Ltd.
1. Introduction Practically, shrinkage strains measurement of specimen in the first twelve hours right after mixing is quite hard because of the fact that only after reaching a minimum strength can the strain be attached. Hence, most shrinkage strain measurements started from the time when the molds were casted with specimens and technical norms for determining such quantities are based on a certain age for starting the shrinkage measurement. Our work presented here was to learn more about early age shrinkage of mortar by using the fiber Bragg gratings (FBGs). Nowadays, this technique hasn’t been put forward as a new shrinkage testing method due to its complicated preparations and relatively high costs for buying those fragile FBG sensors, we hope our experiments can help conquer some obstacles in the research of concrete. 1.1. Working principle of fiber Bragg grating Since 1978, Hill et al. [1] have fabricated the first fiber Bragg grating (FBG) with a laser beam. Nowadays, FBGs are widely applied in structural health monitoring and sensor development. For Bragg grating in a typical single mode silica optical fiber, the linear relationship between wavelength shift DkB , strain De, and temperature DT can be expressed by
⇑ Corresponding author. E-mail address: [email protected] (H. Pei). http://dx.doi.org/10.1016/j.conbuildmat.2016.05.089 0950-0618/Ó 2016 Published by Elsevier Ltd.
DkB ¼ ce De þ cT DT kB
ð1Þ
where ce and cT are the calibration coefficients for strain and temperature, respectively [2]. 1.2. Previous studies on the early age shrinkage measurement As is well known, early age properties are big issues for concrete structures especially for large-scale concrete structures such as dams, shearing wall, and nuclear reactor [9]. To study the early age shrinkage in cementitious materials, researchers focused on the measurement of early age shrinkage by using different sensing technology [11,10]. Loukili et al. [12] initiated a new approach to monitor autogenous shrinkage of mortar at an early age considering temperature history. A new type of device was proposed and developed to measure the shrinkage at different temperatures. However, the thermocouple is prone to be disturbed by the resistor.
2. Experiments In every set of experiments, we use two fiber Bragg gratings sensors to measure the strain change and the temperature change separately. As well known, force and temperature changes resulted from the shrinkage of mortar can influence the length of the FBGs sensors, causes the changes of distances between those gratings caved on the fiber sensors, so that they reflect light of a different wavelength. Thus, by analyzing the change of wavelength of the reflected light, we are able to know the strain and temperature change in the specimen.
148
H. Pei et al. / Construction and Building Materials 120 (2016) 147–149
2.1. Experiment setup
2.5. Strain measurement
The very first step of the experiment is making the most important but also most fragile fiber sensors [7,8,5,6,4,3]. Actually what we did is simply connecting a fiber with gratings on it to a fiber that can be connected to the interrogator which is linked to the computer to collect data. Though sounds simple, it’s not that easy. As the fibers are fragile, we need to be very careful during the process. Firstly, we cut off a length of the protection cover to expose a length of the fiber. Then we use the high precision cleaver to cut one end of both the main fiber and the fiber with gratings on it to ensure that the connecting planes are flat. After that we put both fibers on the single fiber fusion splicer to fuse them together. Finally, to protect the junction, we cover it with a protective jacket. Then we can see a peak appear on the screen of the computer, which means that we successfully connect the two fiber and the preparation of the FBGs sensor is now done.
We take the other FBG sensor and insert it into the other thin copper tube. This time what we need to do is different from the previous one that we use to measure the temperature change. After inserting the sensor we slowly pull the copper cube from the bottom to make sure that the fiber sensor is embedded in the mortar. Of course this sensor will be affected not only by the shrinkage strain but also the temperature unavoidably. However, we can still analyze the strain as we can know how the temperature change influences the fiber sensor from the other sensor.
2.2. Get the mould prepared In this experiment, we use a cylindrical hollow stainless-steel case which contains four parts: the top, the bottom and the two semi-circle side walls, as our mould. What we did here is merely putting two layers inside the mould, one cling wrap layer and one silver paper layer. There are two purposes for this step. The first is that during the shrinkage of the specimen, there must be friction between the mortar and the inside surface of the mould. Putting these two layer can help significantly reduce the friction to ensure more precise and persuasive data. Secondly, these two layers can prevent the sticky mortar from sticking to the mould, so that the mould can be reused again. Also, we need to insert two thin copper cubes in the mould as the tunnels in advance for inserting the FBGs sensors in later step.
2.3. Specimen preparation There are totally 2 sets of experiments, in each set there are two experiments. The compositions of specimens in different experiments of the same set are basically the same but proportion of water differs in each set. In the first set of experiment, masses for MgO, KDP, Na2B4O7-10H2O and sand are accordingly 1550 g, 668 g, 168 g, 2120 g. For water, the masses are 901.2 g and 1351.8 g respectively in two experiments, corresponding to the water-solid ratios 0.2 and 0.3 accordingly. And for the second set, we replace KPP with NPP and set the two water-solid ratios to be 0.2 and 0.25, corresponding to 901.2 g and 1126.5 g of water. After weighing all these compositions, we then pour all of them except water into the pot of the mixer. Turn on the mixer and wait for 3–5 min before we pore the water into the pot and wait for another 3–5 min. Then we need to cast the mixed specimen into the prepared die as soon as possible or the specimen will solidify quickly (Fig. 1).
2.4. Temperature measurement One FBG sensor was inserted in the thin copper tube that we put in the die in advance, adjust the height, and leave the copper cube in the specimen (Fig. 1). As is well known, copper is good conductor of heat. Also with the protection of copper, this FBG sensor won’t be affected by the shrinkage of mortar, so that it shows the temperature change of the mortar only, which will allow us to minimize the influence of temperature while analyzing the influence of strain.
3. Experimental results and discussion As mentioned above, there are two sets of experiments. In one set of experiments we used KDP as one of the components of mortar, while in the other set we use NDP instead. Also, in each set of experiments we set two different water-solid ratios. So it’s not difficult to see that KDP/NDP and the water-solid ratio are the two independent factor in our experiments. When we consider this factor, we need to fix the water-solid ratio. As mentioned above, the water-solid ratios in the first set of experiment are 0.2 and 0.3. Thus, let’s pick the experiments in each set whose water-solid ratios are 0.2 and 0.3 for comparison. Here are the two figures (see Figs. 2 and 3). Actually, data here are not the direct data from the sensors. Instead, they are the result of calculations that involve the two sets of data of temperature change and the strain so that they are eliminated from the influence of temperature and show the strain only. Comparing two figures above, it’s easy to figure out the differences. There is an obvious peak appearing approximately 2 h after casting in the first figure while the curve in the second figure is quite smooth. This may indicate that KDP can probably help accelerate the shrinkage during the solidification process. Also, there is an increase of strain in the figure, which means that the specimen containing KDP experienced an expanding period during the solidification. The same situation didn’t appear in the second figure, so we may infer that the specimen containing NDP kept shrinking before reaching a steady stage. Both curves tend to be level over a long period of time. When considering the second factor, similarly we need to apply control variables method. Here we only analyze the first set of experiments where we use KDP. The two figures are as followed (Figs. 4 and 5). The differences are also quite obvious. We can see that it takes longer time for the curve in the second figure (about 2 h) to reach the lowest point than the curve in the first figure (about 1.5 h). Thus, we can infer that the larger the water-solid ratio, the longer the shrinking period will last. Also, the curve in the first figure has a trend of increasing before reach a steady stage while the second curve tend to decrease before becoming steady.
0
0
200
400
600
800
1000
-200
Micro strain
-400 -600 -800 -1000 -1200 -1400 -1600 -1800
Elapsed time (minute) Fig. 1. Simultaneous measurement of thermal strain and temperature.
Fig. 2. NDP, water-solid ratio: 0.2.
1200
1400
H. Pei et al. / Construction and Building Materials 120 (2016) 147–149
0
0
200
400
600
800
1000
1200
-200
4. Conclusions Based on the analysis above, we can have the following conclusions.
-400
Micro strain
149
-600
a) Mortar containing KDP will shrink remarkably and rapidly soon after casting while mortar containing NDP mere shrink gradually. b) Mortar containing KDP will experience a period of expanding right after the rapid shrinkage while mortar containing NDP will keep shrinking until reaching a steady stage. c) For mortar containing the same materials (KDP or NDP), the larger the water-solid ratio is, the longer it will take for the mortar to reach a steady stage.
-800 -1000 -1200 -1400 -1600
Elapsed time (minute) Fig. 3. NDP, water-solid ratio: 0.3.
Acknowledgement 200
0
1000
2000
3000
4000
5000
6000
Micro strain
0 -200
References
-400 -600 -800 -1000
Elapsed time (minute) Fig. 4. KDP, water-solid ratio: 0.2.
0
0
100
200
300
400
-50
Micro strain
-100 -150 -200 -250 -300 -350 -400 -450
The financial support from National Natural Science Foundation of China under No. 51408148, Dalian University of Technology under No. DUT16RC(3)029 and China Ministry of Science and Technology under 2015CB655104 are greatly acknowledged.
Elasped time (minute) Fig. 5. KDP, water-solid ratio: 0.3.
500
600
[1] K.O. Hill, F. Fujii, D.C. Johnson, B.S. Kawasaki, Photosensitivity on optical fiber waveguides: application to reflection filter fabrication, Appl. Phys. Lett. 32 (10) (1978) 647–649. [2] A. Othonos, K. Kalli, Fiber Bragg Gratings: Fundamentals and Applications in Telecommunications and Sensing, Artech House, London, 1999. [3] H.F. Pei, Z.J. Li, B. Zhang, H.Y. Ma, Multipoint measurement of early age shrinkage in low w/c ratio mortars by using fiber Bragg gratings, Mater. Lett. 131 (2014) 370–372. [4] D. Luo, Z. Ismail, Ibrahim. Zainah, Added advantages in using a fiber Bragg grating sensor in the determination of early age setting time for cement pastes, Measurement 46 (10) (2013) 4313–4320. [5] Y.W. Yun, Y. Jang, Research on early age deformation of high performance concrete by fiber Bragg grating sensor, KSCE J. Civ. Eng. 12 (5) (2008) 323–328. [6] Y.W. Yun, Y. Jang, W.W. Wang, Early-age autogenous shrinkage of highperformance concrete columns by embedded Fiber Bragg-Grating sensor. Research Paper Structural Engineering, KSCE J. Civ. Eng. 16 (6) (2012) 967–973. [7] A.C.L. Wong, P. Childs, W. Terry, N. Gowripalan, G.D. Peng, Experimental investigation of drying shrinkage and creep of concrete using fibre-optic sensors, Adv. Struct. Eng. 10 (3) (2007) 219–228. [8] A.C.L. Wong, P.A. Childs, R. Berndt, T. Macken, G.D. Peng, N. Gowripalan, Simultaneous measurement of shrinkage and temperature of reactive powder concrete at early-age using fibre Bragg grating sensors, Cement Concr. Compos. 29 (6) (2007) 490–497. [9] D.P. Bentza, M.R. Geikerb, K.K. Hansenb, Shrinkage-reducing admixtures and early-age desiccation in cement pastes and mortars, Cem. Concr. Res. 31 (2001) 1075–1085. [10] E. Holt, M. Leivo, Cracking risks associated with early age shrinkage, Cement Concr. Compos. 26 (2004) 521–530. [11] D.P. Bentz, A review of early-age properties of cement-based materials, Cem. Concr. Res. 38 (2008) 196–204. [12] A. Loukili, D. Chopin, A. Khelidj, J.Y. Le Touzo, A new approach to determine autogenous shrinkage of mortar at an early age considering temperature history, Cem. Concr. Res. 30 (2000) 915–922.