Fujita Technical Research
Re po rtNo. 5 72 0 21㻌㻌

Basic Properties of Cement Paste Mixed withCalcium Hydroxide-Ettringite Composite-Type Expansive Additive㻌㻌㻌㻌㻌

Kohsuke Handa㻌㻌

AbstractIn this study, we targeted a calcium hydroxide and ettringite composite-type expansive additive (EA) andobtained the basic characteristics of the EA mixed cement paste in order to create a method for calculating
volume expansion based on the hydration reaction of a PC-EA system. Expansion strain, setting time, andcompressive strength were measured. In addition, we observed the state of the EA after hydration using amicro-CT scanner and scanning electron microscope, and elucidated the expansion mechanism.
Our results show that strain rapidly increased and compressive strength decreased when the replacement
ratio of the EA (Crep) exceeds 6.4%. At the same time, radial cracks were generated from the hydrated EA
particles, suggesting that the EA itself grew to expand the cement paste. Although no ettringite wasconfirmed inside the EA when the Crep was 5.1%, when the Crep was 10.3%, ettringite was formed verticallyfrom the surface of C3A with a large amount of pores. These results show that simultaneous formation ofettringite and pores causes rapid expansion.
㻌㻌Keywords：

Expansiveadditive,Calcium

hydroxide,Ettringite, Micro-CT scanning, SEM

㻌
㻌

−35−

Fujita Technical Research Report No.57㻌

§１㻚㻌㻵㻺㼀㻾㻻㻰㼁㻯㼀㻵㻻㻺㻌

EA. These included expansion strain, setting time,㻌

compressive strength, and static modulus of CP mixed withIn order to maintain the durability and aesthetics ofEA. In addition, the state of EA after hydration wasreinforced concrete structures over a long period of time, itobserved using a micro-CT scanner and scanning electron

is necessary to prevent the occurrence of cracks such as

microscope (SEM) to elucidate the expansion mechanism.

drying shrinkage cracking. For example, reducing drying
shrinkage strain is effective in preventing cracks, and§２㻚㻌㻱㼄㻼㻱㻾㻵㻹㻱㻺㼀㻿㻌–㻌㼀㻱㻿㼀㻵㻺㻳㻌㻹㻱㼀㻴㻻㻰㻿㻌

expansive additive (EA) can be used for this purpose.

㻌Although there are many types of EA, calcium hydroxide-

2.1 Sample preparation

ettringite composite-type EA is an admixture for concrete

All samples were prepared using moderate-heat Portlandthat has long been used, and its components are mainly

cement (PC) adapted JIS R 5210 [4] as Japanese standard, EA

composed of free-lime (f-CaO), anhydrite (CS), and(powder), Polycarboxylic acid-based super plasticizer (Ad),hydraulic minerals such as calcium aluminate (C3A) orand deionized water. The water-binder ratio was 0.45. The

calcium aluminoferrite (C4AF) [1]. These minerals change

applied CP mix design is shown in Table 1. All samples were

into calcium hydroxide (CH) and ettringite (AFt)

cured at room temperature (20 °C). The CP for micro-CT

respectively. They have a large volume evolution, and thus

scanning and SEM was casted in a cylindrical resin bottle withgive a cement paste (CP) a macroscopic volume expansion

24 mm diameter and 39 mm height.

that compensates for shrinkage.

㻌Up to now, regarding studies on the volume change

2.2 Setting timemechanism of CP mixed with EA, Yamamoto et al.

In the expansion by EA, the force caused by this expansion is,

proposed the radius evolution of the EA from measurement

unless it is a completely enclosed space, transmitted to the rebar

data such as the reaction degree of each mineral and volume

or restrained member only when the mortar matrix is hardenedof CH and AFt [2]. In addition, Choi calculated theand transmits the expansion pressure. That is, even if theexpansion strain of CP by mathematical modeling based on

unhardened paste expands, no stress is generated, so that it has

Yamamoto's data [3]. However, some challenges remain,

no meaning within the structural design. Therefore, in thissuch as that the radius evolution proposed by Yamamoto isstudy, we focused on the expansion that occurs after hardening

not a value calculated based on the chemical reactionof CP begins.

formula, and the particle size distribution is not taken into

The modified initial setting time determined by the modified

consideration.

Vicat Needle Test was adopted for the starting age ofThis study aims to create a method for calculating thehardening. Instead of the water-cement ratio that produces thevolume expansion of CP based on the hydration reaction“normal consistency” paste proposed in JIS R 5201 [5], theand radius evolution of the calcium hydroxide-ettringitewater-binder ratio was kept constant at 0.45 and the test wascomposite-type EA. In this study, experiments wereconducted. This standard is almost the same as ASTM C191-conducted to measure the basic properties of CP mixed with13 [6], with slightly different conditions. The diameter of theTable 1: Mix design for cement paste specimen and compressive strength
Name

Replacement
Waterratio for cement
Binder ratio
CrepWater(weight.%)(%)

Composition

Compressive strength

PCEAAd

[MPa]

(g/L)

(g/L)

(g/L) (mL/L) (B×%) 1 day

3 days7 daysReference0%590.91313.2

0.0

4.42

12.1

21.7

EA26

2.57%

590.6

1278.7

33.7

3.97

14.2

23.8

EA51

5.14%

590.3

1244.3

67.5

5.71

15.6

23.6

EA64

6.43%

590.2

1227.2

84.3

6.98

14.1

23.7

45%

7.2

0.55

EA103

10.29%

589.7

1175.7 134.8

4.10

8.7

13.2

EA109

10.93%

589.6

1167.1 143.2

5.11

8.4

11.7

EA129

12.86%

589.4

1141.4 168.4−36−－㻞－㻌

Not conducted㻮㻭㻿㻵㻯㻌㻼㻾㻻㻼㻱㻾㼀㻵㻱㻿㻌㻻㻲㻌㻯㻱㻹㻱㻺㼀㻌㻼㻭㻿㼀㻱㻌㻹㻵㼄㻱㻰㻌㼃㻵㼀㻴㻌㻯㻭㻸㻯㻵㼁㻹㻌㻴㼅㻰㻾㻻㼄㻵㻰㻱㻙㻱㼀㼀㻾㻵㻺㻳㻵㼀㻱㻌㻯㻻㻹㻼㻻㻿㻵㼀㻱㻌㼀㼅㻼㻱㻌㻱㼄㻼㻭㻺㻿㻵㼂㻱㻌㻭㻰㻰㻵㼀㻵㼂㻱㻌needle for initial setting is 1.13 mm. For the modified initialtime tended to be faster when the Crep was up to 6.4%, but whensetting time, the material age when the penetration depth of thethe Crep exceeded 6.4%, the setting time became slower as theVicat needle was 1 mm from the bottom was adopted.㻌

Crep increased.㻌㻌㻌

2.3 Expansion strain

3.2 Expansion strain

Expansion strain of CP is measured using a 50 x 400 (x-axis

Test results of expansion strain at 7 days of age are shown indirection) x 10 mm specimen. A 10-mm-square aluminum barFig. 1. For all strains, the strain at the modified initial setting

was installed to the end of the specimen, and the change intime was set to 0. The strain increases sharply when thelength of x-axis was measured by a non-reaction force LVDT.

replacement ratio of EA (Crep) exceeds 6.4%.㻌

In order to reduce the frictional force, the CP was casted into aFig. 2 shows the percentage of strain for each age when thepolyester film and a Teflon sheet was installed between theexpansion strain at 7 days is set to 100%. It can be seen that theform on the bottom and the specimen.

percentage of expansion strain up to 0.5 day on the whole is㻌different between the Crep up to 6.4% and higher than that. This

2.4 Compressive strength

result shows that the reaction mechanism changes depending

Compressive strengths were measured using a cylindricalon the replacement ratio.

specimen of 50 (diameter) x 100 (height) mm. 24 hours after
casting, the CP specimens were carefully removed from their

3.3 Compressive strength

plastic molds, sealed in polyethylene plastic film.

Test results of compressive strength at 1 day, 3 days, and 7

2.5 Observation by micro-CT scanning

to reference is shown in Fig. 3. Compressive strength tended toSlices with a thickness of 2-3 mm were cut from thedecrease when the Crep exceeded 6.4%.

days of age are shown in Table 1 and strength ratio comparedsample in a resin bottle and then ground using a thin

16

sectioning machine. Next, a micro-dicing machine was usedeach bar was approximately 0.92 to 1.02 mm. The bars wereimmersed in isopropanol until testing. Phoenix Nanotom m
was used for the test.

Setting time [hrs]and slices were processed into square bars. The length ofFinal setting time
Modified initial setting time
Approximation expression

14121082.6 Observation and elemental analysis by E-SEM

6At 3 days of age, the sample was crushed with a hammer

4to a size of about 5-10 mm, and hydration was stopped with

0246810Replacement ratio of EA [%]liquid nitrogen. The sample was immediately placed in afreeze-dryer and dried for 1 month. One month later, theinitial setting timeeach sample was grinded and polished on a lapping table

60000

with 6 µm, 3 µm, 1 µm, and 0.25 µm diamond paste. In

50000

between each paste, the samples were submerged in ethanol

40000

mm/mm [x10-6]

vacuum defoaming and cured. After the resin had hardened,

70000

and ultrasonicated to remove debris. Following polishing,samples were kept in a desiccator until testing. Philips XL
30 ESEM was used for testing.
㻌3000020000
10000
0§３㻚㻌㻱㼄㻼㻱㻾㻵㻹㻱㻺㼀㻿㻌㻙㻌㻾㻱㻿㼁㻸㼀㻿㻌-10000㻌
Test results of setting time are shown in Fig. 1. The setting

14Figure 1: Relationship between Crep and modifiedsample was impregnated with epoxy resin while performing

3.1 Setting time120246810
Replacement ratio of EA [%]1214Figure 2: Relationship between Crep and expansion
strain at 7 days of age−37−－㻟－㻌Fujita Technical Research Report No.57㻌

3.4 Observation by micro-CT scanning100%

A cross-section image obtained by CT scanning is shown in

90%

Occupation of strain [%]Fig. 4, and a 3D image of a specimen of each Crep is shown in
Fig. 5. The cube in Fig. 5 has a side of 1 mm, which is㻌

approximately the same as the width of the specimen. The㻌observation results in Photo 5 show that microcracks increase㻌when the Crep is 10.3% compared to 8.4%. Microcracks are㻌

radially generated from the aggregated portion of the hydration

80%
70%

1d-2d50%40%

0.5d - 1d30%
20%- 0.5d10%

products. Hydration products such as these are not generated in0%

the case of PC alone, and it is considered that the EA particles

EA26

EA51

EA64

EA103 EA109 EA129

Specimenhave grown. This result shows that the strength decrease isFigure 3: Expansion strain percentage of duration tocaused by the expansion of the EA particles themselves.

Compressive strength ratio to reference

2d-60%

7 days of age

1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2

1d02

3d7d4
6810
Replacement ratio of EA [%]1214Figure 4: Relationship between Crep and compressive

Figure 6: CT-scanning image of hardened cement

strength

Replacement ratio of EA : 8.4%
Measurement age: 3 days
Compressive strength ratio : 0.91

Compressive strength ratio toreference

paste bar (Crep = 10.3%)

1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2

1d03d

Replacement ratio of EA : 10.3%
Measurement age: 3 days
Compressive strength ratio : 0.71

7d246810 12
Replacement ratio of EA [%]14Figure 5: 3D CT-scanning image of hardened cement paste bar−38−－㻠－㻌㻮㻭㻿㻵㻯㻌㻼㻾㻻㻼㻱㻾㼀㻵㻱㻿㻌㻻㻲㻌㻯㻱㻹㻱㻺㼀㻌㻼㻭㻿㼀㻱㻌㻹㻵㼄㻱㻰㻌㼃㻵㼀㻴㻌㻯㻭㻸㻯㻵㼁㻹㻌㻴㼅㻰㻾㻻㼄㻵㻰㻱㻙㻱㼀㼀㻾㻵㻺㻳㻵㼀㻱㻌㻯㻻㻹㻼㻻㻿㻵㼀㻱㻌㼀㼅㻼㻱㻌㻱㼄㻼㻭㻺㻿㻵㼂㻱㻌㻭㻰㻰㻵㼀㻵㼂㻱㻌

Mixture of C3A,
C4AF andAnhydrite

3.5 Observation and elemental analysis by E-SEMFig. 7 shows BSE images of a raw EA particle, Fig. 8 and Fig.
9 show a hydrated EA particle at 3 days of age.
The EA particles have a structure in which f-CaO is the main
constituent mineral, and the gaps are filled with C3A, C4AF,and anhydrite.
From Fig. 8, it can be confirmed that the precipitation positionof each hydration product is the same as that of f-CaO, C3A,and C4AF, which are the origins of each product present in theraw EA particles. Therefore, it can be inferred that mostminerals do not dissolve in solution and are converted to50μmf-CaO

hydration products on the spot.

Figure 7: Raw EA particle

Fig 8 (d) S

Fig 8 (c) Al

Fig 8 (b) CaACHAFt,
AFm
CH(a) BSE image of hydrated EA
Figure 8 (a)-(d): Element mapping images ofhydrated EA particle

Crep = 10.3%50μm

Figure 9: Hydrated EA particle at 3 days of age (Crep = 10.3%)

AFt

AFm

Crep = 5.1%50μm

Figure 10: Hydrated EA particle at 3 days of

Crep = 10.3%5μm

Figure 11: Ettringite and pores generated aroundC3A in EA at 3 days of ageage (Crep = 5.1%)−39−－㻡－㻌Fujita Technical Research Report No.57㻌

From observation results of EA Crep = 10.3% (Fig. 9), weREFERENCES

confirmed a larger amount of AFt was produced than in 5.1%

㻌(Fig. 10). (For example, a part surrounded by the red dash line

Journal Paper:[1] Minoru MORIOKA, Yasuhiro NAKASHIMA, Takayuki
HIGUCHI, Masataka EGUCHI, Etsuo SAKAI and Masaki
DAIMON: ‘Characteristics of Expansive Additives in theSystem of Free Lime-Hydraulic Compound-Anhydrite’,Tokyo: Journal of the Society of Inorganic Materials, Japan,
2003, Vol. 10, 225-232[2] Kenji YAMAMOTO, Minoru Morioka, Etsuo SAKAI andMasaki DAIMON: ‘Expansion Mechanism of Cement
Added with Expansive Additive’, Tokyo: Concrete Researchand Technology, 2003, Vol. 14, No. 3, 23-31[3] Hyeonggil Choi, Heesup Choi, Myungkwan Lim, Takafumi
Noguchi, Ryoma Kitagaki: ‘Modeling of volume changes ofconcrete mixed with expansive additives’, Construction andBuilding Materials, 2015, 266-274
Standards：[4] JIS R 5210, Portland cement, 2009, 22 pages[5] JIS R 5201, Physical testing methods for cement, 1997, 46pages[6] ASTM C191-13, Standard Test Methods for Time of Settingof Hydraulic Cement by Vicat Needle. West Conshokocken:
American Society for Testing and Materials, 2013, 8 pagesin Fig. 9.) The enlarged image of the formation location of AFt
is shown in Fig. 11. Mono-sulphate (AFm) exists on the surfaceof C3A, and needle-like AFt grows vertically from above. In
addition, a large quantity of pores formed simultaneously
around the AFt. This result shows that rapid strain expansion
occurring near Crep exceeding 6.4% is caused by verticallygenerated AFt with pores. Also, as with Delayed Ettringite
Formation, we have concluded that anhydrite dissolves inwater once and AFt can be produced only when the sulphate
ion concentration exceeds a certain threshold.

§４㻚㻌㻯㻻㻺㻯㻸㼁㻿㻵㻻㻺㻿㻌㻌㻙 The expansion strain increases sharply when thereplacement ratio of EA (Crep) exceeds 6.4%.
㻙 The setting time tended to be faster when the Crep was up to6.4%, but when the Crep exceeded 6.4%, the setting time
became slower as the Crep increased.
㻙 Compressive strength tended to decrease compared toreference when the Crep exceeded 6.4%.
㻙 From the cross-section image of Crep 10.3% obtained by CT
scanning, microcracks are radially generated from theaggregated portion of the hydration product. This resultshows that the strength decrease is caused by the expansionof the EA particles themselves.
㻙 From the image of the formation location of AFt in EA
particles of Crep 10.3% paste, AFm exists on the surface ofC3A, and needle-like AFt grows vertically from above. In
addition, a large quantity of pores formed simultaneously
around the AFt. This result shows that rapid strain
expansion occurring near Crep exceeding 6.4% is caused bythis vertically generated AFt with pores. Also, as with
Delayed Ettringite Formation, we have concluded thatanhydrite dissolves in water once and AFt can be produced
only when the sulphate ion concentration exceeds a certain

Short commentthreshold.

Understanding and modeling hydration㻌mechanisms and microstructures will

Acknowledgements

greatly㻌
I would like to express my sincere gratitude to Associate
Professor Guang Ye of Delft University of Technology andKohsuke
Handa

CMMB group members for much helpful advice, andtechnicians who supported the experiments.

helptopredict

concrete

deterioration. I believe this to be the㻌−40−－㻢－㻌

valuable perspective that cannot be
obtained from macro experiments alone.