Proceedings of 1st International Symposium for Color Science and Art 2019

Fundamental Study on Colored Concretefor Structural Building Members
Hiroshi JinnaiTokyo Polytechnic Univ., 1583 Iiyama, Atsugi, Kanagawa 243-0297, JapanABSTRACT
Focusing on the mortar portion, which determines thecolor of colored concrete, the author experimentallyinvestigated color development and color changes overtime. This investigation led to the following two
conclusions. 1) It is possible to manufacture coloredmortar with high compressive strength that can be used toconstruct high-rise RC buildings of 40 to 60 stories, and 2)
the color of colored mortar changes as the result of drying
after demolding, but the denser the structure of the mortar
and the greater its compressive strength, the lesspronounced the color change.

Photo1 Colored Concrete (Colored Cement paste)

1. INTRODUCTION
Reinforced concrete buildings are often clad with tiles
or the like as a cosmetic exterior material. However,accidents such as tiles coming off walls due to aging
deterioration are far from infrequent. Therefore, the author
decided to conduct research to develop technology for theconstruction of major structural members such as columns
and beams of buildings using pigment colored concretethat does not require exterior cladding materials.

Compressive Strength of 20 degree
seal-cured specimen（MPa）

Photo2 University logo mark made fromcolored concrete (Colored mortar)

2. COLORED CONCRETE USED IN THIS STUDY
本Colored concrete is originally defined as a mixture ofcement, pigment, coarse aggregate, fine aggregate, andwater. However, depending on the type of experimental
data that are desired, there are cases where the use ofcoarse aggregate and fine aggregate in the mix is notrequired for experiments. Thus, in this study, cured
cements mixed with pigments are collectively referred toas colored concrete, and colored cement paste andcolored mortar are treated as types of colored concrete.

160140

The age of 1year

120
100
80
60
40
20
0
W/B=0.5

W/B=0.4
WhiteBlue

W/B=0.3
Green

W/B=0.2

Yellow

Fig. 1 Compressive test results of Colored concrete(Colored mortar)
80

3. EXPERIMENT 1
In Experiment 1, the compressive strength and color
changes of mortar to which pigment was added wereinvestigated. In all, four colors, namely pigment-free white,as well as pigmented blue, green, and yellow, were used.
The dosage of pigment was that recommended by themanufacturer. The water-binder ratio (W/B: ratio of themass of water to the mass of cement) of mortar was set tofour levels: 0.2, 0.3, 0.4, and 0.5.
Mixing was carried out in a room with temperature of 20±3℃. Next, the specimens for the compressive strength
test underwent sealed curing in a curing room at 20℃, andthe specimens for color measurement were stored in a75
W/B=0.5

Ｌ*70

W/B=0.4

65

W/B=0.360

W/B=0.255
50110100Age (Days)

1000

Fig. 2 Example of color changes over time(Blue specimen: L* value)45

Proceedings of 1st International Symposium for Color Science and Art 2019

curing chamber at the temperature of 20℃ and humidity of60%.
The results of the compressive strength test of coloredmortars at the age of 1 year as shown in Fig. 1. While thecolored mortars to which pigment was added had slightly
lower strength than basic white mortar, compression
strength of about 140 MPa was achieved. This level ofstrength is sufficient for the construction of high-rise RC
buildings of 40 to 60 stories.
As an example of the measurement of color changes
over time, Fig. 2 shows the L* value measurement results
for the blue specimen. In the L*a*b* color space, the L*
value represents the lightness of the color, with 0
indicating black and 100 indicating white. In L*a*b*measurement, the color immediately after demolding wasalmost the same regardless of the water-binder ratio forany of the specimens. On the other hand, as time passed
after demolding, the color changed due to drying, and inspecimens with large water-binder ratio, which are more
prone to drying, the increase in L* value was remarkable.

Dosage ofPigment

W/B
0.5

W/B
0.2

11/2

1/4

1

1/2

1/4

Water binder ratio Water binder ratio
0.5
0.2* Water binder ratio(W/B) = Mass of water/Mass of binder

Fig.3 Parameter of experiment

4. EXPERIMENT 2
In Experiment 2, the influence of the amount of pigmentused was investigated. Three dosages of additive wereused, using the manufacturer recommended dosage asthe base. Two water-binder ratios, 0.2 and 0.5, wereadopted for each mortar.
The experiment parameters are shown in Fig. 3. The
pigment dosages were the manufacturer recommended
dosage, one half of that dosage, and one quarter of that
dosage. Photos 3 and 4 show pictures showing the actual
test specimen placed in the same positions as in Fig. 3.
Photo 3 was taken immediately after demolding 1 day after
pouring, i.e. at the material age of 1 day. Photo 4 wastaken after six months of storage in a curing chamber at
the temperature of 20℃ and humidity of 60%.
As long as the base mortar is white, mortar of abeautiful color can be achieved even when reducing thepigment dosage to about one-fourth of the manufacturer
recommended value. Further, looking at the 1/4 pigment
blue specimens indicated by the red arrows, we can seethat the color of the specimens with W/B of 0.5 is darker
than that of the specimens with W/B of 0.2 at the age of 1day. However, as the specimen with W/B of 0.5, which ismore prone to water loss, dries as the days pass, its color
depth becomes lesser than that of the specimen with W/Bof 0.2. These results show that the results obtained inExperiment 1 are reproducible.

Photo3 Colors of specimens at the age of 1day
(Comparing the colors of the specimens with 1/4 of themanufacturer recommended pigment dosage, which
are indicated by the red arrows, the specimens with
W/B of 0.5 are darker in color than the specimens with
W/B of 0.2.)

5. CONCLUSIONS
1) It is possible to manufacture colored mortar with highcompressive strength that can be used to constructhigh-rise RC buildings of 40 to 60 stories.
2) The color of colored mortar changes as the result ofdrying after demolding, but this tendency is lesspronounced the denser the structure of the mortar andthe greater its compressive strength.

Photo4 Colors of specimens at the age of 6 months(Comparing the colors of the specimens with 1/4 of the
manufacturer recommended pigment dosage, which
are indicated by the red arrows, the specimens withW/B of 0.5 become lighter in color than the specimens
with W/B of 0.2 over time)46