480 Revista Română de Materiale / Romanian Journal of Materials 2016, 46 (4), 480 - 484

PROPRIETĂȚILE MECANICE ȘI CONTRACȚIA LA USCARE

A BETONULUI AUTOCOMPACTANT CU ADAOS DE CENUȘĂ
MECHANICAL PROPERTIES AND DRYING SHRINKAGE
OF SELF-COMPACTING CONCRETE CONTAINING FLY ASH
CAI JUN1,2, LI GENGYING1
1
Department of Civil Engineering, Shantou University, Shantou 515063, China
2
College of Urban, Rural Planning and Architectural Engineering, Shangluo University, Shangluo 726000, China

Self-compacting concrete (SCC), also known as self-consolidating concrete, can be classified as an advanced construction
material. SCC is a highly flowable concrete that can achieve full compaction without the need of vibration. In this study, the
influence of fly ash on workability, mechanical properties and drying shrinkage of SCC specimens were investigated. The amount
of fly ash was varied from 0% to 60% by mass of the binder material. Workability of SCC was characterized by the slump flow and
the V-funnel tests. Test results showed that the workability of fresh SCC is improved by increasing the amount of fly ash.
Compressive strength, splitting tensile strength and flexural strength decrease with the increase of fly ash. Fly ash can obviously
reduce the drying shrinkage of SCC.

Keywords: self-compacting concrete, mechanical properties, drying shrinkage.

1. Introduction Fly ash is a byproduct of the coal combustion

process at power generation facilities. As a
cementitious material, fly ash has been used as a
Self-compacting concrete, also known as partial replacement in concrete. The use of concrete
self-consolidating concrete, is the most advanced containing fly ash has been increasing due to the
trend in the field of concrete. SCC is a highly technical and economical advantages. Fly ash can
flowable concrete that can fill every corner of improve the durability of concrete, prevent alkali
formwork under its own weight without the need of aggregate reaction and reduce total material costs
vibration, and consolidate without any segregation. [9]. Cement industry is highly energy consumer and
The three material attributes of SCC are flowability, contributes with about 5% in the global carbon
passing ability and stability. SCC has good flow dioxide emissions. Carbon dioxide is the primary
ability and can pass through gaps between greenhouse gas which is responsible for climate
reinforcements. SCC is an extension of traditional change. As a partial replacement for cement, use of
concrete technology and offers improved fly ash has an favorable influence on the
engineering properties. Since its invention in the late environment. In this study, the effect of fly ash on
1980's, SCC has developed rapidly because of its workability, compressive strength, splitting tensile
obvious advantages [1-4]. SCC offers many benefits strength, flexural strength and drying shrinkage of
confronted by the conventional concrete, including SCC were investigated.
shorter construction time, lower labor costs, better 2. Experimental program
working environment, eliminating the vibration and
improving the quality of concrete [5-7]. SCC is an 2.1 Materials and mix proportion
advanced concrete building material that is regarded
as the most revolutionary development in the Ordinary Portland cement was used in the
concrete industry in recent decades. SCC has been experimentals. Fly ash was used as a partial
widely applied in high-rise buildings, bridges, replacement of Portland cement. The specific
tunnels, hydraulic structures and precast concrete surface area of cement and fly ash was 462 m2/kg
construction. SCC plays an important role in and 565 m2/kg, respectively [10,11]. The main
infrastructure and the application of SCC has grown chemical composition of cement and fly ash is
tremendously [8]. presented in Table 1.


Autor corespondent/Corresponding author,
E-mail: deyi2665@126.com
Cai Jun, Li Gengying / Proprietățile mecanice și contracția la uscare a betonului autocompactant cu adaos de cenușă 481

Table 1

Chemical composition of Portland cement and fly ash.

Chemical analysis
SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O Loss on ignition
(wt. %)
Portland cement 19.5 4.4 6.22 65.9 1.5 1.09 0.30 1.09
Fly ash 56.5 20.1 8.2 9.7 1.98 0.35 0.48 2.69
Table 2

Mixture proportions of SCC.

Proportions Coarse Fine SP
(% by mass of binder) Cement Fly ash Water
Mixture aggregate aggregate (% by mass
(kg/m3) (kg/m3) (kg/m3)
Cement Fly ash (kg/m3) (kg/m3) of binder)
SCC-0 100 0 586 0 211 759 812 0.72
SCC-20 80 20 457 115 206 759 812 0.72
SCC-40 60 40 334 222 200 759 812 0.72
SCC-60 40 60 217 325 195 759 812 0.72

The coarse aggregate was crushed stone beam is loaded at one-third span point. Span of the
with a maximum size of 20 mm and the fine beam is three times its depth.
aggregate was natural sand with a maximum size of Beams (100 × 100 × 515 mm) were used to
5 mm. The fineness modulus of sand was 2.28. The evaluate the drying shrinkage of SCC. Length
four mixtures were designed and the replacement change measurements were taken using a dial
rate of fly ash varied from 0% to 60% by mass of the gauge mounted along the longitudinal axis of the
binder, consisting of cement and fly ash. SCC specimens. Drying shrinkage tests were
Polycarboxylic ether superplasticizer (SP) was used conducted in accordance with Chinese Standard
in all mixtures to obtain the required workability. A GB/T 50082-2009. The drying shrinkage rate is
constant water-to-binder ratio was maintained at defined as:
0.36 for all mixtures. The details of the mixture L L
proportions are given in Table 2.  0 t (1)
Lb
2.2 Test methods L0 - the initial length of specimens.
The slump flow and the V-funnel tests were Lt - the length of specimens at the age of time t .
used to evaluate the workability of fresh SCC Lb - the gauge length of specimens.
mixtures. The slump flow test aims at determining
3. Results and discussion
the filling ability of SCC. Filling ability is the ability of
SCC to flow into all spaces within the formwork 3.1 Workability of fresh SCC
under its own weight. The apparatus consist of The slump flow diameter and V-funnel time of
abrams cone and base plate. The internal fresh SCC are shown in Figures 1 and 2,
upper/lower diameter of abrams cone is 100/200 respectively. Slump flow diameter represents the
mm and has a height of 300 mm. The flow time of yield stress and V-funnel time indicates the plastic
the V-funnel test is the period a defined volume of viscosity [12].
SCC needs to pass a narrow opening. About 12 liter
of fresh SCC is needed to perform the V-funnel test.
Cubes (100 × 100 × 100 mm) were used to
evaluate the compressive strength and splitting
tensile strength, and beams (100 × 100 × 400 mm)
were used to evaluate the flexural strength in
accordance with Chinese Standard GB/T 50081-
2002. The SCC specimens were cast and cured at
a temperature of 20 °C and tested at ages of 7 and
28 days. Three specimens were tested at each age
for each mixture. The compression and splitting
tension tests were performed using a digital
compression machine with a capacity of 3000 kN.
The flexural strength test is used to estimate the
load at which the SCC specimens may crack. SCC Fig. 1 - Effect of fly ash content on slump flow.
482 Cai Jun, Li Gengying / Mechanical properties and drying shrinkage of self – compacted concrete containing fly ash

Fig. 2 - Effect of fly ash content on V-funnel time.

Fig. 3 - Effect of fly ash content on compressive strength.
As can be seen in the Figure 1, slump flow
values of all mixtures meet the design requirements.
The maximum slump flow value is approximately
790 mm when the amount of fly ash is 60% by mass
of the binder. The slump flow value can be
increased by adding fly ash. In the Figure 2, the V-
funnel flow of fresh SCC needs lesser time with the
increase of fly ash content, indicating the decrease
in plastic viscosity.
Workability of the mixtures containing fly ash
was better than that of the mixture without fly ash.
The use of fly ash reduces the water demand for a
given workability. Therefore, SCC containing fly ash
will have an increased workability at constant water-
to- binder ratio.
Fig. 4 - Effect of fly ash content on splitting tensile strength.

3.2 Compressive strength than that of mixtures containing fly ash. The splitting
The results regarding the compressive tensile strength decreases with the increase of fly
strength test are showed in Figure 3. For 7 and 28 ash content.
days compressive strength, SCC containing no fly The lowest 28 days splitting tensile strength
ash achieved maximum strength. The addition of fly is approximately 2.8 MPa when 60% of the binder
ash decreases compressive strength of SCC due to material is fly ash. Compared to mixture containing
the dilution effect. no fly ash, the addition of 20%, 40% and 60% fly
The maximum 7 days compressive strength ash by mass of the binder causes the decrease of
is 35.0 MPa. In comparison with the mixture without 28 days splitting tensile strength with 18.2%, 29.5%
fly ash, the amounts of 20%, 40% and 60% fly ash and 36.4%, respectively. The amounts of 20%, 40%
by mass of the binder cause the diminish of 7 days and 60% fly ash by mass of the binder cause the
compressive strength with 11.5%, 26.7% and diminish of 7 days splitting tensile strength with
53.6%, respectively. The maximum 28 days 23.2%, 36.1% and 52.9%, respectively. The rate of
compressive strength is 48.3 MPa. Compared to decrease of splitting tensile strength diminished
mixture containing no fly ash, the addition of 20%, with increasing age of curing.
40% and 60% fly ash by mass of the binder causes
the decrease of 28 days compressive strength with 3.4 Flexural strength
9.1%, 15.3% and 28.5%, respectively. The rate of The results regarding the flexural strength
decrease of compressive strength diminished with of the specimens with different fly ash content are
increasing curing time. shown in Figure 5. As can be seen in this Figure,
the fly ash content influences the flexural strength
and the increase of fly ash leads to a diminish of
3.3 Splitting tensile strength flexural strength, the more so as the fly ash content
The results regarding the splitting tensile is greater.
strength test are showed in Figures 4. All of the The maximum 7 and 28 days flexural
mixtures showed an increase in splitting tensile strength is 2.51 MPa and 3.10 MPa, respectively. In
strength with increasing age of curing. The splitting comparison with the mixture without fly ash, the
tensile strength of mixture without fly ash is higher amounts of 20%, 40% and 60% fly ash by mass of
Cai Jun, Li Gengying / Proprietățile mecanice și contracția la uscare a betonului autocompactant cu adaos de cenușă 483

Fig. 5 - Effect of fly ash content on flexural strength.

Fig. 6 - Effect of fly ash content on drying shrinkage.
the binder cause the diminish of 28 days flexural
properties and drying shrinkage of SCC. Based on
strength with 9.7%, 21.6% and 39.2%, respectively.
the results obtained in this study, the following
The addition of 20%, 40% and 60% fly ash by mass
conclusions can be drawn:
of the binder causes the decrease of 7 days flexural
The addition of fly ash can significantly
strength with 15.1%, 24.7% and 54.3%,
improve the workability of SCC. The higher the
respectively.
percentage of fly ash, the higher the workability of
SCC.
3.5 Drying shrinkage
The compressive strength, splitting tensile
The results relating to the drying shrinkage
strength and flexural strength diminish with the
of investigated SCC with fly ash content are shown
increase of fly ash content because of the dilution
in Figure 6. Drying shrinkage is considered as an
effect. SCC containing no fly ash gave the highest
important durability property and a major reason for
value of compressive strength, splitting tensile
the deterioration of concrete structures [13-15].
strength and flexural strength at 7 and 28 days of
Cracking of concrete due to drying shrinkage
age.
results in higher repair costs and shorter service life
Fly ash has a positive effect on the drying
of concrete structures. Drying shrinkage tests were
shrinkage and reduces the drying shrinkage of
conducted for a duration of 28 days. The addition of
SCC. The drying shrinkage decreases with the
fly ash has a beneficial effect on the drying
increase of fly ash content at all ages of SCC.
shrinkage of SCC. All mixtures indicates similar
trend in the evolution of drying shrinkage. As can be
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