Scattering-Filling Stone Concrete: Mechanism, Experiment and Utilization
Weiguo Shen1,2,3, a, Zhenguo Yang3,b , Zhifeng Yang1,c,Jiangfeng LI3,d, Liu
Cao3,e,Chuan Zhang3,f
1. State Key Laboratory of Silicate Materials for Architecture, Wuhan University of Technology, Wuhan
430070, China;
2. WUT-UC Berkeley Joint Laboratory on Concrete Science and Technology, Wuhan 430070China;
3. Material Science and Engineering School, Wuhan University of Technology, Wuhan 430070, China;
a. [email protected],[email protected],[email protected],[email protected],e.10
[email protected],[email protected],
Keywords: coarse aggregates; scattering-filling stone process; aggregate interlocking concrete;
strength; shrinkage; interfacial transition zone
Abstract. The coarse aggregate volume fraction in conventional plastic concrete is controlled relatively
low to ensure a required workability, but its low aggregate content play negative roll on the service
properties of the concrete. In this paper, we revealed the mechanism of a coarse aggregate interlocking
concrete prepared by Scattering- Filling Stone Concrete (SFSC), it can keep the fresh concrete its
workability but increase its service performance by scattering coarse aggregate during the concrete
casting, the experimental and engineering application of SFSC indicated that: the strength of concrete
prepared with this method increases obviously whereas the shrinkage decreases significantly when 20%
cement dosage is saved. The SFS process was utilized in a highway pavement, the core of the concrete is
very dense and no obvious defect could be found when 8% pavement concrete was replaced by coarse
aggregate. The SFSC is a type of low carbon concrete.
Introduction
Concrete is arguably the most widely used manufactured
materials in the world, the production processes of concrete
result in tremendous environmental impact, cement is the
most remarkable ingredient in the concrete which has the
largest resource consumption, energy intensity, green house
gases and acid rain gases emission [1,2,3], the manufacture of
Portland cement (PC) is responsible for up to 10% of
anthropogenic CO2 emissions worldwide, to prepare qualified
concrete with low cement content is a very effective approach
to reduce the total environment impact of the concrete even
the human activity CO2 emission. The concrete is a three
phased material: aggregate particles, interfacial transitional
zone (ITZ) and cement paste matrix [4], the coarse aggregate
is the strength framework of the plain concrete and it is the
structure unit with highest strength, volume stability,
durability and lowest cost in the most concrete [5,6]. As a
composition material, the concrete’s hydration heat,
shrinkage, permeability and creep will decrease, whereas the
strength, elasticity modulus and anti-cracking will increase
with the increase of coarse aggregate content [7,8,9]. The
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Fig.1. Schematic diagram of the
scattering-filling concrete placing
process
conventional plastic or fluidal concrete is prepared by mixing the binders (cement and mineral
admixture), fine aggregate, coarse aggregate and water together then placing and vibrating the mixture to
fabricate a consolidated matrix. In order to keep the fresh mixture a reasonable flowability and avoid
gravity segregation, the aggregate content in the conventional concrete (especially those high strength
high performance concrete) keeps relatively low [10], the total aggregate volume fraction in high
performance concrete is around 65% [11], and the coarse aggregate volume ratio is around 40%, so the
aggregates can’t act fully as the matrix structure of the concrete, the high volume fraction of cement paste
increases the permeability, creep and drying shrinkage of the concrete [11]. The first author invented a
new concrete placing process named scattering-filling stone method: adding 10~30% (by the volume of
the finished concrete) of coarse aggregate while the concrete is being poured, paved or placed, then
vibrating the matrix to form a consolidated concrete [12,13,14] (illustrated in Figure 1). This concrete
content 10~30% less cement than the conventional concrete so it is a typical low carbon concrete, in this
paper, the mechanism of concrete is revealed, the experiment and engineering utilization of this technology
is reported.
The mechanism of the coarse aggregate interlocking concrete
As illustrated in figure 2, with the increase coarse aggregate in the concrete, the workability will
became worse, to keep a reasonable workability, the w/c ratio need to increase therefor its strength of the
concrete deduced. Whereas the increase of the coarse aggregate make the strength, modules of concrete
increase but the permeability, shrinkage, creep, hydration heat reduce. Simplified it, the increase of
coarse aggregate make worse the workability but make better the service performance.
Figure 2 The mechanism of Scatering-Filling Stone Concrete
This new SFS process is a solution to this dilemma, the concrete is designed, mixed and ship with
traditional method, so the fresh concrete keep the workability of itself, when the concrete is cast, the
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coarse aggregate (stone, it can be coarser than the original coarse aggregate in the concrete) is scattered in,
the finished concrete has high coarse aggregate content, so the service performance increased. First of all,
the coarse aggregate volume fraction increases dramatically in this type of concrete when more than 20%
of coarse aggregate is scattered in the mixture, the coarse aggregates can interlock with each other, the
friction forces among the aggregate contribute to the strength enhance in a certain extent. The second, the
coarse aggregate distributes more evenly in this kind of concrete than the concrete prepared with
conventional process. With the vibration, the segregation of the coarse aggregate toward the bottom of
the form and the of the cement paste toward the top may result in the conventional concrete [17], the
surface of the concrete will be very weak, but when scatting-filling process is applied, the coarse
aggregate will fill evenly at the top of the form. The third, the addition of extra amount of air dry coarse
aggregates acts as somewhat water reducer, not only reduces the W/C of the paste close to the aggregate
and make the paste stronger so the ITZ of the concrete is enhanced. With the volume fraction of the
aggregate increasing, as a composite material, the concrete will become stronger and stiffer.
Experimental study
120
110
100
90
80
70
60
50
40
30
20
10
0
450
7D-00
Shrinkage ratio ×10-6
Comprissive strength (MPa)
The conventional concretes with strength grade varying from C30-C80 are prepared with various
kinds of aggregates, cement, mineral admixture and mixing proportions, the aggregate interlocking
concretes are prepared with scattering-filling stone process by adding 20% volume ratio of coarse
aggregates to substitute the conventional concretes mixtures, the 7 day and 28 day strengths of those
concretes with different content of adding coarse aggregate contents are illustrated in Figure 2 (a).
7D-20
28D-00
28D-20
400
350
300
250
200
150
100
0%
20%
50
10%
30%
0
C30
C35
C40
C50
C60
C70
0
C80
50
100
time/d
150
200
a. The strength of the concretes
b. the shrinkage of concretes
Fig.3. The strength and shrinkage of original concrete or concrete prepared with SFS
It can be found that the strengths of all those concretes with different mix proportions increase
obviously with the 20% (the volume ratio of scattering concrete in the finished concrete) adding
aggregate ratio only different in the extent. The increasing ratio can be as high as 25%. It is easy to find
that concretes with 50-100 MPa have been prepared with only 362~440 Kg/m3 of cement or binder when
20% coarse aggregate is scattered to substitute the original concrete mixtures through some simple
calculation, this can be never achieved with the conventional concrete placing process. The
scattering-filling stone can prepare concrete with very high coarse aggregate, although the “pre-placed
aggregate” concrete process [16] can prepare concrete with as low cement dosage as this process, but it
can only prepare low or middle strength concrete. The scattering-filling stone method can produce
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consolidated concrete with less cement but higher strength and performances at the same time, the
decrease on cement dosage not only give the concrete good cost competitive but also good environmental
harmonization.
The shrinkage crack of concrete sometime results in damage of concrete structures, increasing of the
aggregate can reduce the crack of concrete [17], the shrinkage curves of the concretes with different
scattering-filling stone replacement volume fractions are illustrated in Figure 3 (b), which indicates that
with the increase of the replacement volume fraction of the scattering-filling stone, the shrinkage of the
concrete decreases significantly. With increasing of the volume fraction of the extra coarse aggregate is
added to the concrete, the shrinkage of the concrete decreases markedly. The aggregate scattering-filling
process is a very effective approach to reduce the shrinkage of the high strength concrete, which is highly
desired by engineers [17].
The utilization of Scattering-Filling Stone Concrete
The scattering-filling stone concrete was used in the pavement concrete in the Provencal highway
project 305 in Xiangyang, Hubei (Figure 4), the mix proportion of the original concrete and
Scattering-Filling Stone Aggregate Concrete is listed in Table 1.
Table 1 The mixing proportion of original and Scattering-Filling Stone Concrete
Concrete
type
cement
(kg/m3)
Crushed stone
(kg/m3)
Water
(kg/m3)
Sand
(kg/m3)
Sand ratio
W/C
Ordinary
380
1211
167
652
0.35
0.44
SFSC
350
1323
154
600
0.31
0.44
The Scattering-Filling Stone Concrete is construction with a process nearly the same as the ordinary
concrete, the only difference is this process need to scatter 8% of coarse aggregate by volume under at the
surface of the base course of the pavement before the pavement concrete is cast. The pavement cores
specimens were drilled 29 days after the ordinary and SFSC pavement were cast, the strength of those
cores are listed at table 2, the cores of SFSC pavement have higher mean strength than that of the
ordinary pavement.
Table 2. The strength of core of the pavement at 29 day
Core Site
Distance to
middle (m)
Highth of core
(mm)
Spilting strengh
t(MPa)
Flexual strenght
(MPa)
K101+791
0.2
205
3.41
5.14
K101+780
1.5
214
3.39
5.12
K101+752
0.2
207
3.34
5.06
K101+740
0.2
220
3.33
5.05
K101+732
0.2
224
3.25
4.97
K101+721
0.9
217
3.18
4.90
2F
d m  l m ;
Note: the spilting strength is calculated by:
f  1.607  1.035 f sp
The flexural strength is writon: c
f sp 
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Mean flexual (MPa)
5.11
(Scattering-Filling
Stone Pavement)
4.97(Ordinary
Concrete Pavement)
Figure 4. The building site of SFSC pavement
8% to 10% of cement can be saved when SFSC is used in the pavement, the pavement has higher
crack resistance than the ordinary concrete, the segregation of the motor and aggregate is not so obvious,
there are nearly no water bleeding above the surface of the pavement as usually. It is well known that the
pavement concrete has very low slump, and not so high strength, there are nearly no the motor more than
needed in pavement concrete, whereas, this SFC process can be used and get good technical and
economic benefit. If we can invent an equipment to fulfil the scattering- filling stone process in the
flowing especially the pump concrete, much more aggregate can be scattered and filled in the concrete,
and much more cement can be saved, the performance of concrete can be improved more remarkably.
Nearly all concrete except the roll compact and no fine concrete can use this process, if this concrete have
the opportunity to be applied in all the possible concrete project, more than 15% of cement can be saved,
around 1% of the anthropogenic CO2 can be saved. It is promising to be a low carbon solution to the
concrete industry.
Conclusions
This article relates to a new type of SFSC process developed by the first author, the mechanism,
experimental study and engineering application of this process is reported. The following conclusions
can be drawn:
1.The increase coarse aggregate volume fraction increase the service performances but reduce the
workability of fresh concrete, the SFSC keep the workability of fresh concrete but increase the service
performance of the concrete at the same time.
2.C30~C80 concrete with higher strength is prepared but lower cement dosage is prepared with
scattering-filling stone method, the dry shrinkage of the aggregate interlocking concrete decrease with
the increase of volume ratio of the extra adding aggregate.
3.The application of SFSC in highway pavement indicate this process can be successfully used and
increase the strength of the pavement 8-10% cement can be saved.
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Acknowledgments
The author acknowledges the funding support of Hubei Highway Bureau, Guangdong Transportation
Ministry (2011-03-057, 2012-02-006) and the Key Laboratory of Road Structure & Material Ministry of
Transport.
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