Fumoto, Takayuki

Yamada, Masaru

Osaka City University Repository

Mem. Fac. Eng., Osaka City Univ., Vol. 44, pp. 79 - 82 (2003)
Strength and Drying Shrinkage of Concrete Used Recycled Aggregate
Takayuki FUMOTO* and Masaru YAMADA**
(Received September 30, 2003)
Synopsis
The influence of recycled aggregate on concrete properties is not clear; therefore, at present, the conventional
concept is to use recycled aggregate for only low-strength concrete. In order to expand the usage range of
recycled aggregate, the influence of qualities of recycled aggregate on properties concrete must be clarified.
Therefore, the present study examined strengths and drying shrinkage of normal and high-strength concrete used
ordinary aggregate and recycled aggregate. The results show a linear relation between the compression or
splitting tensile strength of concrete of a given slump and crrw in the region of compression strength 30-70
N/mm2 or tensile strength 3-6 N/mm2• In addition, the length change rate per unit cement volume shows close
correlation with crrw, in which 1W is the sum of water content and total water absorption of fine and coarse
aggregate.
KeyWords: recycled aggregate, normal-strength concrete, high-strength concrete, strength, drying shrinkage
1. Introduction
Use of recycled aggregate is expected to increase, in view of consumption of natural aggregate. In addition,
Recycling of demolished concrete is effective for reducing environmental impact and land reclamation. As
compared with natural aggregate, recycled aggregate has lower density in oven-dried condition and higher water
absorption. These tendencies are attributed to cement paste attached the particles. Concrete used recycled aggregate
has lower strength and higher drying shrinkage strain than conventional concrete, and the reasons for these are
unknown. So, at present, the conventional concept is to employ recycled aggregate only for low-strength concrete.
However, the amount of demolished concrete is expected to increase, requiring expan'sion of the range of
application for concrete used recycled aggregate. For that reason, it needs to be clear the influence of qualities of
aggregate on properties of concrete. Therefore, the present study investigated relationships between water
absorption of aggregate and the strength or drying shrinkage strain of hardened concrete, which of compressive
strength was the region of 30 -70 N/mm2•
2. Test Procedures
The aggregate used in this study was described in Table 1. As aggregate, we used 2 kinds of natural sand (NSI and
NSC) and a crushed stone (NCT). In addition, we used 2 kinds of recycled fine aggregate and one kind of recycled
coarse aggregate, called RSa ,RSb, and RCb. RSa was recycled fine aggregate produced in a recycling plant. RSd
and RCb were 0.15-2.5 mm and 5-25 mm diameter particles that were crushed from demolished concrete by use of
a jaw crusher and a cone crusher. Here, the source of the demolished concrete was a 45-year-old building.
Concrete samples were produced from NSI, NCT, and ordinary portland cement at the mixture proportions in
Table 2. When other kinds of aggregate were used, the aggregates were used in the same mixture proportions in
volume as the substituted aggregate. Properties of fresh concrete were adjusted to the target values at each WIe by a
polycarboxylic acid type super plasticizer, a ligninsulfonic acid type air-entraining agent, a water-reducing
admixture, and a supplementary air-entraining agent. Table 2 shows the target values. Concrete was prepared by
mixing ordinary cement, fine aggregate, and coarse aggregate in a revolving-paddle mixer for 30 seconds, adding
* Research Associate, Division of Civil Engineering, Department of Urban Engineering
** Professor, Division of Environmental Urban Engineering, Department of Urban Engineering
79
Table 1 Kinds and physical properties of aggregates used in this study
Density in Water
Kind of aggregate Symbol oven-dried absorption Source of raw material
condition
(g/cm 3) (%)
NSI 2.52 2.74 River sand from Ibi river
Ordinary
NSC 2.55 1. 65 River sand from Fujian, China
Fine RSa 2.18 8.10 Plant for recycled aggregate
aggregate Recycled
RSb 1. 99 11.4 Building erected in 1957
Coarse Ordinary NCT 2.66 1.07 Crushed stone from Takatsuki city
aggregate Recycled RCb 2.43 3.40 Bui Iding erected in 1957
Table 2 Mixture proportions of NSI and NCT in this study
Water I cement ratio, w/e (%) 50 42 35 25
Cement total wa ter, C/TW 1.68 2.03 2.44 3.44
s/a (%) 42.3 40. 7 39.3 45.2
Water content, W 155 162 162 162
Cement content, C 310 386 463 648
Fine aggregate content, S 754 693 665 697
Unit Coarse aggregate content, G 1073 1054 1071 881Quantity Polycarboxyl ic acid type super plasticizer or(kg/m3) Ligninsulfonic acid type ai r-entraining agent CxO.25*1 CxO. 25*1 CXO.7*2 Cx2.8*2
(weight percent)
Supplementary air-entraining agent CxO.002 CxO.0025 CxO.0005 CxO.0035(weight percent)
Target value of slump or slump flow (mm) 120± 20 120±20 180±20 600 ± 50
Target value of air content (%) 5±1 5±1 3±1 3±1
*1 Ligninsulfonic acid type air-entraining agent
*2 Polycarboxyl ic acid type super plasticizer
influence of recycled fine aggregate, tests were carried out for concrete with NCT at W/C = 25, 35 and 50%.
Properties of hardened concrete were measured; specifically, compressive and splitting tensile strength, and
length change under dried condition. Dimensions of concrete specimens were 0100 x 200mm for compressive
strength measurement, 0150 x 150mm for splitting tensile strength measurement, and 100 x 100 x 400mm for
length change measurement. All specimens were cured in water at 20oC. Strengths were measured after curing for
28 days. In addition, in the test of length change under dried conditions, the specimens were dried at 200C and 60%
humidity after curing for 7 days, and strain of the specimens by drying was measured.
3. Results and Discussions about Compressive and Splitting Tensile Strengths
Fig.1 shows the relationship between C/W and compressive strength. In spite of kinds of fine aggregate,
compressive strength increased with increasing C/W. In each case, the relationship was almost expressed by a
straight line. In addition, the water absorption of aggregate has great influence on compressive strength.
Therefore, an appropriate index was introduced. The quantity of water absorbed by all aggregate in concrete was
calculated. The result was added to water content, yielding the total quantity of water in concrete, called TW. The
ratio of Cement content to TW was defined as cement / total water ratio (crrw). Expression (1) shows the
80
calculation of crrw.
TW = W + s x Ds x ws + g x Dg x wg (1)
Where, TW is total water content, W is water content, s is content by volume of fine aggregate, Ds is density of
fine aggregate in the oven-dried condition, ws is water absorption of fine aggregate, g is content by volume of coarse
aggregate, Dg is density of coarse aggregate in the oven-dried condition, and wg is water absorption of coarse
aggregate.
Fig.2 shows the relationship between crrw and compressive strength. In both case, the relationship was linear
when compressive strength was 30 - 70 N/mm2• The kind of aggregate had no influence to the relation. However,
when compressive strength exceeds 70 N/mm2, the compression strength of concrete used recycled coarse aggregate
decreased to approximately 80% that using ordinary coarse aggregate. The supposed reason was thought that
recycled coarse aggregate was inferior to ordinary coarse aggregate in particle strength. In other words, it is desired
that high particle of strength coarse aggregate is used in high-strength concrete.
Similarly, as shown in Fig.3, the splitting tensile strength showed a linear relationship with crrw, when splitting
tensile strength was 3 - 6 N/mm2•
100
~ 90~
E,
80z~
~ 70~bD
c
Q)
~ 60~
CI) ( S , G )
Q) 50 ~ (NSI,NCT)>
CI)
--f=- (NSC, NCT)CI) 40Q)
-0 - (RSa, NCT)~
c.
- -G - (RSb, NCT)E 300
--e- (NS I, RCb)u
20
2 2.5 3 3.5 4
Cement/water ra t ia
Fig.l Relationship between compressive strength and cement / water ratio
7
".......
~ ( S , G )E, X (NS I, NCT)~6 + (NSC, NCT)
..s::: o (RSa, NCT)~
bD D (RSb, NCT)c
Q) 5 e (NS I, RCb)~
~
CI)
Q) Q
- 4 I
CI) ~.c:Q)~ ~WNN_ R2=0. 78 (W/C=50, 42%
bD 3c [] In W/C=35,25%
~
------Ordinary coarse aggregate~
- - - Recycled coarse aggregate
c. 2
en 1 1.5 2 2.5 3 3.5 4
Cement/total water ratio
4
+
1.5 2 2.5 3 3.5
.Cement/total water ratio
• IF
~.~ ----- R2=O. 93 (W/C=50, 42%)
t) In W/C=35, 25%
CJ -----Ordinary coarse aggregate
- - - Recycled coarse aggregate
( S , G )
X (NS I, NCT)
+ (NSC, NCT)
o (RSa, NCT)
D (RSb, NCT)
e (NS I, RCb)
20"---------..a-...-------...a.------''----......
1
~
~ 70
c:
Q)
~ 60
CI)
~ 50
CI)
~ 40
~
C.
E8 30
1OO........-......---.--....----.--~t--- ....
~ 90
E,
.::; 80
Fig.2 Influence of cement / total water ratio on compressive
strength
Fig.3 Relationship between splitting tensile strength and
cement / total water ratio
81
4. Results and Discussion about Drying Shrinkage
Next, the drying shrinkage of recycled concrete was investigated. As shown in Fig.4, length change rate tended to
decrease with increasing CIW. As compared with the case where ordinary aggregate was used,. when recycled fine
aggregate of high water absorption was used, the length change rate became large. According to a previous study,
not only water content but also cement content influences drying shrinkage strain. Then, paying attention to the
amount of cement, a length change rate per unit cement volume was computed. As shown in Fig.5, the results clarify
a strong correlation between crrw and length change per unit cement volume. The above results suggest that the
properties of hardened concrete used recycled fine and coarse aggregate are greatly influenced by crrw, which
takes into consideration the amount of water absorption of aggregate.
As the result of this study, if amount of water absorbed to aggregate is considered, a part of properties of concrete
used recycled fine and coarse aggregate will be able to be controlled. So, the recycled aggregate can be used for
normal-strength concrete. But, in case of high-strength concrete, it is difficult to use recycle coarse aggregate
because particle strength influenced concrete strength.
10 10
en ~
....J
.::s:. 9 "" D ( S , G )CD - - 8 __ :t 9CD -
~ .......... OX X (NS I, NCT)c:CD 8 ....... -- 0 8 + (NSC, NCT)~
---., ....... Q,)'-e-"' o (RSa, NCT)
..- -~'~ ::::s'-«S 7 Q,)_"'C D (RSb, NCT)+JoC: 7
CD~
---
~ .... ~>~ ~ X e (NS I, RCb)..- I Q,)~"'C~ ~6 bDQ,)Q) 6
X c: e'-CD ~ «SQ,)~~ '-' 5 ~u"'C.s::::~~ 5«S ( S , G ) ~..c: +Jc:"'C XU 4 ~::::S5 4
-----x--- (NS I , NCT) -+- (NSC, NCT) Q,)~..c: ....JQ,)C12 R2=0.89..-
-E) - (RSa, NCT) - D- (RSb, NCT) a.~bD 3 Q) 3E:: Q)
CD --e - (NS I, RCb) ~ X
....J
to2 C"':) 22 2.5 3 3.5 4 -"' 1 1.5 2 2.5 3 3.5 4«S
Cement/water ra t i 0 Cement/total water ratio
Fig. 4 Change in length change rate with increase in cement
/ water ratio
Fig.5 Influence of cement/total water ratio on length change
per unit cement volume
5. Conclusion
1) A linear relation existed between the compression or splitting tensile strength of concrete of a given slump and the
ratio of cement content to amount of total water in concrete (crrw), within the compression strength range of
30-70 N/mm2 or tensile strength 3-6 N/mm2•
2) The length change per unit cement volume was closely correlated with crrw.
References
1) Takayuki FUMOTO, etc.: Influence of Quality of Recycle Fine Aggregate on Properties of Concrete, No.24,
Vol.l, pp.1233-l238, 2002.
2) Kenji Izumo: Drying shrinkage of various mortar, Proceeding of Annual Conference of the Japan Society of Civil
Engineers No. 57, V-65l, pp.130l-l302, 2002.
82


Strength and Drying Shrinkage of Concrete Used Recycled Aggregate

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Strength and Drying Shrinkage of Concrete Used Recycled Aggregate

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