PSU-UNS International Conference on Engineering and
Environment - ICEE-2007, Phuket May10-11, 2007
Prince of Songkla University, Faculty of Engineering
Hat Yai, Songkhla, Thailand 90112Abstract: A statistical analysis was made using the
results of experimental factorial design about the volume of permeable voids (VPV) of recycled aggregate concrete samples using the proceedings of ASTM C 642-97. The recycled aggregates were made from crushed and sieved concrete, mortar and red ceramic. The proposed model shows that the VPV increased for all recycled concrete samples and the recycled red ceramic coarse aggregate is the most influential and the recycled mortar fine aggregate is the lesser one.
Key Words: recycled aggregate concrete, volume of
permeable voids (VPV), modeling
1. INTRODUCTION
A new development model has been adopted in many nations, taking care of the natural resources exploitation and the waste generation, among other factors that deplete the nature, which is called sustainable development.
The use of recycled aggregate is incresing in all over the world as a new way to promote sustainable development. But in the development of products where the raw material comes from recycled materials, the durability is a fundamental aspect to be assessed [1].
The durability of concrete is a difficult task since it is affected by many variables. However, the durability cannot be measured directly, for it isn't an intrinsic property of the concrete but an attribute. It can be evaluated through the behavior of the material when submitted to certain exposure conditions [2].
Maybe, the most important of those factors is the capacity of the concrete to resist the flow of fluids through it. Properties of the concrete as a porous material depend not only on their constituents but also on its pore structure [3].
Volume of permeable void in concrete is adopted as a way to specify the durability of concrete in bridge structures [4].
2. OBJECTIVES
The objective of this paper is to model the volume of permeable voids (VPV) of recycled aggregate concretes obtained from the ASTM C 642-97. These values of VPV could be used to classify the durability of recycled aggregate concretes.
3. EXPERIMENTAL PROGRAM
It was identified seven independent variables, which are: the fine and the coarse recycled aggregate of red ceramic, the fine and the coarse recycled aggregate of mortar, the fine and the coarse recycled aggregate of concrete and the water/cement ratio. Table 1 shows fine aggregates characteristics and Table 2 shows coarse aggregates characteristics, which were determined by Brazilian Standards.
Recycled concretes were produced using a design of experiments. The complete experimental design to study the total effect of all those 7 factors on the dependent variable is an experiment factorial design 2k [5;6]. The execution of that design consists in accomplishing 27 concrete mixtures, in other words, 128 mixtures. Due to time and cost limitations, the solution found to make the execution of the experimental phase possible, with high degree of reliability of results, was the use of the composed design of second order.
The base of the composed design of second order is a factorial design 2k, fractional or complete, where it is added to this last one, all the 2k vertexes of a star and the central points [5;6]. For this experimental design, it was adopted a fractional factorial design and the central points. Table 3 shows the 50 mixtures used in this experimental program, which varies the content and the type of aggregate and the water/cement ratio.
Before making every concrete, a volume compensation of recycled aggregates was made because the simple replacement of natural aggregates mass by
VOLUME OF PERMEABLE VOIDS
MODELING OF RECYCLED
AGGREGATE CONCRETE
Antonio Eduardo B. Cabral
1*, Valdir Schalch
2, Denise C. C. Dal Molin
3,
José L. D. Ribeiro
3, R. Sri Ravindrarajah
41
Ceará Technological Federal Center (CEFET/CE), Department of Civil Construction, Brazil
2
São Paulo State University (USP), Engineering College of São Carlos (EESC), Brazil 3
Rio Grande do Sul Federal University (UFRGS), Department of Civil Engineering, Brazil 4
recycled aggregates mass would result in mixtures with larger volumes of recycled aggregates, once the specific gravity of the recycled aggregates is smaller than the specific gravity of the natural ones, thus demanding more water and cement to produce equivalent mixtures to the mixture with natural aggregates.
The recycled aggregates were moistened 10 minutes before the mixture, with 80% of the water that would be absorbed in 24 hours by the recycled aggregate mass. This procedure was necessary in order not to modify the water/cement ratio by using the recycled aggregates.
The type V-ARI (according Brazilian Standards) cement was used.
Table 1 Fine aggregates characteristics.
Method
NM 30/00 NBR 9776/87
NM 45/02
Aggregate type Absorption (%)
Specific Gravity
Bulk Density (kg/m3)
Natural 0.42 2.64 1,440 Recycled concrete 7.55 2.56 1,540
Recycled mortar 4.13 2.60 1,440 Recycled red ceramic 10.69 2.35 1,460
Table 2 Coarse aggregates characteristics.
Method
NM 53/02 NM
53/02
NM 45/02
Aggregate type Absorption (%)
Specific Gravity
Bulk Density (kg/m3)
Natural 1.22 2.87 1,560 Recycled concrete 5.65 2.27 1,430
Recycled mortar 9.52 2.01 1,390 Recycled red ceramic 15.62 1.86 1,260
Table 3 Concrete mixtures defined according to the
design of experiments.
% of coarse aggregate % of fine aggregate Mix w/c
N. C RC. M N. C RC. M 01 0.46 100 0 0 0 100 0 0 0 02 0.74 100 0 0 0 0 0 100 0 03 0.74 100 0 0 0 0 100 0 0 04 0.46 100 0 0 0 0 50 50 0 05 0.74 0 0 0 100 0 0 0 100 06 0.46 0 0 0 100 0 0 50 50 07 0.46 0 0 0 100 0 50 0 50 08 0.74 0 0 0 100 0 33 33 33 09 0.46 0 0 100 0 0 0 0 100 10 0.74 0 0 100 0 0 0 50 50 11 0.74 0 0 100 0 0 50 0 50 12 0.46 0 0 100 0 0 33 33 33 13 0.74 0 0 50 50 100 0 0 0 14 0.46 0 0 50 50 0 0 100 0 15 0.46 0 0 50 50 0 100 0 0 16 0.74 0 0 50 50 0 50 50 0 17 0.46 0 100 0 0 0 0 0 100 18 0.74 0 100 0 0 0 0 50 50
Table 3 Concrete mixtures defined according to the
design of experiments – continuation.
% of coarse aggregate % of fine aggregate Mix w/c
N. C RC. M N. C RC. M 19 0.74 0 100 0 0 0 50 0 50 20 0.46 0 100 0 0 0 33 33 33 21 0.74 0 50 0 50 100 0 0 0 22 0.46 0 50 0 50 0 0 100 0 23 0.46 0 50 0 50 0 100 0 0 24 0.74 0 50 0 50 0 50 50 0 25 0.46 0 50 50 0 100 0 0 0 26 0.74 0 50 50 0 0 0 100 0 27 0.74 0 50 50 0 0 100 0 0 28 0.46 0 50 50 0 0 50 50 0 29 0.74 0 33 33 33 0 0 0 100 30 0.46 0 33 33 33 0 0 50 50 31 0.46 0 33 33 33 0 50 0 50 32 0.74 0 33 33 33 0 33 33 33 33 0.60 0 50 25 25 0 33 33 33 34 0.60 0 0 50 50 0 33 33 33 35 0.60 0 25 50 25 0 33 33 33 36 0.60 0 50 0 50 0 33 33 33 37 0.60 0 25 25 50 0 33 33 33 38 0.60 0 50 50 0 0 33 33 33 39 0.60 0 33 33 33 0 50 25 25 40 0.60 0 33 33 33 0 0 50 50 41 0.60 0 33 33 33 0 25 50 25 42 0.60 0 33 33 33 0 50 0 50 43 0.60 0 33 33 33 0 25 25 50 44 0.60 0 33 33 33 0 50 50 0 45 0.80 0 33 33 33 0 33 33 33 46 0.40 0 33 33 33 0 33 33 33 47 0.60 0 33 33 33 0 33 33 33 48 0.60 0 33 33 33 0 33 33 33 49 0.46 25 25 25 25 25 25 25 25 50 0.74 25 25 25 25 25 25 25 25 N: natural C: recycled concrete RC: recycled red ceramic M: recycled mortar
For each concrete mixture, two specimens were molded following the proceedings of the ASTM C 157-
93. After 24 hours, the specimens were demolded and
left in a curing chamber for 28 days. After that, the specimens were moved to a controlled moisture and temperature chamber (50% R.H.; 23ºC) for 224 days, when they were used to determine the VPV.
4. RESULTS
The results obtained for the VPV of the 50 concrete mixtures are shown in Figure 1.
The results of the treatment were defined in agreement with the factorial design, which allows test linear and quadratic terms. The accomplished analysis also allowed to test linear and non linear models, for the dependent variables. For a better understanding of the model, it was made an name abbreviation of independent and dependent variables that are in the Table 4.
the simplest model. The obtained model is described in Equation 1.
0 5 10 15 20 25 30
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
Mi
x
tu
re
s
VPV (%)
Figure 1 VPV of concrete mixtures.
Table 4 Aggregates symbols used.
Variable Symbol
Name Type
rmc recycled mortar coarse
aggregate independent
rmf recycled mortar fine
aggregate independent
rcc recycled concrete coarse
aggregate independent
rcf recycled concrete fine
aggregate independent
rrcc recycled red ceramic coarse
aggregate independent
rrcf recycled red ceramic fine
aggregate independent
w/c water/cement ratio independent
VPV volume of permeable voids dependent
VPV=15,1.(w/c0,23).
(1+0.40.rcc+0.64.rrcc+0.47.rmc). (1+0.30.rcf+0.29.rrcf+0.20.rmf)
(1)
In that model, the percentage of replacement of the fine or coarse aggregates for those recycled should be informed in the scale of 0 (0%) to 1 (100%), while the water/cement ratio is expressed in the usual scale, varying from 0.4 to 0.8. It should be observed that the sum of replacement percentile of natural aggregates by recycled ones should be 1 (100%) as a maximum value, for each aggregate type (coarse and fine).
5. DISCUSSION
Figure 2 presents the VPV of concrete as function of water cement ratio and recycled aggregate type for 50% and 100% of replacement. Table 5 shows the performance of those concrete samples compared to referential concrete when varing the tenor of replacement of recycled aggregate concrete but fixing the water/cement ratio.
In agreement with the presented model, when the natural aggregates replacement is made by those recycled, an increase on the VPV of the obtained concrete is observed. When the natural coarse aggregate is substituted by those recycled coarse ones, it produces a greater effect than the fine aggregate replacement, as it can be observed in function of the magnitude of the model coefficients.
12 14 16 18 20 22 24
0,46 0,6 0,74
w/c
VP
V (
%
)
Ref 50% rcc 50% rrcc 50% rmc 100% rcc
100% rrcc 100% rmc 50% rcf 50% rrcf 50% rmf
100% rcf 100% rrcf 100% rmf
Figure 2 Behavior of the VPV in function of the water
cement ratio and of the tenors of replacement of the natural aggregates for the recycled ones.
Table 5 Performance of recycled aggregate concrete
about VPV when varying the tenor of replacement and fixing the water/cement ratio
Recycled aggreagte type Tenor of
replacement rmc rcc rrcc rmf rcf rrcf
0% 1.00 1.00 1.00 1.00 1.00 1.00
50% 1.24 1.20 1.32 1.10 1.15 1.15
100% 1.47 1.40 1.64 1.20 1.30 1.29
Figure 2 and Table 5 show that the recycled red ceramic coarse aggregate has the worse performance, for the same water/cement ratio, increasing the VPV in 32% and 64% for 50% and 100% of replacement, respectively. This behavior is caused probably due to the angular aggregates shape, even having the same grading of the others. This shape doesn’t provide an efficient grain package and, thus, it produces concrete with more amounts of voids.
aggregates was a little lower than for concrete samples with recycled red ceramic coarse aggregate, reaching an increasing around 22% and 44% for 50% and 100% of replacement, respectively.
The best result was done by the concrete with recycled mortar fine aggregate, which incrased the VPV in only 10%, for 50% of replacement, and 20% for a 100%. The other recycled fine aggregates increased the concrete’s VPV around 15% and 30%, for 50% and 100% of replacement, respectively.
As it can be seen in Figure 2, if the tenor and the type of aggregate is fixed, the VPV values will vary linearly when the water cement ratio modify. The greater the water cement ratio, the greater the VPV, once there is more available water in the concrete, the concrete becomes more permeable. This behavior can be confirmed observing the values in Table 6, once the concrete that has water cement ratio equal to 0.60 and 0.74 has the VPV increased 6% and 12%, respectively. These results are in agreement with other authors results [9].
Table 6 Performance of recycled aggregate concrete in
relation to VPV with water/cement ratio varying and constant tenor of replacement
Water/cement ratio VPV increasing
0.46 1.00 0.60 1.06 0.74 1.12
However, the combined effect of the water cement ratio and the natural aggregate’s replacement decrease when the water/cement ratio increases. This means that for high water/cement ratios, the recycled aggregates influence less in the VPV, once there is already enough free water to enable the formation of a porous sctructure. Tables 7 and 8 show the increase in VPV values when varing the water cement ratio and the percentage of replacement.
Table 7 Increasing in VPV values when varing the
water/cement ratio and the percentage of replacement of natural coarse agregates to recycled coarse aggregates
Recycled coarse aggregate
50% 100%
w/c Ref. rcc rrcc rmc rcc rrcc rmc 0,46 1,00 1,20 1,32 1,24 1,40 1,64 1,47 0,60 1,06 1,28 1,40 1,31 1,49 1,74 1,56 0,74 1,12 1,34 1,47 1,38 1,56 1,83 1,64
Table 8 Increasing in VPV values when varing the
water/cement ratio and the percentage of replacement of natural fine agregates to recycled fine aggregates
Recycled fine aggregate
50% 100%
w/c Ref. rcf rrcf rmf rcf rrcf rmf 0,46 1,00 1,15 1,15 1,10 1,30 1,29 1,20 0,60 1,06 1,22 1,22 1,17 1,38 1,37 1,28 0,74 1,12 1,28 1,28 1,23 1,45 1,44 1,34
As it can be seen analyzing the data in Table 7 and 8, the worst result is showed to the replacement of natural coarse aggregate to recycled red ceramic coarse aggregate, once the VPV increases 83%, 74% and 64% for 100% of replacement, for water cement ratio equal to 0.46, 0.60 and 0.74, respectively.
The best performance was obtained by the recycled mortar fine aggregate, nevertheless the VPV was increased in 28%, 22% and 15% for 100% of replacement, for water cement ratio equals to 0.46, 0.6 and 0.74, respectively.
5. CONCLUSION
The replacement of natural aggregates by the recycled ones, incresed the VPV of all concrete samples. The replacement of the coarse aggregates influences more the VPV's concrete behavior than the replacement of the fine ones. The recycled red ceramic coarse aggregate had the worst performance and the recycled mortar fine aggregate the best.
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