1 Introduction
2 Materials
2.1 Cement
SiO2 | Al2O3 | Fe2O3 | CaOtotal | MgO | SO3 | K2O | Na2O | C3S | C2S | C3A | C4AF |
---|---|---|---|---|---|---|---|---|---|---|---|
19.8 | 5.14 | 2.3 | 64.9 | 0.9 | 3.4 | 1.1 | 0.005 | 58 | 13 | 10 | 6.99 |
2.2 Aggregates
Sand | G1 | G2 | GR1 | GR2 | |
---|---|---|---|---|---|
Dry bulk density (kg/m3) | 2,550 | 2,510 | 2,510 | 2,240 | 2,240 |
Water absorption, ω
a
(%) | 1.7 ± 0.03 | 1.6 ± 0.07 | 1.8 ± 0.05 | 8.2 ± 0.5 | 6.5 ± 0.4 |
Fineness modulus | 2.82 | – | – | – | – |
2.3 Superplasticizer
3 Mix Method and Concrete Proportions
-
only coarse natural aggregates are replaced by recycled ones with three volumetric replacement ratios 30, 65 and 100 %;
-
the granular skeleton is constituted of a ternary mixture of sand and two gravels G1 (4/10 mm) and G2 (10/20 mm);
-
at fresh state, all concretes are of S4 workability class where the target slump with the Abrams’s cone is 18 ± 1 cm. According to the standard NF EN 206-1 the slump for a S4 flowability is comprised between 16 and 21 cm;
-
at hardened state a compressive strength comprised between 35 and 43 MPa must be guaranteed at the age of 28 days;
-
concretes are designated for XF2 class of environmental exposure according to the standard NF EN 206-1, where water to cement ratio (W/C) is lower than or equal 0.5 and the minimum cement content is higher than 300 kg/m3.
3.1 Optimization of Water to Cement Ratio
3.2 Optimization of Solid Skeleton
Sand | Natural aggregates | Recycled aggregates | |||
---|---|---|---|---|---|
G1 | G2 | GR1 | GR2 | ||
Packing density | 0.894 ± 0.027 | 0.885 ± 0.002 | 0.886 ± 0.001 | 0.866 ± 0.002 | 0.875 ± 0.011 |
NAC | RAC30 | RAC65 | RAC100 | |
---|---|---|---|---|
0.67 | 0.82 | 1.51 | – | |
0.50 | 0.53 | 0.67 | – | |
– | 0.82 | 1.51 | 1.50 | |
– | 0.52 | 0.67 | 0.67 |
3.3 Mix Proportions of all Components
NAC | RAC30 | RAC65 | RAC100 | |
---|---|---|---|---|
Cement (kg/m3) | 360 | 360 | 427 | 448 |
Effective water, Weff (kg/m3) | 180 | 180 | 180 | 180 |
Additional water, w
a
(kg/m3) | – | 10 | 42 | 53 |
Sand (kg/m3) | 703 | 780 | 957 | 930 |
Natural aggregates G1 (4/10 mm) (kg/m3) | 346 | 227 | 88 | – |
Natural aggregates G2 (10/20 mm) (kg/m3) | 692 | 429 | 131 | – |
Recycled aggregates GR1 (4/10 mm) (kg/m3) | – | 86 | 145 | 218 |
Recycled aggregates GR2 (10/20 mm) (kg/m3) | – | 164 | 218 | 326 |
Superplasticizer (kg/m3) | 1.25 | 1.25 | 1.25 | 1.25 |
Effective water/cement (Weff/C) | 0.50 | 0.50 | 0.42 | 0.40 |
Total water/cement (W/C) | 0.50 | 0.52 | 0.52 | 0.52 |
Paste volume (%) | 29.6 | 30.6 | 36.0 | 37.8 |
Theoretical density (kg/m3) | 2,280 | 2,236 | 2,188 | 2,155 |
Experimental density (kg/m3) | 2,287 ± 3 % | 2,224 ± 2 % | 2,190 ± 1 % | 2,159 ± 1 % |
3.4 Test Methods
4 Test Results
4.1 Properties of the Fresh Concretes
Mix | Slump (cm) | Air content (%) |
---|---|---|
NAC | 18 ± 0.7 | 1.6 ± 0.3 |
RAC30 | 19.3 ± 1.5 | 1.8 ± 0.1 |
RAC65 | 18.5 ± 1.0 | 2.0 ± 0.2 |
RAC100 | 20 ± 1.4 | 2.5 ± 0.2 |
4.2 Properties of the Hardened Concrete Specimens
4.2.1 Water Porosity
4.2.2 Compressive Strength
4.2.3 Elastic Modulus
4.2.4 Flexural and Splitting Tensile Strengths
4.2.5 Analysis of Peak Strain and Stress–Strain Relationship Under Compression
5 Prediction of Stress–Strain Relationship and the Applicability of EC2
Author | Nature of aggregates | Test conditions | Compressive strength (MPa) | Elastic modulus (MPa) |
---|---|---|---|---|
Ali et al. (1990) | Natural | Not communicated | 16.7 | 13,820 |
25.3 | 19,980 | |||
27.7 | 23,530 | |||
32.0 | 33,980 | |||
43.5 | 44,550 | |||
Assié (2004) | Natural | Stress rate 0.5 MPa/s | 22.6 | 28,400 |
40.6 | 36,400 | |||
55.1 | 38,200 | |||
69.2 | 36,100 | |||
Belén et al. (2011) | Natural | Controlled load rate 8.77 kN/s | 44.81 | 34,374 |
31.92 | 30,645 | |||
80 % natural + 20 % recycled | 43.74 | 33,192 | ||
31.71 | 29,598 | |||
50 % natural + 50 % recycled | 37.45 | 30,321 | ||
32.35 | 27,459 | |||
Recycled | 40.54 | 24,817 | ||
30.13 | 25,935 | |||
El-Hilali (2009) | Natural | Stress rate 0.5 MPa/s | 35.12 | 25,130 |
42.12 | 32,660 | |||
56.46 | 34,660 | |||
60.84 | 37,660 | |||
61.00 | 38,660 | |||
77.95 | 48,850 | |||
31.26 | 27,260 | |||
38.18 | 33,660 | |||
53.46 | 35,660 | |||
59.31 | 39,660 | |||
60.52 | 40,330 | |||
75.21 | 51,260 | |||
30.32 | 29,800 | |||
36.68 | 35,330 | |||
52.56 | 36,660 | |||
55.72 | 40,330 | |||
57.51 | 41,660 | |||
71.95 | 53,230 | |||
Casuccio et al. (2008) | Natural | Stress rate | 18.10 | 27,100 |
37.50 | 33,100 | |||
48.40 | 39,900 | |||
Recycled | 18.00 | 23,400 | ||
36.40 | 28,800 | |||
44.40 | 34,200 | |||
Recycled | 15.40 | 22,600 | ||
35.70 | 28,300 | |||
43.80 | 32,700 | |||
Cedolin and Cusatis (2008) | Natural | Not communicated | 28.50 | 24,200 |
33.70 | 32,680 | |||
49.60 | 28,690 | |||
54.80 | 28,600 | |||
Wee et al. (1996) | Natural | Strain rate 0.07 mm/min | 42.7 | 37,600 |
63.2 | 41,800 | |||
70.2 | 43,000 | |||
65.1 | 41,500 | |||
70.5 | 40,400 | |||
69.7 | 41,500 | |||
71.5 | 41,400 | |||
63.6 | 42,600 | |||
85.9 | 45,000 | |||
90.2 | 44,400 | |||
78.3 | 44,300 | |||
85.9 | 44,300 | |||
81.2 | 43,900 | |||
88.1 | 44,500 | |||
81.6 | 43,800 | |||
82.6 | 44,200 | |||
84.8 | 47,200 | |||
85.6 | 45,600 | |||
96.2 | 46,600 | |||
46.4 | 35,200 | |||
65.8 | 40,800 | |||
73.9 | 41,600 | |||
87.6 | 44,500 | |||
93.1 | 45,400 | |||
95.3 | 45,200 | |||
100.6 | 45,800 | |||
102.1 | 46,100 | |||
102.8 | 46,700 | |||
106.3 | 48,400 | |||
104.2 | 46,300 | |||
92.8 | 45,800 | |||
94.6 | 47,300 | |||
94 | 46,300 | |||
96.6 | 46,500 | |||
91.5 | 45,900 | |||
93.6 | 47,100 | |||
91.7 | 46,000 | |||
119.9 | 49,100 | |||
125.6 | 50,900 | |||
Gesoglu et al. (2002) | Natural | 77.2 | 47,100 | |
71.5 | 48,000 | |||
66.5 | 46,800 | |||
70.7 | 47,300 | |||
61.8 | 45,400 | |||
68.9 | 47,600 | |||
59.1 | 40,900 | |||
62.2 | 45,400 | |||
75.8 | 43,000 | |||
67.7 | 48,200 | |||
53.6 | 46,200 | |||
57.9 | 44,500 | |||
92.9 | 46,400 | |||
94 | 48,300 | |||
97.7 | 47,000 | |||
102 | 48,800 | |||
93.7 | 50,500 | |||
86.2 | 47,100 | |||
87.9 | 43,000 | |||
82.7 | 45,400 | |||
79.1 | 44,700 | |||
85.3 | 45,000 | |||
86.9 | 46,100 | |||
90.7 | 48,100 | |||
89.5 | 47,600 | |||
87.8 | 45,400 | |||
90.3 | 45,000 | |||
95.2 | 50,800 | |||
92.2 | 50,000 | |||
97.6 | 49,300 | |||
87.5 | 48,500 | |||
87.2 | 41,100 | |||
80.4 | 43,200 | |||
86.5 | 44,200 | |||
83.9 | 44,300 | |||
80.9 | 44,600 | |||
84.5 | 45,300 | |||
85.7 | 45,100 | |||
Wu et al. (2001) | Natural | Not communicated | 98.2 | 48,200 |
70.4 | 39,500 | |||
65.8 | 36,200 | |||
60.5 | 31,500 | |||
62.1 | 31,000 | |||
44.8 | 37,500 | |||
43.2 | 28,300 | |||
46.6 | 30,100 | |||
45.0 | 29,000 | |||
Shannag (2000) | Natural | 68.0 | 38,500 | |
77.0 | 47,200 | |||
86.0 | 43,800 | |||
86.0 | 42,300 | |||
89.5 | 38,600 | |||
90.5 | 36,200 | |||
Baalbaki et al. (1991) | Natural | 105.0 | 42,000 | |
106.0 | 44,000 | |||
111.0 | 41,000 | |||
99.3 | 45,000 | |||
99.7 | 42,000 | |||
95.3 | 40,000 | |||
98.0 | 40,000 | |||
103.0 | 40,000 | |||
90.8 | 42,000 | |||
89.2 | 41,000 | |||
Domingo-Cabo et al. (2009) | Natural | Not communicated | 42.8 | 32,153 |
20 % recycled + 80 % natural | 42.7 | 31,178 | ||
50 % recycled + 50 % natural | 41.3 | 31,204 | ||
Recycled | 41.8 | 31,589 | ||
Fares (2009) | Natural | Stress rate 0.5 MPa/s | 36.6 | 36,110 |
52.7 | 39,000 | |||
40.8 | 43,930 | |||
Etxeberria et al. (2007) | Natural | UNE 83-304-84 | 29.0 | 32,561,7 |
25 % recycled + 75 % natural | 28.0 | 31,300,4 | ||
50 % recycled + 50 % natural | 29.0 | 28,591,7 | ||
Recycled | 28.0 | 27,764 | ||
Evangelista and de Brito (2007) | Natural | NP EN 12390-5 | 59.3 | 35,500 |
30 % recycled + 70 % natural | 57.1 | 34,200 | ||
Recycled | 54.8 | 28,900 | ||
Gomez-Soberon (2002) | Natural | Not communicated | 39.0 | 29,700 |
15 % recycled + 85 % natural | 38.1 | 29,100 | ||
30 % recycled + 70 % natural | 37.0 | 27,800 | ||
60 % recycled + 40 % natural | 35.8 | 26,600 | ||
Recycled | 34.5 | 26,700 | ||
Karihaloo et al. (2006) | Natural | Not communicated | 55.0 | 36,900 |
60.0 | 38,300 | |||
100.0 | 43,000 | |||
Natural | 18.5 | 26,772 | ||
33.2 | 28,832 | |||
58.0 | 35,794 | |||
31.3 | 29,940 | |||
47.4 | 33,720 | |||
82.8 | 40,570 | |||
32.6 | 28,790 | |||
45.8 | 33,400 | |||
85.7 | 39,570 | |||
34.9 | 26,510 | |||
55.3 | 31,580 | |||
66.9 | 34,350 | |||
88.8 | 38,140 | |||
Martínez-Lage et al. (2012) | Natural | Controlled strain rate 16 µε/s | 30.5 | 29,500 |
50 % recycled +50 % natural | 26.8 | 24,190 | ||
Recycled | 20.4 | 19,765 | ||
Zhao et al. (2008) | Natural | Not communicated | 43.8 | 31,400 |
43.4 | 39,200 | |||
50.9 | 35,700 | |||
56.4 | 35,900 | |||
50.2 | 41,000 | |||
50.8 | 38,900 | |||
40.0 | 33,600 | |||
51.7 | 39,600 | |||
Dong and Keru (2001) | Natural | Not communicated | 60.5 | 34,900 |
60.5 | 32,700 | |||
62.1 | 35,000 | |||
83.6 | 44,900 | |||
98.2 | 45,100 | |||
63.0 | 39,800 | |||
72.5 | 46,100 | |||
77.4 | 38,500 | |||
76.5 | 40,300 | |||
70.2 | 42,800 | |||
73.8 | 36,600 | |||
75.1 | 38,600 | |||
77.0 | 35,200 | |||
76.8 | 39,700 | |||
90.3 | 48,700 | |||
91.2 | 42,600 | |||
96.7 | 41,700 | |||
85.5 | 42,100 | |||
113.7 | 48,000 | |||
35.9 | 29,600 | |||
43.3 | 28,900 | |||
45.8 | 34,700 | |||
58.0 | 33,000 | |||
59.7 | 34,000 | |||
Wardeh et al. (2010) | Natural | Strain rate 1 mm/min | 46.5 | 35,000 |
Praveen et al. (2004) | Natural | Not communicated | 36.7 | 27,527 |
54.6 | 33,470 | |||
70.8 | 37,614 | |||
Shen et al. (2009) | Natural | Loading rate 10 kN/s | 28.6 | 25,130 |
40.0 | 29,840 | |||
57.9 | 32,040 | |||
32.1 | 25,420 | |||
42.2 | 26,000 | |||
52.1 | 30,020 | |||
48.8 | 27,800 | |||
56.0 | 28,670 | |||
68.8 | 33,030 | |||
Kang et al. (2014) | Natural | ASTM C39/C39 M | 65.4 | 37,700 |
15 % recycled + 85 % natural | 59.4 | 36,200 | ||
30 % recycled + 70 % natural | 48.4 | 32,800 | ||
Natural | 38.6 | 29,200 | ||
15 % recycled + 85 % natural | 32.7 | 29,200 | ||
30 % recycled + 70 % natural | 31.7 | 26,500 | ||
50 % recycled + 50 % natural | 29 | 25,300 |
Author | Nature of aggregates | Test conditions | Compressive strength (MPa) | Strain at peak stress |
---|---|---|---|---|
Belén et al. (2011) | Natural | Controlled strain rate 16 µε/s | 44.8 | 0.00190 |
31.9 | 0.00174 | |||
80 % natural + 20 % recycled | 43.7 | 0.00189 | ||
31.7 | 0.00199 | |||
50 % natural + 50 % recycled | 37.5 | 0.0019 | ||
32.4 | 0.00195 | |||
Recycled | 40.5 | 0.00219 | ||
30.1 | 0.00216 | |||
Martínez-Lage et al. (2012) | Natural | Controlled strain rate 16 µε/s | 30.5 | 0.0021 |
50 % natural + 50 % recycled | 26.8 | 0.0023 | ||
Recycled | 20.4 | 0.0025 | ||
Wee et al. (1996) | Natural | Strain rate 0.07 mm/min | 63.2 | 0.00216 |
70.2 | 0.0021 | |||
65.1 | 0.00216 | |||
70.5 | 0.00206 | |||
69.7 | 0.00212 | |||
71.5 | 0.00213 | |||
63.6 | 0.00228 | |||
85.9 | 0.00226 | |||
90.2 | 0.00243 | |||
78.3 | 0.00232 | |||
85.9 | 0.00231 | |||
81.2 | 0.00224 | |||
88.1 | 0.00227 | |||
81.6 | 0.00211 | |||
82.6 | 0.00216 | |||
84.8 | 0.00252 | |||
85.6 | 0.00232 | |||
96.2 | 0.00237 | |||
73.9 | 0.00243 | |||
87.6 | 0.00243 | |||
93.1 | 0.00244 | |||
95.3 | 0.00242 | |||
100.6 | 0.00258 | |||
102.1 | 0.00256 | |||
102.8 | 0.00247 | |||
106.3 | 0.00251 | |||
104.2 | 0.00249 | |||
92.8 | 0.00242 | |||
94.6 | 0.00228 | |||
96.6 | 0.00232 | |||
91.5 | 0.00228 | |||
93.6 | 0.00219 | |||
91.7 | 0.00266 | |||
119.9 | 0.00275 | |||
125.6 | 0.00273 | |||
Dhonde et al. (2007) | Natural | Stress rate 0.25 MPa/s | 31.2 | 0.00147 |
38.5 | 0.00178 | |||
50.5 | 0.00194 | |||
77.6 | 0.00191 | |||
Praveen et al. (2004) | Natural | Not communicated | 36.7 | 0.002 |
54.6 | 0.0023 | |||
70.8 | 0.0025 | |||
Ali et al. (1990) | Natural | Not communicated | 16.7 | 0.0018 |
25.3 | 0.0021 | |||
27.7 | 0.0021 | |||
32.0 | 0.0022 | |||
43.5 | 0.0022 | |||
Prasad et al. (2009) | Natural | Strain rate | 23.3 | 0.00197 |
39.6 | 0.00235 | |||
Suresh Babu et al. (2008) | Natural | Strain rate | 25.0 | 0.001905 |
31.0 | 0.00207 | |||
31.5 | 0.00209 | |||
25.8 | 0.00199 | |||
28.0 | 0.00203 | |||
Carreira and Chu (1985) | Natural | Not communicated | 20.7 | 0.0018 |
30.5 | 0.0018 | |||
49.5 | 0.00195 | |||
Carreira and Chu (1985) | Natural | Not communicated | 10.7 | 0.0015 |
20.0 | 0.0019 | |||
34.8 | 0.0022 | |||
46.9 | 0.0021 | |||
52.4 | 0.00195 |
6 Conclusion
-
The use of recycled aggregates up to 30 % does not affect the demand of water of concrete, but generates a reduction of 14 % of the compressive strength. By increasing the replacement ratio, the cement content increases to maintain constant W/C ratio causing an increase in the compressive strength which counterbalances the negative effect of recycled aggregates.
-
Recycled aggregate concretes had lower elastic modulus, splitting and flexural tensile strength than normal aggregate one.
-
The strain–stress curves under uniaxial compression show that the post-cracking branch is more spread out compared to NAC. In addition, the peak-strain increases by increasing the replacement ratio. These phenomena are explained by the more progressive and diffuse damage of concrete due to the presence of recycled aggregates.