Durability and Time-Dependent Properties of Low-Cement Concrete
Abstract
:1. Introduction
2. Research Significance
3. Experimental Program
3.1. Concrete Formulation
3.2. Workability and Mechanical Properties of Concrete
3.3. Durability and Time-Dependent Tests
4. Results and Discussion
4.1. Shrinkage
4.2. Creep
4.3. Water Absorption by Immersion
4.4. Capillary Water Absorption
4.5. Carbonation
4.6. Lifetime of Structures and Minimum Concrete Cover Regarding Carbonation
5. Conclusions
- Shrinkage: (i) LCC concrete with high compactness of 0.86 and reduced powder dosage (250 kg/m3) promotes reduced shrinkage, tending to increase with the increase of cement dosage; however, in concrete with powder dosage of 350 kg/m3, the increase of compactness tends to gradually decrease shrinkage; (ii) due to the inadequacy of the EC2 prediction of shrinkage, compared to experimental values, a correction is proposed to improve the curves development, where a βshape coefficient assumes different values (0.06 for concrete with powder of 350 kg/m3 and 0.08 for concrete with powder of 250 kg/m3); (iii) beyond the parameters considered by the concrete codes, the concrete compactness has a noticeable influence on the amplitude of concrete shrinkage, mainly when combined with reduced binder powder (250 kg/m3) and very reduced cement dosage, where the experimental/prediction ratio of shrinkage can go down to 0.4.
- Creep: (i) the granulometric reference curve (Faury vs. Alfred), in concrete with reduced binder powder (250 kg/m3), does not have a relevant influence on the evolution and amplitude of creep coefficient; (ii) similarly to the known behavior of current concrete, the creep coefficient is highly influenced by the concrete strength; thus, LCC presents reduction of creep coefficient for concrete with high compactness (0.86) and higher cement dosage (175 kg/m3), which has also higher strength; (iii) a divergence between the shape of the creep curve experimentally obtained and that according to EC2 is noticeable; however, the shape of the creep curve can be improved significantly by adjusting the αt coefficient on βc (t,t0) parameter, from 0.30 to 0.15, for LCC; (iv) there is a huge difference between experimental and EC2 predicted values for the creep of LCC, mainly in concretes with lower cement dosage and with lower compactness (0.80 to 0.81), thus with higher W/B ratio, the creep being ratio experimental/code around 0.3; (v) W/Ceq ratio has a significant influence on that difference, therefore, a corrective parameter is proposed to be included on the β (fcm) coefficient of EC2 to significantly improve the code prediction, namely , which was obtained by correlation analysis.
- Water absorption by immersion: (i) the increase of compactness has a great influence on the reduction of water absorption, since the values for concretes with lower compactness (0.80 to 0.81) are close to 15% and those values reduce to below 10% for concretes with compactness of 0.86; (ii) the W/Ceq ratio also has an influence on absorption, although it is less significant; thus, the relation that incorporates compactness and that ratio, (W/Ceq)0.2/Compactness6, proved by correlation analysis, has high influence on water absorption.
- Water absorption by capillarity: (i) high compactness of LCC combined with higher cement dosage significantly reduces the capillary absorption; (ii) fly ash addition as partial replacement of cement also promotes a significant decrease in capillary absorption; however, its excessive dosage may jeopardize the concrete performance regarding capillarity; (iii) the capillary coefficients of the LCC characterized allow all concretes to be classified as high quality, except the one with reduced compactness (0.81) and very reduced cement dosage (75 kg/m3).
- Carbonation resistance: (i) maintaining the cement dosage, compactness increase has a significant influence on reducing carbonation depth, since the LC series (concrete with high compactness of 0.86 and with 250 kg/m3 of binder powder) exhibits much lower carbonation depth than the corresponding C series (concrete with lower compactness and 350 kg/m3 of binder powder); (ii) maintaining the binder dosage, the carbonation depth decreases with the increase of cement or equivalent cement dosages, since it reduces the W/Ceq ratio; (iii) the higher the amount of fly ash incorporated in the concrete, replacing cement dosage, the lower the carbonation resistance, because it increases the carbonation velocity; (iv) it is possible to produce concrete with good structural performance, with low binder powder of 250 kg/m3 and only 175 kg/m3 of cement dosage, developing higher carbonation resistance, in circa 10%, than current formulation concrete with 250 kg/m3 of cement dosage and binder powder of 350 kg/m3.
- Minimum cover required to avoid corrosion induced by carbonation: (i) it is necessary to use a minimum cement dosage, since only concretes with cement dosage equal or higher than 175 kg/m3 (even though with very different formulation parameters) have adequate resistance to carbonation for general exposure; for those concretes the minimum required covers are lower than those presented in EC2, reaching differences of up to 17 mm; (ii) the compactness increase has also high influence on reducing the minimum cover, since it increases the concrete strength and carbonation resistance; reducing the concrete compactness implies increasing the cover, even if higher cement dosage is used; the LCC with 175 kg/m3 of cement and compactness of 0.86 presents much higher resistance to carbonation compared to that of all formulated concrete, including those with equivalent cement dosage between 200 and 250 kg/m3.
- Lifetime of structures due to carbonation exposure: (i) higher cement dosages promotes longer lifetime; concretes with at least 175 kg/m3 of cement dosage have, submitted to XC2 and XC3 conditions, service lifetime values above the minimum, for current (50 years) and special (100 years) structures and, for XC2, the values are quite high; (ii) for special structures and under XC4 in wet conditions, only the LC175 and C250 have adequate performance, the first due to the high compactness and the latter due to higher cement dosage, being the only mixtures with an expected lifetime of more than 100 years.
- LCC mixtures with a good performance and a long lifetime: (i) concrete with at least 175 kg/m3 of cement dosage reveals adequate combined mechanical, time-dependent and durability performances; (ii) concrete LC175 (with high compactness of 0.86 and powder dosage of only 250 kg/m3) is revealed to be the most eco-efficient of the concretes studied herein, since for current and special structures, and for any type of XC exposure, it is possible to reduce the cover below the standard minimum, presenting a long lifetime; (iii) the amount of cement can be reduced between 37.5% and 42%, depending on the environmental exposure classes XC, comparing the LCC concrete which contains only 175 kg/m3 of cement with the minimum recommendation of 280 kg/m3, for XC2 and XC3, and 300 kg/m3 for XC4.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Constituents | LC75 | LC75F | C75 | LC125 | LC125F | C125 | LC175 | LC175F | C175B | C200B | LC250A | C250 |
---|---|---|---|---|---|---|---|---|---|---|---|---|
C (kg/m3) | 75 | 75 | 75 | 125 | 125 | 125 | 175 | 175 | 175 | 200 | 250 | 250 |
Lf (kg/m3) | 75 | 75 | 75 | 125 | 125 | 125 | 75 | 75 | 100 | 150 | - | 100 |
FA (kg/m3) | 100 | 100 | 200 | - | - | 100 | - | - | 75 | - | - | - |
SKY (kg/m3) | 2.3 | 2.3 | 0.7 | 2.5 | 2.5 | 0.8 | 2.6 | 2.6 | 2.1 | 1.0 | 0.8 | 1.0 |
W (kg/m3) | 118 | 118 | 169 | 118 | 118 | 169 | 118 | 118 | 128 | 144 | 179 | 169 |
S0/3 (kg/m3) | 44 | 587 | 286 | 44 | 671 | 371 | 44 | 747 | 181 | 186 | 218 | 492 |
S0/4 (kg/m3) | 1068 | 308 | 585 | 1080 | 244 | 520 | 1084 | 210 | 762 | 742 | 817 | 427 |
G4/8 (kg/m3) | 284 | 78 | 106 | 287 | 82 | 110 | 288 | 98 | 92 | 96 | 278 | 116 |
C6/14 (kg/m3) | 623 | 1050 | 798 | 631 | 1049 | 797 | 633 | 997 | 894 | 869 | 587 | 795 |
Total aggregates (kg/m3) | 2018 | 2023 | 1774 | 2042 | 2047 | 1798 | 2048 | 2053 | 1929 | 1893 | 1900 | 1831 |
W/C | 1.57 | 1.57 | 2.26 | 0.94 | 0.94 | 1.35 | 0.67 | 0.67 | 0.73 | 0.72 | 0.72 | 0.68 |
Equiv.-cement, Ceq (kg/m3) | 85 | 85 | 85 | 125 | 125 | 142 | 175 | 175 | 198 | 200 | 250 | 250 |
W/Ceq | 1.39 | 1.39 | 1.99 | 0.94 | 0.94 | 1.19 | 0.67 | 0.67 | 0.65 | 0.72 | 0.72 | 0.68 |
W/B | 0.47 | 0.47 | 0.48 | 0.47 | 0.47 | 0.48 | 0.47 | 0.47 | 0.37 | 0.41 | 0.72 | 0.48 |
Compactness | 0.86 | 0.86 | 0.81 | 0.86 | 0.86 | 0.81 | 0.86 | 0.86 | 0.86 | 0.84 | 0.80 | 0.81 |
LCC Mixtures | fcm,7 (MPa) | fcm,28 (MPa) | fcm,56 (MPa) | Ecm (GPa) | fctm,f (MPa) | fctm,sp (MPa) | Slump (mm) | D_Comp |
---|---|---|---|---|---|---|---|---|
LC75 | 11.6 | 20.6 | 26.5 | 37.4 | 3.2 | 1.5 | - | 1.21 |
LC75F | 15.7 | 22.1 | - | 28.7 | - | - | 50 | - |
C75 | 7.6 | 15.2 | 20.5 | - | 2.1 | 0.7 | 90 | - |
LC125 | 25.2 | 28.9 | 33.9 | 40.6 | 4.5 | 2.3 | - | 1.23 |
LC125F | 26.4 | 29.4 | - | 34.5 | - | - | 45 | - |
C125 | 14.3 | 20.3 | 26.5 | - | 3.6 | 1.5 | 120 | - |
LC175 | 35.0 | 44.7 | 50.2 | 42.4 | 6.9 | 3.4 | - | 1.25 |
LC175F | 36.8 | 45.9 | - | 38.2 | - | - | 65 | - |
C175B | 36.2 | 50.1 | 52.9 | 47.9 | 5.7 | 3.2 | 107 | - |
C200B | 32.9 | 38.2 | 39.1 | 41.3 | 5.8 | 3.0 | 110 | - |
LC250A | 25.8 | 30.5 | 34.3 | 38.1 | 5.1 | 2.2 | - | 1.16 |
C250 | 34.9 | 39.1 | 41.5 | 36.5 | 5.4 | 2.9 | 80 | - |
Cd (mm) | |||||
---|---|---|---|---|---|
LCC Mixtures | Days | ||||
3 | 7 | 14 | 28 | 42 | |
LC75 | 10.0 | 15.0 | 23.3 | 36.5 | 43.3 |
C75 | 17.5 | 22.5 | 39.0 | 49.9 | - |
LC125 | 5.5 | 11.0 | 15.3 | 21.8 | 26.4 |
C125 | 10.0 | 15.5 | 20.0 | 27.8 | 33.5 |
LC175 | 2.0 | 3.5 | 5.8 | 9.0 | 10.0 |
C175B | - | 4.8 | - | 10.3 | 12.9 |
C200B | - | 5.3 | - | 12.3 | 14.7 |
LC250A | 4.5 | 6.5 | 10.3 | 15.8 | 18.1 |
C250 | 3.5 | 5.0 | 8.3 | 10.0 | 11.0 |
RC65 (kg·year/m5) | ||||||
---|---|---|---|---|---|---|
LCC Mixtures | - | - | Days | - | - | Average |
3 | 7 | 14 | 28 | 42 | ||
LC75 | 15 | 15 | 13 | 10 | 11 | 13 |
C75 | 5 | 7 | 5 | 6 | - | 5 |
LC125 | 49 | 29 | 30 | 29 | 30 | 33 |
C125 | 15 | 14 | 17 | 18 | 18 | 17 |
LC175 | 370 | 282 | 209 | 170 | 207 | 248 |
C175B | - | 153 | - | 129 | 125 | 125 |
LC250A | 73 | 82 | 66 | 56 | 63 | 68 |
C200B | - | 123 | - | 91 | 15 | 80 |
C250 | 121 | 138 | 101 | 138 | 171 | 134 |
Intended Service Lifetime | Propagation Time and Period of Initiation | XC2 (Wet, Rarely Dry) | XC3 (Moderate Humidity) | XC4 (Dry Regime) | XC4 (Wet Regime) |
---|---|---|---|---|---|
tg = 50 years (RC2) | tp (years) | 10 | 45 | 15 | 5 |
tic (years) | 92 | 12 | 80 | 105 | |
tg = 100 years (RC3) | tp (years) | 20 | 90 | 20 | 10 |
tic (years) | 224 | 28 | 224 | 252 |
Minimum Cover cmin,dur (mm) | ||||||||
---|---|---|---|---|---|---|---|---|
Structural Class | Current Structures (Class S4) | Special Structures (Class S5) | ||||||
Exposure Classes | XC2 | XC3 | XC4 (Dry Reg.) | XC4(Wet Reg.) | XC2 | XC3 | XC4 (Dry Reg.) | XC4 (Wet Reg.) |
EC2 | 25 | 25 | 30 | 30 | 30 | 35 | ||
LC75 | 34 | 51 | 69 | 77 | 45 | 78 | 106 | 111 |
C75 | 50 | 75 | 102 | 114 | 67 | 115 | 156 | 163 |
LC125 | 21 | 32 | 43 | 48 | 29 | 49 | 66 | 70 |
C125 | 30 | 45 | 61 | 67 | 40 | 68 | 93 | 97 |
LC175 | 8 | 12 | 16 | 18 | 10 | 18 | 24 | 25 |
C175B | 11 | 16 | 22 | 25 | 15 | 25 | 34 | 36 |
LC250A | 15 | 22 | 30 | 34 | 20 | 34 | 46 | 49 |
C200B | 13 | 19 | 25 | 28 | 17 | 29 | 39 | 41 |
C250 | 11 | 16 | 22 | 24 | 14 | 24 | 33 | 35 |
Structural Class | Current and Special Structures (Classes S4 and S5) | ||||
---|---|---|---|---|---|
Type of Cement | CEM I; CEM II/A (1) | ||||
Exposure Class | XC2 | XC3 | XC4 (Wet and Dry Reg.) | ||
EN 206 | Minimum dosage of C (kg/m3) | 280 | 280 | 300 | |
Maximum W/C ratio | 0.60 | 0.55 | 0.50 | ||
- | - | Total powder (kg/m3) | Equivalent dosage of cement, Ceq (kg/m3) | W/Ceq | |
- | Concretes | LC75 | 250 | 85 | 1.39 |
LC125 | 125 | 0.94 | |||
LC175 | 175 | 0.67 | |||
LC250A | 250 | 0.47 | |||
C75 | 350 | 85 | 2.25 | ||
C125 | 142 | 0.97 | |||
C175B | 198 | 0.73 | |||
C200B | 200 | 0.72 | |||
C250 | 250 | 0.68 |
Structural Class | Current Structures (Class S4, RC2, 50 Years) | Special Structures (Class S5, RC3, 100 Years) | |||||||
---|---|---|---|---|---|---|---|---|---|
Exposure Class | XC2 | XC3 | XC4 (Dry Reg.) | XC4 (Wet Reg.) | XC2 | XC3 | XC4 (Dry Reg.) | XC4 (Wet Reg.) | |
Concretes | cmin,dur (mm) | 25 | 30 | 30 | 35 | ||||
LC75 | tg (years) | 25 | 46 | 19 | 9 | 42 | 91 | 25 | 15 |
C75 | 15 | 46 | 17 | 7 | 27 | 91 | 22 | 12 | |
LC125 | 75 | 48 | 29 | 19 | 114 | 94 | 37 | 27 | |
C125 | 33 | 47 | 21 | 11 | 53 | 92 | 27 | 17 | |
LC175 | >>>> 200 | 69 | 179 | 169 | >> 200 | 119 | 216 | 206 | |
C175B | >> 200 | 57 | 86 | 76 | >> 200 | 104 | 105 | 95 | |
LC250A | >> 200 | 51 | 49 | 39 | >> 200 | 98 | 60 | 50 | |
C200B | >> 200 | 54 | 67 | 57 | >> 200 | 101 | 82 | 72 | |
C250 | >> 200 | 58 | 92 | 82 | >> 200 | 105 | 113 | 103 |
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Robalo, K.; Soldado, E.; Costa, H.; Carvalho, L.; do Carmo, R.; Júlio, E. Durability and Time-Dependent Properties of Low-Cement Concrete. Materials 2020, 13, 3583. https://doi.org/10.3390/ma13163583
Robalo K, Soldado E, Costa H, Carvalho L, do Carmo R, Júlio E. Durability and Time-Dependent Properties of Low-Cement Concrete. Materials. 2020; 13(16):3583. https://doi.org/10.3390/ma13163583
Chicago/Turabian StyleRobalo, Keila, Eliana Soldado, Hugo Costa, Luís Carvalho, Ricardo do Carmo, and Eduardo Júlio. 2020. "Durability and Time-Dependent Properties of Low-Cement Concrete" Materials 13, no. 16: 3583. https://doi.org/10.3390/ma13163583