Materials and Design 40 (2012) 109–116
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The effect of coarse aggregate gradation on the properties of self-compacting concrete Hui Zhao a,⇑, Wei Sun a, Xiaoming Wu b, Bo Gao b a b
School of Materials Science and Engineering, Southeast University, Nanjing, Jiangsu 210096, China Jiangsu Transportation Research Institute, Nanjing, Jiangsu 211112, China
a r t i c l e
i n f o
Article history: Received 4 January 2012 Accepted 20 March 2012 Available online 30 March 2012 Keywords: A. Concrete E. Mechanical properties E. Environmental performance
a b s t r a c t The aim of this paper is to assess the effect of coarse aggregate gradation (A/B ratio, size 5–10 mm coarse aggregate weight/size 10–20 mm coarse aggregate weight) on the properties of self-compacting concrete (SCC). For this purpose, four SCC mixtures with A/B ratio for 4/6, 5/5, 6/4, 7/3 were prepared, the bulk density of aggregate with various A/B ratios was investigated, the effect of A/B ratio on the fresh properties, mechanical properties, porosity and durability properties of SCC was studied. The test results indicated that aggregate with A/B ratio for 6/4 has a maximum bulk density of aggregate, with the change in A/B ratio from 4/6 to 7/3, the initial slump flow, blocking and segregation ratio are decreasing, while the wet density of fresh SCC are increasing. SCC with A/B ratio for 6/4 had a maximum mechanical properties, least porosity, carbonation depth, chloride ion diffusion coefficient. Moreover, the damage of SCC under drying–wetting cycles was evaluated, it was found that SCC with various A/B ratios has a resemble behavior on resistance damage against drying–wetting cycles. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Self-compacting concrete (SCC) has been widely used in civil engineering. SCC can spread to a long distances under its own weight without the need of vibration, therefore, SCC can fill the formwork and encapsulate reinforcement without any bleeding or segregation [1]. Furthermore, application of SCC cannot only lower the noise level on the construction site but also diminish the effect on the environment [2–4]. The introduction of SCC is a major technological advance, which leads to a better quality of concrete and a faster, more economical concrete construction process [5]. The coarse aggregate is the main ingredient in SCC, besides cement, mineral admixture, fine aggregate and Superplasticizers (SPs). The coarse aggregate gradation (A/B ratio, size 5–10 mm coarse aggregate weight/size 10–20 mm coarse aggregate weight) has a larger effect on fresh, mechanical and durability properties of SCC. Nowadays, some research results about the effect of A/B ratio on the properties of concrete have been established, however, the related researches are focused on ordinary concrete (OPC), lightweight concrete (LWC), high-strength concrete (HSC) and high-performance concrete (HPC) [6–12], information about the effect of A/B ratio on the properties of SCC is less documented, therefore, the effect of A/B ratio on the fresh properties, mechanical
⇑ Corresponding author. Tel.: +86 18913806637. E-mail address:
[email protected] (H. Zhao). 0261-3069/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.matdes.2012.03.035
properties, porosity and durability properties of SCC needs more investigate. In this study, fly ash (F) was used to replace 20% Portland Cement, in all SCC mixtures, the binder materials content was kept at 460 kg/m3, the water-to-binder (W/B) ratio by weight is 0.35, the weight ratio of fine aggregate-to-total aggregates is 0.39. Four different A/B ratio (4/6, 5/5, 6/4, 7/3) were used, the bulk density of aggregate with various A/B ratios was investigated, the effect of A/ B ratio on the fresh properties, mechanical properties, porosity and durability properties of SCC was studied, the damage of SCC with various A/B ratios under drying–wetting cycles was also assessed, the relationship between relative compressive strength–relative dynamic elasticity modulus and relative compressive strength– mass loss of SCC under drying–wetting cycles were analyzed. 2. Methodology 2.1. Materials 2.1.1. Cement (C) Ordinary Portland Cement (OPC) according to BS EN 197 [13] was used in this study. The chemical compositions and physical properties of cement are presented in Table 1. 2.1.2. Fly ash (F) Fly ash (F) was used as mineral admixture, which was produced as a by-products during the generation of electricity from a local
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H. Zhao et al. / Materials and Design 40 (2012) 109–116
Table 1 The chemical compositions and physical properties of cement and fly ash. Sample
SiO2
Chemical composition (%) Cement (C) 25.69 Fly ash (F) 56.79 Sample
Specific gravity (g/cm3)
Physical properties Cement (C) 3.01 Fly ash (F) 2.31
Al2O3
CaO
Fe2O3
MgO
SO3
K2O
Na2O
Loss on ignition
6.73 28.21
56.07 <3
3.16 5.31
1.75 5.21
1.78 0.68
0.83 1.34
0.26 0.45
2.97 6.0
Blaine fineness (cm2/g)
3520 3960
Compressive strength (MPa)
Flexural strength (MPa)
3d
7d
28d
3d
7d
28d
27.1 –
38.9 –
50.6 –
5.8 –
7.6 –
8.3 –
coal-fired power plant. The chemical compositions and physical properties of fly ash are given in Table 1. 2.1.3. Superplasticizer (SP) In this study, a polycarboxylate polymer (PCA) with long combtype side chain was used as SP. PCA polymer is the liquid product with a solid content of 20% and has water-reducing ratio of over 30%. 2.1.4. Aggregates The river sand (maximum size of 5 mm) and the natural crushed stone (size 5–10 mm and 10–20 mm) sourced from china were used as fine aggregate and coarse aggregate. The particle size distribution and physical properties of fine and coarse aggregates are presented in Table 2.
0.02 0.017
aggregates were dried at 110 ± 5 °C temperature to constant mass, then, coarse aggregates (size 5–10 mm, size 10–20 mm) were mixed with fine aggregate for 3 min according to certain mix proportions in Table 3, finally, aggregate was filled into 7 L container by three times, each time fill a one-third portion of container, aggregate in the container was compacted by blow 20 times with a metal tamping rod, surplus aggregate was removed from the top of container. The compacted bulk density of aggregate is calculated according to the following equation:
M¼
ðm2 m1 Þ V
ð1Þ
where M = Bulk density of aggregate, kg/m3; m2 = Mass of aggregate plus the container, kg; m1 = Mass of container, kg; V = Volume of container, m3 2.4. Samples preparation and curing conditions
2.2. Mixture proportions In this study, in all SCC mixtures, the binder materials content was kept at 460 kg/m3, which fly ash (F) was used to replace 20% OPC. The water-to-binder (W/B) ratio by weight is 0.35. The amount of total aggregates was maintained at 1780 kg/m3. The weight ratio of fine aggregate (FA)-to-total aggregates (TAs) is 0.39. Four SCC mixtures with A/B ratio for 4/6, 5/5, 6/4, 7/3 were prepared. The mix proportions of SCC are shown in Table 3. 2.3. Bulk density of aggregate The compacted bulk density of aggregate were determined using ASTM C 29/C 29 M-97 test method [14], first, fine and coarse
Table 2 The particle size distribution and physical properties of fine and coarse aggregates. Sieve size (mm)
Stability (%)
Cumulative pass amount (%) Fine aggregate
Coarse aggregate
River sand
5–10 mm
10–20 mm
20 15 10 5 4.75 2.36 1.18 0.6 0.3 0.15 Fineness modulus
– – – 100 95.4 82.8 72.2 52.2 31.0 3.2 2.46
– 100 94 21 6 – – – – – –
95 32 8 4 – – – – – – –
Physical properties Density-OD (kg/m3) Density-SSD (kg/m3) Water absorption (%)
2580 2620 0.80
2635 2680 1.20
2598 2640 1.18
Abbreviations: OD – Density at absolutely dry condition, SSD – Density at saturated surface dry condition.
The components of SCC mixture were batched by weight, cement and fly ash were premixed with fine aggregate and coarse aggregate for 1 min, then, the entire amount of mixing water with the dissolved PCA SP was added and mixed for 3 min, finally, SCC mixture was mixed for an additional 2 min, resulting in a total mixing period of 6 min. Before casting, a variety of test were conducted to determine fresh properties of SCC, i.e. initial slump flow, L-box test, segregation ratio and wet density, SCC samples were cured at 20 °C in molds covered by a polyethylene film to prevent moisture loss according to GOST10180 [15], the samples were removed from the mold after 24 h and cured in a humidity room at a temperature of 20 °C with a relative humidity of 90 ± 5% until the age of testing. 2.5. Test methods 2.5.1. Fresh properties 2.5.1.1. Workability. The initial slump flow test of fresh SCC was conducted according to BS EN 12350 Part 2 [16]. The initial slump flow value of fresh SCC is represented by the mean diameter (measured in two perpendicular directions) of SCC after lifting the standard slump cone. 2.5.1.2. L-box test. The L-box test was performed in accordance with FNARC standards. During the test, fresh SCC was allowed to flow upon the release of a trap door from the vertical section to the horizontal section by a few reinforcement bars of L-shape box. The height of concrete at the end of the horizontal section was compared to the height of concrete remaining in the vertical section. 2.5.1.3. Segregation ratio test. The GTM screen stability test method developed by the French contractor (GTM) [17] was used to assess the segregation resistance of fresh SCC. The method consisted of taking 10 L of SCC and allowing the concrete to stand for 15 min
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H. Zhao et al. / Materials and Design 40 (2012) 109–116 Table 3 Mix proportions of SCC. Mix
W-1 W-2 W-3 W-4
Binders (kg/m3) C
F
368 368 368 368
92 92 92 92
Fine aggregate (kg/m3)
693.81 693.81 693.81 693.81
Coarse aggregate (kg/m3) 5–10 mm (A)
10–20 mm (B)
434.4 544 651.6 760.2
651.6 544 434.4 325.8
in the bucket covered with a lid to prevent evaporation, then, half of SCC mixture was poured onto 5 mm sieve of 350 mm diameter, which sat on a sieve pans on a weighing scale. After 2 min, the mass of mortar passed through the sieve was measured and expressed as a percentage of the weight of the original sample on the sieve. 2.5.1.4. Wet density test. The wet density of fresh SCC was determined using BS EN 12350 Part 6 test method [18]. 2.5.2. Mechanical properties 2.5.2.1. Compressive strength. SCC samples of 100 mm cubes were prepared. The compressive strength test was carried out at the ages of 3, 7, 28, 90 days and after drying–wetting cycles of 0, 15, 30, 45, 60 days according to BS EN 12390 Part 3 [19]. 2.5.2.2. Flexural strength test. SCC samples of 150 mm 150 mm 550 mm prisms were prepared. The flexural strength test was carried out at the ages of 3, 7, 28, 90 days according to BS EN 12390 Part 5 [20]. 2.5.2.3. Dynamic elasticity modulus test. The dynamic elasticity modulus of SCC were tested after drying–wetting cycles of 0, 15, 30, 45, 60 days according to the method described in ASTM C 215 [21]. 2.5.3. Water porosity measurements of SCC Water porosity test was carried out according to the vacuum saturation method [22–24], the cylindrical samples of u50 mm 100 mm were cured in a humidity room at a temperature of 20 °C with a relative humidity of 90 ± 5%, the water porosity test was conducted at curing periods of 3, 7, 28 days. On the scheduled day, the test samples were prepared by cutting cylindrical samples into two halves and cutting 40 ± 2 mm thick slice, u50 mm 40 mm cylindrical samples were dried at 100 ± 5 °C until constant weight, then, samples were placed in desiccators under vacuum (negative) pressure of 1 bar for 3 h, de-aired water was introduced to submerge samples and maintaining negative pressure for a further 3 h, finally, the pressure is released to atmospheric level and samples are left submerged overnight to ensure full saturation. The water porosity of samples was calculated using to the following equation:
P¼
ðW sat W dry Þ 100 ðW sat W wat Þ
ð2Þ
where: P is the water porosity (%), Wsat is the weight of saturated sample in air, Wdry is the weight of sample in oven at 100 ± 5 °C, and Wwat is the weight of saturated sample in water. 2.5.4. Durability properties 2.5.4.1. Accelerated carbonation test. The three 100 mm 100 mm 300 mm prismatic samples of SCC curing 26 days were dried 48 h at 60 °C temperature according to GBJ 82-85 standards [25], the accelerated carbonation test of SCC samples was performed in a chamber with a CO2 concentration = 20 ± 3%, RH = 70 ± 5% and T = 20 ± 3 °C, the half face of SCC samples was sealed
Superplasticizer dosage (%)
Water (kg/m3)
FA/TA (%)
1.4 1.4 1.4 1.4
161 161 161 161
39 39 39 39
with heating the paraffin, leaving the other face exposed to carbonation, then, SCC samples were put into the accelerated carbonation chamber. The accelerated carbonation test was carried out at 3, 7, 14, 28 day exposure durations. 2.5.4.2. Rapid chloride migration (RCM) test. The three u100 mm 200 mm cylinder samples of SCC were used for rapid chloride migration (RCM) tests, SCC samples were cured in a humidity room at a temperature of 20 °C with a relative humidity of 90 ± 5% for 21 days according to NT BUILD 355 [26]. The test samples were prepared by first cutting the cylinder samples into two halves and cutting 50 ± 2 mm thick slice from one half, then, 50 ± 2 mm thick slice samples continued to cure 7 days immersing in the water. In the test days, the samples were measured with the voltage preset at 30 V for 24 h or 48 h, SCC sample pieces were split and 0.1 N AgNO3 was sprayed. Twenty measurement points were installed regularly on the split surface at the 5 mm interval to give the mean penetration depth of chloride ion, the formula (3) was used to calculate chloride ion diffusion coefficient (DRCM0).
DRCM0 ¼ 2:872 106
pffiffiffiffiffi Thðxd a xd Þ t
pffiffiffiffiffiffi a ¼ 3:338 103 Th
ð3Þ
DRCM0—Chloride migration coefficient (m2/s) T—Average value of the initial and final temperatures in the anolyte solution (K) h—Thickness of the specimen (m) xd—Average value of the penetration depth (m) T—Test duration (s) a—Faraday constant
2.5.4.3. Drying–wetting cycles test. The test of drying–wetting cycles was carried out according to the method described in the preliminary research [27,28]. SCC samples were cured in a humidity room at a temperature of 20 °C with a relative humidity of 90 ± 5% for 28 days. For each cycle, SCC samples were dried at 80 ± 5 °C and 50–60% relative humidity for 14 h, then, immersed in water at 20 ± 5 °C for 10 h. The damage of SCC with various A/ B ratios under drying–wetting cycles were assessed by relative compressive strength, relative dynamic elasticity modulus and mass loss. The following Eqs. (4)–(6) were used to calculate the relative compressive strength, relative dynamic elasticity modulus and mass loss.
Relative compressive strength ¼ F cu0 =F cun
ð4Þ
(Fcu0—The 28-days compressive strength of SCC, Fcun-The compressive strength of SCC after drying–wetting cycles of 0, 15, 30, 45, 60 days).
Relative dynamic elasticity modulus ¼ EO =En
ð5Þ
(EO-The 28-days dynamic elasticity modulus of SCC, En-The dynamic elasticity modulus of SCC after drying–wetting cycles of 0, 15, 30, 45, 60 days)
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Mass loss ¼ ðW 0 W n Þ=W 0
ð6Þ
(WO-The 28-days weight of SCC, Wn-The weight of SCC after drying– wetting cycles of 0, 15, 30, 45, 60 days). 3. Results and discussion 3.1. The effect of A/B ratio on the bulk density of aggregate The bulk density of aggregate with various A/B ratios are presented in Fig. 1, it can be seen from Fig. 1 that the bulk density of aggregate with various A/B ratios range from 2376 kg/m3 to 2478 kg/m3, A/B ratio has a evidently affected on the bulk density of aggregate, with the change of A/B ratio from 4/6 to 6/4, the bulk density of aggregate is drastically increasing due to more finer coarse aggregate particles filled into the void between the larger size particles of coarse aggregate (this is called filling effect), when A/B ratio in coarse aggregate is above 6/4, the bulk density of aggregate start to decrease with A/B ratio further increased, this can be attributed to this fact that, when A/B ratio is greater than 6/4, more finer coarse aggregate added result in the particles of coarse aggregate to be pushed apart and attain a lower bulk density of aggregate, aggregate with A/B ratio for 6/4 has a maximum bulk density of aggregate for 2478 kg/m3. 3.2. The effect of A/B ratio on the properties of fresh SCC The test results of initial slump flow, L-box test, segregation ratio and wet density of fresh SCC are shown in Table 4. It is evident from Table 4 that initial slump flow of fresh SCC is decreasing with the change in A/B ratio from 4/6 to 7/3, this may be attributed to this fact that size 5–10 mm coarse aggregate has a higher water absorption capacity than size 10–20 mm coarse aggregate, with the increase of size 5–10 mm coarse aggregate content in SCC, more free water are absorbed into size 5–10 mm coarse aggregate, thus reduce initial slump flow of SCC. Moreover, it can be seen from Table 4 that blocking ratio values of all SCC mixtures are between 0.92 and 0.98 in L-box test, the blocking ratio of all SCC mixtures meet the minimum acceptance value of 0.80, which is as per EFNARC standards, SCC with various A/B ratios achieves adequate passing ability, bleeding and segregation of fresh SCC become no obvious with the increase of A/B ratio. Meantime, it also shows in Table 4 that the wet density of SCC with A/B ratio for 4/6, 5/5, 6/4, 7/3 are 2420 kg/m3, 2436 kg/m3, 2441 kg/m3, 2456 kg/m3, the wet density of SCC are increasing with the increase of size 5–10 mm coarse aggregate content in SCC, this behavior can be explained by this fact that size 5–10 mm coarse aggregate has a higher density (SSD = 2680 kg/m3) than size 10– 20 mm coarse aggregate (SSD = 2640 kg/m3).
Bulk density of aggregate kg/m3
2500
2450
3.3. The effect of A/B ratio on the mechanical properties of hardened SCC 3.3.1. Compressive strength development of SCC The compressive strength development of SCC with A/B ratio for 4/6, 5/5, 6/4, 7/3 are presented in Fig. 2, the test results indicate that the compressive strength of SCC with various A/B ratios are increasing at curing periods of 3, 7, 28, 90 days, the early compressive strength development of SCC with various A/B ratios are very rapid, 3-days and 7-days compressive strength of SCC with A/B ratio for 4/6 can reach 36.5 MPa and 44.4 MPa, it is 72.1%, 87.8% compressive strength of SCC at curing period of 28 days, while the compressive strength of SCC with A/B ratio for 7/3 at curing periods of 3, 7 days can reach 40.8 MPa and 46.1 MPa, it is 78.8% and 89.0% of 28-days compressive strength of SCC, the compressive strength of SCC are also growing at late curing age. Meantime, the change in A/B ratio has some effect on the compressive strength at curing periods of 3, 7, 28, 90 days, compressive strength of SCC is increasing with the increase in A/B ratio from 4/6 to 6/4 at the same curing period, when A/B ratio is greater than 6/4, compressive strength of SCC has a gradual downward trend, SCC with A/B ratio for 6/4 has a maximum compressive strength at curing periods of 3, 7, 28, 90 days. This may be attributed to this fact that SCC with A/B ratio for 6/4 has a maximum particle bulk density and less porosity (15.33%, 14.17%, 13.3% at curing periods of 3, 7, 28 days, seen from Fig. 4) [29]. 3.3.2. Flexural strength development of SCC The flexural strength development of SCC are shown in Fig. 3, it can be seen from Fig. 3 that flexural strength of SCC with various A/ B ratios are grow at curing periods of 3, 7, 28, 90 days. The change in A/B ratio has some effect on the flexural strength at the same curing period, the flexural strength of SCC with A/B ratio for 4/6, 5/5, 6/4, 7/3 are 8.95 MPa, 9.26 MPa, 9.33 MPa and 9.28 MPa at curing period of 3 days, SCC with A/B ratio for 6/4 has a maximum flexural strength at curing period of 3 days, a similar tendency to increase and then gradual downward in flexural strength with the increase of A/B ratio is also found for SCC at the curing periods of 7, 28, 90 days. 3.4. The effect of A/B ratio on the water porosity of SCC The results of water porosity of SCC with various A/B ratios at the curing periods of 3, 7 28 days are shown in Fig. 4. It can be observed that the porosities of all SCC mixture reduce with the increase of curing period, at the curing period of 7 days, SCC with A/B ratio for 4/6, 5/5, 6/4, 7/3 has 15.22%, 14.84%, 14.17%, 14.41% of porosity, respectively, with the increase of curing period, the porosities of SCC with A/B ratio for 4/6, 5/5, 6/4, 7/3 reduce to 14.17%, 13.79%, 13.30%, 13.53% at the curing period of 28 days. Base on test result of the porosity at the different curing period, it can be found that SCC with A/B ratio for 6/4 has least porosity value in all curing period. 3.5. The effect of A/B ratio on the durability properties of SCC
2400
2350
2300 A/B=4:6
A/B=5:5
A/B=6:4
A/B=7:3
Coarse aggregate gradation Fig. 1. The bulk density of aggregate with various A/B ratios.
3.5.1. Carbonation depth of SCC In order to study the effect of A/B ratio on carbonation depth of SCC, the carbonation depths of SCC with A/B ratio for 4/6, 5/5, 6/4, 7/3 at all tested ages are shown in Fig. 5. From Fig. 5, it can be seen that the carbonation depths of SCC with various A/B ratios are increasing at carbonation periods of 3, 7, 14, 28 days, when A/B ratio is increasing from 4/6 to 6/4, the carbonation depth of SCC has a gradually decreasing, when A/B ratio is more than 6/4, carbonation depth of SCC has a increasing trend at same carbonation time, SCC with A/B ratio for 6/4 exhibits lowest
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H. Zhao et al. / Materials and Design 40 (2012) 109–116 Table 4 Properties of fresh SCC with various A/B ratios. A/B ratio
Initial slump flow (mm)
5–10 mm (A)
10–20 mm (B)
434.4 544 651.6 760.2
651.6 544 434.4 325.8
826 802 786 775
L-box test Ratio (%)
Time (s)
0.96 0.95 0.92 0.90
18.2 18.3 18.5 18.7
A/B=4:6 A/B=5:5 A/B=6:4 A/B=7:3
60
Segregation ratio (%)
Wet density (kg/m3)
10.3 9.7 9.3 8.7
2420 2436 2441 2456
A/B=4:6 A/B=5:5 A/B=6:4 A/B=7:3
8
Carbonation depth (mm)
Compressive strength (MPa)
4/6 5/5 6/4 7/3
Coarse aggregate (kg/m3)
50 40 30 20
6
4
2
10 0
0 3
7
90
28
0
Curning time (days)
8 6 4 2 0 90
28
Curning time (day)
2
3.0
-12
2.5
Chloride ion diffusion coefficient 10
Flexural strength (MPa)
10
7
15
20
25
30
Fig. 5. The carbonation depths of SCC with various A/B ratios.
m /s)
A/B=4:6 A/B=5:5 A/B=6:4 A/B=7:3
3
10
Carbonation time (day)
Fig. 2. The compressive strength development of SCC with various A/B ratios.
12
5
2.0 1.5 1.0 0.5 0.0
A/B=4:6
Fig. 3. The flexural strength development of SCC with various A/B ratios.
A/B=5:5
A/B=6:4
A/B=7:3
Coarse aggregate gradation Fig. 6. The chloride ion diffusion coefficient of SCC with various A/B ratios.
A/B=4:6 A/B=5:5 A/B=6:4 A/B=7:3
The water porosity (%)
18 16 14
B ratio for 6/4 has a maximum particle bulk density and less porosity, so that a lower carbonation depth can be found on SCC with A/B ratio for 6/4.
12 10 8 6 4 2 0 3
7
28
Curning time (days) Fig. 4. The water porosity development of SCC with various A/B ratios.
carbonation depth at carbonation periods of 7, 14, 28 days, which carbonation depth of SCC with A/B ratio for 6/4 is 2.97 mm, 5.14 mm, 6.22 mm at test ages of 7, 14, 28 days. This behavior can be explained by this fact that carbonation depth of SCC has a close relationship with porosity of concrete [30–32], SCC with A/
3.5.2. Chloride ion diffusion coefficient of SCC From Fig. 6, it can be seen that the chloride ion diffusion coefficient of SCC with A/B ratio for 4/6, 5/5, 6/4, 7/3 are 2.78 1012 m2/s, 2.52 1012 m2/s, 2.23 1012 m2/s, 2.45 1012 m2/s, the chloride ion diffusion coefficient of SCC is decreasing with the change in A/B ratio from 4/6 to 6/4, A/B ratio in SCC is above 6/4, there are an increasing trend at the chloride ion diffusion coefficient. SCC with A/B ratio for 6/4 has least the chloride ion diffusion coefficient for 2.23 1012 m2/s, it may attributed to this fact that SCC with A/B ratio for 6/4 has highest compressive strength and less porosity in all SCC sample, so that SCC with A/B ratio for 6/4 has lowest chloride ion diffusion coefficient [33–36]. 3.5.3. The damage of SCC under drying–wetting cycles 3.5.3.1. Relative compressive strength of SCC under drying–wetting cycles. The relative compressive strength of SCC with A/B ratio for
4/6, 5/5, 6/4, 7/3 measured after drying–wetting cycles of 0, 15, 30, 45, 60 days are shown in Fig. 7. From Fig. 7, it can be seen that the relative compressive strength evolution curves of SCC under drying–wetting cycles include two stages, at the initial stage of drying–wetting cycles, the relative compressive strength of SCC with various A/B ratios are increasing with the change in drying– wetting cycles, which it indicates that more cement hydration products appear and hardened SCC become more compact. After drying–wetting cycles of 30 days, the relative compressive strength of SCC with A/B ratio for 4/6, 5/5, 6/4, 7/3 are decreasing with the increase of drying–wetting cycles days, it may be due to this fact that, after drying–wetting cycles of 30 days, the effect of thermal stress, moisture expansion, drying shrinkage on SCC become more and more significant [37,38]. 3.5.3.2. Relative dynamic elasticity modulus of SCC under drying– wetting cycles. The relative dynamic elasticity modulus evolution curves of SCC with various A/B ratios under drying–wetting cycles are presented in Fig. 8, it can be seen from Fig. 8 that the relative dynamic elasticity modulus of SCC with A/B ratio for 4/6, 5/5, 6/ 4, 7/3 have an upward trend at the initial phase of drying–wetting cycles, a gradual downward trend can be found in the relative dynamic elasticity modulus of SCC after drying–wetting cycles of 30 days. It indicates that the residual cement particles continue to hydration and fill microporosity of SCC during drying–wetting cycles of 30 days [39,40], after drying–wetting cycles of 30 days, the effect of thermal stress on hardened SCC become stronger, microcrack appear on the surface of SCC, therefore, the relative dynamic elasticity modulus of SCC with various A/B ratios begin to decrease.
The relative dynamic elasticity modulus
H. Zhao et al. / Materials and Design 40 (2012) 109–116
A/B=4:6 A/B=5:5 A/B=6:4 A/B=7:3
1.15 1.10 1.05 1.00 0.95 0.90 0.85 0
10
20
30
40
50
60
Drying-wetting cycle days Fig. 8. The relative dynamic elasticity modulus evolution curves of SCC with various A/B ratios under drying–wetting cycles.
A/B=4:6 A/B=5:5 A/B=6:4 A/B=7:3
0.9 0.8 0.7
The mass loss
114
0.6 0.5 0.4 0.3 0.2 0.1 0.0 0
10
20
30
40
50
60
Drying-wetting cycle days
3.5.3.4. The analysis of relationship between relative compressive strength–relative dynamic elasticity modulus and relative compressive strength–mass loss of SCC under drying–wetting cycles. The relationship
Fig. 9. The mass loss evolution curves of SCC with various A/B ratios under drying– wetting cycles.
The relative dynamic elasticity modulus
3.5.3.3. Mass loss of SCC under drying–wetting cycles. The mass loss evolution curves of SCC with various A/B ratios under drying–wetting cycles are given in Fig. 9. It shows, at the initial stage, that the mass loss of SCC with A/B ratio for 4/6, 5/5, 6/4, 7/3 are increasing with the increase of drying–wetting cycles days, after drying–wetting cycles of 30 days, the mass loss of SCC reduce with the change in drying–wetting cycles from 30 days to 60 days. It can be explained by the fact that, at the initial phase of drying–wetting cycles, the residual cement particles in SCC continue to hydrate, the soluble materials are leached from hardened SCC, after drying– wetting cycles of 30 days, the cement hydration reaction of SCC is completely finished and SCC begins to absorb water, so that mass loss of SCC with A/B ratio for 4/6, 5/5, 6/4, 7/3 will reduce.
1.2 A/B=4:6 (y = 0.2993e
1.0028x
2
A/B=4:6
1.1
R = 0.9458)
A/B=5:5
A/B=5:5 (y = 0.2754e
1
1.0586x
2
A/B=6:4
R = 0.9243)
A/B=7:3 A/B=6:4 (y = 0.5696e
0.4569x
2
R = 0.8079)
0.9
A/B=7:3 (y = 0.5101e
0.5385x
2
R = 0.8221
0.8
1
1.1
1.2
1.3
1.4
1.5
The relative compressive strength
The relative compressive strength Fig. 10. The relationship between relative compressive strength and relative dynamic elasticity modulus of SCC under drying–wetting cycles.
A/B=4:6 A/B=5:5 A/B=6:4 A/B=7:3
1.35 1.30 1.25 1.20 1.15 1.10 1.05 1.00 0
10
20
30
40
50
60
Drying-wetting cycle days Fig. 7. The relative compressive strength evolution curves of SCC with various A/B ratios under drying–wetting cycles.
between relative compressive strength–relative dynamic elasticity modulus and relative compressive strength–mass loss of SCC with various A/B ratios under drying–wetting cycles are presented in Figs. 10 and 11. It can be seen from Fig. 10, an exponential relation exists between relative compressive strength (x) and relative dynamic elasticity modulus (y) of SCC under drying–wetting cycles, the fitting formula of SCC with A/B ration for 4/6, 5/5, 6/4, 7/3 are y = 0.2993e1.0028x, y = 0.2754e1.0586x, y = 0.5696e0.4569x and y = 0.5101e0.5385x with the high correlation coefficients (R2 = 0.9458, R2 = 0.9243, R2 = 0.8079 and R2 = 0.8221). These test results are consistent with previous several results [41–43].
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References
1.2 2
A/B=7:3(y = -26.613x + 61.538x - 34.624 2
The mass loss (%)
1
R = 0.9261)
2
A/B=6:4 (y = -24.779x + 57.069x - 31.915 2
2
R = 0.9131)
0.8
/B=5:5(y = -14.767x + 33.702x - 18.412 2
R = 0.9785) 2
0.6
A/B=4:6(y = -8.7392x + 19.185x - 9.7794 2
R = 0.8386)
A/B=4:6
0.4
A/B=5:5 A/B=6:4
0.2
A/B=7:3 0
1
1.05
1.1
1.15
1.2
1.25
1.3
1.35
The relative compressive strength Fig. 11. The relationship between relative compressive strength and mass loss of SCC under drying–wetting cycles.
Fig. 11 shows that this is second-order polynomial relationship between the relative compressive strength (x) and mass loss (y) of SCC under drying–wetting cycles, the fitting formula of SCC with A/B ratio for 4/6, 5/5, 6/4, 7/3 are y = 8.7392 x2 + 19.185 x 9.7794, y = 14.767 x2 + 33.702 x 18.412, y = 24.779 x2 + 57.069 x 31.915 and y = 26.613 x2 + 61.538 x 34.624 with R2 = 0.8386, R2 = 0.9785, R2 = 0.9131 and R2 = 0.9261, it indicates high correlation. 4. Conclusions In this study, the bulk density of aggregate with various A/B ratios was investigated, fresh properties, mechanical properties, porosity and durability properties of SCC with various A/B ratios were determined, the test results are as follows. Aggregate with A/B ratio for 6/4 has a maximum bulk density of aggregate for 2478 kg/m3. With the change in A/B ratio from 4/6 to 7/3, the initial slump flow, blocking and segregation ratio of SCC are decreasing, while the wet density of fresh SCC are increasing. The compressive strength of SCC with various A/B ratios develop ranging from 36.5 to 41.5 MPa, from 44.4 to 46.5 MPa, from 50.6 to 53.6 MPa and from 58.7 to 60.3 MPa at curing periods of 3, 7, 28, 90 days. The flexural strength development of SCC are from 8.95 to 9.33 MPa, 9.56 to 9.82 MPa, 10.68 to 10.85 MPa and 11.58 to 11.71 MPa at curing periods of 3, 7, 28, 90 days. The porosities of all SCC mixture are between 13.30% and 14.17% at curing period of 28 days. SCC with A/B ratio for 6/4 has a maximum compressive strength, flexural strength and lowest porosity at all curing periods. With the change in A/B ratio from 4/6 to 7/3, the carbonation depth and the chloride ion diffusion coefficient of SCC are gradual decrease, then, there are gradual increase trend. SCC with A/B ratio for 6/4 exhibits the lowest carbonation depth and least chloride ion diffusion coefficient. Under drying–wetting cycles, relative compressive strength, relative dynamic elasticity modulus and mass loss of SCC with various A/B ratios have an upward trend at the initial phase of drying–wetting cycles, then, a gradual downward trend can be found in the relative compressive strength, relative dynamic elasticity modulus and mass loss of SCC. SCC with various A/B ratios have a resemble behavior on resistance damage against drying–wetting cycles. Acknowledgements This project was supported by western traffic science and technology projects (Chinese, No. 2006ZB01-2). The provision of PCA Superplasticizer by Jiangsu Bote New Materials Co, Ltd. is gratefully acknowledged. The authors thank Prof. Wei Sun, who is the academician of China National Engineering Research Institute, her sponsorship and support made this study possible.
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