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Strength properties and micro-structural analysis of self-compacting concrete made with iron slag as partial replacement of fine aggregates
Construction and Building Materials 127 (2016) 144–152
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Strength properties and micro-structural analysis of self-compacting concrete made with iron slag as partial replacement of fine aggregates Gurpreet Singh ⇑, Rafat Siddique Ph.D Department of Civil Engineering, Thapar University, Patiala, Punjab, India
h i g h l i g h t s Utilization of iron slag in self-compacting concrete (SCC). Iron slag (10–40%) improved the strength properties of SCC. Iron slag improves the microstructure of SCC.
a r t i c l e
i n f o
Article history: Received 22 February 2016 Received in revised form 15 August 2016 Accepted 30 September 2016
Keywords: Iron slag River sand Compressive strength Splitting tensile strength Flexural strength Modulus of elasticity Microstructure
a b s t r a c t The iron and steel rolling mills are the main source of the production of iron slag. This paper presents the results on an experimental program carried to explore the possibility of use of iron slag as partial replacement of fine aggregate (sand) in self-compacting concrete (SCC). SCC mixes were designed and fine aggregates were replaced with 0, 10, 25, and 40% iron slag. Tests were performed to evaluate the fresh properties, strength properties and micro-structural analysis of SCC. Properties such as slump flow, V-funnel, U-box, L-box, compressive strength, splitting tensile strength, flexural strength and modulus of elasticity were examined. Results indicated that compressive strength, splitting tensile strength and flexural strength of self-compacting concrete improved with incorporation of iron slag at all the curing ages. SEM and XRD analysis were done to examine the microstructure, which indicated that use of iron slag made the microstructure of SCC denser. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Concrete is compacted by vibrations in order to expel entrapped air, making it denser and homogeneous because compaction is necessary to produce durable concrete [1]. Full compaction is difficult due to heavy reinforcement, as a result self-compacting concrete (SCC) was developed in early 1980’s [2]. Self-compacting concrete (SCC) can be defined as a concrete which can be placed with its own weight with or without vibration. It facilitates and ensures proper filling and good structural performance of heavily reinforced congested members. Natural sand (fine aggregates) is getting depleted due to increased consumption of concrete. As a result, substitutes of natural sand are being explored by using waste materials and industrial byproducts. Strength and durability properties are significantly affected by type of fine aggregates [3]. There are several
⇑ Corresponding author. E-mail address: [email protected] (G. Singh). http://dx.doi.org/10.1016/j.conbuildmat.2016.09.154 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
types of industrial byproducts which can be used as fine aggregates in concrete. One such byproduct is iron slag (IS). During the production of iron in blast furnace, blast Furnace Slag is formed when iron ore or iron pellets, coke and a flux (either limestone or dolomite) are melted together in a blast furnace. When the metallurgical smelting process is complete, the lime in the flux has been chemically combined with the aluminates and silicates of the ore and coke ash to form a non-metallic product called blast furnace slag. During the period of cooling and hardening from its molten state, BF slag can be cooled in several ways to form any of several types of BF slag products. So, the objective of a blast furnace is to produce iron, and iron slag is a by-product in this process. Particle size ranges from fine sand to fine gravel. The appearance and particle size distribution of iron slag are similar to that of river sand. The principal constituents of iron slag are silica (SiO2), alumina (Al2O3), calcium (CaO), and magnesia (MgO), which make up 95% of the composition. Small elements entail manganese, iron, and sulfur compounds, as well as trace amounts of several others. Cooling of the slag along with its chemical composition affects its
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Fig. 1. SEM morphology of ordinary Portland cement.
physical properties. There are three additional types of slag in blast furnace: Air-cooled blast furnace quote, Air cooled blast furnace slag rip rap, Slag cement. The rough vesicular texture of slag provides larger surface area in comparison to smoother aggregates which provides good bond with Portland cement as well as high stability in asphalt mixtures [4]. Literature survey indicates that there is no published work related to use of iron slag in self-compacting concrete. Literature review was concentrated on use of slag in concrete as well as self-compacting concrete. Few authors [5–8] reported the effect of types of slags such as electric arc furnace slag [5], iron slag [6], steel slag [7], and iron filing [8] on the properties of mortar and concrete, whereas use of slags in self-compacting concrete have been reported by few authors Wang and Lin [9], Sideris et al. [10], Boukendakdji et al. [11], and Valcuende et al. [12]. Pellegrino et al. [5] concluded that strength properties of concrete made with electric arc furnace slag exhibited comparable (or even better) than conventional concrete made with natural sand. Human and Siddique [6] reported that partial replacement of fine aggregates with iron slag significantly enhanced strength properties and permeability of mortar. Maslehuddin et al. [7]
145
reported that compressive strength of concrete made with steel slag (as coarse aggregates) is better than that of concrete made with lime stone aggregate. Moreover, the improvement in tensile strength of steel slag concrete was not significant. Alzaed [8] concluded that there was gradual increase in compressive strength with addition of iron filling. Compressive strength increased by 17% with 30% of iron filling; however, there was no significant effect on the tensile strength. Wang and Lin [9] indicated that fresh concrete properties and compressive strength of self-compacting high strength concrete (SCHSC) made with 15% furnace slag is higher than control mix. Sideris et al. [10] concluded that use of ladle furnace slag improved fresh concrete properties and as well as compressive strength of SCC. Boukendakdji et al. [11] described that use of ground granulated blast furnace slag in replacement with cement is good for fresh and strength properties of SCC. Valcuende et al. [12] concluded that at early ages the compressive strength of SCC using granulated blast furnace slag as fine aggregates is similar to the SCC made with fine aggregates, but at 90 and 365 days, the strength is higher. As there has not been published work on the use of iron slag in self-compacting concrete, he aim of the present research work was to ascertain the suitability of iron slag as a partial replacement of sand in self-compacting concrete. 2. Experimental detail 2.1. Materials used 2.1.1. Cement Ordinary Portland cement 43 grade conforming to BIS: 81121989 [13]. SEM morphology and EDS spectrum of cement are shown in Figs. 1 and 2, respectively. Physical and chemical properties of cement are given in Table 1. 2.1.2. Fine aggregates River sand (Tokka sand name commonly used in Punjab, India) was used as fine aggregates. They were collected from Chandigarh, Punjab, near Ghaggar River. The specific gravity and fineness modulus of river sand were 2.57 and 2.62 respectively. Sand used for SCC complied with requirements for grading zone-III of BIS: 383-1970 [14]. 2.1.3. Coarse aggregates Coarse aggregates were collected from chapar-kandi quarry located near Ravi River, Punjab, India. The specific gravity and
Fig. 2. EDS spectrum of ordinary Portland cement.
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and river sand are shown in Fig 3. Fineness modulus iron slag is 2.83.
Table 1 Chemical composition and physical properties of cement. Chemical composition
Physical properties
Content CaO SiO2 Al2O3 Fe2O3 MgO LOI
%age 65.7 21.3 6.01 2.2 0.8 4
Color Setting time (min) Initial Final Specific gravity Standard consistency Soundness Le-chat expansion (mm)
Grey 68 278 3.01 34% 3
Table 2 Physical properties of river sand and iron slag. Property
River Sand
Iron Slag
Specific gravity Water absorption by mass (%) Fineness modulus Unit Weight (kg/m3) Appearance
2.57 3.65 2.49 1800 Light grey
2.49 18.54 2.38 2000 Black, glassy more vesicular when granulated
river sand
iron slag
100
% passing
75
2.1.5. Fly ash Class F fly ash was used, having main chemical compounds CaO (12%), SiO2 + Fe2O3 + Al2O3 (71%), Loss of ignition less than 4% and physical properties of fly ash are grey in color, particle size less than 45 lm. 2.1.6. Admixture Auramix-400 low viscosity high performance super-plasticizer based on polycarboxylic technology is used where high water reduction and long workability retention are required, and it has been developed for use in SCC, pumper concrete and high performance concrete, etc. It is light yellow colored liquid with 6.0 pH (min.) value and 0% chloride content. 3. Mixture proportions The mixture proportion of SCC was selected by trial mixes. Control mixture achieved strength of 36.25 MPa at the age of 28 days. Sand was replaced with iron slag by mass in SCC and 10% of fly ash replaced by cement. Fixed quantities of cement, fly ash and coarse aggregates i.e., 455 kg/m3, 45 kg/m3, 760 kg/m3 respectively were used in concrete samples. Fixed water powder ratio of 0.44 and admixture of 1.2% by weight of powder were applied in all SCC mixes. Mix proportions of self-compacting concrete are given in Table 3. 4. Testing procedures
50
25
0 10
100
1000
particle size Fig. 3. Grading of sand and iron slag.
maximum size of coarse aggregates used in this research was 2.69 and 12 mm respectively.
2.1.4. Iron slag Iron slag was collected from Dhiman iron and steel rolling mills, Mandi-Gobindgarh, Fatehgarh Sahib, Punjab India. Iron slag was screened to remove the oversized particle and material passing through 4.75 mm sieve was used in manufacturing of concrete. The major chemical compounds in iron slag are Fe2O3 (66.88%), SiO2 (6.98%), Al2O3 (2.94%), CaO (0.8%), CO2 (22.40%) and physical properties of iron slag used in this research shown in Table 2. Iron slag is brittle and lighter than river sand. River sand and iron slag were dried in oven at 100 °C for 24 h and then cooled down to room temperature before using in concrete. Grading of iron slag
Before casting, the entire test molds were cleaned and oiled properly. These were firmly tightened to correct dimensions before casting. Care was taken that there is no gap left from where there is any possibility of escape of slurry. The ingredients of concrete were mixed in 0.08 cu-m capacity mixer. Testing for SCC involved four mixture compositions using 228 samples (108 cubes of 15 15 15 cm size, 72 cylinders of 15 cm diameter and 30 cm height, and 36 beams of 50 10 10 cm size and 12 cylinders of 10 cm diameter and 20 cm height). 4.1. Fresh properties Immediately after casting, SCC mixtures were examined for fresh concrete properties by slump test, V-funnel test, U-box and L-box as per EFNARC [15]. 4.2. Hardened properties Cubes of 150 mm 150 mm 150 mm size were casted for examining compressive strength. Cylinders of size 150 mm 300 mm were casted for measuring splitting tensile strength, modulus of elasticity. Beams of size 100 mm 100 mm 500 m were casted for measuring flexural strength. Compressive strength and flexural strength of concrete specimen were measured at 7, 28
Table 3 Mixture proportion of SCC. Mixture
Cement (kg/m3)
Fly Ash (kg/m3)
W/P ratio
Sand (kg/m3)
Iron Slag (kg/m3)
Iron Slag (%)
Coarse aggregates (kg/m3)
Admixture (%)
SCC-CM SCC-IS10 SCC-IS25 SCC-IS40
455 455 455 455
45 45 45 45
0.44 0.44 0.44 0.44
960 864 720 576
0 96 240 384
0 10 25 40
760 760 760 760
1.2 1.2 1.2 1.2
IS-iron Slag (10, 25, 40 are the percentage replacement of iron slag with river sand).
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Mixture ID
Slump flow (mm)
L-box (H2/H1)
U-box (H1-H2)
V-funnel (sec.)
SCC-CM SCC-IS10 SCC-IS25 SCC-IS40
774 733 723 687
0.9 0.87 0.86 0.85
32 33 35 35
11 11 12 13
U-box (H2-H1) mm
36
Table 4 Fresh concrete properties.
35 34 33 32 31 30 0
10
Fig. 6. Effect of iron slag on U-box values.
700 650
0
10
25
40
Iron slag (%) Fig. 4. Effect of iron slag on slump values.
Compressive strength (MPa)
Slump flow (mm)
40
750
600
50
7 days
28 days
91 days
40 30 20 10 0 0
10
25
40
Iron slag (%)
0.9
L-box (H2/H1)
25
Iron slag (%)
800
Fig. 7. Effect of iron slag on compressive strength.
0.88 0.86
of powder. The results of fresh properties of self compacting concrete are given in Table 4 and shown in Figs. 4–6.
0.84 0.82 0.8 0
10
25
40
Iron slag (%) Fig. 5. Effect of iron slag on L-box values.
and 91 days, modulus of elasticity of concrete specimen were measured at 28 and 91 days as per BIS: 516-1959 [16]. Splitting tensile strength concrete specimen was measured at 7, 28 and 91 days as per BIS: 5816-1999 [17]. For, modulus of elasticity of concrete, the cylinder specimen was loaded at the rate of 13 MPa/min until an average stress of (C + 0.5) MPa was achieved, where C is one-third of average compressive strength of cube. The load was maintained for one minute and then reduced gradually. The load was applied a second time at the same rate until the average stress of (C + 0.15) MPa was reached.
5. Result and discussion 5.1. Fresh concrete properties The properties of SCC at fresh stage were evaluated by flow ability, passing ability and consistency of SCC incorporating different percentages of iron slag. The evaluation of fresh concrete properties is done by slump flow test, L-box test, U-box test and Vfunnel test. It was perceived that inclusion of iron slag in self compacting concrete mixture decreased the workability. All fresh concrete properties are in good quality resemblance as per European procedure, ENFNARC [15]. Mixtures were tested for fresh concrete properties. The content of water-powder ratio was 0.44 and admixture was 1.2% by weight
5.1.1. Slump flow In case of slump flow, all mixtures of SCC shows slump flow in the range of 680–780 mm (Fig. 4) are within the limits (650– 800 mm) given by EFNARC [15]. This indicated good quality deformability. Iron slag particles are more granulated and sharp edged as compared to river sand. The rough texture and complicated shape of iron slag particles plays a significant role in increasing the inter-particle friction cause jamming of concrete particles. Wang and Lin [9] reported that slump flow diameter of all SCC mixtures was in the range of 550–770 mm; whereas Tomasiello and Felitti [23] and Boukendakdji et al. [11] reported that slump flow diameter was in the range of 650–770 mm.
5.1.2. L-box The L-box ratio for all the SCC mixtures was between 0.84–0.91 and within boundaries of EFNARC [15] range (0.8–1.0). The result shows (Fig. 5 and Table 4) that blocking ratio increased with the increase in replacement percentage of iron slag. Tomasiello and Felitti [23] reported L-box ratios of all SCC mixtures in the range of 0.70 to 0.86. Sideris et al. [10] observed L-box ratio of all SCC mixtures using ladle furnace slag as filler material in the range of 0.84 to 1.
5.1.3. U-box The variation on height of concrete in two compartments of Ubox was found in the range of 32–35 mm. The results of U-box of SCC mixtures were inside the limits of EFNARC [15]. The U-box test results are shown in Table 4 and Fig. 6. It can be observed that values increase with the increase of replacement percentage of iron slag with river sand. Boukendakdji et al. [11] reported the variation on height in U-box compartments in the range of 23 to 39 mm.
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5.1.4. V-funnel Time in V-funnel test increases as iron slag level is increased as replacement of sand. The test results are given in Table 4. Results show that time ranges between 11 and 13 s. The results of Vfunnel test of SCC mixtures were inside the limits as per EFNARC [15]. Fadaee et al. [18] reported V-funnel time range of 8–12 s. with the replacement of copper slag with cement. Boukendakdji et al. [11] reported all five mixes of SCC exhibited flow time values inside the range of 4 to 14.8 mm.
Splitting tensile strength (MPa)
148
5
7 days
28 days
91 days
4 3 2 1 0 0
6. Strength properties
10
25
40
Iron slag (%) 6.1. Compressive strength Compressive strength test results presented in Fig. 7 show that the strength development pattern of iron slag at all levels of sand replacement with iron slag is similar to the control mixes. It is observed that compressive strength increase in increase with iron slag content. At 7 days, SCC mixtures containing 10, 25, 40% iron slag as fine aggregates gained 3, 8, and 16% respectively more compressive strength as compared to 7 days SCC mixture without iron slag. At the curing age of 28 days, SCC mixtures containing 10, 25 and 40% iron slag as fine aggregates gained 1%, 13 and 20% respectively more compressive strength as compared to 28 days SCC mixture without iron slag. At the age of 91 days, SCC mixtures containing 10, 25 and 40% iron slag as fine aggregates gained 2, 11% and 16% respectively more compressive strength as compared to 91 days SCC mixture without iron slag. At the curing age of 28 days and 91 days, the increase in compressive strength percentage of SCC mixtures containing iron slag is more than control mixes. With increasing age, reactive silica in iron slag reacts with alkali calcium hydroxide produced by hydration of cement and forms calcium silicate and aluminates hydrates. The formation of stable calcium silicate and aluminates hydrates by chemical reaction between cement pastes constitutes and aggregates result in filling the voids in the interfacial transition zone and in improving its compressive strength. Alzaed [8] evaluated the effect of iron filling (0, 10, 20 and 30%) on the compressive strength of concrete. The compression tests were carried out on standard cubes (15 15 15 cm). Compressive strength of concrete increased gradually when iron filling is added in concrete mix. Compressive strength increased 17% when 30% of iron filling. Wang and Lin [9] presented an experimental study in which 0, 15 and 30% of furnace slag were replaced with cement to obtain better results of SCC. It was concluded that compressive strength of SCC with 15% of cement replaced by furnace slag is higher than that of control group (13% increment in compressive strength). The compressive strength results of this investigation are similar with those reported in previous studies by Sideris et al. [10]. 6.2. Splitting tensile strength Splitting tensile strength test results presented in Fig. 8 shows that the strength development pattern of iron slag, at the all levels of sand replacement with iron slag, is similar to that control mixes. The test results indicate that replacement of river sand with iron slag in SCC improved the splitting tensile strength. At the curing age of 7 days, SCC mixtures containing 10, 25 and 40% iron slag as fine aggregates gained 19, 28 and 34% respectively more splitting tensile strength as compared to 7 days SCC mixture without iron slag. At the curing age of 28 days, SCC mixtures containing 10, 25 and 40% iron slag as fine aggregates gained 3.5, 16 and 21% respectively more splitting tensile strength as compared to 28 days SCC mixture without iron slag. At the age of 91 days, SCC
Fig. 8. Effect of iron slag on splitting tensile strength.
mixtures containing 10, 25 and 40% iron slag as fine aggregates gained 3, 20 and 23% respectively more splitting tensile strength as compared to 91 days SCC mixture without iron slag. Splitting tensile strength of SCC mixture made with iron slag is higher than control mix al all ages (7,28 and 91 days). Devi and Gnanavel [19] carried out a research to find the effect of steel slag on the engineering properties of conventional concrete with partial replacement of coarse and fine aggregates up-to 50%. It was concluded that splitting tensile strength results of this study are more satisfactory. Similar findings of splitting tensile strength results were reported by Alzaed [8]. Furthermore, splitting tensile strength and compressive strength ratios are calculated and given in Table 5. At the age of 28 and 91 days the splitting tensile strength of all iron slag mixes as well as control mix was nearly 7.5% and 8.5% respectively of their compressive strength. Test result shows that splitting tensile strength and compressive strength ratio decreases with the increase of curing age and it increases with replacement of iron slag as compared to control mix.
6.3. Flexural strength test Flexural strength test results are shown in Fig. 9 show similar increment in flexural strength as in case of compressive strength and splitting tensile strength. At 7 days, SCC mixtures containing 10, 25 and 40% iron slag as fine aggregates obtained 2.5, 12 and 18% more flexural strength as compared with control mix. At 28 days, SCC mixtures containing 10%, 25%, 40% iron slag as fine aggregates obtained 1, 5 and 14% more flexural strength as compared with control mix. At the curing age of 91 days, SCC mixtures containing 10, 25 and 40% iron slag as fine aggregates obtained 2.5, 8 and 11.5% more flexural strength as compared with control mixture. Kothei and Malathy [21] presented the results of SCC made with 10 to 100% of steel slag as replacement with fine aggregates. It was concluded that up to 40% replacement of fine aggregates with steel slag gives the better results of flexural strength. These results are comparable with the results of this study and similar finding of flexural strength results was reported by Pai et al. [22]. In this research, flexural strength increases with the increase of iron slag content. It is clear that the flexural tensile strength
Table 5 Splitting tensile strength and compressive strength ratios. SCC Mixture
SCC-CM SCC-IS10 SCC-IS25 SCC-IS40
Splitting tensile strength/compressive strength ratio (%) 7 days
28 days
91 days
5.7 6.8 7.3 7.3
7.6 7.8 7.8 7.7
7.5 7.6 8.5 8.3
149
Flexural strength (MPa)
5
7 days
28 days
Modulus of elasticity (GPa)
G. Singh, R. Siddique / Construction and Building Materials 127 (2016) 144–152
91 days
4 3 2 1 0 0
10
25
31
SCC CM
30
SCC-IS10
28 27 26 25 24 23 7
40
28
Modulus of elasticity (GPa)
28 days
91
Curing age (days) Fig. 11. Modulus of elasticity verses age.
Fig. 9. Effect of iron slag on flexural strength.
7 days
SCC-IS40
29
Iron slag (%)
31 30 29 28 27 26 25 24 23
SCC-IS25
91 days
CSH Gel
Voids 0
10
25
40
Ettringite
Iron slag (%) Fig. 10. Effect of iron slag on modulus of elasticity.
increases when the compressive strength and age of the concrete increases. Moreover, the increase in the flexural strength is higher than the corresponding increase in the compressive strength at same age of concrete. The percentage increase in flexural tensile strength increases with the increase of level of concrete strength. It is due to the different concrete compression and flexure failure mechanism of low and high strength concrete. Under the flexure loading, the cracks are initiated in the interfacial zone at low stresses and extend into the mortar matrix at high stresses and the resistance to cracks propagation results from the cement paste only.
Modulus of elasticity is the property that influences the safety durability, density and service life of reinforced concrete, Patel et al. [20]. Modulus of elasticity of concrete mixtures was measured at the curing age of 7 days, 28 days and 91 days. The test results are shown in Figs. 10 and 11. Even though the compressive strength was not strongly affected, the modulus of elasticity of concrete increased approximately linearly with the increase in replacement levels of sand with iron slag. The modulus of elasticity of iron slag concrete mixtures was higher than that of control concrete mixture. Modulus of elasticity of control mixture at 7 days curing age was 25.51 GPa, when 10, 25 and 40% of fine aggregates was replaced with iron slag modulus of elasticity of SCC increased to 25.62 GPa, 26.07 GPa and 26.17 GPa respectively. At 28 days curing age, the modulus of elasticity of control SCC was 27.90 GPa when 10%, 25% and 40% of fine aggregates was replaced with iron slag modulus of elasticity of SCC increased to 28.19 GPa, 28.71 GPa and 28.87 GPa. At 91 days curing age, the modulus of elasticity of control SCC was 28.10 GPa when 10, 25 and 40% of fine aggregates was replaced with iron slag modulus of elasticity of SCC increased to 28.78 GPa, 29.43 GPa and 29.70 GPa. SCC made with iron slag gives more modulus of elasticity values as compared to control mixture.
Fig. 12. SEM Image Of SCC (Without Iron Slag) At 28 Days.
Voids Calcium hydroxide
6.4. Modulus of elasticity
CSH Gel
Voids
Calcium hydroxide
CSH Gel
Fig. 13. SEM image of SCC (without iron slag) at 91 days.
7. Microstructure The hardened property of concrete depends on its intrinsic microstructure. The concrete structure is principally affected by the hydration period, water cement ratio, addition of mineral admixture and type of cement used in the production of concrete. Scanning electron micrograph (SEM) can provide both topographic and compositional analysis of material. In this research broken pieces of concrete generated by crushing were mounted on the SEM stub and images were obtained using SE image mode. SEM
150
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CSH Gel
Dense CSH Gel
Calcium hydroxide CSH Gel
Fig. 14. SEM image of SCC (with 10% of iron slag) at 28 days.
Fig. 17. SEM image of SCC (with 25% of iron slag) at 91 days.
CSH Gel Calcium hydroxide
Voids CSH Gel CSH Gel
Voids
Ettiringite
Fig. 15. SEM image of SCC (with 10% of iron slag) at 91 days.
Fig. 18. SEM image of SCC (with 40% of iron slag) at 28 days.
Voids
Ettiringite
CSH Gel
Fig. 16. SEM image of SCC (with 25% of iron slag) at 28 days.
Fig. 19. SEM image of SCC (with 40% of iron slag) at 91 days.
images of SCC-CM, SCC-IS10, SCC-IS25, and SCC-IS40 are shown in Figs 12–19 at the curing age of 28 and 91 days. These micrographs show that clear spread of CSH gel, voids and formation of ettringite in void spaces. Fig. 12 shows SCC mixture without iron slag replacement at the age of 28 days. In this figure micro voids, spread
of CSH gel in some areas and formation of ettringite in void spaces can be observed. Fig. 13 shows the same mixture proportion at the age of 91 days. Micro pores/voids, CSH gel and plates of calcium hydroxide were observed in the image. Fig. 14 shows SCC mixture with 10% iron slag replacement at the age of 28 days. Image being a
G. Singh, R. Siddique / Construction and Building Materials 127 (2016) 144–152
3000 2500 Q
Q
500
P
Q/CSH
1000
Q/C Q/CAO
1500
CS C/CSH
Intensity
2000
Q Q
P
Q
Q Q
0 0
10
20
30
40
50
60
70
80
90
2 Theta angle Fig. 20. XRD spectra of SCC control mixture. (P- Calcium hydroxide, CSH-calcium silicate hydrates, Q- quartz, CS-calcium silicates, CAO- calcium oxide).
Intensity
2000 Q
1500
C
P CQ
Q/CSH
Q
CSH CSH
1000
P
Q Q
Q
50
60
70
P
0 0
10
20
material used. The X-ray diffraction technique was used to analyze the SCC Control mixture without iron slag and SCC with 40% iron slag at the age of 28 days. The XRD was done using a Panalytical X’Pert pro, with Cu Ka, radiation at SAI labs, Thapar University, Patiala. The X’Pert High Score Plus software was used to identify the phases. The cement paste was separated from concrete samples and was sieved through 90 lm sieve. The XRD were conducted for diffraction angle 2 Theta range between 10° and 90°. XRD diffractograms of powder cement paste of SCC control mixture and SCC containing 40% iron slag are presented in Figs. 20 and 21. The XRD shows the presence of quartz, calcium silicate hydrates, calcium hydroxide, calcium silicates and calcite. One major problem encountered in the qualitative analysis of all SCC mixtures was overlapping of diffraction peaks. XRD analysis of all the mixtures shows that there is no qualitative change in the phases present. 9. Conclusions The present experimental study was carried out to investigate the factibility of using iron slag as a replacement of fine aggregates in SCC. Experiments were conducted by replacing fine aggregates with iron slag in varying percentages in SCC. Test result indicates that iron slag is a good candidate to be used in partial replacement of fine aggregates in production of structural self compacting concrete of grade between M30 and M40. Based on the analysis of test results, the following conclusions can be drawn.
2500
500
151
30
40
80
90
2 Theta angle Fig. 21. XRD spectra of SCC mixture with 40% iron slag (P- calcium hydroxide, CSHcalcium silicate hydrates, Q- quartz, CS-calcium silicates, C-calcite).
more mature paste with limited space and well formed crystals. Fig. 15 depicts the same mixture proportion at the age of 91 days. The formation of ettringite in void spaces and CSH gel can observed widely spread. Fig. 16 shows SCC mixture with 25% iron slag replacement at the age of 28 days. Well formed crystals were observed. Furthermore a similar mixture proportion at the age of 91 days is illustrated in Fig. 17. It was observed that dense CSH gel was fully spread over the micrograph leading to highly uniform and dense structure. The CSH formation serves as a thin pliable sheet of material. This would make concrete more resistant to aggressive environment. Fig. 18 shows SCC mixture with 40% iron slag replacement at the age of 28 days. Image shows more mature paste with low porosity. Fig. 19 shows the same mixture proportion at the age of 91 days. In this figure, ettringites with its needle like habit and calcium hydroxide crystals showing their characteristic cleavage can be observed. CSH gel and ettringite needles are identified.
8. X-ray diffraction X-ray diffraction is one of the most powerful tools for identifying unknown crystalline phases. By comparing the positions and intensities of the diffraction peaks against a library of known crystalline phases, the target material can be recognized. In addition, multiple phases in sample can be identified and quantified. XRD analyses were conducted to identify the components of SCC mixtures and
The results show that slump values, U-box values and L-box values decreased with the increase in level of iron slag. V-funnels test value of time is increased as the iron slag content dose. The rough texture and complicated shape of particles of iron slag, which plays a significant role in increasing the interparticle friction. The above factor contributed lowering the slump, L-box and U-Box and increase passing time in V-funnel values. Therefore, it can be concluded that decrease in workability of SCC on use of iron slag. Compressive strength, splitting tensile strength and flexural strength increase with increase of iron slag percentage. The maximum increase in compressive strength is 20% at all ages (7, 28 and 91 days) with 40% replacement. Splitting tensile strength of SCC improved at all the curing ages on use of iron slag as fine aggregate in partial replacement of river sand. At early curing age of 7 days, splitting tensile strength and compressive strength ratio increased with the increase in levels of sand replacement with iron slag in SCC. However, with the progress of curing age of 28 days, the effect of inclusion of iron slag in SCC on splitting tensile strength and compressive strength ratio is not so predominant. Again at 91 days, splitting tensile strength and compressive strength ratio increased with the increase in levels of sand replacement with iron slag in SCC. The modulus of elasticity of iron slag concrete mixtures was higher than that of control SCC mixture at all the curing ages. Images of SEM show the well crystal formation with increase in iron slag content and age and microstructure gets denser due to the formation of ettrinigite in void spaces.
References [1] The Concrete Society, BRE, Technical report No.62 ‘‘Self-compacting concrete: a review”, Day RTU, Holton IX, Eds. Camberley, Surrey 2005: GU17 9AB, UK. [2] H. Okamura, M. Ouchi, Self-compacting Concrete, development, present use and future, in: A. Skarendhal, O. Petersson (Eds.), Proc. First International RILEM Symposium on self-compacting concrete (Stockholm, Sweden), RILEM Publications S.A.R.L, 1999, pp. 3–14. [3] A.M. Nevile, Properties of Concrete, third ed., ELBS and Longman, Singapore, 1989.
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[4] R.S. Kalyoncu, U.S geological survey mineral year book, Slag-iron and steel, 2000. [5] C. Pellegrino, V. Gaddo, Mechanical and durability characteristics of concrete containing EAF slag as aggregates, Cem. Concr. Compos. 31 (2008) 663–671. [6] T. Human, R. Siddique, Properties of mortar incorporating iron slag, Leonardo J. Sci. 23 (2013) 53–60. [7] M. Maslehuddin, M. Alfarabi, M. Shammem, M. Ibrahim, M. Barry, Comparison of properties of steel slag and crushed lime stone aggregate concrete, Constr. Build. Mater. 17 (2003) 105–112. [8] A.N. Alzaed, Effect of iron filling in concrete compression and tensile strength, Int. J. Res. Dev. Eng. Technol. 13 (4) (2014). [9] H.Y. Wang, C.C. Lin, A study of fresh and engineering properties of self compacting high slag concrete(SCHSC), Constr. Build. Mater. 42 (2013) 132– 136. [10] K.K. Sideris, C. Tassos, A. Chalzopoulos, Production of durable self compacting concrete using ladle furnace slag (LFS) as filler material, in: 7th Scientifictechnical conference material problem in civil engineering (MATBUD’2015) 2015,108, pp. 592–597. [11] O. Boukendakdji, S. Kenai, E.H. Kadri, F. Rouis, Effect of slag on the rheology of fresh SCC, Constr. Build. Mater. 23 (2009) 2593–2598. [12] M. Valcuende, F. Benito, C. Parra, I. Minano, Shrinkage of self-compacting concrete made with blast furnace slag as fine aggregates, Constr. Build. Mater. 76 (2015) 1–9. [13] BIS: 8112-1989, Indian standard 43 grade OPC specifications, New Delhi, India, Bureau of Indian standards, 1989.
[14] BIS: 383-1970, Indian standard specifications for coarse and fine aggregates from natural sources for concrete New Delhi, India, Bureau of Indian standards, 1970. [15] EFNARC, Specifications and Guidelines of Self Compacting Concrete, EFNARC, UK, 2005, pp. 1–32. [16] BIS: 516-1959, Indian standard method of test for strength of concrete, New Delhi, India, Bureau of Indian standards, 1959. [17] BIS: 5816-1999, Splitting tensile strength of concrete method of test, New Delhi, India, Bureau of Indian standards, 1999. [18] M. Fadaee, R. Mirhosseini, R. Tabatabaei, M.J. Fadaee, Investigation on using copper slag as part of cementitious material in SCC, Asian J. Civil Eng. (BHRC) 16 (13) (2015) 368–381. [19] V.S. Devi, B.K. Gnanavel, ‘‘Properties of concrete manufactured using steel slag” 12th global congress on manufacturing and management, GCMM 2014, Procedia Eng. 97 (2014) 95–104. [20] A. Patel, P. Bhuva, E. George, D. Bhatt, Compressive strength and modulus of elasticity of self compacting concrete, in: National conference on recent trends in engineering and technology, 2011. [21] L Kothei, R. Malathy, Mechanical properties of self-compacting concrete with partial replacement of natural sand by steel slag, Int. J. Earth Sci. Eng. 05 (03) (2012) 635–639. [22] B.H.V. Pai, M. Nandy, A. Krishnamoorthy, P.K. Sarkar, C.P. Ganapathy, Experimental study on Self-compacting concrete containing industrial byproduct, Eur. Sci. J. 10 (12) (2014). [23] S. Tomasiello, M. Felitti, EAF slag in self compacting concrete, Facta Universitatis Series: Archit. Civil Eng. 8 (2010) 13–20.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Strength properties and micro-structural analysis of self-compacting concrete made with iron slag as partial replacement of fine aggregates Gurpreet Singh ⇑, Rafat Siddique Ph.D Department of Civil Engineering, Thapar University, Patiala, Punjab, India
h i g h l i g h t s Utilization of iron slag in self-compacting concrete (SCC). Iron slag (10–40%) improved the strength properties of SCC. Iron slag improves the microstructure of SCC.
a r t i c l e
i n f o
Article history: Received 22 February 2016 Received in revised form 15 August 2016 Accepted 30 September 2016
Keywords: Iron slag River sand Compressive strength Splitting tensile strength Flexural strength Modulus of elasticity Microstructure
a b s t r a c t The iron and steel rolling mills are the main source of the production of iron slag. This paper presents the results on an experimental program carried to explore the possibility of use of iron slag as partial replacement of fine aggregate (sand) in self-compacting concrete (SCC). SCC mixes were designed and fine aggregates were replaced with 0, 10, 25, and 40% iron slag. Tests were performed to evaluate the fresh properties, strength properties and micro-structural analysis of SCC. Properties such as slump flow, V-funnel, U-box, L-box, compressive strength, splitting tensile strength, flexural strength and modulus of elasticity were examined. Results indicated that compressive strength, splitting tensile strength and flexural strength of self-compacting concrete improved with incorporation of iron slag at all the curing ages. SEM and XRD analysis were done to examine the microstructure, which indicated that use of iron slag made the microstructure of SCC denser. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction Concrete is compacted by vibrations in order to expel entrapped air, making it denser and homogeneous because compaction is necessary to produce durable concrete [1]. Full compaction is difficult due to heavy reinforcement, as a result self-compacting concrete (SCC) was developed in early 1980’s [2]. Self-compacting concrete (SCC) can be defined as a concrete which can be placed with its own weight with or without vibration. It facilitates and ensures proper filling and good structural performance of heavily reinforced congested members. Natural sand (fine aggregates) is getting depleted due to increased consumption of concrete. As a result, substitutes of natural sand are being explored by using waste materials and industrial byproducts. Strength and durability properties are significantly affected by type of fine aggregates [3]. There are several
⇑ Corresponding author. E-mail address: [email protected] (G. Singh). http://dx.doi.org/10.1016/j.conbuildmat.2016.09.154 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
types of industrial byproducts which can be used as fine aggregates in concrete. One such byproduct is iron slag (IS). During the production of iron in blast furnace, blast Furnace Slag is formed when iron ore or iron pellets, coke and a flux (either limestone or dolomite) are melted together in a blast furnace. When the metallurgical smelting process is complete, the lime in the flux has been chemically combined with the aluminates and silicates of the ore and coke ash to form a non-metallic product called blast furnace slag. During the period of cooling and hardening from its molten state, BF slag can be cooled in several ways to form any of several types of BF slag products. So, the objective of a blast furnace is to produce iron, and iron slag is a by-product in this process. Particle size ranges from fine sand to fine gravel. The appearance and particle size distribution of iron slag are similar to that of river sand. The principal constituents of iron slag are silica (SiO2), alumina (Al2O3), calcium (CaO), and magnesia (MgO), which make up 95% of the composition. Small elements entail manganese, iron, and sulfur compounds, as well as trace amounts of several others. Cooling of the slag along with its chemical composition affects its
G. Singh, R. Siddique / Construction and Building Materials 127 (2016) 144–152
Fig. 1. SEM morphology of ordinary Portland cement.
physical properties. There are three additional types of slag in blast furnace: Air-cooled blast furnace quote, Air cooled blast furnace slag rip rap, Slag cement. The rough vesicular texture of slag provides larger surface area in comparison to smoother aggregates which provides good bond with Portland cement as well as high stability in asphalt mixtures [4]. Literature survey indicates that there is no published work related to use of iron slag in self-compacting concrete. Literature review was concentrated on use of slag in concrete as well as self-compacting concrete. Few authors [5–8] reported the effect of types of slags such as electric arc furnace slag [5], iron slag [6], steel slag [7], and iron filing [8] on the properties of mortar and concrete, whereas use of slags in self-compacting concrete have been reported by few authors Wang and Lin [9], Sideris et al. [10], Boukendakdji et al. [11], and Valcuende et al. [12]. Pellegrino et al. [5] concluded that strength properties of concrete made with electric arc furnace slag exhibited comparable (or even better) than conventional concrete made with natural sand. Human and Siddique [6] reported that partial replacement of fine aggregates with iron slag significantly enhanced strength properties and permeability of mortar. Maslehuddin et al. [7]
145
reported that compressive strength of concrete made with steel slag (as coarse aggregates) is better than that of concrete made with lime stone aggregate. Moreover, the improvement in tensile strength of steel slag concrete was not significant. Alzaed [8] concluded that there was gradual increase in compressive strength with addition of iron filling. Compressive strength increased by 17% with 30% of iron filling; however, there was no significant effect on the tensile strength. Wang and Lin [9] indicated that fresh concrete properties and compressive strength of self-compacting high strength concrete (SCHSC) made with 15% furnace slag is higher than control mix. Sideris et al. [10] concluded that use of ladle furnace slag improved fresh concrete properties and as well as compressive strength of SCC. Boukendakdji et al. [11] described that use of ground granulated blast furnace slag in replacement with cement is good for fresh and strength properties of SCC. Valcuende et al. [12] concluded that at early ages the compressive strength of SCC using granulated blast furnace slag as fine aggregates is similar to the SCC made with fine aggregates, but at 90 and 365 days, the strength is higher. As there has not been published work on the use of iron slag in self-compacting concrete, he aim of the present research work was to ascertain the suitability of iron slag as a partial replacement of sand in self-compacting concrete. 2. Experimental detail 2.1. Materials used 2.1.1. Cement Ordinary Portland cement 43 grade conforming to BIS: 81121989 [13]. SEM morphology and EDS spectrum of cement are shown in Figs. 1 and 2, respectively. Physical and chemical properties of cement are given in Table 1. 2.1.2. Fine aggregates River sand (Tokka sand name commonly used in Punjab, India) was used as fine aggregates. They were collected from Chandigarh, Punjab, near Ghaggar River. The specific gravity and fineness modulus of river sand were 2.57 and 2.62 respectively. Sand used for SCC complied with requirements for grading zone-III of BIS: 383-1970 [14]. 2.1.3. Coarse aggregates Coarse aggregates were collected from chapar-kandi quarry located near Ravi River, Punjab, India. The specific gravity and
Fig. 2. EDS spectrum of ordinary Portland cement.
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and river sand are shown in Fig 3. Fineness modulus iron slag is 2.83.
Table 1 Chemical composition and physical properties of cement. Chemical composition
Physical properties
Content CaO SiO2 Al2O3 Fe2O3 MgO LOI
%age 65.7 21.3 6.01 2.2 0.8 4
Color Setting time (min) Initial Final Specific gravity Standard consistency Soundness Le-chat expansion (mm)
Grey 68 278 3.01 34% 3
Table 2 Physical properties of river sand and iron slag. Property
River Sand
Iron Slag
Specific gravity Water absorption by mass (%) Fineness modulus Unit Weight (kg/m3) Appearance
2.57 3.65 2.49 1800 Light grey
2.49 18.54 2.38 2000 Black, glassy more vesicular when granulated
river sand
iron slag
100
% passing
75
2.1.5. Fly ash Class F fly ash was used, having main chemical compounds CaO (12%), SiO2 + Fe2O3 + Al2O3 (71%), Loss of ignition less than 4% and physical properties of fly ash are grey in color, particle size less than 45 lm. 2.1.6. Admixture Auramix-400 low viscosity high performance super-plasticizer based on polycarboxylic technology is used where high water reduction and long workability retention are required, and it has been developed for use in SCC, pumper concrete and high performance concrete, etc. It is light yellow colored liquid with 6.0 pH (min.) value and 0% chloride content. 3. Mixture proportions The mixture proportion of SCC was selected by trial mixes. Control mixture achieved strength of 36.25 MPa at the age of 28 days. Sand was replaced with iron slag by mass in SCC and 10% of fly ash replaced by cement. Fixed quantities of cement, fly ash and coarse aggregates i.e., 455 kg/m3, 45 kg/m3, 760 kg/m3 respectively were used in concrete samples. Fixed water powder ratio of 0.44 and admixture of 1.2% by weight of powder were applied in all SCC mixes. Mix proportions of self-compacting concrete are given in Table 3. 4. Testing procedures
50
25
0 10
100
1000
particle size Fig. 3. Grading of sand and iron slag.
maximum size of coarse aggregates used in this research was 2.69 and 12 mm respectively.
2.1.4. Iron slag Iron slag was collected from Dhiman iron and steel rolling mills, Mandi-Gobindgarh, Fatehgarh Sahib, Punjab India. Iron slag was screened to remove the oversized particle and material passing through 4.75 mm sieve was used in manufacturing of concrete. The major chemical compounds in iron slag are Fe2O3 (66.88%), SiO2 (6.98%), Al2O3 (2.94%), CaO (0.8%), CO2 (22.40%) and physical properties of iron slag used in this research shown in Table 2. Iron slag is brittle and lighter than river sand. River sand and iron slag were dried in oven at 100 °C for 24 h and then cooled down to room temperature before using in concrete. Grading of iron slag
Before casting, the entire test molds were cleaned and oiled properly. These were firmly tightened to correct dimensions before casting. Care was taken that there is no gap left from where there is any possibility of escape of slurry. The ingredients of concrete were mixed in 0.08 cu-m capacity mixer. Testing for SCC involved four mixture compositions using 228 samples (108 cubes of 15 15 15 cm size, 72 cylinders of 15 cm diameter and 30 cm height, and 36 beams of 50 10 10 cm size and 12 cylinders of 10 cm diameter and 20 cm height). 4.1. Fresh properties Immediately after casting, SCC mixtures were examined for fresh concrete properties by slump test, V-funnel test, U-box and L-box as per EFNARC [15]. 4.2. Hardened properties Cubes of 150 mm 150 mm 150 mm size were casted for examining compressive strength. Cylinders of size 150 mm 300 mm were casted for measuring splitting tensile strength, modulus of elasticity. Beams of size 100 mm 100 mm 500 m were casted for measuring flexural strength. Compressive strength and flexural strength of concrete specimen were measured at 7, 28
Table 3 Mixture proportion of SCC. Mixture
Cement (kg/m3)
Fly Ash (kg/m3)
W/P ratio
Sand (kg/m3)
Iron Slag (kg/m3)
Iron Slag (%)
Coarse aggregates (kg/m3)
Admixture (%)
SCC-CM SCC-IS10 SCC-IS25 SCC-IS40
455 455 455 455
45 45 45 45
0.44 0.44 0.44 0.44
960 864 720 576
0 96 240 384
0 10 25 40
760 760 760 760
1.2 1.2 1.2 1.2
IS-iron Slag (10, 25, 40 are the percentage replacement of iron slag with river sand).
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Mixture ID
Slump flow (mm)
L-box (H2/H1)
U-box (H1-H2)
V-funnel (sec.)
SCC-CM SCC-IS10 SCC-IS25 SCC-IS40
774 733 723 687
0.9 0.87 0.86 0.85
32 33 35 35
11 11 12 13
U-box (H2-H1) mm
36
Table 4 Fresh concrete properties.
35 34 33 32 31 30 0
10
Fig. 6. Effect of iron slag on U-box values.
700 650
0
10
25
40
Iron slag (%) Fig. 4. Effect of iron slag on slump values.
Compressive strength (MPa)
Slump flow (mm)
40
750
600
50
7 days
28 days
91 days
40 30 20 10 0 0
10
25
40
Iron slag (%)
0.9
L-box (H2/H1)
25
Iron slag (%)
800
Fig. 7. Effect of iron slag on compressive strength.
0.88 0.86
of powder. The results of fresh properties of self compacting concrete are given in Table 4 and shown in Figs. 4–6.
0.84 0.82 0.8 0
10
25
40
Iron slag (%) Fig. 5. Effect of iron slag on L-box values.
and 91 days, modulus of elasticity of concrete specimen were measured at 28 and 91 days as per BIS: 516-1959 [16]. Splitting tensile strength concrete specimen was measured at 7, 28 and 91 days as per BIS: 5816-1999 [17]. For, modulus of elasticity of concrete, the cylinder specimen was loaded at the rate of 13 MPa/min until an average stress of (C + 0.5) MPa was achieved, where C is one-third of average compressive strength of cube. The load was maintained for one minute and then reduced gradually. The load was applied a second time at the same rate until the average stress of (C + 0.15) MPa was reached.
5. Result and discussion 5.1. Fresh concrete properties The properties of SCC at fresh stage were evaluated by flow ability, passing ability and consistency of SCC incorporating different percentages of iron slag. The evaluation of fresh concrete properties is done by slump flow test, L-box test, U-box test and Vfunnel test. It was perceived that inclusion of iron slag in self compacting concrete mixture decreased the workability. All fresh concrete properties are in good quality resemblance as per European procedure, ENFNARC [15]. Mixtures were tested for fresh concrete properties. The content of water-powder ratio was 0.44 and admixture was 1.2% by weight
5.1.1. Slump flow In case of slump flow, all mixtures of SCC shows slump flow in the range of 680–780 mm (Fig. 4) are within the limits (650– 800 mm) given by EFNARC [15]. This indicated good quality deformability. Iron slag particles are more granulated and sharp edged as compared to river sand. The rough texture and complicated shape of iron slag particles plays a significant role in increasing the inter-particle friction cause jamming of concrete particles. Wang and Lin [9] reported that slump flow diameter of all SCC mixtures was in the range of 550–770 mm; whereas Tomasiello and Felitti [23] and Boukendakdji et al. [11] reported that slump flow diameter was in the range of 650–770 mm.
5.1.2. L-box The L-box ratio for all the SCC mixtures was between 0.84–0.91 and within boundaries of EFNARC [15] range (0.8–1.0). The result shows (Fig. 5 and Table 4) that blocking ratio increased with the increase in replacement percentage of iron slag. Tomasiello and Felitti [23] reported L-box ratios of all SCC mixtures in the range of 0.70 to 0.86. Sideris et al. [10] observed L-box ratio of all SCC mixtures using ladle furnace slag as filler material in the range of 0.84 to 1.
5.1.3. U-box The variation on height of concrete in two compartments of Ubox was found in the range of 32–35 mm. The results of U-box of SCC mixtures were inside the limits of EFNARC [15]. The U-box test results are shown in Table 4 and Fig. 6. It can be observed that values increase with the increase of replacement percentage of iron slag with river sand. Boukendakdji et al. [11] reported the variation on height in U-box compartments in the range of 23 to 39 mm.
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5.1.4. V-funnel Time in V-funnel test increases as iron slag level is increased as replacement of sand. The test results are given in Table 4. Results show that time ranges between 11 and 13 s. The results of Vfunnel test of SCC mixtures were inside the limits as per EFNARC [15]. Fadaee et al. [18] reported V-funnel time range of 8–12 s. with the replacement of copper slag with cement. Boukendakdji et al. [11] reported all five mixes of SCC exhibited flow time values inside the range of 4 to 14.8 mm.
Splitting tensile strength (MPa)
148
5
7 days
28 days
91 days
4 3 2 1 0 0
6. Strength properties
10
25
40
Iron slag (%) 6.1. Compressive strength Compressive strength test results presented in Fig. 7 show that the strength development pattern of iron slag at all levels of sand replacement with iron slag is similar to the control mixes. It is observed that compressive strength increase in increase with iron slag content. At 7 days, SCC mixtures containing 10, 25, 40% iron slag as fine aggregates gained 3, 8, and 16% respectively more compressive strength as compared to 7 days SCC mixture without iron slag. At the curing age of 28 days, SCC mixtures containing 10, 25 and 40% iron slag as fine aggregates gained 1%, 13 and 20% respectively more compressive strength as compared to 28 days SCC mixture without iron slag. At the age of 91 days, SCC mixtures containing 10, 25 and 40% iron slag as fine aggregates gained 2, 11% and 16% respectively more compressive strength as compared to 91 days SCC mixture without iron slag. At the curing age of 28 days and 91 days, the increase in compressive strength percentage of SCC mixtures containing iron slag is more than control mixes. With increasing age, reactive silica in iron slag reacts with alkali calcium hydroxide produced by hydration of cement and forms calcium silicate and aluminates hydrates. The formation of stable calcium silicate and aluminates hydrates by chemical reaction between cement pastes constitutes and aggregates result in filling the voids in the interfacial transition zone and in improving its compressive strength. Alzaed [8] evaluated the effect of iron filling (0, 10, 20 and 30%) on the compressive strength of concrete. The compression tests were carried out on standard cubes (15 15 15 cm). Compressive strength of concrete increased gradually when iron filling is added in concrete mix. Compressive strength increased 17% when 30% of iron filling. Wang and Lin [9] presented an experimental study in which 0, 15 and 30% of furnace slag were replaced with cement to obtain better results of SCC. It was concluded that compressive strength of SCC with 15% of cement replaced by furnace slag is higher than that of control group (13% increment in compressive strength). The compressive strength results of this investigation are similar with those reported in previous studies by Sideris et al. [10]. 6.2. Splitting tensile strength Splitting tensile strength test results presented in Fig. 8 shows that the strength development pattern of iron slag, at the all levels of sand replacement with iron slag, is similar to that control mixes. The test results indicate that replacement of river sand with iron slag in SCC improved the splitting tensile strength. At the curing age of 7 days, SCC mixtures containing 10, 25 and 40% iron slag as fine aggregates gained 19, 28 and 34% respectively more splitting tensile strength as compared to 7 days SCC mixture without iron slag. At the curing age of 28 days, SCC mixtures containing 10, 25 and 40% iron slag as fine aggregates gained 3.5, 16 and 21% respectively more splitting tensile strength as compared to 28 days SCC mixture without iron slag. At the age of 91 days, SCC
Fig. 8. Effect of iron slag on splitting tensile strength.
mixtures containing 10, 25 and 40% iron slag as fine aggregates gained 3, 20 and 23% respectively more splitting tensile strength as compared to 91 days SCC mixture without iron slag. Splitting tensile strength of SCC mixture made with iron slag is higher than control mix al all ages (7,28 and 91 days). Devi and Gnanavel [19] carried out a research to find the effect of steel slag on the engineering properties of conventional concrete with partial replacement of coarse and fine aggregates up-to 50%. It was concluded that splitting tensile strength results of this study are more satisfactory. Similar findings of splitting tensile strength results were reported by Alzaed [8]. Furthermore, splitting tensile strength and compressive strength ratios are calculated and given in Table 5. At the age of 28 and 91 days the splitting tensile strength of all iron slag mixes as well as control mix was nearly 7.5% and 8.5% respectively of their compressive strength. Test result shows that splitting tensile strength and compressive strength ratio decreases with the increase of curing age and it increases with replacement of iron slag as compared to control mix.
6.3. Flexural strength test Flexural strength test results are shown in Fig. 9 show similar increment in flexural strength as in case of compressive strength and splitting tensile strength. At 7 days, SCC mixtures containing 10, 25 and 40% iron slag as fine aggregates obtained 2.5, 12 and 18% more flexural strength as compared with control mix. At 28 days, SCC mixtures containing 10%, 25%, 40% iron slag as fine aggregates obtained 1, 5 and 14% more flexural strength as compared with control mix. At the curing age of 91 days, SCC mixtures containing 10, 25 and 40% iron slag as fine aggregates obtained 2.5, 8 and 11.5% more flexural strength as compared with control mixture. Kothei and Malathy [21] presented the results of SCC made with 10 to 100% of steel slag as replacement with fine aggregates. It was concluded that up to 40% replacement of fine aggregates with steel slag gives the better results of flexural strength. These results are comparable with the results of this study and similar finding of flexural strength results was reported by Pai et al. [22]. In this research, flexural strength increases with the increase of iron slag content. It is clear that the flexural tensile strength
Table 5 Splitting tensile strength and compressive strength ratios. SCC Mixture
SCC-CM SCC-IS10 SCC-IS25 SCC-IS40
Splitting tensile strength/compressive strength ratio (%) 7 days
28 days
91 days
5.7 6.8 7.3 7.3
7.6 7.8 7.8 7.7
7.5 7.6 8.5 8.3
149
Flexural strength (MPa)
5
7 days
28 days
Modulus of elasticity (GPa)
G. Singh, R. Siddique / Construction and Building Materials 127 (2016) 144–152
91 days
4 3 2 1 0 0
10
25
31
SCC CM
30
SCC-IS10
28 27 26 25 24 23 7
40
28
Modulus of elasticity (GPa)
28 days
91
Curing age (days) Fig. 11. Modulus of elasticity verses age.
Fig. 9. Effect of iron slag on flexural strength.
7 days
SCC-IS40
29
Iron slag (%)
31 30 29 28 27 26 25 24 23
SCC-IS25
91 days
CSH Gel
Voids 0
10
25
40
Ettringite
Iron slag (%) Fig. 10. Effect of iron slag on modulus of elasticity.
increases when the compressive strength and age of the concrete increases. Moreover, the increase in the flexural strength is higher than the corresponding increase in the compressive strength at same age of concrete. The percentage increase in flexural tensile strength increases with the increase of level of concrete strength. It is due to the different concrete compression and flexure failure mechanism of low and high strength concrete. Under the flexure loading, the cracks are initiated in the interfacial zone at low stresses and extend into the mortar matrix at high stresses and the resistance to cracks propagation results from the cement paste only.
Modulus of elasticity is the property that influences the safety durability, density and service life of reinforced concrete, Patel et al. [20]. Modulus of elasticity of concrete mixtures was measured at the curing age of 7 days, 28 days and 91 days. The test results are shown in Figs. 10 and 11. Even though the compressive strength was not strongly affected, the modulus of elasticity of concrete increased approximately linearly with the increase in replacement levels of sand with iron slag. The modulus of elasticity of iron slag concrete mixtures was higher than that of control concrete mixture. Modulus of elasticity of control mixture at 7 days curing age was 25.51 GPa, when 10, 25 and 40% of fine aggregates was replaced with iron slag modulus of elasticity of SCC increased to 25.62 GPa, 26.07 GPa and 26.17 GPa respectively. At 28 days curing age, the modulus of elasticity of control SCC was 27.90 GPa when 10%, 25% and 40% of fine aggregates was replaced with iron slag modulus of elasticity of SCC increased to 28.19 GPa, 28.71 GPa and 28.87 GPa. At 91 days curing age, the modulus of elasticity of control SCC was 28.10 GPa when 10, 25 and 40% of fine aggregates was replaced with iron slag modulus of elasticity of SCC increased to 28.78 GPa, 29.43 GPa and 29.70 GPa. SCC made with iron slag gives more modulus of elasticity values as compared to control mixture.
Fig. 12. SEM Image Of SCC (Without Iron Slag) At 28 Days.
Voids Calcium hydroxide
6.4. Modulus of elasticity
CSH Gel
Voids
Calcium hydroxide
CSH Gel
Fig. 13. SEM image of SCC (without iron slag) at 91 days.
7. Microstructure The hardened property of concrete depends on its intrinsic microstructure. The concrete structure is principally affected by the hydration period, water cement ratio, addition of mineral admixture and type of cement used in the production of concrete. Scanning electron micrograph (SEM) can provide both topographic and compositional analysis of material. In this research broken pieces of concrete generated by crushing were mounted on the SEM stub and images were obtained using SE image mode. SEM
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CSH Gel
Dense CSH Gel
Calcium hydroxide CSH Gel
Fig. 14. SEM image of SCC (with 10% of iron slag) at 28 days.
Fig. 17. SEM image of SCC (with 25% of iron slag) at 91 days.
CSH Gel Calcium hydroxide
Voids CSH Gel CSH Gel
Voids
Ettiringite
Fig. 15. SEM image of SCC (with 10% of iron slag) at 91 days.
Fig. 18. SEM image of SCC (with 40% of iron slag) at 28 days.
Voids
Ettiringite
CSH Gel
Fig. 16. SEM image of SCC (with 25% of iron slag) at 28 days.
Fig. 19. SEM image of SCC (with 40% of iron slag) at 91 days.
images of SCC-CM, SCC-IS10, SCC-IS25, and SCC-IS40 are shown in Figs 12–19 at the curing age of 28 and 91 days. These micrographs show that clear spread of CSH gel, voids and formation of ettringite in void spaces. Fig. 12 shows SCC mixture without iron slag replacement at the age of 28 days. In this figure micro voids, spread
of CSH gel in some areas and formation of ettringite in void spaces can be observed. Fig. 13 shows the same mixture proportion at the age of 91 days. Micro pores/voids, CSH gel and plates of calcium hydroxide were observed in the image. Fig. 14 shows SCC mixture with 10% iron slag replacement at the age of 28 days. Image being a
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2 Theta angle Fig. 20. XRD spectra of SCC control mixture. (P- Calcium hydroxide, CSH-calcium silicate hydrates, Q- quartz, CS-calcium silicates, CAO- calcium oxide).
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material used. The X-ray diffraction technique was used to analyze the SCC Control mixture without iron slag and SCC with 40% iron slag at the age of 28 days. The XRD was done using a Panalytical X’Pert pro, with Cu Ka, radiation at SAI labs, Thapar University, Patiala. The X’Pert High Score Plus software was used to identify the phases. The cement paste was separated from concrete samples and was sieved through 90 lm sieve. The XRD were conducted for diffraction angle 2 Theta range between 10° and 90°. XRD diffractograms of powder cement paste of SCC control mixture and SCC containing 40% iron slag are presented in Figs. 20 and 21. The XRD shows the presence of quartz, calcium silicate hydrates, calcium hydroxide, calcium silicates and calcite. One major problem encountered in the qualitative analysis of all SCC mixtures was overlapping of diffraction peaks. XRD analysis of all the mixtures shows that there is no qualitative change in the phases present. 9. Conclusions The present experimental study was carried out to investigate the factibility of using iron slag as a replacement of fine aggregates in SCC. Experiments were conducted by replacing fine aggregates with iron slag in varying percentages in SCC. Test result indicates that iron slag is a good candidate to be used in partial replacement of fine aggregates in production of structural self compacting concrete of grade between M30 and M40. Based on the analysis of test results, the following conclusions can be drawn.
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2 Theta angle Fig. 21. XRD spectra of SCC mixture with 40% iron slag (P- calcium hydroxide, CSHcalcium silicate hydrates, Q- quartz, CS-calcium silicates, C-calcite).
more mature paste with limited space and well formed crystals. Fig. 15 depicts the same mixture proportion at the age of 91 days. The formation of ettringite in void spaces and CSH gel can observed widely spread. Fig. 16 shows SCC mixture with 25% iron slag replacement at the age of 28 days. Well formed crystals were observed. Furthermore a similar mixture proportion at the age of 91 days is illustrated in Fig. 17. It was observed that dense CSH gel was fully spread over the micrograph leading to highly uniform and dense structure. The CSH formation serves as a thin pliable sheet of material. This would make concrete more resistant to aggressive environment. Fig. 18 shows SCC mixture with 40% iron slag replacement at the age of 28 days. Image shows more mature paste with low porosity. Fig. 19 shows the same mixture proportion at the age of 91 days. In this figure, ettringites with its needle like habit and calcium hydroxide crystals showing their characteristic cleavage can be observed. CSH gel and ettringite needles are identified.
8. X-ray diffraction X-ray diffraction is one of the most powerful tools for identifying unknown crystalline phases. By comparing the positions and intensities of the diffraction peaks against a library of known crystalline phases, the target material can be recognized. In addition, multiple phases in sample can be identified and quantified. XRD analyses were conducted to identify the components of SCC mixtures and
The results show that slump values, U-box values and L-box values decreased with the increase in level of iron slag. V-funnels test value of time is increased as the iron slag content dose. The rough texture and complicated shape of particles of iron slag, which plays a significant role in increasing the interparticle friction. The above factor contributed lowering the slump, L-box and U-Box and increase passing time in V-funnel values. Therefore, it can be concluded that decrease in workability of SCC on use of iron slag. Compressive strength, splitting tensile strength and flexural strength increase with increase of iron slag percentage. The maximum increase in compressive strength is 20% at all ages (7, 28 and 91 days) with 40% replacement. Splitting tensile strength of SCC improved at all the curing ages on use of iron slag as fine aggregate in partial replacement of river sand. At early curing age of 7 days, splitting tensile strength and compressive strength ratio increased with the increase in levels of sand replacement with iron slag in SCC. However, with the progress of curing age of 28 days, the effect of inclusion of iron slag in SCC on splitting tensile strength and compressive strength ratio is not so predominant. Again at 91 days, splitting tensile strength and compressive strength ratio increased with the increase in levels of sand replacement with iron slag in SCC. The modulus of elasticity of iron slag concrete mixtures was higher than that of control SCC mixture at all the curing ages. Images of SEM show the well crystal formation with increase in iron slag content and age and microstructure gets denser due to the formation of ettrinigite in void spaces.
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