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Strength, durability, and micro-structural properties of concrete made with used-foundry sand (UFS)
Construction and Building Materials 25 (2011) 1916–1925
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Strength, durability, and micro-structural properties of concrete made with used-foundry sand (UFS) Rafat Siddique a,⇑, Yogesh Aggarwal b, Paratibha Aggarwal b, El-Hadj Kadri c, Rachid Bennacer d a
Civil Engineering Department, Thapar University, Patiala 147004, India Civil Engineering Department, National Institute of Technology, Kurukshetra, India c Department of Civil Engineering, University of Cergy Pontoise, Neuville-sur-Oise, 95031 Cergy-Pontoise, France d Civil Engineering, LMT-Ecole Normale Supérieure – Cachan, 61 av. du président Wilson, F-94235 Cachan Cedex, France b
a r t i c l e
i n f o
Article history: Received 21 August 2010 Received in revised form 21 October 2010 Accepted 13 November 2010 Available online 16 December 2010 Keywords: Concrete Foundry sand Strength properties Durability properties Microstructure
a b s t r a c t This paper presents the design of concrete mixes made with used-foundry (UFS) sand as partial replacement of fine aggregates. Various mechanical properties are evaluated (compressive strength, and splittensile strength). Durability of the concrete regarding resistance to chloride penetration, and carbonation is also evaluated. Test results indicate that industrial by-products can produce concrete with sufficient strength and durability to replace normal concrete. Compressive strength, and split-tensile strength, was determined at 28, 90 and 365 days along with carbonation and rapid chloride penetration resistance at 90 and 365 days. Comparative strength development of foundry sand mixes in relation to the control mix i.e. mix without foundry sand was observed. The maximum carbonation depth in natural environment, for mixes containing foundry sand never exceeded 2.5 mm at 90 days and 5 mm at 365 days. The RCPT values, as per ASTM C 1202-97, were less than 750 coulombs at 90 days and 500 coulombs at 365 days which comes under very low category. Thereby, indicating effective use of foundry sand as an alternate material, as partial replacement of fine aggregates in concrete. Micro-structural investigations of control mix and mixes with various percentages of foundry sand were also performed using XRD and SEM techniques. The micro-structural investigations shed some light on the nature of variation in strength at the different replacements of fine aggregates with foundry sand, in concrete. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Concrete is the most widely used man-made product in the world, and is second only to water as the world’s most utilized substance. Slightly more than a ton of concrete is produced each year for every human being on the planet, some six billion tons a year. Concrete is an affordable and reliable material that is applied throughout the infrastructure of a nation’s construction, industrial, transportation, defense, utility, and residential sectors. Fundamentally, concrete is economical, strong, and durable. Although concrete technology across the industry continues to rise to the demands of a changing marketplace, the industry recognizes that considerable improvements are essential in productivity, product performance, energy efficiency, and environmental performance. The industry will need to face and overcome a number of institutional, competitive, and technical challenges. One of the major challenges, with the environmental awareness and scarcity of space for landfilling, is the wastes/byproduct utilization as an alternative to disposal. ⇑ Corresponding author. Tel.: +91 175 239 3207; fax: +91 175 236 4498. E-mail address: [email protected] (R. Siddique). 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.11.065
Throughout the industrial sector, including the concrete industry, the cost of environmental compliance is high. Introduction of use of industrial by-products such as foundry sand, fly ash, bottom ash, and slag can result in significant improvements in overall industry energy efficiency and environmental performance. Foundry sand is high quality silica sand with uniform physical characteristics. It is a by-product of ferrous and non-ferrous metal casting industries, where sand has been used for centuries as a molding material because of its thermal conductivity. Foundries successfully recycle and reuse the sand many times in a foundry. When the sand can no longer be reused in the foundry, it is removed from the foundry and is termed as foundry sand. Usedfoundry sand can be reused in various applications as an alternative to sending it to landfill, and reuse options are well established in England, Europe and North America. Reuse options include cement manufacture, asphalt, concrete, bricks and free-flow fill for certain construction applications. Some of these alternatives are starting to be adopted in India, but is still in early stage. Overseas examples show that it is not only better for the environment but is profitable for the foundry to use the sand alternatively. These foundries have significantly reduced the volume of waste sand
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going to landfill and actually offset the total cost of transporting the sand ‘in’ and ‘out’. The objectives of this study are to investigate the effect of use of foundry sand as partial replacement of fine aggregates in various percentages (0–60%), on concrete properties such as mechanical and durability characteristics of the concrete along with microstructural analysis with XRD and SEM. Application of used-foundry sand in concrete will lead to diversion of large amounts of usedfoundry sand from land filling to manufacturing of concrete. 3. Experimental methods The effect of using foundry sand as partial replacement of fine aggregates in various percentages, on concrete was investigated. Also, the effect of incorporating foundry sand in concrete on the mechanical, durability properties and microstructure were evaluated.
3.1. Materials and mix proportions Portland Pozzolana Cement (53 MPa) conforming to Indian standard specifications IS: 1489-1991 was used. Consistency was 27%, specific gravity was 3.56 and fineness as per specific surface of cement was 354 m2/kg. Locally available natural sand with 4.75 mm maximum size was used as fine aggregate. It fulfilled the requirements of ASTM C 33-02a and crushed stone with 20 mm maximum size was used as coarse aggregate. The properties of fine aggregates and coarse aggregates were found to conform to IS: 383-1970 with specific gravity of sand as 2.63 and coarse aggregate as 2.77. Unit weight of sand and coarse aggregate was 1890 and 1650 kg/m3, respectively. Fineness modulus was observed to be 3.03 for sand and 6.74 for coarse aggregates. Locally available foundry sand was used as partial replacement of fine aggregates (regular sand). Foundry sand with specific gravity
Table 1 Chemical properties of foundry sand. Constituents
% by weight (used in present study)
Requirements as per American foundry men’s society, 1991
Loss on ignition Silica (SiO2) Iron oxide (Fe2O3) Alumina (Al2O3) Calcium oxide (CaO) Magnesium oxide (MgO) Sulphate Chloride
2.15
5.15% (max)
78.81 4.83
87.9% 0.94%
6.32
4.70%
1.88
0.14% (min)
1.95
0.3%
0.05 0.04
0.09% –
2.61, unit weight 1638 kg/m3 and fineness modulus 1.78 was used. The foundry sand showed lower fineness modulus and bulk density than the regular sand. As per the particle size distribution of the foundry sand, the size corresponding to 50% of passing (d50) was around 33 lm and average diameter of foundry sand particle was observed to be 28.8 lm. Table 1 gives the chemical composition of foundry sand. A polycarboxylic ether based superplasticizer of CICO brand complying with ASTM C-494 type F, IS: 9103 – 1999 and IS: 2645-2003 was used. Seven mix proportions were prepared. First was control mix (without foundry sand), and the other six mixes contained foundry sand. Fine aggregate (sand) was replaced with foundry sand by weight. The proportions of fine aggregate replaced ranged from 10% to 60% at the increment of 10%. Mix proportions are as given in Table 2. The control mix without foundry sand was proportioned as per Indian standard specifications IS: 10262-1982, to obtain a 28-day cube compressive strength of 36 MPa. Hand mixing was done for the all the concrete mixes. 3.2. Testing procedure Fresh concrete properties such as slump flow, compaction factor, vee-bee consistometer were determined according to an Indian Standard specification IS: 11991959. The results are presented in Table 2. The 150 mm concrete cubes and 150 300 mm cylinders were cast for compressive strength, and 150 300 mm cylinders for split-tensile strength. After required period of curing, the specimens were taken out of the curing tank and their surfaces were wiped off. The various tests performed were compressive strength test of cubes (150 mm side), cylinders (150 mm 300 mm), and split-tensile strength of cylinders (150 mm 300 mm) at 28, 90, and 365 days, as per IS: 516-1959. The cylinders (100 mm 200 mm) were cast for rapid chloride penetration resistance test and were sliced 2-in. (51-mm) thick of 4-in. (102-mm) nominal diameter. Rapid chloride penetration resistance test (according to ASTM C 120297) covered the determination of the electrical conductance of concrete to provide a rapid indication of its resistance to the penetration of chloride ions. The test method consisted of monitoring the amount of electrical current passed through 2-in. (51-mm) thick slices of 4-in. (102-mm) nominal diameter cores or cylinders for a 6-h period. A potential difference of 60 V dc was maintained across the ends of the specimen, one of which was immersed in a sodium chloride solution, the other in a sodium hydroxide solution. The total charge passed, in coulombs, was related to the resistance of the specimen to chloride ion penetration. The cylinders (150 mm 300 mm) were cast for carbonation test. Carbonation test of depth of color less region using phenolphthalein indicator was determined using the cylinders (150 mm 300 mm) as per RILEM CPC-18 [11]. After casting, test specimens were covered with plastic sheets and left in casting room for 24 h at room temperature and demolded and cured in water for 28 days. After that, specimens were air cured (open environment) for the required age say till 90-days or 365-days, and then were split. The freshly split surface was cleaned and sprayed with a phenolphthalein pH indicator. The indicator was a phenolphthalein 1% ethanol solution (1 g phenolphthalein and 90 ml ethanol (95.0 V/V%) diluted in water to 100 ml. The average depth ‘Xp’ of the colorless phenolphthalein region was measured from three points, perpendicular to the two edges of the split face, immediately after spraying the indicator. X-ray diffraction analysis (XRD) was done on Philips PW 1140/09. Diffractometer operated at 35 kV, using Cu ka radiation and Ni filler. The samples for X-ray diffraction analysis were prepared in powdered form. The concrete sample was taken from the inner core of the matrix. X-ray diffraction is a non-destructive technique used to determine the elements present in any particular substance. X-ray diffraction is based on the fact that, in a mixture, the measured intensity of a diffraction peak is directly proportional to the content of the substance producing it (Soroka
Table 2 Mix proportions of concrete mixes containing UFS. Mix no.
CM
F10
F20
F30
F40
F50
F60
Cement (kg/m3) Foundry sand (%) Foundry sand (kg/m3) Water (kg/m3) W/C Sand SSD (kg/m3) Coarse aggregate(kg/m3) Superplasticizer(kg/m3) Slump (mm) Compaction factor Vee-bee consistometer (sec) Air temperature (°C) Concrete temperature (°C) Fresh concrete density (kg/m3) pH value 90-days 365-days
350 0 0 175 0.5 605 1260 1.75 30 0.83 5.98 23 25 2437.7
350 10 60.5 175 0.5 544.5 1260 1.75 30 0.88 4.40 26 29 2414.0
350 20 121.0 175 0.5 484.0 1260 1.75 30 0.84 4.98 27 27 2419.2
350 30 181.5 175 0.5 423.5 1260 1.75 30 0.85 4.97 20 23 2426.8
350 40 242.0 179.24 0.512 363.0 1260 1.75 30 0.81 5.65 22 24 2420.1
350 50 302.5 185.6 0.53 302.5 1260 1.75 30 0.81 5.34 22 24 2416.1
350 60 363.0 196.2 0.56 242.0 1260 1.75 20 0.78 6.25 34 28 2402.2
11.70 11.80
11.73 11.75
11.75 11.91
11.75 11.57
11.72 11.60
11.72 11.40
11.90 11.42
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[12]). Since 2d is a known constant, the 2h setting of each peak corresponds to a certain wave length. The scanning electron microscopic studies of various concrete samples and constituent materials were carried out using Philips XL20 Scanning Electron Microscope. The concrete specimens were first cured in water for 365 days and then oven dried at 105 °C for 24 h.
4. Results and discussions 4.1. Fresh concrete properties The effect of using foundry sand as partial replacement of fine aggregates in various percentages, on concrete was investigated. Also, the effect of incorporating foundry sand in concrete on the mechanical, durability properties and microstructure were evaluated. 3.1. Materials and mix proportions Portland Pozzolana Cement (53 MPa) conforming to Indian standard specifications IS: 1489-1991 was used. Consistency was 27%, specific gravity was 3.56 and fineness as per specific surface of cement was 354 m2/kg. Locally available natural sand with 4.75 mm maximum size was used as fine aggregate. It fulfilled the requirements of ASTM C 33-02a and crushed stone with 20 mm maximum size was used as coarse aggregate. The properties of fine aggregates and coarse aggregates were found to conform to IS: 383-1970 with specific gravity of sand as 2.63 and coarse aggregate as 2.77. Unit weight of sand and coarse aggregate was 1890 and 1650 kg/m3, respectively. Fineness modulus was observed to be 3.03 for sand and 6.74 for coarse aggregates. Locally available foundry sand was used as partial replacement of fine aggregates (regular sand). Foundry sand with specific gravity 2.61, unit weight 1638 kg/m3 and fineness modulus 1.78 was used. The foundry sand showed lower fineness modulus and bulk density than the regular sand. As per the particle size distribution of the foundry sand, the size corresponding to 50% of passing (d50) was around 33 lm and average diameter of foundry sand particle was observed to be 28.8 lm. Table 1 gives the chemical composition of foundry sand. A polycarboxylic ether based superplasticizer of CICO brand complying with ASTM C-494 type F, IS: 9103 – 1999 and IS: 2645-2003 was used. Seven mix proportions were prepared. First was control mix (without foundry sand), and the other six mixes contained foundry sand. Fine aggregate (sand) was replaced with foundry sand by weight. The proportions of fine aggregate replaced ranged from 10% to 60% at the increment of 10%. Mix proportions are as given in Table 2. The control mix without foundry sand was proportioned as per Indian standard specifications IS: 10262-1982, to obtain a 28-day cube compressive strength of 36 MPa. Hand mixing was done for the all the concrete mixes. 3.2. Testing procedure Fresh concrete properties such as slump flow, compaction factor, vee-bee consistometer were determined according to an Indian Standard specification IS: 1199-1959. The results are presented in Table 2. The 150 mm concrete cubes and 150 300 mm cylinders were cast for compressive strength, and 150 300 mm cylinders for split-tensile strength. After required period of curing, the specimens were taken out of the curing tank and their surfaces were wiped off. The various tests performed were compressive strength test of cubes (150 mm side), cylinders (150 mm 300 mm), and split-tensile strength of cylinders (150 mm 300 mm) at 28, 90, and 365 days, as per IS: 516-1959. The cylinders (100 mm 200 mm) were cast for rapid chloride penetration resistance test and were sliced 2-in. (51-mm) thick of 4-in. (102-mm) nominal diameter. Rapid chloride penetration
resistance test (according to ASTM C 1202-97) covered the determination of the electrical conductance of concrete to provide a rapid indication of its resistance to the penetration of chloride ions. The test method consisted of monitoring the amount of electrical current passed through 2-in. (51-mm) thick slices of 4-in. (102mm) nominal diameter cores or cylinders for a 6-h period. A potential difference of 60 V dc was maintained across the ends of the specimen, one of which was immersed in a sodium chloride solution, the other in a sodium hydroxide solution. The total charge passed, in coulombs, was related to the resistance of the specimen to chloride ion penetration. The cylinders (150 mm 300 mm) were cast for carbonation test. Carbonation test of depth of color less region using phenolphthalein indicator was determined using the cylinders (150 mm 300 mm) as per RILEM CPC-18 [11]. After casting, test specimens were covered with plastic sheets and left in casting room for 24 h at room temperature and demolded and cured in water for 28 days. After that, specimens were air cured (open environment) for the required age say till 90-days or 365-days, and then were split. The freshly split surface was cleaned and sprayed with a phenolphthalein pH indicator. The indicator was a phenolphthalein 1% ethanol solution (1 g phenolphthalein and 90 ml ethanol (95.0 V/V%) diluted in water to 100 ml. The average depth ‘Xp’ of the colorless phenolphthalein region was measured from three points, perpendicular to the two edges of the split face, immediately after spraying the indicator. X-ray diffraction analysis (XRD) was done on Philips PW 1140/ 09. Diffractometer operated at 35 kV, using Cu ka radiation and Ni filler. The samples for X-ray diffraction analysis were prepared in powdered form. The concrete sample was taken from the inner core of the matrix. X-ray diffraction is a non-destructive technique used to determine the elements present in any particular substance. X-ray diffraction is based on the fact that, in a mixture, the measured intensity of a diffraction peak is directly proportional to the content of the substance producing it (Soroka [12]). Since 2d is a known constant, the 2h setting of each peak corresponds to a certain wave length. The scanning electron microscopic studies of various concrete samples and constituent materials were carried out using Philips XL20 Scanning Electron Microscope. The concrete specimens were first cured in water for 365 days and then oven dried at 105 °C for 24 h. 4. Results and discussions 4.1. Fresh concrete properties The workability of fresh concrete is a composite property which includes the diverse requirements of stability, mobility, compactibility, placeability, and finishability. Slump is a measure indicating the consistency or workability of concrete. Slump for control mix CM was 30 mm and for the F mixes it was observed to be 30 to 40 mm. The compaction factor values for control mix, and F mixes corresponded to the slump flow values as per Table 2. The presence of finer foundry sand particles in concrete lead to the increase in the water demand, as compared to the regular sand particles. Thus, to maintain the workability within specified range, the water content was constant till F30 and thereafter increased. The values of vee-bee time for control mix CM, and F mixes corresponds to the slump flow values and compaction factor values as per ACI Committee 211 [13]. 4.2. Mechanical properties 4.2.1. Compressive strength. Cube compressive strength results of mixes made with various percentages of foundry sand i.e., CM (0% FS), F10 (10% FS), F20 (20% FS), F30 (30% FS) F40 (40% FS), F50 (50% FS), F60 (60% FS), at ages of 28, 90 and 365 days are shown in Table 3. There is marginal decrease in the compressive
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strength of concrete mixes with the inclusion of foundry sand as replacement of regular sand. The maximum strength was obtained at 30% foundry sand in all the replaced mixes and was more than control mix at 28 days, 90 days and 365 days. The strength variation for the various percentages of replacements was observed to be linearly increasing from 10% to 50% with different behaviour of mix F30, attaining a comparatively high strength almost closer or more than the strength of the CM mix. The strength of F60 mix reduced drastically. The strengths of F30, F40, and F50 mixes were observed to be more than the strength of CM mix at the ages of 28 days, 90 days and 365 days. Also, the strength of F20 mix was also observed to be more than the strength of CM mix at 365 days. Lam et al. [14] reported gain of strength between 7 days and 90 days for normal concrete (slump about 75 mm) as 72% which is characteristic of normal concrete. At 90 days, the rate of gain was closer to that of control mix and at 365 days, the rate of gain for all the F mixes was higher than the CM mix. As in cube compressive strength, the cylinder compressive strength as indicated in Table 2 of mix F30 was highest among all F mixes, at all ages of 28, 90 and 365-days and even higher than control mix CM at 365-days. Also, linear increase of 28-day, 90day, and 365-day strength was observed from F10 to F50 except for mix F30. F mixes showed the 28-day cylinder compressive strengths between 0.64 to 0.70 times; the 90-day cylinder compressive strengths between 0.65 to 0.76 times and the 365-day compressive strengths between 0.67 to 0.74 times the corresponding cube compressive strength of concrete. The increase in compressive strength (cube and cylinder) with the inclusion of foundry sand could probably be due to the fact that foundry sand was finer than regular sand which resulted in the denser concrete matrix. Inclusion of foundry sand has not adversely affected the 28-day compressive strengths of concrete mixes made with foundry sand, but has shown a linear increase between mixes F10 and F50 depending upon the foundry sand content.
4.2.2. Split-tensile strength. The results for split-tensile strength are shown in Table 4. The variation in the split-tensile strength with foundry sand content was similar to that observed in the case of the compressive strength. When compared to control mix CM, it was observed that F30, F40, and F50 mixes showed higher strength at 28 days, 90 days, and 365-days. The optimum replacement of sand with foundry sand can no doubt be assumed as F30, as it has attained highest strength among all mixes at all ages. A decrease in strength for mix F60 is observed, after a linear increase of split-tensile strength from F10 to F50, except F30 mix at all ages. 28-day split-tensile strength of showed decrease of 11.5%, 4.8% and 17.30% for F10, F20 and F60 mixes and increase of 24.03%, 19.23%, and 14.42% for F30, F40 and F50 mixes, in comparison with the strength of the control mix CM. At 90 days, a decrease of 11.65%, 4.51%, and 18.79% for mixes F10, F20, and F60 and increase of 25.18%, 22.55%, and 19.92% for F30, F40, and F50 was observed
when compared to control mix CM. Split-tensile strength was found to increase with age. For F mixes, the ratio of split-tensile strength to cube compressive strength of concrete varied from 6% to 7% with 5% for F60 mix. It was reported that for normal strength mixes, the ratio of splittensile strength to cube compressive strength of concrete is in the range of 7–9% (Mehta & Monterio, [15]). Compressive strength is assumed as an adequate index for all types of strength, and therefore a direct relationship ought to exist between the compressive and tensile strength of a given concrete. It has been observed that relationship among various types of strength is influenced by factors like the methods by which the tensile strength is measured (i.e., direct tension test, splitting test, or flexure test), the quality of concrete (i.e., low-, moderate- or high-strength), the aggregate characteristics (e.g., surface texture and mineralogy), and admixtures (e.g., air-entraining and mineral admixtures). In the present study, the relationship between compressive strength and split-tensile strength were found to correspond to that of normal concrete i.e. the ratio of tensile-tocompressive strength ratio was observed to be lying between 5% and 7% for F mixes, due to the inclusion of foundry sand in F mixes, affecting the type of fine aggregate in the concrete mix. 5. Durability 5.1. Carbonation The test results on the carbonation depth of concrete specimens measured until 12 months are represented by the values of corresponding carbonation coefficient (C). C is inversely proportional to the carbonation resistance of concrete and was estimated using the empirical relationship,
X ¼ CðTÞ0:5
ð1Þ
where X is the tested carbonation depth (mm), T the period of exposure (month), C is the corresponding carbonation coefficient (mm/ month0.5). This formula is based on the square-root-t-law, which is generally used to compare the carbonation resistance of concrete and has been adopted by numerous researchers (Sulapha et al. [16]; Wee et al. [17]; Castroa et al. [18]). The results of carbonation depth in natural environment are expressed in Fig. 1, at 90 and 365 days. It can be seen that the carbonation depth increases with an increase in the age. Similar results have been reported for the control mix that carbonation increases with age (Corinaldesi and Moriconi [19]). From Fig. 1, it is evident that foundry sand incorporation of its own demonstrated increase in carbonation depth with increase in percentage of foundry sand in F mixes. For every increase in 10% foundry sand i.e. mix F10 to F60, there is at an average 0.17 mm increase in carbonation depth in F mixes at 90 days. Similarly, at 365 days at an average 0.33 mm increase in carbonation depth was observed in F mixes. The maximum carbonation depth observed for F mixes was for F60 mix (containing 60% foundry sand)
Table 3 Cube and cylinder compressive strength of concrete mixes. Mix
CM F10 F20 F30 F40 F50 F60
28-day (MPa)
90-day (MPa)
365-day (MPa)
Cube
Cylinder
Cube
Cylinder
Cube
Cylinder
36.27 31.05 32.52 38.03 36.42 37.14 29.86
26.35 21.87 22.68 24.94 23.58 24.17 20.73
43.91 37.25 40.08 46.59 44.23 45.18 33.13
30.50 26.17 28.00 30.44 29.57 29.89 25.28
44.42 43.09 47.08 54.15 50.12 51.71 36.19
31.94 30.76 33.18 36.40 35.50 36.10 27.09
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Table 4 Split tensile strength of concrete mixes. Mix
28-day (MPa)
90-day (MPa)
365-day (MPa)
CM F10 F20 F30 F40 F50 F60
2.08 1.84 1.98 2.58 2.48 2.38 1.72
2.66 2.35 2.54 3.33 3.26 3.19 2.16
2.97 2.66 2.86 3.50 3.42 3.33 2.52
was about 2.17 mm at 90 days and 5 mm at 365 days, which is far less than the cover of reinforcing steel bars to cause corrosion. The typical values for coefficient C never exceeded 1.5, so as per Table 5, the concrete can be adjudged as good concrete (Castroa et al. [18]). Thus, it was observed that the carbonation depth of maximum 5 mm observed at 365-day age, in the present study was very less as compared to carbonation depth observed from literatures. Also, pH value for various mixes ranged between 11.72 and 11.90 at 90 days and 11.40 and 11.80 at 365 days. 5.2. Rapid chloride penetration resistance The ability of concrete to resist the penetration of chloride ions is a critical parameter in determining the service life of steel-reinforced concrete structures exposed to deicing salts or marine environments. The effect of fly ash on the mass transfer properties of concrete has been well documented; however, no documentation of foundry sand as replacement of fine aggregates in concrete mixes is available. The measurement concerns the chloride ions that come into concrete and also those flowing through the samples. The RCPT value of F mixes containing foundry sand at the age of 90 and 365 days is shown in Fig. 2. It can be seen that the RCPT value decreases with increase in age. At 90 days, the RCPT value for F mixes was found to more than that of CM mix except for F20 and F30 mixes. The maximum value was observed for F60 mix. It is observed that cement type, w/c ratio, curing condition, and testing age have effect on chloride permeability of concrete. The normal concretes or the concrete with various additives could vary in above parameters thereby effecting RCPT values. The F mixes in the present study showed very less RCPT value thereby indicating good permeability on addition of foundry sand in concrete.
Carbonation Depth (mm)
5.3. X-ray diffraction (XRD) studies of mixes The X-ray diffraction pattern and analysis of the concrete mixes i.e. control mix, and F mixes at 365 days are shown in Fig. 3a–g. In all the mixes, C2S, C3S, and C4AF peaks are not visible indicating that they are totally consumed. Also, the consumption of lime is indicated due to lowering of pH from 13 to between 10.9 and 12. As shown in Fig. 3a–g, SiO2 peak indicating free silica, in CM mix was observed at 1800. For the F10 mix almost same peak was obtained as the addition of foundry sand was nominal. For F20 mix,
5
90 Days
4
365 Days
3 2 1 0 0
10
20
30
40
50
60
Foundry Sand (%) Fig. 1. Variation of carbonation depth for CM & F mixes at different ages.
increase in peak was observed to 3700. It was observed that for F30 mix the peak was minimum at 1300 in all mixes indicating the maximum utilization of silica in C–S–H gel. The F40 mix showed the peak increase to 5000. Again a decrease in intensity peak was observed for F50 mix at 1600 and finally for F60 mix it was observed to increase to 3800.
5.4. SEM analysis The type, amount, size, shape, and distribution of phases present in a solid constitute its microstructure. It is the application of transmission and scanning electron microscopy techniques which has made it possible to resolve the microstructure of the materials to a fraction of 1 lm. Although, concrete is the most widely used structural material, its microstructure is heterogeneous and highly complex. Also, the microstructure–property relationships in concrete are not fully developed. Original microstructure and morphology of the hydrate mixes were observed on fractured surfaces. Fractured small samples were mounted on the SEM stubs with gold coating. It is well known that, the calcium–silica–hydrate (C–S–H) is major phase present. The factors that influence the mechanical behaviour of C–S–H phases are: size and shape of the particles, distribution of particles, particle concentration, particle orientation, topology of the mix, composition of the dispersed/continuous phases and the pore structure. Considering various scanning electron microscope images, assume that the bright and dark matter in the images stands for C–S–H gel/paste and inert aggregates, and the medium dark particles are for foundry sand particles. The assumptions regarding presence of particles is based on the facts that these medium dark particles are seen in almost every sample except the control mix CM (every sample except the control mix CM contains foundry sand). These assumptions can be justified based on the fact that the basic structure of the concrete in all the samples is the same i.e. the mix designed for the control mix has been kept constant in all the samples changing only the foundry sand percentages in these mixes. Fig. 4 is micrograph of control mix i.e. the SEM image at 1.5 KX magnifications. It shows the formation of proper C–S–H gel in various stages. The gel formation is clearly visible in the micrograph. The encircled portions represent the voids while rest of the picture consists of C–S–H gel and inert aggregates (both fine and coarse). In the micrograph C–S–H gel i.e. the bright masses with nodules and big chalky gel parts are spread over the entire micrograph. Also, it is evident from various literatures, that the C–S–H gel gets spread over the aggregates thus acting as binder for the paste. Fig. 5a, micrograph of F10 mix shows two major features. Firstly, the number of voids in the mix has significantly reduced (the big voids as seen in the control mix are not visible) and secondly, the C–S–H gel paste is not as widely spread as it was in the control mix showing some aversion to the binder paste but more importantly the effect of foundry sand has been negative on the strength because of lesser quantity of foundry sand than the optimum amount of the foundry sand required, this is clearly evident from the mechanical properties as all the strengths of the mix has deteriorated significantly. The microstructure also shows the presence of foundry sand particles of various sizes at various places. The decrease in strength could be attributed to the non formation of proper C–S–H gel as compared to CM mix microstructure. Although, at few places the formation of C–S–H gel could be detected as the percentage of the foundry sand added was only 10%. Fig. 5b, micrograph of F10 mix at higher (2.50 KX) magnification clearly indicates that the increased fluidity in the paste has tremendously reduced its capacity for attaining higher strength because lesser amount of paste is available than required in addition to the foundry sand.
R. Siddique et al. / Construction and Building Materials 25 (2011) 1916–1925 Table 5 Typical value of C for Poor, average and good concrete Castroa et al., 2000. C (mm/yr
0.5
)
Concrete
Charge Passed (Coulombs)
>9 9>C>6 <6
Poor Average Good
800 90 Days
365 Days
700 600 500 400 300 200 0
10
20
30
40
50
60
Foundry Sand (%) Fig. 2. Variation of charge passed for CM & F Mixes at different ages.
Fig. 6, micrograph of F20 mix shows the presence of more foundry sand particles at various places since the percentage of the foundry sand increased to 20%. Also, formation of C–S–H gel at very few places can be observed in the microstructure. The C–S–H gel shows better spread than in the previous mix and formation of nodules is also higher than in the previous mix. The combined effect of both can be correlated to the strength values obtained for this mix, though the strength has been higher than the previous mix but it is still less than the control mix, this evidently states that the amount of the foundry sand is still less than that required for the mix to be optimum. Fig. 7 shows three observations different from the previous mixes. Firstly and the foremost is the significant formation of tendrils (the pointed thin strands), secondly the paste has spread very finely and firmly throughout the sample, and lastly the effect of combined paste and foundry sand has led to a formation of higher strength concrete. The formation of tendrils has been attributed to various factors, but in literature (Lea’s, [20]) the most prominent of these being the quick-set, that is the mix may have subjected itself to some chemical as well as physical changes to modify the profoundness as well as initial setting of the mix, i.e. the mix due to its reactivity has given a quickset. Secondly, if these tendrils are neglected, then the C–S–H paste behind shows some distinct characteristics that were non-existent in earlier mixes, the C–S–H gel is more finely spread than before, this spread plus the extra amount of availability of the gel has resulted in higher strength, even higher than the control mix. This mix has shown a tremendous response to the foundry sand and highest strength among all the mixes. Due to the C–S– H gel formation at its best the mix became denser which caused increase in the strength, thereby attributing to the maximum strength of F30 mixes in all F mixes. There is indication of prefect reaction of all the components in this mix. This finding is in accordance with the mechanical tests results obtained for strength. Fig. 8 is micrograph of F40 mix shows the presence of foundry sand particles at various places in mixed state and as separate particles, but prominently visible. It is observed that mix is not penetrated by foundry sand at many places. The gel formation could be seen at some places in the micrograph. Firstly, the foundry sand in the sample has spread out rather than confirming to the mix, this
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has led to an abrupt disrupting of the paste. The paste in this case has shown nodules formation, because of the more amount of foundry sand present than is needed for the equilibrium to be set. The excess amount of foundry sand has come out of the gel leading to a disrupture in the paste, which finally comes down in the form of lower strength of the sample, when compared to previous mix. Fig. 9, a micrograph of F50 mix shows the formation of good C– S–H gel but slightly less than that observed in F30 mix. Also, the strength observed in F50 mix is slightly less than that observed in F30 mix. The mix also shows a dense matrix with no pores or cracks. The gel formation is clearly visible at all places in the micrograph. Mix with 50% replacement of the foundry sand, has further attempted on itself to regain the equilibrium again. In this mix, the C–S–H gel further has reconciled itself leading to some increase in strength and betterment of the paste. This further increase in strength and high equilibrium can be attributed to equilibrium formation (both physical and chemical) have increased the limit to a higher value, thus increasing the strength and increasing the quality of the paste as is clear from the micrograph. Fig. 10 is micrograph of F60 mix showing the presence of bigger and more foundry sand particles at various places. The decrease in strength could be attributed to the development of micro cracks at different places due to coming out of foundry sand particles as is clearly visible from the micrograph. The proper C–S–H gel formation is not visible in the micrograph. The microstructure of F60 mix is also porous and weak and the equilibrium of the system has finally collapsed leading to a failure, with the lowest strength and visible micro cracking. The marked areas with the polygons in the micrograph represent microcracks. Thus, more than 50% of sand replacement by foundry sand leads to significant reduction in strength. The microstructure of control mix, and F mixes has shown formation of C–S–H gel at various places and some micro cracks were also observed in 60% replacement mixes. EDX analysis indicated that various mixes showed Ca/Si ratios as 1.88 (CM); 2.47(F10); 2.15(F20); 1.87(F30); 1.97(F40); 1.89(F50); 10.0(F60). Low Ca/Si ratio (1.88) C–S–H gel was formed in CM mix. The reactivity of the foundry sand was more since high contact areas allow more reactivity between the activated CaO and SiO2 to produce C–S–H. Low Ca/Si ratio C–S–H gel phase in the CM mix and almost equal Ca/Si ratio in F30 mix show higher reactivity and thus attaining higher strength as compared to other F mixes. It could be observed that the variation of Ca/Si C–S–H was in correlation with mechanical properties of different F mixes. In fact, in the present study the mixes with amount of replacement of sand more than 50% with foundry sand, also lead to crumbling at the time of curing. These results simply imply that more than 50% replacement of sand by foundry sand leads to flaws in concrete, but the best mixture in any case is inarguably the 30% replacement mix. Further, F30 mix showed large formation of C–S–H gel thus, development of dense microstructure. The fibrous C–S–H formation acts as a thick impermeable membrane for the ingress of chloride ions into concrete. This makes the concrete more resistant to aggressive environment as observed from RCPT values also. 6. Conclusion The following conclusions could be arrived at from the study: 1. The fresh properties for all the mixes were observed to be comparative with the control mix. The replacement of fine aggregate with foundry sand was found to be optimum at 30% and should not exceed 50%. The rate of gain was closer to that of control mix at 90 days and at 365 days the rate of gain for all the mixes with foundry sand was higher than the CM mix.
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R. Siddique et al. / Construction and Building Materials 25 (2011) 1916–1925
(a)
(b)
(c)
(d)
Fig. 3. X-ray diffraction patterns of various F mixes.
R. Siddique et al. / Construction and Building Materials 25 (2011) 1916–1925
(e)
(f)
(g)
Fig. 3 (continued)
2. The compressive strengths of cubes and cylinders, and splittensile strengths were observed to increase with age. The various strengths were found to be marginally lower than the control mix at 28 days, which increased with age and at 365 days, was either higher or equal to control mix, thus enabling the use of foundry sand as construction material for structures and also indicating that the strength difference between foundry sand concrete specimens and control concrete specimens became less distinct after 28 days. 3. The concrete with foundry sand F mixes showed good resistance to carbonation and rapid chloride penetration resistance as per ASTM C 1202-97 was observed under the category of very low. Thus, these by-products can be easily utilized in concrete, enhancing the durability properties of concrete.
Fig. 4. Micrograph of CM (1.50 KX).
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Fig. 5a. Micrograph of F10 mix (1.50 KX).
Fig. 5b. Micrograph of F10 mix (2.50 KX).
Fig. 8. Micrograph of F40 mix (1.50 KX).
Fig. 9. Micrograph of F50 mix (1.50 KX).
Fig. 6. Micrograph of F20 mix (1.50 KX). Fig. 10. Micrograph of F60 mix (1.50 KX).
Fig. 7. Micrograph of F30 mix (1.50 KX).
4. In all the mixes, C2S, C3S, and C4AF peaks were not visible indicating that they are totally consumed. Also, the consumption of lime was indicated due to lowering of pH from 13 to between 11.40 and 11.80 at 365 days. 5. The presence of calcium hydroxide was not detected in any of the mixes, which confirmed the consumption of calcium hydroxide in the hydration reaction, making dense micro structure and additional development of C–S–H gel, causing increased strength and resistance to aggressive environment. 6. The microstructure as studied by SEM for concretes with foundry sand has shown the reduced voids and C–S–H gel paste is not as widely spread when compared to control mix. 7. Also, presence of foundry sand particles could be seen at various places in various F mixes. Better spread of C–S–H gel and formation of nodules was observed to increase from F20 to F50 mix with maximum for F30 mix.
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8. The formation of maximum tendrils in F30 mix could be attributed to quick set. Also, the findings of SEM were in accordance with the mechanical test results obtained for strength. Micro cracks were observed in the mix F60. 9. A good correlation between SEM micrographs and mechanical properties was observed. Results of this investigation suggest that used-foundry sand could be very conveniently used in making good quality concrete and construction materials. Even though the strength development is marginally less for foundry sand at some percentages of replacements, it can be equated to lower grade of normal concrete and making utilization of waste material justifies the concrete mix-development. Foundry sand used as fine aggregates replacement enables the large utilization of waste product. References [1] Naik TR, Parikh DM, Tharaniyil MP. Beneficial utilization of used foundry sands as construction materials. Report No. CBU-1992-22, Center of by-product utilization, Dept Civil Eng Mech University of Wisconsin, Milwaukee; 1992. [2] Javed S, Lovell CW. Use of waste foundry sand in civil engineering. Transport research record 1486. In: Washington, DC: Transportation Res Board; 1994b. p. 109–3. [3] Naik TR, Patel VM, Parikh DM, Tharaniyii MP. Utilization of used foundry sand in concrete. J Mater Civil Eng 1994;6(2):254–63. [4] Naik TR, Singh SS, Ramme BW. Performance and leaching assessment of flow able slurry. J Environ Eng 2001:359–68.
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[5] Khatib JM, Ellis DJ. Mechanical properties of concrete containing foundry sand. ACI special publication SP-200. American Concrete Institute; 2001. p. 733–48. [6] Naik TR, Kraus RN, Chun YM, Ramme BW, Singh SS. Properties of field manufactured cast-concrete products utilizing recycled materials. J Mater Civil Eng ASCE 2003:400–7. [7] Naik TR, Kraus RN, Chun YM, Ramme WB, Siddique R. Precast concrete products using industrial by-products. ACI Mater J 2004;101(3):199–206. [8] Bakis R, Koyuncu H, Demirbas A. An investigation of waste foundry sand in asphalt concrete mixtures. Waste Mange Res 2006;24:269–74. [9] Fiore S, Zanetti MC. Foundry wastes reuse and recycling in concrete production. Am J Env Sci 2007;3(3):135–42. [10] Siddique R, Schutter GD, Noumowe A. Effect of used-foundry sand on the mechanical properties of concrete. Cons Build Mater 2009;23:976–80. [11] RILEM Committee CPC-18. Measurement of hardened concrete carbonation depth. Mater Struct 1988;18: 453–5. [12] Soroka I. Portland cement paste and concrete. Macmillan Press Ltd; 1979. [13] ACI Committee 211. Recommended practice for selecting proportions for normal and heavy weight concrete. J Am Concr Inst 1977;71(11):59–60. [14] Lam L, Wong YL, Poon CS. Effect of fly ash and silica fume on compressive and fracture behaviours of concrete. Cem Concr Res 1998;28(2):271–83. [15] Mehta PK, Monterio PJM. Concrete microstructure, properties, and materials. Tata McGraw-Hill Edition; 2006. [16] Sulapha P, Wong SF, Wee TH, Swaddiwudhipong S. Carbonation of concrete containing mineral admixture. J Mater Civil Eng 2003;15(2):134–43. [17] Wee TH, Suryavanshi AK, Logendran D. Pore structure controlling the carbonation of a hardened cement matrix blended with mineral admixture. Adv Cem Res 1999;11(2):81–95. [18] Castroa P, Sanjuan MA, Ganesca J. Carbonation of concrete in Mexico Gulf. Build Env 2000;35:145–9. [19] Corinaldesi V, Moriconi G. Influence of mineral additions on the performance of 100% recycled aggregate concrete. Constr Build Mater 2009;23:2869–76. [20] Hewlett Peter C, editor. Lea’s chemistry of cement and concrete. Jordan Hill, Oxford OX2 8DP: Butterworth-Heinemann Lincare House; 2001.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Strength, durability, and micro-structural properties of concrete made with used-foundry sand (UFS) Rafat Siddique a,⇑, Yogesh Aggarwal b, Paratibha Aggarwal b, El-Hadj Kadri c, Rachid Bennacer d a
Civil Engineering Department, Thapar University, Patiala 147004, India Civil Engineering Department, National Institute of Technology, Kurukshetra, India c Department of Civil Engineering, University of Cergy Pontoise, Neuville-sur-Oise, 95031 Cergy-Pontoise, France d Civil Engineering, LMT-Ecole Normale Supérieure – Cachan, 61 av. du président Wilson, F-94235 Cachan Cedex, France b
a r t i c l e
i n f o
Article history: Received 21 August 2010 Received in revised form 21 October 2010 Accepted 13 November 2010 Available online 16 December 2010 Keywords: Concrete Foundry sand Strength properties Durability properties Microstructure
a b s t r a c t This paper presents the design of concrete mixes made with used-foundry (UFS) sand as partial replacement of fine aggregates. Various mechanical properties are evaluated (compressive strength, and splittensile strength). Durability of the concrete regarding resistance to chloride penetration, and carbonation is also evaluated. Test results indicate that industrial by-products can produce concrete with sufficient strength and durability to replace normal concrete. Compressive strength, and split-tensile strength, was determined at 28, 90 and 365 days along with carbonation and rapid chloride penetration resistance at 90 and 365 days. Comparative strength development of foundry sand mixes in relation to the control mix i.e. mix without foundry sand was observed. The maximum carbonation depth in natural environment, for mixes containing foundry sand never exceeded 2.5 mm at 90 days and 5 mm at 365 days. The RCPT values, as per ASTM C 1202-97, were less than 750 coulombs at 90 days and 500 coulombs at 365 days which comes under very low category. Thereby, indicating effective use of foundry sand as an alternate material, as partial replacement of fine aggregates in concrete. Micro-structural investigations of control mix and mixes with various percentages of foundry sand were also performed using XRD and SEM techniques. The micro-structural investigations shed some light on the nature of variation in strength at the different replacements of fine aggregates with foundry sand, in concrete. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Concrete is the most widely used man-made product in the world, and is second only to water as the world’s most utilized substance. Slightly more than a ton of concrete is produced each year for every human being on the planet, some six billion tons a year. Concrete is an affordable and reliable material that is applied throughout the infrastructure of a nation’s construction, industrial, transportation, defense, utility, and residential sectors. Fundamentally, concrete is economical, strong, and durable. Although concrete technology across the industry continues to rise to the demands of a changing marketplace, the industry recognizes that considerable improvements are essential in productivity, product performance, energy efficiency, and environmental performance. The industry will need to face and overcome a number of institutional, competitive, and technical challenges. One of the major challenges, with the environmental awareness and scarcity of space for landfilling, is the wastes/byproduct utilization as an alternative to disposal. ⇑ Corresponding author. Tel.: +91 175 239 3207; fax: +91 175 236 4498. E-mail address: [email protected] (R. Siddique). 0950-0618/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2010.11.065
Throughout the industrial sector, including the concrete industry, the cost of environmental compliance is high. Introduction of use of industrial by-products such as foundry sand, fly ash, bottom ash, and slag can result in significant improvements in overall industry energy efficiency and environmental performance. Foundry sand is high quality silica sand with uniform physical characteristics. It is a by-product of ferrous and non-ferrous metal casting industries, where sand has been used for centuries as a molding material because of its thermal conductivity. Foundries successfully recycle and reuse the sand many times in a foundry. When the sand can no longer be reused in the foundry, it is removed from the foundry and is termed as foundry sand. Usedfoundry sand can be reused in various applications as an alternative to sending it to landfill, and reuse options are well established in England, Europe and North America. Reuse options include cement manufacture, asphalt, concrete, bricks and free-flow fill for certain construction applications. Some of these alternatives are starting to be adopted in India, but is still in early stage. Overseas examples show that it is not only better for the environment but is profitable for the foundry to use the sand alternatively. These foundries have significantly reduced the volume of waste sand
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going to landfill and actually offset the total cost of transporting the sand ‘in’ and ‘out’. The objectives of this study are to investigate the effect of use of foundry sand as partial replacement of fine aggregates in various percentages (0–60%), on concrete properties such as mechanical and durability characteristics of the concrete along with microstructural analysis with XRD and SEM. Application of used-foundry sand in concrete will lead to diversion of large amounts of usedfoundry sand from land filling to manufacturing of concrete. 3. Experimental methods The effect of using foundry sand as partial replacement of fine aggregates in various percentages, on concrete was investigated. Also, the effect of incorporating foundry sand in concrete on the mechanical, durability properties and microstructure were evaluated.
3.1. Materials and mix proportions Portland Pozzolana Cement (53 MPa) conforming to Indian standard specifications IS: 1489-1991 was used. Consistency was 27%, specific gravity was 3.56 and fineness as per specific surface of cement was 354 m2/kg. Locally available natural sand with 4.75 mm maximum size was used as fine aggregate. It fulfilled the requirements of ASTM C 33-02a and crushed stone with 20 mm maximum size was used as coarse aggregate. The properties of fine aggregates and coarse aggregates were found to conform to IS: 383-1970 with specific gravity of sand as 2.63 and coarse aggregate as 2.77. Unit weight of sand and coarse aggregate was 1890 and 1650 kg/m3, respectively. Fineness modulus was observed to be 3.03 for sand and 6.74 for coarse aggregates. Locally available foundry sand was used as partial replacement of fine aggregates (regular sand). Foundry sand with specific gravity
Table 1 Chemical properties of foundry sand. Constituents
% by weight (used in present study)
Requirements as per American foundry men’s society, 1991
Loss on ignition Silica (SiO2) Iron oxide (Fe2O3) Alumina (Al2O3) Calcium oxide (CaO) Magnesium oxide (MgO) Sulphate Chloride
2.15
5.15% (max)
78.81 4.83
87.9% 0.94%
6.32
4.70%
1.88
0.14% (min)
1.95
0.3%
0.05 0.04
0.09% –
2.61, unit weight 1638 kg/m3 and fineness modulus 1.78 was used. The foundry sand showed lower fineness modulus and bulk density than the regular sand. As per the particle size distribution of the foundry sand, the size corresponding to 50% of passing (d50) was around 33 lm and average diameter of foundry sand particle was observed to be 28.8 lm. Table 1 gives the chemical composition of foundry sand. A polycarboxylic ether based superplasticizer of CICO brand complying with ASTM C-494 type F, IS: 9103 – 1999 and IS: 2645-2003 was used. Seven mix proportions were prepared. First was control mix (without foundry sand), and the other six mixes contained foundry sand. Fine aggregate (sand) was replaced with foundry sand by weight. The proportions of fine aggregate replaced ranged from 10% to 60% at the increment of 10%. Mix proportions are as given in Table 2. The control mix without foundry sand was proportioned as per Indian standard specifications IS: 10262-1982, to obtain a 28-day cube compressive strength of 36 MPa. Hand mixing was done for the all the concrete mixes. 3.2. Testing procedure Fresh concrete properties such as slump flow, compaction factor, vee-bee consistometer were determined according to an Indian Standard specification IS: 11991959. The results are presented in Table 2. The 150 mm concrete cubes and 150 300 mm cylinders were cast for compressive strength, and 150 300 mm cylinders for split-tensile strength. After required period of curing, the specimens were taken out of the curing tank and their surfaces were wiped off. The various tests performed were compressive strength test of cubes (150 mm side), cylinders (150 mm 300 mm), and split-tensile strength of cylinders (150 mm 300 mm) at 28, 90, and 365 days, as per IS: 516-1959. The cylinders (100 mm 200 mm) were cast for rapid chloride penetration resistance test and were sliced 2-in. (51-mm) thick of 4-in. (102-mm) nominal diameter. Rapid chloride penetration resistance test (according to ASTM C 120297) covered the determination of the electrical conductance of concrete to provide a rapid indication of its resistance to the penetration of chloride ions. The test method consisted of monitoring the amount of electrical current passed through 2-in. (51-mm) thick slices of 4-in. (102-mm) nominal diameter cores or cylinders for a 6-h period. A potential difference of 60 V dc was maintained across the ends of the specimen, one of which was immersed in a sodium chloride solution, the other in a sodium hydroxide solution. The total charge passed, in coulombs, was related to the resistance of the specimen to chloride ion penetration. The cylinders (150 mm 300 mm) were cast for carbonation test. Carbonation test of depth of color less region using phenolphthalein indicator was determined using the cylinders (150 mm 300 mm) as per RILEM CPC-18 [11]. After casting, test specimens were covered with plastic sheets and left in casting room for 24 h at room temperature and demolded and cured in water for 28 days. After that, specimens were air cured (open environment) for the required age say till 90-days or 365-days, and then were split. The freshly split surface was cleaned and sprayed with a phenolphthalein pH indicator. The indicator was a phenolphthalein 1% ethanol solution (1 g phenolphthalein and 90 ml ethanol (95.0 V/V%) diluted in water to 100 ml. The average depth ‘Xp’ of the colorless phenolphthalein region was measured from three points, perpendicular to the two edges of the split face, immediately after spraying the indicator. X-ray diffraction analysis (XRD) was done on Philips PW 1140/09. Diffractometer operated at 35 kV, using Cu ka radiation and Ni filler. The samples for X-ray diffraction analysis were prepared in powdered form. The concrete sample was taken from the inner core of the matrix. X-ray diffraction is a non-destructive technique used to determine the elements present in any particular substance. X-ray diffraction is based on the fact that, in a mixture, the measured intensity of a diffraction peak is directly proportional to the content of the substance producing it (Soroka
Table 2 Mix proportions of concrete mixes containing UFS. Mix no.
CM
F10
F20
F30
F40
F50
F60
Cement (kg/m3) Foundry sand (%) Foundry sand (kg/m3) Water (kg/m3) W/C Sand SSD (kg/m3) Coarse aggregate(kg/m3) Superplasticizer(kg/m3) Slump (mm) Compaction factor Vee-bee consistometer (sec) Air temperature (°C) Concrete temperature (°C) Fresh concrete density (kg/m3) pH value 90-days 365-days
350 0 0 175 0.5 605 1260 1.75 30 0.83 5.98 23 25 2437.7
350 10 60.5 175 0.5 544.5 1260 1.75 30 0.88 4.40 26 29 2414.0
350 20 121.0 175 0.5 484.0 1260 1.75 30 0.84 4.98 27 27 2419.2
350 30 181.5 175 0.5 423.5 1260 1.75 30 0.85 4.97 20 23 2426.8
350 40 242.0 179.24 0.512 363.0 1260 1.75 30 0.81 5.65 22 24 2420.1
350 50 302.5 185.6 0.53 302.5 1260 1.75 30 0.81 5.34 22 24 2416.1
350 60 363.0 196.2 0.56 242.0 1260 1.75 20 0.78 6.25 34 28 2402.2
11.70 11.80
11.73 11.75
11.75 11.91
11.75 11.57
11.72 11.60
11.72 11.40
11.90 11.42
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[12]). Since 2d is a known constant, the 2h setting of each peak corresponds to a certain wave length. The scanning electron microscopic studies of various concrete samples and constituent materials were carried out using Philips XL20 Scanning Electron Microscope. The concrete specimens were first cured in water for 365 days and then oven dried at 105 °C for 24 h.
4. Results and discussions 4.1. Fresh concrete properties The effect of using foundry sand as partial replacement of fine aggregates in various percentages, on concrete was investigated. Also, the effect of incorporating foundry sand in concrete on the mechanical, durability properties and microstructure were evaluated. 3.1. Materials and mix proportions Portland Pozzolana Cement (53 MPa) conforming to Indian standard specifications IS: 1489-1991 was used. Consistency was 27%, specific gravity was 3.56 and fineness as per specific surface of cement was 354 m2/kg. Locally available natural sand with 4.75 mm maximum size was used as fine aggregate. It fulfilled the requirements of ASTM C 33-02a and crushed stone with 20 mm maximum size was used as coarse aggregate. The properties of fine aggregates and coarse aggregates were found to conform to IS: 383-1970 with specific gravity of sand as 2.63 and coarse aggregate as 2.77. Unit weight of sand and coarse aggregate was 1890 and 1650 kg/m3, respectively. Fineness modulus was observed to be 3.03 for sand and 6.74 for coarse aggregates. Locally available foundry sand was used as partial replacement of fine aggregates (regular sand). Foundry sand with specific gravity 2.61, unit weight 1638 kg/m3 and fineness modulus 1.78 was used. The foundry sand showed lower fineness modulus and bulk density than the regular sand. As per the particle size distribution of the foundry sand, the size corresponding to 50% of passing (d50) was around 33 lm and average diameter of foundry sand particle was observed to be 28.8 lm. Table 1 gives the chemical composition of foundry sand. A polycarboxylic ether based superplasticizer of CICO brand complying with ASTM C-494 type F, IS: 9103 – 1999 and IS: 2645-2003 was used. Seven mix proportions were prepared. First was control mix (without foundry sand), and the other six mixes contained foundry sand. Fine aggregate (sand) was replaced with foundry sand by weight. The proportions of fine aggregate replaced ranged from 10% to 60% at the increment of 10%. Mix proportions are as given in Table 2. The control mix without foundry sand was proportioned as per Indian standard specifications IS: 10262-1982, to obtain a 28-day cube compressive strength of 36 MPa. Hand mixing was done for the all the concrete mixes. 3.2. Testing procedure Fresh concrete properties such as slump flow, compaction factor, vee-bee consistometer were determined according to an Indian Standard specification IS: 1199-1959. The results are presented in Table 2. The 150 mm concrete cubes and 150 300 mm cylinders were cast for compressive strength, and 150 300 mm cylinders for split-tensile strength. After required period of curing, the specimens were taken out of the curing tank and their surfaces were wiped off. The various tests performed were compressive strength test of cubes (150 mm side), cylinders (150 mm 300 mm), and split-tensile strength of cylinders (150 mm 300 mm) at 28, 90, and 365 days, as per IS: 516-1959. The cylinders (100 mm 200 mm) were cast for rapid chloride penetration resistance test and were sliced 2-in. (51-mm) thick of 4-in. (102-mm) nominal diameter. Rapid chloride penetration
resistance test (according to ASTM C 1202-97) covered the determination of the electrical conductance of concrete to provide a rapid indication of its resistance to the penetration of chloride ions. The test method consisted of monitoring the amount of electrical current passed through 2-in. (51-mm) thick slices of 4-in. (102mm) nominal diameter cores or cylinders for a 6-h period. A potential difference of 60 V dc was maintained across the ends of the specimen, one of which was immersed in a sodium chloride solution, the other in a sodium hydroxide solution. The total charge passed, in coulombs, was related to the resistance of the specimen to chloride ion penetration. The cylinders (150 mm 300 mm) were cast for carbonation test. Carbonation test of depth of color less region using phenolphthalein indicator was determined using the cylinders (150 mm 300 mm) as per RILEM CPC-18 [11]. After casting, test specimens were covered with plastic sheets and left in casting room for 24 h at room temperature and demolded and cured in water for 28 days. After that, specimens were air cured (open environment) for the required age say till 90-days or 365-days, and then were split. The freshly split surface was cleaned and sprayed with a phenolphthalein pH indicator. The indicator was a phenolphthalein 1% ethanol solution (1 g phenolphthalein and 90 ml ethanol (95.0 V/V%) diluted in water to 100 ml. The average depth ‘Xp’ of the colorless phenolphthalein region was measured from three points, perpendicular to the two edges of the split face, immediately after spraying the indicator. X-ray diffraction analysis (XRD) was done on Philips PW 1140/ 09. Diffractometer operated at 35 kV, using Cu ka radiation and Ni filler. The samples for X-ray diffraction analysis were prepared in powdered form. The concrete sample was taken from the inner core of the matrix. X-ray diffraction is a non-destructive technique used to determine the elements present in any particular substance. X-ray diffraction is based on the fact that, in a mixture, the measured intensity of a diffraction peak is directly proportional to the content of the substance producing it (Soroka [12]). Since 2d is a known constant, the 2h setting of each peak corresponds to a certain wave length. The scanning electron microscopic studies of various concrete samples and constituent materials were carried out using Philips XL20 Scanning Electron Microscope. The concrete specimens were first cured in water for 365 days and then oven dried at 105 °C for 24 h. 4. Results and discussions 4.1. Fresh concrete properties The workability of fresh concrete is a composite property which includes the diverse requirements of stability, mobility, compactibility, placeability, and finishability. Slump is a measure indicating the consistency or workability of concrete. Slump for control mix CM was 30 mm and for the F mixes it was observed to be 30 to 40 mm. The compaction factor values for control mix, and F mixes corresponded to the slump flow values as per Table 2. The presence of finer foundry sand particles in concrete lead to the increase in the water demand, as compared to the regular sand particles. Thus, to maintain the workability within specified range, the water content was constant till F30 and thereafter increased. The values of vee-bee time for control mix CM, and F mixes corresponds to the slump flow values and compaction factor values as per ACI Committee 211 [13]. 4.2. Mechanical properties 4.2.1. Compressive strength. Cube compressive strength results of mixes made with various percentages of foundry sand i.e., CM (0% FS), F10 (10% FS), F20 (20% FS), F30 (30% FS) F40 (40% FS), F50 (50% FS), F60 (60% FS), at ages of 28, 90 and 365 days are shown in Table 3. There is marginal decrease in the compressive
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strength of concrete mixes with the inclusion of foundry sand as replacement of regular sand. The maximum strength was obtained at 30% foundry sand in all the replaced mixes and was more than control mix at 28 days, 90 days and 365 days. The strength variation for the various percentages of replacements was observed to be linearly increasing from 10% to 50% with different behaviour of mix F30, attaining a comparatively high strength almost closer or more than the strength of the CM mix. The strength of F60 mix reduced drastically. The strengths of F30, F40, and F50 mixes were observed to be more than the strength of CM mix at the ages of 28 days, 90 days and 365 days. Also, the strength of F20 mix was also observed to be more than the strength of CM mix at 365 days. Lam et al. [14] reported gain of strength between 7 days and 90 days for normal concrete (slump about 75 mm) as 72% which is characteristic of normal concrete. At 90 days, the rate of gain was closer to that of control mix and at 365 days, the rate of gain for all the F mixes was higher than the CM mix. As in cube compressive strength, the cylinder compressive strength as indicated in Table 2 of mix F30 was highest among all F mixes, at all ages of 28, 90 and 365-days and even higher than control mix CM at 365-days. Also, linear increase of 28-day, 90day, and 365-day strength was observed from F10 to F50 except for mix F30. F mixes showed the 28-day cylinder compressive strengths between 0.64 to 0.70 times; the 90-day cylinder compressive strengths between 0.65 to 0.76 times and the 365-day compressive strengths between 0.67 to 0.74 times the corresponding cube compressive strength of concrete. The increase in compressive strength (cube and cylinder) with the inclusion of foundry sand could probably be due to the fact that foundry sand was finer than regular sand which resulted in the denser concrete matrix. Inclusion of foundry sand has not adversely affected the 28-day compressive strengths of concrete mixes made with foundry sand, but has shown a linear increase between mixes F10 and F50 depending upon the foundry sand content.
4.2.2. Split-tensile strength. The results for split-tensile strength are shown in Table 4. The variation in the split-tensile strength with foundry sand content was similar to that observed in the case of the compressive strength. When compared to control mix CM, it was observed that F30, F40, and F50 mixes showed higher strength at 28 days, 90 days, and 365-days. The optimum replacement of sand with foundry sand can no doubt be assumed as F30, as it has attained highest strength among all mixes at all ages. A decrease in strength for mix F60 is observed, after a linear increase of split-tensile strength from F10 to F50, except F30 mix at all ages. 28-day split-tensile strength of showed decrease of 11.5%, 4.8% and 17.30% for F10, F20 and F60 mixes and increase of 24.03%, 19.23%, and 14.42% for F30, F40 and F50 mixes, in comparison with the strength of the control mix CM. At 90 days, a decrease of 11.65%, 4.51%, and 18.79% for mixes F10, F20, and F60 and increase of 25.18%, 22.55%, and 19.92% for F30, F40, and F50 was observed
when compared to control mix CM. Split-tensile strength was found to increase with age. For F mixes, the ratio of split-tensile strength to cube compressive strength of concrete varied from 6% to 7% with 5% for F60 mix. It was reported that for normal strength mixes, the ratio of splittensile strength to cube compressive strength of concrete is in the range of 7–9% (Mehta & Monterio, [15]). Compressive strength is assumed as an adequate index for all types of strength, and therefore a direct relationship ought to exist between the compressive and tensile strength of a given concrete. It has been observed that relationship among various types of strength is influenced by factors like the methods by which the tensile strength is measured (i.e., direct tension test, splitting test, or flexure test), the quality of concrete (i.e., low-, moderate- or high-strength), the aggregate characteristics (e.g., surface texture and mineralogy), and admixtures (e.g., air-entraining and mineral admixtures). In the present study, the relationship between compressive strength and split-tensile strength were found to correspond to that of normal concrete i.e. the ratio of tensile-tocompressive strength ratio was observed to be lying between 5% and 7% for F mixes, due to the inclusion of foundry sand in F mixes, affecting the type of fine aggregate in the concrete mix. 5. Durability 5.1. Carbonation The test results on the carbonation depth of concrete specimens measured until 12 months are represented by the values of corresponding carbonation coefficient (C). C is inversely proportional to the carbonation resistance of concrete and was estimated using the empirical relationship,
X ¼ CðTÞ0:5
ð1Þ
where X is the tested carbonation depth (mm), T the period of exposure (month), C is the corresponding carbonation coefficient (mm/ month0.5). This formula is based on the square-root-t-law, which is generally used to compare the carbonation resistance of concrete and has been adopted by numerous researchers (Sulapha et al. [16]; Wee et al. [17]; Castroa et al. [18]). The results of carbonation depth in natural environment are expressed in Fig. 1, at 90 and 365 days. It can be seen that the carbonation depth increases with an increase in the age. Similar results have been reported for the control mix that carbonation increases with age (Corinaldesi and Moriconi [19]). From Fig. 1, it is evident that foundry sand incorporation of its own demonstrated increase in carbonation depth with increase in percentage of foundry sand in F mixes. For every increase in 10% foundry sand i.e. mix F10 to F60, there is at an average 0.17 mm increase in carbonation depth in F mixes at 90 days. Similarly, at 365 days at an average 0.33 mm increase in carbonation depth was observed in F mixes. The maximum carbonation depth observed for F mixes was for F60 mix (containing 60% foundry sand)
Table 3 Cube and cylinder compressive strength of concrete mixes. Mix
CM F10 F20 F30 F40 F50 F60
28-day (MPa)
90-day (MPa)
365-day (MPa)
Cube
Cylinder
Cube
Cylinder
Cube
Cylinder
36.27 31.05 32.52 38.03 36.42 37.14 29.86
26.35 21.87 22.68 24.94 23.58 24.17 20.73
43.91 37.25 40.08 46.59 44.23 45.18 33.13
30.50 26.17 28.00 30.44 29.57 29.89 25.28
44.42 43.09 47.08 54.15 50.12 51.71 36.19
31.94 30.76 33.18 36.40 35.50 36.10 27.09
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Table 4 Split tensile strength of concrete mixes. Mix
28-day (MPa)
90-day (MPa)
365-day (MPa)
CM F10 F20 F30 F40 F50 F60
2.08 1.84 1.98 2.58 2.48 2.38 1.72
2.66 2.35 2.54 3.33 3.26 3.19 2.16
2.97 2.66 2.86 3.50 3.42 3.33 2.52
was about 2.17 mm at 90 days and 5 mm at 365 days, which is far less than the cover of reinforcing steel bars to cause corrosion. The typical values for coefficient C never exceeded 1.5, so as per Table 5, the concrete can be adjudged as good concrete (Castroa et al. [18]). Thus, it was observed that the carbonation depth of maximum 5 mm observed at 365-day age, in the present study was very less as compared to carbonation depth observed from literatures. Also, pH value for various mixes ranged between 11.72 and 11.90 at 90 days and 11.40 and 11.80 at 365 days. 5.2. Rapid chloride penetration resistance The ability of concrete to resist the penetration of chloride ions is a critical parameter in determining the service life of steel-reinforced concrete structures exposed to deicing salts or marine environments. The effect of fly ash on the mass transfer properties of concrete has been well documented; however, no documentation of foundry sand as replacement of fine aggregates in concrete mixes is available. The measurement concerns the chloride ions that come into concrete and also those flowing through the samples. The RCPT value of F mixes containing foundry sand at the age of 90 and 365 days is shown in Fig. 2. It can be seen that the RCPT value decreases with increase in age. At 90 days, the RCPT value for F mixes was found to more than that of CM mix except for F20 and F30 mixes. The maximum value was observed for F60 mix. It is observed that cement type, w/c ratio, curing condition, and testing age have effect on chloride permeability of concrete. The normal concretes or the concrete with various additives could vary in above parameters thereby effecting RCPT values. The F mixes in the present study showed very less RCPT value thereby indicating good permeability on addition of foundry sand in concrete.
Carbonation Depth (mm)
5.3. X-ray diffraction (XRD) studies of mixes The X-ray diffraction pattern and analysis of the concrete mixes i.e. control mix, and F mixes at 365 days are shown in Fig. 3a–g. In all the mixes, C2S, C3S, and C4AF peaks are not visible indicating that they are totally consumed. Also, the consumption of lime is indicated due to lowering of pH from 13 to between 10.9 and 12. As shown in Fig. 3a–g, SiO2 peak indicating free silica, in CM mix was observed at 1800. For the F10 mix almost same peak was obtained as the addition of foundry sand was nominal. For F20 mix,
5
90 Days
4
365 Days
3 2 1 0 0
10
20
30
40
50
60
Foundry Sand (%) Fig. 1. Variation of carbonation depth for CM & F mixes at different ages.
increase in peak was observed to 3700. It was observed that for F30 mix the peak was minimum at 1300 in all mixes indicating the maximum utilization of silica in C–S–H gel. The F40 mix showed the peak increase to 5000. Again a decrease in intensity peak was observed for F50 mix at 1600 and finally for F60 mix it was observed to increase to 3800.
5.4. SEM analysis The type, amount, size, shape, and distribution of phases present in a solid constitute its microstructure. It is the application of transmission and scanning electron microscopy techniques which has made it possible to resolve the microstructure of the materials to a fraction of 1 lm. Although, concrete is the most widely used structural material, its microstructure is heterogeneous and highly complex. Also, the microstructure–property relationships in concrete are not fully developed. Original microstructure and morphology of the hydrate mixes were observed on fractured surfaces. Fractured small samples were mounted on the SEM stubs with gold coating. It is well known that, the calcium–silica–hydrate (C–S–H) is major phase present. The factors that influence the mechanical behaviour of C–S–H phases are: size and shape of the particles, distribution of particles, particle concentration, particle orientation, topology of the mix, composition of the dispersed/continuous phases and the pore structure. Considering various scanning electron microscope images, assume that the bright and dark matter in the images stands for C–S–H gel/paste and inert aggregates, and the medium dark particles are for foundry sand particles. The assumptions regarding presence of particles is based on the facts that these medium dark particles are seen in almost every sample except the control mix CM (every sample except the control mix CM contains foundry sand). These assumptions can be justified based on the fact that the basic structure of the concrete in all the samples is the same i.e. the mix designed for the control mix has been kept constant in all the samples changing only the foundry sand percentages in these mixes. Fig. 4 is micrograph of control mix i.e. the SEM image at 1.5 KX magnifications. It shows the formation of proper C–S–H gel in various stages. The gel formation is clearly visible in the micrograph. The encircled portions represent the voids while rest of the picture consists of C–S–H gel and inert aggregates (both fine and coarse). In the micrograph C–S–H gel i.e. the bright masses with nodules and big chalky gel parts are spread over the entire micrograph. Also, it is evident from various literatures, that the C–S–H gel gets spread over the aggregates thus acting as binder for the paste. Fig. 5a, micrograph of F10 mix shows two major features. Firstly, the number of voids in the mix has significantly reduced (the big voids as seen in the control mix are not visible) and secondly, the C–S–H gel paste is not as widely spread as it was in the control mix showing some aversion to the binder paste but more importantly the effect of foundry sand has been negative on the strength because of lesser quantity of foundry sand than the optimum amount of the foundry sand required, this is clearly evident from the mechanical properties as all the strengths of the mix has deteriorated significantly. The microstructure also shows the presence of foundry sand particles of various sizes at various places. The decrease in strength could be attributed to the non formation of proper C–S–H gel as compared to CM mix microstructure. Although, at few places the formation of C–S–H gel could be detected as the percentage of the foundry sand added was only 10%. Fig. 5b, micrograph of F10 mix at higher (2.50 KX) magnification clearly indicates that the increased fluidity in the paste has tremendously reduced its capacity for attaining higher strength because lesser amount of paste is available than required in addition to the foundry sand.
R. Siddique et al. / Construction and Building Materials 25 (2011) 1916–1925 Table 5 Typical value of C for Poor, average and good concrete Castroa et al., 2000. C (mm/yr
0.5
)
Concrete
Charge Passed (Coulombs)
>9 9>C>6 <6
Poor Average Good
800 90 Days
365 Days
700 600 500 400 300 200 0
10
20
30
40
50
60
Foundry Sand (%) Fig. 2. Variation of charge passed for CM & F Mixes at different ages.
Fig. 6, micrograph of F20 mix shows the presence of more foundry sand particles at various places since the percentage of the foundry sand increased to 20%. Also, formation of C–S–H gel at very few places can be observed in the microstructure. The C–S–H gel shows better spread than in the previous mix and formation of nodules is also higher than in the previous mix. The combined effect of both can be correlated to the strength values obtained for this mix, though the strength has been higher than the previous mix but it is still less than the control mix, this evidently states that the amount of the foundry sand is still less than that required for the mix to be optimum. Fig. 7 shows three observations different from the previous mixes. Firstly and the foremost is the significant formation of tendrils (the pointed thin strands), secondly the paste has spread very finely and firmly throughout the sample, and lastly the effect of combined paste and foundry sand has led to a formation of higher strength concrete. The formation of tendrils has been attributed to various factors, but in literature (Lea’s, [20]) the most prominent of these being the quick-set, that is the mix may have subjected itself to some chemical as well as physical changes to modify the profoundness as well as initial setting of the mix, i.e. the mix due to its reactivity has given a quickset. Secondly, if these tendrils are neglected, then the C–S–H paste behind shows some distinct characteristics that were non-existent in earlier mixes, the C–S–H gel is more finely spread than before, this spread plus the extra amount of availability of the gel has resulted in higher strength, even higher than the control mix. This mix has shown a tremendous response to the foundry sand and highest strength among all the mixes. Due to the C–S– H gel formation at its best the mix became denser which caused increase in the strength, thereby attributing to the maximum strength of F30 mixes in all F mixes. There is indication of prefect reaction of all the components in this mix. This finding is in accordance with the mechanical tests results obtained for strength. Fig. 8 is micrograph of F40 mix shows the presence of foundry sand particles at various places in mixed state and as separate particles, but prominently visible. It is observed that mix is not penetrated by foundry sand at many places. The gel formation could be seen at some places in the micrograph. Firstly, the foundry sand in the sample has spread out rather than confirming to the mix, this
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has led to an abrupt disrupting of the paste. The paste in this case has shown nodules formation, because of the more amount of foundry sand present than is needed for the equilibrium to be set. The excess amount of foundry sand has come out of the gel leading to a disrupture in the paste, which finally comes down in the form of lower strength of the sample, when compared to previous mix. Fig. 9, a micrograph of F50 mix shows the formation of good C– S–H gel but slightly less than that observed in F30 mix. Also, the strength observed in F50 mix is slightly less than that observed in F30 mix. The mix also shows a dense matrix with no pores or cracks. The gel formation is clearly visible at all places in the micrograph. Mix with 50% replacement of the foundry sand, has further attempted on itself to regain the equilibrium again. In this mix, the C–S–H gel further has reconciled itself leading to some increase in strength and betterment of the paste. This further increase in strength and high equilibrium can be attributed to equilibrium formation (both physical and chemical) have increased the limit to a higher value, thus increasing the strength and increasing the quality of the paste as is clear from the micrograph. Fig. 10 is micrograph of F60 mix showing the presence of bigger and more foundry sand particles at various places. The decrease in strength could be attributed to the development of micro cracks at different places due to coming out of foundry sand particles as is clearly visible from the micrograph. The proper C–S–H gel formation is not visible in the micrograph. The microstructure of F60 mix is also porous and weak and the equilibrium of the system has finally collapsed leading to a failure, with the lowest strength and visible micro cracking. The marked areas with the polygons in the micrograph represent microcracks. Thus, more than 50% of sand replacement by foundry sand leads to significant reduction in strength. The microstructure of control mix, and F mixes has shown formation of C–S–H gel at various places and some micro cracks were also observed in 60% replacement mixes. EDX analysis indicated that various mixes showed Ca/Si ratios as 1.88 (CM); 2.47(F10); 2.15(F20); 1.87(F30); 1.97(F40); 1.89(F50); 10.0(F60). Low Ca/Si ratio (1.88) C–S–H gel was formed in CM mix. The reactivity of the foundry sand was more since high contact areas allow more reactivity between the activated CaO and SiO2 to produce C–S–H. Low Ca/Si ratio C–S–H gel phase in the CM mix and almost equal Ca/Si ratio in F30 mix show higher reactivity and thus attaining higher strength as compared to other F mixes. It could be observed that the variation of Ca/Si C–S–H was in correlation with mechanical properties of different F mixes. In fact, in the present study the mixes with amount of replacement of sand more than 50% with foundry sand, also lead to crumbling at the time of curing. These results simply imply that more than 50% replacement of sand by foundry sand leads to flaws in concrete, but the best mixture in any case is inarguably the 30% replacement mix. Further, F30 mix showed large formation of C–S–H gel thus, development of dense microstructure. The fibrous C–S–H formation acts as a thick impermeable membrane for the ingress of chloride ions into concrete. This makes the concrete more resistant to aggressive environment as observed from RCPT values also. 6. Conclusion The following conclusions could be arrived at from the study: 1. The fresh properties for all the mixes were observed to be comparative with the control mix. The replacement of fine aggregate with foundry sand was found to be optimum at 30% and should not exceed 50%. The rate of gain was closer to that of control mix at 90 days and at 365 days the rate of gain for all the mixes with foundry sand was higher than the CM mix.
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R. Siddique et al. / Construction and Building Materials 25 (2011) 1916–1925
(a)
(b)
(c)
(d)
Fig. 3. X-ray diffraction patterns of various F mixes.
R. Siddique et al. / Construction and Building Materials 25 (2011) 1916–1925
(e)
(f)
(g)
Fig. 3 (continued)
2. The compressive strengths of cubes and cylinders, and splittensile strengths were observed to increase with age. The various strengths were found to be marginally lower than the control mix at 28 days, which increased with age and at 365 days, was either higher or equal to control mix, thus enabling the use of foundry sand as construction material for structures and also indicating that the strength difference between foundry sand concrete specimens and control concrete specimens became less distinct after 28 days. 3. The concrete with foundry sand F mixes showed good resistance to carbonation and rapid chloride penetration resistance as per ASTM C 1202-97 was observed under the category of very low. Thus, these by-products can be easily utilized in concrete, enhancing the durability properties of concrete.
Fig. 4. Micrograph of CM (1.50 KX).
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Fig. 5a. Micrograph of F10 mix (1.50 KX).
Fig. 5b. Micrograph of F10 mix (2.50 KX).
Fig. 8. Micrograph of F40 mix (1.50 KX).
Fig. 9. Micrograph of F50 mix (1.50 KX).
Fig. 6. Micrograph of F20 mix (1.50 KX). Fig. 10. Micrograph of F60 mix (1.50 KX).
Fig. 7. Micrograph of F30 mix (1.50 KX).
4. In all the mixes, C2S, C3S, and C4AF peaks were not visible indicating that they are totally consumed. Also, the consumption of lime was indicated due to lowering of pH from 13 to between 11.40 and 11.80 at 365 days. 5. The presence of calcium hydroxide was not detected in any of the mixes, which confirmed the consumption of calcium hydroxide in the hydration reaction, making dense micro structure and additional development of C–S–H gel, causing increased strength and resistance to aggressive environment. 6. The microstructure as studied by SEM for concretes with foundry sand has shown the reduced voids and C–S–H gel paste is not as widely spread when compared to control mix. 7. Also, presence of foundry sand particles could be seen at various places in various F mixes. Better spread of C–S–H gel and formation of nodules was observed to increase from F20 to F50 mix with maximum for F30 mix.
R. Siddique et al. / Construction and Building Materials 25 (2011) 1916–1925
8. The formation of maximum tendrils in F30 mix could be attributed to quick set. Also, the findings of SEM were in accordance with the mechanical test results obtained for strength. Micro cracks were observed in the mix F60. 9. A good correlation between SEM micrographs and mechanical properties was observed. Results of this investigation suggest that used-foundry sand could be very conveniently used in making good quality concrete and construction materials. Even though the strength development is marginally less for foundry sand at some percentages of replacements, it can be equated to lower grade of normal concrete and making utilization of waste material justifies the concrete mix-development. Foundry sand used as fine aggregates replacement enables the large utilization of waste product. References [1] Naik TR, Parikh DM, Tharaniyil MP. Beneficial utilization of used foundry sands as construction materials. Report No. CBU-1992-22, Center of by-product utilization, Dept Civil Eng Mech University of Wisconsin, Milwaukee; 1992. [2] Javed S, Lovell CW. Use of waste foundry sand in civil engineering. Transport research record 1486. In: Washington, DC: Transportation Res Board; 1994b. p. 109–3. [3] Naik TR, Patel VM, Parikh DM, Tharaniyii MP. Utilization of used foundry sand in concrete. J Mater Civil Eng 1994;6(2):254–63. [4] Naik TR, Singh SS, Ramme BW. Performance and leaching assessment of flow able slurry. J Environ Eng 2001:359–68.
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[5] Khatib JM, Ellis DJ. Mechanical properties of concrete containing foundry sand. ACI special publication SP-200. American Concrete Institute; 2001. p. 733–48. [6] Naik TR, Kraus RN, Chun YM, Ramme BW, Singh SS. Properties of field manufactured cast-concrete products utilizing recycled materials. J Mater Civil Eng ASCE 2003:400–7. [7] Naik TR, Kraus RN, Chun YM, Ramme WB, Siddique R. Precast concrete products using industrial by-products. ACI Mater J 2004;101(3):199–206. [8] Bakis R, Koyuncu H, Demirbas A. An investigation of waste foundry sand in asphalt concrete mixtures. Waste Mange Res 2006;24:269–74. [9] Fiore S, Zanetti MC. Foundry wastes reuse and recycling in concrete production. Am J Env Sci 2007;3(3):135–42. [10] Siddique R, Schutter GD, Noumowe A. Effect of used-foundry sand on the mechanical properties of concrete. Cons Build Mater 2009;23:976–80. [11] RILEM Committee CPC-18. Measurement of hardened concrete carbonation depth. Mater Struct 1988;18: 453–5. [12] Soroka I. Portland cement paste and concrete. Macmillan Press Ltd; 1979. [13] ACI Committee 211. Recommended practice for selecting proportions for normal and heavy weight concrete. J Am Concr Inst 1977;71(11):59–60. [14] Lam L, Wong YL, Poon CS. Effect of fly ash and silica fume on compressive and fracture behaviours of concrete. Cem Concr Res 1998;28(2):271–83. [15] Mehta PK, Monterio PJM. Concrete microstructure, properties, and materials. Tata McGraw-Hill Edition; 2006. [16] Sulapha P, Wong SF, Wee TH, Swaddiwudhipong S. Carbonation of concrete containing mineral admixture. J Mater Civil Eng 2003;15(2):134–43. [17] Wee TH, Suryavanshi AK, Logendran D. Pore structure controlling the carbonation of a hardened cement matrix blended with mineral admixture. Adv Cem Res 1999;11(2):81–95. [18] Castroa P, Sanjuan MA, Ganesca J. Carbonation of concrete in Mexico Gulf. Build Env 2000;35:145–9. [19] Corinaldesi V, Moriconi G. Influence of mineral additions on the performance of 100% recycled aggregate concrete. Constr Build Mater 2009;23:2869–76. [20] Hewlett Peter C, editor. Lea’s chemistry of cement and concrete. Jordan Hill, Oxford OX2 8DP: Butterworth-Heinemann Lincare House; 2001.