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Influence of parameters on surface resistivity of concrete
Cement & Concrete Composites 62 (2015) 134–145
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Cement & Concrete Composites journal homepage: www.elsevier.com/locate/cemconcomp
Influence of parameters on surface resistivity of concrete Pratanu Ghosh ⇑, Quang Tran Department of Civil and Environmental Engineering, California State University, Fullerton, CA 92834, USA
a r t i c l e
i n f o
Article history: Received 9 September 2014 Received in revised form 22 June 2015 Accepted 29 June 2015 Available online 3 July 2015 Keywords: Surface resistivity Geometric adjustment factor Probe spacing SCM HPC Pozzolan
a b s t r a c t Several studies have investigated different techniques for measuring electrical properties of concrete which is an important physical property related to chloride induced corrosion in reinforced concrete structures. This research examined the surface resistivity (SR) and the bulk electrical resistivity (BR) of concrete cylinders for several ternary mixtures at different testing ages. In addition, this study evaluated the influence of various significant parameters namely geometric size, probe spacing, replacement levels of silica fume and metakaolin in ternary based cementitious mixtures on the SR of concrete. New recommendation has been proposed for chloride ion permeability classification on the basis of electrical resistivity and compared with widely used Florida and Louisiana DOT classification. Overall, this study will enable researchers and state highway agencies to use non-destructive SR and BR measurement technique as a potential tool to evaluate ternary based high performance concrete (HPC) mixtures and predict the corrosion rate. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Over the last two decades, different techniques have been proposed to examine the electrical properties of concrete [1–4]. These experiments are easy to perform due to their straightforward working procedure. One of the more established destructive test methods that are currently performed based on electrical concepts is the Rapid Chloride Permeability Test (RCPT) [5–6]. This test method involves placing a saturated concrete specimen, typically 102-mm diameter and 51-mm thick, between electrodes in different solutions and integrating the charge that is passed over a six hour testing period [5]. While this test is still widely used, there are a few shortcomings that have been pointed out [7,8]. One of the existing non-destructive methods of determination of concrete resistance to the chloride ion penetration is the electrical resistivity by Wenner probe device. The Florida Department of Transportation has developed a method to standardize procedures for collection of resistivity readings [9]. Experimentation using the Wenner device on 529 sample sets was conducted by Kessler et al. at the Florida Department of Transportation to investigate whether resistivity can be used as a quality control measure in place of the RCPT6 [10]. Tikalsky et al. completed a recent study on different binary and ternary based HPC mixtures electrical resistivity testing and found that resistivity data is well correlated with RCPT data for different binary and ternary based HPC mixtures [11]. Marriaga ⇑ Corresponding author. E-mail address: [email protected] (P. Ghosh). http://dx.doi.org/10.1016/j.cemconcomp.2015.06.003 0958-9465/Ó 2015 Elsevier Ltd. All rights reserved.
et al. studied the reliability of the RCPT and resistivity test on the basis of chloride resistance of Ground Granulated Blast Furnace Slag (GGBFS) mixtures with different levels of cement replacements. They established that the electrical resistivity and the total charge passed is an indirect measure of the chloride penetration suitable for both OPC and GGBS mixtures [12]. Rupnow et al. recently showed that the better precision of Wenner probe resistivity meter from their experimental investigation of single laboratory and multi laboratory measurements and surface resistivity test shows lower variability than rapid chloride permeability test with different HPC mixtures [13]. Paredes et al. conducted rigorous round robin program to document the repeatability and reproducibility of surface measurements data on 12 different PCC mixtures in several laboratories [14]. Darren et al. established effectiveness of electrical resistivity technique for HPC to obtain a relationship with chloride diffusivity in order to evaluate the quality of the concrete. Their findings showed a high correlation coefficient in the range between 0.94 and 0.99, representing the suitability of using electrical resistivity technique to evaluate the quality control of high performance concrete and prediction of corrosion rate [15]. Another possible method is to measure electrical resistance of concrete cylinder by using plate electrodes on the end of the sample [16,17]. This test can be performed by utilizing conductive medium and needs to be remembered that surface finish needs to be flat as much as possible for proper contact pressure and sponges were used between sample and plates to obtain better contact. Recently, Spragg et al. analyzed variability studies on 12 different cementitious mixtures for BR and SR and correlation
P. Ghosh, Q. Tran / Cement & Concrete Composites 62 (2015) 134–145
was established at testing ages of 28,56 and 91 days. Additionally, the effect of electrode resistance was discussed. It was noticed that the effect is not significant on high resistivity concrete [18]. The research presented here focused on evaluation of the BR and the SR of various ternary based cementitious mixtures by two different instruments on two different sizes of cylinders. Influence of variation of replacement level of metakaolin and silica fume (3–12%) on the BR and the SR was also investigated from 7 to 91 days. The main aim of this research is to show the SR measurement as a promising non-destructive quality control tool for durability measurement and also as an alternative solution of the RCPT and other long term migration testing to evaluate corrosion activity in a quicker and simpler way. The other purpose of this study is to identify multiple design solutions in terms of durability that result in long-life of reinforced concrete bridge decks throughout the nation. 2. Materials Twenty-three different types of ternary and binary cementitious mixtures including the control mixture of 100% portland cement with a water/cementitious materials ratio of 0.44 were designed to provide a wide range of values for this experimental program. This water-cementitious materials ratio is typical for exposed bridge deck and substructure concrete. All mixtures contained 335 kg/m3 of cementitious material with a Coarse Aggregate Factor (CAF) of 0.67. Limestone coarse aggregate of size (75 mm) meeting ASTM C33 No.67 gradation and ASTM C33 silica sand were used. All supplementary cement materials (SCMs) were replaced by mass. Tests were performed on mixtures using:
Type II–V cement (TII–V) Ground granulated blast furnace slag of grade 120 (G120S) Class F fly Ash (F) Silica fume (SF) Metakaolin (M)
Due to sulfate attack problems in California, it is mandatory to use Type II–V cement instead of Type I cement. The selection of mixture design was based on concrete mixtures meeting basic technical properties and also representing a diverse range of solutions to investigate long term durability. The basic mixture parameters were coded into the label names of the mixtures with percentage of each cementitious material, e.g. 75TII-–V/20F/5SF means 75% Type II–V Cement, 20% Class F fly ash and 5% Silica Fume. A high-range water reducing admixture (Glenium 7700) and an air entraining agent (MBVR AE90) were used to meet better workability and durability performance specifications. All mixtures were cast according to ASTM C192 practice. Three cylinders of 100 mm 200 mm and two cylinders of 150 mm 300 mm were prepared for testing the SR and the BR resistivity measurement at ages of 7, 14, 28, 56 and 91 days. The cylinders were demolded after 24 ± 2 h and they were continuously cured in lime water tank.
135
as suggested by AASHTO TP-95 for lime water curing condition. All cylinders were removed from lime water tank on the specified testing days and tested at surface saturated dry (SSD) condition at 23° ± 2 °C by 4 point Wenner probe meter. Readings were taken two times with 0, 90, 180 and 270 degree angles of circular face of each concrete cylinder. Data was collected by Wenner probe meter using a probe spacing of 50 mm, instead of 38 mm as recommended by FDOT. The whole experimental process was easy to set up and it took less than thirty minutes to complete. Three 100 mm 200 mm and two 150 mm 300 mm cylinders were tested for each concrete mixture for the SR measurement. The equipment works on low frequency alternating current which is flowing between the outer electrodes and measures the potential difference between two inner electrodes. Assuming that the concrete cylinder has homogeneous semi-infinite geometry (the dimensions of the element are exceptionally large in comparison of the probe spacing), and the probe depth is far less than the probe spacing, the concrete cylinder resistivity (q) can be computed as:
V I
q1 ¼ 2pa ¼ 2paR1
ð1Þ
where, a is the probe spacing (cm); V is the applied voltage (Volt); I is the current (A); and R1 is the surface resistance (Ohm). Fig. 1 shows Wenner probe instrument with its working methodology.
3.2. Merlin meter for bulk resistivity measurement Merlin meter was utilized to measure the BR of concrete specimens of 100 mm 200 mm size. It is another non-destructive instrument and manufactured by Germann Instruments. At the testing ages of 7, 14, 28, 56, and 91 days, the concrete cylinders were removed from lime water tank and tested at SSD condition. Similar to the SR, a multiplier of 1.1 is also applied for all BR data due to lime water curing condition. For the BR measurement, readings were obtained two times by swapping two ends of the concrete specimen within the clamp attached to the electrode and the data logger attached to the computer directly records the bulk conductivity or its inverse the BR. Once the measurement is taken in first few seconds, the BR reading appears unstable and increases at faster rate. It usually takes one or two minutes for the data to become stable and then it is recorded. While conducting the experiment, it is important to check and calibrate the meter by the verification cylinder provided by the manufacturer. An alternating current source is used to apply the current at a fixed frequency of 325 Hz through the specimen. The instrument is set up with a voltmeter to measure the voltage drop V, across the specimen and an ammeter to measure the current I. BR is computed using Ohm’s law from voltage and current passed as follows:
q¼
VA A ¼R IL L
ð2Þ
3. Experimental work 3.1. 4-point Wenner probe for surface electrical resistivity measurement The SR measurement was performed by commercially available non-destructive Wenner 4 probe Surface Resistivity (SR) meter, manufactured by Proceq. Florida testing methodology was implemented for the SR measurements at 7, 14, 28, 56, and 91 days for 100 mm 200 mm and 150 mm 300 mm cylinders except for curing condition and probe spacing of the Wenner probe instrument. A multiplier of 1.1 was used for electrical resistivity data
where q is the bulk electrical resistivity (Kohm cm), R is resistance (Kohm), I is current (A), L is length of the specimen (cm), V is the voltage drop (Volt) and A is cross section area of the specimen (cm2). Fig. 2 shows schematic diagram of fundamental physics involved for measurement of the BR. Here, BR data is involved in order to show that SR can be used as precise and consistent as BR by means of comparing between the corrected SR using geometric correction factor and actual bulk resistivity, which is BR. Thus SR can be used for the analysis of durability indicated criteria in order to show the variation of the resistivity in different mixtures.
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Fig. 1. SR testing instrument with (a) 4-point Wenner probe instrument and (b) testing concrete specimen.
a
b
c
d Handle
Sponges
e
Fig. 2. Merlin meter with (a) concrete specimen, (b) calibration cylinder, (c) testing concrete specimen, (d) Merlin software, and (e) schematic diagram.
4. Results
4.2. Bulk resistivity data
4.1. Surface resistivity data
The BR measurement by Merlin meter was conducted after completion of the SR measurement on the same three 100 mm 200 mm concrete cylindrical specimens. It is to be noted that the configuration of Merlin instrument is not capable to accommodate cylinder of 150 mm 300 mm size. Table 3 shows the average BR data of ternary mixtures with fixed amount of Class F fly ash (20%) or slag G120 (35%) combined with various amount of metakaolin or silica fume replacement (3%, 5%, 7%, 10% and 12%). Some data were missing in this table as the instrument was sent back to the manufacturer for maintenance purpose.
Tables 1 and 2 show average SR and standard error data of all the mixtures at 7,14,28,56 and 91 days to investigate short-term and long-term durability. While the standard error of SR appears to increase over time, it is still significantly small compared to the average SR. This feature indicates the reliability and confidence of using SR as indirect measure of short-term and long-term durability. This investigation will help researchers or concrete industry people to understand the role of silica fume and metakaolin as a second supplementary cementitious material in ternary mixtures.
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P. Ghosh, Q. Tran / Cement & Concrete Composites 62 (2015) 134–145 Table 1 Surface resistivity of 100 mm 200 mm concrete cylindrical specimens. No.
Mixture ID
Surface resistivity of 100 mm 200 mm specimens (Kohm cm) 7 days
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
100 TII–V 80TII–V/20F 77TII–V/20F/3M 75TII–V/20F/5M 73TII–V/20F/7M 70TII–V/20F/10M 68TII––V/20F/12M 77TII–V/20F/3SF 75TII–V/20F/5SF 73TII–V/20F/7SF 70TII––V/20F/10SF 68TII–V/20F/12SF 65TII–V/35G120S 62TII–V/35G120S/3M 60TII–V/35G120S/5M 58TII–V/35G120S/7M 55TII–V/35G120S/ 10M 53TII–V/35G120S/ 12M 62TII–V/35G120S/3SF 60TII–V/35G120S/5SF 58TII–V/35G120S/7SF 55TII–V/35G120S/ 10SF 53TII–V/35G120S/ 12SF
14 days
28 days
56 days
91 days
Average
Standard error
Average
Standard error
Average
Standard error
Average
Standard error
Average
Standard error
13.8 13.9 19.9 22.5 34.8 28.4 33.4 19.4 13.2 16.3 22.0 15.4 18.7 21.1 31.9 23.9 50.2
0.3 0.3 0.2 0.2 0.4 0.3 0.5 0.5 0.5 0.2 0.2 0.2 0.2 0.3 1.0 0.2 1.2
16.9 17.9 32.6 32.9 49.9 41.2 52.0 25.9 26.5 24.9 39.7 27.2 26.9 43.5 48.8 54.1 84.5
0.4 0.3 0.3 0.2 0.7 0.5 0.7 0.7 0.4 0.3 0.3 0.3 0.2 0.4 1.6 0.4 1.9
20.7 24.0 47.2 44.5 68.2 54.0 70.7 36.7 48.2 48.2 67.5 64.0 30.7 75.0 55.2 94.4 118.7
0.6 0.4 0.4 0.3 0.6 0.4 0.9 1.2 0.5 0.6 0.8 0.5 0.3 0.4 1.9 0.5 2.9
23.1 29.1 68.7 61.1 88.1 78.5 95.0 75.8 81.2 73.7 120.3 104.3 45.6 95.3 106.3 130.9 159.1
0.5 0.4 1.3 0.5 0.8 1.1 0.9 1.6 1.4 1.0 1.3 0.7 0.5 0.7 2.0 0.9 3.7
25.4 44.9 108.7 98.7 109.4 110.4 109.0 105.0 119.0 109.0 184.2 159.6 49.7 99.6 125.0 152.0 224.9
0.5 0.7 1.1 0.9 1.1 1.0 1.3 1.9 1.6 1.5 3.4 1.6 0.4 1.0 2.1 1.3 2.9
36.7
0.4
84.3
2.7
110.0
1.4
181.1
2.8
214.3
2.5
23.5 32.0 31.6 27.9
0.4 1.0 0.4 0.3
46.4 53.6 52.4 42.0
1.1 0.8 0.6 0.4
70.5 74.0 78.5 74.6
1.1 0.7 1.1 0.8
73.1 109.1 98.8 135.8
0.9 1.3 1.4 2.6
92.9 148.4 129.0 154.5
1.7 2.1 3.5 2.3
31.8
0.2
55.6
0.8
87.3
1.0
133.1
2.6
158.2
2.4
Table 2 Surface resistivity of 150 mm 300 mm concrete cylindrical specimens. No.
Mixture ID
Surface resistivity of 150 mm 300 mm specimens (Kohm cm) 7 days
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
100 TII–V 80TII–V/20F 77TII–V/20F/3M 75TII–V/20F/5M 73TII–V/20F/7M 70TII–V/20F/10M 68TII–V/20F/12M 77TII–V/20F/3SF 75TII–V/20F/5SF 73TII–V/20F/7SF 70TII–V/20F/10SF 68TII–V/20F/12SF 65TII–V/35G120S 62TII–V/35G120S/3M 60TII–V/35G120S/5M 58TII–V/35G120S/7M 55TII–V/35G120S/ 10M 53TII–V/35G120S/ 12M 62TII–V/35G120S/3SF 60TII–V/35G120S/5SF 58TII–V/35G120S/7SF 55TII–V/35G120S/ 10SF 53TII–V/35G120S/ 12SF
14 days
28 days
56 days
91 days
Average
Standard error
Average
Standard error
Average
Standard error
Average
Standard error
Average
Standard error
9.1 8.8 12.0 15.4 23.2 17.0 23.8 11.5 13.8 9.4 14.3 12.2 15.2 13.0 22.6 14.5 31.0
0.2 0.1 0.1 0.2 0.3 0.2 0.3 0.2 0.1 0.2 0.3 0.1 0.3 0.2 0.4 0.2 0.4
10.9 11.9 18.3 21.7 32.6 30.1 37.3 15.0 17.4 13.9 27.1 21.0 18.5 28.0 35.2 35.1 52.2
0.2 0.3 0.2 0.2 0.4 0.3 0.6 0.3 0.2 0.1 0.6 0.2 1.2 0.3 0.5 0.3 0.8
14.4 14.7 30.0 31.2 48.7 37.8 50.2 22.9 31.1 29.2 42.6 46.6 25.9 48.5 44.0 65.3 72.8
0.3 0.2 0.2 0.3 0.6 0.4 0.7 0.4 0.5 0.4 1.0 0.7 0.5 0.5 1.1 0.6 1.6
15.4 17.8 40.4 39.9 59.5 58.6 69.3 44.2 59.2 45.9 76.4 80.1 37.0 65.1 75.9 93.2 104.6
0.3 0.4 0.3 0.3 0.6 0.5 0.9 0.7 0.9 0.4 1.7 1.0 0.7 1.1 1.4 0.8 1.9
16.7 28.0 65.3 67.2 69.6 71.4 78.1 62.7 76.8 69.7 127.1 116.6 39.6 69.5 85.2 105.6 144.8
0.5 0.8 0.4 0.7 1.1 2.9 1.2 0.9 0.9 0.5 2.9 1.8 0.7 0.7 1.3 1.0 2.8
– – 18.5 – 20.5 –
– – 0.2 – 0.3 –
– – 28.9 – 31.9 –
– – 0.3 – 1.7 –
(–) means unavailability of data due to inadequate materials during mixing day.
– – 48.9 – 55.3 –
– – 0.3 – 0.5 –
– – 60.4 – 94.8 –
– – 0.6 – 1.1 –
– – 79.1 – 112.4 –
– – 0.8 – 0.9 –
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Table 3 Bulk resistivity of 100 mm 200 mm concrete cylindrical specimens by Merlin instrument. No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Mixture ID
100 TII–V 80TII–V/20F 77TII–V/20F/3M 75TII–V/20F/5M 73TII–V/20F/7M 70TII–V/20F/10M 68TII–V/20F/12M 77TII–V/20F/3SF 75TII–V/20F/5SF 73TII–V/20F/7SF 70TII–V/20F/10SF 68TII–V/20F/12SF 65TII–V/35G120S 62TII–V/35G120S/3M 60TII–V/35G120S/5M 58TII–V/35G120S/7M 55TII–V/35G120S/ 10M 53TII–V/35G120S/ 12M 62TII–V/35G120S/ 3SF 60TII–V/35G120S/ 5SF 58TII–V/35G120S/ 7SF 55TII–V/35G120S/ 10SF 53TII–V/35G120S/ 12SF
Bulk resistivity of 100mm 200mm specimens by Merlin (Kohm cm) 7 days
14 days
28 days
56 days
91 days
– 5.3 7.5 8.8 – 10.9 13.0 7.9 5.4 6.3 – 6.1 7.6 6.8 11.8 8.3 –
– 7.1 12.3 12.9 – 16.1 20.6 11.3 9.9 9.1 15.5 10.3 10.2 14.3 31.8 18.4 30.6
7.5 8.5 18.2 17.2 25.3 – 27.4 17.3 18.5 17.8 26.9 23.9 12.2 25.2 – 33.0 46.8
8.9 10.4 – – 32.8 32.1 34.6 30.4 33.3 27.4 50.4 38.0 17.2 32.9 38.8 49.6 64.8
9.5 – 41.0 37.9 40.1 41.3 41.3 42.0 44.5 40.5 82.1 58.3 18.6 36.3 47.7 56.8 81.7
12.9
19.6
40.7
67.3
82.9
8.7
12.0
20.6
27.5
33.3
13.3
21.2
31.1
44.8
68.6
12.2
20.7
30.9
42.2
62.1
11.2
12.3
28.9
50.7
56.8
11.6
21.5
33.5
48.9
63.3
(–) means unavailability of data due to maintenance of Merlin instrument.
4.3. Beneficial effect of ternary mixtures compared to binary and OPC mixtures Generally, the electrical resistivity of concrete mixtures increases over time. Figs. 3–6 show variation of the SR of OPC, binary, and ternary mixtures at 28 and 91 days for both 100 mm 200 mm and 150 mm 300 mm cylindrical specimens. As recognized from Figs. 5 and 6, some data for 150 mm 300 mm cylinders are missing due to unavailability of the instrument for maintenance purpose. Fig. 3 shows results of the SR of OPC, binary and ternary mixtures in 20% Class F with varying amounts of metakaolin replacements (3–12%) at 28 and 91 days for both 100 mm 200 mm and 150 mm 300 mm concrete cylinder specimens. It is observed that development of the SR for two different cylinder sizes have a common rate of development trend. Moreover, the SR of OPC and binary mixtures developed at a slow rate from 28 to 91 days compared to ternary mixtures. The SR of OPC developed from 20 to 25 Kohm cm and that of binary mixture from 24 to 29 Kohm cm from 28 to 91 days. At 28 and 91 days, the SR of binary mixtures is better than OPC, additionally, the SR of ternary mixtures with metakaolin is significantly higher than both OPC and binary mixtures. For instance, the SR of binary mixture at 28 days is 24 Kohm cm, while the lowest and highest SR of ternary mixtures is 1.9 and 3 times of the binary mixture. Fig. 4 shows results of the SR of OPC, binary and ternary mixtures with various amounts of silica fume replacements in 20% Class F fly ash at 28 and 91 days for both cylinder specimen sizes. Again, the SR of ternary mixtures is significantly higher than OPC and binary mixtures. In addition, it is observed that SR development rate of class F fly ash mixtures with various amounts of silica
fume replacement is slightly better than of metakaolin replacement. Fig. 5 depicts the SR of OPC, binary and ternary mixtures in 35% G120S with varying amounts of metakaolin replacement (3–12%) at 28 and 91 days for both sizes. It is noticed that binary mixture with 35% slag has resistivity more than 10.1 and 24.3 Kohm cm higher than the OPC at 28 and 91 days for 100 mm 200 mm specimen. Replacing more cements by metakaolin in ternary mixtures with 35% slag provided remarkable results. 10% or more replacement of cement by metakaolin in ternary mixtures, the SR increases 88 and 175.2 Kohm cm more than that of binary mixture for 100 mm 200 mm concrete cylinder. The ternary mixture with 5% metakaolin obtained lowest SR at 28 days while it is still 24.4 Kohm cm higher than the binary mixture. At 91 days, lowest SR in ternary mixtures is observed as 49.9 Kohm cm and this is still significantly higher than binary and OPC mixtures. Fig. 6 shows results of the SR of OPC, binary and 35% slag G120 based ternary mixtures with varying amounts of silica fume replacement (3–12%) at 28 and 91 days for both sizes. It is observed that replacing cement by silica fume in ternary mixtures with constant proportion of 35% slag provided better SR values compared to binary and OPC mixtures. Ternary mixture with 12% silica fume obtained highest SR at 28 and 91 days for 100 mm 200 mm specimens. Some ternary mixtures obtained the SR values more than 150 Kohm cm at 91 days for 100 mm 200 mm size and this remarkable improvement is attributed to beneficial effect of silica fume combined with slag in ternary mixtures for significant reduction of permeability. 4.4. Influence of geometric shape on SR Surface resistivity is generally measured in a laboratory on a rounded cylinder using the Wenner probe device, the outer two probes measure the current and two center probes measures the potential drop. In field investigation, probe is applied on a wide concrete slab where slab width is substantially larger than the probe spacing and there is no interference from the reinforcing steel. On the other hand, in laboratory investigation probe is generally applied on a finite shaped cylinder body. Sometimes commercially available instruments come with different probe spacing and it is measured on different cylinder sizes. Therefore, it is necessary to understand that there is significant difference between electrical resistivity data of different sizes of cylindrical concrete samples and semi-infinite bridge deck slab due to their geometric shape difference and probe spacing. Study performed by Morris et al. [19] explored an adjustment factor (K) to convert the experimental lab resistivity data performed on concrete cylinder to eliminate the geometrical shape difference between a wide thick slab and concrete cylinder as below. This study will develop to a new permeability classification based on FDOT and LADOT standard of measured surface resistivity data on 150 mm 300 mm cylinder size on short term (28 days) and long term (91 days). This is explained in details in Chapter 4.5.
qapp ¼
qmeasured k
ð3Þ
where qapp is the apparent value or bulk resistivity, qmeasured, is the measured surface resistivity, K is a cell constant correction factor, which is a function of the inter probe distance, a and the geometry of the concrete body investigated. In this study, nineteen mixtures were chosen for the SR testing from 7 to 91 days to observe the influence of specimen size on measured SR. Three cylinders of 100 mm 200 mm and two cylinders of 150 mm 300 mm were examined. The geometric factor for 150 mm 300 mm specimens with probe spacing of 50 mm
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b
120
Measured SR (Kohm-cm)
Measured SR (Kohm-cm)
a
100 80 60 40 20 0
120 100 80 60 40 20 0
Mixtures 100mmx200mm
Mixtures
150mmx300mm
100mmx200mm
150mmx300mm
Fig. 3. SR of OPC, binary and Class F based ternary mixtures with different amounts of metakaolin replacement (a) 28 days (b) 91 days.
b
200
Measured SR (Kohm-cm)
Measured SR (Kohm-cm)
a
160 120 80 40 0
200 160 120 80 40 0
Mixtures 100mmx200mm
Mixtures 100mmx200mm
150mmx300mm
150mmx300mm
Fig. 4. SR of OPC, binary and Class F based ternary mixtures with different amounts of SF replacement (a) 28 days (b) 91 days.
b
Measured SR (Kohm-cm)
Measured SR (Kohm-cm)
a
240 200 160 120 80 40 0
240 200 160 120 80 40 0
Mixtures
Mixtures 100mmx200mm
150mmx300mm
100mmx200mm
150mmx300mm
Fig. 5. SR of OPC, binary and slag based ternary mixtures with different amounts of metakaolin replacement (a) 28 days (b) 91 days.
is computed following the same approach as established by Morris et al. [19] and is shown in Fig. 7. Fig. 8–12 indicates correlation between the ratio of the SR of 150 mm 300 mm cylinders/K2 and the SR of 100 mm 200 mm cylinder/K1. K1 (2.63) and K2 (1.69) are geometric correction factor
corresponding to specific cylinder sizes. It is observed that the coefficient of determination (COD) at 7 days is 0.9 while it increases to 0.94 at 14 days and 0.96 at 28 days. After 28 days, it remains stable around 0.95 which demonstrates that the two ratios are strongly correlated with each other. The red line indicates the
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b
Measured SR (Kohm-cm)
Measured SR (Kohm-cm)
a
200 160 120 80 40 0
200 160 120 80 40 0
Mixtures
Mixtures 100mmx200mm
100mmx200mm
150mmx300mm
150mmx300mm
Fig. 6. SR of OPC, binary and slag based ternary mixtures with different amounts of SF replacement (a) 28 days (b) 91 days.
Surface resistivity 150 mm x 300 mm / K2 (Kohm-cm)
Surface resistivity 150 mm x 300 mm / K2 (Kohm-cm)
Fig. 7. Determination of cell constant correction K to determine SR with different cylinder size [19].
25
y = 0.940x R² = 0.90
20
15
10
5
0
0
5
10
15
20
Actual K
Fig. 8. Correlation between measured SR/K 150 mm 300 mm concrete specimens at 7 days.
of
30
20
10
0
0
10
K by Morris et al. (1996)
Linear (1:1 line) 100 mm 200 mm
y = 0.999x R² = 0.94
20
30
40
Surface resistivity 100 mm x 200 mm / K1 (Kohm-cm)
25
Surface resistivity 100 mm x 200 mm / K1 (Kohm-cm)
K by Morris et al. (1996)
40
and
1:1 line. The slopes of the trend lines with solid and hollow circle points represent theoretical geometric correction factor by Morris et al. [19] and actual experimental geometric correction factor between two cylinder sizes. It has been observed that resistivity of specific geometric size cylinder divided by corresponding geometric correction factor are in close proximity to 1:1 line at all ages. Thus, the trend line equation can be rewritten as y = x,
Actual K
Fig. 9. Correlation between measured SR/K of 150 mm 300 mm concrete specimens at 14 days.
Linear (1:1 line) 100 mm 200 mm
and
resulting in Eq. (4). From Eq. (3), the ratio of two SR can be rewritten as below.
q100200ða¼50 mmÞ 2:63 ¼ ¼ 1:56 q150300 ða¼50 mmÞ 1:69
ð4Þ
4.4.1. Effect of different probe spacing on the SR Dimension of probe spacing has also some influence on the SR and the correction factor K, which is determined in Fig. 8. Here,
141
Surface resistivity 150 mm x 300 mm / K2 (Kohm-cm)
Surface resistivity 150 mm x 300 mm / K2 (Kohm-cm)
P. Ghosh, Q. Tran / Cement & Concrete Composites 62 (2015) 134–145
60
y = 1.018x R² = 0.96
50 40 30 20 10 0
0
10
20
30
40
50
60
Actual K
Surface resistivity 150 mm x 300 mm / K2 (Kohm-cm)
Fig. 10. Correlation between measured SR/K 150 mm 300 mm concrete specimens at 28 days.
of
80 70 60 50 40 30 20 10 0
0
10
20
30
40
K by Morris et al. (1996)
Linear (1:1 line) 100 mm 200 mm
and
50
60
70
80
90
100
Actual K
Fig. 12. Correlation between measured SR/K 150 mm 300 mm concrete specimens at 91 days.
of
Linear (1:1 line) 100 mm 200 mm
and
4.5. Chloride ion permeability classification for FDOT/LADOT with different probe spacing and specimen size
80
y = 1.076x R² = 0.95
70
Table 4 and 5 summarize chloride ion permeability classification at 28 and 91 days on the basis of Eqs. (4) and (6). Two new classifications have been added for chloride ion permeability class: one for conversion of the SR data from 38 mm to 50 mm and the SR data for permeability classification for 150 mm 300 mm specimens. LADOT study only showed chloride ion permeability classes at 28 days and FDOT’s report provided the SR data at 28 and 91 days. Thus, Table 4 expresses the recommended SR for both DOT(s) and Table 5 shows the SR data for FDOT classification [9,20].
60 50 40 30 20 10 0
y = 1.053x R² = 0.95
90
Surface resistivity 100 mm x 200 mm / K1 (Kohm-cm)
Surface resistivity 100 mm x 200 mm / K1 (Kohm-cm)
K by Morris et al. (1996)
100
0
10
20
30
40
50
60
70
80
Surface resistivity 100 mm x 200 mm / K1 (Kohm-cm)
K by Morris et al. (1996)
Actual K
Fig. 11. Correlation between measured SR/K 150 mm 300 mm concrete specimens at 56 days.
of
4.6. Authors’ proposed recommendations for chloride ion permeability class
Linear (1:1 line) 100 mm 200 mm
and
the SR measurement was performed by the Wenner probe meter with probe spacing of 50 mm. The geometric correction factor K is determined as 2.63 for 100 mm 200 mm concrete cylinder and it is marked in red1 in Fig. 13 [19]. Recently, Florida Department of Transportation (FDOT) and Louisiana Department of Transportation (LADOT) investigated the SR using the similar testing instrument like Wenner probe with the probe spacing of 38 mm. Thus, the correction factor, K applied to obtain apparent resistivity is 1.95 for 38 mm probe spacing and it is also depicted in Fig. 13. In summary, for 38 mm and 50 mm probe spacing, the apparent resistivity can be computed in Eq. (5).
qapp ¼
q100200ða¼50 mmÞ 2:63
¼
q100200ða¼38 mmÞ 1:95
ð5Þ
From Eq. (5), the SR of 100 mm 200 mm specimen with 50 mm probe spacing can be correlated with 38 mm probe spacing and it can be expressed in Eq. (6).
2:63 q100200ða¼38 mmÞ 1:95 ¼ 1:35 q100200ða¼38 mmÞ
q100200ða¼50 mmÞ ¼
ð6Þ
Using Eq. (6), the SR for each permeability class with 38 mm probe spacing can be converted to 50 mm probe spacing. 1 For interpretation of color in Fig. 13, the reader is referred to the web version of this article.
Merlin instrument manual developed chloride ion permeability classification beyond 56 days on the basis of development of the BR data and it is shown in Table 6. The reason for choosing beyond 56 days was to ensure complete development of pozzolanic reaction for different pozzolans or supplementary cementitious materials (SCMs) in binary and ternary based cementitious mixtures. Following Table 6, which is obtained from Merlin manual, and ASTM C1202 standard, authors recommended new chloride ion permeability classification at 91 days (beyond 56 days) and it is shown in Tables 7 and 8. Table 7 also includes results of the SR measured by 4-point Wenner probe tester at 91 days, and the BR by Merlin meter at 91 days for all cementitious mixtures. There were only three permeability classes obtained: moderate, low and very low. In addition, Table 7 included the ratio between the SR and the BR for all mixtures, which is close to the theoretical geometric correction factor K (2.63) developed by Morris et al.[19]. Average value of the ratio or geometric correction factor for all mixtures is 2.6. This ratio can be useful to obtain the limits for all permeability classes by multiplying the BR limit by 2.6 per Merlin manual. Table 8 shows results of recommended surface resistivity permeability classes for specimens at 91 days and converted the SR from FDOT as obtained in Table 5. It is to be noted that the authors’ recommended SR limit in high, moderate and low permeability classes are very close to recommended SR from FDOT while the recommended SR in very low and negligible limit classes are significantly different from FDOT. As an example, it can be concluded that a mixture must have the SR higher than 55 Kohm cm instead of 50 Kohm cm to be qualified as a very low permeability class for chloride ion ingress.
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Fig. 13. Determination of cell constant correction K to determine SR with different probe spacing [19].
Table 4 Chloride ion permeability classes on the basis of 28 day SR measurement. Chloride ion permeability classification
High Moderate Low Very Low Negligible
Surface resistivity for 100 mm 200 mm specimen (Kohm cm) FDOT/LADOT recommendation for a = 38mm
Converted SR for a = 50 mm
<12 12–21 21–37 37–254 >254
<16 16–28 28–r50 50–343 >343
Surface resistivity for 150 mm 300 mm specimen (Kohm cm) (a = 50 mm)
<10 10–18 18–32 32–220 >220
Table 5 Chloride ion permeability classes on the basis of 91 day SR measurement. Chloride ion permeability classification
High Moderate Low Very Low Negligible
Surface resistivity for 100 mm 200 mm specimen (Kohm cm) FDOT recommendation for a = 38 mm
Converted SR for a = 50 mm
<11 19–11 19–37 37–295 >295
<15 15–26 26–50 50–398 >398
Surface resistivity for 150 mm 300 mm specimen (Kohm cm) (a = 50 mm)
<10 10–17 17–32 32–255 >255
4.7. Influence of percentage replacement level of SF and metakaolin on the surface electrical resistivity Figs. 14–21 demonstrate the variation of the SR at different levels of SF and metakaolin replacements (from 3% to 12%) in 20% Class F and 35% G120S based ternary mixtures. Figs. 14–21 results on average of 24 measurements for surface resistivity data for 3 samples of 100 mm 200 mm cylinder size (3 cylinders ⁄ 8 data points = 24 data points) and average of 16 data points (2 cylinders ⁄ 8 data points = 16 data points) of 2 samples for 150 mm 300 mm cylinder size. Eight curves are presented to observe the influence of time on the SR at each testing day. The dash lines represent the lower limit of very low (VL) permeability class recommended by the authors and FDOT. Figs. 14 and 15 show the variation of the SR over time at various amount of metakaolin replacements in 20% Class F fly ash mixtures for 100 mm 200 mm and 150 mm 300 mm concrete cylindrical specimens. It is noticed that at 28 days, ternary mixtures with metakaolin replacements more than 7% have the SR values greater
Table 6 BR permeability classes for 100 mm 200 mm specimens beyond 56 days as per Merlin manual [21]. Manual [21]
Merlin bulk resistivity (Kohm-cm)
High Moderate Low Very low Negligible
<5 5–10 10–21 21–207 >207
Table 7 BR and SR permeability classes at 91 days for 100 mm 200 mm specimens. Mixture ID
Chloride ion penetration classfication
BR by Merlin (Kohm cm)
SR (Kohm cm)
SR/BR ratio
100 TII–V 65TII–V/35G120S 62TII–V/35G120S/3SF 62TII–V/35G120S/3M 75TII–V/20F/5M 73TII–V/20F/7M 73TII–V/20F/7SF 77TII–V/20F/3M 70TII–V/20F/10M 68TII–V/20F/12M 77TII–V/20F/3SF 75TII–V/20F/5SF 60TII–V/35G120S/5M 55TII–V/35G120S/10SF 58TII–V/35G120S/7M 68TII–V/20F/12SF 58TII–V/35G120S/7SF 53TII–V/35G120S/12SF 60TII–V/35G120S/5SF 55TII–V/35G120S/10M 70TII–V/20F/10SF 53TII–V/35G120S/12M 80TII–V/20F Average
Moderate Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low
9.50 18.63 33.34 36.28 37.86 40.09 40.52 40.99 41.30 41.35 42.01 44.46 47.75 56.84 56.85 58.26 62.12 63.28 68.61 81.72 82.08 82.95 –
25.42 49.74 92.86 99.61 98.68 109.42 108.96 108.67 110.44 109.01 104.96 118.99 125.02 154.50 151.96 159.55 128.95 158.25 148.45 224.90 184.17 214.29 44.95
2.68 2.67 2.78 2.75 2.61 2.73 2.69 2.65 2.67 2.64 2.50 2.68 2.62 2.72 2.67 2.74 2.08 2.50 2.16 2.75 2.24 2.58 – 2.60
than VL limit from FDOT. However, from author’s recommendation it is observed that only the mixtures with 7% and 12% metakaolin have the SR greater than VL limit. For ternary mixtures with more than 3% metakaolin replacement for both specimen sizes, it takes 56 days to obtain SR higher than VL limits whereas, the binary mixture was still below VL limit until 91 days. Additionally, mixtures containing 7% and 12% metakaolin replacements provided similar SR values at most testing days and all ternary mixtures provided SR values close to each other at 91 days. These interesting features illustrate that 7% metakaolin replacement in 20% Class F fly ash mixtures may be chosen as an optimum solution.
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P. Ghosh, Q. Tran / Cement & Concrete Composites 62 (2015) 134–145 Table 8 FDOT’s and Authors’ surface resistivity permeability classes’ recommendation for 100 mm 200 mm and 150 mm 300 mm specimen at 91 days (a = 50 mm).
Measured SR (Kohm-cm)
High Moderate Low Very Low Negligible
SR for 100 mm 200 mm specimens (Kohm cm)
SR for 150 mm 300 mm specimens (Kohm cm)
FDOT’s recommendation (a = 50 mm)
Author’s recommendation (a = 50 mm)
FDOT’s recommendation (a = 50 mm)
Author’s recommendation (a = 50 mm)
<15 15–26 26–50 50–398 >398
<13 13–26 26–55 55–538 >538
<10 10–17 17–32 32–255 >255
<8 8–17 17–36 36–350 >350
120
7 days
100
14 days
80
28 days
60
56 days
40
91 days
20 0 0
3
6
9
12
Metakaolin replacement (%)
VL limit (author's) VL limit (FDOT)
Fig. 14. Variation of the SR at different amount of metakaolin replacement in 20% Class F fly ash mixtures for 100 mm 200 mm specimens.
100
7 days
80
14 days
Measured SR (Kohm-cm)
Chloride ion permeability classification
200
7 days
160
14 days 28 days
120
56 days
80
91 days 40 0
0
3
6
9
12
Silica fume replacement (%)
Fig. 16. Variation of the SR at different amount of SF replacement in 20% Class F fly ash mixtures for 100 mm 200 mm specimens.
28 days 56 days
40
91 days 20 0 0
3
6
9
Metakaolin replacement (%)
12
VL limit (author's) VL limit (FDOT)
Fig. 15. Variation of the SR at different amount of metakaolin replacement in 20% Class F fly ash mixtures for 150 mm 300 mm specimens.
Figs. 16 and 17 show variation of the SR over time at various amounts of SF replacements in 20% Class F fly ash mixtures for 100 mm 200 mm and 150 mm 300 mm concrete specimens. It is observed that at 28 days, for both sizes, ternary mixtures with more than 10% silica fume have SR values greater than the VL limits recommended by authors and FDOT. Additionally, SR values at different amounts of silica fume replacements are close to each other at 7 days. SR increases as the amount of SF replacement level increases up to 10% and then it decreases when the replacement exceeds 10%. For 150 mm 300 mm specimens, trends of the SR development look similar to those of 100 mm 200 mm specimens except at 28 and 56 days, where the SR of 12% silica fume mixtures are slightly greater than those of 10% silica fume mixtures. These interesting features illustrate that 10% SF in Class F fly ash mixtures might be an optimum solution in ternary mixtures. Figs. 18 and 19 show how measured SR varies over time at various amount of metakaolin replacements (3–12%) in 35% G120S based ternary mixtures for both specimen sizes. It is observed that
Measured SR (Kohm-cm)
Measured SR (Kohm-cm)
140
60
VL limit (author's) VL limit (FDOT)
7 days
120
14 days
100
28 days 80 60
56 days
40
91 days
20
VL limit (author's) VL limit (FDOT)
0
0
3
6
9
Silica fume replacement (%)
12
Fig. 17. Variation of the SR at different amount of SF replacement in 20% Class F fly ash mixtures for 150 mm 300 mm specimens.
at 14 days, most binary and ternary mixtures obtained the SR below the VL limits except the mixtures with 10% and 12% metakaolin replacement for both specimen sizes. Further, an interesting feature observed from 7 to 28 days shows that it is not possible to recognize whether higher amount of replacement of metakaolin has any beneficial effect on the SR. However, at 56 and 91 days, this beneficial feature is clearly evident except at 12% metakaolin replacement at 91 days for 100 mm 200 mm specimens. Figs. 20 and 21 show variation of the SR over time at 3% to 12% silica fume replacement for both sizes of concrete cylindrical specimens in 35% slag G120 based ternary mixtures. For both specimen sizes, most ternary mixtures achieved high SR values at 28 days and exceeded the proposed VL limits. At 56 days, 10% silica fume replacement provided highest SR value of 135.8 Kohm cm for 100 mm 200 mm and 94.8 Kohm cm for 150 mm 300 mm respectively, and these are significantly higher than SR values at 5% replacement level. At 91 days for 150 mm 300 mm, the SR of 10% silica fume replacement is remarkably higher than that of 5%
Measured SR (Kohm-cm)
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P. Ghosh, Q. Tran / Cement & Concrete Composites 62 (2015) 134–145
240
7 days
200
14 days
160
28 days
120
56 days
80
0
3
6
9
12
Metakaolin replacement (%)
VL limit (author's) VL limit (FDOT)
Fig. 18. Variation of the SR at different amount of metakaolin replacement in 35% G120S mixtures for 100 mm 200 mm specimens.
Measured SR (Kohm-cm)
160
7 days 14 days
120
28 days 80
56 days 91 days
40
0
0
3
6
9
12
Metakaolin replacement (%)
VL limit (author's) VL limit (FDOT)
Measured SR (Kohm-cm)
Fig. 19. Variation of the SR at different amount of metakaolin replacement in 35% G120S mixtures for 150 mm 300 mm specimens.
200
7 days
160
14 days
120
28 days 56 days
80
91 days 40 0
0
3
6
9
12
Silica fume replacement (%)
VL limit (author's) VL limit (FDOT)
Fig. 20. Variation of the SR at different amount of SF replacement in 35% G120S mixtures for 100 mm 200 mm specimens.
Measured SR (Kohm-cm)
5. Conclusion
91 days
40 0
replacement level. However, for 100 mm 200 mm specimens, the mixtures with 5%, 10% and 12% silica fume replacements have SR values very close to each other. Therefore, the optimum solution would be to implement 10% silica fume in slag based ternary mixtures.
1. This research demonstrates the influence of several parameters namely probe spacing, specimen size on electrical resistivity for several ternary based cementitious mixtures over extended period of time. 2. Ternary mixtures have promising future for implementation in future bridge decks and pavements to delay chloride induced corrosion process as all ternary mixtures obtained very low level permeability class with respect to remarkable SR development. 3. This study established that 7–10% replacement of metakaolin and SF in ternary mixtures with 20% fly ash or 35% slag provides an optimum solution for achieving very high SR values with respect to chloride induced corrosion. 4. Experimental ratio of the SR between 100 mm 200 mm and 150 mm 300 mm specimens closely matches with theoretical ratio developed by previous established research. This study provides confidence for future researchers and concrete industry personnel to interpret the SR data in a convincing way for different sizes of concrete cylindrical specimens. 5. New recommendation for chloride ion permeability class on the basis of the BR and the SR proposed by authors’ enable future researchers to develop several ternary based high performance concrete (HPC) mixtures as a potential solution for durable reinforced concrete bridge decks. 6. It is easy to understand the role of SCM as a second component in binary mixtures to achieve the optimum resistivity and to observe its role in hydration process and the rate of pozzolanic reaction. However, combination of two SCMs with Portland cement in ternary mixtures create more complicated behavior of the mixtures as three different materials have different particle sizes, chemical composition and hydration reaction mechanisms. 7. In future, thorough microstructural investigation of mixtures can be performed for proper justification to understand the complex behavior, development and comparison of SR of ternary mixtures at different days.
Acknowledgement
120
7 days
100
14 days
80
28 days
The authors would like to thank CSUF’s grant office for the intramural grant to support this research. The authors also would like to thank BASF, Lehigh Cement Company, Mitsubishi Cement Corporation, Headwaters, and CMT Research Associates, LLC for their generous donation of materials namely Type II–V cements, grade 120 slag, grade 100 slag, Class C and Class F fly ash, and silica fume and chemical admixtures.
56 days
References
60 40
91 days
20 0
0
3
6
9
Silica fume replacement (%)
12
VL limit (author's) VL limit (FDOT)
Fig. 21. Variation of the SR at different amount of SF replacement in 35% G120S mixtures for 150 mm 300 mm specimens.
[1] E. Hammond, T.D. Robson, Comparison of electrical properties of various cements and concretes, The Engineer 199 (1955) 78–80. [2] Y. Shimizu, An electrical method for measuring the setting time of portland cement, Concrete 32 (1928) 111–113. [3] J. Calleja, Effect of current frequency on measurement of electrical resistance of cement pastes, J. Am. Conc. Inst. 24 (1952) 329–332. [4] W.J. Weiss, J.D. Shane, A. Mieses, T.O. Mason, S.P. Shah, Aspects of monitoring moisture changes using electrical impedance spectroscopy, in: Second Symposium on the Importance of Self Desiccation in Concrete Technology, Lund, Sweden, 1999.
P. Ghosh, Q. Tran / Cement & Concrete Composites 62 (2015) 134–145 [5] ASTM C1202, Standard Test Method for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration, ASTM International, West Conshohocken, PA, 2010. [6] AASTHTO T277, Standard Method of Test for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration, American Association of State Highway and Transportation Officials, Washington, D.C., 2007. [7] J.D. Shane, C.D. Aldea, N.F. Bouxsein, T.O. Mason, H.M. Jennings, S.P. Shah, Microstructural and pore solution changes induced by the rapid chloride permeability test measured by impedance spectroscopy, J. Concr. Sci. Eng. 1 (2) (1999) 110–119. ISSN: 1295-2826. [8] K.A. Snyder, C. Ferraris, N.S. Martys, E.J. Garboczi, Using impedance spectroscopy to assess the viability of the rapid chloride test for determining concrete conductivity, J. Res. NIST 105 (4) (2000) 497–509. [9] FM 5-578, Florida Method of Test for Concrete Resistivity as an Electrical Indicator of its Permeability, Florida Department of Transportation, Tallahassee, Florida, 2004. pp. 1–4. [10] R.J. Kessler, R.G. Powers, M.A. Paredes, Resistivity measurements of water saturated concrete as an indicator of permeability, in: Corrosion 2005, NACE International, Houston, TX, 2005, p. 10. [11] P. Tikalsky, P. Taylor, S. Hanson, P. Ghosh, Development of Performance Properties of Ternary Mixtures: Laboratory Study on Concrete. Phase II report of National Concrete Pavement Technology Center. Iowa State University, Ames, IA, July 2011, pp. 1–209. [12] J.L. Marriaga, P. Claisse, E. Ganjian, Application of traditional techniques on chloride resistance assessment of GGBS concrete, in: Proceedings of Second International Conference on Sustainable Construction Materials and Technologies, Università Politecnica delle Marche, Ancona, Italy, June 28–30, 2010, p. 1911–1921.
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[13] P.J. Icenogle, T.D. Rupnow, Development of a precision statement for concrete surface resistivity, in: Proceedings of 92nd TRB Annual Meeting, Paper No. 121078, Washington D.C., January 23–26, 2012, pp. 1–11. [14] M. Paredes, N. Jackson, A. El Safty, J. Dryden, J. Joson, H. Lerma, J. Hersey, Precision statements for the surface resistivity of water cured concrete cylinders in the laboratory, J. Adv. Civ. Eng. Mater. 1 (1) (2012) 23. [15] T.Y. Darren, B. Lim, D. Sabet, D. Xu, T. Susanto. Evaluation of high performance concrete using electrical resistivity technique, in: Proceedings of 36th Conference on our World in Concrete & Structures Singapore, August 14–16, 2011. [16] M.D. Newlands, M.R. Jones, S. Kandasami, T.A. Harrison, Sensitivity of electrode contact solutions and contact pressure in assessing electrical resistivity of concrete, Mater. Struct. 41 (2008) 621–632. [17] R.B. Polder, Test methods for on-site measurement of resistivity of concrete – a RILEM TC-154 technical recommendation, Mater. Struct. 33 (10) (2000) 603– 611. [18] R.P. Spragg, J. Castro, T. Nantung, M. Paredes, J. Weiss, Variability Analysis of the Bulk Resistivity Measured Using Concrete Cylinders, JTRP Technical Reports, Publication FHWA/IN/JTRP-2011/21. [19] W. Morris, E. Moreno, A. Sagues, Practical evaluation of resistivity of concrete in test cylinders using a Wenner array probe, Cem. Conc. Res. 26 (12) (1996) 1779–1787. [20] AASHTO TP 95, Standard Method of Test for Surface Resistivity of Concrete’s Ability to Resist Chloride Ion Penetration, American Association of State Highway and Transportation Officials, Washington, D.C., 2011. [21] Merlin Test System, Operation Manual, Germann Instruments, Copenhagen, Denmark, March 1, 2010.
Contents lists available at ScienceDirect
Cement & Concrete Composites journal homepage: www.elsevier.com/locate/cemconcomp
Influence of parameters on surface resistivity of concrete Pratanu Ghosh ⇑, Quang Tran Department of Civil and Environmental Engineering, California State University, Fullerton, CA 92834, USA
a r t i c l e
i n f o
Article history: Received 9 September 2014 Received in revised form 22 June 2015 Accepted 29 June 2015 Available online 3 July 2015 Keywords: Surface resistivity Geometric adjustment factor Probe spacing SCM HPC Pozzolan
a b s t r a c t Several studies have investigated different techniques for measuring electrical properties of concrete which is an important physical property related to chloride induced corrosion in reinforced concrete structures. This research examined the surface resistivity (SR) and the bulk electrical resistivity (BR) of concrete cylinders for several ternary mixtures at different testing ages. In addition, this study evaluated the influence of various significant parameters namely geometric size, probe spacing, replacement levels of silica fume and metakaolin in ternary based cementitious mixtures on the SR of concrete. New recommendation has been proposed for chloride ion permeability classification on the basis of electrical resistivity and compared with widely used Florida and Louisiana DOT classification. Overall, this study will enable researchers and state highway agencies to use non-destructive SR and BR measurement technique as a potential tool to evaluate ternary based high performance concrete (HPC) mixtures and predict the corrosion rate. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Over the last two decades, different techniques have been proposed to examine the electrical properties of concrete [1–4]. These experiments are easy to perform due to their straightforward working procedure. One of the more established destructive test methods that are currently performed based on electrical concepts is the Rapid Chloride Permeability Test (RCPT) [5–6]. This test method involves placing a saturated concrete specimen, typically 102-mm diameter and 51-mm thick, between electrodes in different solutions and integrating the charge that is passed over a six hour testing period [5]. While this test is still widely used, there are a few shortcomings that have been pointed out [7,8]. One of the existing non-destructive methods of determination of concrete resistance to the chloride ion penetration is the electrical resistivity by Wenner probe device. The Florida Department of Transportation has developed a method to standardize procedures for collection of resistivity readings [9]. Experimentation using the Wenner device on 529 sample sets was conducted by Kessler et al. at the Florida Department of Transportation to investigate whether resistivity can be used as a quality control measure in place of the RCPT6 [10]. Tikalsky et al. completed a recent study on different binary and ternary based HPC mixtures electrical resistivity testing and found that resistivity data is well correlated with RCPT data for different binary and ternary based HPC mixtures [11]. Marriaga ⇑ Corresponding author. E-mail address: [email protected] (P. Ghosh). http://dx.doi.org/10.1016/j.cemconcomp.2015.06.003 0958-9465/Ó 2015 Elsevier Ltd. All rights reserved.
et al. studied the reliability of the RCPT and resistivity test on the basis of chloride resistance of Ground Granulated Blast Furnace Slag (GGBFS) mixtures with different levels of cement replacements. They established that the electrical resistivity and the total charge passed is an indirect measure of the chloride penetration suitable for both OPC and GGBS mixtures [12]. Rupnow et al. recently showed that the better precision of Wenner probe resistivity meter from their experimental investigation of single laboratory and multi laboratory measurements and surface resistivity test shows lower variability than rapid chloride permeability test with different HPC mixtures [13]. Paredes et al. conducted rigorous round robin program to document the repeatability and reproducibility of surface measurements data on 12 different PCC mixtures in several laboratories [14]. Darren et al. established effectiveness of electrical resistivity technique for HPC to obtain a relationship with chloride diffusivity in order to evaluate the quality of the concrete. Their findings showed a high correlation coefficient in the range between 0.94 and 0.99, representing the suitability of using electrical resistivity technique to evaluate the quality control of high performance concrete and prediction of corrosion rate [15]. Another possible method is to measure electrical resistance of concrete cylinder by using plate electrodes on the end of the sample [16,17]. This test can be performed by utilizing conductive medium and needs to be remembered that surface finish needs to be flat as much as possible for proper contact pressure and sponges were used between sample and plates to obtain better contact. Recently, Spragg et al. analyzed variability studies on 12 different cementitious mixtures for BR and SR and correlation
P. Ghosh, Q. Tran / Cement & Concrete Composites 62 (2015) 134–145
was established at testing ages of 28,56 and 91 days. Additionally, the effect of electrode resistance was discussed. It was noticed that the effect is not significant on high resistivity concrete [18]. The research presented here focused on evaluation of the BR and the SR of various ternary based cementitious mixtures by two different instruments on two different sizes of cylinders. Influence of variation of replacement level of metakaolin and silica fume (3–12%) on the BR and the SR was also investigated from 7 to 91 days. The main aim of this research is to show the SR measurement as a promising non-destructive quality control tool for durability measurement and also as an alternative solution of the RCPT and other long term migration testing to evaluate corrosion activity in a quicker and simpler way. The other purpose of this study is to identify multiple design solutions in terms of durability that result in long-life of reinforced concrete bridge decks throughout the nation. 2. Materials Twenty-three different types of ternary and binary cementitious mixtures including the control mixture of 100% portland cement with a water/cementitious materials ratio of 0.44 were designed to provide a wide range of values for this experimental program. This water-cementitious materials ratio is typical for exposed bridge deck and substructure concrete. All mixtures contained 335 kg/m3 of cementitious material with a Coarse Aggregate Factor (CAF) of 0.67. Limestone coarse aggregate of size (75 mm) meeting ASTM C33 No.67 gradation and ASTM C33 silica sand were used. All supplementary cement materials (SCMs) were replaced by mass. Tests were performed on mixtures using:
Type II–V cement (TII–V) Ground granulated blast furnace slag of grade 120 (G120S) Class F fly Ash (F) Silica fume (SF) Metakaolin (M)
Due to sulfate attack problems in California, it is mandatory to use Type II–V cement instead of Type I cement. The selection of mixture design was based on concrete mixtures meeting basic technical properties and also representing a diverse range of solutions to investigate long term durability. The basic mixture parameters were coded into the label names of the mixtures with percentage of each cementitious material, e.g. 75TII-–V/20F/5SF means 75% Type II–V Cement, 20% Class F fly ash and 5% Silica Fume. A high-range water reducing admixture (Glenium 7700) and an air entraining agent (MBVR AE90) were used to meet better workability and durability performance specifications. All mixtures were cast according to ASTM C192 practice. Three cylinders of 100 mm 200 mm and two cylinders of 150 mm 300 mm were prepared for testing the SR and the BR resistivity measurement at ages of 7, 14, 28, 56 and 91 days. The cylinders were demolded after 24 ± 2 h and they were continuously cured in lime water tank.
135
as suggested by AASHTO TP-95 for lime water curing condition. All cylinders were removed from lime water tank on the specified testing days and tested at surface saturated dry (SSD) condition at 23° ± 2 °C by 4 point Wenner probe meter. Readings were taken two times with 0, 90, 180 and 270 degree angles of circular face of each concrete cylinder. Data was collected by Wenner probe meter using a probe spacing of 50 mm, instead of 38 mm as recommended by FDOT. The whole experimental process was easy to set up and it took less than thirty minutes to complete. Three 100 mm 200 mm and two 150 mm 300 mm cylinders were tested for each concrete mixture for the SR measurement. The equipment works on low frequency alternating current which is flowing between the outer electrodes and measures the potential difference between two inner electrodes. Assuming that the concrete cylinder has homogeneous semi-infinite geometry (the dimensions of the element are exceptionally large in comparison of the probe spacing), and the probe depth is far less than the probe spacing, the concrete cylinder resistivity (q) can be computed as:
V I
q1 ¼ 2pa ¼ 2paR1
ð1Þ
where, a is the probe spacing (cm); V is the applied voltage (Volt); I is the current (A); and R1 is the surface resistance (Ohm). Fig. 1 shows Wenner probe instrument with its working methodology.
3.2. Merlin meter for bulk resistivity measurement Merlin meter was utilized to measure the BR of concrete specimens of 100 mm 200 mm size. It is another non-destructive instrument and manufactured by Germann Instruments. At the testing ages of 7, 14, 28, 56, and 91 days, the concrete cylinders were removed from lime water tank and tested at SSD condition. Similar to the SR, a multiplier of 1.1 is also applied for all BR data due to lime water curing condition. For the BR measurement, readings were obtained two times by swapping two ends of the concrete specimen within the clamp attached to the electrode and the data logger attached to the computer directly records the bulk conductivity or its inverse the BR. Once the measurement is taken in first few seconds, the BR reading appears unstable and increases at faster rate. It usually takes one or two minutes for the data to become stable and then it is recorded. While conducting the experiment, it is important to check and calibrate the meter by the verification cylinder provided by the manufacturer. An alternating current source is used to apply the current at a fixed frequency of 325 Hz through the specimen. The instrument is set up with a voltmeter to measure the voltage drop V, across the specimen and an ammeter to measure the current I. BR is computed using Ohm’s law from voltage and current passed as follows:
q¼
VA A ¼R IL L
ð2Þ
3. Experimental work 3.1. 4-point Wenner probe for surface electrical resistivity measurement The SR measurement was performed by commercially available non-destructive Wenner 4 probe Surface Resistivity (SR) meter, manufactured by Proceq. Florida testing methodology was implemented for the SR measurements at 7, 14, 28, 56, and 91 days for 100 mm 200 mm and 150 mm 300 mm cylinders except for curing condition and probe spacing of the Wenner probe instrument. A multiplier of 1.1 was used for electrical resistivity data
where q is the bulk electrical resistivity (Kohm cm), R is resistance (Kohm), I is current (A), L is length of the specimen (cm), V is the voltage drop (Volt) and A is cross section area of the specimen (cm2). Fig. 2 shows schematic diagram of fundamental physics involved for measurement of the BR. Here, BR data is involved in order to show that SR can be used as precise and consistent as BR by means of comparing between the corrected SR using geometric correction factor and actual bulk resistivity, which is BR. Thus SR can be used for the analysis of durability indicated criteria in order to show the variation of the resistivity in different mixtures.
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Fig. 1. SR testing instrument with (a) 4-point Wenner probe instrument and (b) testing concrete specimen.
a
b
c
d Handle
Sponges
e
Fig. 2. Merlin meter with (a) concrete specimen, (b) calibration cylinder, (c) testing concrete specimen, (d) Merlin software, and (e) schematic diagram.
4. Results
4.2. Bulk resistivity data
4.1. Surface resistivity data
The BR measurement by Merlin meter was conducted after completion of the SR measurement on the same three 100 mm 200 mm concrete cylindrical specimens. It is to be noted that the configuration of Merlin instrument is not capable to accommodate cylinder of 150 mm 300 mm size. Table 3 shows the average BR data of ternary mixtures with fixed amount of Class F fly ash (20%) or slag G120 (35%) combined with various amount of metakaolin or silica fume replacement (3%, 5%, 7%, 10% and 12%). Some data were missing in this table as the instrument was sent back to the manufacturer for maintenance purpose.
Tables 1 and 2 show average SR and standard error data of all the mixtures at 7,14,28,56 and 91 days to investigate short-term and long-term durability. While the standard error of SR appears to increase over time, it is still significantly small compared to the average SR. This feature indicates the reliability and confidence of using SR as indirect measure of short-term and long-term durability. This investigation will help researchers or concrete industry people to understand the role of silica fume and metakaolin as a second supplementary cementitious material in ternary mixtures.
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P. Ghosh, Q. Tran / Cement & Concrete Composites 62 (2015) 134–145 Table 1 Surface resistivity of 100 mm 200 mm concrete cylindrical specimens. No.
Mixture ID
Surface resistivity of 100 mm 200 mm specimens (Kohm cm) 7 days
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
100 TII–V 80TII–V/20F 77TII–V/20F/3M 75TII–V/20F/5M 73TII–V/20F/7M 70TII–V/20F/10M 68TII––V/20F/12M 77TII–V/20F/3SF 75TII–V/20F/5SF 73TII–V/20F/7SF 70TII––V/20F/10SF 68TII–V/20F/12SF 65TII–V/35G120S 62TII–V/35G120S/3M 60TII–V/35G120S/5M 58TII–V/35G120S/7M 55TII–V/35G120S/ 10M 53TII–V/35G120S/ 12M 62TII–V/35G120S/3SF 60TII–V/35G120S/5SF 58TII–V/35G120S/7SF 55TII–V/35G120S/ 10SF 53TII–V/35G120S/ 12SF
14 days
28 days
56 days
91 days
Average
Standard error
Average
Standard error
Average
Standard error
Average
Standard error
Average
Standard error
13.8 13.9 19.9 22.5 34.8 28.4 33.4 19.4 13.2 16.3 22.0 15.4 18.7 21.1 31.9 23.9 50.2
0.3 0.3 0.2 0.2 0.4 0.3 0.5 0.5 0.5 0.2 0.2 0.2 0.2 0.3 1.0 0.2 1.2
16.9 17.9 32.6 32.9 49.9 41.2 52.0 25.9 26.5 24.9 39.7 27.2 26.9 43.5 48.8 54.1 84.5
0.4 0.3 0.3 0.2 0.7 0.5 0.7 0.7 0.4 0.3 0.3 0.3 0.2 0.4 1.6 0.4 1.9
20.7 24.0 47.2 44.5 68.2 54.0 70.7 36.7 48.2 48.2 67.5 64.0 30.7 75.0 55.2 94.4 118.7
0.6 0.4 0.4 0.3 0.6 0.4 0.9 1.2 0.5 0.6 0.8 0.5 0.3 0.4 1.9 0.5 2.9
23.1 29.1 68.7 61.1 88.1 78.5 95.0 75.8 81.2 73.7 120.3 104.3 45.6 95.3 106.3 130.9 159.1
0.5 0.4 1.3 0.5 0.8 1.1 0.9 1.6 1.4 1.0 1.3 0.7 0.5 0.7 2.0 0.9 3.7
25.4 44.9 108.7 98.7 109.4 110.4 109.0 105.0 119.0 109.0 184.2 159.6 49.7 99.6 125.0 152.0 224.9
0.5 0.7 1.1 0.9 1.1 1.0 1.3 1.9 1.6 1.5 3.4 1.6 0.4 1.0 2.1 1.3 2.9
36.7
0.4
84.3
2.7
110.0
1.4
181.1
2.8
214.3
2.5
23.5 32.0 31.6 27.9
0.4 1.0 0.4 0.3
46.4 53.6 52.4 42.0
1.1 0.8 0.6 0.4
70.5 74.0 78.5 74.6
1.1 0.7 1.1 0.8
73.1 109.1 98.8 135.8
0.9 1.3 1.4 2.6
92.9 148.4 129.0 154.5
1.7 2.1 3.5 2.3
31.8
0.2
55.6
0.8
87.3
1.0
133.1
2.6
158.2
2.4
Table 2 Surface resistivity of 150 mm 300 mm concrete cylindrical specimens. No.
Mixture ID
Surface resistivity of 150 mm 300 mm specimens (Kohm cm) 7 days
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
100 TII–V 80TII–V/20F 77TII–V/20F/3M 75TII–V/20F/5M 73TII–V/20F/7M 70TII–V/20F/10M 68TII–V/20F/12M 77TII–V/20F/3SF 75TII–V/20F/5SF 73TII–V/20F/7SF 70TII–V/20F/10SF 68TII–V/20F/12SF 65TII–V/35G120S 62TII–V/35G120S/3M 60TII–V/35G120S/5M 58TII–V/35G120S/7M 55TII–V/35G120S/ 10M 53TII–V/35G120S/ 12M 62TII–V/35G120S/3SF 60TII–V/35G120S/5SF 58TII–V/35G120S/7SF 55TII–V/35G120S/ 10SF 53TII–V/35G120S/ 12SF
14 days
28 days
56 days
91 days
Average
Standard error
Average
Standard error
Average
Standard error
Average
Standard error
Average
Standard error
9.1 8.8 12.0 15.4 23.2 17.0 23.8 11.5 13.8 9.4 14.3 12.2 15.2 13.0 22.6 14.5 31.0
0.2 0.1 0.1 0.2 0.3 0.2 0.3 0.2 0.1 0.2 0.3 0.1 0.3 0.2 0.4 0.2 0.4
10.9 11.9 18.3 21.7 32.6 30.1 37.3 15.0 17.4 13.9 27.1 21.0 18.5 28.0 35.2 35.1 52.2
0.2 0.3 0.2 0.2 0.4 0.3 0.6 0.3 0.2 0.1 0.6 0.2 1.2 0.3 0.5 0.3 0.8
14.4 14.7 30.0 31.2 48.7 37.8 50.2 22.9 31.1 29.2 42.6 46.6 25.9 48.5 44.0 65.3 72.8
0.3 0.2 0.2 0.3 0.6 0.4 0.7 0.4 0.5 0.4 1.0 0.7 0.5 0.5 1.1 0.6 1.6
15.4 17.8 40.4 39.9 59.5 58.6 69.3 44.2 59.2 45.9 76.4 80.1 37.0 65.1 75.9 93.2 104.6
0.3 0.4 0.3 0.3 0.6 0.5 0.9 0.7 0.9 0.4 1.7 1.0 0.7 1.1 1.4 0.8 1.9
16.7 28.0 65.3 67.2 69.6 71.4 78.1 62.7 76.8 69.7 127.1 116.6 39.6 69.5 85.2 105.6 144.8
0.5 0.8 0.4 0.7 1.1 2.9 1.2 0.9 0.9 0.5 2.9 1.8 0.7 0.7 1.3 1.0 2.8
– – 18.5 – 20.5 –
– – 0.2 – 0.3 –
– – 28.9 – 31.9 –
– – 0.3 – 1.7 –
(–) means unavailability of data due to inadequate materials during mixing day.
– – 48.9 – 55.3 –
– – 0.3 – 0.5 –
– – 60.4 – 94.8 –
– – 0.6 – 1.1 –
– – 79.1 – 112.4 –
– – 0.8 – 0.9 –
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Table 3 Bulk resistivity of 100 mm 200 mm concrete cylindrical specimens by Merlin instrument. No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Mixture ID
100 TII–V 80TII–V/20F 77TII–V/20F/3M 75TII–V/20F/5M 73TII–V/20F/7M 70TII–V/20F/10M 68TII–V/20F/12M 77TII–V/20F/3SF 75TII–V/20F/5SF 73TII–V/20F/7SF 70TII–V/20F/10SF 68TII–V/20F/12SF 65TII–V/35G120S 62TII–V/35G120S/3M 60TII–V/35G120S/5M 58TII–V/35G120S/7M 55TII–V/35G120S/ 10M 53TII–V/35G120S/ 12M 62TII–V/35G120S/ 3SF 60TII–V/35G120S/ 5SF 58TII–V/35G120S/ 7SF 55TII–V/35G120S/ 10SF 53TII–V/35G120S/ 12SF
Bulk resistivity of 100mm 200mm specimens by Merlin (Kohm cm) 7 days
14 days
28 days
56 days
91 days
– 5.3 7.5 8.8 – 10.9 13.0 7.9 5.4 6.3 – 6.1 7.6 6.8 11.8 8.3 –
– 7.1 12.3 12.9 – 16.1 20.6 11.3 9.9 9.1 15.5 10.3 10.2 14.3 31.8 18.4 30.6
7.5 8.5 18.2 17.2 25.3 – 27.4 17.3 18.5 17.8 26.9 23.9 12.2 25.2 – 33.0 46.8
8.9 10.4 – – 32.8 32.1 34.6 30.4 33.3 27.4 50.4 38.0 17.2 32.9 38.8 49.6 64.8
9.5 – 41.0 37.9 40.1 41.3 41.3 42.0 44.5 40.5 82.1 58.3 18.6 36.3 47.7 56.8 81.7
12.9
19.6
40.7
67.3
82.9
8.7
12.0
20.6
27.5
33.3
13.3
21.2
31.1
44.8
68.6
12.2
20.7
30.9
42.2
62.1
11.2
12.3
28.9
50.7
56.8
11.6
21.5
33.5
48.9
63.3
(–) means unavailability of data due to maintenance of Merlin instrument.
4.3. Beneficial effect of ternary mixtures compared to binary and OPC mixtures Generally, the electrical resistivity of concrete mixtures increases over time. Figs. 3–6 show variation of the SR of OPC, binary, and ternary mixtures at 28 and 91 days for both 100 mm 200 mm and 150 mm 300 mm cylindrical specimens. As recognized from Figs. 5 and 6, some data for 150 mm 300 mm cylinders are missing due to unavailability of the instrument for maintenance purpose. Fig. 3 shows results of the SR of OPC, binary and ternary mixtures in 20% Class F with varying amounts of metakaolin replacements (3–12%) at 28 and 91 days for both 100 mm 200 mm and 150 mm 300 mm concrete cylinder specimens. It is observed that development of the SR for two different cylinder sizes have a common rate of development trend. Moreover, the SR of OPC and binary mixtures developed at a slow rate from 28 to 91 days compared to ternary mixtures. The SR of OPC developed from 20 to 25 Kohm cm and that of binary mixture from 24 to 29 Kohm cm from 28 to 91 days. At 28 and 91 days, the SR of binary mixtures is better than OPC, additionally, the SR of ternary mixtures with metakaolin is significantly higher than both OPC and binary mixtures. For instance, the SR of binary mixture at 28 days is 24 Kohm cm, while the lowest and highest SR of ternary mixtures is 1.9 and 3 times of the binary mixture. Fig. 4 shows results of the SR of OPC, binary and ternary mixtures with various amounts of silica fume replacements in 20% Class F fly ash at 28 and 91 days for both cylinder specimen sizes. Again, the SR of ternary mixtures is significantly higher than OPC and binary mixtures. In addition, it is observed that SR development rate of class F fly ash mixtures with various amounts of silica
fume replacement is slightly better than of metakaolin replacement. Fig. 5 depicts the SR of OPC, binary and ternary mixtures in 35% G120S with varying amounts of metakaolin replacement (3–12%) at 28 and 91 days for both sizes. It is noticed that binary mixture with 35% slag has resistivity more than 10.1 and 24.3 Kohm cm higher than the OPC at 28 and 91 days for 100 mm 200 mm specimen. Replacing more cements by metakaolin in ternary mixtures with 35% slag provided remarkable results. 10% or more replacement of cement by metakaolin in ternary mixtures, the SR increases 88 and 175.2 Kohm cm more than that of binary mixture for 100 mm 200 mm concrete cylinder. The ternary mixture with 5% metakaolin obtained lowest SR at 28 days while it is still 24.4 Kohm cm higher than the binary mixture. At 91 days, lowest SR in ternary mixtures is observed as 49.9 Kohm cm and this is still significantly higher than binary and OPC mixtures. Fig. 6 shows results of the SR of OPC, binary and 35% slag G120 based ternary mixtures with varying amounts of silica fume replacement (3–12%) at 28 and 91 days for both sizes. It is observed that replacing cement by silica fume in ternary mixtures with constant proportion of 35% slag provided better SR values compared to binary and OPC mixtures. Ternary mixture with 12% silica fume obtained highest SR at 28 and 91 days for 100 mm 200 mm specimens. Some ternary mixtures obtained the SR values more than 150 Kohm cm at 91 days for 100 mm 200 mm size and this remarkable improvement is attributed to beneficial effect of silica fume combined with slag in ternary mixtures for significant reduction of permeability. 4.4. Influence of geometric shape on SR Surface resistivity is generally measured in a laboratory on a rounded cylinder using the Wenner probe device, the outer two probes measure the current and two center probes measures the potential drop. In field investigation, probe is applied on a wide concrete slab where slab width is substantially larger than the probe spacing and there is no interference from the reinforcing steel. On the other hand, in laboratory investigation probe is generally applied on a finite shaped cylinder body. Sometimes commercially available instruments come with different probe spacing and it is measured on different cylinder sizes. Therefore, it is necessary to understand that there is significant difference between electrical resistivity data of different sizes of cylindrical concrete samples and semi-infinite bridge deck slab due to their geometric shape difference and probe spacing. Study performed by Morris et al. [19] explored an adjustment factor (K) to convert the experimental lab resistivity data performed on concrete cylinder to eliminate the geometrical shape difference between a wide thick slab and concrete cylinder as below. This study will develop to a new permeability classification based on FDOT and LADOT standard of measured surface resistivity data on 150 mm 300 mm cylinder size on short term (28 days) and long term (91 days). This is explained in details in Chapter 4.5.
qapp ¼
qmeasured k
ð3Þ
where qapp is the apparent value or bulk resistivity, qmeasured, is the measured surface resistivity, K is a cell constant correction factor, which is a function of the inter probe distance, a and the geometry of the concrete body investigated. In this study, nineteen mixtures were chosen for the SR testing from 7 to 91 days to observe the influence of specimen size on measured SR. Three cylinders of 100 mm 200 mm and two cylinders of 150 mm 300 mm were examined. The geometric factor for 150 mm 300 mm specimens with probe spacing of 50 mm
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b
120
Measured SR (Kohm-cm)
Measured SR (Kohm-cm)
a
100 80 60 40 20 0
120 100 80 60 40 20 0
Mixtures 100mmx200mm
Mixtures
150mmx300mm
100mmx200mm
150mmx300mm
Fig. 3. SR of OPC, binary and Class F based ternary mixtures with different amounts of metakaolin replacement (a) 28 days (b) 91 days.
b
200
Measured SR (Kohm-cm)
Measured SR (Kohm-cm)
a
160 120 80 40 0
200 160 120 80 40 0
Mixtures 100mmx200mm
Mixtures 100mmx200mm
150mmx300mm
150mmx300mm
Fig. 4. SR of OPC, binary and Class F based ternary mixtures with different amounts of SF replacement (a) 28 days (b) 91 days.
b
Measured SR (Kohm-cm)
Measured SR (Kohm-cm)
a
240 200 160 120 80 40 0
240 200 160 120 80 40 0
Mixtures
Mixtures 100mmx200mm
150mmx300mm
100mmx200mm
150mmx300mm
Fig. 5. SR of OPC, binary and slag based ternary mixtures with different amounts of metakaolin replacement (a) 28 days (b) 91 days.
is computed following the same approach as established by Morris et al. [19] and is shown in Fig. 7. Fig. 8–12 indicates correlation between the ratio of the SR of 150 mm 300 mm cylinders/K2 and the SR of 100 mm 200 mm cylinder/K1. K1 (2.63) and K2 (1.69) are geometric correction factor
corresponding to specific cylinder sizes. It is observed that the coefficient of determination (COD) at 7 days is 0.9 while it increases to 0.94 at 14 days and 0.96 at 28 days. After 28 days, it remains stable around 0.95 which demonstrates that the two ratios are strongly correlated with each other. The red line indicates the
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b
Measured SR (Kohm-cm)
Measured SR (Kohm-cm)
a
200 160 120 80 40 0
200 160 120 80 40 0
Mixtures
Mixtures 100mmx200mm
100mmx200mm
150mmx300mm
150mmx300mm
Fig. 6. SR of OPC, binary and slag based ternary mixtures with different amounts of SF replacement (a) 28 days (b) 91 days.
Surface resistivity 150 mm x 300 mm / K2 (Kohm-cm)
Surface resistivity 150 mm x 300 mm / K2 (Kohm-cm)
Fig. 7. Determination of cell constant correction K to determine SR with different cylinder size [19].
25
y = 0.940x R² = 0.90
20
15
10
5
0
0
5
10
15
20
Actual K
Fig. 8. Correlation between measured SR/K 150 mm 300 mm concrete specimens at 7 days.
of
30
20
10
0
0
10
K by Morris et al. (1996)
Linear (1:1 line) 100 mm 200 mm
y = 0.999x R² = 0.94
20
30
40
Surface resistivity 100 mm x 200 mm / K1 (Kohm-cm)
25
Surface resistivity 100 mm x 200 mm / K1 (Kohm-cm)
K by Morris et al. (1996)
40
and
1:1 line. The slopes of the trend lines with solid and hollow circle points represent theoretical geometric correction factor by Morris et al. [19] and actual experimental geometric correction factor between two cylinder sizes. It has been observed that resistivity of specific geometric size cylinder divided by corresponding geometric correction factor are in close proximity to 1:1 line at all ages. Thus, the trend line equation can be rewritten as y = x,
Actual K
Fig. 9. Correlation between measured SR/K of 150 mm 300 mm concrete specimens at 14 days.
Linear (1:1 line) 100 mm 200 mm
and
resulting in Eq. (4). From Eq. (3), the ratio of two SR can be rewritten as below.
q100200ða¼50 mmÞ 2:63 ¼ ¼ 1:56 q150300 ða¼50 mmÞ 1:69
ð4Þ
4.4.1. Effect of different probe spacing on the SR Dimension of probe spacing has also some influence on the SR and the correction factor K, which is determined in Fig. 8. Here,
141
Surface resistivity 150 mm x 300 mm / K2 (Kohm-cm)
Surface resistivity 150 mm x 300 mm / K2 (Kohm-cm)
P. Ghosh, Q. Tran / Cement & Concrete Composites 62 (2015) 134–145
60
y = 1.018x R² = 0.96
50 40 30 20 10 0
0
10
20
30
40
50
60
Actual K
Surface resistivity 150 mm x 300 mm / K2 (Kohm-cm)
Fig. 10. Correlation between measured SR/K 150 mm 300 mm concrete specimens at 28 days.
of
80 70 60 50 40 30 20 10 0
0
10
20
30
40
K by Morris et al. (1996)
Linear (1:1 line) 100 mm 200 mm
and
50
60
70
80
90
100
Actual K
Fig. 12. Correlation between measured SR/K 150 mm 300 mm concrete specimens at 91 days.
of
Linear (1:1 line) 100 mm 200 mm
and
4.5. Chloride ion permeability classification for FDOT/LADOT with different probe spacing and specimen size
80
y = 1.076x R² = 0.95
70
Table 4 and 5 summarize chloride ion permeability classification at 28 and 91 days on the basis of Eqs. (4) and (6). Two new classifications have been added for chloride ion permeability class: one for conversion of the SR data from 38 mm to 50 mm and the SR data for permeability classification for 150 mm 300 mm specimens. LADOT study only showed chloride ion permeability classes at 28 days and FDOT’s report provided the SR data at 28 and 91 days. Thus, Table 4 expresses the recommended SR for both DOT(s) and Table 5 shows the SR data for FDOT classification [9,20].
60 50 40 30 20 10 0
y = 1.053x R² = 0.95
90
Surface resistivity 100 mm x 200 mm / K1 (Kohm-cm)
Surface resistivity 100 mm x 200 mm / K1 (Kohm-cm)
K by Morris et al. (1996)
100
0
10
20
30
40
50
60
70
80
Surface resistivity 100 mm x 200 mm / K1 (Kohm-cm)
K by Morris et al. (1996)
Actual K
Fig. 11. Correlation between measured SR/K 150 mm 300 mm concrete specimens at 56 days.
of
4.6. Authors’ proposed recommendations for chloride ion permeability class
Linear (1:1 line) 100 mm 200 mm
and
the SR measurement was performed by the Wenner probe meter with probe spacing of 50 mm. The geometric correction factor K is determined as 2.63 for 100 mm 200 mm concrete cylinder and it is marked in red1 in Fig. 13 [19]. Recently, Florida Department of Transportation (FDOT) and Louisiana Department of Transportation (LADOT) investigated the SR using the similar testing instrument like Wenner probe with the probe spacing of 38 mm. Thus, the correction factor, K applied to obtain apparent resistivity is 1.95 for 38 mm probe spacing and it is also depicted in Fig. 13. In summary, for 38 mm and 50 mm probe spacing, the apparent resistivity can be computed in Eq. (5).
qapp ¼
q100200ða¼50 mmÞ 2:63
¼
q100200ða¼38 mmÞ 1:95
ð5Þ
From Eq. (5), the SR of 100 mm 200 mm specimen with 50 mm probe spacing can be correlated with 38 mm probe spacing and it can be expressed in Eq. (6).
2:63 q100200ða¼38 mmÞ 1:95 ¼ 1:35 q100200ða¼38 mmÞ
q100200ða¼50 mmÞ ¼
ð6Þ
Using Eq. (6), the SR for each permeability class with 38 mm probe spacing can be converted to 50 mm probe spacing. 1 For interpretation of color in Fig. 13, the reader is referred to the web version of this article.
Merlin instrument manual developed chloride ion permeability classification beyond 56 days on the basis of development of the BR data and it is shown in Table 6. The reason for choosing beyond 56 days was to ensure complete development of pozzolanic reaction for different pozzolans or supplementary cementitious materials (SCMs) in binary and ternary based cementitious mixtures. Following Table 6, which is obtained from Merlin manual, and ASTM C1202 standard, authors recommended new chloride ion permeability classification at 91 days (beyond 56 days) and it is shown in Tables 7 and 8. Table 7 also includes results of the SR measured by 4-point Wenner probe tester at 91 days, and the BR by Merlin meter at 91 days for all cementitious mixtures. There were only three permeability classes obtained: moderate, low and very low. In addition, Table 7 included the ratio between the SR and the BR for all mixtures, which is close to the theoretical geometric correction factor K (2.63) developed by Morris et al.[19]. Average value of the ratio or geometric correction factor for all mixtures is 2.6. This ratio can be useful to obtain the limits for all permeability classes by multiplying the BR limit by 2.6 per Merlin manual. Table 8 shows results of recommended surface resistivity permeability classes for specimens at 91 days and converted the SR from FDOT as obtained in Table 5. It is to be noted that the authors’ recommended SR limit in high, moderate and low permeability classes are very close to recommended SR from FDOT while the recommended SR in very low and negligible limit classes are significantly different from FDOT. As an example, it can be concluded that a mixture must have the SR higher than 55 Kohm cm instead of 50 Kohm cm to be qualified as a very low permeability class for chloride ion ingress.
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Fig. 13. Determination of cell constant correction K to determine SR with different probe spacing [19].
Table 4 Chloride ion permeability classes on the basis of 28 day SR measurement. Chloride ion permeability classification
High Moderate Low Very Low Negligible
Surface resistivity for 100 mm 200 mm specimen (Kohm cm) FDOT/LADOT recommendation for a = 38mm
Converted SR for a = 50 mm
<12 12–21 21–37 37–254 >254
<16 16–28 28–r50 50–343 >343
Surface resistivity for 150 mm 300 mm specimen (Kohm cm) (a = 50 mm)
<10 10–18 18–32 32–220 >220
Table 5 Chloride ion permeability classes on the basis of 91 day SR measurement. Chloride ion permeability classification
High Moderate Low Very Low Negligible
Surface resistivity for 100 mm 200 mm specimen (Kohm cm) FDOT recommendation for a = 38 mm
Converted SR for a = 50 mm
<11 19–11 19–37 37–295 >295
<15 15–26 26–50 50–398 >398
Surface resistivity for 150 mm 300 mm specimen (Kohm cm) (a = 50 mm)
<10 10–17 17–32 32–255 >255
4.7. Influence of percentage replacement level of SF and metakaolin on the surface electrical resistivity Figs. 14–21 demonstrate the variation of the SR at different levels of SF and metakaolin replacements (from 3% to 12%) in 20% Class F and 35% G120S based ternary mixtures. Figs. 14–21 results on average of 24 measurements for surface resistivity data for 3 samples of 100 mm 200 mm cylinder size (3 cylinders ⁄ 8 data points = 24 data points) and average of 16 data points (2 cylinders ⁄ 8 data points = 16 data points) of 2 samples for 150 mm 300 mm cylinder size. Eight curves are presented to observe the influence of time on the SR at each testing day. The dash lines represent the lower limit of very low (VL) permeability class recommended by the authors and FDOT. Figs. 14 and 15 show the variation of the SR over time at various amount of metakaolin replacements in 20% Class F fly ash mixtures for 100 mm 200 mm and 150 mm 300 mm concrete cylindrical specimens. It is noticed that at 28 days, ternary mixtures with metakaolin replacements more than 7% have the SR values greater
Table 6 BR permeability classes for 100 mm 200 mm specimens beyond 56 days as per Merlin manual [21]. Manual [21]
Merlin bulk resistivity (Kohm-cm)
High Moderate Low Very low Negligible
<5 5–10 10–21 21–207 >207
Table 7 BR and SR permeability classes at 91 days for 100 mm 200 mm specimens. Mixture ID
Chloride ion penetration classfication
BR by Merlin (Kohm cm)
SR (Kohm cm)
SR/BR ratio
100 TII–V 65TII–V/35G120S 62TII–V/35G120S/3SF 62TII–V/35G120S/3M 75TII–V/20F/5M 73TII–V/20F/7M 73TII–V/20F/7SF 77TII–V/20F/3M 70TII–V/20F/10M 68TII–V/20F/12M 77TII–V/20F/3SF 75TII–V/20F/5SF 60TII–V/35G120S/5M 55TII–V/35G120S/10SF 58TII–V/35G120S/7M 68TII–V/20F/12SF 58TII–V/35G120S/7SF 53TII–V/35G120S/12SF 60TII–V/35G120S/5SF 55TII–V/35G120S/10M 70TII–V/20F/10SF 53TII–V/35G120S/12M 80TII–V/20F Average
Moderate Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low Very Low
9.50 18.63 33.34 36.28 37.86 40.09 40.52 40.99 41.30 41.35 42.01 44.46 47.75 56.84 56.85 58.26 62.12 63.28 68.61 81.72 82.08 82.95 –
25.42 49.74 92.86 99.61 98.68 109.42 108.96 108.67 110.44 109.01 104.96 118.99 125.02 154.50 151.96 159.55 128.95 158.25 148.45 224.90 184.17 214.29 44.95
2.68 2.67 2.78 2.75 2.61 2.73 2.69 2.65 2.67 2.64 2.50 2.68 2.62 2.72 2.67 2.74 2.08 2.50 2.16 2.75 2.24 2.58 – 2.60
than VL limit from FDOT. However, from author’s recommendation it is observed that only the mixtures with 7% and 12% metakaolin have the SR greater than VL limit. For ternary mixtures with more than 3% metakaolin replacement for both specimen sizes, it takes 56 days to obtain SR higher than VL limits whereas, the binary mixture was still below VL limit until 91 days. Additionally, mixtures containing 7% and 12% metakaolin replacements provided similar SR values at most testing days and all ternary mixtures provided SR values close to each other at 91 days. These interesting features illustrate that 7% metakaolin replacement in 20% Class F fly ash mixtures may be chosen as an optimum solution.
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P. Ghosh, Q. Tran / Cement & Concrete Composites 62 (2015) 134–145 Table 8 FDOT’s and Authors’ surface resistivity permeability classes’ recommendation for 100 mm 200 mm and 150 mm 300 mm specimen at 91 days (a = 50 mm).
Measured SR (Kohm-cm)
High Moderate Low Very Low Negligible
SR for 100 mm 200 mm specimens (Kohm cm)
SR for 150 mm 300 mm specimens (Kohm cm)
FDOT’s recommendation (a = 50 mm)
Author’s recommendation (a = 50 mm)
FDOT’s recommendation (a = 50 mm)
Author’s recommendation (a = 50 mm)
<15 15–26 26–50 50–398 >398
<13 13–26 26–55 55–538 >538
<10 10–17 17–32 32–255 >255
<8 8–17 17–36 36–350 >350
120
7 days
100
14 days
80
28 days
60
56 days
40
91 days
20 0 0
3
6
9
12
Metakaolin replacement (%)
VL limit (author's) VL limit (FDOT)
Fig. 14. Variation of the SR at different amount of metakaolin replacement in 20% Class F fly ash mixtures for 100 mm 200 mm specimens.
100
7 days
80
14 days
Measured SR (Kohm-cm)
Chloride ion permeability classification
200
7 days
160
14 days 28 days
120
56 days
80
91 days 40 0
0
3
6
9
12
Silica fume replacement (%)
Fig. 16. Variation of the SR at different amount of SF replacement in 20% Class F fly ash mixtures for 100 mm 200 mm specimens.
28 days 56 days
40
91 days 20 0 0
3
6
9
Metakaolin replacement (%)
12
VL limit (author's) VL limit (FDOT)
Fig. 15. Variation of the SR at different amount of metakaolin replacement in 20% Class F fly ash mixtures for 150 mm 300 mm specimens.
Figs. 16 and 17 show variation of the SR over time at various amounts of SF replacements in 20% Class F fly ash mixtures for 100 mm 200 mm and 150 mm 300 mm concrete specimens. It is observed that at 28 days, for both sizes, ternary mixtures with more than 10% silica fume have SR values greater than the VL limits recommended by authors and FDOT. Additionally, SR values at different amounts of silica fume replacements are close to each other at 7 days. SR increases as the amount of SF replacement level increases up to 10% and then it decreases when the replacement exceeds 10%. For 150 mm 300 mm specimens, trends of the SR development look similar to those of 100 mm 200 mm specimens except at 28 and 56 days, where the SR of 12% silica fume mixtures are slightly greater than those of 10% silica fume mixtures. These interesting features illustrate that 10% SF in Class F fly ash mixtures might be an optimum solution in ternary mixtures. Figs. 18 and 19 show how measured SR varies over time at various amount of metakaolin replacements (3–12%) in 35% G120S based ternary mixtures for both specimen sizes. It is observed that
Measured SR (Kohm-cm)
Measured SR (Kohm-cm)
140
60
VL limit (author's) VL limit (FDOT)
7 days
120
14 days
100
28 days 80 60
56 days
40
91 days
20
VL limit (author's) VL limit (FDOT)
0
0
3
6
9
Silica fume replacement (%)
12
Fig. 17. Variation of the SR at different amount of SF replacement in 20% Class F fly ash mixtures for 150 mm 300 mm specimens.
at 14 days, most binary and ternary mixtures obtained the SR below the VL limits except the mixtures with 10% and 12% metakaolin replacement for both specimen sizes. Further, an interesting feature observed from 7 to 28 days shows that it is not possible to recognize whether higher amount of replacement of metakaolin has any beneficial effect on the SR. However, at 56 and 91 days, this beneficial feature is clearly evident except at 12% metakaolin replacement at 91 days for 100 mm 200 mm specimens. Figs. 20 and 21 show variation of the SR over time at 3% to 12% silica fume replacement for both sizes of concrete cylindrical specimens in 35% slag G120 based ternary mixtures. For both specimen sizes, most ternary mixtures achieved high SR values at 28 days and exceeded the proposed VL limits. At 56 days, 10% silica fume replacement provided highest SR value of 135.8 Kohm cm for 100 mm 200 mm and 94.8 Kohm cm for 150 mm 300 mm respectively, and these are significantly higher than SR values at 5% replacement level. At 91 days for 150 mm 300 mm, the SR of 10% silica fume replacement is remarkably higher than that of 5%
Measured SR (Kohm-cm)
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P. Ghosh, Q. Tran / Cement & Concrete Composites 62 (2015) 134–145
240
7 days
200
14 days
160
28 days
120
56 days
80
0
3
6
9
12
Metakaolin replacement (%)
VL limit (author's) VL limit (FDOT)
Fig. 18. Variation of the SR at different amount of metakaolin replacement in 35% G120S mixtures for 100 mm 200 mm specimens.
Measured SR (Kohm-cm)
160
7 days 14 days
120
28 days 80
56 days 91 days
40
0
0
3
6
9
12
Metakaolin replacement (%)
VL limit (author's) VL limit (FDOT)
Measured SR (Kohm-cm)
Fig. 19. Variation of the SR at different amount of metakaolin replacement in 35% G120S mixtures for 150 mm 300 mm specimens.
200
7 days
160
14 days
120
28 days 56 days
80
91 days 40 0
0
3
6
9
12
Silica fume replacement (%)
VL limit (author's) VL limit (FDOT)
Fig. 20. Variation of the SR at different amount of SF replacement in 35% G120S mixtures for 100 mm 200 mm specimens.
Measured SR (Kohm-cm)
5. Conclusion
91 days
40 0
replacement level. However, for 100 mm 200 mm specimens, the mixtures with 5%, 10% and 12% silica fume replacements have SR values very close to each other. Therefore, the optimum solution would be to implement 10% silica fume in slag based ternary mixtures.
1. This research demonstrates the influence of several parameters namely probe spacing, specimen size on electrical resistivity for several ternary based cementitious mixtures over extended period of time. 2. Ternary mixtures have promising future for implementation in future bridge decks and pavements to delay chloride induced corrosion process as all ternary mixtures obtained very low level permeability class with respect to remarkable SR development. 3. This study established that 7–10% replacement of metakaolin and SF in ternary mixtures with 20% fly ash or 35% slag provides an optimum solution for achieving very high SR values with respect to chloride induced corrosion. 4. Experimental ratio of the SR between 100 mm 200 mm and 150 mm 300 mm specimens closely matches with theoretical ratio developed by previous established research. This study provides confidence for future researchers and concrete industry personnel to interpret the SR data in a convincing way for different sizes of concrete cylindrical specimens. 5. New recommendation for chloride ion permeability class on the basis of the BR and the SR proposed by authors’ enable future researchers to develop several ternary based high performance concrete (HPC) mixtures as a potential solution for durable reinforced concrete bridge decks. 6. It is easy to understand the role of SCM as a second component in binary mixtures to achieve the optimum resistivity and to observe its role in hydration process and the rate of pozzolanic reaction. However, combination of two SCMs with Portland cement in ternary mixtures create more complicated behavior of the mixtures as three different materials have different particle sizes, chemical composition and hydration reaction mechanisms. 7. In future, thorough microstructural investigation of mixtures can be performed for proper justification to understand the complex behavior, development and comparison of SR of ternary mixtures at different days.
Acknowledgement
120
7 days
100
14 days
80
28 days
The authors would like to thank CSUF’s grant office for the intramural grant to support this research. The authors also would like to thank BASF, Lehigh Cement Company, Mitsubishi Cement Corporation, Headwaters, and CMT Research Associates, LLC for their generous donation of materials namely Type II–V cements, grade 120 slag, grade 100 slag, Class C and Class F fly ash, and silica fume and chemical admixtures.
56 days
References
60 40
91 days
20 0
0
3
6
9
Silica fume replacement (%)
12
VL limit (author's) VL limit (FDOT)
Fig. 21. Variation of the SR at different amount of SF replacement in 35% G120S mixtures for 150 mm 300 mm specimens.
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