PERFORMANCE OF HIGH-STRENGTH CONCRETE INCORPORATING MINERAL BY-PRODUCTS* Tarun R. Naik Director, Center for By-Products Utilization

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1 PERFORMANCE OF HIGH-STRENGTH CONCRETE INCORPORATING MINERAL BY-PRODUCTS* By Tarun R. Naik Director, Center for By-Products Utilization Viral M. Patel Research Associate, Center for By-Products Utilization and Larry E. Brand Former Graduate Student Department of Civil Engineering and Mechanics College of Engineering and Applied Science The University of Wisconsin-Milwaukee P.O. Box 784 Milwaukee, WI Telephone: (414) Fax: (414) * Paper submitted for presentation and publication for the Research in Progress Seminar at the ACI, National Convention, Washington, D.C., March 15-19, 1992.

2 PERFORMANCE OF HIGH-STRENGTH CONCRETE INCORPORATING MINERAL BY-PRODUCTS Tarun R. Naik *, Viral M. Patel ** and Larry E. Brand *** ABSTRACT This research was undertaken to investigate performance of high-strength concrete incorporating mineral admixtures, fly ash and silica fume. For modern construction, the use of new construction materials is increasing to achieve economy and improved final results. An extensive literature search was carried out to review various engineering properties of high-strength concrete. In this study, three different mix proportions for high-strength concretes were developed. One mix was proportioned with fly ash consisting of one third of total cementitious materials, and was designed to achieve 10,000 psi (70 MPa) compressive strength at 28 days. The other two mixes included both fly ash and silica fume to obtain 11,000 psi (77 MPa) and 12,000 psi (85 MPa) compressive strength at 28 days. All mixes were produced at a ready mixed concrete plant. Various tests, to determine physical properties of as delivered * Director, Center for By-Products Utilization, College of Engineering and Applied Science, University of Wisconsin-Milwaukee, Milwaukee, WI. ** Research Associate, Center for By-Products Utilization. *** Former Graduate Student.

3 concrete, such as slump, density, air-content, etc. were carried out. Twenty-seven 6 x 12 in. (150 mm x 300 mm) cylinders were cast for each mix for measuring modulus of elasticity and compressive strength of concrete at various ages. Additional twenty-seven 6 x 12 in. (150 mm x 300 mm) cylinders were also cast for measuring splitting tensile strength for each mix at various ages. Furthermore, forty-six 4 x 8 in. (100 mm x 200 mm) cylinders were cast and tested for compressive strength for each mix for various ages up to one year. Testing work is still in progress to obtain long-term strength properties. Standard 6 x 12 in. (150 mm x 300 mm) cylinder tests data are compared with 4 x 8 in. (100 mm x 200 mm) cylinders; and all cylinder test results are also compared with 4 x 8 in. (100 mm x 200 mm) cores obtained from companion concrete structural members. All tests were conducted in accordance with appropriate ASTM standards. Core test specimens obtained from beams made with the three mixes were also tested for chloride permeability using the AASHTO T-227 test method. Test results revealed that high-strength concrete can be made using high volumes of Class C fly ash to obtain strength levels in the range of 14,000 psi (100 MPa) at 1 year age and beyond. Reinforcement corrosion potential data are also planned for up to five years of this study. All of the available data is analyzed and graphs are plotted to derive useful conclusions and recommendations for testing and use of high-strength concrete with and without fly ash and silica fume. 3

4 INTRODUCTION Engineers are continuously faced with increasing demands for improved efficiency and reduced construction costs from private and public sectors. As a result, the use of high-strength concrete to accommodate higher stress levels is increasing. Until recently concrete with a strength in excess of 6000 psi (42 MPa) at 28 days was rarely available from a ready mixed concrete producer. However, in recent years high-strength concrete has gradually evolved; and, it is being put to a wider use. This has been made possible due to developments in concrete making materials and cost effective utilization of high-strength concretes. DEFINITION OF HIGH-STRENGTH CONCRETE High-strength concrete, as defined by the ACI, is a normal weight concrete which has an uniaxial compressive strength of 6000 psi (42 MPa) or greater at 28 days (1). However, concrete with a compressive strength higher than that which is ordinarily available in a region could also be regarded as high-strength concrete. More recently, some people define concrete with a compressive strength of 8000 psi (56 MPa) and above as high-strength concrete. Even though 6000 psi (42 MPa) was selected as the lower limit by the ACI Building Code, it is not intended to imply that there is a drastic change in material properties, its behavior, or production techniques, that 4

5 occur at this level of compressive strength. In reality, all changes that take place above 6000 psi (42 MPa) represent a gradual process which starts with the "normal-strength" concretes and continues into high-strength concretes. SCOPE There are distinct advantages in using concrete with higher compressive strengths in both reinforced, prestressed, and precast concrete construction. Despite extensive research carried out over the years and availability of low-cost production techniques of high-strength concrete, the full utilization of this engineering material has not been realized. This has been particularly so in prestressed and precast concrete construction applications in which there would be some distinct advantages with the use of high-strength concrete. A possible reason why full utilization has not occurred is that the practicality of everyday use of high-strength concrete, particularly greater than 10,000 psi (70 MPa), has not yet been fully determined, with or without the use of high-strength reinforcing steel. Also, adequate changes in various building code specifications, such as ACI Building Code, to provide for better performance of structures using high-strength concretes has not yet been accomplished. Therefore, requirements for code equations and structural design considerations must also be evaluated to determine their applicability with higher strength concretes in the concrete 5

6 industry (2). For example, equations for allowable tensile strength, shear strength, and modulus of elasticity for a given value of compressive strength must be developed for high-strength concrete. This research answers some of these concerns. This paper reviews and presents results from a research project carried out at the Center for By-Products Utilization at the UW-Milwaukee to determine the properties of fresh and hardened high-strength concrete. The project included 10,000, 11,000, and 12,000 psi (70, 77 and 84 MPa) concrete mixes. Tests completed on each mix were, axial compressive strength of cast cylinders, modulus of elasticity, and splitting tensile strength. Cores were taken from beams cast with the same mixes and were tested for compressive strength to be compared with the cylinder test results. All results were compared with the available ACI Code equations for calculating these properties based upon the concrete compressive strength. These three concretes were also tested to determine the rapid chloride ion permeability at one year age. CONCRETE MIX PROPORTIONING This section details mix proportions tested in this project. The research project consisted of three different mix proportions to achieve nominal strengths of 10,000 psi (70 MPa) and higher at the 28-day age. The production concrete was proportioned in 6

7 consultation with a silica fume supplier and a ready-mixed concrete company located in Milwaukee, Wisconsin. Production of high-strength concrete using conventional batching equipment and techniques requires better quality of materials (i.e., low coefficient of variation) and accuracy in the batching of the mix, particularly in measuring moisture level in the fine aggregates. The materials used in the mixes were locally available. Previous research has shown that the selection of raw materials is extremely important for high-strength concrete (3, 4, 5). The type and brand of cement also influences the workability and the strength of concrete (6,7,8). Type I Portland cement from a regional supplier, for which prior test data were available (3,4,5), was used in all mixes. Properties and type of both coarse aggregates and fine aggregates used in the production of concrete are also important. The fine and coarse aggregate used in the project met the requirements of ASTM C-33. Washed natural sand and coarse aggregate at SSD condition were used for all mixes. The maximum 1/2" size coarse aggregate was crushed limestone with a compressive strength of 35,000 psi. The water/cementitious ratios used in the past studies for the production of high-strength concretes have been lower than 0.35 (3, 4, 5, 9). In this study, the w/c ratio included fly ash and/or silica fume with the cement to provide a water/cementitious ratio of less than

8 One-third of the total cementitious materials was a Type C fly ash (with CaO of about 26%) for the 10,000 psi (70 MPa) mix. The other two mixes had both the Type C fly ash and a silica fume included as a partial replacement of cement in the concrete. The Class C fly ash from the Pleasant Prairie Power Plant in Wisconsin was used in this study. Since silica fume is very fine, it was added in slurry form, i.e. initially mixed with water. This excess water was accounted for in calculating the water/cementitious ratio. The concrete tested was not air entrained because the structural elements were for indoor use. Various other admixtures, a retarder and a superplasticizer, were also added to the concrete to lower the water/cementitious ratio and to achieve a high workability of 6" (150 mm) slump or higher. Details of all the mixes are given in Table 1. CASTING AND CURING OF TEST SPECIMENS A number of tests were conducted on fresh and hardened concrete. The temperature of the concrete and the ambient air was measured at the time of casting of test specimens. The slump, density, and air content of all the three concretes were also measured in accordance with applicable ASTM standards. These values are presented in the Table 1. Mechanical and elastic properties of hardened concrete were 8

9 determined, Tables 2-6. There were two different diameters of cylinders tested for comparison, Fig. 1. Twenty seven 6 x 12 in. (150 mm x 300 mm) cylinders were cast in reusable cast-iron molds for measuring the compressive strength and the modulus of elasticity. Another twenty eight 6 x 12 in. (150 mm x 300 mm) cylinders were cast in plastic molds for measuring the splitting tensile strength of concrete. Also, forty-six 4 x 8 in. (100 mm x 200 mm) cylinders were cast in cast iron molds for compressive strengths of concrete at various later test ages. All specimens were prepared in accordance with ASTM and then sprayed with a curing compound ("confilm") to the exposed surface which minimizes evaporation of the mix water from the concrete surface. The cylinders were then covered with plastic bags and immediately placed in a lime-saturated water tank at a temperature of 73 F ± 3 F (27 C ± 1.5 C). All specimens were stripped after 24 hours and stored in the lime-saturated water tank until the time of test. One cylinder of each size and from each mix was used for measuring the maturity of the concrete in order to compare it with the maturity of in-situ concrete in structural beam elements. The temperature probes were inserted into the cylinders and beams soon after the top surface was finished. 9

10 PROPERTIES OF HARDENED CONCRETE Compressive Strength Two sizes of cylindrical specimens were tested in accordance with ASTM C-39 to determine the compressive strength of concrete. Three 4 x 8 in. (100 mm x 200 mm) cylinders were tested at each of the following test ages: 1, 3, 7, 14, 28, 56, 91, 182, and 365 days, to determine the compressive strength of the three concrete mixes. Three 6 x 12-in cylinders were tested at each test age for compressive strength up to 28-day age. Compressive strength tests are scheduled for 2,3,4 and 5 years. All the tests were done using a Tinius-Olsen compressive testing machine meeting C-911 ASTM requirements. The test results are presented in Tables 2, 3 and 4. The strength of these mixes plotted against their test ages is shown in Fig. 2, 3 and 4. As seen from the Fig. 2, 3 and 4, the desired compressive strengths were achieved between 28 and 35 days. It was possible to obtain such high strengths by using a high cementitious content, addition of finer additives like fly ash and silica fume and a lower w/c ratio in combination with a superplasticizer. This resulted in a denser matrix and better bond between the aggregate and the mortar matrix surrounding it. Also the higher compressive strength of the aggregates contributed to the higher compressive strength of these concretes. 10

11 The compressive strength of low cementitious factor, low-strength, concrete may not significantly increase after 91 days while the compressive strength of high cementitious factor, high-strength, concrete keeps increasing significantly up to approximately 180 days and then it starts leveling off. This is because of high-cementitious content which continues to hydrate over a longer period of time. Tensile Strength The 6 x 12 in. (150 mm x 300 mm) cylinders were tested to determine the splitting tensile strength of concrete. Splitting tensile strength tests were conducted in accordance with the ASTM C-496, at 1, 3, 7, 14, 28 and 56 days. Three cylinders were tested at each test age. All cylinders were tested wet. Detailed test data are given in Tables 2, 3, and 4. Fig. 5, 6 and 7 show variation of the tensile strength with age of concrete. As can be expected, the tensile strength increased with increasing age. Fig. 8 compares the test results with the ACI Eqn based upon the compressive strength: fct= 6.7 (f'c) 1/2, where fct is the predicted splitting tensile strength from the compressive strength, f'c. Fig. 8 shows that the ACI Eqn underpredicts the tensile strength of the 10,000 psi (70 MPa) and higher strength concrete. This is believed to be due to a denser matrix, as well as improved aggregate mortar bond resulting in better tensile strength for 11

12 concrete containing fly ash with or without silica fume. The tested specimens showed that more than 95% of the aggregates failed in tension indicating excellent aggregate mortar interface bond. Very few aggregate bond failures were observed after 14-day age of concrete. After 28 days of curing, the increase in tensile strength was at a diminishing rate for all mixes. A new equation needs to be developed to reliably estimate the tensile strength of the high strength concrete. It can be observed from Fig. 8 the ACI Eq. overpredicts the tensile strength of concrete at strength lower than 6000 psi (42 MPa). The measured splitting tensile strengths were about 10-12% of the compressive strength up to about 6,000 psi (42 MPa) compressive strength. On the other hand, the tensile strength, measured as a percentage of the compressive strength, reduced to about 6% for higher compressive strengths. Similar results have been reported earlier (10). Modulus of Elasticity The standard cylinders cast in cast-iron molds were tested to determine the static modulus of elasticity and compressive strength of concrete. All the tests for the modulus of elasticity were carried out in accordance with the ASTM C-469. These tests were conducted at 1, 3, 7, 14, 28, 35, and 56 days. Three cylinders were tested 12

13 at each test age. For all mixes, at 1 and 3 day ages, the cylinders were capped using a regular-strength sulfur capping compound. While for all other tests, a high strength sulfur capping compound was used. This capping compound was recommended by the manufacturer for concrete with compressive strengths of 6000 psi to psi (40 to 115 MPa). Test specimens were air dried on the top and bottom surfaces for capping. They were then capped and tested wet, after reimmersing them for sufficient amount of time in the water tank. The strains in the concrete were measured up to approximately 70% of the compressive strength at that test age. The secant modulus of elasticity was then calculated by measuring the slope of the line joining the points with stress corresponding to 0.40 fc' and stress at 50 millionths strain, per ASTM C-469. This value was then rounded off to the nearest 50,000 psi. The test results are reported in Table 5. The modulus increased, as expected, with increasing age at a decreasing rate after 14-day age. The modulus of elasticity determined for each stress-strain curve at each strength is plotted against the compressive strength at each age and compared with the ACI Eqn , Fig. 9. E c = 33 w 1.5 (f'c)½ It is clear from the Figure 9 that the ACI equation overpredicts the modulus of elasticity after about 5,000 psi (35 MPa) compressive strength of concrete. Hence the prediction of the deflection of 13

14 structural members would be lower than actual, thereby predicting reduced ductility for high-strength concrete members. It is apparent that the modulus of elasticity of high-strength is lower than predicted than that of normal strength (less than 5000 psi, 35 MPa) concrete. This is due to the fact that there are fewer microcracks in the normal strength concrete at a given strain thereby increasing its modulus of elasticity. Also it is observed from Table 5 that the modulus of elasticity increases at a decreasing rate after 14-day age. COMPRESSIVE STRENGTH FROM CORE TESTS Concrete cores of 4" (100 mm) nominal diameter were cored using a diamond tipped drill bit from beams cast from these three concrete mixes. Care was taken to avoid cutting the reinforcement. The direction of coring was perpendicular to the direction of casting of concrete beams. These cores were then conditioned and tested in accordance with the ASTM Test C-42 and C-39. The length-to-diameter (l/d) ratios for the cores were maintained at two. High-strength sulfur capping compound was used to cap these cores. All cores were tested in the same Tinus Olsen compression testing machine as the cylindrical cast specimens. The details of the core specimens and tests data are given in the Table 6. A core numbering system was devised for ease of identification. The numbering consists of two numbers: B-N., where "B" is the beam # cored, and "N" is the number of core. Three cores were tested from each beam. A correction factor 14

15 was used to predict the equivalent cylinder compressive strength of the beam concrete (12). The correction factor was chosen from the Table 7 which is arrived at from the ACI and Ref. 12. This corrected strength test value was used to compute the nominal cylinder compressive strength based upon the core compressive strength. It can be observed from the tests that the core strengths are lower than the cylinder strengths at an equivalent age, Tables 2, 3, 4, and 6. At higher design strengths, the core strengths were much lower than the equivalent age cylinder strengths. Thus as the concrete strengths increases, a higher correction is required to express the core strength in terms of equivalent cylinder strength (12). RAPID CHLORIDE PERMEABILITY TESTING All three series of concrete under investigation were tested in accordance with AASHTO T 277 procedure to determine the chloride ion permeability of concrete mixes. Values for chloride permeability rating of concretes, as established by AASHTO (11), are listed below: Permeability Rating Negligible Very Low Low Charge, Coulombs Less than 100 Coulombs 100 to 1,000 Coulombs 1,000 to 2,000 Coulombs 15

16 Moderate High 2,000 to 4,000 Coulombs Greater than 4,000 Coulombs The rapid chloride permeability test data obtained for this series of concrete under study is presented in Table 8. The Mix 1 tested to pass an average total charge of 259 Coulombs. The Mix 2 and 3 showed an average total charge of 263 Coulombs and 260 Coulombs, respectively. Thus, according to AASHTO rating, all mixes had "very low chloride ion permeability". The plot of test time versus the total charge passed for Mix 1, 2 and 3 at the age of one year is shown in Figure 10. CONCLUSIONS On the basis of the research reviewed and test results obtained, use of high-strength concrete in the construction industry would definitely be of a great advantage. However, before this is done on a full scale, further research and modifications are required for the building codes and specifications. From this project it can be concluded that high-strength concrete can be manufactured with a low water/cementitious ratio and use of superplasticizer to achieve high workability. However, finishability of the concrete was a problem due to loss of effect of the superplasticizer. 16

17 17

18 The desired compressive strength for all mixes were achieved at about 35 days of age. At later ages, the compressive strengths of concretes with fly ash only and concretes with both fly ash and silica fume were almost the same. The tensile strength increased with increasing age. However, the tensile strength measured as a percentage of the compressive strength for all mixes reduced to about 6% of the compressive strengths as compared to about 10-12% for concretes below 6000 psi compressive strengths. The modulus of elasticity is overpredicted by the ACI equation for concretes with compressive strengths above 5000 psi. It is also observed that the modulus of elasticity increases at a decreasing rate after 14 days of curing. Core tests indicated that the core compressive strengths were lower than the cylinder strengths. This is true for all concretes. As the concrete strength increases a larger correction was required for the cores tests. From the analysis of test results it is concluded that concretes containing mineral admixtures have very low chloride ion permeability. The test results of indicated that all the mixes had almost the same chloride ion permeability. Thus it can be concluded that concretes containing Class C fly ash only and concretes containing 18

19 both fly ash and silica fume have nearly the same chloride ion permeability. Thus the compressive strength of concrete at higher strength have a negligible influence on the rapid chloride ion permeability of concrete. Concretes containing mineral admixtures have a dense matrix and hence a lower chloride ion permeability, especially at later ages. LIST OF REFERENCES (1)ACI Committee 363, "State-of-the Art Report on High-strength Concrete, " ACI Journal, Proceedings V. 81, No. 4, July-August 1984, pp (2)Anderson, A.R., "Research Answers Needed for Greater Utilization of High-Strength Concrete," PCI Journal, V. 25, No. 4, July-August 1980, pp (3)Naik, T.R., and Ramme, B.W., "Effects of High-Lime Fly Ash Content on Water Demand, Time of Set, and Compressive Strength of Concrete", ACI Materials Journal, Vol. 87, No. 6, November/December 1990, pp (4)Naik, Tarun R., and Ramme, Bruce W., "Setting and Hardening of High Fly Ash Content Concrete", 8th International Coal Ash 19

20 Utilization Symposium, ACAA, Washington, D.C., (5)Naik, T.R., and Ramme, Bruce W., "High Early Strength Fly Ash Concrete for Precast/Prestressed Products", PCI Journal, Nov. Dec. 1990, pp. (6)Chicago Committee on High-Rise Buildings, "High-Strength Concrete in Chicago High-Rise Buildings", Task Force Report No. 5, Chicago, IL, February 1977, 63 pages. (7)Hester, W., "High-Strength Air-Entrained Concrete", Concrete Construction, February 1977, pp (8)Freedman, S., "High-Strength Concrete", Modern Concrete, Oct., Nov., Dec. 1970, and Jan., Feb (9)Perenchio, W.I., "An Evaluation of Some of the Factors Involved in Producing very High-Strength Concrete", Bulletin No. RD014, Portland Cement Association, Chicago, IL, 1973, 7 pages. (10)ACI Committee 363, "Research Needs for High-Strength Concrete," ACI Materials Journal, V. 84, November-December 1987, pp (11)AASHTO, "Specifications for Materials Testing", FHWA,

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22 (12)Naik, T.R., "Evaluation of Factors Affecting High-Strength Concrete Cores", Proceedings of the First Materials Engineering Congress, ASCE, Denver, CO, August, 1991, pp REP

23 TABLE 1: CONCRETE MIX AND TEST DATA CONCRETE SUPPLIER: Central Ready-Mix Concrete Co., Milwaukee, WI. Mix Number Nominal Strength, psi 10,000 11,000 12,000 Cement, Type I, lbs./cu.yd Fly Ash, Type C, lbs./cu.yd Silica Fume, lbs./cu.yd Slurry, gallons Water, lbs./cu.yd Water to cementitious ratio Sand, SSD, lbs./cu.yd 1,200 1,280 1,250 1/2" Max. crushed limestone, SSD, lbs./cu.yd. 1,650 1,700 1,700 Slump, inches 6 7-1/4 10-1/2 Air Content, % Air Temperature, Deg.F Concrete Temperature, Deg.F Concrete Density, pcf ASTM Type A Retarding Admixture, oz/cu.yd ASTM Type F Super Plasticizing Admixture, oz./cu.yd. S.I. Units: 1 lbs/cu yd. = kg/cu m. 1 Liter = x 10 3 oz. 1 inch = 25.4 mm 1 Deg. C = ( F - 32)/1.8 23

24 1 lbs/cu. ft. = kg/cu. m. TABLE 2: Concrete Strength Test Data, 10,000 psi (70 MPa) Specified Strength Test Age Days Compressive Strength, psi 4" x 8" Cyls 6" x 12" Cyls Actual Average Actual Average X Splitting Tensile Strength, psi Actual Average X Discarded S.I. Units: 24

25 1 psi = MPa 25

26 TABLE 3: Concrete Strength Test Data, 11,000 psi (77 MPa) Specified Strength Test Age Days Compressive Strength, psi 4" x 8" Cyls 6" x 12" Cyls Actual Average Actual Average Splitting Tensile Strength, psi Actual Average S.I. Units: 1 psi = MPa 26

27 TABLE 4: Concrete Strength Test Data, 12,000 psi (85 MPa) Specified Strength Test Age Days Compressive Strength, psi 4" x 8" Cyls 6" x 12" Cyls Actual Average Actual Average Splitting Tensile Strength, psi Actual Average S.I. Units: 1 psi = MPa 27

28 TABLE 5: Modulus of Elasticity Test Data Age, Average E, psi* Average E, psi* Average E, psi* Days f'c = 10,000 psi f'c = 11,000 psi f'c = 12,000 psi 1 3,750,000 3,700,000 3,650, ,050,000 4,100,000 3,950, ,850,000 5,150,000 5,000, ,400,000 5,750,000 5,650, ,450,000 6,000,000 6,150, ,700,000 6,050,000 6,100, ,750,000 6,000,000 5,800,000 S.I. Units 1 psi = MPa 1 in. = 2.54 cms * Average of three tests 28

29 TABLE 6: CORE STRENGTH TEST DATA* Test Performed in Accordance with the ASTM Test C-42 (Compressive Strength) Center for By-Products Utilization, UWM Core Number Age Days l/d ratio** Core Compressive Strength (psi) *** Correction Equival. Cyl. Compressive Strength (psi) Average (psi) , , , ,120 9, , , , , , ,789 10, , , , , , ,080 11, , , , , , ,800 10, , , , , , ,531 14, , , , , , ,872 13, , , , , , ,715 14, , , , , , ,654 12, , , , , , ,145 12, , , , , , ,524 16, , , , , , ,394 18, , , , , , ,808 12, , , , , , ,495 15, , , ,06 8, , ERR ERR , , , , , , ,220 15, , , , , , ,615 13, , ,138 29

30 * All cores were drilled in a direction perpendicular to the direction of casting the concrete structural beam element. ** Length measured after capping of the cores. *** See Table 7 - Correction for determining equivalent cylinder ("design") strength. l/d correction was not required per ASTM C-42. S.I. Units 1 psi = MPa 1 in. = 2.54 cms 30

31 TABLE 7: Equivalent Cylinder Strength Correction Factor for Core Strength (Ref. 12). Core Correction Factor Strength, psi for Core Strength* 3, , , , , , , *To obtain equivalent 6" x 12" (150 mm x 300 mm) Cylinder Strength. 31

32 TABLE 8: Rapid Chloride Ion Permeability Test Data Mix Number Beam Core Number Test Slice Location Maximum Current During Test (Amperes) Actual Total Charge Passed (Coulombs) Average Total Charge Passed (Coulombs) AASHTO Chloride Permeability Designation** 1 6 Top Upper Lower Bottom Very Low 2 16 Top Upper Lower Bottom* Very Low 3 23 Top Upper Lower Bottom Very Low * Discarded because of a crack ** Per AASHTO T-277 (Ref. 9) Permeability Rating Charge, Coulombs Negligible Very Low Low Moderate High Less than 100 Coulombs 100 to 1,000 Coulombs 1,000 to 2,000 Coulombs 2,000 to 4,000 Coulombs Greater than 4,000 Coulombs REP