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Guidelines for Early-Opening-to-Traffic Portland Cement Concrete for Pavement Rehabilitation (2005)

Chapter: Chapter 3 - Performance Considerations Related to the Durability of EOT Concrete

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Suggested Citation:"Chapter 3 - Performance Considerations Related to the Durability of EOT Concrete." National Academies of Sciences, Engineering, and Medicine. 2005. Guidelines for Early-Opening-to-Traffic Portland Cement Concrete for Pavement Rehabilitation. Washington, DC: The National Academies Press. doi: 10.17226/13543.
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Suggested Citation:"Chapter 3 - Performance Considerations Related to the Durability of EOT Concrete." National Academies of Sciences, Engineering, and Medicine. 2005. Guidelines for Early-Opening-to-Traffic Portland Cement Concrete for Pavement Rehabilitation. Washington, DC: The National Academies Press. doi: 10.17226/13543.
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Suggested Citation:"Chapter 3 - Performance Considerations Related to the Durability of EOT Concrete." National Academies of Sciences, Engineering, and Medicine. 2005. Guidelines for Early-Opening-to-Traffic Portland Cement Concrete for Pavement Rehabilitation. Washington, DC: The National Academies Press. doi: 10.17226/13543.
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Suggested Citation:"Chapter 3 - Performance Considerations Related to the Durability of EOT Concrete." National Academies of Sciences, Engineering, and Medicine. 2005. Guidelines for Early-Opening-to-Traffic Portland Cement Concrete for Pavement Rehabilitation. Washington, DC: The National Academies Press. doi: 10.17226/13543.
×
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Suggested Citation:"Chapter 3 - Performance Considerations Related to the Durability of EOT Concrete." National Academies of Sciences, Engineering, and Medicine. 2005. Guidelines for Early-Opening-to-Traffic Portland Cement Concrete for Pavement Rehabilitation. Washington, DC: The National Academies Press. doi: 10.17226/13543.
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14 CHAPTER 3 PERFORMANCE CONSIDERATIONS RELATED TO THE DURABILITY OF EOT CONCRETE A number of material characteristics impact the behavior of EOT concrete. Various test methods can be used to deter- mine these characteristics, including methods to assess the strength, shrinkage, durability, microstructure, and absorbtion/ permeability characteristics of the mixture. 3.1 STRENGTH The mechanical behavior of EOT concrete is commonly assessed through measurement of its compressive or flexural strength. Although concrete strength is not directly related to durability, strength criterion are an important consideration in deciding when a pavement can be opened to traffic. This is especially true where concrete strength is not assessed in days or weeks, but in hours. By definition, early strength is readily attainable in EOT concrete mixtures; however, if any concrete is loaded prematurely, its long-term performance will be com- promised. Therefore, EOT concrete repair materials must meet or exceed criterion set for opening strength. Concrete strength is essentially a function of the constitu- tive materials used, their proportions, temperature, and time of hydration. Strength development is typically accelerated in mixtures by using high cement content, low w/c ratios, and accelerating admixtures. High curing temperatures also pro- mote rapid strength gain. The compressive strength test on cylindrical specimens, described in AASHTO T 22, is the most common strength test made on concrete. For pavement applications, the flex- ural strength test (AASHTO T 97 [third-point loading test] or AASHTO T 177 [center-point loading test]) is often used. The major limitation to the use of flexural strength is that the specimens are more difficult to properly prepare, and thus the variability within the test is higher. As discussed in Chapter 2, the compressive and flexural strengths are both commonly used as strength criterion in SHA specifications for EOT concrete. 3.2 SHRINKAGE The total shrinkage that occurs in a concrete mixture is composed of several types of shrinkage that occur at differ- ent ages in the life of the material. Although shrinkage of concrete cannot be totally eliminated (excluding the use of expansive cements), it can be reduced or controlled by the use of an appropriate mix design and proper construction tech- niques. Controlling shrinkage contributes to crack prevention, which helps prevent the physical and chemical attack of con- crete. This section discusses three types of shrinkage that can affect EOT concrete mixtures: plastic, drying, and autogenous. 3.2.1 Plastic Shrinkage Plastic shrinkage is the result of free, or “bleed,” water evaporating from the surface of concrete faster than it appears during finishing operations (Kosmatka et al. 2002). Gener- ally, an evaporation rate of 0.5 kg/m2/hour (0.1 lb/ft2/hour) or more is considered critical (Mindess et al. 2003). If the amount of evaporation is significant, small irregular cracks can form over the entire surface of the concrete. These cracks, although at first isolated to the slab surface, can progress into full-depth cracks under the influence of additional shrinkage and/or traffic loading. They also provide pathways for chem- ical attack by destroying the water tightness of the concrete. Generally, the potential for plastic shrinkage is increased by elevated temperatures (both concrete and air), low relative humidity, high wind velocity, a low w/c ratio, and high cement content (Mindess et al. 2003). Many of these factors are accentuated with EOT concrete installations. This concern is thus particularly important. Any factor that either increases the rate of evaporation or decreases the rate of bleed water rising to the surface makes the concrete more susceptible to plastic shrinkage cracking. Plastic shrinkage can be virtually eliminated by maintaining a wet surface during finishing operations and initial curing (Neville 1996, Mindess et al. 2003), but this is almost impossible to do under EOT con- crete construction limitations. Instead, curing compounds are used to minimize evaporation. Curing compounds must be applied early and uniformly, thoroughly coating the exposed concrete surface. 3.2.2 Drying Shrinkage Drying shrinkage occurs after the paste has hardened and results from the strain produced by the loss of water from the

15 hardened material (Mindess et al. 2003). The factors that influence drying shrinkage that are most relevant to EOT con- crete materials are the aggregate volume/cement content, the w/c ratio, admixtures, aggregate characteristics, and curing. According to Neville (1996), the most important influence on shrinkage is the restraint provided by the aggregate. The amount of restraint provided directly relates to the aggregate volume; as the aggregate volume decreases (with a commen- surate increase in cement paste volume), the amount of shrink- age increases. The w/c ratio also directly and significantly affects drying shrinkage, with lower w/c ratio mixtures having reduced shrinkage (Neville 1996, Mindess et al. 2003). Thus, EOT concrete mixtures will benefit from the low w/c ratio that they commonly employ. For a given aggregate source and vol- ume, the w/c ratio of concrete is one of the most important parameters for limiting drying shrinkage. Holding all other factors equal, a lower w/c ratio reduces the amount of evap- orable water available to cause drying shrinkage of concrete mixtures (Neville 1996). Kosmatka et al. (2002) approach this issue a little differently, stating that the most important factor affecting drying shrinkage is the amount of water added per unit volume of concrete and that shrinkage can be mini- mized by keeping the amount of added water low. Obviously, the aggregate volume, the w/c ratio, and the water added all relate to each other, but the main objective is to minimize the amount of evaporable water in the mixture. There is an AASHTO provisional test method for assess- ing the potential for cracking due to drying shrinkage. The test is specified in AASHTO PP 34-99, “Standard Practice for Estimating the Crack Tendency of Concrete.” In this test, ring specimens are molded and the top and bottom faces of the rings are covered to prevent moisture loss other than through the outside circumferential area. A steel ring inside the con- crete specimen restrains the concrete specimen as it shrinks. This restraint results in internal tangential tensile stresses, which will cause the concrete to crack if its tensile strength is exceeded (Kraai 1985). The time to cracking and the width and length of these cracks represent the damaging effect. 3.2.3 Autogenous Shrinkage Concrete with a low w/c ratio can undergo a process of self- desiccation that can lead to autogenous shrinkage (Mindess et al. 2003). This process is characterized by the removal of water from the capillary pores through the internal use of water in the formation of hydration products. Autogenous shrink- age is relevant to EOT concrete materials because it seems to increase at higher temperatures, in mixtures with higher cement contents, and in mixtures made with finer cements (Neville 1996). In the past, this type of shrinkage was considered to be quite rare and of little consequence because its contribution to total shrinkage was small. But because low w/c ratios are often used in modern concrete, including EOT concrete, there has been speculation that autogenous shrinkage might be partly contributing to microcracking. Unlike drying shrinkage, autogenous shrinkage increases as the w/c ratio decreases. This increase may be particularly relevant for EOT concrete mixtures, which in some cases have w/c ratios as low as 0.32. Similar to drying shrinkage, autogenous shrinkage only occurs in the paste fraction of the concrete. Thus, the rela- tive volume of aggregate to paste can directly impact the magnitude of the measured autogenous shrinkage. Because concrete made with higher volumes of aggregate have less measured autogenous shrinkage due to increased restraint, increased cement contents generally result in increased auto- genous shrinkage. 3.3 DURABILITY The performance of EOT concrete repairs can be adversely affected by the concrete’s lack of durability (i.e., ability to maintain its integrity in the environment in which it was placed). In general, durability problems can be attributed to either physical or chemical mechanisms, although the two mechanisms often act together to bring about the develop- ment of distress. Furthermore, problems with completely dif- ferent causes may develop simultaneously, thereby compli- cating the determination of the exact cause(s) of material failure. The information presented in this section is based on research conducted for the FHWA (Van Dam et al. 2002a, Van Dam et al. 2002b). Only material-related distress that can be directly attributed to the unique properties of EOT concrete are discussed, including freeze-thaw deterioration, deicer scaling/deterioration, and sulfate attack. Certain types of material-related distress, such as alkali-aggregate reac- tivity and corrosion of embedded steel, can be significantly affected by some characteristics of EOT concrete mixtures (e.g., high–cement-content and chloride-based accelerators). These topics are not addressed in these guidelines. 3.3.1 Freeze-Thaw Deterioration Freeze-thaw deterioration is caused by the deterioration of saturated cement paste under repeated freeze-thaw cycles. The mechanisms responsible for internal damage resulting from freeze-thaw actions are not fully understood, but the most widely accepted theories stipulate the development of internal stress in the concrete as a result of hydraulic or osmotic pres- sures caused by freezing. A review of the literature related to these phenomena is provided by Marchand et al. (1994). Deterioration of the cement paste due to freeze-thaw dam- age manifests itself in the form of scaling, map cracking, or severe cracking and deterioration, most commonly occurring at joints where moisture is more readily available. The addi- tion of an air-entraining agent (an admixture that introduces a system of dispersed, microscopic spherical bubbles in the concrete) could effectively prevent this deterioration if a suf- ficient air-void system forms.

16 Measurements of the total air content of fresh concrete are made during construction. Three AASHTO test meth- ods are available for measuring the air content of fresh con- crete during construction: AASHTO T 152, AASHTO T 196, and AASHTO T 121. These methods, however, do not deter- mine whether the air is truly entrained or entrapped or whether an adequate air-void system has been developed to protect the concrete against freeze-thaw damage. A test method that has been under investigation for a number of years provides a means for measuring the air-void system parameters for fresh concrete. The test equipment, known as the Air-Void Analyzer (AVA), has received mixed reviews (Price 1996, Magura 1996). The only currently accepted method to characterize the air-void system in the hardened concrete is through micro- scopic analysis in accordance with ASTM C 457, “Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete.” The freeze- thaw resistance of hardened concrete is often tested using AASHTO T 161, “Resistance of Concrete to Rapid Freezing and Thawing,” which is used to assess the resistance of con- crete specimens to rapidly repeated cycles of freezing and thawing. Only Procedure A in the standard, in which the spec- imens are frozen and thawed in water, should be used (TRB 1999). Many SHA’s have modified this procedure to address their specific needs and experiences. 3.3.2 Deicer Scaling/Deterioration Deicer scaling/deterioration is typically characterized by scaling or crazing of the slab surface due to the repeated application of deicing chemicals in a freeze-thaw environ- ment. Although the exact causes of deicer scaling are not known, this scaling is believed to be primarily a form of phys- ical attack similar to paste freeze-thaw deterioration. Both thermal stress and osmotic pressures are accentuated, mag- nifying the conventional freeze-thaw phenomena (Mindess et al. 2003, Pigeon and Plateau 1995). It has also been spec- ulated that pressure exerted by salt crystallization in voids is a contributing factor (Hansen 1963). Recent studies suggest that chemical degradation of the cement paste may also be occurring, resulting in dissolution of calcium hydroxide, coarsening of the concrete pore system, and potentially the formation of deleterious compounds. Deicer scaling/deterioration is more likely to occur if the concrete was over-consolidated or improperly finished— actions that create a weak layer of paste or mortar just below the finished surface (Mindess et al. 2003). Even adequately air-entrained concrete can be susceptible to the development of deicer scaling. Recommendations for the prevention of deicer scaling include providing a minimum cement content of 335 kg/m3 (564 lb/yd3) and using a maximum w/c ratio of 0.45, both of which are common in EOT concrete mixtures. Providing adequate curing and a minimum of 30 days of con- crete “drying” before applying deicing chemicals is also rec- ommended (ACPA 1992). ASTM C 672, “Scaling Resis- tance of Concrete Surfaces Exposed to Deicing Chemicals,” is the most commonly used test to investigate the scaling potential of concrete. 3.3.3 External Sulfate Attack External sulfate attack results when external sulfate ions (present in groundwater, soil, deicing chemicals, etc.) pen- etrate into the concrete and react with the hydrated cement paste. Although the mechanism of sulfate attack is complex, sulfate attack is likely caused by two chemical reactions: (1) the formation of gypsum through the combination of sul- fate and calcium ions and (2) the formation of expansive ettrin- gite through the combination of sulfate ions and hydrated cal- cium aluminate (ACI 2003b). In either case, the reaction leads to an increase in solid volume that can be very destructive to the hardened paste. In EOT concrete repairs, deterioration due to external sul- fate attack would likely first appear as cracking near joints and slab edges, generally within a few years of construction. Fine longitudinal cracking may also occur parallel to longi- tudinal joints. Actions taken to prevent the development of distress due to external sulfate attack include reducing the tri- calcium aluminate (C3 A) content in the cement or using poz- zolanic materials to reduce the quantity of calcium hydrox- ide (CH) in the hydrated cement paste. Both these actions are not easily accomplished in EOT concrete mixtures, and if calcium chloride accelerator is used, even greater amounts of CH are formed. A w/c ratio should be less than 0.45 to help mitigate external sulfate attack (ACI 2003b). Performance testing using ASTM C 452 and C 1012 should be considered to examine the sulfate resistance of portland cements and combinations of cements and pozzolans/slag, respectively. These tests only evaluate the cementitious mate- rials. There is currently no standard test to evaluate the sul- fate resistance of the mixture. 3.3.4 Internal Sulfate Attack Internal sulfate attack is similar in many ways to external sulfate attack, except that the source of the sulfate ions is internal. Potential internal sources of sulfate are (1) the slowly soluble sulfate contained in the cement, aggregate, or other concrete constituents (such as fly ash) and (2) the decompo- sition of primary ettringite due to high curing temperatures. Secondary ettringite formation (SEF) and delayed ettrin- gite formation (DEF) might both be considered types of internal sulfate attack that result for different reasons. SEF is commonly a product of concrete degradation, characterized by the dissolution and subsequent precipitation of ettringite into available void space and into preexisting microcracks. SEF is possible if the concrete is sufficiently permeable and saturated, allowing for the dissolution and precipitation

process to occur. Although most experts agree that secondary ettringite formation will not generate sufficient expansive pressures to cause concrete fracture, its presence in the air- void structure may limit the ability of the paste to resist freeze-thaw deterioration (Ouyang and Lane 1999). DEF, on the other hand, can lead to destructive expansion within the paste, resulting in microcracking and separation of the paste from aggregate particles. DEF is most often associ- ated with steam curing the concrete because primary ettringite will not properly form at elevated temperatures (Thaulow et al. 1996, Klemm and Miller 1997). After the concrete has cured and temperatures are reduced to ambient conditions, sulfates and aluminate phases in the paste may react to form expansive ettringite, disrupting the concrete matrix. It is still speculative, however, whether cast-in-place concrete can experience DEF. But there is little doubt that under certain conditions (e.g., thick slab, high cement content, and high ambient temperature), EOT concrete may experience temper- atures in excess of that required for DEF during curing, espe- cially if curing blankets are used during summer placements. The manifestation of internal sulfate attack is character- ized by a series of closely spaced, tight map cracks, with wide cracks appearing at regular intervals. DEF can only be identified through petrographic microscopic analysis in accor- dance with ASTM C 856, “Standard Practice for Petrographic Examination of Hardened Concrete.” 3.4 MICROSTRUCTURE For the most part, concrete mechanical properties and dura- bility are controlled by the paste microstructure. Detailed dis- cussions of concrete microstructure can be found in Mindess et al. (2003) and Mehta and Monteiro (1993). The hydrated cement paste microstructure that binds the aggregates together consists of solid phases and a pore system. The solid phases, which consist of both unhydrated cement grains and the related hydration products, can be characterized by type, size, and relative percentages. The number of unhydrated cement grains increases markedly in high–cement-content, low–w/c- ratio EOT concrete mixtures. While a variety of hydration products exist in cement paste, the primary phases of interest in determining the behavior of concrete are calcium-silicate- hydrate (C-S-H), calcium hydroxide (CH), and calcium sul- foaluminates (ettringite [AFt] and monosulfate [AFm]). The nature of the solid phases in a cement paste changes with time. At time zero, when the anhydrous cement grains first come into contact with the mix water, the microstructure con- sists of the unhydrated cement particles surrounded by water. As hydration proceeds, space that was initially water-filled is progressively occupied by hydration products. The cement paste pore structure can generally be classified into three distinct groups: cement gel pores, capillary pores, and air voids (Neville 1996). The paste/aggregate interfacial transition zone and microcracking represent additional ele- ments of the concrete pore structure. The pores within the C-S-H, referred to as gel pores or interlayer hydration space, make up the smallest individual elements of the total cement paste porosity. Their characteristics cannot be altered by changing mix design parameters. In contrast, capillary porosity can be significantly modi- fied by altering mixture properties, especially the w/c ratio. The capillary pore system is the space between anhydrous cement grains that is filled with water and not hydration prod- ucts. This system is typically irregular in both shape and spa- tial distribution, with the pore sizes and connectivity depen- dent on the size of the initial water-filled space (a direct function of the w/c ratio) and on the degree of hydration. In well-hydrated, low–w/c-ratio systems common in EOT con- crete mixtures, capillary pores will be much smaller than in high–w/c-ratio systems or systems at early stages of hydra- tion (Mehta and Monteiro 1993). The use of admixtures that disperse cement grains, such as water reducers, typically result in smaller, more uniformly distributed capillary pores. The largest elements of the pore structure are the air voids. The air voids are generally classified into two groups, those that are intentionally entrained and those that are unintention- ally entrapped. Entrained air voids are essentially spherical and tend to be randomly distributed throughout the cement paste. They are created through the addition of admixtures specifically designed to produce large quantities of micro- scopic air bubbles when mixed into fresh concrete. While it is virtually impossible to clearly distinguish between entrained and entrapped air voids, quite often voids larger than 1 mm (0.04 in.) in diameter and/or irregular in shape are labeled as entrapped (ASTM C 125). These larger air voids contribute significantly to the total air content of concrete, but not to the frost resistance of concrete. The interfacial transition zone (ITZ) between hydrated cement paste and the coarse aggregate particles is also an important element of the paste microstructure. The ITZ usu- ally has a different microstructure than the rest of the paste system, with a higher proportion of CH and a greater poros- ity than the bulk paste. With time, the highly porous transi- tion zone may become filled with additional hydration prod- ucts resulting from chemical reactions between the cement paste phases and the aggregates (Mehta and Monteiro 1993). Because these reactions reduce the porosity of the interfacial zone and consume calcium hydroxide, they tend to increase the paste strength in this zone. Microcracking of hydrated cement paste may occur rela- tively early in the hydration process (before the paste had gained significant strength) when internal stress exceeds the strength of the paste. Shrinkage and/or thermal strain could produce such stress when restrained by the aggregates. Both autogenous shrinkage and rapid changes in temperature of EOT concrete mixtures could lead to excessive microcrack- ing of the paste. A number of techniques are commonly used to character- ize the microstructure of concrete, including staining and various microscopy techniques (Van Dam et al. 2002b). Of all the available methods, the stereo optical microscope is the 17

18 first major analytical instrument to use when analyzing con- crete. It is used to examine key microstructural features in concrete, including those present in the aggregates, paste, air- void structure, reaction products, and cracks. Often, a petrog- rapher can diagnose durability problems with this approach alone. The stereo optical microscope is also commonly used for determining the air-void system parameters in hardened concrete in accordance with ASTM C 457, “Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete.” The petrographic optical microscope can also be used for evaluating microstructure and identifying the composition or mineralogical characteristics of phases within concrete. How- ever, the petrographic optical microscope requires detailed sample preparation and a highly trained analyst. ASTM C 856, “Practice for Petrographic Examination of Hardened Concrete,” outlines many of the procedures required for the petrographic examination of concrete. Included in ASTM C 856 are sections on qualifications of petrographers, purposes of examination, required apparatus, sampling, sample prepa- ration procedures, microscopical examination, and suggested diagnostic features to examine in concrete. Although ASTM C 856 is very useful and comprehensive, it does not relate observed diagnostic features to specific mechanisms of dis- tress. The analyst must interpret the results obtained (Van Dam et al. 2002b). Like the petrographic optical microscope, the scanning electron microscope (SEM) can be used to identify micro- structural features and cracks in concrete and the composi- tion or mineralogical characteristics of the various phases. Given the high magnification level of a conventional SEM, it would seem ideally suited for studying concrete. However, the instrument operates at a very low pressure (10-6 mm [4 × 10−8 in.] Hg), which dehydrates the concrete when it is placed in the instrument, altering the microstructure. This dehydra- tion can lead to significant cracking and decomposition of certain phases of interest. Specialized SEMs (i.e., the low- vacuum SEM and the environmental SEM) operate at higher relative pressures, reducing this effect to a minimum. How- ever, some cracking and desiccation still occur when these instruments are used, and care should be exercised in inter- preting features seen in SEM images. 3.5 ABSORPTION/PERMEABILITY The absorption characteristics and permeability of con- crete directly influence concrete durability. Concrete that is more permeable to air, water, or other substances is far more likely to suffer some kind of durability distress. The ingress of gases and liquids leads to solubility of some components in the hardened paste, can result in expansive reactions, and in general provides a medium through which ions can be transported. For this reason, changes in mixture design that decrease permeability often lead to an increase in durability. Currently, there is no readily available method to measure concrete permeability. Hooton et al. (2001) summarized the effectiveness of various methods that can be used to assess chloride penetration (only one method measures permeabil- ity) into concrete. In general, tests that accurately modeled chloride ingress were long-term tests that were not suitable for design or construction quality control. The rapid tests exhibited a number of limitations, the most relevant to EOT concrete being that the results were affected by the presence of ions in the concrete such as occurs when common acceler- ators are used. For this reason, simple tests based on absorp- tion offer a potential alternative to permeability testing. Absorption is a measure of the volume of pore space in concrete irrespective of the interconnectivity of the pores (Neville 1996). Although absorption and permeability are related, they are not necessarily correlated. A variety of tech- niques are used for determining the absorption rate of con- crete. One common test is ASTM C 642, “Test Method for Specific Gravity, Absorption, and Voids in Hardened Con- crete,” which is commonly used as a quality control test for precast members (Neville 1996). A related measure of concrete permeability is sorptivity, which measures the rate of absorption of water into the con- crete (Neville 1996). Generally, it is too difficult to mathe- matically model this flow in all but a single direction, and thus sorptivity tests are configured to establish one-directional flow into the specimen (Hooton et al. 2001). Sorptivity tests typically require that the sample be at a standard moisture content before testing is begun. The benefits of sorptivity test- ing are reduced testing time, low equipment cost, and simplic- ity of procedure. The proposed ASTM standard test for sorp- tivity requires only a scale, a stopwatch, and a shallow pan of water (Stanish et al. 1977). A variety of test methods exist for estimating concrete per- meability using the saturated flow of water. The majority of these tests determine permeability by measuring the steady- state flow of water through concrete due to a pressure differ- ential (Neville 1996), but these tests are difficult to conduct, lack good correlations to each other, and are long term or require specialized equipment. The most common rapid chloride penetration test used in North America is AASHTO T 277, “Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration.” Although this test has been accepted by many transportation agencies, it has serious limitations that make it impractical for evaluating EOT concrete. The three main limitations are that (1) the current passed relates to all ions in the pore solu- tion and not just chloride ions, (2) the measurements are made before a steady-state migration is achieved, and (3) the temperature of the specimen increases because of the applied voltage (Stanish et al. 1977). The first limitation is most relevant for the study of EOT concrete, since EOT concrete commonly contains various admixtures that will affect the ion concentration of the pore solution.

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 540: Guidelines for Early-Opening-to-Traffic Portland Cement Concrete for Pavement Rehabilitation examines the proportioning, testing, construction, and other aspects of early-opening-to-traffic (EOT) concrete.

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