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

Chapter: Chapter 2 - State of the Practice for EOT Concrete Repairs

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Suggested Citation:"Chapter 2 - State of the Practice for EOT Concrete Repairs." 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 2 - State of the Practice for EOT Concrete Repairs." 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 2 - State of the Practice for EOT Concrete Repairs." 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 2 - State of the Practice for EOT Concrete Repairs." 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 2 - State of the Practice for EOT Concrete Repairs." 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.
×
Page 9
Page 10
Suggested Citation:"Chapter 2 - State of the Practice for EOT Concrete Repairs." 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.
×
Page 10
Page 11
Suggested Citation:"Chapter 2 - State of the Practice for EOT Concrete Repairs." 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.
×
Page 11
Page 12
Suggested Citation:"Chapter 2 - State of the Practice for EOT Concrete Repairs." 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.
×
Page 12
Page 13
Suggested Citation:"Chapter 2 - State of the Practice for EOT Concrete Repairs." 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.
×
Page 13

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5CHAPTER 2 STATE OF THE PRACTICE FOR EOT CONCRETE REPAIRS Full-depth repair is a commonly used concrete pavement restoration technique for restoring both structural integrity and ride quality to concrete pavements suffering distresses listed in Table 1 (FHWA 2003). By definition, full-depth repairs are made through the entire depth of the pavement slab, are almost always full width across the lane, and have minimum specified lengths dependent upon the design of the existing pavement. After the repair boundaries are demarcated with full-depth saw cuts and the deteriorated concrete is removed, the base is repaired, the load-transfer devices are installed, and new PCC is placed. EOT concrete is commonly used in situations where lane closure must be kept to a minimum. There are a number of sources of information regarding full-depth repair of concrete pavement, including publica- tions by the Federal Highway Administration (FHWA 2003), the American Concrete Pavement Association (ACPA 1995), and the National Highway Institute (NHI 2001). Although these publications do not specifically address EOT concrete, they discuss the selection of candidate projects, the sizing of repairs, the installation of load transfer, material selection, construction procedures, and to some degree performance and cost considerations. Only limited discussions of material selection are contained in these documents, and little if any guidance is provided for assessing the durability characteris- tics of the EOT concrete mixtures. This chapter details the state of the practice for mixture constituents and proportion- ing, construction practices, durability concerns, and test meth- ods commonly used to assess durability. 2.1 MIXTURE CONSTITUENTS AND PROPORTIONS The main difference between EOT concrete and normal paving concrete is that strength gain occurs much more rapidly in EOT concrete, thus more cement, less water, admixtures, and aids to retain heat are commonly used. This section dis- cusses the various constituents and mixture proportioning of EOT concrete. 2.1.1 Constituent Materials For the most part, EOT concrete is composed of the same constituents as normal paving concrete. Coarse and fine aggre- gates are blended with portland cement, water, and admixtures to produce a stiff but moldable mass that hardens through a chemical process referred to as hydration. In the resulting stone-like mass, the aggregates have been bound together by the hydration products formed through chemical reactions between the water and cement. Air is also entrapped and/or entrained, typically making up 5 to 7 percent of the total mix- ture volume. Aggregates Aggregates make up 70 to 80 percent of the total volume of hardened concrete (Folliard and Smith 2003). As such, they have a large impact on the behavior of the composite. Many characteristics and test methods are used to assess aggregates. Folliard and Smith (2003) recommended essential (Level I) and optional/additional (Level II) tests (shown in Table 2) for evaluating aggregates to be used in concrete pavements. The concrete durability can be compromised through aggregate reactivity (alkali-silica or alkali-carbonate reactivity) or aggre- gate susceptibility to freeze-thaw damage. These topics are not covered in these guidelines, but relevant information is available elsewhere (Farney and Kosmatka 1997, ACI 2003a, Folliard and Smith 2003, Schwartz 1987, and Stark 1976). Another aggregate property that may impact EOT concrete durability is the coefficient of thermal expansion (CTE) of the aggregate, which strongly influences the CTE of the concrete. The CTE of a material is defined as the change in unit length per degree of temperature change. Differences in the CTE between aggregate and cement paste can lead to the develop- ment of thermal stresses within the concrete (Mindess et al. 2003) and in extreme cases may result in separation between the aggregate and the paste (Neville 1996). These differen- tial thermal movements—either between the aggregate and cement paste or between different aggregates in the same concrete—could lead to deterioration (Lea 1971). In addi- tion, because the CTE influences the thermal stresses devel- oped in concrete, its consideration is particularly important in EOT concrete pavement materials selection. As previously stated, the CTE of concrete is strongly related to the proportion and type of coarse aggregate used. The CTE for the aggregate is generally lower than the coef- ficient for cement paste. For example, the CTE is approxi- mately 11–13 × 10−6/°C (6.1–7.2 × 10−6/°F) for a quartzite

aggregate and 6 × 10−6/°C (3.3 × 10−6/°F) for a limestone aggre- gate, and in the range of 18–20 × 10−6/°C (10–11 × 10−6/°F) for cement paste (Mindess et al. 2003). Research has led to some correlation between CTE for con- crete and durability of mixtures. Lab tests have shown that concrete having higher CTEs are less resistant to temperature changes than concrete with lower CTEs (Neville 1996). Portland Cement In many applications, the use of a standard AASHTO M 85 Type I cement can provide satisfactory results for EOT concrete repairs. However, Type III cement is commonly used in EOT concrete materials because of its high–early- strength gain. The required chemical properties of Type III cements are similar to those of Type I, but Type III cements are ground more finely to promote the development of higher early strength. In some cases, Type II cements have been used in EOT concrete materials. Regardless of the cement type used, the engineer must carefully evaluate the properties of the cement in the context of the long-term physical and chemical stability and their effect on durability. Standard specifications for blended hydraulic cements are provided in AASHTO M 240. These cements are formed by intimately blending portland cement with fine materials such as ground granulated blast-furnace slag, fly ash or other poz- zolans, hydrated lime, and pre-blended cement combinations 6 of these materials (Kosmatka et al. 2002). These cements have not been commonly used in EOT concrete projects in the United States because of their generally slower rate of hydration. Chemical Admixtures Chemical admixtures—such as air entrainers (AASHTO M 154), accelerators, and water reducers (AASHTO M 194)— are commonly added to EOT concrete mixtures during pro- portioning or mixing to enhance the properties of freshly mixed and/or hardened concrete. Descriptions of these and other chemical admixtures can be found in a number of sources (Kosmatka et al. 2002, Mehta and Monteiro 1993, Mindess et al. 2003). It is reported that cement/admixture interactions are not well understood and that compatibility problems can result in non-durable concrete (Kosmatka et al. 2002, Mindess et al. 2003). Air Entrainers. Air-entraining admixtures are specified and tested under AASHTO M 154 and T 157, respectively. Air-entraining admixtures are added just prior to or during concrete mixing. When a high-range water reducer (HRWR) is used, the air entrainer should be added first to form a sta- ble air-void system that protects the hardened concrete against freeze-thaw damage and deicer scaling (Mindess et al. 2003). The entrained air also improves the workability of the fresh concrete, thus helping reduce segregation and bleeding. The amount of entrained air required to protect normal con- crete depends on the exposure level and the nominal maximum aggregate size. The ACI recommended air contents for frost- resistant concrete (ACI 2003b) are reproduced in Table 3. One concern for EOT concrete mixtures, especially those made with an HRWR, is the ability to achieve a desirable air- void system in high–cement-content mixtures (Whiting and Nagi 1998). Thus, not only should such mixtures be tested for total air, but the spacing factor should also be measured during the mix design process (Mindess et al. 2003). The air content of fresh concrete can be determined using AASHTO T 152 or T 196. Air content alone does not ensure the adequacy of the air-void system, but relatively good cor- relations exist between air content and frost resistance for air- entrained concrete. In recent years, the Air Void Analyzer (AVA) has been used for air-void system characterization in fresh concrete, with some SHAs using it during concrete pave- ment construction (FHWA 1996). The complete air-void sys- tem in hardened concrete can be assessed microscopically using procedures described in ASTM C 457. It has been observed in some mixtures, particularly those of high strength, that adequate freeze-thaw durability exists even though the air-void system parameters are judged to be inadequate. Accelerating Admixtures. Accelerating admixtures meet- ing the requirements of Type C or E in AASHTO M 194 are Pavement Type Distress Type Minimum Severity Level Required for Full-Depth Repair Blowup Corner Break Low Low Low D-Cracking Deterioration Adjacent to Existing Repair Medium Medium Medium Joint Deterioration Medium (with faulting 6 mm [0.25 in.]) Spalling Reactive Aggregate Medium Transverse Cracking Medium (with faulting 6 mm [0.25 in.]) Jointed Plain and Jointed Reinforced Concrete (JPC and JRC) Pavement Longitudinal Cracking High (with faulting 12 mm [0.5 in.]) Blowup Punchout Medium (with faulting 6 mm [0.25 in.]) Transverse Cracking (Steel Rupture) Medium (with faulting 6 mm [0.25 in.]) Localized Distress Medium Construction Joint Distress Medium D-Cracking Longitudinal Cracking High (with faulting 12 mm [0.5 in.]) Continuously Reinforced Concrete Pavement (CRCP) Repair Deterioration High High TABLE 1 General distress criterion for full-depth repair (FHWA 2003)

commonly used in EOT concrete repair materials. The Amer- ican Concrete Institute, in “Chemical Admixtures for Con- crete,” defines an accelerating admixture as “a material added to concrete for the purpose of reducing the time of setting and accelerating early strength development” (ACI 2003c). One group of accelerating admixtures contains a variety of soluble inorganic salts, such as calcium chloride, which is the best known and most commonly used accelerating admixture because it is relatively inexpensive and readily available. However, calcium chloride promotes corrosion of embedded steel and may have other negative effects on concrete dura- bility, including increasing the amount of drying shrinkage (Lackey 1992) and adversely affecting the pore structure (Suryavanshi et al. 1995, Wang and Gillott 1990). These char- 7 acteristics are believed to be at least partly responsible for the reduced freeze-thaw resistance exhibited in some mixtures containing calcium chloride accelerators (Neville 1996). Calcium chloride is commercially available in an anhydrous and a dihydrate form. Commercial anhydrous calcium chlo- ride is typically 94 to 97 percent calcium chloride by weight, whereas commercial flake products, which are close to dehy- drate, typically are composed of 77 to 80 percent calcium chlo- ride by weight (ACI 2003c). Although opinions vary slightly, the optimum dosage recommended is typically 2 percent for Type I calcium chloride (88 percent pure), and 1.5 percent for anhydrous calcium chloride (ACI 2003c, Mindess et al. 2003). Several commercial non-chloride accelerators conforming to AASHTO M 194 Type C requirements for accelerating Level Property Test Method Absorption AASHTO T 84: Specific Gravity and Absorption of Fine Aggregate AASHTO T 85: Specific Gravity and Absorption of Coarse Aggregate Aggregate gradation AASHTO T 21: Sieve Analysis of Fine and Coarse Aggregate Properties of microfines AASHTO T 11: Materials Finer than No. 200 Sieve and Mineral Aggregates by Washing AASHTO T 176: Plastic Fines in Graded Aggregates and Soils by the Use of the Sand Equivalent Test Aggregate shape, angularity, and texture AASHTO T 304: Uncompacted Void Content of Fine Aggregate AASHTO TP 56: Uncompacted Void Content of Coarse Aggregate (As Influenced by Particle Shape, Surface Texture, and Grading) ASTM D 4791: Test Method for Flat and Elongated Particles in Coarse Aggregate Aggregate thermal expansion AASHTO TP-60: Standard Test Method for the Coefficient of Thermal Expansion of Hydraulic Cement Concrete Aggregate abrasion CSA A23.2-23A: Resistance of Fine Aggregate to Degradation by Abrasion in the Micro-Deval Apparatus AASHTO TP 58: Resistance of Coarse Aggregate to Degradation by Abrasion in the Micro-Deval Apparatus AASHTO T 96: Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angles Machine Elastic modulus ASTM C 469: Static Modulus of Elasticity and Poisson’s Ratio of Concrete in Compression Polishing ASTM D 3042: Test for Acid Insoluble Residue in Carbonate Aggregates Aggregate strength British Standard 812 (Part 3): Aggregate Crushing Value Aggregate mineralogy ASTM C 295: Guide for Petrographic Examination of Aggregates for Concrete Alkali-aggregate reactivity ASTM C 295: Guide for Petrographic Examination of Aggregates for Concrete AASHTO T 303: Accelerated Detection of Potentially Deleterious Expansion of Mortar Bars Due to Alkali-Silica Reaction CSA A23.2-26A: Determination of Potential Alkali-Carbonate Reactivity of Quarried Carbonate Rocks by Chemical Composition I Freezing and thawing resistance (D-cracking) CSA A23.2-24A: Unconfined Freezing and Thawing of Aggregates in NaCl Solution AASHTO T 104: Soundness of Aggregate by Use of Sodium Sulfate or Magnesium Sulfate (only magnesium sulfate is recommended) Iowa Pore Index Test Modified Washington Hydraulic Fracture Test (based on modifications detailed by Embacher and Snyder [2001]) Properties of microfines AASHTO TP 57: Standard Test Method for Methylene Blue Value of Clay, Mineral Fillers, and Fines Aggregate mineralogy X-ray diffraction (XRD) analysis Thermogravimetric analysis (TGA) X-ray fluorescence (XRF) analysis Alkali-aggregate reactivity ASTM C 1293: Test Method for Concrete Aggregates by Determination of Length Change of Concrete Due to Alkali-Silica Reaction II Freezing and thawing resistance (D-cracking) AASHTO T 161 (modified Procedure C): Resistance of Concrete to Rapid Freezing and Thawing TABLE 2 Recommended (Level I) and optional/additional (Level II) testing of aggregates for concrete pavements (Folliard and Smith 2003)

admixtures contain calcium nitrate and ammonium calcium nitrate as active ingredients. Others conforming to AASHTO M 194 Type E requirements for water-reducing and acceler- ating admixtures and also conforming to Type C require- ments contain calcium nitrate as a principal active ingredi- ent. Research has shown that calcium nitrite is useful as a corrosion inhibitor in addition to its accelerating capabilities (Neville 1996). Other non-chloride, non-corrosive accelera- tors are available that contain compounds such as triethanol- amine, sodium thiocyanate, and calcium formate. It has been generally observed that concrete microstruc- ture produced in rapidly setting concrete is coarser and com- posed of more soluble hydration products, which in turn is more prone to physical and chemical attack. It is therefore recommended that accelerators be used only when necessary and that the designer/engineer recognize that the use of accel- erators may have a negative impact on the long-term dura- bility of the concrete. Water-Reducing Admixtures. Water-reducing admixtures are added to reduce the quantity of mixing water required to produce concrete of a given consistency. This reduction allows for a reduction in the water-to-cement (w/c) ratio while maintaining a desired slump, thus increasing strength while reducing permeability. A reduction in water content by 5 to 10 percent is obtainable through the use of conventional water reducers that are specified under AASHTO M 194 Type A. This class of water reducer will typically retard set, so accelerators are often added to offset this effect. Water reducers that act as accelerators are specified under AASHTO M 194 Type E. The effect of water reducers on the fresh concrete proper- ties varies with the chemical composition of the admixture, the concrete temperature, cement composition and fineness, 8 cement content, and presence of other admixtures (Kosmatka et al. 2002). For Type A and Type E water reducers, the effect on the air-void structure is unclear, with some sources report- ing either no effect or an improvement (Kosmatka et al. 2002) while others reporting possible adverse effects (Pigeon and Plateau 1995). HRWRs, also called superplasticizers, are specified under AASHTO M 194 Type F and Type G and can reduce water content by 12 to 30 percent. In some instances, they have application in EOT concrete mixtures where high cement contents and low w/c ratios are desired. This is par- ticularly true if the cement is finely ground, as are many Type III cements. One drawback is that air voids produced in con- crete made with HRWRs are often large, which increases the spacing factor and, on occasion, creates instability in the air- void system (Kosmatka et al. 2002, Pigeon and Plateau 1995). Thus, the fresh and hardened concrete properties of mixtures containing water reducers should be thoroughly evaluated during design to determine the extent of detrimental inter- actions that may occur. 2.1.2 State-of-the-Practice Mixture Proportioning This section presents a brief summary of common practice regarding EOT concrete mixture proportioning as presented in publications by the FHWA (2003), ACPA (1995), and the NHI (2001). In these publications, it is noted that EOT con- crete repair materials use similar constituents and propor- tioning as normal paving concrete, except that higher cement contents and lower w/c ratios are common. In addition, mate- rials that lead to accelerated strength gain—such as Type III cement, chemical accelerators, and water-reducing admix- tures—are also used. Specifically, the following items are reported in these publications: Average Air Content, Percent1 Nominal Maximum Aggregate Size, mm (in.) Moderate Exposure2 Severe Exposure3 9.5 (3/8) 6 7.5 12.5 (1⁄2) 5.5 7 19 (3/4) 5 6 25 (1) 5 6 37.5 (11⁄2) 4.54 5.54 75 (3) 3.54 4.54 150 (6) 3 4 1A reasonable tolerance for air content in field construction is ± 1.5 percent. 2Exposure is outdoor in a cold climate where the concrete will be only occasionally exposed to moisture prior to freezing and where no deicing salts will be used. Examples are certain exterior walls, beams, girders, and slabs not in direct contact with soil. 3Exposure is outdoor in a cold climate where the concrete may be in almost continuous contact with moisture prior to freezing or where deicing salts are used. Examples are pavements, bridge decks, sidewalks, and water tanks. 4These air contents apply to the whole as for the preceding aggregate sizes. When testing these concretes, however, aggregate larger than 37.5 mm (11⁄2 in.) is removed by handpicking or sieving and the air content is determined on the minus 37.5 mm (11⁄2 in.) fraction of the mixture. (The field tolerance applies to this value.) From this, the air content of the whole mixture is computed. TABLE 3 Recommended air contents for freeze-thaw distress resistant concrete (ACI 2003b)

• Type I or III cements are commonly used in EOT con- crete. Additional water may be required to enhance work- ability with Type III cements. The use of a water reducer can reduce this need for additional water (ACPA 1995). • Common cement contents for mixtures that are to be opened to traffic within 24 hours range from 385 to 530 kg/m3 (650 to 890 lb/yd3), with more cement being added for earlier opening times. For 24-hour acceler- ated strength concrete, a draft specification stipulates a minimum cement content of 446 kg/m3 (750 lb/yd3) (FHWA 2003). • The w/c ratio in EOT concrete is typically between 0.40 and 0.48. A draft specification for 24-hour accelerated strength concrete stipulates a maximum w/c ratio of 0.45 (FHWA 2003). • An accelerator is commonly employed and is almost a necessity for mixtures that are to be opened in 6 to 8 hours. The most common accelerator is calcium chlo- ride, which is commonly added at 1 percent by weight of cement when the air temperature exceeds 27°C (80°F) and up to 2 percent by weight of cement when the air temperature is lower. Tables 4 and 5 summarize SHA specifications for EOT concrete repair materials for 6- to 8-hour opening time and 20- to 24-hour opening time, respectively. Six- to 8-hour EOT Concrete Table 4 summarizes the mixture characteristics of the 6- to 8-hour EOT concrete specified by 16 SHAs. Although time to opening was frequently stipulated in the specifications, strength requirements were also used. For example, the time- to-opening criterion presented in Table 4 vary from as early as 4 hours (Kansas and Ohio) to as late as 12 hours (Mary- land and Minnesota). In some cases, only a time to opening or a strength criterion was established, and some SHAs used a strength criterion in addition to time to opening. Florida, for example, specified that the compressive strength must exceed 21 MPa (3,000 psi) in 24 hours while allowing a 6-hour time to opening. In New York, the repair was opened to traffic once the surface temperature of the repair reached 65°C (150°F). Although it is difficult to glean from these specifi- cations and special provisions the exact strength require- ments during the initial 6- to 8-hour period, the required com- pressive strength at opening varied from 8.3 to 24.0 MPa (1,200 to 3,500 psi), whereas the required minimum flexural strength (as measured by third-point loading) ranged from 1.8 to 2.8 MPa (260 to 400 psi). In NHI’s PCC Pavement Evaluation and Rehabilitation, both minimum strength requirements and time to opening requirements are recognized as being acceptable (NHI 2001). According to this publication, the flexural strength criterion 9 for opening to traffic is 1.7 MPa (250 psi) for third-point loading and 2.1 MPa (300 psi) for center-point loading, and the compressive strength criterion is 13.8 MPa (2,000 psi) (FHWA 2003). The NHI document also states that having a strength requirement is preferable and that maturity meters or pulse-velocity devices may be useful for monitoring the strength development of very high–early-strength materials (e.g., 4 hours or less of curing time). All of the 16 states except California that specify use of calcium sulfoaluminate (CSA) cement used either Type I or Type III portland cement in the 6- to 8-hour EOT concrete materials. When specified, the minimum cement contents varied, ranging from 440 to 534 kg/m3 (740 to 900 lb/yd3) for Type I and 390 to 490 kg/m3 (660 to 825 lb/yd3) for Type III. The use of accelerators was specified for mixtures contain- ing Type I cement, with the most common accelerator being calcium chloride. Notable exceptions to this standard were New Jersey and Pennsylvania, which prohibited the use of a chloride-based accelerator. Some of the mixtures proportioned with Type III cement did not specify the use of an accelera- tor, relying on the early strength gain of the cement. The w/c ratios for the 6- to 8-hour EOT concrete mixtures vary widely, with maximum values ranging from 0.33 to 0.49. In general, higher w/c ratios were allowed for mixtures containing Type III cement. In no instance was a supplementary cementitious material (e.g., fly ash, ground granulated blast furnace slag [GGBFS], and silica fume) specified for use in 6- to 8-hour EOT concrete mixtures. Admixtures commonly specified for use in 6- to 8-hour EOT concrete mixtures included air entrainers, accelerators, and water reducers. In no case was the type of air-entraining agent specified, but instead air content was specified either directly or through reference to the SHA’s standards for nor- mal paving concrete. The most commonly specified acceler- ator was calcium chloride, either in solution or in flakes. Addition rates ranged from 1 to 2 percent, and in many cases the recommended rate was based on ambient conditions, with cooler temperatures requiring an increase in the calcium chloride added. Other accelerators allowed included non– chloride-based admixtures meeting AASHTO M 194 Type C or Type E. The Type E admixture also acts as a water reducer, having the added benefit of being able to reduce the w/c ratio while maintaining the same workability. Water reducers were not often specified in SHA specifications for 6- to 8-hour EOT concrete materials. When specified, water reducers conforming to AASHTO M 194 Type A, Type D, Type E, or Type F were permitted. In Ohio, which is the one state spec- ifying a Type D admixture, the retardation effect of the admix- ture would likely be offset by the specified high cement content (534 kg/m3 [900 lb/yd3]) and relatively low w/c ratio (<0.40) of the mixtures. As noted previously, there are con- cerns that the use of Type F admixtures (high-range water reducers) may result in instability of the entrained air-void system.

State Mixture Designation Opening Criterion Cement Type Cement Factor w/c Ratio Coarse Aggregate Fine Aggregate Accelerator Air Content Mineral Admixture Water Reducer AR Accelerated Strength >14 MPa (2,000 psi) completed @ 6 hours Type III NS NS NS No. 57 NS CC o Retarder r other NS NS NS NS CA Type FSHCC >2.8 MPa (400 psi) flexural @ 8 hours CSA NS 37.5 or 25 mm (1.5 or 1.0 in.) maximum NS and Type C used NS NS FL Patching >21 MPa (3,000 psi) completed @ 24 hours 6-hour opening NS >446 kg/m3 (750 lb/yd3) < 0.45 57 Stone NS 1% CC or Type C 2 to 6% NS Type F allowed IL Class PP(2) 8-hour opening Type I 440 kg/m3 (740 lb/yd3) < 0.38 1,020 kg/m3 (1,720 lb/yd3) 665 kg/m3 (1,120 lb/yd3) Type E or Type C 4 to 6% NS Type F Class M 5-hour opening Type I or Type II ~470 kg/m3 (790 lb/yd3) ~0.33 CC 5% w/ CC 6.5% w/o NS IA Class FF 5-hour opening Type III ~490 kg/m3 (825 lb/yd3) ~0.43 Volume specified Volume specified Not Allowed 6.0% No Yes KS Accelerated Cure 4- to 6-hour opening Type III >390 kg/m3 (658 lb/yd3) NS NS NS 1 to 2% CC NS NS NS NS MD 6 hours or 7 hours > 17 MPa (2,500 psi) completed @ 12 hours Type I >445 kg/m3 (750 lb/yd3) < 0.42 No. 57 NS CC or NC Type C 5.5% Type F, Melamine MN 3A32HE 12-hour opening time Type I 30% extra NS NS NS Type E 6.5% NS Type E MI Type SLP > 2.0 MPa (290 psi) flexural @ 8 hours Type I 502 kg/m3 (846 lb/yd3) NS MDO T 6A NS NS CC 2% CC CC 5.5% NS NS MO 4 hours > 24 MPa (3,500 psi) completed Type I or III 475 kg/m3 (800 lb/yd3) for Type I NS NS or other NS NS NS NJ VHES > 2.4 MPa (350 psi) flexural @ 6.5 hours Type I w/ accelerator or Type III >390 kg/m3 (658 lb/yd3) 0.37 No. 57 NS NC required 6.5% NS Type F NY Patch Surface temperature of 65oC (150oF) Type III 490 kg/m3 (825 lb/yd3) 0.39 NYDOT CA2 NS 6.0% NS NS NS OH Class FS 2.8 MPa (400 psi) flexural @ 4 hours Type I 534 kg/m3 (900 lb/yd3) < 0.40 No. 57, No. 6, No. 67, or No. 8 NS 1.5% CC or other 6.0% Type D PA Accelerated 8.3 MPa (1,200 psi) completed @ opening 10 MPa (1,450 psi) completed @ 7 hours NS NS NS No. 57 Type A NC allowed 6.0% NS NS TX Class K 2.9 MPa (420 psi) flexural @ 24 hours, Open @ 1.8 MPa (260 psi) flexural Type III 390 kg/m3 ( >502 658 lb/yd3) < 0.49 Grade 2 or 3 Grade 1 FM 2.6 to 2. NS 8 Type C CC NS NS Type A WI Special HES 21 MPa (3,000 psi) completed @ 8 hours NS kg/m3 NS NS or other NS NS NS CC: calcium chloride. CSA: Calcium sulfoaluminate cement. NC: non-chloride. NS: not specified. VHES: very high early strength. TABLE 4 Summary of SHA specifications for 6- to 8-hour EOT repair materials in 2000

State Mixture Designation Opening Criterion Cement Type Cement Factor w/c Ratio Coarse Aggregate Fine Aggregate Accelerator Air Content Mineral Admixture Water Reducer Type I 25% extra AR HES >21 MPa (3,000 psi) completed @ 24 hours Type III NS NS NS NS NS NS GA 24-Hour Accelerated >17 MPa (2,500 psi) completed @ 24 hours Type I or Type III 420 kg/m3 (700 lb/yd3) < 0.45 NS Or Type E 3 to 6% NS NS IL Class PP(1) > 22 MPa (3,100 psi) completed > 4.2 MPa (600 psi) flexural @ 48 hours Type III or Type I NS NS NS ator required NS NS IN High Early 3.8 MPa (550 psi) flexural @ 48 hours Type I or Type III >335 kg/m3 (564 lb/yd3) <0.42 <0.45 NS 5% 10% flyash 15% GGBFS Type A KS Normal Cure 24-hour opening Type I or II >445 kg/m3 (750 lb/yd3) NS NS NS NS NS NS MD 24 hours > 17 MPa (2,500 psi) completed @ 12 hours Type I >475 kg/m3 (800 lb/yd3) NS NS NS Type F MN 3A32HE 24-hour opening time Type I 30% increase NS NS NS NS NS NS NS NS NS NS NS NS NS No NS CC NS Acceler NS NS CC 6.5% NS NS Type A MI Type P-MS > 3.5 MPa (500 psi) flexural @ 24 hours Type I 502 kg/m3 (846 lb/yd3) NS NS below 18oC (65oF) 5. NS NS 6. 5% NS MO 24 hours >24 MPa (3,500 psi) completed Type I 475 kg/m3 (800 lb/yd3) for Type I NS NS NS NS OH Class MS 2.8 MPa (400 psi) flexural @ 24 hours Type I 475 kg/m3 (800 lb/yd3) < 0.43 No. 57, No. 6, No. 67, or No. 8 NS NS NS Type D TX Class K “Modified” 2.1 MPa (300 psi) flexural @ 24 hours Type I or Type III 390 kg/m3 (658 lb/yd3) 335 kg/m3 (564 lb/yd3) < 0.53 Grade 2 or 3 Grade 1 FM 2.3 to 3.1 Type C allowed NS 6.0% Type A or D CC: calcium chloride. GGBFS: ground granulated blast furnace slag. HES: high early strength. NC: non-chloride. NS: not specified. TABLE 5 Summary of SHA specifications for 20- to 24-hour EOT repair materials in 2000

Twenty- to 24-hour EOT Materials Table 5 summarizes the 20- to 24-hour EOT concrete mix- ture characteristics as specified by 11 SHAs. As was true with the 6- to 8-hour EOT concrete mixtures, time to opening with the 20- to 24-hour EOT concrete mixtures is frequently stipu- lated in the specifications, most often being linked to strength requirements. The opening criterion presented in Table 5 lists time to opening that varied from as early as 12 hours to as late as 48 hours. In two cases, only a time to opening crite- rion is provided, but in all other cases, a strength criterion exists in addition to time to opening, or strength is used as the sole criterion for opening. The range in required compressive strength at opening varied from 17 to 24 MPa (2,500 to 3,500 psi), whereas the range in required minimum flexural strength (as measured by third-point loading) was 2.1 to 4.2 MPa (300 to 600 psi). Although some states (Maryland, Missouri, and Ohio) specified the same strength criterion for both the 6- to 8-hour EOT concrete and the 20- to 24-hour EOT concrete, others (Michigan and Arkansas) reported higher strength requirements for the 20- to 24-hour EOT concrete. All of the 11 states required use of Type I, II, or III port- land cement for the 20- to 24-hour EOT concrete. The spec- ified minimum cement content ranged from 335 to 502 kg/m3 (564 to 846 lb/yd3), with only one state, Texas, specifying different minimum cement contents for Type I versus Type III (390 versus 335 kg/m3 [658 versus 564 lb/yd3], respec- tively). The use of accelerators was either not specified or optional for many of these mixtures. Exceptions were Michi- gan, which specified that calcium chloride be used if ambi- ent temperatures fell below 18°C (65°F), and Georgia and Illinois, which specified that an accelerator be used. The w/c ratio for the 20- to 24-hour EOT concrete mixtures were typ- ically higher than those specified for 6- to 8-hour mixtures, ranging from 0.42 to 0.53. None of the states except Indiana approved the use of a supplementary cementitious material (fly ash, GGBFS, and silica fume) for use in 20- to 24-hour EOT concrete. Indiana allowed the use of a 10-percent fly ash or 15-percent GGBFS addition. 2.2 CONSTRUCTION CONSIDERATIONS In addition to the selection and proportioning of constituent materials, specialized construction aspects need to be consid- ered when repairs are constructed with EOT concrete. Con- struction of EOT concrete repairs consists of five basic opera- tions: repair boundary identification and material removal, load transfer installation, batching, finishing, and curing. Although many ways exist to accomplish each task, gener- ally accepted guidelines and practices are presented in a num- ber of publications (ACPA 1994, NHI 2001, FHWA 2003). The following is a brief summary of the sequence used to con- struct full-depth pavement repairs with a particular emphasis on EOT concrete installations. 12 2.2.1 Boundary Identification and Material Removal The first step in the repair process is to identify the extent of deterioration and establish the repair boundaries. Guid- ance is provided in several publications (ACPA 1995, NHI 2001, FHWA 2003), but the critical factor is to ensure that the entire area of deterioration is removed and that minimum repair lengths (1.8 m [6 ft]) are obtained when the repair is dowelled. The width of the patch should always be a full lane width for jointed concrete pavements. Saw cutting and subsequent removal of existing materials depend primarily on the type of pavement being rehabili- tated. In the case of jointed concrete pavement (JCP), a full- depth saw cut with a diamond saw blade is recommended. The result of this process is a smooth surface with reduced potential for spalling during removal. When saw cutting a continuously reinforced concrete pavement (CRCP), two cuts are made at each end of the repair. The first is a partial- depth cut made at the outside edge of the repair area. This cut is followed by a full-depth cut in the interior of the repair at a distance dependent on the lap length requirement (610 mm [24 in.] for tied laps and 200 mm [8 in.] for mechanical or welded laps) (FHWA 2003). Upon completion of the saw cutting, the concrete can be removed by one of two methods. One method involves break- ing up the concrete into small pieces and removing them using hand tools or construction equipment. The other method, called the lift-out method, involves removing the existing slab section in one or more large pieces, thus causing less damage to the subbase than the first method does. After removal of the concrete, the subbase must be care- fully prepared to ensure uniformity of support. If the existing subbase was damaged during removal, it may require the addition and compaction of new subbase material. Often it is difficult to adequately compact a disturbed subbase within the confines of a repair area. If the subbase disturbance is isolated to the very surface, the disturbed material can be removed and replaced with EOT concrete. 2.2.2 Load Transfer Restoration The restoration of load transfer ensures that spalling of the concrete and damage to the subbase does not occur because of rotation or movement of the patch. This restoration can be accomplished by splicing together existing rebar, installing new rebar (in the case of CRCP), or installing dowel bars in JCP (FHWA 2003). Current practice is to drill multiple holes for dowel bars simultaneously using gang-mounted drill bits. Grout is inserted into the hole, the dowel bar is inserted with a twist, and a grout retention disk is used to prevent outflow. Proper dowel bar alignment is critical and must be ensured.

2.2.3 Batching Regardless of whether the EOT concrete materials are batched at the job site or at a batching facility, it is important that the concrete produced be uniform in consistency and that the constituent materials be intimately blended through adher- ence to a proper mixing sequence and time. Also, admixtures must be added to fresh concrete in appropriate dosages and order to avoid potential harmful effects. Concrete-containing, air-entraining admixtures must be sufficiently mixed to ensure the development of an adequate air-void system. Delays in placing the concrete, especially after the accelerator has been added, must be avoided because early setting may negatively impact consolidation of the repair. 2.2.4 Finishing Finishing operations should be performed in a timely fash- ion. It is imperative with EOT concrete, as with other types of concrete, that the surface not be overworked. However, because the high–early-strength materials set rapidly, timing of this step is even more critical. Surfaces that are over- worked often become brittle, more susceptible to abrasion and/or freeze-thaw damage, and may exhibit a lowered resis- tance to chemical attack. Trapping of bleed water must also be avoided. 2.2.5 Curing Internal concrete temperature and moisture directly influ- ence early and ultimate concrete properties, and thus curing takes on special importance in EOT concrete installations. Proper curing provisions are necessary to maintain a satisfac- tory moisture and temperature condition for a sufficient time to ensure proper hydration (FHWA 1994). Compared with normal paving concrete, curing is even more essential to retain moisture and heat necessary for hydration during the 13 early strength gain of EOT concrete materials. Protection against moisture loss becomes critical for EOT concrete repairs if high temperature, low humidity, high winds, or a combination of these environmental conditions exists. Many SHAs use AASHTO M 148 Class A liquid curing compounds for accelerated concrete paving under normal placement conditions. Among these curing compounds, white- pigmented compound (Type II Class A) is the most com- monly used. This material has the potential to create a seal that minimizes evaporation of mixing water when it is applied to the surface and exposed edges of concrete. The white color also assists in reflecting solar radiation during bright days to prevent excessive heat development on the concrete surface. This might not be a desirable outcome for EOT concrete repairs where heat generated by solar radiation accelerates hydration and thus early strength gain. Concrete repairs located in mountainous and arid climates may require heav- ier dosage rates of resin-based curing compound meeting AASHTO M 148, Type 2, Class B requirements. This is largely because concrete in harsher climatic conditions is more susceptible to plastic-shrinkage cracking. An applica- tion rate of 5.0 m2/L (22 yd2/gal) is recommended for these materials (FHWA 2003). In addition to curing compounds, insulating blankets are often used in conjunction with EOT concrete materials to assist in holding in heat produced by the rapidly hydrating cement paste, thereby aiding in early strength development of the concrete. These blankets are often essential when cool ambient temperatures are present. Insulating blankets do not reduce the need for a curing compound, as blankets typically do not decrease the likelihood that plastic-shrinkage crack- ing will occur. Table 6 indicates when insulation is recom- mended based on ambient temperatures and desired opening time (FHWA 1994). It is not recommended to place blankets too soon after applying a curing compound. In warm condi- tions, waiting several hours and placing the blankets as the work progresses is acceptable. Concrete exposed to temper- ature below 4°C (40°F) may need additional blankets. Opening Time, Hr Minimum Ambient Temperature in Period 8 16 <10oC (50oF) Yes No 10–18oC (50–65oF) Yes No No 18–27oC (65–80oF) Yes No Yes Yes No No Yes Yes No No Yes 4824 36 No No No>27oC (80oF) No TABLE 6 Blanket use recommendations (FHWA 1994)

Next: Chapter 3 - Performance Considerations Related to the Durability of EOT Concrete »
Guidelines for Early-Opening-to-Traffic Portland Cement Concrete for Pavement Rehabilitation Get This Book
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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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