Words = 5,450 Tables: (x250) = 1,750 Figures: (x250) = 250 Total = 7,450. Date of Submission = November 15, 2012

Transcription

1 INVESTIGATION OF VERY EARLY OPENING STRENGTH PORTLAND CEMENT CONCRETE PAVEMENT REPAIR WITH THE APPLICATION OF MATURITY TESTING Richard E. Holesinger (Corresponding Author) St. Louis County Department of Highways and Traffic South Meramec Avenue, Saint Louis, Missouri 0 Phone: --0 Fax: --0 rholesinger@stlouisco.com Words =,0 Tables: (x0) =,0 Figures: (x0) = 0 Total =,0 Date of Submission = November, 0

2 Holesinger ABSTRACT The repair of concrete pavement due to utility cuts or deterioration on St. Louis County, Missouri rightof-way consisted of an evaluation of current materials, construction methods and specifications to deliver a durable concrete repair in four to six hours using a concrete maturity meter to determine opening strength. Literature research was performed to assist in improving current four hour opening pavement repair specifications. Material suppliers, contractors and a utility company were consulted on their mixes. The availability/cost of Type III cement and cold-weather placement was a major concern. The evaluation of contractor, state and county pavement concrete repair mix designs, using Type I/II and III cements were tested at the time of placement for concrete temperature, entrained air, and workability. Maturity curves for some common mix designs were constructed to determine the pavement repair s compressive strength at time of opening. A table of opening compressive strengths based on pavement repair thickness and repair length were adopted. Research concluded that at the time of placement a minimum concrete temperature of 0 Fahrenheit is critical in strength gain. The application of non-chloride calcium nitritebased accelerating and polycarboxylate-based high-range water reducing admixture types were evaluated and dosages were estimated using locally available aggregate. Specifications were developed to encourage material supplier development of economical readymix concrete with Type I/II Portland cement. A procedure was also developed to apply the maturity method to mix design performance and verify the pavement repair s opening strength is met in four to six hours. INTRODUCTION Background St. Louis County, Missouri (County) maintains over, lanes miles of concrete pavement (). As these roads reach the end of their performance life, some areas require full-depth concrete repair. At the same time the County s utility infrastructure continues to age. To make repairs or install new service, utilities are required to remove and replace pavement, often the same day, following County standards and specifications. For these repairs the County has specified the use of Type III Portland cement with a chloride-based accelerator, an opening time of four hours and no compressive strength requirement. Success was determined if the pavement repair did not crack after opening. If this condition was observed the contractor was instructed to remove and replace the repair. In some situations the pavement repair was almost immediately overlaid with hot mix asphalt and the repair condition could never be visually evaluated. In 00, concrete maturity testing was applied to County contract pavement repairs to investigate the compressive strength performance. The results were compared to the minimum opening strengths specified in the Missouri Department of Transportation (MoDOT) (). The four hour opening strength, both county-funded and utility repaired, did not meet the MoDOT minimum compressive strength of,000 psi. A review of concrete materials in the four-hour early opening pavement repair concrete was completed. The Type III Portland cement, coarse and fine aggregate material type, classification and batch weights of the County provided mix design were not adjusted. A review of the 0. maximum allowable water/cement ratio was also determined to be acceptable for the Type III cement mix. Admixture review was next. Calcium nitrate-based non chloride water-reducing accelerator (NC-WRA), meeting the requirements of ASTM C Type C and E (), replaced calcium chloride in pavement repair. Admixture dosage was to be determined by the material supplier. Entrained air was specified to be between percent and percent. The minimum concrete temperature of 0 F at the time of placement was reviewed and considered reasonable. After review of the placement of four hour early opening

3 Holesinger 0 concrete pavement was projects were completed during the 00- construction season, additional specification changes to the special provision were needed. 00 Concrete Mix Design The contractor has always been allowed to submit an alternate concrete mix design for review and approval. The range of material parameters are created and specified by contract special provision. The dosage of admixtures to achieve workability and opening compressive strength are determined by the concrete supplier and admixture manufacturer. Before 00, same-day concrete repair required 0 pounds of Type III Portland cement, an approved accelerator, thermal blankets, and a four hour minimum cure. No compressive strength was specified. In 00, modifications were again made to the same-day early opening pavement repair. The County cubic yard mix design for hour opening allowed the mix to use to 0 pounds of Type III Portland cement and a non-chloride water-reducing accelerating admixture meeting ASTM C (), Type C and E (calcium nitrate based). In 00 additional mix design parameters were specified, allowing Type I Portland cement mix designs to be submitted for use. TABLE. Sack Type III Cement Hour Early Opening Concrete Mix Design Material Type Weight (pounds) Portland Cement III 0 Coarse Aggregate Gradation D Limestone 0 Fine Aggregate Class A Mississippi / Missouri river 00 Water Missouri-American Non-Chloride-Water-Reducing Accelerator (NC-WRA) ASTM C Type C & E Manufacturer Recommended Dosage Target Maximum Water/Cement 0. Entrained Air, % ASTM C 0 Manufacturer Recommended Dosage 0 The County determined the maximum water/cement ratio to be 0. for Type I Portland cement mixes. After consultation with local suppliers about their concern of how setting the maximum water/cement value this low might be creating a potential for increased autogenous shrinkage cracking (), the maximum was agreed to remain at 0. for Type III Portland cement mix designs. The concrete slump prior to addition of accelerating admixture was specified as -½ inches. The resulting Type III and Type I Portland cement mix design proportions for a four hour early opening pavement repair are stated in Tables and. The cement content of the Type III mix is at the upper limit of 00 pounds and the Type I mix exceeds the maximum amount recommended by ACI (). The mix design in Table was submitted by local concrete material producers as being used for MoDOT early opening pavement repair. The HRWR, based on polycarboxylate technology, is a more effective water-reducer that can be added at the manufacturing plant (). Contractors are currently adding HRWR on the job site. The specified NCA is calcium-nitrate based. This material accelerates concrete set time. The use of calcium

4 Holesinger nitrite, widely used at pre-cast plants to accelerate strength gain, is incorporated into the NCA listed in Table. However, the use of straight calcium nitrite may reduce the pavement repair s freeze-thaw durability (). One type of NCA used contained a blend of calcium nitrate and calcium nitrite. TABLE 0. Sack Type I/II Portland Cement Hour Early Opening Concrete Mix Design Material Type Weight (pounds) Portland Cement I/II Coarse Aggregate Gradation D Limestone Fine Aggregate Class A Mississippi /Missouri river Water Missouri-American 00 High Range Water Reducer (HRWR - polycarboxylate-based) Non-Chloride Accelerator (NCA - Calcium Nitrate/Nitrite) ASTM C Type A & F and ASTM C 0 Type I ASTM C Type C Manufacturer Recommended Dosage Manufacturer Recommended Dosage Target Maximum Water/Cement Entrained Air, % ASTM C 0 Manufacturer Recommended Dosage The specified minimum temperature of the concrete at the time of placement remained at 0 F (). Curing was specified to be accomplished through the use of moist and thermal curing. Curing compound was to be used for moist curing. Insulating blankets, used throughout the curing period, were used for thermal curing. Typical aggregate gradation properties are listed in Table. The gradation specified for each fine and coarse aggregate material is listed. The coarse aggregates used are crushed limestone of good quality. The fine aggregates are sands from the Mississippi and Missouri rivers that have high alkali-silica reactivity (ASR) Expansion Value Ratings greater than 0. (). These materials have been tested in accordance with Illinois Department of Transportation (IDOT) modified ASTM 0 (0) (IDOT ASR Rating List) (). ASR has the potential to form a water-absorptive gel that expands and fractures concrete over time (). To reduce the impact of ASR specifying supplementary cementitious materials and lowalkali cement (defined in ASTM C 0 () as having an equivalent sodium oxide (Na O) content of no more than 0.0%), Type I/II cements meet this requirement and have been specified. No study has been made on County pavement repair concrete to determine the extent of ASR remediation needs. In the 00 special provision for concrete repair, opening concrete compressive strength was tied to pavement repair thickness (Table ) for the first time. The cure time shall be the time determined to reach the -hour compressive strength. The roadway shall not be opened to traffic in less than hours or until the minimum -hour compressive strength has been attained. The contractor was also allowed to substitute macro-synthetic fiber when welded wire reinforcement was specified. The macro-fibers, Propex NOVOMESH 0, were to be specified on the mix design and added at the concrete plant at a rate of pounds per cubic yard of concrete. The delivery,

5 Holesinger storage, handling and mixing of the fibers in the concrete was to be in accordance with the manufacturer s guidelines. For the first time in 00, concrete maturity was adopted using MoDOT s Standard Specification 0 Strength of Concrete Using the Maturity Method. The contractor performs the maturity testing with the engineer determining the maturity testing frequency. Utilities, their contractors and suppliers began using the revised pavement repair contract special provision specification as the 0 construction season began. 0 Review of Early Opening Pavement Construction The beginning of 0 started with the review of educational needs of construction inspection staff. The importance of proper concrete repair construction methods was emphasized. The proper sawing, repair dimensions, placement of a compacted aggregate base, dowel bar installation, concrete consolidation, moisture curing and thermal curing where discussed. At pre-construction meetings the four-hour early opening pavement special provision was reviewed with the contractor s personnel. TABLE Aggregate Gradation Properties Coarse Aggregate Fine Aggregate Percent Passing by Weight Percent Passing by Weight Sieve Size Minimum Maximum Sieve Size Minimum Maximum inch 00 - / inch 00 - ¾ inch 00 No. 00 / inch No No. 0 No. 0 No. 0 No. 0 No. 0 0 No Reaching the -hour early opening compressive strengths continued to be a concern. Table lists the -hour laboratory compressive strengths by sack ( pounds) of cement. Utility repair concrete was of unknown cement content since inspection at the manufacturing plant was not provided. The Type III cement exhibited the best -hour laboratory tested compressive strength performance with an average of, psi, followed by the Type I/II cement with, psi, and concluding with the unknown utility mixes with, psi. These compressive strengths represented not the in-place strength, but the compressive strength of x cylinders field cast and cured (the maturity data was not regularly made or recorded). While -hour early opening concrete pavement mix designs were improving in compressive strength gain, they still were not demonstrating successful compressive strength results, requiring further review. Minimum Compressive Strength at Hour Early Opening and -days () For pavement repair, the County followed MoDOT s lead in assigning compressive strengths. For a - day compressive strength,,000 psi was assigned for all thicknesses. For a -hour opening compressive strength the use of,000 psi,,00 psi, and,000 psi were assigned to thicknesses of -inches or less, - inches, and 0-inches and greater, respectively. LITERATURE REVIEW Development of Strength-Maturity Relationship In 00 the County purchased maturity testing equipment based on the Nurse-Saul function and began testing using ASTM 0 () to determine early form removal and opening of roadway to traffic. This

6 Holesinger method uses a time-temperature measurement that is correlated to concrete cylinder compressive strengths at various ages. The maturity function and logarithmic equations () are as follows: M(t) = (T a T 0 ) Δt () Where: M(t) = the temperature-time factor (TTF) at age t, C-hours Δt = a time interval, hours T a = average concrete temperature during time interval, Δt, C, and T 0 = the initial datum temperature, C Using Microsoft s Excel trendline logarithmic function the line equation and R value is generated. The equation of the line is in the following format: Y = Aln(X) B () Where: Y = Compressive Strength, psi X = TTF, C-hours A, B = Regression constants Maturity Meter The commercial battery-powered device automatically measures, computes and displays a timetemperature factor. The maturity meter used has a secure means of collecting data that is unalterable. The maturity loggers used provide a maturity value based on Temperature Time Method as detailed in ASTM C 0 (). The loggers continuously log and store maturity data and are accurate to within +/- C when operating in the range of - C to C. The meter has an operating temperature range from - C to 0 C. The meter is capable of continuously taking readings every hour at a minimum and is able to print data and/or download it into a spreadsheet. Maturity Loggers The maturity loggers are used to develop the strength-maturity curve, to verify the maturity curve and to concrete placement. Loggers used are compatible with the maturity meter. The County specifies loggers that make hourly measurements for up to days after activation. Datum Temperature Development In 00, MoDOT s Standard Specification 0 () was adopted and required for four-hour early opening strength concrete pavement. MoDOT specifies an initial datum temperature (T 0 ) of -0 C. This temperature is the temperature at which no active heat of hydration of cement takes place that contributes toward the gain of concrete compressive strength. Carino () indicated that the -0 C datum temperature is not always the best value to use and depends on cement chemistry, type and dosage of admixtures. For each mix mortar cubes are to be made in the laboratory, broken, and the mixes T 0 established. This however is cost-prohibitive and depends on the need for a higher level of accuracy. In most cases a typical value for a datum temperature can be used (). Datum Temperatures and Their Application The maturity datum temperature can be determined in one of two ways. Mortar cubes or concrete test cylinders can be tested by isothermal curing over a range of temperatures following the procedures laid out in ASTM C 0 Annex A Determination of Datum Temperature or Activation Energy (). In the absence of testing for a precise datum temperature (the temperature below which no active hydration of cement is considered to take place), the datum temperature to be applied to the early opening pavement

7 Holesinger 0 TABLE Laboratory Hour Early Opening Compressive Strengths. sack Type III Portland Cement 0. sack Type I/II Portland Cement Unknown Portland Cement Compressive Strength Compressive Strength Compressive Strength Project Date (psi) Project Date (psi) Project Date (psi) AR- //0 0 AR- // 0 Utility // 0 AR- //0 00 AR- // 00 Utility // 00 AR- //0 0 AR- // 0 Utility // 0 AR- /0/0 0 AR- // 00 Utility // 00 AR- /0/0 0 AR- // 0 Utility // 0 AR- /0/0 0 AR- // 0 Utility // 0 AR- //0 0 AR- /0/ 0 Utility /0/ 0 AR- //0 0 AR- /0/ 00 Utility /0/ 00 AR- //0 0 AR- // 0 Utility // 0 AR- //0 0 AR- // 0 Arithmetic Mean (Average)= AR- //0 0 AR- // 0 AR- //0 0 AR- // 0 CR- //0 0 AR- // 0 CR- //0 0 AR- // 00 CR- /0/0 0 AR- // 00 CR- /0/0 0 T0-0- OC // 00 AR- //0 0 T0-0- OC // 0 AR- //0 0 Arithmetic Mean (Average)= AR- //0 0 AR- //0 00 Arithmetic Mean (Average)= repair concrete mix (with very early or high early concrete mixes with accelerating or water-reducing admixtures or additions) needs to be assigned. MoDOT () specifies the use of -0 C for T 0 in all cases. The use of T 0 at -0 C is to be applied to mixes that have their strength gain heavily retarded or mixes with supplementary cementitious materials or admixtures that have a retarding effect on the concrete mix (). So, applying the T 0 of -0 C to four-hour early opening mixes with accelerators and Type III Portland cement seemed inappropriate for four-hour early opening concrete. After performing a literature review two sources were discovered that applied a much higher datum temperature for accelerated concrete mixes. The New Jersey Department of Transportation (NJDOT) performed testing on their Very Early Strength (VES) mixes and concluded that the T 0 falls in the range of and C (). The NJDOT adopted. C for their T 0 when using Maturity testing for their VES mixes (). The IPRF () reported in March 00 that they selected a T 0 of C. The datum temperature of C was adopted for use with very early or high early County concrete mixes with accelerating or water-reducing admixtures or additions. Difficulty in achieving the opening compressive strengths may have been due to the use of the lower datum temperature, but its significance was unknown. A trial was conducted on a 0. sack Type I Portland cement with Grace

8 Holesinger 0 Polarset (Non-corrosive, non-chloride set-accelerating admixture meeting ASTM C Type C ()) using loggers set at -0 C and C to determine how significant the difference would be (Figure ). To achieve,000 psi a compressive strength at a TTF of C-hours was determined on the -0 C logger (lower curve) and C-Days on the C logger (upper curve). The data points were plotted using Microsoft Excel s logarithmic trendline that generated equation for each curve and coefficient of determination (R ). An R value greater than 0.0 is considered an acceptable fit of the maturity data points (). A value less than 0.0 require a review of the data points by the engineer and a determination of removal of any outlier or complete redo of the maturity curve. Extrapolation beyond the strength-ttf data points is not recommended (). 0 FIGURE Maturity Curves at T 0 at C (top) and -0 C. Verification of Logger Accuracy To determine logger accuracy, calibration verification on a random logger is performed. Verify calibration prior to use on a project and as a minimum, on an annual basis by placing a randomly sampled maturity logger in a controlled-temperature water bath and recording whether the indicated result agrees with the known temperature of the water bath. The maturity meter temperature logger must be accurate to within ± C. The verification of accuracy is performed at a minimum of three different temperatures such as C, C, and C (). Compressive Strength Testing Compression testing at the ages specified is performed in accordance with ASTM C (). The

9 Holesinger Engineer may request up to two additional sets of three x specimens for maturity testing. To develop data points for the strength/maturity relationship roughly 0 percent, 0 percent, 0 percent, 0 percent, and 0 percent of the maturity values corresponding to the anticipated required compressive strength for each mix design should be determined (). To achieve equal increments of strength gain between test ages, the Engineer may alter the compressive strength frequencies as follows to account for differences in materials, curing temperature or testing workforce level: Very Early Opening Strength Testing For concrete that is to be placed in service in less than six hours, early opening strength testing is required. At a minimum, compressive strength tests shall be performed on five sets of three x specimens (a minimum of ), and the average strength computed at,,,, and hours. Production may start after the hour compressive strengths have been determined with approval from the Engineer. TABLE Structure Component Frequency Pavement maturity logger per 0 square yards, with a minimum of per day in the last 0 feet of pavement. Pavement Sawing maturity logger per 0 linear feet, with a minimum of per day in the first feet of pavement. Pavement Repair maturity logger per 0 patches, with a minimum of logger per day in the last pavement repair. Structural A minimum of maturity logger at the end of the pour, with other loggers available to be placed as directed by the Engineer. Placement of Maturity Loggers For pavement and pavement repairs, maturity loggers shall be embedded at approximately mid-depth and inches from the edge of the pavement. Loggers are not to be attached directly to steel as the steel temperature will impact the sensor temperature (). For determination of compressive strength for saw cutting of pavement joints, maturity loggers shall be embedded at approximately one-third the slab depth as determined from the surface of the finished pavement and inches from the edge of the pavement. Maturity loggers shall be placed at the frequency specified in Table. The frequency table was modified after MoDOT s Standard Specification 0 (). Proportioning, Mixing, Placing and Curing Field-Placed Concrete The maturity method does not account for strength variations due to proportioning, mixing, placing and curing of concrete. Proper methods shall be followed at all times during proportioning, mixing, placing and curing of the field placed concrete. Field-Placed Concrete Mix Requirements Consistent determination and reporting of accurate batch weights has been missing. To mitigate this, a Materials Testing Laboratory inspector must be present at the concrete plant when placement of concrete is to be evaluated using the maturity method to verify that the strength-maturity curve identification number matches the mix being batched. Mix constituents of the field placed concrete shall not change, and mix proportions of the field placed concrete shall not vary more than.0 percent from the concrete mix used to develop the strengthmaturity relationship. The water/cementitious ratio shall not vary more than 0.0 from the mix used to develop the strength-maturity relationship. Determination of the water/cement ratio during production can be difficult due to aggregate stockpile moisture variances. The Engineer may determine the water content of freshly mixed concrete using the microwave oven drying test method in accordance with AASHTO T (0).

10 Holesinger Requiring Immediate Validation of Strength-Maturity Relationship If the mix constituents change more than.0 percent, the water/cementitious ratio changes more than 0.0, the material sources change, or when the mixing operations change, an immediate validation of the strength-maturity curve shall be done in accordance with Validation of Strength-Maturity Relationship. Validation of Strength-Maturity Relationship At a change in mix design or a minimum every seventh day of concrete placement, a validation test shall be conducted to verify that in-place concrete strength is accurately represented by the strength-maturity relationship. The Engineer shall be notified at least one business day in advance of when and where the validation test will be done. Documentation for Validation The Engineer shall document the entrained air, slump, and water content from the batch of concrete tested and any deviations from the original job mix in the presence of the Contractor. Specimens shall cast in accordance with ASTM C (). Specimens for Validation During placement of the field placed concrete, a minimum of four x compressive strength cylinders shall be fabricated and cured as specified in Documentation for Validation. Maturity Logger Location for Validation After a cylinder has been fabricated, a maturity logger shall be inserted. A maturity logger shall be embedded from to inches deep and to within ½ inch of the center of one cylinder for computing the maturity index from the measured temperature history as specified in ASTM C 0 (). After the maturity logger is inserted into the cylinder, the side of the cylinder mold is tamped with a rubber mallet to ensure the concrete comes in contact with the maturity logger. The meter is connected to the logger, the datum temperature is set, and the logger is activated as soon as it comes in contact with the fresh concrete (). The maturity meter is then re-connected to the embedded logger and readings taken and recorded immediately after the corresponding specimens are tested for strength. Strength-Maturity Relationship Validated The average compressive strength of the three cylinders shall be compared to the compressive strength as determined by the strength-maturity relationship. If the predicted compressive strength is within 0 percent of the actual compressive strength, then the strength-maturity relationship will be considered validated (). Strength-Maturity Relationship Above Acceptable If the actual compressive strength is more than 0 percent above the compressive strength as determined by the strength-maturity relationship, then a new strength-maturity relationship may be developed. Strength-Maturity Relationship Below Acceptable If the actual compressive strength is more than 0 percent below the compressive strength as determined by the strength-maturity relationship, cylinders are made to determine opening compressive strengths until a new strength-maturity relationship has been developed. Concrete Temperature After review of Punurai (), the use of F as a minimum initial temperature to reach opening compressive strength at. hours was recommended. To reduce thermal cracking a maximum allowable temperature of 0 F was recommended ().

11 Holesinger Slump As per ACI, the slump before addition of HRWR should be between and inches (). At the time of early opening repair concrete placement that allowable maximum slump should not exceed inches (). Only HRWR should be added to increase slump (). Pavement Repair Preparation In accordance with the research findings of the City of Nashville (00), the slab should be excavated at least foot wider than the utility trench walls () to beyond the zone weakened by the utility excavation. Adoption of this standard while incorporating ACPA ISP s requirement that any utility cuts edge shall be located at least feet away from any joints or pavement edge and if in this zone the repair cur boundary would be extended to the joint or the edge (). Sawing for pavement removal should not be performed more than days in advance of pavement removal since load transfer is removed and additional damage may result to the subgrade or adjoining slabs (). After removal of the broken concrete pavement, the Contractor can be allowed the option of excavating the repair up to inches deeper (). The extra depth allows the Contractor to use a lower concrete opening compressive strength. TABLE ACPA & MoDOT Minimum Opening Strength Needed for Full-depth Repair Compressive Strength for Opening to Traffic, psi a Utility Cut Thickness, inches Utility Cut Length - 0 feet ACPA Table MoDOT Table () Existing Slab Utility Cut Design Length > 0 Thickness, feet inches Requirement for Compressive Strength in hours a,000,00,000,00,00,000,0,0,000,000,000,00 0 or more,000 a The cure time shall be the time determined to reach the compressive strength for opening to traffic. The roadway shall not be opened to traffic in less than hours until the minimum -hour compressive strength has been attained. For County projects, a -inch thick layer of Type aggregate base () is placed on a prepared subgrade and compacted to a minimum of percent of the standard maximum density (). For isolated pavement repair removal and replacement areas where a roller is not practical, the Contractor shall utilize a reversible vibratory plate-type compactor with a minimum centrifugal force rating of 0 pounds to achieve the aggregate compaction specified. When approved by the Engineer, the aggregate base for the isolated pavement repair removal and replacement areas may be compacted by a minimum of four complete reversible vibratory compactor coverages when not over excavated trenches (). Minimum Sawing Compressive Strengths

12 Holesinger Early-age saws can be used when the in-place repair reaches a compressive strength of 0 psi (). This is advantageous because it allows the curing blankets to be placed on the concrete sooner. For crushed, hard aggregate, sawing of pavement joints that result in minimal raveling should be made when the in-place concrete strength reaches 0 psi (). Maturity testing can be used, but consideration of casting a set of compression specimens for or hour breaks should be considered for early opening concrete. TABLE -day Compressive Strengths for Early Opening Pavement Repair Type III Cement Mixes, Project Date psi Project Date Type I/II Cement Mixes, psi CR- //0 0 AR- // 00 CR- //0 0 AR- // 0 CR- /0/0 00 AR- // 0 CR- /0/0 0 AR- // 0 AR- //0 0 AR- /0/ 0 Arithmetic Mean (Average)= AR- /0/ 0 AR- // 0 AR- // 0 AR- // 0 AR- // 0 AR- // 0 AR- // 00 Arithmetic Mean (Average)= 0 Minimum Opening Compressive Strengths The original table of minimum opening compressive strength was derived from MoDOT s Standard Specification.0 Full Depth Repairs (). It did not account for varying lengths of repairs encountered on County roads. The American Concrete Pavement Association (ACPA) Publication TB00-0P Guidelines for Full-Depth Repair () was reviewed and provided a table of strengths for repairs less than 0 feet in length and slabs greater than 0 feet in length and is compared with MoDOT s requirements (see Table ). In accordance with ACI 0R-0 the minimum length for undoweled repairs is feet and the minimum width shall not be less than half the panel wide (). The County requires a full-depth saw cut for all conditions and should consider changing this requirement only for pavements greater than or equal to inches in thickness. -day Compressive Strength The -day compressive strength for four hour early opening pavement repair was originally set at,000 psi (). A review of -day compression test reports from 0- (Table ) was made. There was a significant lack of Type III cement mix design -day compressive strengths. With the exception of two possible outliers, consideration of increasing the -day compressive strength to,000 psi would be more realistic with this type of mix design. Entrained Air Saint Louis County, Missouri is in a severe weathering region and the coarse aggregate used has a nominal maximum size of ¾-inch (). The County specifies an entrained air content of. percent ±. percent, exceeding the requirements of ACI0R-0, Table. (0). This is in part to account for loss of entrained air during the concrete consolidation process. Increasing the -day compressive strength to

13 Holesinger ,000 psi allows a percent reduction in entrained air (). The target entrained air content is recommended to be lowered to. percent ±. percent. This also might serve to slightly increase the four hour early opening compressive strength. The use of Type F HRWR negatively impacts air-void system parameters and their use should be avoided (). Suggested Practices and Recommendations At the completion of the research, the recommendations made for early-opening concrete pavement repair shall be incorporated into the standard specifications and applicable standard drawing revisions. In addition, I suggest the following additional objectives be pursued: Development of a Concrete Maturity Theory and Application course. This course would include concrete maturity theory, application and enforcement of the standard specifications and standard details, operation of the maturity meter and reporting requirements (0). Development of a consistent method of reporting, spreadsheet recording, and database archiving maturity curves and field testing data (0). Incorporate early opening pavement repair into the study of concrete s ability to resist chloride ion penetration in accordance with AASHTO TP () to ensure that the chloride content level is in the low level for submitted mix designs. Development of an early-opening repair classification system based on repair thickness, compressive strength classification, and application temperature. In addition, a specific mix design submittal method, a process of review and field-testing of the mix design before full approval is made, would also be developed. With high cement contents and a low water-cementitious ratio, research the impact that autogenously shrinkage has on early-age cracking of the pavement repair. Determine if the specified opening compressive strength is appropriate for the applied traffic loading anticipated. Acknowledgments This work was supported by the Saint Louis County (Missouri) Department of Highways and Traffic. The author expresses his gratitude to Vince Ogar, Joseph Brouk, Dan Hoernschemeyer, and Art Becker for their efforts in testing and promoting improvements to concrete repair materials and construction through specification improvement and maturity testing. The views expressed by the author do not necessarily reflect those of the sponsor. References. Saint Louis County, January 0 Street and Road Mileage Report, Department of Highways and Traffic, Division of Highway Planning, St. Louis county, Missouri, January (0). MoDOT. Missouri Standard Specification for Highway Construction, Standard Specification Pavement Repair, Missouri highway and Transportation Commission, Jefferson City, Missouri, June (0). ASTM C, Standard Specification for chemical Admixtures for Concrete, ASTM Standards, Vol. 0.0, ASTM, West Conshohocken, Pennsylvania (00a). Van Dam, T.J., Peterson, K.R., Sutter, L.L., Panguluri, A., Sytsma,J., Buch,N., Kowli, R., and Desaraju,P., NCHRP Report 0: Guidelines for Early-Opening-to-Traffic Portland Cement Concrete for Pavement Rehabilitation. National Cooperative Highway Research Program, Transportation Research Board, Washington, D.C., August (00).. ACI.R Accelerated Techniques for Concrete Paving, Reported by Committee, Manual of Concrete Practice, American Concrete Institute, Farmington Hills, Michigan, January (00). ACI E-0, Chemical Admixtures for Concrete, Reported by Committee E-0, Manual of concrete Practice, American Concrete Institute, Farmington Hills, Michigan (00)

14 Holesinger Kurtz, M.A., Constantiner, D., Resistance to Freezing and Thawing cycles and Scaling Resistance of Very Early Strength Concrete, Cement, concrete and Aggregate, Vol., No., ASTM, West Conshohocken, Pennsylvania, December (00). Saint Louis County, St. Louis County Standard Specification for Highway Construction, Standard Specification Section Pavement Repair, Saint Louis County Department of Highways and Traffic, May (00). IDOT. Alkali-Silica Potential Reactivity Rating List, Illinois Department of Transportation, Bureau of Materials and Physical Research, Springfield, Illinois, July (0) 0. ASTM C 0, Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method), ASTM Standards, Vol. 0.0, ASTM, West Conshohocken, Pennsylvania (00). ASTM C 0, Standard Specification for Portland Cement, ASTM Standards, Vol. 0.0, ASTM, West Conshohocken, Pennsylvania (0). MoDOT. Missouri Standard Specification for Highway Construction, Standard Specification 0 Strength of Concrete Using the Maturity Method, Missouri highway and Transportation Commission, Jefferson City, Missouri, June (0). ASTM C 0, Standard Practice for Estimating Concrete Strength by the Maturity Method, ASTM Standards, Vol. 0.0, ASTM, West Conshohocken, Pennsylvania (0). Carino, N.J., The Maturity Method, Chapter in The Handbook of Nondestructive Testing of Concrete, nd Edition, Malhotra, V.M., and Carino, N.J., CRC Press, Inc., Boca Raton, Florida and ASTM International (00). Hsu, C.T., Luke, A., Balaguru, P., FHWA NJ 00-00: Optimization of VES Concrete Final Report, New Jersey Institute of Technology, Newark, New Jersey, January (00).. Trost, S., Using Maturity Testing for Airfield Concrete Pavement and Repair, IRPF Research Report, IRPF-0-G-00-0-, Programs Management Office, Skokie, Illinois (00).. Nixon, J.M., Schindler, A.K., Barnes, R.W., Wade, S.A., Evaluation of the Maturity Method to Estimate Concrete Strength in Field Applications, ALDOT Research Project 0-0, Highway Research Center, Auburn University, February (00). TxDOT, Estimating Concrete Strength by the Maturity Method, Tex--A, Texas Department of Transportation, Austin, Texas, February (00). ASTM C, Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens, ASTM Standards, Vol. 0.0, ASTM, West Conshohocken, Pennsylvania (00) 0. AASHTO T, Water Content of Freshly Mixed Concrete Using Microwave Oven Drying, AASHTO Standards, AASHTO, Washington, D.C. (00). ASTM C, Standard Practice for Making and Curing Concrete Test Specimens in the Field, ASTM Standards, Vol. 0.0, ASTM, West Conshohocken, Pennsylvania (00). Punurai, S., Punurai, W, Hsu,C.T. A Very Early Strength Concrete for Highway Construction, Journal of Testing and Evaluation, Vol., No., ASTM, West Conshohocken, Pennsylvania (00). ACI.R-0, Guide for Selecting Proportions for High-Strength Concrete Using Portland Cement and Other Cementitious Materials, Reported by Committee, Manual of Concrete Practice, American Concrete Institute, Farmington Hills, Michigan (00). MoDOT. Missouri Standard Specification for Highway Construction, Standard Specification 0 Concrete, Missouri highway and Transportation Commission, Jefferson City, Missouri, June (0). City of Nashville, Strategic Plan for Pavement Preservation and Maintenance, City of Nashville, Department of Public Works, Nashville, Tennessee, March (00). American Concrete Pavement Association (ACPA), Utility Cuts for Concrete Pavement.ISP, Skokie. Illinois (00).. American Concrete Pavement Association (ACPA), Concrete Paving Technology-Guidelines for Full-Depth Repair. TB00-0P, Skokie. Illinois ().. Saint Louis County, St. Louis County Standard Specification for Highway Construction, Standard Specification Section 00 Aggregate for Base, Saint Louis County Department of Highways and Traffic, January (00)

15 Holesinger. Saint Louis County, St. Louis County Standard Specification for Highway Construction, Standard Specification Section 0 Aggregate for Base, Saint Louis County Department of Highways and Traffic, November (00) 0. ACI 0R-0, Guide for the Design and Construction of Concrete Parking Lots, Reported by Committee 0, Manual of Concrete Practice, American Concrete Institute, Farmington Hills, Michigan (00). ACI R-0, Building Code Requirements for Structural Concrete, Reported by Committee, Manual of Concrete Practice, American Concrete Institute, Farmington Hills, Michigan (00)