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Maturity Testing

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Maturity testing provides a reliable technique for con­tinuous monitoring of concrete strength gain. The tech­nology offers several advantages over traditional test­ing methods. Most importantly, maturity testing enables any pavement to be opened to traffic without delay, whether or not it is a fast-track project.

The purpose of this publication is to describe the maturity concept and its applications and, by explaining the benefits, encourage widespread implementation by agencies and contractors. Detailed procedures for ma­turity testing are given in the Appendix of this report.

According to a recent survey,[1] concrete maturity concepts are being applied or researched by 32 state De­partments of Transportation (DOTs). The survey also showed that 13 states have adopted protocols or specifi­cations governing the use of this developing technology.

The maturity method is a non-destructive approach for estimating the strength of concrete. This approach does not require as much conventional field-testing of concrete specimens, such as cylinders and beams and is more representative of in-situ conditions. Test beams or cylinders do not necessarily reflect the actual con­crete pavement strength. This is because the concrete in a beam or cylinder is not affected by the heat of hydration of the mass of the pavement and is subject to different moisture conditions during the curing process. The strength determined is that of the specimen, not the strength of the in-situ concrete.

Summary of Benefits

A new concrete pavement can be opened to traffic when it has achieved adequate strength. Determining whether a pavement has adequate strength to be opened to traffic depends on how the strength is meas­ured and knowing when the required strength is reached. Opening without unnecessary delay can result in substantial savings of money and time, and an increase in safety due to shorter exposure of the work zone area to traffic. Iowa Department of Transportation has concluded that maturity testing reduces construc­tion time and traffic delays, and improves public rela­tions during construction.[2] Also, quality assurance (QA) costs can be reduced because the number of beams or cylinders required for the maturity method is less than that needed for quality assurance testing with destruc­tive testing methods.

The use of maturity testing can reduce construction costs. Ansari et al[3] estimated that construction time for highway projects could be reduced by as much as 50%. The authors also concluded that the number of test specimens cast during construction could be reduced by about 75%. Hunt and Mihm[4] state that the savings in Texas have the potential to be remarkable. The benefits and applications of maturity testing are summarized as follows:

  • Identifies earliest possible opening to construction traffic and public use[5][6]
  • Allows determination of optimum time to saw joints[7]
  • Facilitates cold-weather paving applications[11][12]
  • Requires fewer specimens (beams or cylinders) to fabricate and test,[13][14] thus reducing quality assur­ance costs
  • Facilitates earlier agency acceptance and payment to contractor[15]
  • Improves public relations by reducing closure time for construction
  • Improves safety by reducing the exposure time of the work zone area to traffic

The Maturity Concept

The maturity method accounts for the combined effects of time and temperature on concrete strength develop­ment. The strength of a given concrete mixture that has been properly placed, consolidated, and cured, is a function of its age and temperature history.

The maturity concept has been around for many years and has proven to be a useful tool in several specialties within the concrete industry. This is espe­cially true among fabricators of prestressed and other prefabricated concrete products where it is essential to obtain strength information at an early date and with minimal cost.

Early research was conducted in 1951 by Saul[16] who introduced and defined the term “maturity” as fol­lows during his investigation on steam curing of con­crete: “the maturity of concrete may be defined as its age multiplied by the average temperature above freezing* that it has maintained.” From this definition, he went on to develop the law of strength gain with maturity: “Concrete of the same mixture at the same maturity (measured as temperature-time) has approxi­mately the same strength whatever combination of temperature and time goes to make up that maturity.” Over the years, Saul’s work has been confirmed and refined by other researchers.[17][18]

Maturity testing provides strength evaluation by the monitoring of internal concrete temperature in the field. The basis of maturity is that each concrete mixture has a unique strength-time/temperature relationship.[19][20][21][22][23][24] Therefore, for concretes of a specific mixture, the same strength will develop at a given maturity value.

The maturity value is the sum of the degree-hours from initial concrete placement to a given time during the curing process. Reference 13[25] provides an excel­lent discussion of the history and development of the concepts.

Based on field case studies[26] conducted in sev­eral states, it is clear that maturity can predict concrete strengths. The Iowa Department of Transportation has been using the method for several years and found it to give consistent and reproducible results.[27][28]

The application of computers introduces a low cost method of analyzing the strength gain that is taking place in concrete structures or pavements. This is especially of interest for pavements, where it is essen­tial to evaluate strength at early ages in order to deter­mine the time at which they may be opened to traffic.

Two maturity functions are commonly used for computing the maturity index. The first is the Nurse-Saul equation that calculates the time-temperature factor (TTF) using the following equation:


M(t) = ∑ (Ta-To)Δt

where:

M(t) = temperature-time factor (TTF) at time t, degree-days or degree-hours

Δ t = time interval, days or hours

Ta = average concrete temperature during time interval, °C or °F

To = datum temperature at which it is assumed that concrete ceases to gain strength with time; the value of -10°C (14°F) is most commonly used.

This equation (Nurse-Saul) is the most popular pro­cedure in use by state DOTs.[29][30] When this equation is used, the concrete strength is related to the logarithm of TTF.

The other maturity function, the Arrhenius equation, is used to calculate the “equivalent age” maturity index. Equivalent age represents the equivalent duration of curing at the reference temperature that would result in the same value of maturity as the curing period at a given average temperature.

Equation 2

te = ∑e-Q(1/Ta-1/Ts)Δt

where:

te = equivalent age at standard or reference temperature, days or hours

e = 2.718

Q = apparent activation energy divided by the gas constant, (E/R), °K

E = apparent activation energy, J/mole R = universal gas constant = 8.314 J/mole°K

K = absolute temperature, Kelvin, °K= °C+273.15

Ta = average concrete temperature during time interval, Δt, °K

Ts = standard or reference temperature, °K

Δt = time interval, days or hours


With this equation, a different function (hyperbolic rather than logarithmic) is used to relate concrete strength to equivalent age. The Arrhenius equation is used less commonly for concrete pavement work in the United States.[31][32] According to Carino,[33] the Arrhenius relationship may be more appropriate when a wide variation in concrete temperature is expected. More information is available in ASTM C 1074,[34] ASTM C 918,[35] and AASHTO T 276.[36]

A thorough discussion of the applications of the maturity functions, their limitations, and accuracy is given in Reference 13[37].

Maturity Testing Procedure

Figure 1. Schematic of maturity testing.
Figure 2. Typical plot from maturity data.[38] (100 psi = 0.69 MPa)
Figure 3. Handheld computer for embedded microprocessors.

Guideline procedures for maturity testing are given in the Appendix of this report, including a protocol[39] based on the Iowa DOT method for concrete paving applications. Procedures are also given in ASTM C 1074[40] and References 3[41], 13[42] and 20[43].

The maturity method is a two-step process (Figure 1). First, a relationship is established between the maturity values and the concrete strength as meas­ured by tests of beams or cylinders. The development of the maturity-strength curve is done at the beginning of construction using project materials. The application covers only one mixture. If there are changes in mate­rial sources, mix proportions, or mixing equipment, another correlation must be run.

Preliminary testing is necessary before a techni­cian can accurately analyze concrete in the field. Using the actual job mixture concrete materials, test speci­mens are prepared with thermocouples or micro­processors embedded in them. The temperatures are monitored and beams or cylinders are broken to develop a relationship between the strength values and the temperature-time factor (TTF). The strength-maturity equation is developed by performing strength tests at various ages, computing the corresponding temperature-time factors at the test ages, and plotting the strength as a function of the logarithm of the tempera-ture-time factor. A best-fit line is then plotted through the data, as shown in Figure 2. Test data from one field project[44] indicate that the maturity curves may be more reproducible when using compressive strengths rather than flexural strengths.

The second step is instrumenting and monitoring the concrete pavement. Temperature probes or microprocessors are embedded in the concrete and the tem­perature is measured periodically.

Installation of thermocouples is a relatively simple matter. Thermocouple wires are attached to a small wooden dowel and inserted to the desired depth (see “Location of Test Probes”) in the fresh concrete, shortly after placement. Alternatively, a wooden stake can be driven into the base and the thermocouple wires attached to the portion of the stake that will be covered by the concrete. The lead wires are then attached to the device, which may be located at some distance away. The lead wires may be placed in a shallow groove troweled into the pavement surface to allow for pavement finishing and texturing without interference.


Installing self-contained microprocessors is also as simple as inserting them to the desired depth. They may be secured to a wooden dowel if necessary to ensure that the depth is correct. The data (lead) wires must extend out of the pavement slab for later connection to the handheld computer or data reader. Embedded microprocessors contain a memory chip, temperature sensor, microcomputer and battery. Some handheld computers can be pre-programmed with the maturity curve to output strength directly from maturity data stored in the microprocessors. The equipment is capable of logging the temperature and/or maturity as long as the battery remains effective, typically several months (Figure 3).

Maturity Test Equipment

Maturity meters automatically monitor and record concrete temperature as a function of time. Acceptable devices include thermocouples or thermostats con­nected to strip-chart recorders or digital data loggers. Commercially available devices automatically compute and display information that can be used as an index to strength, either flexural or compressive.

Several maturity devices are available which con­tinuously measure the concrete temperature and calcu­late the maturity automatically at least once every hour. The meters can also display the maturity value digitally at any point in time. Depending on the meter used, sev­eral different locations can be monitored simultane­ously. Some maturity meters can be set up to use either the Nurse-Saul or the Arrhenius maturity equation.

Figure 4 shows one of the popular maturity meters. This and similar meters are microprocessor-based, bat­tery operated data collection systems. They typically have several channels for temperature measurement, and calculate the maturity value for each channel for many hours of elapsed time. The devices record the tem­perature for each channel every hour and can print out the data on a battery-operated printer or download the data to a computer. Some of the devices use low-cost type “T” thermocouple wire to measure temperature changes in the concrete. Figures 5 through 7 show devices in use.

Location of Test Probes

The location and depth of the thermocouple wire (or embedded microprocessor) are dependent on the use of the data. Cable[45] has made the following recom­mendations:

  • The thermocouple (or embedded microprocessor) should always be placed at least 300 mm (1 ft) from the edge of the pavement.
  • Decisions regarding the timing of joint sawing should be based on data from a thermocouple (or embedded microprocessor) placed within 25 mm (1 in.) of the concrete surface.
  • Measurements taken at mid-depth of the concrete are useful in the determination of the average strength of the slab and should be used in the determination of pavement opening times.
  • Thermocouples can be mounted easily on wood dowels and inserted to the required depth in the concrete. They are left in the slab after measure­ments have been completed.
  • The thermocouples (or embedded microproces­sors) should be inserted at longitudinal intervals of 150 to 300 m (500 to 1,000 ft) to account for varia­tions in placement time along the project and to provide estimates of the best time to saw joints in each interval or section.


Measurement Frequency and Data Collection

Figure 8. Contractor taking pavement temperature.

The desired frequency of taking maturity or tempera­ture measurement readings depends upon the setting characteristics of the concrete, the urgency for opening to traffic and the type of maturity equipment in use.

Embedded microprocessors typically record tem­peratures and/or maturity values at pre-programmed times after placement, such as every 2 hours for the first three days, every four hours for the fourth through sixth day, etc. Depending on the manufacturer, the frequency may not be adjustable. Data from the microcomputer in the embedded probe is transferred to a handheld unit, which can then transfer the data to a personal computer where it can be compiled into a report for the engineer and contractor. One version of the newest technology uses wireless transmission of the data from the probes to a centrally-located personal computer.

As a minimum, the technician should record data readings twice per day, once in the morning and once before leaving the job site (Figure 8). As the technician and crew become knowledgeable of the setting char­acteristics of the concrete they will understand when to take more frequent measurements to pinpoint when the concrete has met opening strength requirements. More frequent readings, taken every two hours for example, may be beneficial for tracking strength development in fast-setting mixtures. If the saw crew intends to monitor the concrete surface temperature to objectively identify the sawing window, frequent readings may be neces­sary during the first 12-24 hours after placement.

More information on recording the temperature and maturity data is provided in Appendix A and B.

Opening to Traffic Criteria

The concrete strength criterion for opening to traffic varies mainly with the type of traffic: construction vehi­cles or public vehicles. However, many other factors also affect the actual target strengths:

  • Type, weight and number of anticipated loads during early-age period
  • Location of loads on slab
  • Pavement design (new construction, unbonded overlay, bonded overlay or overlay on asphalt)
  • Slab thickness
  • Foundation support (modulus of subgrade reac­tion, k)
  • Edge support condition (widened lane or tied curb & gutter or tied concrete shoulder)


Flexural strength as low as 1.0 MPa (150 psi) in third-point loading is acceptable if the pavement will carry only automobiles. If the pavement will carry trucks, a flexural strength of up to 4.5 MPa (650 psi) may be necessary for thinner slabs. Appendix C provides tables listing required opening strengths for both construction and public traffic.

For most concrete pavement applications, flexural strength is the most appropriate structural strength cri­terion for evaluating load capacity. Flexural strength values provide an assessment of the tensile strength at the bottom of the slab where wheel loads induce tensile stresses. For that reason, this document lists opening criteria in terms of third-point flexural strengths.[46]


Implementation

As is the case for many developing technologies and new testing procedures, at the outset, involved parties may be uncomfortable with the associated changes or uncertain of the interpretation of the results. Agency officials can distribute literature to contractors and concrete producers to help make them more familiar with the technology. Reference 13[47] identifies and discusses four items that are important actions to be completed prior to full implementation:

  1. Train QC/QA personnel.
  2. Develop maturity curves for various concrete mix­tures and conditions.
  3. Complete trial field projects.
  4. Achieve a level of confidence and become com­fortable with fundamentals.


Summary

The maturity concept is a technology that can be used as a tool for quality control and quality assurance[48] of newly placed concrete pavements. DOT represen­tatives throughout the United States have reported[49] that maturity is being used to predict critical concrete strengths for actions such as opening the pavement to traffic, timing of joint sawing, structural acceptance, and formwork removal for highway structures.

The method is a useful, accurate means of esti­mating the in-situ concrete strength. Due to its simple application using readily available equipment, the ma­turity concept should continue to grow in all applications where the knowledge of maturing concrete strength is advantageous to reducing construction costs and time schedules.

There is a need for specifying agencies and paving contractors to become familiar with maturity testing techniques. The payoffs associated with this tech­nology will be of benefit to agencies, contractors, and the motoring public.

2 The results of flexural strength tests using ASTM C 78 are very sen­sitive to the preparation of the test beams and testing procedures. Many agencies realize this shortcoming and use the more consis­tent compressive strength test (ASTM C 39) to evaluate concrete for acceptance and opening. To use the criteria presented in this publication, it may be necessary to develop a correlation between compressive strength and flexural strength in the laboratory for each unique mix. The following equation is often used to convert compressive strength to third-point flexural strength.

fr = C(f'cr)0.5

Where:

fr = flexural strength (modulus of rupture) in third-point loading, MPa (psi).

f'cr = required average compressive strength, MPa (psi).

C = A constant between 8 and 10 for normal mixtures [for high-strength concrete C ranges from 7.5 to 12 (11.7 recom­mended)].


Appendix A

Guideline Procedure for Testing the Strength of PCC Using Maturity

General

This guide outlines the procedure for using the maturity concept as a non-destructive test method for estimating concrete strength. It is based on the Iowa DOT Materials Instructional Memorandum 383.

Maturity testing is a two-step procedure. First, a relationship must be established between the maturity values and the concrete strength as measured by destructive methods (that is, through testing of beams or cylinders). The develop­ment of the maturity-strength curve is done in the field at the beginning of construction using project materials and the project proportioning and mixing equipment. The second step is the instrumentation of the concrete to be measured. Temperature probes or microprocessors are installed in the concrete and the temperature is measured. From those measurements, along with the age at which the measurements were taken, maturity values are determined. A maturity meter or temperature-measuring device and a computer or calculator may also be used to determine the maturity values.

The contractor and the agency jointly develop a plan for performing the maturity testing. The plan includes:

  1. The contractor is responsible for the development of the maturity curve. The curve development is monitored by the contracting agency.
  2. The temperature monitoring process of the constructed pavement is the responsibility of the contractor and moni­tored by the contracting agency.


For concrete furnished from a mixing plant (portable or stationary), which is in place prior to construction of the specified project, a maturity curve may be established ahead of actual construction of the specified project. The test specimens should be cast with concrete made from the same plant and using the same materials source as will be used in the spe­cific project. The contractor should inform the agency and provide them an opportunity to observe the development of the maturity curve.

Establishment of Maturity-Strength Relationship

To establish a maturity-strength relationship for a concrete mix, a maturity meter or a thermal meter and a strength testing machine are needed. The following procedure is used: [Note: Before using any maturity meter, check to be sure the datum temperature is set to -10°C (14°F)].

1. Cast a minimum of twelve specimens per ASTM C 192 (cylinders or beams). Test the entrained air content and slump of the concrete being used to cast the specimens. Record these values. The concrete shall meet specifi­cations. The specimens shall be cast from a batch of at least 3 m3 (4 cu. yd).
2. Embed a thermocouple wire or maturity microprocessor near each end of a test beam (when flexural strength is to be determined) or cylinder to monitor the temperature. This specimen will be the last to be tested. The instru­ments should be inserted to approximately mid-depth and such that they are approximately along the axis about 75 mm (3 in.) from each side and each end. Secure any wires to prevent them from being inadvertently pulled out of the specimen. The average of the two readings will be used in the development of the maturity-strength curve. When a thermal meter is used, the measured temperature should be substituted into Equation A1 to obtain values of maturity. The Maturity Data Recording Sheet at the end of this appendix may be used in this determination. When a maturity meter is used, the meter computes the values. Twelve (12) test specimens shall be tested as described in #4 below.


M(t) = ∑ (Ta-To)Δt

where:

M(t) = temperature-time factor (TTF) at time t, degree-days or degree-hours
Δ t = time interval, days or hours
Ta = average concrete temperature during time interval, °C or °F
To = datum temperature at which it is assumed that concrete ceases to gain strength with time; the value of -10°C (14°F) is most commonly used.
3. Cast and cure the beams (or cylinders) at the plant site in accordance with ASTM C 31. Test in accordance with ASTM C 39 or C 78 (for cylinders or beams, respectively). This allows the maturity meter to be protected from the weather and theft. The meter can be stored in a lab trailer or vehicle with the probes run outside to the specimens. The specimens shall be covered with plastic immediately after casting and prior to form removal. If possible, wet burlap should be placed over the surfaces of the specimens under the plastic. The forms shall be removed the fol­lowing day. Cure all specimens in a pit of wet sand after form removal, until they are tested.
4. Determine maturity values and strengths at four different ages. Test three specimens for strength at each age and calculate the average measured strength at each age. The maturity value shall be calculated from a temperature reading at the time the specimen is tested for strength. When a thermal meter is used, the temperature used to calculate the maturity shall be determined at 2- to 3-hour intervals for the first 24 to 36 hours and at least twice per day thereafter. The tests shall be spaced such that they are performed at somewhat consistent intervals of time and span a range of strength that includes the opening strength desired.


The first test (test 1), for normal paving mixtures, should be performed at an age of about twelve (12) hours when warm ambient temperatures prevail, i.e., 26-32°C (80-90°F). During cooler conditions, the first test may be per­formed at the beginning of the day following the casting of test specimens.
Additional test specimens may be cast at a later time and tested at earlier ages to add data to the strength-matu-rity relationship as an aid to determining the appropriate time to saw.
5. Plot the measured strength against the corresponding values of maturity at different ages, as determined by the maturity meter, microprocessor data log, or by hand methods. The TTF number corresponding to the target opening strength is used to determine when the pavement has reached opening strength.
An example Maturity-Strength Development form is included at the end of this appendix. The contractor/contractor representative should sign the form and give copies to the Project Engineer and his designates.

Field Procedure

Equipment (for one test location)

  1. 12 – 150 mm x 150 mm x 500 mm (6 in. x 6 in. x 20 in.) beam molds, or 12 – 150 mm (6 in.) diameter, 300 mm (12 in.) long cylinders
  2. 1 each shovel (square point), rubber hammer, or equivalent, and wood float or equivalent
  3. 1 each hydraulic testing machine – third point flexural or compressive
  4. 1 each embedded microprocessor, or Type T thermocouple wire
  5. 1 each maturity meter, or handheld data logger
  6. 1 each hand-held thermometer
  7. 7. Connectors


Placement of Temperature Probes or Microprocessors

Probes or microprocessors may be placed at any point along the pavement slab. A minimum of two probes should be installed in each day’s placement. On days when there is a large difference between daytime high temperatures and nighttime low temperatures, placing additional probes near the beginning of the day’s run and at a point near the midday location will provide information that is helpful to those sawing the pavement, as well as to those determining the opening time. It has been found that concrete placed at different times of the day does not always gain strength at the same rate.

For thermocouple probes, strip the coating from each end of the two wires and twist the ends together before inserting them into the fresh concrete. Insert the temperature probe into the concrete until the end is at approximately the pavement mid-depth and at least 0.5 m (1.5 feet) from the edge of the pavement. The wire ends are the points at which the temperature measurement is taken. Insertion may be accomplished by attaching the wire ends to a wooden dowel and embedding it into the slab. Check to ensure the concrete is consolidated around the dowel. The portion of the dowel that protrudes above the pavement should be cut or broken off after the testing is completed.


Data Collection

The probe wire leads not placed in the concrete should be connected to a plug unless the temperature-measuring device must be connected to the probe directly with bare wires. The plug is then inserted into the maturity meter or thermal meter. Normally a thermal meter can be used to collect field data. Follow the manufacturer’s instructions to con­nect the device.

When a thermal meter is used, the wire is connected to the meter each time a temperature is taken. Then the wire is disconnected and the value recorded on a Maturity Data Recording Sheet (see example in Figure A1). Appendix B pro­vides a blank Maturity Data Recording Sheet.

Do not disconnect the wire from the maturity meter until the test is completed. The data collection must be uninterrupted. Also, the maturity meter must be protected from rain or water or permanent damage may result.

When a thermal meter is being used, the initial temperature of the concrete shall be measured and recorded as soon as the wires are placed. Temperature readings should be taken in the morning and late afternoon (when the technician first arrives on the project and before the technician leaves for the day) as a minimum for standard paving mixtures. For fast-setting mixtures, readings should be taken every few hours, depending on weather conditions. If a maturity meter is being used, it should be connected to the probe as soon as possible to begin data collection.


Measuring the Maturity

The maturity number can be read directly from the maturity meter or handheld reader, or calculated from the temperature readings obtained by the thermal meter. This number is then used to enter the strength-maturity chart that was established as described previously and a strength is then estimated. It is important to follow manufacturer’s instructions for initializing and using the instruments.


Implementation

Pavement placed on the first day during development of the strength-maturity curve may be opened when either of the following criteria has been met:

  1. The TTF of the slab meets or exceed the opening TTF as determined by the strength-maturity curve being devel­oped.
  2. At a particular test age, the average strength of the three beams used for development of the strength-maturity curve meets or exceeds the required opening strength.


Validation

Once per month, validation tests should be conducted by the agency to determine if concrete strength is being ade­quately represented by the current maturity curve. Cast and cure three (3) specimens using the same procedure and manner as used to develop the current maturity curve. Test all three specimens as closely as possible to the maturity value which was determined to represent the opening strength of the pavement.

The original curve is considered to be valid if the average of these tests is:

  • For flexural strength validation – within 0.34 MPa (50 psi) of the original maturity curve at the TTF.
  • For compressive strength validation – within 3.4 MPa (500 psi) of the original maturity curve at the TTF.


If the average value does not meet that criteria (the average of the tests is higher or lower), a new maturity curve should be developed. An example validation of the maturity curve is included in Figure A2.

This validation procedure is an assurance procedure in that it is not an acceptance test, but merely a check. If the test results indicate a new curve must be developed, this should be done in a timely manner. The original curve should be used until new specimens are cast and the implementation procedure is followed.


Factors Requiring a New Curve

Changes in material sources, proportions, and mixing equipment all affect the maturity curve or function of a given con­crete mixture. Therefore, development of a new maturity curve is generally required for any change to a concrete mixture.


Development of a new maturity curve due to material source and proportion changes in a concrete mixture may be waived by use of the validation procedure. If the average strength is greater than the original maturity curve at the TTF for which the validation spec­imens were tested, a new curve will not be required. A new curve will be required if the average strength is less than the original curve at the TTF for which the val­idation specimens were tested.

Appendix B

MATURITY DATA RECORDING SHEET

Maturity11.png

Appendix C

Traffic Opening Criteria

The following tables provide opening strength criteria for construction and public vehicle traffic. No studies have been made to determine early-age opening criteria for aircraft traffic. The Federal Aviation Administration's current specifications (AC-150/5370) allow opening to traffic at 3.8 MPa (550 psi) flexural strength.

Construction Traffic

The types of construction vehicles and equipment that might use pavement early include concrete hauling trucks, water trucks and saws. Most saws are very light and are inconsequential in terms of stress loading. Even the largest span saws do not induce significant concrete fatigue at very early ages except when operating on slabs less than 175 mm (7.0 in) thick. The 80 kN (18,000 lb) single-axles and 151 kN (34,000 lb) tandem axles (TAL) on con­struction trucks induce much higher stresses. Table C1 provides opening criteria for span saw and truck loads and assumes that these loads will occur at least 0.6 m (2.0 ft) from the edge of the slab.

Table C1. Flexural strength requirements for opening concrete pavements to use by construction traffic. Span saw cri­teria allows 0.5 percent fatigue consumption. Truck axle criteria allows 1.0 percent fatigue consumption.[50]

REQUIRED FLEXURAL STRENGTH FOR OPENING, MPa (psi)
Slab Thickness
mm (in.)
Foundation support, k
MPa/m (psi/in.)
To Support Span Saw Loadsa MPa (psi) To Support Legal 151 kN (34,000 lb) Tandem Axle Loads MPa (psi)
10 Loads 50 Loads
150 (6.0) 27.2 (100) 1.5 (210) 2.8 (410) 3.2 (460)
54.3 (200) 1.3 (190) 2.5 (360) 2.7 (390)
135 (500) 0.8 (100) 2.1 (300) 2.0 (300)
165 (6.5) 27.2 (100) 1.3 (190) 2.5 (360) 2.7 (390)
54.3 (200) 1.1 (160) 2.1 (310) 2.4 (350)
135 (500) 1.0 (150) 2.1 (300) 2.1 (300)
175 (7.0) 27.2 (100) 1.0 (150) 2.1 (300) 2.3 (340)
54.3 (200) 1.0 (150) 2.1 (300) 2.1 (300)
135 (500) 1.0 (150) 2.1 (300) 2.1 (300)
175 (7.0) (see a below) 27.2 (100) 1.0 (150) 2.1 (300) 2.1 (300)
54.3 (200) 1.0 (150) 2.1 (300) 2.1 (300)
135 (500) 1.0 (150) 2.1 (300) 2.1 (300)

A. Can open slabs greater than 175 mm (7.0 in.) thick to construction trucks at a flexural strength of 2.1 MPa (300 psi) or greater with 0.6 m (2.0 ft) offset from slab edges.

Public Vehicle Traffic

Public traffic includes many different vehicles. To determine the acceptable opening strength for public traffic requires an estimate of the number of loads to be applied or allowed before the concrete reaches design strength.

Table C2 provides opening criteria for municipal and highway pavements to public traffic. To use the table requires estimates of anticipated traffic volume, slab thickness and foundation support. The table assumes a 0.6 m (2.0 ft) offset of traffic from the lane edge. Wide truck lanes, tied concrete shoulders and curb and gutter all serve to reduce load stresses to levels equivalent to a 0.6 m (2.0 ft) traffic offset. If the pavement design does not include these features, the contractor can place barricades to prevent edge loads. Normally the contractor may remove the barricades after the concrete flexural strength reaches 3.0 MPa (450 psi). However, it may be necessary to wait for the concrete to gain full design strength on thin municipal pavements that require more than 4.5 MPa (650 psi) flex­ural strength for opening.

Table C2. Flexural strength requirements for opening concrete pavements to use by public traffic.[51] Traffic is estimate of the total one-way ESAL’s that will use the pavement truck lane between time of opening and time concrete reaches design strength (usually 28-day strength).

REQUIRED FLEXURAL STRENGTH FOR OPENING, MPa (psi)
Slab Thickness
mm (in.)
Foundation Support, k
MPa/m (psi/in.)
To Support Estimated ESAL’s Applied Before Achieving Specified Strengthb
100 500 1000 2000 5000
MUNICIPAL
150 (6.0) 27.2 (100) 3.4 (490) 3.7 (540) 3.9 (570) 4.1 (590) 4.3 (630)
54.3 (200) 2.8 (410) 3.1 (450) 3.2 (470) 3.4 (490) 3.6 (520)
135 (500) 2.3 (340) 2.6 (370) 2.6 (370) 2.8 (400) 3.0 (430)
165 (6.5) 27.2 (100) 3.0 (430) 3.2 (470) 3.4 (490) 3.6 (520) 3.8 (550)
54.3 (200) 2.4 (350) 2.7 (390) 2.8 (410) 3.0 (430) 3.1 (450)
135 (500) 2.1 (300) 2.2 (320) 2.3 (330) 2.4 (350) 2.6 (370)
175 (7.0) 27.2 (100) 2.6 (370) 2.8 (410) 3.0 (430) 3.1 (450) 3.3 (480)
54.3 (200) 2.1 (310) 2.3 (340) 2.5 (360) 2.6 (370) 2.8 (400)
135 (500) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.2 (320)
190 (7.5) 27.2 (100) 2.3 (330) 2.6 (370) 2.6 (380) 2.8 (400) 3.0 (430)
54.3 (200) 2.1 (300) 2.1 (300) 2.2 (320) 2.3 (330) 2.4 (350)
135 (500) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300)
200 (8.0) 27.2 (100) 2.1 (300) 2.3 (330) 2.3 (340) 2.5 (360) 2.6 (380)
54.3 (200) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.3 (330)
135 (500) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300)
HIGHWAY
200 (8.0) 27.2 (100) 2.6 (370) 2.8 (410) 3.0 (430) 3.1 (450) 3.2 (470)
54.3 (200) 2.1 (310) 2.3 (340) 2.4 (350) 2.6 (370) 2.7 (390)
135 (500) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (310)
215 (8.5) 27.2 (100) 2.3 (340) 2.6 (370) 2.6 (380) 2.8 (400) 3.0 (430)
54.3 (200) 2.1 (300) 2.1 (300) 2.2 (320) 2.3 (330) 2.4 (350)
135 (500) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300)
225 (9.0) 27.2 (100) 2.1 (300) 2.3 (330) 2.4 (350) 2.5 (360) 2.7 (390)
54.3 (200) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.2 (320)
135 (500) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300)
240 (9.5) 27.2 (100) 2.1 (300) 2.1 (300) 2.2 (320) 2.3 (330) 2.4 (350)
54.3 (200) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300)
135 (500) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300)
255 (10.0) 27.2 (100) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.2 (320)
54.3 (200) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300)
135 (500) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300)
+265 (+10.5) (see b below) 27.2 (100) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300)
54.3 (200) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300)
135 (500) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300) 2.1 (300)

B. Can open slabs greater than 265 mm (10.5 in) thick to traffic at a flexural strength of 2.1 MPa (300 psi) or greater with barri­cade protection of free edges. Reduce opening strengths by 30% [2.1 MPa (300 psi) minimum] if no barricades protect free edges, but the pavement includes a 14 ft wide or greater truck lane and/or tied concrete shoulders.

References

  1. Tepke, David and Tikalsky, P. J., “Concrete Maturity Progress: A Survey of Departments of Transportation,” Paper No. 01-2939, presented at 80th Annual Meeting of Transportation Research Board, TRB Record 1775, Washington D. C., Dec. 2001.
  2. Cable, J. K., Evaluation of Maturity and Pulse Velocity Measurements for PCC Traffic Opening Decisions, Iowa DOT Project HR-380, Iowa Department of Transportation, March 1998.
  3. Ansari, F., et al, Development of Maturity Protocol for Construction of NJDOT Concrete Structures, Final Report to New Jersey Deportation of Transportation, Dec. 1999.
  4. Hunt J. E. and Mihm, A. M., “Concrete Maturity Testing in Texas Project,” Better Roads, vol. 69, no.3, March 1999.
  5. Okamoto, P., et al, Guidelines for Timing Joint Sawing and Earliest Loading for Concrete Pavement, Volume 1 – Final Report, FHWA-RD-91-O79, Federal Highway Administration, Washington, D.C., Feb. 1994.
  6. Cole, L. and Okamoto, P., “Flexural Strength Criteria for Opening Concrete Roadways to Traffic,” TRB Record 1478, Transportation Research Board, 1996.
  7. Okamoto, P., et al, Guidelines for Timing Joint Sawing and Earliest Loading for Concrete Pavement, Volume 1 – Final Report, FHWA-RD-91-O79, Federal Highway Administration, Washington, D.C., Feb. 1994.
  8. Fast Track–Fast Pay, American Concrete Pavement Association, Skokie, IL, June 1986.
  9. Fast-Track Concrete Pavements, TB004 P, American Concrete Pavement Association, Skokie IL, 1994.
  10. Accelerated Rigid Pavement Techniques, State of the Art, FHWA SA-94-080, Federal Highway Administration, Dec. 1984.
  11. “Cold-Weather Concreting,” ACI 306 R-88, ACI Manual of Concrete Practice, Part 2, American Concrete Institute, Farmington Hills, MI, 1997.
  12. Hulshizer, A. J., “Benefits of Maturity Method for Cold-Weather Concreting,” Concrete International, March 2000.
  13. “Handbook on Non-Destructive Testing,” NDT Workshop at ACPA 29th Annual Meeting, Federal Highway Administration, Washington, D.C., Dec. 1992.
  14. Tikalsky, P. J., et al, “Using the Concrete Maturity Meter for QA/QC,” Final Report, University-Based Research and Technology Transfer Program, The Pennsylvania State University, Jan. 2001.
  15. Fast Track–Fast Pay, American Concrete Pavement Association, Skokie, IL, June 1986.
  16. Saul, A. G. A., “Principles Underlying the Steam Curing of Concrete at Atmospheric Pressure,” Magazine of Concrete Research (London), Vol. 2, No. 6, March 1951.
  17. Carino, N. J. and Tank, R. C., “Maturity Functions for Concretes Made with Various Cements and Admixtures,” ACI Materials Journal, Vol. 89, No. 2, American Concrete Institute, March-April 1992.
  18. Nurse, R. W., “Steam Curing of Concrete,” Magazine of Concrete Research, Vol.1, No. 2, June, 1949.
  19. Okamoto, P., et al, Guidelines for Timing Joint Sawing and Earliest Loading for Concrete Pavement, Volume 1 – Final Report, FHWA-RD-91-O79, Federal Highway Administration, Washington, D.C., Feb. 1994.
  20. “Handbook on Non-Destructive Testing,” NDT Workshop at ACPA 29th Annual Meeting, Federal Highway Administration, Washington, D.C., Dec. 1992.
  21. Carino, N. J. and Tank, R. C., “Maturity Functions for Concretes Made with Various Cements and Admixtures,” ACI Materials Journal, Vol. 89, No. 2, American Concrete Institute, March-April 1992.
  22. Carino, N. J., “Prediction of Concrete Strength at Later Ages,” Significance of Tests and Properties of Concrete and Concrete-Making Materials, STP 169 C, American Society of Testing and Materials, West Conshohocken, PA, 1994.
  23. Temperature Management of Slabs, Final Report, Special Project 201, Federal Highway Administration, Washington D.C. June 1994.
  24. Maturity Method, State of the Practice, Federal Highway Administration, Washington, D.C., Jan. 1990.
  25. Tikalsky, P. J., et al, “Using the Concrete Maturity Meter for QA/QC,” Final Report, University-Based Research and Technology Transfer Program, The Pennsylvania State University, Jan. 2001.
  26. Crawford, G. L. and Wathne, L. G., “Use of Non­destructive Testing for Concrete Pavements,” 7th International Conference on Concrete Pavements, Orlando, FL, Sept. 2001
  27. Cable, J. K., Evaluation of Maturity and Pulse Velocity Measurements for PCC Traffic Opening Decisions, Iowa DOT Project HR-380, Iowa Department of Transportation, March 1998.
  28. “Method of Testing the Strength of Portland Cement Concrete Using the Maturity Method,” Materials Instructional Memorandum 383, Iowa Department of Transportation, Office of Materials, Oct. 3, 2000.
  29. Tepke, David and Tikalsky, P. J., “Concrete Maturity Progress: A Survey of Departments of Transportation,” Paper No. 01-2939, presented at 80th Annual Meeting of Transportation Research Board, TRB Record 1775, Washington D. C., Dec. 2001.
  30. “Handbook on Non-Destructive Testing,” NDT Workshop at ACPA 29th Annual Meeting, Federal Highway Administration, Washington, D.C., Dec. 1992.
  31. Tepke, David and Tikalsky, P. J., “Concrete Maturity Progress: A Survey of Departments of Transportation,” Paper No. 01-2939, presented at 80th Annual Meeting of Transportation Research Board, TRB Record 1775, Washington D. C., Dec. 2001.
  32. Saul, A. G. A., “Principles Underlying the Steam Curing of Concrete at Atmospheric Pressure,” Magazine of Concrete Research (London), Vol. 2, No. 6, March 1951.
  33. Carino, N. J., “The Maturity Method: Theory and Applications,” Cement, Concrete, and Aggregates, vol. 6, no. 2, Winter, 1984.
  34. “Practice for Estimating Concrete Strength by the Maturity Method,” ASTM C 1074, 1998 Annual Book of Standards, Vol. 4.02, American Society of Testing Materials, West Conshohocken, PA.
  35. “Test Method for Measuring Early-Age Compressive Strength and Projecting Later- Age Strength,” ASTM C 918, 1997 Annual Book of Standards, Vol. 4.02 American Society of Testing and Materials, West Conshohocken, PA.
  36. “Measuring Early-Age Compressive Strength and Projecting Later-Age Strength,” AASHTO T 276-83, Methods of Sampling and Testing, American Association of State Highway and Transportation Officials.
  37. Tikalsky, P. J., et al, “Using the Concrete Maturity Meter for QA/QC,” Final Report, University-Based Research and Technology Transfer Program, The Pennsylvania State University, Jan. 2001.
  38. “Method of Testing the Strength of Portland Cement Concrete Using the Maturity Method,” Materials Instructional Memorandum 383, Iowa Department of Transportation, Office of Materials, Oct. 3, 2000.
  39. “Method of Testing the Strength of Portland Cement Concrete Using the Maturity Method,” Materials Instructional Memorandum 383, Iowa Department of Transportation, Office of Materials, Oct. 3, 2000.
  40. “Practice for Estimating Concrete Strength by the Maturity Method,” ASTM C 1074, 1998 Annual Book of Standards, Vol. 4.02, American Society of Testing Materials, West Conshohocken, PA.
  41. Ansari, F., et al, Development of Maturity Protocol for Construction of NJDOT Concrete Structures, Final Report to New Jersey Deportation of Transportation, Dec. 1999.
  42. Tikalsky, P. J., et al, “Using the Concrete Maturity Meter for QA/QC,” Final Report, University-Based Research and Technology Transfer Program, The Pennsylvania State University, Jan. 2001.
  43. Crawford, G. L. and Wathne, L. G., “Use of Non­destructive Testing for Concrete Pavements,” 7th International Conference on Concrete Pavements, Orlando, FL, Sept. 2001.
  44. Crawford, G. L. and Wathne, L. G., “Use of Non­destructive Testing for Concrete Pavements,” 7th International Conference on Concrete Pavements, Orlando, FL, Sept. 2001.
  45. Cable, J. K., Evaluation of Maturity and Pulse Velocity Measurements for PCC Traffic Opening Decisions, Iowa DOT Project HR-380, Iowa Department of Transportation, March 1998.
  46. Cable, J. K., Evaluation of Maturity and Pulse Velocity Measurements for PCC Traffic Opening Decisions, Iowa DOT Project HR-380, Iowa Department of Transportation, March 1998.
  47. Tikalsky, P. J., et al, “Using the Concrete Maturity Meter for QA/QC,” Final Report, University-Based Research and Technology Transfer Program, The Pennsylvania State University, Jan. 2001.
  48. Tikalsky, P. J., et al, “Using the Concrete Maturity Meter for QA/QC,” Final Report, University-Based Research and Technology Transfer Program, The Pennsylvania State University, Jan. 2001.
  49. Tepke, David and Tikalsky, P. J., “Concrete Maturity Progress: A Survey of Departments of Transportation,” Paper No. 01-2939, presented at 80th Annual Meeting of Transportation Research Board, TRB Record 1775, Washington D. C., Dec. 2001.
  50. “Early Opening of PCC Pavements to Traffic,” Final Report, Special Project 201, Federal Highway Administration, Washington D.C., June 1994.
  51. “Early Opening of PCC Pavements to Traffic,” Final Report, Special Project 201, Federal Highway Administration, Washington D.C., June 1994.