6−43 Requirements for mass concrete construction include laboratory testi ng, thermal modeling, temperature monitoring, and providing concrete temperature control before, during, and after placement. All testing shall be performed at a laboratory with recognized AASHTO accreditations for performing the required tests (AASHTO T22, AASHTO T23, AASHTO T121, AASHTO T152, ASTM C1064, ASTM C1074), with the provision that no exception is taken by the Engineer with the Contractor’s choice of laboratory. The peak temperature is defined as the average of the values measured at any given time by the two temperature sensors placed at the lo cation of the highest tem perature as determined by the thermal model for the structural element. The highest acceptable peak temperature is 155°F. The differential temperature is defined as the difference in values measured at any given time between the temperature sensor(s) in any giv en location (or the average, if two sensors placed in the location) in the structural element and the peak temperature as defined above. The highest acceptable differential temperature until the completion of temperature control is 35°F. The performance-based differential temperature is defined as a limit that changes as the concrete gains strength, determined as a function of the established maturity curve for the mix. The benefit of this method is a potential acceleration of the production schedule over the use of a fixed limit. This option may be considered by the Engineer, with the proper submission of an implementation plan for the process as described herein, after the contractor has demonstrated compliance with the specifications of the concrete mix during batching, placement and curing.
607.02 Materials and Equipment.
607.02.1 CONCRETE. The concrete shall meet the app licable material requirements of SECTION
808 and SECTION 601 . Unless specified in the contract documents, calcium nitrite based corrosion inhibitor shall not be used in Mass Concrete mixtures. Any proposed mixture adjustment that meets the requirement in SECTION 601 for a new approval of the mix design will also require a new approval of the mass concrete temperature control plans per this specification. 607.02.2 TEMPERATURE AND MATURITY RECORDING. Primary temperature measuring loggers shall be designed specifically for determining the maturity of concrete in accordance with ASTM C1074. They shall operate in the range of 0°F to 212°F to an accuracy of +/- 1°F and internally record the time and temperature at a minimum of 1 hour intervals for a minimum of 90 days. Each logger shall have a unique serial number and shall upon download of the information using the compatible reader or other appropriate data connection, produce a secure (unalterable) Windows PC-readable file that identifies the logger by its serial number and the start date. Software shall be provided to develop maturity curves to predict strength and display the temperature versus time data for all of the loggers in a given placement. The data leads shall be sized to reach from the logger's installed location to an accessible site where a handheld reader can be employed. A data cable that can connect the loggers to a notebook computer or other standard mobile device will be considered equivalent to a handheld reader, providing a Windows PC-readable file can be created that can be transferred to a Windows PC. The Contractor shall provide a reader and nec essary software for the exclusive use of the Engineer. The reader and software provided for t he Engineer shall become the property of the State at the completion of the project. The loggers selected by the Contractor shall have the capability to use battery operated 6−44 Wireless Remote Boxes for the downloading of data. The transmission range of the system shall be sufficient to provide a reliable connection to both the Contractor’s and Engineer’s field offices. A Windows PC-Compatible Wireless System Radio Base Station shall be provided and capable of downloading the data file as described above. The Wireless System Radio Base Station shall be maintained by the Contractor for monitoring the mass concrete placement. An additional Wireless System Radio Base Station shall also be provided for the Engineer’s field office. The additional device and associated software provided for the Engi neer shall become the property of the State at the completion of the project. The requirement for a wireless communications system may be waived by the Engineer, if the Engineer determines that access to the placement does not warrant it. The Contractor shall provide the Engineer recording equipment that will allow intermediate downloading of measurements to a computer without restarting the logger. The recording equipment provided for the Engineer shall become the property of the State at the completion of the project. An automatic temperature monitoring syst em shall be provided with email, phone, or text message alarm capability to notify the Contractor when temperature control limits are about to be exceeded. The Contractor must submit technical literature on the complete maturity logger system, including the loggers, handheld reader, wireless sy stem, software and any other components to the Engineer for approval prior to the first mass concrete placement. This shall include manufacturer contact information for the responsible technical representative and product performance history showing at least one year of successful use of the complete system on a minimum of three projects with mass concrete placements comparable to those within the scope of this project. Contact information shall be provided for the project owners. No mass concrete placements shall proceed until approval of the maturity logger system has been given in writing by the Engineer.
607.03 Submittals.
607.03.1 Mass Concrete Temperature Control Plans. As part of the submittals, the Contractor
shall submit a “Mass Concrete General Temperatur e Control Plan" for approval prior to the first mass concrete placement and shall be stamped by a Rhode Island Registered Professional Engineer. This shall show the general procedures proposed for temperature control. A "Mass Concrete Specific Temperature Control Plan" shall be prepared for each unique placement and shall be based on the general plan. Each specific temperature control plan shall provide guidance for the Contractor, developed based on a concrete hy dration temperature model, to indicate when the peak and differential temperatures might exceed the specification limits. The guidance shall provide specific concrete placement temperature restrictions based on anticipated ambient temperatures and other environmental factors, passi ve and active cooling, and insulation practices that could produce peak or differential temperatures that require remedial action. Guidance shall also be provided on appropriate remedial actions to be taken when concrete temperatures approach specification limits. At a minimum, these guidelines shall take effect when the concrete peak temperature reaches 3°F below the specification limit of 155°F and when the differential temperature reaches 2°F below the specification limit of 35°F or the temperature value at the specified maturity, for the variable differential limit, (if approved). Each specific plan shall be submitted for approval prior to the placement and shall be stamped by a Rhode Island Registered Professional Engineer. Costs related to the development of Mass Concrete Temperature Control Plans shall be considered incidental to the project, and will not be paid for separately. Approval of any Mass Concrete Temperature C ontrol Plan by the Engineer will not relieve the Contractor of his responsibility to maintain concrete temperatures within specification limits. 6−45
a.General Mass Concrete Temperature Control Plan. The General Mass Concrete Temperature Control Plan shall include the following:
1.Concrete mixture proportions, indicating aggregate sources and physical properties, cementitious material sources, and admixture product names and doses for each concrete mixture. The Class MC concrete mixture design and prequalification test results shall be submitted for approval separately.
2.Anticipated mass concrete placement schedule, including proposed concrete mixture adjustments for the full range of conditions that may occur during placement and curing operations.
3.Concrete temperature rise for each mixture shall be tested directly in an adiabatic concrete calorimeter cast from laboratory trial batches using the same material sources and proportions as intended for use on the project.
4.Concrete compressive strength development in standard moist curing environment (73.5 ± 3.5 deg F) at 3, 7, 14, 28, and 56 days for each mixture, based on the average of three 6” x 12” cylinders for each age. Cylinders shall be cured and tested per AASHTO T22. Cast a temperature sensor in the center of two additional cylinders and cure these cylinders alongside those used for compressive strength. Record the average temperatures of the cylinders hourly. Report the compressive strength and maturity for each specimen at each test age and the average values.
5.Calculate and report the concrete strength development-maturity equation for each mixture from the standard cured strength results as described in ASTM C 1074 "Estimating Concrete Strength by the Maturity Method".
6.Demonstration Mock-up(s) shall be performed at least 60 days prior to the first scheduled Mass Concrete Placement. The Contractor shall cast at least one mock-up to verify that the concrete thermal properties and temperature c ontrol procedures required for the Mass Concrete General Temperature Control Plan are adequate to m eet the specification limits. The mock-up(s) shall use the same concrete mixture proportions and materials, form materials, curing materials, and monitoring devices defined in the General Temperature Control Plan, and shall use the same batching and placing operation to be used for the project. The mock-up shall be a cube or other element measuring 4 ft or more in the least dimension. Temperature monitoring of the mock-up shall be as specified in the General Mass Concrete Temperature Control Plan and shall continue for at least seven (7) days. As a minimum, the demonstration mock-up shall be insulated with R-20 insulation on all sides. If alternate insulation, cooling, or curing options are proposed, a separate demonstration mock-up cube shall be cast and instrumented for each alternate. The engineer responsible for the design of the temperature control plan shall be present at the placement for each mock-up. Sensor placement:
a.Two sensors shall be located at the center of the mock-up. The average of these two shall be used.
b.Two sensors shall be located within one inch from the top surface located directly above the center of mass sensors. The average of these two shall be used.
c.Two sensors shall be located within one inch from the center of a vertical face. The 6−46 average of these two shall be used.
d.Two sensors shall be located in an upper corner of the cube. The average of these two shall be used.
e.One sensor shall be used to record the ambient temperature. This sensor shall be placed at approximately ten (10) feet from the placement, in a shaded area. Note: A 5°F or greater variation between sensors of a paired set, or erratic variations or outright failure of a sensor shall be brought to the attention of the Engineer immediately upon discovery of the problem. At the time of the notification, the Contactor shall provide the Engineer with a course of corrective action for approval. If the approved corrective action requires that the data from one sensor in a pair no longer be used, the other functioning sensor shall be used solely for the peak and maximum differential temperature measurements . From the concrete batched for the mock-up, the Contractor shall have tests conducted for air content (AASHTO T152), placement temperature (ASTM C1064, unit weight (AASHTO T121) and fabricate cylinders (per AASHTO T23) from the same concrete by an ACI Certified Concrete Field Technician Level I. The cylinders shall be tested for compression strength by an AASHTO Accredited independent concrete testing laboratory (AASHTO T22) at 3,7, 14, 28, and 56 days. The Contractor shall coordinate the mock-up with the Engineer, and shall provide the State at least one week advance notice of the casting date. The Engineer shall be provided the opportunity to witness the placement and functioning of temperature recording sensors prior to casting, and may perform concrete property tests on companion samples selected by the Engineer. If a mix design has been approved for mass concrete placement prior to the scheduled first placement for this project and the testing confor ms to these standards, the Engineer may waive the requirement of Subsection 607.03.1(a.1) through 607.03.1(a.6) . However, any requirements for testing/analysis added after the aforementioned mix design was approved shall still be performed, with the exception that mix designs previous ly approved using data derived from semi-adiabatic testing will not require re-testing per the above requirements. If the approved mix design has already had a mock-up performed previously and the criteria matches that for the applicable temperature control plan, the Engineer may accept the results of the previous mock-up instead of running a new one. A letter report documenting the concrete properties and temperatures developed in the mock-up compared against the thermal analysis contained in the General Mass Concrete General Temperature Control Plan models shall be submitt ed as part of the General Temperature Control Plan. Any revisions/corrections required to the General Mass Concrete Temperature Control Plan for differing ambient conditions shall be outlined in the letter report. Strength results may be submitted separately. If the project involves four or less unique mass concrete placement designs, the Engineer may waive the requirement for a General Mass Concrete Temperature Control Plan. If waived, the Specific Mass Concrete Temperature Control Plans shall meet all of the requirements listed above.
b.Specific Mass Concrete Temperature Control Plans . Each Specific Concrete Temperature Control Plan shall include the following:
1.Form and form liner R-value and anticipated time of form removal.
2.Insulating material(s) R-value and anticipated periods of use. 6−47
3.Curing procedure and duration.
4.Thermal modeling analysis for typical placement scenarios shall be provided. The analysis shall incorporate, but not be limited to: A range of anticipated ambient placement temperatures, anticipated water temperatures for active cooling, effects of water temperature for placements in water, effects of convection cooling in locations where high winds may be a factor, anticipated concrete placement temperatures, assumed R-values for concrete forms and insulation, and shall calculate maximum core and surface tem peratures vs. time after placement. The impact of planned construction activities, su ch as form removal, shall be included in the analysis. Concrete strength at form removal shall be estimated from the maturity relationship using the lowest calculated maturity value shown by the sensors placed within the concrete.
5.Drawings identifying temperature monito ring locations for each placement, and product data for all sensors and recording instrumentation shall be provided. With the exception of the ambient sensor, the sensors shall be installed in pairs for the redundancy. The minimum number of automated temperature monitoring locations shall be nine (9) per element for placements less than 500 yd 3, and seventeen (17) for placements 500 yd3 or larger. Minimum sensor locations are noted below. Each of the sensors in a pair shall be placed in separate locations, no less than 6” and no more than 18” apart: The relative locations shall be as shown for the mock-ups.
a.Two sensors shall be placed in the center of thermal mass of the placement, where the peak temperature will occur. This location shall be based on the isocurves developed for the model, with the approval of the Engineer. The average of the two will be used to determine the peak temperature at any given time and to measure the maximum temperature differential in the placement based on the difference between the peak temperature and each sensor location at any given time. The average of the two sensors shall be used.
b.Two sensors shall be placed at the location as determined by isocurves developed for the model that shows the point where the lowest temperature is predicted during temperature control. The average of the two sensors shall be used.
c.Two sensors shall be located within one inch from the top surface located directly above the center of thermal mass sensors. This location may be adjusted, based on the isocurves developed for the model, with the approval of the E ngineer. The average of the two sensors shall be used.
d.Two sensors shall be located within one inch from the center of vertical formed surfaces at mid-height. This location may be adjusted, based on the isocurves developed for the model, with the approval of the Engineer. The average of the two sensors shall be used.
e.One sensor shall be used to record the ambient temperature. This sensor shall be placed at approximately ten (10) feet from the placement, in a shaded area.
f.The Contractor shall also provide up to four (4) additional sensor pairs to be located at the discretion of the Engineer.
g.Use similar sensor distribution for placements greater than 500 yd 3. Note: A 5°F or greater variation between sensors of a paired set, or erratic variations or outright failure of a sensor shall be brought to the attention of the Engineer immediately upon 6−48 discovery of the problem. At the time of the notification, the Contactor shall provide the Engineer with a course of corrective action for approval. If the approved corrective action requires that the data from one sensor in a pair no longer be used, the other functioning sensor shall be used solely for the peak and maximum differential temperature measurements. Following a mass concrete pour, the Engineer may require the Contractor to perform thermal modeling analysis of the placement using actual concrete and ambient temperatures to evaluate the effects of construction practices such as, but not limited to, form removal or curing. If required, this shall be performed at no additional cost to the State. Procedures for achieving temperature restrictions including contingencies for severe weather events shall be provided. Procedures may incorporate either active (cooling pipes) or passive control methods (insulation, tenting, venting, etc.) or both. The Temperature Control Plan shall show the expected duration of all temper ature control measures for each model condition provided. If cooling pipes are proposed, submit detailed description of the system describing the layout and size of pipes, anticipated coolant flow rate, temperature of the raw coolant source, pump size, flow and recirculation control equipment, instrumentation, coolant temperature control procedure, and contingency plans.
607.03.2 Performance-Based Variable Temperature Differential Limit. After the Contractor has
established, to the satisfaction of the Engineer, that proper control can be maintained of the concrete mix properties, including curing temperatures, the Contractor shall have the option of submitting a plan to use performance-based criteria for a variable differential limit, based on the concrete strength as determined by the maturity at any given time. This will supersede the 35°F limit. Failure to maintain proper temperature cont rol under this plan will result in reversion to the 35°F limit for subsequent placements until such time that the Contractor demonstrates to the Engineer that causes for the loss of control have been identified and corrected. Temperature control will be considered to have failed if one of the following conditions occurs: • The differential exceeds the variable value by more than 3°F at any time during the first 40 hours after placement. • The differential exceeds the variable value by more than 5°F at any time after the first 40 hours after placement during temperature control. • The differential exceeds the variable value by 2°F or more for any period of 8 hours or more at any time during temperature control. • Cracking of the placement determined to be the result of thermal issues will also be considered to be failure of the temperature control and will result in reversion to the 35°F limit, as well as triggering the provisions specified in Subsection 607.05.4 . Plan Submission Requirements. The Contractor’s written implementation plan shall include complete back-up data such as, but not limited to, listing of all assumptions used in the analysis, published reference documents, coefficient of the thermal expansion for the mix being placed, tensile strength development versus matu rity equations for the mix being placed, elastic modulus versus maturity equations for the mix bei ng placed, example implementation of the method using a predicted thermal gradient analysis and complete test data justifying the prediction equations for the proposed mixture. Each placement shall also include a specific plan with an assumed restraint factor, consideration of the pl acement geometry and other factors that can affect 6−49the differential limit. The other factors shall include, but not be limited to, anticipated concrete placement temperature, ambient temperatures, cooling water temperature (if active cooling is used), convection effects from wind and design elements of the temperature control plan. For acceptable demonstration of the submission of an implementation plan, the Contractor may use a mass concrete pour defined and conducted using the 35°F differential limit. The gradients predicted in the thermal model for the performance-based temperature limit shall match the actual temperatures to the satisfaction of the Engineer. It shall have as a minimum a set of at least eleven temperature/maturity sensors. Locate sensors as follows:
1.At the location of the maximum temperature, at least one sensor shall be placed as defined in Subsection 607.03.1(b.5.a) ;
2.Near the formed surface, at least one sensor shall be placed as defined in Subsection
607.03 1(b.5.b);
3.Near the top surface\, at least one sensor shall be placed as defined in Subsection
607.03 1(b.5.c) ;
4.A minimum of two equally spaced between the location of the maximum temperature and top surface sensor in an approximate straight-line configuration;
5.A minimum of two equally spaced between the location of the maximum temperature and formed surface sensor in an approximate straight-line configuration;
6.At the location of the minimum temperature, at least one sensor shall be placed as defined in Subsection 607.03.1(b.5.d) ;
7.A minimum of two equally spaced between the location of the maximum temperature and the location of the minimum temperature, in an approximate straight-line configuration;
8.One sensor shall be used to record the ambient temperature remote from the placement, as defined in Subsection 607.03.1(b.5.e) . For items 1, 2, 3 and 6, the sensors may be the same as those used for the actual temperature control of the placement as specified in Subsection 607.03.1(b). While redundant sensors are not required, failure at any of the r equired locations without a backup will invalidate the results. The performance-based temperature limit plan sha ll be submitted for approval prior to the first placement for which it is proposed to be used and shall be stamped by a Rhode Island Registered Professional Engineer. Should the plan be approved by the Engineer, this will become the standard sensor distribution for as long as this plan is in effect and shall be used to verify the accuracy of the performance-based temperature limit plan thermal model for each placement. The plan shall show a relationship between the maturity and the appropriate maximum acceptable temperature differential that will prevent cracking of the concrete. The relationship shall be shown in tabular form, at intervals of one (1) °F for the first forty (40) hours after placement and two (2) °F for more than forty (40) hours after placement. to a minimum of fourteen (14) days. The maturity value used to determine the appropriate differential at any given time shall be the lowest measured within the placement.
607.04 CONSTRUCTION METHODS. Applicable construction requirements for SECTION 808;
6−50 CAST-IN-PLACE STRUCTURE CONCRETE MASONRY and SECTION 601; PORTLAND CEMENT CONCRETE shall apply, with the following additions:
607.05 Temperature Control Requirements.
607.05.1 Temperature Control. Mass concrete temperature control shall be monitored by maturity
loggers cast into the concrete, as described in Subsection 607.03.1 . Use of low heat concrete mixtures, pre-cooling of the concrete, insulated curing blankets, insulated forms, cooling pipes, and other measures may be necessary to satisfy the temperature control requirements. The Contractor shall notify the Engineer immediately when temperature control limits are exceeded. Complete concrete temperature records for each placement including the secure files generated by the automated temperature sensors shall be provided to the Engineer. The Engineer shall be provided unobstructed access to temperature sensors at any time to verify compliance with temperature control criteria.
a.When forms are placed in water, the forms and insulation shall be waterproof or otherwise protected against water absorption. The required combined form and insulation R-Value shall be determined through thermal analysis prior to placement using forecasted temperatures to meet the requirements to maintain the maximum peak and differential temperatures within the limits defined in its specification.
b.The temperature of the concrete at placement must not exceed 65°F for cold weather placements, nor 85°F for hot weather placements, unless active temperature control precautions are employed. All active temperature control piping shall be non-metallic and shall be filled with a non-shrink grout on the RIDOT Approved Products List upon completion of cooling operations. The temperature of the concrete at placement sha ll be within the acceptable range of values shown in the temperature control plan for the structural element.
c.Temperature sensors shall be maturity loggers as described in Subsection 607.02.2 . The logger shall be programmed with the appropriate datum temperature.
d.Wiring for loggers that must be cast into the concrete shall be secured to reinforcing or otherwise protected to prevent damage during concrete placement. The method of protection of the wires cast into the concrete shall be approved by the Engineer and shall use methods satisfactory to the Engineer. Wiring for loggers shall be clearly labeled to identify the location within the form at both ends before being placed into the form. Ambient temperature sensors shall be located no closer than 10 feet from the Mass Concrete Placement and shall be placed as to provide an accurate measurement of the environmental condition. Wire runs outside of concrete shall be encased in conduit where necessary to prevent damage during subsequent construction operations.
e.The Contractor shall not perform installa tion and verification checks for operation of any loggers unless the Engineer is present. The Contractor shall provide as-built versions of the temperature control plans showing the location of the loggers as identified by the unique serial numbers. Upon completion of monitoring all visible wires shall be removed from the concrete and any conduit penetrations filled with a non-shrink grout on the RIDOT Approved Product List.
Source: Rhode Island Standard Specifications (Bluebook), 2024 Edition. Pages 295–302 of 826.