2013 Spec Change Summary Concrete - Minnesota Department of ...

Minnesota Department of Transportation
Office of Materials & Road Research
1400 Gervais Avenue, MS 645
Maplewood, MN 55109
Memo
TO:
Resident Engineers, Materials Engineers, and State Aid Engineers
FROM:
Maria Masten, Concrete Engineer
DATE: March 5, 2013
SUBJECT:
2013 Concrete Specification Change Highlights
The concrete related specifications for the 2013 construction year have been completed and are
available on Special Provisions Office website, www.dot.state.mn.us/pre-letting/prov/pdf/sp2005.pdf.
Special Provisions Office started inserting the new specifications in MnDOT Contracts beginning with
the January letting. Specification 2301 and 2461 have deleted the 2005 spec book in their entirety and
been replaced with a Special Provisions.
Please share with Project Engineers/Supervisors, Construction Inspectors and Lab Personnel. Feel free
to contact me if you have any questions.
New/Updated Computerized Speadsheets for 2013
• Concrete Ready-Mix Plant QC Workbook
• Concrete Ready-Mix Plant QA Workbook
• Weekly Report of Low Slump Concrete Overlays
• Concrete Mix Design Request Form
• Weekly Concrete Report
• Concrete Pavement Rehab Weekly Report – Tracks repair pay quantities – Coming soon
• Gradation Testing for Contractor Designed 3U18 (Not pre-bagged) – Coming soon
Prior to doing work on a project, be sure and download all the spreadsheets from the website. Do not
use previous spreadsheets in case they have changed.
http://www.dot.state.mn.us/materials/concreteforms.html
http://www.dot.state.mn.us/materials/concretemixdesigns.html
2013 Changes to Schedule of Materials Control
I have included a separate attachment copy with the highlighted changes for concrete. There are 3
major changes:
• Cementitious and admixture samples will be taken when certifying a ready-mix plant each
construction season.
• Producer gradations have been reduced to 1 coarse and 1 fine gradation per 200 cubic yards
• Testing requirements for paving out of a certified ready-mix plant have been clarified
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2013 Concrete Spec Changes
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2301 Concrete Pavement Changes
2301.3.A.6 MIT-SCAN T2 Non-Destructive Testing Device
The Contractor shall furnish a MIT-SCAN T2 non-destructive testing device having the ability
to measure the location of concrete reinforcement, dowel bars and concrete pavement thickness in a
single device. Agency and Contractor personnel shall mutually use this non-destructive testing device
several times a day during concrete pavement construction.
The Contractor shall perform the following in the hardened concrete:
(1) For transverse joints the entire paved width
(1.1) On first day, Scan one joint out of every five joints to verify dowel bar alignment and
process.
(1.2) If first day is acceptable, scan one joint out of every 500 feet as well as scan one joint
out of every five joints on a 500 foot random segment each day for the remainder of
the project.
(1.3) If a joint is found to have dowel bars out of acceptable alignment tolerances, scan
joints on both sides until alignments meets acceptable tolerances.
(2) For longitudinal L1T joints
(2.1) On first day, scan 75 feet out of every 1000 feet, as well as scan one 500 foot random
segment, to verify tie bar alignment and process.
(2.2) If first day is acceptable, scan 75 feet out of every 5000 feet as well as scan one 500
foot random segment each day for the remainder of the project.
(2.3) If a panel is found to have 2 or more tie bars missing or out of acceptable alignment
tolerances, scan joints on both ends until 5 consecutive panels meets acceptable
alignment tolerances.
Contact the Concrete Engineer for recommendations if alignment tolerances are not met.
Agency observations do not relieve the Contractor of the requirement to properly place the
concrete reinforcement and dowel bars as shown in the plans. In addition, the Department reserves the
right to reject the pavement in accordance with 1503, “Conformity with Plans and Specifications” and
1512, “Unacceptable and Unauthorized Work.”
The Engineer will not provide additional payment for furnishing the above equipment for the
Department's use.
Comments on spec change: The Contractor’s felt we were asking for more testing from them
than was necessary. They proposed a minimum testing rate on the hardened concrete and this is
the final resolution. We still reserve the right to test more and the Concrete Unit has 4 MIT-
Scan T2’s that can be used during 2013 construction.
2301.3.E.2 Concrete Ingredient Summaries
If delivering bulk cementitious materials directly to the concrete batching plant in railroad cars or
sealed transport trucks, submit copies of the bill of ladings to the Engineer on the same day received
from the transporting company.
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2013 Concrete Spec Changes
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Advise the Engineer of the method and schedule of cementitious material unloading. Do not
unload cementitious materials until the Engineer approves the operation.
Each day of concrete pavement production, provide the Engineer with a production summary in an
electronic format that includes the following:
(1) Daily total concrete produced in cubic yards for each concrete mixture type.
(2) Daily total ingredient quantities (aggregate, cementitious and water) including the percent
overrun/underrun.
The Contractor shall provide final project total quantities for (1) and (2) to the Engineer at the end
of the Project.
Comments on spec change: We have deleted the requirement for Contractor cement cut-offs.
We will use the daily material summaries for verification of materials, printed from the batch
plant computer.
2301.3.F.2 Air Content
Maintain the air content of Type 3 paving concrete at the specified target of 7.0 percent
±1.5 percent of the measured volume of the plastic concrete before consolidation in accordance 1503,
“Conformity with Contract Documents.”
Comments on spec change: Clarified the Target Air Content of 7% for paving is BEFORE
CONSOLIDATION. The Air Content after the Air Loss Correction Factor (ACF) needs to be
maintained above 5.5%. For example, if the air content before consolidation was 7% and the air
content behind the paver was 5% using an ACF of 2%, the Contractor would be required to
increase the air content before consolidation to a minimum of 7.5%.
2301.3.I.1 Pavement Texture
The Engineer will provide the Contractor with the locations using a random number multiplied by
length of the sublot within 24 hours of pavement placement.
Comments on spec change: The industry requested adding a timeframe for getting random
numbers for sand patch testing from the Agency.
Complete surface texture testing no later than 48 h after pavement placement unless otherwise
approved by the Engineer. Refer to Table 2301-13 for the acceptance criteria of texture depths below
the specification limits. If the Engineer determines by visual inspection, that areas not represented by
random testing appear to not meet the minimum requirements of Table 2301-13, the Engineer reserves
the right to require additional testing in those specific areas to determine compliance.
Comments on spec change: Changed surface texture testing requirement to within 48 hours.
Added language that more clearly allowed the Engineer to direct spot testing if texture is
suspect.
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2013 Concrete Spec Changes
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2461 Structural Concrete Changes
2461.2.E
Concrete Admixtures
The Contractor may use the following admixtures listed on the Approved/Qualified Products List:
(1) Type A, “Water Reducing and Mid Range Water Reducing Admixtures,”
(2) Type B, “Admixtures Identified as Hydration Stabilizers,”
(3) Type D, “Water Reducing and Retarding Admixtures”
(4) Type S, “Viscosity Modifying Admixtures.”
Use of any other admixtures in the concrete requires approval of the Concrete Engineer unless
otherwise required by or allowed in the Contract.
When incorporating admixtures into the concrete:
(1) Use admixture dosage rates recommended by the manufacturer.
(2) Add all admixtures at the plant.
(3) Provide admixture additions at the job site that are the same products as originally
incorporated into the mix.
(4) Use calcium chloride in concrete as approved by the Engineer, in conjunction with the
Concrete Engineer. Do not use calcium chloride in units containing prestressing steel or in
bridge superstructure concrete.
Comments on spec change: In January of 2012, we started allowing the Contractor to use Type
D admixtures at their discretion. This is in addition to allowing Type A, B, and S admixtures as
described above. We also require all admixtures be added at the plant unless the Contract
allows otherwise. Some contracts allow other admixtures – refer to your Contract.
2461.2.F.2
Contractor Designed
Design the concrete mix based on an absolute volume of 27.00 cu. ft ± 0.10 cu. ft [1.000 cu. m ±
0.003 cu. m] for the following:
(1) Concrete paving mixes in accordance with 2301, “Concrete Pavement;”
(2) Concrete mixes with an anticipated or required 28-day compressive strength of at least
5,000 psi [34 MPa];
(3) Precast concrete in accordance with 2405, “Prestressed Concrete Beams,” 2412, “Precast
Concrete Box Culverts,” 3236, “Reinforced Concrete Pipe,” 3238, “Precast Concrete Box
Culverts,” 3621, “Concrete Masonry Units,” 3622, “Sectional Concrete Manhole and Catch
Basin Units,” and 3630, “Precast Concrete Median Barriers;”
(4) Colored concrete;
(5) Stamped concrete;
(6) Cellular Concrete Grout – Controlled Low Strength Material (CLSM);
(7) Extended Delivery Times Beyond 90 minutes; and
(8) Concrete as otherwise required by the contract.
Comments on spec change: MnDOT will continue to design all mixes unless otherwise specified
in the Contract or included in this list.
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2013 Concrete Spec Changes
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2461.3.F.3
Certified Ready-Mix Plant Program
Complete all concrete plant documentation utilizing the Concrete Ready-mix Plant QC Workbook
available from the MnDOT Concrete Engineering website. Electronically submit the QC Workbook to
the Engineer by the Tuesday immediately following the previous week’s production.
Comments on spec change: Added requirement for QC Producer to use computerized
spreadsheets and email all workbooks to the Engineer weekly during production.
2461.3.G.3 Delivery Requirements
Place concrete into the work in accordance with the following:
(1) Type 1 Concrete—within 90 min of batching, and
(2) Type 3 Concrete— within 90 minutes of batching when all admixtures are added at the plant at
the manufacturer’s recommended dosage rates listed on the Approved Products list. If the haul
time does not facilitate mixing and placing the concrete within 90 minutes, test the concrete in
accordance with 2461.3E1a.
The Contractor may transport Type 3 concrete in non-agitating equipment if the concrete is
discharged within 45 min of batching.
Batch time starts when the batch plant or the transit mix truck adds the cement to the other batch
materials.
Comments on spec change: In January of 2012, we modified the specifications to allow all
concrete to be placed within 90 minutes of batching.
2461.3.G.4
Field Adjustments
Do not add additional mixing water once the concrete is 60 min old.
Comments on spec change: Unwritten rule is we will allow up to 2 gallons of water additional
for field admixture adjustments.
Mix the load a minimum of 5 minutes or 50 revolutions at mixing speed after addition of any
admixture.
Comments on spec change: There is no longer a maximum of 150 revolutions at mixing speed.
For concrete with slumps of greater than 1 inch (25 mm) do not make water adjustments after
approximately 1 cubic yard (1 m 3 ) is discharged.
For concrete with slumps of 1 inch (25 mm) or less, the Engineer will allow water adjustments as
necessary to facilitate placement.
Comments on spec change: For example, we anticipate the Contractor making water
adjustments throughout the pour for Slipform Barrier providing the mix design allows
additional water.
The Engineer will test the concrete for compliance with 2461.3.G.6, “Consistency,” and
2461.3.G.7, “Air Content,” in accordance with the following:
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(1) If the test taken by the Engineer passes, the Engineer will continue verification testing in
accordance with the Schedule of Materials Control.
(2) If the test taken by the Engineer fails, make adjustments and perform any quality control
testing before the Engineer performs a final test. Acceptance or rejection of the truck is based
on the Engineer’s final test result.
(3) The Engineer will test up to two additional trucks in accordance with items (1) and (2) above.
(4) If the concrete does not meet the specification after those three trucks, the Engineer will reduce
their verification testing rate to once per truck for acceptance for the remainder of the pour.
Comments on spec change: Implemented in 2011. Significant changes for Inspector. The
primary focus was eliminating testing every truck multiple times for the Inspector.
Curing Requirements for 2301, 2521, 2531, and 2406
E Concrete Curing and Protection
After completing final finishing operations, cure all exposed concrete surfaces. Use one of the
following curing methods:
(1) Place the membrane curing compound conforming to 3754, “Poly-Alpha Methylstyrene
(AMS) Membrane Curing Compound,” or 3755, “Linseed Oil Membrane Curing Compound,”
within 30 minutes of concrete placement or once the bleed water has dissipated, unless the
Engineer directs otherwise in accordance with 2521.3.E.1.a, “Membrane Curing Method.”
Place the membrane curing compound on the edges within 30 minutes after permanent
removal of the forms or curing blankets, unless the contract requires otherwise.
(2) Place plastic curing blankets or completely saturated burlap curing blankets as soon as
practical without marring the surface in accordance with 2521.3.E.1.b, “Curing Blanket
Method.”
Failure to comply with these provisions will result in the Engineer applying a monetary deduction
in accordance with 1503, “Conformity with Contract Documents,” and 1512, “Unacceptable and
Unauthorized Work.” If the contract does not contain a separate contract item for Structural Concrete,
the Department will apply a monetary deduction of $50.00 per cubic yard ($65.00 per cubic meter) or
50 percent of the Contractor-provided invoice amount for the concrete in question, whichever is less.
Whenever weather conditions are such as to cause unusual or adverse placing and finishing
conditions, expedite the application of a curing method or temporarily suspend the mixing and placing
operations, as the conditions require.
If necessary to remove the coverings to saw joints or perform other required work, and if the
Engineer approves, remove the covering for the minimum time required to complete that work.
E.1 Curing Methods
E.1.a Membrane Curing Method
Before application, agitate the curing compound as received in the shipping container to obtain a
homogenous mixture. Protect membrane curing compounds from freezing before application. Handle
and apply the membrane curing compound in accordance with the manufacturer’s recommendations.
Apply the curing compound with an approved airless spraying machine in accordance with the
following:
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(1) At a rate of 1 gal per 150 sq. ft (1 L per 4 m²) of surface curing area.
(2) Apply homogeneously to provide a uniform solid white opaque coverage on all exposed
concrete surfaces (equal to a white sheet of typing paper). Some Mn/DOT approved curing
compounds may have a base color (i.e. yellow) that cannot comply with the above
requirement. In this case, provide a uniform solid opaque consistency meeting the intent of the
above requirement.
(3) If the curing compound is damaged during the curing period, immediately repair the damaged
area by re-spraying.
The Engineer will approve the airless spraying machine for use if it is equipped with the following:
(1) A re-circulating bypass system that provides for continuous agitation of the reservoir material,
(2) Separate filters for the hose and nozzle, and
(3) Multiple or adjustable nozzle system that provides for variable spray patterns.
If the Engineer determines that the initial or corrective spraying may result in unsatisfactory
curing, the Engineer may require the Contractor to use the blanket curing method, at no additional cost
to the Department.
E.1.b
Curing Blanket Method
After completion of the finishing operations and without marring the concrete, cover the concrete
with curing blankets. Install in a manner that envelops the exposed concrete and prevents loss of water
vapor. After the concrete has cured, apply membrane curing compound to the concrete surfaces that
will remain exposed in the completed work.
E.2 Protection Against Rain
Protect the concrete from damage due to rain. Have available, near the site of the work, materials
for protection of the edges and surface of concrete. Should any damage result, the Engineer will
suspend operations until the Contractor takes corrective action, and may subject the rain-damaged
concrete to 1503, “Conformity with Contract Documents,” and 1512, “Unacceptable and Unauthorized
Work.”
E.3 Protection Against Cold Weather
If the national weather service forecast for the construction area predicts air temperatures of 36 °F
[1 °C] or less within the next 24 h and the Contractor wishes to place concrete, submit a cold weather
protection plans.
Protect the concrete from damage, including freezing due to cold weather. Should any damage
result, the Engineer will suspend operations until the Contractor takes corrective action, and may
subject the damaged concrete to 1503, “Conformity with Contract Documents,” and 1512,
“Unacceptable and Unauthorized Work.”
E.3.a
Cold Weather Protection Plan
Submit a proposed time schedule and plans for cold weather protection of concrete in writing to
the Engineer for acceptance that provides provisions for adequately protecting the concrete during
placement and curing. Do not place concrete until the Engineer accepts the cold weather protection
plans.
Comments on spec change: Implemented in 2011. Significant changes for Inspector and
Contractor – PLEASE REVIEW.
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