minimum of 3 gallons per cubic yard of calcium nitrite solution . The minimum 28 day compressive strength shall be 5,000 psi, unless otherwise state d in the Contract. Material for reinforcing shall meet the requirements of Standar d Specification Section - Reinforcing Steel or Section 709.02 - Welded Steel Wir e Fabric. Only one mat of steel is required for concrete member thicknesses of seven inches or less; two mats of steel, one at each face, are required for con crete member thicknesses greater than seven inches. Grout materials, rapid setting concrete patching materials, and geotextiles shall be one of the products listed on the Department's Qualified Products List (QPL). Quality Control and Quality Assura nce Quality Control (QC) is the responsibility of the Contractor. The Quality Control Inspector (QCI) shall inspect all aspects of the work. The Contractor shall generate a nonconformance report (NCR) for materials and/or workmanship that is nonconforming. The NCR shall describe the nonconformance and the proposed corrective action. Copies of the NCR shall be provide d to the Department’s Quality Assurance Inspector (QAI) and the Fabrication Engineer for review. Nonconforming material and/or workmanship shall be corrected or replaced. In the event that an item fabricated under this Specification d oes not meet the Contract requirements but is deemed suitable for use by the Department, it may be accepted in accordance with Section 106.8, Non-Conforming Work, of the Stan dard Specifications. Acceptance is the prerogative of the Department. The Departmen t will conduct Quality Assurance (QA) in accordance with Standard Specification Subsection 106.5. Testing deemed necessary by the Department that is in addition to the m inimum testing requirements will be scheduled to minimize interference with th e production schedule. The QAI will perform acceptance sampling and testing and will witne ss or review documentation, workmanship and testing to assure the Work is be ing performed in accordance with the Contract Documents.
The QAI has the authority to reject materials and products that do not meet the Contract requirements, including Work rejected due to denial of access o r the lack of adequate notice of the beginning of production. The acceptance of material or workmanship by the QAI will not prevent subsequent rejection, if the Work is later found to be unacceptable. The Contractor shall provide a private office at the fabricatio n plant for the QAI in accordance with the Facilities for Inspection requirements in S tandard Specification Section 535. Construction The precast units shall be manufactured at a faci lity that has had a minimum of five years of experience in producing similar type p roducts. The plant shall meet the requirements of AASHTO M-157. Facilities that are cer tified by the Precast/Prestressed Concrete Institute (PCI) or the National Pr ecast Concrete Association
The Contractor shall notify the Department of the planned start of production date of the precast units a minimum of two weeks prior to beginning production for in-Maine work and a minimum of three weeks prior to beginning production for out- of-Maine work. If the production schedule changes, notify the Fabrication Engineer no less than three Working Days prior to the initial production start-up date. Any Work d one without the QAI present will be rejected. Advise the F abrication Engineer of the produ ction schedule and any
changes to it. If Work is suspended on a project, the Fabrication Engineer will require 72 hours of notice prior to the resumption of Work. The Contractor shall calibrate all production equipment on the following schedule, unless there is reason to believe calibration should be performed sooner: Water gauges- every 90 days; admixture dispensers- every 90 days; concrete cy linder compression testing machine- annually; batch plant scales- every six months. Us e proving rings, load cells and solid standard weights, as applicable. The calibration shall b e performed by a testing laboratory acceptable to the Department, using calibration equi pment the accuracy of which is traceable to a National Institute of Standards and Technolog y (NIST) standard. Provide calibration certifications to the QAI prior to beginning fabric ation. All precast members for a distinct system or Contract Pay Item, including end blocks, steps, caps, box culverts, arch sections, wall units, or other elements, shall be manufactured from the same material sources of aggregates, brand and type of cement and color pigment. Gradations of coarse and fine aggregates shall be furnished to the QAI prior to beginning work and at least once per week thereafter. Concrete mix designs shall be submitted for review and approval by the Department prior to use. Reinforcing steel shall be fabricated, handled, and placed in a ccordance with Standard Specification Section 503, Reinfor cing Steel, and the reviewed Working Drawings. Forms shall be sufficiently rigid and accurate to maintain the member's dimensions. All forms shall be well built, substantial and unyielding, securely braced, strutted and tied to prevent motion and distortion while concrete is being placed in them. Corners within the forms shall be fitted with consistent width chamfer strips of 5 /8 inch ± 1/8 inch mitered at their intersections; all exposed corners shall be chamfered. F orms shall be treated with a bond breaking agent; they shall be clean and free of foreign ma terial. Recess metal inserts and form ties a minimum of one inch, unless noted otherwise in the Contract. The QAI is not responsible for verifying the locatio n of inserts or other hardware installed for the convenience of the Contractor. Curing The units shall be cured by one of the following methods:
of the Precast/Prestressed Concrete Institute Manual for Qualit y Control for Plants and Production of Structural Precast Concrete Products (MNL 116 ), Section 4.20. Moist cure the concrete until it has reached design strength.
Do not use membrane-forming curing compounds without the approval of the Fabrication Engineer. If membrane-forming curing compounds are authorized, follow the requirements of MNL 116 and the curing compound manu facturer’s published recommendations.
Section 4.19, except as modified herein.
After initial set, the temperature gain of the concrete shall n ot exceed 40 F per hour. Initial set shall be determined in accordance with ASTM C403, Standard Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance; a strength gain of 500 psi indicates initial set. The maximum all owable concrete temperature shall be 160 F. Concrete temperature shall be measured during curing with recording thermometers. In order to qualify for accelerated cure, the concrete temperature shall attain a minimum temperature of 120 F; that temperature shall be maintained for a minimum of 8 hours and the concrete shall achi eve a minimum of 80 percent of design strength.
The accelerated curing cycle shall be considered complete when the method of supplying heat is stopped and/or the concrete temperature drops below 120°F. Two cylinders shall be tested immediately upon completion of the ac celerated cure cycle. Products that have not achieved all of the above criter ia shall be moist cured until the concrete has achieved design strength.
If the precast units have achieved 80 percent of design strengt h during the accelerated curing cycle, no further curing will be required. The forms shall remain in place until the concrete attains a mi nimum compressive strength of 3,000 psi. Concrete Testing Acceptance of structural precast units, for e ach day’s production, will be determined by the Department, based on compliance with this specification and satisfactory concrete testing results. At least once per week, the QAI will make 2 concrete cylinders (6 cylinders when the Contract includes permeability requirements) for use by the Dep artment; cylinders shall be standard cured in accordance with AASHTO T23 (ASTM C31). The Q AI will perform entrained air content and slump flow testing, determine water-c ement ratio and determine temperature of the sampled concrete at the time of cylinder cas ting. All testing equipment required by the QAI to perform this testing shall be in accorda nce with Standard Specification Section 502.041, Testing Equipment. In addition, the Contractor shall provide a slump cone meeting the requirements of AASHTO T 119. Providi ng and maintaining testing and curing equipment shall be considered incidental to the work and no additional payment will be made. Quality Control test cylinders shall be made and tested in acc ordance with the following standards: AASHTO T 22 (ASTM C39) Test Met hod for Compressive Strength of Cylindrical Concrete Specimens AASHTO T23 (ASTM C31) Practice for Making and Curing Concrete T est Specimens in Field AASHTO T141 (ASTM C172) Practice for Sampling Freshly Mixed Con crete AASHTO T152 (ASTM C231) Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method