NPCA Staff Report
The NPCA Quality Assurance Committee is dedicated to a continuous improvement plan for the certification program and makes timely and necessary changes each year to answer the never-ending call for higher quality from owners and specifiers across the country. In 2015, we will again raise the bar on quality and move our industry forward with our precast concrete plant certification program.
The latest edition will include many editorial changes and important updates, but perhaps the most significant is the new grading scheme found in the Standardized Grading Tables for all critical sections of the manual. Changes include updates to how critical sections are weighed. According to NPCA Quality Assurance Chairman Richard Alvarado, who is assistant general manager and quality control director for Western Precast Concrete Inc. in El Paso, Texas, updates need to be incorporated into the manual each year to fulfill requirements for continuous improvement and to recognize requests received from DOTs.
“The audit and certification programs are always under review by sources such as the QA Committee, DOTs that require certification, regional specifying agencies and member plants that participate in the programs,” he said. “The system of continuous monitoring directs the evolution of the certification program. It is a living document that changes to meet the ever-changing requirements of the industry.”
Committee member Andy Wieser added that DOTs enjoy seeing a program that challenges precast concrete plants to strive for improvement.
“We believe the new grading schedule will accomplish this,” he said. “To verify to the DOTs that a certified plant will be using approved materials, we will be requiring a third-party testing company to obtain credentials.”
The benefits for maintaining a strong quality control program are that the requirements stand up to the most stringent specification and evolving technologies and practices.
“There will be very little change in the inspection process,” Wieser said. “The inspectors will just be using different grading percentages in the standardized grading tables for critical sections. The scores will be affected very little for some plants and substantially for others.
“All the plants have to do is follow the requirements of the NPCA QC Manual and they will have a positive inspection process.”
“I do encourage anyone who isn’t clear to contact NPCA with questions,” Alvarado added.
Major updates to the NPCA Quality Control Manual for Precast Concrete Plants that will be incorporated into the 12th Edition are shown at right in italics.
5.1.1 Raw Material & Test Records
Records of incoming raw materials and certifications, credentials of third party personnel and calibration records for third party and/or plant owned test equipment shall be kept by the precast plant for a minimum of three (3) years. These records shall at a minimum include the following:
a. Cement mill certificates
b. Aggregate reports
c. Mix water potability or suitability tests
d. Chemical admixture and supplementary cementitious material certifications
e. Reinforcement mill certifications
f. Joint sealant, gasket and connector supplier reports
g. Accessories supplier reports
h. Batching records or ready-mixed concrete delivery tickets
i. Buy America Provisions as required by specific project
j. Certificate of compliance for all lifting inserts
k. Laboratory Accreditation or ACI certificates and test equipment calibration records of any third party firm or testing agency.
126.96.36.199 Independent Third Party Testing Laboratory
Third party laboratories may be accredited to ISO/IEC 17025, or the applicable AASHTO laboratory accreditation.
Plants that employ a third party laboratory for testing and/or calibration services shall, at a minimum, obtain the credentials of personnel performing the testing and the calibration records for the equipment used.
Technicians from a third party laboratory performing plastic concrete testing at the precast facility shall provide a current ACI Field Technician Level I certification. Technicians from a third party laboratory performing compressive strength testing and/or aggregate testing shall provide an appropriate and current ACI certification for the testing being performed along with a current equipment calibration certificate.
Plants subject to owner specific certification and testing requirements shall have appropriate documentation on file for auditor review.
5.2.2 Moisture Content
188.8.131.52 Conventional and/or Dry-Cast Concrete
For conventional and/or dry-cast concrete, aggregate surface moisture content (i.e., water in excess of that absorbed by the aggregates) shall be determined at least once per day in accordance with ASTM C70, “Standard Test Method for Surface Moisture in Fine Aggregate,” by alternate methods such as moisture meters or probes, or by ASTM C566, “Standard Test Method for Total Evaporable Moisture Content of Aggregate by Drying.” Drying aggregate using a microwave or hot plate shall be permitted in addition to using an oven.
For conventional and/or dry-cast processes when aggregate bins fitted with moisture probes or meters, aggregate surface moisture content shall be determined a minimum of once per week in order to validate moisture probe calibration.
184.108.40.206 Self-Consolidating Concrete
For SCC processes when aggregate bins are fitted with moisture probes or meters used with automatic mixing water adjustment systems, the aggregate surface moisture content shall be determined a minimum of once per week in order to validate moisture probe or meter calibration. Moisture tests shall be performed in accordance with ASTM C70, “Standard Test Method for Surface Moisture in Fine Aggregate,” or by ASTM C566, “Standard Test Method for Total Evaporable Moisture Content of Aggregate by Drying.” Drying aggregate using a microwave or hot plate shall be permitted in addition to using an oven. Samples for moisture tests shall be taken as close as possible to the area where the probe is located.
For SCC processes made without moisture probes or meters and automatic mixing water adjustment systems, the aggregate surface moisture content shall be determined at least once a day prior to making the first SCC batch and then once every four hours of elapsed time after the first batch, while SCC is being mixed. Moisture tests shall be performed in accordance with ASTM C70, “Standard Test Method for Surface Moisture in Fine Aggregate,” or by ASTM C566, “Standard Test Method for Total Evaporable Moisture Content of Aggregate by Drying.” Drying aggregate using a microwave or hot plate shall be permitted in addition to using an oven. In addition, Slump Flow and VSI tests shall be performed in accordance with section 220.127.116.11 for every three batches of SCC produced (This is to ensure that moisture fluctuations of aggregates are accounted for correctly). In lieu of this additional Slump Flow and VSI testing, moisture tests may be performed as specified in this section every three batches.