SOURCE APPROVALS FOR AGGREGATES
GENERAL
Written source approval is required for PCC crushed stone, PCC gravel, PCC fine aggregate, and revetment (forms are available at: https://iowadot.gov/construction_materials/Materials-forms or in the appendices of this IM). Only those sources, which can provide aggregates consistently compliant with the applicable specification shall be approved.
For proportioned aggregates, aggregate sources shall not be blended to produce a single stockpile. An aggregate source is defined by an individual A-number. For PCC, approved ledges shall not be blended without written approval.
A. A producer request for source approval shall be made, in writing, to the appropriate District Materials Engineer with a copy to Geology Section, Construction and Materials Bureau in Ames, Iowa.
B. Following documentation of the basis of approval (described below), the District Materials Engineer will respond to the Chief Geologist with supportive evidence and recommendations to:
1. Approve the source
2. Not approve the source, or
3. Request that specific additional information is obtained as a basis for a final decision
C. Upon the signature of the Chief Geologist, the approval will be returned to the District Materials Engineer who will return the signed document to the aggregate producer.
A. Source approvals shall describe, in detail, any physical limitations of the subject source and any special production methods, or restrictions required to produce specification material.
B. Preliminary source approvals may be issued whenever sufficient quality information is available. This will expedite the development of new sources or ledges by establishing the primary quality level without requiring production material to be available. A final source approval will follow only after adequate amounts of compliant material have been produced. Aggregate producers may quote from ledges with preliminary approvals assuming full responsibility for the timely delivery of compliant materials to the projects in question.
C. A new or updated source approval will be required if the aggregate durability of a quarry ledge changes or a new bed grouping is approved. The source approval remains with the source. Any changes in management of the source may be documented by letter and will be recorded in IM T203, with a copy maintained in the District source files and Geology Section of the Materials Laboratory. Changes to production restrictions, resulting from joint producer/District quality control discussions, may also be documented by letter, which will be signed by the producer and the District Materials Engineer. A copy of this letter will be maintained in the District source file and Geology Section of the Materials Laboratory.
D. For crushed stone, the ledges shall contain no more than 5% noncompliant materials within the approved bedding planes. At least 95% of carbonate coarse aggregate particles produced by crushing rock shall be derived from ledges in which the rock complies with the requirements for the durability class for which it is being produced.
E. When processing coarse aggregate for PCC no material larger than the gradation top size may be removed from the product unless allowed by the source approval. When processing multiple PCC products simultaneously, crush to 1.5” nominal before fractionating. Removal of other products may be allowed by the District Materials Engineer if the PCC durability meets or exceeds the original full-face Durability Class and the production method is documented in an amended source approval.
F. Limestone and Dolomite sources greater than 100 miles from the nearest Iowa DOT District Materials Office or area inspection laboratory may not be allowed to furnish aggregate to Iowa DOT projects. These may be considered too distant to provide source monitoring by Department employees as required in Materials IM 209.
The basis of approval shall be by one of three methods or combination of methods:
1. Service History
2. Geologic Correlation
3. Testing
A. Approval by Service History
1. Aggregate will be considered durable when it does not contribute to the premature deterioration in concrete. Durability classes will be assigned on the basis of qualifying performance in air-entrained concrete pavements of appropriate age.
2. Meet the durability requirements of Article 4115.01.
B. Approvals by Geologic Correlation
1. Sources may be approved based on geologic correlation to a source with an established service history.
2. Sources may be approved if there is a satisfactory similarity to any approved source with no aggregate-related deterioration as determined by the Department through pavement coring and petrographic examination.
C. Approvals by Chemical & Physical Testing
Aggregate sources without qualifying performance records or satisfactory similarity to any approved source can be provisionally assigned to a Durability Class based on physical and chemical tests meeting the following requirements:
|
DURABILITY CLASS |
QUALITY |
TEST LIMITS |
TEST METHOD |
|
Class 2 |
Salt susceptibility quality |
Max. 4.5 |
Iowa 223 |
|
|
Secondary Pore Index |
Max. 30 |
Iowa 219 |
|
Class 3 |
Salt susceptibility quality |
Max. 1.5 |
Iowa 223 |
|
|
Secondary Pore Index |
Max. 25 |
Iowa 219 |
|
Class 3i |
Salt susceptibility quality |
Max. 1.0 |
Iowa 223 |
|
|
Secondary Pore Index |
Max. 20 |
Iowa 219 |
NOTE: If there is a discrepancy in classification between Quality Number and Pore Index classification, the source will be assigned to the lower Durability Class.
An approved Portland cement concrete aggregate must have pore index test results of no greater than 25 for a Durability Class 3i and no greater than 30 for a Durability Class 3 or Class 2.
A pore index failure will trigger an investigation of possible changes to ledge quality and if proper ledge control has been maintained. If the ledge has been properly controlled, a second stockpile sample can be obtained and tested. If the second sample fails, the approval may be suspended until complying test results are obtained or a pavement performance review has been performed with results matching the PCC durability class of the source approval.
A. Quality
For Fine Aggregate (glacial sands) for Portland Cement Concrete (4110), meet the requirements in the Table below. Sampling for approval should be a minimum of three samples taken at a frequency of one per 2,000 tons or one per week once the working depth has been established.
|
Fine Aggregate Quality |
Test Limits |
Test Method |
|
Shale and Coal |
2.0% (maximum) |
B. Gradation
The fineness modulus must be no lower than 2.60. A target fineness modulus (or base-line) will be established for each source at the time of approval. The target should be the average of at least 5 Iowa DOT gradations taken at the sampling frequency outlined in Paragraph A. Establishing the target may be supplemented using Producer gradations. Sources with a variation of the fineness modulus of lower than 0.2 and greater than 0.25 from the proposed target will not be approved until the variability is eliminated.
C. The DME may approve a gravel source to allow up to 20 percent crushed particles in the fine aggregate with the concurrence of the Chief Iowa DOT Geologist. This allowance would require a new source approval with a revised target fineness modulus.
Meet the following requirements:
· The proportioning must be through a controlled and measured process.
· The crushed material must be from an approved Class 3 or 3i source with not less than 70 percent igneous and metamorphic particles and meeting the requirements of Article 4115 of the Standard Specifications. The crushed material must be from the same source as the natural fine aggregate.
· The fine aggregate angularity as determined using AASHTO T 304 (modified) may not exceed 40%.
· The crushed fine aggregate must meet Gradation 1 and the fineness modulus restrictions listed in this section.
· The crushed material must be compared to the uncrushed and tested using ASTM C 1260 Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) and shall not exceed the uncrushed results by 0.10% which is the Precision and Bias of the Test Method. Testing must be done by a certified independent laboratory at the expense of the Producer and reported directly to the DOT Testing Engineer.
A. Existing
sources with a fine aggregate approval must establish a target fineness modulus,
as described above. This should be done using Iowa DOT gradations which may be
supplemented with Producer gradations if a correlation exists. Variation from
the target fineness modulus should be monitored by both the aggregate Producer
and Iowa DOT personnel.
B. Variation of the fineness modulus of lower than 0.2 and greater than 0.25 from the target should be investigated. Variability in fineness may result in rejection of the stockpile.
A. Source approvals, written by the appropriate District Materials Engineer, shall be required for limestone, dolomite, and quartzite materials. The source approvals shall identify the ledges and the types of revetment for which they are approved.
B. The basis of approval shall be by one of the three methods stipulated in 4130.01:
1. Service History
2. Test Plot Performance (see Appendix F for construction guidelines)
3. Testing
C. All revetment stone from ledges containing conglomerate or breccia, where the performance history has not been established shall be evaluated using a two-year wet test plot before approval. Conglomerate and breccia shall be defined as any rock that contains clasts (i.e., fragments or pieces) of a pre-existing material.
D. The distribution of approvals will include the producer and the Materials Engineer.
E. The District may place restrictions on the revetment approval prohibiting winter production of revetment.
F. When subsequent performance indicates the source approval to be in error it shall be modified or rescinded as necessary.
G. For Erosion stone or stone for Gabion baskets the only requirements are the stone shall not exceed a maximum C-Freeze test limit of 15 when tested in accordance with Iowa 211 Method C and the abrasion maximum shall not exceed 50% when tested in accordance with AASHTO T96.
H. Material meeting the specifications for any of the revetment classes can be certified for use as Erosion Stone or Gabion stone. Otherwise meet the requirements of Article 4130.03 through 4130.08 as appropriate.
A. Approvals by Service History
1. The source approvals shall document the location, age, and sources of all usage forming the basis of the approvals.
2. The historical usage must conform to the revetment class approved.
B. Approvals by Test Plot Performance
1. Test plots may be of any size that incorporates all beds of the ledge under evaluation.
2. For Class A, B, C, D, and E revetment, the test plots must be constructed in an environment of wetting and drying cycles combined with seasonal freezing and thawing cycles that meet with the approval of the District Materials Engineer.
3. The test plots will be evaluated after two years and shall have no more than 25% of the stones showing cracks or fractures.
C. Approvals by Testing.
1. A record of Alumina Content (Iowa DOT Test Method 222) or freeze and thaw tests (Test Method 211, Method A) and Iowa Pore Index Tests (Test Method 219) should exist such that the District Materials Engineer is assured of reasonable conformance to the specifications. When no record exists, test results may be secured from production samples; ledge samples (block stoning), or samples from rock cores.
2. When the source test plot or service history is not available, the virgin stone shall meet the following requirements on stone crushed to 3/4 inch to 1 1/2inch (19 mm to 37.5 mm) nominal maximum sizes:
|
REVETMENT TYPE |
REVETMENT QUALITY |
TEST LIMITS |
TEST METHOD |
|
|
Alumina |
0.7 |
Iowa 222 |
|
Class A, B, C, and E revetment |
A Freeze |
10 |
Iowa 211, Method A |
|
|
Secondary Pore Index |
25 |
Iowa 219 |
|
Class D revetment |
C Freeze |
10 |
Iowa 211, Method C |
NOTE: Revetment may pass either Alumina or A-Freeze for compliance.
The abrasion loss for all revetment shall not exceed 50% when tested in accordance with AASHTO T96.
A. When appropriate, and after review and concurrence of the Geologist, the District Materials Engineer may establish source approval procedures, including production restrictions.
B. A copy of such source approvals, and any subsequent changes to them, shall be provided to the Geologist in the Construction and Materials Bureau.
C. The District aggregate source files should retain all documentation of materials approved for production, including production equipment, production methods, restrictions, etc.