The Table of Contents for this section is available.
(A) General:
Fine aggregate shall consist of natural sand or manufactured sand having clean, durable, hard, uncoated particles, or other inert materials having similar characteristics. Manufactured sand shall be produced from fractured stone material. Fine aggregate shall be free from dirt, wood, paper, burlap, and all other foreign material.
The aggregates shall be stockpiled either at the producer's plant or at the batch plant site for at least 24 hours before being used in the concrete, in order to permit excess water to drain and the moisture content to become uniform. No new material shall be added to the stockpile during the 24 hour period. When the aggregates have a low and uniform moisture content and the consistency of the concrete can be satisfactorily controlled without stockpiling the aggregates for 24 hours, the minimum stockpiling period may be reduced or waived entirely by the Engineer.
The Division of Highways' list of approved sources of fine aggregate shows the fineness modulus of each aggregate as established by the producer. Fine aggregate having a fineness modulus varying more than 0.2 from the established value shall not be used until appropriate adjustments in the concrete mix proportions are made. Blending fine aggregates to obtain the required gradation will be permitted, provided test results of each aggregate meet the durability requirements and test results of the combination indicate acceptable quality. Blending shall be accomplished by weighing separately at the time of batching or by other means acceptable to the Engineer.
(B) Soundness:
When subjected to 5 cycles of the soundness test the weighted average loss shall be not more than 15 percent.
(C) Deleterious Substances:
The amount of deleterious substances shall not exceed the following:
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| 2.0 by weight (Natural sand) | |
| 1.0 by weight (Manufactured sand) |
The percentage of deleterious substances will be determined in accordance with AASHTO T112.
(D) Organic Impurities:
The color of each source of fine aggregate will be determined annually in accordance with AASHTO T21. Should the fine aggregate show a darker color than that of samples previously approved from the same source, its use shall be withheld until tests acceptable to the Engineer have been made to determine whether the quality of sand is still acceptable.
(E) Mortar Strength:
All fine aggregate, except fine aggregate to be used in concrete for portland cement concrete pavement, shall meet the requirements of this subarticle.
Mortar made with the fine aggregate shall have a compressive strength at the age of 3 and 7 days using Type III portland cement, or 7 and 28 days using Type I or II portland cement, of not less than 95 percent of that developed by a comparison mortar. The comparison mortar shall be made of the same cement and graded Ottawa sand with a fineness modulus of 2.40 plus or minus 0.05. It shall have the same water-cement ratio and consistency as the test mortar. Testing of the mortar strength will be done in accordance with AASHTO T71 modified to provide for comparison mortar using graded Ottawa sand meeting the above requirements.
Fine aggregate failing to meet the requirements of the preceding paragraph for structural strength may be used with the approval of the Engineer, provided that when tested in concrete cylinders the resultant concrete at 14 days is found to have equal or better strength than cylinders made with an identical mix using an acceptable sand.
(F) Gradation:
Natural sand shall meet the gradation requirements for standard size No. 2S fine aggregate.
Manufactured sand shall meet the gradation requirements for standard size No. 2MS fine aggregate.
(G) Blending Manufactured Sand:
Manufactured sand may be blended with natural sand or another manufactured sand by weighing separately at the time of batching or by other means acceptable to the Engineer. The blended sand shall meet the gradation requirements for No. 2MS fine aggregate. Natural sand used in the blend shall not contain more than 3 percent passing the No. 200 sieve. Manufactured sand used in the blend shall not contain more than 8 percent passing the No. 200 sieve.
(H) Siliceous Particle Content:
Manufactured sand shall have a siliceous particle content of not less than 25 percent when used in concrete surfaces exposed to traffic. The siliceous particle content will be determined by NCDOT Chemical Procedure C-9. Copies of this test procedure are available upon request from the Materials and Tests Unit.
(A) General:
Coarse aggregate shall consist of crushed stone, crushed or uncrushed gravel, crushed air-cooled blast furnace slag, or other inert materials having similar characteristics. Washing to remove clay, loam, dust, and similar adherent materials will be required for all coarse aggregate for portland cement concrete unless otherwise permitted by the Engineer in writing. Coarse aggregate shall be free from dirt, wood, paper, burlap, and all other foreign material.
The aggregates shall be stockpiled either at the producer's plant or at the batch plant site for at least 24 hours before being used in the concrete in order to permit excess water to drain and the moisture content to become uniform. No new material shall be added to the stockpile during the 24 hour period. Where the aggregates have a low and uniform moisture content and the consistency of the concrete can be satisfactorily controlled without stockpiling the aggregates for 24 hours, the minimum stockpiling period may be reduced or waived entirely by the Engineer.
Coarse aggregate from different sources shall not be mixed, nor shall it be used in alternate batches, except where permitted by the Engineer in writing. Blending of coarse aggregates to obtain the required gradation will be permitted provided the different sizes are from the same source. Blending shall be accomplished by weighing separately at the time of batching or by other means acceptable to the Engineer.
(B) Soundness:
When subjected to 5 cycles of the soundness test the weighted average loss shall be not more than 15 percent.
(C) Deleterious Substances:
The amount of deleterious substances shall not exceed the following:
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The percentage of deleterious substances will be determined in accordance with AASHTO T112.
(D) Resistance to Abrasion:
Crushed stone or gravel shall have a percentage wear of not more than 55 percent.
(E) Aggregate Sizes:
(1) General:
The Contractor may, at his option, use either standard size No. 57 or No. 67 coarse aggregate in Class AA, A, B, or S concrete, unless otherwise indicated in the contract. Standard size No. 78M may also be used in any of these classes where so permitted by the Engineer. The Contractor shall use standard size No. 78M aggregate in Class M concrete.
(2) Machine Placed Curb, Curb and Gutter, and Paved Ditch:
The Contractor shall use standard size No. 78M coarse aggregate in concrete for machine placed curb, curb and gutter, and paved ditch.
(3) Prestressed and Precast Concrete:
All coarse aggregate used in prestressed and precast concrete shall pass a 1 inch sieve.
(4) Use of More Than One Size:
All concrete used in a single component of any structure shall be made with the same size aggregate.
(5) Portland Cement Concrete Pavement:
The Contractor shall use standard size No. 57M coarse aggregate
in concrete for portland cement concrete pavement unless otherwise
approved by the Engineer.