South Carolina - Asphalt Paving

Key Concepts

Compaction tests - Standard Proctor (ASTM D-698 / AASHTO T 99): a 5.5-lb rammer with a 2-in. circular base dropped 25 times from 12 in. onto each of three equal layers in a cylindrical steel mold with a 4.0-in. inside diameter and 4.59-in. height (Construction Equipment Guide, Ch. 5, COMPACTION TESTS; Construction Planning, Equipment, and Methods 9th ed., pp. 181–182). - Modified Proctor (ASTM D-1557 / AASHTO T 180): a 10-lb rammer dropped 18 in. on each of five equal layers, applying approximately five times greater energy than the standard test (Construction Equipment Guide, Ch. 5, COMPACTION TESTS).

Equipment selection by material - Smooth-drum vibratory rollers: semi-cohesive soils with up to about 10% of the material having a PI of 5 or greater (Construction Equipment Guide, Ch. 5, Smooth-Drum Vibratory Soil Compactors). - Padded-drum vibratory soil compactors: effective with up to 50% of the material having a PI of 5 or greater (CPEM 9th ed., p. 213). - Pneumatic rollers: the four parameters needed to determine compacting ability are wheel load, tire size, tire ply, and tire inflation pressure. Because contact area varies with air pressure, total weight or weight per wheel is not a satisfactory indicator (CPEM 9th ed., p. 217). - Tamping/tamping-foot rollers: working speed 8 to 12 mph; generally two to three passes on an 8- to 12-in. lift; four passes may be needed in poorly-graded plastic…

Key Concepts

Prime and tack coats - Before laying HMA on existing pavement or unsealed surface treatment, uniformly apply tack coat with distributor spray bars at 0.05 to 0.15 gal/sy (SC-T-86); lesser amounts on new pavements, greater on older. All nozzles fully open and turned at the same angle to the spray bar, approximately 30 degrees; existing surface must be dry and thoroughly cleaned (SCDOT 401.4.18, p. 209). - A prime coat is not required when HMA is placed directly on the subgrade (401.4.18). - Normal prime application: 0.20 to 0.60 gal/sy, penetrating to fill base voids and act as a waterproof barrier (CPEM 9th ed., p. 728). Tack: 0.03 to 0.06 gal/sy of residual asphalt cement; too heavy causes layers to creep (p. 729). Seal coats: 0.10 to 0.20 gal/sy. - Elevated spray-bar nozzles are set 15 to 30 degrees from the horizontal axis of the spray bar so fans do not intermix (CPEM pp. 727–728).

Single asphalt surface treatment sequence (SCDOT 406.4.4, p. 233): clean surface → apply CRS-2P at 0.28–0.35 gal/sy → immediately spread Aggregate No. 789 at 15–20 lbs/sy (No. 89M 12–15 lbs/sy; lightweight 6–12 lbs/sy) → roll with pneumatic rollers in tandem → roll until aggregate firmly seated → remove excess aggregate.

Key Concepts

Pavement courses. The asphalt structure generally consists of two or more courses: a surface (top or riding) course and underlying binder course(s); a binder course is placed between the base and surface courses. A friction course is the top surface layer, usually less than 1 in. thick, to improve skid resistance and smoothness. A leveling course is placed over a distressed roadway or unbound base to improve profile prior to resurfacing (CPEM 9th ed., Chapter 14 glossary, Pages 689–691).

SCDOT course designations. HMA Intermediate Course is furnished and paid for as Type A, Type B, or Type C (Subsections 402.5 and 402.6, Pages 218–219). HMA Surface Course designations under Section 403 are Types A, B, CM, C, D, and E. If included in the Contract, HMA Surface Course Type C or D is used for Ditch Paving (Subsection 403.2.2, Page 220).

Binder content by base course type. Asphalt Base Course Types A and B: percent asphalt binder in the total mixture usually ranges from 4.0% to 5.5% (Subsection 310.2.4, Page 186). Asphalt Base Course Type C: 4.3% to 5.7% (Subsection 309.2.3); its screenings must pass a ½-inch sieve with a minimum of 90% passing the No. 4 sieve (Subsection 309.2.2.2, Page 182).

South Carolina — Asphalt Paving

Key Concepts

Making liquid asphalt (CPEM p. 702) - Two methods reduce asphalt cement to a liquid state: cutbacks and emulsions. - A cutback is a blend of asphalt cement and a fuel product; rapid, medium, and slow cure cutbacks are formulated by diluting with a petroleum thinner such as gasoline, naphtha, diesel, or fuel oil. Environmental concerns over volatile organic compounds have diminished their use. - Emulsions are produced using a colloidal mill to break asphalt cement into very fine "globules." The globules are introduced into water that has been treated with an emulsifying agent — a soap-like material that keeps the globules suspended. Emulsions have largely displaced cutbacks due to cost, safety, and environmental concerns. - Of the many AASHTO grades, SS-1 and SS-1h are the predominant asphalt emulsions used for prime and tack coats.

Primary applications of emulsion asphalt cements (CPEM p. 703) Prime coats, tack coats, and binder for surface treatments, slurry seals, and cold patch materials. For prime and tack coats and surface treatments, the binder is applied by spraying with a distributor truck. (Hot-mix asphalt concrete uses heated asphalt cement, not emulsion.)

Key Concepts

Full-depth HMA patching (SCDOT 401.4.14, p. 208). Remove deteriorated pavement to the width/length determined by the RCE with the face of the cut straight and vertical. Minimum patch size 6 ft × 6 ft, with at least 25 ft between patches. If unstable material is found below the plan depth, remove more as directed and backfill with material meeting Section 305, Graded Aggregate Base, compacted in layers not exceeding 4 inches with vibratory compactors. Thoroughly tack the sides of the existing pavement, then place patch material in layers not exceeding 3 inches, compacting each layer with a vibratory compactor and pneumatic roller. Patches are opened and filled the same day, with the roadway opened to traffic late that same day. Do not apply mixture on a wet or frozen surface.

Milling and planing (SCDOT 401.4.12 and 401.4.13). Establish the longitudinal profile of the milled surface with a skid sensor on the side of the cut; clean the milled surface of all loose particles and tie into drives and intersections. For planing: build a test section of at least 500 feet first; create a corduroy texture with grooves spaced no greater than 0.2 inches center to center; maximum depth high to low on the planed surface is ⅛ inch; extra planing for small depressed areas is not required if those un-textured areas total **no more than 5% of the total treated…

Key Concepts

Mixture proportioning and w/cm - When SCMs are used, w/cm = weight of water ÷ total weight of all cementitious materials (portland cement, fly ash, ground slag, silica fume). Worked example from the source: 270 lb water ÷ (425 lb cement + 125 lb fly ash) = 0.49 (Page 36). - Exposure category W1 — concrete in contact with water where low permeability is required: maximum w/cm 0.50, minimum compressive strength 4000 psi (28 MPa) (Table 2.5, Page 24). - Rule of thumb: adding 1 gal of water per cubic yard increases slump about 1 in. and reduces compressive strength about 150 psi (1.0 MPa), plus increased shrinkage (Page 24). - Most specifications allow only one addition of water, limited so slump stays within the specified range without exceeding the w/cm; follow with 30 revolutions of the drum at mixing speed (Chapter 11, Page 174).

Aggregates - Maximum size coarse aggregate is limited to the least of: one-fifth the narrowest dimension between form sides, three-quarters the space between reinforcing bars, or one-third the depth of a slab-on-ground (Page 18). - Lightweight aggregate when saturated holds water equal to 30 to 35 percent of its dry weight; presoak to 70 to 80 percent of total absorption. Slump loss greater than 2 in. during pumping indicates inadequate presoaking (Chapter 11, Pumping Lightweight Concrete).