PRECAST CONCRETE SECTION 612 253 SECTION 612 — PRECAST CONCRETE
612.1Description.
This work consists of providing and installing precast structures and precast, prestressed structures.
612.2Materials.
recommendation.
612.3Construction.
612.3.1 Submittals.
concrete beams. Include the following, as applicable:
positions of embedded items or reinforcement. Show required concrete cover.
PRECAST CONCRETE SECTION 612 254 6. bill of materials including all accessories; and
registered Delaware professional engineer.
Use AASHTO HL93 loading or Delaware legal load, whichever governs.
accordance with the latest version of the AASHTO Manual for Bridge Evaluation.
612.3.2 General Manufacturing Requirements.
and approved by the Department to manufacture the units.
Department to manufacture prestressed primary load carrying members.
storage, transportation, and erection, are subject to the inspection and approval process. Defective construction that may adversely affect the strength of a member or its performance in the bridge structure will result in rejection.
conditioning, lighting, electrical outlets, wireless internet access, bottled drinking water, a desk and chair for each occupant, and a lockable file cabinet for the engineer’s exclusive use.
prestressed units during the process of transporting, unloading, and installing the members. Handle precast units only by lifting devices provided especially for th is purpose. Provide proper dunnage for storing precast units.
612.3.3 Precast Concrete Elements.
associated elements such as footings, headwalls, toewalls, and baffles.
bending, distortion, or induced stress during lifting, moving, and placing the sections.
PRECAST CONCRETE SECTION 612 255 3. Provide shear keys at all wingwall -to-wingwall and structure -to-wingwall joints. Prepare shear keys with an exposed aggregate surface.
contract or by ASTM C1577, as applicable.
inches from the end of each unit.
a minimum of 2 -inches of clear cover.
Post -tension precast arches in accordance with the manufacturer's recommendations.
1-foot distance from any joint. Retain elevations in accordance with the contract. Provide weep holes of 4 -inch PVC pipe and with a 2 -inch fall from back to front. Alternately, provide a 6 -inch sleeve for field installation of weep holes.
Cure precast elements in accordance with approved plant quality control plans.
each side and to all headwalls, end faces, and exposed faces in accordance with Section 613.
than 1/8 -inch per foot of internal span, with a maximum of 5/8 -inch for all sizes through 7 -feet internal span, and a maximum of 3/4 -inch for internal spans greater than 7 -feet.
maximum of 1/2 -inch in any unit.
that the cover over the reinforcement on the external surface of the top slab shall be no less than 2 -inches for earth covers less than 3 -feet, except where ASTM C1577 is applicable.
permissible variation in diameter of any reinforcement shall conform to the tolerances prescribed in the ASTM specification for that type of reinforcement.
coarse aggregate. Construct a foundation consisting of coarse aggregate in accordance with the contract. PRECAST CONCRETE SECTION 612 256 2. For box culverts, place toe walls beneath the bottom slab at the inlet and outlet. Connect by dowels epoxy grouted into the bottom slab in accordance with the contract. Place a 1 -inch non- shrink grout leveling pad before placing the culvert. Contain the coarse aggregate in place beneath the culvert while completing adjacent excavations for wingwalls using formwork or other acceptable means. Fill voids between the bottom slab of the culvert and the coarse aggregate with flowable fill before backfilling.
approved by the engineer in the field. Place the precast sections in a continuous line of units with a smooth interior free of appreciable irregularities. If necessary, shim units to maintain a difference of 1/2 -inch or less between the soffits of adjacent units.
with a 1/2 -inch maximum gap between units. The maximum allowable post - tensioning force is 28,900 -pounds. Upon completion of post -tensioning, verify the tolerance for the assembled units is plus or minus 1 -inch per 50 linear feet and a maximum of plus or minus 2 -inches for culverts over 100 feet long. For rigid frame and arch structures, ensure that the outer edge of the frame units matches the outer edge of the fo oting units.
Provide bolted connections consisting of a minimum of two, 3 -foot x 2 -foot x 1/4 -inch plates per joint with at least eight, 3/4 -inch bolts per plate. Place bolts a maximum of 3 -inches from the joint or edge of plate. Do not use slotted holes in the plates. Secure anchor bolts using cast -in hardware or field drill holes. Where joints between precast units exceed 1/2 -inch after installation, repair with non -shrink g rout or Class A concrete.
days of 5,000 PSI to fill the shear keys. Before applying the grout, clean and wet the surfaces. Do not allow standing water to remain in the area receiving grout. During grout placement, prevent material from falling on the roadway, into the waterway, or on the railroad area below. Prepare, place, and cure in accordance with the manufacturer's recommendations.
that the joint wrap stays in place during backfilling.
footing keyways, and all other holes or pockets. Cover grout filled locations on the fill face with joint wrap material a minimum length and width of 9 -inches.
allow a difference in backfill height of more than 1 -foot.
612.3.4 Precast Prestressed Concrete Load -carrying Members.
surfaces with an in -form retarder to create an exposed aggregate surface. PRECAST CONCRETE SECTION 612 257 2. Provide beam dap details that show beams resting level on bearing devices and details for non - bearing areas as necessary. Provide batter to make beam ends vertical when installed.
cover unless noted otherwise in the contract. Adjust reinforcing bar spacing to clear embedded accessories.
strands.
ultimate pullout capacity of 11,900 -pounds each. Adjust threaded inserts or bar locations by 1/2-inch to avoid conflicts. Note any deviations from this plan on the working drawings.
installation of stay -in-place forms or falsework. The stay -in-place form manufacturer shall determine the size, type, spacing, and location of the appurtenances.
for beams that will have a concrete deck cast -in-place on the beams. Provide a float finish for beams planned for overlays of waterproofing membranes, hot mix riding surfaces, or thin concrete.
approximately 500 pounds per strand, before applying full pre -tensioning. Measure the stress using a dynamometer or other approved means. Use the initial tension as a check against elongations computed and measured. After this initial tensioning, stress the group of strands until attaining the required elongation and jacking pressure. Measure the stress induced in the strands using jacking gauges and by elongations o f the strands. The calculated stress based on the elongation should closely match the gauge reading.
measuring the pre -stressing strand elongation to at least the nearest 1/16 -inch. Provide documentation to show that the jacking equipment and gauges used in manufa cturing the pre-stressed members received calibration by a reputable testing laboratory. Allow for all possible slippage or relaxation of the anchorage in the interpretation and analysis of the elongations and jacking pressures.
jacking pressure and the elongation measurement, check the entire operation and determine the source of the error before continuing.
place the concrete in the form. Only place concrete when the temperature is between 50 and 85 degrees F. Maintain cable or strand stresses between anchorages until the concrete reaches a minimum compressive strength of 80 percent of the 28 -day compressive strength and the process of transferring the pre -stress to the member has begun. PRECAST CONCRETE SECTION 612 258 e. Immediately after the concrete attains initial set, in accordance with AASHTO T197, steam cure members under a suitable enclosure to contain the live steam and minimize moisture and heat loss. Provide steam of 100 percent relative humidity. Do not disch arge steam directly onto concrete or form. Ensure that the temperature within the enclosure increases at a rate not exceeding 40 degrees F per hour until reaching a maximum temperature of 140 to 160 degrees F. Maintain the maximum temperature until the con crete has reached the specified release strength. After attaining release strength, gradually decrease the temperature within the enclosure at a rate not to exceed 40 degrees F per hour, until the temperature is no more than 30 degrees F above the ambient temperature. Record curing temperatures throughout the process.
moisture. Do not allow the concrete to dry or cool before de -tensioning. In all de -tensioning operations, keep the pre -stressing forces nearly symmetrical about the vertical axis of the member. De -tension in a manner that minimizes sudden or shock loading and limit the maximum eccentricity about the vertical axis to 1 strand. Remove or loosen forms, ties, inserts, hold -downs, or other devices that would restrict longitudinal movement of the members along the bed during de -tensioning.
paint with either an approved bitumastic compound or waterproofing compound. Fill strand recesses with pneumatically applied mortar. As an alternate, use an approved epoxy mortar covering the ends of strands with a minimum thickness of 1/8 -inch.
beams, in accordance with Section 613.
no case less than 3 working days after the placing concrete in the forms. Maintain the members horizontally at all times during handling, moving, storing, and shipping.
dowel holes, as shown in the contract, in accordance with Section 612.3.3.C.6. Do not allow loads on prestressed elements until the grout has cured.
612.4Method of Measurement.
retaining wall placed and accepted using plan quantities of cubic yards of concrete. The Department will measure box culverts and associated elements such as toe walls, headwalls, and baffles as part of the box culvert. The Department will measure footings and headwalls for rigid frames as part of the rigid frame. PRECAST CONCRETE SECTION 612 259 B. The Department will not measure the quantity of precast concrete arch, precast concrete retaining wall for arches, or prestressed reinforced concrete members.
612.5Basis of Payment.
other materials, contractor’s alternate designs, fabricating, transporting, and placing the units on site. The Department will consider anything not mea sured separately as incidental to the respective item.
ITEM DESCRIPTION UNIT 612000 PRECAST CONCRETE BOX CULVERT CY 612001 PRECAST CONCRETE RIGID FRAME CY 612002 PRECAST CONCRETE ARCH LS 612010 PRECAST CONCRETE RETAINING WALL CY 612011 PRECAST CONCRETE RETAINING WALL FOR ARCHES LS 612020 PRESTRESSED REINFORCED CONCRETE MEMBERS, SOLID SLABS LS 612021 PRESTRESSED REINFORCED CONCRETE MEMBERS, VOIDED SLABS LS 612022 PRESTRESSED REINFORCED CONCRETE MEMBERS, BOX BEAMS LS 612023 PRESTRESSED REINFORCED CONCRETE MEMBERS, BULB T BEAMS LS 612024 PRESTRESSED REINFORCED CONCRETE MEMBERS, NEXT BEAMS LS