6-178 SECTION 671 – DRY CAST SEGMENTAL BLOCK WALL Reserved SECTION 672 - PRECAST CONCRETE BLOCK GRAVITY WALL
672.01 Description The work under this item shall consist of design, fabrication,
furnishing and construction of a Precast Concrete Block Gravity Wall in accordance with these specifications and in close conformance with the lines an d grades shown on the Plans, or established by the Resident. The Precast Concrete Block Gra vity Wall shall consist of facing blocks made of wet cast concrete made from Portland ceme nt, water, chemical admixtures, and aggregates, supported on concrete leveling pads , and if required, geosynthetic-reinforced backfill. Included in the scope of the precast gravity wall construction are: geotechnical design of any wall with a expos ed height greater than 4.5 feet or as specified on the Plans, all grading necessary for wall construction, compaction of the wall foundation soil, backfill, piped drainage, construction of leveling pads, and block wall i nstallation. The top of the upper row of blocks shall be at or above the top of the face el evation shown on the Plans.
672.02 Quality Assurance The wall system shall be one of the approved
combinations of facing block and soil reinforcement systems not ed in the Plans or on the Department’s Qualified Products List (QPL). Alternate wall sys tems will not be considered for this Item. All design calculations and Shop Drawings shall be signed, che cked, and sealed by a Professional Engineer licensed in the State of Maine. The Contractor shall require the wall design-supplier to provi de an on-site, qualified experienced technical representative to advise the Contractor c oncerning proper installation procedures. The technical representative shall be on-site duri ng initial stages of installation and thereafter shall remain available for consultation as neces sary for the Contractor or as required by the Resident.
672.03 Materials Materials for walls shall meet the requiremen ts of the following
sections of Division 700: Gravel Borrow 703.20 Crushed Stone, ¾ -Inch 703.13 Underdrain Pipe 706.06 or 706.09 Reinforcing Steel 709.01 Reinforcement Geotextile 722.01 Drainage Geotextile 722.02 The Contractor is cautioned that all of the materials listed a re not required for every Precast Concrete Block Gravity Wall. The Contractor shall furn ish the Resident a Materials 6-179 Certification Letter certifying that the applicable materials c omply with this section of the specifications. Materials shall meet the following additional requirements: 672.031 Concrete Units The Materials Certification Letter desc ribed above shall contain the date of concrete casting, a lot identification number, comp ressive strength results, and entrained air results. All prefabricated concrete units shall c onform to the requirements of Section 712.061 with the following exceptions: Materials. Materials are modified as follows: The maximum water cement ratio shall be 0.42, use of calcium ni trite is not required, and the minimum 28 day compressive strength shall be 4600 psi. Paragraph 3 of Materials is not applicable to this Section. Quality Control and Quality Assurance. Quality Control and Qual ity Assurance is modified as follows: delete the paragraph that begins with “The contractor shall provide a private office…” Curing. Curing requirements are modified as follows: Replace the first sentence in the paragraph which begins “Forms shall remain …” with the following: The forms shall remain in place until the conc rete has gained sufficient strength such that removal of the forms and subsequent handling will not damage the units. Add the following paragraph at the end of the Curing section: Face texture of the units shall be a formed finish on all expo sed surfaces. Pigment shall be added during the casting process of the concrete unit to achieve a consistent shade of gray or other color as determined by the Resident. Concrete Testing. Concrete testing requirements are modified a s follows: Replace the paragraph which begins “The Contractor shall cast a minimum of 8 ….” With the following: The Contractor shall make and test at least one set of cylinde rs for every 50 CY of production concrete used to cast the concrete units. Replace the paragraph which begins “At least once …” with the following: The Contractor shall make four cylinders for use by the Depart ment to represent every 200 CY or fraction thereof. Tolerances. Maximum dimensional deviation of formed unit dimen sions shall be ½ - inch or 2 percent or the manufacturer’s published tolerances, w hichever is less. Units not meeting the specified tolerances will be rejected.