6-225 SECTION 681 – PRECAST AGGREGATE-FILLED, CONCRETE BLOCK GRAVITY WALL
681.01 Description The work under this item shall consist of the design, fabrication,
furnishing and construction of a Precast Aggregate-filled Concr ete Block Gravity Wall in accordance with these specifications and in conformance with th e lines and grades shown on the Plans, or established by the Resident. The Precast Aggrega te-filled Concrete Block Gravity Wall shall consist of blocks made of Structural Precast concrete made from Portland cement, water, chemical admixtures, and aggregates, supported o n 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 an exposed 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 concrete wal l unit installation. The top of the upper row of concrete wall units shall be at or above the t op of the face elevation shown on the Plans.
681.02 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.
681.03 Materials Materials for walls shall meet the requiremen ts of the following
sections of Division 700: G r a v e l B o r r o w 703.20 Crushed Stone, ¾ -Inch 703.13 U n d e r d r a i n P i p e 706.06 or 706.09 Reinforcing Steel 709.01 Structural Precast Concrete Units 712.061 Reinforcement Geotextile 722.01 Drainage Geosynthetic 722.02 The Contractor is cautioned that all of the materials listed a re not required for every Precast Aggregate-filled Concrete Block Gravity Wall. The Cont ractor shall furnish the 6-226 Resident a Materials Certification Letter certifying that the a pplicable materials comply with this section of the specifications. Materials shall meet the f ollowing additional requirements: 681.031 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 wat er cement ratio shall be 0.42, use of calcium nitrite is not required unless the desi gn of the concrete wall units requires fabrication with reinforcing steel, the minimum 28-day compressive strength shall be 4600 psi. Paragraph three of Materials is not applicable to this Section . Quality Control and Quality Assurance. Quality Control and Qua lity Assurance is modified as follows: delete the paragraph which begins with “Th e contractor shall provide a private office…” Curing. Curing requirements are modified as follows: Replace the first sentence in the paragraph which begins “Form s shall remain …” with the following: The forms shall remain in place until the c oncrete has gained sufficient strength such that removal of the forms and subseque nt 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 exposed surfaces. Pigment shall be added during the casting process of the concrete unit to achieve a co nsistent shade of gray or other color as determined by the Resident. Concrete Testing. The concrete testing requirements are modif ied as 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 cylinder s for every 50 CY of production concrete used to cast the concrete units. Replace the paragraph which begi ns “At least once …” with the f ollowing: The Contractor shall make four cylinders for use by the Departm ent to represent every 200 CY or fraction thereof.