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Lower ratios may be possible with use of high-range water reducers.  Revise ratio as required.

2.

Maximum Water-Cementitious Materials Ratio:  0.45.

Water absorption indicates susceptibility to weather staining.  The limit in paragraph below, corresponding to 6 percent by weight, is suitable for average exposures.  Different parts of a single panel cannot be produced with different absorptions.  Verify that fabricator can produce units with lower water absorption because special consolidation techniques to increase concrete density are required.

E.

Water Absorption:  6 percent by weight or 14 percent by volume, tested according to PCI MNL 117.

Lightweight backup mixes must be compatible with normal-weight face mixes to minimize bowing or warping.  Retain lightweight concrete backup mixes if required or as an option if satisfactory durability and in-service performance are verified by fabricator.

F.

Lightweight Concrete Backup Mixes:  Proportion mixes by either laboratory trial batch or field test data methods according to ACI 211.2, with materials to be used on Project, to provide lightweight concrete with the following properties:

Retain subparagraph below or revise to suit Project.  Higher-strength mixes may be available; verify with fabricators.

1.

Compressive Strength (28 Days):  5000 psi (34.5 MPa).

Increase or decrease unit weight as required.  Coordinate with lightweight-aggregate supplier and architectural precast concrete fabricator.  Lightweight concretes with lightweight and normal-weight aggregate in mix will usually be heavier than unit weight below.

2.

Unit Weight:  Calculated equilibrium unit weight of 115 lb/cu.ft. (1842 kg/cu.m), plus or minus 3 lb/cu.ft. (48 kg/cu.m), according to ASTM C 567.

G.

Add air-entraining admixture at manufacturer’s prescribed rate to result in concrete at point of placement having an air content complying with PCI MNL 117.

H.

When included in design mixes, add other admixtures to concrete mixes according to manufacturer’s written instructions.

2.14

 MOLD FABRICATION

A.

Molds:  Accurately construct molds, mortar tight, of sufficient strength to withstand pressures due to concrete-placement and vibration operations and temperature changes and for prestressing and detensioning operations.  Coat contact surfaces of molds with release agent before reinforcement is placed.  Avoid contamination of reinforcement and prestressing tendons by release agent.

Delete form liners unless needed to produce exposed surface finish.

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