A.
Portland Cement.
Portland cement shall be Type I or Type III and be in accordance with the current specifications for Portland cement in ASTM C150. Type IA or Type IIIA Portland cement shall be used when air entrainment is specified and shall conform to the current specifications for Portland cement in ASTM C175.
B.
Fly Ash.
When fly ash is used, “cement” shall be defined as “cement plus fly ash”. Fly ash shall be Type C from a source approved by the Texas Department of Transportation and shall not exceed 25% of the absolute volume of the “cement plus fly ash”. Fly ash is not permitted when white Portland cement is required.
C.
Water.
Water used for mixing in concrete shall be clean and free from injurious amounts of oils, acids, alkalis, salts, organic materials, or other substances that may be deleterious to concrete or reinforcement. Water which is suitable for drinking or ordinary household uses is acceptable. Nonpotable water shall not be used for mixing in concrete. The maximum water/cement ratio shall be 0.50.
D.
Admixtures.
Calcium chloride or admixtures containing chloride are strictly prohibited. Provide admixtures in accordance with the following:
1.
Air-entraining Admixtures.
Use admixture which conforms to the requirements of ASTM C260.
2.
Chemical Admixtures.
Chemical admixtures used as retarders, accelerators, water-reducing agents, or a combination of these, shall conform to the applicable provisions of ASTM C494 and/or ASTM C1017.
3.
Admixtures shall be charged into the mixer as solutions and shall be measured accurately. The liquid shall be considered a part of the mixing water.
E.
Aggregates.
Use coarse aggregate from only one (1) source and fine aggregate from only one (1) source for all exposed concrete in a single structure. Use of pit run gravel as an aggregate will not be permitted. Both fine and course aggregates in normal weight concrete shall conform to the requirements of ASTM C33 and shall be as follows:
1.
Coarse Aggregate.
Course aggregates shall consist of crushed stone, gravel, crushed gravel or a combination of these. Gravel and crushed gravel shall consist of clean, hard, durable particles, free from adherent coating, thin or elongated pieces, soft or disintegrated particles, dirt, organic or injurious matter. Crushed stone shall consist of the clean, dustless product resulting from crushing stone. There shall be no adherent coatings, clay, loam, organic or injurious matter.
2.
Fine Aggregate.
Fine aggregate shall consist of a sand or mixture of sand with or without a mineral filler. The sand or mixture of sand in fine aggregate shall be clean, hard, durable, uncoated grains that are free from lumps.
F.
Curing Compound.
When required, provide commercial curing compound that will not permanently discolor the concrete and is in accordance with the provisions set forth in ASTM C309.
G.
Sheet Material for Curing Concrete.
When required, provide waterproof paper, polyethylene film or white burlap-polyethylene sheeting in accordance with provisions set forth in ASTM C171.
H.
Patching Grout.
Provide a non-shrink, non-slump, quick-setting patching mortar to repair small defects in concrete work. Master Builders’ “Embeco 153,” or preapproved equal, is acceptable for use as a patching grout. Sand used in patching grout shall be in accordance with the provisions set forth in ASTM C144.
I.
Proportioning and Mixing of Concrete.
Proportion and mix ingredients in a manner that will produce a concrete having the proper placability, durability, strength, appearance, and other specified properties. Proportion ingredients to produce a homogenous mixture that will readily work into corners and angles of forms and around reinforcement when placed and consolidated and will not segregate or have excessive water collect on the surface. Proportion materials in accordance with the procedures outlined in ACI 613, “Recommended Practice for Selecting Proportions for Concrete.” All materials will be proportioned and mixed with the intention of producing a concrete with the minimum specified twenty-eight (28) day compressive strength, or greater.
1.
Normal Weight Structural Concrete.
In addition to the above requirements for proportioning and mixing concrete, normal weight structural concrete shall be mixed in accordance with the provisions of ASTM C94, “Standard Specification for Ready-Mixed Concrete.” The use of an on site batch plant is strictly prohibited without the prior approval of the Engineer or designated representative of the Engineer. Any specified or approved admixtures shall be mixed and proportioned in the concrete in accordance with the manufacturer’s instructions and the applicable reference standards.
2.
Concrete Riprap.
Concrete riprap shall be proportioned and mixed in accordance with the provisions for normal weight concrete.
3.
Pneumatically Placed Concrete.
In addition to any of the following requirements, the cement, sand, admixtures, and water to be used for pneumatically place concrete shall conform to the requirements previously outlined in this specification. Pneumatically placed concrete shall be proportioned as follows:
a.
Type I.
One (1) part cement (minimum) to four (4) parts sand (by volume).
b.
Type II.
One (1) part cement (minimum) to five (5) parts sand (by volume).
The type to be used shall be designated on the plans. At the time of mixing, the sand shall contain from three (3) to six (6) percent moisture. When visual inspection indicates that lumps or oversized particles are going into the machine, all materials shall be thoroughly mixed and passed through a 1/4-inch sieve before being placed in the machine. The minimum mixing time for each batch shall not be less that 1-1/2 minutes after the sand and cement are in the drum when the drum rotates at a peripheral speed of two-hundred (200) feet per minute. Completely discharge each batch before recharging. Clean the mixer at regular intervals to remove all adherent material from the mixing vanes and from the drum. No water shall be added to the mix after mixing and before application. Discard any mixed material that has exceeded the forty-five (45) minute maximum time to placement.
(Ordinance 2007-106, App. B, adopted 3/20/07)