This is the first in a series entitled: Contractor's Soap Box; question-and-answer columns dealing with the insights, struggles and professional experiences facing concrete contractors in their never-ending quest to master the sometimes fickle nature of the beast! We believe you will benefit from the positive nature of this column and that much can be learned from each of these professionals.
Periodically, we will feature one of America's top concrete contractors and present him with a list of questions sure to spark your attention. This issue we feature Dave Rossetti, Sr. from D.J. Rossetti Concrete, Albany, New York. His company has been voted one of the top 100 concrete contractors in America by his peers for five straight years.
We thank Dave for his willingness to share his hard earned wisdom with our many readers, and for his company's ongoing dedication to excellence in the concrete business! The following is a Q&A discussion between myself and Dave Rossetti.
D.J. Rossetti, Inc. is in its 25th year of business. They specialize in construction of commercial, institutional and retail concrete floors and in airport concrete paving, roads and bridge decks. They have been ranked in the top 100 Contractors for the past five years by Concrete Construction. They are now also specializing in polished and dyed concrete as a certified FGS PermaShine installer. With extensive experience in stamped/imprinted decorative concrete, D.J. Rossetti, Inc. is also a Bomanite franchise partner for their concrete topping system.
JV. Dave, what are your thoughts about the use of float blades verses combination blades or pans?
Rossetti. We prefer the use of pans for the first two or three passes over the floor. The number of passes is based on the F number required for the project. We then prefer to use combination blades for the balance of the finishing. This gives us flexibility in utilizing less finishing machines on a given placement. We get F numbers of 50 to 125 depending on how many times we check rod the floor.
JV. What is your position on the use of fly ash in concrete floor mixes?
Rossetti. Understanding when to use fly ash in concrete slab mix designs is necessary because it can be equally helpful or harmful in finishing concrete slabs, depending upon conditions. In hot weather placements the use of 17% of quality fly ash slows the initial set of the concrete, thus giving the finisher a larger window for finishing. It also slows down the rate of hydration for curing purposes and will give better long term strength gain. We have found fly ash to be a great aid when we are forced to steel trowel finish either air-entrained regular weight concrete or lightweight concrete. It helps prevent delamination of the concrete finish, which is a common problem when finishing air entrained concrete.
JV. What is your preference on the type of aggregate: crushed stone versus gravel?
Rossetti. We prefer to use a crushed stone mix. Although we have had some success with gravel mixes, we find that they tend to shrink and curl more. The effect of this can be overcome by placing the saw cut control joints closer together. I feel the reason for this is that it takes more cement and sand paste to fill the larger gaps between the round stones, and with more cement paste, more shrinkage occurs.
JV. What are your feelings about adding chloride verse non-chloride accelerators?
Rossetti. We still prefer the use of calcium chloride when allowed by the project engineer. It just works better and we have not seen any finishing problems associated with its use.
JV. What kind of mix design do you like for polished floors?
Rossetti. The best mix design that I can recommend is what I call "Old Fashioned Concrete:" cement, sand, stone and water. We do not use any chemical admixtures in our polished concrete mix design unless we are forced to place the slab by pumping the concrete. The mix we recommend is a 4000 psi with low cement content of 520 lbs. ASTM size #57 crushed stone at about 2000 lbs. Sand should be low at about 1300 lbs., maximum water should be at a .52 w/c ratio = 270.4 lbs. This will need to be adjusted somewhat to allow for local specific gravity of materials, but it is a good guideline. The slump of this mix is typically about 5". The mix above is for slabs on grade that will be placed out of the truck chute or by concrete buggies. For a pumpable mix we recommend to add the use of a high-range water reducer, one that will not create any micro-air. The dosage should be kept low; typically 8 to 10 oz. per 100 pounds of cement. The cement content in a pumpable mix needs to go up to 564 lbs. The #57 stone would then come down to 1800 lbs and the sand would go up to 1455 lbs. The w/c ratio would stay at .52 = 293.3 lbs.
JV. Thanks, Dave, for sharing your experiences with us. I am sure our readers will gain much from your hard earned insights gathered over your many years of perfecting your craft.
Rossetti. Glad to help. I think this is a great idea. I hope more contractors accept your invitation in future issues of Concrete News. We love the publication.
Dave Rossetti, Sr.
D. J. Rossetti, Inc.
11 Stone Break Road
Malta, New York 12020.
If you have questions you'd like the experts to address in the future, please email them to me at email@example.com.
© 2007 L&M Construction Chemicals, Inc. | ConcreteNews September 2007.