Answers to 7 questions
on industrial concrete floors
THE wearing surface is the critical part of any industrial concrete floor. It takes all the abuse that a building full of workers and their equipment can produce. And, if that floor surface is not up to the job, it will break down completely and expensively.
Repair and replacement of a wear- ing surface can cost more than the ori- ginal floor itself. Add production de- lays and plant downtime and the total can become staggering. Obviously, you save by building the right floor in the first place.
Here are some basic guides for making the right choice of a wearing surface to meet the majority of indus- trial flooring needs.
What are the main considerations in floor design?
There are two main aspects of floor design to consider. First, there are the compressive and flexural strengths which make the floor structurally sound. Here enter such factors as live and dead loads, the sub-base, slab thickness, reinforcement, column spacing, and strength of the concrete itself. All of these make up an engin- eering consideration varying with each structure.
Second, there are the strength re- quirements of the surface which deter- mine the abrasion and impact resis- tance of the floor in actual use. Since the wear resistance and impact streng- th partially depend on surface streng- th, the use of 4500-5000 psi concrete is a must, even though lower strength concrete might meet basic structural requirements. Special surface aggre- gates are also recommended to further increase wear resistance. Experience has proved the sound long-run econo- mics of using high strength concrete for industrial floor use.
How do one-course (monolithic) and two-course (granolithic) floors compare?
concrete
The monolithic floor usually costs less to begin with, and it can be placed by any conscientious general contrac-
The answers in this article have been provid- ed by The Master Builders Company Ltd.. Toronto, Ontario, Canada.
Far East BUILDER, August 1971
tor with proper equipment. It ade- quately resists light traffic when it is properly finished high strength con- crete. However, wear resistance can be boosted up to 8 times when a metallic armoured surface is applied to the freshly floated concrete.
On the other hand, a granolithic floor allows for a base slab of lower strength concrete to meet structural requirements, surfaced with a specially prepared topping to meet high point load conditions. The need for high point load support automatically in- volves the need for metallic aggregates in the wearing surface for added abra- sion and impact resistance. The two- course floor also permits the builder to place the base slab earlier, making it easier for the contractor to complete construction. As the building nears completion, the contractor can install the special topping.
How can dusting be avoided?
There are two basic kinds of dust- ing: (1) the powdering of the cement matrix through low strength, improper curing, and/or excessive trowelling of wet mixes; (2) the fracturing and pul- verising of brittle aggregates in a floor surface which has broken down under wear. Each
Each type of disintegration means almost certain floor replace- ment eventually.
Improper curing is an invitation to dusting. It often begins in job specifi- cations which do not require the con- tractor to cure floors properly. At the same time, excessive trowelling of a wet mix brings "fines" to the top, pro- ducing a low strength surface prone to dusting. Dusting from poor curing can be temporarily alleviated by using a chemical hardener of the fluosilicate type. However, this treatment hardens only the matrix by reacting with the free lime in it. The treatment does not render the aggregates tougher or less brittle. The use of chemical hardeners should be restricted to maintenance. Proper curing can eliminate need for liquid hardeners, but liquid hardeners cannot replace the benefits of proper curing.
Even properly cured floors will sometimes dust through the pulveris-
ing of brittle aggregate and matrix. To prevent this, the answer is the incor- poration of specially prepared, size- graded metallic aggregates into the sur- face of the freshly floated concrete floor. Because the metallic aggregate is tough, ductile and malleable, it will not fracture under abrasion and im- pact. Furthermore, the application of a metallic aggregate shake (the dry cement-aggregate mixture) markedly lowers the water/cement ratio of the concrete near the surface resulting in a surface strength more than double that of the concrete below. Even though this treatment eliminates dusting, an iron-armoured floor must also be pro- perly cured, preferably with a quality membrane curing compound exceed- ing ASTM requirements for moisture retention.
How can concrete floors be made oil- resistant and easy to clean?
Concrete is a porous substance con- taining a network of tiny capillary channels. The wetter the mix used in constructing a floor, the more perme- able the hardened concrete will be. Floating and troweiling makes the sur- face skin denser and helps reduce ab- sorption as long as the surface remains intact. But, as the surface wears with age and use, the capillary openings are exposed and absorption increases. Concrete sealers can help fight this condition, but the main obstacle to their use besides cost and incoveni- ence is that they must be applied to an absolutely clean surface. This, of course, is nearly impossible with a floor that has been in use.
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To combat the problem, combined curing and sealing compounds are available which are applied initially to cure and seal concrete floors.
Can a floor surface be both durable and non-slip?
A smooth, hard-trowelled finish is more durable than a conventional non- slip finished floor. However, it does tend to be more slippery when wet or spotted with oil and grease. The effec- tiveness of embedding abrasive aggre- gate in floors depends on the wearing away of the cement matrix, exposing
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