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FMC: FAQs
Q. How much does a yard of concrete weigh?^
A. 3800-4000 lbs per yard
Q. How much can a FMC truck haul?^
A. 10 yards
Q. What is the length of a FMC truck? ^
A. Front discharge mixer, 35 ft; Rear discharge mixer, 31ft
Q. How does FMC calculate concrete? ^
A. Length x Width x Depth (fraction of foot-example 4 in would be 4/12=0.33) Divided by 27. Add 10-15% for spillage/waste and variations in sub-grade.
Q. What kinds of cracking occur in concrete surfaces?*
A. Concrete, like other construction materials, contracts and expands with changes in moisture content and temperature, and deflects depending on load and support conditions. When provisions for these movements are not made in design and construction, cracks can occur. Some forms of common cracks are: plastic shrink cracking, cracks due to improper jointing, cracks due to continuous external restraint, basement floor cracks, D-cracks from freezing and thawing, craze cracks and settlement cracks. Cracks rarely affect structural integrity. Most random individual cracks look bad and although they permit entrance of water, they do not lead to progressive deterioration. They are simply unsightly. Closely spaced pattern cracks or D-cracks due to freezing and thawing are an exception and may lead to ultimate deterioration.
Rules to minimize cracking:
* Design the members to handle all anticipated loads
* Provide proper control and isolation joints
* In slab-on-grade work, prepare a stable sub-grade
* Place and finish according to established rules
* Protect and cure the concrete properly
Q. What is hot weather concreting?*
A. Hot weather concreting is any period of high temperature in which special precautions need to be taken to ensure proper handling, placing, finishing and curing of concrete. Hot weather problems most frequently occur in the summer, but are associated with high winds and dry air that occur at any time, especially in arid or tropical climates. Hot weather conditions can produce a rapid rate of evaporation of moisture from the surface of the concrete and accelerate the setting time. Generally, high relative humidity tends to reduce the effects of high temperature.
Rules for hot weather concreting:
- Concrete mixture designs may include various admixtures
- Adequate manpower to quickly place, finish and cure the concrete
- Limit the addition of water at the job site - add water only on arrival at the job site to adjust the slump. Later additions should be avoided; in no instance should they exceed 2 or 2 1/2 gallons per cubic yard. Never add water to concrete that is more than 1 1/2 hours old.
- Slabs on grade should not be placed on polyethylene sheeting. If a vapor barrier is required, a bed of damp sand should be placed over it.
- Finish as soon as the sheen has left the surface; start curing as soon as finishing is completed. Continue curing for at least 3 days: cover to prevent evaporation, or use a liquid membrane curing compound or cure slabs with water. The addition of white pigment to membrane curing compounds will help by reflecting heat away from the concrete surface.
- Moisten the sub-grade, forms and reinforcement prior to placement. However, avoid standing water.
- Protect field test cylinders by shading and preventing evaporation. Field curing boxes with ice or refrigeration may be used to ensure required 60-80F for cylinders.
- Do not use accelerators
Q. What is finishing?*
A. Finishing is the operation of consolidating, leveling and creating a concrete surface of desired texture and hardness. The finish can be strictly functional or decorative.
Rules to finish concrete:
- FLOAT the concrete as soon as it has been struck-off. A float is a wood or metal tool used to further level the concrete surface and to embed the large aggregate. On small jobs a float is hand-held; on larger jobs a long-handled bull float may be used. One or two passes should be enough to smooth and level the surface without sealing the concrete. Floating must end before visible bleed water rises to the surface.
- WAIT for the concrete to stop "bleeding". Bleeding occurs as the solids in the concrete settle. All other finishing operations must wait until the concrete has stopped bleeding and the water sheen has left the surface. Any finishing operations done while the concrete is still bleeding will result in later problems such as dusting, scaling, crazing and blisters. The waiting period depends on: the amounts of water, cement and chemical admixtures in the concrete; and the weather.
- EDGE the concrete all the way around. Spade the concrete next to the form gently with a small mason's trowel and then use the edging tool to give the concrete rounded edges.
- JOINT the concrete by grooving it. The jointer should have a blade one-fourth the depth of the slab (1 inch deep joints on a 4 inch slab). Use a straight piece of lumber as a guide. A shallow-bit groover should only be used for decorative grooves.
- TROWEL the concrete according to its end use. For sidewalks, patios and driveways, troweling may not be required. Repeated passes with a steel trowel will produce a smooth floor that will be slippery when wet. For a smooth floor make successive passes with a smaller steel trowel and increased pressure. Excessive troweling may create dark "trowel burns". Tilting the trowel will cause an undesirable "chatter" texture.
- TEXTURE the concrete surface after floating (for sidewalks, patios or driveways) or after troweling (for interior flatwork) with a coarse or fine push-broom to give a non-slip surface.
- NEVER sprinkle water or cement on concrete while finishing it. This may cause dusting or scaling.
- CURE the concrete as soon as all finishing is completed and the water sheen has left the surface.
Q. What is discoloration?*
A. Surface discoloration is the non-uniformity of color or hue on the surface of a single concrete placement. It may take the form of dark blotches or mottled discoloration on flatwork surface, gross color changes in large areas of concrete caused by a change in the concrete mix or light patches of discoloration caused by efflorescence. In this context, it is not intended to include stains caused by foreign material spilled on a concrete surface.
Rules to prevent discoloration:
- Minimize or eliminate the use of high-alkali content cements
- Avoid calcium chloride or chloride-bearing chemical admixtures
- Forms with different rates of absorption will cause shading differences on the surface.
- A change in the type or brand of a form release agent can also change concrete color.
- Eliminate trowel burning of the concrete
- Not properly or uniformly cured concrete may develop discoloration.
- Moisten absorptive sub-grades, follow proper curing procedures and add proper protection from drying from the wind and sun
Q. What is precast concrete?*
A. Precast concrete is concrete cast before reaching its final position. Precast construction is used to produce a wide variety of structural elements such as wall panels, bridge girders, pipes, poles, crash barriers, lift stations, etc.
Q. What is pervious concrete?**
A. Pervious concrete does not contain fine aggregate. It typically has a voids content of 15%-35%. This ensures that the concrete has the unique ability to allow storm water to pass through its mass into the ground underneath. Pervious concrete offers significant environmental benefits as it reduces the requirement for drainage facilities. It facilitates the recharge of ground water and the filtration process purifies the water as it percolates below.
Q: What are some uses for pervious concrete? **
A: Pervious concrete has been successfully used for low-volume streets, driveways, sidewalks, golf cart paths, retaining walls, slope protection and French drains. It can also be utilized for a variety of paving projects.
Q. What is the difference between cement and concrete? ***
A. Cement is actually an ingredient of concrete. Concrete is a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and portland cement. Cement comprises from 10 to 15 percent of the concrete mix, by volume.
Q. How do you remove stains from concrete? ***
A. Stains can be removed from concrete with dry or mechanical methods, or by wet methods using chemical or water.
Common dry methods include sandblasting, flame cleaning and shotblasting, grinding, scabbing, planing and scouring. Steel-wire brushes should be used with care because they can leave metal particles on the surface that later may rust and stain the concrete.
Wet methods involve the application of water or specific chemicals according to the nature of the stain. The chemical treatment either dissolves the staining substance so it can be blotted up from the surface of the concrete or bleaches the staining substance so it will not show.
Q. What are the decorative finishes that can be applied to concrete surfaces?***
A. Color may be added to concrete by adding pigments-before or after concrete is place-and using white cement rather than conventional gray cement, by using chemical stains, or by exposing colorful aggregates at the surface. Textured finishes can vary from a smooth polish to the roughness of gravel. Geometric patterns can be scored, stamped, rolled, or inlaid into the concrete to resemble stone, brick or tile paving. Other interesting patterns are obtained by using divider strips (commonly redwood) to form panels of various sizes and shapes rectangular, square, circular or diamond. Special techniques are available to make concrete slip-resistant and sparkling.
Q. What are ICF's (Insulated Concrete Forms) ? ****
A. ICF's are basically forms for poured concrete walls, that stay in place as a permanent part of the wall assembly. The forms, made of foam insulation or other insulating material, are either pre-formed interlocking blocks or separate panels connected with plastic ties. The left-in-place forms not only provide a continuous insulation and sound barrier, but also a backing for drywall on the inside, and stucco, lap siding, or brick on the outside.
 ICF’s are poured concrete wall forms that become a permanent part of the wall assembly. The forms, made of foam insulation or other insulating material, are either pre-formed interlocking blocks or separate panels connected with plastic ties. The forms provide continuous insulation and a sound barrier, and also reinforce backing for drywall on the inside, and stucco, lap siding or brick on the outside.
ICF for Homeowners
- Lower heating/cooling costs due to high thermal mass buffers
- Minimal air infiltration due to continuous air barriers
- No convection currents within wall cavities
- One-third less outside noise, compared to fiberglass-filled frame walls
- Safe and solid, withstand hurricanes, tornadoes and fires
- Many insurance carriers offer home owner policy discounts on ICF homes
- Low maintenance, less repair and no rusting
- Environmentally friendly, with fewer building products, reduced site debris and lower energy requirements
- No toxic emissions
ICF for Builders
- Versatile and flexible designs, yet accept tradition exterior finishes
- International standard for past 30 years and code-accepted in US and Canada
- Successful in every region and climate, from Orlando to Calgary
- Lightweight, fast to learn, easy to use. Requires less skill and labor than a wood-frame house
- Easy to cut/insert holes, chases and rectangles
- Fast and easy drywall fastening, lap siding and mid-course corrections
- Stable and competitive concrete prices
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