Winter Concreting Tips1. Plan in advance. Have equipment and materials ready before cold weather hits. Be set with heaters, insulating materials and enclosures.
2. Use air-entrained concrete.
3. Don’t place concrete on a frozen sub-base. Be sure that all ice, snow and frost are removed from surfaces the concrete will touch.
4. For durability, the fresh concrete should be kept at 55ºF. or higher for thin sections. Consider using high-early strength concrete.
5. Cure concrete to prevent loss of moisture. When heated enclosures are used, provide extra moisture by sprinkling or use steam for heating.
Vent salamanders and other fuel-burning heaters. Concrete should be allowed to cool slowly to prevent thermal cracking.
6. Do not use “antifreeze” compounds in an attempt to lower the freezing point of concrete.
7. Leave the forms in place as long as the job schedules permit. Re-shoring is necessary until concrete reaches required design strength.
8. Keep job condition records. Record, at least twice daily: weather conditions, temperatures of the air and the concrete surface.
9. If the concrete is to cure below 60ºF, water reducers or retarders may prolong the set.
10. The use of calcium chloride or admixtures containing soluble chlorides is not recommended under certain conditions:
• In concrete containing aluminum or pre-stressing strand because of corrosion.
• Where discoloration of troweled surfaces cannot be tolerated.
• Where galvanized steel will remain in permanent contact with the concrete.
• In concrete subjected to alkali-aggregate reaction or exposed to soils or water containing sulfates.
11. Concrete placed in late fall or winter should not be exposed to salts applied as deicers or salts which drip from parked vehicles.
To cure concrete is to preserve the concrete through the process of hydration. This process increases the strength and durability of
a concrete slab. Hydration sets up a chemical reaction between the cement mixture and water, thus causing the concrete to harden.
Proper CuringA) Begin to cure concrete once the cement mixture has been poured into the form you are using. Whether you are pouring a slab for a foundation, a
driveway, a concrete deck around a swimming pool or any other form, the process is the same. Finish the concrete to prepare it for curing by raking it
out level. Leveling works the rocks in the cement mixture down to the bottom and brings the actual cement mixture up. Water will form on top, but this
water evaporates quickly. You must keep the concrete moist to allow the concrete time to harden and set.
B) Keep the concrete moist by using any of several methods. Water hoses and sprinklers can be used to keep a light mist falling on the concrete. Buckets
of water can be poured over the concrete. You can dip big brooms into the buckets of water and sprinkle water over the concrete. This watering of the
concrete is the hydration process that must be used when you want to cure concrete. The final quality of the concrete will be determined by how well it
is cured during hydration.
C) Retain moisture on the concrete with some kind of covering on top of the concrete. Any material such as burlap, canvas, straw or sand can be used to
cover the poured concrete. Keep it damp while you are waiting for the concrete to cure.
D) Pay attention to the color of the concrete as it hardens. You can usually tell when concrete has cured by the way its color lightens.
Tips & WarningsCuring concrete can take anywhere from several hours to seven days, depending on the size and type of form you are pouring. Weather also plays a factor. The colder the temperature, the longer it takes to cure concrete.
Basic Hot Weather Concreting Tips1. Plan in advance. Have equipment and materials ready before the hot weather arrives.
2. Keep the subgrade and forms moist so they will not absorb water from the mix.
3. Keep sunshades and windbreaks available and use them whenever possible.
4. Have everything prepared before the mobile mix truck arrives. Don’t make the truck wait for you.
5. Concrete should be placed, struck off and darbyed immediately.
6. Use evaporation retardants, fogging or misting with water, or cover with a vapor-proof sheet after screeding. This will help prevent rapid drying,
crusting, plastic shrinkage and rubber sets.
7. Temporary covers, like continuously moistened burlap, may be placed over the fresh concrete & removed in small sections ahead of the finishers.
8. Substituting a burlap drag or broom finish will eliminate other high risk finishing practices, such as smooth trowel finish.
9. Curing should take place when the surfaces are hard enough to resist marring.
10. Seal with a good, quality sealer a minimum of 30 days after placing and curing.
11. Remember to protect the crew in high temperatures. Drink plenty of fluids and be careful with long exposure to the sun.
There are always brief stretches of weather during any season when it is not feasible or advisable to place concrete.
Finishing Concrete Flatwork Tips• Consult our team of experts on selecting the correct concrete mix for your project.
• After placing and consolidating concrete, use a wood or metal screed with a straight edge to strike off and level the concrete.
• Immediately float the surface with a wood or metal float. A metal bullfloat is best for large slabs. Pushing and pulling the float edge
across the slab, smoothes the small ridges left by the screeding step.
• Edge the concrete with an edging tool if a round smooth edge is desired. Run the edger back and forth, using the form as a guide.
• Cut the control joints. The grooving tool should be 1/4th the depth of the slab. Or, control joints may be sawed later.
• Finish or trowel the concrete as desired for function, serviceability & attractiveness, according to its end use.
• Exterior slabs (driveways, patios, sidewalks, etc.) should be sloped to drain properly.
• A broomed finish will give a non-slip textured surface when wet.
• Garage or warehouse floors usually need to be level and quite smooth.
• Repeated passes with a steel trowel and increased pressure will produce a very smooth surface.
• Do not sprinkle water or cement on the concrete while finishing it.
• Cure the concrete as soon as all finishing is completed and the water sheen has left the surface.
• Our staff has information on special finishes such as; exposed aggregate, (t-5) integral color, stamped or patterned. Just ask!
If you are unsure of your finishing abilities and seek assistance with your concrete project, feel free to contact our office for names of qualified concrete finishers and contractors.
Crack ControlConcrete expands and shrinks with changes in moisture and temperature. The overall tendency is to shrink and this can cause cracking. Irregular cracks are unsightly and difficult to maintain but generally do not affect the integrity of the concrete.
Joints are simply pre-planned cracks. Joints in concrete slabs can be created by forming, tooling, sawing, or by the placement of joint formers. The National Ready Mixed Concrete Association recognizes that cracks in concrete cannot be prevented entirely, but they can be controlled and minimized by properly designed joints.
The NRMCA recommends the maximum joint spacing should be 2 1/2 ft. times the thickness of the slab. Or, a 4 inch thick slab joint spacing should be about 10 feet. It is recommended that maximum joint spacing be limited to 15 feet. Sections should be somewhat square. The length of a section should not exceed 1 1/2 times the width.
Plan exact location of all joints, including timing of contraction and joint sawing before construction. Provide isolation joints between slabs and columns, walls and footings, and at junctions of driveways with walks, curbs or other obstructions.
In its simplest form, concrete is a mixture of paste and aggregates (sand & rock). The paste, composed of cement and water, coats the surface of the fine (sand) and coarse aggregates (rocks) and binds them together into a rock-like mass known as concrete. A remarkable trait to this process is that concrete is plastic, and can be molded or formed into any shape when newly mixed, becoming strong and durable when hardened. This versitality explains why concrete can build skyscrapers, dams, bridges, sidewalks, superhighways, and homes.
The key to achieving a strong, durable concrete rests on careful proportioning and mixing of the ingredients. A concrete mixture without enough paste to fill all the voids between the aggregates will be difficult to place and will produce a honeycombed surface, rough and porous concrete. A mixture with an excess of cement paste will be easy to place and will produce a smooth surface; however, the resulting concrete will be more likely to crack and be uneconomical.
A properly proportioned concrete mixture will possess the desired workability for the fresh concrete and the required durability and strength for the hardened concrete. Typically, a mixture is by volume about 10 to 15% cement, 60 to 75% aggregates and 15 to 20% water. Entrained air bubbles in many concrete mixtures may also take up another 5 to 8 percent.
Portland cement’s chemistry comes to life in the presence of water. Cement and water form a paste that surrounds & binds each particle of sand and stone. Through a chemical reaction of cement and water called hydration, the paste hardens and gains strength. The character of concrete is determined by the quality of the paste. The strength of the paste, depends on the ratio of water to cement. Water-cement ratio is the weight of the water divided by the weight of the cement. High-quality concrete is produced by lowering the water-cement ratio as much as possible without sacrificing the workability of fresh concrete.
Generally using less water produces a higher quality concrete provided the concrete is properly placed, consolidated & cured.
Besides portland cement, concrete may contain other cementitious materials that include fly ash, a waste byproduct from coal burning electric power plants; ground slag, a byproduct of iron and steel manufacturing; and silica fume, a waste byproduct from the manufacture of silicon or ferro-silicon metal. Some of these cementitious materials are similar to the volcanic ashes the Romans mixed with lime to obtain their cement binder. Some of these structures still exist today!
The concrete industry uses these materials (normally disposed in land-fills) to the advantage of concrete. The materials participate in the hydration reaction and significantly improve the strength, permeability and durability of concrete.
"Proportioning Mix Mobiles” - Mobile Volumetric Plants“Mix Mobile” are truck-mounted, volumetric batching and continuous mixing units. These “plants-on-wheels” often supply small-volume or specialty pours and offer the convenience of freshly mixed concrete in fairly precise quantities. The unit consists of a truck with bins of sand, coarse aggregate, cement, water, and admixtures. The aggregate bins have longitudinal belts at the bottom of the sand, and as well as coarse aggregate bins that drag the aggregate to separate adjustable gates at the rear of the bin. The speed of the belts is connected to a feeder in a cement bin, and all three materials drop down into a mixer. Flow meters control the introduction of water and admixtures
Protect Your SkinProtect your self from irritation and chemical burns when working with fresh concrete. Severe burns can result with on-going contact between fresh concrete and skin surfaces, eyes, and clothing.
• Avoid direct skin contact with sand and aggregate, they are very abrasive to your skin.
• Don’t handle wet cement directly.
• Wear protective clothing, such as waterproof gloves, long-sleeved shirts, and long pants to keep the concrete from making contact with your skin.
• Wear rubber boots if you must stand in the fresh concrete while it is being placed, screeded, or floated to prevent skin contact.
• Use waterproof pads to protect your skin, knees, elbows, or hands from contact with fresh concrete during finishing.
• Get minor burns treated by a physician, if they persist, seek immediate medical help.
• Flush eyes and skin that come in contact with fresh concrete immediately with clean water.