Frequently Asked Questions
What is the difference between cement and concrete?
Although the terms cement and concrete often are used interchangeably, cement is actually an ingredient of concrete. Concrete is basically a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and portland cement. Concrete gets stronger as it gets older. Portland cement is not a brand name, but the generic term for the type of cement used in virtually all concrete, just as stainless is a type of steel and sterling a type of silver. Through a process called hydration, the cement and water harden and bind the aggregates into a rocklike mass. This hardening process continues for years meaning that concrete gets stronger as it gets older.
So, there is no such thing as a cement sidewalk, or a cement mixer; the proper terms are concrete sidewalk and concrete mixer.
How is portland cement made?
Materials that contain appropriate amounts of calcium compounds, silica, alumina and iron oxide are crushed and screened and placed in a rotating cement kiln. Ingredients used in this process are typically materials such as limestone, marl, shale, iron ore, clay, and fly ash.
The kiln resembles a large horizontal pipe with a diameter of 10 to 15 feet (3 to 4.1 meters) and a length of 300 feet (90 meters) or more. One end is raised slightly. The raw mix is placed in the high end and as the kiln rotates the materials move slowly toward the lower end. Flame jets are at the lower end and all the materials in the kiln are heated to high temperatures that range between 2700 and 3000 Fahrenheit (1480 and 1650 Celsius). This high heat drives off, or calcines, the chemically combined water and carbon dioxide from the raw materials and forms new compounds (tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite). For each ton of material that goes into the feed end of the kiln, two thirds of a ton then comes out the discharge end, called clinker. This clinker is in the form of marble sized pellets. The clinker is very finely ground to produce portland cement. A small amount of gypsum is added during the grinding process to control the cement’s set or rate of hardening.
What does it mean to “cure” concrete?
Curing is one of the most important steps in concrete construction, because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only if water is available and if the concrete’s temperature stays within a suitable range. During the curing period-from five to seven days after placement for conventional concrete-the concrete surface needs to be kept moist to permit the hydration process. New concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.
Can it be too hot or too cold to place new concrete?
Temperature extremes make it difficult to properly cure concrete. On hot days, too much water is lost by evaporation from newly placed concrete. If the temperature drops too close to freezing, hydration slows to nearly a standstill. Under these conditions, concrete ceases to gain strength and other desirable properties. In general, the temperature of new concrete should not be allowed to fall below 50 Fahrenheit (10 Celsius) during the curing period.
What is air-entrained concrete?
Air-entrained concrete contains billions of microscopic air cells per cubic foot. These air pockets relieve internal pressure on the concrete by providing tiny chambers for water to expand into when it freezes. Air-entrained concrete is produced through the use of air-entraining portland cement, or by the introduction of air-entraining agents, under careful engineering supervision as the concrete is mixed on the job. The amount of entrained air is usually between 4 percent and 7 percent of the volume of the concrete, but may be varied as required by special conditions.
Why does concrete crack?
Concrete, like all other materials, will slightly change in volume when it dries out. In typical concrete this change amounts to about 500 millionths. Translated into dimensions-this is about 1/16 of an inch in 10 feet (.4 cm in 3 meters). The reason that contractors put joints in concrete pavements and floors is to allow the concrete to crack in a neat, straight line at the joint when the volume of the concrete changes due to shrinkage.
Will concrete harden under water?
Portland cement is a hydraulic cement which means that it sets and hardens due to a chemical reaction with water. Consequently, it will harden under water.
How do you control the strength of concrete?
The easiest way to add strength is to add cement. The factor that most predominantly influences concrete strength is the ratio of water to cement in the cement paste that binds the aggregates together. The higher this ratio is, the weaker the concrete will be and vice versa. Every desirable physical property that you can measure will be adversely effected by adding more water.
What are the decorative finishes that can be applied to concrete surfaces?
Color may be added to concrete by adding pigments-before or after concrete is placed-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.
Inuslated Concrete Block Questions
What’s an insulating concrete form (ICF)?
ICFs are polystyrene forms that stack like blocks with steel rebar inside. Once these blocks are assembled, concrete is poured into the hollow core of the block to create walls. They are either shaped into pre-formed interlocking blocks or separate panels connected with plastic ties. These left-in-place forms not only provide continuous insulation on both sides of the wall, but also provide a backing for drywall on the inside and stucco, lap siding or brick on the outside.
How many ICF homes have been built?
Approximately 128,000 ICF homes have been built in North America since the early 90’s. Today, it represents approximately 3% of North America housing starts. The rate of growth has been steadily increasing year over year at a rate of close to 40%. Over 100 distributors and manufacturers of ICF systems serve the Canadian market.
Can an ICF home be built year-round?
Yes. An ICF home can be built at any time of the year. Unlike wood-framed construction, there is no warping when exposed to dampness from rain or snow and the technology exists to properly cure cement in any kind of weather.
What types of exterior finishes can an ICF home have?
An ICF home will accept any traditional exterior finish including brick wood and vinyl siding, stucco and stone as well as many other. The options are endless.
How can an ICF home save me money?
An ICF home keeps heat in during the winter and cool air in during the summer. This feature, combined with radiant in-floor heating, can save money on your annual energy bills.
What makes the ICF system so energy efficient?
ICF provides the best of construction techniques with modern building technology. ICF homes surpass and standard home in energy efficiency because of the combination of natural thermal mass and an in-floor radiant heating systems. This system heats from the floor up, which makes for a healthier living environment by reducing the amount of mould and dust in the air.
How does the cost of an ICF home compare to that of a framed home?
The initial cost of an ICF home is slightly more than a traditional framed house. However, when you consider the savings you’ll have in your energy bills, and ICF home will actually end up saving you money in the long run.
Is ICF considered an environmentally friendly method of building?
It’s estimated a 3,800 square foot home saves up to 25 large trees when compared to conventional construction. Concrete is inert, non-toxic, and produced from abundant natural and recycled materials. ICF homes use 40% less energy and reduce greenhouse gas emissions.
How does the homeowner benefit from this type of construction?
An ICF home offers a very quiet living environment. Studies have shown that compared to a typical wood-frame house, only about one-third as much sound penetrates an ICF wall. The home is a more secure structure as ICF is resistant to high winds and major storms. There is flexibility in design selection because ICF homes allow for larger windows with deep window sills; and with concrete as a flooring system allows for wider, more open spaces.