Let’s talk about something rock-solid. Let’s talk about concrete. It is an important subject because, according to ScienceDirect, concrete is the most consumed material globally, with three tons used per person per year worldwide. And in construction, twice as much concrete is used as in all other building materials combined. Thirty billion tons of concrete are used worldwide each year.
Questions and Answers About Concrete
First, many people confuse cement and concrete. Cement is an ingredient in concrete. Concrete is the final product used for roads, sidewalks, etc. So, there aren’t any “cement trucks,” only “concrete trucks.” And no “cement sidewalks,” only “concrete sidewalks.”
What Is Cement?
Cement is a powder, a hardening ingredient used in concrete. It reacts with the water used in the concrete formula, essentially becoming the “glue” that holds the components together and making the substance strong when cured.
Portland cement is the generic term used, although it doesn’t come from any place named “Portland.” Cement is typically composed of 60 percent lime/limestone, 25 percent silica, 5 percent alumina, and 10 percent other materials like gypsum and iron oxide.
What Is Concrete?
Concrete is the combination of cement powder, water, and aggregates. The aggregates include sand, gravel, or crushed stone. Cement comprises 10 to 15 percent of the concrete mix, whereas aggregates comprise 60 to 75 percent of the mix. The balance is water—clean water with no impurities, salt, or organic material that could compromise the integrity and strength of the concrete.
The mixture hardens through hydration, where the components are hardened into a solid rock-like mass. The concrete continues to get harder as it gets older.
Why Is Concrete so Valuable?
Concrete has a lot going for it because it’s:
- Highly durable and resilient.
- Low maintenance.
- Versatile, enabling its use in many shapes, textures, forms, and surfaces.
- Easily cured; it hardens at ambient temperatures.
- Useful in underwater construction.
- Usable in high-temperature construction projects.
- Effective in making buildings quieter.
- Effective in enhancing building safety.
What Does it Mean to “Cure” Concrete?
Proper curing of concrete is essential to achieve its strength and durability and to have good surface integrity. Curing is the process of hardening, which results from a chemical reaction between the cement and water, called hydration.
The ambient temperature must be kept within a specific range during the hydration process, and the concrete surface must be kept moist. Proper curing takes five to seven days after the concrete is poured. If the air temperature is too hot, too much water can evaporate from the concrete. If the temperature is too cold, hydration stops.
What Causes Concrete to Crack?
If too much water is used in the concrete mix, excess water can evaporate, and the concrete will shrink too rapidly. Cracks can be of two types: crazing cracks and shrinkage cracks. Crazing cracks are a network of fine cracks or fissures on the concrete surface caused by shrinkage of the surface layer of concrete.
Shrinkage cracks are caused by changes in moisture in the concrete. Additionally, cracks can result from improper finishing and poor planning in the pouring or forming of the concrete.
How Is the Strength of Concrete Measured and How Much Weight Can Concrete Support?
The durability of concrete reflects its ability to support loads. Its strength is measured in pounds per square inch (PSI), with higher numbers representing higher strength. For example, most contractors use concrete rated between 3,000 and 5,000 PSI for residential applications like garage floors and driveways, thus supporting weights between 3,000 and 5,000 pounds.
Conventional concrete has a strength of 7,000 PSI or less; concrete with PSI levels between 7,000 and 14,500 PSI is considered high-strength concrete. In each case, the standard is that desired concrete strength should be achieved in 28 days to attain substantial hydration, although concrete will continue to gain strength over a longer period.
Concrete can be made stronger by adjusting the ratio of water to cement. The higher the water to cement ratio in the mixture, the weaker the concrete will be. The lower the ratio, the stronger the cement will be. Concrete strength also depends on the quality of the aggregates in the mixture.
Is There a Way to Reinforce Concrete?
Concrete can be reinforced and strengthened by adding rebar for structural reinforcement. It can also be strengthened by using fiber or wire mesh or by being mixed with fly ash.
How Is Concrete Measured?
It is measured by the cubic yard, 3 feet by three 3 by 3 feet, equaling 27 cubic feet. A cubic yard of concrete will weigh about 4,000 pounds. An expert contractor will be able to properly estimate the amount of concrete needed for a specific project.
How Can Concrete Be Protected from the Aggressive Effects of Acids?
Few things have deteriorating effects on concrete. However, most acids do. The most important thing is to choose the right concrete formulation, a quality mix with maximum chemical resistance. Protective treatments, including coatings and sealers, can be applied to keep acids or other corrosive substances from contacting and damaging the concrete.
Can Stains Be Removed from Concrete?
Stains can be removed using a variety of methods. Dry methods include sandblasting, scabbing, shot blasting, grinding, and scouring. Of course, care must be used not to excessively impact and damage the surface. Wet methods include the use of water and chemicals that are specific to a stain.
Is All Concrete Gray?
The natural color of concrete is gray due to the iron or manganese components in the cement formula. Other colors can certainly be added, and the iron and manganese lowered or removed.
Can Decorative Finishes Be Applied to Concrete?
In addition to changing the color of concrete, colorful aggregates can be added to the surface of the concrete, and textured finishes can be applied, ranging from a smooth polish to a rough gravel-like texture. Additionally, patterns can be stamped, rolled, or inlaid on the concrete surface to look like brick, tile, or stone. Also, divider strips can be used to create other patterns.
What Can McConnell & Associates Do for You?
For just about every surface under your feet, McConnell & Associates can help you. Since 1965, McConnell & Associates has been restoring, beautifying, and protecting surfaces throughout the Midwest. That includes restoring and repairing concrete sidewalks, curbs and gutters, resurfacing tennis courts, installing new running tracks, and protecting paved and sports surfaces.
McConnell & Associates is the regional expert in preventative maintenance, including asphalt installation, maintenance and repair, seal coating, crack filling, patching, paving, striping and markings. We also do concrete repair, curb & gutters, concrete sealing, and speed bumps.
We can install and maintain everything from a backyard tennis court to a complete athletic complex for a school or community center.
Contact McConnell & Associates with offices in Kansas City, St. Louis, Pevely, and Wichita. McConnel now leads the industry with premium pavement, concrete, and sports surface products and services. We offer the depth of experience to make your project a success.