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Frequently Asked Questions

Concrete

Q. How do I maintain my concrete installation? Show Answer

All concrete installations should be maintained regularly to assure the preservation of a high quality, long –lasting surface. Resealing and other maintenance is required periodically, depending on a number of factors including volume and intensity of traffic, UV exposure, geographic location and weather conditions.

Q. What does it mean to "cure" concrete? Show Answer

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.

Q. Why does concrete crack ? Show Answer

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. When concrete is placed on supporting soil or around steel reinforcement, the concrete mass is prevented from shrinking. This restraint creates internal forces exceeding the strength of concrete. Cracks form to relieve these forces.

Q. Does the presence of cracks indicate a structural problem? Show Answer

In most instances, the answer is no. Very narrow "hairline" cracks are aesthetic in nature and do not indicate any structural problem. Cracks that have movement where one side of the crack moves relative to the opposite side should be investigated by a professional engineer.

Q. Can I replace wire mesh with fibers? Show Answer

The answer depends on the intended purpose of installing wire mesh. If control joint spacing exceeds 30 times the concrete thickness, then wire mesh should be used to hold random cracks together. If control joint spacing does not exceed 30 times the concrete thickness, wire mesh can be omitted and fiber can be used to reduce surface cracking resulting from rapid evaporation (plastic shrinkage cracking) and improve fatigue strength.

Q. How heavy is concrete? Show Answer

Approximately 145 # for each cubic foot. A full 5 gallon pail is about 2/3 of a cubic foot it will weigh almost 100 #. An average size wheelbarrow will weigh about 500 #. A cubic yard (27 cubic feet) weighs almost 2 tons.

Q. Where has pervious concrete been used? Show Answer

Pervious concrete pavements have been identified dating back to 1985. There may be older existing projects still waiting to be identified, though. The confusion is that back then the product was known by such names as no-fines concrete, enhanced porosity concrete (EPC) and even "popcorn concrete." The NRMCA is in the process of compiling a national database of pervious concrete projects.