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Concrete Division
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Concrete’s history dates back to the Roman Empire, and while the basic of concrete have largely remained the same, technological advances of today have made this product into one of the most versatile and used building materials available throughout the world.
The words “concrete” and “cement” are often confused. Cement is the gray powder that, when mixed with water, binds the sand and rock together to create concrete. Concrete is the world’s most prolific building material. This “liquid stone” can be shaped to make roads, bridges, dams, hospitals, and homes. It is extremely strong and durable. The longevity of concrete means less maintenance and replacement when compared to other building products. These properties contribute to the environmental value of concrete versus most any other building material available today.
Concrete consists of a mixture of aggregate (sand and gravel), cement and water. Concrete can be cast in almost any shape desired and once hardened it becomes a structural element. “Ready-mix” concrete is a prescribed mix of aggregate, cement, water and often other admixtures and products that enhance the properties and characteristics of concrete.
Ready Mix Concrete is sold by volume, not weight. The measurement standard for Ready Mix Concrete is the cubic yard. A ready mix plant makes concrete with a computerized batching system. As the ready mix plant weighs the dry materials (aggregate and cement), it begins to meter in the liquid materials (water and admixtures) into the mixer. Once the system achieves the correct weights for the dry materials, the plant discharges the dry materials into the mixer where they are blended with the liquid ingredients into a homogenous mix.
Ready Mix Concrete is typically delivered from a plant to the construction location with a specialty vehicle called a mixer truck. The most noticeable feature of a mixer truck is the large drum that houses the concrete. The inside of these drums are fitted with spiral blades. When the drum is rotated in one direction, the concrete is pushed deeper into the drum, agitating the mix and keeping it in its plastic state. When the drum rotates in the other direction, blades force the concrete out of the drum. Chutes are often used to guide the viscous concrete into place. A Mixer truck typically weights approximately 30,000 pounds and can carry roughly 40,000 pounds of concrete (10 cubic yards)
Here at Ferndale Ready Mix & Gravel, we have three primary concrete divisions:
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Common Flatwork Questions
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DELAMINATION
Delaminations are similar to blisters. Delaminated areas result from water and air getting trapped between a prematurely closed surface. Delaminations are very difficult to detect during finishing and become apparent after the concrete surface has dried and the delaminated area is crushed under traffic. The primary cause of delamination is finishing the surface before the bleeding of water and air has occurred |
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SCALING
Scaling is the general loss of surface mortar due to freezing and thawing. The aggregate is usually clearly exposed and often stands out from the concrete. Scaling is primarily a physical action caused by pressure from water freezing within the concrete. |
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SPALLING
Spalling is a deeper surface defect than scaling, often appearing as circular or oval depressions on surfaces or as elongated cavities along joints. Spalls are caused by pressure or expansion with the concrete, bond failure in two-course construction, impact loads, fire or weathering.
Improperly constructed joints and corroded reinforcing steel are two common causes of spalling | |
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DISCOLORATION
Factors found to influence discoloration are calcium-chloride admixtures, cement alkalies, Hard-troweled surfaces, inadequate or inappropriate curing, variation of the water cement ratio at the surface, and changes in the concrete mix. Weather can have a large effect on discoloration. Humidity, cloud cover, and temperature can affect the color of the cured concrete. Uneven or equally place subgrade material may affect the color. Shadows from adjacent buildings or trees often affect the color. Often discoloration from these causes appears soon after placing the concrete. | |
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CRACKING
There are several reasons why cracking can occur, listed below are the main types of cracking and their causes:
- PLASTIC SHRINKAGE CRACKING – Plastic shrinkage cracks are caused by a rapid loss of water from the surface of concrete before it has set. The critical condition exists when the rate of evaporation of surface moisture exceeds the rate at which rising bleed water can replace it.
- SUB-GRADE SETTLEMENT – Insufficiently compacted subgrades and soils susceptible to frost heave or swells, producing cracks in slabs.
- CRAZING – Crazing, a network pattern of fine cracks that do not penetrate much below the surface, is caused by minor surface shrinkage. Crazing is not structurally serious and does not ordinarily indicate the start of future deterioration. Low humidity, high air temperature, hot sun or drying wind, either separately or in any combination, can cause rapid surface drying that encourages crazing.
POPOUTS
A popout is a conical fragment that breaks out of the surface of the concrete leaving a hole that may vary in size. Popouts usually occur when a piece of porous rock absorbs moisture or freezes under moist conditions. The rock’s swelling creates internal pressure sufficient enough to rupture the concrete surface. Most popouts appears within the first year after placement. Popouts are considered a cosmetic detraction and generally do not affect the service life of the concrete
CURLING
Curling is the distortion (rising up) of a slab’s corners and edges due to differences in moisture content or temperature between the top and bottom of a slab.
DUSTING
Dusting is the development of a fine powdery material that easily rubs off the surface of hardened concrete. Dusting is the result of a thin, weak layer called laitance, composed of water, cement, and fine particles. Dusting is caused by 1) floating and troweling concrete with bleed water on the surface, 2) water applied during finishing, 3) exposure to rainfall during finishing, 4) spreading dry cement over the surface to accelerate finishing, 5) a low cement content, 6) too wet a mix, 7) lack or proper curing, 8) carbonation during winter concreting caused by unvented heaters, 9) freezing of the surface, and 10) dirty aggregate.
BLISTERS
Blisters are bumps, or varying size, which appear when bubbles of entrapped air or water rise through the unhardened concrete and get trapped under an already sealed, airtight surface. Blistering is commonly caused by an excessive amount of entrapped air held within the concrete, insufficient vibration during compaction, overuse of vibration, or finishing when the concrete is still spongy. |
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