How to solve common concrete defects

Veronica R

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Concrete is a versatile and durable artificial stone which is made by mixing aggregate and water. It can be cast to form almost any shape and is used not just to build structures, but for driveways, built-in furniture, roads, sidewalks, dams and bridges. Concrete is economical, can withstand high temperatures and is wind, water and fire resistant. Of all the manmade materials in the world, concrete is still the most widely used. However, concrete isn't without its disadvantages. Problems, either from poor workmanship or environmental factors, that may arise when building with concrete may be remedied.

Water Seepage and Discoloration

Porous concrete or cinder block foundation walls in a basement can be affected by water seepage and damage from basement flooding due to cracked floors or locations with a high water table. Fix problems with water seepage, which also occur due to lateral pressure and window wells, by installing an exterior waterproofing membrane applied to the outside of foundation walls. Using quality waterproof paint designed for porous concrete also helps to stop water infiltration.

Concrete's blotchy and uneven color develops when consistency is not maintained in mix proportioning, not finishing the concrete at the right time, using recycled materials as cement replacements, excessive troweling, or the addition of flaked calcium chloride to accelerate concrete's setting time. Discoloration can be prevented by maintaining consistency in placing, finishing and curing. Liquid calcium chloride should be used instead of flaked, which does not dissolve easily and causes dark spots.

Scaling and Crazing

Scaling is a defect characterized by peeling or pitting of the concrete surface. It usually results from exposure to weathering, using de-icing chemicals to remove snow and ice, faulty concrete finishing, or water seeping into porous concrete exposed to repetitive freeze-thaw cycles. To prevent surface scaling, concrete has to have a minimum compressive strength of 4,500 psi. To withstand the damaging effects of freeze-thaw cycles and deicing salts concrete should contain tiny air bubbles known as air entrainment, which increases the durability of hardened concrete. Use the correct sequence for placing and finishing the concrete and avoid using de-icing chemicals.

Crazing, or craze cracks, is a pattern of small cracks on the concrete's surface caused by drying out of the surface due to rapid moisture loss due to the surface being exposed to low humidity during placement, using too many placing tools, when the concrete's surface has higher water content than that of the interior concrete or the hot sun. Prevent crazing by covering the concrete with plastic or burlap until it is ready for finishing and start to cure as soon as possible using a spray-on monomolecular curing compound, drier, or stiffer mix. Minimize the amount of troweling of the surface, and to prevent overworking the surface, use a broom finish, which is high-traction surface that provides slip resistance.

Cracking and Shrinking

Cracking and shrinking can cause strength loss. Cracking, which is mainly caused by shrinkage due to drying, and according to the Concrete Foundations Association of North America, is also caused by "thermal contraction, restraint to shortening, subgrade settlement, and applied loads." To reduce cracking, use the lowest amount of mix water required and only use calcium chloride as an accelerating admixture when necessary. Do not use rapid drying or pour concrete on a frozen surface as this will increase cracking. Contraction joints, which control the location of the cracking caused by changes in the slab dimensions should be placed accordingly at reasonable intervals.

Shrinking is caused by a high rate of water evaporation from the concrete's surface, using the wrong concrete mixture, humidity, wind velocity and temperature of concrete. It also creates curling or warping, which distorts concrete slabs by upward or downward bending of the edges. Erecting windbreaks for protection of damaging effects of wind, minimizing placing and finishing time, curing as soon as possible after finishing, and using low-shrinkage aggregate in the mix can help to reduce shrinkage. Likewise, the proper placement of contraction joints and using shrinkage compensating cement can also help prevent shrinkage.

Despite problems, what is the best part about using concrete as a building material?

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