There are many factors to take into consideration when placing concrete, one of which I personally had never thought of was the challenges in placing concrete on a windy day. It is often a challenge because the top may of the pour may cure faster than the bottom as the water evaporates out of the concrete. This uneven evaporation of water allows for the pour to shrink at different rates causing cracks. The compaction of the subgrade, or ground the concrete is poured on top of, is very important. Uneven spots can cause tension in the concrete as it shrinks. This tension is caused by the concrete catching on the low spots were the structure cannot easily shrink.
Kenneth Wayne Meyer offers a few simple tips in his article to help prevent large visible cracks from developing. First you must ensure that you fully compact your substructure. This can be done using a garden tiller which will loosen the topsoil. He then suggests using a walk behind compactor to compact the soil to a firm solid state. This firm solid compaction will ensure that no soft spots in the soil are present which may cause a low spot once the concrete is poured. Once you have compacted your subgrade to a sufficient point, add a layer of sand to allow for even friction throughout the subgrade. This layer of sand should also be leveled.
Now that the subgrade has been completely compacted and allows for an even frictional force throughout, you are ready to set in your reinforcing. Meyer suggests using wire mesh panels because they are easier to work with and keep on the top half of the slab. After your rebar has been set you are ready to start your pour.
To ensure that you have a good pour and your concrete cures the same throughout, it is important to wet the bed of sand which was laid to level the subgrade. If the bed of sand is not wet down before beginning your pour, the water in the concrete mix will be sucked down away from the concrete into the sand bed, allowing for the bottom of the slab to cure faster than the top.
After your pour has been completed, it is important to protect your slab from high winds, direct sunlight, rain, and any other harmful elements that may allow for temperature or evaporation variants while curing.
Finally it is time to put the finishing touches on your new concrete structure. Contraction Joints should be added to a depth of 1/4th the depth of the slab and on intervals 25 to 30 times the depth of the concrete. Cracks in concrete appear in the weakest areas, these Contraction Joints provide weak areas in the concrete providing for somewhere for the concrete to move. After two weeks have passed and the slab has completely cured, the joints can be sealed. Sealant will provide a cushion for the joints to move while at the same time protection the joint from water and ice penetration.
By following these simple yet effective tips we can all hope to avoid some of these larger eyesores.
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