Concrete Dusting in Construction: Causes & Preventive Measures
Hardened concrete surfaces form fine, powdery dust or chalk, which can be swept away easily. Although dusting can occur both inside and outside a building structure, it is more problematic when it occurs inside.
A thin, weak layer of water, cement, and fine particles, referred to as laitance, causes dusting on concrete surfaces. As a result, dusting risks increase with any element that reduces concrete strength, especially the top layer. Concrete bleeds when finished, is placed on non-absorptive surfaces, and is not properly cured.
Creating a durable, wear resistant concrete surface can prevent dusting on concrete surfaces. In order to achieve this, curing should be done properly, premature finishes avoided, water cement ratios should be kept low, and dry cement should not be added to facilitate finishing.
Dusting Causes in Concrete
Wrong Concrete Placement
When concrete is poured over a polyethylene vapor retarder or non-absorptive subgrade, normal absorption by the subgrade is reduced, bleeding occurs, and hence dusting of the concrete surface is a possibility.
Concrete's strength may be decreased by carbonation caused by carbon dioxide from construction machinery in enclosed spaces, such as gasoline engines and mixer engines.
Too Much Water Addition in the Concrete Mixture
A concrete surface with too much water may result in excessive water and fines resulting from excessive bleed water. As a result, there is a weak, permeable surface layer that has low wear resistance.
Before bleeding the concrete ends, carry out the final finishing operation. As a result, the top layer of concrete will have a greater water-cement ratio, reducing its strength.
Likewise, troweling on cold concrete after it has been humidified will reduce its strength.
A cold concrete floor in a basement will condense water when it is poured in cold weather and fairly high humidity.
When the surface skin is insufficiently cured, it disintegrates under foot traffic and creates a dusting mess.
Low Cement Ratio
Dusting is common in mixes with low cement content.
Freshly placed concrete may become weak when exposed to rain, snow, drying wind, and freezing.
Exact Finishing Process
The surface of plastic concrete should not be sprinkled with dry cement to absorb bleed water. Concrete bleeding can be reduced by using air-entrained concrete, modifying the mix proportions, or accelerating the setting process.
Whenever the concrete surface is wet or bleeding, do not finish it.
You can follow screeding with bull floating immediately; otherwise, bleed water will be absorbed into the concrete due to delayed bull floating. Use a jitterbug rather than a tamper to avoid bringing excess mortar to the surface of the concrete surface.
Exact Curing Method
Concrete is properly cured using a curing regime such as a liquid membrane curing compound, water, wet burlap, or other curing materials.
Low water Cement Ratio to the Concrete
For a strong, durable, and wear resistant surface, use concrete with a low water-cement ratio. It is important to combine the concrete mixture in such a way that it provides the specified strength without excessive bleeding.
Slump values should be limited to 125 mm in general. Higher values are permissible if they do not result in unacceptable bleeding. A low water to cement ratio can be achieved by adding water-reducing admixtures to concrete.
To learn more, watch the following video tutorial.
Video Source: Spray-Lock Concrete Protection
Avoid Concrete Placement in dry Surfacee
Concrete should not be placed directly over polyethylene vapor retarder or non-absorptive sub grades. Before concrete is placed on a vapor retarder or non absorptive subgrade, place 75mm to 100mm of trim able, compactable fill.
The absorptive subgrade should be lightly dampened if it has a high evaporation rate. Subgrades should not collect water on their surfaces.
Do not Pour Concrete in Cold Weather
Adding accelerating admixture to concrete mixtures in cold weather is recommended unless the temperature is over 10°C.