In this article What is dusting in concrete?We will look for answers to questions such as, what are the causes and what are the measures to be taken against it. Concrete; Cement is an important building material obtained by mixing water and aggregates (sand, gravel, etc.) under appropriate conditions. In some cases, additional minerals and some chemicals may be added if deemed necessary. (See Concrete Additives) If all components are mixed in the required proportions, cement and water will react with each other to form a hard rock-like substance called concrete. Concrete can maintain its structure for a long time under suitable conditions. However, there are some problems that affect the life of the material.
Due to the internal and external effects of the concrete surface, an increase in water/cement or, more precisely, an increase in the water/binder ratio will reduce the surface strength and form an unstable layer. The abrasion resistance of this layer is poor and the adhesion performance of the cement particles decreases. As a result, fine materials, especially cement, fall off the surface and form dust. Dust is a nasty situation that is more common in ground concrete and concrete pavements. In addition, breathing dust with a high cement content is harmful to health.
What are the Causes of Dusting in Concrete?
Dust in concreteThis happens when the water content of the concrete surface exceeds the required one. Deteriorated concrete becomes resistant to abrasion and dust forms on the concrete surface. Dust seriously affects the service life of concrete. When it comes to health, it should be avoided as inhaling concrete dust is very harmful. There are many potential reasons for this to happen. Causes of dust formation in concrete Let’s consider the issue in parts:
- Since the surface treatment is done before the concrete sweating ends, a hardened layer is formed on the concrete surface that can prevent the evaporation of sweat. This layer traps sweat and causes an increase in the water-cement ratio, creating a low-strength concrete surface.
- This dusting problem is frequently seen in concrete poured on low water absorption or polyethylene coated floors. As a result of this situation, the concrete starts to sweat more and problems begin to occur. If the cure is insufficient, there is not enough water on the surface to hydrate the cement and a weak layer is formed.
- If the air temperature is higher than the concrete temperature and there is moisture in the environment, condensation will form on the concrete surface and the surface water-cement ratio will increase.
- Inadequate ventilation conditions in closed areas will slow down the sweat on the concrete surface.
- Carbon dioxide gas emitted from various vehicles causes problems such as carbonation. Such situations are also seen as factors that reduce the strength and durability of the concrete surface.
- Due to insufficient curing, a weak layer forms on the concrete surface and the surface strength is weakened.
- Since the concrete is not protected in cold weather conditions, the concrete may freeze and the surface strength will decrease, causing problems. (See Concrete casting in hot and cold weather)
- Before the concrete solidifies, dusting may occur as a result of the increase in the surface water-cement ratio due to the effect of precipitation.
- Compared to cement, the specific gravity of fly ash is quite low. Therefore, in concrete with high fly ash content, low specific gravity fly ash has high surface density, while low binder ratio has weaker surface strength.
- Dust in concrete Among the reasons, insufficient compression of the concrete is also counted.
What are the Precautions to be Taken Against Dusting in Concrete?
- When the concrete continues to sweat, no fine work should be done on it.
- During the surface treatment process, it is necessary not to sprinkle water on the surface.
- The surface must be protected from adverse environmental conditions.
- Dust in concrete For this purpose, the ventilation of the concrete structure must be taken into account and all suitable conditions must be carefully ensured.
- In cold weather, the temperature of the concrete should be around 10 degrees.
- The surface of the concrete structure must undergo an effective curing process for a sufficient period of time.
- Don’t let your concrete dry too fast! Cover your newly poured concrete with damp burlap.
- After removal from the mold, keep the concrete element out of direct sunlight and wind for as long as possible.
- Once (and only) the concrete has initial set and hardened, spray a fine mist of water to keep the surface moist.
- Avoid using additional water when finishing your fresh concrete. The surface can be polished more easily and may appear to have a quality surface finish, but this normally only causes serious dusting and concrete surface strength problems and should be avoided at all costs.
- Do not use too much release agent on the molds. In addition to dusting, it also causes other problems such as surface voids and discoloration.
How is the Concrete Surface Repaired After Dusting in Concrete?
- Dust in concrete If the surface is formed, it can be removed up to the solid layer below by scraping the surface as a thin layer or by pressurized water or sandblasting. Also, 7 to 8 centimeters thin cementitious coating or epoxy coating can be applied if needed.
- As a solution to the dusting problem, surface hardener or dust remover products can be used. This practice will not completely cure bad surfaces, but will significantly reduce the problem. Surface hardeners usually contain sodium silicate or fluorinated silicate structures. These components react with the hydration product Ca(OH)2. These applications should be applied to concretes that are at least 28 days old and should be followed during the application.