Bursau M., Hartsevich N., Dimitriadi N., Ivashko L.
https://doi.org/10.35579/2076-6033-2020-12-03
ABSTRACT
The article represents the analysis results of the main reasons for formation of the concrete products surface defects, caused by the physical and chemical interaction of the agent components and concrete at the interaction boarder with the mould, as well as describes the ways to prevent them. As a result of the performed analysis, the reasons for the defects formation of the concrete products surfaces were detected and analysed: grease stains, blowholes, concrete dyeing, loose deposit (scab), rusty stains on the surface of the finished product, destruction of the concrete surface layer of the finished product.
It was found out that the defects formation on the concrete surface of the finished product is caused by the following factors: a mismatched blend composition of the mould release agent, not considering the technological peculiarities of the concrete product manufacturing, an insufficient or excessive agent consumption.
The article provides the practical recommendations, allowing to significantly decrease or exclude a possibility of the defects formation on the surface of the finished concrete and reinforced concrete products.
As a result of the performed studies it was found out that the consumption within 7-10 g/m2 of the agent active material will ensure proper demoulding of the product, and at the consumption more than 20-30 g/m2 the following can be often observed: grease stains form on the concrete surface, the colour changes, the concrete surface layer looses etc.
Dyeing of the concrete surface can be caused by the following: dyeing components in the agent; presence of the substances in the agent, capable of the physical and chemical interaction with the concrete mixture components.
In most cases the surface blowholes on the concrete are the result of the air bubbles concentration at the interaction boarder between the concrete mixture and mould release agent. The size of the bubbles depends to a certain degree on the release agent. Adding of the surface active substances to the agent composition will contribute to the bubbles split to the tiniest sizes (less than 1 mm).
The surface active substances in the agent, as well as calcium and aluminium ions in the concrete will contribute to the formation of the scab on the concrete surface. The volume of the scab decreases when adding fatty acid to the agent composition.
After stripping of the concrete and reinforced concrete products, their surfaces can be exposed to the rust stains, appeared as a result of the surface dyeing with the steel mould corrosion products. The mould corrosion can appear if the applied mould release agent does not have enough capability to protect them from corrosion under the conditions of the moulded products solidification, especially, in case of the steam treatment. In order to ensure the anticorrosion protection of the steel moulds, corrosion inhibitors are added to the agent composition.
Destruction of the finished product surface layer is caused by the physical and chemical interaction of the agent components and concrete mixture. In case of improper ratio of the agent components, the reaction products in the form of a thin loose deposit layer can accumulate on the concrete and(or) mould surface. In case of proper ratio of the agent components, the layer of the reaction products is so thin that it cannot be seen visually. The obtained results of the studies can be used as the basis for development of the mould release agents’ formulation.
Keywords: concrete mixture, mould release agent, adhesion reduction, defects on the concrete products surface, ways to prevent possible defects.
For citation: Bursau M., Hartsevich N., Dimitriadi N., Ivashko L. Analysis of the Reasons for the Surface Defects of the Concrete And Reinforced Concrete Structures, Caused By the Physical And Chemical Effect of the Agents on the Concrete Mixture at the Interaction Boarder with the Mould. In: Contemporary Issues of Concrete and Reinforced Concrete: Collected Research Papers. Minsk. Institute BelNIIS. Vol. 12. 2020. pp. 45-60. https://doi.org/10.35579/2076-6033-2020-12-03
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ISSN 2076-6033 (Print)