With the development of building ecological and environmental protection, return to nature, green and low-carbon design concept, green concrete products with the same concept are gradually rising in the construction industry, especially the development and application of imitation, color, modeling and other decorative concrete. People have higher and higher requirements for concrete appearance. In addition to modeling design, color can improve the visual effect of concrete. A lot of research on concrete coloring technology has been done at home and abroad, and many kinds of colorants and their coloring technology suitable for decorative concrete have been proved by practical engineering application. At present, concrete coloring technology mainly includes inorganic pigment, color cement, color aggregate, chemical colorant and coating.
1 inorganic pigment
Inorganic pigment is a kind of pigment whose main component is one or several inorganic oxides, in which metal constitutes an important part of molecule. From the point of view of concrete properties, the pigments for concrete should be hydrophilic, alkali resistant, ACID resistant, thermal stability, frost resistance, easy to disperse, not easy to fade, strong adaptability to the external environment, and have no obvious influence on the development of concrete strength. Inorganic pigments for concrete mainly include Iron Oxide, chromium oxide, titanium nickel yellow, titanium chromium brown, cobalt blue, cobalt green, copper chromium black, etc., which are widely used in the production of roofing tiles, concrete building bricks, courtyard blocks, paving plots, etc.
Inorganic pigment coloring is relatively simple. Color concrete can be prepared by directly adding pigment into concrete, mixing evenly, forming and curing. However, it should be noted that the proportion of pigment and cement should be strictly controlled. If the additive is selected, the compatibility of pigment and additive should be paid attention to, so as to reduce the probability of color spots or stripes.
Concrete in the atmosphere, light and heat and many other environmental factors, the surface will occur frost, also known as the phenomenon of Pan alkali. In the process of concrete drying and hardening, the hydration reaction of cement occurs, and the strength development substances such as hydrated calcium silicate, ettringite and calcium hydroxide are formed. If the drying and hardening continue, the water will move along the pores to the concrete surface. In the process of water evaporation, the soluble calcium hydroxide will stay on the surface and contact with carbon dioxide in the air to form white calcium carbonate, namely pan alkali. The reaction formula is shown in formula (1).
Ca(OH) +CO CaCO +H O (1)
In order to make the concrete surface more beautiful, some measures can be taken to reduce the possibility of this phenomenon
(1) Wash the sand surface with water and use soft water if possible;
(2) The introduction of air entraining agent and waterproof agent can reduce the water consumption of concrete, reduce the water content of concrete surface, increase the compactness of concrete, and make the concrete surface smoother and more uniform in color.
Inorganic pigments are widely used in concrete projects as concrete colorants. For example, using ordinary portland cement, inorganic pigments and ordinary aggregate as the main raw materials, C20 ~ C60 cement-based color concrete products which can be used in a large area have been successfully prepared and applied to the floor of Chengdu music Park, with a single construction area of more than 1000m.
2 color cement
Color cement is used to color concrete as a whole, showing a variety of colors, patterns and textures, simulating natural materials and textures, and depicting a variety of patterns at will, so as to realize the harmonious coexistence of architecture, humanity and natural environment. It is widely used to decorate indoor and outdoor concrete floor, wall, scenic spots, such as garden, relief, square, sidewalk, parking lot, building exterior wall, roof and other decoration and transformation projects.
The concrete made of color cement is color concrete. In order to meet the requirements of architectural art concrete, white cement, color aggregate and Color Pigment are added to adjust the color of color concrete. By changing the depth of aggregate and pigment, the color concrete with different visual effects can be mapped through the principle of light and shadow irradiation; by adopting appropriate mold molding, certain process methods and aggregate decoration forming means, the line and texture of concrete can be highlighted.
The color permeable concrete prepared by color cement and coarse aggregate is mostly used in pavement, which is more beautiful and decorative on the basis of the permeability and environmental protection of sponge city.
3 color aggregate
The color aggregate itself has a distinctive natural color, and its application in decorative concrete can skillfully show the natural effect. By using its own shape and luster, it can realize the aesthetic feeling of natural pavement which can not be carved artificially, and it can realize the scene of combining with the natural environment without more decoration. Generally, colored aggregate is used to prepare decorative wall, slab and exposed permeable concrete pavement.
The common color concrete aggregates are pebbles, crushed stones, glass, recycled bricks, etc. the surface layer of the color exposed concrete prepared by it is the color aggregate exposed by water washing before the final setting, which can not only ensure that the color does not fade for a long time, but also form diffuse reflection to the strong light, reducing the reflection intensity of the wall and road surface.
4 chemical colorants
Chemical colorants for concrete can react inside and on the surface of concrete to form a permanent color. They can be used in residential beach like rock colored concrete floors (Figure 2) and bowling alley colored concrete floors. It can be used on a pre treated surface to form a unique appearance that no other material can have. At present, the commonly used chemical colorants are divided into two kinds: concrete ion colorant and concrete penetration colorant.
4.1 ion colorant for concrete
Concrete ion colorants, as the name suggests, react with minerals in concrete to form chromogenic substances, forming a stable color structure, and have the characteristics of anti-aging, natural color stability, color fastness and environmental adaptability. The commonly used ion colorants are mainly composed of metal ions, oxidants, wetting agents, etc., which are widely used in concrete products and indoor and outdoor color.
With the contact between the colorant and the concrete, on the one hand, it neutralizes and changes the alkaline environment of the concrete surface, reduces the surface tension between the colorant and the concrete, promotes the chemical reaction between the oxidant and the alkaline mineral calcium hydroxide of the concrete, increases the stability of the colorant on the concrete surface, and reduces the cost On the other hand, the oxidant in the colorant (in this paper, Hydrogen Peroxide is taken as an example) ionizes some electrons with weak ionization constant. At this time, the oxidant acts as a ligand, and the electron transfer attracts metal ions to react with the oxidant to form a stable complex on the concrete surface, thus forming a stable color concrete. The reaction equation is as follows
Coloring construction method:
(1) The concrete must be dry, and its surface shall be polished and cleaned before coloring. (2) In order to prevent color mixing, protective measures should be taken at non coloring parts. (3) Large area coloring with spray, small area coloring can use brush, brush in the form of circle. (4) The reaction time was 2-8 H. (5) When the coloring reaction is completed, 2% sodium bicarbonate water solution can be sprayed to neutralize the excess colorant, and washed with high-pressure water gun. (6) If seal curing treatment is needed, it can be carried out after the colorant is completely dried (more than 24h, and the drying time should be appropriately extended in low temperature environment). (7) Construction is prohibited in windy, rainy and hot weather.
4.2 concrete penetration colorant
Concrete penetrating colorant is a kind of colorant with organic pigment and penetrating agent as the main components, which can effectively penetrate into the surface and interior of concrete to form a stable structure with rich color and gorgeous color. It has good anti ultraviolet ability and wear resistance, and is widely used in concrete products and indoor and outdoor floor coloring.
Using the same coloring method, the concrete penetrating colorant is sprayed on the surface of the concrete to be colored, and the colorant diffuses to the surrounding and penetrates into the concrete at the same time; under the action of the penetrating agent, the surface tension of the concrete is reduced, the flow resistance of the colorant is reduced, the penetration is smoother, and the coloring is more uniform and stable.
Coloring construction method:
(1) The concrete must be dry, and its surface shall be polished and cleaned before coloring.
(2) In order to prevent color mixing, protective measures should be taken at non coloring parts.
(3) After the colorant is sprayed evenly, if you want to continue spraying to increase the color, you need to dry the colorant completely (more than 24 hours, low temperature environment, appropriate extension of drying time), then you can carry out the second coloring, in order to achieve the best coloring effect.
(4) After the colorant is completely dried, the concrete surface shall be polished by high-speed polishing machine to the required gloss.
(5) If seal curing treatment is needed, it can be carried out after the colorant is completely dried (more than 24h, and the drying time should be appropriately extended in low temperature environment).
(6) Construction is prohibited in windy, rainy and hot weather.
(7) Regular waxing maintenance should be carried out to maintain the durability and beauty of the colored floor.
5 coatings
The concrete coloring coatings are mainly latex, rubber, polyurethane, epoxy and other coatings, with a wide range of color choices and rich layers, mainly for the wall and board facing. In view of the air, water and other environmental factors in our country, it is appropriate to select water-based polyurethane coating with waterproof, strong chemical resistance, strong adhesion, aging resistance, stain resistance, good construction performance and green environmental protection to brush the concrete exterior wall. If the coloring structure is basement, indoor and other concrete structure with less ultraviolet light, the waterborne epoxy coating with strong corrosion resistance and adhesion can be selected.
The paint is evenly mixed and sprayed on the concrete surface to be colored by brushing, showing the color of the paint itself. On the other hand, the coating penetrates into the concrete structure, blocks the capillary pores, and crosslinks each other in the film-forming process, so as to ensure the perfect coating quality, effectively shield the concrete corrosion caused by the external corrosion of steel bars, carbon steel and other adverse factors, strengthen the surface of concrete substrate, prolong the life of concrete, and improve the durability of concrete. However, after a period of wind and rain, the surface layer of paint colored concrete is easy to fall off and fade, which affects the coloring effect.
Painting method:
(1) The coating must be thoroughly stirred before use.
(2) The concrete surface shall be polished and cleaned (to increase the coating adhesion).
(3) In order to prevent color mixing, protective measures should be taken at non coloring parts.
(4) Strictly control the thickness of painting to prevent exceeding the "foaming limit".
(5) Ensure good ventilation and fire protection measures (the solvent in the coating is easy to burn).
epilogue
Concrete coloring should be considered according to the actual coloring position, area, material, external conditions and other factors. Different colorants and coloring techniques should be selected under different conditions. In particular, if we want to design the concrete coloring modeling with special effects such as beach and weathering erosion, we can easily get the coloring effect required by the design by choosing the chemical colorant of the concrete first and cooperating with the mold pouring technology.
