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Color difference prevention and maintenance of color permeable bricks

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更新时间:2018年05月29日11:48:51 打印此页 关闭 Hits: 1788 Updated: May 29, 2018 11:48:51 Print this page Close
In recent years, with the needs of the construction of a harmonious society in China, the requirements for urban beautification have become higher and higher. Colorful concrete permeable bricks have been laid on urban sidewalks because of their high strength, beautiful colors, convenient construction, and low prices. Concrete permeable bricks generally use plastic mold pouring vibration molding and steel mold press molding. In the production process, some common quality problems, such as color difference, have severely affected the application quality of permeable bricks . Based on the collaborative industry practice, this article set out from the perspective of the production enterprise to comment on the cause and prevention of the typical quality common problem of color difference in the permeable bricks cast by molds.
1 Reasons for the color difference of concrete permeable bricks
After inquiry and research on many concrete permeable bricks , it is proved that the cause of the chromatic aberration of permeable bricks is very messy. During the entire process from the quality of raw materials, concrete pouring, protection, and paving, chromatic aberration may occur.
1.1 Impact of raw materials
1.1.1 Effect of pigments Iron oxide pigments, with their excellent coloring function, have a small impact on the flexural strength of cement concrete, and also have the benefits of absorbing ultraviolet rays and protecting the base material in the system from degradation and low price. It has been liked by manufacturers of permeable bricks , so most of the permeable bricks now use iron oxide pigments. Pigments are the main factor for the coloring of permeable bricks , so the stability and the control of the amount of iron oxide pigments have the primary effect on the occurrence and prevention of chromatic aberration of permeable bricks .
1.1.2 Impact of cement
Cement is the primary cementitious material of permeable bricks , and it is also one of the primary factors affecting the quality of permeable bricks . Generally, cement with higher surplus strength should be selected, and because the surface cement has a certain effect on the coloration of pigments, the color should be selected. Light cement, when producing white, yellow, green, etc.
When color permeable bricks , white cement should be used. Because the color difference between cement and pigment is not adhered to, the cement measurement error will also cause the strength to be unstable. Therefore, the cement measurement error should be controlled within 1%. Cement generally has an appropriate alkali content, and the alkali in cement easily reacts with iron oxide pigments, which inevitably affects the color rendering of the pigments.
1.1.3 Impact of Aggregate Grading
The color of the aggregate will also have a certain effect on the color of the permeable brick. After producing light-colored permeable bricks such as white and yellow, only light-colored aggregates such as dolomite and quartz sand can be used. Dark-colored permeable bricks should be dark Aggregate.
1.2 Impact of Production Construction Elements
1.2.1 collaboration ratio
When the pigment is not full, the denser the pigment distribution, the stronger the color of the permeable brick produced. Pigment fullness is generally 8% ~ 10%. The accuracy of the collaboration ratio directly affects the proportion of the pigment in the mixture, and the depth of its color varies naturally.
1.2.2 Water-cement ratio
In the case of too little water, it is difficult to ensure that the pigment is in full contact with water, it is difficult to distribute the pigment uniformly in the concrete, and it is difficult to uniformly color the pigment; while in the case of too much water, the pigment will be diluted, resulting in the lightness of the permeable brick .
1.3 Impact of protection measures
After the permeable brick is poured, after the protection of time, the pigment and concrete form a stable unity. After exposure to sunlight and air, the color fades slowly and to a lesser extent. The production process of permeable bricks molded by vibration molding The middle demolding time is the time that the surface layer is in contact with the air, so the longer the demolding time, the better the light resistance of the permeable brick (Figure 1).

In the early stage of pouring protection, the pigment has not yet formed a stable body with the concrete. The sun exposure may cause the stability of the pigment to decrease, and its surface color is difficult to ensure.
1.4 Environmental impact
1.4.1 Temperature and humidity
The environment around the production site is primarily temperature and humidity. Permeable bricks are particularly moldable. The permeable bricks have a large water ash. When the temperature is lower than 0 ° C, the surface concrete is likely to freeze, which will cause frostbite.
Alkali easily reacts with pigments, causing the color of the surface layer to change. When the temperature is too high, the stability of the pigment will change during the mixing process of the pigment with water and cement, resulting in severe discoloration of the surface layer of the permeable brick . After the permeable brick is released from the mold, the excessive humidity will increase the formation of a small layer of water droplets on the surface of the permeable brick . The water droplets will react with carbon dioxide and calcium carbonate in the air to form water-soluble calcium bicarbonate. As a result, the moisture of the surface concrete is lost too quickly, and it is difficult to ensure the normal color development of the pigment.
1.4.2 Back to alkali
Alkali reversion is a phenomenon in which many fine white powders appear on the surface of colorful concrete permeable bricks after a period of production, and is the most common phenomenon in the production of colorful concrete permeable bricks . The effect mechanism is as follows: During the hydration process of Portland cement, many calcium hydroxides are formed
Calcium hydroxide is a very soluble substance. In the early stage of cement-based material cohesion and hardening, the leisure water will gradually move outward along the internal pores to compensate for the evaporated water on the surface. In this process, , Will definitely bring out the calcium hydroxide dissolved in it
After reaching the surface of the material, calcium hydroxide will also chemically react with carbon dioxide and moisture in the air to form a white pile of calcium carbonate that is insoluble in water and adheres to the surface of the permeable brick . This is a common surface whitening phenomenon. It continues to react with carbon dioxide and water in the air to generate Ca [(HCO) 3] 2 dissolved in water. After being washed away by rain, the brightness is weakened and the color is degraded.
1.4.3 Surface brightness
The degree of smoothness of the surface of the concrete permeable brick is not the same, and the degree of reflection under the illumination of natural scattered light is also different, which will also affect people's perception of color. The decisive effect on the brightness of the concrete surface is the smoothness of the mold.
The concrete permeable brick molds are generally made of polypropylene and polyethylene mixtures or engineering plastics ABS. The smoothness of these molds is inversely proportional to the number of applications.
2 Color difference control of concrete permeable bricks
After the above analysis of the cause of the color difference of the concrete permeable bricks , it can be seen that the color difference of the permeable bricks is messy. In the production process, it is not composed of a single element, but it is often an effect composed of multiple elements together. Therefore, the occurrence of chromatic aberration of concrete permeable bricks should not be simply attributed to single factors such as poor material selection, construction problems, or harsh environment. Inductive skills should be adopted in terms of material coordination of permeable bricks , selection of construction materials, and protection methods. Ways to control.
2.1 Raw material collaboration ratio planning and material selection
The coordinated ratio planning of colorful surface concrete should adopt the orthogonal test method to quickly and accurately determine the composition ratio of each component, especially the amount of pigment. This is of great significance for the color control of permeable bricks . Materials are the basis for excellence in engineering quality. In the selection of materials, it is necessary to choose a manufacturer with production qualification and stable quality. For all raw materials entering the construction site, it is necessary to have a product quality certificate, which should be done together. Sampling re-inspection and material verification of raw materials to ensure product appearance quality. Specific issues should be noted:
(1) Choosing a reliable pigment factory is a condition to ensure common colors. When conditions permit, you can go to the pigment production plant to investigate, select samples for analysis, and conduct trial production. After understanding its function, select a pigment production plant with stable and reliable quality and a large production plan as the designated supply plant. When purchasing other pigments, factors such as durability should be considered together, or color changes and surface color irregularities will occur during the stacking process.
(2) When the general cement and white cement enter the factory, sampling should be carried out, and the content of free Ca O should be checked seriously. The cement exceeding the standard should not be selected. Together, low-alkali cement should be used as much as possible.
(3) Pigments and cement should be stored in a monotonous ventilated place to prevent agglomeration; if agglomeration occurs, use should be stopped.
(4) The batch size of the gravel grading should be consistent among the batches. The mud content of the gravel should be strictly controlled. Generally, the sand cannot exceed 1%, and the gravel cannot exceed 0.5%.
2.2 Production process control
Calibration of measuring equipment on time to reduce measurement errors. The sand and gravel should be screened before construction to reduce the sand and mud content. To ensure the same mixing time for the same batch, generally stir for 3 ~ 5min; the pigment should be added correctly when mixing. The pigment should be premixed with the cement aggregate before participating in the water. If the pigment is added after adding water, it will be briefly agglomerated. Pigments are loose and uneven. Liquid admixtures should also be mixed with water before participating in the mix.
The pouring time of the bottom concrete should be well controlled. If the distance between the bottom and the surface concrete is too long, it will cause the surface concrete to condense when the bottom layer is poured. The adhesion between the two layers is not good. After freezing and thawing, the surface layer will fall. Short, the surface concrete is too soft, which will cause the bottom concrete to penetrate the surface layer, and the demolished surface will form the surface speckle (the local color of the stone is white).
2.3 Protection methods
After the concrete is poured and before the demoulding, the protection method generally adopts natural protection. This time has a particularly important impact on the color uniformity and stability. It should be severely avoided by wind, rain and direct sunlight. It should be dried in the natural shade to prevent water exposure. . After demoulding, it should be transferred in time. When transferring and stacking, the concrete permeable bricks should be stacked in a "well" shape. There should be a certain distance between the bricks and the bricks to maintain ventilation, so as to facilitate the evaporation of the remaining water in the bricks. The surface of the place where the permeable bricks are piled up should be solid, smooth, and drained smoothly, and rainproof measures should be set up.
2.4 Environmental factors
Concrete should be poured within 5 ~ 30 ℃, and the production of concrete permeable bricks should be prevented when the minimum temperature is lower than 0 ℃. In different seasons and climates, it is necessary to adjust the water-cement ratio in a timely manner. This is particularly important for plastic permeable bricks . In humid climates such as rainy days, water consumption should be appropriately reduced; in monotonic climates with high temperatures, water consumption should be increased as appropriate. The mold deformation and smoothness of the concrete permeable bricks are inversely proportional to the number of uses. The more the number of turnovers, the poorer the brightness of the permeable bricks . Therefore, the number of uses of the mold should be severely restricted. The number of use of the general mold during construction should not exceed 20 Times.
3 Effect verification after implementing relevant control measures
Figures 2 and 3 show that the uniformity and stability of the color of the permeable bricks are greatly different between the two batches produced by the relevant skills before and after the test.
4 Conclusion
There are many factors that affect the color quality of permeable bricks , such as collaboration ratio planning, quality of raw materials, construction technology, protection, environmental factors, etc. As long as they are comprehensively controlled, they can ensure their color quality. The production quality of permeable bricks involves all aspects of the production of the enterprise, only
Some enterprise leaders attach great importance to product quality, establish a quality assurance system and related reward and punishment systems, and work together to improve the quality of employees. All operations are carried out in accordance with standardized processes to ensure the accuracy of the operation of each process. Beautiful and uniform concrete permeable brick .
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