1, introduction
The concrete has been applied in many fields for many years, to its research is more and more thorough. To construction unit is mainly from the appearance quality of many years of unremitting efforts, but in concrete construction and use there are still many misunderstanding, this paper has many misconceptions regarding the use of ordinary cement concrete made from it, the apparent color sets out undertake an analysis, offer a few opinion, from the concrete appearance the quality of the paper draws some control method thereof, hope that the majority of the construction personnel can be reference and guidance.
In 2, the surface color of concrete forming mechanism
Concrete component production process more: Cement ( cementitious materials and aggregate ) water and adding some additives through mixing, mixing materials after pouring, vibrating, curing molding. Concrete plays a filling of cementitious materials -- cement surrounds the entire aggregate, the surface of the concrete member is filled with grout of cement, so the color is the color of the surface of concrete structures, it is color. Color depth through the water, the cement composition and construction measures and environmental changes to implement.
Concrete in addition to primary also filled with other colors. The concrete existence a lot of capillary pore. Concrete structures in the detachment of the whole protection conditions, long-term exposure to natural environment, along with the hardening process and the excess moisture evaporation, on its surface infiltration and formed many, the size of the capillary pore, the light refraction, reflection, from the pores is mainly reflecting the aggregate, coarse aggregate the color of rock.
In 3, the reasons for the formation of the surface color of concrete
( a ) the color of rock apparent effect
Here the bedrock according to original state is divided into two kinds, one kind is the result of chemical processing before the cement raw material of bedrock, one is only through physical processing of aggregate rock. The production of cement raw material burning before bedrock including raw material and clinker after firing and additional admixture. Due to geographical and geological effect around the cement production, raw materials are the existence of differences, contained in the material such as chromium, iron and other mineral elements content of different, thus leads to the same level of cement in the various components in the existence of differences. This last form is the concrete surface colors exist fundamental difference: white, gray, red, green and other colors. Here it should be pointed out that here means that the cement is widely used instead of ordinary cement, special cement.
As a concrete framework -- aggregate, due to material limited: coarse aggregate -- limestone, granite, quartzite, fine aggregate -- river sand, sand and rock crushing gravel etc.. The same due to geographical and geological conditions and effects, aggregate component is complex, therefore in the concrete interior through the refraction of light, reflecting the reflected color not the same. As a result of aggregate water mud wraps, bare area is small, through the pores of the refracted light area is smaller, so in the concrete surface to form color is a light color of rock aggregate.
These because of the limited conditions, impossible to concrete color consistency, and spend a lot of manpower and material resources are selected, so the construction of the only recognized this phenomenon.
( two) the apparent influence of construction technology of color
Construction technology of concrete construction measure by template, color, water cement ratio, the influence of environment temperature, the following are analyzed.
The 1 template
Concrete molding must be used to meet the requirements of the template. While construction in addition to the template using the isolation agent will depend on a variety of other substances, such as dirt, dust, paint: metal parts and the corrosion, but the concrete reaches a certain strength, these substances are then attached to the surface of the concrete member, forming a variety of unsightly blemishes, serious will directly affect the appearance of components quality. Even worse if the template in use without cleaning up clean, clean, use in each template, concrete surface will form a rough surface, while the template on the dirt is also getting more and more thick and even stepped away, resulting in concrete component surface form ugly stepped pattern, seriously affecting the appearance quality of concrete structures. In the course of the template is relatively smooth condition, the concrete surface color is not only the primary colors, and due to the effect of isolating agent, in the surface of concrete structures will be prominently displayed, so the isolation agent choose particularly important.
A template is difficult to do integrity, thus the template will be among the joint. Due to manufacturing, use, maintenance and other causes between the template seam is not close, in the concrete pouring process, through close parts of the slurry leakage, water leakage; the slurry erosion and with concrete curing for the evaporation of water, in the joint does not close in part forming pitted, foundry or in Cheng Qing black or spotted coat surface form ( it is not dense state ).
2construction measures
In the concrete construction, because of the use of tools such as improper, vibration rod contacts the template vibrated, will be formed on the surface of concrete vibration rod seal, and affect the component appearance effect. Due to the vibration of concrete caused by the segregation of concrete appearance of line shape, form a crack shape affects the appearance, and often cause unnecessary troubles and doubts.
Because concrete inhomogeneity or because of pouring process appear longer intervals, resulting in concrete is formed between the blue-white color difference, not all of the.
Due to the construction of the vibrational transition, resulting in segregation of concrete or piebald shape ( stone outside the dew point ), a large area of the state, is not only the appearance of poor quality and strength of concrete is reduced a lot.
3 water cement ratio
In order to facilitate the construction, concrete must have certain construction slump, in admixture circumstances is bound to increase water content and cement content; even the admixture, in the configuration of high strength concrete, such as mixing the mixture, also need more cement content. But with the cement hydration and strength of growth as well as various environmental changes, water evaporation of the concrete, formed in the concrete many pores, and in the formation of pores at the same time, in the pores within the precipitation of Ca ( OH )2crystal, so that through the refraction of light, on the surface of the concrete form of white or gray color, the separated crystal more color more white.
Portland cement water shortly after, mixing water becomes saturated solution of calcium hydroxide, is precisely the alkali and the supersaturated solution of calcium hydroxide, calcium hydroxide from a supersaturated solution crystallization, at the same time from cement ingredient: C3S and C2S react with water can be seen, generate more to calcium hydroxide. Obviously, there will be more Ca ( OH )2crystal precipitation.
2(3CaO.SiO2) + 6H2O -3CaO.2SiO2.3H2O+3Ca ( OH )2
2(3CaO.SiO2) + 4H2O -3CaO.2SiO2.3H2O+Ca ( OH )2
Cement dosage is bigger, more crystals, color is light.
4in the external conditions
In the concrete construction, cement hydration reaction by the environmental impact, especially under temperature influence. When the ambient temperature is relatively low, the raw materials: concrete coarse aggregate, the water temperature is lower, at the same time by mixing equipment, transportation equipment, containers, model of the endothermic effect of concrete into the mould, the final temperature is lower, the hydration reaction is slow, slower growth in strength, high strength concrete is spent a long time, hydration reaction adequately, precipitation of Ca ( OH )2less, so the concrete forming after the appearance of color is blue. In contrast, when the temperature is high, concrete material absorbs more heat, high temperature, at the same time by mixing equipment, transportation equipment, containers, to model the effect of the pouring of concrete, caused by high temperature, hydration reaction is fast, high heat of hydration in concrete internal temperature rises rapidly, precipitation of Ca ( OH )2more, so the color more performance for the gray, concrete although within a short period of time to reach a higher strength, but later growth limited. In actual construction, the project and so on, at the same time in order to reduce costs, and take the steam or other heat preservation measures of conservation, but notable is: temperature should not only on concrete heating and ignore the material temperature, thus warming measures should work along both lines. Select a reasonable concrete die-entering temperature and curing temperature on the strength of concrete, the most favorable growth, meet the needs of the entire construction schedule. That is to say, in the conditions permit, as far as possible the nature conservation, the environmental temperature is low, respond to raw material and equipment for heating, forming on the concrete heating maintenance, maintain a certain humidity; in a high temperature environment, deal with the raw materials, equipment such as cooling, no need to concrete heating maintenance at the same time, must strengthen water conservation.
4, concrete appearance quality control
The appearance quality of concrete due to cement, aggregate effect, is the natural quality; and construction conditions, random changes, unsteady quality. So the appearance quality control only from the construction measure proceed with, from the various construction conditions and the cement itself hydration reaction precipitation of Ca ( OH )2 crystal, eventually is affected by all kinds of external conditions, the internal concrete will form the destructive effect, causing damage in concrete structures. Therefore to control Ca ( OH )2 is the most important and primary.
The Qinghai-Tibet railway bridge and circular concrete pole concrete durability test results show that: the addition of fly ash or silica fume can make full use of Ca ( OH )2, not only to reduce the amount of cement, and higher strength of concrete, and the color is not mixed with fly ash before dark.
Through the use of special white isolation agent products -- bridge, turnout, poles, the appearance of contrast, compared the effect of uniform, consistent color, appearance, and completely replace oil and soap water as isolation agent.
The nature conservation and low temperature maintenance of railway, road and bridge appearance quality color observation and comparison, a summer high temperature time and steam curing contrast, nature conservation and low temperature maintenance of product color is deeper than the high temperature curing appearance color, close to the nature.
Based on mobility ( low water consumption ) concrete products and high fluidity concrete appearance quality comparison, small mobility products appearance color is deeper than the high flow of product appearance.
5, conclusion
In order to meet the requirements of construction and durability of concrete, i.e., to maintain the fluidity of concrete, but also control the water cement ratio, therefore in the construction should use a lot of high efficiency water reducing agent, in order to control the water cement ratio to good purpose, reduction of Ca ( OH )2. In the use of water reducing agent at the same time, requirements are added into fly ash or silica fume, improve concrete strength and increase the durability of concrete, consumption of cement hydration reaction precipitation of excess Ca ( OH )2. In the concrete before the construction of the local climate, seasonal temperature distribution were fully investigated, in order to make heating and cooling preparation; at the same time the temperature observation and construction measures of adjustment; control concrete temperature in order to control Ca ( OH )2precipitation amount to. Based on the model of clean, keep its smooth, use and concrete color consistent sound isolation agent to keep the surface of the concrete member color consistency. Through the development and implementation of a detailed operating guidelines, to avoid the vibration of concrete segregation. Through the development and implementation of a detailed steel stick measures to ensure concrete construction by slurry leakage, water leakage and less dense parts and variegated. Through the development and implementation of concrete construction plan, reduce or even avoid the discontinuous concrete construction, avoid chromatism. Through the electronic measurement and increased detection of moisture content frequency, control of concrete homogeneity, avoid chromatism. Through the control of the fine aggregate content of impurities, to avoid unnecessary noise.
Through this kind of measure control, to reflect concrete color concrete good appearance quality, economical and beautiful and durable.
Reference.
[1] GBJ10" standard" code for design of concrete structures
[2] GB175" silicate cement, ordinary portland cement standard"
[3] GB1596" used in concrete and cement fly ash" standard
[4] edited by Liu Bingjing" concrete" people traffic press