1 Introduction
With the improved quality of life, people living environment beautification, concrete appearance quality problems have gradually attached importance to by people, a people in concrete structure for decoration, beautification of structure; on the other hand again to focus on concrete appearance quality improvement, especially the present expressway, railways and other large construction projects, has the appearance quality of concrete as a quality engineering construction is an important aspect of the construction, the construction unit, many of the technical staff of the appearance quality of concrete project to tackle key problem group, in-depth construction site, on a number of higher frequency, influence the appearance quality defects in wide range of anatomical diagnosis, have made certain result, also accumulated certain experience, but the color or deep or shallow, area or big or small, very irregular shape to exposed on the surface of the concrete and the effects of extensive concrete surface stain ( i.e. surface color ), is not well solved, it gradually becomes the influence of large volume concrete construction quality a obstacle. At present, how to effectively overcome the concrete surface stain, ensure the concrete surface color uniformity, is the lack of experience, but also some reference information. After many years of accumulation, the authors in this paper enumerates some US and peer in the construction of concrete has encountered problems, as well as how to analyze, solve these problems.
2concrete nature
The color of concrete, mainly cement color formation. Ordinary concrete often gray, but as a result of cement raw materials vary, but the gray depth slightly difference. In the evaluation of concrete color, usually with a reference color, the color change before the " color". The method is in a glass plate pouring concrete, after being dry, from the glass surface to see the colors as the base color; can also use dry concrete section color as the base color. The site through the concrete color to judge the degree of color change in size.
The 3 surface discoloration reasons and prevention measures
Concrete hardening in the surface, some spots are gradually formed. Because of the changes with the concrete composition, length of time, the external environment condition is different, so the concrete surface stain variety. Despite the stain species complex, but the site of common concrete surface stain from the formation depth is divided, in general can be divided into two categories:
(1) surface type. Which is concrete color difference only occurs in the surface of concrete, the concrete washing and polishing to eliminate their differences.
(2) deep. Mainly from the internal concrete, have a certain depth, is the concrete itself color differences, no reliable method to remove it.
The 3.1surface type.
Because the concrete organization for multiple hole quality, surface relatively rough, very easy to absorb water or adhesion of dust, from the initial template, the release agent to form after the external environment pollution, the common surface stains, mainly from pollution.
The 3.1.1 template rust pollution
Due to wet environment template brushing cannot very good preventing partial oxidation to rust, the color was brown.
According to the causes of surface rust, rust preventing method:
(1) the construction template brushing should be timely, quality and the use of good mold release agent, such as an epoxy resin type such as release agent, to prevent rust source.
(2) once the concrete appearance of stain, should be timely treatment. Usually the surface area available steel brush in larger range, using1:10 oxalic acid solution was scrubbed after machine grinding wheel, in order to restore the color of concrete.
3.1.2release agent pollution
The use of the site of release agent of many types, quality or not. Commonly used oil release agent, has a certain degree of dyeing, is also the pollution problem. Such as the use of diesel as demoulding agent, the surface color of concrete with multiple dark; the oil (usually the more viscous, not easy to brush off ) as demoulding agent, surface color white. Construction and empirical evidence for the use of the hydraulic oil is oil release agent in concrete surface color pollution the smallest breed.
The release agent of the pollution, the usual approach is:
(1) uses the high quality release agent. Currently used on site quality release agent for epoxy resin type release agent, does not pollute the concrete, smooth surface, uniform color, and can be repeatedly inverted. When the hydraulic oil is used as demoulding agent, try to choose good quality varieties.
(2) according to the proportion of use. Because the diesel and oil as demoulding agent, each with varying degrees of color difference, in the use of the process, such as no suitable quality release agent, can use a certain proportion mix to reconcile its color, usually and diesel oil by 1: 4ratio of mixture, also can get better effect of color.
(3) due to the low quality of the release agent pollution area is larger, surface treatment of the difficulty. Small area deep color available phosphoric acid solution, on the concrete surface to scrub, and then the steel brush in addition to, make it become white, after the restoration of concrete color. Like the color of light pollution, can use bleaching agent for cleaning.
3.1.3environment pollution
Concrete is a highly contaminated material. In the city, factory smoke and dust sewage in many places, the most serious pollution, influence area is also the most widely. Usually on the external environment pollution caused by concrete surface stains, such as dust pollution, pollution, water pollution and so on moss, processing technology is not difficult, but the repeated pollution possibility is big. The only effective way is to minimize the various sources of pollution, purifying the environment, to protect the concrete color is not or less affected by the damage.
3.2deep
Concrete deep stains, not pollution, but the concrete internal composition changed, once the concrete surface form a stain, basically use simple flushing polishing method cannot eliminate, theoretically can prevent such spots occur. On the concrete effects of deep stain for many reasons, there are common:
3.2.1cement quality changes
(1) the quality of cement stability. The cement factory production process is poor, or the small production supply situation, cause cement quality is not stable, often fluctuate, cement component changes, extremely easy to cause the concrete surface stain generation. Said from some kind of degree, cement color basically decided the color of concrete, concrete deep stain, mainly from the cement composition changes ( aggregate of concrete the effect of color color than cement ). Usually the color of cement with chemical composition and production condition changes, its color is mainly composed of a cement composition of iron oxide and magnesium oxide content and the proportion of them and, once the component content and proportion, color changes drastically. Of course, the cement clinker firing temperature, cooling rate and fineness of cement also has certain effect, but the impact is small.
(2) different types of different manufacturers of cement mixtures. The construction site cement preparation is insufficient, or the original cement manufacturers supply timely, occurrence of cement mixed phenomenon. Ordinary portland cement is generally green gray, slag cement, fly ash cement is in Portland cement mixed with gray color of the blast furnace slag, fly ash, although the basic grey but still with the ordinary portland cement colors vary, the same species of different manufacturers of cement production, due to differences, can not mix, construction if there are mixed, the concrete probability will increase dramatically.
In order to prevent cement changes, major measures:
(1) strictly control the source of cement, avoid different kinds of different manufacturers of cement mixtures. The cement to use advanced production technology, strong production supply capacity of the manufacturers, the cement can not guarantee the quality of the manufacturers, to be replaced. In general, the small factory production because of the restriction conditions and supply ability is limited, the production of cement is difficult to guarantee the quality of long-term stability and all components are not dramatic fluctuations, especially some small factories in tight supply often put all sorts of things together phenomenon, once supply will near small manufacturers cement into my door, temporary alternative supply.
(2) strengthen the cement color detection. The site often have different batches of cement color but there were significant differences between the phenomenon, sometimes gray, sometimes is gray green, sometimes black, this phenomenon in some formal manufacturers too good not to stop. Thus the desired site each into a batch of cement, to the color visual contrast and concrete color test, such as color change greatly, should be banned.
3.2.2mixing quality difference
Usually used in concrete cement quality under the condition of changing, mixing quality on the surface of concrete the effect of color dominates. The main factors include:
(1) the influence of water to cement ratio changes. Due to the water are not accurate, concrete when dry thin, water cement ratio variation. In general, the water-cement ratio is small ( less than 40mm concrete slump ) dry after multiple is gray green color, relatively deep, water cement ratio ( slump is greater than 160mm ) concrete dry hard mostly gray, light color. The construction of concrete water cement ratio changes often make the structure concrete appearance disc and the disc between the color differences.
(2) the concrete internal texture of inequality. Concrete mixing quality of concrete internal adverse effects throughout the homogeneity change, extremely easy to cause the difference in colour, which is why the same disk pouring concrete structure surface color will appear the reason of the obvious difference of.
On concrete mixing poor quality control, mainly:
(1) the site concrete mixing station should do concrete mix amount of each component accurately, especially water accurately, ensure that the water cement ratio in small range.
(2) strict control of concrete mixing quality, appropriate to extend the concrete mixing time, ensure that the mixing quality.
3.2.3construction joint
In the concrete deep stain effect more obvious, in addition to concrete quality reasons, that is the structure on the construction joint. Construction joints of concrete is usually near the deep color, and a band of plaque, and the pouring of concrete thickness is basically the same, especially the effect of concrete appearance. The main causes of:
(1) the site pouring operation is not continuous. Because the construction arrangement of improper or inconvenient construction and other reasons, led to the construction of concrete halt in a long time, the interface between concrete has emerged early coagulation. If the initial setting of the concrete implementation of forced vibration, easily destroying the concrete hardening mechanism, leading to the hydration reaction is slow, make the color burn.
(2) the concrete setting time is short. Because concrete addition of retarders or retarding time enough, in the long-distance transportation or temperature is higher in the summer, the most prone to concrete construction joint.
The main preventive measures:
(1) the reasonable arrangement of construction, avoid long time interrupt, make sure that the site pouring continuous operations.
(2) improving the performance of concrete. On the transport distance and the high temperature of summer, concrete mixed with a certain amount of retarder, prolong the setting time of concrete, to respond to the site of all kinds of unexpected events.
4Conclusion
In recent years, concrete surface stain has gradually caused the construction unit, construction units attached great importance to, and many units to as one of scientific research subjects for research. From the years of construction unit treatment of concrete surface stain practice, deeply realize the fact that although the concrete surface stain factors perplexing, treatment becomes difficult, but as long as the site is not a problem, the construction units can seriously, combine the actual situation at the scene, an antidote against the disease, treatment of concrete surface stain problem can also be smoothly done or easily solved.
The original author: Peng Qing
Source: concrete to