Problem description:
Want to know how to improve the properties of cement so that it is not easy to peel off! ! !
Analysis:
1824, British engineer asp obtained the first cement patent, which marked the invention of cement. The invention of cement provided a material basis for the development of building engineering, which made it develop from land engineering to underwater and underground engineering. Cement has been invented for more than 100 years, and it has been the most widely used cementing material.
Cementitious material refers to the material that can bind bulk materials (such as sand and stone) or bulk materials (such as bricks and tiles) into a whole in building engineering.
Cement is in powder form. After mixing with water, it can change from plastic slurry to hard stone through physical and chemical processes, and can glue bulk materials into a whole. It is a good mineral cementing material. Cement can be hardened not only in air, but also in water to maintain and develop its strength. Therefore, cement is a kind of hydraulic cementing material, which can be used in ground, underground and underwater projects.
In order to meet the needs of different construction projects, the variety of cement is increasing, reaching more than 200 kinds. Therefore, cement is usually classified according to the following characteristics.
(1) According to the main hydraulic substances of cement: Portland cement (mainly calcium silicate), aluminate cement (mainly calcium aluminate), sulphoaluminate cement (mainly calcium sulphoaluminate), etc. Because of their different hydraulic substances, their properties are also different, such as aluminate cement with fast setting speed. High early strength, good heat resistance and sulfate corrosion resistance; The volume of sulphoaluminate cement will expand after hardening.
(2) According to the purpose of cement, it can be divided into general cement (used in general construction projects, mainly five kinds of portland cement) and special cement (refers to cement slurry suitable for special purposes, such as dam cement, oil well cement, masonry cement, etc. ) and special cement (cement with outstanding performance, such as expansive cement, low-heat cement, colored cement, white cement, etc. ).
Among many kinds of cement, portland cement is the most basic and used cement, and it is also commonly used in interior decoration. In addition, white cement and colored cement were used in the decoration.
I. Cement
Cement can be divided into black cement, white cement and colored cement by color. Black water mud is mostly used for building walls, burning walls and sticking tiles. White cement is mostly used for decorative purposes such as filling brick joints. Colored cement is mostly used in water surface or wall surface and some artificial ground decoration projects, such as terrazzo.
Cement is divided into different labels according to different adhesion.
Cement can also be divided into many kinds according to its composition: portland cement, ordinary portland cement, slag cement, pozzolanic cement and fly ash cement. Our commonly used cement is ordinary portland cement and portland cement. Ordinary portland cement is generally used, and the weight of ordinary bags is 50kg.
In April of 20001year, the state formulated a new cement labeling standard. The new general cement standards are: GB 175- 1999 portland cement, ordinary portland cement, GB 1344- 1999 slag portland cement, pozzolanic portland cement and fly ash portland cement, and GB12958-65439. Six cement standards implement the strength grade expressed in MPa, such as 32.5, 32.5R, 42.5R, 42.5 r, etc. Therefore, the value of strength grade is the same as the lowest value of 28-day compressive strength index of cement. The new standard also plans the strength grade of cement in China. Portland cement is divided into three strength grades and six types, namely 42.5, 42.5R, 52.5, 52.5R, 62.5R and 62.5r. The other five cements are also divided into three grades and six types, namely 32.5, 32.5R, 42.5R, 52.5r and 52.5r respectively. ..
After testing, the State Building Materials Bureau concluded that the strength grade of the new cement standard and the cement grade of the old cement standard have the equivalent relationship in the following table:
GB 175-92 GB 175- 1999
725(R) 62.5(R)
625(R) 52.5(R)
525(R) 42.5(R)
425(R) 32.5(R)
Second, sand.
Sand, also called sand, is an essential material in cement mortar. If there is no sand in cement mortar, the setting strength of cement mortar is almost zero.
Sand can be divided into fine sand, medium sand and coarse sand according to specifications. Sand with a particle size of 0.25-0.35 mm is fine sand, medium sand with a particle size of 0.35-0.5 mm and coarse sand with a particle size of more than 0.5 mm. Generally, medium sand is recommended for home decoration.
Sand can be divided into sea sand, river sand and mountain sand from the source. In building decoration, the state prohibits the use of sea sand. Although the sea sand is clean, its salinity is high, which has a great influence on the engineering quality. Distinguishing whether it is sea sand mainly depends on whether the sand contains tiny shells of the sea. Because of the rough surface of mountain sand, the cement bonding effect is good, but the composition of mountain sand is complex, and most of them contain organic impurities such as soil. Therefore, it is recommended to use river sand in general decoration projects. The surface roughness of river sand is moderate, relatively clean and less impurities. Generally, the sand purchased from the market must be screened with a net before use.
Third, additives.
The purpose of cement mortar additive is to enhance its cohesiveness and elasticity. The main varieties are:
1) 107 glue (polyvinyl formal), because 107 glue contains poison and pollutes the environment, at present, some cities in China have begun to ban the continued use of 107 glue.
2) White latex (polyvinyl acetate emulsion) has better performance than 107, but its price is relatively high.
Four, the deployment of cement mortar
Generally speaking, the proportion of cement mortar in home decoration is about 1:3 (cement: sand), and the amount of water added should be determined according to the visual feeling of the site, neither too dry nor too thin. The proportion of additives shall not exceed 40%.
Verb (abbreviation of verb) red brick
Red bricks are generally made of red clay, and their colors are not exactly the same according to the soil quality in different places. Generally speaking, bricks made of red soil and cinder are stronger.
Because the production of red brick needs clay, which will destroy farmland or natural vegetation to some extent, and the problem of structural bearing capacity, the country has begun to ban the use of red brick in buildings, but the author has reservations about the use of hollow brick in kitchen and bathroom interior walls, because the problems caused by it are endless.
The plane of red brick is 225* 105*70mm (tolerance 5 mm).
Six, hollow brick
Hollow brick is the main wall material widely used in construction industry in recent years. Because of its advantages of light weight and low consumption of raw materials, it has become the first choice recommended by the Ministry of Construction. Like red bricks, the common raw materials of hollow bricks are clay and cinder ash, and the general specification is 240 *115 * 90 mm.
Seven, caulking agent
Color joint filler is a one-component cement-based polymer modified dry-mixed mortar. Showing off powder is usually sold in small bags in China. Although it was listed earlier abroad, it is still a new thing in China. It is durable, waterproof and compressive, and it is a substitute for ordinary joint filling material white cement. It can be used in advanced decoration projects and can fill the gaps of various stones and tiles. There are two deployment methods:
1, proper amount of water (about 5.5 ~ 6.5 liters), and fully stir until it is even and paste-free.
2. First, add water into the bucket, then slowly add the powder, and keep stirring until it is even without particles and becomes paste. Then let it stand for 5 ~ 10 minutes, and stir it a little before use.
The gap of joint sealant should not be less than 1mm, preferably1-5 mm. There is also a wide joint practice, that is, the gap is 6-12 mm.
Overview of cement:
1, the history of cement is not long, only 100 years, but the development is amazing.
2, cement varieties
1) consists of the following parts:
① Portland cement
There are six categories: Portland cement, ordinary Portland cement, pozzolanic Portland cement, fly ash Portland cement, slag Portland cement and composite Portland cement.
② Aluminate cement
③ Clinker-free (less clinker) cement
2) according to the purpose is divided into:
① Ordinary cement
② Special cement
Portland cement and ordinary portland cement
Definition: All hydraulic cementing materials made of Portland cement clinker, 0-5% limestone or granulated blast furnace slag and appropriate amount of gypsum are called Portland cement. That is to say, there are two kinds of portland cement abroad: no admixture P I and admixture P II with no more than 5%.
Unqualified cement: fineness, final setting, insoluble matter, loss on ignition, too much mixture and too low strength.
Portland cement mixed with the mixture (composite portland cement)
(1) Definition: In order to improve some properties of portland cement, increase the variety of cement, expand the application scope of cement, and achieve the purpose of reducing cost and increasing output, a proper amount of additives can be mixed into hard portland cement clinker, which can be ground together with gypsum to make different kinds of portland cement, which is referred to as portland cement with additives for short.
(2), the type of mixed materials
1, active mixture, divided into
Granular blast furnace slag
Pozzolanic mixture
flyash
2. Inert mixture (also called filling mixture), such as quartz sand, limestone and clay. And the mixture of granulated blast furnace slag, fly ash and volcanic ash that does not meet the technical requirements.
(3) Types of mixed cement
1, slag portland cement, hereinafter referred to as slag cement, code name PS.
All hydraulic cementing materials made of portland cement clinker, granulated blast furnace slag and appropriate amount of gypsum are slag portland cement.
2. Pozzolanic cement, hereinafter referred to as pozzolanic cement, code-named PP.
Any hydraulic cementing material made of portland cement clinker, pozzolanic mixture and appropriate amount of gypsum is pozzolanic portland cement.
3. Fly ash portland cement, hereinafter referred to as fly ash cement, code-named PF.
All hydraulic cementing materials made of portland cement clinker, fly ash and appropriate amount of gypsum are slag portland cement.
Performance and application of fly ash cement
1), fly ash cement has slow setting and hardening, low early strength and high late strength, even catching up with or obviously surpassing portland cement.
2) Fly ash has a small specific surface area and a small water absorption capacity, so this cement is dry and has a strong crack resistance.
3), fly ash cement bleeding faster, easy to cause water loss cracks, in the early stage of hardening should strengthen maintenance, and take certain technical measures.