Common types of cement have many varieties. Decorative cement also has the distinction between white portland cement and colored portland cement. In addition, the principle of purchasing cement and mortar and sand is also very important.
The main technical performance index of cement
(1) Specific gravity and bulk density: The specific gravity of ordinary cement is 3:1, and the bulk density is usually 1300 kg/m3.
(2) Fineness: refers to the thickness of cement particles. The finer the particles, the faster the hardening and the higher the early strength.
(3) Condensation time: The time required for cement to add water to start coagulation is referred to as the initial setting time. The time required to complete the stirring from the addition of water is called the final setting time. The initial setting time of Portland cement is not earlier than 45 minutes and the final setting time is not later than 12 hours.
(4) Strength: Cement strength should meet national standards.
(5) Volume stability: refers to the uniform performance of cement volume change in the hardening process. The cement contains many impurities and will produce uneven deformation.
(6) Heat of hydration: The effect of cement and water will produce an exothermic reaction. In the process of cement hardening, the constant release of heat is called heat of hydration.
Commonly used cement varieties
(1) Portland cement: Portland cement clinker containing calcium silicate as the main component is added by adding a proper amount of gypsum.
(2) Ordinary portland cement: It is made of Portland cement clinker, added with appropriate amount of gypsum and mixed materials.
(3) Slag Portland cement: It is made from Portland cement clinker, mixed with appropriate amount of granulated blast furnace slag and gypsum.
(4) Fly ash portland cement: Made from Portland cement clinker and fly ash, mixed with appropriate amount of gypsum and ground.
Common cement marking
There are various types such as 225, 275, 325, 425, 525, 625 and so on. Their tensile strength is different because of different varieties, the number is different, and the MPa value is between 2.8-4.5 and 3.4-8.0.
Decorative cement varieties
Decorative cement is often used to decorate the surface of a building. It is simple to construct, convenient in shape, easy to maintain, and inexpensive. The varieties are as follows:
(1) White Portland cement: Calcium silicate as the main component, plus a small amount of iron clinker and the appropriate amount of gypsum ground.
(2) Color Portland cement: White Portland cement clinker and high-quality white gypsum, mixed with pigments and admixtures, are ground together. Common color additive pigments are iron oxide (red, yellow, brown, black), manganese dioxide (brown, black), chromium oxide (green), cobalt blue (blue), ultramarine blue (indigo), peacock blue (sea blue) ), carbon black (black) and so on.
Decorative cement is similar to Portland cement in that it has the same construction and maintenance, but it is relatively easy to pollute and the instruments and tools must be clean.
Cement mortar application and purchase
In home decoration, cement mortar is used for floor tiles, wall tiles and masonry, etc. It not only enhances the adsorption capacity of the surface material and the base layer, but also protects the internal structure. At the same time, it can be used as a leveling layer for building rough surfaces. So in the renovation project, cement mortar is an essential material.
Many people believe that the greater the proportion of cement in the entire mortar, the stronger its adhesiveness, and therefore often disagree with the decoration company in terms of how much cement is used. In actual fact, in the case of paste tiles, if the cement number is too large, when the cement mortar condenses, the cement absorbs a large amount of water. At this time, the ceramic tile surface moisture is easily absorbed and cracked, shortening the service life. Cement mortar should generally be stirred at a ratio of cement:sand=1:2 (volume ratio). At present, there are many varieties of cement on the market, such as Portland cement, ordinary portland cement, and slag portland cement, etc. Silicate cement is commonly used for home decoration.
The principle of buying cement and sand
In order to ensure the quality of cement mortar, the cement must be paid attention to whether it is 425 Portland cement produced by Dachang. Sand should be selected sand, the sand thickness of the particles is very suitable for use in cement mortar. Many customers think that the better the sand, the better the mortar is, in fact, a misunderstanding. Too fine sand adsorption capacity is not strong, can not produce a large friction and stick to the tile.
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