As is known, is now on the market, Russia has an acute shortage of cement, so many traders have started to supply cement from China, where there is significant excess capacity and the number of producers in the hundreds and thousands of plants.
Some manufacturers of quality cement is much less than that and such party is not uncommon for our country. Send them back economically inefficient, and use and sell as high-quality cement is simply criminal.
For obvious reasons, the term transportation of cement can be about 1 month, and more. It is not clear how much this cement was lying in a warehouse, waiting for loading operations. Cement any brand and any manufacturer in possession of losing 5 to 15% of its activity per month. And the more cement brand, the greater the loss in percentage terms. Within six months of storage M600 and M500 and M400 are transformed into M200, if not lower. The process is not only from moisture, but also under the influence of atmospheric carbon dioxide, multilayer packaging paper this does not save.
Our company offers design and supply of equipment for the continuous activation of cement, allowing them to extend vintage cement and stabilize its basic characteristics. This equipment is also easy to return vintage old, obsolete cement.
Activation cement is also advisable in any local production with the use of cement, which in its activation characteristics and performance on the technique EMC
substantially exceed the primary, according to our estimates of up to 20%.
Grinding of cement additives today assumed the character of the epidemic, the response to it will come later. Quality supplements are not controlled - ash unstable and contain unburned coal, natural raw materials must be taken with the permission of the state and too fragmented, not including production, transportation, etc. costs. High quality cement implies a set of properties, not only 28 day's compressive strength of cubes. Really fine grinding increases the rate of hydration and a quick set of strength, reduces the proportion of unreacted clinker concrete. But at the same time, the rheology of cement varies greatly, and he can not have properties that allow you to transport it in the silo and then submit a feeder in the mixer. Moreover, rapid hydration can create problems fast setting. Moreover, rapid hardening can lead to excessive heating of concrete. In the thin material of a more complex chemical composition than the traditional Portland cement, during prolonged exposure can go crystallization processes with the fall of strength - no one was slowly occurring processes in such complex compositions, thermodynamics of such systems do not already know. If such materials used in structural concrete - the trouble is inevitable. When it comes - is unknown. Experience the classic concrete has gained more than a century excerpts. What will happen in 10 years with new materials, a broad-based - no one can predict.
On energy conservation by mechanochemical technology in this case should not speak. The cost of energy (fed in the form of electrical energy to the motor of the mill) is on the order of 1000 kcal per kg.
The phenomenon of mechano-chemical synthesis - the threshold. For heavy elements is, as for the light that make up the cement, - no, rather little is because requires energy to 2 orders of magnitude greater. Using the term "mechanochemical treatment of cement - this is the usual ribbon. When these energy costs this is likely to homogenize the components of the cement mixture at the level of dispersion of the order of several microns (less than for only some soft minerals such as gypsum). Such a characteristic finely with silicate cement additives, as the duration of preservation of properties during storage, it is very doubtful (decontamination of cement due to hydration of calcium oxide followed by carbonization is determined by the specific surface area, which is much higher than in the case of finely cement) and is not really needed. Such materials have been reasonably prepared prior to use for their own use and not for sale on the market. Obviously, the use of special cements for structural concrete for the multi-storey building is dangerous.
Mechanical activation of cement - this term is now used and not always applied correctly.
Briefly the essence is as follows. Cement - a mixture of minerals with high content of calcium, specifically, it consists mainly of Ca3S, Ca2S, Ca3A, Ca4AF. When grinding clinker introduced gypsum to retard setting, as well as slag (amorphous glass mainly of SiO2). The stone is formed by hydration of minerals, the composition of gidrozolnyh minerals with particle sizes in nm is very different from the composition of minerals to lower calcium content. In other words, to obtain the active material - cement, without a huge increase in volume during hydration and hardening, bind calcium oxide in these minerals. When hydration is formed excess calcium in the form of calcium hydroxide, which is not desirable - is carbonization, and its strength is generally lower than other components.
Therefore, the concrete must enter active additives, which are called pozzolan, to bind this excess calcium hydroxide. Slag in the USSR was added automatically to dispose of slag metallurgy, as well as to make Portland cement hunter. In the U.S., the introduction of concrete pozzolanic additives - the case of producers of concrete. Enter usually ash carryover, because They not only have a high reactivity (mostly glass), but spherical particles, which gives the plasticity of the concrete and reduces water consumption for a good placement of concrete. However, the ash in the states tend to have high quality, in particular, they are slightly cheaper than cement and missed them.
Added to concrete and ash worse than that for the environment (reducing emissions of nitrogen oxides and sulfur) energy produced at low temperatures. As a result of coal burning is greater than the limiting value of 3.5%. Therefore, they cleaned from coal special Electroseparators, bring the contents of coal to the required 3.5%. To reduce air trapping these particles of coal, which further reduces the strength of concrete, introduce organic additives.
Our ash have a very strong variation in composition and dispersion, ie do not meet the standards and are not suitable for inclusion in concrete without testing each batch of ash (which kills the whole economy automatically). But they were usually obtained at high temperatures of combustion, they have a lot of spherical particles. Energy receives energy, and ash for their departure, the servicing of which they pierce through the cost of monopoly.
Concrete - a composite material, which provided a multi-modal filling space. The denser - the higher the strength. Rubble - about 2 cm, 1 mm sand, binder about 50 microns. It is logical to add siliceous or glass additives spherical shape at the level of less than 10 microns (for submicron particle additives form values obviously no longer has). Then they perform several useful functions: a plasticizer, an absorber of excess calcium hydroxide, a filler (reduces pore size, and thus greatly increases the strength).
Returning to mechanical activation.
Fresh cement activate pointless - the chemical activity is quite inadequate. Usually, the mechanical activation of cement to understand the growth of activity after treatment in a ball mill. This increase is associated with a decrease in the average particle size by grinding and / or disaggregation. Effect of mixed concrete for durability and economy.
Stale cement has a low activity for several reasons: aggregation primarily of fine particles (in the preparation of concrete the size of the particles of binder close to the sand, so the composite optimal structure is not formed, a lot of time, high water consumption, a weak supersaturation and low strength in the end); carbonization surface due to active absorption of moisture from the air first, followed by carbon dioxide - peel reduces the rate of reaction of particles of clinker minerals with water during mixing. Mechanical activation of cement increases the activity of stale at times due to disaggregation of binding particles and damage (removal) of the surface crust of carbonate.
When activated, a ball mill grinding inevitably particles, and this has both positive and negative sides. The growth of the content of fine particles that react with water very quickly, in practice, can have negative consequences - between the preparation of concrete and its styling may be a considerable time, and early seizure leads to the need for a further excess of water (which is the pore and weakening). < br>
How to do it right? First, the cement grinding in ball mills from the manufacturer is optimal for the economy - further grinding economically impractical - normal size distribution of particles is shifted toward smaller sizes too high a price (an obvious yield plateau dispersion time of grinding). If you are going to do it ourselves, the more the economy will be negative. Therefore, machining activation is necessary only stale cement, purchased at low prices is not in peak season, and this should be done before using, since fall in activity after the activation will go even faster. On what equipment is to be done? Not in ball mills, and in the apparatus of a free kick. Even disintegrator yields positive results - but it is not grinding, but mainly the disaggregation of large particles. Fine particles are generally swaps idling - and that in this case is not bad.
Better to use EMC
- it does the same thing, but:
rotor one, manufacturing and service times easier;
called fingers work all, and not just the first 2 rows, as in the disintegrator;
air, he rides in a circle almost without loss, without a dusty environment the most active component;
large fraction, which only makes sense to grind, you can select and then drive on the cycle.
As a result, we have the optimal grain size of cement - without too much grinding, disaggregated mass without large particles that are barely functional as a binding material - because of the intimate size of the sand and slow hydration (after many years in conventional concrete is 20 percent of unreacted cement mainly Ca2S).