Everything about white cement

  About cement and chemisty again…

On this page already mentioned some of the so-called “chemistry" used for cement. These few words are not enough to really understand some dependencies that are associated with attempts to improve or eliminate certain characteristics that give different additives for mortars, concrete etc.

Cement - itself is the most important because it is the basis on which we interact. Cements as we know there are many types, and each of them has its extras, the quality and composition of some of them depends on the way the burned coal or used the biomass (or add-ons like "bio" or "eco" - usually in the form of various types of plants, which are to replace coal in the reduction of emissions of harmful substances). For people trying to create something better, more interesting than plain concrete, it is a very clear signal, ba - even a requirement that does not apply cements type CEM II and "worse", only focus on those marked CEM I.

Unfortunately, even if it will be used cement the cleanliness classes should be taken into account that, as nicely defines the european standard amount "of sugar in sugar" or clinker in cement is at least 95%, which is really different additives can represent up to 5% of the cement. In theory, it means nothing, but in practice it can mean a lot.

Interestingly, one of the producers is in its offer two (in theory the same) cements, numbered alike, and in the same class. The brief description of bagged cement we read that the base for the production is the "limestone ground." In the cement sold in bulk have this information does not exist. For us it is quite important that even if the words the information would not be included in any technical data and safety data sheets, which this cementing a "dog duty" to make our request, then we are sure that in the bagged cement to meet the relatively high limestone content, which only theoretically, this limit is 5% of these.

I write theoretically, because really very few customers purchasing cement in bags checked the cement in the laboratory, and the warehouse, which sells the cement has (indeed quite legally and lawfully) documents made available by the manufacturer.

To further confuse the essence of the matter - all cement behaves differently with regard to the same reaction chemistry and resistance to "overdose". It can be assumed that the greater the strength of the cement, the more sensitive it will be to "flexibility" in dosage. It is very important that if the cement is "resistant" to the overdose, it should not disturb us certain processes, certain behaviors "mistakes" in the amount, the more important the more ingredients added to the mix.Cement can also be "resistant" to use what we "throw" to him. This means that the line behind which begins the expected response can not only be shifted (much larger quantities), but very thin - that is, very quickly start to unwanted processes. These can be too fast hardening, or lack thereof, too strong liquidation or the contrary.

Cement can also be "resistant" to use what we "throw" to him. This means that the line behind which begins the expected response can not only be shifted (much larger quantities), but very thin - that is, very quickly start to unwanted processes. These can be too fast hardening, or lack thereof, too strong liquidation or the contrary.All this means that starting to use a particular brand of cement offered by a particular manufacturer, first there is an absolute need for empirical verification of its behavior relative to what we have, then strict adherence to the same cement. Any change can mean a large or very large problems, the mastery of which can take even not only days but long weeks.

The basic types of chemicals that can be found include plasticizers. Their main task is to reduce the required amount of mixing water required to be able to perform the desired component or product to mortar (also self-leveling) could be ready for use. Their composition is different, and depending on the strength and scope often lists the term "plasticizer" and "superplasticizer". The latter, as its name suggests, of course, much more strongly affects the mix, a lot more changes its properties. Quite common "ailment" plasticizers and their stronger brethren is fragile delay the initial setting time of the cement, which is offset by an increase in strength even early or final, frost resistance, etc.

Few overlooked link division, sometimes even not take into account is their use. Some of them are designed for concrete products, including concrete block, concretes, screeds and mortars.

For us this is an important division. As the concrete elements should not be so called "cancers" or "badly flooded" plays of the sides on elements, the plasticizers intended for this purpose to facilitate. Concrete commodity that does not require for an increased emphasis on self-compacting and facilitate spill, sometimes tilting. Finally, plasters - plasticizers often to have a replacement in this role lime.

That's what their type is selected, it will be used, and must depend strictly on what in the end we get what is to be created. Bad choice (after all there is to cement, or more broadly, mortars and concretes) will make all the work - eg. in the case of architectural concrete - simply go to waste, because these will be offset by the effects of which were to provide the quality and purpose of the concrete.

Each plasticizer, each plant has two very important documents that must be read before any measure is applied. The first is a technical data sheet, the second - a safety data sheet. It's one we will learn about composition, interactions, and most importantly about what exactly it is intended for. It is in them will be found as the most important information, ie what is the scope and terms of use.

Such information is usually in the form of "comprises 0.1 to 1.5% based on the amount of cement, the recommended usage is 0.8%."

What does it mean? The manufacturer has conducted research in the field and fed him that the measure fulfills its purpose; perhaps they also included a broader range, but above the 1.5% of the used type of cement (what it was - we do not know), there were, for example, difficulties in maintaining proprietary blends. The studies have also shown that the range in which the change is soon limited value of 0.8%.

Producing unusual mixes, concrete - we can not suggest a "recommended" using - perhaps the amount of the class of cement will cause only the upper value of ensuring that its properties are desirable. Limit 1.5% (in this example) is applying the information that everything above is happening on his own responsibility, that is, you may find that it will reach exactly what he wanted, and you may find that on the contrary, because there will be processes which will destroy everything.

Foaming agents - these are measures to make him blend behave more like a liquid and less like a solid or with poor ductility, at a significantly reduced amount of water needed for the process. Usually also they have plasticizing properties, but sometimes not so much as "classical" plasticizers.

You can meet with their use both as a "two in one" and "complement" to the plasticizer. In the latter case, clear and obvious is to see how the two agents they influence each other. If, in theory, resulting from the already mentioned documents (card and characteristics) that there is no theoretical contraindications to their use, they can be combined, but you need to carefully examine how mutually reinforce their action.

In such cases, you join two powerful types of chemicals, it is very important how "clean" the cement as it can easily prove that even small additions in the form of limestone or other "dust", "slag" or "only God knows what" specified by the manufacturer as "secondary" - ie an amount of less than 5%, will cause such changes and such chemical processes, for which we have not dreamed of in his darkest nightmares. Unfortunately, sometimes finding out whether (and how so, what) are these "invalid" extras in the amount of 5%, like fighting with windmills, and can be almost impossible.

Foaming agents are used widely for self-compacting concretes, self-leveling screeds etc. however, almost norm is that each type of application is important differences in the use of such chemicals, just as in the already mentioned plasticizers.

Accelerators time / early setting time - sometimes regarded as a means of supporting the use of mortar / concrete in winter conditions, as accelerated setting time means that the concrete has started to involve in pace "here and now" or start by itself to heat through even heat during bonding and not freezing.

Their use should be very cautious. In extreme cases their use may mean that a mortar or a mixture will bind us now with stirring, even in a concrete mixer. This will occur if they are used in cements, which are really large initial increases in strength, and the temperature will reach "up" several - several degrees above zero. It can then happen that not only will destroyed a large part of concrete, but also the machine in which it was prepared. There cements, where the strength after 24 hours reaches well above 20 MPa, and still adding the accelerator to strengthen.

Apart from this, you may find that the wrong use of such measures will increase all the problems that arise from rapid increases in strength: they belong to the group of micro-cracks in the concrete, excessive cramps, lack of ability to control the water demand of cement.

Aerators - their primary role is appropriate aeration mix or making it in concrete, in mortars will create a small air bubbles to improve the hardiness required very often in plaster or adhesives. As the side or secondary effects of such measures is also a plasticizing mortar, allowed her to easily fought incurring - they are often used instead of plasticizers in mortars, as they allow for the use of these inferior types of cement with various additives.

These air bubbles in these mortars are a place in which to settle unwanted salts (efflorescence, raids) resulting from the fact that the cements are alkalis, and their composition is usually far from perfect.

Number aerator which is used, and usually it is nearly-acting, due to the fact how much of these bubbles, that is, what degree of aeration of this mortar is to be. In extreme cases it is more than 40%.

Here arises a few thoughts on how to change the quality of cement, such as the elimination of certain used for hundreds of years ingredients violently forced a modification to a lesser extent, concrete, and the huge mortars.

Even in the mid-twentieth century and at the beginning of the more what almost entirely suited for both plasticity and aeration was slaked lime. It is now almost eliminated at all and replaced by substitutes plasticizing and aerating agents, and biocidal compounds, not to let grow algae in mortars. Historically, not even in the 20s exterior plaster composed of two layers thick: syringe for about 20-30 mm, based on strictly lime mortar usually with some natural additives (casein glues, charcoal, et al.) or cement lime mortar . The second layer was overhead - slightly thinner layers (approx. 20 mm) slightly weaker. It could also be a mortar or limestone or lime - cement. On syringe it is differed mostly filler, rather than sharp and coarse sand, used much finer sands, sometimes called masonry.

At the moment, the market can meet the two "main variations" on the external plaster, often referred to even as a "renovation".

In the first case it is merely a dry mixture on the basis of white or gray cement, with a small addition of plasticizer, or even without a nearly 1: 1 (2) 7 (9). The amount of water which is such a mixture intended, usually oscillates between 6 liters per 25 kg bag + - 0.5-1 l. It is almost a blend of the same composition as he had in the 80s could be found on every construction site which it was done by a team performing plasters in every house, except that in that case hydrated lime was replaced with slaked lime "traditionally". Progress.

In the second case, the composition is much more impressive. Can be read through the cement (in an amount of from dozen to nearly twenty percent), the filler (sand etc.) and ground limestone, dolomite or, generally, what is the version of a calcium compound in solid form and occurs in nature. In addition, it is pure chemistry: aerator (as mentioned works like a pores maker, and as plasticizes) and strong plasticizer together with the addition, one of whose many uses is the "softening" a water, it is sometimes even a biocide. It is surprising just what is used plasticizer, limestone (or something similar) and that softener. Their final performance and the use of very specific proportions make as a result of various reactions limestone contained in the adhesive or mortar evolve into a relationship reminiscent of his behavior and appearance slaked lime traditionally and very much like acting. Determinant of such a " very unusual" composition is accurately determined amount of water that must be applied to mortar unfit for use. As for the construction conditions, it is almost Apothecary, because you can meet the description of 25 kg 4 l + - 0.2 liters, which is basically a measurement error on the bucket, where only approximately in the form of bars molded into the plastic or metal is marked quantity.

One would like to say - what times, such chemistry. At the same time it shows total ignorance of what is now the terms of operation of the "old and traditional" chemistry.

On the other hand - this example shows vividly and clearly, how fragile is the line and how narrows the border with the addition of any further measure which aims to modify the mortar or concrete in the desired direction for us. In extreme cases, concrete ultra high strength this boundary clear is with that fragile line and there is no room or margin for any mistake, ba - even dosing must be done in a strictly determined order, as well as mixing time, which has the task of this water - usually with chemistry - spread.

The aforementioned compounds are either in powder or liquid. The method and procedure are also well defined. Basically, there are three forms of interference:

  • If the compound is in liquid form, it is almost always, almost the only existing rule is to add so-called mixing water, or water that is to be added to the mixture prepared beforehand. Dosage (ie how many installments, the length of the mixing time etc.) follows from a formula developed by us and the mix of data that declared by the manufacturer. You should not add the first chemical liquid together with the water, then in the absence of the desired effect we add only water alone. This can take revenge very soon, as early as during pouring it turns out that there is too much water, and the mixture is too liquid. In this case, added "extra" water must have a lot more time to connect with the added chemistry, which is already in the mix, to enhance its operation. If you think that it has been added too little chemistry, it should wait for a few moments and wait patiently until a mortar or a mix is better mixed (some recipes say, up to ten minutes), or add water, but slowly and well mixed with the whole chemistry which was to be added to the mix. The whole process of change should be faster and better enable us to assess the pace of the changes that occur in the forthcoming portion of concrete or mortar
  • The agent may be in dry form - that is to add it to the dry ingredients and very thorough mixing before the addition of the mixing water. Of course, check if there are any requirements for the order or not. You may find out that you first need to add the "thickest" ingredients, and the smallest at the end, or first mixed with cement, then add to the pre-prepared ingredients. All such reservations should be included in the instructions for use, which should be given at the time of purchase. In this case, the problem may be the addition to the already mixed with the water mixture as the delay in response to the application of usual large or very large.
  • Quite rare, but still - the supplement is in dry form, but to work, before adding it should be dissolved under certain conditions, to then add to the mixing water and only to the mixture. In this case, they apply for any reservations which have been expressed earlier.

Polypropylene fibers /glass fibers - this is not a "chemistry" in its pure form, but rather supplement replacing reinforcement, but because of the fact that it is currently very popular addition, as will be generally described.

These fibers in theory are neutral, resistant to external conditions, basically not much they can hurt. Added to the concrete (no longer in theory) increase resistance to fire, frost, compression, abrasion, during transport, in the same mix improves even distribution of various fractions of stone, and improve and accelerate penetration of water during mixing.

It seems that differ only in thickness and length but it is not. Some of them may be coated with a special humidifiers referred to as lubricants, others do not. Very easy to find then the differences in the application. These are the first example. For vibro concrete elements, self compacting concrete. These gentle wetting of the surface, and a large water absorption allows the unfavorable conditions (relatively dry mix, low w / c) effectively combine with a little water and blend in with the existing mix (in the case of the elements of the press - it happens under pressure machine second - under the same pressure of the concrete mix). Taken to reach this kind of polypropylene fibers allow you to "squeeze the water out of each other." Much larger amount of water can cause them to "stick together".

Others - witjout wetted surfaces make it easy to spread, even if the amount of water in the mixture is high.

Detailed information about a specific type of fiber should be included in the SDS and sheet, and any questions you should answer technologist working for a manufacturer or a general agent. If you have not, no, you can try to call the local producer and find out what exactly are the differences between one and the other types of fibers. Some general and technical information concerning these specific properties will be the same for each of the manufacturers, which will see the key differences that are associated with each type that is on offer and choose the one most suitable for us.

At the end you have to mention that the composition of the concrete mix, of course, outside of cement - that is what is the fill - thickness (granulation), fill type, humidity, amount of each component also has an impact on how they will be data-ons to keep it "how much water will be squeezed out of the proverbial stone," and how much you will need to add is how will finally during mixing behaved our concrete.

This means that there really is not one rule speaking what and how much you have to be metered, how and how much mixed. Very many factors affect the reactions that occur between individual components. Yes, in the production of concrete or mortar will be noticed certain directions in which reactions will follow, but the exact result will almost always be depended on:

  • cement
  • the type and amount of added to the mixture
  • the composition of the mixture
  • its original moisture content

which will be the result of practice, which will support the theory. It says that the cleaner cement, more decent additions (composition, quality, description, producer), more reproducible both qualitatively and quantitatively the composition or formulation of our concrete, and the humidity "output" has become - the less unpleasant and unpredictable surprises will come across on the road.

Also keep in mind that in such trials and subsequent production of the most important literature, with which you have become familiar, is in order:

  • technical data sheet cement (composition, parameters, properties)
  • technical characteristics of the card and the chemistry that we use
  • technical data sheet and characteristic properties of the other additives

They indirectly affect the composition of the mix and what, how much and when it will be added. That's all the help you get the desired effect, even in the form of such architectural concrete what we want or the mortar (sometimes on a "traditional" ingredients), as required by the specification for the facility where the works are carried out.

Knowledge work because the two sides: one allows us to take full advantage of all the modern chemistry that exists, or the other to understand the wisdom of those who have used often forgotten, and usually much cheaper and easier method - also for use on a typical construction site.

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