لخّصلي

Concrete shrinkage is partly reversible (water reabsorption) and partly irreversible (chemical bonding). Irreversible shrinkage stems from absorbed water loss within calcium silicate hydrate micropores, and carbonation shrinkage occurs when calcium hydroxide reacts with carbon dioxide, causing water evaporation and reduced pH. Carbonation shrinkage is influenced by CO2 levels, permeability, and humidity (optimal around 50%). Shrinkage is also affected by factors like specimen size (smaller specimens shrink more), relative humidity (higher humidity reduces shrinkage), and the presence of aggregate and reinforcement. Adding slag to concrete reduces plastic shrinkage due to lower water needs; its effect on dry shrinkage is less consistent across studies. Porosity and permeability change with age, affecting shrinkage. Further research is needed on cement composition, curing, and the long-term effects of using slag, which is a significant supplementary cementing material but whose production might decrease due to environmental regulations. A six-page report on slag in Turkey is assigned for next week, covering its history, availability, properties, current use, and potential alternative applications.

How can we convert? It is, some of them is irreversible, some of them is reversible. Reversible means that when the concrete shrinks due to the loss of water, when we put the concrete inside the water, some of them, some of the shrinkage will come back. Please, read the notes, you know, due to the last weeks. Even you put the concrete inside the water, some of the shrinkage is irreversible. The irreversible shrinkage is coming from the chemical development of chemical bonds between the cement chain. Therefore, if there is no isotropic water is involved between the calcium silicate hydrate, no irreversible drying. But for longer drying period, some of the shrinkage is irreversible. Not coming. And evaporation of free water from the capillary pores, water which is not physical water in macro pores, does not yield considerable drying shrinkage. But losing the free water from the micro capillary pores, not macro pores, from the calcium silicate hydrates, this leads to shrinkage. Therefore, the absorbed water loss is the main reason. The absorbed water loss from the micro pores, from the calcium silicate hydrate gels, are the main reason of the drying shrinkage. Another shrinkage is the carburetion shrinkage. If you remember from the cement product, one of the main hydration product is calcium hydroxide, from the three calcium silicate and decalcium silicate hydration. When this calcium hydroxide reacts with carbon dioxide and water, what's going to happen? Calcium carbon plus water. When this water evaporates, carburetion shrinkage happens. As a result of the carburetion, concrete loses some of the calcium hydroxide. This is long form, this is short form. And water, as a result, carbonation, calcium carbonate is formed. pH or passive alkalinity of the water is reduced. There will be a risk of corrosion, plus there will be a risk of carbonation shrinkage and cracks. Carbonation shrinkage depends on the carbon dioxide in the paint. Permeability of the system, relative humidity of the paint, and humidity of the system. All of these parameters affect the carbonation shrinkage. Carbonation cannot occur effectively if the pores are full of water, because carbon dioxide cannot enter inside the pores. If the pores are empty, there is no water, again, carburetion will not occur. Carburetion only happens at intermediate humidity level, about 50%. Because for the carburetion reaction, water is needed, and carbon dioxide is needed. If the water is full, no carburetion. If there is no water, no carburetion. Intermediate, the highest level of carburetion is obtained at intermediate humidity level, around 50%. So, we have the book of Professor Mehra, country book. I can share this book, electronic version of this book with you, and please read it. Shrinkage cream, type of the shrinkage. If you look at here, the growth of the paint, what does it mean, the growth of the paint? For example, we have the concrete elements and the foundation layer. Or we have the concrete elements and the steel part inside the concrete elements. Or we have the concrete elements, and in both sides, it is fixed. So this means that the growth rate will be higher. If there is no growth rate, the concrete will have more cracks. But if the concrete is not ready to move, there will be a crack. And the growth rate is supplied by aggregate, sometimes by reinforcement, by foundation, etc. All of these parameters will reduce the shrinkage parameters of the concrete. Here, effect of relative humidity, relative humidity percentage. You can see here, when the relative humidity is around 100% of the time, there is no shrinkage. With 70, less amount of shrinkage. With 50, much more higher shrinkage. Therefore, relative humidity is one of the main parameters which improves the shrinkage of the concrete. Or, specimen size. If the specimen size is big, the movement of water from inside the concrete to outside, atmosphere, is difficult. If the specimen is thin, for example, big pavement, thin one, the movement of water is very easy. For that reason, small specimen shows higher shrinkage than the bigger specimen. Because the drive takes longer time, wetting is much faster. This means that the reversal part of the drive shrinkage by drive through the walls can be recovered, but by wetting. For example, as I said to you, if you remember all the last weeks, let's look at the shrinkage behavior of the concrete. This is the time, this is the shrinkage. It looks like this one. This is the drive. When it is wetting, what there is left, this is the reversal. Shrinkage, this is even worse. The drive needs too long time, but when you put the concrete inside the water, the wetting is very quick. For that reason, the reversal of shrinkage will come back quickly, but the reversal of shrinkage will remain for an infinite period of time. And plastic, let's go back to slag in terms of different point of shrinkage. Most of all, the plastic shrinkage is less for concrete with slag. This is due to the decreased water requirement. Less mixing water, less plastic shrinkage. For dry shrinkage, available test results indicated that replacement of ornaments and by slag has little or no influence. If reduced, the potential effects could be the slight increase in dry shrinkage. However, from the level as books reported, 10% less dry shrinkage, but we can say similarly. Generally, difference in conclusion from different research due to the test conclusions. And the topic of effect of cement based on shrinkage from different point of views can be good research topic. Effects of the finds of cement based material, composition, curing period, curing characteristics, etc. These are the things that the researchers need to study for a long period of time. What about the porosity and permeability? At early age, Portland cement and slag cement results were more porosity because low reaction. At later age, volume of porous 3 to 5 nanometer size slag is more porous slag. This means that porous structure is remarkably changed. Small size pores are high. Small means that there is good permeability. Small means that there is not permeability. Pores are relatively large, discontinuous and thin walled in systems with porous cement. This is another research, one of them is Uchikawa, the other one is Portland. And as I said to you, pores structure yields less permeability. Therefore, use of the nature photograph or use of the slag behaves very similar. This is the final notes for this week. And you need to prepare, you have to look at one of them I mentioned a bit before, compared to slag and Uchikawa. This is the second one, around six page reports I expect from you for the next week. Source and history of use of slag in Turkey. Availability and capacity. Properties of each slag. Current taste profile. And any supply of plastic slag products for other usage, for aggregating or for other usage. Please make a search and prepare a short report for the next week. Okay, so this is the slag. Slag is one of the most important mineral. At least for now, maybe in future, because of the coal combustion, due to the environmental regulation is reduced. And slag production will reduce because steel factor is one of the main sources of the carbon dioxide emissions. But now, slag is one of the main supplementary cement materials. And we can obtain a very good behavior with the use of the slag. So, let's hope we have an impressive report.