MOOC Materials Characterization 5.3: Masonry. Composition
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MOOC Materials Characterization 5.3: Masonry. Composition

September 22, 2019

Welcome to topic 4 of module 5 of characterization of masonry works. In this topic, we are going to characterize the composition of the elements that compose masonry. In the first place we are going to study mortars. The first test we perform on mortars is an x-ray diffraction test in which we will obtain the crystalline components of the mortar. In the test, we observe that we have the components of the binder that are dolomite and calcite and aggregate components, which are plagioclase quartz and phyllosilicates. Then we perform the thermogravimetric tests in which the piece is subjected to a gradual heating and we are going to see the isothermal peaks that we have to apply to maintain the curve of rising temperature and the weight losses that occur in those peaks. These peaks are often due to phase changes In the graph we see the pink curve corresponding to the energy to be applied to the sample to maintain that curve and in green color these weight losses. In the image we have the thermogravimetric curve of the first mortar sample of corresponding to the first construction phase. That is, according to historical studies, the masonry works built between the fifteenth and eighteenth centuries. Up to 100 degrees, we can see the weight losses and the endothermic peaks of the heat to be applied to evaporate the water; up to 420 degrees we see the endothermic peaks of the crystallization of the salts. At 700 degrees centigrade we have a first decomposition peak of the dolomite binder, and at 800 degrees centigrade we have the decomposition peak of the calcite. If we look at the green graph, we can obtain the percentages of weight loss in each phase change, corresponding to the percentage of that component in the total mixture. And we observe how at the calcite peak, there is a 23 percent weight loss. Finally, the waste that is will not be lost is the aggregate or quartz, which is 65 percent. Then, if we have 23% of lime and 25% of aggregate, we will have that the proportion of our mortar in the first phase is a lime aggregate proportion of 1 to 2,
corresponding with a poor binder mortar If we observe the sample of the mortar of the second period, built between the nineteenth and twentieth centuries, we observe the same peaks, but only in the case of calcite, the weight loss that occurs is of 34.23 percent, while the waste is soluble, or at least it is not lost by the heat, because it is quartz, and it is the 60%. Therefore it is a mortar with a proportion ratio lime aggregate of 1 to 1.3 So, the mortar of the second period has a greater amount of binder, therefore, it has better resistances for being a higher quality mortar. From the analysis of the mortar samples using the scanning electron microscope we observed, on the one hand, that no crystals of calcium hydroxide can be seen, which means that after all those years, everything in the calcium hydroxide has been carbonated. On the other hand, we also do not observe hydrated calcium silicate gel. If we carry out a historical study of the introduction of cement in Spain, because sch is a product of cement hydration, we observe that in 1835, the first natural cement factory in Spain is opened in Bajo Urola, in the Basque country. The first Portland cement factory in Spain was opened in 1898 in Tudela Veguín and and finally the first Portland cement factory in Granada is the one of Inocencio Romero de la Cruz in Atarfe, which opened in 1921. Therefore, we can conclude that most probably the masonry woks were built in the eighteenth century, or rather in late, or early twentieth century, because there is no cement sample in our masonry work, and cement once it entered Spain was started to be used in almost all masonry works relegating lime to the background. As for the bricks, if we observe the x-ray diffraction we can see, on the one hand the components of the clay aggregate, which are the quartz caliches, which is the calcite, and finally the components of the clay which are philisilicates, gehlenite, wallastonite, diopside and hematite. If we subject a piece of brick from the first phase to the thermogravimetric test we again obtain the curve of both endothermic peaks and weight loss in which we can observe up to a thousand degrees Celsius the evaporation of the water it can have. At 800 degrees, the weight loss due to the calcite of the caliches that can be in the ceramics takes place. In that same graph we observe many endothermic peaks; a peak at five hundred degrees, another one at 700 degrees, and all these peaks are due because during the burning of the ceramic piece, all the parts of the piece did not get to be heated up to that temperature. This indicates that the piece was not heated in its burning process at very high temperatures. Or that those temperatures did not reach the whole piece. However, if we look at a piece manufactured later, with masonry work from the second phase, from the nineteenth century or the twentieth century, we see the same peaks of the 100 degrees of water, and the 300 degrees of calcite, but peaks at 500 and 600 degrees do not appear. The first peak that appears is at 900 degrees, and this tells us that the piece was heated to a temperature higher than a higher burning temperature and therefore is a better piece. This is because in the nineteenth century in Spain the furnaces or kilns of lower draught or inverted flame were introduced. These are furnaces where the fuel used is usually wood or coal. Fuel was burned from the bottom and it had to pass through an air draught which produced higher temperatures in the furnace, and therefore the clay was burnt at a higher temperature so that much more compact and resistant ceramics were achieved. Therefore, as a conclusion of the study we observe that the masonry works of the eighteenth century are of brick masonry with lime caissons, presenting low temperature burnt bricks , and mortars with low calcium aggregates ratios, such as ratios between 1-2 or 1-2.5 , and mortar densities of 1.23 grams per cubic centimeter. However, those same masonry works built in the nineteenth century are much better. They are masonry works with bricks burnt at a higher temperature, and mortars with a higher proportion in binder. In our case, the mortar had a lime-aggregate ratio of 1 to 1.3 and therefore with apparent densities of 1.78 grams per cubic centimeter.

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