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SANTANA, Patric Souza [1], CARVALHO, Frank Alison de [2], PRAT, Bernat Vinolas [3], VIEIRA, Flaviana Tavares [4] Prensas de máquinas
SANTANA, Patric Souza. et al. Influence of vibration on the molding of soil-cement specimens: Under the results of water absorption and simple compressive strength tests. Multidisciplinary Scientific Journal Knowledge Center. Year 04, Ed. 12, Vol. 02, pp. 102-116. December 2019. ISSN: 2448-0959, Access link: https://www.nucleodoconhecimento.com.br/engenharia-civil/solo-cimento
The constant development of innovations in materials and services in the construction sector makes it possible to carry out increasingly efficient actions, leading to the presentation of products at a lower cost, whilst also meeting the specifications governed by the regulations that cover the sector in question, in addition to each increasingly meet concepts of sustainability and economic viability. Following this ideal, the project proceeded with the manufacture of cylindrical specimens of material classified as soil-cement, through the application of vibrations/impacts during their molding, to be subsequently subjected to water absorption and resistance to simple compression tests. , in order to verify the influence of vibration action. This action aimed to result in better densification of the material in a cylindrical format and, consequently, better resistance to compression and lower porosity, items that were confirmed in the tests mentioned above, meeting the technical specifications required in regulations applied to soil-cement blocks. Finally, it was verified that by adopting vibration action in the production process, greater efficiency of the product was obtained from soil and cement inputs, since, by comparing the data obtained, it was possible to quantitatively verify the positive influence of vibrations on the absorption of water and in the resistance of the test specimens.
Keywords: soil-cement, vibration, water absorption, simple compressive strength.
Resulting from changes in the rocks of the Earth's crust, resulting from mechanical or chemical actions, soils present in both granulometric and chemical diversities depending on the rock and the actions that produced it (Salgado, 1975). Applied to civil construction, soil presents itself as a multipurpose material, or even one of significant versatility, considering that through the addition of water and, if necessary, a binder, it can have different moldings and purposes, including the production of baked bricks or blocks. or not.
As noted in Minke (2012), the use of land in various constructions dates back thousands of years prior to the Christian era, and continues today mainly in countries with low rainfall and among those with low-income populations. As it is a versatile and at the same time multipurpose material, even during excavation to lay foundations, it can be removed and worked on so that it can provide the execution of masonry, furniture and even the construction of the building's roof, providing the interior of the residence with satisfactory conditions of resistance, temperature, humidity, aesthetics, among others.
Due to the lack of some physical properties, there may be a need to apply certain additives to provide certain products with the characteristics necessary to adapt them to regulatory standards, providing greater durability, especially with regard to water absorption parameters. and simple compressive strength. One of the binders adopted for soils to modify their mechanical characteristics (permeability and resistance to compression) is Portland cement, considering that it acts as a waterproof stabilizer, and the higher the clay content present in the soil, the greater will be the amount of cement necessary to produce the stabilizing effect, interfering with the clay's bonding forces. By adding Portland Cement to the soil, a mixture called soil-cement (SOUZA et al. 2008) is obtained in varying proportions.
In the composition of soil-cement, soil is the material that enters in the greatest proportion, and must be selected in a way that allows the lowest possible consumption of cement (SOUZA et al. 2008), which makes the composition more economically viable, considering the cost of Portland cement. The use of this becomes more viable compared to the use of pure soil, since this mixture is capable of having greater resistance and durability due to the cement not having organic components in its composition and the crystallization that is generated when the cement is in the process of It heals, thus meeting the soil's needs for physical properties.
The approach to using soil mixed with cement has already been studied and tested in different ways, as demonstrated in several articles and bibliographies that confirm the viability of this alloy in sustainable and economic terms (Grande, 2003; Santana et. al. , 2018). Another aspect to take into account is the possibility of using other materials in the soil-cement mixture that make the product even more sustainable: tire rubber fiber (Pereira et al., 2015), pet waste (da Silva et. l ., 2017), construction waste (Souza et. al., 2008; Martins et. al., 2016) and marble waste (Santos, 2015). However, there are no studies that demonstrate a numerical comparison of parts or specimens made with the soil-cement mixture that point out the interference generated due to a percussive compaction of the material, with vibrations being added that are intended to accommodate the components thereof. . The development of equipment that addresses the reported technique can be considered a lack, since in the current market almost all equipment does not adopt some type of machinery that addresses the use of vibrations for the manufacture of more compact masonry pieces related to the classified input. as soil-cement.
In this project, the materials used were soil obtained on the premises of the Federal University of Vales do Jequitinhonha and Mucuri (UFVJM) on the JK Campus – Diamantina MG. Portland Cement Type CPIII 32 (32MPa after 28 days of curing in conventional mortar), cylindrical mold with an internal diameter of 5 cm, percussive load device with a mass of 1kg, Marte AD5000 semi-analytical balance with 0.01g precision, drying oven with air circulation and renewal model AL-102-250, tray for hydrating specimens and EMIC DL10000 electronic press (10,000Kgf or 100KN of allowable load) for compression testing.
For a numerical comparison of two samples (with and without the application of vibrations during the production of test specimens), the most applicable option is the differentiation of the results of the water absorption and compression tests of two groups of samples. For this comparison, the number of specimens that would have to be produced was defined, which were 16, being subdivided into 8 common samples and 8 influenced by vibrations during the production of the specimens. These numbers were stipulated in order to meet a minimum number of comparisons of at least 6, in the event of damage to the parts or discard due to the appearance of data that differed greatly from the then average results.
When preparing the specimens used in the tests to obtain data, parameters were established that should be used for the production of the soil-cement mixture, such as a percentage of cement of 15% of the total mass (100g), a percentage of 85% of soil, and humidity of 15% in relation to the weight of 100g. The percentage of cement was defined at 15% due to the granulometric characteristics of the soil obtained with NBR 7181. As seen in Table 1, according to a study carried out at the Soil Fertility Laboratory of the Federal University of the Jequitinhonha and Mucuri valleys, the percentages of clay and silt combined presented as greater than 20% and less than 30%, sample 1 is disregarded due to its discrepancy in relation to the other samples, but it is noted that its result is close to 20%.
Table 1: Study regarding soil granulometry at the Federal University of Vales do Jequitinhonha and Mucuri
After the process of establishing the parameters, the process of producing the soil-cement composition and molding the specimens began based on the selection of the materials that would be used. At this stage, the standards established by ABNT regarding Soil samples – preparation for compaction and characterization tests – NBR-6457 were used in order to granulometrically separate the soil to be used. The soil was taken to the greenhouse for the humidity control procedure, with the soil having a humidity of less than 5% and more than 3%, so that it could later be selected with the aid of a No. 4 sieve (4.8mm). mesh). Considering that it is a material sold within standards, Portland Cement type CPIII 32 was considered to have a humidity of 0% and a particle size that completely passes through the No. 4 mesh sieve (4.8mm). With the selection of materials already completed, both were weighed individually.
After weighing, the soil was mixed with the cement following the instructions of NBR-12024 Soil-cement – Molding and curing of cylindrical specimens, and for this both materials were combined in a plastic container devoid of moisture until it was determined that the mixture was at a point where there was a homogeneous color and then water was added, obeying the percentage stipulated for the formation of the hydrated soil-cement composite, which is 15% in relation to the weight of the dry components.
With the compound already prepared, the portions were placed in cylindrical molds for the test specimen molding process, also following ABNT regulations according to NBR-12024. The pressure to which the compound was exposed to compact the specimen for cylindrical formatting in this stage was 42N/cm², this value was established based on the pressure used to manufacture soil-cement type bricks specified in NBR 8492 .
For the preparation of specimens influenced by the application of vibration, the compound preparation and molding process was identical, however, after pressing, the cylindrical molds received impacts on their upper face, simulating vibrating actions. Such impacts were generated by collisions of masses weighing 1 kg that were released at an established height of 1 m. With the aid of gravity, the mass reached the specimen at a force of 9.8N and a speed of 3.13m/s, considering that the height of the cylindrical metallic mold is 15cm and that it was located close to the ground. Such parameters refer to an equivalence of kinetic energy (Ec) of 48.02J.
After molding the specimens, they were extracted from the molds and placed on benches for initial curing, being hydrated taking due care to avoid surface changes due to the action of water. All specimens were duly identified using crayons. To carry out the curing process, NBR-12024 was adopted, which determines that they must be maintained for 7 days at a temperature of approximately 23°C, with air humidity greater than 95%.
In order to promote knowledge and facilitate the choice of the type of soil stabilization to be adopted as a solution in a given situation, this article makes an interpretative and comparative analysis between some stabilization processes. This is a study based on a bibliographical review that presents the point of view of national and international authors on soil stabilization, relies on traditional concepts and classifications that have already been consolidated, and also brings new stabilization methods that are still being studied. and researched in the scientific community.
After the curing process, tests were carried out with each specimen, starting with the water absorption and porosity test, which aims to determine how much water is absorbed by the specimen, having been the same immersed in water. In this experiment, Equation 1 provided by NBR-12024 6 was used, which informs
Mbu: Weight of the saturated sample
To obtain the data that were inserted in Equation 1, the specifications contained in NBR-8492 were adopted. The specimens were taken to an oven for 72 hours, at a temperature of approximately 105°C, and subsequently weighed, thus obtaining the dry weight (Mbs) of the specimen. To determine the wet weight of the samples (Mbu), the specimens were immersed in water for 24 hours and followed by removal and removal of surface water using a damp flannel, presenting them as saturated.
For the simple compression test, the specifications of NBR 10836 were adopted, which defines the need for capping the specimens, immersion in water and subsequent breaking of the specimens in a compatible press. The specimens were capped using cement, sand and water mortar, which was applied to both sides, top and bottom, which would receive the compression loads. The capping was cured and the specimens were subsequently immersed in water according to regulatory specifications, and they were removed from the water immediately before the individual rupture of each specimen. For breaking, an electronic press from the manufacturer EMIC model DL10000 was adopted (10,000Kgf or 100KN of allowable load). For each specimen, three diameter measurements were collected with standardized readings referring to an average diameter that made it possible to define the area of load application.
Once the test piece was positioned in the press, it was activated with an applied load of 0.25Mpa or 2.55 kgf/cm², avoiding the occurrence of maximum instantaneous load. All press displacement and maximum applied load readings were made using software provided by the press manufacturer. The maximum load was determined by setting the maximum load value obtained even if the displacement of the press was maintained, with no further change in the applied load. Adopting the basic pressure formulation that refers to the coefficient of force over area, the tension given in KN/mm² and MPa was obtained for each test body in order to facilitate the comparison of results specified by regulations pertinent to the production of test bodies. proof and soil-cement blocks.
When verifying the data, tables were created containing the information obtained. In the set of Tables 2 and 3 it is possible to analyze the difference in water absorption obtained for specimens classified as common and for those in which vibrations were applied during the compaction molding process.
Table 2: Data from water absorption tests of common samples (without vibration).
Table 3: Data regarding the water absorption test of samples influenced by vibrations.
With such data, it is possible to verify that the test specimens that were exposed to vibrations obtained numerically inferior results compared to common samples that feature lower porosity. Based on this information, it is possible to conclude that the impacts generated greater compaction of the granules and thus influenced the water absorption of the sample, reducing it, since the average percentage of water absorption of common samples was 22.30% ± 0.89, higher than the 16.00% ± 1.36 obtained in samples influenced by vibrations caused by impacts.
The water absorption of samples that were influenced by impacts decreased by approximately 30%. This value allows us to verify that the distances between the components of this sample and its volume are smaller in relation to the other group, however their density is greater, as can be seen in the following data that indicate the average density of each group ( see table 4).
Table 4: comparison of mass and density averages
Regarding the results of the simple compression test, the values obtained in samples exposed to vibrations also obtained better results compared to the results of samples without vibration. The results obtained are shown in the following tables, which present the following data: three measured diameters of each specimen (D1, D2, D3); the average diameter (MD); the area referring to the average diameter (ADM); the maximum load allowed by the test piece in N (newtons – LOAD N); the calculation of the compressive stress (δ), which mathematically is given by F/A (N/mm² or MPa) and finally the corrected pressure (corrected δ).
Note that there are two columns indicating the calculation of the pressure necessary for rupture in Tables 5 and 6. This demonstration is explained by the existence of the correction factor that must be applied to cylindrical specimens that do not fit the standard indicated. The height needs to be twice as large as the diameter. Thus, based on the data provided by NBR 7680, a correction factor of 1.375 for common samples and 1.5 for samples influenced by vibration can be extracted, so these data were applied in Equation (2). The correction value is given by the relationship between height/diameter and thus compared to the data provided by NBR 7680.
Table 5: Compression test of samples classified as common (without vibrations).
Table 6: Compression test of samples influenced by vibration
Analyzing the data from the compression test, it can be seen that the values obtained for the samples that were influenced by vibration proved to be more resistant. The average of the values obtained in each group of test specimens prove this fact, since the average pressure necessary to break the common test specimens was 1.65 N/mm² ± 0.30 and for the specimens that received the influence of vibrations due to impacts was 3.52 N/mm² ± 0.68. It was therefore found that the samples influenced by extra vibrations required loads approximately 132% higher to break compared to those applied to common samples.
In a comparative analysis, adopting the parameter called Fbk, which is the minimum characteristic value of compressive rupture stress of a set of concrete blocks tested NBRs 6136 and 12025, adopting Equation (3) we would have the following results: characteristic resistance of the specimens without vibration at 1.3MPa and 2.87MPa for the specimens that were influenced by impacts.
Fbk = Characteristic Compressive Strength of Concrete
i = n/2, see n for pair
i = (n-1) /2, if n is odd
Graph 1 shows the correlation between porosity (abscissa) and resistance (ordinate) to simple compression of the specimens detailed above. There is a distinction between two groups of data that appear at a certain distance from each other. It is observed that the one with the lowest water absorption has the highest values of compressive resistance, and on the other hand, the one with the highest porosity has the lowest values for compressive resistance.
Graph 1: Correlation between resistance (Y-Axis – MPa) and water absorption (X-Axis – %)
The improvement indicated by the tests carried out on the specimens is due to greater compaction due to impacts that more intensely densify the grains that form the soil-cement samples. For this conclusion, the values obtained in the mean and standard deviation of water absorption and the force required for the specimens to be ruptured were based on the values obtained. In these tests, the numbers obtained in samples influenced by extra vibrations were significantly better, as can be seen. analyze in the following table.
Table 7: Comparison of test results averages for sample groups.
The influence of impacts on specimens is due to greater compaction that can be visually observed due to the smaller size compared to other samples. The difference in question can be up to 0.8 cm between the two types of samples. This difference can be illustrated in figure 1. It is noteworthy that the samples obtained average volumes of 4.71cm³ for samples influenced by impacts and 6.28cm³ for samples without influence of impacts.
Figure 1: Side profile of the cylinder formed by the samples. A difference can be noted between the concentration of granules in each specimen based on the average densities and their difference in height.
In view of the above, it is understood that the numerical analysis of this comparison can have several applications such as use in constructions and in new fields of study, as this experiment showed the advantages of the presence of vibration in soil-cement specimens as to the parameters of water absorption and compressive strength. It must be taken into account that according to NBR 6136, the minimum compressive strength fbk values for sealing blocks is 2 Mpa. In this study, the specimens molded using vibration complied with this minimum value, reaching up to 2.87 Mpa. However, specimens molded without vibration cannot be purchased with this regulatory limitation. Because the fbk value obtained was 1.3 Mpa.
The information obtained from this experiment can be used as a basis for future research as parameters for the manufacture of modular parts, such as some types of bricks and plates, since with such analysis it will be possible to create parts that support greater weight loads and with lower water absorption rates. Another application of this research would be the collection of data regarding maximum compaction and its influence on the specimens, given that there will be pressures in which compaction will no longer be possible and whether this would be harmful to the samples.
Therefore, the greater compaction caused by vibrations in the samples interferes with them, increasing their resistance due to densification, since the experiment indicates that there is probably a relationship where denser specimens tend to require greater loads to be ruptured compared to other bodies. less dense samples, but with the same composition.
ABNT – Brazilian Association of Technical Standards. NBR 6136. Hollow Simple Concrete Block for Structural Masonry. Rio de Janeiro, 2007.
ABNT – Brazilian Association of Technical Standards. NBR 06457. Soil samples – preparation for compaction and characterization tests. Rio de Janeiro, 2006.
ABNT – Brazilian Association of Technical Standards. NBR 07181. Soil: Granulometric Analysis. Rio de Janeiro, 1984.
ABNT – Brazilian Association of Technical Standards. NBR 7680-1 – Concrete – Extraction, Preparation, Testing and Analysis of Testing of Concrete Structures Part 1: Resistance to Axial Compression. Rio de Janeiro, 2015.
ABNT – Brazilian Association of Technical Standards. 08492. Solid Soil-Cement Brick. Determination of Resistance to Compression and Water Absorption. Rio de Janeiro, 1984c.
ABNT – Brazilian Association of Technical Standards. NBR 10836 – Hollow Soil-Cement Block Without Structural Function – Determination of Compressive Resistance and Water Absorption. Rio de Janeiro, 1994.
ABNT – Brazilian Association of Technical Standards. NBR NBR 12024. Soil-Cement – Molding and Curing Cylindrical Specimens. Rio de Janeiro, 1992.
ABNT – Brazilian Association of Technical Standards. NBR NBR 12025. Soil-Cement – Simple Compression Test of Cylindrical Specimens. Rio de Janeiro, 1990.
DOS SANTOS, CW; SUZART, PV; SILVA, FN Technological trends for the process of preparing composites based on soil-cement and banana fiber for the manufacture of bricks and related technologies through research in patent documents. Bahia: Cadernos de Prospecção, 2013. 36-44 p.
GRANDE, Fernando Mazzeo. Manufacture of modular soil-cement bricks by manual pressing with and without the addition of silica fume. 2003. PhD Thesis. University of São Paulo.
MARTINS, LUANE RICARTE, F. de F. Fernandes, and AML Silva. “Use of construction and demolition waste to stabilize soil in Iranduba to make soil-cement bricks.” Scientific Technical Congress of Engineering and Agronomy – CONTECC. 2016.
MINKE, G. Earth construction manual. Design and technology of sustainable architecture. Translated from the 2006 English edition by António Moura. 1st ed. 2012. 151 p.
PEREIRA, Adriana Maria, FAZZAN, João Victor, and FREITAS, Verônica de. “Analysis of the feasibility of using tire rubber fiber as reinforcement in cement soil bricks.” National Journal of City Management 3.20 (2015).
SALGADO VIEIRA, Lucio. Soil science manual. No. 631.4 S35. 1975.
SANTANA FILHO, César Carlos, et al. “Brick soil-cement-contemporary notes in terms of Brazil.” (2018).
SANTOS NETO, José Lima dos. “Improvement of soil-cement brick, with the addition of marble and granite cutting residue (RCMG).” (2015).
SILVA, Jonas Soares da, SENA, Rilson José de, and LAURSEN, Anderson. “MECHANICAL EVALUATION OF SOLID SOIL-CEMENT BRICK CONTAINING PET WASTE.” Veredas Favip-Electronic Science Magazine 10.1 (2017): 69-83.
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[1] Bachelor of Science and Technology. Graduating in Geological Engineering.
[2] Master's degree from the Master's program in Health, Society and Environment at UFVJM, degree in Civil Engineering (Kennedy School of Engineering).
[3] PhD in Civil Engineering from the Construction Engineering department of the Polytechnic University of Catalonia (UPC) (Barcelona, Spain), Master in civil engineering from UPC, specialization in project management from Fundação Getulio Vargas (FGV – Brazil), degree in Civil engineering from UPC.
[4] PhD in Inorganic Chemistry at UFMG, Master in Agrochemistry at UFV, Degree in Chemistry and degree in Natural Sciences at UFSJ.
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