Papers by Keyword: Shrinkage

Abstract: This paper deals with the stress analysis and prediction of crack formation caused by the development of hydration heat and shrinkage in the expansion block of the Nové Heřminovy dam. During the design of the concrete gravity dam, extensive analysis were carried out in order to predict the occurrence of cracks induced by hydration heat development and shrinkage within the first 10 years after the start of construction. The aim of the analysis was to predict the location, depth, and width of cracks under given conditions and to provide recommendations for minimizing crack formation in the structure. In the first stage, a parametric study on a sectional model was carried out, which led to the optimization of technological procedures and the concreting schedule. Subsequently, a global model of a typical gravity block of the dam was created to simulate the boundary conditions of the structure as accurately as possible during construction and subsequent operation, and to obtain results regarding stress distribution and areas with a risk of cracking. The analysis was performed using nonlinear numerical calculations in ATENA software, while also incorporating transport analysis of temperature and environmental humidity.

Abstract: Thermosets play an important role in composite processing, adhesive bonding and coating. In all these applications, shrinkage my cause a significant amount of residual stress, leading to distortion, reduced load carrying capacity and cracking. The chemical curing reaction is accompanied by a reduction in volume called “chemical shrinkage”. If curing is performed at elevated temperature, cooling to ambient conditions afterwards is accompanied by “thermal shrinkage” and further shrinkage due to so-called “physical ageing”. A skillful combination of available methods makes it possible to separate chemical shrinkage in the viscous state from shrinkage in the gelled and vitrified state. Modeling of the time-and temperature-dependent properties is the prerequisite for the prediction and control of residual stresses caused by shrinkage in thermoset polymers.

Abstract: The umbu tree (Spondias tuberosa) belongs to the Anacardiaceae family and is part of the plant biodiversity of Brazilian biomes, such as the Caatinga. Some research related to the nutritional aspects of the pulp of this fruit is found in the literature. On the other hand, studies related to the drying of the seed of this fruit are still rare. Since drying is generally the first step before flour production, which will allow extraction of its nutrients, this work proposes a detailed description of this step. For this purpose, two solutions are proposed (analytical and numerical) for the diffusion equation in cylindrical coordinates, with boundary conditions of the third kind. For the analytical solution, three parameters were considered: the effective constant mass diffusivity (), the convective mass transfer coefficient for the north and south interfaces of the cylinder (), and the convective mass transfer coefficient for the east and west interfaces of the cylinder (). For the numerical solution, the effective diffusivity was considered as a function of the local moisture content (), the convective mass transfer coefficient was assumed to be equal for all interfaces (), and shrinkage was incorporated into the model. The convective mass transfer coefficients obtained through analytical solution show a greater convective effect at the top of the cylinder representing the seeds. Through the results obtained by the numerical solution it can be assumed that due to the heterogeneity of products such as umbu seeds, shrinkage can also be influenced by changes in sample porosity during processing.

Abstract: This study evaluates the impact of replacing natural sand (NS) with quarry waste sand (QWS) or recycled concrete sand (RCS) at varying substitution rates (0%, 25%, 50%, 75%, and 100%). The analyzed properties include Abrams cone slump, superplasticizer demand (SP), rheological and tribological parameters, mechanical strength, capillary water absorption, and shrinkage. The results show that QWS-based concrete exhibits better workability and requires less superplasticizer, whereas RCS-based concrete necessitates a higher admixture dosage. Both QWS sand and RCS sand significantly enhance the rheological and tribological properties of concrete Moreover, QWS sand provides higher mechanical strength than NS sand, with a strength gain of up to 16% at full replacement (100% QWS sand) at 90 days. Conversely, RCS sand reduces compressive strength by 28.6% at 28 days. and negatively affects porosity and capillary water absorption. However, these negative effects are mitigated when the RCS sand replacement is limited to 25%. QWS sand-based concrete exhibits slower shrinkage and reduced deformability compared to NS sand-based concrete. Predictive strength models were established based on experimental parameters, displaying a high correlation coefficient and a low root mean square error. Replacing NS sand with QWS sand or RCS sand reduced production costs, lowered carbon emissions, minimized waste, and preserved natural resources, offering a sustainable approach for concrete applications.

Abstract: Accurately predicting the water-binder ratio (W/B ratio) is crucial for achieving rice husk ash supplemented concrete structures' desired strength and durability. This study introduces an innovative approach for W/B ratio prediction, utilizing cutting-edge machine learning algorithms in combination with Explainable Artificial Intelligence (XAI) techniques. The research employs hybrid ensemble learning models, including Random Forest (RF), CATBoost (CB), Whale Optimization Algorithm-optimized RF (RF-WOA), and Moth Flame Optimization-optimized CB (CB-MFOA). The results indicate that these hybridized models significantly outperform the standalone models (RF and CATBoost) and traditional empirical methods (feret’s law, Abram’s law and bolomey’s method), with the CB-MFOA model achieving the highest accuracy, demonstrated by an R-value of 0.9984 during the calibration phase. In the verification phase, the CB model excelled with an R-value of 0.966. In addition to model performance, the study integrates XAI methods to explain the predictions and identify the key factors influencing the w/b ratio. Cement was found to be the most critical variable, enhancing the accuracy of the CB-MFOA model. The findings confirm that the proposed method improves prediction precision and provides engineers with a reliable tool to optimize concrete mix designs, thereby improving the durability and sustainability of concrete. This research contributes to the broader field of concrete technology by advancing the application of AI-based solutions in civil engineering and related fields.

Abstract: Creep and shrinkage of concrete are important parameters for verification of ultimate and serviceability limit states. The prediction models which can be found in design codes, are applicable for ordinary concrete types. Unusual concrete types, like e.g., white concrete can be used, but their properties should be investigated by experimental testing. The paper is focused on measurement of shrinkage and creep of white and grey concrete of the same strength class. The experiments showed that both, creep and shrinkage of white concrete are higher than those of ordinary grey concrete. The measured shrinkage strains were compared with predicted shrinkage strains using various prediction models.

Abstract: Nowadays, the requirements of scaffolds and bone grafts are increasing along with large defects increasing every year. Furthermore, large defects that occur in human bones are customary. However, this obstacle can be overcome by using 3D printing. This study aims to investigate the morphology, deviation dimension, shrinkage and hardness of hydroxyapatite (HA)/collagen composite, which these materials mimic with human bone. HA/collagen composite was printed using three-dimensional bioprinting based on extrusion with a print speed of 10 mm/min and a layer height of 0.5 mm. The composition of HA and collagen material is 70% and 30%, respectively, where this composition mimics natural bone. Morphology and dimension of HA/collagen composite were obtained by transmission electron microscope. Moreover, the deviation dimension and shrinkage were measured using the Miviewcap optical microscope and software Image J. The resulting HA/collagen composite clearly showed that collagen was in the form of fibers while HA was in an irregular shape. The average width and length of collagen were 5.98 + 0.20 nm and 82.48 + 6.23 nm, respectively. Moreover, the Average width and length of HA were 21.85 + 0.53 nm and 23.30 + 1.33 nm. The average deviation dimension in the X, Y, and Z axes was 2.69%, 1.40%, and 24.12%. Furthermore, shrinkage was 12.27%, 10.18%, and 19.06% on the X, Y, and Z axes. The average hardness of specimen 1 and 2 of HA/collagen composite were 0.0021594 HV.

Abstract: Pollution problems caused by industrial production of leather tanneries are an important environmental issue. In the present paper we propose to study effects of tannery sludge (TS) addition in manufactured clay bricks applying a mixture design formed by different proportions of four components: Clay, two types of sand and TS. The analysis leads to an optimal practical mixture of around 10% of TS, 20% of sand and 70% of clay and this to remain with an acceptable aspect, an admissible water absorption below 15%, an admissible total shrinkage (drying and after fire) lower than 8%, a tensile strength higher than 5MPa and a thermal conductivity of 0.93 Wm^-1K^-1, 15% lower than the reference mixture with 0% of TS. Experimental results indicate that a temperature cycle firing up to 950°C can lead to higher tensile strength and lower water absorption compared to a cycle that reaches only 850°C. Furthermore, incorporating (TS) in the fired brick manufacturing process can lead to significant energy saving. Additionally, it was observed that a moderate inclusion of TS can enhance evaporation process. Keywords : Mixture design, Tannery Sludge (TS); Clay bricks ; Evaporation ; Strength; Water absorption; Shrinkage; Leaching; Energy.

Abstract: This paper presents a case study of solar drying of hydroxide sludge in the region of Marrakesh, Morocco. The experiments of solar greenhouse drying processes of the hydroxide sludge were studied in summer and winter seasons. The representative samples were in three volumes. The greenhouse sludge dryer was designed and constructed as a horticultural plant. Results showed that the dry of the three samples was reached in only 13 hours in summer and 25 hours in winter. The time of solar greenhouse drying registered was significantly lower compared to several studies. The higher values of drying rate were obtained in early hours of experiments in summer. The maximum ranges obtained were 0.25 kg water/kgDS.h for the hot season and 0.020 kg water/kgDS.h for the cold season. The important influence of the temperature had a greater effect with wind speed on drying rate. The sludge water evaporation caused a large volume reduction with a shrinkage during the processes in both seasons.

Abstract: In Engineering Schools, labs for teaching forming processes by means of material conservation methods are generally equipped with the appropriate equipment and tools to exemplify the theory received in class. However, the use of simulation techniques to complement the formation is not usually widely extended, since their learning is not usually trivial.One of the material conservation forming processes is sand casting. This process is of great educational significance, since the theory that defines it sets the basis for understanding other related moulding processes. In this context, the use of simulations of the moulding process allows the visualization of practical examples, helping to explain more clearly the theoretical information explained in class.Therefore, in this research a simulation assisted analysis has been developed using the Inspire Cast by Altair software, of teaching parts made in sand casting. First of all, students have been shown by means of simulations, the defects that can be originated in a part manufactured by sand casting. The study has been carried out by redesigning the risers involved in the distribution system of the process, by means of the Chvorinov's rule.Finally, a series of conclusions have been achieved, among which the following one stands out: if the functional performance of the part manufactured by sand casting is to be taken into account, the cooling modulus criterion must be selected for the design of the riser. Although, in principle, the material required for moulding is much larger, the defects generated in the part will be considerably reduced.