Influence of Monolith Length on Temperature Field of Concrete Gravity Dams

This paper examines the influence of monolith length on the temperature field of concrete gravity dams built using the block method. The developed 3D model is capable of conducting a thermal analysis of a 95.0 m high concrete gravity dam built using the block method, where each newly cast block represents a new analysis phase. The calculation accounts for the period of construction, the filling of the reservoir, and the service for a total duration of about 5 years. The thermal properties of the material, the influence of cement hydration heat, the temperature of the surrounding rock mass, the temperature of the fresh concrete mixture, and the corresponding boundary conditions defining a heat transfer were taken into account. The height and width of the blocks, as well as the sequence of concreting, were considered invariable, while the length of the blocks (dimension in the direction of the dam’s axis equal to the monolith length) varied, with values of 10.0, 12.5, 15.0, and 20.0 m. The obtained calculation results for the control nodes showed that the maximum reduction in the monolith length (from 20.0 m to 10.0 m) caused a decrease in the maximum temperature values of the concrete (from 1.6 to 3.4 °C, depending on the control node). Also, the results showed that, by reducing the length of the monolith, there was a delay in the moment at which the maximum temperature values of the concrete appeared in the selected control node. The delay in reaching the maximum, in relation to the 10.0 m long monolith, was from 7 days (for points on the crest dam) to 49 days (for points in the central zone of the monolith) for the other considered monolith lengths. The above indicates the importance of concrete temperature control for longer monoliths, especially during construction in extreme air temperatures. The main contribution of the conducted analysis is the development of insight into temperature field changes depending on monolith length, which can help engineers during the design and construction of new, as well as the maintenance of existing, dams

Termička analiza gravitacione betonske brane u fazi izgradnje i eksploatacije

Rezime: Termičko ponašanje gravitacionih betonskih brana presudno zavisi od početnih i graničnih uslova, karakteristika mešavine i dimenzija blokova. U radu je prikazan prostorni numerički model za faznu tеrmičku analizu visoke gravitacionе bеtonskе branе. Za usvojеnе dimеnzijе blokova, rеdoslеd bеtoniranja i dinamiku građеnja određivano je tеmpеraturno poljе, uzimajući u obzir toplotu hidratacije betona i sadеjstvujuću stеnsku masu. Na osnovu dobijenih rezultata, dati su zaključci i preporuke za proračun temperaturnog polja kod gravitacionih betonskih brana.Summary: The thermal behavior of concrete gravity dams crucially depends on the initial and boundary conditions, the characteristics of the mixture and the dimensions of the blocks. This paper presents numerical model for transient thermal analysis of a high concrete gravity dam. The temperature field was determined for the predefined dimensions of the blocks and placement schedule, taking into account hydration heat and the surrounding rock mass. Based on the obtained results, conclusions and recommendations for concrete gravity dams thermal analysis are given

Long-Term Thermal Stress Analysis and Optimization of Contraction Joint Distance of Concrete Gravity Dams

Results of the conducted research aiming to demonstrate the methodology of optimization of dam monolith length (distance between contraction joints), through monitoring the thermal tensile stresses during construction and service life of a concrete gravity dam that is built using the block method, are presented in this paper. A 3D space–time numerical model for phased thermal stress analysis is employed in a large concrete gravity dam case study. For the adopted block dimensions, schedule, and dynamics of construction and material parameters, the thermal stress analysis is conducted, taking into account the following: thermal physical properties of the material, the cement hydration process, heat exchange with the external environment and the reservoir, and self-weight of the structure. The main advantage of the proposed methodology is the possibility of controlling the cracks resulting from thermal tensile stresses in the monolith of a concrete gravity dam, by optimizing the monolith’s length to minimize the zones in which the tensile capacity of concrete is exceeded. The results obtained from the temperature field analysis show that the maximum temperature increase in the dam’s body results from the cement hydration process in combination with summer air temperatures in the construction phase. The aforementioned factors account for the increase in temperature of up to 45.0 ◦C, while during winter cooling of the structure occurs due to lower temperatures, especially in the surface zones. The results of the stress field analysis show that the extreme values of thermal tensile stresses are present in the process of a sudden or gradual cooling of the concrete when shrinkage occurs. Finally, it is shown that the reduction of the monolith length by 5.0 m (from 20.0 m to 15.0 m) results in a decrease in the extreme thermal tensile stress values by an average of 0.70 MPa (up to 12.0%) in winter and an average of 1.10 MPa (up to 20.0%) in summer; while for the entirety of the analyzed time period, results in a decrease in the extreme thermal tensile stress values by an average of 16.0% (0.93 MPa)

Assisted phytostabilization of Pb-contaminated soil using brushite-metakaoiln geopolymer materials and Festuca rubra

Lead (Pb) is one of the most common environmental pollutants and high concentrations of this element can cause numerous symptoms of phytotoxicity. Inorganic amendments immobilize metal/metalloid ions and reduce their bioavailability in the soil by increasing pH or by adsorbing them. Adsorption mechanisms include chemical precipitation, ion exchange, and crystal growth. In this experiment, geopolymer materials were newly synthesized from a natural raw kaolinite clay with 2, 4, and 6 wt % (GPB2, GPB4, and GPB6) of pure brushite addition. Previous research has shown that brushite-metakaolin geopolymer materials can be successfully synthesized and that they have significant efficiency in removing lead ions from aqueous solutions. Plant samples were grown under controlled conditions in eight different series using commercial substrate and seeds. Four series contained lead-contaminated soil and were treated with brushite-metakaolin geopolymer materials, while the other four series, which contained uncontaminated soil, were also treated with brushite-metakaolin geopolymer materials and served as control series. The plant samples were taken after six weeks. Lead concentrations in the different plant and soil samples were analyzed using an absorption spectrophotometer (AAS). BCF, BAF and TF were calculated from the results obtained. Moreover, physiological and biochemical experiments were carried out and total antioxidant capacity, total phenols, free proline and photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids) contents were measured in different plant samples. The results show different responses to metal/metalloid toxicity in the control and treated plant samples, confirming that there is a significant influence of brushite-metakaolin geopolymer materials on the phytostabilization efficiency of Festuca rubra. Phytostabilization is an ecofriendly and cost-effective technique that allows the metals/metalloids to be immobilized in the soil by plants, preventing their migration into the surrounding ecosystem and reducing the chances of them entering the food chain.Twenty-First Young Researchers’ Conference - Materials Science and Engineering: Program and the Book of Abstracts; November 29 – December 1, 2023, Belgrade, Serbi

Korelativni odnosi za definisanje deformabilnosti stene

In the framework of geotechnical investigations of the rock mass at the partition site MHE Bočac 2 (BiH), Jelašnica dams on the same river in southern Serbia and nine partition sites of hydroelectric power plants on the river Ibar, detailed geotechnical investigations of the rock mass were carried out. They included exploration drilling with the definition of quasihomogenic zones within the drilled core, determination of RQD for each separated quasi-chemical zone, dilatometric tests in each well, seismic ventilation between exploratory wells or seismic carotid, core testing by the Point Load method and laboratory tests of the single-axial strength of the samples. By connecting the results of the one-axial strength, the velocity of the elastic waves and the quality of the rockl mass (RMR), i.e. these indirect data for defining the deformability of the rock masses with the obtained results of in situation deformability testing, with the results of dilatometric tests, the analysis of correlation bonds is carried out which is applied in engineering geological or geotechnical practice. As is known, in engineering practice, the following correlations are used to define the deformation module: D = f(RMR); D= f(RMR,σci); D= f(Vp) i D = f(Vp, σci). After the analysis, a correlation was applied which included all three indirect data and it gave the closest data for defining the deformability of the rock mass.U okviru geotehničkih istraživanja stenske mase na pregradnom mestu MHE 'Bočac 2‟ (BiH), brane 'Jelašnica' na istoimenoj reci u južnoj Srbiji i na devet pregradnih mesta hidroelektrana na Ibru (Srbija) izvršena su detaljna geotehnička ispitivanja stenske mase. Ona su obuhvatila: istražno bušenje sa definisanjem kvazihomogenih zona u okviru izbušenog jezgra, određivanje RQD-a za svaku izdvojenu kvazihomogenu zonu, dilatometarska ispitivanja u svakoj bušotini, seizmičko prozračivanje između istražnih bušotina ili seizmički karotaž, ispitivanje jezgra metodom PointLoad i laboratorijska ispi-tivanja jednoaksijalne čvrstoće uzoraka. Na navedenim istražnim lokacijama teren grade različite ste-nske mase. Teren pregradnog mesta MHE 'Bočac 2' je izgrađen od krednih krečnjaka, teren brane 'Jelašnica' od paleozojskih gnajseva, a teren hidroelektrana na Ibru od mezozojskih peridotita i serpentinita. Povezivanjem rezultata jednoaksijalne čvrstoće, brzine elastičnih talasa i kvaliteta stenske mase (RMR), odnosno ovih posrednih podataka za definisanje deformabilnosti stenskih masa sa do-bijenim rezultatima ispitivanja deformabilsnosti in situ, tj. Sa rezultatima dilatometarskih ispitivanja, urađena je analiza korelacionih veza koja se primenjuje u inženjeresko-geološkoj odnosno geotehničkoj praksi. Kao što je poznato, u inženjerskoj praksi primenjuju se sledeće korelacije za definisanje modula deformacije: D=f(RMR); D=f(RMR,); D=f(Vp) i D=f(Vp, ). Nakon analize, primenjena je korelacija, koja je obuhvatila sva tri posredna podatka i ona je dala najbliže podatke za definisanje deformabilnosti stenske mase. Sva navedena ispitivanja deformabilnosti metodom dilatometra, geofizička ispitivanja i inženjersko-geološko kartiranje jezgra i okolne stenske mase izvršena su od strane Instituta za vodoprivredu 'Jaroslav Černi' iz Beograda

A method of determining parameters of Bofang model on the example of "Bileca" reservoir

In this research paper, measurement data of air and water temperatures and water levels for "Bileca" reservoir for a period between 1967. and 2017. are presented. Based on the averaged measurement data values, an analytical expressions for amplitude of periodic temperature variation of "Bileca" reservoir are derived and an average annual temperature, as a function of the observed depth, is obtained, based on Bofang model. The obtained results allow thermal stress analysis, which represents an important factor for stability and safety monitoring of dams

Removal of Cs Ions from Aqueous Solutions by Using Matrices of Natural Clinoptilolite and its Safe Disposal

The possibility to use natural zeolite - clinoptilolite as a host material for radioactive Cs immobilization has been investigated. Cs-exchanged form of clinoptilolite which was prepared by treatment of clinoptilolite powder with 0.25 M CsCl solution was compacted. Both, powder and powder compact of exchanged clinoptilolite were thermally treated at 1200 C-0. The XRPD analysis showed that Cs was successfully immobilized after heat treatment by formation of stable cesium dodecaoxo-alumopentasilicate in both, powder sample and compact. The newly formed compound showed satisfactory Cs ions retention during leaching test. The sintered compact showed somewhat better resistance to Cs leaching than the thermally treated powder. The compressive strength of sintered compact was close to 200 MPa which is more than enough for easy handling and safe storage

Long-Term Thermal Stress Analysis and Optimization of Contraction Joint Distance of Concrete Gravity Dams

Results of the conducted research aiming to demonstrate the methodology of optimization of dam monolith length (distance between contraction joints), through monitoring the thermal tensile stresses during construction and service life of a concrete gravity dam that is built using the block method, are presented in this paper. A 3D space–time numerical model for phased thermal stress analysis is employed in a large concrete gravity dam case study. For the adopted block dimensions, schedule, and dynamics of construction and material parameters, the thermal stress analysis is conducted, taking into account the following: thermal physical properties of the material, the cement hydration process, heat exchange with the external environment and the reservoir, and self-weight of the structure. The main advantage of the proposed methodology is the possibility of controlling the cracks resulting from thermal tensile stresses in the monolith of a concrete gravity dam, by optimizing the monolith’s length to minimize the zones in which the tensile capacity of concrete is exceeded. The results obtained from the temperature field analysis show that the maximum temperature increase in the dam’s body results from the cement hydration process in combination with summer air temperatures in the construction phase. The aforementioned factors account for the increase in temperature of up to 45.0 °C, while during winter cooling of the structure occurs due to lower temperatures, especially in the surface zones. The results of the stress field analysis show that the extreme values of thermal tensile stresses are present in the process of a sudden or gradual cooling of the concrete when shrinkage occurs. Finally, it is shown that the reduction of the monolith length by 5.0 m (from 20.0 m to 15.0 m) results in a decrease in the extreme thermal tensile stress values by an average of 0.70 MPa (up to 12.0%) in winter and an average of 1.10 MPa (up to 20.0%) in summer; while for the entirety of the analyzed time period, results in a decrease in the extreme thermal tensile stress values by an average of 16.0% (0.93 MPa)