Deividas Rumsys

In the present trend of constructing taller and longer structures, the application of lightweight aggregate concrete is becoming an increasingly important advanced solution in the modern construction industry. In engineering practice, the analysis of lightweight concrete elements is performed using the same algorithms that are applied for normal concrete elements. As an alternative to traditional engineering methods, nonlinear numerical algorithms based on constitutive material models may be used. The paper presents a comparative analysis of curvature calculations for flexural lightweight concrete elements, incorporating analytical code methods EN 1992-1 and ACI 318-19, as well as a numerical analysis using the constitutive model of cracked tensile lightweight concrete recently proposed by the authors. To evaluate the adequacy of the theoretical predictions, experimental data of 51 lightweight concrete beams of five different programs reported in the literature were collected. A comparison of theoretical and experimental results showed that the most accurate predictions are obtained using numerical analysis and the constitutive model proposed by the authors. In the future, the latter algorithm can be used as a reliable tool for improving the design standard methods or numerical modeling of lightweight concrete elements subjected to short-term loading.

This study is focused on the experimental investigation of compressive strength and durability properties of lightweight concrete mixtures with fine expanded glass and expanded clay aggregates using different microfillers. The paper proposes the relationships between the compressive strength and density of concrete mixtures with different proportions of the lightweight aggregates mentioned above. The performed experimental studies have revealed the tendencies of possible usage of different amounts of fine lightweight aggregates and their combinations in the production of concrete mixtures depending on the demands of practical application. Following the requirements for structural concrete subjected to environmental effects, durability properties (alkaline corrosion and freeze–thaw resistance) of the selected concrete mixtures with expanded glass aggregate were studied. The results of the experimental investigations have shown that durability of tested concrete specimens was sufficient. The study has concluded that the mixtures under consideration can be applied for the production of structural elements to which durability requirements are significant.

In recent years, along with the global development of the Circular Economy concept and in order to minimise the quantity of waste disposed, waste recovery and reuse of recovered materials as raw materials in various industries while preserving the natural resources is strongly encouraged. One of the strands in development of these trends is the reuse of slag (bottom ash) produced from municipal waste incineration in concrete mixes. The article gives a brief overview of the possibilities for the use of slag produced during the municipal waste incineration for the formation of concrete mixes. A brief overview of global experience in this area has been provided. The technological process of waste incineration in Lithuania and the chemical composition of the resulting ash have been described in general terms. The results of preliminary tests of concrete mixes with bottom ash performed at Vilnius Gediminas Technical University have been presented. The tests performed show that a properly selected content of bottom ash can be used as a substitute for fine aggregates in concrete mixes. The initial results give impetus to further research in the field of application of secondary raw materials for concrete mixes.

The present paper investigates experimental mechanical properties of lightweight concrete mixes produced with expanded glass aggregate. Different concrete mixtures (totally 12) from normal weight to extremely lightweight structural concrete have been made. The sand by its volume was replaced with the expanded glass. All specimens were tasted after 7 and 28 days of hardening to identify flexural and compressive strength. Density of concrete mixes ranged from 1458 to 2347 kg/m3, and the compressive strength of 40×40×40 mm cubes ranged from 40 to 103 MPa. As a result, strength and density relationship of lightweight concrete was obtained. The performed experimental investigations on freeze­thaw resistance and alkaline corrosion have shown good durability of the designed mixes.

The paper deals with analysis of structural lightweight concrete. New lightweight concrete mixture made with expanded clay aggregate has been proposed and applied for experimental rein-forced concrete beams. Totally 8 beams with different rein-forcement ratios (0.309%, 0.557%, 0.895% and 1.255%) were tested under short-term four point bending loading. Stress-strain behavior of the beams under considerations has been investigated. Average strains at 4 different levels of pure bend-ing zone and vertical displacements at 12 different points of the beam were measured. During the test, deformations and crack-ing of the pure bending zone were additionally observed using high-speed digital video cameras. The data obtained by cameras were analyzed using digital image correlation technique. Applying the test data bending moments and curvature diagrams were derived for each beam. The obtained relationships were compared with theoretical results calculated using design code methods LST EN and STR. Using the inverse algorithm developed by VGTU, tension reinforced lightweight concrete stress and strain diagrams were obtained, which were adapted to numerical modeling by software ATENA. Moment and curvature diagrams obtained by finite elements program were compared with experimental moment and curvature diagrams. Good agreement between both diagrams has been obtained. Straipsnyje aprašytas naujai sukurtas konstrukcinis lengvasis betonas ir jo panaudojimas eksperimentinių armuotojo lengvojo betono sijų gamybai. Atlikti trumpalaike apkrova veikiamų plieniniais strypais armuotų lengvojo betono sijų eksperimentiniai tyrimai, kuriuose nagrinėtas sijų įtempių ir deformacijų būvis. Laboratorijoje išbandyti 8 lenkiamieji elementai, kurių armavimo procentai: 0,309 %, 0,557 %, 0,895 % ir 1,255 %. Tyrimų metu matuotos vidutinės elemento deformacijos grynojo lenkimo zonoje 4 skirtinguose lygmenyse bei sijų poslinkiai ties atramomis, jėgos pridėjimo vietose ir viduriniame pjūvyje (iš viso 12 matavimo taškų). Bandymo metu grynojo lenkimo zonos deformacijos bei pleišėjimas papildomai stebėti greitaeige vaizdo kamera. Gauti rezultatai panaudoti sudarant eksperimentines lenkimo momentų ir kreivių diagramas, kurios palygintos su teoriškai apskaičiuotomis taikant Lietuvoje galiojančių LST EN ir STR projektavimo normų metodikas. Taikant VGTU sukurtą atvirkštinio uždavinio algoritmą, gautos tempiamo armuotojo lengvojo betono įtempių ir deformacijų diagramos, kurios pritaikytos atliekant skaitinį modeliavimą baigtinių elementų programa ATENA. Gautos momentų ir kreivių diagramos baigtinių elementų programa palygintos su eksperimentų metu gautomis momentų ir kreivių diagramomis. Gautas geras šių diagramų sutapimas.