Parametric analysis capacity of anchors in tension andshear at fiber reinforced ultra high strength concretefactorial analysis and neural networks

У дисертацији је разматран проблем носивости анкера на чупање и смицање у бетону веома високих чврстоћа. Издвојена су три параметра који имају значајан утицај на носивост анкера. Реализовано је обимно експериментално истраживање, које је конципирано тако да се даље може користити у нумеричким анализама. Закључци су изведени на основу нумеричке анализе и дефинисања утицаја варираних параметара помоћу неуронских мрежа и факторијалног експеримента.U disertaciji je razmatran problem nosivosti ankera na čupanje i smicanje u betonu veoma visokih čvrstoća. Izdvojena su tri parametra koji imaju značajan uticaj na nosivost ankera. Realizovano je obimno eksperimentalno istraživanje, koje je koncipirano tako da se dalje može koristiti u numeričkim analizama. Zaključci su izvedeni na osnovu numeričke analize i definisanja uticaja variranih parametara pomoću neuronskih mreža i faktorijalnog eksperimenta.The dissertation discusses the problem of load anchors to pulling out and shearing in ultra high strength concrete. Allocate three parameters that have a significant impact on the load capacity of anchors. Realized an extensive experimental research, which is designed so that could be used in numerical analysis. Conclusions are drawn on the basis of a numerical analysis, and defining the influence of varying the parameters using the neural network and the factorial experiment

Concrete mix design for reconstruction of northwest breakwater in the Tripoli harbour - Libya

Reconstruction of Northwest breakwater in the Tripoli Harbour - Libya (about 4500 m long) required manufacture of various concrete elements (cubes and accropodes) in total amount of 550 000 m(3). Volumes of cubes were 6,3 m(3), 8,5 m(3) and 12,7 m(3), volumes of accropodes were 6,3 m(3) and 9,0 m(3). After preliminary trials and trial production, an optimum mix proportion was chosen, in compliance with technical specification requirements. One of the main causes for concrete blocks cracking is the temperature difference between core and external surface of the blocks, so new blocks with new mix proportions were made (three variations in cement content). Temperature was measured at three characteristic points: in the middle of the cube, in the middle of vertical outer surface and in the middle of horizontal upper edge. Finally, optimal proportions of the constituent materials were adopted

The estimation of compressive strength of normal and recycled aggregate concrete

Procena čvrstoće pri pritisku se postavlja kao važan zadatak proizvođačima betona, naročito pri projektovanju betonskih mešavina i obezbeđenju zahtevanog kvaliteta proizvedenog betona. U radu je prikazano poređenje eksperimentalnih rezultata čvrstoće pri pritisku betona sa prirodnim i recikliranim agregatom sa rezultatima dobijenim na osnovu jednačina prikazanih u tehničkoj regulativi. Prikazan je koeficijent determinacije eksperimentalnih podataka i rezultata dobijenih na osnovu preračuna prema jednačinama datim u EN 1992-1-1, ACI 209 i tabeli za preračun datoj u SRPS U.M1.048. Prikaz zavisnosti čvrstoće pri pritisku betona na osnovu jednačina datih u radu se odnosi na određivanje zavisnosti u odnosu na vrstu upotrebljenog cementa i starosti betona negovanog na konstantnoj temperaturi.Estimation of concrete strength is an important issue in ready-mixed concrete industry, especially, in proportioning new mixtures and for the quality assurance of the concrete produced. In this article, on the basis of the existing experimental data of compressive strength of normal and recycled aggregate concrete and equation for compressive strength calculating given in Technical regulation are compared. The accuracies of prediction by experimental data obtained in laboratory as well as by EN 1992-1-1, ACI 209 and SRPS U.M1.048 are compared on the basis of the coefficient of determination. The determination of the compressive strengths by the equation described here relies on determination of type of cement and age of concrete with the constant curing temperature

Frost resistance of concrete with crushed brick as aggregate

Predmet istraživanja su betoni spravljeni sa recikliranom opekom kao agregatom. Eksperimentalni rad je obuhvatio više vrsta betona spravljenih sa istom količinom cementa (385 kg/m3) i istom konzistencijom (sleganje oko 1 cm). Kao agregat je korišćena reciklirana opeka i kombinacija reciklirane opeke i prirodnog rečnog agregata. Posmatran je uticaj upotrebljenih frakcija drobljene opeke i njihovog procentualnog učešća na čvrstoću pri pritisku, upijanje vode i otpornost prema dejstvu mraza. Na osnovu rezultata eksperimentalnih istraživanja može se zaključiti da se primenom reciklirane opeke kao agregata dobija novi kompozitni materijal sa zadovoljavajućim fizičko - mehaničkim karakteristikama.The investigation included concrete made by using recycled brick as aggregate. Experimental work included several types of concrete made with the same cement content (385 kg/m3), and same consistency (slump about 1 cm). Recycled brick and combination of natural river aggregate and recycled brick were used as aggregates. The influence of percentage and grain size of crushed brick aggregate on concrete compressive strength, water absorption and frost resistance were observed. On the basis of the results obtained during experimental research, a general conclusion can be drawn that the application of recycled concrete as aggregate can lead to new composites with satisfactory physical-mechanical properties

ESTIMATION POSITION AND DIAMETER OF REBAR BY MODERN NON-DESTRUCTIVE TECHNIQUES

Ultrasonic testing of concrete by modern equipment has grown in importance in recent years in non-destructive testing. Measuring concrete cover thickness and estimating steel rebar position and diameter is main focus for assessment of existing reinforcement concrete facilities. Voids, entrained air and potential delamination are important to detect in order to evaluate the quality of the executed concrete members. This paper presents the latest two modern non-destructive techniques – ultrasonic tomography and electromagnetic pulse induction – suitable for testing reinforcement concrete members. The capabilities of these techniques for locating defects, reinforcement bars and determining their size in unilaterally accessible concrete members are described

Resistance of CEM III/B based materials to acid attack

Cementni materijali u poljoprivrednim i drugim industrijskim objektima izloženi su dejstvu kiselina. Zbog toga vek konstrukcija zavisi od trajnosti maltera ili betonskih elemenata u agresivnoj sredini. U radu je predstavljena otpornost na koroziju koja je uzrokovana sulfatnom, nitratnom, ureom, mlečnom i sirćetnom kiselinom. Skenirajuća elektronska mikroskopija (SEM) korišćena je da se ispita efekat agresivnih rastvora na mikrostrukturu i mehaničke osobine maltera. Hemijska otpornost prizmi od maltera i dve vrste betona testirana je prema metodi Koch-Steinegger. Kako je uslov za otpornost na agresivne rastvore taj da zatezna čvrstoća maltera nije manja od 70% u odnosu na referentne prizme negovane u vodi, može se zaključiti da su malter i beton, napravljeni sa CEM III/B, u ovom istraživanju otporni na sve kiseline kojima su tretirani. .Cement based materials in the agricultural and other industrial structures are exposed to acid attack. That is the reason why the service life of structure depends on the durability of mortar or concrete elements in aggressive environment. Resistance to corrosion caused by sulphate, nitrate, carbamide, lactic acid and acetic acid was presented. Optical and scanning electron microscopy (SEM) was used to examine the effect of aggressive solutions on the microstructure and mechanical properties of mortar. The chemical resistance of mortar prisms and two types of concrete were tested according to the Koch-Steinegger method. As the condition for resistance in aggressive solution is that flexural strength of mortar prisms is no less than 70 % compared to referent prisms cured in water it can be concluded that mortar and concrete made with CEM III/B in this investigation are resistant to all treated acids

Determination of the effects of the rebar-cement bond parameters variation in UHPFRC using FA and ANN

The experimental study included the design and production of ultra-high-performance steel fiber-reinforced concrete (UHPFRC). The physical and mechanical properties of UHPFRC were investigated in a laboratory setting. To investigate the properties of UHPFR concrete, three types of concrete and over 70 samples were used. Following that, samples were created to test the anchors' load-bearing performance. Six concrete slabs with a total of 108 pre-installed anchor samples and six concrete slabs with 108 post-installed chemical anchor samples were created. The analysis of the test findings comprised all individual results as well as the definition of the relationship between the anchor's tensile load capacity and other parameters. To accurately determine the individual influence of the investigated factors as well as their combined impact, a factorial experiment, and artificial neural networks were used in addition to normal statistical numerical studies. It was determined that both approaches offer advantages. The results obtained show matches in certain parts. Due to the way data is processed in different ways, there are also significant differences between them

Properties of composite cement with commercial and manufactured metakaolin

Metakaolin kompozitni cementi su pripremljeni zamjenom Portland cementa s dodatkom 5 ÷ 35 % metakaolina (MK), proizvedenog toplinskom aktivacijom / kalcinacijom domaće kaolinske gline, i komercijalnog matakaolina (CMK). Karakteristike metakaolin kompozitnih cemenata ocijenjene su na osnovu ispitivanja vremena (početka i kraja), tlačnih čvrstoća (u starosti od 2, 7, 28, 90 i 180 dana) i postojanosti volumena, te u usporedbi s kontrolnim cementom (Portland cement - CEM I). Nakon 28 dana, veću vrijednost tlačne čvrstoće pokazali su uzorci cementa pripremljeni s dodatkom CMK, te s dodatkom do 25 % MK u odnosu na kontrolne uzorke.Metakaolin composite cements were prepared with 5 to 35 % replacement of ordinary Portland cement with metakaolin (MK), manufactured by thermal activation/calcination of domestic kaolin clay, and commercial matakaolin (CMK) . Performance of the composite cements was evaluated through the setting time (initial and final), compressive strengths (for ages 2, 7, 28, 90 and 180 days) and soundness, and compared with control cement (Portland cement – CEM I). After 28 days, compressive strength was higher than that for control cement for cements prepared with addition of CMK, and with addition of up to 25 % MK

Some properties of ultra-high strength concrete

Značajno mesto u primeni novih materijala u građevinarstvu zauzima upotreba betona ultra visokih čvrstoća. Struktura, svojstva i tehnologija izrade ove vrsta betona se intenzivno proučava poslednjih petnaest godina. U ovom radu je prikazana mogućnost dobijanja betona ultra visokih čvrstoća na osnovu eksperimentalnih istraživanja primenom komponentnih materijala dostupnih u Srbiji. Spravljene su tri serije uzoraka sa različitim vrstama cemenata. Korišćena su čelična vlakna dužine 8mm i poprečnog preseka 0.175mm. Prikazana su fizičko-mehanička svojstva betona ultra visokih čvrstoća i analizirana je mikrostruktura ovog kompozita.Modern civil engineering is characterized with increased application of Ultra-high strength concrete (UHSC). Structure, properties and manufacturing technologies of UHSC are intensively analyzed in the last fifteen years. Possibilities of getting UHSC designed with the materials that are available in Serbian market, were tested in the experimental work; they are shown in this paper. Three series of samples were made with different types of cement. Steel fibers were used: length 8 mm, diameter 0.175 mm. Physical-mechanical properties of UHSC are presented and microstructure of concrete was observed, as well

Evaluation of air content on concrete compressive strength with classical approach and neural networks

Mnogi parametri utiču na karakteristike svežeg i očvrslog betona. Jedan od najvažnijih svakako jeste poroznost betona. Poroznost svežeg betona meri se količinom uvučenog vazduha. Uticaj uvučenog vazduha na beton i njegovu pritisnu čvrstoću istraživali su mnogi svetski istraživači. Na bazi tih istraživanja, izdvojene su dve, u praksi najviše korišćene, formule. Tehnike mekog programiranja, a posebno neuronske mreže, s formiranim bazama podataka laboratorijskih ispitivanja betona, otvaraju novi pristup u predviđanju uticaja količine uvučenog vazduha u svežem betonu na njegovu čvrstoću pri pritisku.Many parameters influence on the characteristics of fresh and hardened concrete. One of the most important characteristic of concrete is its porosity. Measure the porosity of fresh concrete is measured by the amount of entrained air. The effect of entrained air in concrete on compressive strength investigated by many authors. On the bases these works we have two formulas applicable in practice. Soft programming techniques especialy neural networks and the formation of databases related to the testing in laboratories for concrete opened up new approaches in predicting the impact of the quantity of entrained air in concrete on compressive strength