Mechanisms and modelling of concrete damage due to freezing

Dan je pregled mehanizama oštećenja betona od smrzavanja bez dodatka soli za odmrzavanje, prikazani su neki modeli pomoću kojih se može predvidjeti nastajanje oštećenja. Na osnovi mehanizama pojave oštećenja i mjerenja, izrađeni su modeli čija je svrha predviđanje trajnosti betonskih konstrukcija izloženih utjecaju smrzavanja. Pokazuje se da je zbog mikrostrukture betona koja se mijenja i brojnih parametara koji utječu na razvoj degradacije betona teško napraviti uspješan model.An overview of mechanisms of concrete damage due to freezing, but without presence of deicing salt, is presented. Some models enabling prediction of concrete damage are described. The models aimed at predicting durability of concrete structures exposed to freezing action have been developed based on modelling and measurement of damage mechanisms. However, the authors stress that is quite difficult to develop a successful model due to concrete microstructure which is subject to changes, and also because of a multitude of parameters that are responsible for the degradation of concrete

AN IMPROVED NANOSCALE TRANSMISSION LINE MODEL OF MICROTUBULE: THE EFFECT OF NONLINEARITY ON THE PROPAGATION OF ELECTRICAL SIGNALS

In what manner the microtubules, cytoskeletal nanotubes, handle and process electrical signals is still uncompleted puzzle. These bio–macromolecules have highly charged surfaces that enable them to conduct electric signals. In the context of electrodynamic properties of microtubule, the paper proposes an improved electrical model based on its cylindrical structure with nano–pores in its wall. Relying on our earlier ideas, we represent this protein–based nanotube with the surrounding ions as biomolecular nonlinear transmission line with corresponding nanoscale electric elements in it. One of the key aspects is the nonlinearity of associated capacitance due to the effect of shrinking/stretching and oscillation of C–terminal tails. Accordingly, a characteristic voltage equation of electrical model of microtubule and influence of capacitance nonlinearity on the propagation of electrical pulses are numerically analyzed here

Interlaboratory tests and their implementation

U radu je objašnjena svrha međulaboratorijskih ispitivanja i opisan postupak pripreme, provedbe, vrednovanja i izvještavanja o rezultatima. Prikazana je i primjerima potkrijepljena statistička analiza rezultata koja je u skladu s priznatim normama i uputama. Opisana je analiza rezultata ispitivanja metodom raspona i srednjih vrijednosti te metodom ANOVA. Rad je namijenjen ispitnim laboratorijima koji žele organizirati međulaboratorijsko ispitivanje i/ili sudjelovati u njemu.The purpose of interlaboratory tests is described and the procedures for preparation, implementation, evaluation and reporting of results, are described. The statistical analysis of results, compliant with recognised standards and recommendations, is presented and backed by appropriate examples. The analysis of test results using the value range and mean value method, and the ANOVA method, is described. The paper is targeted at testing laboratories that wish to organize interlaboratory testing campaigns and/or participate in such testing

Interlaboratory testing of stone aggregate grading

Prikazani su rezultati međulaboratorijskog ispitivanja granulometrijskog sastava kamenog materijala frakcije 0 – 4 mm obrađeni metodom analize varijance (ANOVA). Eksperiment je planiran trofaktorskim stupnjevitim modelom. Procijenjene su varijance ponovljivosti i obnovljivosti te prijelazne varijance među nizovima rezultata dobivenih u različitim uvjetima obnovljivosti. Iskazivanje prijelazne varijance važno je radi određivanja utjecaja heterogenosti agregata na svakoj razini ispitivanja.Results of interlaboratory testing of the stone aggregate fraction 0 – 4 mm, analysed by variance analysis method (ANOVA), are presented. The experiment was planned with the three-factor staggered- nested model. The repeatability and reproducibility variances, and intermediate precision variances among ranges of results obtained under various reproducibility conditions, were estimated. The estimation of intermadiate variance is significant for determining the influence of heterogeneity of aggregates at each level of testing

Influence of composition on the deformability of asphalt

Opisana je obrada rezultata mjerenja najveće dubine kolotraga koji se stvaraju na asfaltnim uzorcima različitog sastava. Otpornost na stvaranje kolotraga mjerena je uređajem malih dimenzija postupkom B prema normi HRN EN 12697-22, a sastav uzorka određen je prostornim modelom u kojemu su komponente izražene volumenskim koncentracijama. Statističkom obradom rezultata mjerenja nađena je ovisnost dubine kolotraga o sastavu asfaltnog uzorka koja vrijedi za sve ispitane uzorke.The analysis of results obtained by measuring biggest rutting depths determined on asphalt samples of different composition is described. The resistance to rutting was measured with a small size device according to procedure B as specified in HRN EN 12697-22, and the sample composition was determined through space model in which components are expressed as volume concentrations. The correlation between the rutting depth and the asphalt sample composition, applicable to all samples subjected to testing, was determined through statistical analysis of results

Determining thickness of asphalt and concrete layers by non-destructive method

Prikazano je istraživanje mogućnosti uporabe nerazorne metode ispitivanja zasnovane na refleksiji i transmisiji zvučnih valova u svrhu mjerenja debljine asfaltnih i betonskih slojeva. Opisana teorija odziva slojevitih konstrukcija na točkasti udarac male energije potvrđena je mjerenjima na uzorcima i probnom polju. Utvrđeno je da je moguće mjerenje debljine slojeva asfalta i betona uz ograničenja vezana uz temperaturu pri ispitivanju i razlike akustičnih impedancija slojeva.The study of possible use of a non-destructive method of testing, based on reflection and transmission of sound waves, for measuring thickness of asphalt and concrete layers, is presented. The described theory of response of multi-layer structures to low-energy point impact has been confirmed through measurements on samples and test section. It has been established that measurement of thickness of asphalt and concrete layers is possible, with limitations relating to testing temperature and differences in acoustic impedance of layers

CONSTRUCTION AND TESTING OF THE MEASUREMENT SYSTEM FOR EXCAVATOR PRODUCTIVITY

Hidraulični bager jedan je od najčešće korištenih strojeva u rudarstvu, graditeljstvu i geotehnici. Kao takav korisnicima predstavlja i važnu stavku u troškovima goriva i održavanja. Detaljna mjerenja učinka ovoga stroja izvode se u svrhu poboljšanja efikasnosti odnosno uštede. Mjerni sustav s takvom svrhom može biti složen i skup, tražiti specijalnu opremu proizvođača stroja te ne postoji kao gotovo rješenje koje bi omogućavalo praćenje radnih parametara poput trajektorije lopate, sila i energije kopanja, visine radnoga čela i sl. Iz toga razloga osmišljen je i testiran sustav za praćenje radnih parametara i učinka bagera. Sustav se sastoji od triju pretvornika linearnoga pomaka i triju pretvornika tlaka, za mjerenje produljenja i tlakova hidrauličnih cilindara, te jednoga žiroskopa za mjerenje kuta zakretanja bagera. Pretvornici su spojeni na jedinicu za prikupljanje podataka, opremljenu SD karticom i 12-bitnim AD pretvaračem. Jedinica je bazirana na Atmega328 mikrokontroleru, što omogućava primjenu Arduino sučelja za programiranje i razvijenih biblioteka koda. Mjerni sustav testiran je laboratorijski radi određivanja točnosti, rezolucije i moguće brzine uzorkovanja podataka. Tlakovi mogu biti mjereni u rasponu 0 bar – 500 bar s točnošću od 0,026 % MO i rezolucijom 0,15 bar. Izvlačenje cilindra može biti mjereno u rasponu 0 mm – 2300 mm, s točnošću od 0,087 % MO i rezolucijom 0,58 mm. Točnost mjerenja kuta zakretanja iznosi 1,2° po okretu ili 0,33 % MO. Testirana brzina uzorkovanja iznosi 39 Hz – 588 Hz, ovisno o programskome kodu.hydraulic excavator is one of the most used machines in mining, construction and geotechnics. Monitoring its productivity can provide benefits such as savings in fuel consumption and maintenance, cost optimization of working parameters and a higher working efficiency. A measurement system for such a purpose can be complex and expensive, as it requires special equipment from the manufacturer and does not exist as an out of the box solution that would measure working parameters such as bucket trajectory, digging energy, digging force, etc. A measuring system was designed to monitor productivity and gather working parameters. It consists of three pressure transmitters for measuring cylinder pressures, three draw wire sensors for cylinder elongations, one inertial measurement unit for the measurement of swing angle and one logger unit for data acquisition and storage. The logger unit, equipped with an SD card module and 12-bit AD converter, is based on Atmega328 microcontroller, which allows for the usage of Arduino IDE and already developed libraries. The system was tested in a laboratory to determine its accuracy, resolution and usable sample rate. Cylinder pressure can be measured in the range of 0-500 bar with an excellent accuracy of 0.026 % FSO and 0.15 bar resolution. Cylinder elongation can be measured in the range 0-2300 mm with an accuracy of 0.087 % FSO and 0.58 mm resolution. Swing angle measurement accuracy is 1.2° per circle or 0.33 % FSO. The usable sample rate of the system is found to be 39 Hz-588 Hz, depending on the logger executing code

Eksperimentalno određivanje granica detekcije „Impact - Echo" metode

This paper presents results of experimental investigation of detection limits for „Impact-echo" method, used for the determination of damages in reinforced concrete structures. An experimental reinforced concrete field with embedded damages of different type and size, built in at different depths was designed and manufactured at the Institute IGH in Zagreb. Also, a device named "MECHAHIT" for automatic generation of ball impacts with reproducible contact time and contact force was designed and constructed. Measured re-sponses are processed by different spectral analysis methods. Based on parametric evalu-ation of results, the detection limits are determined. It is shown that the use of "MECHAHIT" device and alternative spectral analysis methods improve signal-to noise ratio, extend de-tection limits and improve the presentantion of the measurements.U radu su prikazani rezultati eksperimentalnog odredivanja granica detekcije „Impact—echo" metode kod pronalaženja oštećenja u armiranobetonskim konstrukcijama. Za provodenje eksperimentalnih istraživanja, u Institutu IGH u Zagrebu, projektiran je i izraden armiranobetonski eksperimentalni poligon s ugradenim oštećenjima različitih vrsta i veličina, smieštenih na različitim dubinama. Konstruiran je i uredaj nazvan „MECHAHIT" kojim se automatski generiraju udarci ponovljivog kontaktnog vremena i kontaktne sile. lzm-jereni odazivi su obradeni različitim spektralnim metodama. Na osnovi parametarske studije rezultata odredene su granice detekcije. Utvrdeno je da se primienom uredaja „MECHAHIT" i alternativnih metoda spektralne analize postiže pobolišanie prezentacije signala, uklanjan-inje šuma i proširenje granica detekcije