Wyniki wyszukiwania - BazTech

1

Badanie eksperymentalne belki sprężonej wykonanej z fibrobetonu o wysokiej wytrzymałości

Urban Tadeusz, Gołdyn Michał, Krawczyk Łukasz

Inżynieria i Budownictwo

|

2024

|

R. 80, nr 4

256--261

PL

W artykule zaprezentowano wyniki badań belki sprężonej wykonanej z fibrobetonu o wysokiej wytrzymałości. Belkę o przekroju dwuteowym wysokości 0,2 m i długości 2,8 m badano w schemacie czteropunktowym do osiągnięcia nośności na zginanie. Element sprężono jednym splotem Y1860S7 średnicy ø 012,5. W fibrobetonie zastosowano włókna proste KrampeHarex® DM12,5/0,175. Określono wytrzymałość betonu zarówno na ściskanie (fc ≈ 110 MPa), jak i na rozciąganie w próbie rozłupywania (fct,sp ≈ 17,5 MPa) oraz trójpunktowego zginania (ft,fl ≈ 11,9 MPa). Po wykonaniu i sprężeniu belki rejestrowano zmiany odkształceń na powierzchni elementu przez 19 dni, po czym przystąpiono do badania niszczącego, w trakcie którego rejestrowano ugięcia i odkształcenia elementu. Zniszczenie było następstwem zginania i wynikało z uplastycznienia zbrojenia sprężającego, a następnie uformowania się jednej rysy zlokalizowanej. Obliczenia nośności w świetle reguł normy SIA 2052 z wykorzystaniem sprężysto-plastycznego modelu zachowania fibrobetonu wykazały dobrą zgodność z wynikami eksperymentu.

EN

The paper presents experimental results prestressed beam made of high-strength fiber reinforced concrete. The I-shaped beam with a height of 0.2 m and a length of 2.8 m was tested in a four-point scheme until the bending load capacity was achieved. The element was prestressed with one tendon Y1860S7 with a diameter of ø 012.5. The fiber reinforced concrete was made with KrampelHarex® DM12.5/0.175 fibers. Concrete was tested in compression (fc ≈ 110 MPa) and in tension, checking the resistance in both the splitting test (fct,sp ≈ 17.5 MPa) and the three-point bending test (fc,fl ≈ 11.9 MPa). After fabrication and prestressing of the beam, changes in strains on the element's surface were observed for 19 days, after which destructive test was conducted. During the test deflections and deformations of the element were recorded. The failure was as a result of bending and followed yielding of the prestressing strand and the subsequent formation of one localised crack. The calculation of the load carrying capacity in the light of the SIA 2052 standard, assuming the elasto-plastic material model of the fibre reinforced concrete, showed good agreement with the experimental results.

2

Research on the design method of flexural capacity of RC beams strengthen by ultra-high performance concrete

Wang Jiawei, Ying Feifei

Archives of Civil Engineering

|

2024

|

Vol. 70, nr 1

487--507

EN

Due to the increase in traffic volume, load level, and service life of existing bridges, the bending bearing capacity of reinforced concrete beams (hereinafter referred to as RC beams) has decreased, leading to safety issues. In order to solve the problem of insufficient flexural bearing capacity of RC beams, this article adopts the method of ultra-high performance concrete (UHPC) flexural strengthening RC beams, establishes a finite element model of UHPC-RC reinforcement system, and conducts stress analysis with reinforcement thickness, reinforcement range, reinforcement form, and reinforcement height as parameters to determine the optimal scheme of the reinforcement system. Based on the calculation results, a theoretical formula for the maximum principal stress and maximum deflection of the reinforcement system is proposed. To verify the feasibility of the plan, a reinforcement design was carried out on an existing beam, and it was found that the bending bearing capacity of the RC beam increased by 21%; the high tensile strength of UHPC and the addition of steel fibers have a good limiting effect on cracks; The steel plate of the reinforcement system can be used as a template, reducing construction costs and having good economy.

3

Parameter analysis and design method of ultra-high performance concrete shear strengthening RC beams

Wang Jiawei, Wang Ziqian, Ying Feifei, Yu Haitao

Archives of Civil Engineering

|

2024

|

Vol. 70, nr 2

431--445

EN

In recent years, bridge safety accidents caused by insufficient shear bearing capacity of bridges have attracted increasing attention. The main causes include internal factors such as insufficient bridge section and deterioration of steel bars, as well as external factors, for example, vehicle load surge and improper maintenance. To address this issue to some degree, this article adopts the method of strengthening RC beams with ultra-high performance concrete (UHPC) and conducts parameter analysis using finite element method, taking into consideration the influence of four parameters: reinforcement material, reinforcement thickness, reinforcement length, and reinforcement form on the shear strengthening characteristics of RC rectangular beams. After obtaining the optimal reinforcement plan through parameter analysis, the author applied the research results to an existing bridge with insufficient shear strength. It then turned out that the shear bearing capacity of the reinforced bridge’s inclined section increased by approximately 27.1%. Simple and fast in construction, this reinforcement method is one of the methods that is effective to increase cross-section reinforcement; besides, it features good economic characteristics and applicability.

4

Investigation on cracking performance of UHPC overlaid concrete deck at hogging moment zone of steel-concrete composite girders

Wan Zhiyong, Guo Guohe, Wang Zhiguo, He Shaohua, Tan Juliang, Hou Libo

Archives of Civil Engineering

|

2023

|

Vol. 69, nr 4

445--457

EN

The concrete deck at the negative bending moment region of a continuous steel-concrete composite girder bridge is the weakest part of the structure. Introducing ultra-high performance concrete (UHPC) to the hogging region may overcome the shortage and break through the bottleneck. This paper explores the cracking performance of steel-concrete composite girders with concrete slabs topped by a thin layer of UHPC subjected to a negative bending moment. A real continuous composite girder bridge is briefly introduced as the engineering background, and the cracking characteristic of the concrete deck over the middle piers of the bridge is numerically modeled. Approaches to strengthen the cracking performance of the concrete deck at the hogging region through topping UHPC overlays are proposed. The effectiveness of the approaches is examined by conducting a series of numerical and experimental tests. Numerical results indicate that the normal concrete (NC) deck near the middle forums of the bridge would crack due to the large tensile stress from negative bending moments. Replacing the top concrete with an identical-thick UHPC overlay can increase the cracking resistance of the deck under the moment. As the thickness of the UHPC overlay increased from 6.0 cm to 12.0 cm, the maximum shear stress at the UHPC overlay-to-NC substrate interface under different load combinations was decreased by 56.3%~65.3%. Experimental results show that the first-cracking load of the composite beam using an NC-UHPC overlaid slab was 2.1 times that using an NC slab. The application of a UHPC overlaid deck can significantly improve the crack performance of the steel-concrete composite girder bridge.

5

Cracking control technique for continuous steel-concrete composite girders under negative bending moment

Cai Min, Li Wenjie, Wan Zhiyong, Sheng Jianjun, Tan Juliang, Ma Chao

Archives of Civil Engineering

|

2023

|

Vol. 69, nr 3

239--251

EN

Continuous steel-concrete composite girder can fully utilize material strength and possess large spanning ability for bridge constructions. However, the weak cracking resistance at the negative bending moment region of the girder seriously harms its durability and serviceability. This paper investigates practical techniques to improve the cracking performance of continuous steel-concrete composite girders subjected to hogging moment. A real continuous girder was selected as the background bridge and introduced for numerical analysis. Modeling results show that under the serviceability limit state, the principle stress of concrete slabs near the middle piers of the bridge was far beyond the allowable material strength, producing a maximum tensile stress of 10.0 MPa. Approaches for strengthening concrete decks at the negative moment region were developed and the effectiveness of each approach was assessed by examing the tensile stress in the slabs. Results indicate that the temporary counterweight approach decreased the maximum tensile stress in concrete slabs by 22%. Due to concrete shrinkage and creep, more than 65% of the prestressed compressive stresses in concrete slabs were finally dispersed to the steel beams. A thin ultra-high performance concrete (UHPC) overlay at the hogging moment region effectively increased the cracking resistance of the slabs, and practical engineering results convicted the applicability of the UHPC technique.

6

Investigation on the effect of silane coupling agent treatment of steel fibers on the durability of UHPC

Du Shuang, Luan Congqi, Yuan Lianwang, Du Peng, Zhou Zonghui, Wang Jinbang

Archives of Civil and Mechanical Engineering

|

2023

|

Vol. 23, no. 2

art. no. e118, 2023

EN

Ultra-high performance concrete (UHPC) is a type of cementitious material that has been specifically engineered to achieve exceptional mechanical properties and durability through optimized particle filling. However, the addition of steel fibers to the UHPC matrix creates a transitional region at the interface. Previous research has indicated that the use of silane coupling agents (SCA) on the surface of steel fibers is a promising approach for improving the bonding properties between the fibers and the matrix. This study aims to explore the impact of varying amounts of untreated steel fibers versus those that have undergone SCA treatment on the durability of UHPC. The findings indicate that treating steel fibers with SCA significantly narrows the pore space between the matrix and steel fibers, as well as enhances the production of hydration products on the steel fiber surface. Furthermore, this treatment facilitates the formation of a compact transition zone between the UHPC matrix and steel fibers. The electrochemical corrosion resistance, chloride ion penetration resistance, frost resistance, and sulfate erosion resistance of UHPC are all enhanced by this method. As a result, the durability of UHPC is significantly improved, making it an extremely promising avenue of research.

7

Pierwsze krajowe zastosowanie nawierzchni betonowej na obiektach mostowych

Siwowski Tomasz, Szydło Antoni, Rajchel Mateusz

Materiały Budowlane

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2022

|

nr 4

70--73

PL

Coraz więcej dróg w Polsce ma nawierzchnię betonową, natomiast na mostach położonych w ciągu tych dróg nadal jest układana nawierzchnia bitumiczna ze względu na brak krajowych technologii. Powoduje to określone komplikacje technologiczne i eksploatacyjne. W artykule przedstawiono przegląd nawierzchni betonowych, stosowanych na mostach drogowych na świecie. Na tym tle opisano pierwsze krajowe zastosowanie nawierzchni betonowej wykonanej na kilku obiektach mostowych w ciągu drogi ekspresowej S-7.

EN

More and more roads in Poland have a concrete pavement. However, due to the lack of national technologies, bituminous pavement is still being laid on the bridges located along these roads. This causes certain technological and operational complications. The article presents an overview of concrete pavements used on road bridges around the world. Against this background, the first domestic application of concrete pavement, made on several bridge structures along the S-7 expressway, was described.

8

Wybrane charakterystyki dynamiczne kładek dla pieszych z pomostami z betonu UHPC

Pańtak Marek

Inżynieria i Budownictwo

|

2022

|

R. 78, nr 11-12

568--573

PL

W artykule przedstawiono wybrane charakterystyki oraz wyniki badań i analiz dynamicznych dwóch kładek dla pieszych wzniesionych z wykorzystaniem betonu UHPC. Zobrazowano wpływ wykorzystania betonu UHPC na parametry dynamiczne kładek dla pieszych.

EN

The article presents selected characteristics and the results of dynamic tests and analyses of two footbridges built with the use of UHPC concrete. The influence of the use of UHPC concrete on the dynamic parameters of footbridges was depicted.

9

Fire performance of ultra‑high performance concrete: effect of fine aggregate size and fibers

Zhang Dong, Tan Kang Hai

Archives of Civil and Mechanical Engineering

|

2022

|

Vol. 22, no. 3

art. no. e116

EN

This study conducted a thorough investigation on the combined effects of fine aggregate (FA) size, steel fiber, and polypropylene (PP) fiber on the spalling behavior and mechanical properties of ultra-high-performance concrete (UHPC) at high temperature. FAs with 0.6, 2.36, and 4.75 mm were incorporated with steel fibers or PP fibers in UHPC. Test results showed that the synergistic enhancement in spalling prevention of UHPC at high temperature was only found in the combination of PP fiber and large-sized FA. Large-sized FA not only increased the fraction of microcracks but also enhanced their connectivity in UHPC with PP fibers, thus increasing the permeability and improving the spalling resistance at high temperature. This reduced the required PP fiber content for spalling prevention. Besides, steel fibers and large-sized FAs had a combined negative effect on mechanical properties above 600 °C, resulting in even lower mechanical properties at 900 °C compared to UHPC without any fiber and UHPC with PP fibers. Microstructural observation also found that the degradation of steel fibers and microcracks generated by expansion of aggregate both severely damaged the microstructures of UHPC at 900 °C. By contrast, adding PP fibers reduced compressive strength of UHPC below 600 °C due to the voids left by the decomposition of PP fibers, but it did not affect compressive strength at 900 °C, as the cracks in the matrix was enlarged, which reduced the negative effect of PP fibers.

10

Experimental study on demountable steel ultra‑high performance concrete composite slabs under hogging moment

Guo Jun‑Yuan, Wang Jun‑Yan, Wang Yan-Bo, Gao Xiao‑Long, Bian Chen

Archives of Civil and Mechanical Engineering

|

2022

|

Vol. 22, no. 3

art. no. e137

EN

Demountable steel-concrete composite structures have attracted much attention from researchers because of its fast construction, demountability and environmental friendliness. Using ultra-high performance concrete (UHPC) in the hogging moment regions of demountable steel-concrete composite structures might improve their crack resistance and flexural performance. In this study, the cracking behavior, failure mode, stiffness, ultimate strength and relative slip of demountable steel-UHPC composite slabs with different stud spacings and longitudinal reinforcement ratios under hogging moment were experimentally investigated. A welded steel-UHPC composite slab was also tested to compare its behavior with the demountable slabs. The test results show the demountable steel-UHPC composite slabs have excellent crack control ability under hogging moment due to the slip of threaded headed stud and the strain hardening behavior of UHPC; the relative slip is directly associated with the stud spacing and controlled by the friction and shear force of threaded headed studs. As compared to the welded composite slab, the demountable composite slab can be easily separated after loading, the flexural capacity is slightly smaller, while the crack control ability is better and the ductility is higher. A constitutive model considering the reduction of tensile strength of UHPC after reinforcement was adoptedl the design formulas were developed to predict the elastic limit and the ultimate moment, and the bending stiffness of the demountable composite slabs under hogging moment. The test results verify the applicability of the proposed constitutive model of UHPC and design formulas.

11

Problemy napraw i wzmocnień żelbetowych podpór mostowych

Jarominiak Andrzej

Inżynieria i Budownictwo

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2020

|

R. 76, nr 12

580--590

PL

Omówiono rezultaty ankiety przeprowadzonej w USA na temat problemów utrzymania podpór mostów. Przedstawiono uszkodzenia i niektóre metody naprawy podpór żelbetowych, w tym stosowanie ultrazapraw cementowych z włóknami węglowymi lub szklanymi (UHPFRC) oraz omawia przyczyny małej trwałości napraw i metody jej zwiększenia: ekstrakcję chlorków, ochronę katodową zasilaną prądem ze źródła zewnętrznego i ochronę systemami anod galwanicznych.

EN

The article informs about the results of the survey conducted in the USA on the problems of maintenance the bridge substructures, lists the damage and informs about some methods of repairing reinforced concrete of these structures, including Ultra-High Performance Fibre Rein-forced Concrete, discusses the reasons for the low durability of repairs and methods of increasing it: chloride extraction, impressed current cathodic and galvanic anodes systems protection.

12

Elastyczność nowoczesnych rozwiązań konstrukcyjnych z wykorzystaniem prefabrykatów betonowych

Janczura K.

Materiały Budowlane

|

2018

|

nr 1

74--76

13

Analiza możliwości zastosowania betonu z proszków reaktywnych w konstrukcji mostowej

Stankiewicz B., Średniawa W.

Cement Wapno Beton

|

2018

|

R. 23/85, nr 6

496--510

PL

Zastosowanie w praktyce, ultra wysokowartościowych betonów z proszków reaktywnych (BPR) prowadzi do zmniejszenia masy własnej elementów konstrukcyjnych do ⅓ lub ½ masy własnej profili konstrukcyjnych z betonu tradycyjnego, zastosowanego w tych samych warunkach obciążenia. Na szczególną uwagę zasługuje rola włókien w BPR, dzięki którym wytrzymałość na ściskanie i rozciąganie elementu kompozytowego wzrasta wyraźnie. Odporność zmęczeniowa jest większa gdyż włókna powstrzymują powstanie rys, w konstrukcjach obciążonych dużymi siłami dynamicznymi. Włókna stalowe powinny stanowić podstawowy składnik przenoszący obciążenia, ale przede wszystkim zapewniać integralność strukturalną. W pracy przeanalizowano wariant wielomodułowej konstrukcji kładki dla pieszych, z dźwigarem nośnym kratownicowym. Pas górny konstrukcji stanowią dwie belki betonowe z BPR, połączone z płytą pomostu również wykonane z BPR. Pas dolny stanowi pojedynczy pręt o przekroju kołowym, również wykonany z BPR, natomiast krzyżulce wykonane są z rur okrągłych, ze stali nierdzewnej.

EN

Practical use of ultra-high-performance reactive powders concretes (RPC) leads to the reduction of the own mass of structural elements to ⅓ or ½, of the own mass of structural profiles from traditional concrete, analyzed under the same load conditions. Particularly noteworthy is the role of fibers in RPC concretes because the compressive and tensile strength of a composite element increases significantly. Fatigue resistance is higher due to the ability of the fiber to reduce crack propagation, in structures loaded under important dynamic forces. Steel fibers are required to act as the primary load bearing component, but above all to ensure structural integrity. In the work the variant of the multimodule structure of the footbridge with a truss carrying girder is analyzed. The top stripe of the structure consists of two concrete beams from RPC connected to the bridge deck with RPC. The lower belt is a single rod with a circular cross section, also made of RPC concrete, while as the crossbars round stainless steel pipes are applied.

14

Betony z proszków reaktywnych i ich zastosowanie w konstrukcjach zespolonych

Denisiewicz A.

Przegląd Budowlany

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2014

|

R. 85, nr 11

18--23

PL

Pierwsza część pracy o charakterze przeglądowym ma na celu prezentację wciąż mało znanego w naszym kraju materiału, jakim jest beton z proszków reaktywnych (BPR). Omówiono cechy charakterystyczne oraz podstawowe właściwości fizyczne i mechaniczne BPR. Wskazano dotychczasowe i planowane (będące w sferze badań) zastosowania tego materiału w szeroko pojętych konstrukcjach zespolonych. W pracy przedstawiono również wyniki własnych badań doświadczalnych BPR, które miały na celu sprawdzenie możliwości wykonania betonu z proszków reaktywnych w „warunkach placu budowy”, tzn. bez stosowania mieszarek intensywnych lub próżniowych oraz bez wykonywania zabiegów pielęgnacyjnych (obróbka cieplno – wilgotnościowa, ciśnieniowa).

EN

The first part of the paper presents reactive powder concrete (RPC), rather unpopular in Poland. The basic physical and mechanical characteristics of RPC are discussed. The current and planned uses of the reactive powder concrete in the composite constructions are indicated. The second part of the work shows the results of the own RPC experimental research. The tests are to check possibility to produce reactive powder concrete with such parameters that it can be included in the group of high-quality materials with the use of an ordinary freefall concrete mixer without special treatment procedures such as heat-moisture treatment and pressure treatment.

15

New Generation Cementitious Composites with fibres – properties and application

Zych T.

Czasopismo Techniczne. Architektura

|

2014

|

R. 111, z. 8-A

85--102

EN

The paper presents the properties of new generation cementitious composites with fibres, such as "bendable concrete" (ECC, Engineered Cementitious Composites) (plastic, not brittle but resistant to cracking material) with the addition of polyvinyl alcohol (PVA) fibres, high performance concrete (HPC) with glass fibres, reactive powder concrete (RPC) (characterized by ultra-high compressive strength, above 200 MPa) with short steel fibres. The detailed characteristics of the composition of the cement matrix and the role of fibres in the formation of the composite properties are described. Various applications of the composites as structural and architectural materials are also given.

PL

W artykule przedstawiono właściwości najnowszej generacji kompozytów cementowych z dodatkiem włókien, m.in. "betonów zginalnych" (ECC) (plastycznych, a nie kruchych przy zginaniu, odpornych na pękanie) z włóknami polialkoholowinylowymi (PVA), wysokowartościowych betonów (HPC) z włóknami szklanymi, betonów z proszków reaktywnych (RPC) (cechujących się ultrawysoką wytrzymałością na ściskanie − powyżej 200 MPa) z krótkimi włóknami stalowymi. Szczegółowo scharakteryzowano skład matrycy cementowej oraz opisano rolę, jaką spełniają włókna w kształtowaniu właściwości kompozytu. Pokazano możliwości zastosowania kompozytów jako materiałów konstrukcyjnych oraz architektonicznych.

16

Ultra-high performance concrete – properties and technology

Zdeb T.

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2013

|

Vol. 61, nr 1

183-193

EN

The paper deals with information concerning properties and technology of a new generation cementitious composite i.e. Ultra-High Performance Concrete. High performance here means both high strength and high durability under the influence of environmental factors. This group of composites is mainly represented by Reactive Powder Concretes (RPC), which show both outstanding durability and mechanical properties. Characteristic features of RPC are mainly due to the very low water-cement ratio, which involves application of superplasticizer, significant reduction of aggregate grains size as well as hydrothermal treatment. In the first part of the paper selected properties of RPC are compared to ordinary concrete and to other groups of new generation concrete. Moreover, fundamental technological factors influencing properties of RPC are described as well. The second part deals with the RPC developed at Cracow University of Technology. The presented test results are mainly focused on the influence of steel fibres content on mechanical properties of reactive powder concrete and hydrothermal treatment on composites microstructure. The quantitative and qualitative evaluation of this relationship expand the knowledge of the UHPC technology. Finally, the third part presents the most significant and newest structures which have been erected with the use of RPC.

17

Rozwój mikrostruktury podczas hydratacji ultra BWW

Pfeifer C., Moeser B., Stark J.

Cement Wapno Beton

|

2010

|

R. 15/77, nr 3

123-131

PL

Przeprowadzono obserwacje mikrostruktury próbek betonu z proszków reaktywnych po różnym okresie hydratacji, przy zastosowaniu najnowszych typów mikroskopów skaningowych. Są to mikroskopy o zmiennej próżni i z zastosowaniem pary wodnej, o wysokiej zdolności rozdzielczej. W wyniku badań stwierdzono, że dodatek superpastyfikatora znacznie opóźnia proces hydratacji i zakłóca wzrost kryształów ettringitu. W początkowym okresie hydratacji ziarna klinkieru < 2 um ulegają częściowemu lub całkowitemu rozpuszczeniu, co powoduje powstawanie pustek z otoczkami w mikrostrukturze matrycy. Wiązanie pomiędzy matrycą i kruszywem jest bardzo mocne i w strefie przejściowej nie występują pory. Natomiast reakcja pucolanowa pyłów krzemionkowych jest słabo zaawansowana, z uwagi na mały stosunek w/c.

EN

The UHPC microstructure, after different time of hydration, was examined with high resolution SEM imaging techniques. ESEM in WET mode for early hydration process and NanoSEM for extremely dense microstructure. The obtained results have shown that high addition of superplasticizer caused the strong retardation of hydration process. The growth of ettringite is also influenced. At early hydration the clinker particles < 2 um are often partially or completely dissolved, resulting in hollow shells formation in the microstructure. The bond between matrix and aggregate is very strong and the interfacial zone shows no gaps. However, the pozzolanic reaction of silica fume shows low advancement, because of water shortage caused by very small w/b ratio.