Ball-shaped concretions ("cannon balls") commonly occur in a marine, organic carbon-rich sedimentary sequence (Innkjegla Member) of the Carolinefjellet Formation (AptianAlbian) in Spitsbergen. The sedimentologic, petrographic and geochemical investigation of these concretions in the Kapp Morton section at Van Mijenfjorden gives insight into their origin and diagenetic evolution. The concretion bodies commenced to form in subsurface environment in the upper part of the sulphate reduction (SR) diagenetic zone. They resulted from pervasive cementation of uncompacted sediment enriched in framboidal pyrite by non-ferroan (up to 2 mol% FeCO3) calcite microspar at local sites of enhanced decomposition of organic matter. Bacterial oxidation of organic matter provided most of carbon dioxide necessary for concretionary calcite precipitation (δ13CCaCO3 ≈ -21%VPDB). Perfect ball-like shapes of the concretions originated at this stage, reflecting isotropic permeability of uncompacted sediment. The concretion bodies cracked under continuous burial as a result of amplification of stress around concretions in a more plastic sediment. The crack systems were filled by non-ferroan (up to 5 mol% FeCO3) calcite spar and blocky pyrite in deeper parts of the SR-zone. This cementation was associated with impregnation of parts of the concretion bodies with microgranular pyrite. Bacterial oxidation of organic matter was still the major source of carbon dioxide for crack-filling calcite precipitation (δ13CCaCO3 ≈ -19% VPDB). At this stage, the cannon-ball concretions attained their final shape and texture. Subsequent stages of concretion evolution involved burial cementation of rudimentary pore space with carbonate minerals (dolomite/ankerite, siderite, calcite) under increased temperature (δ18OCa,Mg,FeCO3 ≈-14% VPDB). Carbon dioxide for mineral precipitation was derived from thermal degradation of organic matter and from dissolution of skeletal carbonates (δ13CCa,Mg,FeCO3≈ - 8‰ VPDB). Kaolinite cement precipitated as the last diagenetic mineral, most probably during post−Early Cretaceous uplift of the sequence.
This article looks at the semantic space of abstract and concrete concepts from the perspective of distributed models of conceptual representations. It focuses on abstract metaphorical classes and the mechanisms through which these concepts are processed. When the metaphor X is a Y is understood, X is included in the abstract metaphorical class of Y. This metaphorical class is abstract because the most of semantic features of Y are filtered out through a suppressiveoriented mode of processing. It is suggested that abstract metaphorical classes of living things are usually defined by a single or a very small set of semantic features. Therefore, such metaphorical classes are highly abstract. On the other hand, abstract metaphorical classes of nonliving things are defined by a relatively larger cluster of semantic features. Therefore, abstract metaphorical classes of nonliving things have a relatively higher degree of concreteness compared to those of living things. In other words, abstract metaphorical classes of living things and nonliving things are rather different in terms of nature and the structure of semantic space.
Statistical conformity criteria for the compressive strength of concrete are a matter of debate. The criteria can have prejudicial effects on construction quality and reliability. Hence, the usefulness of statistical criteria for the small sample size n = 3 is questioned. These defects can cause a reduction in the quality of produced concrete and, consequently, too much risk for the recipient (investor). For this reason, the influence of conformity control on the value of the reliability index of concrete and reinforced concrete has been determined. The authors limited their consideration to the recommended standards PN-EN 206-1, PN-EN 1992 and ISO 2394 method of reliability index, which belongs to the analytical methods FORM (First Order Reliability Method). It assumes that the random variables are defined by two parameters of the normal distribution or an equivalent normal: the mean and the standard deviation. The impact of conformity control for n = 3 for concrete structures, designed according to the Eurocode 1992, for which the compressive strength of concrete is the capacity dominant parameter (sensitivity factor of dominating resistance parameter according to the FORM is 0.8), has been determined by evaluation of the reliability index.
In the recent years structural health monitoring (SHM) has gathered spectacular attention in civil engineering applications. Application of such composites enable to improve the safety and performance of structures. Recent advances in nanotechnology have led to development of new family of sensors – self-sensing materials. These materials enable to create the so-called “smart concrete” exhibiting self-sensing ability. Application of selfsensing materials in cement-based materials enables to detect their own state of strain or stress reflected as a change in their electrical properties. The variation of strain or stress is associated with the variation in material’s electrical characteristics, such as resistance or impedance. Therefore, it is possible to efficiently detect and localize crack formation and propagation in selected concrete element. This review is devoted to present contemporary developments in application of nanomaterials in self-sensing cement-based composites and future directions in the field of smart structures.
To investigate the mechanical properties of tunnel lining concrete under different moderate-low strain rates after high temperatures, uniaxial compression tests in association with ultrasonic tests were performed. Test results show that the ultrasonic wave velocity and mass loss of concrete specimen begin to sharply drop after high temperatures of 600°C and 400°C, respectively, at the strain rates of 10‒5s‒1 to 10‒2s‒1. The compressive strength and elastic modulus of specimen increase with increasing strain rate after the same temperature, but it is difficult to obtain an evident change law of peak strain with increasing strain rate. The compressive strength of concrete specimen decreases first, and then increases, but decreases again in the temperatures ranging from room temperature to 800°C at the strain rates of 10‒5s‒1 to 10‒2s‒1. It can be observed that the strain-rate sensitivity of compressive strength of specimen increases with increasing temperature. In addition, the peak strain also increases but the elastic modulus decreases substantially with increasing temperature under the same strain rate.
Concrete is generally produced using materials such as crushed stone and river sand to the extent of about 80‒90% combined with cement and water. These materials are quarried from natural sources. Their depletion will cause strain on the environment. To prevent this, bottom ash produced at thermal power plants by burning of coal has been utilized in this investigation into making concrete. The experimental investigation presents the development of concrete containing lignite coal bottom ash as fine aggregate in various percentages of 25, 50, and 100. Compressive, split tensile, and flexural strength as part of mechanical properties; acid, sulphate attack, and sustainability under elevated temperature as part of durability properties, were determined. These properties were compared with that of normal concrete. It was concluded from this investigation that bottom ash to an extent of 25% can be substituted in place of river sand in the production of concrete.
The article presents research results of the strength parameters of HPC achieved in various research conditions. The research was carried out on substantially different samples, both as to the size as the slenderness ratio. Moreover, the assessment of the effect of speed of a load on strength parameters as well as other factors which in a significant way show the difference in the strength values was made. For comparison, the results were also applied to the relations known in ordinary concrete.
This paper deals with the prevention of failure of structural elements made of reinforced concrete. It discusses preservice cracks in the concrete decks of an underground parking facility. The cracks were assessed by analyzing their morphology. The results were used to determine the crack causes and the mechanisms of their initiation and growth. Some design solutions to prevent or reduce the occurrence of pre-service cracks are also presented.
The rheological properties of self-compacting concrete are closely influenced by temperature and the time. Previous studies which aim was to research the effect of temperature on self-compacting concrete workability, showed that the behaviour of fresh SCC at varying temperatures differs from that of normal vibrated concrete. The paper presents the study of rheological properties of fresh self-compacting concrete mixtures made with portland, blast furnace and component cement. Two types of superplasticizers were used. It was proven that temperature has a clear effect on workability; it can be reduced by selecting the appropriate superplasticizer and cement.
Self-curing concrete SC is a concrete type that can be cured without using any external curing regimes. It can perform by several methods such as using lightweight aggregate or chemical agents. In this research chemical curing agent is used to produce SC. This paper reports the results of a research study conducted to evaluate the effect of sulfates on the performance of self-curing concrete compared to ordinary concrete. Samples are immersed in sodium sulfate Na2S04 solution of 4% concentration. Results are measured in terms of compressive strength, tensile strength, flexural strength and mass loss. It was found that the rate of strength loss is noticed at ordinary concrete compared to SC concrete. Sulfate resistance is improved when using self-curing concrete. This improvement appears to be dependent on using a chemical curing agent.
The ductility of High Performance Concrete (HPC) can develop both in tension and compression.This aspect is evidenced in the present paper by measuring the mechanical response of normalvibrated concrete (NC), self-compacting concrete (SC) and some HPCs cylindrical specimensunder uniaxial and triaxial compression. The post-peak behaviour of these specimens is definedby a non-dimensional function that relates the inelastic displacement and the relative stress duringsoftening. Both for NC and SC, the increase of the fracture toughness with the confinement stressis observed. Conversely, all the tested HPCs, even in absence of confinement, show practically thesame ductility measured in normal and self-compacting concretes with a confining pressure. Thus,the presence of HPC in compressed columns is itself sufficient to create a sort of active distributedconfinement.
In the recent years a tendency for design of increasingly slender structures with the use of high performance concrete has been observed. Moreover, the use of high performance concrete in tunnel structures, subject to high loads with possibility of extreme loads occurrence such as fire, has an increasing significance. Presented studies aimed at improving high performance concrete properties in high temperature conditions (close to fire conditions) by aeration process, and determining high temperature impact on the concretes features related to their durability. In this paper it has been proven that it is possible to obtain high performance concretes resistant to high temperatures, and additionally that modification of the concrete mix with aerating additive does not result in deterioration of concrete properties when subject to water impact in various form.
The Silurian Pelplin Formation is a part of a thick, mud-prone distal fill of the Caledonian foredeep, which stretches along the western margin of the East European Craton. The Pelplin Formation consists of organic carbon- rich mudstones that have recently been the target of intensive investigations, as they represent a potential source of shale gas. The Pelplin mudstones host numerous calcite concretions containing authigenic pyrite and barite. Mineralogical and petrographic examination (XRD, optical microscopy, cathodoluminoscopy, SEM-EDS) and stable isotope analyses (δ13Corg, δ13C and δ18O of carbonates, δ34S and δ18O of barite) were carried out in order to understand the diagenetic conditions that led to precipitation of this carbonate-sulfide-sulfate paragenesis and to see if the concretions can enhance the understanding of sedimentary settings in the Baltic and Lublin basins during the Silurian. Barite formed during early diagenesis before and during the concretionary growth due to a deceleration of sedimentation during increased primary productivity. The main stages of concretionary growth took place in yet uncompacted sediments shortly after their deposition in the sulfate reduction zone. This precompactional cementation led to preferential preservation of original sedimentary structures, faunal assemblages and early- diagenetic barite, which have been mostly lost in the surrounding mudstones during burial. These components allowed for the reconstruction of important paleoenvironmental conditions in the Baltic and Lublin basins, such as depth, proximity to the detrital orogenic source and marine primary productivity. Investigation of the concretions also enabled estimation of the magnitude of mechanical compaction of the mudstones and calculation of original sedimentation rates. Moreover, it showed that biogenic methane was produced at an early-diagenetic stage, whereas thermogenic hydrocarbons migrated through the Pelplin Formation during deep burial.
Numerical analysis of the tensioning cables anchorage zone of a bridge superstructure is presented in this paper. It aims to identify why severe concrete cracking occurs during the tensioning process in the vicinity of anchor heads. In order to simulate the tensioning, among others, a so-called local numerical model of a section of the bridge superstructure was created in the Abaqus Finite Element Method (FEM) environment. The model contains all the important elements of the analyzed section of the concrete bridge superstructure, namely concrete, reinforcement and the anchoring system. FEM analyses are performed with the inclusion of both material and geometric nonlinearities. Concrete Damage Plasticity (CDP) constitutive relation from Abaqus is used to describe nonlinear concrete behaviour, which enables analysis of concrete damage and crack propagation. These numerical FEM results are then compared with actual crack patterns, which have been spotted and inventoried at the bridge construction site.
An automated method for crack identification and quantitative description of crack systems in concrete was developed in order to aid a service life assessment of concrete elements in structures. Flat polished specimens for crack analysis were impregnated with epoxy resin containing fluorescent dye. The examination of the crack system was performed in ultraviolet light using a stereomicroscope and an Image Pro Plus image analysis system on specimens cored out of several concrete structures. The laboratory tests were performed on cast specimens to establish correlations between water penetration and chloride diffusion and crack system parameters. The analysis of cracks in concrete cores taken from structures resulted in interesting conclusions based on the crack width distribution and crack localization with respect to steel reinforcement. The method was found very effective to support standard concrete diagnostics methods.
The behaviour of concrete under quasi-static loadings for uniaxial compression, tension and planestress conditions is studied. The failure criteria of concrete are discussed as well as the methodsof constitutive parameters identification are elaborated. The attention is focus on an energeticinterpretation of selected failure criteria. The numerical example with concrete damage plasticitymaterial model is shown.
The paper describes experimental research of slab-column connections examined on specimendesigned as a part of reinforced concrete structure with flat slabs. The aim of the research wasto verify the efficiency of slab reinforcement concept against punching shear by increasing slab’smechanical reinforcement ratio by applying additional external reinforcement in the form of carbonfiber reinforced polymer (CFRP) strips. The capacity enhancement in comparison to unstrengthened slab obtained 36%.
In the design of asphalt mixtures for paving, the choice of components has a remarkable importance,as requirements of quality and durability must be assured in use, guaranteeing adequate standardsof safety and comfort. In this paper, an approach of analysis on the aggregate materials using fractal geometry is proposed. Following an analytical and an experimental approach, it was possible to find a correlation betweencharacteristics of the asphalt concrete (specific gravity and porosity) and the fractal dimension ofthe aggregate mixtures. The studies revealed that this approach allows to draw the optimal fractal dimension and, conse-quently, it can be used to choose an appropriate aggregate gradation for the specific application;once the appropriate initial physical parameters are finalized. This fractal approach could be employed for predicting the porosity of mixed asphalt concretes,given as input the fractal characteristics of the aggregate mixtures of the concrete materials.
This study investigates the use of steel fibers and hybrid composite with a total fibers content of 2% on the high strength flowing concrete and determines the density, compressive strength, static modulus of elasticity, flexural strength and toughness indices for the mixes. The results show that the inclusion of more than 0.5% of palm fibers in hybrid fibers mixes reduces the compressive strength. The hybrid fibers can be considered as a promising concept and the replacement of a portion of steel fibers with palm fibers can significantly reduce the density, enhance the flexural strength and toughness. The results also indicates that the use of hybrid fibers (1.5 steel fibers + 0.5% palm fibers) in specimens increases significantly the toughness indices and thus the use of hybrid fibers combinations in reinforced concrete would enhance their flexural toughness & rigidity and enhance their overall performances.
The paper focuses on different approaches to the safety assessment of concrete structures designed using nonlinear analysis. The method based on the concept of partial factors recommended by Eurocodes, and methods proposed by M. Holicky, and by the author of this paper are presented, discussed and illustrated on a numerical example. Global safety analysis by M. Holicky needs estimation of the resistance coefficient of variation from the mean and characteristic values of resistance, and requires two separate nonlinear analyses. The reliability index value and the sensitivity factor for resistance should be also identified. In the method proposed in this paper, the resistance coefficient of variation necessary to calculate the characteristic value of resistance may be adopted from test results and the resultant partial factor for materials properties, and may be calculated according to Eurocodes. Thus, only one nonlinear analysis from mean values of reinforcing steel and concrete is required.
This investigation is carried out to evaluate the repair and strengthening the techniques of elliptical paraboloid reinforced concrete shells with openings. An experimental program of several different techniques in repair and strengthening is executed. The materials, which are considered for strengthening, are; Glass fiber reinforced polymers GFRP at different position of the shell bottom surface, steel strip and external tie. They loaded by four concentrated loads affected on the corners of the opening. The initial and failure loads as well as the crack propagation for the tested shells at different loading stages, defl ections and failure load for repaired and shells are recorded. A non-linear computer program based on finite element techniques is used to study the behavior of these types of shells. Geometric and materials nonlinearities are considered in the analysis. The efficiency and accuracy of computer program are verified by comparing the program results with those obtained experimentally for the control shell with opening and strengthened shells.
Article presents the results of the effect of humidity on early shrinkage of normal concrete with variable W/C ratio. As known for a long time, shrinkage is dependent of many factors. One of them is the W/C ratio and the quantity of water which is located in the concrete mix. In article there were discussed changes taking place in the concrete mix, the methods of research and the partial results obtained by the authors of the paper. Shrinkage is a phenomenon well known and studied by various research centers. The total amount of shrinkage may depend on various factors such as humidity, temperature, composition of the concrete mix, the W/C ratio, the size of the item. The study was conducted to determine the amount of shrinkage in its early stages. It is very important for concrete floors contractors, precast manufacturers to start at the right time finishing work and prevent the formation of shrinkage cracks.
The paper presents the description of structure and the selected problems of the technical condition, as well as the strength analysis of the thin-walled reinforced concrete shell which has been making a covering of the main hall of the Gdynia Seaport Building through the last 80 years. The rectangle projection of four single curvature shells of the dome was shaped out of mutual perpendicular intersection of two cylindrical shells. The analysis of the state of stress and deformations was carried out using the special model worked out in MES considering the combination of loads, the thermal ones included. For the long lasting loads (the deadweight of the dome), the computed results of static quantities were confronted with analytical results obtained according to F. Dischinger’s method. This method had been applied by the DYWIDAG Company in Berlin and its branch in Katowice (Poland) who designed the Gdynia Dome. The computational analysis and the assessment of the technical state, along with laboratory pH tests of concrete, made it possible to carry out the overall evaluation of durability and safety of operation of the Gdynia Seaport Dome through the next decades.
In the paper, the method of a numerical simulation concerning diagonal crack propagation in con-crete beams was presented. Two beams reinforced longitudinally but without shear reinforcement were considered during the Finite Element Method analysis. In particular, a nonlinear method was used to simulate the crack evaluation in the beams. The analysis was performed using the commercial program ANSYS. In the numerical simulation, the limit surface for concrete described by Willam and Warnke was applied to model the failure of concrete. To solve the FEM-system of equations, the Newton-Raphson method was used. As the results of FEM calculations, the trajectories of total stains and numerical images of smeared cracks were obtained for two analyzed beams: the slender beam S5 of leff = 1.8 m and the short beam S3k of leff = 1.1 m. The applied method allowed to generate both flexural vertical cracks and diagonal cracks in the shear regions. Some differences in the evaluation of crack patterns in the beams were observed. The greater number of flexural vertical cracks which penetrated deeper in the beam S5 caused the lower stiffness and the greater deformation in the beam S5 compared to the short beam S3k. Numerical results were compared with the experimental data from the early tests performed by Słowik . The numerical simulation yielded very similar results as the experiments and it confirmed that the character of failure process altered according to the effective length of the member. The proposed numerical procedure was successfully verified and it can be suitable for numerical analyses of diagonal crack propagation in concrete beams.
A large number of infrastructural concrete buildings are protected against aggressive environments by coating systems. The functionality of these coating systems is mainly affected by the composition and thickness of the individual polymeric layers. For the first time ever, a mobile nuclear magnetic resonance (NMR) sensor allows a non-destructive determination of these important parameters on the building site. However, before this technique can be used on steel-reinforced concrete elements, the potential effect of the reinforcement on the measurement, i.e. the NMR signal, needs to be studied. The results show a shift of the NMR profile as well as an increase of the signals amplitude in the case of the reinforced samples, while calculating the thickness of concrete coating leading to identical results.