Showing papers in "Brittle Matrix Composites in 2012"

Design of UHPC using artificial neural networks

Abstract: Ultra-high performance concrete (UHPC) results from the mixture of several constituents giving rise to a highly complex material in hardened state. The higher number of constituents in relation to current concrete, together with a higher number of possible combinations and relative proportioning, makes the behavior of this type of concrete more difficult to predict. Until now, most of the proposed mixture design methods are based on a trial and error procedure, which is expensive and work intensive. Moreover, these methods are not efficient in predicting neither the consistency in fresh state nor the strength in hardened state, and do not consider the effect of curing on the latter. The main objective of the research study herein described is to build an analytical model, based on artificial neural networks (ANN), to predict the required performance of UHPC. Specifically, back-propagation neural networks (BPNN) are adopted to model the relation between the input and the output parameters of UHPC, for two different curing conditions, including heat treatment and water storage. In order to train the neural network, a total set of 53 different mixtures were designed. It is concluded that the developed model can be used as a reliable method to predict the performance of UHPC.

Evaluation of durability to wet/dry cycling of cement mortar composites reinforced with nanofibrillated cellulose

Abstract: In this work, the evaluation of the durability to wet-dry cycling exposure of cement composites reinforced with nanofibrillated cellulose comparing the results with composites reinforced with conventional cellulose fibres at the micro-scale level has been performed. For this purpose, cement mortar composites reinforced with cellulose fibres from conventional sisal pulp and cellulose nanofibres prepared by the application of a high intensity refining process have been prepared. The mechanical performance of the composites prepared was tested after 7 days of cure treatment and after 5 wet-dry cycles. The cement mortar composites reinforced with the nanofibrillated cellulose exhibited higher flexural strenght and flexural modulus but lower values of fracture energy than the ones reinforced with the conventional sisal fibres. No significant improvements of the durability were found for the composites prepared with nanofibrillated cellulose.

Electric and thermoelectric properties of cement composites with expanded graphite

Abstract: The electric resistance and thermoelectric properties of cement composites with addition of expanded graphite were. The expanded graphite was obtained from intercalated graphite by rapid heating in different conditions. The influence of thermal treatment on thermoelectric properties was measured. The cement pastes were prepared in the two different ways, either by mixing together expanded graphite and cement, or by rubbing compounds together in order to obtain smaller particles of graphite (even nanometric size) during mixing. The bulk density and electric and thermoelectric properties of cement pastes with addition of expanded graphite were measured. The results of investigations show that the electric properties of composites are strongly influenced by the conditions of thermal expansion as well as by the technique of preparation.

Influence of mineral additives on concrete carbonation

Abstract: The aim of the paper was to show the important aspect of treating waste additives as the main way to achieve sustainable development in the concrete technology. The author considers the effects of minimizing the use of cement replacing it with waste additives, on the concrete durability. The depth of carbonation is adopted as the possible measure of durability. Results of accelerated and natural tests of carbonation progress for concrete with normal and fluidal fly ash, silica fume and blast furnace slag are shown, influence on carbonation of the additive type, its content in concrete and its role (cement or aggregate substitution) is discussed. The important impact of early water curing on depth of carbonation is stated also.

The role of deicing salts on the non-linear moisture diffusion coefficient of cementitious materials during drying

Abstract: The drying of cementitious materials is of interest in volume change (i.e., shrinkage) research. However, the movement of water due to drying and wetting also plays a significant role in many durability related problems (e.g., corrosion, alkali silica reactivity, freezing and thawing). Many factors can influence the drying and wetting process in concrete including: pore structure, environmental conditions, and liquid properties. This paper describes the influence of the liquid properties on the drying process. Specifically, this work examines the non-linear moisture diffusion coefficient that is used in a differential equation that describes drying. This paper describes how the non-linear moisture diffusion coefficient is influenced by the presence of deicing salts solutions. The relationship between the equilibrium relative humidity and the solution properties is also discussed in this paper. A higher degree of saturation was observed for the samples containing deicing salt solutions, as compared to the plain samples at any given humidity. The presence of deicing salt causes a shift of the non-linear moisture diffusion coefficient as a function of relative humidity. The non-linear moisture diffusion coefficient curves have near zero rates of drying at low relative humidity with a rapid increase in drying rate as the relative humidity is increased (especially near the equilibrium relative humidity) followed by diffusion coefficient of 0 between RHeq and 100% RH.

Study on the properties of cement mortars with basalt fibres

Abstract: The results of research concerning flexural strength, work of fracture and compressive strength of basalt fibre reinforced cement mortars as well as basalt fibre resistance in alkaline environment are presented in the paper. Basalt fibres, 5 mm and 12 mm long, with the amount of 0.4 kg/m3, 1 kg/m3, 2 kg/m3 were used as the reinforcement of 3, 7 and 28-day mortars. It was found that the addition of fibres caused the increase in flexural strength (up to 20%), the reduction in compressive strength (up to 15%) and the properties tested were determined by the length of fibres whereas the influence of the fibre content was insignificant. The examination of basalt fibre resistance in alkaline environment (10% sodium hydroxide solution at 60 °C during 10 days) pointed out the chemical degradation of basalt fibres in the form of reduction of fibre diameter and formation of the deposit on the surface of fibre. The microscopic observations and ED XRF spectra did not confirm the presence of any polymer coating on the surface of fibres that could enable the effective anchorage (bond) of basalt fibres to the matrix and could protect fibres against the destruction in the alkaline environment of cement matrix.

Influence of blended cements on the concrete resistance to carbonation

Abstract: The influence of high calcium fly ash as clinker replacement in blended cements on the resistance of concrete structures to the carbonation is presented. The paper concerns of five blended cements made with different contents of supplementary cementitious materials: high and low calcium fly ash and ground granulated blastfurnance slag and one reference cement – Portland cement. The aim was to study the carbonation depth on several concretes designed with a constant water to binder ratio and with various blended cements. Additionally, the prediction of the maximum carbonation depth was proposed. The evaluation of the microstructure was performed using optical microscopy on thin sections in transmitted light. The best results according to the resistance to carbonation achieved the concretes made with Portland-fly ash cement where 14.3 % of high calcium fly ash was used. CEM II/A-W can be used to prove the fc28 and resistance to carbonation for XC3 class.

Numerical simulation of chloride-induced corrosion initiation in reinforced concrete structures with cracks

Abstract: Steel corrosion is a major problem with concrete structures. For concrete structures exposed to chlorides, once a critical chloride concentration is reached at the steel surface, corrosion starts to occur. For a given cover thickness, the corrosion initiation time depends on the chloride diffusivity. For different kinds of concrete, the diffusivity Do at the un-cracked state has been measured. However, in reinforced concrete design, concrete members are allowed to crack in tension. Once cracking occurs, chloride can also diffuse through the crack at a faster rate governed by the crack diffusivity Dcr. Recent experiments have shown that Dcr is a function of the crack width. In the present study, finite element analysis is performed to study the effect of cracking on corrosion initiation in concrete with different values of Do. For various crack width and cover thickness, the time for critical chloride concentration to be reached at steel intersected by the crack is determined. Based on the simulation results, we will derive the empirical equation for an effective diffusion coefficient (Deff) which can be employed directly in the solution of the one-dimensional diffusion equation to calculate the corrosion initiation time. The study will provide a convenient but accurate approach for predicting corrosion initiation under real world situations where cracks are present in a concrete structure.

Influence of mixture composition on shrinkage cracking of lightweight self-consolidating concrete

Abstract: This paper presents a part of the results from a broader study dealing properties of lightweight self-consolidating concrete. Various self-consolidating mixtures were considered by replacing a part of fine and coarse aggregate with light-weight aggregate. The workability of SCC was evaluated using the slump flow test, V-fimnel test and J-ring test. For verification of concrete segregation the concrete specimens were cutting and a visual evaluated of the distribution of coarse aggregates. Free shrinkage of concrete has been investigated using beam specimens 50 × 50 × 250 mm on Graf-Kaufman test. Restrained shrinkage cracking performance was tested using ring specimens (ASTM CI581), which had an inner steel ring instrumented with an electrical strain gauge to monitor stress rise in the concrete due to drying shrinkage under restrained conditions.

Influence of alkali silica reaction on the chemistry of pore solutions in mortars with and without lithium ions

Abstract: This paper presents the results of the investigation of the chemistry of pore solutions of mortars containing both reactive and non-reactive aggregate. The effects of lithium ions (Li+) on chemical compositions of the pore solutions were also explored. In order to accelerate the A SR, all experiments were performed at 55 °C. The compositions of the pore solution were measured at short intervals for the period of up to 120 days. The results showed clear difference between the composition of the pore solution of the mortar with non-reactive aggregate (control mortar) and the mortar containing reactive aggregate. The concentrations of Na+, K+ and OH− ions in the reactive systems without Li+ ions continuously decreased until they reached certain threshold level at which point they stabilized. The time of the stabilization of chemistry of pore solution in the reactive systems coincided with the time of the ultimate expansion of mortar bars of the same composition. When LiNO3 was added as a source of Li+ ions, the consumption of Na+ and K+ ions was significantly reduced. However, the concentrations of Li+ and OH− ions in the pore solution decreased over time.

Reactive powder concrete – change in compressive strength and modulus of elasticity at high temperature

Abstract: : This paper presents the results from an experimental study on the behaviour of Reactive Powder Concretes (RPC) at high temperature. The exposure to high temperature is related to the potential risk of fire. A previous study has shown that RPC is prone to spalling in such circumstances and for this reason polypropylene fibres were used in RPC concrete to prevent this occurring. The addition of PP fibres reduces the risk of spalling due to an increase in permeability, however it reduces the initial compressive strength of the RPC material by approx. 20 %. The results demonstrate that the strength of concrete along with the modulus of elasticity decrease with increasing temperature. Two experimental concretes were prepared and prismatic specimens, 40x40x80 mm in size, were cast from each mixture and tested in compression after being submitted to the high temperature. The relative value of compressive strength course for both types of concrete shows a similar development. The change in modulus of elasticity with temperature was determined from the stress-strain relationship and compared with the dynamic modulus of elasticity determined with the use of a Pundit plus ultrasonic pulse velocity defectoscope.

Shape simulation of granular particles in concrete and applications in DEM

Abstract: Aggregate occupies at least three-quarters of the volume of concrete, so its impact on concrete’s properties is large. The sieve curve traditionally defines the aggregate size range. Another essential property is grain shape. Both, size and shape influence workability and the mechanical and durability properties of concrete. On the other hand, the shape of cement particles plays also an important role in the hydration process due to surface dissolution in the hardening process. Additionally, grain dispersion, shape and size govern the pore percolation process that is of crucial importance for concrete durability Discrete element modeling (DEM) is commonly employed for simulation of concrete structure. To be able doing so, the assessed grain shape should be implemented. The approaches for aggregate and cement structure simulation by a concurrent algorithm-based DEM system are discussed in this paper. Both aggregate and cement were experimentally analyzed by X-ray tomography method recently. The results provide a real experimental database, e.g. surface area versus volume distribution, for simulation of particles in concrete technology. Optimum solutions are obtained by different simplified shapes proposed for aggregate and cement, respectively. In this way, reliable concepts for aggregate structure and fresh cement paste can be simulated by a DEM system.

The influence of non-metallic and metallic fibres on the mechanical properties of cement mortars

Abstract: Compared to concrete, the compressive strength is not a very important property of cement mortar. It is very important that mortar forms a complete, strong, and durable bond with the building material elements, because it is used as an adhesive and sealant material. The physical and mechanical properties of cement mortar, especially flexural strength, toughness, tensile strength, reduction of plastic as well as drying shrinkage, can be enhanced by the use of randomly dispersed fibres, such as steel, carbon or polymer. In the present research there were investigated cement mortars modified with randomly dispersed polypropylene and steel fibres in different volume fraction used both separately and in a hybrid system. The conducted research proved that the low modulus polypropylene fibres with good flexibility added to cement matrix resulted in good properties of fresh mortar and caused the reduction of early age cracking. The beneficial effects of flexible fibres could be attributed to their high aspect ratio and increased fibre availability at a given volume fraction due to their low density. Because of low stiffness, these fibres are particularly effective in controlling the propagation of micro-cracks. It was found that the hybrid combination of metallic and nonmetallic fibres can offer potential advantages in improving cement matrix properties, such as the ultimate strength and toughness of composites.

Porosity of green concrete based on a gap-graded blend

Abstract: Portland cement (PC) production contributes by about 6% to global emissions of C02. Reduction of the PC content in the binder exerts therefore a direct positive effect on such emissions. Partial replacement of the Portland cement by pozzolanic mineral admixtures has been proven a possible option. The green character is even reinforced by making use of incinerated vegetable waste, such as rice husk ash (RHA). Moreover, as a result of the gap-grading effect on particle packing density with RHA as the fine component, high strength concrete can be achieved with RHA-blended cement. This has been published earlier, so the paper only briefly covers these aspects. Characteristics of the capillary pores developed in the hydrating binder have direct impact on the transport-based durability properties. However, assessment of such pore characteristics of the RHA-blended cement constitutes a complicated problem, especially in experimental approaches. This paper, therefore, presents a new economic approach to conduct such investigation on the realistically produced cementitious materials in virtual reality. The fresh packed state of the paste’s particles is simulated by a discrete element modeling (DEM) system, HADES. The hydration of a (blended) cement is simulated by a so-called ‘extended integrated particle kinetics model’ (XIPKM). Pore characteristics, such as topology, location distribution, degree of percolation and fraction of main channels in the pore network, are explored by a new modern approach named ‘double random multi-tree structuring’ (DraMuTS). The size distribution of throats that significantly limit the transport in the pore network system is derived from star volume measurements. Four examples of plain PC and of RHA-blended PC with two w/b ratios are presented. The expected positive effects on transport-based durability issues due to RHA-blending are discussed.

The effect of super absorbent polymers on the performance of immature cementitious mortars

Abstract: Construction industry like any other area of economic and social life undergoes continuous alterations and improvements in order to successfully comply with the requirements of sustainable development. Consumers demand more durable, less labour and service intensive materials at a competitive price. To meet these expectations numerous new composite materials have been developed over the last couple of decades, including cementitious materials modified by superabsorbent polymers (SAP). The paper presents part of the larger research project on the performance of cementitious mortars containing two types of superabsorbent polymers (SAP) as the internal curing agent.SAP A is a copolymer of acrylamide and acrylic acid and SAP B is a polymer based on acrylic acid. Research work presented in this paper involves macro and micro scale characterisation of polymer modified mortars. The microstructural features were studied with application of the Mercury Intrusion Porosimetry and the Scanning Electron Microscopy techniques. Analyses of pore size distribution in mortars of different ages are accompanied by the analyses of strength and autogenous shrinkage development as well as early density changes in immature mortars by the X-ray absorption method. The investigations confirmed the positive effect of SAP A on the reduction of autogenous shrinkage and microcrack propagation. Limited absorption/desorption abilities of SAP B cannot reassure continuous supply of water and hence the performance of SAP B mortars was comparable with the reference samples. The effect of both SAPs on strength development proved to be negligible.

Modelling of fracture in fibre-cement based materials

Abstract: In this paper a model is presented to simulate fracture of fibre reinforced cement based materials. The model is based on a lattice-type fracture model. Fibres are explicitly implemented as separate elements connected to the cement matrix via special interface elements. With the model multiple cracking and ductile global behaviour are simulated of the composite material. Variables in the model are the fibre dimensions and properties, the fibre volume in the composite, the bond behaviour of fibres and matrix and the cement matrix properties. These properties are obtained by testing, which will be described in the paper. The model is used as a design tool for creating fibre cement based composites with any desired mechanical behaviour.

Chloride penetration resistance of concrete mixtures with recycled concrete aggregates

Abstract: Disposal of aged concrete pavements involves great cost and (due to volumes involved) can be detrimental to environment when all of this material is deposited in landfills. It is therefore cost-effective to recycle crushed concrete as coarse aggregates (referred hereafter as RCA) to replace natural aggregates (NA) during construction of new concrete pavements. This approach reduces the need for quarrying of natural aggregates and saves space in the landfills. The main focus of this study was on determining the chloride penetration resistance of pavement concretes containing various levels (0, 30 and 100%) of RCA as a replacement for NA. All concrete mixtures used in this study were designed to meet the fresh properties and flexural strength requirements specified for pavements by the Indiana Department of Transportation (INDOT). The resistance to chloride ion penetration was determined using two electrical migration tests: rapid chloride permeability (RCP) test (as per ASTM C1202) and non-steady state migration test (as per NT BUILD 492). Before the initiation of the RCP test, all specimens were first subjected to 250 mV AC potential scan using Solartron™ 1260 gain-phase impedance analyzer. The impedance spectra (collected over a frequency range of 0.1 Hz to 10 MHz) were used to obtain bulk resistance (Rb) of the concrete. The steady state diffusion coefficients were calculated using RCP test data in Nernst-Plank and empirical equations. The general trends obtained from the chloride penetration resistance results indicate that initial current values from RCP test can be used to predict the performance of concretes containing RCA. Mixtures with 30% RCA performed similar to 0% RCA mixture while the resistance to chloride penetration of concrete with 100% RCA was somewhat reduced.

Influence of aggregate type on the durability of concrete made of blended cements with calcerous fly ash

Abstract: The influence of aggregate type on the compressive strength, the resistance to chloride penetration and the scaling resistance with de-icing salts of concrete made with blended cements with calcerous fly ash was investigated. The range of investigation included the air entrained concrete with water to cement ratio w/c = 0.45 with the prototype blended cements containing the additives of calcerous fly ash, siliceous fly ash and ground granulated blast furnace slag. Concrete specimens were cured during first 3 days in water and then in the air of 40% RH until 28 and 90 days. Frost-salt scaling tests were performed using 3% NaCl solution. The air void microstructure was quantitatively evaluated. The results revealed the influence of blended cement type on the properties of concrete with different type of aggregates.

Experimental study of shear failure mechanism in concrete beams

Abstract: In this paper, recent results of the experimental investigation, which was aimed at disclosing some aspects of shear failure mechanism in concrete beams reinforced longitudinally, are presented. The aim of the test was to investigate the influence of a shear span-to-depth ratio and a beam size on failure mode and shear capacity in the tested beams. It has been found that the shear span-to-depth ratio a/d is an important parameter, which significantly affects the shear failure mechanism in the investigated members. This fact was presented in several scientific papers. However, the second important parameter, which must be taken into account when analysing reinforced concrete beams without stirrups, is the size of the member. The “size effect”, which is described in professional literature as a decrease of shear strength with an increase of the members depth, is not evaluated sufficiently enough. The effective length-to-depth ratio leff/d, which has been identified in this paper, also has a considerable influence on the contributions of the shear resistance mechanism and thus the ultimate shear capacity. In this paper it has been shown that members characterized by the same a/d but different leff/d can fail in a different way.

Behavior of hybrid fiber ECC panels subjected to low and high velocity projectile impact—a review

Abstract: This paper reviews the results of recent laboratory research studies focusing on the behavior of hybrid fiber Engineered Cementitious Composite (ECC) panels subjected to low- and high-velocity projectile impact. The reviewed laboratory studies include high-velocity (300-700 m/s) small-size projectiles impact tests conducted on 0.30 × 0.17 m hybrid fiber ECC prismatic panels of various thicknesses (representing a section of a door or wall), low-velocity large projectile impact tests conducted on both full scale hybrid fiber ECC blast/shelter panels (2.0 × 1.0 × 0.05-0.1 m), and 1/3 scale hybrid fiber ECC strengthened masonry wall panels (1.0 x 1.0 x 0.1 m). Recent results obtained from dynamic tensile tests of hybrid fiber ECC coupon specimens are also reviewed to assess the effect of strain rate on the material uniaxial tensile behavior. The reviewed test results demonstrate the potential value of hybrid fiber ECC for providing better functionality as protective material in aspects such as increased shatter resistance with damage reduction due to scabbing and spalling, as well as significantly-improved cracking behavior, resistance against multiple impacts, and energy absorption associated with distributed microcracking in comparison to concrete.

Durable concrete structures with cracks which heal themselves

Abstract: Concrete is one of the most widely used construction materials due to its excellent mechanical properties and relatively low cost. However, concrete is prone to crack formation. These cracks do not impair the structural integrity, but they endanger the durability of the structure as aggressive liquids and gasses may enter via these cracks and cause degradation. Therefore, crack repair is needed but these repair works increase the cost of concrete structures by 50% as they are labour intensive and because the structure becomes in discuse during repair. Accordingly, in this research it was investigated whether cementitious materials can be modified so that cracks heal themselves. Therefore, healing agents were encapsulated by brittle capsules and embedded inside the cementitious matrix in the zones where cracks were expected. When the matrix starts cracking, the capsules break and release their content, leading to crack repair. Water absorption measurements were performed to evaluate the healing efficiency. The amount of absobed water was determined by gravimetrical measurements and visualized by X-ray radiography. When samples with untreated cracks were placed with their cracked surface in a water reservoir, it was noticed from the radiographs that water penetrated very fast into the cracks. For samples with self-healing properties no water entered into the cracks. Moreover, even in the zone alongside the crack no water entry was noticed. Therefore, it can be concluded that self-healing of concrete cracks can be used to prevent the ingress of liquids and to prevent subsequent damage to the matrix.

Safe cement composites SRCC - the rope effect in HPFRC concrete

Abstract: The main motivation for this work was the attempt to limit the rapid destruction of brittle high performance concrete UPC and, in consequence, to obtain SRCC (safe rope effect cement composite) In the high performance fiber reinforced cement composites HPFRC deflection and flexural strength are increased The rope effect in HPFRC results in a highly deflected damaged specimen with multicracking effect and with post-peak load at bending exceeding that corresponding to the first crack, which enables to obtain cement composite with the ability to absorb additional energy after the appearance of the macrocrack The SRCC paste and mortar were presented in the previous paper This paper shows different effects of the strengthening of cement concrete with dispersed synthetic structural polypropylene fibers 19 and 54 mm long The possibility to control multicracking and the crack propagation process using the rope effect for SRCC composites, which eliminates the catastrophic process of the destruction of composite, was presented and a new possibility of the strengthening effects assessment was suggested

Effects of mechanical properties of ASR damaged concrete on structural design

Abstract: The paper reports on an experimental investigation of concrete with three slow reacting aggregates (greywacke, quartz-porphyrite, crushed gravel). The specimens were stored in a fog room at 40 °C for 560 days. The compressive strength, the tensile strength, the static modulus of elasticity, and the dynamic modulus of elasticity were measured at certain intervals. The results show how these mechanical properties are affected by the alkali-silica reaction (ASR). It turned out that the dynamic modulus of elasticity cannot be used for the prediction of deterioration due to ASR. However, when the compressive and tensile strengths and the static modulus of elasticity have been determined a re-evaluation of an ASR affected structure can be performed.

Influence of fibres on rheological and mechanical properties of self-compacting concrete

Abstract: The paper presents results of tests on self-compacting mixtures with the addition of steel fibres (Steel Fibre Reinforced Self-Compacting Concrete). Four types of steel fibres at 3 levels of the volume ratio are considered. The results include studies on samples belonging to classes of slump flow SF, classes of viscosity T 500 , and rheological tests. The studies were based on application of two rheometers for rheological properties of concrete mixtures - BT2 Rheometer and Viskomat XL. Additionally, a study of compressive strength f cm,28 and flexural strength f fl was carried out on concrete SFRSCC. These studies have confirmed the possibility of using steel fibres in concrete SCC while maintaining the assumed technological parameters for concrete mixtures and, above all, their workability.

Influence of calcerous fly ash on concrete resistance to migration of chlorides

Abstract: The use of caleerous fly ash from brown coal combustion in Belchatow Power Plant in Poland as additive to concrete mix was studied. The strength and the resistance to chloride penetration into concrete was investigated at water to binder ratio from 0.45 to 0.60. Caleerous fly ash both in unprocessed form and grinded to specified specific surface was used for partial replacement of cement up to 30% of mass. To evaluate the concrete resistance to chloride ion penetration the standard method of determination of chloride migration coefficient from non-steady-state migration test according to NT Build 492 was used. Test results revealed a substantial improvement of the resistance to chloride penetration into concrete containing calcerous fly ash. The resistance was higher for increased replacement level and decreased water-to-cement ratio.

Modelling the influence of composition on rheological parameters and mechanical properties of fibre reinforced polymer-cement mortars

Abstract: Fibre reinforced polymer-cement compositions for self-levelling flooring are studied. The individual and combined effects of dispersible polymer powder with properties of binder and superplasticiser, of various methylcelluloses, and of polypropylene fibre on effective viscosity of the mix and mechanical properties of the hardened mortar are evaluated and analysed. Used for analysis are multifactor experimental-statistical models built on the data obtained for 18 mixes (of the same workability) in the designed experiment and describing the fields of rheological model parameters, of strength, and other criteria in composition coordinates. The models have made it possible to simulate material behaviour in computational experiments, to reveal and evaluate the correlations of the properties for different technological conditions, to find individual and compromise optima.

Shape assessment in concrete technology by Fourier analysis

Abstract: Particle packing has been recognized to influence mechanical and durability properties of cementitious materials, which are generally favored by optimum packing density. Particle size is a common denominator in such studies. Unfortunately, so far, particle shape has not been extensively and unambiguously evaluated in these approaches. Part of it is definitely due to the interconnected nature of size and shape as well as the missing of a clear methodological framework. Nevertheless, various strategies for assessment of shape are available. Capabilities of available advanced computer-simulation systems render possible considering differently-shaped particles. This will make it possible studying in an economic way the effect of shape on properties of densely packed aggregate or binder particles at low w/c ratios. So, shape assessment is becoming an even more relevant issue in structural studies of concrete. This paper presents a somewhat underrated approach to the assessment of shape of (aggregate) particles, i.e. Fourier analysis. A new shape index is proposed.

Assessment of pore characteristics in virtual concrete by path planning methodology

Abstract: This paper will discuss novel techniques for pore network exploration and the assessment of topological and geometrical characteristics relevant for durability estimation. The discussed methods are applicable to DEM-produced cementitious materials in which binder particle are realistically dispersed. This cannot be achieved by the in concrete technology popular random generator-based systems. Development of the discussed techniques was inspired by the path finding algorithms developed in robotics. The presented techniques are called double random multiple tree structuring (DraMuTS) and random node structuring (RaNoS). The path finding algorithms are adapted to the porosimetry problem and as a consequence modified to exclude time-consuming iterations. Moreover, path finding will take place starting from a large number of positions to enhance the economy of the approach.

Microhardness testing procedure applied to blended cement based matrix

Abstract: In the paper a new method of determination of cement paste microhardeness is presented. It includes the procedure of systematic indentation with a Vickers tip and a statistical processing of population of obtained results. The tested specimens were cast with different kinds of blended cements, containing high calcium fly ash (HCFA) as one of major components. Differences in values of microhardeness obtained for six series of tested specimens mixes are discussed and compared with compressive strength of investigated materials.

Behavior of polymer modified reactive powder concrete exposed to oil products

Abstract: Reactive powder concrete, RPC, demonstrates greatly ultra-high strength and improved durability characteristics compared with traditional or even high performance concrete. The main purpose of the present investigation is to modify RPC by adding styrene butadiene rubber, SBR, as a polymer in percentages 6, 12, 14, and 18 by weight of cement to the original mixture. An experimental work had carried out to investigate the behavior and durability of the polymer modified reactive powder concrete, PMRPC, exposed to two types of oil products (gas oil and kerosene) in comparison with the original RPC. Metakaolin was used as a pozzolanic material. Teasing program was designed to include compression, initial surface absorption, total absorption, and permeability tests. The test period was extended to 180 days. Moreover, drying shrinkage strain was measured up to the age of 90 days. Tested specimens were grouped in three series after the age of 28 days. The first continued to be cured with water, meanwhile, the second cured with gas oil and the third with kerosene. The experimental results showed that, the PMRPC mixes exhibited superior performance in all tested properties than the original RPC, especially when exposed to oil products. This behavior could be related to the role of the polymer in filling the pores and cracks and thus improving the surface condition. It was concluded that the optimum percentage of added SBR was 14%. In addition, it was found experimentally that SBR could totally replace the highrange water reducing admixture in PMRPC. Finally, the main conclusion reached was that PMRPC could be used to construct durable oil storage tanks or at least be used as lining layers for storage tanks.