Effect Of Concrete Composition Research Articles

Effect of concrete composition on drying shrinkage behavior of ultra-high performance concrete

The concrete compositions have great effects on the drying shrinkage behavior of ultra-high performance concrete (UHPC). Five factors including water-to-binder ratio (w/b) and contents of steel fiber, superplasticizer, silica fume and fly ash were considered to evaluate their influences on the drying shrinkage behaviors of UHPC in this investigation. Based on the drying shrinkage test results, the effect degrees of these factors were analyzed by the gray relation entropy analysis. Then the microstructure and pore distributions of UHPC samples were measured by scanning electron microscope and mercury intrusion porosimetry for mechanism analyses. The results reveal that a lower w/b or higher content of fly ash is conducive to achieving a reduction in drying shrinkage of UHPC, while the additions of superplasticizer and silica fume have an adverse effect on drying shrinkage, resulting in increased drying shrinkage, and the effect of steel fiber on drying shrinkage is not monotonic, its optimum dosage is 50 kg/m3 in this work and a lower or higher amount will cause an increased DSS of UHPC compared with the one with an optimum dosage. The five factors can affect the drying shrinkage behavior of UHPC by principally changing the microtopography and internal pore structure of the concrete matrix, according to the gray relation entropy analysis, the effect degrees of studied factors on drying shrinkage of UHPC are as follows: w/b > superplasticizer > silica fume > fly ash > steel fiber.

Effect of Concrete Composition on the Thermodynamic Binding of Dopamine: A DFT Study.

Concrete has long been a standard in construction projects. However, increasing the binding of cement paste to the concrete aggregate (a collection of geological materials containing, e.g., gravel, sand, etc.) remains an open area of research, as this is a common failure point in concrete-based infrastructure. One solution is the application of an adhesive into the mix that not only is capable of binding under aqueous conditions but can aid in the binding of the aggregate to the cement paste. Bioinspired catecholic-type molecules have been shown to be an ultrastrong adhesive, even under wet conditions, and would, in principle, be an ideal candidate to use. In this study, we examine how dopamine (a molecule with a catechol functionality) binds to various oxides found in concrete mixtures. We find that dopamine binds preferentially to alkaline earth oxides; thus, for concrete mixtures rich in these minerals dopamine would be an ideal candidate for improved adhesion.

INFLUENCE OF CONCRETE COMPOSITION ON THE CORROSIVE STATE OF THE STEEL ARMATURES AND DURABILITY OF REINFORCED CONCRETE STRUCTURES

The influence of the composition of the concrete mixture on the state of reinforcing steel as the main problem of corrosion of reinforced concrete structures is considered. The main attention is paid to the need for individual and mandatory consideration of the influence of the properties of additives to concrete on the passivation of reinforcing steel. The purpose of conducting studies to determine the effect of concrete composition on the state of reinforcing steel is to analyze the causes of corrosion of reinforcement, determine the influence of the environment, apply appropriate prevention of this phenomenon and use methods to determine the corrosion state at the design stage of building structures for which reinforced concrete is used. The composition of concrete, in addition to the standard set in various quantitative combinations (cement, gravel, sand, water) today it is advisable to use special additives. Due to their correct and proportional application, you can create a mixture with significantly improved characteristics: with increased frost resistance, strength, durability, with accelerated or delayed setting of the mixture, etc. Nevertheless, you should not forget that the individuality of the composition of additives could affect the ability of concrete to passivate reinforcing steel. It is possible to eliminate the possibility of reducing the passivation of concrete by testing reinforced concrete samples for its protective properties in relation to the reinforcement. The test method is based on the passivation of reinforcing steel in an alkaline environment and consists in evaluating the protective effect of a sample of concrete in relation to a sample of steel reinforcement by comparing data obtained with a change in potential depending on changes in the density of electric current passing through the sample. The issue of quality and durability of reinforced concrete structures, both technically and economically, is attracting increasing attention of builders. It is obvious that in most cases an increase in the initial cost of manufacturing the structure and its reliable protection is economically justified, if this allows reducing the number and cost of repairs during operation. Keywords: reinforcement, corrosion, concrete, reinforced concrete, concrete additive, concrete composition, corrosion state of reinforcement, durability of reinforced concrete structures.

The effect of concrete composition on laser scabbling

Laser concrete scabbling is the process by which the surface layer of concrete may be removed through the use of a low power density laser beam. The main aim of this investigation was to establish relationships between laser interaction time and volume removal for a wide range of material compositions, including different w/b ratios, binder compositions (OPC/PFA), aggregate/binder ratios and coarse aggregate sizes. The results show that 25% replacement of ordinary Portland cement with pulverised fuel ash and/or a reduced water/binder ratio improves the efficiency of scabbling of cement pastes. Mortars and cement pastes were seen to scabble at a constant rate, whereas concretes experienced a peak rate, after which volume removal reduced dramatically. Basalt aggregate concrete was less susceptible to laser scabbling than limestone aggregate concrete. The effects of composition on the mechanisms which drive laser scabbling are discussed. It is suggested that pore pressure spalling governs behaviour in cement pastes, and thermal stress spalling is more dominant in mortar specimens. The driving force responsible for laser scabbling of concretes is developed within the mortar.

Neutron streaming along ducts and labyrinths at the JET biological shielding: Effect of concrete composition

Abstract Experiments and Monte Carlo simulations were performed at the Joint European Torus (JET) in order to validate the computational tools and methods applied for neutron streaming calculations through penetrations in the JET Hall biological shielding. In the present work the sensitivity of the simulations on the hydrogen and boron content in concrete shielding was investigated. MCNP code was used to simulate neutron streaming along the JET Hall personnel entrance labyrinth for deuterium–deuterium and deuterium–tritium plasma sources for different concrete wall compositions. Neutron fluence and ambient dose equivalent along the labyrinth were calculated. Simulation results for the “as built” JET concrete composition were compared against measurements performed using thermoluminescence detectors. This study contributes to the optimization of the radiation shielding of JET and, furthermore, provides information from JET experience that may assist in optimizing and validating the radiation shielding design methodology used in its successor fusion devices ITER and DEMO.

Photoneutron production and backscattering in high density concretes used for radiation therapy shielding

In the current study, the effect of high density concretes on photoneutron productions in radiation therapy was studied using Monte Carlo simulations. The photon and neutron spectra of an 18 MeV photon beam of the Varian linac head were used for all simulations. Ordinary and five high density concretes made of high density elements were simulated. The studied concretes consisted of Magnetite, Datolite–Galena, Magnetite–Steel, Limonite–Steel, and Serpentine. Our results showed that photoneutron production in these concretes strongly depends on their composition. It appears that the application of high density elements with higher probability for photoneutron production, such as Fe and Pb, increases the photoneutron production in concrete walls of radiation therapy bunkers. Further studies on the effect of concrete composition on photoneutrons in radiation therapy room are recommended.

Mixing of high performance concrete: effect of concrete composition and mixing intensity on mixing time

At present the use of ultra high performance concrete (UHPC) is limited to a small number of special applications. This is essentially due to the time needed to blend the UHPC mix which is considerably longer than required for ordinary concrete. The present investigations aimed at the determination of the composition features which result in the longer mixing time of UHPC. The individual components of the concrete mix (silica fume, quartz flour, water, superplasticizer and coarse aggregate) were systematically varied in order to investigate their effect on the mixing time needed to achieve optimal flow properties. Besides concrete composition, the effect of mixing tool speed was considered. The shortest necessary mixing time (stabilisation time) was calculated from the evolution of the power applied to the tool during mixing. It was confirmed that high w/c values resulted in short stabilisation times. In addition, the contents of silica fume and quartz flour as well as the type of cement and superplasticizer affected the stabilisation time significantly. It was possible to describe the effect of the individual variables in terms of the relative solid concentration ϕ/ϕmax which depends on concrete composition. This is the ratio of the actual volumetric concentration of solids in the concrete mix ϕ to the maximum possible concentration of solids ϕmax calculated from the volumes of particles (particle size distribution). The relative solid concentration is the basis of a model for the calculation of the mixing time of UHPC of a given composition and for given tool speed. High tool speeds and low actual concentrations of solids shorten the stabilisation time.

Effect of Concrete Composition on FRP/Concrete Bond Capacity

Effect of Concrete Composition on FRP/Concrete Bond Capacity

Effect of concrete composition on durability in natural acidic environment

The durability of concretes from the precast industry was studied in environmental conditions simulating wetting/ drying in a natural acidic environment. The industrial concretes were dry concrete and fluid concrete, both having cement content of 265 kg/m3. They were compared with conventional concrete of 360 kg/m3 cement content, with all the concretes studied having the same water/cement ratio of 0·47. Ageing in the mild acidic environment did not result in any detrimental effect and in some cases even a positive influence was observed. These differences were discussed in terms of the micro-structural observations. The strength was largely independent of the type of concrete, reflecting their similar water/cement ratio. However, permeability and performance with regard to carbonation and chloride penetration was significantly better in the industrial concretes, and this was attributed to their lower cement content. This trend suggests that the current standards that set the requirements for minimum cement content for durability should be revisited.

Justification and refinements of model B3 for concrete creep and shrinkage 1. statistics and sensitivity

Model B3 for creep and shrinkage prediction in the design of concrete structures, presented as a RILEM Recommendation inMater Struct.28 (1995) 357–365, is calibrated by a computerized data bank comprising practically all the relevant test data obtained in various laboratories throughout the world. The coefficients of variation of deviations of the model from the data are distinctly smaller than for the latest CEB model, and much smaller than for the previous ACI model (which was developed in the mid-1960's). The effect of concrete composition and design strength on the model parameters is identified as the main source of error. The model is simpler than the previous models (BP and BP-KX) developed at Northwestern University, yet it has comparable accuracy and is more rational.