Influence Of Admixtures Research Articles

Influence of mineral admixtures on impact strength of self-compacting concrete under elevated temperatures

Self-Compacting Concrete (SCC) is a special type of concrete that can be placed in its own weight and compacted without any vibrations. One of the biggest problems of its use in structures subject to high temperatures was the fire resistance of SCC materials. The grade of concrete used for this study is M20. Different replacement methods was adopted for the comparative performance study of supplementary mineral admixtures such as Fly Ash (FA), Silica Fume (SF) and Meta-Kaoline (MK). Fine aggregate and coarse aggregate are replaced with FA by 5% and 3% respectively. Fine aggregate is replaced with SF by 3%. Fine aggregate and coarse aggregate are replaced with MKby 4% and 2% respectively. Specimens are casted in cylinders of 150mm diameter and 63.5mm heightand cured for 28 days. After 28 days, specimens were heated in the muffle furnace at 500, 750 and 1000°C. Then all the specimens were tested and observed for impact strength, colour change and weight loss.

Tailoring electrostatic surface potential and adsorption capacity of porous ceramics by silica-assisted sintering

In this study, we apply silica-assisted sintering to develop porous yttria stabilized zirconia (YSZ) ceramics with tailored electrostatic surface potential and adsorption capacity as a promising alternative to chemical functionalization. The porous bodies were formed by partial sintering at 1050 °C and were investigated regarding the influence of admixtures of silica particles on sintering behavior, microstructural evolution and the resulting mechanical and surface properties of the material, particularly the surface potential. With increasing silica concentration, the sintering mechanism was gradually changed from solid state to liquid phase sintering, due to the wetting of YSZ by liquid silica and a resulting inhibition of mass transport, particle growth and diffusion-induced densification. Most importantly, due to the silica layer development, the isoelectric point (IEP) of the YSZ/silica material surfaces was systematically shifted towards the IEP of silica from pH 9.4 to 1.2 resulting in a more pronounced negative surface potential at neutral pH. The relationship between surface IEP and silica concentration was mathematically described using the IEPs of the starting materials, the YSZ particle radius and the glass layer thickness. This estimation allows us to tailor the surface coverage of the YSZ matrix with silica as well as the resulting electrostatic surface potential. We further demonstrate how the applied processing route can be effectively used to develop ceramics with specified adsorption capacities for protein immobilization for use in filtration, bioprocessing or biomaterial applications.

Compressive Strength of Interlocking Concrete Pavement Block influenced by Admixtures

The interlocking concrete pavement blocks are quite commonly used to construct the pedestrian walkways and parking lots of transport infrastructure. Such blocks need adequate compressive strength to withstand the design live loads. In this paper, the influence of admixtures on the compressive strength of the blocks are studied through a series of laboratory investigations. The M35 grade of concrete conforming to the Indian Standard code of practice has been used with a standard superplasticizer as admixtures added at specified weights. The study implied that the use of admixtures alters the compressive strength of concrete blocks significantly.

The Effect of Mixed Doping on the Microstructure and Electrophysical Parameters of the Multicomponent PZT-Type Ceramics.

This work shows the influence of admixture on the basic properties of the multicomponent PbZr1−xTixO3 (PZT)-type ceramics. It presents the results of four compositions of PZT-type material with the general chemical formula, Pb0.99M0.01((Zr0.49Ti0.51)0.95Mn0.021Sb0.016W0.013)0.9975O3, where, in the M position, a donor admixture was introduced, i.e., samarium (Sm3+), gadolinium (Gd3+), dysprosium (Dy3+) or lanthanum (La3+). The compositions of the PZT-type ceramics were obtained through the classic ceramic method, as a result of the synthesis of simple oxides. The X-ray diffraction (XRD) pattern studies showed that the obtained multicomponent PZT materials have a tetragonal structure with a P4mm point group. The microstructure of the obtained compositions is characterized by a well crystallized grain, with clearly visible grain boundaries. The composition with the admixture of lanthanum has the highest uniformity of fine grain microstructure, which positively affects its final dielectric and piezoelectric properties. In the multicomponent PZT-type ceramic, materials utilize the mixed (acceptor and donor) doping of the main compound. This dopiong method has a positive effect on the set of the electrophysical parameters of ceramic materials. Donor dopants W6+ (at positions B) and M3+ = Sm3+, Gd3+, Dy3+, and La3+ (at positions A) increase the dielectric and piezoelectric properties, while the acceptor dopant Sb3+ (at positions B) increases the time and temperature stability of the electrophysical parameters. In addition, the suitable selection of the set of admixtures improved the sinterability of the ceramic samples, as well as resulted in obtaining the required material with good piezoelectric parameters for the poling process. This research confirms that all ceramic compositions have a set of parameters suitable for applications in micromechatronics, for example, as actuators, piezoelectric transducers, and precision microswitches.

On the influence of acidic admixtures in furfural on the performance of MgAl mixed oxide catalysts in aldol condensation of furfural and acetone

Aldol condensation of furfural and acetone is often used as a model reaction to test acid-base properties of solid catalysts. The present study describes the effect of furfural acidity on the catalytic performance of MgAl mixed oxides. Three furfural sources differing in their acidity were used and compared in aldol condensation at T = 55 °C and acetone to furfural molar ratio of 10. The furfural conversion over MgAl mixed oxides depended on the acidity of the furfural source, and the catalysts were partially consumed for neutralization of acid admixtures present in furfural. Only for some furfurals could the furfural conversion be improved by distilling the as-received furfural prior to the aldol condensation experiments. Moreover, the storage of the freshly distilled furfural during a few days, even in a closed flask and at a dark place, resulted in a substantial decrease in furfural conversion in aldol condensation. The results indicate that the distillation of the as-received furfural is an effective method to control the performance of basic catalysts at comparable reaction conditions only for some furfurals. Furthermore, the storage of the freshly distilled furfural has to be performed with care to avoid its re-oxidation.

Influence of concrete admixture on the bond strength of reinforced concrete submitted to high temperature

Abstract High temperatures can affect the macro and micro structural properties of reinforced concrete. This work aimed to analyze the bond strength behavior after high temperature exposure of two classes of concrete, the conventional 30 MPa and the high compressive strength 65 MPa concrete. The pullout test proposed by RILEM CEB / FIP RC6 (1983) was used for the evaluation of the compressive strength and modulus of elasticity. The influence of temperature on the physical-mechanical properties of concrete samples under a simulated fire situation was also studied for the evaluation of the resistant capacity in a post-fire situation. In addition to the analysis at 28 days, samples of the 30 MPa (group I) and 65 MPa (group II) classes were also investigated at 90 days exposed to room (23 °C), 400 °C and 800 °C temperatures. The bond strength curve was similar to that of compressive strength, where, at 400 °C, there was no statistical difference regarding room temperature and, at 800 °C, there was significant loss of strength in all cases. At 90 days age there was a loss of bond strength of 51 and 40 % for groups I and II, respectively. At 800°C the reductions were above 50 % in compressive strength and above 80 % in the modulus of elasticity, for both groups. These results show the structural impairment under high temperature. Comparing the test 28 and 90 days ages, there was no significant influence of age on the bond and compressive strength of the concretes.

Effects of Single and Compound Electrolyte Electrolyzed Cathode Waters on Mechanical Property and Hydration Reaction of Concrete

In this study, two kinds of different electrolyzed cathode water were used to prepare the concrete, the effects on mechanical property and hydration reaction of concrete were determined ultimately. Taking the influence of air-entraining admixture into consideration, the blank control test was also conducted. The experiment results showed that the single and compound electrolyte electrolyzed water both can effectively improve the strength of ordinary concrete, and the differences in strength between these two kinds of electrolyzed water concrete were not significant. To a small extent, the air-entraining admixtures would affect the activity of electrolyzed water and decrease the growth ratio of strength due to resistance effect. TG/DTA results test showed the calcium hydroxide amount of electrolyzed water concrete was obviously higher than that of natural tap water concrete at each age. In other words, the electrolyzed water in concrete can promote and boost the hydration reaction to produce more C–S–H gels and calcium hydroxide, leading to strength improvement and porosity reduction of concrete. In addition, the influence of the reaction between CO2–3 ions in electrolyzed water and calcium hydroxide on the increase of strength was little.

Study on the role of activators to the autogenous and drying shrinkage of lime-based low carbon cementitious materials

In order to improve the recycling of industrial solid wastes in the build materials area, the long-term development of auotogenous and drying shrinkage of lime-based low carbon cementitious materials (LCMs) was investigated in this work. In addition, the influence of chemical admixture (Na2SO4 and NaOH) on the shrinkage behavior of LCMs was systemically studied and compared. Moreover, the hydration kinetics, evolution of the compositions of hydration products and microstructure of LCM were investigated and analyzed to reveal the mechanism of the shrinkage behavior of LCM. The results showed that LCMs have lower autogenous and drying shrinkage value compared to those of Portland cement (PC). The addition of Na2SO4 to the LCM mixture further mitigated the shrinkage value of the LCM, especially for autogenous shrinkage. Na2SO4 in the LCM led to an additional number of ettringite (AFt) crystals formed in the paste at the early age, and the autogenous shrinkage of LCM was effectively decreased due to the compensation effect of the AFt on the shrinkage. Moreover, a large number of AFt crystals as skeletons embedded in the C(A)SH gel contributed to restricting the shrinkage of the paste. However, NaOH in the LCM caused the alkali activated reaction of the slag particles in the LCM and resulted in a LCM microstructure with fewer AFt crystals and more fine pores. Thus, the NaOH increased the autogenous and drying shrinkage of the LCM to some extent.

Influence of admixtures on properties of concrete and optimization using response surface methodology

The study presented here shows the influence of River Sand, M-sand and Admixtures on the properties of concrete which were analyzed. The effect of admixture content on concrete properties was evaluated with two types of admixtures independently. Metakaolin (MK) content was varied at 0%, 5%, 10% and 15% whereas Waste Paper Sludge Ash (WPSA) content was varied from 0%, 6%, 12% and 18%. Response surface methodology was employed to optimize the compressive strength, permeability and sorptivity of concrete when both admixtures (MK+WPSA) were varied simultaneously. The relationship between the concrete properties and level of materials added was derived using a Face Centered Central Composite Design with three levels and three factors. Based on desirable properties obtained in experimental part of the study, the factors considered in the design was M-Sand (0%, 50%, 100%), MK (0%, 5%, 10%), WPSA (0%, 6%, 12%). From the experimentally obtained data, prediction models based on regression analysis were developed which enables the establishment of response contours showing the interaction between the different parameters investigated. The contour plots were overlaid to distinguish the combination of proportions that gives ideal performance of concrete for water-repellency and strength

Permeability of Concrete and Correlation with Microstructure Parameters Determined by 1H NMR

Water and gas permeability coefficients of concrete with different water‐binder (w/b) ratios and admixtures were measured by a self‐designed test device based on the steady‐state flow method for liquid and the method of differential pressure in stability for gas, respectively. In addition, the micropore structure of concrete was determined by 1H nuclear magnetic resonance (NMR). Results indicated that there are good correlations between water and gas permeability of concrete with different w/b ratios, with correlation coefficient greater than 0.90. Better correlations between water permeability and segmental contributive porosity ranged from 10 to 100 nm and 100 to 1000 nm can be identified, but the gas permeability is more relevant to the segmental contributive porosity ranging from 100 to 1000 nm. Moreover, the correlation between water permeability and contributive porosity for each pore diameter is always better than that of gas permeability. The influence of admixtures on the relationship between permeability and pore size distribution of concrete is significant. Moreover, water permeability coefficient is one or two orders of magnitude lower than the gas permeability coefficient.

Microstructure of biopolymer-modified aerial lime mortars

Cellulose-based viscosity-modifying admixtures are used on daily basis in a wide range of building materials, dominantly in pre-mixed mortar systems. Lately, alternative admixtures such as different “gums” have emerged. In building materials, the gums have similar viscosity-enhancingeffects as cellulose ethers with different efficiency. Various ways of production, as well as diverse working mechanisms of the biopolymers are to be considered while choosing the most suitable admixture for the intended use. Influence of alternative admixtures in several doses on the microstructure of lime mortars was studied in this paper. Mortars were prepared with the same workability and the air content in fresh mortar was determined, for it can have notable impact on microstructure of hardened mortar. Hydroxypropyl derivative of chitosan showed air entraining ability, while the carboxymethyl derivative reported slight decrease in amount of air entrained into the mixture. In the case of diutan gum, the most water-demanding admixture, the percentage of entrained air dropped with growing dose. Admixture addition increased the volume of pores in diameter lower than 0.1 μm, and in region of pores around 10 μm. Only the diutan gum affected the distribution of capillary pores, which are typical for lime mortars. Hygric properties were in correlation with air content values.

Utilization plasters with superabsorbent admixture to moderate moisture level in constructions

The level of indoor humidity has to meet several criteria according to the preservation of a healthy indoor climate for building inhabitants. On top of that, the undesired moisture content is associated with a proliferation of various organisms which results in an adverse effect on the durability of building materials. Facing the impact of climate change and excessive energy consumption associated with building maintenance, the employment of passive moderation techniques takes place to avoid the usage of energy-demanding HVAC devices. The application of advanced materials such as superabsorbent polymers (SAPs), commonly used in diapers or other hygiene products, can bring a very effective solution for this issue overcoming. In this paper, the effect of 0.5; 0.1 and 1.5 wt.% dosages of SAPs incorporated into a cement-lime plaster are studied to evaluate the material performance in the sense of moisture moderation. First, the basic material properties, moisture transport and storage properties, thermal conductivity and specific heat capacity are determined to access the influence of SAP admixtures on the functional performance of studied plasters. Consequently, the experimentally accessed results are further employed for the computational modeling analysis which evaluates the capability of studied plasters for the moderation of moisture content in constructions.

ВЛИЯНИЕ МЕХАНИЧЕСКИХ ПРИМЕСЕЙ В РАБОЧЕЙ ЖИДКОСТИ НА ИЗНОС И ЗАЕДАНИЕ ЗОЛОТНИКОВЫХ ПАР ГИДРОПРИВОДОВ АВИАЦИОННОЙ ТЕХНИКИ

ВЛИЯНИЕ МЕХАНИЧЕСКИХ ПРИМЕСЕЙ В РАБОЧЕЙ ЖИДКОСТИ НА ИЗНОС И ЗАЕДАНИЕ ЗОЛОТНИКОВЫХ ПАР ГИДРОПРИВОДОВ АВИАЦИОННОЙ ТЕХНИКИ

Effect of crystalline admixture, fly ash, and PVA fiber on self-healing capacity of concrete

The ability of concrete admixtures to self-heal is an important way to improve concrete durability. The influence of crystalline admixture (CA), fly ash (FA) and PVA fiber on the self-healing capacity of early-age cracks in concrete was studied. The compressive strength recovery, electrical resistivity recovery, and morphology of crack surfaces were used to evaluate of early-age cracking in concrete. In this research four mixes are cast, control mix (M1), 0.1% of PVA fiber by volume mix (M2), 20% partial replacement of cement with fly ash mix (M3) and 2% of CA by mass of cement mix (M4). The cracks were formed by applying the compressive load for early-age cracks after 3 days of curing. Self-healing products are studied using scanning electron microscopy (SEM). It was observed that all admixtures show self-healing capacity to some extent. The results showed that the recovery of compressive strength and electrical resistivity of the cracked CA concrete samples has the highest self-healing capability due to the presence of calcium carbonate and C-S-H gel which were confirmed by SEM analysis.

Влияние вводного скрещивания казахского белоголoвого скота с герефордами уральского типа на пищевую ценность мясной продукции

Влияние вводного скрещивания казахского белоголoвого скота с герефордами уральского типа на пищевую ценность мясной продукции

Improving the resistance of concrete for sleepers to the formation of delayed and secondary ettringite, the alkali-silica reaction, and electric corrosion

The paper reports results of examining the influence of modifier admixtures on the corrosion resistance of concrete for reinforced concrete sleepers based on the criteria of electric resistance, resistance to alkaline corrosion and corrosion due to the crystallization of delayed and secondary ettringite. This study was conducted within the framework of resolving the issue on premature destruction of reinforced-concrete sleepers caused by the progressing crack formation at the stage of heat treatment and subsequent operation. It has been established that the introduction of pozzolanic admixtures containing active Al 2 O 3 in their formulation to the composition of concrete for sleepers makes it possible to minimize the risk of corrosion predetermined by the reaction between aggregates’ silica and alkali and corrosion as a result of crystallization of delayed and secondary ettringite. The high efficiency of pozzolanic admixtures containing active Al 2 O 3 regarding the specified types of corrosion is due to binding alkali into the insoluble alkaline hydroalumosilicates, contributing to the compaction of the system with a decrease in the content of Na + /K + ions in the solution. A decrease in the content of alkali in the porous solution predetermines blocking the «alkali-silica reaction» and increasing the temperature of ettringite stability to higher values. This reduces the potential number of secondary ettringite forming cycles and the probability of delayed ettringite formation. The alternative mechanism of action of active Al 2 O 3 on pozzolan implies binding the SO 4 2– and Ca 2+ ions from a porous solution into low-sulfate forms of calcium hydro-sulfoaluminates, which excludes the crystallization of delayed and secondary ettringite. Reducing the consumption of cement and water through the use of admixtures-plasticizers makes it possible to increase the electrical resistivity of the modified concrete for sleepers above the level of a control composition without admixtures. The obtained results provide an opportunity to ensure the design durability of concrete in reinforced-concrete sleepers through their comprehensive modification by plasticizers and active mineral admixtures that contain active Al 2 O 3

Lanthanide Luminescence Revealing the Phase Composition in Hydrating Cementitious Systems.

The hydration process of Portland cement in a cementitious system is crucial for development of the high‐quality cement‐based construction material. Complementary experiments of X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM) and time‐resolved laser fluorescence spectroscopy (TRLFS) using europium (Eu(III)) as an optical probe are used to analyse the hydration process of two cement systems in the absence and presence of different organic admixtures. We show that different analysed admixtures and the used sulphate carriers in each cement system have a significant influence on the hydration process, namely on the time‐dependence in the formation of different hydrate phases of cement. Moreover, the effect of a particular admixture is related to the type of sulphate carrier used. The quantitative information on the amounts of the crystalline cement paste components is accessible via XRD analysis. Distinctly different morphologies of ettringite and calcium−silicate−hydrates (C−S−H) determined by SEM allow visual conclusions about formation of these phases at particular ageing times. The TRLFS data provides information about the admixture influence on the course of the silicate reaction. The dip in the dependence of the luminescence decay times on the hydration time indicates the change in the structure of C−S−H in the early hydration period. Complementary information from XRD, SEM and TRLFS provides detailed information on distinct periods of the cement hydration process.

Capillary suction induced water absorption and chloride transport in non-saturated concrete: The influence of humidity, mineral admixtures and sulfate ions

Concrete structures in marine environments are gravely jeopardized by chloride attack caused by capillary suction. To investigate the erosion of concrete induced by capillary suction under various factors, seawater and NaCl-Na2SO4 solution were used as corrosive solution to obtain the evolution law of water absorbed amount and chloride content in concrete with different water to binder ratio, fly ash and slag dosages and internal relative humidity. The results show that the decrease of internal relative humidity leads to the increase of seawater absorbed by capillary suction in a brief period, and boost rapid growth of chloride content in surface of concrete. For early age (28 d) concrete specimens, when the fly ash dosage is 0–30% or the slag dosage is 0–50%, the water absorption rate and chloride content of concrete are more likely to drop with the dosage increasing. Furthermore, under short-time capillary suction condition, SO42− has a minor impact on water absorption of concrete, while slightly increases the chloride content. However, the chloride content does not evolve coincidently with the change of SO42− concentration. Moreover, within a brief exposure period, the chloride content linearly develops with absorbed sweater amount, and it is inappropriate to use chloride diffusion coefficient to reflect the chloride transport rate of concrete under capillary absorption effect.

Experimental study of different admixture effects on the properties of uranium mill tailing solidified bodies

To study the influence of admixtures, including blast furnace slag, quicklime, and fly ash, on the properties of solidified uranium mill tailings, the mechanical strength, permeability coefficient, and radon exhalation rate of solidified samples were measured after curing and storage for 28 days. The results showed that, with increased admixture dosage, the curing degree of the solidified body improved, mechanical strength increased, and permeability coefficient and radon exhalation rate decreased. At the same dosage of the three additives, the optimized curing degree in the blast furnace slag samples with 25% dosage had the properties of blast furnace slag samples, which was in accordance with China GB 14569.1-2011 standards that provide theoretical reference and decision evidence for the future management of uranium tailing impoundment/decommissioning treatment.

Strength Characteristics of Slag Based Steel Fiber Reinforced Concrete with Partial Replacement of Steel Slag in Coarse Aggregate

The current research work represents the various test results from an experimental program for the influence of mineral admixture, stone dust, steel slags and rapid hardening (accelerator) type of chemical admixtures along with the inclusion of steel fibers for various mixture proportions on the mechanical properties of concrete. The different strength properties considered the cubical size for compressive strength, prism for flexural rigidity and monitored the ultrasonic pulse velocity test including water absorption (sorptivity) test for different curing days was evaluated. The outcome results for concrete shows that when the percentage of steel slag is increased then there will be a good workability in fresh concrete than normal aggregates. In overall 100% of stone dust, if the portion of steel slag is more than 40% with replacement of coarse aggregate and binding material as slag will lead to minimum workability, there is no change in the proceding workability area in the further addition of super plasticizer. Also, the study indicates that the crimped steel fiber matrix interaction gives considerable results to enhance the bending stress in flexural rigidity caused by the introducing of steel fibers.