Admixture Dosage Research Articles

The Influence of Admixtures on the Technological Properties of Fresh Concrete Mixture

In this research superplasticizing (SP), air voids removing (AVR), viscosity modifying (VM) and air entraining admixtures (AE) were used. The dosage of admixtures was chosen from minimum to maximum values recommended by the manufacturers. To sum up, 7 concrete mixture compositions with SP, 6 with AVR and 6 with VM and the last 6 with AE admixture were prepared. Water and cement ratio for all the compositions was kept at the same value. According to the results obtained, the usage of SP admixture resulted in significant increase of mixture`s slump and flow however it reduced mixture`s air content and increased its density. Concrete mixture`s properties: slump and flow were almost not affected by the increase of AVR and VM admixtures, however the air content slightly decreased and the density of concrete mixture slightly increased. With the incline of air entraining admixture, mixture`s slump, flow and air content increased, but the density declined. The authors of this study wanted to express the importance of the close link between concrete mixture`s technological and rheological properties. According to the yield stress of concrete mixture it is possible to prognosticate the future problems or various outcomes during or after the concrete mixture`s casting process. DOI: http://dx.doi.org/10.5755/j01.ms.21.4.5170

Study on the Tensile Creep Model of the Admixture of Early-Age Concrete and Application Simulation

With respect to the recent issue related to the lack of research on tensile creep model of the admixture concrete at early age and simulation, the admixture influence function with factor of the admixture dosage was established based on composite exponential function as reference model based on existed creep rules and appropriate assumption. It has been proposed that contributing factor, c, quantitatively represented the sensitivity of concrete creep changes to the admixture and correlation between concrete creep and the admixture. The model fitting was then made after tensile creep experiment by adding different admixtures such as fly ash, slag, silica fume and polypropylene fiber in contract to reference concrete test. It indicated that the model exhibited a good fitting performance, which is practical and useful as well as readily adopted by simulation. Meanwhile, the contributing factor also demonstrated quantitatively the variation among the effect of the admixtures (fly ash, slag, silica fume and polypropylene fiber) on the tensile creep of the concrete. Finally, the model was applied to an as-built concrete project for extended simulation, the results indicated that tensile creep can effectively improve the distribution of surface tensile stress and alleviate detrimental effect due to day-night temperature differences.

Utilization of high volume of industrial slag in self compacting concrete

This paper presents the results of an experimental investigation carried out to study the influence of industrial slag on the rheological, self-compactability and strength properties of self-compacting concrete (SCC) incorporating high volume replacements of industrial slag up to 90%. The rheological properties such as plastic viscosity and yield stress were evaluated using ICAR rheometer. The effect of high range water reducing admixture (HRWR) dosage, and the self-compactability properties such as T50, slump flow, V-funnel flow times and L-box blocking ratio were also investigated. The results illustrated that plastic viscosity decreased with the increase of the percentage of slag and the yield stress was nearly zero for all the replacements studied. The compressive strengths determined for the SCCs demonstrated that high strength SCC of more than 100 MPa at 30% and low strength SCC of 20 MPa at 90% replacement can be realized by utilizing slag appropriately.

Properties of SCC prepared using natural pozzolana and industrial wastes as mineral fillers

The high unit cost of self-consolidating concrete (SCC) resulting from the use of conventional filler materials, such as fly ash or silica fume, has been identified as the main hindrance to its widespread use particularly at places where these materials are not available locally. To achieve economy in the production of SCC, it is highly desirable to explore possibility of using alternative materials as mineral fillers through the evaluation of technical and economic benefits of SCC made with these materials. This paper presents the results of a study conducted to evaluate the performance of ternary SCC mixtures prepared using some industrial wastes as mineral fillers which include limestone powder, cement kiln dust, bag house dust, pulverized steel slag and metakaolin, each in conjunction with natural pozzolana. The mechanical properties and durability characteristics of the SCC mixtures satisfying the requirements of self-compactability at optimally selected dosages of chemical admixtures were evaluated. Except the SCC mixture incorporating bag house dust, the early and later-age strengths of the other SCC mixtures were found to be very high. Further, the good corrosion resistance exhibited by the developed SCC mixtures showed that the high performance SCC mixtures can be prepared utilizing these industrial wastes as mineral fillers.

Effect of atmospheric pressure on air content and air void parameters of concrete

The effects of atmospheric pressure changes on the air-entraining capability of air-entraining admixtures and the air void parameters of hardened concrete are studied using a low-pressure test chamber to simulate plateau environments with thin air and low atmospheric pressure. Results indicate that the atmospheric pressure of the environment significantly affects the performance of air-entraining admixtures. The air content of fresh concrete decreases by approximately 20–49% when the atmospheric pressure is 50 kPa with respect to when at normal atmospheric pressure (101 kPa). The air content of fresh concrete decreases linearly as atmospheric pressure drops. The air void parameters of concrete mixed when atmospheric pressure is low are worse than when it is mixed under normal atmospheric pressure. However, when the air content of hardened concrete reaches a certain value (4%) as the dosage of air-entraining admixtures is increased, the spacing factor could achieve freezing–thawing resistance (300 μm). The enhanced surface tension of liquids at low atmospheric pressure may contribute to the decreased air-entraining capability of air-entraining admixtures.

Design and performance of ternary blend high-volume fly ash concretes of moderate slump

One approach to increasing the sustainability of concrete construction is to replace a significant portion of the ordinary portland cement (OPC) with a supplementary cementitious material, such as fly ash. This paper presents mixture proportions and measured properties for a series of six high-volume fly ash (HVFA) concretes, five containing a ternary component of a fine limestone powder, with cement replacement levels of 40% or 60% by volume, targeting moderate slump (150mm) applications. Special emphasis is given to electrical resistivity measurements, comparing measurements conducted in a uniaxial vs. a surface configuration, and assessing the capability of measurements of the bulk resistance of the fresh concrete to anticipate setting times in these HVFA mixtures. The degree to which relationships exist between compressive strength and either cumulative heat release or uniaxial resistivity are presented. In general, ternary blend HVFA concretes can be formulated to provide acceptable strengths at both early ages and over the longer term, with an increased resistivity that implies an enhanced durability and increased service life. However, to achieve moderate slumps at the requisite lower water-to-cementitious material ratios, high dosages of high-range water-reducing admixtures (HWRA) will likely be required, which can negatively impact early-age properties (e.g., setting time and 1 d strengths). Thus, optimum mixture proportioning will require the careful selection and evaluation of the available HRWRA products, both individually and in potential combinations. Finally, another viable route to reducing cement content is to increase the aggregate volume fraction, as demonstrated by the OPC control concretes investigated in this study where aggregate volume fraction was increased from 70% to 72.5%, concurrently achieving a 10% reduction in cement content. In the ternary blend HVFA mixtures, further increases to 75% aggregates were possible, resulting in overall cement reductions (per unit volume of concrete) of between 45% and 63%.

Factorial Design Approach in Proportioning Prestressed Self-Compacting Concrete.

In order to model the effect of mixture parameters and material properties on the hardened properties of, prestressed self-compacting concrete (SCC), and also to investigate the extensions of the statistical models, a factorial design was employed to identify the relative significance of these primary parameters and their interactions in terms of the mechanical and visco-elastic properties of SCC. In addition to the 16 fractional factorial mixtures evaluated in the modeled region of −1 to +1, eight axial mixtures were prepared at extreme values of −2 and +2 with the other variables maintained at the central points. Four replicate central mixtures were also evaluated. The effects of five mixture parameters, including binder type, binder content, dosage of viscosity-modifying admixture (VMA), water-cementitious material ratio (w/cm), and sand-to-total aggregate ratio (S/A) on compressive strength, modulus of elasticity, as well as autogenous and drying shrinkage are discussed. The applications of the models to better understand trade-offs between mixture parameters and carry out comparisons among various responses are also highlighted. A logical design approach would be to use the existing model to predict the optimal design, and then run selected tests to quantify the influence of the new binder on the model.

Sodium salt admixtures for enhancing the foaming characteristics of sodium lauryl sulphate

This study identifies admixtures to enhance the effectiveness of Sodium Lauryl Sulphate (SLS) as a foaming agent by increasing the foam density and stability. Sodium hydroxide, sodium carbonate and sodium chloride were chosen based on common ion effect to increase the viscosity of the foaming solution in order to achieve ASTM recommended range of foam density. Response surface methodology is used to study the responses like viscosity, foam density and foam stability of all the admixtures. Viscosity is observed to have a linear relationship with foam density, bubble size distribution and stability. Foam density increases with the dosage of admixture, irrespective of foam generation pressure (FGP). Use of appropriate dosage of these admixtures with SLS provides the foam density specified by ASTM. Relatively lesser dosage of NaOH is sufficient to achieve ASTM recommended foam density, which is attributed to the fact that mole percent of sodium in NaOH is higher than NaCl and Na2CO3. The stability of the foam has also been demonstrated through a typical mix of foam concrete.

Effect of Sand Content on Properties of Self-Consolidating, High-Performance Cementitious Mortar

The workability and compressive strength of a high-performance cementitious mortar (HPCM) produced by using a natural siliceous sand were studied as a function of sand content [expressed as sand-to-cementitious materials ratio (s/cm)], silica fume (SF) content, and high-range water reducing admixture (HRWRA) dosage. The purpose of this study was to maximize the proportion of sand content without negatively affecting workability and mechanical and durability properties when these characteristics were achieved at a low cost. Test results indicated that the workability of HPCM became less sensitive to sand content when the SF content increased. Statistical analysis showed that the compressive strength of self-consolidating HPCM was not significantly affected by sand content up to a certain maximum level, which was dependent on the HRWRA and SF dosage. On the basis of combined consideration of both workability and compressive strength, the maximum s/cm ratio to produce a self-consolidating HPCM with SF content at 0%, 10%, and 20% was 1.6, 1.6, and 2.0, respectively. Also, increasing the sand content was helpful in improving the durability of HPCM, because chloride ion permeability and drying shrinkage decreased.

SP제 및 물시멘트비 영향을 고려한 초유동 콘크리트의 흐름 실험 및 해석

ABSTRACT In this research, flow experiments and simulation of highly flowable concrete has been attempted using a viscoplastic particle method varying with dosages of SP admixture and water-cement (W/C) ratios. Rheological and flow characteristics of flowable concrete manufactured in domestic products of cement, aggregates, and SP admixtures were investigated by experimental programs varying with mix proportions. From experiment, the predictive model of rheological characteristics of flowable concrete has been newly proposed considering with the effects of the W/C ratio and the dosage of SP admixture, and the effect of mixing proportion has also been incorporated into shear stress and strain rate curve of flowable concrete in the current method. A series of L-box flow test of highly flowable concrete varying with dosages of SP admixture and W/C ratios was compared with the proposed model. Keywords : highly flowable concrete, particle method, water-cement ratio, SP admixture, L-box flow test

Testing dynamic segregation of self-consolidating concrete

Segregation is a common problem in self-consolidating concrete, which often uses a high dosage of high-range water-reducing admixture to achieve high flow and passing ability. Dynamic segregation, when the aggregate lags behind in flowing concrete, may be distinguished from static segregation, when the aggregate sinks in concrete at rest. In this study, a flow trough was developed to measure dynamic segregation. The trough was found to provide a promising method for measuring this behavior. Static and dynamic segregation were not always found to occur simultaneously, and the slump flow test was not always sufficient to detect dynamic segregation, especially over a long travel distance. A simple procedure was proposed to set the maximum flowing distance based on mix proportions and the flow trough results.

Effect of Slag on the Rheological and Strength Properties of Self-Compacting Concrete

This study deals mainly deals with the rheological and strength properties of self-compacting concrete (SCC) incorporating high volume replacements of slag. Plastic viscosity and yield stress were evaluated using ICAR rheometer. The effect of high range water reducing admixture (HRWR) dosage, the time to reach 500 mm diameter (T50), the final slump flow, V-funnel flow times and L-box blocking ratio were also investigated and studied in this research program. The results show that the plastic viscosity decreases with the increase of the percentage of slag and the yield stress was nearly zero for all the replacements studied. The compressive strengths determined for the SCCs demonstrate that high strength SCC of more than 100 MPa can be realized by using slag appropriately.

Research on the Effects of Admixture on Concrete Permeability

At present, our country norms on the permeability of concrete is mainly determined by its strength, without considering the influence of admixtures on the permeability. This paper studies the permeability of different strength concrete rules of different kinds and dosage of admixture. The results show that, the permeability of concrete is closely related to the w/b, but also it has a strong correlation with admixture dosage, the relevance between the permeability of concrete and the kinds of admixture is relatively small. The results of this paper can provide some reference value to the relevant standards of durability in our country.

Effect of Admixture Dosage and Specimens Age on Mechanical Fracture Parameters of Lime Mortars Enhanced by Burnt Clays

In the restoration of historic buildings with priorities of historic preservation there exists an effort to modify the mortars by admixtures which are in compliance with historical materials and techniques. Therefore the specimens were made from lime mortar modified by brick powder or metakaolin. The reference mixture used only hydrated lime while the other mixtures were enhanced by brick powder or metakaolin in the amounts of 25, 50 and 100 % of the weight of hydrated lime. This paper presents the results of three-point bending fracture tests obtained by using double-K fracture model. The specimen’s age was 90 and 150 days.

Characterization of heat-treated self-compacting concrete containing mineral admixtures at early age and in the long term

Self-compacting concretes (SCCs) are increasingly used in the field of prefabrication, although the final strength of the heat-treated concrete is less than that of reference samples that have been cured in normal conditions. The aim of this work is to contribute to the improvement of the mechanical behavior of this kind of SCC. This paper presents the effect of the incorporation of local mineral admixtures on the behavior of heat-treated SCC at an early age (1day) and in the long term (28 and 180days). The characteristics of the SCC in the fresh and hardened states were also studied. The adopted heat-treatment cycle attained a maximum temperature of 60°C and a total duration of 24h. Three additions to the cement at the levels of 20% and 40% were used. They were fine limestone (LF), granulated slag (GS), and crystallized slag (CS). The fresh states characteristics of SCC are affected by the nature and dosage of the mineral admixture. In the hardened state, the comparison between the elaborated SCC and the control SCC without addition and without heat treatment showed an overall gain in strength at early age and minimal loss in the long term. The CS with a dosage of 40% allowed to the heat-treated SCC to be the less porous and the more resistant one compared to the elaborated SCCs. The use of LF appears to be more favorable if its incorporation is limited to below 20%. The GS is also favorable with 20% and it can be more beneficial if its fineness exceed that of the cement powder.

Influence of Silica Fume on Mechanical Property of High Performance Concrete

Silica fume is a by-product in the production of ferrosilicon and industrial silicon material. With the ultrafine physical structure of and high volcanic ash activity, silica fume is more important admixture in concrete improving the strength and durability of concrete, and it is widely used in high performance concrete engineering. Influence of silica fume on mechanical property of high performance concrete is investigated in this paper. Experimental results show that the strength of concrete increases significantly when suitable dosages of admixtures is applied.

품질변동에 따른 병용계 자기충전 콘크리트의 유동특성에 관한 실험적 연구

The purpose of this study is to investigate experimentally the variation factors range having influence on the rheological properties of the combined self-compacting concrete according to materials quality, weighting error and site conditions. Two types cement (blast-furnace slag cement and belite cement), lime stone powder as binder and the optimum mix proportions in the preceded study are selected for this study. Also, variations for sensitivity test are as followings; (1) Concrete temperature 3 cases (2) Surface moisture of sand 5cases (3) Fineness modulus of sand 5cases (4) Specific surface of lime stone powder 3cases (5) Dosage of chemical admixture 5cases. Slump flow (650±50 mm), 500 mm reaching time ((7±3 sec), V-type flowing time (15±5 sec) and U-box height (min. 300 mm) are tested for sensitivity. As test results, the variations range for quality control are as followings. (1) Concrete temperature; 10∼20℃(below 30℃) (2) Surface moisture of sand; base±0.6% (3) Fineness modulus of sand; 2.6±0.2 (4) Dosage of chemical admixture; base±0.2% (5) Specific surface of lime stone powder 6000 cm 2 /g. Compared with two types cement including based belite cement (binary type) and based slag cement (ternary type), the combined self-compacting concrete used belite cement type is most stable in the quality control because of high contents for lime stone powder and C2S. It is to propose a control scheme of the combined self-compacting concrete in the actual construction work.

Influence of matrix flowability, fiber mixing procedure, and curing conditions on the mechanical performance of HTPP-ECC

In this study, the influences of matrix flowability, fiber mixing procedure, and curing conditions on the mechanical properties of Engineered Cementitious Composites (ECC) made with High Tenacity Polypropylene (HTPP) fibers are investigated. While the HTPP-ECC examined in this study possesses moderate compressive strengths (30–70MPa), their tensile ductility (1.91–3.91%) is similar to that of ECC with Polyvinyl Alcohol (PVA) fibers. For the purpose of controlling matrix flowability, different dosages of HRWR admixture were introduced to a matrix with fly ash/cement weight ratio of 2.8 and water/cementitious material weight ratio of 0.23. Dogbone-shaped and 50mm cube specimens were used to investigate uniaxial tensile and compressive properties of HTPP-ECC, respectively. Test results showed that control of flowability in a certain range is required to achieve robust tensile ductility. A further improvement in tensile ductility and mechanical properties of HTPP-ECC was achieved through water-curing instead of air curing typically used for PVA-ECC. The basic mechanisms that enhance tensile ductility of HTPP-ECC through flowability control, mixing procedure modification, and water-curing are discussed from the view point of micromechanics underlying ECC design, with supporting evidence from fiber bridging stress–crack width (σ–δ) relations.

Compensation Effect of Expansive Agent on Shrinkage of Self-Compacting Concrete

The compensation effect of expansive agent on shrinkage of self-compacting concrete (SCC) are studied. The deformation of Concrete was tested by concrete comparator, and the qualitative and quantitative analysis of hydration products were done by X-ray diffractometer (XRD). The results show that the dosages of mineral admixture and curing conditions affect the application results of expansive agents markedly. SCC samples containing expansive agent cured in the water are expanding within the test time. In the case of watering condition and natural curing condition, the samples are always shrinkage within test time, but mineral admixtures have a good effect to resist the shrinkage of SCC. Microstructure analysis show that ettringite content is reduced slightly due to the reduction of the alkalinity of SCC resulted by more mineral admixture. However, when at water curing condition, humidity inside SCC is much higher, which makes ettringite content larger even though with more mineral admixture. So, curing is the most important factors for the micro-expansion of SCC containing expansive agent.

Reutilization of RFA of Construction Waste in Cement Mortar

The effect of some factors(dosage and grain size of recycled fine aggregate of construction waste, content of mineral admixture) on the properties of cement mortar was studied. The results indicated that when recycled fine aggregate particles gradation was areaⅡ, replacement percentage (sand) was 60%,dosage of mineral admixture was 36%, compared with blank sample, the 28d flexural strength and the compressive strength of cement mortar samples were increased by 30.7% and 37.2%, respectively. Micro-morphology of section on cement mortar was observed by SEM. Identifying the hydration products through XRD was carried out.