Admixture Dose Research Articles

Mechanical processing of wet stored fly ash for use as a cement component in concrete

Wet storage effects on fly ash mean that processing may be necessary to achieve the physical properties required for use in concrete. This paper considers drying, de-agglomeration and milling of various wet stored fly ashes at laboratory and pilot/benchtop scales, towards meeting these. In the laboratory, different batch quantities and milling times with as-received/pre-screened materials were examined using a ball mill. Greater particle size reductions were obtained with increased milling time but at gradually reducing rates. Pre-screening and batch quantity had relatively minor effects on particle size reductions, with small differences also found between wet and dry stored fly ash. Extended milling time resulted in a darkening of colour; slight increases in loss-on-ignition, the main oxides content and crystalline components; reductions in water requirement (to a point); and greater reactivity. Similar effects were generally noted in concrete for the superplasticising admixture dose to achieve a target slump and compressive (cube) strength. At pilot/benchtop scale, a dryer-pulveriser and spiral jet mill were used, which gave general agreement with the behaviour noted in the laboratory, but with the effects tending to be less. Fineness levels in Standards were achievable, with subsequent performance in concrete, appearing to depend on the milling process used.

PARAMETRIC STUDIES ON VARIOUS FACTORS AFFECTING COMPRESSIVE STRENGTH OF GEOPOLYMER CONCRETE

Concreteisbecomingmoreandmoreindemandasinfrastructurefacilities are being developed. Its good. It is a known fact that themanufacture of OPC uses a big amount of energy and natural resourcesandalsoemitsasignificantamountofcarbondioxideintotheatmosphere.Therefore,itscrucialtocomeupwithalternativestoenvironmentallyfriendlyconcrete.Flyashisusedtocreatetheinorganic alumino-silicate substance known as geopolymer. India has alargesupplyofflyash,oneoftherawmaterialsusedtomakegeopolymerbinders,althoughithasonlyjustbeguntobeused.Therefore, in order to produce concrete that is more environmentallyfriendly, it is imperative to make the effort to use this by-product. Inordertoimproveitsoverallperformance,thisresearchdetailstheexperimentalworkcarriedoutbycasting20differentgeopolymerconcretemixturestoassesstheimpactofdifferentparametersimpactingitscompressivestrength.Therehavebeenstudiesonanumber of parameters, including the ratio of alkaline liquid to fly ash,sodium hydroxide concentration, sodium silicate to sodium hydroxideratio, curing time,curing temperature,dose of superplasticizer, restperiod, and additional water content in the mix. According to the testresults,compressivestrengthimproveswithincreasedcuringtime,temperature, rest time, and sodium hydroxide solution concentrationwhile decreasing with increased water to geopolymer solids by massand admixture dose. The workability of new geopolymer concrete isenhanced by the use of a naphthalene-based superplasticiser. It wasfurtherdiscoveredthatakeyfactorinreachingtheoptimumcompressivestrengthofthegeopolymerconcretemixisthewatercontent.

Optimization of mix proportion of basic magnesium sulfate cement-based high-strength coral concrete

The diverse morphology of coarse coral aggregate and its complex pore structure cause uncertainty in the performance of coral aggregate concrete (CAC). Crushing coarse coral aggregates into fine aggregates may be an effective measure to achieve high performance CAC. This paper investigates the morphological parameters of single-size coral sand particles by numerical characterization and statistical analysis. The relationship between coral sand particle gradation and CAC performance is explored. Basic magnesium sulfate cement was used as the cementitious material, and compound-oriented coral sand (zone II medium sand) was used as the fine aggregate. Through a response surface method design, the flexural and compressive strengths of the synthesized basic magnesium sulfate cement-based high-strength CAC at 28 d achieve 13.1 and 79.1 MPa, respectively. The results show that the particles larger than 0.6 mm in the coral sand could enhance the flexural strength of CAC, while smaller (<0.6 mm) particles are more beneficial to the compressive strength. The particle gradation of group II½ is more likely to enable the coral sand to achieve a tightly packed state. After optimization by the response surface method, the critical proportioning parameters for achieving excellent mechanical properties of basic magnesium sulfate cement-based CAC are obtained: α-MgO:MgSO4 molar ratio of 8.3–9.5, cement ratio of 1.11–1.35 and admixture dose of 1.58–2.02%. Further, the recommended ratio is given in the 3D space under the ternary interaction. This method can provide a novel approach for designing and manufacturing high-performance CAC.

Microstructure Study for Effect of Local Admixture in Concrete Durability

Concrete permeability plays the main role in concrete durability because of the entry of harmful substances such as chlorides, sulfates, carbon dioxide (CO2), oxygen (O2). Concrete permeability is affected by factors such as size and proportion of aggregate, type, and quantity of cement, water-cement ratio, type and dose of admixture used, which help concrete have a high life. This research aims to investigate the effect of local admixture prepared to improve concrete properties, especially reducing the permeability of concrete using its proven effectiveness in salt attack. This research studies the effect of this admixture on concrete microstructure for several concrete specimens. This chemical admixture, which contains calcium oxide (CaO), chloride (Cl), and others, helps obtain a good performance of concrete. Adding calcium oxide (CaO) plays an important role in improving the physicochemical properties of concrete. An increase in the compressive strength was observed for all specimens. Incorporating additives without CaO to concrete has been shown to decrease its strength. In the present study, concrete showed higher compressive strength than other concrete, which has not contain this admixture which may be explained by the larger quantity of CaO in the cement.

Overview on evaluation of the mechanical, durability properties and microstructure of Nano-Silica assimilated cement composites (Nano-SAC)

The Cement composites (CC) are the ubiquitous material in the world because of nanostructured, multi-phase, composite material that ages over time. CC as a construction material is most heterogeneous and the advent of nanotechnology offers substantial advances in concrete. In this framework, the application of Nanotechnology has its prominence in the construction industry, due to the enhanced characteristics of CC. Several studies have attempted to incorporate a variety of nanomaterials in CC and investigated the enhancement of mechanical and durability properties. Most importantly, the use of Nano-Silica (NS) has high significance in enhancing the mechanical properties, making the composite a durable material due to high pozzolanic behaviour and influence on the microstructure of CC. Hence, this paper reviews the prior development and current findings of Nano-Silica (NS) incorporated CC. The effect of Nano-Silica on mechanical and durability properties of the cement composites by varying microstructural characteristics are discussed. Furthermore, due to compact microstructure and accelerated hydration, and impermeable microstructure and higher strength durability is enhanced. Finally, the paper also describes the limitation that the optimum dose of the Nano-silica varies with its size, type, and dose of admixture, water to binder ratio, which is still contradictory. Additionally, the incorporation of Nano-silica is a potential breakthrough in building materials for a specific application. This article shed light on optimum dose in cement composite for specific types and sizes of Nano-silica particles.

Concrete Water-Reducing Admixtures between Laboratory and Site.(Dept.C)

This research was planned to study the effect of water-reducing admixtures on the properties of cement paste and concrete. These properties included setting time of cement paste, consistency of fresh concrete and compressive strength of hardened concrete. The main veritables taken into consideration in this study were cement content, water/cement ratio and admixture/cement ratio. A comparison was made between the properties of concrete according to the usage of the optimum dose of the admixture as a result of the experimental test results and the properties of concrete when the dose recommended by the producer was used. Great improvement was achieved in both the workability of fresh concrete and the compressive strength of hardened concrete when optimum dose of the water-reducing admixture was used which depends on many factors among which are the cement content and water content. The initial and the final setting time of cement increase with the increase of the water-reducing admixture in the cement poste. However, the limits of the setting time recommended by the specifications have to be taken into consideration when determining the optimum dose of the admixture.

Organic phosphorus compounds as heat release regulators in hardening shielding concrete

Abstract The paper presents the results of the study of the influence of the addition of retarding superplasticising admixture based on triisobutyl phosphate and modified phosphonates on the amount of heat generated by hardening shielding concrete. A four-point measurement of the heat generated during the hardening of concrete with an admixture dose of 0, 0.5, 1.0 and 2.0% by weight of the cement was made and the concurrent measurement of the heat released by the hardening cement paste was measured with an isothermal calorimeter. Based on the results from the calorimeter, the effect of the admixture on the temperature field in the hardening concrete mass elements was simulated for different aggregates. The results indicate that the admixture clearly lowers the temperature gradient in hardening mass concrete. In the simulations, the most clear effect was achieved in the case of concrete with barite aggregate, where the gradient value was reduced from 10°C/m to 8°C/m for an admixture content equal to 2.0%.

Effect of some prepared superplasticizers on the rheological properties of oil well cement slurries

Three superplasticizers namely: cyclohexanone glyoxylic sulfanilate (CGS), acetone glyoxylic sulfanilate (AGS) and melamine glyoxylic sulfanilate (MGS) were prepared and characterized using FT-IR. The prepared admixtures were evaluated as additives for improving the rheological properties of oil well cement. The effect of temperature (25°, 45° and 65 °C) and admixture dose (0.25, 0.5, 0.75 and 1%) were determined on the apparent viscosity, plastic viscosity and yield stress. The results showed that the prepared superplasticizers, CGS, AGS and MGS decreased these parameters. The results concluded that the CGS, AGS and MGS admixtures act as retarders and dispersant for oil well cement. The three prepared admixtures exhibited high enhancement on the rheological properties which mean that it can use in oil cementing processes.

Development of Lateral Prestress in High-Strength Concrete-Filled FRP Tubes

This paper reports on an experimental investigation into the axial and lateral strain development of fiber reinforced polymer (FRP) confined high-strength concrete (HSC) with prestressed FRP shells. A total of 24 aramid FRP (AFRP)-confined concrete specimens were manufactured as concrete-filled FRP tubes (CFFTs) with instrumentation to measure the strain variations during application of prestress, removal of end constraints and progressive prestress losses. Prestressed CFFT specimens were prepared with three different dose rates of expansive mineral admixture to create a range of lateral prestress applied to AFRP tubes manufactured with sheet thicknesses of 0.2 or 0.3 mm/ply and referred to as lightly- or well-confined, respectively. In addition to these three levels of prestress, non-prestressed companion specimens were manufactured and tested to determine baseline performance. The experimental results from this study indicate that lateral prestressing of CFFTs manufactured with HSC can be achieved by varying the expansive mineral admixture dose rate with a lateral prestress of up to 7.3 MPa recorded in this study. Significant strain variations were measured during removal of the end constraints with up to 700 microstrain recorded in the axial direction. Finally, the measurement of prestress losses for the month following prestress application revealed minimal progressive losses, with only 250 and 100 με recorded for the axial and hoop strains, respectively.

Effect of some prepared superplasticizers (Cyclohexanone Based) on compressive strength and physico-chemical properties of oil well cement pastes

Two different superplasticizers particularly cyclohexanone formaldehyde sulfanilate (CFS) and cyclohexanone glyoxylic sulfanilate (CGS) were prepared; also, their effect on mechanical and physico-chemical properties of oil well cement was assessed. The chemical structures were affirmed by FTIR technique. The designed chemical compounds were predestined as superplasticizers for cement pastes. The pastes were made by superplasticizer (CFS or CGS) addition to cement by the ratios of 0, 0.25, 0.50, 0.75, and l.00 as mass% of cement. The water of consistency, setting time, chemically combined water content (Wn), the hydration rate and compressive strength of the admixed hardened pastes were predestined at various time periods. The phase composition was intended by DSC and XRD techniques. The results revealed that as the admixture dose rate increases the demand cement paste water of consistency decreases. Also, as the admixture addition rate increases the chemically combined water content decreases, so the rate of hydration decreases; meanwhile compressive strength magnitudes increase accounting for the low water/cement (initial porosity) of the sample.

Waste glass powder as partial replacement of cement for sustainable concrete practice

Abstract Million tons of waste glass is being generated annually all over the world. Once the glass becomes a waste it is disposed as landfills, which is unsustainable as this does not decompose in the environment. Glass is principally composed of silica. Use of milled (ground) waste glass in concrete as partial replacement of cement could be an important step toward development of sustainable (environmentally friendly, energy-efficient and economical) infrastructure systems. When waste glass is milled down to micro size particles, it is expected to undergo pozzolanic reactions with cement hydrates, forming secondary Calcium Silicate Hydrate (C–S–H). In this research chemical properties of both clear and colored glass were evaluated. Chemical analysis of glass and cement samples was determined using X-ray fluorescence (XRF) technique and found minor differences in composition between clear and colored glasses. Flow and compressive strength tests on mortar and concrete were carried out by adding 0–25% ground glass in which water to binder (cement + glass) ratio is kept the same for all replacement levels. With increase in glass addition mortar flow was slightly increased while a minor effect on concrete workability was noted. To evaluate the packing and pozzolanic effects, further tests were also conducted with same mix details and 1% super plasticizing admixture dose (by weight of cement) and generally found an increase in compressive strength of mortars with admixture. As with mortar, concrete cube samples were prepared and tested for strength (until 1 year curing). The compressive strength test results indicated that recycled glass mortar and concrete gave better strength compared to control samples. A 20% replacement of cement with waste glass was found convincing considering cost and the environment.

EFFECT OF SOME PREPARED SUPERPLASTICIZERS (ACETONE BASED) ON PHYSICO-CHEMICAL AND MECHANICAL PROPERTIES OF OIL WELL CEMENT PASTES

This study aims to prepare two different superplasticizers particularly acetone formaldehyde sulfanilate (AFS) and acetone glyoxylic sulfanilate (AGS); also, their effect on physico-chemical and mechanical properties of oil well cement was studied. The chemical structures were confirmed by FTIR technique. The prepared compounds were evaluated as superplasticizers for cement pastes. The cement pastes were prepared by the addition of the prepared admixtures; AFS or AGS, to cement by the ratios of 0, 0.25, 0.50, 0.75, and l.00 as mass % of cement. The water of consistency, combined water content, the rate of hydration and compressive strength of the hardened pastes were determined at different time intervals. The phase composition and microstructure of the hardened pastes were studied by DSC and XRD techniques. The results revealed that as the admixture dose rate increases the demand water for consistency of the cement paste decreases. Also, as the admixture addition rate increases the chemically combined water content decreases, so the rate of hydration decreases; meanwhile compressive strength increases due to the low initial porosity of the sample.

Compatibility issues of cement with water reducing admixture in concrete

Summary Multiple brand of cement and water reducing admixtures are available in the market, even though these cements and admixture comply with the respective codal provisions there performance are not same in the concrete for each and every brand of cement and water reducing admixture, even if quality and source of other ingredients of concrete is kept same. This has created a lot of confusion among the user about what type/brand of admixture is used with what type/brand of cement and what should be optimum dose of admixture. Common problem associated with incompatibility issue is flash setting, delayed setting, rapid slump loss, improper strength gain and cracking, these not only effect the strength of the concrete but also the durability of the structure. Hence, in the present study different brand/type of cement and water reducing admixture available in the market is used to find study the compatibility issue and optimum dose of admixture. To achieve this marsh cone test has been performed. Test results indicate that the optimum dose of admixture vary from 0.9 to 1.1% of the weight of cement with different type/brand of cement and type/brand of admixture.

Influence of Portland cement characteristics on air-entrainment in fly ash concrete

A study examining air-entrainment in fly ash concretes combined with different Portland cements (PCs) is described. Tests were carried out (using five PCs, ten fly ashes and a standard chemical reagent (to entrain air)) on paste suspensions (foam index), mortar and concrete to quantify the material effects. Preliminary tests indicated that the foam index increased with the fineness (specific surface area (SSA) (by nitrogen adsorption Brunauer–Emmett–Teller (BET) method)) of the PC used (varied by grinding) with fly ash. Reductions in the property were found with increasing alkali content in the paste suspensions (by sodium hydroxide addition), which tended to be slightly greater with higher SSA/lower alkali content fly ash. Tests on the wider range of PCs and fly ashes gave a strong correlation between their combined SSA and foam index, with their combined alkali content having less effect on the latter. The influence of fineness was again apparent in the mortar tests, which also showed that when PC and fly ash were of comparable SSA, a change in either material had a similar effect on air-entrainment. However, fly ash had an increasing influence as the difference in this between materials became greater. The results also suggest that air losses after mixing tend to increase with the SSA of PC + fly ash (and hence admixture dose). Similar effects were generally noted in the tests made on concrete. A possible approach to controlling air-entrainment in fly ash concrete may therefore be to ensure that its SSA is similar to that of the PC with which it is used. A test method to enable this to be evaluated is suggested.

The contribution of genetic diversity to subdivide populations living in the silk road of China.

There are several indigenous ethnic populations along the silk road in the Northwest of China that display clear differences in culture and social customs, perhaps as a result of geographic isolation and different linguistic traditions. However, extensive trade and other interactions probably facilitated the admixture of different gene pools between these populations over the last two millennia. To further explore the evolutionary relationships of the 13 ethnic populations residing in Northwest China and to reveal the features of population admixture, the 9 most-commonly employed CODIS loci (D3S1358, TH01, D5S818, D13S317, D7S820, CSF1PO, vWA, TPOX, FGA) were selected for genotyping and further analysis. Phylogenetic tree and principal component analysis revealed clear pattern of population differentiation between 4 populations living in Sinkiang Uighur Autonomous Region and other 9 populations dwelled in the upper regions of Silk Road. R matrix regression showed high-level gene flow and population admixture dose exist among these ethic populations in the Northwest region of China. Furthermore, the Mantel test suggests that larger percent of genetic variance (21.58% versus 2.3%) can be explained by geographic isolation than linguistic barriers, which matched with the contribution of geographic factors to other world populations.

A ketamine–propofol admixture does not reduce the pain on injection compared with a lidocaine–propofol admixture

Propofol injection pain is a well-known problem in pediatric anesthesia. Premixture of lidocaine with propofol although effective does not abolish injection pain in all children. Promising results have been reported with pretreatment of the vein with ketamine. The purpose of this prospective, double-blind randomized, clinical trial with active control was to evaluate the efficacy of premixing propofol with ketamine in the prevention of injection pain in children. After ethics committee and parental approval and children's assent, 116 children, aged 1-12 years, were randomly allocated to receive an IV induction dose of admixture of racemic ketamine 0.5 mg x ml(-1) (ketamine group) or lidocaine 1 mg x ml(-1) in propofol 10 mg x ml(-1) (lidocaine group). The outcome measures were signs and symptoms of injection pain (primary outcome: the incidence of injection pain), hemodynamic and respiratory parameters, and adverse effects during anesthesia induction (secondary outcomes). Patients' characteristics were similar in the two groups. Fewer children (13/58) in the lidocaine group than in the ketamine group (26/58) (mean difference 23%, 95% CI for difference 6-40%, P = 0.018) developed pain on injection of propofol. There were no differences in hemodynamic parameters between the two groups. One child in the lidocaine group developed laryngospasm, but no other adverse events were recorded. Injection pain was twice as common with ketamine-propofol admixture than with lidocaine-propofol admixture.

Effectiveness of shrinkage-reducing admixtures on Portland pozzolan cement concrete

Drying shrinkage causes tensile stress in restrained concrete members. Since all structural elements are subject to some degree of restraint, drying shrinkage is regarded to be one of the main causes of concrete cracking. The purpose of the present study was to evaluate the effectiveness of SRA in reducing drying shrinkage strain in Portland pozzolan cement concrete. The major variables examined included slump, admixture type and dose, and specimen size. The measured results indicate that any of the admixtures used in the study significantly reduced shrinkage. Concrete manufactured with shrinkage reducing admixtures shrank an average of 43% less than concrete without admixtures. As a rule, the higher the dose of admixture, the higher was its shrinkage reduction performance. The experimental results were compared to the shrinkage strain estimated with the ACI 209, CEB MC 90, B3, GL 2000, Sakata 1993 and Sakata 2001 models. Although none of these models was observed to accurately describe the behaviour of Portland pozzolan cement concrete with shrinkage reducing admixtures, the Sakata 2001 model, with a weighted coefficient of variation of under 30%, may be regarded to be roughly adequate.