Low Slump Research Articles

Power Performance of AlGaN/GaN High‐Electron‐Mobility Transistors with AlN Buffer on SiC Substrate at 3.5 GHz

Herein, a 3.5 GHz (S‐band) power performance is reported on an AlGaN/GaN high‐electron‐mobility transistor (HEMT) with AlN buffer on SiC substrate. A 4 inch epi‐wafer is grown by high‐temperature metal–organic chemical vapor deposition. The fabricated devices with a 400 nm gate and direct current and radio‐frequency (RF) characteristics are examined. These device shows a transconductance of 233 mS mm−1and a maximum drain current of 820 mA mm−1. The pulsed current–voltage (I–V) characteristic shows a low slump ratio with a 0.36% and 2.2% forZ1andZ2, respectively. The power performance shows output power = 5.5 W mm−1with 54.3% power added efficiency, and VDSwas 50 V. The potential of an AlN buffer HEMT is demonstrated by the results for use in next‐generation high‐power RF devices.

Concrete with Coconut Fibre Treated with Sodium Hypochlorite – Compressive and Flexural Strength

Concrete needs to be reinforced to improve its engineering qualities. Coconut fibres were employed for this study since they are widely accessible and come in big numbers. The study compares the qualities of plain concrete and concrete reinforced with coconut fibre based on a laboratory experiment. Better management of these waste fibres will result from using coconut fibres. Two types of coconut fibre treatment were employed – treatment with tap water and treatment with sodium hypochlorite. It is found in this study that adding 1% of coconut fibre does not increase the concrete strength after 7 and 14 days of curing. However, it was discovered that using 1% coconut fibres treated using tap water increased the compressive and flexural strength of the concrete after 28 days of curing by roughly 4% and 3%, respectively. Compressive and flexural strength development agrees very well with each other. Hence, it is concluded that 1% was the ideal fibre concentration (by weight of cement) to obtain a better 28th day of compressive and flexural strength, although not for 7 and 14 days. However, concrete with the highest strengths demonstrated a very low slump value, only 20 mm. A smaller or bigger slump value showed smaller concrete strengths.

Performance evaluation of alkali activated slag based recycled aggregate pervious concrete

The present study attempts, a detailed evaluation of the strength performance of Alkali Activated Slag based Pervious Concrete (AASPC) mixes, containing fly ash and ground granulated blast furnace slag (GGBS) as binders. Fly ash and GGBS, by-product obtained from thermal power plants and steel industries respectively, is incorporated in the AASPC mixes as a full replacement to ordinary Portland cement (OPC). Initially OPC and AASPC mixes are designed to obtain M30 grade. OPC based pervious concrete is considered as control concrete. Pervious concrete is a type of concrete that has a high-water permeability and a higher void content than regular concrete.Experiments investigates the effect of the addition of Recycled Coarse Aggregate (RCA) on the physical and mechanical properties of alkali activated pervious concrete. Certain physical test has been conducted on recycled coarse aggregate to check the quality of aggregates, RCA varying percentage in 0, 25, 50, 75 and 100%, in the mixes. All mixes of alkali activated pervious concrete includes 50% of GGBS and 50% of fly ash from total binder content. Alkali activators used are, sodium hydroxide pellets and sodium silicate liquid. Workability of the alkali activated pervious concrete has a low slump value compare to the control concrete, but the workability of pervious concrete with cement is equal to alkali activated pervious concrete and workability will decreases with increase in RCA percentage because has a high capacity of water absorption. Compressive strength of alkali activated pervious concrete has increased by 23% compared to the OPC based pervious concrete and then there will be a decrease in compressive strength with increase in RCA percentage. The flexural strength and split tensile strength results for both the alkali activated pervious concrete and OPC based concrete shows almost similar values. Permeability and void ratio results shown increase with increase in RCA percentage in AASPC.

Direct ink writing of reinforced polydimethylsiloxane elastomer composites for flexure sensors

AbstractFlexible materials with ideally designed structures and properties through direct ink writing (DIW) offer vast potential for flexible wearable devices, sensors, soft robots, and so on. Despite its common use as a flexible material, Sylgard‐184's poor rheological properties restrict its ability of printing precision models by DIW. Herein, we have improved the viscosity of Sylgard‐184 by adding suitable crosslinkers and silica, which produce inks with high printing quality and a low slump rate (3.75%). In addition, the DIW printing process was investigated, and a theoretical model relating to the basic printing parameters was developed. With the model, it is possible to predict printing parameters for various elastomers. To further demonstrate the application of this strategy to flexible wearable devices, a sensor was printed. The sensor allowed real‐time monitoring of bending angles through bending angle tests. A change from 0 to 135° was detected using this bending sensor. We believe that the results of this research will provide ideas for the high‐quality printing of silicone elastomers.

Effects of Kenaf Fibre on Fresh Properties of Fibrous Concrete

As a result of global quest for sustainable materials to achieve a bio based economy and low carbon foot print environment, the use of fibre to produce fibrous concrete composite has continuously received significant research attention. While several researches have been conducted on metallic and synthetic fibrous concretes, they exhibit several unavoidable drawbacks and bio fibrous concrete has proven to be a better alternative. Therefore, the effect of fibre volume fraction and fibre length on fresh properties of concrete was investigated. The bio fibrous concrete mix was made of six different fibre volume fractions (0.25%, 0.5%, 0.75%, 1%, 1.5% and 2%) and corresponding three different fibre lengths of 25 mm, 50 mm and 75 mm. A concrete mix proportion of grade 30 N/mm2 at 28 days target strength was prepared. A total of 19 different concrete mixes comprising of one PC mix was the control for the experiment, and 18 different mixes of Kenaf bio fibrous concrete composite (KBFCC) at varying fibre volume fraction (vf) and fibre length (lf) were tested. These mixes were tested for workability (slump, compacting factor and Vebe test) and fresh density. The slump and Vebe time for KBFCCs were 5–100 mm and 3–79 seconds respectively. The slump and Vebe time for PC were 120 mm and 3 seconds respectively. A significant drop from 0.951 to 0.809 for fibre length of 25 mm, 0.947 to 0.799 for fibre length of 50 mm and 0.931 to 0.793 for fibre length of 75 mm was observed for the compacting factor value. Though, KBFCC with fibre content below 1% was workable in spite of its low slump, its high Vebe time and low compacting factor. For fibre volume of 1% and above, the workability of concrete decreased and became very stiff with balling effect. It was seen that fresh density of PC concrete (2358 kg/m3) was higher compared to those of KBFCC (2105-2339 kg/m3), however, both values were lower than 2400 kg/m3 threshold specified by the BS code of practice. The study therefore recommended that fibre contents lesser than 1% and 50 mm length can be used in order to have good fresh properties performance.

Interaction of magnetic water and polypropylene fiber on fresh and hardened properties of concrete

Utilizing fibers is an effective way to avoid the brittle behavior of the conventional concrete and can enhance its ductility. In particular, propylene fibers can improve concrete properties, including energy absorption, physical and mechanical properties, controlling shrinkage cracks. The increase of fiber density leads to an increase of the overlapping surface of the fiber of concrete and, in turn, a decrease of cracks developed in the concrete. However, the workability of fiber reinforced concrete tends to be lower than the conventional concrete owing mainly to the hairline thickness and excessive concentration of fibers. The low slump of concrete impedes the construction of reinforced concrete members. In this research, we study if the utilization of magnetic water can alleviate the workability issue of young fiber reinforced concrete. To this end, the compressive and flexural strength of four types of concrete (conventional concrete, fiber reinforced concrete, magnetic concrete, magnetic fiber-reinforced concrete) is studied and compared at three different ages of 7, 14, and 28 days. In order to study the influence of the fiber density and length, a study on specimens with three different fiber density (1, 2, 5 kg of fiber in each cubic meter of concrete) and fiber length (6, 12, 18 mm) is undertaken. The result shows the magnetic fiber concrete can result in an increase of the flexural and compressive strength of concrete at higher ages.

Bond strength and chloride resistance of epoxy and concrete overlays on bridge decks

ABSTRACT The deteriorating condition of infrastructure, combined with fiscal limitations experienced by many agencies, necessitates increased service life of bridges. Maintenance and preservation methods such as overlays and sealers have been known to protect bridge decks from deterioration, while also extending a bridge’s service life. It is important to understand the characteristics of various overlay types to make informed maintenance decisions, thus assessing and comparing the performance of thin epoxy overlays and low slump dense concrete (LSDC) overlays is desirable. To evaluate the performance of these two overlay types, the chloride resistance and long-term bond strength of the overlays were assessed. Three bridges were chosen to install each overlay type, with corresponding field and laboratory evaluations performed. The above tests results indicated that the initial bond strength of both overlays is good, but that the thin epoxy overlays showed decreased performance after 300 F/T cycles. The bond performance of the LSDC remain unchanged for the duration of the freeze–thaw testing, indicating superior long-term performance. As expected, the epoxy overlay performed much better than the LSDC overlay with respect to chloride resistance. These performance metrics are important to keep in mind when selecting maintenance and rehabilitation methods for bridges.

The Application of Electrical Parameters to Reflect the Hydration Process of Cement Paste with Rice Husk Ash.

This paper aims to study the electrical parameters (electrical resistivity and alternating current (AC) impedance spectroscopy) of cement paste with rice husk ash (RHA). The water to cement (Mass ratio of water to cement (w/c)) ratios of the paste in this study varied from 0.4 to 0.5. The mass ratio of rice husk ash in each w/c ratio of specimens ranged from 0% to 15% by t mass of cement. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to determine the microstructures of specimens. Moreover, the slump flow and plastic viscosity of fresh paste were determined. The results indicated that with the increasing dosage of RHA, the fluidity decreased, while the plastic viscosity increased. Meanwhile, a high w/c ratio led to a low plastic viscosity and high slump flow. The electrical resistivity of RHA cement paste gradually ascended with the increasing curing period. The conduction of specimens intricately changed by mixing RHA, a reasonable equivalent circuit was selected to describe the conduction mechanism by AC impedance spectroscopy. Additionally, the results of XRD and SEM showed that RHA could effectively promote the hydration process as well as decrease the size and number of cracks in hardened cement paste.

Bleeding characteristics of high consistency heavyweight concrete mixtures

Bleeding, a type of static segregation derives from density difference of concrete ingredients in fresh state. Due to having this difference higher than normal weight counterparts, heavyweight concrete is more susceptible to bleeding, thus, this type of concrete is commonly produced in low slump values. In order to give a response to advances and demands in concrete technology, heavyweight concrete mixtures with high slump values were designed at various mixture characteristics, and their bleeding characteristics were researched in the study. For this purpose, totally, thirty-five concrete mixtures with ≥150 mm slump values were produced by using common cement replacement materials (silica fume and fly ash), viscosity modifier, and various water/binder ratios at two binder dosages. The mixtures showed excessive bleeding capacities ranged from 0 to 11.7% and bleeding rates ranged from 0 to 5.1 kg/m2/h. Silica fume was found as the most effective admixture for reducing or elimination of the bleeding. Bleeding time generally shorten at high binder content and at high water/binder ratio. It was observed that the bleeding adversely affects the hardened characteristics of heavyweight concrete mixtures.

Investigation on applicability of spherical shaped EAF slag fine aggregate in pavement concrete – Fundamental and durability properties

Electric Arc Furnace oxidizing slag (EAF slag) is a steel manufacturing byproduct. Recently, due to the adoption of new production method, spherical shaped EAF slag has been produced and applicability of this material in concrete requires to be investigated. EAF slag possesses the characteristic property of high density. Moreover, lesser water is required when spherical shaped EAF slag is used in concrete. Considering these characteristics, there is high possibility to apply spherical shaped EAF slag in concrete pavement which requires low slump and high flexural strength. In this experimental study, concrete specimens were casted by replacing sand with spherical and angular shaped EAF slag at a volume ratio of 0.0, 0.3, 0.5 and 1.0 for the water to cement ratio (W/C) and slump of 0.4 and 5 cm respectively. Fresh behavior such as slump, air content, fresh density and bleeding of casted concrete were measured and mechanical and durability properties of casted specimens were tested after the curing age of 3, 7 and 28 days. Results show that both spherical and angular EAF slag have a positive effect on the mechanical properties of concrete. In addition, spherical EAF slag concrete showed improved fresh and durability properties.

Self-Consolidating Paving Grade Geopolymer Concrete

The cement concrete used in the construction of rigid pavement is usually stiff mix with a low slump. The concrete of this type requires a high degree of compaction which is achieved employing needle vibration or roller compaction technique in the field. The vibration technique may sometime leave vibratory trails, and roller compaction concrete produces over or under consolidated concrete, and both methods are also known to be energy intensive. This issues can be overcome by the adoption of self-consolidating concrete for the construction of rigid pavement. However, the self-consolidating paving technique is an uncommon scenario. In this connection, an attempt was made produce a self-consolidating geo-polymer concrete. This paper presents an investigation carried on the novel geo-polymer concrete which is self-consolidating, sustainable and can be espoused for fixed form paving application. The geo-polymer concrete mix used for the study was prepared from class F fly-ash, GGBS, alkaline solution (NaOH and Na2SiO3), coarse aggregate and quarry dust as fine aggregate. The mix was designed to cure at ambient condition and possess a target compressive strength of 40 MPa. The properties of concrete during paste phase and hardened state were investigated and the results of the tests are presented and discussed here. Also reported here are the results of flexural strength test performed on beams sliced out from the micro slabs, which ascertained the self-consolidation of the geo-polymer concrete mix.

Using silica mineral waste as aggregate in a green high strength concrete: workability, strength, failure mode, and morphology assessment

ABSTRACTEnvironmental degradation is a major challenge in the developing countries, which are caused due to unmanaged solid waste, or improper disposal. This study investigates the effect of using silica mineral waste (eco sand) as aggregate in a green high strength concrete, in which properties such as workability, strength, failure mode, and morphology were determined. There was low slump and compacting factor in all the concrete mixtures, however, strength properties were improved with the incorporation of eco sand as a replacement of conventional fine aggregate. Higher strength properties were achieved in the eco sand concrete than the reference mixtures, which occurred at an optimum eco sand content of 25%. The morphology and failure mode of the eco sand concrete showed that there was a significant compactness and constituents parking in the matrix.

Influence of thixotropy determined by different test methods on formwork pressure of self-consolidating concrete

In this experimental study, the influence of thixotropy determined by different test methods on the formwork pressure of self-consolidating concrete (SCC) with varying compositions was investigated. In order to determine the effect of water/binder (w/b) ratio, slump flow diameter and coarse aggregate/total aggregate (CA/TA) ratio on thixotropy and formwork pressure of SCC, fifteen concrete mixtures were prepared. Four different test methods i.e., “structural break-down area” (SBDA), “break-down percentage” (BDP), “drop in apparent viscosity” (DAV) and “yield value at rest” (YVR) were performed to determine the thixotropy of the SCC mixtures. Test results showed that the SBDA, DAV and YVR methods were more appropriate to evaluate the thixotropy of SCC than the BDP method. A strong correlation between thixotropy and formwork pressure was found using SBDA, DAV and YVR methods in SCC mixtures having low w/b ratio. There was a strong relationship between thixotropy determined by SBDA, BDP and DAV methods and formwork pressure in low slump flow SCC mixtures, while thixotropy determined by the YVR method showed good correlation with the formwork pressure in SCC mixtures having high slump flow values. Finally, new models were developed to estimate the formwork pressure of all kinds of mixtures as a function of thixotropy and time. The models were found to be successful for each of the thixotropy measurement method.

Application of Polycarboxylate Superplasticizer in the Concrete

Compared with the traditional water reducer, polycarboxylicwater-reducing agent exhibits the advantages of high water-reducing rate, cement paste fluidity and low slump loss, etc. The structure of polycarboxylates water reducing agent molecular is comb type. Water reducing agent can be used in the molecular design because it has high water reducing rate, low dosage, good slump stability, and have great potential in increase strength. In recent years, it has attracted many researchers' attention. Water reducing agent can block or destroy cement granular flocculation structure, through the surface function, complexation, electrostatic repulsion force and stereo repulsive force. Research on water reducing agent based on the application of poly carboxylic acid can realize functional design of water reducing agent, so as to promote the development of high-performance concrete.

Rheological study of cement paste with metakaolin and/or limestone filler using Mixture Design of Experiments

Several cement pastes with different amounts of metakaolin (MK) and/or limestone filler (LF) were prepared. The water/cementitious materials ratio was maintained constant at 0.3, with addition of 0.5%wt/wt of poly-carboxylate ether (PCE) superplasticizer admixture. The following parameters of the fresh cement pastes were evaluated: the slump and spread, the Marsh funnel time, the plastic viscosity, yield stress, viscoelastic properties and thixotropy. After the curing of 7day old pastes, compressive strength tests were performed according to the Brazilian standard using 50×100mm cylinder specimens. We conclude that LF alone is not able to avoid segregation or bleeding, and there is no difference between cement pastes mixed with LF and pure OPC pastes, in terms of rheology. On the other hand, if one needs low slump and low spread, the use of MK is recommended because this material creates a strong, thixotropic interconnected net inside of the paste, increasing the yield stress and the thixotropy of the cement paste. By adding 5–10%wt/wt MK, the average increase of compressive strength is approximately 45% at 7days, compared to the control (only OPC, water and PCE). The maximum recommended amount of LF or MK substitution in our case was 10%wt.

Effect on Workability of Concrete due to Partial Replacement of Natural Sand with Gold Mine Tailings

Objective: Availability of fine aggregates in its natural form is becoming very scarce. It is becoming a challenging task to meet the demand for fine aggregates in its natural form without exploiting the natural resources. To sustain the construction activity, it becomes very essential to explore the possibility of utilizing alternative materials for fine aggregates. Large quantity of inorganic industrial waste is generated annually. Coal mine wastes, blast furnaces lag, iron ore tailings, red mud, zinc tailings, goldmine tailings etc., are some of the inorganic waste products that are generated. Methods/Statistical Analysis: In this investigation, an attempt is made to replace partially naturals and with gold mine tailings and study the behavior of concrete in the green state. Mix proportion for M25 concrete was obtained as per IS: 10262 guidelines, for normal concrete and concrete containing gold mine tailings as fine aggregates. Findings: Natural fine aggregates were replaced with 10%, 20% and 30% goldmine tailings on weight basis. In all five mixes were obtained and workability studies in the form of slump and compaction factor test were carried out. The slump for normal concrete was 84.33 mm and that for concrete containing gold mine tailings was 16.33 mm. The low slump for concrete containing gold mine tailings alone may be attributed to the presence of fine particles. The slump values for 10%, 20% and 30% replacement levels are 63.6 mm, 44.33 mm and 22.6mm respectively. Similar behavior is observed in the case of compaction factor test also. The decrease in the workability of concrete may be attributed to the increase in the fineness of resulting fine aggregates. Applications/ Improvements: The application of the gold mine tailing in the high scale structures and reduce cement by GMT.

해안제방 시공 중 해수유입에 대한 차수보강 사례분석

In this study, the causes and countermeasures for the leakage of a sea dyke under construction are analyzed. In general, the seabed ground is clearly divided from the embankment but a lot of parts show abnormal zones with low resistivity from the results of electric resistivity survey. Hence the causes of the leakage are considered as following: three-dimensional shear strain behavior, irregular compulsory replacement of the soft seabed ground with low strength and quality deterioration of the waterproof sheets during the closing process. The improvement method is determined by considering the constructability in the seawater and its velocity condition, durability, economic feasibility, similar application cases and so on. Consequently, a combination of low slump mortar and slurry grouting and injection method is selected as an optimum combination. Mixing ratio and improvement pattern are determined after drilling investigation and pilot test. The improvement boundary is separated into general and intense leakage area. The construction is performed with each pattern and the improvement effects are confirmed. The confirmed effects with various tests after completion show tolerable ranges for all of the established standards. Finally, various issues such as prediction of length of the waterproof sheet, installation of it against seawater velocity, etc. should be considered when sea dykes are designed or executed around the western sea which has high tide difference.

프리스트레스트 중공 슬래브와 현장타설된 토핑콘크리트의 수평전단성능 평가

Prestressed hollow-core (PHC) slabs are structurally-optimized lightweight precast floor members for long-span concrete structures, which are widely used in construction markets. In Korea, the PHC slabs have been often used with cast-in-place (CIP) topping concrete as a composite slab system. However, the PHC slab members produced by extrusion method use concrete having very low slump, and it is very difficult to make sufficient roughness on the surface as well as to provide shear connectors. In this study, a large number of push-off tests was conducted to evaluate interfacial shear strengths between PHC slabs and CIP topping concrete with the key variable of surface roughness. In addition, the horizontal shear strengths specified in the various design codes were evaluated by comparing to the test results that were collected from literature.

Effect of Low Atmospheric Pressure on Air Content of Fresh Concrete

The effects of atmospheric pressure changes on the air entraining capability of air-entraining admixtures was 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 the normal atmospheric pressure (101 KPa). The air content of fresh concrete decrease linearly as atmospheric pressure dropped. The higher the air content of fresh concrete mixed in ordinary pressure, the faster the air content of fresh concrete decreases with the drop of air pressure. The concrete with high slump shows more resistance to drop of air-content due to low air pressure than the concrete with low slump. Therefore, in order to meet the design requirements of air content of air-entrained concrete for different constructions in the plateau regions, it is necessary to increase the dosages of air entraining agents to according to different pressure conditions and types of air-entraining agent.

Strength reduction factors for structural rubbercrete

Many researches have been carried out to study the fresh and hardened properties of concrete containing crumb rubber as replacement to fine aggregate by volume, yet there is no specific guideline has been developed on the mix design of the rubbercrete. The experimental program, which has been developed and reported in this paper, is designed and executed to provide such mix design guidelines. A total of 45 concrete mixes with three different water to cement ratio (0.41, 0.57 and 0.68) were cast and tested for fresh and mechanical properties of rubbercrete such as slump, air content, unit weight, compressive strength, flexural strength, splitting tensile strength and modulus of elasticity. Influence of mix design parameters such as percentage of crumb rubber replacement, cement content, water content, fine aggregate content, and coarse aggregate content were investigated. Three levels of slump value (for conventional concrete mixes) has been selected; low, medium and high slump. In each slump level, water content was kept constant. Equations for the reduction factors (RFs) for compressive strength, flexural strength, splitting tensile strength and modulus of elasticity have been developed. These RFs can be used to design rubbercrete mixes based on the conventional mix (0% crumb rubber content)