Workability Of Fresh Concrete Research Articles

RETRACTED: Assessment of the effects of Fe2O3 nanoparticles on water permeability, workability, and setting time of concrete

The purpose of this study is to investigate the percentage of water absorption, velocity of water absorption, coefficient of water absorption, workability, and setting time of binary blended concrete with partial replacement of cement by 0.5, 1.0, 1.5, and 2.0 wt.% of Fe2O3 nanoparticles. The results showed that using Fe2O3 nanoparticles up to maximum replacement of 2.0% produces concrete with improved resistant to water permeability. Fe 2O3 nanoparticles can improve the filler effect and also the high pozzolanic action of fine particles increases substantially the quantity of C—F—H gel. If this phenomenon joints with low water-to-cement ratio, it can improve the microstructure in the interfacial transition zones and thus the value of C—F—H gel results in decreasing the water permeability. The results also show that the workability and setting time of fresh concrete were decreased by increasing the content of Fe2O 3 nanoparticles.

The composite effect of steel fibres and stirrups on the shear behaviour of beams using self-consolidating concrete

Based on the investigation of the influence of steel fibre on the workability of fresh self-consolidating concrete (SCC), this paper presents the experimental results carried out on a series of simply supported SCC rectangular beams, using steel fiber reinforcement with and without stirrups, and subjected to four-point symmetrically placed vertical loads. The major test variables are the steel fibre content and stirrup ratios. The current study on the shear strength of conventional reinforced concrete (RC) beams verifies the shear strength of SCC beams with steel fibres. The investigation indicates that the shear strength significantly increases by increasing the fibre content; the addition of steel fibres in an adequate percentage can change the failure mode from a brittle shear collapse into a ductile flexural mechanism. The stirrups can be partially replaced by steel fibres. The combination of steel fibres and stirrups demonstrates a positive composite effect on the mechanical behaviour. The shear strength recorded experimentally is compared with the value obtained from the proposed formula, and the correlation is satisfactory.

Effects of Ultra-Fine Limestone Powder on Workability and Strength of High Strength Concrete

With the increasing demand for high strength concrete, more attention has been paid to the problem of high viscosity mixture in high strength concrete technology by academic and engineering circles. This project studied the effects of ultra-fine limestone powder on the workability and viscosity of fresh concrete using the ultra-fine limestone powder (LP) obtained by ultra-fine grinding of limestone powder, building sandstone processing waste, as fine mineral admixture of high strength concrete. The experimental results show that the viscosity of fresh high strength concrete with ultra-fine limestone powder decreases significantly. At the same time, the influence of ultra-fine limestone powder on the strength of the concrete at different ages is very little.

굳지 않은 경량골재 콘크리트의 공기량, 유동성 및 블리딩 특성

굳지 않은 경량골재 콘크리트의 다양한 특성에 대한 경량굵은골재 최대크기와 천연모래 치환율의 영향을 평가하기 위해 15배합의 경량골재 콘크리트가 배합되었다. 또한 굳지 않은 경량골재 콘크리트의 유동특성에 영향을 줄 수 있는 경량골재의 내부구조와 공극의 분포 및 시간에 따른 흡수 특성 등이 측정되었다. 실험 결과 경량골재 콘크리트의 초기 슬럼프는 천연 모래 치환율이 증가할수록 감소하였으며, 전경량 콘크리트의 슬럼프는 배합 후 30~60분 사이에 초기 슬럼프의 80%가 감소하였다. 경량골재 콘크리트의 공기량과 블리딩 량은 경량굵은골재 최대크기와 천연 모래 치환율에 중요한 영향을 받았다. 경험식인 ACI 211과 콘크리트표준시방서는 경량골재 콘크리트의 공기량을 과소평가 하였으며, 천연 모래 치환율의 감소할수록 그 과소평가 정도는 증가하였다. 이 연구에 의해 제안된 경량골재 콘크리트의 공기량과 블리딩율에 대한 예측모델은 실험 결과와 잘 일치하였다.

The durability properties of polypropylene fiber reinforced fly ash concrete

This paper reports of a comprehensive study on the durability properties of concrete containing polypropylene fiber and fly ash. Properties studied include unit weight and workability of fresh concrete, and compressive strength, modulus of elasticity, porosity, water absorption, sorptivity coefficient, drying shrinkage and freeze–thaw resistance of hardened concrete. Fly ash content used in concrete mixture was 0%, 15% and 30% in mass basis, and fiber volume fraction was 0%, 0.05%, 0.10% and 0.20% in volume basis. The laboratory results showed that inclusion of fly ash improves; however, polypropylene fiber decreases the workability of concrete. Moreover, polypropylene fiber addition, either into Portland cement concrete or fly ash concrete, did not improve the compressive strength and elastic modulus. The positive interactions between polypropylene fibers and fly ash lead to the lowest drying shrinkage of fibrous concrete with fly ash. Freeze–thaw resistance of polypropylene fiber concrete was found to slightly increase when compared to concrete without fibers. Moreover, fly ash increased the freeze–thaw resistance more than the polypropylene fibers did.

Application of numerical analysis for investigating the relationship between slump values and other rheological properties of fresh concrete

The main concern in working with fresh concrete is the workability during filling of formwork. In this study, the mechanism of segregation during the filling of fresh concrete into formwork is numerically investigated considering the rheological properties of fresh concrete. A mathematical model, which considers fresh concrete as a non-Newtonian fluid that, is used for the investigation of relationship between slump values and rheological properties of fresh concrete. The aggregates are considered as Lagrangian particles whose trajectories determine segregation. This study will provide an insight to the relationships between workability and various rheological parameters of fresh concrete that is, yield stress, segregation, viscosity during filling of fresh concrete into formwork. The relationships between workability and rheological properties during the fill of fresh concrete for both concrete mixtures with no admixtures (MC) and concrete mixtures with admixtures (MCS) are investigated. MCS concrete mixture includes super-plasticizers for the same composition of MC. Cylindrical formworks for three different heights of 50, 100 and 150 cm are employed. It is observed that MCS mixtures have higher slump values and less aggregate segregation (%) compared to MC mixtures for the same compositions of fresh concrete. It is found that, slump values decrease as yield stress increases for both MC and MCS fresh concrete mixtures. When MCS mixtures are used, there is a significant reduction in yield stress compared to MC mixtures. Key words: Non-Newtonian fluid, workability, slump values, aggregate segregation, fresh concrete rheology.

Assessment of the effects of rice husk ash particle size on strength, water permeability and workability of binary blended concrete

This study develops the compressive strength, water permeability and workability of concrete by partial replacement of cement with agro-waste rice husk ash. Two types of rice husk ash with average particle size of 5 micron (ultra fine particles) and 95 micron and with four different contents of 5%, 10%, 15% and 20% by weight were used. Replacement of cement up to maximum of 15% and 20% respectively by 95 and 5 μm rice husk ash, produces concrete with improved strength. However, the ultimate strength of concrete was gained at 10% of cement replacement by ultra fine rice husk ash particles. Also the percentage, velocity and coefficient of water absorption significantly decreased with 10% cement replacement by ultra fine rice husk ash. Moreover, the workability of fresh concrete was remarkably improved by increasing the content of rice husk ash especially in the case of coarser size. It is concluded that partial replacement of cement with rice husk ash improves the compressive strength and workability of concrete and decreases its water permeability. In addition, decreasing rice husk ash average particle size provides a positive effect on the compressive strength and water permeability of hardened concrete but indicates adverse effect on the workability of fresh concrete.

Assessment of the recycling potential of fresh concrete waste using a factorial design of experiments

Recycling of industrial wastes and by-products can help reduce the cost of waste treatment prior to disposal and eventually preserve natural resources and energy. To assess the recycling potential of a given waste, it is important to select a tool capable of giving clear indications either way, with the least time and work consumption, as is the case of modelling the system properties using the results obtained from statistical design of experiments. In this work, the aggregate reclaimed from the mud that results from washout and cleaning operations of fresh concrete mixer trucks (fresh concrete waste, FCW) was recycled into new concrete with various water/cement ratios, as replacement of natural fine aggregates. A 3(2) factorial design of experiments was used to model fresh concrete consistency index and hardened concrete water absorption and 7- and 28-day compressive strength, as functions of FCW content and water/cement ratio, and the resulting regression equations and contour plots were validated with confirmation experiments. The results showed that the fresh concrete workability worsened with the increase in FCW content but the water absorption (5-10 wt.%), 7-day compressive strength (26-36 MPa) and 28-day compressive strength (32-44 MPa) remained within the specified ranges, thus demonstrating that the aggregate reclaimed from FCW can be recycled into new concrete mixtures with lower natural aggregate content.

Influence of MB-value of manufactured sand on the shrinkage and cracking of high strength concrete

The relation between methylene blue (MB) value of MS and its limestone dust content and clay content was investigated. The effects of MB value ranging from 0.35 to 2.5 on the workability of fresh concrete and crack propagation characteristics at the age of 24 hours, and effects on the mechanical properties, dry shrinkage of the harden concrete were tested. The experimental results show that the MB value is not related with the limestone dust content of MS, but in direct proportion to clay content. With the increase of MB value, the concrete workability decreases, and the flexural strength and 7 d compressive strength reduce markedly, whearas the 28 d compressive strength is not affected. When the MB-value is less than or equal to 1.35, the change of the MB-value has a little influence on early plastic cracking and dry shrinkage property of concrete, but when the MB-value is more than 1.35, the tendency of plastic cracking and dry shrinkage is remarkable.

“Effect of Magnetic Water on Engineering Properties of Concrete”

mail: - E Abstract This research investigates the influence of magnetic water on compressive strength and workability (consistence) of concrete. Results show that the compressive strength of concrete samples prepared with magnetic water increases 10-20% more than that of the tap water samples. In the present study, increasing in compressive strength of concrete is achieved when the magnetic strength of water is 1.2 T, and velocity of water current that passes through magnetic field is of 0.71 m/s. It is also found that magnetic water improves the workability (consistency) of fresh concrete.

Advances in Research on Correlation of Workability and Rheology of Fresh Concrete: A Review

A literature review was carried out to identify advances in research on workability of fresh concrete via both experimental tests and modeling, especially high performance concrete and self-compacting concrete. It is concluded that, in order to achieve better understanding of fresh concrete, especially self-compacting concrete (SCC) and high-performance concrete (HPC), a clear methodology of research should be established as the first step. It is suggested that there is no unique workability test method suitable for all the range of fluidity of fresh concrete, and a specific method should be identified for a proper range of fluidity. As to the relationship between fluidity of concrete and that of paste, future research can be conducted in two aspects, i.e. one is the influence of the quantity of paste in concrete, and another is the influence of fluidity of paste affected by a couple of factors.

Advances in Research on Influence of Raw Materials on Workability of Fresh Concrete: A Review

A literature review was carried out to identify advances in research on workability of fresh concrete via both experimental tests and modeling, especially high performance concrete and self-compacting concrete. As to the relationship between fluidity of concrete and that of paste, future research can be conducted in two aspects, i.e. one is the influence of the quantity of paste in concrete, and another is the influence of fluidity of paste affected by a couple of factors. Most literature proved that the flow of concrete depends both on positive effect and negative effect, the former promote fluidity, such as dispersing, filling and lubricating, and the latter restricts fluidity, such as formation of particle coagulation, an increase of wettable surface of solid particles and mechanical interlock.

Properties of concrete made with recycled epoxy/glass particles

This paper is aimed at evaluating the properties and effectiveness of concretes containing recycled epoxy/glass (EG) particles, which were chopped and grounded waste copper‐clad laminates or printed circuit board scrap. Recycled EG particles are divided into two portions according to their size: a substitutive material for natural fine aggregate and ultra fine filler, according to the particle size of 150 μm. The percentages of EG particles substituted for natural fine aggregate for the control mix were 10, 20, and 30 wt.% by considering suitable workability. Concrete strength can be significantly improved with EG particles due to the filling effect of ultra fine particles. However, as the substitute percentage of EG particles increases, the slump of fresh concrete drops and low workability is observed in the mixes with 30% EG particle even though superplasticizer is applied. Resistivity increases and absorption decreases as the percentage of fine EG particles substituted increases. The weight loss from sulfate immersion test reduces with the use of EG particles. Test results indicate that the proper application of EG particles would effectively modify the pore system, reduce permeability, and inhibit ions penetration in concrete. By considering the saving of land‐fill disposal cost of waste epoxy and glass fiber scraps, enhancement of concrete properties, non‐toxic waste leaching, and raw materials cost reduction, the effective utilization of recycled EG particles in concrete would be successfully achieved.

DEVELOPMENT OF LOW-ALKALINE CEMENT USING POZZOLANS FOR GEOLOGICAL DISPOSAL OF LONG-LIVED RADIOACTIVE WASTE

To reduce uncertainties in the safety assessment of the disposal system for long-lived radioactive waste, cement was developed which generates leachates with a lower pH than that of ordinary cement paste. This cement is termed “low-alkaline cement”. Large amounts of pozzolans were used to produce the low-alkaline cement with ordinary Portland cement. Silica fume was found to be an effective pozzolans to reduce pH, but the needed large amount of silica fume reduced the workability of fresh concrete. Therefore, the authors also used fly ash with silica fume, to develop more workable low-alkaline cement, termed high-volume fly ash silica fume cement (HFSC). Two types of HFSC developed showed high compressive strength, smaller drying shrinkage and lower temperature rise than that of ordinary Portland cement. It was confirmed that HFSC could be used as self-compacting concrete. Therefore they can be applied as either structural or backfilling concrete in the disposal system.

Properties of steel fiber reinforced fly ash concrete

This paper reports on a comprehensive study on the properties of concrete containing fly ash and steel fibers. Properties studied include unit weight and workability of fresh concrete, and compressive strength, flexural tensile strength, splitting tensile strength, elasticity modulus, sorptivity coefficient, drying shrinkage and freeze–thaw resistance of hardened concrete. Fly ash content used was 0%, 15% and 30% in mass basis, and fiber volume fraction was 0%, 0.25%, 0.5%, 1.0% and 1.5% in volume basis. The laboratory results showed that steel fiber addition, either into Portland cement concrete or fly ash concrete, improve the tensile strength properties, drying shrinkage and freeze–thaw resistance. However, it reduced workability and increase sorptivity coefficient. Although fly ash replacement reduce strength properties, it improves workability, reduces drying shrinkage and increases freeze–thaw resistance of steel fiber reinforced concrete. The performed experiments show that the behaviour of fly ash concrete is similar to that of Portland cement concrete when fly ash is added.

Effect of chemical structure of polycarboxylate-based superplasticizers on workability retention of self-compacting concrete

In self-compacting concrete (SCC) mixture design, polycarboxylate-based superplasticizers (PC-based SPs) usually guarantee the initial workability. However, the time dependent workability of mixtures principally depends on the chemical structure of PC-based SPs and its compatibility with cement. PC-based SPs are the copolymers of chemical structures, which have the potential to be modified to improve their performances. In this study, three synthetic PC-based SPs were synthesized by using radical polymerisation techniques. The effect of these admixtures on setting time of cement pastes and time dependent workability and strength development of SCCs were investigated, respectively. Test results showed that, from the viewpoint of chemical structure, workability retention performance of PC-based SPs could be manipulated by modifying the bond structure between main backbone and side-chain of copolymer. PC-based SPs with ester bonding was not effective in maintaining fresh concrete workability due to the alkali attack vulnerability of this bond structure. On the other hand, by directly bonding the polyoxyethylene side-chain to the backbone of copolymer, fresh SCCs workability can be effectively maintained at least for a period of 2 h. It should be noted that, in addition to the SP type, water/powder ratios of SCC mixtures were also responsible for the long workability retention performances. Best results were derived from mixtures incorporating 2.3 wt% of P3 type SP. However, some lengthening in setting times and reduction in early strength should also be expected.

Measurement of Workability of Fresh Concrete Using a Mixing Truck.

The main objective of this study is to evaluate the workability of fresh portland cement concrete while it is still in the mixing truck by determining fundamental rheological parameters (plastic viscosity and yield stress). Nine concrete mixtures with different values of yield stress and plastic viscosity were tested in a concrete truck. The measurements made with the truck were based on the typical method of determining the flow behavior in a traditional fluid rheometer; that is, the shear rate in the mixing truck was swept from high to low by varying the rotation speed of the drum. The results of these experiments are discussed and compared with data provided by the ICAR rheometer, a portable rheometer designed for measuring concrete rheology. The test results indicate that the mixing truck equipment is sufficiently sensitive to detect differences in yield stress, slump, and plastic viscosity. However, the plastic viscosity determined by the truck measurement did not correlate with plastic viscosity as measured by the ICAR rheometer, while the yield stress determined by the truck measurement did correlate well with the measured slump and the ICAR rheometer resultsSuggestions are given on how to improve the mixing truck for better use as a rheometer.

Effect of corrosion inhibiting admixtures on concrete properties

The effect of different corrosion inhibiting admixtures on concrete properties is investigated experimentally. Two reference concretes are considered, based on Portland cement, resp., blast furnace slag cement. The effect of four different corrosion inhibiting admixtures is evaluated: a calcium nitrite-based inhibitor, an amino and ester-based organic inhibitor, a aminoalcohol-based inhibitor and a migrating corrosion inhibitor. The properties of the fresh concrete (density, workability and air content) and of the hardened concrete (compressive strength, bending tensile strength, splitting tensile strength and Young's modulus) are evaluated. The obtained results are compared with findings reported in the literature. Some general influences of the different types of corrosion inhibitor admixtures are deduced.

The effects of gradation and admixture on the pumice lightweight aggregate concrete

The usage of lightweight concrete, which has some advantage over ordinary concrete, has increased to a remarkable level in recent years. Many researchers have investigated the possible uses of lightweight concrete in terms of its strength, density and other mechanical and physical properties. The desired quality for lightweight concrete can be obtained through the proper selection of admixtures and proper grading of the lightweight aggregate. In this article, an experimental investigation on the production of moderate-strength lightweight concrete with pumice, according to the ACI standard, is presented. The gradation curves' (which fall within A16–C16 gradation curves, Turkish Standard Code, TS706) performances were investigated in terms of strength and density. The addition of superplasticizer and air-entraining admixtures improved the strength-to-density ratio of the hardened concrete and the workability of fresh concrete. As a result of this study, lightweight concrete blocks having a minimum compressive strength of 6.56 N/mm 2 and a density of 1300 kg/m 3 were obtained.

フレッシュコンクリートの施工性能に関する技術の現状と問題点

フレッシュコンクリートの施工性能に関する技術の現状と問題点