Effect of Low Mixing Speed on the Properties of Prolonged Mixed Concrete

The mixing process of concrete consists of dispersing the constituent ingredients (i.e. cement, admixtures, sand, and gravel) in water to homogeneous and solid product. The properties of the final product depend on mixing parameters such as mixing time and mixing speed. Ready Mixed Concrete (RMC) should be mixed for a long time with limited speed until delivered to the working site. This long time depends on long transport distances and traffic conditions. The present study investigated the effects of long mixing time on the properties of concrete without any change in its proportions during the mixing process and the effects of using the chemical admixtures: super plasticizers and retarders on its effectiveness, using a drum batch mixer. It has two directions of rotation: one for mixing concrete and the other for discharging it. This research identified concrete mixtures with local available materials i.e. cement, sand as fine aggregates, dolomite as coarse aggregates, water and chemical admixtures. Mixtures were prepared with the same cement and water content with constant sand to dolomite ratio with different dosages of chemical admixtures. Chemical admixtures were used to keep concrete flow during mixing. Mixtures were prepared with low mixing speed 1rpm for identified long mixing times more than 90 minutes from adding water to other components Slump and compressive tests were used as measurement tools of fresh and hardened concrete Retempering with extra water or chemical admixtures was prevented through mixing, so mixtures were extracted without target slump value. Findings showed that low mixing speeds made mixtures more effective for long times, the exceeding mixing time led to minimize water to cement ratio due to reduction of water content, and there was an inverse relationship between slump flow and compressive strength in case of no re-tempering. Therefore, slump flow of mixtures decreased by time, but on the other hand, compressive strength enhanced i.e. stiffening took place. The present study proved that the properties of the final product depends on mixing parameters such as mixing time and mixing speed, and that Ready Mixed Concrete (RMC) would be more effective if mixed for a long time with limited speed until transported to the work site. In addition, chemical admixtures with prolonged mixed concrete should be used to improve workability rather than compressive strength.

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Evaluations of All-in-One, Polycarboxylate-Based Superplasticizer with Viscosity Modifying Agents for the Application of Normal-Strength, High-Fluidity Concrete

Applied Sciences ◽

10.3390/app112311141 ◽

2021 ◽

Vol 11 (23) ◽

pp. 11141

Author(s):

Tae-Woong Kong ◽

Hyun-Min Yang ◽

Han-Seung Lee ◽

Chang-Bok Yoon

Keyword(s):

Compressive Strength ◽

Rheological Properties ◽

Yield Stress ◽

Lower Yield ◽

Lower Yield Stress ◽

Slump Flow ◽

Different Types ◽

Long Time ◽

Normal Strength ◽

Physical Phenomena

High fluidity concrete exhibits an excellent self-compacting property. However, the application of typical high-fluidity concrete is limited in the normal strength range (18~35 MPa) due to the large amount of binder. Therefore, it is important to solve these problems by adding a viscosity modifying agent (VMA) with a superplasticizer (PCE), which helps to improve the fluidity of the concrete. In addition, the rheology and stability of the concrete with VMA can be improved by preventing bleeding and segregation issues. Current studies focused on the physical phenomena of concrete such as the fluidity, rheological properties, and compressive strength of normal-strength, high-fluidity concrete (NSHFC) with different types of a polycarboxylate-based superplasticizer (NPCE). The obtained results suggested that the combinations of all-in-one polycarboxylate-based superplasticizers (NPCE) did not cause any cohesion or sedimentation even stored for a long time. The combination of three types of VMA showed the best fluidity (initial slump flow of 595~630 mm) without any segregation and bleeding, and the compressive strength at 28 days was also found to be the highest: 34–37 MPa. From these results, the combination of PCE (2.0%) + HPMC (0.3%) + WG (0.1%) + ST (0.1%) showed an 18% higher plastic viscosity and -4.4% lower yield stress than Plain.

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READY MIXED CONCRETE CONSTITUENT MATERIALS; PLASTICIZING CHEMICAL ADMIXTURES AND EFFECTS ON FRESH AND HARDENED PROPERTIES

Anadolu University Journal of Science and Technology-A Applied Sciences and Engineering ◽

10.18038/aubtda.439551 ◽

2018 ◽

pp. 1-1

Author(s):

Evren Arıöz ◽

Omer Arıöz

Keyword(s):

Chemical Admixtures ◽

Hardened Properties ◽

Ready Mixed Concrete ◽

Mixed Concrete

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Equipment Process of Online Testing Fresh Cement Concrete Rheology

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.857.259 ◽

2013 ◽

Vol 857 ◽

pp. 259-265

Author(s):

Shao Peng Zheng ◽

Bo Tian ◽

Rui Xuan Meng ◽

Rui Fang ◽

Zhi Hao Cheng

Keyword(s):

Compressive Strength ◽

Real Time ◽

Online Monitoring ◽

Mixing Time ◽

Online Testing ◽

Mixing Process ◽

Cement Concrete ◽

Stirring Time ◽

Concrete Mixer ◽

Time Acquisition

Transforming the cement concrete mixer, simulating twin-shaft mixing process on large mixing plant, adding real-time acquisition equipment of torque and speed, and achieving the online monitoring of concrete mixing process. The influences of speed and stirring time on the liquidity of fresh cement concrete was deliberated, so that it were analyzed from three indicators of concrete slump, stirring torque and compressive strength to determine the optimum stirring speed 48r/min, reasonable mixing time 40s ~ 50s, and mixing time less than 100s.

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The Rheological and Mechanical Performances of Concrete Manufactured with Blended Admixtures Based on Phosphonates

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.674.159 ◽

2016 ◽

Vol 674 ◽

pp. 159-164 ◽

Cited By ~ 11

Author(s):

Luigi Coppola ◽

Sergio Lorenzi ◽

Stefano Garlati ◽

Patricia Kara

Keyword(s):

Compressive Strength ◽

Concrete Strength ◽

Threshold Value ◽

Strength Gain ◽

Concrete Mixtures ◽

Flow Table ◽

Mechanical Performances ◽

Ready Mixed Concrete ◽

Compressive Tests ◽

Mixed Concrete

The paper deals with the effectiveness of blended phosphonate-based superplasticizers (PHN) for ready mixed concrete. Two phosphonates (PNH1 and PNH2) were added in different percentage to naphthalene sulphonate (NSF) or polycarboxylates (PCEs) based admixtures to improve both compatibility with different cements and workability retention of concrete. The performance of the obtained concrete mixtures was compared to concretes manufactured with the pure NSF or PCE based admixtures. Concretes with the same initial workability (flow table > 580mm) were produced at a temperature of 20 °C and 30 °C. Workability was measured at 0, 30 and 60 minutes to evaluate the flow retention performances of blended superplasticizers. Compressive tests were carried out to study the influence of the superplasticizer on concrete strength gain at the age of 1, 7 and 28 days. PNH1 in combination with NSF improved workability retention with respect to pure NSF, but caused a reduction in the early compressive strength when the dosage exceeded 0.10% (dry polymer vs. cement mass). Dosage of hybrid PCE-PNH superplasticizers to attain the targeted workability was lower with respect to hybrid PNH1/NSF admixtures. PNH1 was more effective than PNH2 in hybrid PCE admixtures in terms of workability retention. A threshold value for PNH dosage (about 0.18 - 0.20 %) exists also in hybrid PCE superplasticizers, but it is about two times higher than that of hybrid PNH1/NSF.

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A laboratory investigation for potential durability of ready-mixed concrete retempered for air content and workability

Canadian Journal of Civil Engineering ◽

10.1139/l76-061 ◽

1976 ◽

Vol 3 (4) ◽

pp. 570-577 ◽

Cited By ~ 2

Author(s):

B. W. Langan ◽

M. A. Ward

Keyword(s):

Compressive Strength ◽

Laboratory Investigation ◽

Hardened Concrete ◽

Air Content ◽

Spacing Factor ◽

Void System ◽

Air Void ◽

Ready Mixed Concrete ◽

Mixed Concrete

The effects of agitation and retempering on some properties of fresh and hardened concrete are considered.Data are presented on the influence of agitation and retempering with an air-entraining agent on the workability, compressive strength, and air void system in hardened concrete.The results indicate that although agitation reduces air content and increases the spacing factor, the original parameters can be regained by proper retempering. It is shown that any loss in compressive strength due to retempering is accompanied by an increase in potential durability due to the improvement of the air void system.

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Physical Characteristic of Ready Mixed Concrete with Different Replacement Ratio of Recycled Aggregate

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.26-28.345 ◽

2007 ◽

Vol 26-28 ◽

pp. 345-348 ◽

Cited By ~ 2

Author(s):

Seung Joe Yoon ◽

Soo Yeon Seo ◽

Woo Jin Lee

Keyword(s):

Quality Standard ◽

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Concrete Compressive Strength ◽

Replacement Ratio ◽

Air Content ◽

Slump Flow ◽

Standard Set ◽

Ready Mixed Concrete ◽

Mixed Concrete

Researches until now about recycled aggregate have mainly focused on illuminating physical properties and mechanical behaviors of recycled aggregate by experimenting on small batches of mixing. Unfortunately this kind of mixing does not necessarily fit the reality where a large amount of ready-mixed concrete is often made. Therefore, this study carried out an experiment by having a ready-mixed concrete manufacturing company mix a large amount of recycled aggregate that satisfies quality standard set by the MCT of Korea, then verifying the behaviors of recycled aggregate concrete. The target concrete compressive strength was selected as 24MPa had a slump flow for 120±25mm and air content of 5.0±1.5%, that is used most in site. The main experiment variable of this study is to replacement ratio of recycled aggregate(RA). The 27 test specimens were designed with recycled aggregate replacement ratio that had range of coarse recycled aggregate(CRA), 0, 10, 20, 30, 40, and 50%. The result shows that replacing the natural aggregate with the recycled one up to the ratio of 30% satisfies the quality standard for mixing concrete properly.

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THE VARIATION IN THE COMPRESSIVE STRENGTH OF READY MIXED CONCRETE

Advances in Ready Mixed Concrete Technology ◽

10.1016/b978-0-08-020415-4.50036-9 ◽

1976 ◽

pp. 297-300

Author(s):

I. Soroka

Keyword(s):

Compressive Strength ◽

Ready Mixed Concrete ◽

Mixed Concrete

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Superplasticizer for High Strength Concrete

MRS Proceedings ◽

10.1557/opl.2015.324 ◽

2015 ◽

Vol 1768 ◽

Author(s):

Luis E. Rendon Diaz Miron ◽

Maria E. Lara Magaña

Keyword(s):

Compressive Strength ◽

Portland Cement ◽

High Strength Concrete ◽

High Strength ◽

Mineral Admixtures ◽

Normal Strength Concrete ◽

Strength Concrete ◽

Normal Strength ◽

Ready Mixed Concrete ◽

Mixed Concrete

ABSTRACTIn the early 1970s, experts predicted that the practical limit of ready-mixed concrete would be unlikely to exceed a compressive strength greater than 90 MPa [1]. Over the past two decades, the development of high-strength concrete has enabled builders to easily meet and surpass this estimate. The primary difference between high-strength concrete and normal-strength concrete relates to the compressive strength that refers to the maximum resistance of a concrete sample to applied pressure. Although there is no precise point of separation between high-strength concrete and normal-strength concrete, the American Concrete Institute defines high-strength concrete as concrete with a compressive strength greater than 45 MPa. Manufacture of high-strength concrete involves making optimal use of the basic ingredients that constitute normal-strength concrete. When selecting aggregates to obtain high-strength concrete, we consider strength, optimum size distribution, surface characteristics and a good bonding with the cement paste that affect compressive strength. Selecting a high-quality Portland cement and optimizing the combination of materials by varying the proportions of cement, water, aggregates, and admixtures is also necessary. Any of these properties could limit the ultimate strength of high-strength concrete. Pozzolans, such as fly ash and silica fume along with silicic acid, are the most commonly used mineral admixtures in high-strength concrete. These materials impart additional strength to the concrete by reacting with Portland cement hydration products to create additional Calcium Silicate Hydrate (CSH) gel, the part of the paste responsible for concrete strength; finally the most important admixture is polycarboxylate ether as super plasticizer. It would be difficult to produce high-strength ready-mixed concrete without using chemical admixtures. In this paper we study the use of high performance concrete (HPC) to obtain very narrow strong pre-fabricated elements for water conducting channels.

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Influence of Chemical Admixtures on Fresh and Hardened Properties of Prolonged Mixed Concrete

Advances in Materials Science and Engineering ◽

10.1155/2017/9187627 ◽

2017 ◽

Vol 2017 ◽

pp. 1-11 ◽

Cited By ~ 4

Author(s):

Tarek Uddin Mohammed ◽

Tanvir Ahmed ◽

Shibly Mostafiz Apurbo ◽

Tahir Absar Mallick ◽

Farhan Shahriar ◽

...

Keyword(s):

Compressive Strength ◽

Second Generation ◽

Cement Content ◽

Pulse Velocity ◽

Organic Polymer ◽

Chemical Admixtures ◽

Chemical Admixture ◽

Hardened Properties ◽

Mixing Water ◽

Mixed Concrete

Effects of different chemical admixtures on fresh and hardened properties of prolonged mixed concrete and their cost-effectiveness were investigated. Influence of sand to aggregate volume ratio, cement content, and use of chilled mixing water on the properties of prolonged mixed concrete was studied as well. Different concrete mixtures were prepared using five different types of chemical admixture (one water reducer based on lignosulfonate and four superplasticizers based on sulfonated naphthalene polymer, polycarboxylic ether, second-generation polycarboxylic ether polymer, and organic polymer), varying s/a ratio (0.40 and 0.45) and cement content (340 kg/m3 and 380 kg/m3) and using chilled mixing water. Slump tests were performed at 15-minute intervals to assess the fresh performance of each prolonged mixed concrete mixture. 100 mm by 200 mm cylindrical concrete specimens were prepared and tested for compressive strength, Young’s modulus, splitting tensile strength, and ultrasonic pulse velocity. Results indicate that concretes with sulfonated naphthalene polymer-based superplasticizer and second-generation polycarboxylic ether-based superplasticizer show best performances in both fresh and hardened states. Concrete with lignosulfonate-based water reducer exhibits poor performance in comparison with the concretes with superplasticizers. The cost per unit compressive strength of concrete with sulfonated naphthalene polymer-based superplasticizer is lower compared with the concretes with other types of chemical admixture.

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