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

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.

On the Propagation of Lu¨ders Bands in Steel Strips

2000 ◽  
Vol 67 (4) ◽  
pp. 645-654 ◽  
Author(s):  
S. Kyriakides ◽  
J. E. Miller
Keyword(s):  
Yield Stress ◽  
Strain Level ◽  
Finite Element Models ◽  
Localized Deformation ◽  
Lower Yield ◽  
Lower Yield Stress ◽  
Fine Grained ◽  
Steel Strips ◽  
Initiation And Propagation ◽  
Transient Events

The initiation and propagation of Lu¨ders-type localized deformation in thin, fine grained steel strips in tension is studied through combined experimental and analytical efforts. Purely elastic deformation is terminated (upper yield stress) by localized deformation which tends to initiate along preferred directions. The strain level associated with this material instability is limited to two to five percent. When this strain level is achieved locally, the instability propagates via inclined fronts which separate coexisting regions of essentially elastic and plastically deformed materials. Under displacement controlled stretching, one or two fronts propagate in a steady-state manner (lower yield stress). The propagation of one and two fronts are simulated numerically using finite element models in which the material is modeled as a finitely deforming elastoplastic solid with an up-down-up nominal stress-strain response. The simulations capture the major events observed in the experiments such as the initiation process, the propagation of inclined fronts, kinking of the strip and the build up of moments, and the periodic straightening and moment reduction through transient events. This confirms that structural effects play a major role in the evolution of observed events. [S0021-8936(00)01604-4]

The Yield Phenomena of a Medium Carbon Steel under Dynamic Loading

1949 ◽  
Vol 161 (1) ◽  
pp. 165-175 ◽  
Author(s):  
F. V. Warnock ◽  
D. B. C. Taylor
Keyword(s):  
Carbon Steel ◽  
Yield Stress ◽  
Testing Machine ◽  
Strain Curve ◽  
Medium Carbon Steel ◽  
Impact Testing ◽  
Lower Yield ◽  
Lower Yield Stress ◽  
Medium Carbon ◽  
True Shape

The paper describes dynamic tensile tests carried out on a medium carbon steel to determine the true shape of the stress-permanent strain curve for rapid straining. The variation of this curve with change in strain rate, and the progressive deformation of the steel are also studied. An impact testing machine was used, straining being carried out as a series of dynamic loadings, and the stress was measured by means of electrical resistance strain gauges attached directly to the specimens. Comparison is effected between dynamic and static stress-strain curves, the existence of a “dynamic upper yield stress” and a “dynamic lower yield stress” being shown, together with a difference in the rate of strain hardening for the two straining conditions. Non-uniform yielding of the metal is shown to be more pronounced for dynamic straining and, like static yielding, to be an integral part of the lower yield stress phenomenon. The manner in which all these factors are affected by normalizing the steel is shown. A special form of deformation of the steel peculiar to rapid straining is indicated. Theoretical and experimental facts are used to deduce a theory for the observed increases in stress, and the use of these dynamic stresses for design purposes is discussed.

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

2020 ◽  
Vol 6 (8) ◽  
pp. 1581-1592
Author(s):  
Ahmed Mohamed Abd El-Motaal ◽  
Ahmed Abdel-Reheem ◽  
Mohamed Mahdy
Keyword(s):  
Compressive Strength ◽  
Mixing Time ◽  
Mixing Process ◽  
Mixing Speed ◽  
Chemical Admixtures ◽  
Mixing Parameters ◽  
Slump Flow ◽  
Long Time ◽  
Ready Mixed Concrete ◽  
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.

scholarly journals Analysis of the Effect of Various Types of Limestone as a Main Constituent of Cement on the Chosen Properties of Cement Pastes and Mortars

2019 ◽  
Vol 65 (3) ◽  
pp. 75-86
Author(s):  
J. Gołaszewski ◽  
G. Cygan ◽  
M. Gołaszewska
Keyword(s):  
Compressive Strength ◽  
Rheological Properties ◽  
Yield Stress ◽  
Drying Shrinkage ◽  
Plastic Viscosity ◽  
Main Constituent ◽  
Cement Pastes ◽  
Mortar Strength ◽  
The Impact

AbstractThe article is an attempt to compare the impact of the use of various types of limestone as the main constituent of cement on selected mortar properties. Four different limestones were added in amount of 15, 30, 40% to CEM I 42.5 R to obtain limestone cemens. Rheological properties (yield stress, plastic viscosity) of fresh mortar, tensile and compressive mortar strength, early shrinkage, and drying shrinkage were tested. Obtained results indicate that both tensile and compressive strength decreases with the increase of the limestone content in cement. Limestone can worsen or improve workability, depending on distribution of limestone grains. The addition of limestone increases the early shrinkage, but reduces the shrinkage after 28 days. Studies show that the granulation of limestone plays an important role in determining the influence of limestone on mortar properties.

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