scholarly journals Effects of Volume Fraction and Surface Area of Aggregates on the Static Yield Stress and Structural Build-Up of Fresh Concrete

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1551 ◽  
Author(s):  
Irina Ivanova ◽  
Viktor Mechtcherine
Keyword(s):  
Rheological Properties ◽  
Yield Stress ◽  
Surface Area ◽  
Cement Paste ◽  
Volume Fraction ◽  
Fresh Concrete ◽  
Total Surface Area ◽  
Rheological Parameters ◽  
Static Yield ◽  
Static Yield Stress

With increasing interest in the use of additive manufacturing techniques in the construction industry, static rheological properties of fresh concrete have necessarily come into focus. In particular, the knowledge and control of static yield stress (SYS) and its development over time are crucial for mastering formwork-free construction, e.g., by means of layered extrusion. Furthermore, solid understanding of the influences of various concrete constituents on the initial SYS of the mixture and the structural build-up rate is required for purposeful material design. This contribution is concentrated on the effect of aggregates on these rheological parameters. The volume fraction of aggregates was varied in the range of 35% to 55% by volume under condition of constant total surface area of the particles. The total surface area per unit volume of cement paste was equal to 5.00, 7.25 and 10.00 m²/L, conditioned on the constant volume fraction of aggregates. Both variations were enabled by changing the particle size distributions of the aggregates while holding the cement paste composition constant for all concrete mixtures. To characterise the SYS and the structural build-up, constant shear rate tests with a vane-geometry rotational rheometer were performed. It was found that in the ranges under investigation the variation in volume fraction had a more pronounced effect on the static rheological properties of concrete than did the variation in surface area. An accurate mathematical description of the relationship between the initial SYS of concrete and the relative volume fraction of aggregate based on the Chateau–Ovarlez–Trung model was proposed. Challenges in deriving a similar relationship for the structural build-up rate of concrete were highlighted.

scholarly journals Effects of Volume Fraction and Surface Area of Aggregates on the Static Yield Stress and Structural Build-Up of Fresh Concrete

2020 ◽  
Author(s):  
Irina Ivanova ◽  
Viktor Mechtcherine
Keyword(s):  
Rheological Properties ◽  
Yield Stress ◽  
Surface Area ◽  
Cement Paste ◽  
Volume Fraction ◽  
Fresh Concrete ◽  
Total Surface Area ◽  
Rheological Parameters ◽  
Static Yield ◽  
Static Yield Stress

With increasing interest in the use of additive manufacturing techniques in the construction industry, static rheological properties of fresh concrete have necessarily come into focus. In particular, the knowledge and control of static yield stress (SYS) and its development over time are crucial for mastering formwork-free construction, e.g. by means of layered extrusion. Furthermore, solid understanding of the influences of various concrete constituents on the initial SYS of the mixture and the structural build-up rate is required for purposeful material design. This contribution is concentrated on the effect of aggregates on these rheological parameters. The volume fraction of aggregates was varied in the range of 35 to 55 % by volume under condition of constant total surface area of the particles. The total surface area per unit volume of cement paste was equal to 5.00, 7.25 and 10.00 m²/l, conditioned on the constant volume fraction of aggregates. Both variations were enabled by changing the particle size distributions of the aggregates while holding the cement paste composition constant for all concrete mixtures. To characterise the SYS and the structural build-up, constant shear rate tests with a vane-geometry rotational rheometer were performed. It was found that in the ranges under investigation the variation in volume fraction had a more pronounced effect on the static rheological properties of concrete than did the variation in surface area. An accurate mathematical description of the relationship between the initial SYS of concrete and the relative volume fraction of aggregate based on the Chateau-Ovarlez-Trung model was proposed. Challenges in deriving a similar relationship for the structural build-up rate of concrete were highlighted.

Modelling the Yield Stress of Fly-Ash Added Superplasticized Cement Paste at Different Temperatures Using Artificial Neural Network

2022 ◽  
Vol 1048 ◽  
pp. 366-375
Author(s):  
Pavan Chandrasekar ◽  
Anjala Nourin ◽  
Addepalli Sri Naga Bhushana Aravind Gupta ◽  
Bavineni Venkata Jyoshna ◽  
Dhanya Sathyan
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Fly Ash ◽  
Yield Stress ◽  
Cement Paste ◽  
Test Temperature ◽  
Fresh Concrete ◽  
Rheological Parameters ◽  
Different Temperatures ◽  
Artificial Neural

Abstract: Rheology is the science that concerns the flow of liquids, and the distortion of solids under an applied force. The study of the rheology of concrete determines the properties of fresh concrete. The rheological parameters are affected by temperature, stress conditions and several other factors. The main intention of this research is to model the rheological parameters of the fly ash incorporated cement with various types of superplasticizers exposed under different temperatures using an Artificial Neural Network. Test data were generated by performing rheological tests on cement paste at three distinct temperatures (15, 27, 35°C). Mixes were prepared using OPC, fly ash (15, 25, 35%) and superplasticizers of four different families. By conducting experiments, 252 data have been generated by modifying the combination of fly-ash, superplasticizer, and test temperature. Among the 252 data, 80% has been utilized for training and 20% is utilized for predicting the model’s accuracy. The input layer of the model consists of test temperature, the amount of fly ash replaced, cement and water content, and four different groups of superplasticizers. The cement paste’s yield stress was the output parameter of the model. The model generated data has been compared with the experimentally generated data to determine the accuracy of the model.Keywords: Rheology, Fly Ash, Superplasticizer, Temperature, ANN

scholarly journals The Synergistic Effect of Ester-Ether Copolymerization Thixo-Tropic Superplasticizer and Nano-Clay on the Buildability of 3D Printable Cementitious Materials

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4622 ◽  
Author(s):  
Yu Wang ◽  
Yaqing Jiang ◽  
Tinghong Pan ◽  
Kangting Yin
Keyword(s):  
Synergistic Effect ◽  
Yield Stress ◽  
Cementitious Materials ◽  
Rheological Parameters ◽  
Layer By Layer ◽  
Initial Stiffness ◽  
Green Strength ◽  
Nano Clay ◽  
Static Yield ◽  
Static Yield Stress

The shape retention ability of materials deposited layer by layer is called buildability, which is an indispensable performance parameter for successful 3D printable cementitious materials (3DPC). This study investigated the synergistic effect of nano-clay (NC) and thixotropic superplasticizer (TP) on the buildability of 3DPC. The rheological parameters and static yield stress are characterized by the rheology testing, the green strength is measured by a self-made pressure tester, and the fluidity is tested by flow table. Results indicate that NC significantly increases the growth rate of static yield stress and green strength and TP can improve the initial rheological parameters and fluidity, which ensures the initial stiffness and workability of printed materials. The mixture with 7‰ (by mass of cementitious materials) NC and 3‰ TP obtains excellent extrudability and buildability, due to the synergistic effect of NC and TP. Based on the rheology testing and specific printing experiments, a printable window with 1.0 Pa/s~2.0 Pa/s of the rate of static yield stress evolution over time (RST) or 170 mm~200 mm of fluidity is established. This work provides theorical support for the control and evaluation of rheological properties in 3DPC.

Influence of Ground Slag on the Rheology of Mortar

2013 ◽  
Vol 438-439 ◽  
pp. 67-71
Author(s):  
Qian Qian Zhang ◽  
Jian Zhong Liu ◽  
Jia Ping Liu
Keyword(s):  
Film Thickness ◽  
Specific Surface ◽  
Yield Stress ◽  
Surface Area ◽  
Specific Surface Area ◽  
Water Film ◽  
Plastic Viscosity ◽  
Rheological Parameters ◽  
Water Film Thickness ◽  
Binder Ratio

The effects of ground slag with different specific surface area on the rheology of mortar at water-binder ratio of 0.25, 0.28 and 0.30 were investigated, and the combined effects of packing density and solid surface area on the rheology of mortar were evaluated in terms of the water film thickness. The results show that with the increasing of specific surface area of slag (220 m2/kg-784 m2/kg), plastic viscosity and yield stress decrease. The correlations of yield stress and plastic viscosity to the water film thickness are basically linear with high correlation R2 values. The action of the ground slag on the rheology of mortar can be characterized by water film thickness, and with the increasing of water film thickness the rheological parameters decrease.

The Effect of Sulfonated Graphene on the Rheological Properties of Cement Paste

2020 ◽  
Vol 20 (12) ◽  
pp. 7495-7505
Author(s):  
Jia-Ming Wu ◽  
Guo-Jian Jing ◽  
Xiao-Lei Lu ◽  
Tian-Yu Lei ◽  
Shu-Xian Wang ◽  
...  
Keyword(s):  
Rheological Properties ◽  
Cement Paste ◽  
Chemical Interaction ◽  
Cementitious Materials ◽  
Rheological Parameters ◽  
Physical Interaction ◽  
Mechanical And Thermal Properties ◽  
Practical Application ◽  
Sulfonated Graphene ◽  
Modified Graphene

With unique 2D nanostructures and excellent properties, graphene and its derivatives are a class of advanced nanosized reinforcements for cementitious materials. Sulfonated graphene (SG), one of the most important modified graphene materials, possesses sulfonate groups on the surface and significantly improves the mechanical and thermal properties of cement-based composites. It is important to investigate the influence of SG on cement-based materials as it is a prerequisite for practical applications. Herein, SG was prepared and introduced into cement paste to investigate its influence on the rheological properties of cement paste. With the increased addition of SG, a stable slurry was gradually obtained with low fluidity and high rheological parameters. The mechanism of the SG effect on the rheological properties of cement paste was also illustrated. Because of the high specific surface area and sulfonate groups of SG nanosheets, a large amount of flocculated structure was created by the complexing effect, chemical interaction, physical interaction and mechanical interlocking between SG and hydrated/unhydrated cement particles. Furthermore, polycarboxylate ether (PCE) superplasticizer was introduced to ensure fluidity and transportability in the practical application of SG. The results in this work lay a foundation for the practical application of modified graphene in cementitious materials.

LANTHANUM TITANATE NANOPARTICLES ER FLUIDS WITH HIGH PERFORMANCE

2012 ◽  
Vol 26 (13) ◽  
pp. 1250079 ◽  
Author(s):  
DE WANG ◽  
RONG SHEN ◽  
SHIQIANG WEI ◽  
KUNQUAN LU
Keyword(s):  
Yield Stress ◽  
Silicone Oil ◽  
Heating Temperature ◽  
Hydroxyl Group ◽  
Lanthanum Titanate ◽  
Different Temperatures ◽  
Static Yield ◽  
Er Fluids ◽  
Er Fluid ◽  
Static Yield Stress

A new type of electrorheological (ER) fluid consisting of lanthanum titanate (LTO) nanoparticles is developed. The ER fluids were prepared by suspending LTO powder in silicone oil and the particles were fabricated by wet chemical method. This ER fluid shows excellent ER properties: The static yield stress reaches over 150 kPa under 5 kV/mm with linear dependence on the applied DC electric field, and the current density is below 10 μA/cm2. In order to investigate the affect factor on the ER behavior, the LTO powder were heated under different temperatures. The ER performances of two particles treated under different temperatures were compared and the composition changes for those particles were analyzed with TG-FTIR technique. It was found that the static yield stress of the suspensions fell from over 150 kPa to about 40 kPa and the current densities decreased prominently as the rise of the heating temperature. TG-FTIR analysis indicated that polar groups remained in the particles such as alkyl group, hydroxyl group and carbonyl group etc., contribute to the ER effect significantly. The experimental results are helpful to understand the mechanism of the high ER effect and to synthesize better ER materials.

Sign in / Sign up

Export Citation Format

Share Document