scholarly journals Effect of Accelerators on the Workability, Strength, and Microstructure of Ultra-High-Performance Concrete

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 159
Author(s):  
Yonghua Su ◽  
Biao Luo ◽  
Zhengdong Luo ◽  
He Huang ◽  
Jianbao Li ◽  
...  
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Setting Time ◽  
Strength Properties ◽  
Strength Ratio ◽  
Strength Gain ◽  
Ultra High Performance Concrete ◽  
Micro Level ◽  
Early Strength ◽  
Good Workability

The preparation of ultra-high-performance concrete (UHPC) with both high-early-strength and good workability contributes to further promotion of its development and application. This study investigated the effects of different accelerators (SM, alkaline powder accelerator; SF, alkaline powder accelerator containing fluorine; and AF, alkali-free liquid accelerator containing fluorine) on the workability and strength properties of UHPC. The microstructure of UHPC was also characterized by using XRD and SEM. Several dosage levels of accelerators (2%, 4%, 6%, and 8% by mass) were selected. The results indicate that the setting time and fluidity of UHPC are gradually decreased with an increase in accelerators dosage. Compared with fluorine-containing SF/AF, fluorine-free SM evidently facilitates UHPC early strength gain speed. However, the fluorine-containing accelerators have a higher 28 d strength ratio, especially AF. The maximum compressive and flexural strength ratios are obtained at a dosage of 6%, which are 95.5% and 98.3%, respectively. XRD and SEM tests further reveal the effect of different accelerators on the macroscopic properties of UHPC from the micro level.

Evaluation of Setting Time in Ultra High Performance Concrete

2012 ◽  
Vol 525-526 ◽  
pp. 621-624
Author(s):  
Sung Wook Kim ◽  
Jung Jun Park ◽  
Doo Youl Yoo ◽  
Young Soo Yoon
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Setting Time ◽  
Autogenous Shrinkage ◽  
High Strength ◽  
Initial Crack ◽  
Test Method ◽  
Plastic State ◽  
Ultra High Performance Concrete ◽  
Confining Stress

Ultra high performance concrete (UHPC), characterized by a high strength and high ductility, is also subjected to large shrinkage due to its low water-to-binder ratio and its large content in high fineness materials. The large amount of autogenous shrinkage of UHPC can induce crack on structural member when it was restrained with reinforcement and form. However, shrinkage of UHPC in plastic state is not generating confining stress, which is the main cause of initial crack. Normally, the setting time in concrete is an index to distinguish shrinkage which occur confining stress or not. An estimation of setting time is conducted in compliance with ASTM C 403 till now however, that test standard reveals error of results due to discordance of test condition as following with concrete type. This study therefore evaluated setting time of UHPC through the modified test method which was proposed by KICT. Test results and analyses proved a discrepancy of setting time between ASTM and proposed method. The proposed method put faith in evaluation of setting time in accordance with UHPC.

Study on the Compressive Strength and Mixing of Ultra-High Performance Concrete

2013 ◽  
Vol 357-360 ◽  
pp. 825-828
Author(s):  
Su Li Feng ◽  
Peng Zhao
Keyword(s):  
Compressive Strength ◽  
High Performance ◽  
High Performance Concrete ◽  
High Strength ◽  
Strength Properties ◽  
Test Method ◽  
Test Results ◽  
Concrete Compressive Strength ◽  
Ultra High Performance Concrete ◽  
Mixture Ratio

The test in order to obtain liquidity, higher intensity ultra-high performance concrete(UHPC), in the course of preparation, high intensity quartz sand to replace the ordinary sand,reasonable mixture ratio control low water-cement ratio,the incorporation of part of the test piece ofsteel fibers, produced eight specimens . In the ordinary molding and the standard conservation 28d thecase, the ultra-high-performance concrete compressive strength of more than 170MPa.Thepreparation of the test method and test results will provide the basis for further study of the law of themechanical properties of ultra high strength properties of concrete.

Properties of High Performance Concrete Containing Waste Glass Micro-Filler

2014 ◽  
Vol 604 ◽  
pp. 161-164 ◽  
Author(s):  
Genadijs Sahmenko ◽  
Nikolajs Toropovs ◽  
Matiss Sutinis ◽  
Janis Justs
Keyword(s):  
Silica Fume ◽  
High Performance ◽  
Glass Powder ◽  
High Performance Concrete ◽  
Setting Time ◽  
Ground Glass ◽  
Early Age ◽  
Strength Gain ◽  
Fluorescent Lamp

The article discusses possibilities for use fine ground glass obtained from fluorescent lamp utilisation as micro filler in High Performance Concrete (HPC). Investigated mix compositions are based on silica fume (SF) and SF combination with glass powder. Testing results indicates that replacing silica fume by additionally ground fluorescent glass (up to 50%) slightly increasing consumption of water and delaying setting time of cement paste. All HPC mixes with glass powder showing decreased early-age strength and considerable strength gain after long-term hardening. It is concluded, that the best way of glass application in HPC is use fine ground glass powder together with silica fume as complex admixture.

Morphology and Strength of Cement Paste from Clay as Nanomaterial

2014 ◽  
Vol 490-491 ◽  
pp. 19-24 ◽  
Author(s):  
M.S. Muhd Norhasri ◽  
M.S. Hamidah ◽  
A. Mohd Fadzil
Keyword(s):  
Cement Paste ◽  
High Performance ◽  
High Performance Concrete ◽  
Human Life ◽  
Sol Gel ◽  
Hydration Product ◽  
Strength Properties ◽  
Cement Matrix ◽  
The Matrix ◽  
Early Strength

Now days the application of nanomaterials was vastly growing in the development of new material to improve the quality of human life. Particles of nanomaterials which are in nanoscale helps to improve to the characteristics of the existing micro based materials. The application of nanomaterials in the construction were started since in the early 90s when during those time micro based materials was very demanding especially when dealing with High Performance Concrete (HPC). The utilization of nanobased materials improves and reinforces the cement matrix system and performs early strength and also enhances tensile properties of concrete. In this research, two types of clay were used which nanometakaolin and nanometaclay. nanometakaolin were made from sol gel process thats involved milling technique and nanometaclay were supplied by Sigma Aldrich. The mix proportion for clay based cement paste also includes metakaolin as cement replacement material. nanometakaolin and nanometaclay was added as additives from 0, 1, 3, 5, 7, 9 percent (%) from weight of cement and will be compared to OPC as control specimen. nanometakaolin and nanometaclay inclusion in cement paste will be evaluated for morphology effect by using Scanning Electron Microscope (SEM), chemical composition by using X-Ray Fluorescent (XRF) technique and strength properties. From morphology evaluation, the shape of the particles and particularisation of the matrix observed on the nanometakaolin, nanometaclay and plain cement paste were compared. Similarly, the strength of the plain cement paste shows was compared with those of nanometakaolin and nanometaclay. From the results, shows that inclusion of nanometakaolin at 7% additives generates early strength of cement paste and at 28 days of age addition of 1% of nanometakaolin was found to be the optimum addition level. The addition of 1% nanometakaolin acts as an ultra-filler and refines the microstructure of concrete. Furthermore, nanometakaolin also produces a secondary hydration product by optimizing the remaining calcium hydroxide which was not fully removed during the hydration period.

Flexural design of precast, prestressed ultra-high-performance concrete members

PCI Journal ◽  
2020 ◽  
Vol 65 (6) ◽  
pp. 35-61
Author(s):  
Chungwook Sim ◽  
Maher Tadros ◽  
David Gee ◽  
Micheal Asaad
Keyword(s):  
Prestressed Concrete ◽  
High Performance ◽  
High Performance Concrete ◽  
Limit State ◽  
Design Guidelines ◽  
Design Tool ◽  
Supplementary Cementitious Materials ◽  
Ultra High Performance Concrete ◽  
Concrete Members ◽  
Cylinder Strength

Ultra-high-performance concrete (UHPC) is a special concrete mixture with outstanding mechanical and durability characteristics. It is a mixture of portland cement, supplementary cementitious materials, sand, and high-strength, high-aspect-ratio microfibers. In this paper, the authors propose flexural design guidelines for precast, prestressed concrete members made with concrete mixtures developed by precasters to meet minimum specific characteristics qualifying it to be called PCI-UHPC. Minimum specified cylinder strength is 10 ksi (69 MPa) at prestress release and 18 ksi (124 MPa) at the time the member is placed in service, typically 28 days. Minimum flexural cracking and tensile strengths of 1.5 and 2 ksi (10 and 14 MPa), respectively, according to ASTM C1609 testing specifications are required. In addition, strain-hardening and ductility requirements are specified. Tensile properties are shown to be more important for structural optimization than cylinder strength. Both building and bridge products are considered because the paper is focused on capacity rather than demand. Both service limit state and strength limit state are covered. When the contribution of fibers to capacity should be included and when they may be ignored is shown. It is further shown that the traditional equivalent rectangular stress block in compression can still be used to produce satisfactory results in prestressed concrete members. A spreadsheet workbook is offered online as a design tool. It is valid for multilayers of concrete of different strengths, rows of reinforcing bars of different grades, and prestressing strands. It produces moment-curvature diagrams and flexural capacity at ultimate strain. A fully worked-out example of a 250 ft (76.2 m) span decked I-beam of optimized shape is given.

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