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International Concrete Abstracts Portal

Showing 1-5 of 45 Abstracts search results

Document: 

20-485

Date: 

November 1, 2021

Author(s):

Karthik Pattaje Sooryanarayana, Kathleen A. Hawkins, Peter Stynoski, and David A. Lange

Publication:

Materials Journal

Volume:

118

Issue:

6

Abstract:

This study proposes using vibration to facilitate three-dimensional (3D) printing of concrete with coarse aggregate, which could lower material costs and decrease shrinkage compared with current 3D-printed cementitious structures. 3D printing of concrete requires concrete to behave like a fluid during pumping and extrusion but like a solid after extrusion. This difference in behavior could potentially be accommodated by using vibration to control the yield stress of concrete. The objective of this study was to understand the effect of vibration on the concrete yield stress and its implications for 3D printing. In this study, a concrete rheometer was modified to measure the yield stress of concrete during vibration. The results of the study show how the effect of vibration on the yield stress of concrete is dependent on the aggregate volume fraction and the packing of the aggregates. It was also observed that the effect is instantaneous and reversible.

DOI:

10.14359/51734150


Document: 

21-008

Date: 

September 1, 2021

Author(s):

Yifeng Ling and Peter Taylor

Publication:

Materials Journal

Volume:

118

Issue:

5

Abstract:

Although internal vibration has been widely implemented in concrete pavements, reports about concrete deterioration caused by improper vibration have been emerging. This study investigates the transmission of vibration energy, water movement, and air movement in concrete under vibration to provide the experimental basis for a better understanding of vibration in different concrete mixtures. An innovative experimental method was developed to measure energy transmission in concrete. The mixtures varied by air content, slump, and water-reducing admixture addition and were prepared to test the vibration energy, water absorption, and the air-void system for a range of vibrator frequencies. The vibration energy transferred through the mixture generally displayed a linear rise, then a slight drop, and, finally, stability, indicated by both measurements of transferred energy and voltage demand of the vibrator. The magnitude of vibration energy transferred through the mixtures increased with an increasing slump. For all samples tested, water appeared to move away from the vibrator, most markedly with an increasing frequency. There is a clear indication of air movement to the surface of the concrete in all tested samples.

DOI:

10.14359/51732981


Document: 

19-297

Date: 

September 1, 2020

Author(s):

Peng Liu, Min Qu, Fazhou Wang, Guohua Hu, and Chuanlin Hu

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

It is well known that the workability of concrete will decrease when doped with secondary fly ash (FA). The authors reported a new FA composite with surface modification which can improve the fluidity of cement and the workability of concrete. A polycarboxylate (PC) high-range water-reducing admixture (HRWRA), which contained poly ethylene glycol (PEG) side chain, carboxylic groups, and hydroxysilane groups, was synthesized by free radical copolymerization. It was subsequently grafted onto fly ash (FA) beads. The Si-OH groups on the surface of alkali-activated FA beads interacted with the PC molecules through covalent hydroxysilane linkage. In the PC-modified FA beads, new infrared (IR) peaks appeared at 2900 and 1100 cm−1 that were assigned to the vibration of C-H and C-O-C groups, respectively. A peak shift in 29Si NMR from −80 to −86 ppm also confirmed the successful grafting of the PC molecules onto the FA beads. Thermal analyses indicated that each of the PC moieties accounted for 2.1 wt. % of the modified FA beads. Compared with the crude FA and the alkali-activated one, the PC-modified FA significantly improved the workability of the cement paste and enhanced the mechanical properties of the cement after hydration for 7 days. Thus, the PC-modified FA composite could serve as a promising additive for cementitious materials.

DOI:

10.14359/51725974


Document: 

18-244

Date: 

May 1, 2019

Author(s):

Aida Margarita Ley-Hernández and Dimitri Feys

Publication:

Materials Journal

Volume:

116

Issue:

3

Abstract:

Self-consolidating concrete (SCC) is designed to fill any type of formwork and spread into place by its own weight in the absence of mechanical vibration. Due to the high flowability of SCC, it is more susceptible to suffer stability problems compared to conventional vibrated concrete. Dynamic segregation refers to segregation in concrete while being cast into a formwork or due to an impact or drop. In this paper, the main purpose is to understand how rheology governs dynamic segregation of SCC, explaining the effect of different mixture design parameters, by using the tilting box (T-box). Changes in admixture contents, paste volume, aggregate distribution, water-cementitious materials ratio (w/cm), and the width of the T-box have been investigated. The results show that dynamic segregation of SCC is dependent on the paste volume, the grain size distribution, fly ash content, and the width of the formwork, in addition to the rheological properties of the concrete.

DOI:

10.14359/51714507


Document: 

17-194

Date: 

March 1, 2018

Author(s):

George J. Zimmer, Robert Flynn, Eric Musselman, and Jeremy Young

Publication:

Materials Journal

Volume:

115

Issue:

2

Abstract:

Roller-compacted concrete (RCC) is often used to construct hydraulic structures, and in gravity dam applications, a facing system is required to control seepage along lift lines. One facing system that is gaining popularity is grout-enriched RCC (GERCC). This innovative process requires the addition of a neat cement grout to the uncompacted RCC along the face, followed by internal vibration to combine the material. One limitation of GERCC is previous research has shown difficulty in entraining air in this system. This study optimized the grout formulation to develop a stable air void system, and then evaluated the effect of this grout on the freezing-and-thawing resistance of GERCC produced both in the lab and during a field trial. Additionally, various grout placement techniques, grout dosages, and vibration levels were evaluated. The results show that freezing-and-thawing-resistant GERCC can be created when the grout and RCC are thoroughly combined.

DOI:

10.14359/51701236


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