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Home > Publications > International Concrete Abstracts Portal
Showing 1-5 of 68 Abstracts search results
Document:
23-330
Date:
September 1, 2024
Author(s):
Peiyuan Chen, Chunning Pei, Liheng Zhang, Shangkun Li, and Jialai Wang
Publication:
Materials Journal
Volume:
121
Issue:
5
Abstract:
The applications of alkali-activated slag (AAS) face challenges such as poor workability, rapid setting, and high autogenous shrinkage, which require chemical admixtures (CAs) to adjust the performance of AAS. Unfortunately, there are limited specific CAs available to tune AAS properties. To address this gap, this study proposes using a ubiquitous, naturally occurring compound, L-ascorbic acid (LAA), as a multifunctional performanceenhancing additive for AAS to overcome the major challenges of AAS. The findings showed that LAA can function as a retarder, plasticizer, strength enhancer, and autogenous shrinkage reducer for AAS. When 0.5% LAA was added, the compressive strengths of AAS mortars at 3 and 28 days increased by 28.9% and 19.6%, respectively, and the 28-day autogenous shrinkage decreased by 43.1%. Both surface adsorption and ion complexation have been confirmed as the working mechanisms of LAA in hydrated AAS.
DOI:
10.14359/51742041
20-502
November 1, 2021
Flavia Mendonca and Jiong Hu
118
6
Ultra-high-performance concrete (UHPC) is a new class of cementitious material with unique characteristics, including self-consolidation, and excellent mechanical and durability properties. To achieve the desired properties, a very dense internal structure and a very low water-binder ratio (w/b) are necessary. Due to the very different mixture design compared to conventional concrete, it is critical to incorporate different types of chemical admixtures to achieve appropriate fresh concrete behavior of UHPC. To ensure the successful placement of UHPC, it is important to have a good understanding of the workability and rheological characteristics of UHPC with different types and dosages of chemical admixtures. This paper presents a detailed study of the impact of high-range water reducer, workability-retaining admixture, and anti-foaming admixture on the workability and rheological characteristics over different mixture elapsed times. Besides the flowability, both Bingham and modified Bingham models were used to obtain key rheological parameters, including yield stress, viscosity, and thixotropy. Furthermore, the authors developed stability indexes to assess the fiber stability of UHPC in both fresh and hardened states. Based on the experimental results, the paper presented suggested criteria to ensure appropriate flowability and fiber stability for UHPC placement.
10.14359/51734151
20-446
L. S. C. Ko, S. Moro, J. Bury, T. Vickers, B. Sachsenhauser, and S. Mönnig
To ensure a successful outcome when using cementitious materials during three-dimensional (3D) printing operations, the effects of chemical admixtures on rheological and setting behavior must be carefully adjusted to accommodate the needs for pumping, extrusion, deposition, and self-sustainability without the support of formwork. This paper highlights potential solutions offered by chemical admixtures, while discussing various testing methods and important influencing parameters. The impact of commercial polymers on viscosity, initial yield stress, thixotropy, and their variations over time are reported. Influencing factors, such as mixing energy and material interactions, are discussed. Accelerating and strength-enhancing admixtures are used to illustrate the adjustment of setting and early strength development of concrete. Understanding the possibilities of modifying fresh concrete properties will help to improve the robotic construction process as well as the design or adaptation of the printing equipment.
10.14359/51733121
18-310
September 1, 2019
M. Moini, K. Sobolev, I. Flores-Vivian, S. Muzenski, L. T. Pham, S. Cramer, and M. Beyene
116
Durability and long-term performance of concrete exposed to deleterious ions and environmental conditions are major concerns. The rapid chloride permeability (RCP) test is commonly used in specifications in the United States to evaluate the permeability of concrete. To evaluate the critical factors that control the service life of structures, the investigation of various concrete mixtures is required. In this paper, the performance of 54 concrete mixtures containing three types of water-reducing admixtures, two types of aggregates, and two levels of cement contents are evaluated in the RCP and freezing-and-thawing tests and the air void structure of selected mixtures are analyzed. It was found that the use of supplementary cementitious materials (SCMs) significantly enhances the performance of concrete mixtures in the RCP test. In addition, mixtures containing up to 30% of Class C fly ash and 50% slag content achieved exceptional durability performance in both RCP and freezing-and-thawing (F-T) tests. The “very-low” RCP values were found for mixtures containing Class F fly ash and polycarboxylate ether (PCE) admixture.
10.14359/51716828
18-371
July 1, 2019
Mona Zahedi and Farshad Rajabipour
4
Concerns over the availability and quality of conventional fly ash for use in concrete has become widespread in recent years. Fluidized bed combustion (FBC) ash, with its annual U.S. production exceeding 14 million tons, could serve as a reasonable alternative. In this study, two compositionally different fly ashes from circulating FBC (CFBC) power plants were evaluated for their compliance with the ASTM C618 standard and their impact on the fresh and hardened properties of concrete. The pozzolanic reactivity of the fly ashes was also quantified based on the emerging RILEM test method. These fly ashes met the chemical and physical requirements of ASTM, except for elevated LOI (in both fly ashes) and elevated SO3 (in one fly ash). Despite this, concrete with proper slump, air content, and strength development could be produced by proper dosing of chemical admixtures. The elevated SO3 was found not to produce deleterious expansions.
10.14359/51716720
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