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International Concrete Abstracts Portal

Showing 1-5 of 350 Abstracts search results

Document: 

20-011

Date: 

November 1, 2020

Publication:

Materials Journal

Volume:

117

Issue:

6


Document: 

20-044

Date: 

November 1, 2020

Publication:

Materials Journal

Volume:

117

Issue:

6


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: 

19-504

Date: 

September 1, 2020

Author(s):

C. Gunasekera, W. Lokuge, M. Keskic, N. Raj, D. W. Law, and S. Setunge

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

So far, alkali-activated concrete has primarily focused on the effect of source material properties and ratio of mixture proportions on the compressive strength development. A little research has focused on developing a standard mixture design procedure for alkali-activated concrete for a range of compressive strength grades. This study developed a standard mixture design procedure for alkali-activated slag-fly ash (low-calcium, Class F) blended concrete using two machine learning techniques: artificial neural networks (ANN) and multivariate adaptive regression spline (MARS). The algorithm for the predictive model for concrete mixture design was developed using MATLAB programming environment by considering the five key input parameters: water/solid ratio, alkaline activator/ binder ratio, Na-Silicate/NaOH ratio, fly ash/slag ratio, and NaOH molarity. The targeted compressive strengths ranging from 25 to 45 MPa (3.63 to 6.53 ksi) at 28 days were achieved with laboratory testing using the proposed machine learning mixture design procedure. Thus, this tool has the capability to provide a novel approach for the design of slag-fly ash blended alkali-activated concrete grades matching to the requirements of in-place field constructions.

DOI:

10.14359/51727019


Document: 

19-374

Date: 

September 1, 2020

Author(s):

D. Marcon Neto, C. Effting, A. Schackow, I. R. Gomes, G. Aurélio Cifuentes, and D. Ganasini

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

In this work, concretes with high levels of fly ash replacing portland cement were elaborated. The concretes’ properties in the fresh state (consistency, workability, and heat of hydration) and in the hardened state (compressive strength, modulus of elasticity, conductivity, void index, water absorption, and density) were measured. Microstructural and thermal characterization were performed. Numerical simulations were performed to analyze the heat exchange during the cement hydration process. Statistical analysis was adequate, and a proposed regression model was validated for the high-volume fly ash concrete, with 60% replacing the portland cement. This concrete presented values of mechanical strength (33.38 ± 3.99 MPa) and modulus of elasticity (38.58 ± 0.81 GPa) which confirms its use as structural concrete. This concrete showed low heat of hydration, a reduction of 23% in relation to the reference concrete (without fly ash) during its curing process, and its microstructure presented a lower level of cracking.

DOI:

10.14359/51725783


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