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International Concrete Abstracts Portal

Showing 1-5 of 247 Abstracts search results

Document: 

20-028

Date: 

November 1, 2020

Publication:

Materials Journal

Volume:

117

Issue:

6


Document: 

19-135

Date: 

September 1, 2020

Author(s):

Barbara Kucharczyková, Hana Šimonová, Petr Frantík, and Dalibor Kocáb

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

This paper focuses on the comparison of experimentally obtained data with the shrinkage model B4 designed by a research group led by Professor Z. P. Bažant. Two cementitious materials, one having a high water-cement ratio (w/c) and one having a low w/c, were prepared for the experiment. Intentionally, the test specimens were not protected from drying during the entire period of measurement. Test results confirmed that the actual shrinkage process as measured does not correspond with the prediction model, especially during its early age. Shrinkage during the plastic and semi-plastic stages of the solidification process is not reflected in the predicted shrinkage curve. However, if the start time of the evaluation of the experimental data corresponds to the time of maximum derivatives of the temperature, length changes, and ultrasonic pulse velocity curves, better correspondence between the experiment and prediction model is observed for material with a low w/c. However, this approach does not improve the correspondence between the experiment and numerical prediction in the case of material with a high w/c.

DOI:

10.14359/51724622


Document: 

19-354

Date: 

September 1, 2020

Author(s):

Edward G. Moffatt, Michael D. A. Thomas, Andrew Fahim, and Robert D. Moser

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

This paper presents the durability performance of ultra-high-performance concrete (UHPC) exposed to a marine environment for up to 21 years. Concrete specimens (152 x 152 x 533 mm [6 x 6 x 21 in.]) were cast using a water-cementitious materials ratio (w/cm) in the range of 0.09 to 0.19, various types and lengths of steel fibers, and the presence of conventional steel reinforcement bars in select mixtures. Laboratory testing included taking cores from each block and determining the existing chloride profile, compressive strength, electrochemical corrosion monitoring, and microstructural evaluation. Regardless of curing treatment and w/cm, the results revealed that UHPC exhibits significantly enhanced durability performance compared with typical high-performance concrete (HPC) and normal concretes. UHPC prisms exhibited minimal surface damage after being exposed to a harsh marine environment for up to 21 years. Chloride profiles revealed penetration to a depth of approximately 10 mm (0.39 in.) regardless of exposure duration. Electrochemical corrosion monitoring also showed passivity for reinforcement at a cover depth of 25 mm (1 in.) following 20 years.

DOI:

10.14359/51727022


Document: 

19-355

Date: 

September 1, 2020

Author(s):

Diogo Henrique de Bem and Ronaldo A. Medeiros-Junior

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

No widely accepted method is available to assess the efflorescence in small-scale mortar specimens. Thus, the analysis and determination of parameters that actually have an influence on the occurrence of efflorescence in cementitious materials become difficult to be accomplished, especially considering that its appearance in natural field conditions can take months or even years to happen. This paper has the objective to compare eight small-scale accelerated test methods for the assessment of efflorescence in lime-cement mortars and then to evaluate their sensibility to variations in the mixture composition. The results show that the method in which a water column introduces pressure produced the highest amount of efflorescence in the smallest time. The method was able to clearly identify the impact of silica fume towards the refinement of the porous microstructure and the efflorescence reduction. This study demonstrates that 28 days is enough time to finalize the accelerated testing proposed.

DOI:

110.14359/51724627


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


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