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International Concrete Abstracts Portal

Showing 1-5 of 262 Abstracts search results

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: 

19-347

Date: 

September 1, 2020

Author(s):

Yusheng Zeng, Ser Tong Quek, Aiping Tang, and Xianyu Zhou

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

Freezing-and-thawing (F-T) resistance is a key parameter in evaluating the durability of concrete. The response of concrete under F-T environment varies depending on the mixture proportion and materials used. This paper focuses on the F-T behavior and damage resistance of normal-strength (NC), high-strength (HSC), high-performance (HPC), and ultra-high-performance (UHPC) concrete. The mechanisms causing F-T damage are discussed, specifically based on expansion of freezable water under negative temperature and thermal stress arising from differences in the coefficient of thermal expansion of cement and aggregates. To quantify damage, two parameters—namely, mass loss ratio (MLR) and relative dynamic elastic modulus (RDEM)—are compiled for different classes of concrete. Results show that UHPC exhibited much lower increase in MLR and reduction in RDEM than NC and HPC, respectively. The effects of F-T loading on other mechanical properties of concrete such as compressive strength, flexural strength, tensile strength and stress-strain relationship are also investigated in this paper as possible parameters to help characterize F-T resistance. It is found that F-T will decrease the peak stress but increase the peak strain, and the flexural strength has the fastest loss rate for NC, HPC, HSC and UHPC, respectively. As concrete under F-T environment is often exposed to chloride, the significance of sodium chloride (NaCl) concentration and chloride diffusion coefficient (CDC) on HSC and UHPC under NaCl solution are studied. UHPC exhibits better resistance on chloride diffusion after F-T action due to denser internal pore structure. To improve the F-T resistance of concrete, the performance of two supplementary cementitious admixtures, fly ash and silica fume, to partially replace cement are studied. Results show that the appropriate fly ash replacement of 10 to 30% or silica fume replacement of 5 to 10% is found to enhance the F-T resistance. In addition, introducing fibers such as PVA or PP can improve the F-T resistance significantly, although using the wrong proportion may have a negative effect. Using combined admixture of polyvinyl alcohol and polyethylene fiber with 1.5% volume in cement-based composites reduces strength degradation caused by F-T loadings.

DOI:

10.14359/51725781


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: 

19-328

Date: 

July 1, 2020

Author(s):

Jedadiah F. Burroughs, Charles A. Weiss Jr., John E. Haddock, and W. Jason Weiss

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

This study presents the application of an analytical model to describe the rheological behavior of cement pastes containing silica fume at replacement rates of up to 30% by mass. The analytical model hypothesizes how water interacts with particles in a cementitious system. The coating thickness of water surrounding each particle in the system is estimated. This coating thickness is shown to correlate strongly with measured rheological properties when fit to the Herschel-Bulkley model. To calculate coating thickness, it is necessary to account for the water absorbed by nonhydraulic components in the system, whether aggregate, supplementary cementitious materials, or mineral. The results suggest that silica fume particles may be absorptive, and this absorption capacity, although small, must be considered when designing water-starved cementitious materials. The experimental investigation involved the rheological testing of three water-binder ratios (0.20, 0.30, 0.45), three silica fume replacement levels (10%, 20%, 30%), and eight different silica fume products.

DOI:

10.14359/51724626


Document: 

18-417

Date: 

May 1, 2020

Author(s):

Kamran Amini, Kristen Cetin, Halil Ceylan, and Peter C. Taylor

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

This paper compiles results from three different laboratory studies and employs multivariate regression analyses to model the effect of mixture parameters and concrete hardened properties on saltscaling performance. The correlations between concrete hardened properties and mixture proportions were also studied. The modeled mixture parameters included water-cementitious materials ratio (w/cm), slag cement, and air content. Concrete performance was evaluated through abrasion resistance, sorptivity, compressive strength, and salt scaling tests. According to the results obtained in this study, concrete scaling performance is affected, in the order of importance, by w/cm, slag-cement replacement, and air content. In addition, concrete hardened properties, especially abrasion resistance, were found useful in making reliable salt-scaling predictions. Based on the results derived from the regression analyses and the discussions provided in the reviewed literature, recommendations are given for proportioning of concrete to obtain adequate performance with respect to compressive strength, abrasion resistance, sorptivity, and salt-scaling resistance. In addition, the relationship between concrete properties, ingredients, and effective mechanisms are investigated.

DOI:

10.14359/51724614


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