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International Concrete Abstracts Portal

Showing 1-5 of 31 Abstracts search results

Document: 

18-192

Date: 

March 1, 2019

Author(s):

Meysam Najimi and Nader Ghafoori

Publication:

Materials Journal

Volume:

116

Issue:

2

Abstract:

The current study aims to assess the transport and durability properties of alkali-activated concretes made with hybrid aluminosilicate precursors having different proportions of natural pozzolan as a low-calcium precursor and ground-granulated blast furnace slag as a high-calcium precursor, which are activated with different concentrations and combinations of sodium hydroxide and sodium silicate. The studied parameters included precursor combination (natural pozzolan/slag combinations of 30/70, 50/50, and 70/30), sodium hydroxide concentration (1, 1.75, and 2.5 M), and activator combination (sodium hydroxide/sodium silicate combinations of 70/30, 75/25, and 80/20). The resulting concrete mixtures were tested for slump flow, setting time, compressive strength, absorption, rapid chloride penetration, rapid chloride migration, resistance to sulfuric acid attack, chloride-induced corrosion, and frost resistance. Mercury intrusion porosimetry and X-ray diffraction were used to justify the observed behaviors. The performance of alkali-activated natural pozzolan/slag concretes was also compared with that of a reference concrete made with solely portland cement binder. In view of overall performance, an equal proportion of natural pozzolan and slag (50/50) and a 30/70 combination of sodium silicate and sodium hydroxide proved to be the optimum precursor and activator combinations. The optimum sodium hydroxide concentration was dependent on the precursor and activator combinations as well as the expected fresh, strength, transport and durability performance. In terms of the measured transport properties (that is, absorption, chloride penetration depth, and passing charges) and resistance to acid attack and chloride-induced corrosion, all the studied alkali-activated concretes performed considerably superior to the reference portland cement concrete. In the case of frost resistance, only alkali-activated concretes with 50 and 70% slag performed superior to the reference portland cement concrete.

DOI:

10.14359/51714455


Document: 

17-432

Date: 

January 1, 2019

Author(s):

Qi Cao, Quanqing Gao, Jinqing Jia, and Rongxiong Gao

Publication:

Materials Journal

Volume:

116

Issue:

1

Abstract:

To improve the early-age cracking resistance of self-consolidating concrete (SCC), this paper investigated the effects of an expansive agent (EA), fibers, and the interaction between EA and fibers on the cracking behavior of restrained SCC caused by plastic shrinkage based on the slab test. Twenty-one types of samples were prepared, including one control group, two EA contents (6 and 8% of the mass fractions of cementitious materials), three steel fiber contents (0.25, 0.50, and 0.75% by volume), three polypropylene fiber contents (0.05, 0.10, and 0.15% by volume), three hybrid fiber contents, and nine combinations of EA (8% of the mass fraction of cementitious materials) and fibers. The initial cracking time and propagation of cracks over time were both observed. Test results indicate that an increase of EA dosage presents no significant improvement on early-age cracking resistance capability. Compared with steel fiber (SF), polypropylene fiber (PP) with equivalent fiber factors was particularly effective in reducing the nominal total crack area. In general, crack reduction factors of fiber-reinforced expansive self-consolidating concrete (FRESCC) are 70% greater than that of SCC containing fiber only. It indicates that the combination of EA and fibers enable SCC to present better early-age cracking resistance.

DOI:

10.14359/51710957


Document: 

17-129

Date: 

January 1, 2018

Author(s):

M. Abdur Rasheed and S. Suriya Prakash

Publication:

Materials Journal

Volume:

115

Issue:

1

Abstract:

This paper presents the stress-strain behavior of structural synthetic fiber-reinforced cellular lightweight concrete (CLC) stack-bonded prisms under axial compression. Masonry compressive strength is typically obtained by testing stack-bonded prisms under compression normal to its bed joint. CLC prisms with cross-sectional dimensions of 200 x 150 mm (7.87 x 5.90 in.) with an overall height of 470 mm (1.54 ft) were cast with and without different dosages of synthetic fiber reinforcement. Polyolefin was used as a structural fiber reinforcement at different volume fractions (vf) of 0.22, 0.33, 0.44, and 0.55% with and without microfiber dosage of 0.02%. Experimental results indicate that the presence of fibers helps in the improvement of strength, stiffness, and ductility of CLC stackbonded prisms under compression. Test results also signify that the hybrid fiber reinforcement provides better crack bridging mechanism both at micro and macro levels when compared to only macrofibers. Simple analytical models were developed for stress-strain behavior of CLC blocks and stack-bonded CLC prisms based on the experimental results with and without fibers under compression.

DOI:

10.14359/51701241


Document: 

15-426

Date: 

May 1, 2017

Author(s):

Stamatina G. Chasioti and Frank J. Vecchio

Publication:

Materials Journal

Volume:

114

Issue:

3

Abstract:

In recognition of the gradual and multi-scale process of cracking, this paper investigates the beneficial effects of fiber hybridization on the basic mechanical properties of concrete. Allowing for these benefits in the mechanical performance may potentially lead to reduced production and construction costs. An experimental investigation was undertaken involving normal-strength concrete in which two types of steel fibers were used: high-strength straight steel microfibers with a length of 13 mm (0.51 in.), and hooked-end macrofibers with a length of 30 mm (1.18 in.). Comparisons between hybrid steel fiber-reinforced concrete (HySFRC) specimens and monofiber counterparts with the same total volumetric ratio highlight its superior performance. Synergy in compression is identified by an enhanced confinement mechanism, in tension by improved post-cracking resistance at both low and high crack openings, and in bending through enhanced fracture toughness. Additionally, a variant of the dogbone-type specimen for tests in direct tension was developed. The novel configuration is more suitable for concrete containing fibers and it is easy to construct and test.

DOI:

10.14359/51689479


Document: 

15-402

Date: 

November 1, 2016

Author(s):

Mohammad H. Rafiei, Waleed H. Khushefati, Ramazan Demirboga, and Hojjat Adeli

Publication:

Materials Journal

Volume:

113

Issue:

6

Abstract:

Costly and time-consuming destructive methods of sampling, curing, and testing under hydraulic jacks are often used to determine concrete properties. Computational intelligence techniques provide the ability to estimate concrete properties quickly at almost no cost. This paper presents a state-of-the-art review of statistical, pattern recognition/machine learning, evolutionary algorithms, and hybrid approaches for estimation of concrete properties such as strength, adhesion, flow, slump, and serviceability using previously collected data. Advantages and disadvantages of the methods are delineated.

DOI:

10.14359/51689360


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