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International Concrete Abstracts Portal

Showing 1-5 of 47 Abstracts search results

Document: 

18-247

Date: 

July 1, 2020

Author(s):

Nattapong Paewchompoo, Wanchai Yodsudjai, and Prinya Chindaprasirt

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

The objective of this research was to clarify the mechanism of concrete cover cracking time due to reinforcement corrosion in steel fiber-reinforced concrete. An experimental study and analytical study were conducted. For the experimental study, 3 in. (76.2 mm) diameter and 6 in. (152.4 mm) length cylindrical concrete specimens with reinforcement placed in the middle were prepared. Conventional and steel fiber-reinforced concrete with three levels of compressive strength were used in the study. A strain gauge was installed along the specimen’s circumference and the corrosion of reinforcement was accelerated using anodic DC current. Concrete surface strain and impressed anodic current were recorded via a data logger and a multimeter, respectively. Concrete cover cracking time was also investigated. After corrosion acceleration, reinforcement weight loss was evaluated and internal pressure due to the reinforcement corrosion product was calculated. The analytical study was conducted using finite element with four-node bilinear plane strain in a two-dimensional (2-D) model. In the finite element method (FEM) model, the reinforcement was removed and the internal pressure result from the expansion of corrosion products was applied, similar to the problem of cylinder under constant internal pressure. The relationship between concrete surface strain and internal pressure from the analytical study was compared with the experimental study. It was found that corrosion current density of the reinforcement embedded in the fiber-reinforced concrete was higher than that of conventional concrete. Concrete cover cracking time increased with increase of concrete tensile strength. In addition, the relationship between concrete surface strain and the internal pressure could be predicted by the FEM results within an acceptable margin of error.

DOI:

10.14359/51724620


Document: 

19-057

Date: 

May 1, 2020

Author(s):

A. Pczieczek, C. Effting, A. Schackow, I. Ribeiro Gomes, and D. V. Ferronato da Silva

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

This work aimed to analyze the physical and mechanical properties of mortar with the addition of fly ash and rubber concentrations used on building walls. The mortars had 5 and 10% of fine aggregate mass replaced by rubber and added fly ash in proportions of 10 and 20% according to the volume of cement. Ground fly ash addition in the mortar, in turn, increased the compressive strength by 18% at 28 days compared to the reference mortar, assuring a greater durability against sulfate attacks and presenting lower mass loss during exposure to sodium sulfate. The mortar containing 20% of ground fly ash and 5% of rubber presented tensile adhesion strength of 0.33 MPa at 65 days. A numerical simulation of the mortar microstructure was carried out using the finite element method to study its thermomechanical behavior. Stress distribution and cracking field of the model were also obtained.

DOI:

10.14359/51724594


Document: 

18-322

Date: 

September 1, 2019

Author(s):

Mahmoud Shakouri, Naga Pavan Vaddey, and David Trejo

Publication:

Materials Journal

Volume:

116

Issue:

5

Abstract:

The binding of chlorides by the hydration products of cement in concrete is one of the factors that affects the rate of chloride ingress, which in turn can influence the time to corrosion initiation of reinforcing steel in concrete. Theoretical assessments of the influence of chloride binding on the chloride ingress and service life estimates are often based on empirically developed chloride binding isotherms to account for the interaction between the concrete matrix and external chlorides. While being useful, these assessments disregard the binding influence of admixed chlorides that may be present in the concrete from the early stages of hydration. It is suspected that the presence of free admixed chlorides can influence the diffusivity of chlorides in concrete. This work focuses on determining the binding behavior of admixed chlorides and proposes a modified diffusion model that takes chloride binding from admixed and external chlorides into consideration.

DOI:

10.14359/51716833


Document: 

17-390

Date: 

September 1, 2018

Author(s):

Chun-Qing Li, Hassan Baji, and Shangtong Yang

Publication:

Materials Journal

Volume:

115

Issue:

5

Abstract:

Hydraulic conductivity of concrete can be used as a key indicator in assessment of service life of concrete structures. In this paper, a probabilistic investigation on hydraulic conductivity of concrete is conducted, allowing for variation in hydraulic properties of concrete constituents. Concrete is modeled as a three-phase composite at mesoscale, consisting of mortar, aggregates, and the interfacial transition zone (ITZ). A finite element (FE) method is developed to calculate the hydraulic conductivity of concrete, which is then verified using available experimental results. Based on a large pool of samples generated from Monte Carlo simulation, a conceptual model relating hydraulic conductivity of concrete to aggregate volume fraction ratio and hydraulic conductivity of mortar and the ITZ is proposed. It is shown from the probabilistic-based sensitivity analysis that hydraulic conductivity and thickness of the ITZ are among the most influential factors affecting the bulk hydraulic conductivity of concrete. It is also shown that for high aggregate volume fraction ratios, due to increasing volume of the ITZ, the coefficient of variation of hydraulic conductivity can be as high as 0.36.

DOI:

10.14359/51706938


Document: 

17-336

Date: 

July 1, 2018

Author(s):

Jun Xu and Fumin Li

Publication:

Materials Journal

Volume:

115

Issue:

4

Abstract:

The diffusivity of chloride ions within the surface layers of concrete (skins) and internal concrete are noticeably different. The diffusivity of chloride ions in the skins follows a gradual change, while it remains stable in internal concrete. In this paper, an N-layered inclusion model, which was divided into finite elements, is presented for the prediction of the diffusivity of concrete with inhomogeneous skins of concrete. The validity of the model is verified with experimental data. Furthermore, a multiphase series-parallel coupling improved model of composite materials was developed and used to calculate the apparent diffusion coefficient of concrete. The proposed improved model satisfied the upper limits of the parallel model as well as the lower limits of the series model, and was compared to the available experimental data to verify rationality and more accuracy than the N-phase sphere model. Finally, a sensitivity analysis was performed on several parameters.

DOI:

10.14359/51702195


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