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International Concrete Abstracts Portal

Showing 1-5 of 270 Abstracts search results

Document: 

22-379

Date: 

March 15, 2024

Author(s):

Joseph Jean Assaad and Marianne Saba

Publication:

Materials Journal

Abstract:

This paper assesses the suitability of geopolymers (GPs) for use as adhesives for ceramic tile fixing, including their compliance to relevant EN 12004 specifications. Two series prepared with different percentages of metakaolin (MK), blast furnace slag (BFS), and limestone materials activated by an alkaline NaOH/Na2SiO3 solution are investigated. Tested properties included the thixotropy, setting, compressive strength, open time, and adhesion bond strength under different exposure conditions (i.e., dry, wet, heat, or freeze/thaw cycles). Compared to cement-based mortars containing adjusted proportions of cellulose and redispersible polymers, the GPs exhibited higher thixotropy reflecting additional energy for spreading the material over the substrate, yet better maintaining of the alternating patterns of ripples and grooves at rest. The bond strengths tested under different exposure conditions were remarkably high for the MK-based GP, given the fine MK particle sizes that foster geopolymerization and cross-linking of solid bonds in the hardened structure. The BFS-based GP exhibited relatively lower bond strengths (compared to MK) due to coarser particles. Such results can be of interest to civil engineers and manufacturers of ready-to-use building materials that aim at reducing the Portland cement footprint while assuring the performance and sustainability of tiling applications.

DOI:

10.14359/51740702


Document: 

22-073

Date: 

December 1, 2023

Author(s):

Zhenwen Xu and Dongming Yan

Publication:

Materials Journal

Volume:

120

Issue:

6

Abstract:

External bonding with fiber-reinforced polymer (FRP) offers a potential solution to mitigate the detrimental effects caused by load impact and corrosion, which can weaken the bond strength of reinforced concrete structures. However, existing models need to be improved in addressing the FRP confinement mechanism and failure modes. As a solution, the proposed model employs stress intensity factor (SIF)-based criteria to determine the internal pressure exerted on the steel-concrete interface during various stages of comprehensive concrete cracking. Critical parameters are evaluated using weight function theory and a finite element model. A bond-slip model is introduced for the FRP-concrete interface and reasonable assumptions on failure plane characteristics. The internal pressure model employed demonstrates that FRP confinement has the ability to generate dual peaks in stress distribution and modify their magnitude as the confinement level increases. The proposed predictive model demonstrates superior performance in failure modes, test methods, and wrap methods for assessing bond strength with FRP confinement. The accuracy of this model is indicated by an integral absolute error (IAE) of 9.6% based on 125 experimental data, surpassing the performance of the other three existing models. Moreover, a new confinement parameter is introduced and validated, showing an upper bound of 0.44 for enhancing FRP bond strength. Additionally, a general expression validating the bond strength model with FRP confinement is established, allowing for the prediction of bond length.

DOI:

10.14359/51739144


Document: 

22-043

Date: 

November 1, 2022

Author(s):

W. K. Toledo, A. Alvarez, G. J. Gonzales, C. M. Newtson, and B. D. Weldon

Publication:

Materials Journal

Volume:

119

Issue:

6

Abstract:

This work investigated the effects of substrate surface moisture condition and texture on ultra-high-performance concrete overlay bond strength. This investigation was performed in three parts that studied extreme substrate moisture conditions, partially dried substrate moisture conditions, and surface texture. These studies investigated the effects of substrate surface moisture conditions, from dry to a surface with a thin layer of free moisture, and surface textures that provided various aggregate exposure conditions on overlay bond strength. Direct tension pull-off tests were conducted to assess overlay bond strength. Results for specimens with exposed fine aggregate surface textures showed that visibly moist substrate surfaces facilitated development of excellent bond strengths, and adequate bond was achieved for conditions with a thin layer of free moisture. For specimens with saturated surface-dry conditions, acceptable bond was achieved with a slightly exposed fine aggregate texture and increasing bond strength was observed with increasing aggregate exposure.

DOI:

10.14359/51736004


Document: 

14-163

Date: 

September 1, 2022

Author(s):

Lars Elof Bryne and Björn Lagerblad

Publication:

Materials Journal

Volume:

119

Issue:

5

Abstract:

Shotcrete (sprayed concrete) differs from ordinary cast concrete through the application technique and the addition of set accelerators that promote immediate stiffening. The bond strength development between shotcrete and rock is an important property that depends on the texture of the rock, the type of accelerator, and application technique. This investigation focuses on the development of the microstructure in the interfacial transition zone (ITZ) and the strength of the bond at the shotcrete-hard rock boundary. The results show that the bond strength is related to the hydration process—that is, the strength gain of the shotcrete—and remains low before the acceleration period of the cement hydration. With a scanning electron microscope (SEM), it is possible to observe changes over time for the early development of the interfacial zone, both before and after proper cement hydration. Results from tests with wet-sprayed concrete on granite rock are presented. The test method—using both bond strength and the SEM to investigate the development of the microstructure at the ITZ—is interesting, but has to be more broadly examined. Different mixtures, accelerators, and rock types have to be used.

DOI:

10.14359/51688826


Document: 

21-412

Date: 

September 1, 2022

Author(s):

Naseeruddin Haris and Sangeeta Gadve

Publication:

Materials Journal

Volume:

119

Issue:

5

Abstract:

Corrosion of steel reinforcing bars in reinforced concrete (RC) structures is a matter of concern among practicing engineers and researchers are perpetually working over it. The development length of reinforcing bars at joints of RC structural frames are more prone to severe corrosion. Due to this, the design stress that needs to be developed in reinforcing bars is largely reduced. In addition, the development lengths of reinforcing bars create congestion at frame joints. This paper is an attempt to overcome these issues. In this paper, an epoxy-grouted nut coupler system is proposed that generates the required design stress in reinforcing bars with a very short development length at end anchorages, due to which congestion of the reinforcing bar at the joints can be avoided. The experimental investigation on the effect of corrosion on bond strength and development length of reinforcing bar in this epoxy-grouted nut coupler is also carried out by performing pullout tests. Statistical models are developed to predict the bond strength between the coupler and reinforcing bar corroded to different levels. This epoxy-grouted nut coupler is an effective tool for developing required stress in reinforcing bars by reducing the actual development length of reinforcing bars in the case of new structures. It is also useful and convenient in regeneration of stress in reinforcing bars at end anchorages that has been lost in corrosion-damaged structures.

DOI:

10.14359/51735977


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