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International Concrete Abstracts Portal

Showing 1-5 of 211 Abstracts search results

Document: 

20-375

Date: 

September 1, 2021

Author(s):

Karthik H. Obla and Colin L. Lobo

Publication:

Materials Journal

Volume:

118

Issue:

5

Abstract:

The resistivity of concrete is gaining acceptance as an easier and more reliable method to measure the penetrability of water and dissolved chemicals into concrete. This study evaluates the surface and bulk resistivity of concrete specimens prepared from mixtures with varying levels of penetrability or transport properties. Test specimens were conditioned by different methods as permitted by the standards. In Part 1, the results indicate that, based on measured resistivity, concrete mixtures are classified for transport properties similar to ASTM C1202. Resistivity measurements were less variable. Changes in the resistivity of specimens placed in simulated service conditions for 1 year are also evaluated. Comparisons were also made on resistivity measured on smaller specimens obtained from different locations of a cylindrical specimen. In Part 2, the impact of various specimen conditioning techniques allowed by the standards on the degree of saturation, resistivity, and characterization of concrete for transport properties are discussed.

DOI:

10.14359/51732934


Document: 

20-376

Date: 

September 1, 2021

Author(s):

Karthik H. Obla and Colin L. Lobo

Publication:

Materials Journal

Volume:

118

Issue:

5

Abstract:

The resistivity of concrete is evolving as a reliable method to measure the penetrability of water and dissolved chemicals into concrete. In Part 1 of this two-part paper, the results of the bulk and surface resistivity of specimens conditioned by different methods were compared to the results of chloride ion penetrability by ASTM C1202, and the precision of test determinations was reported. In Part 2, the results illustrate how changing the specimen conditioning method can change how concrete mixtures are characterized for chloride ion penetrability or transport properties. For the different mixtures evaluated, specimens subjected to the same curing condition had different degrees of saturation levels at the end of the conditioning period. Correcting the measured resistivity for degree of saturation, however, led to inaccurate mixture classification. The paper recommends a preferred specimen conditioning method for the resistivity test.

DOI:

10.14359/51732935


Document: 

20-438

Date: 

July 1, 2021

Author(s):

Yao Luan, Takumi Arasawa, Hiroshi Mutsuyoshi, and Rikako Kawana

Publication:

Materials Journal

Volume:

118

Issue:

4

Abstract:

Cracks in concrete structures increase the penetration of water and deleterious ions, leading to accelerated deterioration. An innovative repair method using bacteria is currently gaining attention. In this method, CO2 is released by bacteria and reacts with calcium ions (Ca2+) to form CaCO3, which heals cracks by deposition. In this study, alkali-silica reaction (ASR)-induced cracks were repaired using two types of bacterial material, containing yeast and Bacillus, respectively. Microbial grouts containing these bacteria were prepared and used to impregnate mortar surfaces with ASR-induced cracks. The cracks were observed to be healed over time, and water absorption and gas permeability were reduced after repair. Thermogravimetric analysis (TGA) revealed that the main precipitate was CaCO3, while mercury intrusion porosimetry (MIP) indicated that the CaCO3 also densified the surface layer of the mortar by refining the pore structure. After repair, the specimens were immersed in water and NaOH solutions to test whether re-expansion occurred. The results showed that when immersed in 0.1 mol/L NaOH or water, the repaired specimens exhibited less expansion than the unrepaired ones.

DOI:

10.14359/51732798


Document: 

20-254

Date: 

March 1, 2021

Author(s):

Vineet Shah and Allan Scott

Publication:

Materials Journal

Volume:

118

Issue:

2

Abstract:

Magnesium silicate hydrate (M-S-H) formed by the reaction between magnesium oxide and amorphous silica in water imparts strength-binding characteristics similar to that of portland cement (PC). Analysis of both the mechanical and durability parameters of MgO-SiO2 binder is essential for its adoption as an alternative cementitious material. This study investigates the mechanical and transport properties of MgO-SiO2 binder concrete. Silica fume and metakaolin were used as amorphous silica sources in the binder. The implications of the addition of magnesium carbonate in MgO-SiO2 binder concrete was also investigated. Along with the compressive strength, other hardened properties of concrete including elastic modulus, shrinkage, porosity, sorptivity, permeability, and resistivity were measured at 7, 28, and 90 days. The overall performance of the concrete was improved through the use of metakaolin instead of silica fume in terms of compressive strength, elastic modulus, and shrinkage. The transport properties of the magnesium oxide and metakaolin mixture were found to be better or similar compared to PC, which was attributed to the refined pore structure and lower porosity. The addition of magnesium carbonate further helped to improve the overall performance of the concrete through likely the formation of hydrotalcite type phases.

DOI:

10.14359/51730418


Document: 

19-503

Date: 

March 1, 2021

Author(s):

Ablam Zidol, Monique T. Tognonvi, and Arezki Tagnit-Hamou

Publication:

Materials Journal

Volume:

118

Issue:

2

Abstract:

It has been demonstrated in recent studies that, unlike general-use cement (GU), glass powder (GP) performs better in concrete mixtures with high water-binder ratios (w/b) in terms of both mechanical properties and chloride ion permeability. This paper aims to deepen investigations on the behavior of concrete incorporating GP in aggressive outdoor environments such as chloride ion diffusion, carbonation, and sulfates as a function of w/b. For comparison purposes, concretes containing conventional supplementary cementitious materials (SCMs) such as Class F fly ash (FFA) and ground-granulated blast-furnace slag (GGBFS) along with control concrete were also studied. In general, GP-based concretes behaved as those containing SCM. Indeed, despite their high w/b, concrete incorporating GP better withstands sulfate attack than the reference. This was mainly attributed to the low chloride permeability of such concretes. Also, as commonly observed with SCM concretes, carbonation was higher with GP-based concrete and increased with w/b.

DOI:

10.14359/51729326


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