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International Concrete Abstracts Portal

Showing 1-5 of 651 Abstracts search results

Document: 

SP-362_70

Date: 

June 18, 2024

Author(s):

Nader Ghafoori, Ariful Hasnat, and Aderemi Gbadamosi

Publication:

Symposium Papers

Volume:

362

Abstract:

This paper examines the influence of harvested fly ash on the properties of mortar and concrete. Class F and harvested fly ash were used at the substitution rate of 20% by weight of Portland cement. The investigated properties included heat release, consistency, setting time, compressive strength at different testing ages, absorption, the volume of permeable voids, surface resistivity, and drying shrinkage. The results revealed that the harvested fly ash produced the lowest released heat of hydration and longest setting times. Mixtures containing harvested fly ash displayed lower strength at all curing ages. Compared to traditional fly ash, harvested fly ash showed inferior transport properties for both absorption rate, permeable voids, and surface resistivity. Mixtures containing harvested fly ash showed comparable 120-day drying shrinkage when compared with the companion mortars made with traditional fly ash.


Document: 

SP-362_68

Date: 

June 18, 2024

Author(s):

Troian Viacheslav, Gots Volodymyr, Bruno Alex, Panek Rafał, and Flatt Robert J.

Publication:

Symposium Papers

Volume:

362

Abstract:

It is known that the use of recycled coarse aggregates (RCA) can raise a variety of problems, which are mainly due to the porosity of the old mortar contained in RCA. One of the simpler ways to solve these problems is the pre-wetting of RCA, which allows not only to minimize disadvantages but also to obtain the advantages associated with the effect of internal curing. Undoubtedly, the strongest positive effect of pre-wetted RCA is on the rheology of recycled concrete. But there are also possible positive effects of internal curing for strength and durability of blended cement concretes, which require longer curing times compared to normal Portland cement concrete. In this paper, we mostly study the influence of porous RCA on the rheology of cement paste, based on slag cement with a 75% slag content. For this purpose, the absorption properties of RCA of different sizes were studied. From this, mathematical dependences of the workability of cement systems on w/c and time could be obtained. These further underline the positive effect of pre-wetting of RCA with regard to retaining the workability of cementitious systems. This lays the basis for a broader study of pre-wetting RCA on the rheology of mixtures, strength, and durability to be covered in future publications.


Document: 

SP-362_44

Date: 

June 14, 2024

Author(s):

Dena Shalaby, Émilie Garneau, Mathieu Fiset, Joao Augusto Lago Araujo Seixas, Ahmed Rahem

Publication:

Symposium Papers

Volume:

362

Abstract:

The Production of Portland cement used in concrete and the large amount of industrial waste generated worldwide represent critical environmental and economic issues. The reuse of bauxite residue generated during alumina production by Bayer’s process to replace Portland cement and produce sustainable and environmentally friendly geopolymer concrete is a promising solution. This paper presents the development and characterization of bauxite residue and class F fly ash-based geopolymer mortar and concrete. The parameters studied for the mixture proportions are the bauxite residue to class F fly ash ratio, the water-to-binder ratio, and the curing condition, in terms of duration and temperature. Then, the compressive strength of the geopolymer mortar and concrete is characterized with experimental tests. Results show that, with appropriate mixture proportions and curing conditions, a large amount of bauxite residue (up to 70%) can be used to replace fly ash and obtain geopolymer concrete with improved quality characteristics that meet the construction field’s sustainable development criteria.


Document: 

SP-362_24

Date: 

June 6, 2024

Author(s):

Harald Justnes, Tobias Danner, Elise Marie Rong Anfinsen, Aleksandra Marie Høye, Margrethe Munch-Ellingsen, and Mehrdad Torabzadegan

Publication:

Symposium Papers

Volume:

362

Abstract:

The objective is to elucidate the effect of calcium nitrate CN on cement replaced with 50% blast furnace slag (ggbs). The influence of 2 and 4% CN accelerator on hydration development of these binders was investigated by isothermal calorimetry, X-ray diffraction, and thermogravimetry. The strength development of mortar with two different ggbs blended binders cured at 20°C was followed and the influence of CN was discussed. Concrete with 50% of a third ggbs, 0, 2, and 4% CN and w/c = 0.46 was cured at +5°C and compressive strength development was measured. CN led to lower mortar strength at 1 day at 20°C, but higher strength from 3 days onwards. Mortar with two different ggbs achieved the same strength at 7 and 28 days when added 4% CN. However, CN increased the 1-day strength of concrete cured at +5°C. Since ggbs is accelerated by high pH, the somewhat lower 1-day strength in mixes with CN is probably caused by the immediate precipitation of hydroxyl ions by calcium to portlandite leading to a lowering of the pH. CN led to more ettringite formation and AFm phases at 1-day sealed curing and the calcium hydroxide content was reduced. Reasons for calcium hydroxide reduction are discussed.


Document: 

SP-355_14

Date: 

July 1, 2022

Author(s):

Harald Justnes, Tobias Danner

Publication:

Symposium Papers

Volume:

355

Abstract:

The long-term stability of aluminum metal in binders intended for concrete has been studied. Aluminum was cast in paste where 55% cement was replaced by calcined smectitic clay. After 7 days of curing several samples were submersed in either distilled water or in a 6% NaCl solution. After 1 year of submersion, the microstructure of samples submitted to both exposure conditions was analyzed. Chloride corresponding to 1.5-2% Cl- of cement mass had reached the Al-bar. The surface of the Ø 10 mm aluminum bar had corroded to a depth of less than 10μm, irrespectively if it was submerged in water or in 6% NaCl. There was no sign of intergranular corrosion. The hydrated binder consisted of amorphous calcium silicate hydrate gel and crystalline layered double hydroxides of hydrocalumite-type. When cured in water, the crystals were a mix of hemi- and mono-carboaluminate, but when stored in 6% NaCl, the carbonate/hydroxide was partly replaced by chloride. There was a dense binder zone formed around the ≈ 15 μm oxide layer of the aluminum bar richer than the overall binder in aluminum. Some of the alumina formed on the metal surface may have been partly dissolved by alkalis and precipitated/reacted with the nearest binder region and densified it and thus preventing further reaction.

DOI:

10.14359/51736020


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