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International Concrete Abstracts Portal

Showing 1-5 of 732 Abstracts search results

Document: 

SP-349_03

Date: 

April 22, 2021

Author(s):

Hamza Beddaa, Amor Ben Fraj, Francis Lavergne and Jean Michel Torrenti

Publication:

Symposium Papers

Volume:

349

Abstract:

Dredged river sediments can be considered as a promising alternative for conventional aggregates in concrete. However, the effect of sediments’ properties and particularly their organic matter (OM) content on those of the concrete have to be assessed. Indeed, the organic weight fraction of organic matter in sandy sediments dredged in the Seine watershed is highly variable as it varies from 0 wt% to 10 wt% of the dry matter. This research aims at assessing the effects of humic substances (HS) on the early age behavior of a cement paste. HS are organic compounds resulting from the chemical, physical and microbiological transformation of animals and plants residues and which are also the most representative component of sediments organic matter. A soluble HS, potassium humate, is added as partial substitution of cement; 0.2 wt%, 0.5 wt% and 1 wt%. The results indicate that HS causes a delay of both chemical and autogenous shrinkages by retarding the hydration process. In addition, the chemical shrinkage amplitude is not significantly affected by the presence of HS in the mixture, while the autogenous shrinkage is decreased especially for the high w/b (water/binder; binder=cement+HS) ratios, due to bleeding. Furthermore, for high rates (2% and 3%), this bleeding could generate a delay of setting between the top and the bottom of the sample causing cracks due to a restrained shrinkage in the upper part of the sample.


Document: 

SP-349_31

Date: 

April 22, 2021

Author(s):

Tim Schade and Prof. Dr. Bernhard Middendorf

Publication:

Symposium Papers

Volume:

349

Abstract:

Compared to normal concrete, packing density optimised Ultra High Performance Concretes have a high shrinkage up to 1 mm/m due to their high cement content. Especially in the first 24 hours approximately 80 % of the final shrinkage is reached which reduces the early strength due to microcracks. Instead of additives within the scope of this research work, parts of normal portland cement (NPC) were substituted by Calcium Sulfoaluminate (CSA) Cement and Calcium Aluminate (CA) Cement with the aim to reduce shrinkage of UHPC-mixture as well as a fast setting. CSA-cements with low CO2 footprint are characterised by their fast strength development and expansion behaviour due to early ettringite formation. X-ray diffraction was used to study the phase development. The influence on the shrinkage value was measured by shrinkage tests. In addition, the development of the microstructure was investigated by scanning electron microscopy. Finally, the influence on the strength development was correlated by ultrasonic measurement. These techniques allow a prediction of the setting process in the early stages. Finally, an environmentally friendly NPC-CSA blend could be developed which, in addition to high early strength, also achieves low shrinkage. Furthermore, the influence of the ettringite formation on the microstructure could be determined.


Document: 

SP-349_43

Date: 

April 22, 2021

Author(s):

Yassine El Khessaimi, Youssef El Hafiane, and Agnès Smith

Publication:

Symposium Papers

Volume:

349

Abstract:

Ye’elimite-rich cements or calcium sulfoaluminate cements (CSA) are commercialized to prepare shrinkage compensation and self-stressing concretes. Moreover, CSA cements show environmentally friendly characteristics associated to their production, which include reduced CO2 footprint. The expansive behavior of CSA cements is mainly controlled by ettringite amount, produced upon hydration of the key-phase, ye’elimite [Ca4(Al6O12)SO4]. This paper presents, on one hand, the optimal conditions for the synthesis of highly pure ye’elimite by solid state reactions, and on the other hand, it shows a fundamental description of ye’elimite formation mechanisms. Another aspect of the study encompasses the influence of fineness and citric acid addition on ye’elimite phase dissolution, then on hydrates composition of lab made ye’elimite-rich cement. For the fineness effect study, a highly fine and pure ye’elimite was originally synthetized by sol-gel methods. Various experimental techniques were performed to conduct the different aspects of the present study, namely XRD-Quantitative Rietveld analysis, Thermal analysis (TGA, DTA and Dilatometry), SEM (BSE imaging and EDS mapping), BET analysis, PSD by laser diffraction, and Image analysis (2D porosity and 2D PSD).


Document: 

SP-349_35

Date: 

April 22, 2021

Author(s):

Alexandre Rodrigue, Josée Duchesne, Benoit Fournier and Benoit Bissonnette

Publication:

Symposium Papers

Volume:

349

Abstract:

Alkali-activated slag/fly ash concretes activated with combined sodium silicate and sodium hydroxide show good mechanical and durability properties in general. When tested in terms of resistance to freezing and thawing cycling in watersaturated conditions, the concretes tested in this study show final values of relative dynamic modulus averaging 100% after 300 cycles. However, all tested concretes showed poor performance towards freezing and thawing in presence of de-icing salts with only one tested mixture showing a final average scaling value below 0.5 kg/m². Early-age microcracking is observed on all tested concretes and is correlated to high values of autogenous shrinkage in equivalent paste mixtures. Increasing the fly ash content reduces both the observed autogenous shrinkage and early-age cracking. Low drying shrinkage values ranging from 470 to 530 μm/m after 448 days of measurements at 50% RH and 23°C are noted. The use of fly ash in these alkali-activated concretes reduces the expansion levels of concrete specimens incorporating alkali-silica reactive aggregates. With increasing fly ash contents (20, 30 and 40% replacement), decreasing expansions are observed for any given reactive aggregate. In general, the durability properties measured in this study were improved by partially substituting slag with fly ash as binder material.


Document: 

SP-343_28

Date: 

October 1, 2020

Author(s):

Kitazawa, K.; Sato, Y.; Naganuma, K.; Kaneko, Y.

Publication:

Symposium Papers

Volume:

343

Abstract:

This paper attempts to investigate the effectiveness of Steel Chip Reinforced Polymer Cementitious Composite (SCRPCC) to reduce the seismic drift of high rise building by employing finite element method. Steel chips are produced when a steel plate is precisely machined on a numerically controlled lathe. To verify the influence of drying shrinkage on the structural performance of entire buildings, seismic response analyses of a 22-story RC wall building subject to drying shrinkage cracking are conducted. The analyzed building was damaged in 1985 Mexico Earthquake. In the analyses, drying shrinkage is considered by conducting the drying shrinkage cracking analyses before dynamic seismic vibration analyses to examine the influence of drying shrinkage. For each case of the analyses, two kinds of materials are used; ordinary concrete and SCRPCC. The shrinkage of 8,400-day drying period induces cracks in the walls of top floor as well as the first floor. The maximum drift of the building is increased in the NS direction by the shrinkage cracking while reduced in the EW direction. The maximum total drift of the building during the seismic vibration is reduced by 3.5% in the NS direction and 8.9% in the EW direction by using the SCRPCC instead of the ordinary concrete. The average crack width of the building is reduced by 11.1% by the SCRPCC.


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