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International Concrete Abstracts Portal

Showing 1-5 of 382 Abstracts search results

Document: 

SP-349_22

Date: 

April 22, 2021

Author(s):

Malene T. Pedersen, Barbara Lothenbach, and Frank Winnefeld

Publication:

Symposium Papers

Volume:

349

Abstract:

In this work, a non-ferrous metallurgical slag has been characterized and its reactivity has been assessed and compared to current SCMs. Additionally, the hydration of a blend of portland cement with 30 wt. % replacement by slag was investigated for hydration kinetics, hydrate phase assemblage and mechanical strength up to 91 days using isothermal calorimetry, XRD and compression tests. The reactivity tests revealed pozzolanic reactivity of the slag and a dissolution behavior comparable to fly ash. The hydrate phase assemblage of the PC-slag blend showed a difference in the AFm phases forming compared to the portland cement reference, which was suggested to be due to the incorporation of Fe. The compressive strength after 28 days of hydration was correlated with the cumulative heat after 7 days of hydration and then compared to current SCMs. Also these results show that the non-ferrous metallurgical slag compares to siliceous fly ash. Hence, this work shows that Fe-rich non-ferrous slags are suitable candidates as SCMs in portland cement.


Document: 

SP-349_21

Date: 

April 22, 2021

Author(s):

Laura Caneda-Martínez, Moisés Frías, Mª Isabel Sánchez de Rojas, Javier Sánchez, and César Medina

Publication:

Symposium Papers

Volume:

349

Abstract:

The current exponential growth in cement demand and the gradual reduction in the availability of the supplementary cementitious materials (SCMs) conventionally employed in the cement sector (fly ash, blast furnace slag, etc.) have brought awareness over the need to find alternative sources of pozzolanic materials. Whereas the use of calcined kaolinitic clays (metakaolinite) could represent an excellent substitute for the traditional SCMs, the environmental and economic cost associated with kaolinite extraction thwarts the development of this course of action. Conversely, the clayey wastes obtained in the coal mining industry could represent an inexpensive and environmentally sound raw material for the production of recycled metakaolinite, promoting at the same time a Circular Economy model.

This work describes the physical and durable properties of binary mortars prepared with different substitution levels (20 % and 50 %) of thermally activated coal mining waste (600 ºC/2 hours), placing emphasis on their chloride resistance. The results show that the differences observed in the pore network and in the mineralogical composition of the blended matrices result in a superior resistance to chloride ingress and, therefore, in a decrease in the risk of corrosion of the subsequent structures and an increase in their service life.


Document: 

SP-349_53

Date: 

April 22, 2021

Author(s):

Thomas, M.D.A., Smith, D. and Moffatt, E.G., Kasaniya, M.

Publication:

Symposium Papers

Volume:

349

Abstract:

This paper presents data on the durability of concrete produced using ground glass as a pozzolan. Various sources of glass were used including soda glass, E-glass and Pyrex glass. All the materials showed excellent pozzolanic activity when ground to pass 75-microns. The use of ground glass resulted in substantial reductions in permeability and chloride penetrability, and improved resistance to sulfate attack. Air-entrained concrete containing glass showed good freeze-thaw resistance. Low alkali E-glass and borosilicate glass were effective in preventing deleterious expansion due to alkali-silica reaction (ASR). Bottle glass, which contains substantial amounts of alkali, was not efficacious with regards to ASR. The inclusion of bottle glass results in very substantial increases to the pore solution alkalinity and this can result in substantial increases in expansion in concrete containing reactive aggregate and low-alkali cement. It is shown that the accelerated mortar bar test is not suitable for evaluating the impact of high-alkali materials on ASR as the alkalis contributed by the cementing materials are released when the mortar bars are masked by the conditions of the test (first immersed in hot water and then in hot NaOH solution).


Document: 

SP-349_29

Date: 

April 22, 2021

Author(s):

Isabel Sánchez, Marina Casas Angulo, Mario Ramírez, Raquel Vigil de la Villa, Rosario García-Giménez, Isabel Sonsoles de Soto García, Moisés Frías and Antonio Zapardiel

Publication:

Symposium Papers

Volume:

349

Abstract:

The use of kaolinite as a pozzolanic activator in the hydration of cement is widely established. The optimum calcination conditions and the scientific basis of the reaction kinetics for the systems metakaolinite (MK)/lime, used as a standard system, and metakaolinite (MK)/cement have been set. These treatments reach their maximum effectiveness in the presence of non-altered calcite. The objective of this research is to determine the influence that calcite has on the pozzolanicity of the kaolinite, in order to do so, different mixtures kaolinite (K)/calcite (Ca) thermally activated at 600ºC and 750ºC for 2 hours were prepared. The products obtained in the pozzolanic reaction were studied with XRD and SEM/EDX analysis. The calcite addition generated an inhibitor effect in the reactivity of natural kaolinite (K) when the thermic activation is at 750°C for 2 hours. The optimal calcination conditions regardless of the proportion of calcite are 600°C/2 hours.


Document: 

SP-349_40

Date: 

April 22, 2021

Author(s):

Victor Poussardin, Michael Paris, Dimitri Deneele, and Arezki Tagnit-Hamou

Publication:

Symposium Papers

Volume:

349

Abstract:

Although normal portland cement is made from natural and recyclable materials its manufacture causes significant pollution, especially because of clinkerization which leads to important CO2 releases into the atmosphere. The use of supplementary cementitious materials (SCMs) to partially replace clinker in normal portland cement and reduce its environmental cost is now well known (e.g., fly ash, metakaolin, glass powder or blast-furnace slag). This study investigates the potential for calcination and reactivity of a carbonate sample containing phyllosilicates. Samples were calcined at different temperatures and investigated using X-ray diffraction (XRD) with Solid State Nuclear Magnetic Resonance (NMR). The results show that the calcination of the sample leads to a dehydroxlation phenomenon of the clay fraction resulting in a change in the coordination of the aluminium atoms. Furthermore, the reaction between the Dolomite and the Palygorskite present in the sample leads to the formation of poorly-crysallized Belite during calcination. Hydration tests on the red-clay sample have demonstrated the hydraulic reactivity of the Belite and the pozzolanic reactivity of the calcined Palygorskite that lead to the formation of hydrates phases (C-S-H ; C-(A)-S-H). The multi-technique analysis applied in this study allows to highlight a direct correlation between the structural modification induced by calcination and the reactivity of the calcined sample.


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