Heat treatment of fresh concrete by radio waves – Avoiding delayed ettringite formation

2017 ◽  
Vol 143 ◽  
pp. 580-588 ◽  
Author(s):  
Björn Höhlig ◽  
Christof Schröfl ◽  
Simone Hempel ◽  
Ina Noack ◽  
Viktor Mechtcherine ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Fresh Concrete ◽  
Radio Waves ◽  
Delayed Ettringite Formation ◽  
Ettringite Formation

Heat Curing and Delayed Ettringite Formation

1994 ◽  
Vol 370 ◽  
Author(s):  
M.C. Lewis ◽  
Karen L. Scrivener ◽  
S. Kelham
Keyword(s):  
Heat Treatment ◽  
Elevated Temperature ◽  
X Ray Diffraction ◽  
Delayed Ettringite Formation ◽  
X Ray ◽  
Preliminary Results ◽  
Ettringite Formation ◽  
Heat Curing ◽  
Xrd Studies ◽  
Over Time

AbstractThis paper reports some preliminary results from a study of the effect of elevated temperature curing on mortars and the phenomenon of delayed ettringite formation (DEF). Mortars made from cements with sulphate levels of 3%, 4%, and 5% and with 5% sulphate and added alkali were cured at 20 and 90° C and subsequently stored in water. Expansion measurements showed a pessimum effect with increasing S03 content. Mortars which expanded showed a corresponding decrease in strength. X-ray diffraction (XRD) studies indicated that no ettringite is present after heat treatment but re-forms over time within the material. However, the ultimate levels of ettringite reached do not correspond to the magnitude of expansion observed. X-ray microanalysis shows that immediately after the heat treatment the aluminate species and most of the sulphate species are incorporated within the C-S-H gel. The concentrations of these species decrease during expansion, such that at the end of expansion the amounts remaining correspond to the presence of AFm phase mixed with C-S-H.

scholarly journals Risk analysis of the delayed ettringite formation in pile caps foundation in the metropolitan region of Recife - PE - Brasil

2016 ◽  
Vol 9 (3) ◽  
pp. 357-394 ◽  
Author(s):  
I. F. Torres ◽  
T. Andrade
Keyword(s):  
Risk Analysis ◽  
Metropolitan Region ◽  
Hardened Concrete ◽  
Chemical Compositions ◽  
Delayed Ettringite Formation ◽  
Ettringite Formation ◽  
Pile Caps ◽  
Foundation Pile ◽  
Physical And Chemical

ABSTRACT Currently, there is an awareness that is critical to assess the durability characteristics of concrete with as much attention as the mechanical properties. The durability of concrete structures can often be affected by chemical attacks, jeopardizing its performance and security. When concrete is subjected to high temperature at early ages, many physical and chemical changes in hardened concrete may occur. It iswidely accepted that concrete subjected to these conditions of temperature and exposed to moisture is prone to cracking due to Delayed Ettringite Formation (DEF). This work aims at providing a DEF risk analysis on foundation pile caps at the Metropolitan Region of Recife - PE. Temperature rise measurement was performed in situ at 5 different caps through datalogger and thermocouples equipments. Furthermore, the Duggan test was performed in order to assess the level of expansion of 3 cements studied: X (CP II E 40), Y (CP II F 32) and Z (CP V ARI RS). Simultaneously, the chemical compositions of these cements and their respective clinkers were quantified by analysis of X-ray fluorescence (XRF). The cement X (CP II E 40) showed the chemical characteristics favoring with more intensity DEF and, as a result, higher level of expansion in the test Duggan. It is noteworthy that incorporation of metakaolin (8% and 16%) and silica fume (5% and 10%) showed mitigating potential of expansions. It is important to point out that all factors related to thermal properties and chemical composition of the concrete used in the region converge to a condition of ideal susceptibility for triggering DEF. Therefore, it is essential at least minimum and basic requirements in the design specification in order to avoid high temperatures in the massive concrete elements, preventing them from delayed ettringite formation.

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