Delayed ettringite formation in massive concrete structures: an account of some studies of degraded bridges

2004 ◽  
Author(s):  
E. Menéndez
Keyword(s):  
Concrete Structures ◽  
Delayed Ettringite Formation ◽  
Massive Concrete ◽  
Ettringite Formation

Diagnosing delayed ettringite formation in concrete structures

2008 ◽  
Vol 38 (6) ◽  
pp. 841-847 ◽  
Author(s):  
Michael Thomas ◽  
Kevin Folliard ◽  
Thano Drimalas ◽  
Terry Ramlochan
Keyword(s):  
Concrete Structures ◽  
Delayed Ettringite Formation ◽  
Ettringite Formation

The Application of Fluorescence Microscopy and Scanning Electron Microscopy in the Detection of Delayed Ettringite Formation in Concrete

2010 ◽  
Vol 636-637 ◽  
pp. 1266-1271
Author(s):  
L. Matos ◽  
António Santos Silva ◽  
D. Soares ◽  
Manuela M. Salta ◽  
José Mirão ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Concrete Structures ◽  
X Ray Diffraction ◽  
Delayed Ettringite Formation ◽  
Thin Sections ◽  
Ettringite Formation ◽  
Heat Cure ◽  
Fluorescence Light ◽  
Scanning Electron

The degradation of concrete structures caused by delayed ettringite formation (DEF) is a problem that nowadays affects many concrete structures worldwide. This pathology is due to the formation of an expansive compound – ettringite - inside the material. This is a hydrated calcium sulphoaluminate produced by the chemical reaction between sulphate ions, calcium hydroxide and alumina present in the Portland cement paste. This product, normally formed during the hydration of cement, presents an acicular morphology (needles) that can be observed by scanning electron microscopy (SEM). However, DEF can also be formed after the setting of the cement causing, in this case, a deleterious expansion of the concrete. This secondary ettringite can also be produced after an excessive heating of the concrete, caused by a high amount of cement or by the use of heat cure. SEM has been used to distinguish between expansive and non expansive ettringite based normally in morphology analysis, since the former is characterized by a compressed or compact nature where the needle shapes disappear or are welded together. Furthermore, the use of other techniques, like X-ray diffraction or micro-XRF, has been limited because the compressed or compact ettringite is badly crystallized or even amorphous and the elemental composition is similar and therefore it is difficult to detect. This article presents a methodology for the diagnosis of DEF using polished concrete thin sections and combining polarised and fluorescence light optical microscopy with SEM-EDS.

Study on the Delayed Ettringite Formation in Massive Shrinkage Compensating Concrete with U-Type Expansive Agent

2011 ◽  
Vol 477 ◽  
pp. 340-347
Author(s):  
Qian Wang ◽  
Zheng Yue Ren ◽  
Zhe Zhang
Keyword(s):  
Thermal Stability ◽  
Water Supply ◽  
Ambient Temperature ◽  
Formation Condition ◽  
Test Results ◽  
Delayed Ettringite Formation ◽  
Massive Concrete ◽  
Ettringite Formation ◽  
Simulated Environments ◽  
Expansive Agent

This paper introduces the research results of the thermal stability and the delayed formation of ettringite in China and abroad. Aiming at the debate of the ettringite delayed formation condition of the massive shrinkage compensating concrete in the engineering field, the decomposition and delayed formation of ettringite were studied in simulated environments in massive concrete and other controlled curing environment. As UEA is the most applied expansive agent in domestic, the massive shrinkage compensating concrete mixed with UEA is selected as the research object. The test results show that, AFM appears in the research specimens when the inner temperature reach 80°C and the ettringite can reform under the condition of rich water supply after the concrete cooling to an ambient temperature. By comparing the test results of different curing environment, some points for attention during the construction of the UEA massive shrinkage compensating concrete are proposed.

scholarly journals Influence of Mineral Additions in the Inhibition of Delayed Ettringite Formation in Cement Based Materials – A Microstructural Characterization

2010 ◽  
Vol 636-637 ◽  
pp. 1272-1279 ◽  
Author(s):  
António Santos Silva ◽  
D. Soares ◽  
L. Matos ◽  
Manuela M. Salta ◽  
L. Divet ◽  
...  
Keyword(s):  
Concrete Structures ◽  
Microstructural Characterization ◽  
Delayed Ettringite Formation ◽  
Ettringite Formation ◽  
Long Term Storage ◽  
Long Term Study ◽  
Heat Curing ◽  
Mineral Additions ◽  
Length Changes

The degradation of concrete structures caused by delayed ettringite formation (DEF) is a problem that affects many concrete structures worldwide [1]. This pathology is due to the formation of expansive ettringite inside the material and is very difficult to deal with, because presently there is no efficient method to repair concrete structures affected by DEF. Hence, there is an urgent need to find preventive methods that may enable the inhibition of DEF in new constructions. This paper presents the findings of a long-term study [2,3] on the expansion rate and microstructure of heat-cured concretes with different amounts of mineral additions, like fly ash, metakaolin, ground granulated blast-furnace slag, silica fume and limestone filler. For this purpose different concrete compositions were produced using the same binder, water/binder (w/b) ratios and aggregate type. The concretes were prepared and subjected to a heat-curing cycle and subsequently to two drying-humidification cycles. After these cycles the concrete specimens were immersed in water for long-term storage at 20 ± 2°C. Length changes of specimens were measured at regular intervals. The microstructures of old heat curing specimens were investigated by optical microscopy and SEM-EDS analysis. The results of the blended-concrete compositions were compared with control compositions, and the conclusions were extracted.

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