Petrographic and Mineralogic Characteristics of Aggregates

Rhoades, Roger; Mielenz, Richard C.

doi:10.1520/stp46210s

Cited by 9 publications

(12 citation statements)

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“…Two groups of minerals found in rock aggregates can cause such reactions. These two groups are carbonates (consisting of fine-grained dolomite and calcite with clay), and silicates (see Mindess et al, 1981;Diamond, 1978;Neville, 1977;BRED, 1982;Rhoades and Mielenz, 1948). All silicate minerals react with strong alkalis to a higher or lesser degrees, though generally three sub-groups of these minerals can react strongly to produce distress in concretes.…”

Section: Snlea Mineralsmentioning

confidence: 99%

“…Cristobalite and coesite which are quite rare minerals are tested to be reactive but however, in practice, they are rarely encountered in aggregates. Silica rich glass found in young volcanics are reactive (Rhoades and Mielenz, 1948;Allen, 1948;Ochard, 1973). BRED (1982) regards "cryptocrystalline" and "microcrystalline" quartz as reactive though Diamond (1978) is of the opinion that the strained varieties of these "two minerals" are likely to cause ASR only.…”

Section: Reactive Siticasmentioning

confidence: 99%

“…Though this mineral is tested to be reactive (Rhoades and Mielenz, 1948), its ravity (in occurrences and amounts) in nature precludes it to be of significance in the cause of ASR.…”

Section: Cristobalitementioning

confidence: 99%

“…This is a rock type rather than a mineral. Acidic volcanic glass and its devitrified equivalents are known to cause ASR (Stanton, 1940(Stanton, (a), 1940; Rhoades and Mielenz, 1948).…”

Section: Acidic Volcanic Glassmentioning

confidence: 99%

“…Alkali silica reactions (ASR) in concrete were first recognised in 1940 (Stanton, 1940a and1940b;Rhoades and Mielenz, 1948) and because of its adversed effects on concretes have been discussed and studied by quite a number of persons (see Neville, 1976;Diamond, 1978;BRED, 1982). This reaction and its worse can cause cracks in concrete and disruption or failure of structures with disastrous results.…”

Section: Introductionmentioning

confidence: 99%

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The mineralogical and petrological factors in Alkali Silica Reactions in concrete

Yeap¹

1992

BGSM

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Reactive silicas which can cause Alkali Silica Reactions (ASR) are opal, Si0 2 rich volcanic glass, chalcedony (or fibrous quartz) and tridymite. Opal is a hydrous cryptocrystalline or colloidal form of silica (Si0 2 nHP) with a water content of around 6% to 10%. Silica-rich volcanic glass is a component of many young volcanic rocks. Chalcedony is a compact variety of silica composed of minute (crypto-or micro-crystalline) crystals of quartz (Si0 2 ) enclosing submicroscopic pores. Tridymite is a rare hexagonal high temperature polymorph of quartz with a S.G. of 2.28.Opaline silica and silica-rich volcanic glass are regarded as the most reactive. Chalcedony, tridymite and some forms of crypto-and microcrystalline quartz occurring in acidic volcanics, chert and flint are regarded as of intermediate reactivity. Strained macrocrystalline quartz can cause ASR but only under certain conditions. A factor which may influence the reactivity of particular aggregate is the proportion of reaction materials that is present in the aggregates. For a very reactive opaline silica the worst expansion may occur when it is found in the order of 2% to 5% (in the coarse aggregate), that is the pessimum. The pessimum for silica-rich volcanic glass is unknown. In the case of the strained macro-crystalline quartz, the pessimum being 100% that is quartzite containing wholly of strained quartz. The pessimum for the intermediate reactive silica is not known, but could well be higher than that of the opaline silica and definitely lower than that of strained quartz.A multitude of rocks can cause ASR and there are many others which will not. Common rock types often used for aggregates can be grouped into: (i) Inherently reactive (ii) Potentially reactive if pessimum amounts of reactive silicas are present and (iii) Innocous unless impregnated by secondary reactive silica minerals. Fine aggregates can also cause ASR to produce distress in concrete.A sweeping ban on all volcanic aggregates for use in concrete may give a false sense of confidence for the control of ASR in Singapore. Banning of alkali rich cement/clinker is a better way of controlling ASR as well as other alkali-aggregate reactions.

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Section: Snlea Mineralsmentioning

confidence: 99%

Section: Reactive Siticasmentioning

confidence: 99%

“…Though this mineral is tested to be reactive (Rhoades and Mielenz, 1948), its ravity (in occurrences and amounts) in nature precludes it to be of significance in the cause of ASR.…”

Section: Cristobalitementioning

confidence: 99%

“…This is a rock type rather than a mineral. Acidic volcanic glass and its devitrified equivalents are known to cause ASR (Stanton, 1940(Stanton, (a), 1940; Rhoades and Mielenz, 1948).…”

Section: Acidic Volcanic Glassmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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