Historical Version s - view previous versions of standard. Work Item s - proposed revisions of this standard. More C This standard is intended to assist in understanding the meaning and significance of the terms. Reference to these descriptions may, however, serve to indicate or prevent gross errors in identification. Identification of the constituent materials in an aggregate may assist in characterizing its engineering properties, but identification alone cannot provide the sole basis for predicting behavior of aggregates in service.

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Designation: C — Copyright ASTM. Standard Descriptive Nomenclature for. Constituents of Concrete Aggregates 1. A number in parentheses indicates the year of last reapproval.

A superscript epsilon e indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the Department of Defense. The descriptions provide a basis for understanding these terms as applied to concrete aggregates. N OTE 1—These descriptions characterize minerals and rocks as they occur in nature and blast-furnace slag or lightweight aggregates that are prepared by the alteration of the structure and composition of natural material.

Referenced Documents. Current edition approved August 10, Published March Originally published as C — Last previous edition C — 86 e 1. This standard has been extensively revised.

The reader should compare this edition with the last previous edition for exact revisions. This standard. Aggregates of any type or combination of types may perform well or poorly in service. Information about con- crete aggregate performance in concrete has been published by ASTM. Classes and Types. Most rocks are composed of several minerals but some are composed of only one mineral.

Certain examples of the rock quartzite are composed exclu- sively of the mineral quartz, and certain limestones are composed exclusively of the mineral calcite. Individual sand grains frequently are composed of particles of rock, but they. These three. Sedimentary rocks may form from pre-existing igneous, metamorphic, or sedimentary rocks.

Silica Minerals. It will scratch glass and is not scratched by a knife. When pure it is colorless with a glassy vitreous luster and a shell-like conchoidal fracture.

It is resistant to weathering and is therefore an important constituent of many sand and gravel deposits and many sandstones. It is also abundant in many light-colored igneous and metamorphic rocks. When X-ray diffraction methods are used, opal may show some evidences of internal crystalline arrangement. The color is variable and the luster is resinous to glassy. It is usually found in sedimentary rocks, especially some cherts, and is the principal constituent of diatomite. The recognition of opal in aggregates is important because it is potentially deleteriously reactive with the alkalies in hydraulic cement paste or with the alkalies from other sources, such as aggregates containing zeolites, and ground water.

The properties of chalcedony are intermediate between those of opal and quartz, from which it can sometimes be distinguished. It frequently occurs as a constituent of the rock chert and is potentially deleteriously reactive with the alkalies in hydraulic cement paste. They are metastable at ordinary temperatures and pressures. C They are rare minerals in aggregates except in areas where volcanic rocks are abundant. A type of cristobalite is a common constituent of opal.

Tridymite and cristobalite are potentially deleteriously reactive with the alkalies in hydraulic cement paste. They are important constituents of all three major rock groups, igneous, sedimentary, and metamorphic. Since all feldspars have good cleavages in two directions, particles of feldspar usually show several smooth surfaces.

All feldspars are slightly less hard than, and can be scratched by, quartz and will, when fresh, easily scratch a penny. The various members of the group are differentiated by chemical composition and crystallographic properties. The feldspars orthoclase, sanidine , and microcline are potassium aluminum silicates, and are frequently referred to as potassium feldspars. The plagioclase feldspars include those that are sodium aluminum silicates and calcium alumi- num silicates, or both sodium and calcium aluminum silicates.

Potassium feldspars and sodium-rich plagioclase feldspars occur typically in igneous rocks such as granites and rhyolites, whereas, plagioclase feldspars of higher calcium content are found in igneous rocks of lower silica content such as diorite, gabbro, andesite, and basalt.

Ferromagnesian Minerals. They include the minerals of the amphibole, pyroxene, and olivine groups. The most common amphibole mineral is hornblende; the most common pyroxene mineral is augite; and the most common olivine mineral is forsterite. Dark mica, such as biotite and phlogopite, are also considered ferromagnesian minerals. The amphibole and py- roxene minerals are brown to green to black and generally occur as prismatic units.

Olivine is usually olive green, glassy in appearance, and usually altered. These minerals can be found as components of a variety of rocks, and in sands and gravels. Olivine is found only in dark igneous rocks where quartz is not present, and in sands and gravels close to the olivine source.

Micaceous Minerals. The mica minerals of the muscovite group are colorless to light green; of the biotite group, dark brown to black or dark green; of the lepidolite group, white to pink and red or yellow; and of the chlorite group, shades of green. Another mica, phlogopite, is. The mica minerals are common and occur in igneous, sedi- mentary, and metamorphic rocks, and are common as minor to trace components in many sands and gravels.

Vermiculite a mica-like mineral forms by the alteration of other micas and is brown and has a bronze luster.

Clay Minerals. Members of several groups, par-. Some clays are made up of alternating layers of two or more clay groups. Random, regular, or both types of interlayering are known. They are formed by alteration and weathering of other silicates and volcanic glass. The clay minerals are major constituents of clays and shales. They are found disseminated in carbonate rocks as seams and pockets and in altered and weathered igneous and metamorphic. Some of these aggregates will disintegrate when wetted.

Rocks in which the cementing matrix is principally clay, such as clay-bonded sandstones, and rocks in which swelling clay minerals smectite are present as a continuous phase or matrix, such as in some altered volcanics, may slake in water or may disintegrate in the concrete mixer. Rocks of this type are unsuitable for use as aggregates.

Rocks having these properties less well developed will abrade considerably during mixing, releasing clay, and raising the water requirement of the concrete containing them. When such rocks are present in hardened concrete, the concrete will manifest greater volume change on wetting and drying than similar concrete containing non-swelling aggregate.

Zeolites Laumontite and its partially dehydrated variety leon- hardite are notable for their substantial volume change with wetting and drying. Both are found in rocks such as quartz diorites and some sandstones. Carbonate Minerals. They have rhombohedral cleavage, which results in their breaking into fragments with smooth parallelogram shaped sides. Calcite is soluble with vigorous effervescence in cold dilute hydrochloric acid; dolomite is soluble with slow effervescence in cold dilute hydrochloric acid and with vigorous effervescence if the acid or the sample is heated or if the sample is pulverized.

Sulfate Minerals. Gypsum is usually white or colorless and characterized by a perfect cleavage. Gypsum may form a whitish pulverulent or crystalline coating on sand and gravel. It is slightly soluble in water.

Anhydrite is harder than gypsum. Gypsum and anhydrite occurring in aggregates can cause sulfate attack in concrete and mortar. Pyrite is found in igneous, sedimentary, and metamorphic rocks; marcasite is much less common and is found mainly in sedimentary rocks; pyrrhotite is less common but may be found in many types of igneous and metamorphic rocks.

Pyrite is brass yellow, and pyrrhotite bronze brown, and both have a metallic luster. Pyrite is often found in cubic crystals. Marcasite readily oxidizes with the liberation of sulfuric acid and formation of iron oxides, hydroxides, and, to a much smaller extent, sulfates; pyrite and pyrrhotite do so less readily. Marcasite and certain forms of pyrite and pyrrhotite are reactive in mortar and concrete, producing a brown stain accompanied by a volume increase that has been reported as.

Iron Oxide Minerals, Anhydrous and Hydrous. Another common iron-bearing mineral is black, weakly magnetic, ilmenite FeTiO 3. Magnetite and ilmenite are important acces- sory minerals in many dark igneous rocks and are common detrital minerals in sediments.

Hematite is frequently found as an accessory mineral in reddish rocks. The presence of substantial amounts of soft iron-oxide minerals in concrete aggregate can color concrete various shades of yellow or brown. Very minor amounts of iron minerals color many rocks, such as ferruginous sandstones, shales, clay-ironstones, and granites. Magnetite, ilmenite, and hematite ores are used as heavy aggregates. They may be divided into two classes: 1 plutonic, or intrusive, that have cooled slowly within the earth; and 2 volcanic, or extrusive, that formed.

Volca- nic rocks frequently contain glass.


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ASTM C294 - 19

The descriptions provide a basis for understanding these terms as applied to concrete aggregates. When appropriate, brief observations regarding the potential effects of using the natural and artificial materials in concrete are discussed. Information about lightweight aggregates is given in Specifications C , C , and C See Descriptive Nomenclature C

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