- Author
-
Kessler, D. W.
|
Hockman, A.
|
Anderson, R. E.
- Title
- Physical Properties of Terrazzo Aggregates.
- Coporate
- National Bureau of Standards, Washington, DC
- Report
-
BMS 98,
May 20, 1943,
21 p.
- Keywords
-
aggregates
|
physical properties
|
tests
|
void spaces
- Abstract
- Terrazzo specifications seldom afford ade4quate control over the quality of the aggregates, and since troubles sometime occur that are attributed to faulty aggregates, this investigation was undertaken to supply data on certain properties of the marbles used for making terrazzo chips. Comparative data are given on 77 samples of the commonly used products. Samples were supplied by 24 producers representative of various quarries in 12 States. The abrasive resistance, bulk specific gravity, absorption, and toughness tests were made on the rock in the original condition, and the percentage of dust, percentage voids, and thickness grading tests were made on samples of No. 2 chips. Moisture-expansion tests were made on a few samples, including two thought to be faulty. Thermal coefficients were determined for one sample in three directions at right angles to each other. A few samples were found to be rather low in abrasive resistance and friable enough to produce a considerable amount of dust in their shipping containers. Bulk specific gravity and absorption values varied considerably for the entire series and also for samples of similar mineral compositions. The percentages of voids in chips of No. 2 aggregateds were determined for samples when poured into a volumetric measure and also when compacted by vibraing. The void space obtained for loose chips is assumed to be comparable to that of portions measured by workmen in mixing, whereas the values for the vibrated samples give an indication of the minimum amount of cement paste required in a well-rolled terrazzo floor. Since it is commonly believed that flat or thin chips are undersirable, a test was devised to separate samples of No. 2 aggregates (chips passing 3/8 in. and retained on 1/4-in. mesh) into four thicknesses. The percentages of particles in each of these fractions show characteristic differences for samples that are similar in other properties. The shape of the particles seems to bear no relation to the type of crushing equipment used, but is a characteristic of the rock. A few terrazzo slabs were made with chips of unusual thickness distribution and were cut thourgh the middle for studying the orientation of flat or elongated chips in the finished product. These show a tendency for such particles to assume horizontal positions when the terrazzo mixture is rolled, and thus interfere with the removal of excess cement paste. One sample showed a large expansion while absorbing water, the amount being about equal to that of a 70 deg C temperature change, but the expansions for other samples were comparatively low. Contractions of the samples while drying were about the same as expansions while soaking. Thermal-expansion measurements on an impure calcite marble over the range -24 deg to +60 deg C gave variable coefficients over different temperature intervals, and for different directions in the stone. The highest coefficient (0.0000087) was obtained when the specimen was cooled from 60 deg to 0 deg C.