Tímarit Verkfræðingafélags Íslands


Tímarit Verkfræðingafélags Íslands - 01.10.1959, Blaðsíða 21

Tímarit Verkfræðingafélags Íslands - 01.10.1959, Blaðsíða 21
TlMARIT VFl 1959 71 MOBERG P0Z20LANS by Hörður Jónsson' and Haraldur Ásgeirsson*. Móberg is a rock formation which is found in abun- dance in Iceland. This volcanic glass substance of dif- ferent morphological stages has in earlier tests exhibited decisive pozzolanic activities (1). As the use of pozzolans may be of considerable im- portance (2) in future constructions in this country it was decided to conduct some research on pozzolans at this laboratory. This interim report is prepared in order to present the data already obtained and to contemplate what further studies should be carried out. Natural pozzolans are not used intentionally in Ice- land, in spite of numerous possible advantages. One reason being perhaps the inability to judge pozzolans except by long time performance tests (3,4). Pozzolans, however, often enter unintentionally into concretes as silty impurities in basaltic aggregates. In the fall of 1956 fifteen samples were collected for pozzolanic testing. These samples were gathered from the neighbourhood of power plants already planned, in the vicinity of Hvítá and Thjórsá rivers and from locations near Reykjavik. Of these samples, twelve were of moberg, one of rhyolitic pumice, one of pumice and volcanic ash and one of olivine rich sand. Table I lists more precisely localities where these samples were taken. They were selected in a close collaboration with the geologist of the Institute, Mr. Tomas Tryggvason, who has prepared the petro- graphic descriptions included in table I. From the numerous methods adapted for pozzolans, the following physical and chemical tests were performed: 1. Chemical analysis (5). 2. Surface area determinations (6). 3. Dissolved silica and reductions in alkalinity (7). 4. Ability to combine with lime (8). 5. Solubility in boiling 5% HCl (9). 6. Mortar specimens were made in accordance with 1 Chemical Engineer at the University Reseai’ch Institute. - in charge of the Material Testing Division of the University Research Institute. DIN 1164 (German specification) except that in these 15 and 30 per sent of the cement was re- placed with pozzolans. The mortars were cured in a saturated lime solution for 3, 7, 28, 90, 180 and some for 360 days. (10). 7. Free lime in 180 day mortars (11). 8. Lime mortar strength determinations (12). For preparation of mortars two grades of standard sand were used, marked sample 16 and sample 17. No. 16 is a quax-tz sand (German cement spec.) and 17 is Ottowa silica sand (A.S.T.M. cement spec.). These sands were used as reference samples in a number of tests. The cement used was type I Danish Portland cement. Additional test under way is the pyrex glass aggregate expansion test (13). ,,A pozzolan is a silicous or silicous and alumineous material, which in itself possesses little or no cementi- tious value, but will in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties“ (A.S.T.M. standards 1958, Part 4, page 195). It can be seen frorn this defination that pozzolans can be complex materials. It is therefore to be anticipated that these do respond diffei'ently to different tests. It is also well known that both chemical and physical met- hods of testing pozzolans have a large number of re- coginzed limitations (13). Some of these test are arbitrary ones obtained from experience with one or moi-e types of pozzolans, (13, 14). Others are designed to reveal a more genei'al character (15, 23.). The data already obtained in this investigation and the trends seen are presented in the following graphs, tables and discussions. 1. Results of chemical analysis are shown in table II. These analysis do not indicate any well defined re- lation to pozzolanic activity as exhibited by other tests. The Chemical composition of the mobei'g is a basaltic one and resembles some Italian pozzolans as shown in Chemistry of Cement and Concrete by Lee and Desch (16), p. 359. Free and ci'ystalline water (13) does not seem to influence to any noticeable extent the pozzo- lanic activity.

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