SHOTCRETE: SHRINKAGE IN SPRAYED SAMPLE SLABS
Key words: Shotcrete, shrinkage, test method
1 SCOPE 6 EQUIPMENT
This method describes a means of determining shrinkage of Moulds, distortion-proof and watertight of non-water absor-
shotcrete. bent material (such as steel, specially treated wood or plastic)
with an internal length and width = 400 ± 10 mm and a height
2 APPLICATIONS of 50 ± 5mm.
One of the uses of this method is for preliminary investigations
of shrinkage in different types of shotcrete. The expression Measuring tips of rustproof metal for glueing onto the con-
"shrinkage of shotcrete" as determined in accordance with crete surface.
this method refers to the shrinkage in length or volume ob-
tained when a sprayed slab is dried. Water bath for the specimens with a temperature of
20 ± 1 ºC
3 REFERENCES Climate chamber for the test specimens with a temperature
Steel fiber concrete, Testing and assessment. (cap 5.1 of 20 ± 1 ºC and a relative humidity of 50 ± 5 %.
Shrinkage) Alemo, Holmgren, Skarendal
SS 13 72 15 Measuring equipment for determination of the change in
Shrinkage length of the test specimens from one occasion of measure-
ment to another with a precision within ± 0,01 mm.
SS 13 72 20
Concrete testing - Hardened shotcrete - Com- 7 SAMPLE PREPARATION AND TESTING
pressive strength of shotcrete test specimens
7.1 Spraying of sample slabs
Sample slabs are sprayed in the stipulated shotcrete quality
4 DEFINITIONS and with the stipulated equipment, at right angles to the bot-
"Shrinkage of concrete" is defined as the decrease in length or tom of the mould. The shotcrete is sprayed into the mould in
volume obtained in conjunction with the drying of the con- one or more layers with no time interval between the layers.
crete. The maximum thickness of the sample slabs should be
50 mm. At least two test slabs of each shotcrete quality should
5 THE PRINCIPLE OF THE TEST METHOD
Test slabs are sprayed to the desired thickness, but maximum 7.2 Curing of the sample slabs
50 mm, in a mould of non-absorbent material, and are then During the first 24 hours there must be a sufficient supply of
stored in water for one week. During the water storage period water on the surface of the shotcrete. During the subsequent
test specimens are sawn out and steel tips attached to both 6 days the sample slabs are stored in a water bath with a
sides of the test specimen. After 7 days the test specimens are temperature of 20 ± 1 ºC with the exception of the time re-
removed from the water bath and the progress of shrinkage is quired to saw the slabs and attach the measuring tips. During
established. this period the samples are kept continually moist.
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NORDTEST METHOD NT BUILD 352 2
7.3 Manufacture of test specimens 8 RESULTS
During the curing period, square test specimens with 250 mm At least the following information is to be given about each test
sides are sawn, and four measuring tips attached in a square specimen:
fashion to each flat side, so that the measuring length
a) the marking of the test specimen
between the tips is approximately 200 mm. The tips are
placed symmetrically so that length measurements take place and for each test specimen and measurement occasion
parallel with the edge of the test specimens. b) age
c) shrinkage, i.e. the mean value of the decrease in length
of the eight measurement sections in relation to the cor-
responding length at the age of 7 days.
Any report submitted is to contain at least the following infor-
a) name and address of the test laboratory
Faulty test specimens are discarded. The number of faulty
b) date and identification number of report
specimens and the cause of discarding are noted.
c) test method (Nordtest number and title)
When the test specimens are 7 days old they are removed deviations from the method description, if any
from the water-bath and placed in the curing chamber.
e) name and address of commissioning party
Immediately after the removal they are measured along the f) name of tester and method of test specimen manufac-
eight measuring sections with the measuring equipment ture
against the measuring tips. Changes in length of the test name of manufacturer of shotcrete
specimens are then noted, with a precision of ± 0,01 mm
h) composition of the shotcrete
unless otherwise specified, when the test specimens are 14,
21, 35, 63, 119, and 231 days old (i.e. 2 x 7, 4 x 7, 8 x 7, i) date of receipt and test
16 x 7, and 32 x 7, days after the first measurements are j) test results
k) other information which may influence the assessment
When measurements are carried out the measuring equip-
ment is to be of the same temperature as the test specimens. l) assessment of results if requested in the commission.