Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
Test method for drying shrinkage of cement mortar
This standard is applicable to the comparison of drying shrinkage performance of different cements.
The drying shrinkage of cement mortar measured in this standard is determined by measuring the length change of 1:2.5 plastic mortar specimen of 25×25×280mm (both ends are equipped with spherical nail head) with comparator after the specimen is cured in dry air.
When the specimen used for determination of drying shrinkage performance is placed in dry air, the temperature is 20±3℃ and the relative humidity is 60±5%. The temperature and humidity shall be checked and recorded every day.
I. Instruments
1. Mortar mixer
See the requirements of GB 177-77 Test method for strength of cement mortar, clause 1, article 1.
2. Shock table, truncated-cone round mold and mold sleeve, cylindrical tamper and caliper, which shall all meet the requirements of GB 2419-81 Test method for fluidity of cement mortar, clause 1.
3. Test mold: triple test mold made of metal material (as shown in figure 1), that may be disassembled and shall be numbered. The inner wall dimension of each part is 25×25×280mm. There is small hole for installation of measuring nail head on top of mold and the position of the small hole must ensure that the measuring nail head is on the center line of the specimen. The measuring nail head is made of stainless steel or copper and has specification as shown in figure 2.
Figure 1 Triple test mold
Figure 2 Nail head
The depth of measuring nail head into the specimen shall be 15±1mm. The distance between inner sides of nail heads shall make the valid specimen length be 250±2.5mm.
4. Tamper: there are two kinds, i.e. square tamper and notched tamper; see figure 3; both are made of metal materials. The compression area of square tamper is 23×23mm. The notched tamper is used to tamp and measure mortars on both ends of the nail head.
5. Three-edge scraper, see the requirements of GB 177-77 Test method for strength of cement mortar.
6. Comparator (as shown in figure 4): composed of dial indicator and bracket. The minimum scale value of dial indicator is 0.01mm and its measuring range is 10mm.
Note: It is allowed to use other types of length measuring instruments, but the accuracy must meet the above requirements. In arbitration inspection, the comparator shall prevail.
Figure 4 Comparator
1——dial indicator; 2——bracket
II. Determination of water consumption for cement mortar
7. The water consumption for cement mortar is determined according to the fluidity of mortars; cement mortar is prepared in accordance with the requirements of GB 177-77, article 15.
8. The fluidity of cement mortar is determined in accordance with the requirements of GB 2419-81, articles 7, 8 and 9.
9. Take the average of two perpendicular diameters as the diffusion diameter at mortar bottom; if the average is between 130~140mm, it is the water consumption for normal consistency; if less than 130mm or larger than 140mm, it is required to add or reduce water for redetermination until the diffusion diameter is between 130~140mm.
III. Molding of cement mortar specimen
10. Three molded specimens are required for the determination of drying shrinkage of cement mortar. 350g of cement specimen and 875g of standard sand shall be weighed for each 3 specimens. The mortar is prepared in accordance with the requirements of GB 177-77, article 15.
Place the uniformly mixed mortar into the test mold with both ends installed with head nail and coated with a layer of machine oil on the inner wall by two layers. Fill the first layer of mortar to a depth of about 2/3 of the height of the test mold. First, scratch the mortar back and forth with a knife to make it become tight (in particular, both sides of the nail head shall be scratched for more times), and then tamp from the inner side of the nail head with a 23×23mm tamper, i.e. tamp from one end to the other sequentially for 10 times (in total 20 times when counting from both directions) between the tails of two nail heads; tamp on each side of the nail head with notched tamper for 2 times, then fill the second layer of mortar. After the test mold is filled with mortar, scrape evenly with a knife. The depth of knife stroke shall go beyond the surface of the first layer of mortar, and then tamp on the specimen with the tamper sequentially for 12 times (in total 24 times when counting from both directions). In each tamping, first make the tamper contact the mortar surface then tamp with force. The tamping must be uniform and stable and hit is not allowed. After tamping, fill the test mold with the left mortars and scrape with three-edge scraper; mark it and place it in curing box with temperature of 20±3℃ and relative humidity of more than 90% for curing.
I. Instruments II. Determination of water consumption for cement mortar III. Molding of cement mortar specimen VI. Demolding and curing of the specimen VII. Measurement of specimen length change VIII. Result calculation Additional explanation:
Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
Test method for drying shrinkage of cement mortar
This standard is applicable to the comparison of drying shrinkage performance of different cements.
The drying shrinkage of cement mortar measured in this standard is determined by measuring the length change of 1:2.5 plastic mortar specimen of 25×25×280mm (both ends are equipped with spherical nail head) with comparator after the specimen is cured in dry air.
When the specimen used for determination of drying shrinkage performance is placed in dry air, the temperature is 20±3℃ and the relative humidity is 60±5%. The temperature and humidity shall be checked and recorded every day.
I. Instruments
1. Mortar mixer
See the requirements of GB 177-77 Test method for strength of cement mortar, clause 1, article 1.
2. Shock table, truncated-cone round mold and mold sleeve, cylindrical tamper and caliper, which shall all meet the requirements of GB 2419-81 Test method for fluidity of cement mortar, clause 1.
3. Test mold: triple test mold made of metal material (as shown in figure 1), that may be disassembled and shall be numbered. The inner wall dimension of each part is 25×25×280mm. There is small hole for installation of measuring nail head on top of mold and the position of the small hole must ensure that the measuring nail head is on the center line of the specimen. The measuring nail head is made of stainless steel or copper and has specification as shown in figure 2.
Figure 1 Triple test mold
Figure 2 Nail head
The depth of measuring nail head into the specimen shall be 15±1mm. The distance between inner sides of nail heads shall make the valid specimen length be 250±2.5mm.
4. Tamper: there are two kinds, i.e. square tamper and notched tamper; see figure 3; both are made of metal materials. The compression area of square tamper is 23×23mm. The notched tamper is used to tamp and measure mortars on both ends of the nail head.
5. Three-edge scraper, see the requirements of GB 177-77 Test method for strength of cement mortar.
6. Comparator (as shown in figure 4): composed of dial indicator and bracket. The minimum scale value of dial indicator is 0.01mm and its measuring range is 10mm.
Note: It is allowed to use other types of length measuring instruments, but the accuracy must meet the above requirements. In arbitration inspection, the comparator shall prevail.
Figure 4 Comparator
1——dial indicator; 2——bracket
II. Determination of water consumption for cement mortar
7. The water consumption for cement mortar is determined according to the fluidity of mortars; cement mortar is prepared in accordance with the requirements of GB 177-77, article 15.
8. The fluidity of cement mortar is determined in accordance with the requirements of GB 2419-81, articles 7, 8 and 9.
9. Take the average of two perpendicular diameters as the diffusion diameter at mortar bottom; if the average is between 130~140mm, it is the water consumption for normal consistency; if less than 130mm or larger than 140mm, it is required to add or reduce water for redetermination until the diffusion diameter is between 130~140mm.
III. Molding of cement mortar specimen
10. Three molded specimens are required for the determination of drying shrinkage of cement mortar. 350g of cement specimen and 875g of standard sand shall be weighed for each 3 specimens. The mortar is prepared in accordance with the requirements of GB 177-77, article 15.
Place the uniformly mixed mortar into the test mold with both ends installed with head nail and coated with a layer of machine oil on the inner wall by two layers. Fill the first layer of mortar to a depth of about 2/3 of the height of the test mold. First, scratch the mortar back and forth with a knife to make it become tight (in particular, both sides of the nail head shall be scratched for more times), and then tamp from the inner side of the nail head with a 23×23mm tamper, i.e. tamp from one end to the other sequentially for 10 times (in total 20 times when counting from both directions) between the tails of two nail heads; tamp on each side of the nail head with notched tamper for 2 times, then fill the second layer of mortar. After the test mold is filled with mortar, scrape evenly with a knife. The depth of knife stroke shall go beyond the surface of the first layer of mortar, and then tamp on the specimen with the tamper sequentially for 12 times (in total 24 times when counting from both directions). In each tamping, first make the tamper contact the mortar surface then tamp with force. The tamping must be uniform and stable and hit is not allowed. After tamping, fill the test mold with the left mortars and scrape with three-edge scraper; mark it and place it in curing box with temperature of 20±3℃ and relative humidity of more than 90% for curing.
Contents of GB 751-1981
I. Instruments
II. Determination of water consumption for cement mortar
III. Molding of cement mortar specimen
VI. Demolding and curing of the specimen
VII. Measurement of specimen length change
VIII. Result calculation
Additional explanation:
