1 Scope
This document specifies the method outline, apparatus, materials, laboratory conditions, specimen forming, specimen maintenance, frost resistance testing, processing of test results, calculation of frost resistance parameters and permissible deviations from the test method for the frost resistance of cementitious sand.
This document applies to the testing of the frost resistance of general purpose silicate cements under water freezing and water thawing conditions.
2 Normative references
The following documents constitute the essential provisions of this document through the normative references in the text. Among them, note the date of the reference document, only the date of the corresponding version applies to this document; do not note the date of the reference document, its latest version (including all the revision of the list) applies to this document.
GB 175 General purpose silicate cements
GB/T 17671 Test method for the strength of cementitious sand (ISO method)
GB/T 50082 Standard for test methods for long-term performance and durability of ordinary concrete
JC/T 243 Concrete Frost Resistance Test Equipment
JC/T 681 Planetary cementitious sand mixer
JC/T 682 cementitious sand test body forming and vibrating table
JC/T 723 Cement sand vibrating table
JC/T 726 Cement sand test moulds
JC/T 960 Automatic pressure testing machine for cementitious sand strength
3 Terms and definitions
The terms defined in GB/T50082 and the following terms and definitions apply to this document.
3.1
Dynamic modulus of elasticity
The coefficient of proportionality between stress and strain in the elastic deformation phase of a material under dynamic loading conditions.
3.2
relative dynamic modulus of elasticity
The ratio of the dynamic modulus of elasticity of a specimen before and after freezing and thawing as calculated by resonance testing, usually expressed as a percentage of the square of the fundamental frequency of vibration of the specimen.
4 Method summary
Two sets of 40mmX40mmX160mm cementitious sand specimens were formed in parallel according to GB/T 17671 and cured under standard conditions.
After a certain age, the specimens are tested for strength loss, mass loss and relative dynamic modulus of elasticity before and after the freeze-thaw cycle to characterise the frost resistance of the cement.
5 Apparatus and equipment
5.1 Cementitious sand mixer
Shall conform to the provisions of JC/T 681.
5.2 Vibrating table
Shall conform to the provisions of JC/T 682.
5.3 Vibrating table
Shall conform to the provisions of JC/T 723.
5.4 Test moulds
Shall conform to the provisions of JC/T 726.
5.5 Scales
Shall conform to the provisions of GB/T 17671.
5.6 Pressure testing machine
Shall conform to the provisions of JC/T 960.
5.7 Temperature sensor
Temperature sensors (including thermocouples, potentiometers, etc.) should be in the range of -20C ~ 20C to determine the temperature of the centre of the test body, and the measurement accuracy
should be 0.5C.
5.8 Rapid freeze-thaw cycle testing machine
Shall comply with the provisions of JC/T243. The centre of the tester and any one diagonal ends should be equipped with temperature sensors, equipment operation
When the freeze-thaw box in each point of the antifreeze temperature difference should not exceed 2C.
5.9 Test box
The test body box should be a rectangular test box made of elastic rubber material, with an external dimension of 55mmX55mmX220mm, and a semi-circular rubber projection with a radius of 3mm on the inner surface of the test body box. The dimensions of the test box are shown in Figure 1.
5.10 Resonance method dynamic elastic modulus tester
Should comply with the provisions of GB/T50082.
6 Materials
Standard sand and test water, should be in line with the provisions of GB/T17671.
7 Test chamber conditions
Test room temperature. Humidity requirements, should be consistent with the provisions of GB/T17671.
8 Test body forming
Cement sand quality ratio according to the provisions of GB/T17671, each pot of sand molding 3 test body, parallel molding 2 groups, each group of 6. The
Among them, mixed with volcanic ash materials of ordinary silicate cement, volcanic ash silicate cement, fly ash silicate cement and composite silicate cement molding water-cement ratio of 0.50, and the flow rate of sand should not be less than 180mm; when the flow rate of less than 180mm should be adjusted accordingly according to the relevant provisions of GB175.
9 Test body maintenance
Cement test body maintenance according to the relevant provisions of GB/T17671, the maintenance age of 28d. Highly blended mixture (≥ 50%) cement, after consultation with the customer, the maintenance age can be up to 90d, and should be indicated in the test report.
10 Frost resistance testing
10.1 Before freezing and thawing, a reference test body shall be made. That is, according to the requirements of Chapter 7 and Chapter 8 of this document to prepare the same specifications of the cementitious sand test body, and the temperature sensor buried in the centre of the test body. The benchmark test body should be more resistant to freezing than the test body to be tested, and there should be no obvious damage to the test body after 25 freeze-thaws. The freezing and thawing medium of the benchmark test body should be potable water.
10.2 Test body according to Chapter 8 requirements after maintenance to the specified age, take a group of test body according to GB/T17671 relevant requirements to test the cementitious strength (eo) before freeze-thaw; another group of test body for freeze-thaw test.
10.3 freeze-thaw test before the start to wipe off the test body surface moisture, and accurately weigh the test body mass (mo) accurate to a decimal. At the same time, according to the relevant provisions of GB/T50082 method to detect the test body transverse fundamental frequency vibration frequency initial value (fo), and record the test body appearance.
10.4 The cement sand test body will be put into the test body box, injected with drinking water and not over the top of the test body 3mm ~ 5mm. then, it will be put into the freeze-thaw test machine test body frame for freeze-thaw test. Each freeze-thaw cycle should be completed within 2h~4h, and thawing and freezing time should be no less than 1h, freezing and thawing when the central temperature of the test body is controlled at a 18C Shi 2C and 5C earth 2C respectively. each freeze-thaw process, the test body from 3C down to -16C time used should not be less than 1/2 of the freezing time, the test body from -16C up to 3C time used should not be less than 1/2 of the whole thawing time. The freeze-thaw cycle should be 25 times, but the number of freeze-thaws can be increased as necessary, but should be indicated in the test report. The number of freeze-thaw tests should not exceed one per freeze-thaw test due to external causes.
10.5 after the completion of the freeze-thaw test remove the test body to wipe off the surface moisture, test the quality of the test body after the east thaw (m,) and test body transverse fundamental frequency vibration frequency (fi), record the appearance of the test body; and according to GB/T17671 test after the freeze-thaw cement sand strength (e,). The test piece should be prevented from losing water during the testing process, and the test piece to be tested should be covered with a wet cloth.
10.6 Calculate the relative dynamic modulus of elasticity, the rate of strength loss and the rate of mass loss before and after freezing and thawing of the specimen according to Equation (1)~Equation (3) to characterise the frost resistance of the cement.
11 Processing of test results
11.1 Frequency of fundamental vibration
The fundamental frequency of each specimen shall be tested twice in parallel and the results of the two tests shall not exceed 0.5% of the average value, and the average of the two results shall be used as the fundamental frequency of the specimen.
11.2 Compressive strength
The compressive strength is measured as the average of 6 test values for each group of 3 specimens. The rejection and processing of the test values shall be carried out in accordance with the relevant provisions of GB/T17671.
12 Frost resistance parameters calculation
12.1 Relative dynamic modulus of elasticity
The relative dynamic modulus of elasticity of the cement test body is calculated according to formula (1), and the calculation result is accurate to one decimal point:
13 Permissible deviations of the test method
13.1 Repeatability
The permissible deviation in the rate of loss of compressive strength of cement of the same sample tested by the same laboratory, the same operator and the same equipment shall not exceed 5%.
13.2 Reproducibility
The permissible deviation in the rate of loss of compressive strength of cement of the same sample tested by different laboratories, personnel and equipment shall not exceed 7%.
Foreword
1 Scope
2 Normative references
3 Terms and definitions
4 Method summary
5 Apparatus and equipment
6 Materials
7 Test chamber conditions
8 Test body forming
9 Test body maintenance
10 Frost resistance testing
11 Processing of test results
12 Frost resistance parameters calculation
13 Permissible deviations of the test method
