Retarder is a common concrete admixture used to adjust the setting time of concrete and slow down its early setting rate. In concrete construction, concrete needs to be poured into the formwork, then vibrated, leveled and other processes are performed, and finally the concrete is gradually solidified and hardened. If the concrete setting speed is too fast, it will cause problems such as dry cracking and hollowing of the concrete surface, and it will also bring inconvenience to the concrete construction. The retarder can delay the setting speed of the concrete, making the concrete easier to operate during construction, and at the same time improving the strength and durability of the concrete. Common retarders include phosphate, glucose, sodium carbonate, etc. Different retarders are suitable for different concrete projects and construction environments.
Detection performance
The following is a brief introduction to some properties and related test methods that retarders may need to test:
| performance | Test Methods |
|---|---|
| retarding time | According to the requirements of the standard, after mixing the retarder with the concrete, measure the setting time of the concrete, such as ASTM C191. |
| Compressive strength | Using standard test methods, put the concrete mixed with the retarder into the mold, and after the standard curing time, perform the compressive strength test, such as ASTM C39. |
| tensile strength | According to the requirements of the standard, put the concrete mixed with the retarder into the standard test piece, perform the tensile test after curing, such as ASTM C496. |
| Permeability | Standard test methods are used to measure the penetration resistance of concrete mixed with retarders under a certain water pressure, such as ASTM C1202. |
| chemical composition | Use chemical analysis methods to analyze the main chemical composition and content of the retarder, such as XRF analysis. |
Detection method
Retarding time: According to the standard requirements, prepare a certain amount of concrete and retarder, mix the concrete and retarder evenly, then observe the setting of the concrete under the specified temperature and humidity conditions, and record the time when the concrete begins to set and reach a certain strength. This time is the retarding time.
Compressive strength: Mix concrete and retarder evenly according to a certain ratio, then put it into a standard specimen, perform standard curing within a certain period of time, and then use a pressure testing machine to perform a compression test on the specimen to calculate the compressive strength of the concrete.
Tensile strength: Mix concrete and retarder evenly according to a certain ratio, then put it into a standard specimen, perform standard curing within a certain period of time, and then use a Tensile Testing Machine to perform a tensile test on the specimen to calculate the tensile strength of the concrete.
Permeability resistance: Mix concrete and retarder evenly according to a certain ratio, then put it into a standard test piece, and carry out standard curing within a certain period of time. Then put the test piece under a certain water pressure, observe the water seepage on the surface of the test piece, and calculate the permeability resistance of the concrete according to the water seepage.
Chemical composition: The chemical analysis method is used to analyze the composition of the retarder through X-ray fluorescence spectroscopy and other instruments. XRF analysis is a non-destructive analysis method that can quickly and accurately analyze the element content and composition in the sample.
Beichao reminds you: different types of retarders may need to choose different test methods. For example, certain retarders may require testing for toxicity and environmental impact. In the specific detection, the corresponding test method should be selected according to the type and use of the retarder.
