In fact, the current evaluation method for the retarding effect of concrete retarder is still relatively limited, mainly the measurement of retarder setting time and setting time difference.
1. For clean slurry, the standard method is the test specified in "Cement standard consistency water consumption, setting time, stability test method" (GBT 1346-2011) method. The instrument used in this method is a standard Vicat meter. Before measuring the setting time of the concrete retarder, it is necessary to pre-measure the standard consistency water consumption, then prepare the cement slurry according to the standard consistency water consumption, and measure the initial setting and final setting time of the cement slurry.
The advantage of this method is that it is convenient and fast, but the disadvantage is that there is a large human error, which is mainly reflected in the contingency in the operation process and readings, especially in determining The human error in the final setting time is even more obvious.
2. For concrete, the standard method is the test method specified in "Concrete Admixtures" (GB8076-2008). The instrument used in this method is a penetration resistance meter. Before measuring the setting time, the concrete mixture needs to be sieved out of the mortar with a 5mm (round hole sieve) vibrating screen and put into a standard metal cylinder. The penetration resistance value and time can be obtained. Relationship curve, and then find out when the penetration resistance value reaches 3.5MPa, the corresponding time is regarded as the initial setting time; when the penetration resistance value reaches 28MPa, the corresponding time is regarded as the final setting time.
The advantage of this method is that the results are accurate and the error is small. The disadvantage is that the operation process is complicated and time-consuming.
3. With the advancement of science and technology, domestic and foreign scholars also try to use some new methods to evaluate the retarding effect of retarder, such as hydration temperature rise, Although X-ray diffraction, low-field nuclear magnetic resonance, resistance method and other methods are simple and effective, their accuracy still needs to be tested by a large number of engineering practices, and no relevant standards have been formed. Therefore, traditional methods are still the main method in engineering at present.
The setting time difference is the most intuitive manifestation of the effect of the retarder, but the quality of the concrete retarder is not only determined by these two. An ideal concrete retarder should have significant retarding effect when the dosage is small, and the setting time should be highly adjustable within a certain dosage range, and should not produce abnormal condensation phenomena. In addition, it is particularly important that the concrete retarder should be able to significantly delay the initial setting time of the cement slurry and shorten the interval between the initial setting and final setting of the concrete as much as possible. </p
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