Study on early cracking of cement mortar mixed with high efficient water reducer
1. Elliptic ring shrinkage cracking test shows that naphthalene and polycarboxylic acid superplasticizers prolong the initial cracking time of cement mortar, reduces the cracking sensitivity of cement mortar.
When high efficiency water reducing agent dosage phase at the same time, the size of the initial cracking time of cement mortar order: mixed > PC cement mortar mixed with cement mortar > H - UNF C - UNF cement mortar > benchmark samples.
The effect of visible, high efficiency water reducing agent to reduce the cement mortar cracking sensitivity is: poly carboxylic acid class > high concentration type naphthalene series > normal naphthalene series.
2. In a fixed water/cement ratio and cement paste quality, mixing naphthalene series, poly carboxylic acid type high efficiency water reducing agent are increased free shrinkage of cement mortar that will be increased with dosage of high efficiency water reducing agent . Under the same condition of the high efficiency water reducing agent dosage phase, the cement mortar 28 d free shrinkage value for the size of the order: Mix h-unf cement mortar > mix c-un F cement mortar > mix PC cement mortar > reference sample. We can see from that, under the same experimental condition, the effect of high efficiency water reducing agent control volume stability of cement mortar is like below: poly carboxylic acid class > normal naphthalene series BBB 0 high concentration naphthalene system.
3. Within the scope of this test, the mixing of polycarboxylic acid efficient water reducer reduces the maximum crack width of cement mortar, while the mixing of naphthalene system accelerates the development rate of the maximum crack width of cement mortar, during which the 28 d is even higher than that of the reference sample.
4. Under the condition of dry curing, adding high-efficiency water-reducing agent improves the flexural and compressive strength of cement mortar for 28 d, and adding high-efficiency water-reducing agent of polycarboxylic acid, which is more effective in improving the strength of cement mortar for 28 d than adding high-efficiency water-reducing agent of naphthalene system.
What is the difference between water reducing agent and retarder?
Water-reducing agent is a type of admixture that can keep the workability of net cement slurry, mortar and concrete unchanged and can significantly reduce the amount of water used for mixing. It can significantly improve the strength of concrete and improve the frost resistance of concrete as well as impermeability and reduce the amount of cement and so on.
Retarding agent also belongs to the admixture, but it will delay the setting time of concrete without obvious influence on the later strength. Function: the purpose of mixing human retarder in concrete is to extend the hydration and hardening time of cement, so that fresh concrete can maintain plasticity in a longer time,and thus adjust the setting time of fresh concrete.