Adding high-efficient water reducing agent is the most direct and effective means to adjust and optimize the ratio of concrete and improve and strengthen the properties of concrete, which can meet the requirements of most concrete construction at present.
Effect on the workability of concrete
The fluidity of concrete itself is poor. Even if a sufficient amount of water is added, the fluidity of concrete cannot fully meet the construction requirements due to the formation of flocculating substances. It can be known from the action principle of high-efficient water reducing agent that the addition of high-efficient water reducing agent causes the collapse of flocculating substance, makes full use of water, and increases the fluidity of concrete. The high-efficient water reducing agent and concrete are in a stable suspended state, which strengthens the workability of concrete.
The study shows that when the content of the water-reducing agent increases, the slump of concrete also increases, and when the slump increases to a certain degree, it will slow down. Therefore, the use and proportion of efficient water reducing agents need an experimental demonstration, under normal circumstances, water reducing agent content is 0.75%, can obtain the largest slump, and the slump amplitude at this time is also the slump peak of different proportions of water-reducing agent concrete.
Slump and the relationship between weather temperature, performance: high temperature, the activity of water-reducing agent increases, to promote the workability of concrete, making the slump faster; When the temperature is low, molecular motion is slow, and the stimulative action of reducing water agent is reduced, slump speed also becomes slow. Considering the collapse degree and collapse range of concrete, it is reasonable to control the content of High-efficient water reducing agent at 0.5% ~ 0.75%. It is unnecessary to increase the content of high-efficient water reducing agents, which will not increase the effective workability of concrete, and will cause cost waste.
Effect on the setting time of concrete
Concrete setting time is related to the choice of concrete construction, material, machine layout, and construction technology. In general, the condensation time is required to be as short as possible and kept within a range to reduce the compression of materials such as templates.
It is proved that the type and quantity of high-efficient water reducing agents will influence the setting time of concrete to a certain extent. Laboratory cement setting experiments show that:
1. When different types of cement are added with FDN high-efficiency water-reducing agent, the initial setting time of ordinary cement is 182 ~ 265min, and the setting time of slag cement is 291 ~ 420. This time difference has affected the construction organization design; 2. Add FDN high-efficiency water reducing agent into slag cement, when the amount of adding is 0.25%, the measured setting time is 356min (initial) to 483min (final), when the amount of adding is increased to 1.00%, the setting time is 703 (initial) to 801min (final). The results show that the selection and design ratio of high-efficient water reducing agents have a great influence on the setting time of cement.
Therefore, when designing concrete proportion, it is necessary to choose appropriate high-efficient water reducing agents and proportions according to the purpose of use.
Effect on hydration heat of cement
The results show that the cumulative heat of hydration of ordinary cement is 242J/g in 3D and 284J/g in 7d. After the CRS superplasticizer was added, the accumulated hydration heat of ordinary cement was 242J/g in 3d and 275J/g in 7d. It can be seen that the effect of efficient water reducing agent on the hydration heat of cement is not big. Different superplasticizers have different effects on hydration heat, so they should be selected according to the purpose of use.
Effect on the concrete hardening process
Taking the content of superplasticizer as a variable and the compressive strength and workability of concrete as quantitative, the experimenter studied the influence of the content of superplasticizer on the compressive strength of concrete. The experimental results show that when the addition amount of FDN superplasticizer increases from 0.25% to 0.5%, the 3D compressive strength increases from 21.1mpa to 28.9mpa, with a growth rate of 36.9%. The 7d strength increased from 35.6MPa to 44.8MPa, with an increased rate of 25.8%. The 28d strength increased by 13.6% from 51.4MPa to 58.4MPa. The increase of the additional amount of superplasticizer can significantly improve the initial strength and the final strength of concrete.
The study also found that the addition of high-efficient water reducing agent, will also cause the following beneficial effects on concrete: 1. can effectively save the amount of cement, is conducive to the maintenance of concrete molding and crack control; 2. in the same concrete collapse degree and strength of the case, the addition of high-efficient water reducing agent, enhance the fluidity of concrete significantly; 3. Reducing water consumption is beneficial to ensure the age strength and final strength of concrete.
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