When we mix concrete, water-reducing admixture is a very effective admixture, and it is also a widely used admixture. However, there are many types of water-reducing admixtures on the market. The commonly used ones are polycarboxylate water-reducing admixtures. and naphthalene-based water-reducing agents, so what are the differences between the two? Let the staff of Qingdao Dingchang New Materials Co., Ltd. explain to you the differences between polycarboxylate water-reducing agents and naphthalene-based water-reducing agents. Different?
1. Different principles
The water reduction mechanism is different. The polycarboxylate water-reducing agent is mainly based on steric repulsion, while the benzene-based water-reducing agent is mainly based on electrostatic repulsion. In addition to steric repulsion, polycarboxylate superplasticizer also has a strong air-entraining isolation "ball" effect and the effect of reducing solid-liquid interface energy. The benzene-based water-reducing agent is mainly based on electrostatic repulsion and has almost no other beneficial effects on water reduction.
2. Different usage methods
The dosage of polycarboxylate water-reducing agent is between 0.05% ~ 0.3%, and the water-reducing rate is between 25% ~ 35%, up to 40%. The dosage of benzene water reducing agent is 0.3%~1.5%, the recommended content is 0.5%~1.0%, and the water reducing rate is between 15%~30%.
3. Different effects
The slump retention rate of polycarboxylic acid-type high-efficiency water-reducing agent is significantly better than that of naphthalene-type high-efficiency water-reducing agent, and when the same water-reducing rate is reached When , the content of polycarboxylate water-reducing agent is much lower than that of naphthalene-based water-reducing agent.
Test Proof
1. Introduction
High-performance water-reducing agent is an important component of high-performance concrete. With the development of concrete technology, More and more attention is paid to the durability of concrete. To improve the durability, the water-cement ratio of concrete often needs to be reduced. However, the fluidity of concrete still needs to meet the requirements of pumping construction. Therefore, water-reducing agents are required to have high water-reducing effects. , it also needs to be able to control the slump loss of concrete, but general high-efficiency water-reducing agents often fail to meet the requirements.
As a new generation of high-performance water-reducing agent, polycarboxylic acid-based water-reducing agent has a comb-shaped molecular structure, has good adaptability to cement, small dosage, high water-reducing rate, and the prepared concrete can retain slump. It has the characteristics of good stability and workability, and overcomes the shortcomings of naphthalene-based water reducing agents such as formaldehyde in the production. It is especially suitable for the production of high-performance concrete. It has been widely researched and developed rapidly in recent years. However, from the current market Judging from the variety and share of polycarboxylic acid-based water-reducing agents sold, the application and promotion of polycarboxylic acid-based water-reducing agents is still in its infancy, and it has broad application prospects.
In order to better understand the working performance of polycarboxylic acid-based water-reducing agents in concrete, this article conducted experimental research on polycarboxylic acid-based water-reducing agents and naphthalene-based water-reducing agents.
2. Raw materials and mix proportions
2.1 Test raw materials
Cement: Onoda P.O42.5 ordinary Portland cement
Sand: Dongguan river sand, medium sand, fineness modulus 2.6
Stone: 5～20mm gravel
Water: tap water
Water reducing agent: used Two polycarboxylic acids and one naphthalene-based (FDN) water-reducing agent; the CP polycarboxylic acid-based water-reducing agent is provided by Shenzhen Haichuan Engineering Technology Co., Ltd.;
2.2 Cement slurry experiment
According to the "Experimental Method for Homogeneity of Concrete Admixtures" (GB 8077-2000), when W/C is 0.29, measure the cement slurry flow at 4 points within the recommended dosage range of the two types of water reducing agents. The degree of fluidity and the retention of fluidity for 1 hour and 2 hours were used as parameters to characterize its performance, and two dosages were selected for concrete experiments.
2.3 Concrete experiment
Based on the cement slurry experiment results, a representative dosage was selected, and the mix ratio was used to conduct the concrete experiment. Under the condition of controlling the slump of 180±20mm, two samples were tested. Water reduction rate, slump at 1 hour and 2 hours, and compressive strength ratio at 3 days and 7 days for two dosages of similar water-reducing agent.
3. Experimental results and analysis
3.1 Cement slurry experimental results
According to the GB8077-2000 cement slurry experimental method, the recommended dosage of water-reducing agent Add, the results of each dosage are as follows
3.2 Concrete experimental results
Select the dosage of 0.5 and 0.8 of CP from the cement slurry, and choose the dosage of 0.8 and 1.0 for Grace 152 The dosage of 2.0 and 2.5 was selected from FDN, and the mix ratio and other experimental results were obtained through trial mixing.
3.3 Result Analysis
3.3.1 Cement slurry
It can be seen that as the dosage of CP water-reducing agent increases, the fluidity increases, and Judging from the fluidity after 2 hours, there is basically no loss; at a low dosage of 0.5%, the fluidity is already 257mm; at a dosage of 0.7%, the fluidity has greatly improved, reaching 285mm; then although the dosage increase, but the mobility improvement is not significant. From the results, it can be concluded that when the dosage is 0.5%, the fluidity is slightly lost over time, but above 0.7%, there is a greater improvement, and the fluidity is not lost over time.
It can be seen that the fluidity of FDN also increases with the increase of the water-reducing agent dosage, but when the dosage is 2.5%, the fluidity is only 237mm, while the CP when the dosage is 0.5% The fluidity is also higher than it; when the dosage is 1.0%, the fluidity is 197mm, and there is no fluidity after 1 hour; it is also the breaking point of FDN at 1.5%, and when the dosage increases, the fluidity does not change much. .
Through the comparison results, the 0.5% and 0.8% dosage of CP, the 0.8% and 1.0% dosage of Grace, and the 2.0 and 2.5 dosage of FDN were selected for the next step of concrete experimental comparison.
3.3.2 Concrete experiment
The concrete experiment was conducted on water reduction rate, slump change over time, compressive strength ratio, etc.
It can be seen that the water reduction rate of CP with a dosage of 0.5% has reached 28%, and when the dosage is 0.8, the water reduction rate is as high as 35%;However, FDN can only reach 30% when the dosage is 2.5. Under the same solid content conditions, to achieve the same water reduction rate, the dosage of FDN must be much more. Judging from the changes in slump over time, FDN loses quickly, and the slump in 2h is equivalent to the slump in CP1h. In the compressive strength ratio between 3 days and 7 days, the improvement degree of CP and FDN is not much different. From the three projects compared, CP is better than FDN in terms of single project and overall performance.
4. Conclusion
Through the above experimental comparison, the following conclusions can be drawn:
(1) The water reduction rate of polycarboxylic acid-based water-reducing agent is obvious Higher than naphthalene-based water-reducing agent, when achieving the same water-reducing rate, the dosage of polycarboxylic acid water-reducing agent is much lower than that of naphthalene-based water-reducing agent;
(2) Polycarboxylic acid The slump retention of the polycarboxylate water-reducing agent is significantly better than that of the naphthalene-based water-reducing agent. The high-fluidity concrete prepared with the polycarboxylate water-reducing agent can still meet the pumping requirements after 1 hour;
(3) As the dosage increases, the ultimate water-reducing rate of polycarboxylate water-reducing agents is much higher than that of the naphthalene series, and the naphthalene-series water-reducing agent has basically reached the limit when the dosage is about 2.0%, which shows that the polycarboxylate water-reducing agent More suitable for formulating high-strength concrete with low water-cement ratio.
I will share here the difference between polycarboxylate water-reducing agent and naphthalene-based water-reducing agent. Generally speaking, polycarboxylate water-reducing agent has better strengthening effect and shrinkage resistance. However, benzene-based water-reducing agents also have their own advantages. The specific type of water-reducing agent used depends on the actual situation.
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