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The relationship between high efficiency water reducing agents and concrete and its components

With economic development, the construction of highways and bridges has entered a new, higher stage. Its technical standards and quality requirements are becoming increasingly high and refined. Especially in optimizing concrete mix proportions, appropriate admixtures can be added, and the mix proportion can be formulated according to different construction and quality requirements. Whether guiding construction, controlling quality, or improving economic benefits, it will bring immeasurable convenience.

This article focuses on the relationship between high efficiency water reducing agents and concrete and its components.

The influence of high efficiency water reducing agent on concrete

Impact on fresh concrete

Compatibility: Adding high efficiency water reducing agents can increase the fluidity of concrete. The slump of concrete increases with the increase of the dosage of high efficiency water reducing agent, and the maximum increase in slump occurs when the dosage reaches 0.75%. When the dosage is further increased, the slump increases, but the increase tends to be gentle.

The slump loss of concrete mixed with a high efficiency water reducing agent is very rapid, usually within 1 hour, and is even greater at high temperatures. The suitable dosage for general high efficiency water reducing agents is 0.5% to 0.75%. When the amount of cement is large, the suitable dosage is 0.9% to 1.2%. From an economic perspective, the commonly used dosage is around 0.5%.

Setting time: High efficiency water reducing agents have little effect on the setting time of concrete, and the degree of influence varies depending on the type and dosage of high-efficiency water reducing agents; The effect of high-efficiency water reducing agents on the setting of cement varies depending on the type of cement used. As shown in Table 1, the setting time of cement mixed with a high-efficiency water-reducing agent.

Bleeding: Adding high efficiency water reducing agents to concrete can reduce its bleeding rate, while using water reducing agents with causative properties (such as AF and Jian-1) can further reduce it. The concrete mixed with benchmark cement, with FDN, UNF and CRS added, and reduced water consumption, has a water bleeding rate of about 50% of the benchmark concrete.

Air content: Increase the air content of concrete. The air content of CRS, FDN, and UNF increased by about 1%, the content of AF and Jian-1 was 0.75%, and the air content of concrete was about 5%. Also note that adding high-efficiency water-reducing agents to flowing concrete will reduce its air content.

Hydration heat: The hydration heat and peak temperature of cement with a high-efficiency water reducing agent added are similar to those of cement without additives, but the appearance time of the peak is delayed by several hours. An efficient water-reducing agent reduces the heat of hydration of slag cement. Refer to Table 2 for the hydration heat of cement mixed with a high-efficiency water-reducing agent.

Effects on hardened concrete

Compressive strength: Keeping the workability of concrete the same, as the dosage of high efficiency water reducing agent increases, the strength of concrete will improve. In ordinary concrete, when the water-cement ratio and mix proportion are held constant, adding high efficiency water reducing agents will not significantly reduce compressive strength. Refer to Table 4 for the compressive strength (increase and workability) of concrete mixed with high-efficiency water-reducing agents.The water-reducing and enhancing effects of high-efficiency water-reducing agents vary with the type of cement, its mineral composition and its fineness.
The tensile strength, flexural strength, and bond strength of steel bars have all increased to varying degrees.
When maintaining the same compressive strength of concrete, the addition of high-efficiency water-reducing agents has no significant effect on the static elastic modulus of concrete. Even if the compressive strength of concrete increases significantly, the static elastic modulus of concrete does not increase significantly.
By adding high-efficiency water-reducing agents and keeping the cement dosage constant, the early shrinkage of concrete is greater than that of blank concrete, and it becomes similar to blank concrete after 90 days. Concrete mixed with high-efficiency water-reducing agents maintains its strength, with early shrinkage similar to that of blank concrete and later shrinkage smaller.
The creep of concrete mixed with a high-efficiency water-reducing agent is slightly smaller than that of blank concrete.
The long-term strength of concrete mixed with high-efficiency water reducing agents has the same increase as that of blank concrete (the improvement of concrete strength is mainly achieved through the water-cement ratio).
Adding high-efficiency water-reducing agents can reduce the water consumption of concrete. Under certain workability conditions, high-strength concrete and ultra-high-strength concrete with a compressive strength of 100MPa can be manufactured. A small change in the water consumption of ultra-high-strength concrete mixed with CRS (Gumaron resin sulfonate high-efficiency water reducer) can lead to a significant change in flowability. Increasing the water-cement ratio and reducing the cement content appropriately will not have a significant impact on the strength of the concrete.Simultaneously adding high-efficiency water-reducing agents and silica fume can also produce ultra-high-strength concrete with a strength exceeding 100 MPa.High-quality cement and coarse aggregate should be selected as materials for ultra-high-strength concrete. The maximum particle size of coarse aggregate should not exceed 20mm, and quartz stone or crushed stone should be used. When a large amount of cement is used, it is advisable to use coarser sand with a fineness modulus of around 3.0 for preparation.
Anti pile hammer performance: Concrete mixed with high-efficiency water reducing agent CRS has good or at least the same anti hammer performance as blank concrete. Experiments have shown that the crushing height of concrete with CRS added is 0.75cm/impact, while that of blank concrete is 1.02cm/impact.

The influence of concrete components on water reducing agents and high efficiency water reducing agents

Cement Composition

Most high efficiency water reducing agents exhibit stronger water reducing and plasticizing effects in slag cement than in ordinary cement. Experiments conducted by the Nanjing Institute of Water Resources Science have shown that some cements use hard gypsum as a setting agent, while lignin water reducing agents, especially sugar additives, can cause rapid setting or hardening of cement.

Cement fineness

The experiment conducted by the Railway Science Research Institute shows that, under the same conditions, the flowability of cement slurry decreases with increasing cement fineness. When a small dose of water reducer is added, the flowability of the cement slurry still decreases sharply as cement fineness increases. However, when a 1% water reducer is added, the flowability of the cement slurry increases with increasing cement fineness. At the same time, when the specific surface area of cement is about 5000 cm2/g, adding 0.3% water reducer does not increase the flowability of the cement slurry. Only when the water reducer dosage is between 0.5% and 1.0% can the flowability of the cement slurry be significantly increased.

When the particle size of cement particles decreases, the flowability of cement slurry decreases. When a 1% water-reducing agent is added, the flowability of the cement slurry increases as the cement particle size decreases.

As the cement particle size decreases, the amount of water required to achieve the same fluidity increases, and the water reduction rate increases when the cement particle size is less than 10 μ m.

Aggregate fineness modulus and particle shape

The fineness and quality of sand significantly affect the strength, water reduction rate, moisture content, and other properties of benchmark concrete and concrete with admixtures. When the fineness modulus of sand is 2.6-2.9, the water reduction rate is higher and very close; when the fineness modulus is 2.3 or 3.18, the water reduction rate is relatively low.

The water reduction rate of crushed stone concrete mixed with water-reducing agents is higher than that of pebble concrete.

Experiments conducted by the Water Resources Research Institute have shown that, maintaining the same water-cement ratio and workability, there is no significant difference in water reduction rate between crushed stone concrete and pebble concrete mixed with naphthalene-based high-efficiency water-reducing agents.

Temperature

When the temperature is below +5 ℃, it is difficult to achieve the goal of increasing strength by adding high-efficiency water-reducing agents alone, and it will not bring economic and technological effects. Therefore, early strength testing agents should be added.

Ordinary concrete with small cement consumption

Efficient water-reducing agents should be used at a lower dosage of 0.3% to 0.5%, while high-strength concrete should be used at a higher dosage of 0.7% to 1.0%. When adding fly ash to concrete, the dosages of the water-reducing and high-efficiency water-reducing agents should be appropriately increased. The dosage of wood calcium can be increased from 0.25% to 0.30%. When segregation and bleeding occur upon adding a high-efficiency water-reducing agent, the sand ratio can be appropriately increased to restore viscosity and improve concrete workability.

Conclusion-The relationship between high efficiency water reducing agents and concrete and its components

In summary, to prepare concrete that meets construction quality requirements for workability and is relatively economical, it is necessary to strictly control the raw materials. To meet the technical specifications, conduct more experiments and speak with data. Efficient water-reducing agents, cement, sand, and stone each have their own characteristics and influence one another; they are closely related. So we need to be familiar with their characteristics and their relationships, and make strategic plans in order to guide construction correctly and reasonably.