Can admixtures improve concrete defects? Adjustment and workability is a prerequisite

Now is the Internet age. If we want something, we will search it using various search engines. Whether it is Baidu or 360, as long as we enter a keyword, the search volume ranking for this word will automatically appear on the web page. , the higher it is, the more people are searching for it, and this word or question has received more attention.

When we enter concrete on the page, we can find that questions about concrete quality issues still attract the attention of many people, and various solutions to deal with concrete quality defects are often met with dissatisfaction. So, what are the causes of concrete quality problems?

Analysis of the causes of common appearance quality problems of concrete

Causes of deformation of concrete geometric dimensions

(1) The installation of the formwork is not stable and reliable enough, causing the formwork to expand partially during the concrete pouring process;

(2) The vibration is too close to the formwork and the power is high for a long time, causing the formwork to deform and run away;

(3) The template itself is deformed due to long use or improper storage.

　(2) The concrete mixing time is short, the mixing is not uniform, the concrete has poor workability, and the vibration is not dense;

　(3) Improper concrete feeding, such as too much concrete feeding in sequence , there is no segmented and layered pouring, so the vibration is not solid or the cutting and vibrating are not coordinated well, and the cutting is not done before vibrating, causing leakage of vibration, etc., which will cause the concrete to segregate and produce honeycombs;

(4) The pores of the formwork are not blocked or the formwork support is not firm, and the formwork shifts when the concrete is vibrated, causing serious grout leakage, “root rot” and the formation of honeycombs;

(5) The surface of the formwork is rough or If it is not cleaned properly, the steel formwork isolating agent is applied unevenly or is partially missed, causing the concrete surface to be damaged when the formwork is removed;

(6) The wooden formwork is not moistened before pouring concrete or is not moistened enough. The moisture of the concrete in contact with the formwork is sucked away by the formwork, causing the surface to lose too much water and appear pitted;

(7) The joints of the boards are not assembled tightly, resulting in slurry leakage during pouring, along the joints of the boards Pockmarks appear on the concrete surface; the concrete is not vibrated densely, the bubbles are not eliminated, and some of the bubbles stay on the surface of the formwork to form pits.

Analysis of the reasons for the formation of exposed bars on the concrete surface

(2) The structural section is small, the steel bars are too dense and too large, causing stones to get stuck on the steel bars, and the concrete cement slurry cannot fill the surrounding steel bars. , causing exposed reinforcement there;

　(3) Improper mix ratio or improper cutting of materials causes concrete to segregate, lack of slurry in the pouring part or serious leakage of slurry in the formwork, resulting in exposed reinforcement.

Analysis of the causes of gaps and interlayers

(1) Before pouring concrete, the surface of the construction joints was not carefully treated, and the vibration was not enough during pouring;

(2) ) There are debris accumulated on the surface of the old concrete. If it is not cleaned in time, the debris will be mixed into it to form an interlayer when it is poured again.

The aggregates on the surface of the concrete are exposed and the color is uneven and the causes

(1) The inner surface material of the formwork is too soft or highly dense; the sand rate of the concrete mixture is low, discontinuous grading is used, the aggregate is dry or porous, too much coarse aggregate, excessive vibration, etc. will cause aggregate exposure ;

(2) The surface of the formwork has different ability to absorb color, and the color of the material is uneven; adding chloride will form dark stripes, and the rust of the steel bars or steel formwork will contaminate the concrete, causing uneven color;

(3) Due to the bleeding parallel to the surface of the formwork, fine particles are segregated to form sand marks; the formwork does not absorb water, the temperature during construction is low, the mixture has high bleeding property, and there is insufficient sand in the fine aggregate, the air content is low, and the mixture High bleeding, insufficient sand in fine aggregate, low air content, too fast pouring speed, and excessive vibration will produce sand marks.

The powerful advantages of concrete admixtures

Since the usage of naphthalene series water-reducing admixtures accounts for more than 80% of high-efficiency water-reducing admixtures, to simplify the description, high-efficiency water-reducing admixtures Will be collectively referred to as naphthalene series water reducing agent. High-performance water-reducing agents include polycarboxylic acid-based water-reducing agents, aminocarboxylic acid-based water-reducing agents, and other water-reducing agents that can meet the requirements of high-performance water-reducing agents in the “Concrete Admixtures” GB8076-2008 standard. Currently, my country’s high-performance water-reducing agents Performance water-reducing agents are mainly represented by polycarboxylic acid-based water-reducing agents.

With the continuous deepening of technology research and development in the concrete admixture industry in my country, new concrete admixtures are constantly emerging, such as efficient and high-performance water-reducing agents that can reduce concrete water consumption and improve concrete strength. They are used to adjust Retarder and accelerator for concrete setting time, expansion agent and shrinkage reducing agent used to reduce shrinkage and cracking of concrete, air-entraining agent that can improve the freeze-thaw resistance of concrete and extend the service life of concrete, and can be used for construction under negative temperature conditions in winter The antifreeze used, rust inhibitors that can inhibit or reduce the corrosion of steel bars and other metal embedded parts in concrete, etc., can basically meet the performance requirements of various concrete construction under the current conditions in my country.

Because admixtures can effectively improve the properties of concrete and have good economic benefits, they have been widely used in many countries and have become an indispensable material in concrete. Especially with the use of high-efficiency reducers, cement particles can be fully dispersed, water consumption is greatly reduced, and cement potential is fully utilized. As a result, the cement stone is relatively dense, and the pore structure and interface area are…The structure has been well improved, which has greatly improved the physical and mechanical properties of concrete, whether it is impermeability, chloride ion diffusion, carbonization, sulfate corrosion resistance, impact resistance, wear resistance, etc. It is superior to concrete without additives in all aspects. It not only improves strength and workability, but also improves the durability of concrete. Only by adding high-efficiency water-reducing admixtures, it is possible to prepare high-performance concrete with high workability, high strength and high durability.

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