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The adverse effects of mud on polycarboxylate superplasticizer and concrete

Mud comes from various sources, and its components vary. Mud in concrete, sand, and gravel can be divided into three categories: limestone powder, clay, and calcium carbonate. Among them, stone powder is a fine particle with a particle size of less than 75 μ m in machine-made sand. It is the same parent rock as machine-made sand and has the same mineral composition. Its main component is CaCO3, which is a part of the grading composition of machine-made sand.

Limestone powder improves the gradation of fine aggregate in concrete, promotes early hydration, prevents the conversion of ettringite to a single-sulfate type, and enhances early strength and compactness.

The common clays in sand and gravel include montmorillonite, kaolin, and illite. The chemical composition of these three types of clay is aluminosilicate, which is finely dispersed (particle size ≤ 2 μ m), highly hydrophilic, and colloidal. Aluminum silicate is composed of two basic units: tetrahedral silicon oxide chips and octahedral aluminum oxide chips. Due to the different proportions of the two units that make up clay, different types of clay with different properties are formed.

The high mud content of sand and gravel not only seriously affects the early workability and later mechanical properties of concrete, but also causes significant resource and energy waste and increases concrete’s sensitivity to volume cracking. Mud powder is the most easily introduced contaminant in sand and gravel that affects concrete performance. Although we have mandatory standards for the quality of sand and gravel and strictly limit the content of mud powder, due to regional variations in aggregate quality, few sand and gravel produced and supplied on site fully meet the standards, and most need to be adjusted to local conditions.

Study on the working principle of mud powder and polycarboxylate superplasticizer

It is generally believed that the main reason why cement powder affects concrete mixed with lignosulfonate and naphthalene-based water-reducing agents is the adsorption competition between cement powder and cement. There is still no unified explanation for the working principle of mud powder and polycarboxylate superplasticizer. Some scholars believe that the mechanism of action of mud powder and a water-reducing agent is similar to that of cement.

A water-reducing agent adsorbs on the surface of cement or mud powder with anionic groups, but the adsorption amount and rate of mud powder with a water-reducing agent are much greater than those of cement. At the same time, the high specific surface area and layered structure of clay minerals also adsorb more water, reducing free water in the slurry and directly affecting the construction performance of concrete.

The influence of different minerals on the performance of water-reducing agents

Research has shown that only clay-based mud with significant expansion and water absorption properties will have a significant impact on the workability and later mechanical properties of concrete. Common clay minerals in aggregates include kaolinite, illite, and montmorillonite. The sensitivity of the same type of water reducer to mud powder with different mineral compositions varies, and this difference is very important for selecting water reducers and developing mud-resistant water reducers and mud-resistant agents.

The Influence of Mud Powder Content on Concrete Performance

The workability of concrete not only affects its formation, but also its later mechanical properties and durability. The volume of mud powder particles is unstable, shrinking when dry and expanding when wet. As the mud content increases, both polycarboxylate and naphthalene superplasticizers will reduce the water-reducing rate, strength, slump and other properties of concrete, causing significant damage.

According to the national standard “Building Sand” (GB/T14684-2011), when the concrete strength grade is C30 or there are special requirements for frost resistance, impermeability or other properties, the mud powder content in natural sand shall not exceed 3.0%, and the mud block content shall not exceed 1.0%; When the concrete strength grade is less than C30, the mud powder content shall not exceed 5.0% and the mud block content shall not exceed 2.0%.

Exploration of Methods for Concrete Mud Resistance

Mud powder poses a significant threat to concrete performance. Therefore, researchers and construction workers have adopted various methods to mitigate the adverse effects of mud on concrete performance. By studying the concrete preparation process and mix ratio tests, the extent to which mud content affects the adaptability of polycarboxylate superplasticizer is identified. Based on the test results, actual production is guided, and strict control of fine aggregates entering the factory can also ensure that the various properties of concrete meet the construction and technical requirements.

Conclusion-The adverse effects of mud on polycarboxylate superplasticizer and concrete

Therefore, systematically studying the effects of different types of mud on the strength, workability, and durability of polycarboxylate superplasticizers and concrete materials can help achieve effective resource utilization, improve economic benefits, and solve environmental problems.

The study of concrete resistance to mud should be based on compositional differences in mud across regions, and the influence of each mud type on polycarboxylate superplasticizer and concrete performance should be investigated. Targeted superplasticizers or anti-mud agents should be developed, and, in practical applications, the corresponding superplasticizers and anti-mud agents should be selected based on the soil mineral composition in the region.