Effect of acidity and basicity of sand and gravel on water-reducing efficiency of polycarboxylic acid superplasticizer

1. Effect of surface characteristics of sand and gravel on water-reducing efficiency of polycarboxylic acid superplasticizer.

Crushed stone and machine-made sand are often used in the practical application of engineering. Due to the different ways of formation of sand and gravel used in engineering, their surface characteristics-appearance also change greatly. In order to understand the influence of its surface characteristics on the water-reducing performance of polycarboxylic acid superplasticizer, the sand and gravel with the same gradation and the same particle size composition were used to mix the mixture with the same cement, the same polycarboxylic acid superplasticizer and the same amount of cement.

Raw materials. 

1. machine-made sand, river sand fineness modulus 2.7

2. crushed stone and gravel using secondary gradation 4.75mm~9.5mm accounts for 40% 9.5mm 19mm accounting for 60%.

3. Standard cement 310kg is used for cement.

4 Sand ratio 38%.

5 target slump 80mm.

6 polycarboxylic acid content 2%.

The experimental results show that:

(1) the water requirement of pebbles and river sand with the same gradation and grain size is less, while that of macadam and machine-made sand with the same gradation and grain size is higher.

(2) the slump loss of the concrete mixed with pebbles and river sand with the same gradation and grain size is smaller in half an hour, while the slump loss of the concrete mixed with crushed stone and machine-made sand with the same gradation and grain size is larger.

Cause analysis.

Because of the rough surface, large specific surface area and high adsorption to water and admixtures, the content of free radicals in cement clinker is relatively increased, which partly breaks the steric hindrance effect formed by the adsorption of polycarboxylic acid functional groups. So water consumption will increase. At the same time, due to the large amount of polycarboxylic acid adsorbed on macadam, the comprehensive effect of electrostatic repulsion and steric hindrance, adsorption, calcium complexation and sulfonic group complexation in cement slurry system has been weakened.

2. Effect of acidity and basicity of sand and gravel on water-reducing efficiency of polycarboxylic acid.

There are many kinds of sand and gravel, and the chemical composition changes greatly, so it has a great influence on the water-reducing efficiency of polycarboxylic acid, especially the effect of acidity and basicity of sand and stone on the water-reducing efficiency of polycarboxylic acid should be controlled in the actual production process. In order to study the effect of acidity and basicity of sand and gravel on the water-reducing efficiency of polycarboxylic acid, we carried out related experiments.

The same gradation of acid sand and alkaline sand were used to mix cement concrete.

Raw materials.

1 one part of river sand with fineness modulus 2.7 of acidity and basicity.

2. Acid gravel and alkaline gravel are graded in secondary gradation. 4.75mm~9.5mm accounts for 40%, 9.5mm, 19mm, 60% each.

3. Standard cement 310kg is used for cement.

4 Sand ratio 38%.

5 target slump 80mm.

6 polycarboxylic acid content 2%.

The experimental results show that:

(1) the water requirement of acidic sand with the same gradation and grain size is similar to that of alkaline sand with the same gradation and grain size.

(2) the slump loss of the concrete mixed with alkaline sand and gravel of the same gradation and grain size is smaller in half an hour, while the slump loss of the concrete mixed with acid sand and stone of the same gradation and grain size is larger in half an hour.

Cause analysis.

All kinds of functional groups of polycarboxylic acid dissolved in water are basically negative, have negative charge, and can combine with cations to form strong chemical bonds, so they can adsorb each other with alkaline stone to form a stable structure. as a result, the comprehensive effect of electrostatic repulsion and steric hindrance, adsorption, calcium complexation and sulfonic group complexation in cement slurry system has been enhanced. Therefore, alkaline aggregate can improve the water-reducing performance of polycarboxylic acid.

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