In order to study the effect of gradation-thickness of sand and gravel on the water-reducing efficiency of polycarboxylic acid, we carried out related experiments. The cement concrete was mixed with gravel of the same gradation and sand with different fineness modulus.
(1) one copy of river sand with fineness modulus 2.1 and 2.7.
(2) gravel of the same specification and gradation shall be graded in secondary gradation, accounting for 40% of 4.75mm~9.5mm, 9.5mm of 19mm, and 60% of each.
(3) the standard cement 310kg is used for cement.
(4) the same sand ratio is 38%.
(5) 2% of polycarboxylic acid.
The experimental results show that:
1 when the gravel of the same gradation and the same grain size is small, the water demand of the mixed concrete increases, which indicates that the water reducing performance of polycarboxylic acid is greatly reduced.
2 when the sand fineness modulus of the gravel with the same gradation and grain size is small, the slump loss of the mixed concrete is larger in half an hour. This shows that the thickness of sand has a great influence on the stability and fluidity of polycarboxylic acid concrete.
All kinds of functional groups of polycarboxylic acid soluble in water basically have strong adsorption. When the sand fineness modulus is large, the specific surface area increases and can combine with polycarboxylic acid functional groups, which relatively increases the content of free radicals in cement clinker. Thus, the steric hindrance effect formed by the adsorption of polycarboxylic acid functional groups is partially broken. 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.
The mud content, acidity and alkalinity of sand and gravel materials and the thickness of sand all have an impact on the water-reducing effect of polycarboxylate superplasticizer. In order to achieve a better water-reducing effect, the quality of sand and gravel materials should be ensured first in the process of mixing concrete.
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