INFLUENCE OF THE MAXIMUM PASTE THICKNESS AND THE ADDITION OF SUPERPLASTICIZER ON CONCRETE FLOW UNDER VIBRATION(Atena Editora)

Abstract

The manufacture of large self-supporting tiles is carried out by a machine that contains a mobile feed box, which pours the concrete onto a long, open, W-shaped mold (track). As the concrete used does not flow under its own weight, they are hose vibrators are used to provide flowability. Aiming to simulate some conditions of the production process, an adaptation of the L-box test was made, in which a hose vibrator was inserted into the box's reservoir. The compositions used natural fine sand, artificial sand and gravel, in the proportions of 25%: 25%: 50% and 0%: 50%: 50%, by mass. The effects of the aggregate/cement ratio “m” and the addition of a 3rd generation superplasticizer additive based on polycarboxylate were studied. For each of these proportions, “m” values were defined equal to 4.0; 4.5 and 5.0, which reduces the amount of cement by up to 16%. To define the additive levels, the frustum slump test was carried out, which is the reference test in the industry for choosing composition in terms of flowability. The Maximum Paste Thickness (MPT) calculations resulted in negative values, indicating that the mixtures would lack paste between grains larger than 0.150 mm. The amount of superplasticizer required was more consistent with the solids fraction values found than with the cement concentration. The results showed that even the compositions with zero slump presented workability and flowed under vibration. The use of superplasticizer led to a significant decrease in flow time and an increase in mechanical resistance, especially for the lower cement concentration.