THE INFLUENCE OF THE AMOUNT OF POLYPROPYLENE FIBER AND SUPERPLASTICIZER ON THE STRENGTH OF CONCRETES FOR RIGID ROAD SURFACES AND TRANSPORT STRUCTURES

Abstract

The article presents an analysis of the influence of the amount of polypropylene fiber, cement and polycarboxylate-type superplasticizer on the strength characteristics of concrete for rigid road surfaces and transport structures. Portland cement PC II/A-Sh-500R-N, polypropylene fiber Baumesh with a fiber length of 36 mm and a diameter of 0.68 mm, and polycarboxylate-type superplasticizer MC-PowerFlow 3200 were used. A 3-factor experiment was conducted in which the following composition factors were varied: the amount of Portland cement, 300 to 380 kg/m3; the amount of polypropylene fiber Baumesh, 2.5to 3.5 kg/m3 ; the amount of superplasticizer, 1.0 to 1.6% of the cement mass. The compressive strength of fiber-reinforced concretes was determined at the age of 3 and 28 days, and the tensile strength at the age of 28 days. All studied concrete mixtures had equal mobility class P2. The influence of varied factors on the W/C ratio of mixtures was assessed. The amount of Portland cement has the greatest influence on this indicator. Increasing the dosage of superplasticizer from 1.0% to 1.6% allows reducing the W/C ratio by 8-24%. The amount of polypropylene fiber has a limited effect on the W/C ratio. The amount of Portland cement has the greatest influence on the compressive strength of the studied fiber-reinforced concretes. When the dosage of binder is increased from 300 kg/m3 to 380 kg/m3, the strength of fiber-reinforced concretes at the age of 3 increases by 74-80%, the strength at the project age increases by 38-47%. Increasing the amount of superplasticizer provides an increase in compressive strength at an early age by 10-12%, at a project age by 12-14%. Increasing the amount of reinforcing fibers from 2.5 to 3.5 kg/m3 at a high content in the mixture of binder and plasticizer does not significantly affect. By increasing the amount of fiber at a low amount of cement and superplasticizer, the early and project compressive strength of fiber-reinforced concretes increases insignificantly. By increasing the dosage of the binder to 380 kg/m3, the tensile strength of fiber-reinforcedconcretes increases by 9-12%. A similar increase in tensile strength at bending is achieved by increasing the dosage of the superplasticizer from 1.0 to 1.6%. The nature of the influence of polypropylene fiber on this strength indicator is nonlinear. An increase in strength by 9-12% is observed with an increase in fiber dosage from 2.5 kg/m3 to 3.0 kg/m3 both at high and low amount of binder and superplasticizer. It has been established that in general, from the point of view of achieving the highest compressive and tensile strength when bending, it is rational to introduce Baumesh polypropylene fiber in an amount of about 3.0 kg/m3 and MC-PowerFlow 3200 additive in an amount of 1.5-1.6% of the cement mass.