Hidro-abrazivna otpornost betona spravljenog sa recikliranim materijalima i ojačanog mikrovlaknima

Abstract

Durability of hydraulic engineering structures in most part depends on the resistance of concrete surface to mechanical abrasion. Hydro-abrasion represents a surface damage caused by continuous removal of material due to impact of waterborne hard particles. This form of progressive deterioration of concrete surface occurs, to a varying extent, in almost all hydraulic engineering structures. Therefore, hydro-abrasion wear of concrete in general causes reduction of the service life of a hydraulic engineering structure, as well as an increase in operating costs due to the necessary maintenance, and the downtime of the structure during the repair period. In general, little is known about the onset of concrete hydro-abrasion and about development of this damage in time. Presently, there is no standard testing method for hydro-abrasive resistance of concrete in laboratory conditions, which can to a great extent simulate the natural abrasion conditions. Also, the factors representing the physical, mechanical and structural concrete characteristics, and which affect its resistance to wear have not been sufficiently investigated. In the literature is discussed mostly the hydroabrasive resistance of high-strength concretes made with natural crushed or river aggregate, which are reinforced by addition of the silica powder or micro-reinforcement, with a high quantity of cement (higher than 400 kg/m3). The potential for application of recycled materials and reduced quantity of cement for production of the concretes resistant to hydroabrasion is presented in a limited scope. The paper investigates and analyzes the potential for production of cement concrete in which the cement content has been partially replaced by fly ash or silica powder, and where fine river aggregate has been partially replaced by recycled granulated rubbers, with the addition of micro-fiber (steel or polypropylene), with the aim to increase resistance to hydro-abrasive action. Performances of these concretes in fresh and hardened state were compared with the performances of reference concrete without the partial replacement of cement and fine aggregate and without micro-fibers. The tests of hydro-abrasive resistance of concrete was performed on the original apparatus constructed in the Laboratory of building materials at the Faculty of Civil Engineering and Architecture of Niš, which facilitates that the jet of water and sand mixture impacts the concrete tests slab at a high speed. The parametric analysis of the effects of individual mechanical characteristics on the hydro-abrasive resistance of concrete was done. For the purposes of the research, a total of eighteen types of concrete was made, which can be divided into three groups of six mixtures. The first group consists of the concrete mixes where no partial substation of cement was performed, the second group consists of the concrete mixtures where cement was substituted by filter ash, in the amount of 20% in respect to the cement mass, while the third group consists of the concrete mixes where the cement was substituted with the silica powder in the amount of 10% in respect to the cement mass. Within each group, there is a mixture where a part of fine river aggregate was replaced by the granulated recycled rubber in the amount of 10% in respect to the aggregate volume, followed by two concrete mixtures where polypropylene fibers have been added (monofilament to one and fibrillated to the other mixture), then two mixtures where hooked end steel fibers were (in one those are fibers 30 mm long and in the other those are fibers 50 mm long) and finally, there is the concrete mix without partial replacement of the fine river aggregate with recycled rubber and without the addition of fibers. The conclusions are formulated based on the processed and systematized results of the experimental research, and the performed parametric analysis of the effects of individual mechanical characteristics on the hydro-abrasive resistance of concrete. In general, the most intensive effect regarding increase of hydro-abrasive resistance of concrete is achieved by the partial replacement of the fine river aggregate by the recycled granulated rubber. Also, concrete reinforcement with polypropylene fibers contributes to the considerable increase of hydro-abrasive resistance of concrete, whereby the better effect is achieved using the fibrillated fibers. The addition of steel fibers in concrete does not result in a considerable increase of the hydro-abrasion resistance. The concretes made with the partial replacement of cement by fly ash have lower hydro-abrasive resistance in comparison to the reference concrete, while with the addition of polypropylene fibers, their resistance becomes approximately equal to the resistance of the reference concrete. Partial replacement of cement with silica powder contributes to the increase of hydro-abrasive resistance of concrete. The parameters such as compressive strength, flexural strength, splitting tensile strength, tensile strength determined using „Pull-off“ method, static modulus of elasticity and resistance to abrasion wear can be the factors for prediction of hydro-abrasive resistance of concrete, due to the existence of strong. The behavior of concrete exposed to hydroabrasive action cannot be fully predicted based on the „Drop weight“ tests of the impact resistance of concrete. The accelerate abrasion test method implemented in the research is suitable for analysis of hydro-abrasive resistance of concrete.