Fiber-Reinforced RubCon

Fiber composite materials have been widely used in construction in a variety of industries, such as aerospace, automotive, shipbuilding, and chemical processing, for 

FIGURE 2.27 Influence of stirrups percentage on load-bearing capacity of beams for different lengths of a shear zone. (Reprinted from Yu. Potapov, O. Figovsky, Yu. Borisov, A. Polikushkin, and D. Beilin, Influence of Shear Force on the Behavior of Polymer Concrete Beams at Bend, J. Scientific Israel Technological Advantages 4, nos. 3-4 (2002) 25-31. With permission.) 

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Experimental investigations were performed with fiber-reinforced RubCon samples measuring 4 x 4 x 16 cm. Various fiber materials were used steel, polypropylene, rough basalt, and glass. The reinforcement ratio for appropriate fiber materials was adopted according to publicized research [4,11]. The optimal volume of fiber content is 1.0%-1.5% for steel fibers and 1.0-5.0% for glass fibers. 

The strength characteristics of steel fiber-reinforced RubCon depend on the reinforcement ratio p. The results of experiments show that an optimum saturation by fiber reinforcement is in the range of 2%-3%. Fiber clotting is observed at greater volumes of reinforcement, and results in a decrease in RubCon strength and serious constructive defects. 

Resistance of fiber-reinforced RubCon to long-term loading is the principal criterion of its application as a structural material. We investigated creep of plain RubCon at compression earlier. Experiments were continued for the purpose of studying fibrous RubCon creep. 

Asymptotes of the curves give an indication of the fibrous RubCon creep limit. It is interesting to note that the creep coefficient of the plain RubCon creep = 0.77-0.78, whereas for fiber reinforced RubCon it is slightly below creep = 0.74-0.75. In this case the creep limit of fiber-reinforced RubCon at compression ccreep = 74.9-78.4 MPa exceeds the creep limit of plain material ccreep = 66-66.8 MPa. This phenomenon is... 

Chemical Resistance of Steel Fiber-Reinforced RubCon... 

The corrosive environments that were used were water, a 70% solution of sulfuric acid, a 5% solution of phosphoric acid, a 36% solution of hydrochloric acid, and a 25% water solution of ammonia. Chemical resistance of fiber-reinforced RubCon was estimated on test specimens measuring 4 x 4 x 16 cm at exposures of 180 and 360 days at intermediate terms of 10, 30, 60, 90, 180, and 270 days. 

Experimental curves of the mass transfer and chemical resistance of fiber-reinforced RubCon samples are illustrated in Figure 2.61. 

The analysis of the obtained results shows that fiber-reinforced RubCon is a composite hydrophobic material with a coefficient of water resistance of Kcr = 0.995. Decreasing compressive strength was not observed and water absorption was 0.05% on weighing of samples. The small change of weight is due to the hydrophobic surface of RubCon. This is due to the intrinsic properties of the polybutadiene binder, which is not moistened with water. Furthermore, polybutadiene oligomer is nonpolar liquid. 

FIGURE 2.61 (1) Water absorbing of fiber reinforced RubCon, (2) coefficient of water... 

Thus, the basic stages of fiber-reinforced RubCon manufacturing techniques are... 

In the course of our tests we observed various types of RubCon sample destruction depending on the fiber reinforcement material. The application of rough basalt or glass fibers results in brittle destruction of samples, which occurs after fiber breakage. The crack formation moment coincides with the breaking of fibers. It should be noted that crack formation of RubCon samples reinforced with steel or polypropylene fibers occurs much earlier than the fracture of fibers. 

One of the major areas of RubCon application is in structures that operate in aggressive environments where crack resistance of the material is important. Our experiments have shown that steel fibers show the greatest opportunity to increase crack resistance and allow production of a material with high elastic-plastic properties. For this reason, we have undertaken research on the influence of fiber reinforcement ratio and aspect ratio on RubCon strength at compression, tension, and bend. 

The optimal composition of continuously reinforced RubCon from a strength point of view is reinforcement ratio p = 2% maximal particle size of coarse aggregates a = 5 mm. At p > 2%, clotting of fibers is observed, which results in some structural defects. 

To gain a better understanding of the influence of fiber reinforcement on creep of RubCon, we investigated the relationship between values of compressive stresses and creep deformations that are damped out with time. The analysis of the result diagrams (Figures 2.54 and 2.55) shows linear stress-strain dependence of fiber-reinforced and plain RubCon samples at short-term compressive loading. However, creep deformations of these samples do not linearly depend on compressive stress value due to highly elastic deformation of the polybutadiene binder. 

It can be seen in Figure 2.88 that increasing the percentage of fiber reinforcement leads to an increase of agitation time. It is safe to assume that low values of bending strength of RubCon at short fiber-feeding times are related to formation of defects and pores as a result of nonuniform distribution of the fibers. Further increase in... 

We obtained the system of three equations with three unknowns, which can be solved for analytically, where N is the limiting compressive load b is the width of the cross-section of the sample Rk is the compressive strength of RubCon x is the distance from the most compressed fiber to the neutral axis of the cross-section eR is the deformation corresponding to maximal stress from the diagram o - e e is the deformation of extreme compressed fiber os is the tension stress As is the tension zone area of the cross section and h0 is the distance between centers of longitudinal reinforcements. 

To determine the influence of reinforcement on the strength characteristics of RubCon, control samples without reinforcement (size 4 x 4 x 16 cm) were prepared. Figure 2.35 illustrates the dependence tension at bending of RubCon samples reinforced by different kinds of fibers. One can see that the bending... 

A full two-factor experiment was carried out. The varied parameters were the reinforcement ratio p and aspect ratio (relative length) of the fibers L/d the response functions were tensile, compressive, and bending strength of the RubCon samples. During the experiment, the reinforcement ratio and aspect ratio were changed from 1% to 4% in 1% increments, and from 40 to 130 in increments of 30, respectively. 

One can see from Figures 2.90 (a, b) and 2.91 (a, b) that the slump of standard cone decreases with an increase in reinforced fibers in the RubCon mixture with coarse and fine-grained aggregates. This is especially true at relative length of fibers above l/d = 70. At p = 4% and l/d = 130, the slump is practically equal to zero due to formation of a fiber skeleton of mixture components. Rigidity of this skeleton... 

Experimental research was performed on models of reinforced concrete beams (10 x 20 x 120 cm) with polymeric concrete layers. B 25 class concrete was used main longitudinal reinforcement of A-III class was used in the form of two 8-mm diameter rods and the 5-mm diameter stirrups of the same class arranged, so that destruction would be along normal sections. Epoxy-rubber compositions were used as covering layer materials. All compositions were made on ED-20 epoxy-based resin. Besides fiber glass-reinforced plastic glued by ED-20 compositions based on liquid rubbers, RubCon was used. The composition of the polymer layers and some of their mechanical characteristics are given in Table 6.3. 

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