Jakob Šušteršič

Shrinkage of Polypropylene Fiber-Reinforced High-Performance Concrete

In this paper, the results of laboratory investigations into the time development of the shrinkage of polypropylene fiber-reinforced high-performance concrete have been analyzed. The volumetric content of polypropylene fibers contained in the investigated concretes varied from 0 to 0.75%. Within this context, the influence of both dry and previously moistened polypropylene fibers added to the concrete on the shrinkage of the composites was examined. Electronic measurements conducted from the beginning of the hardening of the concrete also covered the early stage of autogenous shrinkage that, in high-performance composites, accounts for a significant part of total shrinkage. To compare the shrinkage of fiber-reinforced concrete with that of a comparable concrete without polypropylene fibers, the shrinkage of such a comparable concrete without fibers was also included in the measurements. The measurement results of the shrinkage of polypropylene fiber-reinforced concrete and of a comparable concrete without polypropylene fibers, as presented graphically in this paper, clearly show that the autogenous as well as the total shrinkage of fiber-reinforced concrete is less than the shrinkage of a comparable concrete without fibers. By increasing the content of the fibers up to 0.5% of the volume of the composite, the shrinkage of the fiber-reinforced concrete was considerably reduced, whereas with further increasing of the fiber content, the shrinkage reduction rate became relatively insignificant. The concrete that had been reinforced by previously moistened polypropylene fibers, which served as an internal water reserve, exhibited a lesser degree of early autogenous shrinkage than the concrete that had been reinforced by dry polypropylene fibers. The drying shrinkage of high-performance concrete, reinforced by previously moistened polypropylene fibers, was, however, approximately twice as large as that of dry polypropylene fiber-reinforced high-performance concrete. Whereas the workability of the composite deteriorated considerably already in the case of a volumetric content of moistened polypropylene fibers greater than 0.25%, in the case of the use of dry polypropylene fibers, this deterioration was even more conspicuous.

Abrasion Resistance of Concrete in Hydraulic Structures

The phenomenon of hydraulic structure concrete abrasion, caused by the water-carried sediment abrasion process, is analyzed in this paper. There was detailed investigation of laboratory procedure adequacy for definition of concrete abrasion level in standard ASTM C1138 hydraulic structures. Assessment was based on comparison of laboratory results and natural condition measurements of concrete abrasion resistance by test plot performance in the Vrhovo hydro power plant (HPP) stilling basin. There was adequacy testing of the concrete built in the HPPs evacuation structures on the Lower Sava River. There was modification of basic concrete composition by pozzolanic or polymer additives, along with granular rubber, polypropylene fibers, steel fibers, and the primary binder. A qualitative similarity was shown in the analysis on concrete abrasion level between field measurements and laboratory simulations, as well as ASTM C1138 laboratory method suitability for concrete abrasion resistance assessment in the spillway of the lower Sava Rivers HPP chain. Quantitative results comparison showed a good correlation between natural environment measurements and laboratory measurements for concrete at 900 days, while this correlation was not confirmed for the concrete at 90 days.

Shrinkage and Creep of Steel Fiber Reinforced Normal Strength Concrete

This paper deals with the results of laboratory research into the time-related development of shrinkage and creep in normal strength concrete that has been steel fiber reinforced with volumetric contents of up to 2.0 % of shorter (l = 16 mm) or longer (l = 30 mm) steel fibers. The experimental research refers to the respective effects of the length and volumetric content of such fibers, as well as to the effect of early water curing conditions on the shrinkage and creep of the composite concerned. The results of the measurement of the autogenous, drying, and total shrinkage and the creep of the tested composites, as well as those corresponding to comparable concrete without fibers, are presented in the paper. The results of the experimental research show that the total shrinkage of such composites is, in general, about 15 % less than that of the comparable plain concrete without fibers. The autogenous shrinkage of the composites was nearly the same, but the drying shrinkage was considerably less than in the case of the comparable plain concrete. However, the creep of these composites differed only minimally from that of the comparable plain concrete.

Efficiency of Polymer Fibers in Lightweight Plaster

In the paper, results of the investigation of fiber-reinforced lightweight plaster (FRLP) with different types of polymer fibers are discussed. The following fibers were used: high-modulus aramid fibers (AR), mid-modulus and high-modulus polypropylene fibers (PP-M and PP-H), polyamide fibers (PA), polyacrylonitrile fibers (PAN), and polyvinyl alcohol fibers (PVA). The behavior of these composites under flexural and compressive load is observed at the age of 28 days and after accelerated aging. Therefore, toughness is evaluated to find out the efficiency of different types of the same volume percentage of fibers but with equal length. Mix proportions of investigated lightweight plasters were the same; only the fiber types were changed. Obtained results show that all used polymer fibers improve toughness of FRLP.

Flexural Behavior and Cracks in Concrete Beams Reinforced with GFRP Bars

Concrete beams reinforced with glass fiber-reinforced polymer (GFRP) bars exhibit large deflections and crack widths compared with concrete members reinforced with conventional steel. Current design methods for predicting deflections under the loading and crack widths developed for concrete structures reinforced with steel may not be used for concrete structures reinforced with GFRP, but some of parameters will be used. Based on this paper research work and past studies, a theoretical correlation for predicting crack width was proposed. Experimental results are focused in examining the two sets of concrete beams with different percent of reinforcement using the GFRP bars. In this case the compare parameters are deflections, cracks, and bearing capacity using the analytical and experimental results. The beams were tested under a static load to examine the effects of the reinforcement ratio and compressive strength of concrete on cracking, deflection, ultimate capacity, and modes of failure.