Roller-compacted concrete (RCCP) is a zero-slump and stiff-dry mixture which is usually placed with an asphalt paver and compacted by conventional vibratory roller compactors to achieve the required density. Typically, the RCCP is constructed without joint. It needs neither forms nor surface finishing, nor does it contain bar reinforcing and dowels. Consequently, considering a proper mix design, load transfer can be achieved through aggregate interlock. Nevertheless, RCCP can be reinforced with fibers in order to improve the durability, flexural strength, load transfer capacity, and so on. Accordingly, this research was conducted to study the effects of fibers on the mechanical properties of RCCP and present a prediction fatigue model based on third-point beam fatigue test. Based on three-point bending test results on notched beam, fiber, cement, and water linearly affect the flexural strength. However, fiber tended to influence the fracture energy more significantly than flexural strength. It was found that stress ratio, fiber content and fracture energy was the significant term to predict fatigue life, respectively.

With the increasing development of concrete structures, properties such as strength and durability of concrete have become particularly important. Therefore, it is necessary to use special concretes and obtain new combinations. Ordinary concrete is brittle and frangible, and if rebar is not used, other materials such as fibers should be added to the mixture to remove the brittleness of the concrete. Fiber is used to control cracks in concrete, which in addition to controlling cracks, improves impact resistance, fatigue, shear, bending, as well as energy absorption of concrete. In this research, fiber concrete made of steel, barchip, and macro synthetic fibers and the combination of each fiber with different volume ratios is subjected to explosive load and the failure rate of each sample and the resistance of fiber concrete with hybrid fibers to explosion have been investigated in laboratory and field. Also, the special electrical resistance of hybrid fiber concrete against the electric current has been evaluated, which can be considered as a measure to evaluate the permeability and parallel absorption of concrete water. The results showed that concrete with macro synthetic fibers had greater explosion resistance than other samples. Also, the electrical resistance of concrete with macro-synthetic fibers has been higher than that of other samples, which will have special applications in corrosive areas with high penetration of chloride ions due to higher electrical resistance and consequently lower permeability. Also, for estimating the cost of fiber performance in concrete, the lowest excess cost of using fibers in concrete was related to the use of 1.5% of the concrete volume of macro synthetic fibers due to the low cost of these fibers and its high resistance to electrical resistance and resistance to explosive load. The use of these fibers in concrete to withstand explosion and electric current has been cost effective.

The improvement of compressive and tensile strength of concrete has a great importance in the construction industry. In this study, cubic samples constructed in a dimension of 150times150times150 mm containing different amounts of macro-synthetic (0. 1 and 0. 15 vol. %) and polymeric fibers (0. 2, 0. 3, and 0. 35 vol. %) by means of seven mix designs. Compressive and splitting tests were performed using a universal testing machine. For each specimen, stress-strain and load-displacement behaviors, absorbing energy, ductility and crack patterns were investigated. In order to analyze the strain variations on the surface of the specimens digital image correlation (DIC) was applied. Moreover, finite element method (FEM) was conducted to evaluate the experimental results. The results of this study show that the presence of fibers in concrete has a significant effect on reducing size and number of cracks, and increases displacement compared to conventional concrete. In addition, displacement at the failure moment in tension and pressure for fiber contained concrete was more than the control specimen. According to the observations, addition of the fibers reduces compressive and tensile strength. However, it is so obvious from the results that by choosing the optimal amount, this reduction would be neglected in comparison with the positive effects of the fibers. Finally, the results indicate an acceptable agreement between the FEM and DIC evaluations. Therefore, considering the low cost and high speed of analysis with FEM and DIC methods, it is possible to combine these two methods as a useful tool to determine the surface characteristics of such specimens.

Roller compacted concrete pavement (RCCP) is a zero-slump and stiff-dry mixture which is usually placed with an asphalt paver and compacted by conventional vibratory roller compactors to achieve the required density. RCCP consistently has a slightly lower cement content than conventional concretes of similar strength. Nowadays, RCCP is used for any type of industrial or heavy-duty pavement and has advantages including cost saving as a result of the construction method and the increased placement speed of the pavement. Therefore, the use of RCCP pavement has become more and more popular in recent years. There are numerous studies on the mechanical properties of fibre reinforced focused on cement paste and normal concrete. However, our understanding of what exactly happens when hybrid fibres used to reinforce RCCP mixes with respect to fracture toughness is quite limited. Accordingly, in this study, three point bending test was carried out on mono and hybrid fibre-reinforced RCCP based on modified two-parameter model to determine the value of Mode I plane-strain fracture toughness of fibre-reinforced RCCP by considering possibility of crack deflection during its propagation through modified two-parameter fracture model. Finally, it can be observed that, for great amount of fracture angle, the application of Two-parameter fracture model instead of modified Two-parameter fracture model cause to an overestimation of the fracture toughness values.

In fiber reinforced self-compacting concrete, fibers and properties such as filling ability create a homogeneous mixture. In this research, 10 mix designs are examined and tested, one of which is related to the control sample and the other 9 designs include steel, macrosynthetic monofilament (MEX 100), and carbon fiber reinforced polymer (CFRP) fibers with volumetric percentages of 0.25, 0.5 and 0.75. The rheological behavior of fresh self-compacting concrete is investigated by rheometer test. Moreover, conventional tests that determine the self-compacting properties of fresh concrete, including slump flow, J-ring, L-box, U-box, and V-funnel tests, are examined. The behavior of hardened concrete is analyzed based on tests to determine mechanical properties (compressive strength and modulus of elasticity). The results indicate adding fibers to fresh concrete reduces the self-compacting and rheological properties of concrete. This effect becomes more visible by increasing the fiber volume ratio so that the greatest effect could be observed in designs containing CFRP fibers. The results of mechanical properties of hardened concrete show adding small amounts of fibers to self-compacting concrete improves some of these properties, while using large amounts of fibers increases ductility and, consequently, decreases compressive strength and modulus of elasticity in self-compacting concrete.

In recent years, the use of Roller–, Compacted Concrete Pavement (RCCP) has developed in road pavement due to its great advantages. Adding fibers to RCC can improve some properties of the concrete, including flexural strength, fatigue resistance, crack growth rate, and shear transfer along cracks and joints. Many experiments have shown the advantages of using fiber-reinforced concrete in RCC, but more information is needed about their behavior in cold regions, and especially the exposure to Freeze-Thaw cycling. Investigation and comparing the effect of polymer fibers on the strength and durability of Roller-Compacted Concrete under Freeze-Thaw cycling are the main goal of the present article. Therefore, specimens with weight percentage of fiber equal to 1, 2. 5, and 4% (by weight of cement) and fibers of to 5, 20 and 40 mm lengths are made. Durability test against a Freeze-Thaw cycling and compressive strength are measured on samples after 7, 28 and 90 days. Analysis of the results shows that the additive fiber increases the compressive strength of the RCC, but decreases its durability against the melting and freezing cycles. Therefore, the use of fibers on RCC in cold regions should be done due accuracy and attention.

The effect of softwood fibers surface characteristics on mechanical properties of cellulosic fibers/polypropylene composite (W.P.C) was studied. Fibers were refined to modify the surface characteristics and to reach four different freeness levels (11, 14, 17 and 21oSR). Then the fibers were compounded with polypropylene using pre-determined levels of 20% fibers and 77% polypropylene and 3% MAPP and samples were made using extrusion molding. The results revealed that refining the fibers will change the strength of the composites. Statistical analysis showed that the impact of the different freeness levels significantly influenced the strength at 99% confidence level. The highest strength levels were reached using fibers with the freeness level of 14oSR.

Nowadays the paper factories, especially factories which use waste papers because of environmental issues and lack of forest sources, need to identify fibers in raw materials to improve quality of recycled papers. In order to evaluate feasibility of fibers identification, papers of 6 Iranian important factories (7 different Kinds of papers) have been sampled. Factories use waste paper for raw materials. Many micro- slides have been prepared from the papers according to ISO 9184-1 (ISO 1990), and many morphological and anatomical characteristics inside Atlases have been used to identify of exotic fibers. Eventually frequency of identified species in papers has been recorded. The result showed that identification of papers is feasible. From the softwoods: Pinu spp., Larix spp., Picea spp. and from the hardwoods: Populs spp., Fagus orientalis, Betula spp., Alnus spp. and Carpinus betulus and from non-woods: Wheat, Corn, Cotton and Rice were the most plentiful species. The number of recycles and processes of refining and beating in paper production process causes fiber destruction and identification of paper fibers especially for species whose shape of fibers (vessel elements and trachids) are very similar, therefore they are not useable for fiber identification.