The validity of the cubic law for laminar flow of fluids through open fractures consisting of parallel planar plates has been established by others over a wide range of conditions with apertures ranging down to a minimum of 0.2 µm. The law may be given in simplified form by Q/Δh = C(2b)3, where Q is the flow rate, Δh is the difference in hydraulic head, C is a constant that depends on the flow geometry and fluid properties, and 2b is the fracture aperture. The validity of this law for flow in a closed fracture where the surfaces are in contact and the aperture is being decreased under stress has been investigated at room temperature by using homogeneous samples of granite, basalt, and marble. Tension fractures were artificially induced, and the laboratory setup used radial as well as straight flow geometries. Apertures ranged from 250 down to 4µm, which was the minimum size that could be attained under a normal stress of 20 MPa. The cubic law was found to be valid whether the fracture surfaces were held open or were being closed under stress, and the results are not dependent on rock type. Permeability was uniquely defined by fracture aperture and was independent of the stress history used in these investigations. The effects of deviations from the ideal parallel plate concept only cause an apparent reduction in flow and may be incorporated into the cubic law by replacing C by C/ƒ. The factor ƒ varied from 1.04 to 1.65 in these investigations. The model of a fracture that is being closed under normal stress is visualized as being controlled by the strength of the asperities that are in contact. These contact areas are able to withstand significant stresses while maintaining space for fluids to continue to flow as the fracture aperture decreases. The controlling factor is the magnitude of the aperture, and since flow depends on (2b)3, a slight change in aperture evidently can easily dominate any other change in the geometry of the flow field. Thus one does not see any noticeable shift in the correlations of our experimental results in passing from a condition where the fracture surfaces were held open to one where the surfaces were being closed under stress.

/pdf/validity-of-cubic-law-for-fluid-flow-in-a-deformable-rock-2ynq4id3hq.pdf

VALIDITY OF CUBIC LAW FOR FLUID FLOW IN A DEFORMABLE ROCK FRACTURE - eScholarship

In order to further broaden the application scope of basalt fiber reinforced concrete (BFRC), prolong service life in complex environment, master development status and sort out development needs, the durability of BFRC in complex environment was systematically summarized. First of all, the reason and damage mechanism of concrete deterioration in a variety of harsh environment are analyzed and grasped. Secondly, the strengthening mechanism of basalt fiber (BF) structure in permeability, carbonization, sulfate erosion, alkali environment, freeze-thaw cycle and high temperature is reviewed in detail, and the strengthening effect and performance of BFRC are discussed from the perspective of macroscopic properties and microscopic pore structure. The addition of BF reduces the generation and development of early microcracks in concrete structures, promotes the densification of structures on a microscopic scale. What's more, the permeability, carbonation resistance, acid and alkali corrosion resistance, frost resistance and high temperature resistance of concrete structures can be significantly improved. Finally, the problems in the current research are summarized and research ideas to cope with the environmental complexity are proposed to provide a research basis for BFRC to maintain excellent performance in the actual complex application scenarios. 

A review on durability of basalt fiber reinforced concrete

This paper presents a comparative study on the effect of steel and polyoxymethylene fibers on the characteristics of Ultra-High Performance Concrete (UHPC). Firstly, based on the modified Andreasen & Andersen packing model, a UHPC with ultra-low cement content is produced. Then, the steel fibers and polyoxymethylene (POM) fibers are added into this UHPC matrix separately and together. The obtained experimental results show that the addition of POM fiber has limited contribution to the compressive strength of UHPC, while it has a positive influence on its flexural strength and high temperature resistance. The results of nanoindentation indicate that POM fiber can slightly disturb the packing skeleton of UHPC and enlarge the ITZ between matrix and fibers. Based on the nanoindentation results, it can be found that the interfacial transition zone (ITZ) is about 50 μm in the case of UHPC with only steel fibers, while this value gradually increase to about 60 μm when POM fiber is added individually. This results further demonstrate that the POM fiber can slightly disturb the packing skeleton of UHPC and enlarge the ITZ between matrix and fibers. Therefore, to efficiently apply the POM fiber in UHPC, it is suggested to combine it with steel fibers and its optimal content should be around 1% (vol.). It can be concluded that it is difficult for POM fiber to fully replace steel fiber in referencing UHPC, while the hybrid fibers should be a good choice to produce excellent UHPC composite. 

Comparative study on the effect of steel and polyoxymethylene fibers on the characteristics of Ultra-High Performance Concrete (UHPC)

/pdf/mechanical-and-fracture-properties-of-steel-fiber-reinforced-463c18pf0w.pdf

Mechanical and fracture properties of steel fiber-reinforced geopolymer concrete

In this study, the effect of adding nano-silica (NS) particles on the properties of concrete containing coal fly ash were explored, including the mechanical properties, impact resistance, chloride penetration resistance, and freezing–thawing resistance. The NS particles were added into the concrete at 1%, 2%, 3%, 4%, and 5% of the binder weight. The behavior under an impact load was measured using a drop weight impact method, and the number of blows and impact energy difference was used to assess the impact resistance of the specimens. The durability of the concrete includes its chloride penetration and freezing–thawing resistance; these were calculated based on the chloride diffusion coefficient and relative dynamic elastic modulus (RDEM) of the samples after the freezing–thawing cycles, respectively. The experimental results showed that the addition of NS can considerably improve the mechanical properties of concrete, along with its freezing–thawing resistance and chloride penetration resistance. When NS particles were added at different replacement levels, the compressive, flexural, and splitting tensile strengths of the specimens were increased by 15.5%, 27.3%, and 19%, respectively, as compared with a control concrete. The addition of NS enhanced the impact resistance of the concrete, although the brittleness characteristics of the concrete did not change. When the content of the NS particles was 2%, the number of first crack impacts reached a maximum of 37, 23.3% higher compared with the control concrete. Simultaneously, the chloride penetration resistance and freezing–thawing resistance of the samples increased dramatically. The optimal level of cement replacement by NS in concrete for achieving the best impact resistance and durability was 2–3 wt%. It was found that when the percentage of the NS in the cement paste was excessively high, the improvement from adding NS to the properties of the concrete were reduced, and could even lead to negative impacts on the impact resistance and durability of the concrete.

https://www.mdpi.com/2079-4991/11/5/1296/pdf

Effect of Nano Silica Particles on Impact Resistance and Durability of Concrete Containing Coal Fly Ash.

Effects of nylon fiber and nylon fiber fabric on the permeability of cracked concrete

Experimental study on the damage permeability of polypropylene fiber-reinforced concrete

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Effects of nylon fiber and nylon fiber fabric on the permeability of cracked concrete

Experimental study on the damage permeability of polypropylene fiber-reinforced concrete