Rebound Hardness Values Research Articles

Comparative Study on NDT Techniques for Evaluation of Concrete Quality Exposed to Marine Environment

Concrete, the primary material used in quay walls, is directly exposed to saline environments. Coping concrete, particularly in areas where periodic berthing and loading/unloading occur, is prone to rapid quality deterioration. Current facility safety and maintenance guidelines assess concrete durability at specific points through sampling, which are intended to represent the entire inspection unit. This paper explores quality management strategies from an areal perspective by applying various non-destructive scanning methods to extensive areas of coping concrete. Ultrasonic array imaging and ground-penetrating radar scanning images revealed significant quality degradation in berthing operation areas, whereas sampling-based ultrasonic pulse velocity and rebound hardness values were less effective in detecting this degradation.

Assessment of carbonate rocks for engineering applications considering mineralogical, geochemical and geotechnical attributes

Due to continuous need of materials for infrastructural development, geomaterials of different origins are used where available. Vast majority of these materials in some countries are predominantly metamorphic and sedimentary in nature. Many of these rocks are of carbonate origin and they are encountered by practitioners worldwide. Therefore, it is very crucial to evaluate the prospect of using carbonate rocks for different applications. In this paper, laboratory tests were conducted on soft and hard carbonate rocks in order to assess their usefulness taking into consideration the mineralogy, geochemistry and geotechnics. The mineralogy is majorly calcite, the fabric is characterized by aggregation of particles to form clusters and the chemical composition is predominantly calcium oxide. The hard carbonate rocks have low porosity, medium dynamic fragmentation, medium to low water absorption, slightly strong rebound hardness value, high uniaxial compressive strength and soft carbonate rocks have low in situ specific volume and compressibility. The carbonate rocks are suitable for cement production. The hard carbonate rocks can be used for infrastructure purposes. The soft carbonate rocks are suitable for use as foundation fill materials and suitable for use as sub-grade materials. However, practitioners must be cautious when using this material as sub-base materials.

The application of small sample theory and confidence interval method to determine the representative mean Leeb rebound hardness value

The application of small sample theory and confidence interval method to determine the representative mean Leeb rebound hardness value

Estimating the uniaxial compressive strength of rocks with Schmidt rebound hardness by considering the sample size

The Schmidt hammer is commonly used for the prediction of unconfined compressive strength and other mechanical properties of rocks from surface rebound hardness values since it is quick, easy, inexpensive, and non-destructive testing method. In this study, metamorphic, sedimentary, and igneous rock samples were collected from various locations in Turkey to predict the rock strength from Schmidt rebound hardness. Schmidt rebound tests were performed on cubic samples with an edge length of 11 cm and uniaxial compressive strength tests were carried out on cubic samples with an edge length of 5 cm in accordance with ASTM and EN standards and suggested procedure by ISRM. New relationship coefficients between unconfined compressive strength and Schmidt rebound hardness values were suggested according to rock type. Finally, some diagrams were developed to be practically used for estimating the uniaxial compressive strength from Schmidt rebound hardness values by considering the sample size obtained from the experimental work.

Analysis of the Leeb Hardness Test Data Obtained by Using Two Different Rock Core Holders

In this study, an investigation was carried out to elucidate if the core holder type affects the measured Leeb hardness values (HL) of rock materials obtained by using the Equotip hardness tester. To achieve this goal, NX-size core specimens of different rock samples were subjected to Leeb hardness testing by employing an ‘Arch-shaped’ and a ‘V-shaped’ core holder. The results indicated a strong degree of linear correlation (R 2 0.95) between mean rebound hardness values determined in the arch-shaped holder (HL A ) and V-shaped holder (HL V ). The maximum difference in HL values obtained from the two holders was 74.2 units on the HL-scale, corresponding to a difference of 10.2 %. Although the differences in magnitudes of HL A and HL V values were small and varied from one rock variety to another, there was a tendency of the V-shaped holder to give relatively lower values. On the other hand, when compared to the minimum values, a higher statistical correspondence was observed between maximum HL A and HL V values. The results also showed that it is possible to predict uniaxial compressive strength of the tested rocks reliably by employing any of the holders.

The effects of moisture, temperature and uniaxial pressure on Schmidt rebound hardness value of rocks

The effects of moisture, temperature and uniaxial pressure on Schmidt rebound hardness value of rocks

Dielectric and hardness measurements of planetary analog rocks in support of in-situ subsurface sampling

Accurate assessment of the subsurface mechanical characteristics and how they correlate with dielectric properties is crucial to optimize future drilling and sampling investigations on planetary bodies. For 12 different types of basaltic rocks with different hardnesses, we use capacitive cells to measure the real part of the dielectric constant over the frequency range 100–1000MHz, and a Schmidt hammer hardness tester to measure the hardness using a scale of 10–100. Our measurements suggest that the real part of the dielectric constant and rock hardness are linearly correlated. Additionally, sample hardness was linearly correlated to density. For a density ranging from 0.82 to 3.05g/cm3, the real part of the dielectric constant ε′ and rebound hardness values R ranged from ε′=1.8–7.6 and R=14.16–68 for the different basalt samples. Hence, high dielectric constants imply a high rock hardness value and vice versa. We concluded that for volcanic surfaces that are analogous to the Martian surface as well as other planetary surfaces, there is an inverse correlation between drilling penetration rate based on the rotary-percussive drill method and the dielectric constant. Dielectric inversion from planetary radar probing experiments proposed herein is a crucial method to locate regions with lowest hardness and hence highest drilling penetration rate in desiccated volcanic planetary subsurfaces. The use of these cross-correlation measurements can optimize future drilling experiments and ensure that they reach their targets of opportunities, minimize losses in drilling performance, or the unnecessary use of power that will be needed for the continuity of the investigation.

Geotechnical and kinematic parameters affecting the coefficients of restitution for rock fall analysis

This paper presents the results of laboratory and field tests regarding the determination of the parameters that influence the trajectory of falling blocks in rockfalls. Coefficients of restitution are considered to be critical parameters in rockfall modeling, but various definitions exist and there is no agreement on which one is more appropriate. In this research, the lamped-mass analysis method was used and coefficients of restitution were calculated using the kinematic definitions. The laboratory testing was performed using a number of common rocks found in Greece. The rock materials tested were characterized by different Schmidt hammer rebound hardness values while the mass of the falling blocks as well as the impact angle and the velocity were altered during the tests in order to estimate the effect of each parameter on the coefficients of restitution. The kinematic coefficient of restitution was compared to the normal coefficient of restitution and was found to be more appropriate when used in correlations. Impact angle was found to significantly affect the trajectory. Finally, a correlation between Schmidt hammer rebound hardness and kinematic coefficient of restitution is proposed whilst a method for estimating the normal coefficient of restitution is suggested including the impacts' angle effect.

P-wave velocity and Schmidt rebound hardness value of rocks under uniaxial compressional loading

P-wave velocity and Schmidt rebound hardness value of rocks under uniaxial compressional loading

The effect of sample size on Schmidt rebound hardness value of rocks

The Schmidt hammer has been commonly used device for hardness determination and for predicting the unconfined compressive strength and other mechanical properties of rocks, due to the fact that it is a quick, easy, inexpensive and non-destructive testing method. Testing is most commonly performed following the ISRM and ASTM standards. The effect of sample size for a consistent hardness value has not been well defined in previous works. ISRM [Rock characterization testing and monitoring ISRM suggested methods, suggested methods for determining hardness and abrasiveness of rocks, Part 3. Oxford: Pergamon; 1981. p. 101–3] suggested that block edge length should have at least 6 cm, while ASTM [Standard test method for determination of rock hardness by Rebound Hammer Method, D5873-05, 2005] indicated at least 15 cm. In this study, in order to analyze the effect of sample size on Schmidt rebound hardness (SRH) property of rocks, rock samples were collected from eight locations. Cubic samples having different edge dimensions of 6, 7, 8, 10, 12 and 15 cm were prepared. In the laboratory, Schmidt hammer tests were conducted according to the suggested procedure by ISRM (1981) together with different methods of recording SRH. By evaluating the measured data, it is showed that the size of the cubic samples significantly affects the SRH values. Edge dimension of the cubic block should be at least 11 cm for determining a consistent hardness value. An equation predicting the consistent hardness value from samples smaller than 11 cm was also suggested.

Evaluation of Schmidt Hammer Rebound Hardness Test Holders

Abstract An evaluation is made of three different holders for Schmidt hammer tests on rock core in the laboratory, including steel angle, V-notch, and semicircular groove holders. The differences are small, but it is shown that the V-notch holder gives consistently higher rebound hardness values. It is also easier and more economical to build. These qualities indicate that the V-notch holder would be a better selection for conventional use.