Rebound Values Research Articles

Geotechnical properties of Lower Eocene limestones, Sinn El-Kaddab Plateau, southwest of Aswan, Egypt

This study investigates physical and mechanical characteristics of Lower Eocene limestone exposed on the Sinn El-Kaddab Plateau, southwest of Aswan. The limestone successions belonging to the upper member of the Dungul Formation attain 120 m in the composite section of the area. Sedimentologically, these limestones are composed of three lithofacies; hemipelagic facies at base composed mainly of wackstone, followed upwards by shallow marine nummulitic packstone and grainstone, and middle ramp facies at top composed mainly of bioclastic grainstone. The average values of the investigated physical properties include true density (2.70 g/cm3), bulk density (2.40 g/cm3), apparent specific gravity (2.66 g/cm3), apparent porosity (10.32%), and water absorption (4.44%). The average investigated mechanical properties values include Schmidt rebound attains (27.46), maximum stress (27.82 N/mm3), and compressive strength (283.77 kg/cm2). Unconfined uniaxial compressive strength and abrasion impact values were derived mathematically from equilibrated curves using Schmidt rebound values. Both limestones of Naqb Dungul and Kalabsha localities are suitable for uses in construction and ornamental purposes as dimension stone such as in floor tiles, interior and exterior cladding, production of bricks and mosaics, and possible non-constructional uses include fillers and pigments. Low values of both abrasions impact value obtained results; unconfined compressive strength and confined compressive strength of the lower facies refer to unsuitability as wear abrasive or road aggregates.

Nondestructive assessment of the compressive strength of concrete with high volume slag

Experimental research was performed to clarify the influence of slag content, type and particle size of coarse aggregate on the rebound value and compressive strength of concrete with high volume slag. Furthermore, a model of rebound strength curve for concrete with high volume slag was established. In addition, the porosity and pore structure of sample surface were analyzed by X-ray computed tomography (X-ray CT) and mercury intrusion porosimetry (MIP), respectively. The results demonstrate that the largest rebound value of the concrete is obtained when the content of slag is 40%. Furthermore, the particle size and type of coarse aggregate have an effect on the rebound value of concrete. When the coarse aggregate is basalt and the particle size is between 10–20 mm, the rebound value is the largest. In addition, when the carbonation depth is large, the rebound strength of concrete with high volume slag is larger than that of the national unified strength curve. The establishment of rebound strength curve of concrete with high volume slag is helpful to improve the accuracy of compressive strength test of slag concrete.

Clast transport history influences Schmidt hammer rebound values

AbstractThe Schmidt hammer (SH) is widely used in geomorphology for relative‐ and calibrated‐exposure age dating surfaces and deposits within landforms. This study employs a laboratory‐based methodology to assess the effects of surface roughness, clast roundness, and clast volume on SH rebound values (R‐values) by analyzing samples from three modern depositional environments (i.e. river, alluvial fan, talus). Each environment contains clasts of Torlesse supergroup greywacke sandstones with distinct roundness and micro‐scale roughness characteristics. Roundness, surface roughness, and clast volume were all found to influence R‐values significantly. The R‐values from different deposit types are statistically significant and could potentially create an apparent age divergence of several thousand years for samples with the same exposure‐age. © 2020 John Wiley & Sons, Ltd.

Assessing the load carrying capacity of concrete anchor bolts using non-destructive tests and artificial multilayer neural network

Concrete anchor bolts play a key role in architecture, construction, mechanical and petrochemical industries. Although much work in the past has been conducted to evaluate the pull-out strength of these bolts using destructive tests, so for very little progress has been achieved in developing a non-destructive testing method that can be used to estimate their pull-out strength. In this regards the presented research work details a truly non-destructive testing procedure that can be adopted to estimate the pull-out strength of concrete anchor bolts. In the presented experimental research work the author details the procedure of combining the Schmidt hammer rebound number along with the ultra-sonic pulse velocity test to identify anchor bolts that have defects and thus lead to lower pull-out strength. 48 anchor bolts of 16 mm and 20 mm diameter with embedment lengths of 50 mm and 70 mm were tested. Ultrasonic pulse velocity readings were recorded before and after the application of Schmidt hammer rebound reading. It was observed during experimentation that samples which showed lower rebound values also depicted reduced ultrasonic pulse velocity for the fixed path length. Since the anchor bolt load carrying strength depends on its diameter, embedment length, its alignment and bond between the steel and concrete, hence by combing the two non-destructive testing methods the researchers were able to identify faculty anchor bolts and successfully access their pull-out strength. Furthermore, an artificial neural network (ANN) was developed to conduct sensitivity analysis of the various parameters effecting the load capacity of anchor bolts in order the identify the most influential factors. A high level of accuracy was achieved between the experimental and predicted load capacity using the developed ANN.

Schmidt hammer and terrestrial laser scanning (TLS) used to detect single‐event displacements on the Pleasant Valley fault (Nevada, USA)

ABSTRACTChanges in surface roughness on carbonate fault scarps often reflect varying durations of subaerial weathering. On the Pleasant Valley fault in central Nevada, the documentation of a surface rupture in 1915, a long recurrence interval of faulting, slow weathering rate, and a relatively high (2–3 m) single‐event displacement make the discrimination of the historical and penultimate slip patches unambiguous. Following from a 2018 study, we used a Schmidt hammer and terrestrial laser scanning (TLS) to further test whether these weathering patterns delineate exposed slip patches on a fault scarp. Results show that Schmidt hammer rebound value ranges (termed ΔR – the difference between minimum and maximum R‐values in repeat impacts at a point), increase by ~8–10 points across the historical–penultimate event transition zone in two separate scarp transects. TLS‐derived surface roughness also indicates a clear difference between the most recent and penultimate events. The average single‐event displacement (SED) estimated using the Schmidt hammer and TLS is 2.85 m at two transect sites and is roughly equivalent to the visually estimated 3 m. While this fault is an ideal case where we know some of the slip history, the results demonstrate that these techniques show promise for discriminating slip patches on larger carbonate fault scarps with longer paleoearthquake histories, and could be used alongside 36Cl cosmogenic exposure‐age dating to improve paleoseismic records on normal faults. © 2019 John Wiley & Sons, Ltd.

Analysis of Compressive Strength of Existing Higher Educational Institutions (HEI) Concrete Column using a Schmidt Rebound Hammer

The Schmidt rebound hammer is principally a surface hardness tester with an apparent theoretical relationship between the strength of hardened concrete block and the rebound number of the hammer. This study analysed compressive strength of some selected concrete columns of Civil Engineering block at Covenant University Ota, using the Schmidt rebound hammer. It is aimed at determining variation in the concrete column strength of the HEI building in relation to standard compressive strength required of a concrete column. Data for the study was collected by carrying our Schmidt rebound hammer test (non-destructive test) on the concrete column within the study area and the rebound value (R) was measured to determine the present compressive strength of the concrete column. In carrying out this experiment, the standard experiment procedure of the Schmidt hammer test was followed. The analysis of the performed nondestructive test on the HEI concrete column was presented through tables and figures. The result of the study shows that there is variation in the compressive strength of the HEI concrete columns sampled using Schmidt rebound hammer test. The result indicated that the average compressive strength gotten through the rebound values of the sampled concrete columns compressive strength falls within the minimum required strength between 25N/mm2 and 30N/mm2 expected of a concrete column of an existing structure. The study therefore, concluded that the concrete columns of the HEI building sampled is safe, stable and it can satisfy the need for which it was built. Furthermore, because of it stability it can resist the load coming to it and this make it habitable for learning.

A new empirical formula for evaluating uniaxial compressive strength using the Schmidt hammer test

The uniaxial compressive strength (UCS) of rock is an important geotechnical parameter for engineering applications. However, how to determine the UCS simply and accurately has drawn the attentions of may researchers. To date, different kinds of indirect methods have been invented to determine the UCS of rocks, and among these methods, estimation of the UCS based on the Schmidt hammer rebound value (Hr) was commonly adopted. In this paper, an insightful analysis of the literature related to UCS estimation using the Schmidt hammer test was conducted, and three stages for the development of UCS estimation using Hr were classified. The drawbacks and merits of different kinds of techniques were analyzed in detail. Then, a data set containing the data for different rock types was collected from references, and to obtain an objective empirical formula, the simulated annealing-gene expression programming (SA-GEP) method was employed to establish the correlation between UCS and Hr. Based on the calculation results, the L-type Schmidt hammer was suggested for use in UCS estimation, and the corresponding empirical formula was established. To confirm validity of the empirical formula, the Schmidt hammer tests and uniaxial compressive tests were conducted separately, the experimental results were in a good agreement with the proposed empirical formula, implying that the proposed empirical formula can be applied in engineering practice.

A Deep Learning Based Method for the Non-Destructive Measuring of Rock Strength through Hammering Sound

Hammering rocks of different strengths can make different sounds. Geological engineers often use this method to approximate the strengths of rocks in geology surveys. This method is quick and convenient but subjective. Inspired by this problem, we present a new, non-destructive method for measuring the surface strengths of rocks based on deep neural network (DNN) and spectrogram analysis. All the hammering sounds are transformed into spectrograms firstly, and a clustering algorithm is presented to filter out the outliers of the spectrograms automatically. One of the most advanced image classification DNN, the Inception-ResNet-v2, is then re-trained with the spectrograms. The results show that the training accurate is up to 94.5%. Following this, three regression algorithms, including Support Vector Machine (SVM), K-Nearest Neighbor (KNN), and Random Forest (RF) are adopted to fit the relationship between the outputs of the DNN and the strength values. The tests show that KNN has the highest fitting accuracy, and SVM has the strongest generalization ability. The strengths (represented by rebound values) of almost all the samples can be predicted within an error of [−5, 5]. Overall, the proposed method has great potential in supporting the implementation of efficient rock strength measurement methods in the field.

Geochemical and physical characterization of lithic raw materials in the Olduvai Basin, Tanzania

The invention and proliferation of stone tool technology in the Early Stone Age (ESA) marks a watershed in human evolution. Patterns of lithic procurement, manufacture, use, and discard have much to tell us about ESA hominin cognition and land use. However, these issues cannot be fully explored outside the context of the physical attributes and spatio-temporal availability of the lithic raw materials themselves. The Olduvai Basin of northern Tanzania, which is home to both a wide variety of potential toolstones and a rich collection of ESA archaeological sites, provides an excellent opportunity to investigate the relationship between lithic technology and raw material characteristics. Here, we examine two attributes of the basin's igneous and metamorphic rocks: spatial location and fracture predictability. A total of 244 geological specimens were analyzed with non-destructive portable XRF (pXRF) to determine the geochemical distinctiveness of five primary and secondary sources, while 110 geological specimens were subjected to Schmidt rebound hardness tests to measure fracture predictability. Element concentrations derived via pXRF show significant differences between sources, and multivariate predictive models classify geological specimens with 75–80% accuracy. The predictive models identify Naibor Soit as the most likely source for a small sample of three lithic artifacts from Bed II, which supports the idea that this inselberg served as a source of toolstone during the early Pleistocene. Clear patterns in fracture predictability exist within and between both sources and rock types. Fine-grained volcanics show high rebound values (associated with high fracture predictability), while finer-grained metamorphics and coarse-grained gneisses show intermediate and low rebound values, respectively. Artifact data from Bed I and II suggest that fracture predictability played a role in raw material selection at some sites, but other attributes like durability, expediency, and nodule size and shape were more significant.

Examine the Correlation between Physico-Mechanical properties of Selected Granite rocks in Ondo State, Nigeria

This research examines the correlation between physico-mechanical properties of some selected granite rocks in Ondo State, Nigeria. Samples were collected at Zibo FM Quarry, Aaye and Samchase Quarry, Itaogbolu and tested in the laboratory for the determination of rock density, hardness, and strength. An average density of between 2.57g/cm3 and 2.67g/cm3 was recorded. Schmidt hammer and Rockwell hardness machine wereused for the determination of rock samples hardness. An average uniaxial compressive strength of rock sample was estimated from the values obtained from Schmidt hammer rebound value. The Hardness test varies from 115.90MPa to 185.00MPa (classified to have high strength) while the average Rockwell hardness varied from 45.1HRA - 57.32HRA. The average point load index ranges from 7.402MPa - 7.505MPa classified to have very high strength. Multiple regression analysis using computer-aided solution (Statistical Package for Social Sciences - SPSS) was used to analyze data obtained from the laboratory and field tests. Five parameters were input into the multiple regression analysis to generate the models. Two parameters which are Schmidt hammer rebound value and Rockwell hardness value out of five parameters are dependent variables, while point load index, uniaxial compressive strength, and density are independent variables. The result of the models developed shows positive correlations – an indication that the hardness of rock gives a significant contribution in drilling bit selection. Keywords : Rock density, Schmidt hardness, Rockwell hardness, uniaxial compressive strength, point load strength, and SPSS

Investigation of engineering properties for usability of Lefke stone (Osmaneli/Bilecik) as building stone

Lefke stone is a sandstone that has been widely used in mosques, madrasas, churches, and houses as building stone. The geological features and engineering properties of Lefke stone outcropped in the southern part of Osmaneli/Bilecik were investigated in field and laboratory studies. Samples acquired during the fieldwork were tested to determine the physical, mechanical, durability, and hygrothermal properties in the laboratory. The mean physico-mechanical properties of Lefke stone yielded apparent density of 2.38 g/cm3, specific gravity of 2.68 g/cm3, total porosity of 11.26%, 2.93% water absorption by weight, uniaxial compressive strength of 94 MPa, flexure strength of 11.45 MPa, a 3.90 MPa point load strength, 4.5–5 Mohs hardness, and field Schmidt hammer rebound value of 36. According to durability tests, Lefke stone is resistant to CaCl2 salt mist but has low resistance to SO2 aging. Salt crystals placed in the discontinuities of the rock caused slight crack growth. The stone’s resistance to crystallization of sodium sulphate salt is low, and an increase in the volume of salts crystallized in the rock results in low corner strengths. A capillary water-absorption value of 0.0016 kg/m2.h places Lefke stone into the category of very low water absorption capacity and permeability. The water vapor diffusion resistance factor (μ) less than 1 indicates that the sandstone has high breathability. Its performance in historical buildings, field observations, and values obtained through laboratory tests confirm that Lefke sandstone can be used as a building stone.

Post-blast Non-destructive Damage Assessment on Full-scale Structural Elements

A damage assessment methodology, based on the Schmidt hammer rebound value, has been developed and applied to evaluate the integrity of different structural elements after a blast event. All the elements (nine slabs, five beams and four masonry walls) were tested at full-scale with scaled distances that range from 0.2 to 2.92 m/kg1/3. The methodology consists of the evaluation of a statistically significant difference between six rebound values before and six after a blast event at each evaluation point. Based on each individual damage value, damage maps have been created using an interpolation tool. The combination of a global damage value with the spalled area based on visual inspection, allows the comparison between different protective solutions against blasting. The methodology presented and validated in this work can be used to evaluate the status of different concrete elements after a blast event such as terrorist attacks and can be also used for determination of the quality of different protective solutions. In terms of the solutions tested, the use of fibers enhances the tensile resistance of specimens. Concrete in beams configuration appears to have less resistance than in slabs, making them more vulnerable against explosives. To reduce the inner spalling in tiling wall areas, and the associated injuries, a good potential solution is the basalt fiber mesh.

Investigation of Mechanical Properties of Shale Rock in Qassim Region, Saudi Arabia

An investigation into the mechanical properties of shale rock from Qassim Province, Saudi Arabia is presented in this paper. Uniaxial compression test, Schmidt hammer test and porosity estimation were carried out. Regarding the compression test, it was found that the strength ranged from 1.98MPa to 8MPa and the strain ranged from 0.53% to 2.5%. Regarding the Schmidt Hammer test, it was found that the rebound values ranged from 22.4 to 25. The measurements of volumetric porosity indicated that the porosity in the shale rock ranged between 19.12% and 24.31%. All the values determined in this project match well with the published values of other studies about shale rock.

Full-scale reinforced concrete slabs: blast effects, damage characterization and numerical modelling

This work investigates the response of a blast loaded reinforced slab with different constructive characteristics. This topic has been well covered during the last years, but there are a reduce number of them that presents blast test at realistic scale. Seven different slabs were tested: three at a scaled distance of 0.79 m/kg1/3, one at 0.41 m/kg1/3 and four with 0.20 m/kg1/3. The three tests with high-scaled distance, used as calibration tests, have been characterized with pressure gauges and accelerometers. These reinforced slabs are the same as the one of low-scaled distance and one of high-scaled distance. Finally, the two tests of low-scaled distance have different reinforcement: steel or polypropylene fibres. The blast effects over the slabs has been characterized with a non-destructive methodology based on the Schmidt hammer. The methodology consists on the evaluation of a statistically significant difference of six rebound values before and six after a blast event for each evaluation point, having 19 evaluation point for each slab face. based on each individual damage value, damage maps have been created using an interpolation tool. This methodology is very useful to quantify the non-visual damage of a structural element and to validate numerical modelling results. In this case, a 3D lagrangian simulation using the lS-DYNA code with the blast load routine called cONWEP was done. The results in the developed model are affected by the scaled distance and by the construction patterns. The blast resistance of the slabs were better when using steel or polypropylene fibres, especially under tensile stresses (bottom part of the slabs).

Evaluating the economy-wide effects of energy efficient lighting in the household sector of Iran

Energy efficient lighting confers significant potential in electricity demand reduction. To increase the diffusion of energy efficient lighting, an LED Replacement Lamps Program is proposed. Free of charge LED lamps are suggested to be distributed to households by government to reduce household electricity demand. Because electricity is heavily subsidized in Iran, the direct benefit of the program for the government will be avoiding the energy subsidy payments. Back-of-the-envelope benefit cost analysis suggests that if potential electricity savings are realized, the program will be profitable. However, the possible rebound effect may negatively impact the program effectiveness through partially offsetting the potential electricity savings. Therefore, the viability of the program depends on the actual electricity savings that may differ from its anticipated levels. A hybrid dynamic general equilibrium model is employed to evaluate the actual economy-wide energy savings. The model has the novelty of endogenously calculating useful energy demand (e.g. lighting, cooling). Energy demand is then derived based on end-use efficiency and useful energy demand. Model results indicate an average economy-wide rebound of 43.8%. Even though the rebound value is high, the program is shown to be profitable.

A laboratory experiment on salt weathering by humidity change: salt damage induced by deliquescence and hydration

A laboratory experiment on salt weathering was carried out under changing humidity conditions. Three types of rock (tuff and dense and porous sandstone) with sodium chloride, sodium sulfate, or magnesium sulfate were subjected to humidity oscillations from 20%RH to 98%RH during 6 h periods at 20 °C. Prior to the weathering experiment, the rock specimens were oven-dried, and the water supply was restricted to only that from the air during the experiment. Salt on the rock specimens was deliquesced/hydrated at almost 100%RH during the high-humidity period and crystallized/dehydrated during the low-humidity period. Sodium chloride, which has high deliquescence ability, caused the most intensive weathering. Porous sandstone with sodium chloride was completely broken down after 100 cycles of humidity changes. The other two types of rock with sodium chloride showed flaking or swelling on their surfaces. For dense sandstone with sodium chloride, the Equotip rebound value decreased as the humidity cycles increased. Sodium chloride has a high susceptibility of deliquescence at humidities of more than 80%RH. Weathering by sodium chloride would occur extensively on the surfaces of stone heritages and geoheritages in humid coastal spray zones. Magnesium sulfate induced a weight loss in porous sandstone, flaking from the surface of tuff, and cracks on the surface of dense sandstone. Sodium sulfate had almost no effect in the humidity-change experiment, although salt efflorescence was obvious. The results for magnesium sulfate, salt deliquescence, hydration, and crystallization in the humidity-change experiment were easily repeated. Magnesium sulfate might have more influence than sodium sulfate when air humidity fluctuates in a short period.

Experimental investigation on the performance of Schmidt hammer test in durability assessment of carbonate building stones against freeze–thaw weathering

Although Schmidt hammer test has been widely used for assessment of weathering state of rocks, its application for evaluation of rock durability remains rare. This study aims at investigating the performance of the Schmidt hammer test in the durability assessment of carbonate building stones against frost weathering. For this purpose, nine types of carbonate rocks were collected from various quarries of Iran and subjected to a series of tests including determination of petrographical, physical, mechanical, ultrasonic, and rebound hardness properties. Moreover, long-term weathering test of freeze–thaw, up to 100 cycles, were carried out and ultrasonic detection was used to detect the weathering-induced damages of rocks. In ultrasonic detections, ultrasonic parameters of maximum amplitude (Amax), spatial attenuation (αs), and compressional wave velocity (Vp) were determined before and after freeze–thaw tests and then their change rates were determined. The change rates of Amax, αs, and Vp including KA, Kα, and KP, respectively, were considered as the functions of the degree of the frost-induced damages of rocks, and consequently as indications of the rock durability. Results showed that there are close correlations between the Schmidt hammer rebound value (Rn) and KA, Kα, and KP. However, the correlation between Rn and KP was weaker than those between Rn and KA and Kα because of the disproportionate response of Vp to the rock deterioration. It was concluded that the Schmidt hammer test is capable to evaluate the durability of carbonate building stones and can be used for a rapid and onsite evaluation of rock durability at different quarry faces. Hence, it allows selecting more durable rocks for different applications in new constructions and also in replacement works in historical sites.

Analysis of Schmidt hammer rebound test results with repetitive impacts for determining the mechanical characteristics of weathered pyroclastic rock surfaces: a case study along the Isotake coast, Japan

Cliffs located along the Isotake coast, Shimane, Japan, are characterized by the development of indents without rockfalls and by the occurrence of rockfalls without indents—even though these cliffs have the same geology. An analytical method was developed to determine the mechanical properties of the rock surfaces of a coastal cliff. Twenty continuous impact repetitions of a Schmidt hammer were applied normal to the cliff surfaces in each test. The results of the tests (26 with indents and 22 without indents) showed a gradual increase in the rebound value with increasing number of repetitions. A new exponential equation was proposed in this study to describe the features of the weathered surfaces. The changes in the results were well approximated by this equation, and the approximation clearly distinguished between the two types of weathered surfaces, with higher rebound values at the surfaces of the cliffs with indents than at the surface of cliffs without indents. The homogeneity and heterogeneity of the surface and inner body of the cliff rock can also be modelled by the coefficients in this equation.

Detection of internal defects of concrete structures based on statistical evaluation of healthy part of concrete by the noncontact acoustic inspection method

A noncontact acoustic inspection method was developed to perform measurements from a long distance (usually about 5 to 7 m but even over 30 m) and detect internal defects (up to 10 cm in depth) of concrete structures using a long-range acoustic device and a laser Doppler vibrometer. An algorithm was also proposed to detect internal defects of concrete by combining two acoustic features, the vibrational energy ratio and spectral entropy obtained by our measurement. However, in actual concrete structures, it is difficult to distinguish a boundary between a healthy part and a defective part owing to influences such as the shape of internal defects, age-induced deterioration, and the surface condition of concrete. Therefore, we propose a method to statistically evaluate the distribution of the healthy part of concrete and extract the healthy part to identify the defective part. By this proposed method, the actual concrete floor slab bridge was measured from 33 m away and some internal defects were detected and visualized. Furthermore, a result for a railroad tunnel was compared with the Schmidt hammer rebound value and elastic wave velocity to verify the validity of the proposed method.

Statistical Analysis of Mechanical and Physical Properties of Igneous Rocks

One of the modern finishing materials for building construction is igneous rock. Thisstudy was focused on determining the relationships between mechanical and physicalproperties of igneous rocks. This incorporates point load strength index Is (50) , UnconfinedCompression Strength (UCS), flexural strength, poisons ratio, dry density, porosity,Schmidt rebound values and P-wave velocity for a wide range of igneous rocks. Thestudy was performed on data collected from the literature. The results showed that theporosity has a significant negative effect on the dry density of rock samples. The bestrelationship was observed between modulus of elasticity and temperature with thecoefficient of determination (R 2 ) of 0.89; it means that the temperature had a greatinfluence on the modulus of elasticity so that increasing temperature causes to decreasein modulus of elasticity of igneous rock. In addition, the weakest relationship wasobserved between flexural strength and p-wave velocity with R 2 of 0.42; whereas, therewas no relationship between UCS and Poisons ratio.