Schmidt Hammer Rebound Research Articles

Evaluation of Self-Compacting Concrete Strength with Non-Destructive Tests for Concrete Structures

Self-compacting concrete (SCC) shows to have some specificities when compared to normal vibrated concrete (NVC), namely higher cement paste dosage and smaller volume of coarse aggregates. In addition, the maximum size of coarse aggregates is also reduced in SCC to prevent blocking effect. Such specificities are likely to affect the results of non-destructive tests when compared to those obtained in NVC with similar compressive strength and materials. This study evaluates the applicability of some non-destructive tests to estimate the compressive strength of SCC. Selected tests included the ultrasonic pulse velocity test (PUNDIT), the surface hardness test (Schmidt rebound hammer type N), the pull-out test (Lok-test), and the concrete maturity test (COMA-meter). Seven sets of SCC specimens were produced in the laboratory from a single mixture and subjected to standard curing. The tests were applied at different ages, namely: 1, 2, 3, 7, 14, 28, and 94 days. The concrete compressive strength ranged from 45 MPa (at 24 h) to 97 MPa (at 94 days). Correlations were established between the non-destructive test results and the concrete compressive strength. A test variability analysis was performed and the 95% confidence limits for the obtained correlations were computed. The obtained results for SCC showed good correlations between the concrete compressive strength and the non-destructive tests results, although some differences exist when compared to the correlations obtained for NVC.

Strength evaluation of granite block samples with different predictive models

Over the last decade, application of soft computing techniques has rapidly grown up in different scientific fields, especially in rock mechanics. One of these cases relates to indirect assessment of uniaxial compressive strength (UCS) of rock samples with different artificial intelligent-based methods. In fact, the main advantage of such systems is to readily remove some difficulties arising in direct assessment of UCS, such as time-consuming and costly UCS test procedure. This study puts an effort to propose four accurate and practical predictive models of UCS using artificial neural network (ANN), hybrid ANN with imperialism competitive algorithm (ICA–ANN), hybrid ANN with artificial bee colony (ABC–ANN) and genetic programming (GP) approaches. To reach the aim of the current study, an experimental database containing a total of 71 data sets was set up by performing a number of laboratory tests on the rock samples collected from a tunnel site in Malaysia. To construct the desired predictive models of UCS based on training and test patterns, a combination of several rock characteristics with the most influence on UCS has been used as input parameters, i.e. porosity (n), Schmidt hammer rebound number (R), p-wave velocity (Vp) and point load strength index (Is(50)). To evaluate and compare the prediction precision of the developed models, a series of statistical indices, such as root mean squared error (RMSE), determination coefficient (R2) and variance account for (VAF) are utilized. Based on the simulation results and the measured indices, it was observed that the proposed GP model with the training and test RMSE values 0.0726 and 0.0691, respectively, gives better performance as compared to the other proposed models with values of (0.0740 and 0.0885), (0.0785 and 0.0742), and (0.0746 and 0.0771) for ANN, ICA–ANN and ABC–ANN, respectively. Moreover, a parametric analysis is accomplished on the proposed GP model to further verify its generalization capability. Hence, this GP-based model can be considered as a new applicable equation to accurately estimate the uniaxial compressive strength of granite block samples.

Shear strength behaviour of rock joint material influenced by different weathering grade

Shear strength parameter is a crucial in designing the rock mass structures such slope and tunnel. Stability of rock mass structure is affected by apparent joint sets and discontinuities present in the rock mass especially when the joint interfaces degraded and physically altered due to weathering effect. The weathered condition imposed on joint surface importantly play the role to control the shear strength characteristic and sliding behaviour. A comprehensive study and focussing on effect of weathering grade to the rock joint surface particularly for granite type of rock was introduced. A set of granite samples were collected from a quarry then been classified into respective grade of weathering based on surface hardness by using Schmidt rebound hammer and rock material density by using PUNDIT test. The standard laboratory testing of direct shear test that accordance to ISRM suggested method were carried out on jointed block samples with different grades of weathering. Detail assessment on rock joint samples were evaluated to characterize the physical appearance of different weathered joint surface condition. The rock joint surface assessment made based on Joint Roughness Coefficient (JRC) then been correlate with thin section petrographical results for justification with respect to mineral composition contents. As the result, the shear strength of weathered rock joint significantly influenced by the weathering grade due to changes of microstructure behaviour of the granite. Moreover, the lower grade of the granite sample has low frictional resistance force to against the sliding, hence indirectly produced low shear strength of the rock joint.

Developing Empirical Models for Uniaxial Compressive Strength Prediction by Using Non-Destructive TestResults

In the current study, uniaxial compressive strength, Schmidt hammer and Sonic velocity tests are performed on NX size rock core samples from Sakesar and Namal formation limestone. Least square regression analysis is used to develop any possible correlations between the destructive and non-destructive test results. Empirical models, for predicting the uniaxial compressive strength of rocks by using the rebound number and P-wave/S-wave velocity, have been developed and evaluated. Analysis shows that the empirical model for predicting UCS with Schmidt hammer rebound number is more reliable over a wide range of strength values for both the formations. Whereas the model that uses P-wave/S-wave velocities is reliable particularly when the strength values are low to medium.

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 Comparison Between Schmidt Rebound Hammer Test and Point Load Index Test (IS50) for the Effectiveness in Estimating the Unconfined Compressive Strength of Intact Rock- A Case Study with respect to Limestone of Early Eocene Nammal Formation, Central Salt

In a bid to find some possible relation of Unconfined Compressive Strength (UCS) with relatively simplelaboratory tests like Point Load Test (PLT) and Schmidt Rebound Hammer Test (SRHT), some 50 core samples ofMiddle Eocene Nammal formation from Central Salt Range in Pakistan were collected and subjected to these testmethods as per respective test standards of International Society of Rock Mechanics (ISRM). The values of SRHT andPLT were separately compared to the respective values of UCS so as to find the linear relations. On the basis of the R2value of Regression Analysis, it has been found that a strong correlation with a high degree of accuracy exists betweenPLT and UCS while the degree of accuracy between SRHT and UCS was found to be low.

A Comparison Between Schmidt Rebound Hammer Test and Point Load Index Test (IS50) for the Effectiveness in Estimating the Unconfined Compressive Strength of Intact Rock- A Case Study with respect to Limestone of Early Eocene Nammal Formation, Central Salt

In a bid to find some possible relation of Unconfined Compressive Strength (UCS) with relatively simplelaboratory tests like Point Load Test (PLT) and Schmidt Rebound Hammer Test (SRHT), some 50 core samples ofMiddle Eocene Nammal formation from Central Salt Range in Pakistan were collected and subjected to these testmethods as per respective test standards of International Society of Rock Mechanics (ISRM). The values of SRHT andPLT were separately compared to the respective values of UCS so as to find the linear relations. On the basis of the R2value of Regression Analysis, it has been found that a strong correlation with a high degree of accuracy exists betweenPLT and UCS while the degree of accuracy between SRHT and UCS was found to be low.

Reliability of empirical equations to predict uniaxial compressive strength of rocks using Schmidt hammer

ABSTRACT While the direct measurement of uniaxial compressive strength (UCS) of rocks is expensive and time-consuming, many empirical equations were developed to predict UCS of rocks by the indirect method such as Schmidt hammer rebound number (RL). However, to the best of our knowledge, the reliability of these equations is not investigated. The aim of this paper is to check the reliability of the available empirical equations to predict UCS for limestone rocks using L-type Schmidt hammer (RL) test. A total of 112 core sample test results of limestone rocks, which were collected from four different borrow areas in Iraq, were measured. Results of this study showed that the equation developed by Arslan et al., 2015 [“Prediction of Durability and Strength from Schmidt Rebound Hammer Number for Limestone Rocks from Salt Range, Pakistan.” Journal of Himalayan Earth Science 48: 1] is the more reliable regression model to predict UCS from RL. Furthermore, the performance of the selected equation is enhanced using the measured values of UCS from this study.

Performance of Foundry Sand Concrete under Ambient and Elevated Temperatures.

Waste foundry sand (WFS) is the by-product of the foundry industry. Utilizing it in the construction industry will protect the environment and its natural resources, and enable sustainable construction. WFS was employed in this research as a fractional substitution of natural sand by 0%, 10%, 20%, 30%, and 40% in concrete. Several tests, including workability, compressive strength (CS), splitting tensile strength (STS), and flexural strength (FS), ultrasonic pulse velocity (USPV), Schmidt rebound hammer number (RHN), and residual compressive strengths (RCS) tests were performed to understand the behavior of concrete before and after exposure to elevated temperatures. Test findings showed that the strength characteristics were increased by including WFS at all the phases. For a substitute rate of 30%, the maximum compressive, splitting tensile, and flexural strength were observed. Replacement with WFS enhanced the 28-day compressive, splitting tensile, and flexural strength by 7.82%, 9.87%, and 10.35%, respectively at a 30% replacement level, and showed continuous improvement until the age of 91 days. The RCS of foundry sand concrete after one month of air cooling at ambient temperature after exposing to 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, and 800 °C was found to be in the range of 67.50% to 71.00%, 57.50% to 61.50%, 49.00% to 51.50%, 38% to 41%, 31% to 35% and 26% to 31.5% of unheated compressive strength values for 0% to 40% replacement of WFS, respectively. The RCS decreases with increasing temperature; however, with increasing WFS, the RCS was enhanced in comparison to the control samples. In addition, the replacement of 30% yielded excellent outcomes. Hence, this study provides a sustainable construction material that will preserve the Earth’s natural resources and provide a best use of WFS.

Destructive and non-destructive experimental investigation of polypropylene fibre reinforced concrete subjected to high temperature

Concrete is an inherently fire-resistant material, which in most cases requires no additional fire protection. However, a long-term exposure to high temperature results in the change in both strength properties and mechanical behaviour of concrete. Most of the experimental studies conducted so far investigated the fire resistance of concrete composites after the fire exposure. Whereas the aim of this paper was to focus on the performance of selected concrete composites, particularly plain concrete and fibre reinforced concrete with polypropylene fibres, exactly at the elevated-temperature state. Namely it concerns reference plain concrete and polypropylene fibre reinforced concrete tested up to 800 °C. Standard destructive tests and non-destructive tests were conducted on cylindrical specimens at hot state immediately after heating-up by using a specific heat treatment. The system used for the heat treatment was composed of ceramic pads, thermocouples the Mannings HTC 70 kW heating and control machine, which provided and regulated the heat transferred to the pads. The main objective of the experimental study was to observe actual material strength during fire situation as well as the reliability of the Schmidt's rebound hammer test when used for testing concrete at elevated temperature. The obtained results are in good agreement with the existing result database of polypropylene fibre reinforced concrete and plain concrete subjected to elevated temperature. The results obtained by the two different testing methods also show good agreement in a certain range of temperatures. As a consequence, in scientific manner, it seems that conducting the Schmidt's rebound hammer test on hot specimen with subsequent standard destructive compression test on the identical specimens cooled down to ambient temperature enable the observation of the compressive strength at hot state and the residual compressive strength after fire exposure on the same specimen. The investigation also demonstrates the benefit of the polypropylene fibres when added to a concrete composite subjected to elevated temperatures. Their presence in a mixture improves concrete spalling resistance and ensures a stable environment with low pore pressure in the concrete microstructure when subjected to elevated temperature and as a consequence the deviation in concrete compressive strength is small. The upcoming experimental investigation will focus on the effect of fibre content on the strength properties of concrete under elevated temperature.

Compressive strength assessment of recycled aggregate concrete using Schmidt rebound hammer and core testing

The main objective of this study was to estimate the compressive strength of recycled aggregate concrete (RAC) by means of Schmidt rebound hammer and core testing. The use of recycled aggregate in concrete has been shown to lead to a decrease in the construction cost and it can reduce the burden on the environment by saving natural aggregates. On the other hand, some non-destructive and semi-destructive techniques, such as Schmidt rebound hammer and core testing, are long-established methods for strength estimation of materials. Thus, the present study intended to obtain the compressive strength of RAC using these methods and then compare it with the results of 150 mm cube specimens. To achieve this goal, after producing concrete mixes with 70% replacement of recycled coarse aggregate, 96 cube specimens and 8 concrete slabs were cast to perform Schmidt rebound hammer, core and cube testing. In addition, the combination of the methods was used to obtain correlations between Schmidt rebound hammer and core testing. The results demonstrate that a multi-variable equation using these tests’ results can efficiently predict the compressive strength of RAC and conventional concrete and is more promising than single-variable equations based on the Schmidt rebound hammer test results.

The determination of alteration extent using minero-petrographical, geochemical, and geomechanical properties in granitic rocks from the Tavşanlı Zone (NW Turkey)

The effects of alteration on granites outcropping around Sivrihisar area within the Tavsanli Zone (NW Turkey) were investigated considering minero-petrographical, geochemical, and geomechanical properties. For this aim, polarizing light microscope, scanning electron microscope, X-ray diffraction, chemical analyses, and geomechanical tests were conducted on the granitic samples. The new petrographic index, referred as feldspar alteration index, was developed from the quantitative ratios of total and altered constituents in feldspar minerals. Based on solution-precipitation processes, plagioclase and alkali feldspar were altered to smectite, sericite, and kaolinite along microfractures, cleavage, twinning, and zoning structure. Anorthite-rich core is more altered than the rim of zoned plagioclase due to higher solubility in water and selective alteration of calcic plagioclase. EDS studies indicate that Na, Si, and Ca decrease and Mg, Al, K, and Fe progressively increase. The normalized values of whole-rock chemical analyses of the granites show depletion of Si, Al, Na, and Ca reflecting the dissolution of plagioclase. Enrichment of Si, Al, Na, Ca, Mg, K, and Fe reveal precipitation of smectite, sericite, and kaolinite minerals during alteration. Minero-petrographical and geochemical changes led to an increase in water absorption and apparent porosity and a decrease in apparent density, P-wave velocity, Schmidt hammer rebound, and compressive strength. Significant relationships between FAI and geomechanical properties (R2 = 0.7116–0.8676), FAI and P-wave velocity index (Ivp) (R2 = 0.8676), and FAI and strength ratio (Rs) (R2 = 0.7614) demonstrate that FAI can be used to determine the alteration degree of granites.

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

The Effect of Fire on Building Materials: The Case-Study of the Varnakova Monastery Cells in Central Greece

The evaluation of the fire impact on building materials is of great scientific and socio-economic importance since fire can result in materials’ chemical and mechanical alterations, which leads to structural stability problems of historical and/or modern construction. This highly increases the cost of rehabilitation interventions. The case study of the Byzantine Monastery of Panagia (Virgin Mary) Varnakova is an example of the fire effect on both historical and newer stone masonries. The Varnakova Monastery is a typical 19th century monastic complex and, during its long history, it has undergone multiple reconstructions after major catastrophic events that have taken place due to its strategic geographical position and its financial and spiritual significance for the region. The last big-scale renovation of the Monastery was conducted between the years 1992 to 2014. However, in January 2017, a devastating fire destroyed the largest part of the monastic cells’ quarter. In this work, a diagnostic study of the different construction phases’ materials comprising the masonries of the monastery cells in their present state is presented. The examination of a series of samples through analytical techniques, such as optical microscopy, X-ray diffraction, thermal analysis, and total immersion tests, along with the use of non-destructive techniques in situ, such as Infra Red Thermography, Digital Microscopy, and Schmidt Hammer Rebound tests, shed light on the preservation state and on the decay of the diverse building materials. In addition, the impact of the fire on their properties was investigated. The results reveal the diversity of the materials used in the historical masonries throughout the centuries, while the combination of analytical and non-destructive techniques demonstrates the damages induced by the fire.

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.

Reusing Iraqi Construction and Aggregates Waste to Manu-facturing Eco-Friendly Polymer Concrete

The recycling and reusing of waste materials to produce suitable materials is very important subjects to scientific research in world now, because the decrease natural resources and create a hole or risk in future of the world. The aim of our research to produce polymer concrete (PC) has high mechanical and physical characteristic. This PC was prepared by using the waste of aggregates and demolitions to make PC have good mechanical and physical characteristic with low cost as compared as cement concrete. In this research different types of construction and demolition waste were used as aggregates replacement (i.e. waste of cement/concrete debris, waste of ceramics and the waste of blocks) while the type of polymer resins (i.e. Epoxy) as cement replacements. The weight percentages of resin were changed within (20, 25 and 30) % to manufacture this polymer concrete. The tests we done like physical such as den-sity and mechanical such as compressive strength, flexural strength. Splitting tensile strength and Schmidt hammer rebound hardness.

Evaluation of concrete made with stone and brick aggregate using non-destructive testing

The quality of concrete can be primarily judged by its compressive strength. Numerous methods of non-destructive testing (NDT) have been developed to approximate the compressive strength of in situ concrete. Schmidt's rebound hammer and ultrasonic pulse velocity methods are frequently used. In the study reported in this paper, both methods were applied and correlated with destructive testing of concrete. The focus of the study was on developing the NDT relationships for concrete made with coarse aggregates consisting of different mixtures of stone and brick aggregates. The correlation between Young's modulus (static, dynamic and shear) and longitudinal pulse velocity was also incorporated for evaluating complete features of the concrete. A number of experiments followed by statistical analyses was made to achieve the same result.

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.

In situ investigation of stone heritage sites for conservation purposes: a case study of the Sz\xe9kesfeh\xe9rv\xe1r Ruin Garden in Hungary

This paper demonstrates the application of in situ diagnostic tools to document stone heritage sites prior to conservation interventions using a Medieval ruin of Central Europe (Székesfehérvár, Hungary). The applied methods included lithological mapping and characterisation and mapping of decay forms as well as in situ measurements of physical parameters such as Schmidt hammer rebound, moisture content and micro-drilling resistance. The combination of these methods allowed the condition assessment of different lithotypes and demonstrated the role of micro-fabric, mineralogical composition and climatic conditions in stone durability. Differences were found in the properties and in the weathering forms of fine-grained and medium-grained porous oolitic limestone and travertine. The black crust observed in porous limestone is less prone to detachment on medium-grained oolitic limestone ashlars, while scaling was observed on fine-grained oolitic limestone blocks. The micro-drilling resistance of exposed porous limestone showed higher drilling resistance at the crust zone (upper 1–2 mm) than below, marking the upper cemented zone, while the drilling resistance of porous limestone under shelter showed an opposite trend. The shelly limestone, the sandy calcarenite and red compact limestone also showed an increase in drilling resistance at the topmost app. 2 mm zone. The applied in situ, non-invasive and micro-destructive techniques helped in the identification of endangered zones at Székesfehérvár, thus, they can provide key information on condition assessment of stones at heritage sites, where sampling is limited and preventive conservation is important.

Issues in Engineering Geological Classification of Weathered Sedimentary Rocks: Case Study of Kati Formation, Parit, Perak

Kati Formation consists of alternating layers of sandstone, siltstone and mudstone that results in non-uniform weathering. The presence of surficial features due to weathering such as iron bands, iron recementation, iron staining and lithobionts coating in an uneven distribution on the outcrop causing more complexity to the heterogeneous sedimentary rocks which are also tectonically deformed. The presence of iron recementation in highly weathered rocks causing the rock strength to be higher than the moderately weathered rocks. Thus, several laboratory tests are conducted in this study to characterise the weathered rocks which are uniaxial compressive strength (UCS), point load strength index, slake durability test, jar slake test and Schmidt hammer rebound test. Among the laboratory tests conducted in this study, slake durability index test, Id2 is the ideal test to characterise the rock samples of different weathering grades as it gives a large range of laboratory test results which is 0.3 % to 15.0 % for completely weathered, 22.0 % to 67.0 % for highly weathered, 68.0 % to 83.0 % for moderately weathered and 87.0 to 98.0 % for slightly weathered to fresh rocks. The values obtained are not affected by the uneven distribution of iron oxide present in the rock samples.