Variation Of Compressive Strength Research Articles

Reliability analysis of jointed rock slope considering uncertainty in peak and residual strength parameters

Stability analysis of rock slopes is a complex problem because of uncertainties involved in the rock mass properties. The probabilistic approach is a rational way to deal with these uncertainties. This article investigates the stability of a rock slope by deterministic and probabilistic approaches by considering uncertainty in peak and residual strength parameters and strength-drop in stress-strain behavior of the rock mass. A Geological Strength Index (GSI) based on a quantitative approach was used to estimate the statistical parameters of peak and residual strength parameters. Reliability index of the slope was then estimated using Hong’s Point Estimate Method coupled with the finite element method. The approach is demonstrated using an important case study of a Himalayan rock slope supporting the piers of the world’s highest railway bridge. It was observed that the factor of safety and reliability index for the slope was highly sensitive to residual strength parameters, and; hence, ignoring strength-drop from the rock mass behavior and uncertainty in residual strength parameters can overestimate the factor of safety and the reliability index of rock slopes. A parametric study is carried out to evaluate the influence of the coefficient of variation of uniaxial compressive strength of intact rock, the Hoek-Brown strength parameter of intact rock, roughness and alteration parameters of the joints on the probability of failure and the reliability index. The approach is verified by comparing the estimated displacements along the slope with in-situ measured displacements observed during field monitoring over the years. The approach used can be extended to the rock slopes or rock slides where high displacements in the slopes are expected due to triggering forces like seismic forces, excavation or structural loads.

Behavior of polyester FRP tube encased recycled aggregate concrete with recycled clay brick aggregate: Size and slenderness ratio effects

Compared with normal aggregate concrete, recycled aggregate concrete (RAC) containing recycled clay brick coarse aggregates (termed as RAC-RCBA) shows very lower compressive strength and larger variation in compressive strength, which hinder the application of RAC-RCBA as structural concrete. This study used polyester FRP (PFRP) as confining material of RAC-RCBA cylinders to improve the strength of RAC-RCBA. The axial compressive behavior of 42 PFRP tube encased RAC-RCBA cylinders (termed as PFRP confined RAC-RCBA) and 24 unconfined RAC-RCBA cylinders were investigated. Compared with conventional glass/carbon FRP (G/CFRP) materials, the main advantages to use PFRP are its much lower material cost and much larger tensile strain capacity. In this study, the experimental parameters considered were: (1) strength, (2) size, and (3) slenderness ratio of RAC-RCBA cylindrical specimens. Statistical analysis was also conducted to investigate the size effect and the slenderness ratio effect. The experimental results indicated that compared with conventional G/CFRP composites, the PFRP had a significantly lower tensile strength and modulus, but a much larger tensile strain at failure. The PFRP tube enhanced the ductility of the RAC-RCBA cylinders remarkably, while the enhancement on the compressive strength of RAC-RCBA by PFRP was not so pronounced as that by carbon/CFRP tubes. It was also found that the size and the slenderness ratio influenced the compressive strength of the RAC cylinders at the transitional point (fct) remarkably, and the fct decreased with the increase in size and slenderness ratio for middle, large and tall sized cylinders. In addition, a size-dependent model for fct was proposed and the predictions fitted well with the experimental results, the applicability of the proposed model for other weakly confined RAC-RCBA was also verified through the comparison with the experimental results of flax FRP tube confined RAC-RCBA.

A Statistical Study on the Compressive Strength of Recycled Aggregate Concrete

In order to explore the effect of RCA on the compressive strength of concrete, two RCAs from different sources are utilized to take experiments in this study. Four groups of concrete, including three RACs incorporated with various RCAs and another one made with natural aggregate (i.e. normal aggregate concrete (NAC)) are tested under an identical laboratory condition. The influence of RCA on the statistical parameters of the compressive strength, including the mean value, the standard deviation and the coefficient of variation are examined in detail. In addition, the fitted normal distribution modelto is used to describe the probability distribution characteristics of the compressive strength of the RACs, and the Monte-Carlo simulation technique is applied to verify the suitability of the normal distribution model for the probability distribution of the compressive strength of RAC. At last, it is summed up that the RCA does not have a significant effect on the variation and probability distribution of the compressive strength of concrete.

Effect of Partial Replacement of Fly Ash by Metakaolin on Strength Development of Fly Ash Based Geopolymer Mortar

This article aims to investigate the compressive strength variation by the addition of metakaolin as a substitute of fly ash in the fly ash based geopolymer mortar. Five, ten and fifteen percent by weight of fly ash was replaced by highly reactive metakaolin. Two type of fly ashes namely, ASTM class F and ASTM class C were used as a base material for the synthesis of geopolymer mortar. Eight molar sodium hydroxide solution mixed with sodium silicate solution was used as alkaline activator. For optimum geopolymerization, mortar was cured at sixty degree Celsius for twenty four hours duration. Results show different behavior of metakaolin replacement on compressive strength for two different types of fly ash based geopolymer mortar. Improvement in compressive strength was seen by addition of metakaolin in ASTM class F fly ash based geopolymer. On the other hand compressive strength was decreased abruptly in fly ash class C based geopolymer up to certain replacement level.

Uniaxial Compressive Strength Variation for Multi-point Support Design and Discontinuity Mapping for Tunnel Stability Analyses and Stope Dilution Assessme

Uniaxial Compressive Strength Variation for Multi-point Support Design and Discontinuity Mapping for Tunnel Stability Analyses and Stope Dilution Assessme

Experimental Study on the Influence of Fly Ash and Slag on Strength of Concrete

Fly ash and slag are the most common admixture in the concrete, which can improve the strength and durability of concrete. The variation of compressive strength, splitting strength and flexural strength of pebble cement concrete were studied in this paper. The results prove that: flay ash and slag can enhance the strength and improve the performance of concrete; fly ash mainly play a role in the early stage of concrete strength growth and slag mainly play a role in the later stage. The research could provide a reference for preparing the high-strength concrete.

The Resistance of Chloride Ion Penetration and the Microstructure of Air-Entrained Concrete

It was investigated that the variation of compressive strength, chloride diffusion coefficient and microstructure of concrete with different water-cement ratio and air content. The experimental results indicate that the bubble distribution and the continuity of the pores in the concrete are greatly affected by the air content in it. It enhanced the discontinuity of the pores and increased the number of tiny bubbles which were independent, closed, stable and equally distributed, as the air content was appropriate. So that it improved the resistance of chloride ion penetration. The chloride diffusion coefficient of C30 concrete whose air content was 5% was only 69.52% of that of theC30 reference concrete. And this effect to C50 concrete was more apparent than C30 concrete.

To Study the Variation in Compressive and Split Tensile Strength of Concrete by Using Various Binders

To Study the Variation in Compressive and Split Tensile Strength of Concrete by Using Various Binders

Influence of temperature history on chloride diffusion in high volume fly ash concrete

This paper presents the influence of temperature history on chloride diffusion of high volume fly ash (HVFA) concrete. Four different curing temperature histories, referenced as SDC (standard curing), SMC (steam curing), OC (outdoor curing) and TMC (massive concrete temperature matched curing), were set. Concretes with different replacement levels of fly ash were cast and cured under the four temperature histories, respectively. The variations of compressive strength, porosity and chloride diffusion coefficient with different ages were determined by experiment. SEM and XRD were used to analyze the microstructure and compositions of hydrated pastes. The results show that the performances of fly ash concrete were influenced by temperature histories. And the influence was more obvious with the addition of replacement level of fly ash. For ordinary concrete, higher accumulated temperature at early age got higher compressive strength, better pore structure and lower chloride diffusion coefficient, but had negative effects at later age compared to SDC. For HVFA concrete, it was beneficial for the development of performances. Although the chloride diffusion coefficient was higher than ordinary concrete at early age, it would become small even lower at later age. And higher accumulated temperature promoted this process. In addition, by utilizing the concept of maturity, good power function relations between chloride diffusion coefficient of fly ash concrete and Maturity were obtained at early age.

Pull-out behaviour of straight and hooked-end steel fibres under elevated temperatures

This paper presents the results of an experimental investigation into the effect of elevated temperature on the steel fibre-matrix bond characteristics. A series of pull-out tests on straight and hooked-end fibres embedded in four different cementitious matrixes, namely normal strength concrete (NSC), medium strength concrete (MSC), high strength concrete (HSC) and ultra-high performance mortar (UHPM) were performed. Ninety days after casting, the specimens were heated to target temperatures of 100, 200, 300, 400, 500, 600, 700 and 800°C, respectively. The initial and residual thermal and mechanical properties of the concrete were investigated. It was shown that while the variation in compressive strength and pull-out response for different temperatures is relatively small up to 400°C, further increase in temperature results in a reduction in the pull-out strength, especially for the temperature >600°C. At 800°C, the maximum pull-out load of the hooked-end fibres with NSC, MSC and HSC decreased by 54%, 64% and 56%, respectively.

Estimation of uniaxial compressive strength of shale using indentation testing

A number of methods have been proposed to indirectly assess the uniaxial compressive strength (UCS) of intact rock in the drilling of oil wells and underground drilling. Indentation testing is a method in which an indentor ‎of a specific diameter penetrates a particle of rock and the force-displacement curve is plotted to determine the critical transition force (CTF). In the present study, 10 shale block samples were collected from a cretaceous shale formation in Iran from which standard cores were prepared and subjected to UCS testing. Cubic particles 4, 5 and 7mm3 in size were cut and entrenched in disks containing resin and a total of 300 indentation tests were conducted on them. Empirical relations for the relation between UCS and CTF were developed for each size. The highest correlation coefficient was recorded for the 7mm3 particles and the lowest for the 4mm3 particles. A simple method is proposed to determine the empirical relationship independent of particle dimensions between UCS and CTF that has a correlation coefficient of 0.78. Verification of the proposed equations show that they predicted UCS with 85% accuracy. A comparison of the proposed relationships and those from previous studies indicates that the empirical relationship between these two variables is influenced by variation in the uniaxial compressive strength and lithology of the different samples.

Confining effect by hot rolled steel and cold formed steel on coconut shell concrete with quarry dust

Properties of concrete using quarry dust as fine aggregate and coconut shell as coarse aggregate were examined. Hot rolled and cold formed steel were used as an external confinement on both conventional concrete and coconut shell concrete mixes. Workability, density of concrete, compressive, flexural and impact resistance were considered and evaluated. Uses of quarry dust in place of sand reduce workability and increase density of concretes. In case of without confinement, the compressive strength variation between cubes strength and cylinders strengths are traditional and it is not if it is confined. Flexural specimen with confinement does not fail and stands enough without any sign of failure in case of hot rolled steel. However, in case of cold formed steel, flexural specimen with confinement enhances approximately nine times of the flexural specimen without confinement and stands enough with ductile manner. Hot rolled and cold formed steel confinement effect is not allowing the impact specimen to form crack and in turn not allows failing the specimen. This study proves that the use of quarry dust in place of sand augmented the mechanical properties of both coconut shells concrete and conventional concrete as well. Confinement effect improves promptly the mechanical properties of concretes.

The Case Study on Cubes Compressive Strength Variations for Different Water Sources in Dares Salaam City, Tanzania

The Case Study on Cubes Compressive Strength Variations for Different Water Sources in Dares Salaam City, Tanzania

Experimental Investigation of Compressive Behaviour of Pier by Partial Replacement of Metakaolin

Objectives:The main focus of our experimental investigation is to study the behavior of a pier based on variations in compressive strength due to partial replacement of cement with metakaolin in order to attain maximum stiffness and strength, so as to withstand the shear forces, bending moments and other related structural response parameters efficiently. Analysis: The round and rectangular specimens were prepared by replacing cement with metakaolin up to 15%. The samples were tested after 7 and 28 days. Findings: Study reveals that with the replacement of 10% metakaolin in both circular as well as rectangular moulds, there is an increase in the load carrying capacity approximately about 19%, when compared with plain reinforced concrete moulds after 28 days. The most important finding is that the replacement of cement by metakaolin up to 10% helped us to attain higher strength after 7 as well as 28 days hence providing us a simple and efficient method of preventing the pier failure by attaining higher strengths. Improvement/Applications: Based on the test results there is remarkable increase in the load carrying capacity of pier which enhances the rigidity of pier in terms of strength and stiffness.

Experimental Investigation of UHPFRC Cube and Cylinder Compression Test at Elevated Temperature

The present paper focuses on compressive strength of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) cube and cylinder under compression testing machine, the experimental determination of test results shows +5% variation in compressive strength, differs from normal concrete +20% the ascending in strength development at an increased age under an elevated temperature of the material is identified with addition of hooked end steel fiber. In this study, the optimized mix design developed and the conversion ratios determined to develop relationship between cube and cylinder. The comparison between mean compressive strength ratio for cube and cylinder has been presented to determine high compressive strength. The research work is carried out to achieve enhanced target compressive strength 180 N/mm2.

Preliminary studies on steel slag as a substitute for coarse aggregate on concrete

The development of science and technology in the field of construction that is rapidly increasing, is always followed by the growing community needs for infrastructure facilities, such as buildings, bridges and other construction. One of the key element in that development is concrete. Due to the rapid development of science and technology in the field of construction, it’s required a building material which has better advantage than the materials of the existing building. To obtain a better building materials, one alternative is the use of waste as aggregate in concrete mixture. In this study the authors using waste steel waste (steel slag) as a substitute for coarse aggregate. Steel slag used is steel waste from PT. Growth Sumatra Industry. The gravel substitution variations is 0%, 15%, and 25% and the testing was done by the slump test, compressive strength and flexural strength of concrete. From the test results obtained optimum compressive strength variation occurs in 25% substitution of steel slag gravel amounted to 40.481 MPa, whereas for the optimum bending capacity contained in variations of 25% substitution of steel slag gravel amounted to 19.592 N / mm 2 . And for optimum slump value obtained on the variation of normal concrete. This shows the workability of the concrete normally higher than the other variation.

Slant shear bond strength between self compacting concrete and old concrete

This experimental investigation aims to study the bond strength between old and new self-compacting concrete (SCC). The first part presents the factors affecting slant shear bond strength between old concrete and new self-compacting concrete. The studied parameters are compatibility between old concrete and new SCC through variation of concrete compressive strength and concrete stiffness, type of bonding agent, roughness of old concrete, and the effect of adding latex and polypropylene fiber to self-compacting concrete. In the second part, the proper specimen of slant shear test is studied. From the test results, cylindrical specimens with 150mm diameter and 300mm height have a minimum coefficient of variation compared with other studied shapes. The concrete compressive strength overlay self-compacting concrete, roughness of old concrete configuration, adding latex and using polypropylene fiber have a significant effect on slant shear bond strength. In addition, the prism specimen represents more reliable value of slant shear strength than cylinder specimen.

Influence of microbial activity on the physical properties and strength of ilmenite and magnetite ores

The influence of microorganisms on the physical properties and strength of ilmenite and magnetite ores was determined in culture studies and laboratory tests of rock parameters such as absorption, porosity, elastic wave velocity, and uniaxial compressive strength. Initial pH condition was determined in the culture experiments, and then abiotic and biotic oxidation tests were performed to determine variations in pH, physical properties, and the strengths of the two ferruginous ore rocks. For ilmenite and magnetite ores, average initial values were, respectively, 0.185% and 0.496% for porosity, 0.046% and 0.123% for absorption, 1919 m/s and 1467 m/s for elastic wave velocity, and 432 MPa and 168 MPa for uniaxial compressive strength. The pH of ilmenite ore at the end of the abiotic and biotic oxidation tests was in the range of 3.82–4.26 and 2.20–2.57, respectively, while that of magnetite ore was 4.02–5.16 and 1.50–1.90, respectively. In magnetite ore, the changes in porosity and absorption due to the biotic oxidation test were larger than those observed in the abiotic oxidation test, while the variations in ilmenite ore due to both tests (abiotic and biotic oxidation) were small. The differences in porosity and absorption between the abiotic and biotic oxidation tests were larger in magnetite ore than in ilmenite ore, while the elastic wave velocity was smaller in magnetite ore than in ilmenite ore. In addition, the variations in uniaxial compressive strength due to the abiotic oxidation test were not significantly different than initial values in both ilmenite and magnetite ores, while variations caused by the biotic oxidation test were relatively large in both ferruginous ore rocks. Our results suggest that variations in the physical properties and strength of ilmenite and magnetite ores are largely dependent on microbial activity.

Compressive behaviour of fibre reinforced plastic with random fibre packing and a region of fibre waviness

A critical limitation of fibre reinforced plastic is its large variability on mechanical performance, especially the longitudinal compressive strength. The influence of fibre random packing and waviness on the compressive strength of UD fibre reinforced plastic is studied in this paper. Three-dimensional geometrically non-linear finite element model is constructed to investigate the compressive behaviour, and an improved approach named Latin hypercube sampling based on random sequential expansion is proposed to generate random fibre distribution across the cross-section. Latin hypercube sampling based on random sequential expansion provides high computation efficiency and good distribution characteristics in comparison to previously proposed methods. Fibre waviness defect with different misalignment angles is also incorporated in the finite element model. It is shown that random fibre packing tends to result in a stochastic detriment of fibre reinforced plastic compressive strength in comparison with uniform fibre packing condition, and the stochastic variation of compressive strength tends to follow normal or lognormal distribution.

Modified Hoek–Brown failure criterion for anisotropic rocks

The direction-dependent strength behavior of anisotropic rocks is a common characteristic. It is essential to develop the model that can describe the nonlinearity as well as the anisotropy in the triaxial strength behavior of the rocks. In the present study, a modified Hoek–Brown failure criterion was developed to describe the triaxial strength behavior of the rocks by the using of anisotropic index (\(\alpha_{\beta }\)). The procedures for determining the failure criterion parameters are introduced. In the model, the estimation of the uniaxial compressive strength at a given angle β was required, so an empirical equation for predicting the variation of the uniaxial compressive strength of anisotropic rocks is presented. The performance of the proposed equation was tested by using a triaxial test database compiled by Singh (Rock Mech Rock Eng 48(4):1387–1405, 2015). The variation of the uniaxial compressive strength was then incorporated into the modified Hoek–Brown failure criterion. Based on the analysis of the extensive triaxial test database, it was possible to accurately predict the strength of anisotropic rocks using limited test data. It is concluded that the modified Hoek–Brown failure criterion has good ability in predicting the strength of anisotropic rocks.