Prismatic Specimens Research Articles

Study of Fresh and Hardened Properties of Concrete Using Cement with Modified Blend of Millet Husk Ash as Secondary Cementitious Material

The growing demand and production of cement have created a significant impact on the environment and the cement production has required huge energy consumptions. Therefore, Pakistan is facing a serious energy crisis. Thus, the researchers are engaged for introducing agricultural/industrial waste materials which possess cementitious properties to reduce not only cement production, but it reduces energy consumption, and helps to protect the environment. The experimental goal of this work was to investigate the fresh and hardened concrete inclusion with MHA as cement replacement at proportions such as 0%, 5%, 10%, 15%, and 20%. In this investigational work, total 180 concrete specimens were prepared with a targeted strength of 25 MPa. However, cube specimen was used for compressive strength, cylindrical samples were used for investigating the splitting tensile strength and prism specimen used for flexural strength of concrete. The results showed the compressive strength was achieved by 30.24 MPa and 28.21 MPa at 5% and 10% of MHA as compared to targeted strength of 25 MPa after 90 days. Similarly, splitting tensile and flexural strength was estimated by 2.64 MPa and 4.26 MPa at 10% of MHA as cement replacement material in concrete after 28 days respectively. Moreover, the water absorption and density of concrete was reduced with rise in content of MHA after 28 days respectively. Besides, the slump was declined as the content of MHA rises.

Estimating unconfined compressive behavior of HMA using soft computing

The mechanical properties of materials such as elastic tangential modulus (Et) and unconfined compressive strength (UCS) can be used to predict their performance during service life. This paper utilizes gene expression programming (GEP) as an alternative method to estimate the unconfined uniaxial compression properties of hot mix asphalt. Short-term static compression was used to evaluate modes of failure and stress–strain relationship of cylindrical and prismatic asphalt concrete specimens due to mixture types, specimen shape, height, temperature, binder type and testing orientation. The results show that cubic specimens tested parallel to the direction of compaction achieved higher compressive strength and peak strains than specimens tested to the perpendicular direction. Cylindrical specimens had greater elastic stiffness than prismatic specimens with similar aspect ratios. The GEP and multiple linear regression approaches for the assessment of UCS and Et concluded satisfactory outcomes. The coefficient of determination (R2) for USC-GEP was 0.887 and 0.908 and similarly Et-GEP of 0.785 and 0.648 was more significant than regression models. The models developed provide a cheap, simple and quick methodology of estimating the stress–strain properties of dense-graded asphalt concrete by eliminating the need for the compression test.

Experimental study on stress-strain curves of seawater sea-sand concrete under uniaxial compression with different strain rates

In order to investigate the mechanical properties of seawater sea-sand concrete (SSC) under uniaxial compression, the SSC prisms with different mix proportions are designed and prepared, and the compressive strength and stress-strain curves under uniaxial compression are tested, in which five loading strain rates 10−5/s, 10−4/s, 10−3/s, 10−2/s, and 10−1/s are selected. The failure patterns of the SSC specimens under different strain rates are discussed, and the peak stress, peak strain (strain at the peak stress), elastic modulus, and ultimate strain are analyzed. The influence of the strain rate and the shell particle content on the stress-strain curves is intensively evaluated. It shows that the peak stress and elastic modulus increase with an increasing strain rate while the peak strain and ultimate strain have no obvious trend. Additionally, the shell particles seem to have contributions to the increase of the compressive strength of SSC base on the test results of cube and prism specimens, but further considerations about this phenomenon are necessary. Finally, the dynamic increase factor (DIF) of characteristic indices of SSC is put forward.

Impact performance of novel multi-layered prepacked aggregate fibrous composites under compression and bending

Multi-layered Prepacked aggregate fibrous composite (MLPAFC) is a new type of concrete, which is prepared in two subsequent stages of aggregate-fibre skeleton prepacking and cementitious grouting. In this study, ten MLPAFC mixtures were prepared in three subsequent layers incorporating different contents of four different types of steel fibres. Long and short hooked-end and crimped steel fibers were adopted with 3.0 and 1.5% dosages for the outer and interior layers, respectively. In-between the three MLPAFC layers, two layers of Glass Fiber Mesh (GFM) were inserted in five of the ten mixtures. The impact response of the MLPAFC mixtures was evaluated using two test methods. In the first, the ACI 544-2R repeated free-falling weight test was followed using disk specimens, while flexural free-falling weight on prism specimens was the second adopted impact test. Moreover, Weibull distribution was used to statistically analyse the discrepancies of the obtained experimental impact records. The impact tests results revealed that MLPAFC can absorb significantly high energy under falling weight impact due to its structure and the dual crack arresting activity of both steel fibers and GFM. The cracking number of impacts of MLPAFC cylindrical specimens without GFM was increased by approximately 530–870% compared reference specimens, while increment percentages reaching 1350% were recorded at failure stage. The impact resistance of MLPAFC prisms under flexural impact was noticeably improved, yet with lower percentages than cylindrical specimens. The insertion of intermediate GFMs let to additional developments in the impact strength of both cylindrical and prism specimens.

Stress–Strain Relationship Model and Gray Entropy Analysis of Recycled Coarse Aggregate Concrete

Abstract In this research, the effects of recycled coarse aggregate (RCA) gradation (5–10 mm, 5–16 mm, 5–20 mm, and 5–31.5 mm), RCA content (30 %, 50 %, and 70 %), fly ash content (10 %, 20 %, and 30%) and water–binder ratio (0.35, 0.4, and 0.45) on the stress–strain constitutive relationship of recycled aggregate concrete (RAC) were analyzed. For this purpose, 45 prism specimens were designed, and then it was obtained by gray relational entropy analysis that the water–binder ratio and RCA content have a considerable influence on RAC’s mechanical and energy absorption properties. A mathematical expression for the stress–strain constitutive relationship of the RAC concerning the four aforementioned factors was developed through experimental investigation and regression analysis. The proposed model is compared with the experimental date, and the result has a good fit.

Influence of temperature on the creep behaviour by macroindentation of Cocos nucifera shells and Canarium schweinfurthii cores (bio-shellnut wastes in Cameroon)

The aim of this study was to show how temperature modifies the mechanical characteristics of the Cocos nucifera (CN) shells and the Canarium schweinfurthii (CS) cores. The test consisted in performing an instrumented macroindentation on prismatic specimens in an adiabatic chamber; the indentation carried out according to four temperature ranges (30 °C, 50 °C, 70 °C, 90 °C). The Oliver and Pharr method is used for the analysis of mechanical parameters in indentation: reduced Young’s modulus, hardness, creep coefficient. These parameters have enabled to estimate indirect characteristics such as toughness and ultimate mechanical stress to be obtained. The creep data are simulated to have the rheological model to these materials by considering the statistical criteria. As a global observation, when the temperature increases, the mechanical parameters decrease; although CN is more sensitive to the temperature gradient than CS, these 2 materials show performances that allow them to be classified as engineering polymer materials according to the Ashby diagram.

Behavior of Self-compacting Mortars Based on Waste Brick Powder

Aims: Study the performance of self-compacting mortar (SCM) using waste ground brick as cement replacement material. Background: Large amounts of brick waste are produced in brick manufacturing plants and construction and demolition sites. The use of these bricks as partial substitution to natural aggregates or after crushing as fines for partial cement substitution could contribute to reduce the problem of waste storage and environmental pollution as well as in the conservation of natural resources. Objective: The objective of this paper is to study the effect of adding waste ground brick on the performance of SCM at the fresh and hardened state. Methods: It is an experimental investigation where mortar specimens where cement was partially substituted by crushed recycled bricks fines recovered from a brick plant. The level of substitution was either 0%, 5%, 10%, 15% 20% and 25% by weight of cement. Workability was measured by slump flow and flow time by V-funnel test. Compressive strength and water absorption by capillary were measured on 40x40x160 mm3 prismatic specimens. Results: The experimental results show that self-compacting mortar can be obtained up to 25% of cement substitution by brick powders. The compressive strength was improved at long term for up to 15% cement substitution by brick powder. The sorptivity coefficient is increased by incorporation of brick waste powder. Conclusion: The substitution of cement by waste ground brick powder up to 15% of waste brick powder has little influence on the rheological parameters of self-compacting mortar and the compressive strength is increased at the long term. Further investigations are underway to study the shrinkage, the long term durability and the pore size distribution by mercury porosimetry.

Application of natural fiber composite materials in the strengthening of reinforced concrete structures

This paper presents an experimental investigation of strengthened reinforced concrete structure by bonded natural fiber composite materials. Nonetheless, the composite plates are externally constituted of a matrix based on epoxy adhesive in which the aligned continuous natural fibers are embedded. In recent years, the natural fibers are of great interest as a result of policies to reduce the negative impact on the environment. They are a renewable source, helping to capture carbon dioxide during their cultivation. Numerous technical, economic, and environmental advantages such as low cost, high strength-to-weight ratio, low density, and non-corrosive properties make them very attractive to use. The objective of this research is to assess the strengthened capacity of natural fibers. This research mainly used hemp and flax natural fibers. So, these natural fibers are an alternative to synthetic reinforcing fibers like carbon fiber or glass fiber, which are widely used in civil engineering. This article briefly presents the results of the tests carried out on concrete prismatic specimens strengthened by external bonding different composite plates based on natural fibers. The tests were presented by examining the influence of reinforcement on the ultimate capacity and the element of rigidity. The results show a significant increase in the ultimate load of the strengthened concrete prismatic specimens compared to the reference specimen. The cracking and failure modes are presented. The results show that the natural fibers are a good alternative to glass and carbon fibers.

Influence of end effect under loading in the intermediate principal stress direction on strainburst behaviors of Beishan granite

In this study, strainburst tests on Beishan granite under different intermediate principal stress (σ 2) loadings were performed using a true-triaxial rockburst system. Rectangular prism specimens were prepared and divided into two groups. For the first group, the specimens were in direct contact with platens. For the second group, the specimen surfaces loaded by σ 2 were daubed with a layer of lubricant to reduce the end friction of the platens. A loading mode, which kept one specimen surface free and applied loads on the other five surfaces of the specimen, was used to simulate the stress state of a rock element on the excavation boundary. A high-speed video camera was then used to capture the failure process of the specimens. The experimental results indicated that as σ 2 increased, the degree of violence of the specimens during failure increases. However, the σ 2-dependent strength and energy release characteristics of the lubricated specimens were significantly different from those of the non-lubricated specimens. The strength of the lubricated specimens was lower than that of the non-lubricated specimens under a given σ 2, and the strength difference between them increased as σ 2 increased. Moreover, the kinetic energy difference of the rock fragments between the non-lubricated and lubricated specimens increased with increasing σ 2.

Monitoring of dielectric permittivity in accelerated alkali-silica reaction concrete with microwave backscattering

Deterioration of concrete due to the alkali–silica reaction (ASR) involves a reaction between alkaline ions in the cement pore solution and non-crystalline silica found in many aggregates. The product of reaction is a porous hydrophilic ASR gel, which causes expansion and cracking of concrete structure. Currently, there is no reliable method for non-destructive evaluation of ASR. We have investigated the feasibility of using relative dielectric permittivity obtained from X-band microwave backscattering of concrete. Advantages of this method of concrete evaluation are that measurements are non-contact and one-sided, and the approach is scalable to arbitrary-size concrete structures. The exploratory study was performed using an unrestrained set of accelerated ASR concrete prism specimens developed according to the ASTM1293 standard. One set of specimens contained no entrained air, while another set was contained entrained air. The specimens were removed from the environmental chamber at different times during a year-long study to create a set of different ASR maturity specimens. Strain measurements were performed on all specimens. Strain data both air entrained and non-air entrained sets were shown to be in close agreement with Larive model of isothermal unrestrained ASR expansion with similar fitting parameters. Relative dielectric permittivity of concrete specimens was correlated with strain data. Both sets show correlation between dielectric permittivity and strain, with stronger linear correlation observed for the air-entrained specimens. Development of such correlation would enable estimating expansion of actual concrete structures from microwave backscattering measurements, which could be used for risk stratification to guide and minimize coring.

The Study on the Whole Stress-Strain Curves of Coral Fly Ash-Slag Alkali-Activated Concrete under Uniaxial Compression.

This study aimed to research the whole stress–strain curves of coral Fly Ash-Slag Alkali-Activated Concrete (CAAC) in different strength grades. Fly ash-slag alkali-activated concrete was used as cementing materials to produce coral aggregate concrete. A monotonic loading test was conducted on the prismatic specimens to obtain elastic modulus (Ec), Poisson’s ratio (μ) and the constitutive relationship of CAAC under uniaxial compression. When the strain of CAAC reached the maximum value, the specimen was split and damaged rapidly. As the strength grade increased, the ratio of residual stress (σri) to peak stress (σ0i) decreased in the range of 0.17–0.28. The Ec of CAAC increased gradually, and μ increased to the peak value and then decreased. According to the test results, the constitutive equation of CAAC can be expressed by piecewise expression, which can better reflect all the experimental characteristics. It was also found that CAAC has many similar characteristics with coral concrete and lightweight aggregate concrete. To improve the strength and toughness of CAAC, some fibers, such as organic fiber, can be added to expand the application of CAAC in engineering projects.

Comparative Flexural Toughness Evaluation of Steel Fibre-Reinforced Concrete

A comparative appraisal of the protocols recommended in the ASTM and Japanese standards for evaluation of flexural toughness of three concrete grades reinforced with steel hooked-end fibres is presented. Target 28-day cube compressive strengths of the three concrete grades were 25 MPa, 35 MPa and 45 MPa and the fibres having an aspect ratio of 80 were used at volume fractions of 0%, 0.13%, 0.19%, 0.25%, 0.31% and 0.38%. Testing for toughness was carried out in the form of displacement-controlled four-point bend tests on prismatic specimens of size 150 mm × 150 mm × 700 mm and stable load–deflection behaviour was obtained only when fibre dosage was at least 0.25%. For fibre volume fractions of 0.25% and more, the toughness parameters obtained from the ASTM and the Japanese standard were comparable. From the results of the comparative study, it is recommended that for an Indian standard, if the toughness characterisation is to be done, then equivalent flexural strength should be considered as the parameter over residual strength. In addition, ‘equivalent flexural strength ratio is also to be considered, since it represents the load retaining capacity of the specimen after the peak load. Nevertheless, equivalent flexural strength is the average flexural strength up to the specified deflection limit which does not specify any post-peak behaviour, hence need not be a characterising parameter for understanding fibre performance in concrete.

Impact resistance of plain and rubberized concrete containing steel and polypropylene hybrid fiber

Hybridization of polypropylene–steel fiber leads to improvements of both the mechanical properties and impact resistance of concrete. This paper provides the results of an experimental impact test, which has been conducted using a low-velocity drop hammer (with an impact velocity of 2.8 m/s) on fiber-reinforced concrete (FRC) and fiber-reinforced rubberized concrete (FRRuC) prisms. Prism specimens, measuring 100 × 100 × 500 mm (depth × width × length), were prepared. The variables were different ratios of micro steel (MS) fiber (0%, 0.75, 0.825, 0.9 %, 1.0 %) and polypropylene (PP) fiber (0%, 0.1 %, 0.175, 0.25 %, 1%) with/without crumb rubber (CR) with a partial replacement of fine aggregate at a ratio of 20 % by volume. FRC with CR produced higher first and final impact energy compared with prisms without CR. By contrast, the density, as well as the compressive and tensile strengths decreased, whereas the voids and water absorption of concrete increased due to the CR replacement. The specimen, which was reinforced with 0.9 % MS + 0.1 % PP hybrid FRRuC, produced high final impact energy of approximately 887.2 J, which was 10 times higher than that of plain concrete ; the impact ductility index was 4.15, which was twice the value of plain concrete. Furthermore, the most significant improvement in mechanical properties was found for specimens with 0.9 % MS + 0.1 % PP hybrid fiber.

Effects of incorporating hybrid fibres on rheological and mechanical properties of fibre reinforced concrete

Hybrid fibre reinforced concrete (HFRC) is one of the most promising construction techniques and repairing material in recent times for the construction industry. Generally, plain concrete has a very low tensile strength and limited resistance to cracking prior to the ultimate load. Fibre hybridization with different types of fibres helps in resisting these cracks in the concrete structures. This research aims to study the rheological and mechanical properties of HFRC made with steel and coconut (coir) fibre in comparison to control concrete. For this purpose, the experimentation was carried out in the laboratory on cylinders and prisms specimens made from conventional (control) concrete and HFRC with 2%, 4%, and 6% of fibre concentration by weight of cement. Besides, the concentration of waste steel fibre was kept at a constant rate of 1% for all of the HFRC mix in this study. The rheological properties of HFRC mixes were obtained by slump test, compacting factor test, ball penetration test, and density test. These properties were then compared to the corresponding properties of control concrete. On the other hand, compressive strength test, splitting tensile test and flexural tests were performed to attain the mechanical properties of HFRC. The test results indicate that the incorporation of hybrid fibres in the concrete decreases the concrete workability compared to the control concrete. The experimental results showed that the compressive strength is improved compared to the control mix whether the splitting and flexural strength shows an 18.36% and 24.87% improvement over the control mix. Finally, the inclusion of optimum content of hybrid fibres that is 2% by weight of cement showed enhancement in the mechanical properties of HFRC in terms of compressive, tensile and flexural strength with compared to control concrete.

Using steel and polypropylene fibres to improve the performance of concrete sleepers

The extensive use of concrete sleepers in transportation and railway projects highlights the significance of repairing and maintaining such elements. The performance of concrete sleepers strengthened with steel and polypropylene (PP) fibres was investigated in this study. A series of compressive tensile and flexural strength tests was carried out on 120 cylindrical and prismatic specimens made from eight design mixes with 1% fibre content. The results indicated that the best mix design in terms of compressive and tensile strengths contained 1% steel fibres and no PP fibres, while the highest flexural strength was achieved with 0·6% steel fibres and 0·4% PP fibres. Moreover, it was found that the inclusion of fibres in concrete sleepers can reduce the amount of prestressed reinforcing bars by 40% and prevent the generation of deep cracks. The combined use of steel and PP fibres was found to enhance flexural strength by 3·5 times.

Experimental study on damping properties of rubber powder modified styrene-acrylic emulsion concrete beam

In this paper, 4.5% rubber powder is added to improve the damping properties of styrene-acrylic emulsion concrete. A total of 66 specimens were manufactured, including eleven groups of prisms and cantilever beam specimens. Through the axial compression test of the prism specimen, the basic mechanical properties of rubber powder modified styrene-acrylic emulsion concrete were studied, and the interface morphology of rubber powder modified styrene-acrylic emulsion concrete was observed by scanning electron microscope (SEM). After the cantilever beam specimen is damaged in different degree, a free vibration test is conducted. The damping properties of beams at various damage stages are discussed. Experimental results show that the addition of styrene-acrylic emulsion enhances the toughness and damping capacity of concrete by about 20.4%, but reduces the compressive strength by about 36%. Meanwhile, when the amount of styrene-acrylic emulsion is increased, it can slow down the rate of cantilever beam stiffness degradation. Rubber powder reduces the compressive strength by about 21.4% and accelerates the degradation of dynamic stiffness while enhancing the damping capacity of concrete by about 20.4%. Through SEM observation, it is found that there are many holes on the surface of cement stone after rubber powder falls off, which is the main reason for the decline in mechanical performance after rubber powder falls off. The nonlinear relationship between the displacement angle and the damage index is established by statistical analysis.

Apparent moduli and strength differences between cylindrical and prism specimens caused by edge confinement effects

Rock samples obtained from excavation and fault damage zones are friable, and it is challenging to obtain cylindrical specimens from such rocks using coring bits in the lab. On the other hand, preparation of prismatic specimens may be less destructive because it does not exert excessive rotational torque around the sides of the rock as in the preparation of cylindrical specimens. Therefore, prism-shaped specimens could become a more favorable sample geometry when working with highly fragile rock samples. However, prism specimens may experience shape-specific boundary effects during mechanical deformation due to the presences of corners and edges, which might cause differences in the measured rock strength and elastic properties compared to a cylindrical specimen. This study aims to investigate how the corners and edges of prism specimens affect the apparent strength and moduli of samples via comparison of laboratory data and finite element modelling results. We find that the prismatic samples can have higher apparent elastic moduli due to the enhanced confinement at the sample edges, which in turn also increases the measured compressional strengths of prism samples compared to cylindrical samples. Whether this apparent strengthening effect influences laboratory data interpretation will also depend on the degree of sample variability and how well specimen edge boundary conditions are controlled.

Rate effect on the stress–strain behavior of concrete under uniaxial tensile stress

AbstractConcrete is a typical rate‐dependent material, and a direct tensile test is the most effective method by which to investigate its tensile performance. In this study, an additional loading device for direct uniaxial tensile tests was designed and fabricated to achieve central loading and determine the descending stage during direct tensile tests. Experimental results prove that the device is reliable and convenient for reuse; it is characterized by its ability to obtain complete stress–strain curves and to be used for many repetitive tests. Initially, 27 prismatic specimens were used to test the compressive strengths and elastic moduli of concrete specimens with designed compressive strengths of 25, 30, and 50 MPa. Next, a total of 256 uniaxial direct tensile tests were carried out, including 101 static tests at a loading strain rate of 10−5 s−1 and 155 dynamic tests at loading strain rates of 10−4 s−1 and 10−2 s−1. A total of 121 complete stress–strain curves were acquired for the 256 direct tensile tests. According to the test results, the SDs of the entire curves of the tensile stress of concrete are presented, and the energy absorption capacities of the specimens were also determined. The effects of the loading rate on the mean and variability of the peak stress, peak secant modulus, elastic modulus, and peak strain were analyzed. With the increase of the strain rate, the other indexes, excluding the peak strain, were found to notably increase.

The effect of specimen geometry on the compressive and tensile strengths of self-compacting rubberised concrete containing waste rubber granules

Self-compacting rubberised concrete (SCRC) has been received great attention in recent years as an environmental remediation to not only fabricate sustainable and durable civil engineering structures, but also to take the very first steps towards resolving the issue of waste tyres abandoned in the nature. As a step forward in evaluating the structural performance of SCRC, the current research investigates the impacts of specimen size and specimen shape on the compressive and tensile strengths of SCRC containing 0%, 10%, and 20% crumb rubber aggregates (i.e., CSCC, SCRC10 and SCRC20) by means of both experimental and fracture mechanics-based theoretical approaches. Cubic specimens with dimension of 100mm and 150mm for assessing the compressive strength, cylindrical specimens with dimension of Φ100×200mm and Φ150×300mm for the both compressive and splitting tensile strengths measurement, and prism specimen with dimension of 100×100×400mm for the flexural strength measurement were casted. The analytical study was performed based on the modified size effect low (MSEL) and adjusting its parameters by applying the experimental results, to establish the correlation between the mechanical properties of SCRC with the geometry of the structural element. Moreover, the relationship between the modulus of rupture and compressive strength of the SCRC has been also pioneered, based on the design codes recommended for the self-compacting concrete. The results show difference between the compressive strength of the cube-shaped specimen with standard cylinder specimen is more significant for mixes with 20% rubber aggregates rather than that for the SCRC with less than 20% rubber aggregate. Increasing the rubber aggregates content led to the significant size effect on the tensile strength of SCRC. The MSEL model predictions are in acceptable agreement for cubic specimen with the experimental data obtained for the CSCC and SCRC10 and for cylindrical specimen, the impact of varying the specimen size on the compressive strength weakened by increasing the rubber aggregate content.

Tensile and flexural performance of concrete members reinforced with polypropylene fibers and GFRP bars

In the present study, an experimental program was carried out to evaluate the influence of the addition of 10 kg/m3 of polypropylene (PP) fibers on the tensile and flexural behavior of concrete members internally reinforced with GFRP bars. Mechanical characterization and pullout tests were performed to determine the properties of the constituent materials and to characterize their interface. In a structural level, direct tensile and four-point bending tests were performed on prismatic specimens to investigate their mechanical response. Throughout the work, digital image correlation (DIC) was used to monitor deformations, crack openings and spacings. A considerable reduction in cracking width and an increased multiple cracking behavior was observed for specimens with fiber addition. The results show also a significant influence of tension-stiffening for specimens subject to tension and bending, whereas a slight increase in structural ductility was observed for the specimens tested in bending. The tests indicate possible influence of the shear lag effect to the bar stiffness.