Variation Of Compressive Strength Research Articles

Experimental study on performance of cast-in-situ recycled aggregate concrete under different sulfate attack exposures

Sulfate attack is a type of widely distributed corrosion to cement-based materials, and the utilization of recycled aggregate concrete is beneficial for reducing construction solid waste and the consumption of natural resources. To study the performance of ordinary cast-in-situ recycled aggregate concrete subjected to sulfate attack under various service conditions, five different exposure conditions, full and partial immersion and drying-wetting cycles for 40 weeks were investigated. The sulfate concentration, compressive strength, mass and diameter variation, and visual appearance of the recycled aggregate concrete cylinders were measured. Furthermore, microscopic analysis of the scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) was carried out to observe the microstructure and corrosion products. The micro observations of the interfacial transition zone (ITZ) were analyzed by SEM and EDS. The evolution of the pore structure under sulfate attack was measured by the MIP test. The results show that the specimens under the partially immersed condition endured the most severe damage, and significant mass loss and scaling were observed due to chemical attack and salt crystallization. The specimens under drying-wetting conditions deteriorated far more rapidly than those under fully immersed conditions. In addition, ettringite, gypsum and micro-cracks were observed regardless of the exposure conditions. However, no evident characteristic of ettringite or gypsum appeared in the ITZ. This paper suggests that the key role of ITZ could be to provide a diffusion path for sulfate due to its high permeability and porosity.

Influence of the molding process and different surface regularization methods on the compressive strength of concrete specimens

Concrete is one of the most important material for civil construction, given its high applicability. C Compressive strength (fc) is one of the main parameters to evaluate the concrete quality. Concrete of the same mixing volume may vary even with the same materials preparation. Concrete specimens molding, and its surface regularization contribute to these variations that are often hard to measure. Therefore, this paper aims to determine the variations in compressive strength of concrete, simulating different processes for casting, initial curing and surface treatment. In stage 1, the specimens were subjected to five surface treatment types, resulting in variations of 30% for concrete fc, whereas grinding specimens reached the highest 28-day compressive strength, so they were carried over to the next stage. In stage 2, specimens were produced as per ABNT NBR 5738 (2015) and with induced errors in casting and initial curing. The specimen produced according to the standard achieved the second-best result, whose 28-day fc was3% lower than that of the similar method, despite leaving the specimen uncovered for the first 24 hours after casting. Specimens produced in metal cylinder form works shows higher results than those produced in polyvinyl chloride molds (PVC).

Durability Properties of Kaolinite Clay - Metakaolin in Concrete

Unfortunately the concrete structures are exposed to fire, which may cause reduce in strength of structural components. In this article , the research , the effect of chloride (NaCl) penetration and temperature variations on metakaolin using in concrete. Here M60 grade concrete mix used and the concrete cubes (150 mm × 150 mm × 150 mm) are cast for cement replacement by metakaolin with 0%, 5%, 10%, 15% and 20%. The 0% specimens are considered as ‘Controlled Specimen’. Then these specimens are tested after 28 and 90 days for various temperature of 100, 200, 300 and 400°C with 1, 2 and 3 hour duration and same cubes are cast for M60 mix proportion and tested for Rapid Chloride Penetration Test and use 5% Sodium Chloride ( NaCl) concentration. The graphical Presentation is clearly shows that variations in compressive strength for cement replacement by metakaolin in concrete for chloride penetration and different temperature. For chloride penetration results shows that up to 10% to 15% replacement of Metakaolin, concrete gives good compressive strength and after it goes on decreasing,. Thus 10% give a desirable percentage of replacement. And also compressive strength drastically increasing with the age of concrete for various temperature exposures.

A novel development of green ultra-high performance concrete (UHPC) based on appropriate application of recycled cementitious material

Recycled construction waste cementitious material (RCWCM) can be considered as a kind of waste solid with potential cementitious characteristics. In the past, landfill and stacking methods were generally used for treating this type of wastes, which is harmful for the sustainable development of construction industry. Hence, based on this premise, an effective method for developing a green Ultra-High Performance Concrete (UHPC) by incorporating RCWCM is addressed in this study. Specifically, dehydrated cementitious powder (DCP) is obtained from heating treatment of RCWCM. Then, the DCP is used to gradually replace the cement and included in the design of UHPC based on Modified Andreasen & Andersen (MAA) particle packing model. Afterwards, the physical and chemical characteristics of the newly produced UHPC are evaluated. The results show that when DCP is used to replace up to 25% cement, the variation of UHPC compressive strength is difficult to be noticed. Corresponding to that, the microstructure and durability of the developed green UHPC are also advanced when the added DCP content is less than 25%. Additionally, the ecological assessment shows that the UHPC incorporating DCP has a relatively small impact on the environment, which provides a broad prospect for the future sustainable development of UHPC.

Compressive strength and grade of concrete in structures

The paper summarizes the experience of the Department of Buildings and Facilities Structures Research in determining the compressive strength and grade of concrete in the structures, which characterize one of the main requirements for ensuring the structures mechanical strength and stability. Their unambiguous interpretation at the stages of concrete composition selection, products manufacture and structures operation leads to a conflict of interests and corruption risks between a concrete producer, a builder and an investor. Two approaches to the concrete strength and grade assessment are considered: the first one reasons from the economic interests of a concrete producer (the possibility of cement saving at a stable well-organized production facility), the second one takes into account the consumer's point of view (design indicators ensuring). The first approach is based on the coefficient of the tested control concrete cubes strength variation declared by the concrete mixture manufacturer. The calculation of the relationship between the average and characteristic compressive resistance of concrete at various coefficients of concrete compressive strength variation and grades showed that this coefficient can significantly change the assessment results. The second approach is based on the use of reference core samples cut directly from the structure, which are tested and interpreted according to established international experience. The difference in strength assessments is shown for the cases with the use of samples tests results selection compared to groups in which the smallest values are removed. Both approaches are analyzed based on the experience of determining the concrete compressive strength grade using the core samples from the entire floor slab in the existing structure and from some its areas; the results were far from straightforward and not consistent with the project. It is necessary to clearly define the areas of application of norms and standards that, firstly, serve the technology and the production market of concrete and concrete and reinforced concrete products, and secondly, ensure obtaining the actual characteristics of existing products, structures and facilities and their conformity to the project. It is advisable, especially for the structures of the higher levels of responsibility and in some controversial matters, to verify the results obtained with the first approach application to the concrete mix test specimens by testing core samples cut from the structures.

Compressive strength and grade of concrete in structures

The paper summarizes the experience of the Department of Buildings and Facilities Structures Research in determining the compressive strength and grade of concrete in the structures, which characterize one of the main requirements for ensuring the structures mechanical strength and stability. Their unambiguous interpretation at the stages of concrete composition selection, products manufacture and structures operation leads to a conflict of interests and corruption risks between a concrete producer, a builder and an investor. Two approaches to the concrete strength and grade assessment are considered: the first one reasons from the economic interests of a concrete producer (the possibility of cement saving at a stable well-organized production facility), the second one takes into account the consumer's point of view (design indicators ensuring). The first approach is based on the coefficient of the tested control concrete cubes strength variation declared by the concrete mixture manufacturer. The calculation of the relationship between the average and characteristic compressive resistance of concrete at various coefficients of concrete compressive strength variation and grades showed that this coefficient can significantly change the assessment results. The second approach is based on the use of reference core samples cut directly from the structure, which are tested and interpreted according to established international experience. The difference in strength assessments is shown for the cases with the use of samples tests results selection compared to groups in which the smallest values are removed. Both approaches are analyzed based on the experience of determining the concrete compressive strength grade using the core samples from the entire floor slab in the existing structure and from some its areas; the results were far from straightforward and not consistent with the project. It is necessary to clearly define the areas of application of norms and standards that, firstly, serve the technology and the production market of concrete and concrete and reinforced concrete products, and secondly, ensure obtaining the actual characteristics of existing products, structures and facilities and their conformity to the project. It is advisable, especially for the structures of the higher levels of responsibility and in some controversial matters, to verify the results obtained with the first approach application to the concrete mix test specimens by testing core samples cut from the structures.

Study on engineering properties of sand strengthened by mixed fibers and polyurethane organic polymer

A considerable number of engineering hazards are caused by loose internal structure of sands. Thus, many researchers have explored a variety of reinforcement methods. A new reinforcement technique was experimentally evaluated in this study. In particular, a hybrid method with a combination of fiber and polymer was studied. Three different types of fibers (sisal, polypropylene, and palm) in combination with varying concentrations of polymers were experimented to improve the internal structure and strength of sand samples reconstituted at different densities. Through a series of laboratory tests, the compressive and tensile strength variations of different combinations were obtained, and the interaction between fibers and polymer inside the sand was evaluated by scanning electron microscopy (SEM). The experimental results show that the tensile and compressive strength of the reinforced sand increases with the increase of the polymer concentration, sample density, and different fiber combinations. This provides some references for future practical engineering applications.

Influences of confining pressure and bedding angles on the deformation, fracture and mechanical characteristics of slate

The physical properties of slate in buildings are affected by its bedding angle and confining pressure. A total of 74 slate specimens with seven bedding angles and five levels of confining pressure were tested in uniaxial and triaxial compression tests. The effects of bedding angle and confining pressure on the mechanical behaviour of the brittle slate were quantified. The test results showed that, with the increase of confining pressure, the compressive strength of rock increased significantly. The variation in compressive strength of slate under confining pressure could be described by the parabolic Mohr-Coulomb strength criterion. The strength of slate is the lowest when the bedding angle is 45°–60°, and greatest when it is below 15°. When unconfined, the fracture angle of slate is 65°–90°. With increased confining pressure, the fracture angle of slate tends to 45° from above. As the bedding angle increases from 0° to 90°, the fracture angle of slate presents a U-shaped curve. When the bedding angle is 75°–90°, the deformation modulus of slate is greatest, and is minimised when the bedding angle is 45°–60°. Even if the confining pressure is low, the deformation modulus of slate is significantly increased compared to that in unconfined conditions. It proves that shotcrete treatment of the rock surrounding a tunnel will greatly improve the supporting effect thereon.

Time-Dependent Variations of Compressive Strength and Small-Strain Stiffness of Sands Grouted with Microfine Cement

AbstractUnconfined compressive strength (qucs) and maximum shear modulus (Gmax), which are essential properties of grouted sands for quality control and stable design, exhibit a nonlinear behavior ...

Determining the Reduction Factor in Predicting the Contribution of Concrete to Shear Strength by Using a Probabilistic Method

The reliability of a structure can be defined as the probability of the structure to fulfil its intended purpose throughout its design lifespan. In the codes, it is aimed to provide the target failure probability by means of safety factors in the form of load factors and strength reduction factors. This paper presents an investigation of the reduction factor for the contribution of concrete to the shear strength of reinforced concrete beams without stirrups designed according to the Turkish Code. In this code, the contribution of concrete to the shear strength is calculated by multiplying the diagonal cracking strength by a reduction factor of 0.8. In this study, based upon a second moment probabilistic analysis procedure, the change in the strength reduction factor was investigated for various coefficients of variation of concrete compressive strength and failure probabilities by using experimental data available in the literature. It is assumed that the considered random variables are statistically independent, and the correlation effects are not taken into account. The results show that the reduction factor decreases with the increase in the coefficient of variation of concrete compressive strength and the reduction factor given by the Turkish Code corresponds to a variation coefficient of 0.12 and a failure probability of 10−6.

Effect of small ply angle variation in tensile and compressive strength of woven GFRP composite: Application of two parameter Weibull distribution

This paper demonstrates the effect of small ply angle variation in tensile and compressive strength of woven Glass Fiber Reinforced Polymer (GFRP) composites. Four different plies of (0/90)4, (±5°)4, (±10°)4, (±15°)4 manufactured by hand lay-up followed by the press molding machine. Samples for the tensile and compressive tests were prepared according to ASTM D3039 and ASTM D3410 standards. Three samples of each laminate were tested on a Universal Testing Machine (UTM) at a steady crosshead speed of 1 mm/min. A digital microscope was used for tracking the sample damage pattern. It was observed that fiber orientation in laminates affects the tensile and compressive strength. Fibers ruptured during tensile testing of specimens and in compressive testing, samples failed due to the separation of longitudinal fibers. The experimental results showed that (0/90)4 ply showed the maximum tensile strength and compressive strength followed by (±5°)4, (±10°)4, (±15°)4. Weibull distribution analysis was used for statistical estimation of the tensile and compressive life of specimens.

Strength characteristics of fiber-reinforced light shotcrete

The article presents the regularities of the flexural and compressive strength variation, as well as the energy intensity of destruction of light heat-shielding vermiculite concrete, depending on the content of polypropylene or basalt fiber. The paper stresses that the greatest increase in flexural strength of 40% is observed at the polypropylene or basalt fiber that the greatest increase in flexural strength of 40% is observed at the polypropylene or basalt fiber of 2 and 2-4% respectively. As the basalt fiber content increases from 1 to 4%, the compressive strength increases from 42 to 83%. The resistance of vermiculite concrete to dynamic bending loads when the polypropylene fiber ranges from 0.5 to 2% by a factor of 2.5 4.2. With basalt fiber content of 1 to 4% the energy intensity of destruction increases 1.5 2.5 times.Specific energy intensity of destruction of samples reinforced with basalt fiber increases by 2.3 ÷ 2.7 times during volumetric destruction of the specimens under study on a vertical pile driver. The regularities obtained in the course of the studies indicate that fiber reinforcement of light heat-shielding vermiculite concrete increase its strength characteristics and thereby expand the scope of its application.

Damage and Degradation of Concrete under Coupling Action of Freeze‐Thaw Cycle and Sulfate Attack

In this study, the mechanical behaviors, failure characteristics, and microstructure of concrete containing fly ash (FA) against combined freeze‐thaw cycles and sulfate attack were studied compared with normal concrete, and the formation rates of corrosion products during coupling cycles were investigated. Results showed that, during the coupling action of freeze‐thaw cycles and sodium sulfate solution, concrete containing 10% fly ash exposed in 5% sodium sulfate solution exhibited better freeze‐thaw resistance. Meanwhile, the variation of compressive strength of concrete during the coupling cycles could be divided into two stages, including the strength enhancement stage and the strength reduction stage. Moreover, the proportion of micropores and capillary pores decreased obviously during combined freeze‐thaw cycles and sulfate attack, and excessive concentration of sodium sulfate solution led to more macropores after high‐frequency freeze‐thaw cycles.

Effect of Coarse Aggregate Sources on the Compressive Strength of Various Grade of Nominal Mixed Concrete

Various grades of nominal mix concrete from low to medium strength are being used in building construction works in Kathmandu Valley. The aim of the study was to investigate the source effect of various types of coarse aggregates on the compressive strength of different grade of nominal mix concrete. Here, 5 different types of coarse aggregates sources were selected (A-Panauti, B-Melamchi, C-Chaukidada, D-Khopasi and E-Kaaldhunga) based on field enquiry and questionnaire survey with suppliers and contractors. Majority of coarse aggregates were angular in shape with a few sub angular and flaky types. From physical test result, most of the coarse aggregates were found to be graded type with partial deviation from the gradation limitation of IS383:1970. Based on specific gravity and dry-rodded bulk density, coarse aggregates can be classified as medium weight aggregates. Mechanical test of aggregate shows all the aggregates are of medium strength with variation in mechanical properties among them. The next stage of study is related to determination of compressive strength. Total 90 concrete cubes of size 15 cm were made of 3 different grades of nominal mix M1 (1:2:4), M2 (1:2:3) and M3 (1:1.5:3) by weight. Water/cement ratio, cement, sand, water were kept constant for each mix ratio while only coarse aggregate sources were chosen as variable. Due to change in aggregate type only, variation in 28 days target compressive strength is found up to 47%. Sample C, D and E showed relatively higher 28 days compressive strength compared to Sample A and B. The results indicate that the coarse aggregate source has significant variation in the compressive strength of various grade of nominal mix concrete. The variation in compressive strength is relatively significant for lean mix concrete (1:2:4 & 1:2:3) compared to rich mix concrete (1:1.5:3). In terms of concrete cube failure mechanism, the cubes made of sample A & B failed by coarse aggregate crushing while the major failure mechanism in sample C, D & E was initiated by bond failure.

Statistical and experimental study for determining the influence of the segregation phenomenon on physical and mechanical properties of lightweight concrete

Lightweight aggregate concrete (LWAC) compaction is a critical stage during concrete production and remains one of the major problems because excessive vibration time can easily produce the segregation phenomenon. LWAC is susceptible to segregation because of the differences between the densities of lightweight aggregates and mortar, influencing the strength and durability of concrete. In the present study, the variation in compressive strength, modulus of elasticity, ultrasonic parameters and segregation indexes were obtained in LWAC compacted with different vibration time. A statistical analysis was applied for establishing the structure of the variable dependence in segregated concretes. The vibration time and the density of the lightweight aggregate used to produce the LWAC can influence the compressive strength depending on the density of the lightweight aggregate used (up to 67% in concretes produced with the lightest aggregate). Based on these parameters and the results obtained experimentally, a simplified expression to estimate the compressive strength is proposed.

Pore Structure Degradation of Different Cement Mortars Exposed to Sulphuric Acid

Acid attack causes the deterioration of construction material surfaces. The objective of this study was to investigate the degradation of different types of cement mortar in terms of variations in pore size distribution obtained by mercury intrusion porosimetry (MIP), mass loss, and compressive strength. The mortars were manufactured with nanosilica, zinc stearate, and an ethyl silicate coating. After curing (28 days), the samples were subjected to acid exposure for 90 days, immersed ina solution (3% w/w) of sulphuric acid (H2SO4). The results indicate that the mortars showed a more refined microstructure, with a higher proportion of smaller pores (<100 nm) compared to the control mortar. The 28-day and 90-day compressive strength variations of mortars were also determined by observing pronounced reduction due to the appearance of expansive compounds responsible for microcracking.

Effect of CaO/SiO2 ratio on phase transformation and properties of anorthite-based ceramics from coal fly ash and steel slag

Anorthite-based ceramics were produced entirely from coal fly ash and steel slag. The effect of the CaO/SiO2 ratio (0.12–0.8) on the phase transitions was examined by adding steel slag to coal fly ash in the range of 10–50 wt%, and a temperature range of 900–1200 °C. The influence of CaO/SiO2 and sintering temperatures on the technological properties were assessed by response surface methodology (RSM) and correlated with the phase changes. The results revealed that anorthite was the main phase for the CaO/SiO2 ratio ranging from 0.12 to 0.56, while at 1200 °C, a ratio of 0.8 involved a high content of gehlenite. RSM showed that the CaO/SiO2 ratio was the main influencing factor on the density, while the variation of apparent porosity and compressive strength were more affected by sintering temperature. The crystallisation of the anorthite phase significantly enhanced the properties of the obtained ceramics, whereas the appearance of gehlenite reduced the mechanical strength. The optimum conditions to fabricate anorthite-based ceramics with suitable properties were found to be a CaO/SiO2 ratio of 0.46 and a temperature of 1188 °C. The optimised anorthite-based ceramic exhibited a low thermal conductivity (0.39 W/m.K) and a dielectric constant of 6.03 at 1 MHz, along with a compressive strength of 41 MPa, which makes this sample a potential candidate for insulator applications.

Change on shear strength of concrete fully immersed in sulfate solutions

Sulfate-caused deterioration on concrete is principally evaluated by measuring the variation of uniaxial compressive strength and longitudinal expansion at different exposure ages. The evolution of concrete shear strength and its components over exposure period in such a sulfate-rich environment is overlooked. This study aims to characterize the time-dependent evolution of concrete shear strength and its components and to identify the possible microscopic deterioration mechanisms corresponding to these macroscopic properties changes under sulfate-exposure conditions. For this study, direct shear tests on concrete specimens subjected to different sulfate-exposure periods were conducted, where the effects of three water-to-binder ratios (w/b of 0.38, 0.45 and 0.52) and four sulfate-exposure periods (0, 3, 6 and 9 months) were considered. Results indicate that the shear strength and its components of concrete specimens under direct shearing are significantly influenced by external sulfate attack (ESA). For example, shear dilation of concrete specimens under direct shearing diminishes over sulfate-exposure period. However, friction component has a slight increase at the early exposure period in sulfate solutions, followed by a rapid drop at the later exposure period. In addition, the failure criterion of concrete specimens is found to be transformed from the bi-linear Mohr-Coulomb (M-C) before exposure to the linear M-C criterion after exposure in sulfate solutions.

PENGARUH PEMANFAATAN ABU PECAHAN TERUMBU KARANG DAN ABU SEKAM PADI SEBAGAI PENGGANTI SEMEN TERHADAP KUAT TEKAN BETON

Portland cement is a relatively expensive type of cement when used on constructions requiring simple requirements. Local material utilization using ash fragments of coral reefs and rice husk ash is one of the solutions. The objectives of this study is to determine the value of concrete compressive strength in each variation of cement replacement used were 2.5%, 5%, 7.5% and 10%, each variation consists of 70% ash fragment of coral reefs and 30% rice husk ash from the volume of cement used. The cube specimen with a size of (15x15x15) cm as many as 20 specimen were prepared. Concrete mixture according to SNI 03-2834-2000 used 0.5 cement water ratio and 60-100 mm of slump. The result of the compressive strength of concrete variation every percentage increase has increased and decreased from the result of the normal concrete compressive strength of 368.24 kg/cm2. Maximum increase occurred in the concrete compressive strength variation 7.5% of 384.76 kg/cm2 and decreased on the concrete compressive strength variation 10% of 367.40 kg/cm2.

Numerical investigation on the cooling-related mechanical properties of heated Australian Strathbogie granite using Discrete Element Method

A series of laboratory tests was carried out to study the cooling-related mechanical properties of Australian Strathbogie granite, which were heated from room temperature to various high temperatures (200, 400, 600 and 800°C) followed by two different cooling methods (exposed in air for slow cooling and put into water for rapid cooling). Using a two-dimensional discrete element code, UDEC, a grain-breakable model was firstly established, in which the grains were made breakable by connecting the centroid and midpoints of edges for each grain. Therefore, both the inter-granular and intra-granular fractures can be handled in the model for capturing the fracturing mechanism of rock under heating or cooling treatment. In the experiments and simulation, three types of granite with different grain sizes were considered, which are fine grain (FG), medium grain (MG) and coarse grain (CG). Besides, the effects of grain size homogeneity and mineral composition were also taken into consideration in the simulation. It was found that the strength and deformation characteristics from the numerical simulation had a good consistency with that from the experiments. For all types of granite, no significant variations in compressive strength and failure strain were found at lower heating temperature (below 400°C) under both slow and rapid cooling conditions. Compressive strength reduced sharply as heating temperature rising from 400 to 800°C, while failure strain exhibited the opposite trend and was more pronounced for rapid cooling. Fracturing analysis indicated that granite exhibited more fractures after heating and cooling treatments compared with that without cooling treatment. Compared with slow cooling, rapid cooling introduced more fractures, especially intra-granular fractures, and damaged rock more severely. CG was found to have more inter-granular fractures but fewer intra-granular fractures than FG and MG granite at all testing temperatures except for 200°C. Granite with heterogeneous grain size distribution exhibited lower strength and more intra-granular fractures than that with uniform grain size distribution after cooled from the same temperature. The increasing quartz content introduced higher mineral heterogeneity in granite during heating and cooling due to thermal expansion differences. Granite with higher quartz content displayed lower strength and more fractures than that with lower quartz content after heating and cooling treatments.