Mechanical Properties Of Concrete Research Articles

Experimental investigation of mechanical properties and multi-objective optimization of electronic, glass, and ceramic waste-mixed concrete.

The utilization of waste from various sources plays an important role in minimizing environmental pollution and civil construction costs. In this research, the mechanical properties of concrete were studied by mixing electronic waste (EW), glass powder (GW), and ceramic tile waste (CW). The effects of weight percentages of EW, GW, and CW are considered to investigate improvements in mechanical properties such as compressive strength (CS), split tensile strength (STS), and flexural strength (FS) of concrete. Taguchi analysis has been applied to predict the optimum composition of waste mixing percentages. The Multi-Objective Optimization Ratio Analysis (MOORA) techniques are applied to estimate the optimum composition of mixing wastes for maximizing the CS, STS, and FS of concrete. It was observed that 10 wt.% of EW, 15 wt.% of GW, and 30 wt.% of CW are predicted as the optimal mixing combinations to obtain a maximum compressive strength of 48.763 MPa, a split tensile strength of 4.178 MPa, and a flexural strength of 7.737 MPa, respectively. Finally, the predicted optimum waste-mixed weight percentages were used to examine the microstructure and various elements in the concrete using SEM and XRD analysis. When compared to conventional concrete, the optimum waste-mixed concrete has improved its compressive strength (38.453%), split tensile strength (41.149%), and flexural strength (36.215%).

Improvement of the mechanical properties of concrete by the addition of Metakaolin and rice husk hydrolyzed using a new method

Improvement of the mechanical properties of concrete by the addition of Metakaolin and rice husk hydrolyzed using a new method

Effect of high temperature on mechanical properties of lithium slag concrete

As the main gel material of concrete, cement is used in an astonishing amount every year in the construction industry. However, a large amount of CO2 is emitted into the atmosphere while producing cement. Therefore, it is the general trend to look for substitutes for cement and develop new green concrete. Lithium slag (LS) is the industrial waste discharged from lithium salt plants. Through testing, it is found that the chemical composition of LS has a high degree of coincidence with ordinary Portland cement (OPC) Therefore, LS can be incorporated into concrete as supplementary cementations material (SCM) to prepare lithium slag concrete (LSC). The pollution of the natural environment caused by a large number of piled-up and landfilled LS is immeasurable. Consuming and using LS in large quantities and with high efficiency not only eliminates the pollution of lithium slag to the natural environment, but also helps to reduce the amount of cement used in green concrete and truly reuse waste resources. In order to study the mechanical properties of post-heated LSC, the test were carried out for LSC specimens after high-temperature. The main influence factors were considered, including the temperatures of 20℃, 100 ℃, 300 ℃, 500 ℃ and 700 ℃, the contents of lithium slag in LSC of 0%, 10%, 20% and 30%, cooling method of LSC after exposure high temperature. The results showed that the mechanical properties of LS concrete specimens were slightly improved at 100 ℃, and when the temperature was 300 ℃ or higher, the damage to the specimens was huge and irreversible. An appropriate amount of LS (20% lithium slag content) could improve the strength of LSC. This paper also studied the relationship between lithium slag content and strengths of LS concrete. The research results show that adding an appropriate amount of LS to concrete improves the mechanical properties of concrete. When the LS replacement rate is 20%, the mass loss rate of LSC after different high temperature treatments was the minimum. The cubic compressive strength, axial compressive strength, and flexural strength of specimens with 20% LS substitution can be increased by 8.16%, 8.33%, and 13.46% after high temperature. The cubic compressive strength, axial compressive strength, and flexural strength of specimens with 20% LS substitution can be increased by 8.16%, 8.33%, and 13.46% after high temperature.

A Comprehensive Review of Plant-Based Biopolymers as Viscosity-Modifying Admixtures in Cement-Based Materials

As the construction industry is facing the challenge of meeting the ever-increasing demand for environmentally friendly and durable concrete, the role of viscosity-modifying admixtures (VMAs) has become increasingly essential to improve the rheological properties, stability, and mechanical properties of concrete. Additionally, natural polymers are ever evolving, offering multiple opportunities for innovative applications and sustainable solutions. This comprehensive review delves into the historical context and classifications of VMAs, accentuating their impact in enhancing the rheological properties, stability, and mechanical properties of concrete. Emphasis is placed on the environmental impact of synthetic VMAs, promoting the exploration of sustainable alternatives derived from plant-based biopolymers. Indeed, biopolymers, such as cellulose, starch, alginate, pectin, and carrageenan are considered in this paper, focusing on understanding their efficacy in improving concrete properties while enhancing the environmental sustainability within the concrete.

Experimental research and theoretical prediction on mechanical properties for recycled GFRP fiber reinforced concrete

Recycled GFRP fiber has increasingly been reused in concrete, necessitating an improvement in its recycling process and an investigation into its effects on the mechanical properties of concrete to achieve higher recycling values. To this end, this study proposed a novel GFRP recycling method that integrates mechanical recycling, water-vibratory separation, and secondary sieving to efficiently remove impurities from GFRP waste. Three different sizes of recycled GFRP fibers (SF, MF, and LF) were sorted from decommissioned GFRP wind turbine blades using the novel recycling method, and their effects of on the mechanical properties of concrete were investigated. The results show that all three types of recycled GFRP fibers increase the strength and toughness of concrete. With equivalent fiber content, the largest recycled GFRP fiber (LF) yields the most substantial reinforcement effect on the mechanical properties of concrete. Specifically, incorporating 1.0 % LF increases the compressive strength, splitting tensile strength, and flexural strength of concrete by 14.0 %, 16.8 %, and 37.0 %, respectively, while also increasing flexural toughness by 2.9 times. In addition, the mechanical properties of recycled GFRP fiber reinforced concrete were theoretically analyzed in this study, and two strength prediction models for recycled GFRP fiber reinforced concrete were established to achieve rapid prediction of concrete strength.

Numerical simulation of concrete strength based on microstructure and mineral composition analysis using micro-CT and XRD technology

The investigation of mechanical properties in porous materials, such as concrete, has been a significant area of interest in the fields of civil engineering and architecture. Traditional macroscopic mechanical testing methods are limited due to destructive experimental conditions, time-consuming procedures, and the inability to characterize internal structures. To overcome these limitations, researchers have utilized microscopic factors with micro-CT and simulation models. Different simulation methods demand mechanical parameters to effectively model the constituent materials; however, there exists variability in the amount and standard values of these input parameters, which leads to a decrease in the reliability of the obtained results. In order to tackle this issue, a novel approach is proposed, which integrates mineral component analysis using X-ray diffraction (XRD) and establishes coefficients to minimize the number of necessary input parameters. Simulation results demonstrate excellent agreement with experimental measurements, accurately reproducing the stages of elastic deformation, failure, and fracture in the stress-strain curve of concrete. Our findings reveal that changes in the concrete skeletal structure, microstructure, and mineral composition significantly influence compressive strength. Coarse aggregates and high-mechanical-performance minerals, in particular, have a substantial impact. Additionally, the mechanical properties show a significant linear relationship with the strength reduction coefficient of aggregates and concrete cores. In conclusion, the proposed method, combining CT scanning and XRD with FDEM, proves to be a reliable and practical approach for accurately assessing the mechanical properties of concrete. This methodology simplifies the intricate processes associated with the time-intensive parameter calibration, leading to a more efficient parameter allocation procedure. As a result, this method enhances concrete design, promotes a better understanding of parameter impacts, and enables accurate prediction of concrete behavior across diverse scenarios.

Chloride Corrosion Process of Concrete with Different Water-Binder Ratios under Variable Temperature Drying-Wetting Cycles.

In this paper, four water-binder ratios (w/b) of 0.29, 0.33, 0.39, and 0.46 were designed. A variable test temperature was implemented in the drying-wetting cycle test according to the temperature fluctuations in the actual service environment, and the constant temperature test was established as the control group. The mechanical properties and chloride corrosion resistance of concrete with different w/b ratios under variable temperature drying-wetting cycles, as well as the microstructure changes, phase composition, and damage mechanism inside the concrete, were investigated. The results showed that the mechanical properties of concrete increased first and then decreased with drying-wetting cycles increasing, whereas the chloride corrosion resistance continued to decline. A higher w/b exacerbated the deterioration of the concrete performance. A higher w/b increased the porosity, chloride diffusion depth, and chloride content, thus reducing the resistance of chloride corrosion. Compared with w/b = 0.29, the compressive strength, splitting tensile strength, mass, and relative dynamic elasticity modulus of w/b = 0.46 exposed to 60 drying-wetting cycles decreased by 54.50%, 52.44%, 0.96%, and 6.50%, respectively, while the porosity, peak chloride content, and erosion depth increased by 45.12%, 70.45%, and 45.00%. Compared with the drying-wetting cycle with a constant temperature, the cumulative damage caused by the drying-wetting cycle with a variable temperature was greater, resulting in more severe deterioration of concrete performance. The increase in the test temperature significantly accelerated the diffusion rate, penetration depth, and chemical binding capacity of chloride ions. After 60 drying-wetting cycles, the peak chlorine content and erosion depth of w/b = 0.46 under variable temperature cycles were 15.38% and 10.32% higher than those under a constant temperature, while the compressive strength, splitting tensile strength, mass, and relative dynamic elastic modulus were reduced by 7.76%, 14.81%, 0.33%, and 2.40%, respectively. Microscopic analysis confirmed that higher w/b and variable temperature cycles accelerated the decay of mechanical properties and the decline of chloride corrosion resistance. According to the numerical fitting analysis, the w/b should be 0.29~0.39 under the condition that the mechanical properties and chloride corrosion resistance of concrete are met.

Uncertainty quantification and global sensitivity analysis of bearing capacity of push-out specimen considering randomness in bond-slip behaviour

As an artificial composite material, the uncertainty in mechanical property of concrete significantly impacts the bond-slip behaviour of the shaped steel concrete structure. To investigate the effect of the uncertainty of concrete mechanical properties on the bearing capacity of push-out specimens, based on the data of a small number of push-out test with identical design parameters, the improved Bootstrap method is utilized to execute sample augmentation for the bond stress-slip curves, and the stochastic bond slip constitutive model is established after considering five parameters (K1, …, K5) in the deterministic bond-slip model as random variables. Simultaneously, considering the randomness in elastic modulus of concrete (Ec), uncertainty quantification (UQ) of the bearing capacities of the push-out specimens is conducted using the arbitrary polynomial chaos (aPC) method. Subsequently, the global sensitivity analysis of the ultimate and residual bearing capacities is accomplished through the aPC surrogate model. The results indicate that the probability distribution types of the parameters in the stochastic bond-slip constitutive model can be arbitrary when considering the randomness of concrete material, and the aPC method with at least a third-order expansion is recommended to execute UQ for the push-out test due to the strong nonlinearty between the bearing capacities and the random parameters. The ultimate bearing capacity is primarily affected by the parameter K2, followed by K4, K3, and K5. Whereas the residual bearing capacity is predominantly influenced by the parameter K4, followed by K5, the remaining parameters exhibit negligible influence. In contrast, K1 and Ec have the greatest influence on equivalent plastic strain of the concrete near the loading end of the push-out specimen.

Synergic Effects of Recycled Concrete Aggregate and Styrene Butadiene Rubber (SBR) Latex on Mechanical Properties of Concrete

These days Sustainable advancement is picking up notoriety all around the globe. To hold characteristic assets, reuse and reusing of development and annihilation squander is the clearest approach to achieve manageability in the development division. Presently, reused aggregate RA is been generating and CDW is its source. As of late, these squanders are reused in present day reusing offices, under great quality control arrangements which could prompt enhance its execution. An investigation is completed about the characteristics of Recycled Aggregate Concrete RAC by utilizing squashing and breaking of concrete waste got from various obliteration locales & junkyard. With the end goal to upgrade the characteristics of RAC there are a few additives called as super plasticizer which are adjoined with concrete. Fixings utilized in particularly this investigation were ordinary sand, common & reused aggregate & additive namely Styrene Butadiene Rubber latex (SBR). Those aggregates are acquired from various assets. Sum of 144 concrete molds in system of 4 collections was framed. Gatherings were structured in such a route along these lines, to the point that the impact of reused coarse aggregate (half, 75 percent, and 100 percent), cement dose and expansion of latex of SBR in factor amounts by the cement weight of (0.5 percent, l percent, 1.5 percent) ought to be appropriately decided. For compressive quality and rupture modulus MOR, tests were done. Prior to the tests performance in the research center a diminishing pattern of twenty five (25) percent in compressive quality was taken note. An impressive decrease was seen in the properties of RAC by utilizing 100% reused aggregate when contrasted with Natural Aggregate Concrete NAC. There was negligible change in Recycled Aggregate Concrete RAC made of 75 percent (%) NA and 25 percent (%) RCA. Yet, there was ideal properties differences of concrete ended with the blend of half NA and half RCA. It was seen in the outcomes that concrete squanders might be used in arrangement of concrete subsequent to reusing them which at that point can be utilized in many concrete structures.

Investigation of foam concrete's mechanical properties and multi-scale damage evolution characteristics under uniaxial loading

The macroscopic mechanical behavior of foam concrete damages its mesoscopic pore structure. To study the macroscopic mechanical properties of foam concrete, a series of uniaxial compression tests were carried out. AE-DIC and SEM characterization were used to reveal the multi-dimensional damage evolution characteristics of foam concrete under load. Furthermore, the porosity response law of the foam concrete damage characteristics was analyzed using the finite element method. The results show a significant linear relationship between the residual and peak stress of foam concrete under uniaxial load (σr = kσp), and the coefficient k decreases with an increase in porosity. During uniaxial compression, tensile and shear damages were dominant on both sides of the yield point of foam concrete. The macroscopic load retention characteristics in the failure stage typically result from microscopic fracture structure reorganization and stress path optimization. The damage-dissipation energy during this period accounts for approximately 100% of absorbed energy. An increase in the porosity led to frequent adjustments in the stress path of the foam concrete, and the tensile damage tended to be significant and diffuse.

Effect of the Inorganic Modification Mode on the Mechanical Properties of Rubber Recycled Concrete.

The reasonable and effective application of waste tires and discarded concrete in concrete is an important branch of green concrete development. This paper investigates the effects of the inorganic modification mode on the basic mechanical properties of rubber recycled concrete based on indoor tests. Inorganic modification, such as water washing, acid washing, and alkaline washing modification, was mainly used to treat and modify rubber particles. The factors affecting the compressive strength, the splitting tensile strength, the flexural strength, the axial compressive strength, and the modulus of elasticity of modified rubber recycled concrete were analyzed. The study results show that the incorporation of recycled aggregates and rubber reduced the mechanical properties of concrete, with the compressive and splitting tensile strengths showing the greatest reductions of 27.36% and 27.24%, respectively. Three modification methods significantly improved the mechanical properties of rubber recycled concrete. The alkali washing modification method was the most effective, maximally improving the mechanical properties of rubber recycled concrete by 7.53-15.51%. The effects of the three modifications on the mechanical properties of concrete were ranked as follows: alkali washing > acid washing > water washing. This study provides a data basis for the practical application of rubber recycled concrete in engineering and a test basis for the development of green concrete.

Corrosion characteristics of concrete by landfill leachates of different ages

Landfill leachate is a highly corrosive pollutant, and the composition of landfill leachate varies greatly between landfill ages. Landfill leachates of different ages pose a corrosive danger to concrete structures. In this study, four landfill leachates of different ages were selected for concrete immersion corrosion tests to elucidate the corrosion characteristics of concrete. Measurements of concrete mechanical property indices were combined with microscopic analysis methods, such as X-ray diffraction and scanning electron microscopy. The effects of the compositional differences of the landfill leachate of different ages and contact times on the concrete were analyzed and evaluated. The test results showed that the young landfill leachate slowed down the hydration process of concrete and promoted the generation of expansive corrosive crystals such as gypsum and calcium sulfate, which changed the internal microstructure of the concrete and caused irreversible damage. Exposure to leachates caused a decrease of the concrete quality, compressive strength, and dynamic elastic modulus to below their initial values. The participation of intermediate and mature landfill leachate in the hydration process of concrete promoted the hydration reaction in the short term. However, with the prolongation of the test period, this enhancement gradually weakened, and at the same time, the sulfate in the landfill leachate and the hydration products generated ettringite, which produced expansion stress on the internal structure of the concrete, destroying the structure and decreasing its strength. The experimental results of this study provide theoretical support for the treatment of different ages of landfill leachates and the design and protection of landfill concrete structures.

Ultra-stable foam enabled by nano silica engineering for foam concrete improvement

Foam concrete is increasingly applied in construction due to its lightweight, good thermal insulation and fire resistance, and environmental sustainability, while its low strength limits its further popularization and applications. To enhance the stability and performance of foam concrete, amphiphilic nano silica (ANS) was employed in this study to modify the sodium dodecyl sulphate (SDS) based foaming agent. Then, the designed foam was utilized to fabricate foam concrete, of which the micro/macro performance was analysed in detail. The results showed that ANS-modified foam exhibited superior stability with a thicker foam wall thickness, contributing to the enhancement of foam stability within the cement matrix. The foam concrete with ANS exhibited higher strength compared to the control groups. The analysis of pore structures revealed that the ANS modification led to a more rounded and homogeneous pore configuration, characterized by an increased proportion of small and medium-sized pores and a decreased average pore size. The increase in pore roundness was accompanied by a reduction in the number of sharp edges of the pores and therefore a reduction in the stress concentration factor, while the moderately sized pore also was more conducive to increasing strength due to its lower stress concentration. As a result, the strength of the concrete is significantly increased. These findings demonstrate the potential of ANS as an effective foam stabilizer for foam concrete production, leading to enhanced foam stability and improved mechanical properties of concrete.

Study on the Effect of Post-Freezing Mechanical Properties of Polypropylene Fibre Concrete Based on BAS-BPNN

An indoor accelerated freezing and thawing test of polypropylene fibre-reinforced concrete in chloride and sulphate environments was conducted using the “fast-freezing method” with the objective of investigating the damage law of the post-freezing mechanical properties of hydraulic concrete structures and studying the effects of different mixing amounts of polypropylene fibres on the mechanical properties of concrete. Furthermore, in order to reduce the cost of concrete tests and shorten the time required for conducting concrete tests, a backpropagation neural network based on a Beetle Antenna Search algorithm (BAS-BPNN) was established to simulate and predict the mechanical properties of polypropylene fibre-reinforced concrete. The accuracy of the model was verified. The results indicate that the order of improvement in the macro-physical properties of concrete due to fibre doping is as follows: PPF1.2 exhibited the greatest improvement in macro-physical properties of concrete, followed by PPF0.9, PPF1.5, PPF0.6, and PC. When the freezing and thawing medium and the number of cycles are identical, all four assessment indexes (R2, RMSE, SI, MAPE) demonstrate that the four groups of polypropylene fibre concrete exhibit superior performance to the control group of ordinary concrete. This indicates that polypropylene fibre can enhance the mechanical properties and freezing resistance of the concrete matrix, delay the process of freezing and thawing damage to the matrix, and extend the lifespan of the matrix, yet cannot prevent the ultimate failure of the matrix. The application of intelligent algorithms to optimise the parameters of an artificial neural network model can enhance its capacity to generalise and predict the mechanical properties of concrete. In terms of the coefficient of determination (R2), the Beetle Antenna Search algorithm (0.9782) outperforms the Particle Swarm Optimization (PSO; 0.9676), the Genetic Algorithm (GA; 0.9645), and the backpropagation neural network (BPNN; 0.9460). The improved backpropagation neural network based on the Beetle Antenna Search algorithm not only avoids the trap of local optimality but also improves the model accuracy while further accelerating the convergence speed. This approach can address the complexity, non-linearity, and modelling difficulties encountered during the freezing process of concrete. Moreover, it offers relatively accurate prediction outcomes at a reduced cost in comparison to traditional experimental methodologies.

Effect of Incorporation of Recycled Polypropylene Plastic on Mechanical Properties of Concrete

Effect of Incorporation of Recycled Polypropylene Plastic on Mechanical Properties of Concrete

Comparing the Properties of Concrete (Experimental Data) Using Machine Learning Algorithms

Concrete is the most widely used construction material throughout the world. Extensive experiments are conducted every year to study the physical, mechanical, and chemical properties of concrete involving a hefty amount of money and time. This work focuses on the utilization of Machine Learning (ML) algorithms to predict various concrete properties for avoiding unnecessary experimentation. In this present work, six mechanical properties of concrete namely modulus of rupture, compressive strength, modulus of elasticity, Poisson’s ratio, splitting tensile strength, and coefficient of thermal expansion are estimated by applying five different ML algorithms viz. Linear Regression, Support Vector Machine, Decision Tree, Random Forest, and Gradient Boosting models on the Wisconsin concrete mixes database. Further, these ML models were evaluated to identify the most suitable model that can reliably predict the mechanical properties of concrete.

Experimental study on Corn Straw Fiber (CSF) toughening EPS concrete

The natural Corn Straw Fiber (CSF), it has the advantages of light weight, high strength, good toughness and renewable, can delay the cracking and improve the toughness of cement-based materials. The effects of different mass fractions of CSF and Expanded-Polystyrene (EPS) particles on the compressive strength, flexural strength, splitting tensile strength and their failure modes, load-displacement curves and toughness of EPS concrete were analyzed by full factorial experimental design method. The compressive toughness index (I0, I1) and fracture energy (Gf) were defined to evaluate the effect of CSF on toughening EPS concrete. The results show that the addition of CSF can improve the compressive strength, flexural strength and cracking toughness of EPS concrete to a certain extent. The maximum compressive strength occurred in the E1F3 specimen with a CSF content of 3 % in Group I, which was 1.12 MPa, and the improvement rate was also the highest among the four groups, reaching 69.7 %. The compressive toughness index I1 also reached its maximum in the E1F3 specimen; The maximum flexural strength occurred in the E3F4 specimen with a 4 % CSF content in Group III, which was 0.885Mpa, with the highest improvement rate of 127.38 %. The maximum fracture energy Gf reached 0.827 in the E3F4 specimen. However, another additive, EPS particles, did not significantly improve the physical and mechanical properties of concrete. According to the SEM images and toughening mechanism analysis, it was discovered that tight adhesion between EPS particles and CSF with cement matrix, and the failure mode of CSF was tensile fracture, which could maximize the effect of CSF high tensile toughness. On the basis of mechanical properties and toughening effect, the relationship formulas between variable factors and strength, toughness index were fitted, and the optimal content of EPS and CSF were determined to be 1.3 % and 3 %, respectively.

A Review on Mechanical Properties of Concrete by Partial Replacement of Cement with Eggshell Powder and Fly Ash

A Review on Mechanical Properties of Concrete by Partial Replacement of Cement with Eggshell Powder and Fly Ash

Mechanical properties of silica fume based concrete: A review

The significant industrial growth accompanying rapid urbanization has spurred a heightened demand for concrete. Cement production, a primary ingredient of concrete, results in substantial carbon dioxide (CO2) emissions. To mitigate this impact, alternative pozzolanic materials like silica fume (SF) can be incorporated. SF, an industrial byproduct, serves as a supplementary cementitious material (SCM), offering benefits of waste recycling. This study aims to comprehensively review the addition of SF as an SCM replacement, with a specific focus on the mechanical properties of concrete. Numerous scientific papers were analyzed and carefully examined from the period of 1998 to 2023, which forms the bibliometric core of this study. The entire scopus database was examined for co-occurrence of keywords and actively contributing countries and results were shown through network diagrams. The effect of SF addition on fresh properties as well as mechanical properties were discussed. The inclusion of SF in range of 10–25% by quantity of cement was found to have increased split tensile strength, compressive strength and flexural strength. However, the addition of SF beyond 25% replacement level can have an adverse impact on the overall characteristics of the composite mix. The present study summarizes the major trends as reported in the available literature where SF has been used as SCM. Apart from finding the general trends, various research gaps have been identified.

MECHANICAL PROPERTIES OF DIFFERENT TYPES OF FIBER-REINFORCED CONCRETE: BENEFITS AND LIMITATIONS

Fibers are widely used in the concrete industry to enhance the mechanical properties of concrete, especially tensile strength and post-cracking behavior. This study evaluates the mechanical performance of steel, glass, polypropylene fibers, and hybrid fiber-reinforced concrete through a detailed literature review. It was found that fiber addition significantly enhances the tensile strength, flexural strength, and ductility of concrete, with variations attributed to the type and volume of fibers used. The impact on compressive strength was minimal. Fibers with high elastic modulus notably improved concrete strength, whereas fibers with lower modulus enhanced concrete’s ductility and toughness. Each fiber type presents unique benefits and limitations concerning mechanical properties, environmental resistance, and cost. Hybrid fiber reinforcement emerged as particularly effective, offering substantial improvements over single-fiber systems, and mitigating some of their inherent limitations. This research aims to provide comprehensive insights into the effects of fiber reinforcement on concrete's mechanical properties, highlighting the distinct benefits and drawbacks of different fiber types.