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The use of recycled materials and industrial by-products as sustainable constituents of cementbased materials could be an environmentally and technically promising solution for application to structural elements. In the present work, the technical and environmental impact of using recycled steel fibers as an alternative to industrial steel fibers for concrete reinforcement was assessed at material level. Numerical simulations were performed to derive the post-cracking constitutive laws of the developed Recycled Steel Fiber Reinforced Concrete (RSFRC) and Industrial Steel Fiber Reinforced Concrete (ISFRC) by inverse analysis of experimental results obtained from three-point notched beam bending tests (3PNBBT), round panel tests supported in three points (RPT-3ps) and double edge wedge splitting tests (DEWST). These simulations were able of fitting with high accuracy the experimental results and consequently to derive the tensile stresscrack width relationships of RSFRC and ISFRC that was used to numerically simulate the bending response of a T-cross section steel RSFRC beam failing in shear. The environmental impact of the incorporation of RSF in concrete in comparison with ISFRC was evaluated using Life Cycle Assessment methodology. The reduction of the environmental impact of the production of RSFRC compared to ISFRC with the same concrete strength class is demonstrated., The 1st author would like to thank the FCT for the financial support through the Research Grants PD/BD/113638/2015 under the Doctoral Program in Eco Construction and Rehabilitation – EcoCoRe.

The characterization of historic mortars applied in construction is required in many situations, namely for their conservation. In this sense, the drilling resistance test has been being ex...

This article aims to characterize the physical, mechanical, and water-resistant behavior of unstabilized and stabilized compressed earth blocks (CEB) produced with partial incorporation of recycled...

An innovative system of pre-cast high performance concrete pre-walls, combined with low-cement cast-in-situ lightweight concrete core, is studied experimentally from the standpoint of the thermophysical properties of the concrete compositions under various hygroscopic conditions. Thermal conductivity, volumetric heat capacity and thermal diffusivity are experimentally determined, by a transient method, for eight concrete compositions in the dry state, hygroscopic and over-hygroscopic ranges. The incorporation of lightweight aggregates in the concrete mixture allowed to reduce the thermal conductivity (up to 53%) and thermal diffusivity (up to 41%), in comparison to normal weight concrete. The moisture content, regardless of the composition of the concrete, impacts negatively the thermal performance, with a rise of both thermal conductivity and diffusivity, which was also captured by analytical expressions. An application study of the pre-walls system to a swimming pool showed reductions of thermal conductance of up to 38% when combining high mechanical performance concrete in the pre-walls with lightweight aggregate concrete with high thermal performance in the core. These results highlight the importance of assessing thermophysical properties in service conditions, with the moisture content effect included, and selecting the types of concrete in composite pre-walls systems to enhance both mechanical and thermal performance.

This paper characterizes the oxygen permeability of structural lightweight aggregate concrete (SLWAC). The influence of different parameters is analysed, namely water/binder (w/b) ratio, type of binder and aggregate, relative humidity, water content and concrete age. The correlation between this and other properties is investigated. The oxygen permeability varied over a broad range. Nevertheless, the oxygen permeability of SLWAC with denser aggregates could be as low as that of normal weight concrete. The influence of the type of aggregate tended to increase with w/b ratio, aggregate porosity and percentage of additions. Small differences between mixtures were masked by the high variability of the test.

This paper aims to characterize the mechanical and physical behavior of non-structural lightweight concrete (NSLWC) produced with volcanic scoria, regarding its application in building’s floors. The density, thermal conductivity, capillary absorption, compressive, tensile and punching strength, elasticity modulus, shrinkage, abrasion resistance and behavior at high temperatures of different NSLWC fill solutions were analyzed. For comparison purposes, conventional NSLWC with expanded clay and expanded polystyrene aggregates were also studied. Despite its greater density and slightly lower abrasion resistance and thermal conductivity, NSLWC with scoria showed similar mechanical strength, less shrinkage, higher punching strength and better behavior at high temperatures than conventional NSLWC.

Steel fibers resulting from the industry of tire recycling can be efficiently employed in concrete to improve its mechanical performance, such as post-cracking load bearing and energy absorption capacity. Under chloride attack, an important aspect of Recycled Steel Fiber Reinforced Concrete (RSFRC) durability is its corrosion resistance. However, the insufficient knowledge on this domain contributes for a conservative design philosophy, which can compromise the cost competitiveness of RSFRC and prevent its application in elements where this occurrence, even eventual, is not acceptable. In the present work, an experimental program was performed with the aim of assessing the corrosion susceptibility of RSFRC including the characterization of the micro-mechanical properties and the corrosion resistance of recycled steel fiber (RSF) by means of nano-indentation testing, electrochemical monitoring techniques and scanning electron microscopy (SEM) analysis. The influence of the small rubber debris attached to the RSF surface was also analyzed by using two distinct pre-treatment methods. The adhesive bond behavior between the RSF and the surrounding self-compacting concrete (SCC) matrix was analyzed by performing monotonic RSF pullout tests. Double edge wedge splitting (DEWS) tests were conducted for evaluating the corrosion effects on the post-cracking response of RSFRC., CiviTest Company and the Scientific and Technological Research Assistance Centre (CACTI) of the University of Vigo. The first author would like to thank the FCT for the financial support through the Research Grant PD/BD/113638/2015. The third author acknowledges the grant SFRH/BSAB/114302/2016 provided by FCT. Part of this work is supported by FCT with the reference project UID/EEA/04436/2013, COMPETE 2020 with the code POCI-01- 0145-FEDER-006941. Finally the support of the FCT through the project PTDC/ECM-EST/2635/2014

This paper addresses the prediction of the carbonation-induced corrosion service life of structural lightweight aggregate concrete (SLWAC) by means of a performance-based approach. Abacuses for the prediction of the service life of SLWAC as a function of the w/c ratio are presented. Limiting values of concrete composition for different carbonation exposure classes are prescribed for an intended service life of at least 50 years. The results reveal that even when pastes of low-to-moderate quality are considered, the carbonation-induced corrosion should not be the mechanism determining the service life of SLWAC structures, as long as appropriate thicknesses of concrete cover are adopted.

In recent years, Energy Performance Building Directives have been published and adopted by all EU member states in order to promote the improvement of the energy performance of buildings within the EU, and thus coping with the growing comfort needs and consequent increase in energy consumption for space heating and cooling. Structural lightweight aggregate concrete (SLWAC), due to its thermal properties, presents itself as an alternative to normal weight concrete (NWC) to reduce the thermal bridging effects as well as the building energy needs to maintain thermal comfort levels in buildings. In this paper, the potential of SLWAC to improve the energy performance of buildings was assessed. An experimental study was carried out in order to determine the thermal properties of five different concrete mixtures, four SLWAC and a reference NWC for comparison purposes. These thermal properties were then used in the two-dimensional heat transfer program Therm and in the whole-building energy simulation program EnergyPlus to assess the impact of SLWAC on the thermal bridge heat losses and building energy needs of a case study. Results showed that SLWAC can improve the energy efficiency of buildings and thus be an attractive alternative to the use of the traditional NWC.

This study aims to characterise the carbonation behaviour of structural lightweight aggregate concrete (SLWAC) produced with different types of aggregate, w/c ratios and types and content of mineral admixtures (silica fume, fly ash, lime filler) by means of accelerated carbonation tests. A new biphasic model to describe the carbonation behaviour of SLWAC is suggested. Based on this model, the carbonation coefficient of SLWAC is estimated as a function of the w/c ratio, for different density classes of lightweight aggregates. It is concluded that the carbonation resistance of SLWAC cannot be properly predicted by its compressive strength and that the carbonation rate is little affected by the type of binder, being appropriate to neglect the contribution of mineral admixtures in carbonation resistance of SLWAC. It is also concluded that even with pastes of moderate quality, the carbonation mechanism should not be relevant to the durability of SLWAC.

This paper's aim is to characterize the freeze–thaw resistance of normal strength and high-strength concrete with partial or total replacement of fine natural aggregate (FNA) by fine recycled concrete aggregate (FRCA). The surface scaling, mass loss, length change, residual ultrasound pulse velocity and residual compressive strength were monitored for different FRCA replacement ratios (0%, 20%, 50% and 100%) subjected to 300 freeze–thaw cycles according to ASTM C666 – Proc. A. In general, the mechanical strength decreases with the incorporation of FRCA, especially in high-strength concrete. Contrary to high-strength concrete, normal strength concrete was not frost resistant, regardless the type of aggregate used. The w/c ratio had a greater influence on the freeze–thaw resistance than the type of aggregate. The air entraining had a slightly beneficial effect on high-strength concrete. Generally, it is concluded that the incorporation of FRCA is not detrimental to the freeze–thaw resistance of concrete. Only the total replacement of FNA by FRCA led to lower residual mechanical strengths after freeze–thaw action than those obtained in reference mixes. However, surface scaling tends to be more severe in concrete with FRCA if it can be saturated near the concrete surface.

For structural elements exposed to chloride environments, an important aspect of Recycled Steel Fiber Reinforced Concrete (RSFRC) durability is the corrosion resistance. In the present work, an experimental program was carried out to evaluate the long-term effects of chloride attack on the post-cracking behavior of RSFRC by performing splitting tensile tests and round panel tests. Two RSFRC mixtures defined based on the packing density optimization were produced with a fiber content of 0.8% and 1% per volume of concrete. The influence of different periods of chloride immersion was investigated, as well as the influence of fiber dispersion at crack surfaces of the specimens. Additionally, a simplified prediction of the long-term chloride penetration depth into uncracked RSFRC under immersion aggressive chloride exposure conditions was estimated. The RSFRC revealed high susceptibility to surface corrosion under the chloride exposure conditions adopted. However, the post-cracking resistance of RSFRC was not significant affected. The addition of RSF had a negligible effect in the diffusion of chloride ions into concrete, and the critical chloride content was higher than that found in conventional reinforced concrete structures., This research was funded by C.F. research grant PD/BD/113638/2015 provided by Fundação para a Ciência e a Tecnologia (FCT) through the Doctoral Program in Eco Construction and Rehabilitation - EcoCoRe, and J.B. through the project ICoSyTec (POCI-01-0145-FEDER-027990) financed by FCT.

This paper characterizes the chloride penetration resistance of structural lightweight aggregate concrete (SLWAC) produced with different types of aggregates and binders, for usual compressive strengths of about 20–65 MPa. Concrete is characterized by means of capillary absorption, electrical resistivity and accelerated chloride migration tests. In general, it was found that the chloride penetration resistance can be substantially affected by the type of binder. Besides the microstructural refinement effect, the mineral admixtures should also affect the ionic composition of the pore solution. The type of aggregate had a little influence on the chloride penetration resistance. Chloride penetration resistance should not be related to the compression strength of concrete. However, chloride diffusion is exponentially related to the w/c ratio, regardless the type of aggregate. The capillarity and resistivity results did not correlate well with those from the chloride migration test. It is concluded that SLWAC with less porous aggregate can be at least as resistant as normal weight concrete.

This study aims to characterise the chloride penetration resistance of structural lightweight aggregate concrete (LWAC) produced with different types, volumes and initial wetting conditions of lightweight aggregates (LWA), types of cement and contents of fly ash and silica fume, w/c ratios and curing conditions. A comprehensive experimental study was carried out involving three types of non-steady-state tests, which simulate different exposure conditions and penetration mechanisms. It is shown that the chloride penetration resistance is mainly affected by the cementitious paste and that high performance LWAC of 30–70 MPa can be produced. Regardless of the type of aggregate, we propose exponential relations to estimate the diffusion coefficient of chlorides. The volume and initial wetting condition of LWA had little influence on the chloride resistance. A long-term higher reduction of the diffusion coefficient was found in less dense LWAC. Reasonable correlations between the non-steady-state tests were obtained. Contrary to what is suggested in some European standards, the concrete strength cannot properly predict the durability behaviour of LWAC.

In this paper, the mechanical and long-term durability behaviour of structural lightweight concrete (LWC) produced with natural lightweight scoria aggregate (LWSA) from the Azores is analysed. Among the properties studied are the compressive and tensile strength, modulus of elasticity, shrinkage, capillary absorption, carbonation and chloride resistance. To this end, a comprehensive experimental study was carried out on different concrete compositions involving common and high-performance structural concrete produced with coarse or coarse and fine volcanic scoria aggregate. Generally, all the mechanical properties worsened with the incorporation of LWSA. It is concluded that the most efficient LWC with LWSA can attain compressive strength up to about 35 MPa. On the other hand, the production of LWC of more than 50 MPa implies a marked reduction in compressive strength for a small reduction in density. The long-term shrinkage increased with the replacement of normal-weight aggregate by LWA and was higher when coarse and fine scoria were used. However, the early age shrinkage can be counterbalanced by the internal curing effect provided by LWSA. The capillary absorption, chloride and carbonation resistance were affected by the high porosity of LWSA. The absence of the outer shell in scoria aggregate and the surface effects during tests can partly explain the lower performance of the LWC. Nevertheless, it is shown that LWC with scoria can be durable, and even for low- to moderate-strength LWC the corrosion induced by carbonation may not be relevant.

A comprehensive experimental study on the concrete–steel bond behaviour of structural expanded clay lightweight aggregate concrete (LWC) was carried out using different compositions, types and initial wetting conditions of lightweight aggregates, anchorage lengths, reinforcement arrangements, strength classes and failure mechanisms. For splitting failure, the bond strength of LWC was about 70% that of normal weight concrete (NWC). But when the confinement is sufficient and pull-out of the reinforcement occurs, the relative performance of LWC and NWC may vary widely. The reduction of the bond strength with LWC was roughly proportional to ρd/2200, where ρd is the concrete dry density. The addition of silica fume had little effect on the LWC bond strength. The bond was impaired when the LWA was pre-soaked. LWC seems to be less affected by the position and orientation of the reinforcement. It is shown that the water/cemet (w/c) ratio has a greater influence on the bond strength than on compressive strength. The bond strength was higher in the lower w/c concrete, regardless of the type of aggregate. Moreover, the bond strength of LWC was more than twice that of NWC of equal compressive strength. It is shown that the application of reduction factors to the LWC bond strength, as suggested in the main standards, may be too unrealistic. A new approach for estimating the LWC bond strength is suggested.

In this paper some of the main long-term properties of concrete produced with recycled aggregates obtained from crushing both structural and non-structural lightweight concrete (LWC) are analysed. The properties studied are drying shrinkage, capillary and immersion absorption, and carbonation and chloride penetration resistance. A comprehensive experimental study was carried out on a series of concrete mixes in which ratios of 20%, 50% and 100% of two types of coarse lightweight aggregates (LWA) were replaced with two types of recycled lightweight concrete aggregates (RLCA). Long-term shrinkage is affected by the paste adhered to LWA and increases as the replacement ratio of LWA with RLCA goes up. However, the internal curing promoted by RLCA reduces the early shrinkage. In terms of durability, the experimental results show that generally all the properties studied decay due to the progressive replacement of structural LWA with RLCA. However, despite the general reduction of long-term properties, recycled lightweight concrete (RLWC) can be also durable, regardless of the type of RLCA. Moreover, it is shown that even for low to moderate strength RLWC the mechanism of carbonation is not a determinant factor for durability. On the other hand, the carbonation and chloride penetration resistance of concrete with non-structural LWA tends to improve with the incorporation of RLCA. It can thus be concluded that RLWC may be a viable and more cost-effective alternative solution, especially given its higher structural efficiency. In addition, RLCA obtained from non-structural LWC can be incorporated in concrete without significantly compromising its durability.

In this paper the tensile strength of Lightweight Aggregate Concrete (LWAC) produced with different types of expanded clay aggregates is characterized. A comprehensive experimental study was carried out on different concrete compositions with mean compressive strengths from 30 to 70 MPa and density classes from D1.6 to D2.0. The influence on the splitting tensile strength and modulus of rupture of the curing conditions and initial wetting of lightweight aggregate is studied. For concretes of equivalent compressive strength, the tensile strength is almost independent of the type of lightweight aggregate. The tensile strength of LWAC was about 0.8–0.85 of that of Normal Weight Concrete (NWC) of equal strength, decreasing to about 0.7 in LWAC with lightweight sand. Contrary to compressive strength, the LWAC with less porous aggregates has lower tensile structural efficiency than NWC. But the tensile structural efficiency of moist-cured concrete is little affected by the volume and wetting conditions of aggregate. There is a reduction in the splitting strength of air-cured concrete that is not predicted in the normalization and it is greater for NWC than for LWAC. However, the modulus of rupture of air-cured LWAC can only be about 0.5–0.8 of that of NWC of equal strength.

The present study aims to characterize the capillary absorption of structural lightweight aggregate concrete (LWAC), taking into account different compositions with lightweight aggregates (LWA) of very distinct porosity. The influence of the following parameters is analysed: the volume and initial water content of LWA; the cement content and its replacement by fly ash or silica fume; the partial replacement of normal weight aggregate by lightweight coarse or fine aggregate; different curing conditions. It is shown that LWAC usually has higher initial and long-term absorption than normal weight concrete (NWC) of the same composition. However, the sorptivity tends to be similar in both concretes, regardless of the type and volume of aggregate and the water/cement of the surrounding paste. Moreover, the sorptivity is lower in LWAC than in NWC of the same strength. It is also shown that the coarser the porosity of the LWA the lower is the capillary action. The capillary absorption is higher in LWAC with pre-soaked LWA and increases as the percentage replacement of cement by fly ash increases and the percentage of silica fume decreases.

A comprehensive experimental study was carried out on the shrinkage behaviour of structural expanded clay lightweight aggregate concrete (LWC), taking into account different compositions, types and initial wetting conditions of lightweight aggregates (LWA). The influence of different compositional parameters on shrinkage, such as the type and volume of aggregate, the w/c ratio, the binder content and the partial replacement of normal aggregates by LWA was analysed. The shrinkage of LWC depends on how the volume of LWA varies. The influence of different pozzolanic materials was also studied, namely, silica fume, nanosilica and fly ash. Depending on the type, content and reactivity of the pozzolanic additions, the shrinkage was higher or lower than that of LWC without admixtures. The initial wetting condition of LWA had little influence on the long-term shrinkage. The LWC with the most porous aggregates is more affected by the cross-section geometry of concrete in that it is more susceptible to differential shrinkage. Current standard expressions did not properly predict the shrinkage behaviour of LWC. Multiplier coefficients of about 1.3 for the most common structural LWA and about 1.6 for more porous LWA are suggested, to take into account the higher long-term shrinkage of LWC.

A comprehensive experimental study on structural lightweight aggregate concrete (SLWAC) was carried out involving more than 50 different compositions of strength classes ranging from LC20/22 to LC60/66 and density classes from D1.4 to D2.0. This study aims to characterize the behavior of SLWAC in compression to define the basis for a new simplified method to estimate the SLWAC strength. The possible failure modes of SLWAC and the influence of the main constituents of concrete on compressive strength are analyzed in detail. The importance of the strength level, the limit strength and the ceiling strength on the mechanical behavior of SLWAC and its structural efficiency are also shown. A biphasic model to estimate the strength of SLWAC is evaluated. High correlations between design and experimental values were obtained for the different compositions with distinct types of LWA.

Current design methods for structural lightweight aggregate concrete (SLWAC) are usually only valid for a limited range of concrete compositions that have previously been subjected to trial tests. The SLWAC mix design is more complex than that of normal weight concrete as more parameters need to be determined. Taking this into account, a simplified design method is proposed for SLWAC made with natural sand. The major advantages of the proposed method are that it is easy to apply and it can be generalized to any type of lightweight aggregate (LWA). For this, three additional design parameters are needed: the strength of LWA in concrete; the limit strength; the SLWAC potential strength. At most, two experimental mixtures are needed to determine these parameters. A biphasic model to estimate the strength of SLWAC is evaluated and high correlations are obtained. The good performance of the suggested method is demonstrated by examples of practical application and by the comparison with experimental results reported by the authors and other investigators.

The objective of this paper is to characterize self-compacting concretes produced with lightweight aggregates (SCLC) available in the Iberian Peninsula. The influence of different compositions on the self-compactability of SCLC is analyzed and some limits are suggested for their formulation. The usual self-compacting tests and additional segregation tests were considered. SCLC of adequate stability and self-compactability could be produced for compressive strengths between 37.4 and 60.8 MPa, density classes D1.8–D2.0 and 490–599 kg/m 3 of fines content with 33% fly ash by weight. Promising results were obtained in the SCLC mechanical characterization.

This article presents a detailed study of the microstructure of Iberian expanded clay lightweight aggregates (LWA). Other than more commonly used mercury porosimetry (MP) and water absorption methods, the experimental study involves optical microscopy, scanning electron microscopy (SEM), and microtomography (μ-CT). Pore connectivity and how it is deployed are shown to some degree, and the pore size spectrum is estimated. LWA are in general characterized by a dense outer shell up to 200 μm thick, encasing an inner cellular structure of 10–100 times bigger pore size. Aggregate pore sizes may span from some hundreds of nanometers up to over 1 mm, though the range of 1–25 μm is more typical. A noteworthy fraction of these pores is closed, and they are mainly up to 1 μm. It is also shown that macropore spatial arrangement is affected by the manufacturing process. A step forward is given to understanding how the outer shell and the inner pore network influence the mechanical and physical LWA properties, particularly the density and water absorption. The joint consideration of μ-CT and SEM seems to be the most appropriate methodology to study LWA microstructure. MP analysis is likely to distort LWA pore spectrum assessment.

Shading devices are used to reflect direct sunlight, reduce glare and prevent overheating. A correctly designed shading system will strongly influence the entire building energy consumption, peak loads and indoor comfort. The use of the venetian blinds is particularly common due to its relatively low cost and high versatility. The present study focuses on the algorithms for calculating both short-wave (solar) and long-wave (infrared) transmittance, absorptance and reflectance of the venetian blinds. The model is based on the net radiation method, allows for different slat discretization schemes and is suitable for integration into the building energy simulation tools. Once the effective optical properties are computed, the system can be regarded as an additional layer in a multilayer glazing system. Computed blind solar transmittance has been compared with other numerical models and in situ experimental results. A general good agreement has been found, except in cases where incident radiation is mostly diffuse. In this study, the effect of different design parameters on effective optical properties of the venetian blinds is also investigated: (a) the sun profile angle, (b) the slat angle and (c) the venetian blind geometry. Moreover, the effect of the discretization of each slat is examined.

The estimation of water absorption in aggregates is still one of the major challenges related to the production of structural lightweight aggregate concrete (SLWAC). At present these predictions are only based on common practice and a more soundly based approach is required. Aggregate absorption is mainly affected by its microstructure, surface characteristics, percentage of broken particles, initial water content and characteristics of the surrounding mortar. These are the key parameters taken into account in this paper, where the absorption of different types of Iberian aggregates with varying initial water content is analysed in detail. Based on experimental tests, and by introducing new parameters which take into account the microstructure and water content of the aggregates, a new procedure for predicting absorption by aggregates in concrete is suggested. This procedure will make it possible to more accurately specify the amount of mixing water to be used in SLWAC production, and it is almost independent of the type of aggregate. Therefore, the proposed method should be easily extended to other types of aggregate. Finally, the proposed method was checked experimentally by producing several concrete mixtures, and the results were promising.

The main aim of this article is to evaluate, argue and criticise the design models and methods concerning the use of CFRP external flexural strengthening of concrete structures proposed in Fib bulletin 14 – Task Group Fib TG9.3 “External bonded reinforcement” [Fib bulletin 14, FIB TG 9.3 FRPEBR. Externally bonded FRP reinforcement for RC structures. Federation Internacionale du beton (Fib), Task Group 9.3 FRP, 2001. p. 130]. The three different approaches of flexural strengthening suggested in the above-mentioned document are checked by comparative studies based on different experimental works published by other researchers and analytical applications. By comparing analytical values with experimental results, we draw important conclusions related to: the evaluation of the suggested approaches in terms of complexity; adaptability to real case studies; accuracy of design models proposed in different approaches, and efficiency and general behaviour of CFRP flexural strengthening reinforcement.

In this paper the compressive strength of a wide range of structural lightweight aggregate concrete mixes is evaluated by the non-destructive ultrasonic pulse velocity method. This study involves about 84 different compositions tested between 3 and 180 days for compressive strengths ranging from about 30 to 80 MPa. The influence of several factors on the relation between the ultrasonic pulse velocity and compressive strength is examined. These factors include the cement type and content, amount of water, type of admixture, initial wetting conditions, type and volume of aggregate and the partial replacement of normal weight coarse and fine aggregates by lightweight aggregates. It is found that lightweight and normal weight concretes are affected differently by mix design parameters. In addition, the prediction of the concrete's compressive strength by means of the non-destructive ultrasonic pulse velocity test is studied. Based on the dependence of the ultrasonic pulse velocity on the density and elasticity of concrete, a simplified expression is proposed to estimate the compressive strength, regardless the type of concrete and its composition. More than 200 results for different types of aggregates and concrete compositions were analyzed and high correlation coefficients were obtained.