The possibility of the use of recycled aggregates from the construction industry in green concrete production is of increasing importance to reduce the negative environmental impact associated with construction and de...The possibility of the use of recycled aggregates from the construction industry in green concrete production is of increasing importance to reduce the negative environmental impact associated with construction and demolition wastes.The objective of this study is to investigate the effect of recycled concrete aggregate(RCA)quality on the properties of hardened concrete properties such as compressive strength,splitting tensile strength,density,water absorption capacity and porosity accessible to water.The RCA used in this study was obtained from the crushing of waste concrete with two different compressive strengths(LRCA obtained from the crushing of waste concrete having compressive strengths below 30 MPa and HRCA obtained from the crushing of waste concrete having compressive strengths above 30 MPa).The natural coarse limestone aggregate was 100%replaced with coarse LRCA and HRCA.As a result of the study,the use of 100%HRCA and%100 LRCA instead of limestone coarse aggregate in the concrete adversely affected its mechanical and physical properties.In addition,HRCA showed better performance in terms of compressive strength,tensile strength,water absorption and porosity compared to the use of LRCA.Furthermore,the percentage of adhered mortar on the surface of LRCA and HRCA was analyzed using a computerized micro tomography device,and it was found that the percentages of attached mortar and aggregates are 61%and 35.5%for LRCA,whilst the attached mortar and aggregate contents for HRCA are 45.9%and 53.7%,respectively.展开更多
Self-compacting concrete(SCC)is a type of concrete which is frequently preferred in different applications due to its advantages such as its fluidity and transition in tight openings between steel reinforcing bars.How...Self-compacting concrete(SCC)is a type of concrete which is frequently preferred in different applications due to its advantages such as its fluidity and transition in tight openings between steel reinforcing bars.However,it is vital that SCC maintains its fresh state characteristics when its transportation phase is taken into consideration.Fiber reinforced in SCC affects the properties of fresh concrete negatively while it had a positive effect on its dynamic properties.In this study,the effect of steel fibers having different aspect ratios on the time dependent fresh properties and mechani-cal properties of self-compacting concrete mixtures was investigated.In addition to the control mixture without fiber,in the mixtures containing fiber,three different twin-hook steel fibers with aspect ratios of 54,64 and 50 were used as 0.6%of total volume.In all of the SCC mixtures,the water/cement ratio,cement dosage and slump-flow value were kept constant.The time dependent rheological properties of the mixtures were investigated.The compressive,split-tensile and flexural strengths as well as fracture energy,the load deflection relation under flexural load and load-crack opening displacement,modulus of elasticity of SCC mixtures were also investigated.Besides,the water absorption capacity and depth of penetration of water under pressure of mixtures were measured.On the basis of the results,the fiber utilization and its aspect ratio had no significant effect on compressive strength and modulus of elasticity of the SCC mixtures.The split-tensile,flexural strengths and fracture energy of SCC mixtures increased by using fiber;the permeability properties of SCC mixture increased by fiber utilization.展开更多
The aim of this study is to determine the radon and natural radioactivity concentra-tions of some building materials and to assess the radiation hazard associated with those mortar materials when they are used in the ...The aim of this study is to determine the radon and natural radioactivity concentra-tions of some building materials and to assess the radiation hazard associated with those mortar materials when they are used in the construction of dwellings.Radon measurements were realized by using LR-115 Type 2 solid state nuclear track detec-tors.Radon activity concentrations of these materials were found to vary between 130.00±11.40 and 1604.06±40.5 Bq m^(-3).The natural radioactivity in selected mortar materials was analyzed by using scintillation gamma spectroscopy.The activity concentrations for 226Ra,232Th and 40K for the studied mortar materials ranged from ND to 48.5±7.0 Bq kg^(-1),ND to 41.0±6.4 Bq kg^(-1)and ND to 720.4±26.8 Bq kg^(-1),respectively.Radium equivalent activities,external and internal hazard indexes,gamma and alpha indexes and absorbed gamma dose rates were calculated to assess the radiation hazard of the natural radioactivity in studied samples.The calculated Raeq values of all samples were found to be lower than the limit of 370 Bq kg-1 set for building materials.The estimated hazard index values were found to be under the unity and the absorbed dose rate values were also below the worldwide average of 84 nGy h^(-1).展开更多
In this study,the effects of recycled glass(RG)and recycled concrete(RC)fine aggregates on the drying-shrinkage,carbonation,high temperature and abrasion resistance of mortar mixtures were investigated comparatively.I...In this study,the effects of recycled glass(RG)and recycled concrete(RC)fine aggregates on the drying-shrinkage,carbonation,high temperature and abrasion resistance of mortar mixtures were investigated comparatively.In addition,durability performance of the mortar mixtures was investigated through micro-structural analysis.For this purpose,9 different mortar mixtures were prepared by replacing 25,50,75 and 100 wt.%of crushed-limestone fine aggregate with recycled glass and recycled concrete aggregates.Except for the abrasion resistance,the RG mixtures showed better durability performance than the control mixture.However,the RC mixtures containing more than 50%recycled aggregate showed lower performance than the control mixture.展开更多
Cement is the most consumed building material in the world.However,cement manufacture is responsible for 5-7%of the world CO_(2)emissions.In this paper,cement was partially replaced by styrene-butadiene rubber(SBR)pol...Cement is the most consumed building material in the world.However,cement manufacture is responsible for 5-7%of the world CO_(2)emissions.In this paper,cement was partially replaced by styrene-butadiene rubber(SBR)polymeric latex in order to reduce cement consumption.Besides,effects of SBR addition on the strength and physical properties of plain mortar exposed to three different curing regimes are presented.Three different curing regimes were applied to the 40×40×160 mm prismatic mortar specimens:(Ⅰ):Specimens were cured in water until the test age(CW),(Ⅱ):after demoulding,specimens were immersed in water for 2 days and kept in ambient temperature until the time of the test(2DWA)and(Ⅲ)involved 2 days of water curing followed by 1 day in an oven at 50℃and subsequentely placing in ambient temperature until the test time(2W1OA).Results showed that combin-ing 2 days of water curing followed by ambient temperature curing(2DWA)along with 3%SBR polymer content showed good performance in terms of compressive strength,water absorption and void content.Moreover,a good performance in terms of flexural strength was observed by combining 2W1OA curing regime with 2%SBR content.However,the detrimental effect of water curing regime(CW)in terms of compressive and flexural strength was also observed with the increase of SBR ratio.展开更多
Steel micro fibers provide strengthening,toughening and durability improve-ment mechanisms in cementitious composites.However,there is not much data in the literature regarding how the extent of their effectiveness ch...Steel micro fibers provide strengthening,toughening and durability improve-ment mechanisms in cementitious composites.However,there is not much data in the literature regarding how the extent of their effectiveness changes depend-ing on the type of matrix being reinforced.For clarifying this point,the influ-ence of a constant volumetric ratio(1%)of 6 mm long steel micro fibers on the performance of 5 mortar mixtures was investigated and were prepared using plain,binary and ternary cementitious systems.A total of 10 mixtures were cast.The mineral admixtures used in the study include silica fume(SF),metakaolin(MK)and a Class C fly ash(FA).While the replacement levels of SF and MK were 10%by weight of the total mass of the binder,this ratio was chosen as 30%for FA.In addition to the behavior of the mixtures under compressive,flexural and impact loads,abrasion,water absorption,chloride ion penetration,freez-ing-thawing resistance and drying shrinkage characteristics of the mixtures were determined.Test results indicate that generally the refinement in the pore struc-ture of the matrix provided by mineral admixtures and the increase in resistance against growth and coalescence of micro-cracks provided by fibers produce a syn-ergistic effect and improve the investigated performances of the mixtures.展开更多
Portland cement is extensively used as a binder in concrete production.However,with Portland cement production,5%of the natural resources used in this produc-tion are consumed,constituting 5-7%of the total CO_(2)emiss...Portland cement is extensively used as a binder in concrete production.However,with Portland cement production,5%of the natural resources used in this produc-tion are consumed,constituting 5-7%of the total CO_(2)emission.In order to mitigate the environmental problems associated with cement production,styrene-butadiene rubber latex was used as cement replacement up to 20%.In this study,compres-sive strength,flexural strength,unit weight,water absorption,open porosity,water sorptivity and the chloride ion permeability of Portland cement mortar mixtures modified by styrene-butadiene rubber(SBR)polymeric latex were investigated.For this purpose,the sand/cement ratio and the water/cement ratio were kept constant as 3/1 and 0.5,respectively.In addition to the control mixture containing no polymer,1,2,3,5,10 and 20 wt.%of cement was replaced with SBR.In this way,seven mortar mixtures were prepared.Mixed curing(wet cure and dry cure)method was applied to the mortar specimens.Results showed that up to a 5%replacement level,it is possible to improve the mechanical properties of cement mortars with SBR latex addition.However,at a 10%and 20%replacement level,SBR had a signifi-cant detrimental effect on the mechanical properties of polymer modified mortars.However,the transport properties decreased with the incorporation rate of SBR latex and the detrimental effect of SBR replacement was more pronounced in 20%SBR mortar mixtures.展开更多
The effect of cement fineness on the fresh state and rheological properties as well as compressive strength of cementitious systems was investigated.A CEM I 42.5R portland cement containing 7.92%C_(3)A and sulfate res...The effect of cement fineness on the fresh state and rheological properties as well as compressive strength of cementitious systems was investigated.A CEM I 42.5R portland cement containing 7.92%C_(3)A and sulfate resisting cement containing 3.58%C(3)A were used.The cements were ground to 4 different Blaine finenesses,ranging from 2800 to 4500 cm^(2)/g.In the absence of water-reducing admixture,the water requirement of mixtures increased with an increase in the cement fineness.Thus,the fresh state properties of the mixtures were affected negatively.However,surprisingly,a reverse behavior was observed in the mixtures containing water-reducing admixtures,that is,an increase of the cement fineness increased the effectiveness of the admixture;consequently,the fresh state properties of the mixtures were improved.This seems to have been caused from the higher adsorption of the admixture on finer cement grains than on the coarser particles.Moreover,as expected,the strength of the mortar and concrete mixtures increased along with the increase in cement fineness and its C3A content.展开更多
Despite the large variations in the behaviors of water-reducing admixtures upon changes in their structures,most previous reports on the cement-admixture compatibility did not provide suficient information on the stru...Despite the large variations in the behaviors of water-reducing admixtures upon changes in their structures,most previous reports on the cement-admixture compatibility did not provide suficient information on the structure of the admixture.Hence,the evaluation and generalization of the reports on the cement-admixture compatibility are challenging.In this study,three different polycarboxylate-ether-based water-reducing admixtures with the same free nonionic content,anionic/nonionic molar ratio,and main chain length and different side chain lengths were produced.The compatibility of these admixtures with a CEM I 42.5R-type cement was investigated.In addition,an analysis of variance was performed on the experiment results to evaluate the contributions of the admixture type,admixture/cement ratio,and elapsing time to the Marsh funnel flow time,mini-slump,slump flow,and compressive strength.The water-reducing admixtures having long or short side chains reduced the initial flow characteristics of the cementitious systems.However,the admixture having the shortest side chain was better with regard to flow retention.The side chain length of the admixture did not have significant effects on the compressive strength and water absorption capacity of the mortar mixtures and mini-slump performances of the cement paste mixtures.Regarding the behaviors of the admixtures in the cementitious systems,an optimal admixture side chain molecular weight is proposed.展开更多
文摘The possibility of the use of recycled aggregates from the construction industry in green concrete production is of increasing importance to reduce the negative environmental impact associated with construction and demolition wastes.The objective of this study is to investigate the effect of recycled concrete aggregate(RCA)quality on the properties of hardened concrete properties such as compressive strength,splitting tensile strength,density,water absorption capacity and porosity accessible to water.The RCA used in this study was obtained from the crushing of waste concrete with two different compressive strengths(LRCA obtained from the crushing of waste concrete having compressive strengths below 30 MPa and HRCA obtained from the crushing of waste concrete having compressive strengths above 30 MPa).The natural coarse limestone aggregate was 100%replaced with coarse LRCA and HRCA.As a result of the study,the use of 100%HRCA and%100 LRCA instead of limestone coarse aggregate in the concrete adversely affected its mechanical and physical properties.In addition,HRCA showed better performance in terms of compressive strength,tensile strength,water absorption and porosity compared to the use of LRCA.Furthermore,the percentage of adhered mortar on the surface of LRCA and HRCA was analyzed using a computerized micro tomography device,and it was found that the percentages of attached mortar and aggregates are 61%and 35.5%for LRCA,whilst the attached mortar and aggregate contents for HRCA are 45.9%and 53.7%,respectively.
基金support provided by Bursa Uludag University Scientific Research Projects Centre(BAP)under grant number KUAP(MH)-2017/11 and AYP(MH)-2016/16.
文摘Self-compacting concrete(SCC)is a type of concrete which is frequently preferred in different applications due to its advantages such as its fluidity and transition in tight openings between steel reinforcing bars.However,it is vital that SCC maintains its fresh state characteristics when its transportation phase is taken into consideration.Fiber reinforced in SCC affects the properties of fresh concrete negatively while it had a positive effect on its dynamic properties.In this study,the effect of steel fibers having different aspect ratios on the time dependent fresh properties and mechani-cal properties of self-compacting concrete mixtures was investigated.In addition to the control mixture without fiber,in the mixtures containing fiber,three different twin-hook steel fibers with aspect ratios of 54,64 and 50 were used as 0.6%of total volume.In all of the SCC mixtures,the water/cement ratio,cement dosage and slump-flow value were kept constant.The time dependent rheological properties of the mixtures were investigated.The compressive,split-tensile and flexural strengths as well as fracture energy,the load deflection relation under flexural load and load-crack opening displacement,modulus of elasticity of SCC mixtures were also investigated.Besides,the water absorption capacity and depth of penetration of water under pressure of mixtures were measured.On the basis of the results,the fiber utilization and its aspect ratio had no significant effect on compressive strength and modulus of elasticity of the SCC mixtures.The split-tensile,flexural strengths and fracture energy of SCC mixtures increased by using fiber;the permeability properties of SCC mixture increased by fiber utilization.
基金funded by the Scientific and Technological Research Council of Turkey(Project number:214M039).
文摘The aim of this study is to determine the radon and natural radioactivity concentra-tions of some building materials and to assess the radiation hazard associated with those mortar materials when they are used in the construction of dwellings.Radon measurements were realized by using LR-115 Type 2 solid state nuclear track detec-tors.Radon activity concentrations of these materials were found to vary between 130.00±11.40 and 1604.06±40.5 Bq m^(-3).The natural radioactivity in selected mortar materials was analyzed by using scintillation gamma spectroscopy.The activity concentrations for 226Ra,232Th and 40K for the studied mortar materials ranged from ND to 48.5±7.0 Bq kg^(-1),ND to 41.0±6.4 Bq kg^(-1)and ND to 720.4±26.8 Bq kg^(-1),respectively.Radium equivalent activities,external and internal hazard indexes,gamma and alpha indexes and absorbed gamma dose rates were calculated to assess the radiation hazard of the natural radioactivity in studied samples.The calculated Raeq values of all samples were found to be lower than the limit of 370 Bq kg-1 set for building materials.The estimated hazard index values were found to be under the unity and the absorbed dose rate values were also below the worldwide average of 84 nGy h^(-1).
文摘In this study,the effects of recycled glass(RG)and recycled concrete(RC)fine aggregates on the drying-shrinkage,carbonation,high temperature and abrasion resistance of mortar mixtures were investigated comparatively.In addition,durability performance of the mortar mixtures was investigated through micro-structural analysis.For this purpose,9 different mortar mixtures were prepared by replacing 25,50,75 and 100 wt.%of crushed-limestone fine aggregate with recycled glass and recycled concrete aggregates.Except for the abrasion resistance,the RG mixtures showed better durability performance than the control mixture.However,the RC mixtures containing more than 50%recycled aggregate showed lower performance than the control mixture.
文摘Cement is the most consumed building material in the world.However,cement manufacture is responsible for 5-7%of the world CO_(2)emissions.In this paper,cement was partially replaced by styrene-butadiene rubber(SBR)polymeric latex in order to reduce cement consumption.Besides,effects of SBR addition on the strength and physical properties of plain mortar exposed to three different curing regimes are presented.Three different curing regimes were applied to the 40×40×160 mm prismatic mortar specimens:(Ⅰ):Specimens were cured in water until the test age(CW),(Ⅱ):after demoulding,specimens were immersed in water for 2 days and kept in ambient temperature until the time of the test(2DWA)and(Ⅲ)involved 2 days of water curing followed by 1 day in an oven at 50℃and subsequentely placing in ambient temperature until the test time(2W1OA).Results showed that combin-ing 2 days of water curing followed by ambient temperature curing(2DWA)along with 3%SBR polymer content showed good performance in terms of compressive strength,water absorption and void content.Moreover,a good performance in terms of flexural strength was observed by combining 2W1OA curing regime with 2%SBR content.However,the detrimental effect of water curing regime(CW)in terms of compressive and flexural strength was also observed with the increase of SBR ratio.
文摘Steel micro fibers provide strengthening,toughening and durability improve-ment mechanisms in cementitious composites.However,there is not much data in the literature regarding how the extent of their effectiveness changes depend-ing on the type of matrix being reinforced.For clarifying this point,the influ-ence of a constant volumetric ratio(1%)of 6 mm long steel micro fibers on the performance of 5 mortar mixtures was investigated and were prepared using plain,binary and ternary cementitious systems.A total of 10 mixtures were cast.The mineral admixtures used in the study include silica fume(SF),metakaolin(MK)and a Class C fly ash(FA).While the replacement levels of SF and MK were 10%by weight of the total mass of the binder,this ratio was chosen as 30%for FA.In addition to the behavior of the mixtures under compressive,flexural and impact loads,abrasion,water absorption,chloride ion penetration,freez-ing-thawing resistance and drying shrinkage characteristics of the mixtures were determined.Test results indicate that generally the refinement in the pore struc-ture of the matrix provided by mineral admixtures and the increase in resistance against growth and coalescence of micro-cracks provided by fibers produce a syn-ergistic effect and improve the investigated performances of the mixtures.
文摘Portland cement is extensively used as a binder in concrete production.However,with Portland cement production,5%of the natural resources used in this produc-tion are consumed,constituting 5-7%of the total CO_(2)emission.In order to mitigate the environmental problems associated with cement production,styrene-butadiene rubber latex was used as cement replacement up to 20%.In this study,compres-sive strength,flexural strength,unit weight,water absorption,open porosity,water sorptivity and the chloride ion permeability of Portland cement mortar mixtures modified by styrene-butadiene rubber(SBR)polymeric latex were investigated.For this purpose,the sand/cement ratio and the water/cement ratio were kept constant as 3/1 and 0.5,respectively.In addition to the control mixture containing no polymer,1,2,3,5,10 and 20 wt.%of cement was replaced with SBR.In this way,seven mortar mixtures were prepared.Mixed curing(wet cure and dry cure)method was applied to the mortar specimens.Results showed that up to a 5%replacement level,it is possible to improve the mechanical properties of cement mortars with SBR latex addition.However,at a 10%and 20%replacement level,SBR had a signifi-cant detrimental effect on the mechanical properties of polymer modified mortars.However,the transport properties decreased with the incorporation rate of SBR latex and the detrimental effect of SBR replacement was more pronounced in 20%SBR mortar mixtures.
文摘The effect of cement fineness on the fresh state and rheological properties as well as compressive strength of cementitious systems was investigated.A CEM I 42.5R portland cement containing 7.92%C_(3)A and sulfate resisting cement containing 3.58%C(3)A were used.The cements were ground to 4 different Blaine finenesses,ranging from 2800 to 4500 cm^(2)/g.In the absence of water-reducing admixture,the water requirement of mixtures increased with an increase in the cement fineness.Thus,the fresh state properties of the mixtures were affected negatively.However,surprisingly,a reverse behavior was observed in the mixtures containing water-reducing admixtures,that is,an increase of the cement fineness increased the effectiveness of the admixture;consequently,the fresh state properties of the mixtures were improved.This seems to have been caused from the higher adsorption of the admixture on finer cement grains than on the coarser particles.Moreover,as expected,the strength of the mortar and concrete mixtures increased along with the increase in cement fineness and its C3A content.
基金The authors express their sincere gratitude to the Scientific and Technological Research Council of Turkey(Grant No.219M425)Bursa Uludag University Science and Technology Center(Grant Nos.AYP(MH)-2016/16,DDP(MH)-2018/9,and DDP(MH)-2019/15).The first author thanks TUBITAK for the scholarship provided by Grant No.217M408 during his PhD study.The authors would like to acknowledge Polisan Construction Chemicals Company and Bursa Ready Mixed Concrete for the provision of the materials and information on their properties.
文摘Despite the large variations in the behaviors of water-reducing admixtures upon changes in their structures,most previous reports on the cement-admixture compatibility did not provide suficient information on the structure of the admixture.Hence,the evaluation and generalization of the reports on the cement-admixture compatibility are challenging.In this study,three different polycarboxylate-ether-based water-reducing admixtures with the same free nonionic content,anionic/nonionic molar ratio,and main chain length and different side chain lengths were produced.The compatibility of these admixtures with a CEM I 42.5R-type cement was investigated.In addition,an analysis of variance was performed on the experiment results to evaluate the contributions of the admixture type,admixture/cement ratio,and elapsing time to the Marsh funnel flow time,mini-slump,slump flow,and compressive strength.The water-reducing admixtures having long or short side chains reduced the initial flow characteristics of the cementitious systems.However,the admixture having the shortest side chain was better with regard to flow retention.The side chain length of the admixture did not have significant effects on the compressive strength and water absorption capacity of the mortar mixtures and mini-slump performances of the cement paste mixtures.Regarding the behaviors of the admixtures in the cementitious systems,an optimal admixture side chain molecular weight is proposed.
