Preparation of C200green reactive powder concrete and its static–dynamic behaviors
Zhang Yunsheng *,Sun Wei,Liu Sifeng,Jiao Chujie,Lai Jianzhong
Jiangsu Key Laboratory for Construction Materials,Southeast University,Nanjing 210096,PR China
a r t i c l e i n f o Article history:
Received 30April 2006
Received in revid form 14June 2008Accepted 16June 2008
Available online 27June 2008
Keywords:C200
Green reactive powder concrete (GRPC)Static mechanical behavior Dynamic tensile behavior
a b s t r a c t
In this paper,a new type of green reactive powder concrete (GRPC)with compressive strength of 200
MPa (C200GRPC)is prepared by utilizing composite mineral admixtures,natural fine aggregates,short and fine steel fibers.The quasi-static mechanical properties (mechanical strength,fracture energy and fiber–matrix interfacial bonding strength)of GRPC specimens,cured in three different types of regimes (standard curing,steam curing and autoclave curing),are investigated.The experimental results show that the mechanical properties of the C200GRPC made with the cementitious materials consisting of 40%of Portland cement,25%of ultra fine slag,25%of ultra fine fly ash and 10%of silica fume,4%volume fraction of steel fiber are higher than the others.The corresponding compressive strength,flexural strength,fracture energy and fiber–matrix interfacial bonding strength are more than 200MPa,60MPa,30,000J/m 2and 14MPa,respectively.The dynamic tensile behavior of the C200GRPC is also investigated through the Split Hopkinson Pressure Bar (SHPB)according to the spalling phenomena.The dynamic testing results demonstrate that strain rate has an important effect on the dynamic tensile behavior of C200GRPC.With an increa of strain rate,the peak stress rapidly increas in the dynamic tensile stress–time curves.The C200GRPC exhibits an obvious strain rate stiffening effect in the ca of high strain rate.Finally,the mechanism of excellent static and dynamic properties gains of C200GRPC is also discusd.
Ó2008Elvier Ltd.All rights rerved.
1.Introduction
Reactive powder concrete (RPC)is an advanced cement bad material,which originally developed in the early 1990s by Bouy-gues’laboratory in France [1].RPC posss ultra-high static and dy-namic strength,high fracture capacity,low shrinkage and excellent durability under vere condition [1–4].The microstructure of RPC is optimized by preci gradation of all particles in the mix to yield maximum compactness [5–11].With the merits,RPC has a great potential prospect in the protective shelter of military engineering and nuclear waste treatment,which has received significant con-cerns from experts across the word [12–14].However,the high cost,complex fabrication technique and high energy demand of RPC verely limit its commercial development and application in the practical engineering [12,15,16].
It is well known that the major components of RPC commonly ud across the world include Portland cement,ultra fine quartz powder (6600l m),silica fume (accounting for 25%or greater weight of the total binders)and small sized steel fibers [17].Obvi-ously,the expensive raw materials are responsible for the high production cost.In addition,the rigorous curing regimes usually
employed in the production of RPC (200°C autoclave curing or 90°C heating curing)result in a very l
ow producing efficiency and high energy consumption [18,19].Therefore,how to increa the ratio of performance to cost is a key problem for the application of RPC in practical engineering.
penIn order to reduce the production cost of RPC,50–60%of Port-land cement is replaced by the cheap composite mineral admix-tures that consist of two or three types of components such as fly ash,slag,and a small dosage of silica fume (10%)in this study.The ultra fine quartz sand with the maximal diameter of 600l m is totally replaced by the least costly and easily obtained natural river sand with the maximal diameter of 3mm.A short and fine steel fiber with much lower price ($2500per ton)than the one ud by France is specially designed and manufactured in Guo Mao steel fiber company in Jiang Xi Province,PR China.In addition,three dif-ferent curing regimes:standard curing (20°C and 100%RH)with low energy consumption,steam curing (90°C heating curing)with medium energy consumption,and autoclave curing (200°C and 1.7MPa pressure)with high energy consumption,are systemati-cally investigated to explore the feasibility of less energy-intensive curing regimes for preparing a novel type of green reactive powder concrete with compressive strength of 200MPa (C200GRPC).
In the past veral decades,there has been an increasing inter-est in investigating the effect of strain rates on the mechanical
0958-9465/$-e front matter Ó2008Elvier Ltd.All rights rerved.doi:10.comp.2008.06.008
*Corresponding author.
E-mail address: (Z.Yunsheng).
Cement &Concrete Composites 30(2008)
831–838
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behavior of concretes under high speed impact load.However,most dynamic tests in the open literatures are related to dynamic compression.In fact,the destruction of concrete structures sub-jected to high speed impact loading is mainly attributed to a low dynamic tensile strength of the concrete,rather than a lack of dy-namic compressive strength.So it is very important to study the dynamic tensile behavior of concrete.However,little literature is available on dynamic tensile behavior of concrete due to the stress concentration and load eccentricity in conducting dynamic tensile tests [20–23].In order to solve the problems,a tensile wave re-flected from the incident compressive one at the free surface of concrete specimen by using Split Hopkinson Pressure Bar (SHPB)is ud to study the dynamic tensile behavior of the C200GRPC in this paper,which is also employed by Klepaczko and Brara [20].2.Experimental 2.1.Raw materials
Four types of cementitious materials are ud in this study:Portland cement (PC)with 28days of compressive strength of 68.9MPa,Silica Fume (SF),Ultra Fine Fly Ash (UFFA),and Ultra Fine Slag (UFSL).Their chemical compositions and physical properties are given in Table 1.
The natural river sand with the maximum size of 3mm is ud in this study to replace the ultra fine quartz sand,which is a nec-essary component to produce RPC reported by published litera-tures.The superplasticizer with the water reducing ratio of 35%produced by Cika Company in Guangzhou,PR China is ud.Steel fibers is specially designed and manufactured by Guo Mao Steel Fi-ber Company in Jiang Xi Province,PR China.The characteristic parameters of the steel fibers are:length (l f )=13mm,diameter (d f )=0.175mm,tensile strength =1800–2000MPa.2.2.Mixture proportions of GRPC
Three different GRPC matrices (M1,M2and M3)are designed.Their compositions are listed in Table 2.Portland cement (50–60%)is replaced by binary or ternary mineral admixtures of fly ash,slag and silica fume.Ultra fine quartz sand is totally replaced by natural river sand.In order to investigate the effect of steel fiber content on the quasi-static and dynamic mechanical properties of GRPC,the volume fraction (V f )of steel fibers is varied from 0%,2–4%.
2.3.Specimens preparation and curing
2.3.1.Specimens preparation
The cementitious materials (Portland cement and composite mineral admixtures)and river sand are first dry-mixed for 1min.Then the water and superplasticizer are put into the pre-mixed powders and mixed for another 3min.Finally,fiber is added into the mixture and mixed for 3min so that fibers are homogenously distributed throughout the fresh mortar.After that,the fresh GRPC paste is cast into steel moulds and compacted using a vibrating ta-ble.The specimens are stored in the conditions (20°C,100%RH)for 24h,then removed from the moulds,and cured in different curing regimes described in Section 2.3.2.
2.3.2.Curing
Three types of curing regimes are employed in the study:(1)Standard curing (curing 1):20°C and 100%RH for 28days.(2)Steam curing (curing 2):90°C and RH =100%for 24h.
lsat(3)Autoclave curing (curing 3):200°C and 1.7MPa pressure for
8h.
garage的音标2.4.Testing methods
2.4.1.Fiber–GRPC matrix interfacial bonding strength
‘‘Dumbbell”shaped specimen,as shown in Fig.1,is prepared to measure the fiber–GRPC matrix interfacial bonding strength according to the Chine standard testing method for steel fiber reinforced mortar.Nine fibers with the proportional spacing are placed in the middle ction of the fresh GRPC matrix along the longitude direction.The average interfacial bonding strength is cal-culated for nine fibers.
2.4.2.Flexural,compressive and tensile strength
Specimens for flexural and compressive tests are 40mm Â40mm Â160mm prisms.Flexural strength and compressive strength are tested according to GB177-85.At first,the three-point bending test is performed to obtain flexural strength.After bending test,the broken specimens with sizes of approximately 40mm Â40mm Â80mm are ud to conduct compressive test.Three sam-ples of each batch are tested.The average value is rved as the fin-ial flexural strength and compressive strength.A clod-loop
Table 1
Chemical composition and physical properties of the four cementitious materials Chemical compositions (%)PC SF UFFA UFSL SiO 220.694.555.034.2Fe 2O 3 4.40.8 5.90.4MgO 0.6 1.0 1.3 6.7Al 2O 3 5.00.331.314.2CaO 65.10.5 3.941.7SO 3 2.20.8 1.5 1.0LOI
1.3 1.0 1.0 1.7Specific surface area (m 2/kg)
417
2200
686
766
Table 2
Compositions of the three GRPC matrices No.PC (%)SF (%)UFFA (%)UFSL (%)Superplasticizer (%)W/B Binder to sand ratio M15002525 1.70.15 1.2M25010040 1.70.15 1.2M3
40
10
25
25
1.7
0.15
1.2
Fig.1.Interfacial bonding strength testing specimen.
832Z.Yunsheng et al./Cement &Concrete Composites 30(2008)831–838
rvohydraulically controlled materials testing machine (Sintech 10/D MTS 810)is ud to conduct flexural and compressive tests.As for tensile strength,similar method for measuring the fiber–GRPC matrix interfacial bonding strength is employed.The direct tensile test is performed on the ‘‘dumbbell”shaped specimen using MTS 810testing machine.Six specimens are prepared for each batch.The average value is ud as the final tensile strength.2.4.3.Fracture energy
The fracture energy can be obtained through three-point bend-ing test for the beam with a notch,as shown in Fig.2.The specimen (40mm Â40mm Â160mm)with a cave of 15mm depth in the middle is ud in this study.The testing span is 150mm and the rate of deformation is 0.02mm/min.The fracture energy G is given by the following equation
G ¼
R d max
Pd d þ12mg d max ð1Þ
where R d max
范玮琪和黑人婚纱照
0Pd d is the work of load P ;12
愚人节英语
mg d max is the work of spec-imen weight;m is the mass of a specimen;d is the deformation;b and h are the width and height of a specimen,and a is the depth of the notch.In this test,b =h =40mm,a =15mm.
2.4.4.Dynamic tensile test
Dynamic tensile test is performed by using SHPB tup on cyl-inder specimen with 70mm in diameter and 500mm in length.The ends of all specimens are carefully grounded in order to assure the parallelism of the end surfaces.A typical SHPB tup to study the dynamic behavior of concrete is outlined in Fig.3.It is com-
pod of gas launcher,projectile,Hopkinson bar and long speci-men.The projectile impact on the Hopkinson bar develops a compressive longitudinal incident wave.The incident wave is then transmitted into the concrete specimen,and a small part is re-flected back to the Hopkinson bar due to the difference of imped-ances.The compressive wave that is transmitted into the specimen is reflected by the specimen free end as a tensile wave.The super-position of the incident compressive wave and the reflected tensile one,generates a tensile stress that grows rapidly in time along the concrete specimen.Due to the wave superposition,the net tensile wave leads to spalling (tensile fract
ure)of the concrete specimen at a certain distance from the free end,where the tensile stress reaches the critical value.The whole process of wave propagation is recorded via the three strain gauges cemented to the Hopkinson bar surface at three specified distances.This arrangement allows for determination of the fracture stress caud by spalling,the stress history in the specimen,the critical time of loading,and the loading rate or strain rate.Dynamic tensile test is performed on C200GRPC with impact velocity between 4.0m/s and 14m/s.For each impact velocity,six specimens are tested.3.Results and discussion
3.1.Static mechanical properties of C200GRPC
3.1.1.Compressive strength
The compressive strengths of various GRPCs made with differ-ent matrices,fiber content,curing regimes and curing ages are measured and given in Fig.4a–d.As can be en in Fig.4a,the types of matrices have an important influence on the compressive strength.Comparing the three types of matrices (M1,M2,and M3),it can be obrved that the matrix M3incorporated with three kinds of ultra fine mineral admixtures (silica fume,fly ash,and slag)at the same time exhibits the highest compressive strength amongst the three types of matrices,who compressive strengths reach 141.
1,155.0,and 158.0MPa,respectively for matrix M3pre-pared under curing 1,curing 2,and curing 3.In addition,the incor-poration of small sized steel fiber,especially in the ca of high volume fraction of fiber,evidently improves the compressive strength of GRPC in various curing regimes,as shown in Fig.4b.The GRPCs with 4%fiber have approximately 30–50MPa increa compared to the GRPC matrices without fiber.As a result,the com-pressive strength of GRPCs can reach 200MPa under curing 1for 180days,or curing 2or curing 3.
Considering the standard curing uring 1(20°C,100%RH)is a gentler curing regime than curing 2and curing 3,the hydration reaction will continue to progress with the develop-ment of curing ages in a long period.In order to investigate the effect of curing ages,the compressive strength of various GRPCs are determined at ages of 28days,90days,and 180days,and dis-played in Fig.4c.It can be en that the compressive strength
has
Fig.2.Schematic diagram of fracture energy test.
Launcher
Projectile
Velocity measuring circuit
Specimen
SR
Dynamic strain apparatus
Data analyzing apparatus
Input bar
Z.Yunsheng et al./Cement &Concrete Composites 30(2008)831–838833
an obvious increa for various GRPCs when curing age increas from28days to90days.After90days,the further prolonging of curing age shows a relatively little strength gain.For example, the compressive strengths of matrix M3GRPC with4%fiber are 183.3,220.3,and228.3MPa at an age of28,90,and180days, respectively.There is a37MPa strength gain when curing age in-creas from28days to90days,while only8MPa gain from90 days to180days.Thus,from the viewpoint of time and energy sav-ing90days of curing ages is enough to achieve most of the ulti-mate strength.
The effects of different curing regimes are also investigated on compressive strength,as shown in Fig.4d.As can be en,GRPC under standard curing regime has the lowest strength.However, when steam curing is employed,compressive strength shows an obvious increa.Through24-hour steam curing,about15–30MPa compressive strength is further gained when compared to the28-day standard curing.Autoclave curing shows more attractive strength enhancement than stream curing.It is only through8-hour autoclave curing that over200MPa compressive strength is achieved for various GRPCs with3%or4%fiber.The above analysis indicates that elevating temperatures can signifi-cantly increa the hydration rate,accelerate rapid formation of hydration products,resulting in high early strength.Although autoclave curing is most effective in improving compressive strength among three types of curing regimes,its high energy con-sumption and complex operation limit the c
uring regime to be extensively applied in practical engineering.Comparatively stan-dard curing has such advantages as easy operation and lower en-ergy consumption.If the curing ages is reasonably prolonged, 200MPa compressive strength can also be achieved.
On basis of the above analysis,the GRPC with the compressive strength of200MPa or greater can be obtained by using60wt.% of ternary composite mineral admixtures consisting of10%silica fume,25%fly ash and25%slag;utilizing natural sand to totally re-place ultrafine quartz powder;incorporating3–4%volume frac-tion of specially designedfine steelfiber;and employing20°C, 100%RH of curing condition for90days.Compared to the RPC commonly ud across the world,the preparation of GRPC is cheaper,practical and easier.The advantages will make GRPC exhi-bit great potentials in thefields of civil engineering,military engi-neering,and nuclear waste treatment.
3.1.2.Flexural strength
Theflexural strengths of various GRPCs are shown in Fig.5(a–d). As can be en,the effects of matrix types,fiber content,curing re-gimes and curing ages on theflexural strength of various GRPCs show a similar tendency as compressive strength,but larger effect is true toflexural strength when compared to compressive strength.The GRPC made with matrix M3and4%fiber can gain 60MPaflexural strength under standard curing for90days.油泵型号
3.1.3.Fracture energy
The fracture energy is an important parameter to describe the resistance to cracking and deforming.The fracture energy of vari-ous GRPCs under curing2and curing3is determined and depicted in Fig.6.It can be en from Fig.6that the fracture energy exhibits a sharp increa when small sized steelfiber is incorporated.Com-paratively,thefiber content,curing regimes and types of matrices have a little influence on the fracture energy.For example,the frac-ture energy reaches31,300J/m2for GRPC with3%volume fraction
834Z.Yunsheng et al./Cement&Concrete Composites30(2008)831–838
offiber,while only0.183J/m2for GRPC withoutfiber.When thefi-ber volume fraction increas from3%to4%,the fracture energy only has an800J/m2gain.
3.1.
4.Interfacial bonding strength
The interfacial bonding strength is one of the important indices to evaluate the bonding property betweenfibers and matrix.Gen-erally,higherfiber–matrix interfacial bonding strength is expected for higherflexural and tensile strengths.The experimental results are shown in Fig.7.As can be en in Fig.7,the types of matrices and the curing regimes,especially for the latter,have a significant impact on thefiber–matrix interfacial bonding strength.The inter-facial bonding strength follows the order:M3>M2>M1and cur-ing3>curing2>curing1.M3matrix cured under curing3can gain the highest interfacial bonding strength,which is14.2MPa.
3.2.Dynamic tensile behavior of C200GRPC
Bad on the experimental results of static mechanical tests,it can be conclude that M3matrix exhibit
s superior mechanical prop-erties(compressive,flexural strengths,fracture energy,and inter-facial bonding)to M1and M2matrices.Thus,it is chon as the optimum C200GRPC matrix and is ud to conduct the dynamic tensile test.
In order to determine the dynamic tensile strength of C200 GRPC,different impact velocity is ud in the range of4–14m/s.
Z.Yunsheng et al./Cement&Concrete Composites30(2008)831–838835
skilletFigs.8–10shows the tensile stress vs.time curve of C200GRPC un-der different impact velocity.When performing the dynamic ten-sile test,the lowest impact 4m/s is first employed,then gradually increa the impact velocity up to the highest im-pact velocity 14m/s.Once one small visible crack is obrved,the corresponding peak stress is recorded and rved as the mini-mal dynamic tensile strength.Table 3shows the peak stress at dif-ferent impact velocity.The minimal dynamic tensile strength is also marked with asterisk,as shown in Table 3.For the purpo of the comparison,the corresponding quasi-static tensile strength is also given in Table 3.In addition,the photos of the C200GRPC are also taken after dynamic tensile tests,as shown in Fig.11.Re-sults show that:r the dynamic tensile strength increas obvi-ously with an increa of impact velocity,which shows high strain rate nsitivity.s the minimal dynamic tensile strength is higher than quasi-static strength,especially for the GRPCs with high fiber content.t the incorporation of steel fiber shows an obvious strength improvement on GRPC matrix.The dynamic ten-sile strength of fiber reinforced GRPC is much larger than that of GRPC matrix without fiber.The failure characteristic of GRPC with fiber is totally different from that of GRPC matrix without fiber:the failure surface is very coar and zigzag for GRPC with fiber.In con-trast,a flat surface can be clearly en for GRPC matri
x without fi-ber.Furthermore,the damage of RPC matrix is also more rious than that of fiber reinforced ones under the same impact velocity.3.3.Mechanism of excellent static and dynamic properties gains of C200GRPC
The above static and dynamic tests show C200GRPC made with 50–60%composite mineral admixtures,natural river sand and standard curing regime (20°C,90%RH),posss excellent static and dynamic properties.The gains of the excellent properties are mainly attributed to two aspects:One is from the compacted matrix made with different types and amounts of ultra fine com-posite mineral admixtures such as silica fume,fly ash and slag.the other is from small sized steel fibers.
3.3.1.Contribution of GRPC matrix
The water-binder ratio of the GRPC matrix prepared in this study is very low,only 0.15,resulting in a very compacted paste after tting and hardening.In addition,60wt.%of composite min-eral admixtures in cementitious matrix could not be ignored.Dur-ing the process of microstructure formation,the compact packing and filling effect,the pozzolanic effect and micro-aggregate effect of the composite mineral admixtures make GRPC matrix denr,lower porosity and less macro-defects,as compared with the one
without mineral admixture incorporation.The effects will fur-ther improve with the development of curing ages,especially in the ca of standard curing regime (curing 1),which results in higher compressive and tensile strength gains when cured under curing 1for 180days than the ones cured under the other two cur-ing regimes.It should be noted that the micro-aggregate effect of fly ash plays an important role at later stages.It is becau only about 20%of the total fly ash that will takes part in pozzolanic reaction,the remaining fly ash particles act as micro-aggregates
Table 3
Dynamic tensile experimental results of C200GRPC with and without fiber Types of GRPCs
Dynamic tensile strength Static tensile strength (MPa)
Impact speed (m/s)
Peak strength (MPa)C200GRPC matrix
6.23 5.83* 5.0
4.09 3.184.01 2.79C200GRPC with 3%fiber
11.0013.92*9.7
10.8113.1710.5512.077.8311.164.259.72C200GRPC with 4%fiber
intuition13.1915.1110.2
resume是什么意思
12.3514.26*11.9314.128.3811.174.56
header card
10.37
Note :The minimum dynamic tensile strength is marked with*asterisk.
836Z.Yunsheng et al./Cement &Concrete Composites 30(2008)831–838
