Flexural Behavior of Reactive Powder Concrete with Hybrid Section T- Beams

Reactive powder concrete (RPC) is unique of the present and greatest signicant improvements in constructions eld, it has usual excessive kindness happening current duration in the world owing toward its higher concrete properties, great ductility, durability, shrinkage, great opposition to corrosion and abrasion. In this experimental investigation is carried out on the way to revision the RPC exural activity with Hybrid Segment T- Beams and the mechanical characteristics of this building material. In order to analyze the belongings of steel ber volumetric ratio, silica fume ratio, tensile steel ratio, hybrid section on RPC T-beam exural eciency, the experimental program included testing ve beams. The study was focused on determining the load-deection behavior, letdown mode, strain supply across the depth of the beams and crack pattern at failure. The results of the volumetric ratio of steel bers and the silica fume ratio were also considered in studying the mechanical properties of RPC mixes. Moreover, a study of hybrid beams showed that use of RPC web and normal concrete in ange eciently improves the performance of T-beams compared to normal concrete T-beams with a percentage rise of 12 percent and hybrid beams have also shown that the use of RPC ange and normal concrete in web eciently improves the display of T-beams associated to regular concrete T-beams with percentages increase of 28%.


INTRODUCTION
Reactive powder concrete (RPC) is unique of the informed and best significant improvements in concrete equipment , it has established excessive consideration in current years in the world owing toward its higher mechanical properties [1,2].RPC is also recognized as ultra high enactment concrete (UHPC) allowing to its more structural presentation.It involves of great measure of cement , fine sand with particle size less than 600 µm , silica fume , fibers, low w/c ratio (less than 0.2) , new generation of superplasticizers and on no account coarse aggregate [3].RPC is quickly rising as an outstanding alternative to conventional concrete and even high strength concrete in many important structural submissions such as bridges, factories and power stations; therefore, there is increasing need to understanding the mechanical properties and structural behavior of this novel production material.Behavior of RPC beams is one of the fields which requires more studies because until this time there are quiet insufficient researches dealing with this field and there is surely absence of evidence about the analysis and design of RPC structural members.Therefore, this paper aims at studying experimentally and theoretically the flexural behavior of simply supported RPC T-beams under static load.In addition, some significant mechanical properties of RPC combination, are also experimentally recognized which institute data needed for the analysis and design of RPC structural members.Reactive powder concrete is a type of concrete which shows superior mechanical and durability properties, this goes to its elements (types and proportions), mixing efficiency, pressing after placing and curing regime.Each step of preparing RPC and each one of RPC components play key and significant part in getting high recital concrete [4] .In 2004, Chan and Chu [5] studied the conclusion of appearances in RPC, containing bond strength , pullout energy ,etc.Various silica fume contents ranging from 0% to 40% were used in the mix proportions Based on the results of bond strength and pullout energy, the optimal silica fume-cement ratio was found to be in between 20% and 30%, given the conditions of this experimental program .At the optimal silica fume dosage (30%), the pullout energy was increased by approximately 100%, whereas the bond strength was increased by 14%.The difference can be attributed to the dissimilar mechanisms of silica fume on supplement energy and on bond strength.In 2007, Gao [6] planned the influence of dynamic loads on the properties of plain RPC and fibers reinforced RPC.The test program included two types of case ; concrete cylinder with dimension height and diameter (150mm×75mm) and small beams with dimension depth, width and length (280mm×70mm× 70mm) with a span of 210mm, The addition of 1.5 %( by volume) of steel fiber significantly increased the flexure strength of RPC.However, there are no helpful belongings on solidity under quasi static and higher rate loading.In 2008, Hoang et al [7] considered guidance of ultra high by using steel fibers enactment concrete (modified RPC, the investigation consequences exhibited that flexural strength and hardiness of excessive enactment concrete is amended by adding of steel fibers.In 2010, Prabha et al [8] planned stress-strain properties of RPC under uniaxial compression.All the tests were approved out on concrete cylinder specimens of size (diameter=100 mm and height= 200mm) in the Universal Testing Machine.Two types of steel fibers ((L ƒ /d ƒ =6/0.16 and 13/0.16) and various dosages of steel fibers (0%,1% and 2% for 13mm, while 1%,2% and 3% for 6mm and a arrangement of 1% of 6mm and 1% of 13 mm and to end a amalgamation of 1% of 6mm and 2% of 13mm) were used in RPC mix.The trials also showed that the elastic modulus of RPC mixes was found to be 21 %( for 2%-6mm) to 24 %( for 2%-13mm) higher than that of RPC without fibers.It was settled that the ratio of ultimate to peak strain was the highest for fibers permutation of 2% 13mm and 1%6mm (4.65) following by 2%13mm (3.81) mix and 3% 6mm (3.73) mixes.The crack pattern confirmations realization of vertical cracks for lower percentages of small fibers reinforcement and diagonal cracks for higher percentages of fibers reinforcement.3% of 6mm and 2% of 13mm seemed to be the optimal fibers contents for RPC as observed from the results gained in this revision.In 2010 Hannawayya [9] offered investigation to study the effects RPC on the concrete properties as a material as well as reviewing the flexural performance of RPC rectangular section beams.The investigational database involved investigating that conclusion of consequence steel fibers volumetric ratio (V f ) and the content silica fume (SF) on some imperative properties of RPC such as compressive strength, uniaxial stress-strain relationship in solidity, splitting tensile strength and modulus of rupture.Supplementary investigational trials were also directed to training the result of V f , SF and longitudinal steel bar ratio (ρ) on the flexural behavior (in terms of load-deflection response, moment-curvature response, failure load and cracking pattern) of simply supported separately reinforced RPC beam having dimensions of 140×125×1400 mm under symmetrical two point load.This research offerings investigational revision on flexural behavior of simply supported RPC T-beams Hybrid Section under simple static load effect as well as studying some important mechanical properties of RPC.In this research, four beams were confirmed to exercise the consequence of steel fibers volumetric ratio (V f ), silica fume ratio (SF), hybrid section on the flexural performance of singly reinforced RPC Tbeams.

Materials: 2.1 Cement:
The castoff in this effort is Iraqi conventional Portland cement (Taasluja) type (I).It is stowed in impermeable plastic containers to evade exposure to altered atmospheric conditions.This cement is tested and checked allowing to the Iraqi Standard Specification (IOS 5:1984) [10].Tables (1) and ( 2) show the chemical and physical properties of this cement.It imitates to the Iraqi specifications.

Silica Fume:
A gray densified silica fume was cast-off, which was introduced from Sika company.Silica fume is an awfully fine dust, its elements are periods minor than cement atoms, continuously cast-off in minor percentage all as incomplete replacement of cement or as an preservative (as cast-off in the current effort) to develop properties.Table (9), chemical is given conformations of silica fume castoff happening this research .The silica fume obeys to the supplies of ASTM C1240-04 [12].

Superplasticizer (S.P.):
A great enactment concrete superplasticizer (entitled High Range Water Reduction Agent HRWRA) established, which is recognized commercially as Glenium 51, is castoff in this revision.Glenium 51 is unrestricted from chlorides and obeys with ASTM C494 type a [13].Table (10) shows the properties of Glenium 51.

Steel Fibers:
High enactment steel fibers were castoff in this investigation, Allowing to ASTM-A820-04 [14], this type of steel fibers is classified as (Type I).Its properties are listed in Table (11).

Steel Bars:
insignificant diameter (ϕ12mm) were castoff as tension reinforcement, while (ϕ6mm) warped steel bars were castoff as stirrups and (ϕ6mm) as oblique reinforcement of flange.The tensile experiments for all these bars are recorded in Table (12).from each nominal diameter are tested to define the average yield stress (f y ) and the ultimate strength (f u ).The investigation consequences of bars (ϕ12mm) satisfy ASTM A615 requirements [15].The test results are, as follows: A typical concrete mixture involving of cement, fine aggregate, coarse aggregate, and water were cast-off to cast the normal and web in hybrid beams (Normal, PRC1, PRC2 and PRC3 ).Control sample in the form of cylinders and prisms were also cast from this mixture.The ( w/c) of this combination was 0.45 and the sizes of cement, fine aggregate and coarse aggregate were 1:1.5:3 (by weight) respectively.

Reactive Powder Concrete Mixes:
Five RPC mixtures were castoff in this revision.Supplies quantities of all mix are recorded in table (13).Several mix proportions were tried to get maximum compressive strength conferring to ASTM C39 [ 16] .The variables castoff in these mixes were the percentage of silica fume ratio (three percentages of silica fume as additive were used 15, 20 and 25%) and the volume ratio of steel fibers (three volume ratios were considered 0, 1 and 2%).Then the involvement process was stopped to shovel the mix by hand and then restarted for 3 additional minutes.This stage was recurrent in three cycles to assure the homogeneity of the combination.After the third cycle, steel fibers were all added by hand although involvement was integrated for 3 minutes.The total partying time was about 25-30 minutes.The normal concrete was mixed using the same mixer according to the conventional mixing of normal concrete.

Experimental Program:
In this research, four samples were established to revision the effect of (Vf), (SF) , hybrid section on the flexural conduct of singly reinforced RPC T-beams.
The beams were separated as listed in table (14).The beams were considered to have suitable sizes that can be industrial, controlled and established as informal as likely.The minimal lengths of the confirmed beams were 1300mm in total distance and 160mm in depth.The web was completed with effective depth and 100mm width, the flange was prepared with 50mm thickness , 220mm flange width, clear span of 1200mm for all beams confirmed underneath exploit of two point loads, the space between two point loads was reserved constant at (400 mm).

Experimental Results and Discussion
The consequences of the investigational experiments approved out in this research to observe and assess the flexural performance of RPC with Hybrid Section T-Beams as well as revising the manual properties of RPC.Belongings of three constraints on the flexural behavior of RPC with Hybrid Section T-Beams, comprising: steel fiber volumetric ratio (V f ), silica fume ratio (SF), hybrid section.
The possessions were premeditated in expressions of load deflection curves, principal crack load, ultimate load, strain dissemination across the depth of the beam at dissimilar load stages, type of beam failure and crack form.

Mechanical Properties of RPC :
Device cases were equipped commencing the same mixture of non fibrous and fibrous concrete for each column specimen.The details of the control specimens were as following: Cubes of 100 mm and cylinder 150× 300mm for compressive strength test of concrete(fc') were used conferring to ASTM C39-03 [17], flexural strength test(fr) (modulus of rupture) is approved out by consuming (100 x 100 x 500 mm) prisms, the experiment is supported out allowing to ASTM C78-02 [18], splitting tensile strength assessment(ft) is achieved on a dimensions with diameter and height (150×300) mm concrete cylinder allowing to the ASTM C496-04 [19],and with diameter and height (150×300) mm for concrete cylinders for dimension of static modulus of elasticity (Ec) allowing to ASTM C469-02 [20].
all the results shown in table (15).

Effect of Concrete Type (Hybrid Section):
To reading the talent of consuming typical concrete composed with RPC in the equivalent section to save part high cost of RPC and to achievement the benefits of the two materials in best technique, four beams were established.The strains in the concrete at midspan section of the tested beams were unrushed at seven unlike stages above the depth every beam as revealed in figures (4) to (7).

Conclusions Based on Experimental Work Results:
1. Influence of steel fiber volumetric ratio on the increase of ultimate deflection reveals that increasing steel fiber volumetric ratio to 2% makes RPC T-beams more ductile and capable of undergoing large deflections before attainment final load resonant ability.This possessions is exact significant structural supporters as it permits concrete to provide warning previously disappointment and avoids unexpected collapse.
2.Although the ultimate midspan deflection increases with increasing steel fiber volumetric ratio, the load-deflection curves of beams with (0, 1 and 2%) steel fiber volumetric ratio reveal that at a particular load level, the deflection decreases with increasing steel fiber volumetric ratio at all stages of loading, due to increasing in stiffness.
3. The increases in first crack load and ultimate load for RPC T-beams with increasing steel fiber volumetric ratio belong to the reason that fibers across the initial flexural cracks restrict growth and extension of the cracks and transmit regularly tensile to the concrete nearby the cracks.This maintains the beam reliability all over the post-cracking steps, therefore the beam resist better load and exhibits more deflection previously disappointment.A larger ductility is achieved with a higher ratio of steel bars.
4.Silica fume with ratios from 15% to 25% has little consequence on the principal crack capacity, ultimate flexural and the midspan deflection of RPC T-beams.On the other hand, growing ratio from 15 to25%, the first crack load, the ultimate flexural strength and the ultimate midspan deflection increase with percentages of 17, 10 and 15% respectively .5.The part below load midspan-deflection curve of RPC T-beam increases with increasing steel fiber volumetric ratio and tensile steel ratio constant.
6. Main crack load, ultimate flexural strength and the ultimate midspan deflection with percentages increase of 22%, 31% and 12% respectively as compared with normal concrete T-beam, when using RPC in the flange with normal concrete in web for hybrid T-section beam show increase 7.Using RPC in the web with normal concrete in the flange for hybrid T-section beam show increase in the first crack load, ultimate flexural strength and the ultimate midspan deflection with percentages increase of 82%, 56% and 28% respectively as compared with normal concrete T-beam.Therefore, using RPC in the web does effectively enhance the performance of T-beams more than the case of RPC in flange.
8. Cracking of RPC beams with higher steel fiber volumetric ratios is associated with multiple cracking, while beams with lower steel fiber volumetric ratios are associated with localized cracking.Effect of silica fume on the crack pattern is not evident.9.The strain distribution across the depth of the mid-span section of RPC beams is around line happening compression zone during the stuffing variety, while in the tension region,it is roughly linear at squat load levels and converts nonlinear at greater load levels owing to cracking.Also the presence of steel fibers leads to an growth in the final concrete strain values at together tension and compression zones but the influence is more pronounced in the tension zone.This can be credited to the enhanced action of steel fibers in tension slightly than in compression and increasing in stiffness and modulus of elasticity.
10.The presence of steel fibers in RPC gives some improvement to its compressive strength.Increasing Vf from 0% to 1% and 2% resulted in an increase in compressive strength of the order 20% and 33% respectively.Although silica fume is a smaller amount operational; growing silica fume ratio starting 15% to 20% and 25 % increases the compressive strength of RPC by only 5% and 8.5% respectively.
11.Under compressive load the failure of nonfiberous RPC is of explosive and brittle nature, while the failure of RPC with steel fibers exhibits ductile behavior.Steel fibers result in more closely spaced cracks, reduces the crack width and improves resistance to deformation.
12. Steel fibers obligate a important consequence on tensile strength of concrete.As steel fibers proportion upsurges from 0% to 1% and 2%, the splitting tensile strength of RPC upsurges by 75% and 139% separately.Silica fume has a minor effect in growing the splitting tensile strength, as upsurges starting 15% , 20% then 25% increase by only 2.32% to 8.77% respectively.
13. Steel fibers have also a significant effect in increasing the modulus of rupture of RPC.As soon as steel fibers ratio rises starting 0% to 1% and 2% modulus of rupture of RPC rises by 129% to 198 % respectively.However silica fume appearances tiny consequence happening the modulus of rapture.As rises from 15% to 20% and 25 rises by only 4% and 9% respectively.
14.The strain distribution across the depth of the mid-span section of RPC beams is nearly direct in the compression region during the course of the charging variety, however happening the tension zone, it is nearly linear at short load levels and develops nonlinear at higher load levels owing to cracking.Also the presence of steel fibers leads to an rise in the ultimate concrete strain values at together tension and compression zones but the influence is more pronounced in the tension zone.This can be recognized to the enhanced action of steel fibers in tension reasonably than in compression.

♣
The letter M denotes Mix; the first number indicates the percentage of steel fiber content (Vf) and the second number indicates the percentage of silica fume (SF).* Percent of cement weight.** S.P.: Superplasticizer, percent of binder (cement + silica fume) weight.*** Percent of mix volume 3.3 Mixing Procedure: RPC was varied by consuming a horizontal turning mixer with (0.1 m 3 ) ability obtainable in the structures laboratory, College of Engineering, Kufa University.
Two beams (RPC2 and RPC3) were castoff to explore inspiration incompletely using RPC on conduct T-beams equally contrast with completely RPC sample (RPC1) and typical sample (Normal), figure(1) shows details of cross-sectional .

Figure ( 2 )
Figure (2): Effect of hybrid section on load deflection curves of T-beams

Figure ( 3 )
Figure (3): Effect of hybrid section on Crack pattern of T-Beams

Table ( 2) :Physical properties of cement used in this study* Physical Properties Test Results Limits of Iraqi SpecificationNo.5/ 1984[10] Specific surface area(Blaine method),(m 2 /kg) 320 230 (Min.) Setting time (vicat's apparatus) Initial setting time (hrs: Min.) Final setting time (hrs : min.)
(6)]dness(Autoclave method),% 0.22 0.8(max) * Chemical and Physical tests analysis have been tested in the materials laboratory of the college engineering , University of Kufa2.2FineAggregate:There are contain two types of fine aggregate are castoff in this revision: 1.For typical concrete combinations of this revision used typical sand from Al-Zubair region in Basrah city was used.The maximum size of this type (4.75mm) with pointed subdivision form and smooth.The arranging of this sort is revealed in Table(3).The consequences specified that the fine aggregate grading was within the supplies of the Iraqi description No.45/1984(11).Table(4)shows the specific gravity, sulfate content, and absorption of fine aggregate.2.For RPC is castoff very fine sand with maximum size (600µm).The classifying of fine aggregate revealed in table (6) Specification No.45/1984[11].Table(6)expressions the physical possessions of the castoff fine aggregate .

Table ( 4): Physical properties of fine aggregate* Physical Properties Test Result Limit of Iraqi Specification No. 45/1984[11]
*The

Table ( 6): Physical and chemical properties of very fine sand Physical Properties Test Result Limit of Iraqi Specification No. 45/1984[11]
(8)]th type maximum size 14mm attained from Sanam mountain region in Basrah city was castoff as coarse aggregate.Table(7)confirmations grading of coarse aggregate which conforms to the Iraqi specification No.45/1984[11].Table(8)illustrates the specific gravity; sulfate content and absorption of coarse aggregate.

Table ( 11): Properties of steel fiber* Configuration Property Specification Description Hooked Length 30 mm Diameter 0.375 mm Density 7800 kg/m 3 Tensile strength 1800 MPa Modulus of elasticity 200GPa Aspect ratio(Lf/Df) 80 *Supplied by the manufacturer 2.7 Water:
Conventional water is process without any additives