The 2nd International Conference on Composites: Characterization, Fabrication and Application (CCFA-2) Dec. 27-30, 2010, Kish Island, Iran IUST
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Effect of Fibers Addition and nano colloidal on Mechanical Properties of SCC Composite 1
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A. A. Maghsoudi*, 2A.R. Dortaj Nejad, M. Maghsoudi3
Associate Prof., 2,3M.Sc. Student, Civil Eng. Dept., Shahid Bahonar University, Kerman, Iran. * (Tel: (+98341) 3320054, E-mail:
[email protected])
Abstract Self compacting concrete, SCC is a relatively new type of concrete that can flow through densely reinforced concrete structural elements under its own weight without need for vibration. It offers very attractive technical benefits when combined with fibers and can create a type of composite material. This paper reports a laboratory investigation on the contribution of nano particles, the polypropylene and two new steel fibers on mechanical properties of SCC composite. The fibers were used as resin in SCC as matrix and the mechanical properties of composite materials such as compressive strength, modules of elasticity and modules of rapture were surveyed. It was concluded that addition of nano colloidal and fibers can improve some of the mechanical properties of self compacting concrete.
Keywords: SCC, nano SCC, polypropylene and steel fibers, mechanical properties, composite.
1- Introduction The concept of the self compacting concrete (SCC), was created and developed at the end of the eighties after the development of new additives. It is a highly workable concrete that can flow through densely reinforced or complex structural elements under its own weight and adequately fill voids without segregation or excessive bleeding, without the need of vibration [1]. SCC has substantial commercial benefits because of ease of placement in complex forms with congested reinforcement [2]. In 1910, Porter first suggested the use of steel fibers in concrete, FRC [3]. However, the first scientific investigation of FRC in United States was done in 1963 [4]. FRC is produced using the conventional hydraulic cements, fine and coarse aggregates, water and discrete discontinuous reinforcing fibers. Fibers, used as reinforcement, can be effective in arresting cracks at both micro and macro-levels. At the micro-level, fibers inhibit the initiation and growth of cracks, and after the micro-cracks coalesce into macro-cracks, fibers provide mechanisms that abate their unstable propagation, provide effective bridging, and impart sources of strength gain, toughness and ductility [5,6] Fiber reinforced concrete (FRC) requires a high degree of vibration to get good compactness. This increases the labor costs and noise pollution at the work site. Moreover, if the reinforcement is dense or the form is intricate in shape, it becomes even more difficult to place and vibrate the concrete. Hence, the development of a SCC fiber reinforced concrete (SCFRC) should make for easier placement of concrete, save labor and avoid noise pollution. SCC offers several economic and technical benefits; the use of steel fibers extends its possibilities [7].
2-Scop of investigation
The lack of experimental work on influence of nano particles and low fiber volume fraction on mechanical properties like as compressive strength, modulus of elasticity and modulus of rupture on nano SCFRC is the aim of this research program.
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The 2nd International Conference on Composites: Characterization, Fabrication and Application (CCFA-2) Dec. 27-30, 2010, Kish Island, Iran IUST
ICI
3-Experimental Work and Results 3-1 Material Concrete The mixture proportion of SCC used is shown in Table 1. The cement Type II, limestone powder (LP) as a binder to enhance viscosity of admixture and two types of aggregates were used in the concrete infill composition with maximum size of 19 mm and 4.75 mm respectively. A poly-carboxylic based high super plasticizer produced by a local manufacturer was used in concrete mixtures. Table 2 presents the overall fresh properties of mix rating obtained for each mix. Table1: Mixture proportions Mix No. SCC
C
kg/m3
604
Aggregate C.A.
F.A.
Nano Silica cc
868
821
1330
kg/m3
kg/m3
LP
Water Lit
PCE Lit
w/c
105
213.4
8.4
0.35
Table 2: Fresh properties rating criteria of SCC Mix No. Slump flow dis. (cm) T50 (Sec.)
SCC
SCCMF1
SCCMF2
SCCMF3
68 4.44
70 4.5
69 4.38
71 4.0
Fibers Three type of macro fibers, two machinery clips metal fibers (with a length of 30 to 50mm), one as straight (Type I), one in the form of spring (type II) and one type of Polypropylene fiber (type III) with a length of 15mm, were used. The machinery metal fibers are not flexible and stainless but are cheap and walk away. The low modulus and slipping fibers are polypropylene ones. They are auto-fibrillating and, although being made of a single piece of polypropylene, they look like a bundle of thinner fibers stuck together. This property provides an improved bond with the cement matrix. The characteristics of fibers are detailed and compared in Table 3. Table 3: properties of the fibers used Fiber type Length Cross section Density Tensile strength
Machinery clips- Type I 30-50 mm Rectangular 1.6*0.03 mm 7.2 t/m3 --
Machinery clips- Type II 30-50 mm Rectangular 1.6*0.03 mm 7.2 (t/m3) --
Polypropylene Type III 15 mm Circular, dia. 0.023 mm 0.91 t/m3 350-400 MPa
3.2 Overall Mix Rating for Fresh Concrete Properties An overall SCC rating system was developed that can be used to group SCC mixes as those with good, medium, and poor fresh properties [1]. Rating criteria were selected for good, moderate and poor ratings. Table 4 shows the selected parameters for each test method and the associated rating criteria. That is, for a given mix, an overall rating of “poor” was assigned if two or more of the individual tests indicated poor ratings for the mix; “good” was assigned if none of the individual tests indicated a poor rating, and if the number of good values from the individual tests exceed the moderate values from the
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The 2nd International Conference on Composites: Characterization, Fabrication and Application (CCFA-2) Dec. 27-30, 2010, Kish Island, Iran IUST
ICI
individual tests; and all other mixes were assigned an overall rating of “moderate”. Table 2 presents the overall fresh properties mix rating obtained for each designed mixes. As a general, the results of Table 2 are indicated that, it is possible to consider the designed FRC mixes as SCC in plastic phase. A typical slump flow diameter test for designed mixes are shown in Figure 1. Table 4: Plastic (fresh) properties rating criteria Test Method Slump flow dia.
Parameter (P)
Nominal
Flow dia. (cm) T50 (sec)
Rating Criteria Good
Moderate
Poor
66
61≤P≤71
71
