SLURRY INFILTRATED FIBER CONCRETE

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1. INTRODUCTION
1.1 General

Slurry infiltrated fiber concrete (SIFCON) is a relatively new special type of high performance steel fiber-reinforced concrete (HPFRC). SIFCON is made by preplacing short discrete fibers in the moulds to its full capacity or to the desired volume fraction, thus forming a network. The fiber network is then infiltrated by a fine liquid cement-based slurry or mortar. The fibers can be sprinkled by hand or by using fiber-dispending units for large sections. Vibration is imposed if necessary during placing the fibers and pouring the slurry. The steel fiber content can be as much as 30 % by volume. In conventional fiber reinforced concrete (FRC), where fibers are mixed together with other ingredients of concrete, this percentage is limited to only about 2 % for practical workability reasons. Because of its high fiber content, SIFCON has unique and superior mechanical properties in the areas of both strength and ductility. The main differences between FRC and SIFCON, in addition to the clear difference in fiber volume fraction, lie in the absence of coarse aggregates in SIFCON which, if used, will hinder the infiltration of the slurry through the dense fiber network. Furthermore, SIFCON contains relatively high cement and water contents when compared to conventional concrete.
Although it is still a relatively new construction product, SIFCON has been
used successfully in a number of areas since the early 1980's. Some of those applications are explosive-resistant containers, security blast-resistance vaults, and repair of structural components, bridge decks, airfield pavements and abrasive-resistance surfaces.


2. PREPARATION
Analogous to preplaced aggregate concrete, SIFCON is preplaced fiber concrete with the placement of steel fibers in a mold or form, or on a 6 substrate, as the initial construction step. Fiber placement is accomplished by hand, or through the use of commercial fiber dispersing units. As stated before, the amount of fibers that can be incorporated depends on fiber dimensions, especially aspect ratio (l/d), fiber geometry, and placement technique. External vibration can be applied during the fiber placement operation.



2.1. Materials And Mix Proportions
The primary constituent materials of SIFCON are steel fibers and cement based
slurry. The matrix can contain:
(a) Only cement (slurry or cement paste).
(b) Cement and sand (mortar).
© Cement and other additives (mainly fly ash or silica fume).
In most cases, high-range water-reducing admixtures (superplasticizers) are
used in order to improve the flowability of the slurry to ensure complete
infiltration without increasing the water-cement ratio (W/C). The dosage of
superplasticizers has the greatest effect on fluidity, cohesiveness and
penetrability of cement slurries.


2.3. Matrix
The matrix of SIFCON does not contain coarse aggregate which, of course, cannot infiltrate through the tiny spaces between the steel fibers. The matrix compositions investigated in literature include cement, cement-sand, cement fly ash, cement- silica fume, cement-sand-fly ash and cement-sand-silica fume .Matrices containing mineral additives such as fly ash or silica fume were found to have better shrinkage characteristics .Typically, silica fume addition is reported to increase the strength, where as the addition of fly ash results in some reduction in strength .Moreover, an increase in the proportion of sand is reported to increase the compressive strength .

2.4. MIX PROPORTIONS
The primary variables in the mix proportioning are fiber content and matrix composition. The fiber volume fraction is commonly controlled by the placement technique and the fiber geometry. The recommended water cement ratio for the slurry (matrix) is 0.4 or less. Superplasticizers (SP) can be used, if necessary, to improve the flowability of the slurry, which should be liquid enough to flow through the dense fiber bed without leaving honeycombs. Only fine sand should be used. Very fine sand of less than 0.5 mm in size is reported to use in preparing mortar SIFCON. If fly ash is used as a cement replacement additive, about 20 % of the cement could be replaced with fly ash. If silica fume is used, the recommended dosage is 10 % by weight of cement. Both Type I and Type III (ASTM) cements can be used.