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  • Effect of alkaline-resistant glass fibre on compressive strength of lightweight foamed concrete

    Hanizam Awang*, Universiti Sains Malaysia, Malaysia

    N M Noordin, Universiti Sains Malaysia, Malaysia

    27th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 29 - 30 August 2002, Singapore

    Article Online Id: 100027027

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  • 27th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 29 - 30 August 2002, Singapore

    Effect of alkaline-resistant glass fibre on compressive strength of lightweight foamed concrete

    Hanizam Awang*, Universiti Sains Malaysia, Malaysia

    N M Noordin, Universiti Sains Malaysia, Malaysia

    Abstract

    This paper presents the finding of an experiment conducted to investigate the effect of glass fibre on compressive strength of foamed concrete which can be used as decorative architectural component for non-load bearing structure. Chopped Strand Alkali-Resistant glass was used in the study with size of 24mm. A cement-to-sand ratio of 1 : 1 was used as a typical design mix with two targeted dry densities of 900 kg/m3 and 1000 kg/m3 were used in the study. Specimens consisting of 126 glass fibre reinforcement concrete cubes (100mm x 100mm x 100mm) were made and subjected to compressive tests at age of 7 and 28 days. Foamed concrete containing fiber glass with compressive strength between 1.3 N/mm2 to 3.1 N/mm2 was produced. The results indicated that there is a significant correlation between strength of concrete and percentage of fibre used. From the different percentage of glass fibre added into foamed concrete, we were able to identify the strength for lightweight foamed concrete made with a 0.45 water-to-cement ratio. The experimental 'findings indicate that the increase of 'fibre content can produce stronger foamed concrete. The results of this study suggest that with further refinements in the mixture designs, there are possibilities of producing foamed concrete using glass fibre.

    Keywords : Foamed, concrete, Alkali- Resistance glass fibre, compressive strength

    1. Introduction.

    Lightweight foamed (or cellular) concrete is normally made from mixing stable foam to slurry of mortar. This action incorporates small-enclosed air bubbles within the mortar thereby making it lighter and possessing special properties such as low thermal conductivity and high fire resistance. Foamed concrete may have densities ranging from as low as 500kg/m3 to as high as 1600kg/m3 . It therefore has a wide range of applications such as material for wall blocks or panels, floor & roof screeds, trench reinstatement, road foundations and also void filling.

    Several important materials are normally used in the production of Lightweight Foamed Concrete (LFC) namely cement, sand, water and stable foam. The type of sand used to make foamed concrete is fine (river) sand which is less than 2mm in size. Ordinary Portland cement is used as a binder material in the production of foamed concrete.

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  • Stable foam that is used in the production of foamed concrete is made by expanding a suitable amount foaming agent (in this case Fine Foam 707) by way of a foaming generator ( Portafoam) developed at the School of Housing, Building and Planning, Universiti Sains Malaysia. The dilution ratio for such a foam agent is 1 :19 and expansion from the foam generator is 25. The pre-formed foam is one of the most important ingredients in the making of foamed concrete and acts as "light" aggregates in the concrete.

    The reduction in dry density of the mortar generally results in lower compressive strength compared to the normal sand-cement mortar and this may range from as low as 0.5 N/mm2 to 12 N/mm2 measured at 28 days for the density range mentioned above.

    As can be seen above the compressive strength of normal foamed concrete is quite low and it would be advantageous if this can be improved. One possibility is by way of addition of fibers in the mix. It is known from previous studies that the inclusion of fibers in a cement mortar can result in increased compressive strength [1]. Raju et af2] also found that the cube compressive strength of concrete increased linearly with the addition of fibers. Similarly applied to foamed concrete it is hoped that the glass fiber would contribute to the load carrying capacity of the material by shear deformation at the fiber - matrix interface thereby contributing to increased strength.

    The type of fiber chosen is alkali-resistant glass fiber because of its suitability, availability and high tensile strength [3]. AR glass fibre in the form of chopped strands was added as one of the ingredients in making foamed concrete in order to improve its compressive strength.

    The objective of this study is therefore to investigate the effect of various proportions of alkali resistant glass fibre on the cube compressive strength of foamed concrete of different density.

    2. Experimental details.

    The study would examine the effectiveness of glass fibre in the improvement of LFC. ASTM Type 1 Ordinary Portland cement (OPC) was used for the experiment. The fine aggregate used was natural sand, that was obtained from a local riverbed . A sieve analysis was carried out to see the suitability of the sand to be used and the percentage passing 5 mm sieve size. The sand falls in zone 3 in accordance with British Standard BS 882: Part 2: 1973 . Norizal [4] have mentioned that the appropriate size of fine aggregate used should be between 0 to 2 mm. In addition, 20% of the total quantity of sand used should preferably be of size less than 0.5 mm. Before the test materials were mixed, the sand was in a saturated surface-dry condition . However a moisture test made on the sand sample showed total water content to be 1.1 'Yo. Figure 1 shows the particles sizes distribution of the river sand used in this study.

    The dry mix (cement and sand) was blended with water which had been fixed using a water-tocement ratio of 0.45. Alkali-Resistant glass fibre was added in stages to this mix using three different percentage (0.2%, 0.4%, 0.6%) and mixing was continued for 5 minutes. The alkali resistant glass which was imported from China was in the form of chopped strand 24 mm in length. The alkali resistance of the glass fiber has been confirmed and approved by the Pre-stressed Concrete Institute (PU) and International GRC Institution

    The wet mortar containing glass fibre was then tested for viscosity using a flow table similar to the ASTM C 230-68 test for mortar. The flow diameter using this test was 20 cm after 3 turns of the handle. Stable foam which had a weight of 40 g/liter was then added to the mix and the mixing process continued thoroughly until a homogenous and smooth texture of foamed mortar was achieved. The foam produced was from using a foam agent (Fine Foam) which diluted with 19 parts of water and expanded using a portable foam generator (known as "Portafoam"). This foam generator uses compressed air to generate foam and was coupled to the holding tank containing the foam chemicals mentioned earlier. A specially designed lance unit connected to the foam generator also ensured smooth stable foam for producing the foamed concrete. The same mixing procedure continued with the other mixes containing different percentages of glass fibre . The design mixes are shown in Table 1.

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  • Figure 1 : Particles Size Distribution of Sand

  • Several specimens were cast from a typical mixture and they consisted mainly of the following:

    Cubes of 100 mm x 1 OOmm x 1 OOmm for compression test

    Cylinders of 334mm x 150mm x 150mm for tensile tests.

    Prisms of 1 OOmm x 500mm x 1 OOmm for flexural strength tests.

    The foamed concrete specimens were de-moulded after one day and stored in a water tank at 20 C until its testing date at the age of 7 and 28 days. Three cubes were tested for the first group which consisted of specimens with a target dry density of 900 kg/m3 and another three from the group with a target dry density of 1000kg/m3 to determine the average strength of the specimens. All tests were performed according to the relevant standards (BS 6073 : Part 2 : 1981). The compressive, tensile and flexural strength of the concrete were determined both at 7 and 28 days, whereas the water absorption test was performed at 28 days. The results presented in this paper are the average compressive strength from three tests.

    3. Test Results and Discussion.

    The result of 7 and 28 days compressive tests are given in Table 2 and Table 3.

    Table 2: The result of compressive strength with different percentage of fibre at 900kg/m3 targeted dry density .

    Percentage of fibre (%) 0.2 0.4 0.6

    Cube compressive strength (N/mm2) days 7 1.3 1.6 2.4 28 1.9 2.1 2.9

    Cylinder tensile strength (N/mm2) days 7 0.2 0.4 0.6 28 0.3 0.5 0.8

    Prism flexural strength ( N/mm2) days 7 1.2 1.8 .6 28 1.6 2.5 3.6

    Water absorption (%) days 28 11.9 18.85 29.78

    Actual dry density (kg/m3) days 28 924 930 912

    Table 3: The result of compressive strength with different percentage of fibre at 1000kg/m3 targeted dry density

    Percentage of fibre (%) 0.2 0.4 0.6

    Cube compressive strength (N/mm2) days 7 28

    1.6 2.25

    2.4 2.8

    2.8 3.0

    Cylinder tensile strength (N/mm2) days 7 28

    0.3 0.5

    0.6 0.7

    0.8 0.9

    Prism flexural st

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