Development of Fibre Reinforced Lightweight Foamed Polymer Concrete
Mufaddal Bagwala1, Tanveer Malik2
1Post-Graduate, Department of Industrial Engineering,
National Institute of Industrial Engineering, Mumbai, India.
2Faculty, Department of Textile Technology,
Shri Vaishnav Institute of Technology and Science, Indore, M.P., India.
Considering normal concrete (NC) the type of concrete need to be vibrated after placing in the formwork, Lightweight concretes have been successfully applied in the building constructions for decades because of their low specific weight in connection with a high strength, a high capacity of thermal insulation and a high durability. The development leading to a self compacting light weight concrete represents an important innovative step in the recent years. This concrete combines the favorable properties of a lightweight concrete with those of a self compacting concrete (i.e., the type of concrete need no vibration after placing in the formwork). Research work is aimed on development of glass fibres reinforced lightweight foamed polymer concrete with the use of ultra light weight aggregates “Expanded Polystyrene (EPS)”. The focus of this paper is to study on fibre reinforced foamed polymer concrete (FRFPC) in terms of constituent materials (foaming agent, cement and other fillers used), mix proportioning, production methods, fresh and hardened properties and wide applications of FRFPC. The results are compared together and with the results observed by other authors. The comparison revealed the superiority of this new composite in improving the compressive and tensile strength.
Keywords: Foamed Polymer Concrete; Expanded Polystyrene (EPS); Glass Fibre Rovings; Pre-foaming Method; Lightweight; Self-Compacting; Self Levelling.
Concrete is the most widely used construction material in the world. Its low cost, ease of application and compressive strength are the principle reasons for its universal acceptance. However it has few shortcomings most of which are attributable to the Portland cement binder. Shortcomings include poor tensile strength, high porosity freeze thaw deterioration, and destruction by corrosive chemicals, etc. The development of new composite materials possessing increased strength and durability when compared with conventional types is a major requirement of applications in repairs and in the improvement of infrastructure materials used in the civil construction industry . Fibre Reinforced Foamed Polymer concrete (FRFPC) is an example of a relatively new material with such high performance. The demand for lightweight concrete in many applications of modern construction is increasing, owing to the advantage that lower density results in a significant benefit in terms of load-bearing elements of smaller cross sections and a corresponding reduction in the size of the foundation.
Foam concrete is either a cement paste or mortar, classified as lightweight concrete, in which air-voids are entrapped in mortar by suitable foaming agent . It possesses high flowability, low self-weight, minimal consumption of aggregate, controlled low strength and excellent thermal insulation properties. By proper control in dosage of foam, a wide range of densities (1600–400 kg/m3) of foamed concrete can be obtained for application to structural, partition, insulation and filling grades. However, it has low compressive strength and poor tensile strength. To overcome this, ultra light weight aggregate Expanded Polystyrene (EPS) is introduced into the mortar and concrete reinforcement is done by using twisted glass fibre rovings.
Expanded polystyrene (EPS) beads are a type of artificial ultra-lightweight, non-absorbent aggregate. It can be used to produce low-density concretes required for building applications like cladding panels, curtain walls, composite flooring systems, and load-bearing concrete blocks. Expanded polystyrene (EPS) concrete is a lightweight concrete with good energy-absorbing characteristics, consisting a discrete air voids in a polymer matrix. It has very high compressive strength. However, polystyrene beads are extremely light, with a density of only 12 to 20 kg/m3, which can easily cause segregation in mixing. Hence some chemical treatment of surface on this hydrophobic material is needed. Other investigators also reported that EPS tends to float and can result in a poor mix distribution and segregation, necessitating the use of admixtures.
Glass fibre is a high performance fiber made from hot air blowing and drawing of molten glass. Its density is 2.58 g/cm3 and is having tensile strength 2.5 times higher than steel. For the past few decades, it has been used extensively for the purpose of reinforcement to improve the tensile strength and thermal insulation of the material.
According to foaming type, lightweight foamed concrete is classified as pre-foaming type foamed concrete which is mixed by pre-foamed foams in cement slurry, after-foaming type foamed concrete which is mixed with foaming agents such as aluminum powder and zinc powder, and mixed-foaming type foamed concrete which is mixed with surface active agent into cement slurry during mixing . In this study, lightweight foamed polymer concrete is manufactured by the pre-foaming type because of its advantages for controlling the quantity of the foam and easiness of placing during construction. The foam agent is the most important factor for the foamed concrete and foam agents are classified as polymer foam agent, protein foam agent and surface active agent. Protein foam agent compounded of animal blood and gelatin is made of several kinds of amino acid and makes about 0.2∼0.8mm size of a pore in the cream at the time of foaming.
The production of stable foam concrete mix depends on many factors viz., selection of foaming agent, method of foam preparation and addition for uniformair-voids distribution, material section and mixture design strategies, production of foam concrete, and performance with respect to fresh and hardened state are of greater significance. With the above aspects in view, this paper classifies the studies on FRFPC related to its constituent materials, mix proportioning, production and fresh state and hardened properties with wide structural applications.
This paper aims to enhance buildability in the building and construction industry by carrying out a systematic and extensive R&D to develop cost-effective high strength fibre reinforced lightweight foamed polymer concrete (FRFPC) with ultra lightweight aggregate (EPS) and reinforcement with twisted glass fibre rovings for various matching applications such as with energy-saving features to improve or maintain good indoor thermal environment in buildings, fire-proof, sound-proof and floating structures etc. One of the key deliverables of this paper is to develop FRFPC for non-structural application for large panel external walls, partition walls, volumetric precast components and closed cell bath units with weight below 1000kg/m3 while satisfying other performance requirements. The study also includes the assessment of FRFPC for structural applications.
Ordinary Portland Cement (OPC) was used. The main chemical composition of (OPC) used in this study are listed in Table 1.
Table 1: Chemical and physical compositions of ordinary Portland cement
Sand particles of size less than 600 microns were taken as fine aggregates. The spherical EPS beads of size 3mm diameter of density 20 kg/m3, compressive strength 0.9 MPa and specific gravity 0.029 was obtained from J.P. Industries. Glass fiber rovings of fineness 110 Tex, Tenacity 85 cN/Tex, tensile strength 2250 MPa and with 5% elongation at break was used for reinforcement. Polycarboxylic ether was used as Binding agent for EPS and Acrylic based Admixture was used to attain early strength in the concrete.
Protein Hydrolization based foaming agent “Green Froth” was used. Foam concrete is produced either by pre-foaming method or mixed foaming method. Pre-foaming method comprises of producing base mix and stable preformed aqueous foam separately and then thoroughly blending foam into the base mix. In mixed foaming, the surface active agent is mixed along with base mix ingredients and during the process of mixing; foam is produced resulting in cellular structure in concrete. The foam must be firm and stable so that it resists the pressure of the mortar until the cement takes its initial set and a strong skeleton of concrete is built up around the void filled with air. The preformed foam can be either wet or dry foam. The wet foam is produced by spraying a solution of foaming agent over a fine mesh, has 2–5 mm bubble size and is relatively less stable. Dry foam is produced by forcing the foaming agent solution through a series of high density restrictions and forcing compressed air simultaneously into mixing chamber. Dry foam is extremely stable and has size smaller than1 mm, which makes it easier for blending with the base material for producing a pumpable foam concrete.
2.3 Proportioning and Preparation of Fibre Reinforced Lightweight Foamed Polymer Concrete (FRFPC)
Often trial and error process is adopted to achieve foamed polymer concrete with desired properties.For a given mix proportion and density, rational proportioning method based on solid volume calculations was used. The optimum design mix ratio was found to be:
C: S: E: W: FA: BA: Ad as 2:2:1:1.2:0.4:0.1:0.1
by volume where, C denotes cement, S denotes sand, E denotes EPS, W denotes water, FA denotes foaming agent, BA denotes binding agent and Addenotes Acrylic based admixture.
2.3.1 Preparation of FPC blocks in Laboratory
For making control samples of above design mix, moulding cube of dimensions 7cm x 7cm x 7cm was used. First of all cement, sand and EPS slurry was prepared by hand mixing. For this, at first cement and sand was mixed in given proportion in the mixing tray. Then calculated quantity of water was added to form slurry. In this slurry, EPS beads of calculated weight were added. Few drops of Polycarboxylic ether (PCE) super plasticizer were incorporated in the mixture to enhance the binding of EPS in the slurry and to avoid segregation. At this time, foaming agent “green froth” was added with water in the foam generator machine FG120 and dry foam was prepared. This foam was added in the slurry with the help of foaming lance and workable foamed polymer concrete was prepared (see figure 1).
2.3.2 Reinforcement of FPC with twisted glass fibre rovings
For making control samples, Glass fibre rovings of twist 1.8 turns per inch were cut in the length of 7 cm. At first, one FPC layer was laid in the moulding cube. Then the glass fibre roving layer was laid manually and it was again covered by FPC layer (see figure 2). This procedure was repeated two times to prepare blocks of FRFPC (see figure 3). These blocks were allowed to dry for 24 hours at room temperature and then were immersed in water for 3 days before the physical and mechanical characterization.
2.4 Testing Methods
2.4.1 Pre-curing Tests
184.108.40.206 Slump Test
The slump test is conducted to determine the workability of the fresh concrete . Depending on the application of the concrete different slumps will be desired, for a FPC a slump of 500 to 700mm is required to level under its self weight and flow around obstructions. At the start of this test the mould needs to be clean and free from dried concrete. The mould, shown in Figure 4, must be placed on a horizontal surface free from vibration and held in place by standing on the foot pieces. The mould is filled in three equal proportions, rod each layer 25 times to the depth of that layer. Once the concrete is level with the top of the surface lift the mould vertically to let the concrete subside. Ensure the time it takes to lift the mould its own height is 3 ± 1 second, without causing any lateral or torsional displacement of the concrete. Immediately measure the average height of the top surface of the collapsed concrete and calculate the difference compared to the height of the mould (300mm). This difference in these two values is known as the slump.
220.127.116.11 L-Box Test
The L-Box test is used to determine the flowability of the freshly mixed FPC in order to verify whether or not the concrete is self compacting . The L-Box, shown in Figure 5, consists of a ‘chimney’ section and a ‘channel section which is separated by a sliding gate, as illustrated in Figure 5. In addition, there are three reinforcement bars located in the channel which are designed to impede the flow of the concrete into the channel, as seen in Figure 6.In order to conduct the test all sides that will be in contact with the concrete should be dampened. Ensure that the sliding gate is completely closed to ensure that there is no premature flow into the channel. The chimney is then filled to the top with the fresh concrete and the surface is leveled. The sliding gate is then raised at a constant rate of 1.5cm/sec. The concrete flows from the chimney into the channel through the reinforcement bars. This is allowed to occur until the concrete has ceased to flow or one minute has passed, whichever occurs first.
The L-Box ratio equals h2/h1, a ratio of one means the concrete has self leveled and a ratio of zero means the concrete has not reached the far wall of the channel. For a concrete to be considered self compacting the ratio of h2/h1 must be between 0.6 and 1.
2.4.2 Post Curing Tests
18.104.22.168 Compression Test
In accordance with AS1012.9.5, the surfaces of test samples which are to come in contact with the loading device platens are to be plane within 0.05 mm tolerance level . Before conducting the compressive test two measurements of the concrete cylinders should be conducted. The measurements should be taken at 90 degrees to each other and be rounded to the nearest 0.2mm. Ensure that the platens of the testing machine are clean and wiped free from any small particles. The surfaces of the specimens to be tested should also be wiped clean ensuring that they are free from any lubricants.
Place the specimen in the testing machine ensuring that its axis is aligned with the center of thrust of the spherically seated platen. Bring the upper platen and the capped specimen together so that uniform bearing is obtained and being to apply a force. The force should be increased continuously at a rate equivalent to 20 ± 2 MPa compressive stress per minute until no increase in force can be sustained. Record the maximum force applied to the specimen as indicated by the testing machine. The maximum force recorded on the specimen can be used to calculate the compressive strength of the concrete. The maximum force divided by the average cross sectional area will result in the compressive strength of the material.
For an accurate result for the compressive strength of a material a minimum of 3 test samples are required. These specimens should be produced in a single mix, exposed to the same curing conditions and tested after 28 days. The compressive strength is calculated to the nearest 0.5 MPa where the strength is above 10 MPa. The average of these three specimens will produce a compressive strength of the material with a probability that 95% will be within 10% of this mean.
22.214.171.124 Tensile Test
AS1012.10.6 details the procedure for determining the tensile strength of the hardened concrete . Figure 7 shows the apparatus used to determine the maximum tensile strength.
Prior to conducting the tensile test three measurements of the specimens diameter need to be recorded to the nearest 0.2mm. In addition to this, the length of the specimen to the nearest millimeter should be taken from two measurements. These length measurements should be taken on the two lengths that will come in contact with the tensile machine. Centre the specimen on the apparatus and lower the upper platen to apply a small force on the specimen. Apply a force that will increase continuously at a steady rate of 1.5 ± 0.15 MPa per minute of indirect tensile stress until the specimen can now longer sustain the load. Record the maximum amount of force applied to the specimen.
In accordance with AS1012.10.6, we can calculate the indirect tensile strength by using the following equation:
In order to obtain an accurate measurement of the tensile strength of the material a minimum of two test samples are required. These specimens should be produced in a single mix, exposed to the same curing conditions and tested after 28 days. Indirect tensile strength is calculated to the nearest 0.1 MPa. The average of these two specimens will produce a tensile strength of the material with a probability that 95% will be within 14% of this mean.
126.96.36.199 Modulus of Elasticity
From the compressive strength testing of the cylinders the modulus of elasticity can be determined experimentally. In accordance with AS1012.17, 40% of the average compressive loading determined in the compressive testing will be used as the maximum test load for the samples. This is to ensure that loading is clear of the plastic deformation zone .
The test sample will be fitted with a strain gauge reading apparatus, as shown in Figure 8, before it is test loaded. The modulus of elasticity can be calculated by using the following equation:
3. Results and Discussion
The results of Pre-Curing tests and Post-Curing tests can be used to classify and study the properties of fibre reinforced foamed polymer concrete (FRFPC):
3.1 Fresh State Properties
As foam polymer concrete cannot be subjected to compaction or vibration the foam concrete should have flowability and self-computability. These two properties are evaluated in terms of consistency and stability of foam concrete, which are affected by the water con-tent in the base mix, amount of foam added along with the other solid ingredients in the mix.
Flow time using marsh cone and flow cone spread tests are adopted to assess the consistency of foamed polymer concrete. These measurements were also related to rheology and it was observed that EPS as filler exhibited 2.5 times higher spread compared to cement-sand mix. This enhanced consistence and rheology is attributed to difference in particle shape and size of fine aggregate. The consistency reduces with an increase in volume of foam in the mix, which maybe attributed to the (i) reduced self-weight and greater cohesion resulting from higher air content and (ii) adhesion between the bubbles and solid particles in the mix increases the stiffness of the mix.
The stability of foamed polymer concrete is the consistency at which the density ratio is nearly one (the measured fresh density/design density), without any segregation and bleeding. This ratio is higher than unity at both lower and higher consistencies due to either stiffer mix or segregation. The stability of test mixes can also be assessed by comparing the (i) calculated and actual quantities of foam required to achieve a plastic density within 50 kg/m3 of the design value and (ii) calculated and actual w/c ratios. The additional free water contents resulting from the foam collapse corresponded to an increase in actual w/c ratio. Thus the consistency of the base mix to which foam is added is an important factor, which affects the stability of mix. This consistency reduces considerably when foam is added and depends on the filler (EPS) size also.
3.2 Physical Properties
3.2.1 Drying Shrinkage
Foamed polymer concrete possesses high drying shrinkage due to the absence of coarse aggregates, i.e., up to 10 times greater than those observed on normal weight concrete. Autoclaving is reported to re-duce the drying shrinkage significantly by 12–50% of that of moist-cured concrete (due to a change in mineralogical compositions) and is essential if the products are required within accept-able level of strength and shrinkage. The shrinkage of foamed polymer concrete reduces with density, which is attributed to the lower paste content affecting the shrinkage in low-density mixes.
3.2.2 Air-Void Systems
The pore structure of cementitious material, predetermined by its porosity, permeability and pore size distribution, is a very important characteristic as it influences the properties such as strength and durability. The pore structure of foamed polymer concrete consists of gel pores, capillary pores as well as air-voids (air entrained and entrapped pores). As foamed polymer concrete being a self flowing and self-compacting concrete and with EPS, the possibility of entrapped air is negligible. The air-voids in the foamed polymer concrete can be characterized by a few parameters like volume, size, size distribution, shape and spacing between air-voids. The FPC was having 80% air voids in the structure with bubble size ranging from 0.3 to 0.8 mm.
Density can be either in fresh or hardened state. Fresh density is required for mix design and casting control purposes. A theoretical equation for finding fresh density may not be applicable as there can be scatter in the results caused by a number of factors including continued expansion of the foam after its discharge, loss of foam during mixing. Many physical properties of foamed polymer concrete related to/depend upon its density in hardened state. While specifying the density, the moisture condition needs to be indicated as the comparison of properties of foamed polymer concrete from different sources can have little meaning without a close definition of the degree of dryness. Density of FRFPC was 607 kg/m3, that is much lower than normal concrete whose dry density is 2700 kg/m3.
3.3 Mechanical Properties
3.3.1 Compressive Strength
The compressive strength decreases exponentially with a reduction in density of foamed polymer concrete. The specimen size and shape, the method of pore formation, direction of loading, age, water content, characteristics of ingredients used and the method of curing are reported to influence the strength of FRFPC in total. Other parameters affecting the strength of foamed polymer concrete are cement–sand and water–cement ratios, curing regime, type and particle size distribution of sand, diameter & density of EPS and type of foaming agent used. The compressive strength of FRFPC developed by us was 28.75 MPa which was comparable to the compressive strength of normal concrete.
3.3.2 Flexural and Tensile Strengths
Splitting tensile strength of glass fibre reinforced foamed polymer concrete (FRFPC) was higher than those of equivalent normal weight and lightweight aggregate concrete This increase is attributed to the improved shear capacity between sand particle and the paste phase. Use of Glass fibers has been reported to enhance the performance with respect to tensile and flexural strength of foamed polymer concrete, provided it is not affecting fresh concrete behaviour and self-compaction. The tensile strength of FRFPC was found to be 647 kg/cm2.
3.3.3 Modulus of Elasticity
The static modulus of elasticity of foamed polymer concrete was comparable to that of normal weight and lightweight concrete, with the value of 24.87 kN/mm2 for FRFPC of density 607 kg/m3 due to the presence of glass fibre rovings for reinforcement.
3.4 Durability of FRFPC
3.4.1 Permeation Characteristics
Water absorption: Water absorption of FRFPC decreases with a reduction in density, which is attributed to lower paste volume phase and thus to the lower capillary pore volume. The water absorption of FRFPC is mainly influenced by the paste phase and not all artificial pores are taking part in water absorption, as they are not interconnected. The oxygen and water vapour permeability of FRFPC have been observed to decrease with increasing EPS content.
Sorptivity: The moisture transport phenomenon in porous materials has been defined by an easily measurable property called Sorptivity (absorbing and transmitting water by capillarity), which is based on unsaturated flow theory. It has been shown that the water transmission property can be better explained by Sorptivity than by permeability. Sorptivity of FRFPC is re-ported to be lower than the corresponding base mix and the values reduce with an increase in foam volume. Also, the sorption characteristic of FRFPC is observed to depend upon the EPS size, pore structure and permeation mechanisms
3.4.2 Resistance to Aggressive Environment
Foam polymer concrete mixture designed at low density taking into consideration of depth of initial penetration, absorption and absorption rate, provided good freeze-thaw resistance. FRFPC has good resistance to aggressive chemical attack due to presence of glass fibres. An accelerated chloride ingress tests suggested that fibre reinforced foam polymer concrete performance is equivalent to that of normal concrete, with enhanced corrosion resistance at lower density.
3.5 Functional Characteristics
3.5.1 Thermal Insulation
FRFPC has excellent thermal insulating properties due to its cellular microstructure, presence of EPS and glass fibers. The thermal conductivity of FRFPC of density 607 kg/m3 is reported to be one-sixth the value of typical cement–sand mortar. Comparison with normal concrete: The thermal conductivity values are 5–30% of those measured on normal weight concrete and range from between 0.1 and 0.7 W/mK for dry densities value of 607kg/m3, reducing with decreasing densities. Thermal insulation of brick wall can be increased by 23% when inner leaf is replaced with foamed polymer concrete of unit weight 607 kg/m3.
Effect of density variation on thermal conductivity: Insulation is more or less inversely proportional to density of concrete. A decrease of concrete dry density by 100 kg/m3 results in a reduction of thermal conductivity by 0.04 W/mK of ultra lightweight aggregate foamed polymer concrete. Altering the mortar/foam ratio affects density which has enormous impact on insulation capacity.
Effect of temperature on thermal conductivity: Thermal insulation is reported to improve with a reduction in temperature. While studying the potential of FRFPC for load bearing insulations for cryogenic applications, influence of temperature variations from 22º to196ºC is reported for an apparent reduction of 26% in thermal conductivity of foam polymer concrete
3.5.2 Fire Resistance
At high temperature the heat transfer through porous materials is influenced by radiation, which is an inverse function of the number of air–solid interfaces traversed. Hence along with its lower thermal conductivity and diffusivity, the FRFPC may result in better fire resistance properties. As compared to normal concrete, lower density of FRFPC is reported to have exhibited better fire resistance. This increased fire resistance is due to presence of fiberglass and EPS. Also, FRFPC never explode or spall when exposed to very high temperature as compared to normal concrete. The FRFPC can resist temperature upto 4200ºC without any deformation in the shape.
4. Comparison of Fibre Reinforced Foamed Polymer Concrete (FRFPC) with Normal Concrete
A comparison between normal concrete and fibre reinforced foamed polymer concrete (FRFPC) of optimal design mix mentioned in this paper is listed in the table 2 for same volume of both type of concretes used as control samples:
Table 2: Comparison of Fibre Reinforced Foamed Polymer Concrete (FRFPC) v/s Normal Concrete
|2.||28 days Compressive Strength (MPa)||34||28.75|
|3.||28 days Tensile Strength (kg/cm2)||390||647|
|4.||Modulus of Elasticity (kN/mm2)||45||24.87|
|5.||Fire Resistance (upto ºC)||1000||4200|
|6.||Thermal Conductivity (W/mK)||0.6 – 4.3||0.1 – 0.7|
|7.||Resistance to Aggressive Environment||Low||High|
|8.||Air-Void System (in %)||1 – 5||80 – 90|
|9.||Bubble Size (in mm)||–||0.8-1.8|
|11.||Cost (INR for 1000 m3 block)||8700 – 9650||1300 – 1470|
5. Applications of Fibre Reinforced Foamed Polymer Concrete (FRFPC)
Due to the absence of gravel and the ball-bearing effect of the foam, FRFPC possesses a high degree of flowability. No vibration is thus required. FRFPC completely fills all gaps and voids in the concrete or mould, fully embedding any hoses, tubes, electrical conduits, windows or door frames. In addition to the mixing and pumping of lightweight concrete, FRFPC offers a mobile mixing and pumping unit, discharging mixes at approximately 12 m3of FRFPC per hour. The rapid mixing and high fluidity of FRFPC facilitates speedy casting of building elements. With the application of vertical molds to cast complete houses in place, omission of vibrating equipment results in the entire walls and roof slab of a building being filled in one step [9-12]. Openings (or the actual frames) for doors and windows as well as ducting and conduits for sanitary and electrical services can be cast in place and firmly embedded in the foamed polymer concrete. Some of the applications where FRFPC can be used widely are:
5.1 Lightweight Concrete Blocks
FRFPC is used for making lightweight blocks in India, China and Thailand. The lightweight FRFPC blocks are mainly used to build partition walls. The lightweight nature of the blocks means that they impose a minimum loading on the building. Foamed concrete blocks also provide good thermal insulation and sound insulation. Blocks can be made with virtually any dimension (see figure 9). For advanced block making factories, a wire cutting machine can be used to efficiently cut large blocks into small blocks.
5.2 FRFPC for Plastering:
FRFPC has low water absorption and a closed cell structure. When it rains, water does not pass through the foamed concrete. When plaster is applied to foamed concrete walls, water remains in the plaster so that the plaster does not crack, which it can do with other types of block.
5.3 Void Filling:
FRFPC is also very useful for void filling. As it is very fluid it will pour into even the most inaccessible places (see figure 10 (a)) It can be used for planned work, but also in emergencies to provide stability and support very quickly.
FRFPC has been used to fill old sewers, basements, storage tanks and voids under roadways caused by heavy rain (see figure 10 (b)). It can be applied even through small openings making the work much easier and cheaper than other methods. If necessary, it can also be pumped into position over considerable distance.
5.4 Roofing Insulation:
A low density mix is chosen and the resulting air content gives the material excellent thermal insulation properties. The low density also has the advantage that it does not significantly add to the overall weight of the roof .
Roofing is probably the most widespread application of FRFPC. Foamed polymer concrete has two benefits when it is used for roofing. The first benefit is that it provides a high degree of thermal insulation. The second benefit is that it can be used to lay a flat roof to falls, i.e. to provide a slope for drainage. In countries where roofs are flat and where roof surfaces are used as part of everyday life, foamed concrete is strong enough to support foot or even vehicular traffic on the roof. FRFPC is also much lighter than slopes made from mortar screeds. This means that a roof with a slope made of FRFPC imposes a lower loading on the structure of the building.
A typical specification for roof insulation is shown here in figure 11:
- Structural Slab
- Lightweight FRFPC laid to falls (50 – 200 mm or more)
- Waterproof membrane
- Tiles (cement or mosaic, spaced for expansion joint with sealant)
5.5 Bridge Abutment
FRFPC is particularly suitable for bridge abutments because it does not impose the large lateral loads, which can be a problem when using traditional granular materials. With traditional abutments, there is a lot of sideways pressure against the bridge walls caused by the materials used and their compaction (see figure 12).
Using FRFPC, the lateral load is practically eliminated, so the bridge walls do not have to be as thick. This in turn means that the wall foundations can be made less massive. Huge cost savings can be achieved by reducing the thickness of the walls, and the size of the foundations. Traditional abutments also experience settlement, both due to compaction of the aggregates by trafficking, and due to the sinking of the whole structure into the ground if the subsoil is soft .
Such settling and sinking causes subsidence of the road, which necessitates costly repair work. When lightweight FRFPC is used there is no settling, and sinking is reduced by adjusting the weight of the abutment by the choice of a suitable mix design.
5.6 Trench Reinstatement
FRFPC is an ideal material for trench reinstatement (the filling of trenches dug in roads when pipes are laid or repairs are carried out). The traditional methods of filling trenches in the roads, i.e. the use of granular fill materials, result in settlement and damage to the road and potentially, to the pipes. With FRFPC there is no settlement; and because the foamed polymer concrete is very fluid, it will fill any voids and cavities in the trench sides (see figure 13).
Also, the excellent load spreading characteristics of FRFPC means that axle loads are not transmitted directly to the services in the trench, so the pipes are not damaged by the weight of traffic.
Traditional granular backfill materials require compaction. FRFPC does not require compaction, so there is no need to use any compactors. This is important since the use of such tools can cause vibration related illnesses among the workers.
5.7 Road Sub-Base
FRFPC can be used to make road structures less heavy (see figure 14). This helps solve the problem where the traditionally heavy road structures cause severe settlement of the road, particularly in areas of soft ground. By constructing the road sub-base from a lightweight material, the overall weight of the structure can be greatly reduced. As FRFPC is very versatile, with a wide range of densities, it has proved to be an ideal, cost effective material for solving this problem.
5.8 Wall Construction
FRFPC can be used for cast in situ walls (see figure 15). These can be made either by using traditional shuttering or hollow polystyrene moulds. This provides a quick and cheap method of building, with the added advantage of excellent thermal insulation . A wall made from 607 kg/m³ density foamed polymer concrete provides the same level of thermal insulation as would a wall made from dense concrete that was 5 times as thick and made from 10 times the quantity of materials as the foamed polymer concrete wall.
FRFPC is an ideal material for tunnel construction and repair (see figure 16). It is used both for the filling of voids created and exposed during tunnelling, and for grouting the finished work, including gaps behind the tunnel lining.
5.10 Floor Construction
FRFPC provides very good material for floor construction (see figure 17). It is ideal for building sub-floors quickly and cheaply and can be used for levelling terrain and raising floor levels as well as for insulation purposes.
5.11 Lightweight Precast Blocks
The traditional method of making lightweight precast blocks involves the addition of aluminum powder to a wet mortar mix, followed by autoclaving. This is not popular due to the pollution it causes. FRFPC is an environmentally friendly alternative as there are no waste products in its production and all the ingredients are non-hazardous.
5.12 Ground Works
FRFPC can be used in various types of ground projects, including stabilizing embankments after landslides, highway widening schemes, land reclamation and filling in of harbours . As it does not sink into soft subsoil, redevelopment can begin much sooner after application than can using traditional methods. For similar reasons, it is also ideal for road foundations.
5.13 Fire Breaks
The excellent fire resistant property of FRFPC makes it an ideal material for fire breaks in buildings where there are large undivided spaces . It is used to prevent flame penetration through the services void between floor and ceiling in modern construction, and also to protect timber floors in old houses.
5.14 Sound Insulation
FRFP Creduces the passage of sound, both from background noise and due to impact (see figure 18). It is, therefore, an ideal material for internal walls and suspended floors in multi-storey buildings, especially ones with communal use .
6. Conclusion and Future Scope
The data presented in this paper show that there is a great potential for the utilization of Expanded Polystyrene (EPS) and twisted glass rovings in the foamed concrete. It is considered this utilization would provide much greater opportunities for value adding and cost recovery as it could be used as a replacement for expensive materials. The following important results can be summarized by the investigation carried out on the FRFPC:
- The density of FRFPC having design mix suggested in this paper was 607 kg/m3.
- The 28 days compressive strength of FRFPC was 28.75 MPa.
- The 28 days tensile strength of FRFPC was 647 kg/cm2.
- The FRFPC was fire resistance upto 4200ºC.
The comparison of results for FRFPC with normal concrete is closed to each others. Hence, FRFPC can be used to replace normal concrete with better efficiency in wide applications which are already discussed in this paper.
The need for developing affordable foaming agent and foam generator is essential to facilitate wider use of foam concrete. There is need to investigate compatibility between foaming agent and chemical admixtures, use of lightweight coarse aggregate and reinforcement including fibres, for enhancing the potential of foam concrete as a structural material.
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