Expanded Polystyrene (EPS) Concrete & Performance Improvements
Expanded polystyrene (EPS) concrete is a kind of lightweight concrete made of organic and inorganic materials. Compared with ordinary concrete, it uses EPS particles in coarse aggregates, so it has lower density, better corrosion resistance, thermal and sound insulation performance. Incidentally, using recyclable EPS in concrete also effectively alleviates the problem of plastic pollution. However, EPS particles have two major weaknesses which seriously restrict the application of EPS concrete and need to be overcome: one is that it is easy to segregate during mixing, the other is its hydrophobicity.
Influencing factors of EPS concrete performance
Water-cement ratio
The water-cement ratio is an important parameter that determines the physical and mechanical properties of concrete. Within a certain range, the flexural strength and compressive strength of EPS concrete decrease with the increase of the water-cement ratio. Workability is poor when the ratio is too small. Whereas with a large ratio, though the concrete will have good fluidity, the EPS particles will float up, and segregation, bleeding will occur. The optimal water-cement ratio concluded by many tests is 0.3-0.5. It is not a fixed value due to the influence of the use of admixtures such as superplasticizers.
Sizes and dosage of EPS particles
EPS is a hydrophobic polymer material difficult to degrade, but with low water absorption and thermal conductivity, and good corrosion resistance. For concrete, the density of EPS particles is very small, only 7-14 kg/m3. In order to achieve both light weight and high strength, it is necessary to deal with the problem of bonding between EPS particles and cement, that is, to ensure that EPS concrete has good viscosity to make EPS particles well-distributed.
The size and dosage of EPS particles are negatively correlated with the strength of EPS concrete. I.e., when the density of EPS concrete is the same, the larger the EPS particle size, the smaller the compressive strength and flexural strength of concrete. And when the mixing ratio is the same, the larger the EPS dosage, the smaller the density, compressive strength, thermal conductivity, the larger the shrinkage and plastic deformation.
Concrete Reinforcing Fibers
The addition of a large number of EPS particles leads to poor mechanical properties of EPS concrete. It has been found that concrete reinforcing fibers can be used to improve.
- Adding polypropylene fibers in EPS concrete can improve the bonding at the interfacial transition zone, reduce the occurrence of stress concentration, and improve the compressive strength and splitting tensile strength of EPS concrete. It also improves concrete’s workability and toughness.
- Carbon fibers have the effect of further enhancing the toughness and tensile properties of EPS concrete.
- Composite fibers can reduce the drying shrinkage, improve the toughness and crack resistance of concrete.
Modifiers
Modifiers are used to change EPS from hydrophobicity to hydrophilicity. Under proper curing conditions, using styrene-butadiene binders to modify concrete can significantly improve its tensile strength.
Mineral admixtures
Silica fume
Silica fume can increase the bond strength between EPS and cement paste, improve the dispersion performance of EPS particles in the cement matrix, and inhibit the floating of the EPS particles. A test shows that silica fume improves the compressive strength of EPS concrete by up to 15%, splitting tensile strength by up to 25%. The suitable amount of silica fume is 10%-15% by mass of cement.
Fly ash
The activity of fly ash is relatively low, and if its content is not controlled, it will easily lead to adverse consequences. Adding an appropriate amount of fly ash can not only improve the overall performance of EPS concrete, but also reduce costs. In addition, compared with ordinary concrete, EPS concrete mixed with fly ash has better chemical resistance, lower corrosion rate, and stronger resistance to chloride ion penetration. The appropriate amount of fly ash is 10%-20% by mass of cement.
Mechanical properties
The mechanical behavior of EPS concrete is different from ordinary lightweight concrete like vermiculite concrete, perlite concrete, ceramsite concrete. EPS concrete is lighter in weight, better in ductility and energy consumption, and can withstand higher compressive forces.
The low strength of EPS aggregates affects the types of defects and strength of EPS concrete. With the increase of EPS content, the plastic deformation ability of the concrete increases gradually. The compression failure process of EPS concrete is gradual, and the concrete specimens can maintain the load under the condition of incomplete disintegration. At low strain, concrete will fail with decreasing strength. When the density of EPS concrete is low, it shows an energy-absorbing characteristic. The stress-strain curve of EPS concrete is similar to that of ordinary concrete, which goes through three processes: elastic stage, stage with cracks, and failure stage. The early compressive strength increases greatly (by 85%). As the compressive strength increases, the slope of the elastic stage of the curve increases.
Thermal and sound insulation
Thermal insulation and fire resistance are important physical properties of EPS concrete. Increasing the volume of EPS can significantly enhance the thermal insulation and fire resistance properties of concrete. It is generally believed that the greater the porosity, the better the thermal insulation effect, but if the EPS content is too high, it may cause air convection and increase the thermal conductivity.
EPS concrete is light weight and porous, so it is inferred that its sound insulation performance should be better. A manufacturer has developed EPS concrete plates with a sound reduction index of 45dB.