Expanded Polystyrene (Expanded Polystyrene referred to as EPS) is a light-weight polymer. It uses polystyrene resin to add a foaming agent, and at the same time it is heated to soften it to generate gas and form a rigid closed-cell structure of foam.
Its processing method can be divided into mode method and extrusion method according to different foaming methods. This uniformly closed cavity structure makes the EPS have the characteristics of low water absorption, good heat preservation, light weight and high mechanical strength. Northern Europe began to use EPS for civil engineering in the late 1960s. In 1971, the Norwegian National Road Research Laboratory (NRRL) used EPS for the first time in the FLOM bridge approach reconstruction project to replace the 1m thick ordinary filler, and successfully controlled the uneven settlement of the bridge head section. Due to the good overall economy and quality effects, the consumption increased rapidly in the 1980s, and countries such as Sweden, Japan, and the Netherlands have already used EPS in highway projects.
Physical and mechanical properties
The density of EPS is determined by the expansion multiple of polystyrene particles in the forming stage, generally between 10~45㎏/m3, and the apparent density of EPS used in engineering is generally 15~30㎏/m3. At present, the density of EPS used as lightweight filler in road engineering is 20㎏/m3, which is 1%~2% of ordinary road filler. Density is an important indicator of EPS, and its various mechanical properties are almost directly proportional to its density.
1.2 Deformation characteristics
According to the experiment, the compression process of EPS under the three-dimensional stress state and the one-dimensional stress state is basically similar. When the axial strain εa=5%, the stress-strain curve has a significant turning point, and the EPS begins to show elastoplasticity. When the confining pressure is very small, the influence on the stress-strain relationship and the yield strength is limited. When the confining pressure exceeds 60KPa, the yield strength decreases obviously, which is obviously different from the change law of soil. When the axial strain εa≤5%, no matter how large the confining pressure is, the volumetric strain εv is close to the axial strain εa, that is, the EPS lateral deformation is small, that is, the Poisson’s ratio is small.
The elastic modulus Es of EPS with bulk density γ=0.2～0.4kN/m3 is between 2.5～11.5MPa. The EPS filling height of the approach project of Danao River Bridge in Guangdong Province exceeds 4m, and the EPS density used is 0.2kN/m3. In order to minimize post-construction settlement, after paving the EPS material layer, fill it with 1.2m of soil for pre-compression. Among them, the average compression settlement of the EPS material layer is 32mm, and the elastic modulus of the EPS can be calculated to be 2.4MPa, and the EPS material is still in the elastic deformation stage. The road section was opened to traffic on a trial basis in October 2000. After 6 months, the actual compression of the EPS material layer changed to an average value of 8mm, indicating that the actual effect of the use of the EPS material was successful as an embankment filler.
EPS has strong independence and is very beneficial to the stability of high slopes. The Swedish bridge design code stipulates that the active and static side pressure coefficients are 0 and 0.4 respectively, and it is not necessary to calculate the passive side pressure. Since the lateral pressure generated by the EPS is small after being compressed vertically, the use of EPS in the subgrade filling of the bridge head section can greatly reduce the soil pressure on the abutment back of the abutment, which is very beneficial to the stability of the abutment.
The friction coefficient f between the EPS block and the sand is 0.58 (dense) to 0.46 (loose) for dry sand, and 0.52 (dense) to 0.25 (loose) for wet sand; f between the EPS block and the block is 0.6 to 0.7 Within range.
1.4 Water and temperature characteristics
The closed cavity structure of EPS determines its good thermal insulation. The biggest feature of EPS used in thermal insulation materials is its extremely low thermal conductivity. The thermal conductivity of various specifications of EPS board is 0.024W/mK~0.041W/mK .
EPS is a thermoplastic resin and should be used below 70°C to avoid thermal deformation and strength reduction. At the same time, this feature can be used for heating wire processing. Flame retardants can be added during production to form flame retardant EPS. The flame-retardant EPS will extinguish itself within 3s after leaving the fire source.
The cavity structure of EPS makes the penetration of water extremely slow. According to the measured data from Norway and Japan, the water absorption rate of EPS (the amount of inhaled water is equivalent to the percentage of its bulk density) is below 1% when not immersed in water; below 4% near the groundwater level; about 10% for long-term immersion . Since the bulk density of EPS is much lower than the bulk density of soil, the 1%-10% increase in bulk density caused by water absorption has negligible impact on the project. EPS helmet
EPS is chemically stable in water and soil and cannot be decomposed by microorganisms; the cavity structure of EPS also makes the penetration of water extremely slow; when exposed to ultraviolet rays for a long time, the surface of EPS will change from white to yellow, and the material is to some extent It is brittle; EPS is stable in most solvents, but it can be dissolved in organic solvents such as gasoline, diesel, kerosene, toluene, and acetone. This shows that the EPS filler needs a good protective layer.