Dr. K M Soni, Retd. ADG, CPWD, New Delhi
Physical Properties of EPS Geofoam Blocks
As per ASTM D6817, foam control is prescribed as EPS12, EPS15, EPS19, EPS22, EPS29, EPS39 and EPS46 for Geofoam blocks. Typical density of EPS geofoam may vary minimum from 11 to 46 kg per cum as per ASTM C303 for different types of foams, hence, the blocks are very light and therefore suitable for areas where weight reduction is required. Due to the light weight (Fig. 1), their handling and placing is easy, making them useful for steps on slabs.
Compressive Resistance and Flexural Strength
The compressive resistance of EPS Geofoam blocks ranges from about 15 kPa to 18.6 kPa at 1% deformation as per ASTM D1621 for different types of foams. As long as combined dead/live loads do not exceed one percent strain, EPS Geofoam blocks do not creep or experience plastic yield. Minimum flexural strength of EPS Geofoam blocks varies from 69 kPa to 517 kPa, as per ASTM C203.
Prescribed minimum oxygen index as per ASTM is 24% by volume.
Water Absorption and Buoyancy
EPS Geofoam has a closed-cell structure that limits water absorption. Due to its density being less than water, uplift forces are to be considered in case of its applications under partial or submerged conditions. In case of surcharge from overlying soils or pavements, overburden may be sufficient to offset uplift forces. However, where uplift forces are significant, anchors or restraining straps may be required to be installed. In case of steps in buildings, such conditions do not arise.
Carefully selected and installed EPS Geofoam blocks are durable. They do not get decomposed and last for long. It is advisable to cover the blocks and not to keep them exposed to sun to avoid degradation. In the steps, they are restrained from displacements by providing GI wire mesh/GI wire fabric which also acts as reinforcement for the concrete being overlaid.
EPS is combustible, so it is important to cover it with non-combustible materials like cement concrete, RCC, stone or tiles. If required, fire retardant paint should be applied over the blocks.
EPS Geofoam blocks can be used as a structural fill material in civil engineering construction such as bridge column formwork, in stay-in-place wall forming, stairs, lecture halls, auditorium and stadium seating, rooftop pools, and plaza decks, with pavers or cast-in-place slabs.
Sometimes, lecture halls, classrooms, and auditoriums are designed on slabs, in which case, the weight of the steps is required to be reduced. In such applications, EPS Geofoam blocks are very suitable. CPWD has used the material in the steps of the lecture halls of the National Institute of Securities Markets (NISM) at Patalganga, Mumbai. Another advantage of such blocks is that they can be cut in the desired shapes.
Recommendations for Use
When used in steps, the blocks should be laid as per the requirements of the risers. In case depth is more, the required number of blocks can be bundled. Thereafter, wire mesh is laid over the blocks on top and sides to keep them in position and also for better bonding with the concrete to be laid over the blocks. Screed or a layer of concrete is then laid over the blocks. Finally, the flooring is provided as per the architectural requirements.
Another use of such blocks is as in-filling of sunken floors of toilets, kitchens, and other similar locations, as the material is light, low water absorbent, and easy to install. EPS blocks are used in ‘stay in place’ formworks. CPWD had included it for steps in DSR 2019 through correction slip no. 5, under the heading ‘New Technologies & Materials’.
ASTM D6817, “Standard Specification for Rigid Cellular Polystyrene Geofoam” and ASTM C578, “Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation”. https://www.achfoam.com/ACH/media/ACH/docs/Tech%20Data/Foam-Control-D6817-C578-Summary.pdf