Practices of making lightweight concrete for sustainability of waste polystyrene is gaining popularity in construction of low weight structures which do not need more compressive strength as compared to conventional concrete structures. Therefore some specialized construction solutions prefer waste polystyrene in lightweight concrete because using this component as aggregate makes the production of lightweight concrete economical and environmentally friendly.
In addition to the lightweight property, it has high thermal insulation, high sound insulation and zero water absorption properties which makes it more supportive in the construction sector by saving additional costs of insulation and sound absorption.
What is Polystyrene or Styrofoam?
The expanded polystyrene EPS is a type of plastic which is 98% air and is 100% recyclable but due to increased cost of transportation and difficulty in handling, its recycling has never been easy over the years. That is why it is the least recycled material in the plastic industry and so most of the waste remains in the landfills and floating around in rivers and seas leaving more dangerous impact on the ecosystem.
Polystyrene takes hundreds of years to decompose and if it decomposes to any extent, it is effectively not 100 biodegradable. But by recycling and reprocessing or using the waste in lightweight concrete solutions, we can significantly reduce environmental pollution and its overall carbon footprint.
Need to study more about how polystyrene is recycled, please click here.
What is Lightweight Concrete?
The term “lightweight” refers to different types of concrete which have “lower density” than normal weight concrete NWC. This reduction in density can be achieved by different methods such as using lightweight aggregate (LWA) in concrete, foamed concrete (FC), and autoclaved aerated concrete (AAC) or by any other techniques that reduce the final specific weight of the product, and thus the achieved weight is less than what we get in normal concrete mixtures.
It is made with lightweight aggregates like perlite (small pebbles of natural glass found in volcanic deposits) volcanic pumice (super-heated high pressurized rock from volcanic eruption), fly ash (powdered byproduct of burning coal), shale (sedimentary rock formed from mud, a mix of flakes of clay minerals), or Leca (lightweight clay burnt at around 1200 degrees centigrade), glass waste and foamed substances mostly polystyrene or Styrofoam.
Lightweight concrete weighs about 90–115 pounds per cubic foot, which is at least 20% lighter than standard concrete. Lightweight Concrete prepared with polystyrene or Styrofoam is popular in earthquake hit areas by replacing bricks and concrete blocks to reduce seismic loads on structures. Here in these areas, this type of concrete is a better substitute of wood posing positive impact on ecosystem.
Historical Overview of Lightweight Concrete
Many experiments have been conducted historically throughout the twentieth century to decrease the weight of concrete without impairing other properties. In the early 1920s, Eriksson experimented with different samples of gas concrete and put the mixtures in an autoclave to speed up the curing process.
The lightweight aggregate concrete was first produced in Denmark in 1939 and became popular due to its relatively higher strength than of gas concrete. Even today there are many ongoing extensive research programs on structural and non-structural lightweight concretes.
Technical Properties of Lightweight Concrete
Lightweight aggregate concretes can be used for both structural and non-structural applications, according to the American Concrete Institute (ACI). For structural lightweight concrete, the minimum recommended 28-day compressive strength and maximum density are 2500 psi and 1840 kg/m3, respectively.
Lightweight concrete made of a material with lower densities and higher air voids in the cement paste are considered as non-structural lightweight concrete and are most likely be used for its insulation and lower weight properties.
Lightweight concrete with compressive strength of less than 2500 psi is considered as non-structural lightweight concrete. While normal or standard concrete has a compressive strength ranging from 3000 to 7000 psi. There are also Ultra High Performance Concretes having a compressive strength of even 10 times the strength of normal concrete.
Where is lightweight concrete used?
It has comparatively lower weight and low compressive strength but scientific researches and experiments have proved that using a hybrid cement mixture of ordinary Portland cement (OPC) and alkali-activated cement (AAC) can improve the compressive strength of concrete.
Lightweight concrete is lighter than regular concrete, mostly used in non-load-bearing structures such as partition walls, false ceilings, aesthetic decors, sun shades, façade, and custom made wardrobes reducing the total dead load on foundations making it ideal for large infrastructures and high-rise buildings.
Normally, the demand for lightweight concrete arises when large structures are built on the soft ground such as paddy fields. Currently, issues related to quality control of lightweight aggregates and decline in the tensile strength of concrete are inhibiting the promotion of its development and widespread acceptance.
However, the strength properties of lightweight concrete with polystyrene waste as fine aggregate have been investigated in new experimental studies and this concern could be wiped out adding a proportion of standard aggregate in concrete mix.
Lightweight concrete is produced using a variety of other methods also like incorporating voids by aeration and adding little or no fine aggregate.
Advantages of Using Lightweight concrete with Polystyrene
- Lightweight concrete is easier to handle and nail, which allows for faster construction.
- It has relatively low thermal conductivity, which helps maintain comfortable indoor temperatures and insulation facility.
- Lightweight concrete helps reduce sound transmission, making it a good choice for applications where noise control is important, such as in floors or walls in multi-story buildings, apartments, or office spaces.
- It has enhanced fire-resistant properties.
- Using large quantities of industrial waste like blast furnace slag, clinker, and fly ash and polystyrene, lightweight concrete helps reduce carbon footprints.
- It is also used in refilling of trenches and excavations.
- It is also recommended in insulation of pipes for providing thermal insulation.
- It is suitable as filling between floor timbers.
- It is also suitable as levelling layer before placement of plain or reinforced concrete in flooring.
- Lightweight concrete can help conserve natural resources by reducing the need for traditional concrete materials like coarse aggregates and sand.
- The Lightweight concrete has faster setting time as compared to standard concrete offering setting time to half which is best suitable for precast products.
- It is suitable for heavy defense structures like Bunkers.
- It has also been considered for use as a core material in sandwich panels, beams, and slabs, as a sub-base material for road pavements and also in floating offshore marine structures.
Disadvantages of Polystyrene Filled Lightweight concrete
- Preparing lightweight concrete need more care and supervision because smallest negligence can cause considerable decrease in quality.
- Due to lesser density, they are not suitable for foundation purposes.
What are the components of Lightweight Concrete?
- Ordinary Portland Cement
- Water
- Polystyrene shredded in small particles as Lightweight Aggregate
- Conventional sand as Fine Aggregate
- Superplasticizers as admixtures for additional strength, segregation control and decreased setting time.
- Supplementary Cementitious Materials like fly ash, slag, silica fumes etc for additional strength
Conclusion
The disposal or recycling of expanded polystyrene or Styrofoam has always been difficult for recycling facilities due to heavier transportation costs. Therefore, a large quantity of polystyrene remains in environment and takes hundreds of years to decompose thus causing serious effects to the ecosystem. The use of this waste in making lightweight concrete is a sustainable effort towards safety of the environment.
The experimental results indicate that it is possible to produce a polymerized concrete with compressive strength above 2100 for 28 days in blocks for paving or in partition walls.
This type of concrete offers significant advantages in terms of thermal and sound insulation, lower density, improved energy efficiency, and reduced material costs, making it an ideal choice for applications in high-rise building construction in seismic areas and in regions requiring effective thermal insulation.
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