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Waste Glass in Concrete
Waste Glass in Concrete: As per a report by the United States Environmental Protection Agency, total waste material production raised from 89 to 260 million tons from 1961 to 2015. In 2015, 27% of waste materials were recycled and 10% were composted. Furthermore, 13% was combustible with energy recovery and 53% has been disposed in landfills.
Steel and batteries are by far the most frequently recyclable wastes. Despite glass is a recyclable material, only 35% of glass waste was recycled. The primary reason for not recycling collected mixed-color waste glass is owing to its chemical components.
Glass containers are typically composed of sand, limestone, soda ash, and cullet. Sand is the primary component of glass and the source of silica. To reduce the melting temperature, some recyclers add soda ash to the mix. The chemical compounds of various glass colors vary slightly, affecting their melting point. As a result, glass containers cannot be recycled appropriately unless they are color-sorted.
Another cause for the inefficiency of glass container recycling is the origin of the waste glass. Typically, discarded glass, like bottles or containers, is mixed together during the collecting process. In order to recycle waste glass, workers must sort it according to its color and kind. It is a lengthy and wasteful procedure.
Another cause why certain waste glass cans are not recycled is contamination. Prior to recycling, they must be devoid of any chemical residue, medication, or other dangerous substance.
Utilization of glass as a pozzolan
To improve the mechanical and durability characteristics of concrete, cementitious ingredients such as pozzolans may be used. When ground to a powder, glass transforms into a natural pozzolan that enhances the fresh and hardened characteristics of concrete.
While the concrete is still in its plastic phase, the use of glass powder increases its workability, requiring lower energy, cost, and duration to cast and solidify the concrete. Whereas the concrete is in hardened state, concrete incorporating glass powder demonstrates increased strength, resistance to freeze-thaw, and resistance to sulfates.
ASR map cracking is seen here because to the existence of waste glass. Variations in degradation are caused by the chemical components of colored glass. Generally, green glass-containing concrete is less distressing owing to the existence of chromium.
Glass powder may be used in replacement of portland cement at a 10-30% replacement ratio by weight. The manufacturing of Portland cement is a significant source of CO2 emissions. Incorporating recycled glass into concrete as a substitute for portland cement benefits the environment in more ways than one by lowering CO2 emissions. Additionally, it helps limit the quantity of waste glass dumped in landfills.
The particle size of the glass powder is critical to its pozzolanic performance. Concrete with finer glass particles has better mechanical and durability characteristics than concrete with coarser glass particles.
ASR and glass aggregates
Apart from powder, discarded glass may also be utilized in concrete as fine or coarse aggregates. Given that aggregates account for around 69% of the volume of concrete, employing glass cullet as aggregate does more than just integrate additional discarded glass into the mix. Additionally, it reduces the amount of energy and time necessary to grind the glass into powder.
However, if the concrete mixture includes glass particles, you should think of a mitigation strategy to reduce the alkali-silica reaction (ASR). ASR gel is the consequence of a chemical interaction between alkalis in portland cement and reactive particles in concrete.
When moisture is there, ASR gel expands and deteriorates the concrete. Due of the high alkali and silica content inherent in the microstructure of glass aggregates, they are considered extremely reactive (Glass has around 70 percent silica and 15 percent sodium.) Generally, green glass-containing concrete is less distressing owing to the existence of chromium.
Getting rid of the ASR reaction
There are numerous methods for minimizing the possibility of a detrimental ASR reaction in concrete using waste glass particles. Using low-alkali portland cement and/or supplemental cementitious materials (SCMs) such as silica fume, fly ash, slag, and metakaolin may help alleviate ASR distress in waste glass aggregate concrete.
Silica fume and metakaolin are the most effective traditional SCMs. Using roughly 10% of either silica fume or metakaolin reduces ASR damage in concrete using 100% glass aggregates by about 90%.
Additionally, you may use glass powder as an SCM in concrete (instead of portland cement) to alleviate ASR distress. It is, however, less effective than standard SCMs. For instance, you may use glass powder for 30% of the portland cement and 100% of the aggregates. This way, you will avoid any ASR damage.
Concrete utilizing glass powder as a cement replacement material has nearly the same strength as concrete with just portland cement. However, it outperforms traditional concrete in terms of durability.
Concrete with glass aggregates has a ten to twenty percent – twenty percent lower strength than concrete using mineral aggregates. This decrease in mechanical qualities is a result of the aggregates’ reduced strength and the lack of bonding between the glass aggregates and the paste in comparison to mineral aggregates.
Glass is better than mineral aggregates
Having said that, you may utilize concrete including waste glass in interior applications (where abrasive materials and moisture are unlikely to be present). Additionally, you may use it for less-strengthening sidewalks, pavements, and curbs. When used inside, this form of concrete prevents the presence of water and, thus, ASR damage.
Take note that utilizing waste glass particles drastically reduces the workability of the concrete mixture. The angular forms of the glass cullets have a detrimental effect on the workability of the concrete mixture. Following that, you must apply a superplasticizer to aid in the placing and consolidation of the concrete.
Concrete employing waste glass aggregates has been demonstrated to be more resistant to abrasion than standard concrete using mineral aggregates. Even if not all mineral aggregates are replaced with glass aggregate, the glass particles will rise to the top of the concrete owing to their lower density than mineral aggregates and the paste.
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