An optimized mix for the manufacture of sustainable aerated concrete blocks using waste rubber powder

Aerated concrete is a type of lightweight concrete in which air bubbles are incorporated into concrete using aluminium powder to make it light in weight. The manufacture of aerated concrete blocks without affecting the quality using waste rubber powder is an efficient waste management method and a vital step towards minimizing environmental pollution caused by the dumping of waste rubber, especially used tyres. There have been only limited studies conducted on using waste rubber powder from used tyres in aerated concrete. The available literature deals with the use of crumb rubber or rubber pieces in concrete for structural applications. Again, fly ash, a waste product from the combustion of coal that would help in reducing the cement content, is also incorporated into the study. This will help in reducing the environmental problems caused by the dumping of fly ash and also reduce the raw material consumption for the manufacture of cement and reduce the emission of CO₂. In this novel experiment, a certain percentage of cement is replaced with fly ash and fine aggregate with waste rubber powder with a view of developing a concrete mix suitable for the manufacture of infill masonry blocks that are sustainable and eco-friendly. Studies were also carried out with aerated binder paste using rubber powder as filler material. In addition to compressive strength, the durability characteristics like water absorption, water permeability, sorptivity, acid and sulphate attacks were evaluated. Microstructure studies were conducted for optimized mixes for finding morphology and porosity characteristics. Various methods were adopted to improve the bonding property of rubber powder, and early strength attainment of the mixes was also studied with optimized mix. From these studies, it is observed that, with 20% replacement of fly ash, 0.75 and 1% of aluminium powder gives the strength requirement for Grade A and Grade B class blocks as per standards. The studies carried out in aerated binder paste exhibit a compressive strength of 6.7 N/mm² with a density of 1302 kg/m³ at 0.5% of aluminium powder and 20% of fly ash, which satisfies the requirements for non-load bearing masonry blocks. The durability parameters are also modified with the incorporation of rubber particles. It is also observed that the strength can be improved with the addition of anhydrous gypsum.