Metallic aluminium in municipal solid waste incineration fly ash as a blowing agent for porous alkali-activated granules.

Porous alkali-activated materials are synthetic aluminosilicates that should be often produced as granules for practical applications. In the present study, municipal solid waste incineration fly ash with ~1.2 wt% of metallic aluminium was used as a novel blowing agent for metakaolin (their ratio ranged from 0% to 100%) with an aqueous sodium silicate solution as the alkali-activator and granulation fluid in high-shear granulation. The compressive strength of all granules was sufficient (≥2 MPa). Water absorption indicated an increase in porosity as the fly ash content increased. However, X-ray microtomography imaging showed no clear correlation between the fly ash content and porosity. The granules exceeded the leaching limits for earth construction materials for antimony, vanadium, chloride and sulphate. Of those, antimony, chloride and sulphate could be controlled by decreasing the ash content, but the source of vanadium was identified as metakaolin. The increase in the fly ash content decreased the cation exchange capacity of the granules. In conclusion, the recommended fly ash content is equivalent to 0.3 wt% of Al0 and the developed granules could be best suited as light-weight artificial aggregates in concrete where the additional binder would provide stabilization to decrease the leaching.

A review on sustainable use of agricultural straw and husk biomass ashes: Transitioning towards low carbon economy.

In order to mitigate the problems associated with the deposition of biomass ashes, it becomes essential to use these materials efficiently. One solution to the problem is utilization of these wastes in the concrete industry. Due to the massive development of infrastructure, the demand for cement is tremendously rising which results in the surge of cement concrete by 30 billion tonnes every year. Plant-based straw and husk ashes are residual waste containing high amounts of silica, which can also be accommodated as a pozzolanic material in concrete. This study presents a complete review of various husk and straw ashes and their impacts on the fresh and hardened properties of concrete including its preparation, microstructure, workability, compressive strength, splitting tensile strength and flexural strength. Special emphasis has been given to the durability characteristics of concrete focussing on porosity, water penetration, carbonation, acid resistance, sulphate, and chloride attack. The data gathered shows that fineness of ashes provides filler and pore refinement effect and gains additional hydration products, resulting in an improvement of the mechanical and durability properties of concrete. The addition of ashes as supplementary cementitious materials in concrete enhances the mechanical performance up to a certain replacement. The optimum level of replacement for rice husk ash, wheat straw ash, and sugarcane straw ash was observed at 10-20%. While wheat husk ash, groundnut husk ash, rice straw ash, and millet husk ash provide optimum strength gains at 10% replacement of OPC. An increase in the replacement content of mostly ashes has a positive effect on water absorption and resistance to acid, sulphate, and chloride attacks.

Turning waste expanded polystyrene into lightweight aggregate: Towards sustainable construction industry.

With the limited supply of energies that we can extract or mine from the earth, low energy consumption building is indeed a demand for the present situation with the use of sustainable building materials. Owing to the frequent use of EPS in the packaging industry, the versatile use of non-biodegradable EPS contributes to increasing global waste generation. In this regard, the utilization of recycled EPS in concrete production can be a sustainable approach to manage embodied energy. EPS is a very lightweight thermal insulating material and is primarily used to prepare lightweight concrete and thermal insulation products in the construction sector. Currently, EPS-based cementitious composites are used in many building structures due to their excellent durability, thermal performance, and sustainability benefits. Several extensive studies have been carried out over a few years to maximize the hardened and durability properties of EPS concrete. With a number of building materials emerging, there is a lack of in-depth review studies on the performance of EPS aggregate concrete. The study underlines the influence of the addition of EPS to lightweight concrete in terms of mechanical, durability, and thermal insulation properties. The main contribution of this article lies in the exploration of subsequent additives, for the production of modified EPS to improve the performance of concrete. Further, the review is expected to provide substantial knowledge on the potential use of EPS, to promote sustainability in the construction sector.

Effects of carbon nanotubes on expanded glass and silica aerogel based lightweight concrete.

This study is aimed to investigate the effect of carbon nanotubes on the properties of lightweight aggregate concrete containing expanded glass and silica aerogel. Combinations of expanded glass (55%) and hydrophobic silica aerogel particles (45%) were used as lightweight aggregates. Carbon nanotubes were sonicated in the water with polycarboxylate superplasticizer by ultrasonication energy for 3 min. Study results show that incorporating multi-wall carbon nanotubes significantly influences the compressive strength and microstructural performance of aerogel based lightweight concrete. The addition of carbon nanotubes gained almost 41% improvement in compressive strength. SEM image of lightweight concrete shows a homogeneous dispersal of carbon nanotubes within the concrete structure. SEM image of the composite shows presence of C-S-H gel surrounding the carbon nanotubes, which confirms the cites of nanotubes for the higher growth of C-S-H gel. Besides, agglomeration of carbon nanotubes and the presence of ettringites was observed in the transition zone between the silica aerogel and cementitious materials. Additionally, flowability, water absorption, microscopy, X-ray powder diffraction, and semi-adiabatic calorimetry results were analyzed in this study.