Untreated Municipal Solid Waste Incineration Ashes for Cement Replacement

This paper characterised the two different ashes, namely Boiler Ash (BOA) and Residue Ash (RA), collected from Qatar's Municipal Solid Waste Incineration (MSWI) plant through a range of detailed analyses (chemical, physical and morphological). The potential utilisation of these raw MSWI ashes as supplementary cementitious material (SCM) in cement-based composites has been investigated by replacement with 0%, 10%, 20%, and 30% by weight of cement. The effect of the replacement levels on workability, setting time, and strength was investigated. Test results showed that setting time increased and workability decreased with the increase of BOA content. On the contrary, RA substitution decreased the setting time and increased the workability. The highest compressive strength was obtained in RA-incorporated mortars at a 10% replacement ratio. Beyond the 10% replacement ratio, RA incorporation significantly reduced the strength. Due to BOA's high unburned carbon content, BOA substitutions reduced the strength of the mortars. However, the impact of the replacement ratio was not as strong as those in RA mortars. Considering setting time, workability, and compressive strength, BOA and RA's optimum percentage of cement replacement was 20% and 10%, respectively. Heavy metal and salt leaching from MSWI ash-incorporated mortars were evaluated by the monolithic tank test. Results indicated that most toxic metals and salts, except Ba and Cl-, were stabilised in the cement matrix

Assessments of the Microstructural and Mechanical Properties of Hybrid Fibrous Self-Consolidating Concretes using Ingredients of Plastic Wastes

This paper focuses on the experimental investigation carried out on self-consolidating concrete (SCC) reinforced with micro-steel fiber and hybrid fibers (combination of micro-steel fiber and recycled high density polyethylene fiber derived from municipal wastes). The physical properties of fresh and hardened concrete including flowability, setting time and durability, the mechanical properties, namely, compressive strength and flexural strength, and microstructural analysis were studied. Micro-steel fiber addition was seen to enhance the flowability of concrete than the non-fibrous and hybrid fiber reinforced concretes. The setting time of SCC mixtures prolonged with the addition of fibers into concrete mixtures. Hybrid fiber reinforced SCC mixtures have displayed reduction in drying shrinkage. The compressive and flexural strengths of the fiber reinforced concretes show a marginal reduction in strength- when compared with the strength of unreinforced concrete. The results of the microstructure analysis clearly demonstrate that the hybrid fibers bond well with the cement matrix and stronger than the bonding between micro-steel fibers and cement matrix

Whole-Field Stress Sensing and Multiscale Mechanics for Developing Cement-Based Composites Containing Recycled Municipal Granular Wastes

Worldwide, there is a growing level of interest to develop sustainable cement-based products and processes in which the usage of natural resources such as sand and limestone are reduced from the current levels. One of the ways to achieve this is by replacing them with suitable inclusions of recycled granular materials from municipal wastes where possible. However, to understand the effects of such inclusions in concrete structures, research advancements are needed to sense and characterise the distribution of stresses (/strains) at the local scale and to establish their links with the fracture and bulk strength characteristics under external loading environments, which is the focus here. In this research, polyethylene (PE)-based granular materials derived from municipal wastes and fly ash obtained from the incineration of municipal solid wastes are used together as secondary raw materials in preparing the concrete mixtures. Photo stress analysis (PSA) is performed here, making non-contact and whole-field digital measurements of maximum shear stress distribution and the directions of the principal stresses at any point of interest on the surface of the samples under external loading. Their links with the fracture toughness and flexural strength of the samples cured at different times are presented. The novel PSA-based stresssensing helps to establish new understandings of the strength characteristics of composites across scales in the future

Application of photonics in determining the strength characteristics of composite concretes

For the sustainable developments of the construction industry, there is a growing need for reducing the usage of the rapidly depleting natural resources in building concrete structures. Re-utilisation of conventional wastes such as different grades of polymeric particulates derived from municipal wastes is being explored as a partial replacement of natural aggregates in making concretes. This poses new challenges to researchers as methods to evaluate the effects of new host particles on the mechanical strength characteristics of composite concretes at microscale and their subsequent effects on their bulk strength are not yet well established. In this research work, municipal polymeric wastes in various forms and fly ash from incineration of municipal solid wastes are used together as secondary raw materials for the preparation of concrete mixtures. The influence of various forms of polyethylene (PE) substitution on the local and global shear stress distribution are sensed whole-field on the cylindrical and notched concrete beams using the principles of photonics. The generic methodology reported here would be of great interest in measuring the strength of concretes and other cementitious composite materials under different loading environments in future. Furthermore, an improved understanding on both microscale stress (/strain) evolution and macro strength characteristics could form a basis to develop new strength theories of composite concretes