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Thailand attaches great importance to the achievement of the 2030 Agenda for Sustainable Development, particularly within the context of the Decade of Action for the SDGs. Additionally, the Office of Natural Resources and Environmental Policy and Planning (ONEP) proposed Thailand’s Nationally Determined Contribution (INDC) Roadmap on Mitigation 2021–2030 to the cabinet in 2015 to achieve 20% (111 metric tons) CO2 emission reduction by 2030 after signing the global agreements. The three main targets of CO2 reduction include energy and transportation, industrial process and product use (IPPU), and waste management. 

Construction industries are responsible for 30 percent of the total global resources, 40 percent of the global energy consumption as well as 30 percent of the total greenhouse gas emission. Concrere is one of the key construction materials and widely used in civil engineering globally, and Portland cement is the major constituent of concrete. The cement industry plays an important role in sustainable development. The industry is considered the largest user of natural resources in the world and the third-largest source of carbon dioxide emissions. An emission factor of 0.47–0.92 tons of CO2 per ton of cement production is approximated. 

Bottom ash is a by-product of coal-fired power-generating plants. During the combustion process, some ash melts; as a result, large particles, namely bottom ash, are precipitated to the water vessel in the furnace underneath. In Thailand, the Mae Moh power plant generates 240,000 tons of lignite bottom ash per year. Meanwhile, the BLCP power plant produces 59,995 tons yearly. Nowadays, most of bottom ash from two power plants is disposed as waste in landfill, thereby causing environmental pollution.

High performance concrete (HPC) was defined as a concrete meeting a special combination of performance and uniformity requirements that cannot always be achieved using conventional constituents and normal mixing, placing, and curing practices. HPC has more specific requirements and characteristics, including good passing and filling abilities, high early strength, volume stability, consistent mechanical properties for a long period, and long service life in a severe atmosphere or environment. Since the term HPC adequately describes improvement in the overall properties, it is more widely used.

As mentioned in earlier, the reduction of concrete volume using high-performance concrete (HPC) is key to achieving global sustainability for the construction industry. Therefore, this study focuses on the upcycling of bottom ash in HPC. If bottom ash can be developed as a super pozzolan as a cement replacement at large volume and an advanced functional aggregate in HPC, a new alternative material will be available for concrete production, and the industrial waste is successfully upcycled. The utilization of bottom ash as a pozzolanic material in concrete has been rarely studied in previous research, unlike fly ash, which has been proven technically viable as a pozzolanic material and is widely used. The concrete mix proportion of HPC contains a combination of cement, pulverized fly ash, silica fume or nano silica, ground granulated blast-furnace slag, and rice husk ash as a binder. Moreover, HPC is normally used for high-rise buildings and other infrastructures, especially for foundations. The size of a foundation for a high-rise building is generally quite large, where inevitably high heat from the hydration reaction is emitted. A large volume of pozzolanic material for this application is often considered. Eventually, this study will cover the use of ground bottom ash as a super-pozzolanic material in self-consolidating HPC with a high volume of cement replacement in order to reduce heat evolution of concrete. The increase of properties of concrete by using super pozzolanic material and decrease the heat evolution of concrete is the importance key to solve the paint point and to fulfill the research gap of HPC. In addition, coarse bottom ash will be applied as a functional aggregate in concrete in order to improve special properties such as internal curing, thermal insulation, and acoustic absorption, which is a potential application of bottom ash for a sustainable construction industry.

If bottom ash can be developed as a super pozzolan for producing HPC at high volume, Portland cement consumption, the cost of concrete, and disposal challenges of bottom ash will be alleviated, and the environment will benefit. Moreover, the upcycling of bottom ash as an advanced functional aggregate to increase the special properties of HPC adds value to bottom ash, providing advantages for future construction. The utilization of bottom ash as both cement and functional aggregate in HPC achieves zero waste from thermal power plants and encourages further study of other by-products from industries, solving more disposal problems. Moreover, the obtained results lay a solid foundation for the use of bottom ash as a raw material to produce HPC and advanced functional concrete.

The main materials for producing HPC in this project are OPC, silica fume, and fly ash as cementitious material with the combination of well-grade river sand, high compressive strength crushed rock, and polycarboxylate ether-based superplasticizer. In this study, the binder content will be approximately 500–800 kg/m3 with a low W/B of 0.25–0.30. The amount of superplasticizer will vary until the flow slump of 650–750 mm, T50 of 2–5 s, and V-Funnel of 6–12 s are achieved. Two types of bottom ash—low and high CaO bottom ash—will be used. Both types will be processed to obtain coarse and fine bottom ash by sieving. Then, the fine bottom ash will be ground for higher fineness to be used as a super pozzolan to replace OPC at the rates of 50 to 80% by weight of total binder in HPC. In addition, nanomaterials may be used to enhance the performance of concrete, such as nano silica or nano calcium carbonate. Subsequently, fiber with various types, lengths, and dosage levels will be also applied in HPC in order to improve tensile strength and shrinkages of concrete. Finally, coarse bottom ash will be used as an advanced functional aggregate in the selected mixture of HPC containing super pozzolan from the ground bottom ash. The utilization of coarse bottom ash as an advanced functional aggregate will be applied in HPC for internal curing, modulus and weight reduction, and thermal insulation improvement. In this research, the experimental program consists of three parts:

Part I: Development of coal bottom ash as a super-pozzolanic material

The aim of this part is to develop the quality of bottom ash for use as a super pozzolan. Two types of bottom ash will be used in this study, which are different in terms of chemical composition (CaO content). Each type of bottom ash will be divided into two groups. The first group is as-received bottom ash, or bottom ash without any processing. The second group experiences the cut-size method, which separates the sample by the different sieve sizes applied. The samples that pass through these sieves are considered cut-size bottom ash. Then, both groups of bottom ashes will be ground to have the same high fineness. Next, the mortar testing will be conducted in response to the first objective of this study, which is to evaluate the pozzolanic reaction of ground bottom ash by investigating the SAI in accordance with ASTM C618. In addition, the microstructure properties of raw power samples and pastes containing ground bottom ash will be studied by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy analysis (EDS), X-ray diffraction analysis (XRD), differential thermal gravimetric (DTA) and thermogravimetric analysis (TGA), mercury intrusion porosimetry (MIP), and degree of reaction (DR) investigation. 

Part II: Investigation on workability, strengths, and durability properties of HPC containing super pozzolan from bottom ash.

The aim of this part is to utilize the bottom ash obtained from Part I as a super pozzolan in HPC. The processed bottom ash will be used to replace OPC at the high level of 50–80% by weight of binder. The target compressive strength of HPC of this study is 80 to 100 MPa. The flow slump of concrete will be maintained between 650–750 mm by adjusting the mix proportion and superplasticizer content. In addition, nanomaterials may be used to enhance the performance of concrete, such as nano silica or nano calcium carbonate. The fresh properties of HPC containing super pozzolan from the processed bottom ash, including loss of slump flow and viscosity in terms of T50 and V-Funnel, will be determined. The mechanical properties of hardened concrete, such as compressive strength, modulus of elasticity, and compression creep behavior, will be investigated. In addition, the durability properties of concrete are significant. The durability of concrete is defined as the ability of concrete to resist deterioration from the environment or from the service in which it is placed while maintaining its desired engineering properties. In this study, the durability of HPC, such as drying shrinkage, water permeability, and chloride resistance, will be investigated.

Part III: Utilization of coarse bottom ash as a functional aggregate in HPC

In this part, the selected mix proportion of concrete in Part II will be developed to produce advanced functional HPC using functional aggregate made from bottom ash i.e., as an internal curing material and as thermal/acoustic insulation material. For internal curing material, low and high CaO coarse bottom ash (retaining a specified sieve from Part I and II) will be immersed in water, saturated lime water, and a mild concentration of sodium hydroxide solution to obtain a saturated-surface-dry condition. Then, the natural aggregate will be replaced by the processed bottom ash and the factors affecting the properties of HPC such as strengths, compression creep, and durability properties will be investigated. For thermal/acoustic insulation, the bottom ash is a porous material with numerous open voids in its particles, its utilization as a functional aggregate can improve the thermal and acoustic insulation of concrete. Therefore, the processed bottom ash retained on a specified sieve will be used to replace natural aggregate in HPC. The thermal conductivity of concrete will be determined using ISOMET 2114 based on ASTM D5930, and the sound absorption coefficient will be measured according to ASTM E1050. The results of this part will be advantageous for future applications of bottom ash in HPC having high thermal insulation and sound absorption needs, such as precast concrete wall and noise barrier concrete in urban roads.