experts embarked on finding ways of producing an alternative building material that is less costly and more sustainable but serves the same purpose as aggregates and cement . One of the suggested ways of achieving sustainability in the construction sector is using waste material as an alternative source of concrete materials . Over the past few years , various construction companies around the world have embraced the use of industrial and natural wastes such as pumice , ceramic tile waste , waste glass , oil palm kernel shells ( OPKS ), and laterite aggregates as building materials [ 4-8 ].
Management of waste poses a serious challenge in Malaysia and the best way to handle this challenge is to put the 3R principle ( Recycle , Reuse and Reduce ) into practice thus encouraging the economic utilisation of waste and lowering storage costs . Currently , approximately 40 % of electricity in Malaysia is generated from coal and it is projected that about 50 % of the country ’ s power supply will be produced from coal by the year 2030 [ 9 ]. The process of generating electricity from coal is harmful to the environment as it involves combustion of huge amounts of coal which results in the release of large volumes of toxic substances such as coal bottom ash into the environment . For the last several decades , Malaysian coal power plants have produced immense amounts of coal bottom ash . For example , Tanjung Bin , which is one of the largest coal power plants in the country , produces about 8,000 metric tonnes of bottom ash and 42,000 metric tonnes of fly ash every month [ 10 ]. The methods used in disposing these huge amounts of toxic by-products are not efficient resulting in the contamination of water , soil , and air as well as harming people and other living organisms . However , bottom ash did not show any negative effects on people when used as a construction material as reported by American Coal Ash Association ( ACAA ) [ 11 ]. Another material used in the production of concrete is sand which is used in large quantities . This could lead to excessive mining of sand from rivers which may result in a gradual depletion of natural resources as well as causing an imbalance in the ecological system [ 12 ]. The production of ash from coal power plants is due to the presence of non-combustible substances in coal , such as alumina , silica and iron with small amounts of magnesium sulphate and calcium . The physical properties of coal wastes are similar to those of granite and sand used in concrete mixes . Therefore , these waste products can be used as a potential replacement for ordinary sand . This is the best way to recycle the waste products and conserve the environment . It also helps to reduce the cost of construction as well as enhance the quality of concrete . A comprehensive study was carried out to examine the key properties of the waste products of coal and to determine their suitability for use in the construction industry as a replacement for aggregates and cement .
METHODOLOGY
Materials ASTM C150-15 , type I Portland cement was used by the manufacturer as a binder [ 13 ]. This comprised of 30 % of coal fly ash used as cement replacement in the concrete mix design based on the optimum strength discovered in previous research [ 14 , 15 ]. Coal bottom ash was used as fully fine and coarse aggregate replacements . The aggregates were used in the saturated surface dry condition during the process of preparing all the specimens . The coal waste was obtained from a coal power plant in southern region of Malaysia . The size of coal waste used as coarse aggregates ranged between 4.75mm to 10mm while the size of coal waste used as fine aggregates was less than 4.75mm . The chemical compositions of the cement and coal fly ash used are shown in Table 1 . Meanwhile , the coarse and fine aggregates used are shown in Figure 1 .
Mix Design The mix design was prepared under a saturated surface in dry conditions where the aggregates were formulated . In addition a water to cement ratio of 0.5 for all the concrete specimens was also formulated . The process of mixing was done at room temperature of around 28 ° C . Table 2 shows the mix proportion of the concrete mixtures . Preparation of test specimens was carried out in cubes measuring 100 x 100 x 100mm . A tamping rod was used to compact the specimens into three layers . A vibrating table was used to apply more vibration of approximately 10s , and after 24 hours , the specimens were cured in water where they were left for seven , 14 and 28 days .
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