Evaluation on engineering properties of geopolymers from bottom ash and rice husk ash

The reactions form chains and rings of alumino-silicate networks in geopolymeric structures. The raw materials used for geopolymerization normally contain high SiO2 and Al2O3 in the chemical compositions such as meta-kaoline, rice husk ash, fly ash, bottom ash, blast furnace slag, red mud, and others. The geopolymer-based material has potentials to replace Ordinary Portland Cement (OPC)-based materials in the future because of its lower energy consumption, minimal CO2 emissions and lower production cost as it utilizes industrial waste resources.
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Evaluation on engineering properties of geopolymers from bottom ash and rice husk ashTạp chí Khoa học công nghệ và Thực phẩm 12 (1) (2017) 81-88EVALUATION ON ENGINEERING PROPERTIES OFGEOPOLYMERS FROM BOTTOM ASH AND RICE HUSK ASHNguyen Van Phuc, Nguyen Hoc Thang*Ho Chi Minh City University of Food Industry*Email: thangnh@cntp.edu.vnReceived: 25 June 2017; Accepted for publication: 18 September 2017ABSTRACTGeopolymerization is the process of reactions among alumino-silicate resources in highalkaline conditions developed by Joseph Davidovits in 1970s. The reactions form chains andrings of alumino-silicate networks in geopolymeric structures. The raw materials used forgeopolymerization normally contain high SiO2 and Al2O3 in the chemical compositions suchas meta-kaoline, rice husk ash, fly ash, bottom ash, blast furnace slag, red mud, and others.The geopolymer-based material has potentials to replace Ordinary Portland Cement (OPC)-basedmaterials in the future because of its lower energy consumption, minimal CO2 emissions andlower production cost as it utilizes industrial waste resources. Moreover, in this paper, coalbottom ash (CBA) and rice husk ash (RHA), which are industrial and agricultural wastes,were used as raw materials with high alumino-silicate resources. Both CBA and RHA weremixed with sodium silicate (water glass) solution for 20 minutes to form geopolymermaterials. The specimens were molded in 5-cm cube molds according to ASTMC109/C109M 99, and then cured at room temperature. These products were then tested forengineering properties such as compressive strength (MPa) and volumetric weight (kg/m3),and water absorption (kg/m3). The results indicated that the material can be consideredlightweight with volumetric weight from 1394 kg/m3 to 1655 kg/m3; compressive strength at28 days is in the range of 2.38 MPa to 17.41 MPa; and water absorption is at 259.94 kg/m3.Keywords: Coal bottom ash, geopolymers, rice husk ash, industrial waste, engineeringproperties.1. INTRODUCTIONGeopolymer is inorganic polymer material based on alumino-silicate networks whichare products of reactions among alumino silicate resources in high alkaline condition.Geopolymer has been recently gaining attention as an alternative binder for OrdinaryPortland cement (OPC) due to its low energy and CO2 burden [1-3]. This binder is alsoreferred by other researchers as alkali-activated pozzolan cements [4] or alkaline activatedmaterials [5] to describe the alkali activation of the solid alumino-silicate raw materials in astrongly alkaline environment. It has been estimated that the use of such geopolymer cementcan reduce about 80% of the CO2 emissions associated with the cement production [3, 6]. Inaddition, its reported advantage over OPC in terms of material performance includes longerlife and durability, higher heat and fire resistance, and better resistance against chemicalattack [3, 7-10]. Unlike Portland cement, the solid component of such binder, which is themain source of reactive alumino-silicates, can be sourced out entirely from industrial wastematerials such as blast furnace slag, fly ash, bottom ash, rice husk ash, and red mud [10-15].81Nguyen Van Phuc, Nguyen Hoc ThangThis research presents the utilization of coal bottom ash and rice husk ash as rawmaterials to produce a geopolymer-based material. These raw materials constitute the blendof the alkali-activated binder in this study. CBA was used as the primary source of reactivealumina and silicate. It is an industrial waste of coal-fired power plants, which is estimated tobe over 125 Mt/year worldwide [16-18]. Rice husk ash was used as the primary source ofreactive silica. It is a by-product of burning agri-waste particularly rice husk, with anestimated generation rate of over 20 million metric tons per year worldwide [19-21]. It ishighly porous, lightweight material with very good pozzolanic properties which is used toproduce cheap insulating refractory materials (e.g., see [22]).2. MATERIALS AND METHODS2.1. MaterialsIn this paper, the CBA waste was obtained from the Tan Rai Power Plant (Lam Dong,Viet Nam). The CBA after being dried for 24 hours were ground in 4 hours by a ball millerand then sieved using a 90 μm-mesh. On the other hand, the rice husk ash (RHA) wasproduced from the burning of rice husk at 650 ºC for one hour in the furnace. The rice huskwas obtained from the agricultural waste in Dong Thap province, a local of the MekongDelta, Vietnam. The burned rice husks were also ground in 30 minutes and sieved afterwardsto produce RHA. Water glass solution (WGS) was from Bien Hoa Chemical Factory, DongNai province, Viet Nam.2.2. Mix proportion and experimental processThrough some preliminary investigations of changes in the ratio of CBA/RHA (e.g. 1/0;0.75/0.25; 0.5/0.5 (or 1/1); 0.25/0.75 and 1/0), most of these ratios did not meet the technicalrequirements, except for the ratio of 1/1. Therefore, this ratio was chosen for all followingexperiments. In detail, a mixture of solid powder with 50% CBA and 50% RHA was mixedwith WGS concentration from 10 to 28% (in weight of liquid powder per solid solution).Table 1 showed the mix proportions and WGS solution using for doing experiments in thisresearch. The effects of WGS proportions were investigated through engineering propertiesof the geopolymer specimens after cured at room condition for 28 days.Table 1. Mix proportions used in the design of experimentsMixtureProportion of solid powders (% in wt)Concentration ofWGS (% in wt,liquid/solid)(Sample)CBARHAG10505010G16505016G22505022G28505028The powdered raw materials were prepared according to the designed proportion and thenmixed with 10 to 28% (by weight of the powdered solid) water glass solution for 20 minutesusing a laboratory cement mixer [23]. Water is also added to adjust the pH value o ...