Malenab, R., Ngo, J., & Promentilla, M.
Materials (2017). In press
The use of natural fibers in reinforced composites to produce eco-friendly materials is gaining more attention due to their attractive features such as low cost, low density, and good mechanical properties, among others. This work thus investigates the potential of waste abaca (Manila hemp) fiber as a reinforcing agent in an inorganic aluminosilicate material known as geopolymer. In this study, the waste fibers were subjected to different chemical treatments to modify the surface characteristics and to improve the adhesion with the fly ash-based geopolymer matrix. Definitive screening design of experiment was used to investigate the effect of successive chemical treatment of the fiber on its tensile strength considering the following factors: (1) NaOH pretreatment; (2) soaking time in aluminum salt solution; and (3) final pH of the slurry. The results show that the abaca fiber without alkali pretreatment, soaked for 12 h in Al2(SO4)3solution and adjusted to pH 6 exhibited the highest tensile strength among the treated fibers. Test results confirmed that the chemical treatment removes the lignin, pectin, and hemicellulose, as well as makes the surface rougher with the deposition of aluminum compounds. This improves the interfacial bonding between geopolymer matrix and the abaca fiber, while the geopolymer protects the treated fiber from thermal degradation.
Kalaw, M., Culaba, A., Hinode, H., Kurniawan, W., Gallardo, S., & Promentilla, M.
Materials (2016). In press.
Geopolymers are inorganic polymers formed from the alkaline activation of amorphous alumino-silicate materials resulting in a three-dimensional polymeric network. As a class of materials, it is seen to have the potential of replacing ordinary Portland cement (OPC), which for more than a hundred years has been the binder of choice for structural and building applications. Geopolymers have emerged as a sustainable option vis-à-vis OPC for three reasons: (1) their technical properties are comparable if not better; (2) they can be produced from industrial wastes; and (3) within reasonable constraints, their production requires less energy and emits significantly less CO₂. In the Philippines, the use of coal ash, as the alumina- and silica- rich geopolymer precursor, is being considered as one of the options for sustainable management of coal ash generation from coal-fired power plants. However, most geopolymer mixes (and the prevalent blended OPC) use only coal fly ash. The coal bottom ash, having very few applications, remains relegated to dumpsites. Rice hull ash, from biomass-fired plants, is another silica-rich geopolymer precursor material from another significantly produced waste in the country with only minimal utilization. In this study, geopolymer samples were formed from the mixture of coal ash, using both coal fly ash (CFA) and coal bottom ash (CBA), and rice hull ash (RHA). The raw materials used for the geopolymerization process were characterized using X-ray fluorescence spectroscopy (XRF) for elemental and X-ray diffraction (XRD) for mineralogical composition. The raw materials’ thermal stability and loss on ignition (LOI) were determined using thermogravimetric analysis (TGA) and reactivity via dissolution tests and inductively-coupled plasma mass spectrometry (ICP) analysis. The mechanical, thermal and microstructural properties of the geopolymers formed were analyzed using compression tests, Fourier transform infra-red spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Using a Scheffé-based mixture design, targeting applications with low thermal conductivity, light weight and moderate strength and allowing for a maximum of five percent by mass of rice hull ash in consideration of the waste utilization of all three components, it has been determined that an 85-10-5 by weight ratio of CFA-CBA-RHA activated with 80-20 by mass ratio of 12 M NaOH and sodium silicate (55% H₂O, modulus = 3) produced geopolymers with a compressive strength of 18.5 MPa, a volumetric weight of 1660 kg/m³ and a thermal conductivity of 0.457 W/m-°C at 28-day curing when pre-cured at 80 °C for 24 h. For this study, the estimates of embodied energy and CO₂ were all below 1.7 MJ/kg and 0.12 kg CO₂/kg, respectively.
Kalaw, M., Culaba, A., Nguyen,H., Nguyen, K., Hinode, H., Kurniawan W., Susan M Gallardo, Michael Angelo B. Promentilla.
ASEAN Journal of Chemical Engineering (2016). In press.
Geopolymers, from industrial wastes such as blast furnace slag, red mud, and coal ash, among others, have emerged as technically viable, economically competitive, and environmentally attractive supplements and even alternatives to ordinary Portland cement (OPC). Furthermore, while the most impact shall be achieved with largescale use in the general building and structural sector, as replacement or supplement to OPC, the properties of these geopolymers may be optimized for special niche applications. One of these applications is for light weight, low thermal conductivity, heat resistant, and moderate strength cement binder for low rise residential buildings. In this study, compressive strength, heat resistance, volumetric weight, mass loss, water absorption and thermal conductivity of geopolymers formed from mixtures of coal bottom ash and rice hull ash (CBARHA) and coal fly ash and rice hull ash (CFA RHA) with sodium silicate solution (modulus 2.5) as activator were evaluated. Using mixture design and the JMP statistical software, the CBARHA combination at a mass ratio of 46% CBA, 32% RHA with 22% WGS gave properties at maximum desirability of 17.6 MPa compressive strength, 1640 kg/m3 volumetric weight, 273 kg/m3 water absorption, 28 MPa compressive strength after high temperature exposure (1000oC for 2 hours) with 4.4% mass loss, and 0.578 W/mK thermal conductivity. On a performance basis, even as the geopolymers are formed as paste, these properties fall within the standards for lightweight OPC based concrete with strength requirements for residential buildings. The low thermal conductivity and higher strength after high-temperature exposure vis-à-vis OPC are additional advantages for consideration.
Sumabat, A., Mañalac, A., Nguyen, H., Kalaw, M., Tan, R., Promentilla, M.
Chem. Eng. Trans (2015). In press.
High CO2 emission and energy intensity from the Portland cement industry has prompted many researchers to develop cleaner and low-emission technologies for a sustainable built environment. Geopolymer technology is one promising solution to produce an alternative cementitious material with lower carbon footprint and reduce the global consumption of Portland cement. Geopolymer can use waste such as red mud, coal ash, rice hull ash, among others, as raw materials for reactive alumina-silicates. At high alkaline condition, these alumina-silicates form a geopolymer cement binder system that hardens at room temperature like Portland cement. However, optimal mix formulation of these raw materials is necessary to produce materials with desired specification for a specific application. This work thus presents a systematic method that integrates the statistical design of experiment, multiple response optimization technique and analytic hierarchy process for product design of geopolymer-based materials. The method is demonstrated using a case study involving a geopolymer from a ternary blend of red mud, rice hull ash, and diatomaceous earth. Aside from the mechanical and thermal properties, production cost, embodied energy and carbon footprint were considered in modeling the product desirability.
Promentilla, M., Kalaw, M., Nguyen, H., Aviso, K., Tan, R
Computer Aided Chemical Engineering (2017). In press.
Geopolymer is an inorganic polymer binder formed from the alkaline activation of reactive alumino-silicate materials resulting in two- or three-dimensional polymeric network. It is a promising alternative to Portland cement-based materials because of its lower embodied energy and carbon footprint with potential for waste valorization. Studies have been done to develop such material with desired engineering specification by using statistical design of experiment and optimizing the process conditions or mix formulation of waste materials. However, it is not only the engineering properties such as its mechanical and thermal properties, but also other properties pertaining to green materials (e.g., embodied energy and carbon footprint) must be considered. Conflicting objectives may also have to be satisfied simultaneously to find a compromised solution in the product design such as that of maximizing the strength and minimizing the volumetric weight. This work thus proposes a weighted max-min aggregation approach to multi-objective optimization of the geopolymer product using fuzzy programming approach. The optimization formulation was introduced such that fuzzy sets represent both the aspired product desirability and soft constraints; the optimal mix is then found by maximizing the simultaneous satisfaction of target properties of the desired product. This work also proposes an extension of such fuzzy optimization formulation wherein the nature of trade-off between improving the product desirability and satisfying the fuzzy constraints are made explicit. The relative importance of the properties as represented by priority weights were derived systematically using Analytic Hierarchy Process (AHP). A case study on a ternary blended geopolymer from coal fly ash, coal bottom ash, and rice hull ash is presented to illustrate the proposed method.
Kalaw, K., Sumabat, A., Nguyen, H., Dungca, J., Bacani, F., Culaba, A., Gallardo, S.,
Promentilla, M.
Proceedings of the DLSU Research Congress.
In the building sector which has been Portland cement (OPC)-based for the past century, geopolymers have emerged to have the potential to become the new norm. Its technical properties have been shown to be comparable if not better and its production results in as much as 80% reduction in CO2 emissions compared to OPC. Moreover, sustainability is accessible since geopolymers, synthesized via alkali activation of amorphous alumino-silicate materials, can be formed from alumina- and silica- rich industrial and agro-industrial wastes such as coal ash and rice hull ash.
Tigue, A., Hinode, H., Kurniawan W., Promentilla, M.
Proceedings of the 10th Regional Conference on Chemical Engineering.
Thermal power plants in the Philippines produce millions of tons of coal fly ash annually which may cause environmental burden if such by-product is not properly managed. Thus, there has been an increasing interest in bulk utilization of fly ash particularly its application for structural fill and building construction materials. In this study, one-part geopolymer technology was proposed as a sustainable solution to use large amount of fly ash for soil stabilization through chemical stabilization process. Such stabilization consists of adding other materials to the soil or chemicals that will alter its properties by physic-chemical reactions between particles and the added materials or by creating a matrix that binds or coats the particles. The most common additives for soil stabilization are cement, lime, cement/lime mixture. On the other hand, geopolymer is a new class of inorganic polymeric materials that has great potential for such application which has an advantage over the traditional soil stabilizer in terms of carbon footprint. It has cement-like properties that are formed from reacting silica-rich and alumina-rich solids in alkaline solution resulting in a slurry mixture of soil and binder that eventually harden into a new strong matrix. This work thus presents some of our recent findings on developing a soil stabilizer using coal fly ash as a geopolymer precursor with a mixture of sodium hydroxide and sodium silicate as alkaline activator. The hardened geopolymer stabilized soil was then subjected to acid attack and then characterized in terms of mineralogical phases and morphology.
Tigue, A., Dungca, J., Hinode, H., Kurniawan W., Promentilla, M.
Proceedings of the 24th Regional Symposium on Chemical Engineering.
A novel approach one-part geopolymer was employed to investigate the feasibility of enhancing the strength of in-situ soil for possible structural fill application in the construction industry. Geopolymer precursors such as fly ash and volcanic ash were utilized in this study for soil stabilization. The traditional geopolymer synthesis uses soluble alkali activators unlike in the case of ordinary Portland cement where only water is added to start the hydration process. This kind of synthesis is an impediment to geopolymer soil stabilizer commercial viability. Hence, solid alkali activators such as sodium silicate (SS), sodium hydroxide (SH), and sodium aluminate (SA) were explored. The influence of amount of fly ash (15% and 25%), addition of volcanic ash (0% and 12.5%), and ratio of alkali activator SS:SH:SA (50:50:0, 33:33:33, 50:20:30) were investigated. Samples cured for 28 days were tested for unconfined compressive strength (UCS). To evaluate the durability, sample yielding highest UCS was subjected to sulfuric acid resistance test for 28 days. Analytical techniques such as X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscope/energy-dispersive X-ray spectroscopy (SEM/EDX) were performed to examine the elemental composition, mineralogical properties, and microstructure of the precursors and the geopolymer stabilized soil.