Aluminosilicate minerals have become an important resource for an emerging sustainable material for construction known as geopolymer. Geopolymer, an alkali-activated material, is becoming an attractive alternative to Portland cement because of its lower carbon footprint and embodied energy. However, the synthesis process requires typically a two-part system for alkali activation wherein the solid geopolymer precursor is mixed with aqueous alkali solutions. These alkali activators are corrosive and may be difficult to handle in the field-scale application. In this study, a one-part geopolymer in which coal fly ash was mixed with solid alkali activators such as sodium hydroxide and sodium silicate to form a powdery cementitious binder was developed. This binder mixed with soil only requires water to form the soil-fly ash (SO-CFA) geopolymer cement, which can be used as stabilized soil for backfill/foundation. This geopolymer product was then evaluated for chemical stability by immersing the material with 5% by weight of sulfuric acid solution for 28 days. Indication suggests that the geopolymer exhibited high resistance against acid attack with an observed increase of unconfined compressive strength even when the immersion time in acidic solution was increased to 56 days. The mineralogical phase, microstructure, and morphology of the material were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), respectively. Results not only confirmed the formation of gypsum due to acid attack but also indicated the dissolution of anorthite and albite that may have caused the microstructure to be composed of sodium aluminosilicate hydrate (N–A–S–H) and calcium (alumino) silicate hydrate (C(–A)–S–H) with poly(ferro-sialate-siloxo) and poly(ferro-sialate-disiloxo) networks. A column leaching test with deionized water was also performed on the soil-fly ash geopolymer to study the leachability of metals in the material. Results showed that arsenic exhibits higher mobility in the geopolymer as compared to that of cadmium, chromium, and lead.

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.

ABSTRACT:The Philippines has an extensive road network which handles most of its passenger and freight movements. Large volumes of aggregate embankment materials of good quality are required to primarily support these transport infrastructures, and this poses threat to the environment. Coal combustion by-products (CCPs) are seen to be its potential alternative mainly due to its vast production and disposal problems in the country. Representative samples of class C fly ash and bottom ash were gathered together with conventional road base materials. Fly ashes were substituted to act as fines; whereas, bottom ash substitutions were varied at different mixture ratios of 0%, 20%, 40%, 60%, 80%, and 100% of fine aggregates. Index properties (i.e. specific gravity, Atterberg limits, and maximum and minimum index densities), compaction characteristics, unsoaked and soaked California Bearing Ratios (CBR), and hydraulic conductivities were obtained for all the blends in order to produce empirical relationships with varying bottom ash content. Results show that the optimum strength can be produced at a blend of 100% bottom ash. However, permeability tests show a considerable decline in hydraulic conductivity with the addition of coal ashes to the typical aggregates. Thus, proper drainage must be carefully applied to these blended embankment materials so as to avoid substantial ingress of water.

This study focuses on the analysis of the soil bearing capacities of the various cities and municipalities of Metro Manila, Philippines. The allowable soil bearing capacities to be used for foundation design were calculated through various theories and studies using geotechnical parameters, such as relative density and angle of internal friction. Standard Penetration Test (SPT) results were used to estimate these geotechnical parameters in order to obtain a good approximation of the soil's bearing capacity. Because of economic constraints, not all low-rise construction projects choose to perform soil exploration. Due to this, soil data are usually lacking and may cause problems when designing shallow foundations of these kinds of structures. In line with this kind of situation, the study can help engineers in designing shallow foundations by providing them a reference of the allowable soil bearing capacity of any area within Metro Manila. This will be able to give them a good idea of the soil's strength in supporting shallow foundations. The allowable bearing capacity of the soil shown in the reference is obtained from collected borehole data within Metro Manila and by using several geotechnical engineering theories. Contour maps of the bearing capacities are then made in order to provide an overview of the soil bearing capacity for shallow foundations. A Geographic Information System (GIS) software database was also made so as to store all the borehole location's data as well as serving another basis for estimation. This can be updated whenever new data is available.

ABSTRACT:Fly ash in the recent decades has become abundant resulting in the improper waste disposal. However, it is also known to be a precursor to the process of geopolymerization which is categorized under waste utilization. Geopolymer has become known for being on par with cement and other chemical stabilizers in terms of strength. It has been used in numerous studies focusing on concrete and on soil stabilization. This study proposes the use of fly-ash-based geopolymer as a stabilizer for silty sand embankment material wherein the process of synthesizing geopolymer is through the dry-mix method. The dry-mix method is another way of producing geopolymer, requiring the aluminosilicate precursors and alkali activators to be in its dry state, and adding water to the dry-mix would result in geopolymerization. The geopolymer was applied on Silty Sand to verify its reaction with the soil and to obtain the effective mix that would enable the soil to be stabilized for embankment use. The effectiveness of this method in soil stabilization was tested through the following tests, the CBR Test (ASTM D1833) and the UCS Test (ASTM D2166). Results have shown improvements of the geopolymer-stabilized soil in terms of the CBR index and the UCS value. The effective geopolymer concentration was found to be at 30% geopolymer concentration which produced the highest increase for the stabilized soil with a maximum CBR index of 34.32% and a maximum UCS value of 1349.74 kPa.