Class C Fly Ash Research Articles

A study on the influencing parameters in developing construction and demolition waste-based geopolymer concretes and their sustainability assessment

Construction and demolition waste (CDW) has been recently identified as a potential aluminosilicate source for geopolymers. However, the available research has mainly focused on developing CDW-based geopolymer pastes and mortars, while studies on geopolymer concretes sourced from CDW have been very limited. Thus, the current study aimed at experimentally identifying different CDW materials suitable for producing geopolymer concretes. Additionally, the study analysed the mechanical, microstructural, and environmental properties of CDW- based geopolymer concrete produced. In this regard, the effect of relevant parameters on the compressive strength development of CDW-based geopolymer concretes was comprehensively investigated, including those related to precursor types/fineness, alkali activator solution, aggregate type/size and curing regimes. Microstructural analyses were also conducted on the selected samples (100% brick waste, 100% tile waste, 100% concrete waste and 75% brick waste + 25% GGBS). Finally, the environmental impact of geopolymer concrete was assessed and compared with similar traditional concrete. Results showed that employing CDWs alone is not suitable to achieve sufficient strengths under all curing regimes. However, the inclusion of 25% GGBS significantly improved the strength performance of CDW-based geopolymer concrete, in comparison to other supplementary cementitious materials (SCMs) such as Class-C fly ash and calcium hydroxide. The particle size of CDWs and concentration of alkaline activators highly affect the performance of CDW-based geopolymer concretes. Utilization of CDWs with particles finer than 75 μm and high concentrations of NaOH (12 M) is recommended to achieve good performance. The results also indicate that almost similar energy is needed for producing CDW-based geopolymer and OPC-based traditional concrete, whereas a huge reduction in CO2 emission (∼40%) was estimated in the case of geopolymers. The outcomes of the current study are expected to contribute to the advancement of geopolymer concrete derived from CDW in addition to providing valuable insights into this type of concrete for practitioners and academics.

Impact of SCMs and fibres in ECC on the fire resistance of hot-jointed SCC/ECC composites

The influence of various supplementary cementitious materials (SCMs) and fibres on the fire resistance of composite systems that combine engineered cementitious composites (ECCs) in tension with self-compacting concrete (SCC) in compression was examined. The study was designed to determine the ideal ECC formulation for optimising mechanical properties and bonding performance at ambient and elevated temperatures. The SCC and ECC were hot-joined without vibration or surface preparation, using a fresh-to-fresh casting method. Modifications to the chemical composition of the ECCs included the addition of class F fly ash (FAF), class C fly ash (FAC) or slag, as well as polyvinyl alcohol (PVA) fibres or steel fibres. The samples were exposed to temperatures of 200°C, 400°C, 600°C and 800°C, followed by comprehensive testing to evaluate their flexural strength, tensile strength and interfacial properties. The results indicate that the incorporation of an ECC layer within the SCC system significantly improved mechanical strength and thermal stability, both at ambient temperatures and under high-temperature conditions. Notably, the addition of FAF (rather than FAC or slag) in the ECC layer offered superior thermal stability and ensured the retention of desirable residual mechanical properties. Moreover, steel fibre reinforcement greatly improved the SCC/ECC bonding, outperforming PVA reinforcement at elevated temperatures.

Class-C fly ash from coal as a partial substitute in cement-based paste and mortar design mix – A case in the Philippines

An indirect way to minimize greenhouse emissions from the cement industry is partially substituting cement with coal fly ash (CFA). Despite CFA being widely studied, the quality, performance, and water requirements, when used in formulating paste and mortar, vary depending on the source. This study assessed CFA from a power plant in the Philippines as a partial substitute for cement. Paste and mortar mixture were designed to have varying CFA-to-binder ratios (CBR) and water-to-binder ratios (WBR). The effect of CBR and WBR on the consistency and workability of fresh paste and mortars were modeled, adopting multivariate non-linear regression to objectively assess the individual and interactive effects. Properties (compressive strength, density, and voids) of hardened mortar formulated with different CBRs but having normal consistency/workability were determined and assessed. Models generated could be used to estimate the WBR required for formulations to achieve normal consistency/workability. The water requirement for mortar formulation to have normal workability may be predicted based on the WBR for paste formulated to have normal consistency. Increased cement replacement with CFA improved the compressive strength, with replacement up to 20 wt% resulting in better performance than pure cement.

Effects of alkali activator types and fly ASH replacement rate on mechanical properties of geopolymer

In this study, C-class fly ash (FA) and ground granulated blast-furnace slag (GGBS)-based geopolymer activated in NaOH and NaOH+Na2SiO3 were used to study setting time, compressive strength, porosity, etc. As a result of comparing the effects of alkali types on FA and GGBS geopolymer composites, NaOH + Na2SiO3 showed increased strength and density compared to NaOH, since the addition of Na2SiO3 provides the silica source to develop more compact structure. For the Class-C FA and GGBS mix, increased fly ash content resulted in prolonged setting times, reduced strength, and loose matrix. In addition, the non-reactivity of calcium in the mixture was observed as the fly ash content increased, leading to strength loss.

Strength-Gain Characteristics and Swelling Response of Steel Slag and Steel Slag–Fly Ash Mixtures

The shear strength and stiffness characteristics of steel slag indicate that it can potentially be utilized as a competent base/subbase material of bound and unbound pavement layers. However, concerns with respect to the utilization of steel slag remain due to its long-term swelling, corrosivity, and leaching characteristics. In this study, long-term swelling and corrosivity tests were performed on basic-oxygen-furnace steel slag (BOFSS) and electric-arc-furnace ladle steel slag [EAF(L)SS] generated in Indiana, USA. In order to reduce the 1D swelling strains of these slags, 5%, 10%, and 20% Class C fly ash (CCFA) and 10% ground rubber replacement ratios were used to prepare steel slag mixtures for testing. The improvement due to CCFA replacement was evaluated by performing unconfined compression and long-term swelling tests on selected steel slag–CCFA mixtures. The seven-day unconfined compression strengths of 90% EAF(L)SS + 10% CCFA and 90% BOFSS + 10% CCFA mixtures were 2,387 and 3,768 kPa, respectively. After nine months of monitoring, the maximum 1D swelling strains of soaked samples of BOFSS and EAF(L)SS mixtures prepared with 10% CCFA replacement were 0.1% or less. The unconfined compression and swelling test results for the steel slag–CCFA mixtures indicated superior strength gain characteristics and negligible swelling strains with time than for steel slags.

Effect of Admixtures (Fly Ash and Super Plasticizer) on Performance of Concrete

Abstract: This research is conducted to study the performance of concrete mix containing Class-C Fly ash and P250 super plasticizer. The concrete mix are also proportioned to have various proportion of cement replacements by fly ash ranging from 10% to 30% by weight and super plasticizer PC250 from 0.5% to 1.5% by weight of cement. The performance of concrete is evaluated with respect to workability and compressive strength by Destructive and Non destructive test (rebound number). At 28 day. Concrete mix containing fly ash and super plasticizer shows consistently higher compressive strength compared to concrete with only fly ash and without fly ash. It has been observed that by addition of fly ash the initial compressive strength is lower because of unhydrated cement, since the addition of fly ash lowers the rate of hydration of cement. According to the analysis of results show that class- C fly ash could be substituted for cement replacement, as the concrete with fly ash 30% and super plasticizer shows 34.19% more strength as compared to non fly ash concrete. Similarly increase in workability also observed upto 240mm slump value.

The innovative Fiber reinforced geopolymer fly ash-based geopolymer in loose sand stabilization

Geopolymer (GP) has recently emerged as a new and environmentally friendly alternative to standard soil stabilization agents such as lime and Ordinary Portland Cement (OPC) to reduce environmental concerns. The addition of fibers to treated soil limits crack propagation, enhancing its strength even further. This study used high calcium class C fly ash (CFA) reacted with 10 M NaOH as a geopolymer (GP) binder to treat weak sand soil. Polypropylene (PP) fibers with a length of 4.5 mm were used as reinforcement in amounts ranging from 0.3 to 1.5%. Microstructure and unconfined compressive strength (UCS) testing were performed on the generated specimens. The study proved the benefits of fiber inclusion in improving the mechanical behavior of the treated weak soil. Superior strength characteristics were observed in GP- treated soil mixes with a binder content of 20% and an Activator/Binder (A/B) ratio of 0.4 reinforced with 1.5% PP fibers by weight, indicating that they can be used as a sustainable alternative to traditional binders in deep soil mixing applications.

Comparison of the performance of class-C and class-F fly ash concrete mixtures produced with crushed stone sand

The use of fly ash as partial replacement of cement in the production of environmentally-friendly concrete is now an established fact. This study investigated the effects of class-C and class-F fly ash at 20 wt% replacement of Portland cement (PC) on the strength and durability characteristics of concrete mixtures incorporating crushed stone sand as fine aggregate. Experimental investigations were carried to compare the effects of class-C and class-F fly ash as partial replacement of cement on the rheology, compressive strength, moisture sorption, abrasion resistance, and microstructural characteristics of the resulting concrete mixtures at various concrete ages.Test results showed that the use of class-C fly ash lowers the workability (slump value) by 26% and entrained air by 33% of the fresh concrete, while the class-F fly didn’t not affect these characteristics when compared with that of control mixture. On the other hand, the use of class-C and class-F fly ash enhanced the later age compressive strength of the resulting mixtures by 23% and 35%, respectively in comparison to control concrete mixture. At 56 days of concrete age, 20% and 29% reduction in the 8-day cumulative moisture sorption and 14% and 19% reduction in mass loss due to abrasion of class-C and class-F based concrete mixtures, respectively, was recorded as compared to that of control mixture. Scanning electron microscopic (SEM) analyses showed enhancement in the microstructure of the concrete mixtures as results of the inclusion of fly ash as partial replacement of PC. Test results also showed superior performance of class-F fly ash on the strength and durability characteristics of resulting concrete mixture as compared to class-C fly ash at equivalent replacement level. The outcome of this study provides insight into the comparative performance of class-C and class-F fly ash based concrete mixtures in fresh and hardened states.

Limestone and class C fly ash blends activated with binary alkalis of Na2CO3–NaOH and MgO–NaOH: Reaction products and environmental impact

Alternative alkaline cements made with composite precursors of limestone (LS) powder and class-C fly ash, activated with commercial powdered sodium silicate or alternative activators of blends of Na2CO3–NaOH and MgO–NaOH were investigated. The limestone-fly ash ratios were of 75–25, 50-50 and 25–75 and the alkaline activators were added at 6, 8 and 10 wt % relative to the total mass of precursors. As the limestone-fly ash ratio decreased, the compressive strength increased, and dosages of activators at 8 and 10% favored high strength gains. The use of Na2CO3–NaOH and MgO–NaOH was more effective than the solid sodium silicate. The curing temperature also influenced the strength; samples cured at 40 °C reached 32 MPa at 28-day with an LS-fly ash ratio of 50-50 and 10% Na2CO3–NaOH, while those activated with 10% MgO–NaOH reached 34 MPa. Thermal analysis (TGA/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) indicated the formation of C,N-(A)-S-H, M-S-H gel, hydrotalcite, and carbonated phases of gaylussite and pirssonite. By using 50 wt% LS a reduction of 80% CO2 emissions can be achieved compared to a Blended Portland cement paste of similar strength, as also proven by two prepared mortars that developed 28-days strengths of 17–19 MPa.

Geopolymer: A Systematic Review of Methodologies.

The geopolymer concept has gained wide international attention during the last two decades and is now seen as a potential alternative to ordinary Portland cement; however, before full implementation in the national and international standards, the geopolymer concept requires clarity on the commonly used definitions and mix design methodologies. The lack of a common definition and methodology has led to inconsistency and confusion across disciplines. This review aims to clarify the most existing geopolymer definitions and the diverse procedures on geopolymer methodologies to attain a good understanding of both the unary and binary geopolymer systems. This review puts into perspective the most crucial facets to facilitate the sustainable development and adoption of geopolymer design standards. A systematic review protocol was developed based on the Preferred Reporting of Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist and applied to the Scopus database to retrieve articles. Geopolymer is a product of a polycondensation reaction that yields a three-dimensional tecto-aluminosilicate matrix. Compared to unary geopolymer systems, binary geopolymer systems contain complex hydrated gel structures and polymerized networks that influence workability, strength, and durability. The optimum utilization of high calcium industrial by-products such as ground granulated blast furnace slag, Class-C fly ash, and phosphogypsum in unary or binary geopolymer systems give C-S-H or C-A-S-H gels with dense polymerized networks that enhance strength gains and setting times. As there is no geopolymer mix design standard, most geopolymer mix designs apply the trial-and-error approach, and a few apply the Taguchi approach, particle packing fraction method, and response surface methodology. The adopted mix designs require the optimization of certain mixture variables whilst keeping constant other nominal material factors. The production of NaOH gives less CO2 emission compared to Na2SiO3, which requires higher calcination temperatures for Na2CO3 and SiO2. However, their usage is considered unsustainable due to their caustic nature, high energy demand, and cost. Besides the blending of fly ash with other industrial by-products, phosphogypsum also has the potential for use as an ingredient in blended geopolymer systems. The parameters identified in this review can help foster the robust adoption of geopolymer as a potential “go-to” alternative to ordinary Portland cement for construction. Furthermore, the proposed future research areas will help address the various innovation gaps observed in current literature with a view of the environment and society.

Water quality implications of the neutralization of acid mine drainage with coal fly ash from India and the United States

Subsurface coal mining often induces the formation of acid mine drainage (AMD) in active and abandoned coal mines while coal combustion generates coal combustion residuals (CCR), including fly ash (FA), with elevated levels of toxic metals. Decades of AMD and CCR production have caused major environmental and human health impacts. Given the typically elevated level of oxides in FA, previous studies have examined its potential to neutralize AMD and remove the associated metals. While the neutralization of AMD through reaction with FA has been demonstrated to successfully remove cationic metals, the fate of oxyanion forming elements are less well studied and is the focus of this study. Here we conducted 49 different experiments in which simulated AMD solutions were interacted with representative U.S. (n = 7) and Indian (n = 6) FA samples through controlled liquid to solid ratios in short-term (24 h) and long-term (up to 5 weeks) lab-scale experiments. We show that Class-F FA, originating from Gondwana and Northeastern Tertiary coals in India, has limited neutralization capacity, while Class-C FA, with high CaO and MgO contents from Powder River coals in the U.S. has the greatest AMD neutralization capacity among the studied fly ashes. The neutralization experiments show that AMD-FA reactions cause the removal of cationic elements (i.e., Fe, Mn, and Al) from solution, while at the same time, leaching oxyanion forming elements (i.e., As, Se, Mo, Cr, B, Tl, and Sb) from the FA, increasing the potential environmental risks from the treated leachates. The magnitude of mobilization of these elements depends on their concentrations in the FA and the pH conditions. We show that using FA from the Appalachian and Illinois coals efficiently neutralizes AMD, but also results in secondary contamination of the treated effluents with oxyanion forming elements to levels exceeding drinking water and ecological standards, which could contaminate the ambient environment, whereas neuralization with Powder River Basin Class-C FA induces only limited contamination.

Geotechnical characterization of sustainable geopolymer improved soil

Abstract Geopolymer (GP) has recently emerged as a novel and environmental friendly alternative to conventional soil stabilization products like lime and Ordinary Portland Cement (OPC), which adversely affect the environment. This article emphasizes GPs produced from high calcium class C fly ash (CFA) and an alkali activator comprising sodium hydroxide and sodium silicate solution for sand stabilization. The experimental program includes a series of unconfined compressive strength (UCS), flexural strength, tensile strength, and microstructural analyses using scanning electron microscopy. Results revealed that UCS, flexural strength, and tensile strength of GP-treated soil were in the range of 2–10, 0.5–2.0, and 0.4–1.2 MPa, respectively (depending on the ratio of fly ash and activator). These strengths were even higher than those of cement-stabilized soil. The microstructural analysis revealed that the formation of dense calcium–sodium alumina–silicate hydrated gel (C, N–A–S–H) is the reason for strength improvement. According to the findings of this study, using a CFA-GP binder for soil improvement is a viable alternative to OPC in geotechnical applications.

Structural parts based on Municipal-Solid-Waste incineration ashes

We investigated a novel processing technique of municipal solid waste incineration (MSWI) ashes. By using two thermodynamic driving forces – a strong alkaline activator and a compaction pressure, the otherwise relatively nonreactive MSWI ashes could form strong solids, with relatively high flexural and compressive strengths. The produced material was dense, with a low defect density. The effects of the compaction pressure range, the alkaline activator amount, and the MSWI fly ash to bottom ash ratio were examined. We also used 5 wt% class-C fly ash, 5 wt% class-F fly ash, and/or 1 wt% epoxy as additives. This study may open a door to advanced MSWI ash upcycling approaches, useful to environmental preservation and sustainability.

Effect of Binary and Ternary Binders on Flow and Strength of Cement Mortar

This paper reports the results of laboratory work on the flow and strength of cement mortars containing binary and ternary blends of portland cement, silica fume (SF), Class C fly ash (CFA) and Class F fly ash (FFA). The cement was partially replaced with 20 and 40 wt.% of fly ash (FA) and 5 wt.% of SF as binary mixtures. Besides, the ternary mixtures contained 15%FA+5%SF and 35%FA+5%SF in place of 20% and 40% cement respectively. Both fly ashes were used in the ternary mixtures, thus, 4 mixtures containing ternary binders were prepared. Two sets of mortar mixtures having either same flow or same water/binder (W/B) ratio as those of the control mixture (containing no mineral admixture) were investigated. In total, 15 mortar mixtures were taken into constitution in the present study. The flow of mixtures was measured immediately after casting. In addition, the 7-and 28-day flexural and compressive strength of the mortar mixtures were determined. The use of SF in binary mixtures with constant W/B ratio provided the highest compressive strength (68 MPa). In ternary mixtures the use of 20%FA+5%SF mixture with constant W/B ratio showed the highest 28-day compressive strength (65 MPa). Among the mixtures with constant W/B ratio, ternary mixtures showed the lowest flow values. Besides, in the mixtures with constant flow, once again, the ternary mixtures had the highest W/B ratio. Both in binary and ternary specimens, the mixtures prepared with FFA had a higher flow than that of the CFA mixtures.

Performance of natural clinoptilolite zeolite in the cementitious materials: A comparative study with metakaolin, fly ash, and blast furnace slag

Different pozzolanic materials possess different chemical and mineralogical compositions and could show different performances in the blended hydrated cementitious materials. In the present study, the performance of natural clinoptilolite zeolite, a popular silica-alumina-based natural pozzolanic material in recent times, was investigated to compare with other commonly available silica-alumina (metakaolin) and silica-calcium (blast furnace slag, and Class C-fly ash) enriched pozzolanic materials in the blended cementitious system. The performance was evaluated on fresh (workability), hydration (setting time and chemical shrinkage), and mechanical (compressive strength) properties of hydrated cementitious materials. Thermogravimetric analysis (TGA) was accomplished to measure the pozzolanic activities of all respective pozzolanic materials. The water absorption, porosity, and chloride ion penetrability of concrete via surface resistivity were measured as the transport properties. For the durability properties, drying shrinkage and the alkali-silica aggregate reaction (ASR) of mortars were investigated. Results revealed that the addition of clinoptilolite zeolite reduced the workability but accelerated the setting time of hydration compared to other pozzolanic materials. Zeolite particles increased the volume of chemical shrinkage compared to other pozzolanic materials due to the particle packing effects. The addition of zeolite led to decreasing the compressive strength due to relatively slow pozzolanic activity compared to the other pozzolanic materials as measured by the TGA analysis. Zeolite blended samples had a similar water absorption and porosity compared to the metakaolin, slag, and fly ash blended samples. All pozzolanic materials were equally effective in reducing the drying shrinkage, while zeolite particles attributed to the internal curing capacity. Overall, clinoptilolite zeolite exhibited excellent resistance to chloride-ion penetrability due to the finer pore size, and a reduction in deleterious expansion due to ASR through cation exchange compared to slag and fly ash particles.

Fly Ash/Paraffin Composite Phase Change Material Used to Treat Thermal and Mechanical Properties of Expansive Soil in Cold Regions

Phase change materials (PCMs) can store large amounts of energy in latent heat and release it during phase changes, which could be used to improve the freeze-thaw performance of soil. The composite phase change material was prepared with paraffin as the PCM and 8% Class C fly ash (CFA) as the supporting material. Laboratory tests were conducted to reveal the influence of phase change paraffin composite Class C fly ash (CFA-PCM) on the thermal properties, volume changes and mechanical properties of expansive soil. The results show that PCM failed to establish a good improvement effect due to leakage. CFA can effectively adsorb phase change materials, and the two have good compatibility. CFA-PCM reduces the volume change and strength attenuation of the soil, and 8 wt.% PCM is the optimal content. CFA-PCM turns the phase change latent heat down of the soil and improves its thermal stability. CFA-PCM makes the impact small of freeze-thaw on soil pore structure damage and improves soil volume change and mechanical properties on a macroscopic scale. In addition, CFA-8 wt.% PCM treated expansive soil has apparent advantages in resisting repeated freeze-thaw cycles, providing a reference for actual engineering design.

Fly Ash Selection and Mix Proportioning for Ambient Cured High Strength In-situ Cast Mono Component Geopolymer Concrete

Potential valorisation of fly ash powders is examined for scalable production of in-situ cast structural member with ambient cured alkali-activated geopolymer concrete. The critical issue of strength variation has been investigated by correlating with the physical and chemical properties of the original fly ash affecting water demand in mix proportion. A Class-F fly ash having fineness of 680 m2/kg Blaine’s specific surface area (SSA) and a low w/b down to 0.16 showed the 28-day strength of 99 MPa. In contrast, medium sized (416-464 m2/kg) fly ash-based mono component concrete produced the strength between 40-47 MPa and that of the coarse (157-326 m2/kg) grade < 20 MPa in the 28-day test. Lower strength was observed in Class-C fly ash containing high proportion of quartz sand exhibiting higher water demand. Results of mix proportioning suggest a higher strength gain with 20-30% increase in fly ash over the minimum cement content specified in the mix design guidelines of IS 456 : 2000 while replacing 15-20% of coarse aggregates by fine aggregates. Unconfined flexural load applied on the three M40 reinforced concrete (RC) beams, viz. mono component, bi-component geopolymer and Portland pozzolana cement showed similar deflection up to 20 kN load.

Experimental Investigation on the Microstructural Properties of Black Cotton Soil Stabilized with Cinder (Scoria) Fines and Class-C Fly Ash

Black cotton soil is one of the significant problematic soil for any civil or geotechnical engineering application in the whole world. In the past several decades, different experimental studies have been carried out on the stabilization of expansive soil and different types of stabilizers like lime, Portland cement, cement fly ash, and lime fly ash were used and applied in highway and others construction. However, those traditional stabilizers are not environmentally friendly thus further scientific study is needed to minimize the percentage of carbon-based stabilizers. The fact that Ethiopia encountered major engineering problems due to these problematic soils many researchers have been conducted a vital study using traditional stabilizers for several years however there is no significant study on the microstructural properties of stabilized black cotton soil. In this study, a scoria fines and class c fly ash are used at different blended groups, for each group, the stabilizer content ranges from 10 to 30%. The liquid limit and plasticity index of the soil has been decreased with the increasing content of class c fly ash (FA) and cinder fines (CF). Especially after the soil treated with 25% of class c fly ash and 25% of cinder fines, the liquid limit has decreased by 51.61% and, the plasticity index by 78.61%, linear shrinkage by 66.58%, and the free swell index decreased by 78.9%. The CBR and UCS value has increased by 86.2% and 83.9%, respectively, and CBR swell reduced by 61.2% with increasing stabilizer content. The microstructural properties of Raw black cotton soil and samples that are selected based on strength and index properties (BCS+FA3, BCS+CF3, BCS+CF+FA3) were observed by Scanning electron microscopy (SEM) imagining device, and the result clearly shows the alteration in fabric and morphology of the sample. After treatment with class c fly ash and cinder fines, the laminated configuration of black cotton soil has changed to more flocculated and coherent mass. Also, the SEM image proves that cinder fines impart a mechanical bonding that forms well-developed floccules and a more porous nature. These types of particle arrangement and clay aggregation bring the improvement in index and strength properties.

Characterisation and properties of class C-fly ash based geopolymer foams: Effects of foaming agent content, aggregates, and surfactant

In this study, GFs were first prepared in two forms; foamed mortars using the graded (GS-) and the river (RS-) sand as aggregates, and a foamed paste (P-). Aluminum (Al) powder, used as the foaming agent, had effects on porosity, pore morphology, and pore size distribution. When the amount of Al was increased, there cracks had formed in the P-GFs so the strength reduction was more drastic than that of the foamed mortars of both types. The sand aggregates acted as the skeletal structure of the GFs strengthening the materials. The attempt to improve the porosity characteristics of the foamed mortars by the addition of the dishwashing liquid surfactant was successful. The pore size of the GS-GFs became smaller and the distribution was more uniform. However, the compressive strength had degraded. Assessment on initial and final setting times, phase formation, and microstructure showed that the geopolymerisation and the C-S-H phase (tobermorite) formation had been retarded when this surfactant was incorporated. This GF also showed the most severe strength degradation in the thermal exposure test. Although all GFs mortars did not show disintegration or spalling of the pieces, microcracks appeared after exposure at 800 °C, and became more remarkable after 1000 °C. The fire resistance test on the 10 mm thick-GF mortar panels showed that the reversed-side temperature remained around 400–450 °C after 30 min of exposure without spalling or catastrophic cracks.

Determining physico-chemical parameters for high strength ambient cured fly ash-based alkali-activated cements

High strength ambient cured alkali-activated cement was developed from original Class-F (ASTM) fly ash using 1:2.5 mass ratio of 16 molar sodium hydroxide and sodium silicate liquid activator with solution to solid binder ratio of 0.36 for in-situ cast application. Graded strength of high, medium and low in the range of 60–103, 30–56 and ≤ 20 MPa were obtained using mono-component original fine, medium and coarse sized fly ashes respectively. The inclusion of 35 wt% GGBS in the medium sized Class-F fly ash improved the strength from 45 MPa to 60 MPa while 100% GGBS showed higher strength of 81 MPa. Chemically, CaO/SiO2 ratio in the composition influenced the fresh and hardened properties of alkali-activated fly ash/GGBS cements. For instance, in the Class-F fly ash (Si/Al=1.55-1.99) based compacts with CaO/SiO2 ratio ≤ 0.03, the strength improved with increasing atomic Al/(Na + K) ratio. Conversely strength decreased with increasing Al/(Na + K) ratio in bi-component fly ash and GGBS based alkali-activated cements where CaO/SiO2 ratio is higher in between 0.17-0.75. Interestingly Si-dissolution from subcrystalline silica or fine quartz from mechanically activated Class-C fly ash did not improve strength. Lignite ash with high specific surface area as obtained in low temperature combustion did not react with high pH alkaline solution indicating need for vitreous aluminosilicate glass. X-ray diffraction and attenuated total reflectance Fourier transform infrared spectroscopic analyses show that plagioclase and C-S-H were the reaction products responsible for strength gain in ambient cured alkali-activated fly ash/GGBS cements.