Class C Fly Ash Research Articles

Masonry composite material made of limestone powder and fly ash

Large amounts of fly ash (FA) and limestone powder (LP) wastes are accumulating in countries all over the world. Most of these wastes are abandoned and cause certain serious environmental problems and health hazards. In this study, LP waste and class-C FA were used to produce a composite material without the addition of portland cement. LP was mixed with the FA at levels of 10, 20 and 30% by volume in the samples. LP and FA were mixed, wetted and compressed under high pressure in a steel mould. The compressive and flexural strengths were measured, and ultrasonic pulse velocity tests were performed on samples at ages of 7, 28 and 90 days. Density, water absorption and thermal conductivity values were also determined for the samples aged for 28 days. Preliminary results obtained from the tests indicate that masonry composites can be produced using LP, FA and water.

Resilient Modulus of Clay Subgrades Stabilized with Lime, Class C Fly Ash, and Cement Kiln Dust for Pavement Design

The effects of different percentages of one traditional additive—hydrated lime—and two by-products—Class C fly ash (CFA) and cement kiln dust (CKD)—on the resilient modulus (Mr) of four different clay subgrades were investigated. It was found that at lower application rates (3% to 6%), the lime-stabilized soil specimens showed highest enhancement in the Mr values. At higher application rates (10% to 15%), however, CKD treatment provided maximum improvements. Three log-log and one semi-log stress-based models were evaluated. Validation of selected models was conducted by using additional soil data. Overall, a semi-log deviatoric and confining stress model was found to show the best acceptable performance. Additional analyses were performed to develop correlations of Mr with compacted specimen characteristics and soil and additive properties. To illustrate the application of the semi-log model, the AASHTO flexible pavement design methodology was used to design asphalt concrete pavement sections.

Laboratory Performance Evaluation of Subgrade Soils Stabilized with Sulfate-Bearing Cementitious Additives

AbstractA laboratory study was conducted on both raw and stabilized soil specimens to evaluate the performance of two subgrade soils stabilized with three different additives, namely, hydrated lime (or lime), class C fly ash (CFA), and cement kiln dust (CKD). Lime, CFA, and CKD have low sulfate (<40 ppm), moderate sulfate (≈3,280 ppm), and high sulfate content (≈28,133 ppm), respectively. Cylindrical specimens were prepared with different percentages of additives and cured for 28 days. Following the curing period, specimens were tested for resilient modulus (Mr), and unconfined compressive strength tests (UCS), representing short-term performance. Long-term laboratory performance (or durability) was evaluated in terms of moisture susceptibility (tube suction test) and three-dimensional (3D) swell during 60-day capillary soaking of cured specimens. At the end of 60 days, the specimens were also tested for Mr and UCS, as additional indicators to long-term subgrade performance. Short-term performance evaluation projected 15 % CKD with the highest improvement after 28 days of curing, while long-term performance evaluation showed 9 % lime providing maximum enhancements in Mr and UCS values after 60 days of capillary soaking. The study further indicated decrease in durability of specimens stabilized with CKD; however, lime and CFA helped by reducing 3D swell and moisture susceptibility. This difference in behavior was attributed to the presence of elevated levels of sulfate in CKD resulting in sulfate-induced heaving of stabilized soil specimens. Mineralogical studies such as scanning electron microscopy and energy dispersive spectroscopy were also used to verify the research findings observed from the macro test results.

Engineering Properties and Moisture Susceptibility of Silty Clay Stabilized with Lime, Class C Fly Ash, and Cement Kiln Dust

A laboratory study was undertaken to evaluate the effectiveness of different percentages of hydrated lime, class C fly ash (CFA), and cement kiln dust (CKD) as soil stabilizers. Cylindrical specimens were compacted and cured for 28 days in a humidity room having a constant temperature and controlled humidity. At the end of the curing period, specimens were tested for resilient modulus (Mr), modulus of elasticity (ME), and moisture susceptibility using tube suction test. The study revealed that the values of Mr, ME, and unconfined compressive strength (UCS) for the stabilized specimens increased with the increase in the amount of the stabilizing agent. It was also found that the increase in Mr, ME, and UCS values varies with the type of stabilizing agents. The CKD-stabilized specimens exhibited a higher increase in Mr, ME, and UCS values than the corresponding values of lime- and CFA-stabilized specimens. Additionally, CKD-stabilized specimens exhibited the least moisture susceptibility in terms of lowest dielectric values as compared to lime- and CFA-stabilized specimens.

Compressive strength and microstructural characteristics of class C fly ash geopolymer

Abstract Geopolymers prepared from a class C fly ash (CFA) and a mixed alkali activator of sodium hydroxide and sodium silicate solution were investigated. A high compressive strength was obtained when the modulus of the activator viz., molar ratio of SiO 2 /Na 2 O was 1.5, and the proper content of this activator as evaluated by the mass proportion of Na 2 O to CFA was 10%. The compressive strength of these samples was 63.4 MPa when they were cured at 75 °C for 8 h followed by curing at 23 °C for 28 d. In FTIR spectroscopy, the main peaks at 1036 and 1400 cm −1 have been attributed to asymmetric stretching of Al–O/Si–O bonds, while those at 747 cm −1 are due to the Si–O–Si/Si–O–Al bending band. The main geopolymeric gel and calcium silicate hydrate (C–S–H) gel co-exist and bond some remaining unreacted CFA spheres as observed in XRD and SEM–EXDA. The presence of gismondine (zeolite) was also observed in the XRD pattern.

Performance of a Stabilized Aggregate Base Subject to Different Durability Procedures

This study examined the effects of two freeze-thaw (FT) laboratory procedures, FT-1 and FT-2, on stabilized aggregate specimens. Cylindrical specimens were stabilized with 10% Class C fly ash (CFA) cured for selected periods and then subjected to either FT-1 or FT-2 cycles. FT-1 and FT-2 procedures consisted of freezing specimens at −25°C for 24 h and thawing them at 21.7°C for another 24 h with a high relative humidity; the only difference was that FT-1 required a membrane around each specimen, while FT-2 required no membranes during freezing and thawing. After being subject to freezing and thawing actions, specimens were then tested for resilient modulus ( MR ) and unconfined compressive strength (UCS) values. Results showed that the MR values of 28-day cured specimens increased as FT-1 cycles increased up to 12, beyond which a reduction in MR values was observed. For 3-day cured specimens the MR increased with FT-1 cycles up to 30. The UCS values of 28- and 3-day stabilized specimens also exhibited the...

A Comparative Evaluation of Various Additives Used in the Stabilization of Sulfate Bearing Lean Clay

Abstract A laboratory study was conducted on both raw and stabilized clay specimens to evaluate short- and long-term performance of three different additives, namely, hydrated lime, class C fly ash (CFA), and cement kiln dust (CKD), for providing better treatment of sulfate rich lean clay. Short-term performance evaluation experiments included Atterberg limits, resilient modulus (Mr), modulus of elasticity (ME), and unconfined compressive strength (UCS), after 28 days of curing. Long-term performance was evaluated in terms of moisture susceptibility (tube suction test) and three-dimensional swell during 120 days of capillary soaking. At the end of 120 days, specimens were also tested for Mr, ME, and UCS, as additional indicators to long-term pavement performance. Short-term performance evaluation projected 15 % CKD with highest improvement, while long-term performance evaluation showed 15 % CFA providing maximum enhancements after 120 days of capillary soaking. The study further indicated swelling of specimens stabilized with lime and CKD; however, CFA helped in reducing the swelling. All the percentages of additives used in the study helped in reducing the moisture susceptibility of clay. Mineralogical studies such as scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction were also used to verify research findings observed from the macro test results.

Alkali-activated complex binders from class C fly ash and Ca-containing admixtures

Processes that maximize utilization of industrial solid wastes are greatly needed. Sodium hydroxide and sodium silicate solution were used to create alkali-activated complex binders (AACBs) from class C fly ash (CFA) and other Ca-containing admixtures including Portland cement (PC), flue gas desulfurization gypsum (FGDG), and water treatment residual (WTR). Specimens made only from CFA (CFA100), or the same fly ash mixed with 40 wt% PC (CFA60-PC40), with 10 wt% FGDG (CFA90-FGDG10), or with 10 wt% WTR (CFA90-WTR10) had better mechanical performance compared to binders using other mix ratios. The maximum compressive strength of specimens reached 80.0 MPa. Geopolymeric gel, sodium polysilicate zeolite, and hydrated products coexist when AACB reactions occur. Ca from CFA, PC, and WTR precipitated as Ca(OH)(2), bonded in geopolymers to obtain charge balance, or reacted with dissolved silicate and aluminate species to form calcium silicate hydrate (C-S-H) gel. However, Ca from FGDG probably reacted with dissolved silicate and aluminate species to form ettringite. Utilization of CFA and Ca-containing admixtures in AACB is feasible. These binders may be widely utilized in various applications such as in building materials and for solidification/stabilization of other wastes, thus making the wastes more environmentally benign.

Study of alkaline hydrothermal activation of belite cements by thermal analysis

The effect of alkaline hydrothermal activation of class-C fly ash belite cement was studied using thermal analysis (TG/DTG) by determining the increase in the combined water during a period of hydration of 180 days. The results were compared with those obtained for a belite cement hydrothermally activated in water. The two belite cements were fabricated via the hydrothermal-calcination route of class-C fly ash in 1 M NaOH solution (FABC-2-N) or demineralised water (FABC-2-W). From the results, the effect of the alkaline hydrothermal activation of belite cement (FABC-2-N) was clearly differentiated, mainly at early ages of hydration, for which the increase in the combined water was markedly higher than that of the belite cement that was hydrothermally activated in water. Important direct quantitative correlations were obtained among physicochemical parameters, such as the combined water, the BET surface area, the volume of nano-pores, and macro structural engineering properties such as the compressive mechanical strength.

Mechanical properties of reactive powder concrete containing mineral admixtures under different curing regimes

Mechanical properties (compressive strength, flexural strength, and toughness) of reactive powder concrete (RPC) produced with class-C fly ash (FA) and ground granulated blast furnace slag (GGBFS) were investigated under different curing conditions (standard, autoclave and steam curing) in this study. Test results indicate that, compressive strength of RPC increased considerably after steam and autoclaving compared to the standard curing. On the other hand, it was observed that steam and autoclave curing decreased the flexural strength and toughness. Increasing the GGBFS and/or FA content improved the toughness of RPC under all curing regimes considerably. Furthermore, SEM micrographs revealed dense microstructure of RPC.

Effect of curing method on characteristics of cold bonded fly ash aggregates

This paper discusses the influence of normal water curing, autoclaving and steam curing on the properties of a typical class-C fly ash aggregate. The 10% fines value, water absorption, and porosity of aggregates are correlated with SEM and XRD results to understand the influence of various factors and material characteristics. An increase in duration of normal water curing significantly improved the aggregate properties. Autoclaving and steam curing resulted in relatively lower enhancement in the properties as compared to normal water cured aggregate. Between the accelerated curing methods, autoclaved aggregate possessed properties closer to the normal water cured aggregate due to the dense microstructure formation. Continuation of normal water curing, after initially subjecting the aggregates to accelerated curing, exhibited only a marginal improvement in the properties.

Laboratory and field assessment of pile run chat from the Tar Creek superfund site stabilized with class C fly ash and cement kiln dust

A combined laboratory and field study was undertaken to assess the suitability of pile run chat as a roadway base material. Chat is mine tailings from the abandoned mines in the Tri-State Mining District involving Oklahoma, Kansas and Missouri. The chat does not have any cohesion and consequently no compressive strength in unconfined form. In this study, pile run chat was stabilized with 10% class C fly ash (CFA) and 10% cement kiln dust (CKD), separately. Results from the laboratory study showed an appreciable increase in the unconfined compressive strength (UCS) and elastic modulus of pile run chat due to cementitious stabilization. CFA stabilized specimens exhibited higher strength than the CKD stabilized specimens. Results from the field tests, namely, Spectral Analysis of Surface Waves (SASW) and Falling Weight Deflectometer (FWD), showed that stabilized chat base layer perform well as part of a pavement structure. It was also found that the field modulus of elasticity, determined from both SASW and FWD, of CFA-stabilized chart base layer were higher than the corresponding values of CKD-stabilized chat base layer.

Activated fly ash/slag blended cement

This paper presents the results of the preparation of an ecological cementing material from granulated blast-furnace slag (GBFS) and Class C fly ash (CCFA). The desulphurization gypsum, calcined at 600–800 °C for 0.5–1.5 h, works as the main ingredient of the activator in the cementing material. The optimized formulation of the cementing material was obtained with the aid of factorial design method: slag, 70%; CCFA, 18%; activator, 12%. The “partial super-fine grinding process” was adopted to improve the performance, i.e., 85% of the mixture is ground to Blaine fineness of 3500 cm 2/g, 15% further ground to around 5000 cm 2/g. The compressive strength of 28 days of the cement mortar is up to 49 MPa and flexural strength 8.4 MPa. The hydration products, investigated by SEM and X-ray diffraction, are mainly ettringite and C–S–H gel.

Environmental Effects on Durability of Aggregates Stabilized with Cementitious Materials

The present study focuses on investigating the effect of freeze–thaw (FT) cycles, referred to as environmental effect in this paper, on aggregates stabilized with various stabilizing agents, namely, cement kiln dust (CKD), Class C fly ash (CFA), and fluidized bed ash (FBA). Cylindrical specimens were compacted and cured for 28 days in a moist room with a constant temperature and controlled humidity. After curing, specimens were subjected to 0, 8, 16, and 30 FT cycles, and then tested for resilient modulus ( Mr ) . Results showed that Mr values of stabilized specimens decreased with increasing FT cycles up to 30. The reasons for such changes are explained by the increase in moisture content during thawing and the formation of ice lenses within the pores during freezing, causing distortion of the matrix of particles. It was also found that the decrease in Mr values varied with the type of stabilizing agents. The CKD-stabilized Meridian and Richard Spur aggregates exhibited a higher reduction in Mr values th...

Stabilization of Sulfate-Containing Soil by Cementitious Mixtures Mechanical Properties

Winn Rock (CaSO4) gravel from a quarry in Winn Parish in north Louisiana was used extensively as a surface course for local parish roads. Stabilization of these roads with Type I portland cement followed by an overlay of asphaltic concrete resulted in heaving. A study was undertaken to investigate the cause or causes of the expansion as well as to identify an alternate means of stabilization. Specimens of representative soil from the affected area were stabilized in the laboratory using various cementitious materials and were cured using a variety of methods. The mix contained 5% to 20% cementitious material. The cementitious materials were Type I portland cement, lime, and supplementary cementing materials such as granulated blast furnace slag (BFS), Class C fly ash (CFA), silica fume, and an amorphous silica (AS). The unconfined compressive strength of the stabilized soil was determined. The effect of size fractions other than the gravel on the expansion was assessed, and the expansion of the specimens over time was monitored. The cement and BFS mixtures almost doubled the compressive strength of the specimens compared with portland cement alone. The finer size fractions were responsible for expansion. The magnitude of expansion was directly proportional to the amount of Type I portland cement, the amount of available moisture, and the curing temperature. Replacement of a part of the portland cement by BFS significantly reduced the amount of expansion even at the highest moisture content. No expansion was detected when CFA and AS partially replaced the cement.