► Sodium hydroxide-activated ground fly ash cured at room temperature can be produced with reasonable strength. ► A 28day compressive strength of 20.0 – 23.0MPa was obtained with NaOH concentration ...in the range 9.5–14.0M. ► Ground fine high calcium fly ash can be used as a source material for making geopolymers cured at ambient temperature.
NaOH-activated ground fly ash geopolymers, cured at room temperature, were studied in this paper. Ground fly ash (GFA), with a median particle size of 10.5μm, was used as source material. NaOH concentrations of 4.5–16.5M (M) were used as an alkali activator. Compressive strength tests and microstructure observations using SEM, EDX, XRD and FTIR were performed. Results indicated that GFA gave higher strength geopolymer paste compared to original fly ash. Ground fly ash could be used as a source material for making geopolymers cured at room temperature. An increase in NaOH concentration from 4.5 to 14.0M increased the strength of GFA geopolymer pastes. Microstructure studies indicated that NaOH concentrations of 12.0–14.0M created new crystalline products of sodium aluminosilicate. The compressive strengths at 28days of 20.0–23.0MPa were obtained with the NaOH concentrations of 9.5–14.0M. Increasing the NaOH concentration beyond this point resulted in a decrease in the strength of the paste due to early precipitation of aluminosilicate products.
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AbstractThis study is centered on the use of ground bagasse ash (GBA) and recycled concrete aggregate (R-CA) as raw materials to produce ecofriendly high-strength concrete (HS-C) with high ...durability. Specifically, GBA with high fineness was used as a replacement for cement up to 50%wt of the binder, and R-CA was used as a coarse aggregate to produce HS-C. The study involved investigating the water permeability and expansion due to the Na2SO4 solution present in the HS-C. The results revealed that R-CA had a clear negative influence on the durability of concrete. However, the expansion and the water permeability of recycled aggregate concrete (RAC) reduced when GBA up to 50%wt of cement was introduced as a replacement, and the values were lower than that of the conventional high-strength concrete (CT). Furthermore, the increase in the compressive strength of concrete resulted from the low incidence of capillary pores and pore connectivity in the cement paste, which was due to the filler effect of pozzolanic or hydration products, had significantly affected the reduction in water permeability, whereas the expansion of concrete was not significantly affected.
This research was conducted to compare geopolymers made from fly ash and ground bottom ash. Sodium hydroxide (NaOH) and sodium silicate (Na
2SiO
3) solutions were used as activators. A mass ratio of ...1.5 Na
2SiO
3/NaOH and three concentrations of NaOH (5, 10, and 15
M) were used; the geopolymers were cured at 65
°C for 48
h. A Fourier transform infrared spectrometer (FT-IR), differential scanning calorimeter (DSC), and scanning electron microscope (SEM) were used on the geopolymer pastes. Geopolymer mortars were also prepared in order to investigate compressive strength. The results show that both fly ash and bottom ash can be utilized as source materials for the production of geopolymers. The properties of the geopolymers are dependent on source materials and the NaOH concentration. Fly ash is more reactive and produces a higher degree of geopolymerization in comparison with bottom ash. The moderate NaOH concentration of 10
M is found to be suitable and gives fly ash and bottom ash geopolymer mortars with compressive strengths of 35 and 18
MPa.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This research demonstrates the effect of fly ash fineness on pore size and microstructure of hardened blended cement pastes. Two sizes of fly ash, original fly ash and classified fly ash were used to ...replace Portland cement type I paste. Test results indicated that the pore sizes of hardened blended cement paste were significantly affected by the rate of replacement and the fineness of fly ash. The replacement of cement by original fly ash decreased the pore sizes of blended cement paste and the incorporation of classified fly ash resulted in a further decrease in the pore sizes of blended cement paste. The X-ray diffraction (XRD) results showed that the blended cement paste with classified fly ash was more effective at reducing the intensity of Ca(OH)
2 than that with the original fly ash. The scanning electron microscope (SEM) results revealed that the hardened blended cement paste containing finer fly ash produced a denser structure than the one containing coarser fly ash.
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The objective of this study is to investigate the use of ground palm oil fuel ash with high fineness (GPA) as a pozzolanic material to produce high-strength concrete. Samples were made by replacing ...Type I Portland cement with various proportions of GPA. Properties such as the compressive strength, drying shrinkage, water permeability, and sulfate resistance, were then investigated. After aging for 28 days, the compressive strengths of these concrete samples were found to be in the range of 59.5–64.3
MPa. At 90-day the compressive strength of concrete containing GPA 20% was as high as 70
MPa. The drying shrinkage and water permeability were lower than those of high-strength concrete made from Type I Portland cement. When the concrete samples were immersed in a 10% MgSO
4 solution for 180 days, the sulfate resistance in terms of the expansion and loss of compressive strength was improved. The results indicated that GPA is a reactive pozzolanic material and can be used as a supplementary cementitious material for producing high-strength concrete.
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This paper presents an experimental investigation on the effect of fly ash fineness on compressive strength, porosity, and pore size distribution of hardened cement pastes. Class F fly ash with two ...fineness, an original fly ash and a classified fly ash, with median particle size of 19.1 and 6.4
μm respectively were used to partially replace portland cement at 0%, 20%, and 40% by weight. The water to binder ratio (w/b) of 0.35 was used for all the blended cement paste mixes.
Test results indicated that the blended cement paste with classified fly ash produced paste with higher compressive strength than that with original fly ash. The porosity and pore size of blended cement paste was significantly affected by the replacement of fly ash and its fineness. The replacement of portland cement by original fly ash increased the porosity but decreased the average pore size of the paste. The measured gel porosity (5.7–10
nm) increased with an increase in the fly ash content. The incorporation of classified fly ash decreased the porosity and average pore size of the paste as compared to that with ordinary fly ash. The total porosity and capillary pores decreased while the gel pore increased as a result of the addition of finer fly ash at all replacement levels.
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Although elevated temperature curing can increase the compressive strength of alkali-activated mortar, its field applications are still limited. In this study, alkali-activated mortars were prepared ...using high calcium fly ash (FA) as a precursor. Small amounts of silica fume were used to partially replace high calcium fly ash at 3–9% by weight to increase the strength of alkali-activated mortar. All mixtures had a liquid to binder ratio of 0.60 and sand to binder ratio of 2.75 by weight. A ratio of NaOH to Na2SiO3 solution was kept at 2:1 by weight. Mortar flow was also held between 105–115 using a superplasticizer. Compressive strength and durability were investigated in terms of acid and sulfate resistance. The effects of silica fume addition and curing temperature on compressive strength were found to be significant. The optimum content of silica fume was 6%, providing compressive strength as high as that of alkali-activated mortars cured at 45 °C. The weight loss of alkali-activated mortar due to sulfuric acid attack decreased with increasing silica fume content and curing temperature. All alkali-activated mortars were found to have a better performance than (ordinary) Portland cement (OPC) mortars and mortars containing 40% FA. Alkali-activated mortars immersed in magnesium sulfate solutions had compressive strength that decreased with an increase in curing temperature. The expansion of alkali-activated mortar due to sodium sulfate attack increased with increasing silica fume content, and the expansion decreased with increased curing temperature. All alkali-activated mortars performed better than OPC mortars after 98 days of sulfate attack.
This research aimed to create value of construction and demolition waste to be able used as a recycled coarse aggregate (RCA) in durable concrete, based on 7-year field investigation in marine site. ...Fly ash was used to substitute Portland cement type I in RCA concrete varied from 0 to 50% by weight of binder with three W/B ratios and comparing to natural aggregate (NA) concrete. Cubical concrete specimens were cast having round steel bars embedded with various concrete coverings to evaluate the durability performances. After 28-day curing, the specimens were placed at a tidal zone in the gulf of Thailand and investigated both mechanical and durability performances at 7-year exposed period. Based on site monitoring, 15–25% fly ash RCA concrete with W/B ratio of 0.40 would be advantaged to resist destruction due to the marine attack when compared with NA concrete with the same water-to-binder ratio.
► Strength due to filler effect for small particles was almost constant with age. ► Filler effect of small particles can enhance the compressive strength. ► Pozzolanic reaction of ground POFA was ...much more pronounced than the filler effect.
This research examines the compressive strength of mortar and how the filler effect and pozzolanic reaction of ground palm oil fuel ash (POFA) contribute to this strength. POFA and river sand were ground to three different particle sizes and used to replace Type I Portland cement at 10–40% by weight of binder to cast the mortar. The compressive strengths of ground POFA and ground river sand mortars were determined at various ages between 7 and 90
days. The results showed that the compressive strength of mortar due to the filler effect of ground river sand was nearly constant during the 7–90
day period for a specified replacement rate of cement. However, the compressive strength of mortar due to the filler effect tended to increase slightly with increased cement replacement. The pozzolanic reaction of ground POFA increased with increasing particle fineness of ground POFA, replacement rate of cement, and age of the mortar. The compressive strength contribution from the pozzolanic reaction of ground POFA was much more pronounced than the contribution from the filler effect when the smallest sizes of both materials were considered.
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► The compressive strength, thermogravimetric analysis and pore size distribution of the blended cement pastes were investigated. ► Blended cement paste with high fineness POFA had a higher ...compressive strength than that with coarse POFA. ► Reduction of Ca(OH)
2 affected the increased peak intensity of the C-S-H and C
2ASH
8 phases with increasing curing time. ► The critical pore size and average pore diameter of the paste containing POFA were lower than those of the OPC paste.
This paper presents the effect of palm oil fuel ash fineness on the microstructure of blended cement paste. Palm oil fuel ash (POFA) was ground to two different finenesses. Coarse and high fineness palm oil fuel ash, with median particle sizes of 15.6 and 2.1
μm, respectively, were used to replace ordinary Portland cement (OPC) at 0%, 20% and 40% by binder weight. A water to binder (
W/
B) ratio of 0.35 was used for all blended cement pastes. The amorphous ground palm oil fuel ash was characterized by the Rietveld method. The compressive strength, thermogravimetric analysis and pore size distribution of the blended cement pastes were investigated. The test results indicate that the ground palm oil fuel ash was an amorphous silica material. The compressive strengths of the blended cement pastes containing coarse POFA were as high as that of OPC cement paste. Blended cement paste with high fineness POFA had a higher compressive strength than that with coarse POFA. The blended cement pastes containing 20% of POFA with high fineness had the lowest total porosity. The Ca(OH)
2 contents of blended cement paste containing POFA decreased with increasing replacement of POFA and were lower than those of the OPC cement paste. In addition, the POFA fineness had an effect on the reduction rate of Ca(OH)
2. Furthermore, the critical pore size and average pore size of blended cement paste containing POFA were lower than those of the OPC cement paste. The incorporation of high fineness POFA decreased the critical pore size and the average pore size of blended cement paste as compared to that with coarse POFA.
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