Biomass fly ash in concrete: Mixture proportioning and mechanical properties

ASTM C 618 prohibits use of biomass fly ashes in concrete. This document compares the properties of biomass fly ashes from cofired (herbaceous with coal), pure wood combustion and blended (pure wood fly ash blended with coal fly ash) to those of coal fly ash in concrete. The results illustrate that with 25% replacement (wt%) of cement by fly ash, the compressive strength (one day to one year) and the flexure strength (at 56th day curing) of cofired and blended biomass fly ash concrete is statistically equal to that of two coal fly ash concrete in this investigation (at 95% confidence interval). This implies that biomass fly ash with co-firing concentration within the concentration interest to commercial coal-biomass co-firing operations at power plants and blended biomass fly ash within a certain blending ratio should be considered in concrete.     

Topological controls on the dissolution kinetics of glassy aluminosilicates

Fly ash which encompasses a mixture of glassy and crystalline aluminosilicates is an abundant supplementary cementitious material (SCM), valuable for replacing ordinary portland cement (OPC) in the binder fraction in concrete. Because higher OPC replacement levels are desired, it is critically important to better understand and quantify fly ash reactivity. By combining molecular dynamics (MD) simulations and vertical scanning interferometry (VSI), this study establishes that the reactivity of the glassy fractions in a fly ash with water (i.e., their aqueous dissolution rate) is controlled by the number of constraints placed on atoms within the disordered aluminosilicate network. More precisely, an Arrhenius‐like dependence of dissolution rates on the atomic network topology is observed. Such topological controls on fly ash reactivity are highlighted for a range of U.S. commercial fly ashes spanning CaO‐enriched and SiO₂‐enriched compositions. The structure‐property relationships reported herein establish an improved framework to control and estimate fly ash‐cement interactions in concrete.     

复合矿物功能掺合料对粉煤灰激活增强的研究

根据激发粉煤灰活性机理研制了一种复合矿物功能掺合料,针对其对粉煤灰活性激发增强效果进行了系统研究。结果表明,用Ⅱ级粉煤灰、复合矿物功能掺合料置代50%以上水泥配制的胶砂、普通混凝土和高性能混凝土的早期强度、后期强度均大幅度提高。其中强度等级C15-C100 的混凝土不仅单方可节约水泥 50%以上,而且其强度较单掺粉煤灰有显著提高,具有显著的经济和社会效益。     

Behavior of low-calcium fly and bottom ash-based geopolymer concrete cured at ambient temperature

This paper presents the results of an experimental study on the behavior of fly ash-, bottom ash- and blended fly and bottom ash-based geopolymer concrete (GPC) cured at ambient temperature. A total of 10 bathes of GPC and a single batch of ordinary Portland cement concrete (OPC) were manufactured. The tests of compressive strength, elastic modulus, flexural strength, workability, drying shrinkage and absorption capacity were carried out to determine the properties of fresh concrete and mechanical and durability-related properties of hardened concrete. Test parameters included the mass ratio of fly ash-to-bottom ash, liquid alkaline-to-coal ash binder ratio, coal ash content and concrete type. The results indicate that the selected parameters significantly affect the microstructure and the behavior of GPCs. It is seen that bottom ash-based GPCs exhibited significantly lower geopolymerization than that of the fly ash-based GPCs, resulting in the inferior behavior of the former compared to the latter.     

Mechanism for performance of energetically modified cement versus corresponding blended cement

The microstructure of cement paste of 50/50 mixes of cement/quartz and cement/fly ash, both ground in a special mill [energetically modified cement (EMC) process] and simply blended, have been studied under sealed curing conditions. The grinding process reduced the size of both cement grains and quartz/fly ash markedly and created flaky agglomerates of high inner surface for the finer particles. EMCs had much higher degree of hydration at 1 day, but similar as blends at 28 days. The pores were much finer for EMC paste due to smaller particles as also reflected in the strength. The morphology of calcium hydroxide in EMC paste appeared more mass like. Pozzolanic reaction was insignificant for quartz in EMC, but increased for fly ash. Thus, improved performance of EMC versus OPC can be explained by increased early hydration and extensive pore size refinement of the hardened binder resulting in reduced permeability and diffusivity for concrete.     

Durability of biomass fly ash concrete: Freezing and thawing and rapid chloride permeability tests

Strict interpretation of ASTM C 618 excludes non-coal fly ashes, such as biomass fly ashes from addition in concrete. Biomass fly ash in this investigation includes (1) cofired fly ash from burning biomass with coal; (2) wood fly ash and (3) blended fly ash (wood fly ash mixing with coal fly ash). A set of experiments conducted on concrete from pure cement and cement with fly ash provide basic data to assess the effects of several biomass fly ashes on the performances of freezing and thawing (F-T) and rapid chloride permeability test (RCPT). The F-T tests indicate that all fly ash concrete has statistically equal or less weight loss than the pure cement concrete (control). The RCPT illustrate that all kinds of fly ash concrete have lower chloride permeability than the pure cement control concrete.     

Use of ground coarse fly ash as a replacement of condensed silica fume in producing high-strength concrete

This paper presents a method of improving coarse fly ash in order to replace condensed silica fume in making high-strength concrete. The coarse fly ash, having the average median diameter about 90-100 μm, yields a very low pozzolanic reaction and should not be used in concrete. In order to improve its quality, the coarse fly ash was ground until the average particle size was reduced to 3.8 μm. Then, it was used to replace Portland cement type I by weights of 0%, 15%, 25%, 35%, and 50% to produce high-strength concrete. It was found that concrete containing the ground coarse fly ash (FAG) replacement between 15% and 50% can produce high-strength concrete and 25% cement replacement gave the highest compressive strength. In addition, the concrete containing FAG of 15-35% as cement replacement exhibited equal or higher compressive strengths after 60 days than those of condensed silica fume concretes. The results, therefore, suggest that the FAG with high fineness is suitable to use to replace condensed silica fume in producing high-strength concrete.     

纳米颗粒粉煤灰绿色混凝土的耐久性试验研究

为配制高性能绿色混凝土,用不同质量分数的粉煤灰（0%~30%）来替代水泥,并在混凝土中掺入不同质量分数纳米颗粒氧化锌（0%~3%）来提高混凝土的抗压强度、抗拉强度和抗氯离子性能。通过制备30组混凝土试块进行试验,得出：1）在粉煤灰替代率相同的情况下,随着纳米颗粒氧化锌含量的增加,纳米颗粒氧化锌粉煤灰混凝土的抗压强度、抗拉强度和抗氯离子性能均逐渐增加。2）在纳米颗粒氧化锌含量相同的情况下,随着粉煤灰替代率的增加,纳米颗粒氧化锌粉煤灰混凝土的抗压强度和抗拉强度均逐渐下降。但纳米颗粒氧化锌粉煤灰混凝土的抗氯离子性能却逐渐提高。因此,当纳米颗粒氧化锌质量分数为1%时,建议粉煤灰的替代率在10%以下;当纳米颗粒氧化锌质量分数为2%时,建议粉煤灰的替代率在20%以下;而纳米颗粒氧化锌质量分数为3%时,建议粉煤灰的替代率仍在20%以下,因此不建议纳米颗粒氧化锌的掺量超过2%。     

活化粉煤灰的研制

提出了机械化学复合活化粉煤灰的新措施。使传统粉煤灰水泥中粉煤灰掺量较大幅度的提高。在５２５＃纯硅酸盐水泥中掺加３５％～４０％经复合活化的粉煤灰仍可生产４２５＃粉煤灰水泥。文中还对该粉煤灰水泥的一些特种性能进行了初步探讨，并对其活化机理提出了一些见解     

粉煤灰再生混凝土中氯离子渗透性能试验研究

通过氯离子自然扩散试验,测定粉煤灰再生混凝土试件中自由氯离子浓度,研究了粉煤灰掺量、干湿循环等因素对粉煤灰再生混凝土中氯离子渗透性能的影响。结果表明:粉煤灰能提高再生混凝土抗氯离子渗透能力,粉煤灰最佳掺量介于10%~30%之间;干湿循环加快了粉煤灰再生混凝土中氯离子的渗透速度;粉煤灰再生混凝土中氯离子浓度随着氯盐溶液侵蚀时间的延长逐渐增大,随着向粉煤灰再生混凝土内部的深入,逐渐降低。     

Carbonation rates of concretes containing high volume of pozzolanic materials

The project studies the influence of fly ash and slag replacement on the carbonation rate of the concrete. The experimental work includes samples of pure Portland cement concrete (CEM I 42,5 R), blast-furnace slag concrete (CEM III-B), and fly ash blended concrete. To reveal the effect of curing on carbonation rate, the concretes were exposed to various submerged curing periods during their early ages. After that, the samples were subsequently exposed in the climate room controlling 20 °C and 50% RH until the testing date when the samples had an age of 5 months. Then, the accelerated carbonation test controlling the carbon dioxide concentration of 3% by volume, with 65% relative humidity were started to perform. The depth of carbonation can be observed by spraying a phenolphthalein solution on the fresh broken concrete surface. Finally, according to Fick's law of diffusion theoretical equations are proposed as a guild for estimating the carbonation rate of fly ash and blast-furnace slag concretes exposed under natural conditions from the results from accelerated carbonation tests.     

低等级粉煤灰的活化处理与应用技术研究

采用物理活化 (机械磨细 )与化学活化 (加复合化学激发剂 )相结合的高效复合活化技术对低等级粉煤灰进行活化处理 ,可得到高活性粉煤灰。该粉煤灰可用于生产高掺量粉煤灰水泥、各种免烧的高强新型绿色墙体材料与地面材料以及配制中低强度等级高掺量粉煤灰混凝土等。     

Effect of nano-silica on the chemical durability and mechanical performance of fly ash based geopolymer concrete

In this study, the effect of nano silica on the short term severe durability performance of fly ash based geopolymer concrete (GPC) specimens was investigated. Four types of GPC were produced with two types of low calcium fly ashes (FAI and FAII) with and without nano silica, and ordinary Portland cement concrete (OPC) concrete was also cast for reference. For the geopolymerization process, the alkaline activator has selected a mixture of sodium silicate solution (Na₂SiO₃) and sodium hydroxide solution (NaOH) with a ratio (Na₂SiO₃/ NaOH) of 2.5. Main objectives of the study were to investigate the effect of usability or replaceability of nano silica-based low calcium fly ash based geopolymer concretes instead of OPC concrete in structural applications and make a contribution to standardization process of the fly ash based geopolymer concrete. To achieve the goals, four types of geopolymer and OPC concretes were subjected to sulfuric acid (H₂SO₄), magnesium sulfate (MgSO₄) and seawater (NaCl) solutions with concentrations of 5%, 5%, and 3.5%, respectively. Visual appearances and weight changes of the concretes under chemical environments were utilized for durability aspects. Compressive, splitting tensile and flexural strength tests were also performed on specimens to evaluate the mechanical performance under chemical environments. Results indicated that FAGPC concretes showed superior performance than OPC concrete under chemical attacks due to low calcium content. Amongst the chemical environments, sulfuric acid (H₂SO₄) was found to be the most dangerous environment for all concrete types. In addition, nano silica (NS) addition to FAGPC specimens improved both durability and residual mechanical strength due to the lower porosity and more dense structure. The FAIIGPC specimens including nano silica showed the superior mechanical performance under chemical environment.     

Performance characteristics of high-volume Class F fly ash concrete

More than 88 million tonnes of fly ash is generated in India each year. Most of the fly ash is of Class F type. The percentage utilization is around 10 to 15%. To increase its percentage utilization, an extensive investigation was carried out to use it in concrete. This article presents the results of an experimental investigation dealing with concrete incorporating high volumes of Class F fly ash. Portland cement was replaced with three percentages (40%, 45%, and 50%) of Class F fly ash. Tests were performed for fresh concrete properties: slump, air content, unit weight, and temperature. Compressive, splitting tensile, and flexural strengths, modulus of elasticity, and abrasion resistance were determined up to 365 days of testing.Test results indicated that the use of high volumes of Class F fly ash as a partial replacement of cement in concrete decreased its 28-day compressive, splitting tensile, and flexural strengths, modulus of elasticity, and abrasion resistance of the concrete. However, all these strength properties and abrasion resistance showed continuous and significant improvement at the ages of 91 and 365 days, which was most probably due to the pozzolanic reaction of fly ash. Based on the test results, it was concluded that Class F fly ash can be suitably used up to 50% level of cement replacement in concrete for use in precast elements and reinforced cement concrete construction.     

Biomass fly ash in concrete: SEM, EDX and ESEM analysis

This document summarizes microscopy study of concrete prepared from cement and fly ash (25% fly ash and 75% cement by weight), which covers coal fly ash and biomass fly ash. All the fly ash concrete has the statistical equal strength from one day to one year after mix. Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX) and environmental scanning electron microscopy (ESEM) analysis show that both coal and biomass fly ash particles undergo significant changes of morphology and chemical compositions in concrete due to pozzolanic reaction, although biomass fly ash differs substantially from coal fly ash in its fuel resources.     

Blended cement using volcanic ash and pumice

This paper reports the results of investigation to assess the suitability of volcanic ash (VA) and pumice powder (VPP) for blended cement production. Tests were conducted on cement where Portland cement (PC) was replaced by VA and VPP within the range of 0 to 50%. The physical and chemical properties of VA and VPP were critically reviewed to evaluate the possible influences on cement properties. The investigation included testing on both fresh and hardened states of cement paste. The standard tests conducted on different PC-VA and -VPP mixtures provided encouraging results, comparable to those for fly ash (FA) cement, and showed good potential of manufacturing blended Portland volcanic ash cement (PVAC) and Portland volcanic pumice cement (PVPC) with higher setting time and low heat of hydration using up to 20% replacement.     

Effect of fine aggregate replacement with Class F fly ash on the abrasion resistance of concrete

This paper presents the abrasion resistance of concrete proportioned to have four levels of fine aggregate replacement (10%, 20%, 30%, and 40%) with Class F fly ash. A control mixture with ordinary Portland cement was designed to have 28 days compressive strength of 26 MPa. Specimens were subjected to abrasion testing in accordance with Indian Standard Specifications (IS: 1237). Tests were also performed for fresh concrete properties and compressive strength. Tests on compressive strength and abrasion were performed up to 365 days.Test results indicated that abrasion resistance and compressive strength of concrete mixtures increased with the increase in percentage of fine aggregate replacement with fly ash. Abrasion resistance of concrete was improved approximately by 40% over control mixture with 40% replacement of fine aggregate with fly ash, and concrete with fine aggregate replacement could be suitably used.     

Properties of concrete produced from multicomponent blended cements

This paper presents a study on the behavior of concrete produced from multicomponent blended cements. These blends were prepared by blending 20–60% ASTM Type I cement with the combination of Class C fly ash and clean coal ash. Two percent to four percent sodium sulfate anhydrite was added to the blends as a chemical activator. Tests were conducted on the prepared concrete for strength development, freezing and thawing resistance, resistance to chloride ion penetration, sulfate resistance, and alkali silica reaction. Test results show that concrete produced from blended cements had equivalent or higher strength than the control mixture at all test ages. Blended cements were effective in controlling expansions due to sulfate attack or alkali silica reaction. They also reduced the deterioration of concrete due to freezing and thawing action and greatly increased the resistance to chloride ion penetration into the concrete.     

钢渣粉和粉煤灰对钢渣混凝土力学性能的影响特点

探讨钢渣粉和粉煤灰等量取代水泥后钢渣混凝土的力学属性变化特点和规律。实验对比表明 :与强度等级为 32 .5的纯水泥钢渣混凝土对比 ,掺入钢渣粉的砼强度略有降低 ,但能改善混凝土的和易性。掺入粉煤灰将增大混凝土的粘聚性和可塑性 ,改善混凝土的和易性 ,减小混凝土的膨胀性。     

Beneficiation of the huge waste quantities of barley and rice husks as well as coal fly ashes as additives for Portland cement

This study aims at benefit from barely husk ash (BHA), rice husk ash (RHA), and coal fly ash (CFA) as a replacement of ordinary Portland cement (OPC) to eliminate the problems associated with cement industry involving energy consuming and air pollution. Three series of cement mixes were prepared from OPC with different contents (0–30 wt.%) of each additive. Different cementing and mechanical properties of the prepared mixes were tested according to the international standard specifications. It was concluded that OPC blended with 15–20 wt.% of BHA, RHA, or CFA show outstanding cementing properties.