Recycled concrete and silica fume make calcium silicate bricks

When old concrete is crushed to coarse aggregate for production of new concrete, approximately 20 weight percent of crusher fines are generated. It has been shown that calcium hydroxide from hydrated cement of such fines reacts in the autoclave with siliceous particles in the fines to give calcium silicate products. Such products are similar in nature to sand-lime bricks. When silica are greatly improved. It has further been shown that crusher fines from recycled concrete do not qualify as hydraulic cements even when ground to cement fineness.     

Comparative assessment of Australian fly ash and conventional concrete bricks

A comparative study of the chemical composition, mineralogy, morphology and crushing strengths of fly ash bricks, conventional concrete bricks and fly ash samples has been undertaken. The main chemicals present in the products were silica and alumina while their main minerals were quartz, mullite, illite, vaterite, and calcite. Elemental analysis by XPS showed that the major elements in the samples were oxygen, silicon, carbon, calcium and aluminium; and scanning electron microscopy revealed that the fly ash samples consist of spherically‐shaped particles with surface attachment containing needle‐like particles. Compared with conventional concrete bricks, fly ash bricks generally have higher atomic silicon and crushing strengths but lower crystalline silica. The implication of the results on the suitability of fly ash bricks as replacements for conventional concrete bricks in the building industry is discussed from the point of view of human health and occupational safety. Copyright © 2004 Society of Chemical Industry     

粉煤灰陶粒混凝土的研究*

本文主要采用粉煤灰陶粒作为骨料来进行轻质高强大流动性混凝土的配合比设计。并对混凝土的工作性和立方体抗压强度进行了分析,从中选出最佳的轻质高强大流动性LC80混凝土配合比,为施工提供参考。     

Application of thermal analysis in investigations on calcium silicate bricks

The principles of differential thermal analysis and thermogravimetric analysis are outlined and two examples of their application to autoclaved calcium silicate products are given. The proportions of calcium hydroxide and calcium carbonate in samples can be estimated. Useful information on calcium hydrosilicate binding materials can be obtained in experiments where the number of variables is strictly controlled.     

五种耐火材料的抗飞灰侵蚀对比试验

为探寻适合在飞灰熔融炉中使用的耐火材料,以提高飞灰熔融炉的使用寿命,采用静态坩埚法,对国内某公司飞灰熔融炉用熔铸锆刚玉砖AZS-41以及有望适用于飞灰熔融炉的高铬砖CRB-86、铬刚玉砖CRCB-30、刚玉砖CB-99和锆英石砖DZB-69进行了抗飞灰侵蚀对比试验,并对侵蚀后试样进行了SEM和EDS分析。结果表明:1)熔铸锆刚玉砖AZS-41因结构致密而具有优异的抗飞灰渗透性,但抗飞灰侵蚀性能差。2)高铬砖CRB-86抗飞灰渗透性较好,因其高含量Cr2O3的存在而具有优异的抗飞灰侵蚀性。3)铬刚玉砖CRCB-30抗飞灰渗透性较差,因高含量且易被飞灰侵蚀的Al2O3的存在而表现出很差的抗飞灰侵蚀性。4)刚玉砖CB-99因显气孔率高,且Al2O3易被飞灰侵蚀,其抗飞灰渗透性和抗飞灰侵蚀性均最差。5)致密锆英石砖DZB-69因结构致密而具有优异的抗飞灰渗透性;但因锆英石相被飞灰中的碱性成分分解以致产生剥落,因此具有较差的抗飞灰侵蚀性。     

An experimental study on strength development of concrete containing fly ash and optimum usage of fly ash in concrete

This paper presents a laboratory study on the strength development of concrete containing fly ash and optimum use of fly ash in concrete. Fly ash was added according to the partial replacement method in mixtures. A total of 28 mixtures with different mix designs were prepared. 4 of them were prepared as control mixtures with 250, 300, 350, and 400 kg/m³ cement content in order to calculate the Bolomey and Feret coefficients (K_B, K_F). Four groups of mixtures were prepared, each group containing six mix designs and using the cement content of one of the control mixture as the base for the mix design. In each group 20% of the cement content of the control mixture was removed, resulting in starting mixtures with 200, 240, 280, and 320 kg/m³ cement content. Fly ash in the amount of approximately 15%, 25%, 33%, 42%, 50%, and 58% of the rest of the cement content was added as partial cement replacement. All specimens were moist cured for 28 and 180 days before compressive strength testing. The efficiency and the maximum content of fly ash that gives the maximum compressive strength were obtained by using Bolomey and Feret strength equations. Hence, the maximum amount of usable fly ash amount with the optimum efficiency was determined.This study showed that strength increases with increasing amount of fly ash up to an optimum value, beyond which strength starts to decrease with further addition of fly ash. The optimum value of fly ash for the four test groups is about 40% of cement. Fly ash/cement ratio is an important factor determining the efficiency of fly ash.     

The composition of the binding material in calcium silicate bricks

Results from the chemical analyses of commercial calcium silicate brick samples are presented. The composition of the binding material in the bricks is consistent with the formation of C? S? H(I) . The strength of the bricks appears to be related to the proportion of voids filled with cementing material.     

Heat evolution of high-volume fly ash concrete

In this paper, the results of a laboratory investigation conducted with heat evolution of high-volume fly ash (HVFA) concrete are presented. Heat evolution of concrete was studied by measuring the temperature increase in concrete under adiabatic curing condition. Characteristic of heat evolution of fly ash concrete was found to be strongly dependent on the replacement level of fly ash and dosage of superplasticizer used to maintain workability. It was also found that using fly ash as cement replacement resulted in a reduction on the maximum temperature rise. Increasing the replacement level of fly ash caused lower temperature rise in concrete. Superplasticizer caused a delay in peak temperature rise time; this is taken as an indicator that high-dosage superplasticizer used in concrete caused retardation in hydration of cement. Concretes having similar ingredients showed similar peak temperature rise whether they are superplasticized or not.     

Reactions of fly ash with calcium aluminate cement and calcium sulphate

The hydration processes in the ternary system fly ash/calcium aluminate cement/calcium sulphate (FA/CAC/C$) at 20 °C were investigated; six compositions from the ternary system FA/CAC/C$ were selected for this study. The nature of the reaction products in these pastes were analysed by X-ray diffraction (XRD) and infrared spectroscopy (FTIR). At four days reaction time, the main hydration reaction product in these pastes was ettringite and the samples with major initial CAC presented minor ettringite but calcium aluminates hydrates. The amount of ettringite developed in the systems has no direct relation with the initial components.     

Utilisation of steel furnace slag coarse aggregate in a low calcium fly ash geopolymer concrete

This paper evaluates the performance of steel furnace slag (SFS) coarse aggregate in blended slag and low calcium fly ash geopolymer concrete (GPC). The geopolymer binder is composed of 90% of low calcium fly ash and 10% of ground granulated blast furnace slag (GGBFS). Mechanical and physical properties, shrinkage, and detailed microstructure analysis were carried out. The results showed that geopolymer concrete with SFS aggregate offered higher compressive strength, surface resistivity and pulse velocity than that of GPC with traditional aggregate. The shrinkage results showed no expansion or swelling due to delayed calcium oxide (CaO) hydration after 320 days. No traditional porous interfacial transition zone (ITZ) was detected using scanning electron microscopy, indicating a better bond between SFS aggregate and geopolymer matrix. Energy dispersive spectroscopy results further revealed calcium (Ca) diffusion at the vicinity of ITZ. Raman spectroscopy results showed no new crystalline phase formed due to Ca diffusion. X-ray fluorescence result showed Mg diffusion from SFS aggregate towards geopolymer matrix. The incorporation of Ca and Mg into the geopolymer structure and better bond between SFS aggregate and geopolymer matrix are the most likely reasons for the higher compressive strength observed in GPC with SFS aggregate.     

粉煤灰泡沫混凝土屋面材料的研究

粉煤灰泡沫混凝土屋面材料具有保温隔热隔音和质轻等性能优势。文章主要探讨了水泥、粉煤灰、膨胀珍珠岩和发泡剂的不同用量对屋面材料体积质量、抗压强度、导热系数等性能的影响,并用熟石灰作为激发剂改善屋面材料性能。试验结果表明,体积质量为700kg/m3级别的泡沫混凝土屋面材料,其28d强度最高可达3.61MPa,导热系数最低至0.15W/(m·K),具有较好的使用性能要求;综合考虑强度和导热系数因素,确定合理的配合比为水泥∶粉煤灰∶膨胀珍珠∶工业熟石灰∶减水剂∶发泡剂=475∶216∶22∶29∶2.4∶0.4。     

Fabrication of low to high duty fireclay refractory bricks from lignite fly ash

The development of refractory bricks made of new materials has recently drawn a lot of interest to address sustainability issues. So, in this study, the recycling of lignite fly ash produced by coal-fired thermal power plants has been investigated to make fireclay refractory bricks. The lignite fly ash and ball clay are the primary raw materials characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray fluorescence (XRF), and differential thermal analysis (DTA). The samples were prepared using a uniaxial hydraulic press, and firing was done in the range of 1000–1200 °C for 2 h. The fired samples were characterized in terms of chemical composition, mineralogical phase, and microstructural using different characterization tools such as XRF, XRD, and SEM. The physical, mechanical, and thermal properties such as linear firing shrinkage, apparent porosity (AP), bulk density (BD), cold crushing strength (CCS), cold modulus of rupture (CMOR), and thermal conductivity of the fired sample were investigated. The linear firing shrinkage, AP, BD, and CCS values were achieved estimated to be 5.32%, 2.10 g m/cc, 15%, and 52 MPa, respectively. The SEM analysis shows dense, rod-like mullite structure and interlocking microstructure of the fired samples. The results were well matched with ASTM standards and commercially available products. So, this promising result indicates lignite fly ash can be used as a potential raw material to produce fireclay refractory bricks.     

Effectiveness of fly ash for strength and durability of concrete

The effectiveness, K, of a fly ash can be defined as the ratio of the amount of cement replaced to the amount of fly ash added, provided the specified requirements of the concrete are maintained. It is generally assumed that the effectiveness of a fly ash can be treated as a constant. This paper presents results on concrete made with various mix proportions using three different cements and fly ash from three different sources. It was found that the K factor of each fly ash in achieving common 28-day compressive strength varies over a wide range depending on the amount of fly ash used, the type of cement, the incorporation of chemical admixtures and the particular strength level chosen. Besides strength, K can also be calculated for other properties. For the materials used in this investigation, the K factors with respect to carbonation were found to be unequal to K factors for strength.     

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.     

Utilising unprocessed low-lime coal fly ash in foamed concrete

This paper describes an extensive laboratory-based investigation into the use of unprocessed, run-of-station, low-lime fly ash in foamed concrete, as a replacement for sand. Foamed concrete with plastic densities ranging between 1000 and 1400 kg/m³ and cube strengths from 1 to 10 N/mm² were tested. It is shown that by using this type of fly ash in this way can significantly enhance many of the properties of foamed concrete, including rheology and compressive strength development, whilst providing almost complete immunity to sulfate attack. Given the high carbon content of this type of fly ash, however, it was found that there was a need to increase greatly the amount of foam required to achieve the specified design plastic density. However, given the relatively low cost of foam production, this is not likely to have significant implications for the use of material.     

粉煤灰微珠掺量对透水混凝土的影响

本文研究了不同粉煤灰微珠掺量对透水混凝土工作性、透水系数、连续空隙率、抗压强度及劈裂抗拉强度的影响。通过单要素控制变量法研究发现：粉煤灰微珠掺量范围在20%～30%时,微珠对透水混凝土工作性及抗压性能的提升作用最为有效。粉煤灰微珠掺量为10%时,透水混土的连通空隙率有明显提高。透水系数与粉煤灰微珠掺量整体呈负相关联系。透水混凝土劈裂抗拉强度受“粉煤灰微珠”掺量的影响较小。     

适用于预拌混凝土的粉煤灰水泥的研制

在去年笔者提出的水泥厂发展混凝土掺和料产业的思路基础上,通过试验研究和经济成本分析,进一步探讨了水泥厂以生产、推广使用粉煤灰水泥的模式发展混凝土掺和料产业的技术经济可行性,并在此基础上研制开发了适用于预拌混凝土的专用粉煤灰水泥。     

低掺量粉煤灰对路面混凝土性能的影响

在路面水泥混凝土中掺入粉煤灰,不仅具有优化资源配置、提高经济效益和改善环保等功能,还可以改善混凝土的和易性、降低混凝土早期的水化温升,其二次水化作用又能改善混凝土的界面结构,从而改善路面混凝土的耐久性能.本文就低掺量粉煤灰对路面混凝土性能影响的试验结果作一介绍和分析.     

Benefits of fly ash utilization in concrete road cover

The world faces a number of environmental issues. Many of these problems are man-made, the results of industrialization and building. There are many ways to help our world to become more environmentally friendly and healthier. Cutting back of carbon dioxide emissions by using less energy consumptive materials in the building industry is one of them. Waste products used as a replacement of old raw materials lead to the less energy consumption and cost saving. The tests results of energy waste (fly ash) exploitability as a partial cement replacement into the concrete cover of pavement is described in this paper. Compressive and flexural strengths at hardened ages of 7, 28, 90 days, chemical resistance, freezing and thawing of fly ash concrete composites were measured and compared with the reference specimen (C 30/37), which met the requirements of STN 73 6123 Building of road element.     

Determination of atomistic deformation of tricalcium silicate paste with high-volume fly ash

We examined the effect of incorporating high-volume fly ash on the atomic arrangement and interatomic deformation behavior of calcium silicate hydrates in tricalcium silicate paste upon exposure to external forces. The interatomic structural changes and strains under compressive load were assessed using synchrotron in situ high-energy X-ray scattering-based atomic pair distribution function analysis. Three different types of strains, which were (a) macroscopic strains from gauges on the surfaces of specimen, (b) strains in a reciprocal space (Bragg peak shift), and (c) strains in real space (PDF peak shift), were compared to each other. All monitored and calculated strains for tricalcium silicate-fly ash (50 wt% fly ash) paste were compared with the counterparts of the pure tricalcium silicate paste. Pair distribution function analysis in the range of r < 10 Å indicated that the atomic arrangement of tricalcium silicate-fly ash was similar to that of synthetic calcium silicate hydrates followed by that of pure tricalcium silicate paste. Moreover, the pair distribution function refinement results revealed that the calcium silicate hydrate structure in tricalcium silicate-fly ash paste was similar to tobermorite 11 Å, unlike that in pure tricalcium silicate paste. The interatomic strain of tricalcium silicate-fly ash in the real space (r < 20 Å) was smaller than that of tricalcium silicate under compression, which suggested that the incompressibility of calcium silicate hydrates at atomistic scale was enhanced by the incorporation of fly ash into it. This was likely to be caused by the increased silicate polymerization of calcium silicate hydrates, which was attributed to the increase in the amount of silicate in their structure via the addition of fly ash.