Influence of fly ash fineness and shape on the porosity and permeability of blended cement pastes

The effects of the fineness and shape of fly ash on the porosity and air permeability of cement pastes were investigated. Pulverized coal combustion （PCC） fly ash and fluidized bed coal combustion （FBC） fly ash classified into three different finenesses were used. River sand with particle size distribution similar to that of fly ash was also used for comparison. Portland cement was replaced with fly ash and ground sand at the dosages of 0, 20wt%, and 40wt%. A water-to-binder ratio （w/b） of 0.35 was used throughout the experiment. The results show that the porosity and air permeability of the pastes are influenced by the shape, fineness, and replacement level of fly ash. The porosity and air permeability of FBC fly ash pastes are higher than those of PCC fly ash pastes. This is due to the higher irregular shape and surface of FBC fly ash compared to the spherical shape and relatively smooth surface of PCC fly ash. The porosity increases with the increase in fly ash replacement level and decreases with the increase in its fineness. The permeability of PCC fly ash pastes decreases with the increase in replacement level and fineness, while for FBC fly ash, the permeability increases with the increase in replacement level. Decreases in porosity and permeability are due to a combined effect of the packing of fine particles and the reaction of fly ash.

Properties of high calcium fly ash geopolymer pastes with Portland cement as an additive

The effect of Portland cement （OPC） addition on the properties of high calcium fly ash geopolymer pastes was investigated in the paper. OPC partially replaced fly ash （FA） at the dosages of 0, 5%, 10%, and 15% by mass of binder. Sodium silicate （Na2SiO3） and sodium hydroxide （NaOH） solutions were used as the liquid portion in the mixture： NaOH 10 mol/L, Na2SiO3/NaOH with a mass ratio of 2.0, and alkaline liquid/binder （L/B） with a mass ratio of 0.6. The curing at 60℃ for 24 h was used to accelerate the geopolymerization. The setting time of all fresh pastes, porosity, and compressive strength of the pastes at the stages of 1, 7, 28, and 90 d were tested. The elastic modulus and strain capacity of the pastes at the stage of 7 d were determined. It is revealed that the use of OPC as an additive to replace part of FA results-in the decreases in the setting time, porosity, and strain capacity of the paste specimens, while the compressive strength and elastic modulus seem to increase.

Influence of Fly Ash and Silica Fume on Water-resistant Property of Magnesium Oxychloride Cement

By incorporation of fly ash or silica fume into magnesium oxychloride （MOC） cement, a high water resistance material can be formed for successful industrial applications. The influences of fly ash and silica fume on water-resistant property were investigated by SEM and EDS. It is found that the incorporation of fly ash or silica fume can improve the water-resistance of the MOC. The improvement of the water resistance of the MOC incorporated with fly ash or silica fume may be attributed to the alumino-silicate 5·1·8 gel or silicate 5·1·8 gel.

Effect of Corrosive Solutions on C-S-H Microstructure in Portland Cement Paste with Fly Ash

By means of ^（29）Si and ^（27）Al magic angle spinning nuclear magnetic resonance（MAS NMR） combined with deconvolution technique, X-ray diffraction（XRD）, scanning electron microscopy（SEM） as well as energy dispersive X-ray system（EDX）, the effect of 5 wt% corrosive solutions（ viz. 5 wt% Na_2SO_4, MgSO_4, Na_2SO_^（4＋）Na Cl and Na_2SO_^（4＋）Na Cl＋Na_2CO_3） on C-S-H microstructure in portland cement containing 30 wt% fly ash was investigated.The results show that, in MgSO_4 solution, Mg2＋ promotes the decalcification of C-S-H by SO_4^（2-）,increasing silicate tetrahedra polymerization and mean chain length（MCL） of C-S-H. However, the substituting degree of Al^（3＋） for Si^（4＋）（Al[4]/Si） in the paste does not change evidently. Effect of Na_2SO_4 solution on C-S-H is not significantly influenced by Na Cl solution, while the MCL and Al[4]/Si of C-S-H in fly ashcement paste slightly change. However, the decalcification of C-S-H by SO_4^（2-） and CO_3^（2-） attack, as well as the activation of fly ash by SO_4^（2-） attack will increase the MCL and Al[4]/Si, which are both higher than that under Na_2SO_4 corrosion, MgSO_4 or Na_2SO_4 ＋Na Cl coordination corrosion.

Applied technique of the cemented fill with fly ash and fine-sands

Traditional stabilization of backfilling material is done by using Portland cement. However, the high price of cement forced mining engineer s to seek cheaper binding materials. Fly ash, which is the indus- trial wast e from thermal power plant, possess the potential activity of jellification, and can b e used in cemented fill as a partial substitute for cement to reduce the fill co s t. Tests were done during the past few years in Xinqiao Pyrite Mine and Phoenix Copper Mine to determine the technology parameters and the suitable content of f ly ash. Specimens with different cement/fly/ash tailings (sands) ratios were tes ted to obtain the strength values of the fill mass based on the analyses of both the chemical composition and physical and mechanical properties of fly ash . The compressive strength of specimens with a ratio of 1∶2∶8 (cement to fly ash to tailings ) can reach 2 MPa after 90 d curing, totally meeting the requiremen t of artificial pillar and reducing the fill cost by 20%-30%.

Self-cementing Mechanism of CFBC Coal Ashes at Early Ages

The self-cementing mechanism at early ages of circulating fluidized bed combustion （CFBC） coal ashes was studied by X-ray diffraction （XRD）, infrared （IR） spectroscopy and chemical method. The results indicate that the amorphous phase is predominant in CFBC coal ashes. The polymerization degree of [SiO4] and [AlO6] of CFBC desulphurization coal ashes is lower than that of those without desulphurization. The contents of the components with fast hydration rate of CFBC desulphurization coal ashes are significantly greater than those of the ashes without desulphurization. This work confirms that the amorphous minerals with high chemical activity are the main causes of the self-cementing property of CFBC desulphurization coal ashes at early ages.

Cement-fly Ash Stabilization of Cold In-place Recycled (CIR) Asphalt Pavement Mixtures for Road Bases or Subbases

For lack of laboratory and field performance data on stabilization of reclaimed asphalt pavement （RAP） aggregate and stabilized soil （S） for road bases and subbases construction, the influences of RAP/S ratio, cement and fly ash content, modifying agent （MA） on the compact, unconfined compressive strength, indirect tensile strength and water stability of the CIR mixtures were investigated. The experimental results showed that the maximum dry density and the optimum moisture content of the mixture changed significantly with the RAP/S ratio and cement-fly ash content. Unconfined compressive strength, indirect tensile strength and water stability were improved significantly by the addition of MA, and the water stability was improved by nearly 20% on average. Scanning electron microscopy（SEM） images indicated that MA accelerated the hydration of cement-fly ash system. Needle-like AFt and fibrous C-S-H gel were observed in the mixtures, which resulted in the cementation effect among the CIR mixture particles and a more compact microstructure. All these could be the cause of high strength of the CIR mixtures with MA.

Effect of Fly Ash on TSA Resistance of Cement-based Material

Thaumasite form of sulfate attack（TSA）is a major concern in evaluating durability of concrete structures subjected to sulfate and carbonate ions.By means of Fourier transform infrared spectroscopy （FT-IR）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,and energy dispersive spectrum（EDS） as well as Raman spectra of erosion substances,effect of fly ash on TSA resistance of Portland cement-based material were investigated.Immersed in magnesium sulfate solution with 33 800 ppm mass concentration of SO 4 2-at 5±2℃for 15 weeks,ratio of compressive strength loss decreased as binder replacement ratio of fly ash increased.Furthermore,when binder replacement of fly ash was 60%,compressive strength increased.When thaumasite came into being in samples with 0,15%binder replacement ratio of fly ash,ettringite and gypsum appeared in those with 30%,45%,60%binder replacement ratio of fly ash.Results mentioned above showed that fly ash can restrain formation of thaumasite and improve TSA resistance of Portland cement-based material sufficiently.

Effect of Nano Silica on Hydration and Microstructure Characteristics of Cement High Volume Fly Ash System Under Steam Curing

The influences of nano silica (NS) on the hydration and microstructure development of steam cured cement high volume fly ash (40 wt%, CHVFA) system were investigated. The compressive strength of mortars was tested with different NS dosage from 0 to 4%. Results show that the compressive strength is dramatically improved with the increase of NS content up to 3%, and decreases with further increase of NS content (e g, at 4%). Then X?ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSCTG), scanning electron microscope (SEM), energy disperse spectroscopy (EDS), mercury intrusion porosimeter (MIP) and nuclear magnetic resonance (NMR) were used to analyze the mechanism. The results reveal that the addition of NS accelerates the hydration of cement and fly ash, decreases the porosity and the content of calcium hydroxide (CH) and increases the polymerization degree of C-S-H thus enhancing the compressive strength of mortars. The interfacial transition zone (ITZ) of CHVFA mortars is also significantly improved by the addition ofNS, embodying in the decrease of Ca/Si ratio and CH enrichment of ITZ.

The Cement Solidification of Municipal Solid Waste Incineration Fly Ash

The chemical composition, the content and the leachability of heavy metals in municipal solid waste incineration （ MSWI） fly ash were tested and analyzed. It is shown that the leachability of Pb and Cr exceeds the leaching toxicity standard, and so the MSWI fly ash is considered as hazardous waste and must be solidifled. The effect of solidifying the MSWI fly ash by cement was studied, and it is indicated that the heavy metals can be well immobilized if the mass fraction of the fly ash is appropriate. The heavy metals were immobilized within cement hydration products through either physical fixation, substhtaion, deposition or adsorption mechanisms.

Properties and Mechanism of CFBC Fly Ash-cement based Stabilizers for Lake Sludge

Circulating fluidized bed combustion（CFBC） fly ash was mixed with cement or lime at a different ratio as a stabilizer to stabilize lake sludge.In order to understand the influences of stabilizers on the lake sludge properties,tests unconfined compressive strength,water stability and SEM observation were performed.The experimental results show that with the increase of the curing time,the strength of all the stabilized specimens increase,especially the samples containing cement.The strength of the specimens is decreased with the increasing of the CFBC fly ash/cement ratio,the optimum ratio between CFBC fly ash and cement is 2：3.The water stability of CFBC fly ash-cement based stabilizers is higher than those of cement and lime.Moreover,the lake sludge stabilization mechanism of CFBC fly ash-cement based stabilizers includes gelation and filling of the hydration products,i e,C-S-H gel and the AFt crystal,which act as benders to solidify those particles together and fill in the packing void of the aggregates.

Modeling and Simulation of Wood and Fly Ash Behaviour as Partial Replacement for Cement on Flexural Strength of Self Compacting Concrete

Flexural strength was monitored and predicted on the application improving concrete strength with wood and fly as partial replacement for cement.The study observed the pressure from the constituent of these locally sourced material that has been observed from the study to influence the flexural strength through the effect from this locally sourced addictives.The study monitors concrete porosity on heterogeneity as it reflect on the flexural strength of self compacting concrete.Other condition considered was the compaction and placement of concrete.These effects were monitored at constant water cement ratio from design mix.The behaviour from this effects on the concrete observed the rate of flexural growth under the influences of these stated conditions.The simulation expressed the reactions of these effects through these parameters monitored to influence the system.Numerical simulations were also applied to the optimum curing age of twenty eight days,while analytical simulation was also applied.This concept is the conventional seven days interval that concrete curing were observed,these are improvement done on the study carried out by experts[16].These locally sourced material were experimentally applied.The simulation predictive values are at the interval of seven days of curing,which was also simulated.The predictive values were compared with the experimental values of the researchers[16],and both values developed best fits correlations.The study is imperative because the system considered the parameters used on experimental and observed other influential variables that were not examined.These were not observed in the experimental procedure.Experts in concrete engineering will definitely find these concept a better option in monitoring flexural strength of self compacting concrete in general.

Geo-environmental application of municipal solid waste incinerator ash stabilized with cement

The behavior of soluble salts contained in the municipal solid waste incinerator(MSWI) ash significantly affects the strength development and hardening reaction when stabilized with cement.The present study focuses on the compaction and strength behavior of mixed specimens of cement and MSWI ash.A series of indices such as unconfined compressive strength,split tensile strength,California bearing ratio(CBR) and pH value was examined.Prior to this,the specimens were cured for 7 d,14 d,and 28 d.The test results depict that the maximum dry density(MDD) decreases and the optimum moisture content(OMC)increases with the addition of cement.The test results also reveal that the cement increases the strength of the mixed specimens.Thus,the combination of MSWI ash and cement can be used as a lightweight filling material in different structures like embankment and road construction.

Effects on Strengths of Cement Mortar When Using Incinerator Bottom Ash as Fine Aggregate

The main purpose of this paper is to study the feasibility of using the Incinerator bottom ash fine aggregate to replace natural fine aggregate in the cement mortar products. The research adopts high cement content mortar to conduct the experiment, in which the weight ratio of cement/aggregate is 1/2. The experiment uses Incinerator bottom ash fine aggregates, which passes through #16 sieve, and natural sand of the same size as the aggregate, and separates mortar specimens in- to two main categories based on different W/C ratio. Moreover, different proportions of furnace slag and F-class are used to replace a portion of cement so as to explore the influence on strength of Incinerator bottom ash aggregates mortar by adding the two admixtures. The study shows that, based on the 1:2 cement/aggregate weight ratio, Incinerator bottom ash fine aggregates mortar, unit weight around 1.8 g/cm3, is 20% lighter natural fine aggregate mortar, unit weight around 2.2 g/cm3. The Incinerator bottom ash fine aggregates mortar can only reach 60%-70% the compressive strength of natural fine aggregates mortar. Direct tensile strength and flexural tensile strength tests are 15% and 30% of compressive strength respectively, due to the irregular strength development, which does not follow general concepts, such as low W/C ratio and mineral admixtures will not necessarily help in strength development in Incinerator bottom ash fine aggregates mortar.

水泥-蔗渣灰-陶瓷粉三元胶凝材料体系早期水化研究

为探究工业固废蔗渣灰、陶瓷粉作为辅助胶凝材料在水泥基材料中的适用性,本文通过单纯型重心设计方法对水泥-蔗渣灰-陶瓷粉三元胶凝体系进行混料设计,并通过凝结时间、水化热与氢核磁共振探究其早期水化性能.研究表明:蔗渣灰与陶瓷粉均会延长水泥浆体的凝结时间,陶瓷粉的延缓幅度更大;水泥浆体水化放热峰会随着蔗渣灰掺量的增加而后移,随陶瓷粉掺量的增加而略微向前移,且蔗渣灰与陶瓷粉的掺入都会使浆体水化放热降低,72h水化程度也会降低;蔗渣灰与陶瓷粉的掺入会增加氢核磁共振信号强度,其中水泥-蔗渣灰组合的信号强度更高.水泥-蔗渣灰-陶瓷粉有较好的协同作用,三元体系可以制备凝结时间符合规范要求、水化热较低的胶凝材料,试验成果为工业固废的绿色应用以及低热混凝土的制备提供参考.

The Influence of Rice Husk Ash on Mechanical Properties of the Mortar and Concrete: A Critical Review

Increasing the population and infrastructure in both emerging and developed countries requires a considerable amount of cement, which significantly affects the environment. The primary materials of concrete (‘cement’) production emit a large quantity of CO2 into the environment. Also, the cost of conventional building materials like cement gives motivation to find geopolymer waste materials for concrete. To reduce harmful effects on the environment and cost of traditional concrete substance, alternative waste materials like rice husk ash (RHA), ground granulated blast-furnace (GGBS), fly ash (FA), and metakaolin (MK) can be used due to their pozzolanic behavior. RHA waste material with a high silica concentration obtained from burning rice husks can possibly be used as a supplementary cementitious material (SCM) in the manufacturing of concrete, and its strong pozzolanic properties can contribute to the strength and impermeability of concrete. This review paper highlights a summary of the positive effect of using RHA as a partial substitute for cement in building construction, as well as its optimal inclusion of enhanced mechanical properties like compressive strength, flexural strength, and split tensile strength of mortar and concrete.

Composition Design for High C_3S Cement Clinker and Its Mineral Formation

A new composition of Portland cement clinker was studied, in which KH, SM and IM was 0.98,2.4 and 2.4 respectively as well as its meal added 1%CuO （in mass）. Fired at 1 200℃,1 350℃,1 400℃ and 1 450℃ for 30 min, the resultant mineral phases component and mineral morphology were analyzed. The performances of the cement which was made of clinker burned at 1 450℃ and fly ash were determined. By means of QXRD, XRD and optical microscopy, it is shown that the clinker burnt at 1 450℃ has the larger size crystals and distinct crystal interface, in which the C3S content is 73.37% and the mineral phases is dominantly C3S, following by minor C2S, C3A and tetracalcium aluminoferrite. The results reveal that a new type of high C3S content clinker can completely be made by traditional temperature-time schedule. The performances of the cement produced from this clinker with addtion of 50% fly ash and 5% gupsum were in agreement with the 32.5 strength grade of Portland fly-ash cement. The results also show that the clinker has a significant effect of saving energy and utilizing waste slag.

Analysis of Pore Structures and Their Relations with Strength of Hardened Cement Paste

Three cement samples were prepared, includi ng OPC consisted of 100wt% portland cement, PFA consisted of 70wt% portland cemen t and 30wt% fly-ash, and CA consisted of 70wt% portland cement and 30wt% modifi ed fly ash. The strength of hardened cement paste of these samples was tested an d their pore structures were determined by a mercury intrusion porosimeter. More over,the data of the pore structures of three samples were comprehensively analy zed. The relations between the pore structures and the compressive strength of t he three samples were studied. The experimental results show that the relations between the porosity determined by the mercury intrusion porosimeter and the com pressive strength are not notable, and the total pore surface area, the average pore diameter and the median pore diameter could be used to explain the differen ce of the strength of the tested samples.

Bond Durability of Carbon-Microfiber-Reinforced Alkali-Activated High-Temperature Cement Adhering to Carbon Steel

The study aims at evaluating the bond durability of a carbon microfiber (CMF)-reinforced alkali-activating calcium aluminate cement (CAC)/fly ash F (FAF) blend cementitious material adhering to carbon steel (CS) under stresses induced by a 350℃ heat-25℃ water cooling cycle. This cementitious material/CS joint sample was originally prepared in an autoclave at 300℃ under a pressure of 8.3 MPa. For comparison, two reference geothermal well cements, Class G modified with silica (G) and calciumaluminum phosphate (CaP), were employed as well reinforced with CMF. In the CAC/FAF blending cement systems, the CAC-derived cementitious reaction products preferentially adhered to CS surfaces, rather than that of FAF-related reaction products. CMF played a pivotal role in creating tough interfacial bond structure of cement layer adhering to CS. The bond toughness also was supported by the crystalline cementitious reaction products including sodalite, brownmillerite, and hedenbergite as major phases, and aragonite, boehmite, and garronite as minor ones. The brownmillerite as an interfacial reaction product between cement and CS promoted the chemical bonding of the cement to CS, while the other phases served in providing the attractive bonding of the cement to CS. The post-stress-test joint samples revealed the formation of additional brown-millerite, aragonite, and garronite, in particular brownmillerite as the major one. The combination of chemical bonding and self-advancing adherence behavior of the cement was essential for creating a better interfacial bond structure. A similar interfacial bond structure was observed with CaP. The crystalline phase composition of the autoclaved cement revealed apatite, zeolite, and ferrowyllieite as major reaction products, and aragonite and al-katoite as the minor ones. Ferrowyllieite was identified as cement/CS interfacial reaction product contributing to the chemical bond of cement, while the other phases aided in providing the attractive bond of cement. After a stress test, two phases, ferrowyllieite and aragonite, promoted the self-advancing adherence of cement to CS. However, the effectiveness of these phases in improving adherence performance of cement was less than that of CAC/FAF blend cement, reflecting the fact that the bond durability of CAC/FAF blend cement was far better than that of the CaP. In contrast, the autoclaved silica-modified G cement consisting of xonotlite, and 0.9 nm-to-bermorite and riversideite, with calcite as the crystalline reaction products, had no significant effect on improving the shear bond strength and the bond’s toughness. No interaction product with CS was found in the cement adhering to CS. After a stress test, the calcite phase acted only to promote the self-advancing adherence of cement, but its extent was minimal compared with that of the other cements, thereby resulting in poor bond durability.