Analysis of the Performances and Optimization of Polyurethane Concrete with a Large Percentage of Fly Ash

The properties of polyurethane concrete containing a large amount of fly ash are investigated,and accordingly,a model is introduced to account for the influence of fly ash fineness,water ratio,and loss of ignition(LOI)on its mechanical performances.This research shows that,after optimization,the concrete has a compressive strength of 20.8 MPa,a flexural strength of 3.4 MPa,and a compressive modulus of elasticity of 19.2 GPa.The main factor influencing 28 and 90 d compressive strength is fly ash content,water-binder ratio,and early strength agent content.

Tests on Alkali-Activated Slag Foamed Concrete with Various Water-Binder Ratios and Substitution Levels of Fly Ash

To provide basic data for the reasonable mixing design of the alkali-activated (AA) foamed concrete as a thermal insulation material for a floor heating system, 9 concrete mixes with a targeted dry density less than 400 kg/m3 were tested. Ground granulated blast-furnace slag (GGBS) as a source material was activated by the following two types of alkali activators: 10% Ca(OH)2 and 4% Mg(NO3)2, and 2.5% Ca(OH)2 and 6.5% Na2SiO3. The main test parameters were water-to-binder (W/B) ratio and the substitution level (RFA) of fly ash (FA) for GGBS. Test results revealed that the dry density of AA GGBS foamed concrete was independent of the W/B ratio an RFA, whereas the compressive strength increased with the decrease in W/B ratio and with the increase in RFA up to 15%, beyond which it decreased. With the increase in the W/B ratio, the amount of macro capillaries and artificial air pores increased, which resulted in the decrease of compressive strength. The magnitude of the environmental loads of the AA GGBS foamed concrete is independent of the W/B ratio and RFA. The largest reduction percentage was found in the photochemical oxidation potential, being more than 99%. The reduction percentage was 87% - 93% for the global warming potential, 81% - 84% for abiotic depletion, 79% - 84% for acidification potential, 77% - 85% for eutrophication potential, and 73% - 83% for human toxicity potential. Ultimately, this study proved that the developed AA GGBS foamed concrete has a considerable promise as a sustainable construction material for nonstructural element.

Durability of Seawater Mixed Concrete with Different Replacement Ratio of BFS （Blast Furnace Slag） and FA （Fly Ash）

Using seawater in concrete can be considered as one of the sustainable approaches in construction industry not only to save the freshwater resource but also to promote the use of abandoned seawater resource, especially in the construction at the uninhabited area close to the sea where the procurement of fresh water is difficult. In this study, durability against chloride attack of seawater mixed concrete with different replacement ratio of BFS （blast furnace slag） and FA （fly ash） is discussed and the life time until the occurrence of corrosion crack is evaluated. The results show that： （1） Chloride penetration rate of seawater mixed specimens with BFS and FA is lower than that of freshwater mixed OPC （ordinary Portland cement） specimens; （2） Oxygen permeability of seawater mixed specimens with BFS and FA is almost the same or lower than that of freshwater mixed OPC specimens; （3） Total life time （corrosion incubation period and propagation period） of seawater mixed specimens with BFS and FA is almost the same or only slightly shorter than that of freshwater mixed OPC specimens. From the results, it was confirmed that the usage of seawater in concrete mixing is feasible in concrete with the appropriate BFS and FA replacement ratio.

Environmental and Cost Advantages of Using Polyethylene Terephthalate Fibre Reinforced Concrete with Fly Ash as a Partial Cement Replacement

Solid waste disposal is an alarming problem in most African countries. Plastic wastes like Polyethylene Terephthalate (PET) bottles and powdered wastes like fly ash are severely persisting environmental hazards. They are brutally polluting the water bodies, landfills, as well as the atmosphere. The construction industry has been working towards improving concrete quality by developing alternative methods like partial cement replacement with different pozzolanic elements as well as using waste fibrous materials. Fly ash and PET bottle fibres are two common waste materials that can be used. This article is a part of a research that studied the combined effects of the addition of PET bottle fibres and fly ash (as a partial cement replacement) on the structural performance of concrete. From a purely engineering point of view, the research results indicate that the utilization and incorporation of PET and fly ash wastes in the construction industry are a viable solution to make concrete quality better. This article presents, beyond the engineering properties and experimental works, the economic and environmental advantages of the addition of these waste materials to the conventional concrete mixture. The addition of PET bottle fibres and fly ash resulted in positive cost implications providing a production cost reduction of 19% over the conventional concrete mixture. The removal of these materials from the environment also showed reduction of the emission of toxic elements to landfills and water bodies that put human, animal and plant lives in danger.

Quantitative Assessment on the Embodied Environmental Impact of Concrete with or without Fly Ash

According to the life cycle assessment and the environmental design method of industry prnduction, a quantitative assessment model for the embodied environmetal impact of concrete with or without fly ash was proposed. The environmental burden impact indicator （ EBII ）, the resources depletion impact indicator （RDII）, and the environmental impact comprehensive indicator （EICI） are defined. The specific environmental impact values of different grade concretes with or wittout fly ash were presented. In the embodied process of concrete with or without fly ash, the key potential environmental impact categories are global warming and dust endsskin, and it is an effective way for reducing the embndied environmental impact of concrete to mix fly ash and lower grade cenwat . The method presented in this paper makes it possible to quantitatively assess the embodied environmental impact of concrete with or without .fly ash. The results calculated in this paper can be used to quantitatively assess the life cycle environmental impact of construction materials and buildings.

Preparation and Properties of Eco-Friendly Aerated Concrete Utilizing High-Volume Fly Ash with MgO and CaO Activators

The associated MgO in limestone is believed to affect the volume stability of cementitious materials at room tem-perature,which limits the utilization of low grade limestone.In this study,MgO was used as an alkali activator instead of partial CaO to prepare the aerated concrete under hydrother mal conditions.The expansion process was studied to evaluate the influence of the raw materials on the gas forming stability of the slurry.The pore structure(porosity,pore size and its distribution)was analyzed by the image method.The physic mechanical properties(density,strength,thermal properties)of concrete with the addition of MgO were comprehensively investigated.Besides,the mineral compositions and morphology of the hydration products were analyzed to demonstrate the infuence mechanism of MgO on the mechanical properties.Experimental results show that the final expansion rate of the slurry decreases with MgO content.A reasonable MgO content,ie,MgO/(MgO+CaO)<20%,con-tributes to improve the compressive strength,attributing to an increased reaction rate to C-S-H gel and tobermor-ite.The addition of MgO causes the thermal conductivity and specific heat to increase.The pore structure is mainly related to the amount of air entraining agent.This study has a significance for the further utilization of magnesium-rich carbonates in the autoclaved building products.

A Study on Strength Properties of Concrete with Replacement of Low C3A Cement by Fly Ash

The chemical composition of cement has a crucial impact on the performance of concrete.Different brands of Portland cement are used for various construction works without prior knowledge of their performance.For economic and environmental reasons,the valorization of fly ash in concrete production has been increasingly studied.The aim of this study is to determine the mechanical performance of the cement in which hydrated cement has been injected,and to assess the environmental benefit of using the waste as a partial replacement.The experimental study consists of replacing cement,with high tricalcium aluminate(C3A)content,with cement with low C3A content.The obtained result shows that it is very feasible to valorize this material and to manufacture eco-environmental cement which has rheological and mechanical characteristics almost similar to or better than that of ordinary cement,where a resistance of 30 MPa has been obtained,after a substitution rate of 50%.The valorization by using cement with low C3A content makes it possible to strengthen the material at a young age and leads to obtain more economical and less polluting cement.

Compressive Strength, Pore Size Distribution and Chloride-ion Penetration of Recycled Aggregate Concrete Incorporating Class-F Fly Ash

The effects of fly ash on the compressive strength, pore size distribution and chloride-ion penetration of recycled aggregate concrete were investigated. Two series of concrete mb：tures were prepared. The concrete mixtures in series I had a water-to-binder ratio and a cement content of 0.55 and 410 kg/ m^3 , respectively. The concrete rnixtures in series II had a water-to-binder ratio and a cement content of 0.45 and 400 kg/ ml respectively. Recycled aggregate was ased as 20% , 50% , and 100% replacements of natural coarse aggregate in the concrete mixtures in both series. In cutdition, fly ash was used as 0% , 25% and 35% by weight replacements of cement. The results show that the compressive strengths of the concrete decreased as the recycled aggregate and the fly ash contents increased. The total porosity and average porosity diameter of the concrete increased us the recycled aggregate content increased. Furtherrruore , an increase in the recycled aggregate content decreased the resistance to chloride ion penetration. Nevertheless, the replacement of cement by 25% fly ush improved the resistance to chloride ion penetration and pore diameters and reduced the total porosity of the recycled aggregate concrete.

Influence of fly ash on early-age cracking behavior of high-flowing concrete

The effects of quality and content of fly ash on the early-age cracking behavior of high-flowing concrete （HFC） were investigated. The early-age cracking behavior of the HFC was analyzed by combining the tests of evaporation capacity and electrical resistivity of the HFC. In these tests, a modified flat-type specimen was adopted. The results show that the HFC will have a lower evaporation capacity when it is mixed with fine fly ash, while it will have a higher evaporation capacity when grade II! fly ash is used as mineral admixture. And the electrical resistivity rate of HFC reduces with the increase of the content of fly ash. A nonlinear relationship exists between the cracking time of HFC and the minimum electrical resistivity. The early-age cracking behavior of HFC with fly ash can be enhanced by appropriately increasing the fine particle content and MgO, K2O, and SO3 contents of fly ash. The optimal content of fly ash, which makes a satisfied early-age cracking behavior of HFC, is obtained. And when the content of fly ash exceeds a critical value, the early-age cracking behavior of HFC will rapidly decrease.

Effect of Fly Ash on Frost-Resistance and Chloride Ions Diffusion Properties of Marine Concrete

It is necessary to pay more attention to the durability of concrete undergoing freeze-thaw cycles and seawater attack simultaneously.Investigated are the effects of water-binder ratio,fly ash（FA）contents and air-entraining agent on resistance to frost and chloride diffusion of marine concrete blended with FA in natural seawater.The results show that fly ash does not improve the frost resistance of concrete but can improve its resistance to chloride diffusion by addition of less than 30%.The resistance to frost and chloride diffusion of FA concrete can be improved with the decrease of water-binder ratio,and FA may improve both of them simultaneously only being mixed with air-entraining agent.A ratio（named as R）of the frost-resisting durability factor to chloride diffusion coefficient can be used to evaluate the durability of marine concrete.Scanning electron microscope（SEM）analyses are consistent with the evaluations by the value of R.

Preparation of Reactive Powder Concrete Using Fly Ash and Steel Slag Powder

To decrease the cement and SF content of RPC by using ultra-fine fly ash （UFFA） and steel slag powder （SS）, the effect of these mineral admixtures on compressive strength of RPC were investigated. The experimental results indicate that the utilization of UFFA and SS in RPC is feasible and has prominent mechanical performance. The microstructure analysis （SEM and TG-DTG-DSC） demonstrated that the excellent mechanical properties of RPC containing SS and UFFA were mainly attributed to the sequential hydration filling effect of the compound system.

Assessment of Curing Efficiency and Effect of Moist Curing on Performance of Fly Ash Concrete

This study was conducted to evaluate the sensitivity of compressive strength,water permeability and electrical resistance of near-surface layer concrete with different fly ash contents to curing conditions.It is shown that the sensitivity to curing condition and fly ash content descends in the following order：difference between internal and surface resistivity （ρ） at 28 days,water permeability and compressive strength;both of longer duration of moist curing and use of fly ash in concrete enhanced the water penetration resistance.It is indicated that the resistivity difference ρ at 28 days can reflect accurately the curing history of fly ash concrete regardless of mix proportions;and use of fly ash in concrete requires longer moist curing duration.

A Study on the Effect of Low Calcium Ultra-fine Fly Ash as a Partial Sustainable Supplementary Material to Cement in Self-compacting Concrete

The aim and scope of the present study were to determine the efficacy of UFFA in evaluating the workability,static and dynamic stabilization properties,retention period,and slump loss of SCC systems in their fresh state,as well as their compressive strength at various ages.Microstructure(SEM and XRD)of blended SCC systems were studied.Also,the thermogravimetry behavior of blended SCC specimens were researched.According to the evaluated results,incorporating up to 20%UFFA into fresh concrete improved its performance due to its engineered fine particle size and spherical geometry,both of which contribute to the enhancement of characteristics.Blends of 25%and 30%of UFFA show effect on the water-binder ratio and chemical enhancer dosage,resulting in a loss of homogeneity in fresh SCC systems.The reduced particle size,increased amorphous content,and increased surface area all contribute to the pozzolanic reactivity of the early and later ages,resulting in denser packing and thus an increase in compressive strength.The experimental results indicate that UFFA enhances the properties of SCC in both its fresh and hardened states,which can be attributed to the particles’fineness and their relative effect on SCC.

Effect of Fly Ash and Early Strength Agent on Durability of Concrete Exposed to the Cyclic Sulfate Environment

The effect of fly ash and early strength agent on resistance of concrete to the cyclic sulfate environment was studied.Concrete specimens made with ordinary portland cement or ordinary portland cement incorporating fly ash with the replacement of 10% or 20%,or 1% early strength agent and fly ash with the replacement of 20%,were made and subjected to 250 cycles of exposure to the cyclic sulfate environment.Concrete properties including loss of mass,chloride ion diffusion coefficient,compressive strength and flexural strength were measured.Microstructure and chemical component of samples were determined by means of X-ray diffraction,scanning electron microscopy and energy dispersive spectroscopy.The experimental results indicated that effect of fly ash on the cyclic sulfate resistance of concretes was mostly dependent on the amount of fly ash.Early strength agent improved performances of concrete with 20% fly ash exposed to cyclic sulfate environment.

Research on the influence of the fly ash on the concrete carbonation

The influence of fly ash on the fresh properties, mechanical properties and carbonation properties were studied in this paper. The performance of a kind of curing agent which was applied to the hardened concrete surface was evaluated. Incorporating large volume of fly ash will risk the concrete carbonation. The curing agent could prevent the concrete carbonation, and the mechanism was explained.

Recycled Aggregate Pervious Concrete: Analysis of Influence of Water-Cement Ratio and Fly Ash under Single Action and Optimal Design of Mix Proportion

Pervious concrete is recommended,which is of great benefit to the ecological environment and human living environment.In this paper,the influences of five water-cement ratios and four fly ash contents to replace the cement by mass with a water-cement ratio of 0.30 on the properties of Recycled Aggregate Pervious Concrete(RAPC)were studied.Following this,based on the Grey relational-Technique for Order Preference by Similarity to an Ideal Solution(TOPSIS)optimization method,the strength,permeability,abrasion loss rate,and material costs of RAPC were adopted as evaluation indices to establish a mix proportion optimization model.The results show that the increase of water-cement ratio and fly ash replacement level of RAPC leads to decreased compres-sive strength while an increase in the permeability and abrasion loss rate.According to test results based on the optimal model 0.30 was identified as the best mix proportion.In addition,ecological-economic analysis of RAPC raw materials was carried out by comparing different natural aggregates.The results of EE(embodied energy)and ECO 2e(embodied CO_(2) emission)pointed out that the combination of recycled aggregate and fly ash leads to sig-nificant ecological and economic benefits.

Accelerated Carbonation Assessment of High-Volume Fly Ash Concrete

The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonation progresses at maximum at a relative humidity of about 60%, the rate may differ in the case of cements blended with SCMs, especially with high-volume fly ash replacements. In this study, the effect of high-volume fly ash concrete exposed to low ambient relative humidity (RH) conditions (57%) and accelerated carbonation (4% CO2) is investigated. Twenty-three concrete mixtures were produced varying in cementitious contents (310, 340, 370, and 400 kg/m3), water-to-cementitious materials ratio (0.45 and 0.50), and fly ash content (0%, 15%, 30%, and 50%) using a low and high-calcium fly ash. The specimens were allowed 1 and 7 days of moist curing and monitored for their carbonation rate and depth through phenolphthalein measurements up to 105 days of exposure. The accelerated carbonation test results indicated that increasing the addition of fly ash also led to increasing the depth of carbonation. Mixtures incorporating high-calcium fly ash were also observed to be more resistant against carbonation than low-calcium fly ash due to the higher calcium oxide (CaO) content. However, mixtures incorporating high-volume additions (50%) specimens were fully carbonated regardless of the type of fly ash used. It was evident that the increase in the duration of moist curing from 1 day to 7 days had a positive effect, reducing the carbonation depth for both plain and blended fly ash concrete mixes, however, this effect was minimal in high-volume fly ash mixtures. The results demonstrated that the water-to-cementitious ratio (W/CM) had a more dramatic impact on carbonation resistance than the curing age for mixtures incorporating 30% or less fly ash replacement, whereas those mixtures incorporating 50% showed minor differences regardless of curing age or W/CM. Based on the compressive strength results, carbonation depth appeared to decrease with increase in compressive strength, but this correlation was not significant.

Comparison of High Performance Fly Ash Concrete Using Nano Silica Fume on Different Mixes

This paper investigates the experimental results on the effect of nano silica fume on compressive strength development of concretes containing high volume fly ash (HVFA). The effect of various silica fumes contents such as 1%, 2% & 3% (wt. %) as partial replacement of cement on the compressive strength of cements is evaluated in the first part. The nano silica fume content which exhibits the highest compressive strength above is used in high volume fly ash concretes containing 30% and 50% class F fly ash. The results show that among three different silica fumes contents, the addition of 1% increases the compressive strength of concretes. The addition of 1% silica fume also increases the early age and 28 days compressive strengths of HVFA concretes.

Effects of GH Admixture on the Early Strength of Fly Ash Concrete and Mortar

The enhancement effects of GH admixture on the early strengths of fly ash concrete and mortar were studied, and the mechanism was analyzed by X-ray diffraction （XRD） and scanning electro microscope （SEM）. Experimental results show that, by the incorporation of GH admixture, both of cement hydration and pozzolanic reaction of fly ash are accelerated, the strengths of fly ash concrete and mortar are enhanced noticeably, especially the early strength. With a mixture design of 200 kg/m^3 OPC （Ordinary Portland Cement ）, 200 kg/m^3 fly ash and 50 kg/m^3 GH admixture, the strength of concrete at 1 d, 3 d and 28 d reaches 25 MPa, 50 MPa and 70 MPa respectively.

Hydration of concrete containing calcium-enriched fly ash at subzero temperature

The compressive strength,hydration products and microstructure of concrete with calcium-enriched fly ash(CEFA) at different temperature were investigated.The result indicates that the hydration products age of 7 d at-15 ℃ are mainly ettringite and C-S-H,and fly ash particles remain original state.Standard curing was adapted after 7 d curing at-15 ℃.At the age of 35 d,C-S-H was found on the surface of fly ash particles.The hydration product of CEFA is mainly C-S-H gel,which can densify the microstructure of concrete.