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.

Effects of water content, water type and temperature on the rheological behaviour of slag-cement and fly ash-cement paste backfill

The pumping ability and placement performance of fresh cemented paste backfill(CPB) in underground mined cavities depend on its rheological properties. Hence, it is crucial to understand the rheology of fresh CPB slurry, which is related to CPB mixture design and the temperature underground. This paper presented an experimental study investigating the effects of binder type, content, water chemical properties and content, and temperature, on the rheological properties of CPB material prepared using the tailings of a copper mine in South Australia. Portland cement(PC), a newly released commercially manufactured cement called Minecem(MC) and fly ash(FA) were used as the binders added to the mine tailing materials. Various amounts of two different water types were added to the mixtures in the preparation of backfill material slurry. Six different temperatures ranging from 5 to 60 °C were to investigate the effect of temperature on CPB rheology. Overall, the increasing water content and decreasing temperature lead to lower yield stress. Based on the results obtained from the rheological properties of CPB slurry, it was found that at room temperature(25 °C), with regards to the unconfined compressive strength(UCS) performance, the replacement of 4% PC mixed CPB(28 days UCS 425 k Pa) to 3% MC mixed CPB(28 days UCS 519 k Pa), reduced the slurry yield stress from 210.7 to 178.5 Pa. The results also showed that the chemical composition of water affects the yield stress of CPB slurry and that MC mitigates the negative effect of mine-processed water(MW) and thus lead to improve the rheological properties of the slurry. However, the results suggested that the rheological properties of a mixture using MC is very sensitive to the water volume and temperature change. Therefore, using MC in backfill requires better quality control in slump mixing.

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.

Effect of temperature on the hydration process and strength development in blends of Portland cement and activated coal gangue or fly ash

This paper describes the results of an investigation into the effect of the variation of curing temperatures between 0 and 60 °C on the hydration process,pore structure variation,and compressive strength development of activated coal gangue-cement blend(ACGC) . Hardened ACGC pastes cured for hydration periods from 1 to 360 d were examined using the non-evaporable water method,thermal analysis,mercury intrusion porosimetry,and mechanical testing. To evaluate the specific effect of activated coal gangue(ACG) as a supplementary cementing material(SCM) ,a fly ash-cement blend(FAC) was used as a control. Results show that raising the curing temperature accelerates pozzolanic reactions involving the SCMs,increasing the degree of hydration of the cement blends,and hence increasing the rate of improvement in strength. The effect of curing temperature on FAC is greater than that on ACGC. The pore structure of the hardened cement paste is improved by increasing the curing temperature up to 40 °C,but when the curing temperature reaches 60 °C,the changing nature of the pore structure leads to a decrease in strength. The correlation between compressive strength and the degree of hydration and porosity is linear in nature.

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.

Influence of Fly Ash Addition on the Hydration of Portland Cement

Influence of fly ash addition on the hydrationof Portland cement clinker,particularly at the initial stage,has been studied on the basis of measured data obtained. Fly ash,considering its active components,was added as a partial replacement of Portland cement at different water/cementitious ratios. The hydration heat was measured in a controlled environmental room of 20 ℃. Both non-evaporable water content and mineral phase were investigated. Data indicate that the amount of fly ash involved in hydration reaction is little at initial stage while it becomes more after 7 d hydration. As hydration reaction is a continuous process,chemical stress results in the disruption of stable structure on the surface of fly ash consisting of Ca,O,Si,Al,C,etc. Additionally,surface of glass beads begins to lose smooth and reacts to blend in with the paste.

硅酸盐熟料-煤矸石/粉煤灰混合水泥水化模型研究

对两种不同3CaO·SiO_2(C_3S)含量的硅酸盐水泥和分别掺有30%(质量分数,下同)煤矸石和30%粉煤灰的混合水泥中水化产物含量变化和形态进行了研究,建立了水化产物量变模型和水化产物形态模型,分析了模型的主要特征和意义。相同龄期,高C_3S硅酸盐水泥比低C_3S硅酸盐水泥生成更多的水化硅酸钙(calcium silicate hydrate,CSH)凝胶和氢氧化钙。含混合材的水泥水化时,CSH凝胶在水化早期和后期有两个增长幅度较大的阶段,并且1年后形成的CSH凝胶量与纯硅酸盐水泥的相当。水泥水化产物与混合材的二次水化反应较慢,研究掺有混合材水泥更长龄期的水化产物含量及结构变化,将有助于理解混合材对水泥性能的作用机理。

碱激发粉煤灰水泥胶凝体系的水化机理分析

通过在粉煤灰掺量比例为50%的粉煤灰-水泥胶凝体系中加入Na2SO4和碱石灰复合激发进行粉煤灰火山灰活性激发试验,研究粉煤灰-水泥胶凝体系的早期强度,并采用衍射分析和扫描电镜分析硬化浆体的微观结构。研究结果表明:Na2SO4和碱石灰复掺具有明显的活性作用,水泥石早期强度显著提高;水泥石中形成了较多的CSH和AFt,未发现AFm生成,说明加入Na2SO4和碱石灰共同激发可有效破坏粉煤灰的玻璃微珠外壳及硅铝网络结构,可增强粉煤灰的潜在活性。

氯化钠对粉煤灰硅酸盐混合水泥活性激发能力和结合方式的试验研究

通过在粉煤灰硅酸盐混合水泥中掺加0.5～4%的氯化钠进行的试验研究表明,氯化钠掺量在1%以下时水泥石早期强度显著提高,具有明显的活性激发和早强作用;在水泥中加入的Cl-约86～90%时,与硅酸盐水泥和粉煤灰形成化学结合状态,4.5～7.7%为游离状态,1.4～5.9%为物理吸附状态;Cl-加入后,水泥石中新形成氯铝酸钙产物,但水泥石中的氯铝酸钙往往与AFm、C-S-H混合生长,未发现单独生成的氯铝酸钙。

Effects of seeding nucleation agent on geopolymerization process of fly-ash geopolymer

Geopolymer, an inorganic aluminosilicate material activated by alkaline medium solution, can perform as an inorganic adhesive. The geopolymer technology has a viability to substitute traditional concrete made of portland cement （PC） because replacing PC with fly ash leads to reduced carbon dioxide emissions from cement productions and reduced materials cost. Although fly ash geopolymer stimulates sustainability, it is slow geopolymerization reaction poses a challenge for construction technology in term of practicality. The development of increasing geopolymerization reaction rate of the geopolymer is needed. The purpose of this study is to evaluate seeding nucleation agents （NA） of fly ash geopolymer that can accelerate polymerization reactions such that the geopolymer can be widely used in the construction industry. Results from the present study indicate that the use of NA （i.e., Ca（OH）2） can be potentially used to increase geopolymerization reaction rate and improve performance characteristics of the fly ash geopolymer product.

Effect of polycarboxylate type of super plasticizer on the hydration properties of composite cements

The work aims to study the effect of polycarboxylate type of super plasticizer on the hydration of composite cements.In this paper we have studied the hydration of 20 wt%fly ash(FA)blended Portland cement in the presence of 0.1 wt%super plasticizer(SP).Water consistency,setting times,non-evaporable water contents,compressive strength,water percolation,and air content measurements were carried out.In addition,Xray diffraction studies were carried out to understand the hydration process.The results indicated the increase in compressive strength of the FA blended Portland cement in the presence of SP and with the increase of the hydration time.

粉煤灰-硅酸盐混合水泥粒度分布分形维数与其比表面积和抗压强度的关系

采用分形理论,研究了6种不同粒度分布的粉煤灰与相同粒度分布的硅酸盐水泥所组成的粉煤灰-硅酸盐混合水泥粒度分布的分形维数及其与比表面积、砂浆抗压强度的关系,以观察粉煤灰的物理作用。结果表明,随着粉煤灰粒度分布的变化,粉煤灰-硅酸盐混合水泥粒度分布分形维数和比表面积、砂浆抗压强度之间呈良好的线性正相关;粉煤灰粒度分布分形维数对砂浆后期强度的影响明显大于其对早期强度的影响。