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.

Utilization of municipal solid waste incineration fly ash in lightweight aggregates

Washing pre-treatrnent of municipal solid waste incineration （MSWI） fly ash blended with shale and sludge was utilized in the manufacture of light-weight aggregates and processed to form ceramic pellets. A formula uniform design was performed to arrange the mixture ratio of the materials. The optimal mixture ratio of the materials was determined by measuring the bulk density, granule strength, and 1 h water absorption of the pellets. It is shown that the optimal mixture ratios of materials, MSWI fly ash, shale, and sludge, are 23.16%, 62.58%, and 14.25% （mass fraction）, respectively. The performance testing indicators of light-weight aggregates are obtained under the optimum mixture ratio： bulk density of 613 kg/m3, granule strength of 821N, and 1 h water absorption of 11.6%, meeting 700 grade light-aggregate of GB/T 17431.2--1998 standard. The results suggest that utilization of MSWI fly ash in light-weight aggregates is an effective method and a potential means to create much more values.

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.

Effect of Glass Powder on Chloride Ion Transport and Alkali-aggregate Reaction Expansion of Lightweight Aggregate Concrete

The effects of glass powder on the strength development, chloride permeability and potential alkali-aggregate reaction expansion of lightweight aggregate concrete were investigated. Ground blast furnace slag, coal fly ash and silica fume were used as reference materials. The re- placement of cement with 25% glass powder slightly decreases the strengthes at ？ and 28 d, but shows no effect on 90 d＇s. Silica fume is very effective in improving both the strength and chloride penetration resistance, while ground glass powder is much more effective than blast furnace slag and fly ash in improving chloride penetration resistance of the concrete. When expanded shale or clay is used as coarse aggregate, the concrete containing glass powder does not exhibit deleterious expansion even if alkali-reactive sand is used as fine aggregate of the concrete.

The Impact of Marine Water on Different Types of Coarse Aggregate of Geopolymer Concrete

This research studies the impact of different types of coarse aggregate on the behavior of geopolymer concrete based on both fly ash (FA) and ground granulated blast furnace slag (GGBFS) in different marine environments. Aiming to solve the problems caused by the construction and demolition waste and the depletion of natural aggregates, in the present study coarse recycled aggregates is used to produce new green concrete with a fly ash-slag based geopolymer. By this examination, the research seeks to improve the quality and productivity of concrete used in construction and hydraulic projects. For this research, four mixtures containing different types of coarse aggregate in two different water environments were used. The utilized mixtures contained natural aggregate concrete (NAC) such as basalt and crushed marble. Also, recycled coarse aggregate concrete (RAC), which totally replaced natural aggregate, was presented in this paper such as crushed concrete and crushed ceramic. For this study, in the sieve analysis;specific and unit weights, was recorded. Furthermore, the mechanical properties were determined, using a compressive test that was conducted on the 7th, 28th, 56th and 90th days at different water environments;potable water (PW) and sea water (SW). Durability test was also performed for total absorption measurement. Results indicated that geopolymer concrete exhibits better strength in marine environments than in those of potable water. Results also showed that crushed marble (CMA) exhibits higher compressive strength and durability.

不同粗骨料取代率下粉煤灰再生混凝土的力学性能研究

为探讨不同再生粗骨料取代率下粉煤灰对再生混凝土力学性能的影响,以及再生混凝土抗折强度与再生粗骨料取代率、水胶比之间的关系,以RC30设计强度等级为基础设计了16组配合比,制作了96块再生混凝土试块,主要进行了再生混凝土的抗压强度试验和抗折强度试验。得出如下结论:随粉煤灰掺量的增加,不同再生粗骨料取代率,抗压强度变化规律有所不同;再生粗骨料取代率为0、30%和40%时,抗压强度随粉煤灰掺量的增加整体呈下降趋势;而当再生粗骨料取代率为50%时,随粉煤灰掺量的增加,抗压强度先减小后增大。粉煤灰掺量大于20%时,天然骨料混凝土的抗压强度急剧下降,而再生骨料混凝土的抗压强度降低幅度均较小,大掺量粉煤灰在再生混凝土中或将有更大的应用空间。通过观察抗折强度试件破坏断面,分析再生混凝土变形破坏特征。粉煤灰的掺入提高了天然骨料混凝土的抗折强度,且掺量为20%强度最高。再生粗骨料取代率为30%时,随粉煤灰掺量变化抗折强度整体呈下降趋势,但下降幅度很小;再生粗骨料取代率为40%和50%时,呈先减后增再减的趋势。天然骨料混凝土的折压比随粉煤灰掺量的增加而提高;再生混凝土折压比随粉煤灰掺量的变化趋势与抗折强度一致,但变化幅度略小。粉煤灰对再生混凝土抗折强度的影响大于抗压强度;再生粗骨料取代率为30%,粉煤灰掺量为10%为较优掺量。提出再生混凝土抗折强度预测式。

粉煤灰化学成分对其抑制碱骨料反应效果影响试验研究

采用快速砂浆棒法,研究了不同化学成分含量粉煤灰抑制碱骨料反应的效果。试验表明:F类粉煤灰抑制碱骨料反应效果明显优于C类粉煤灰,且粉煤灰掺量越高抑制效果越好。统计分析表明,粉煤灰化学成分与其抑制碱骨料反应效果存在很好的相关性,抑制效果与SiO_(2)+Al_(2)O_(3)+Fe_(2)O_(3)总质量分数存在线性正相关,与CaO含量存在线性负相关,与碱含量没有直接相关性。

粉煤灰再生混凝土力学性能试验研究

利用试验检测机构废弃的混凝土试块作为再生粗骨料的原材料,配制不同粗骨料取代率的混凝土,再加入适量粉煤灰,制成试件(取代率分别为0、30%、60%和100%),用于混凝土立方体抗压、劈裂抗拉、轴心抗压和弹性模量试验,通过观察其破坏过程和破坏形态,获取荷载-位移全过程曲线,研究并提出了本构方程。试验结果表明,粉煤灰再生骨料混凝土与天然骨料混凝土相比,各项力学指标随着再生骨料取代率的增大先是呈现增长趋势,当达到峰值后,各项力学指标均下降;两者的应力-应变曲线具有相似的形状,在上升阶段,再生混凝土与天然混凝土的应力-应变曲线变化不大,但在下降段再生混凝土的应力-应变曲线急剧下降。

旋风分离器环形空间顶灰环的流动特性

旋风分离器环形空间内由于二次涡的作用在上部存在一个旋转的顶灰环,不仅会降低分离效率,而且会造成冲蚀磨损。采用有机玻璃制造的PV型旋风分离器(筒体直径D=160 mm)以及丙烯腈待生催化剂和铁矿粉,在入口气速(v_(in))为12~20 m/s、入口气流颗粒质量浓度(C_(in))为10~100 g/m^(3)条件下进行实验,利用高速摄像机考察顶灰环的流动特性。实验结果表明:顶灰环存在周期性脱落现象;脱落周期与入口气速和入口气流颗粒质量浓度有关,且随入口气速增大而增大,随入口气流颗粒质量浓度增大而减小。为进一步分析顶灰环的形成机理,利用Fluent模拟了环形空间的气相流场。结果表明,二次涡对颗粒群的夹带形成了顶灰环,顶灰环颗粒的积累导致顶灰环发生周期性脱落。在模拟分析基础上建立了基于准数关联的顶灰环脱落周期的预测模型。

粉煤灰-矿渣再生混凝土抗压强度及尺寸效应研究

以粉煤灰和矿渣掺入方式和掺量为变量,设计24组C30再生粗骨料混凝土,对再生混凝土的抗压强度进行了研究。试验结果表明,粉煤灰或矿渣单掺时,再生混凝土的抗压强度随矿物掺料的掺量增加呈现先上升后下降趋势,同等掺量下矿渣单掺优于粉煤灰单掺;双掺时保持粉煤灰或矿渣掺量20%不变,再生混凝土立方体和轴心抗压强度随另一种微细矿物掺量的增加同样呈现先上升后下降趋势,双掺较单掺方式对再生混凝土抗压强度的提升效果更佳,且再生混凝土的抗压强度存在明显的尺寸效应。单掺粉煤灰或矿渣时再生混凝土轴心抗压强度和立方体抗压强度换算系数随其掺量增加而增大,双掺则稳定保持在0.85±0.02。此外,论文还建立了不同微细矿物掺料条件下再生混凝土抗压强度换算系数的修正公式,验证结果表明公式预测误差较小。建议实际工程再生混凝土配制采用粉煤灰和矿渣双掺方式,且掺量控制在25%以内。

稻壳灰-废旧砖再生透水混凝土的配合比研究

为探究稻壳灰-废旧砖再生透水混凝土的配合比,采用4因素3水平正交试验,探究水灰比、目标孔隙率、废旧砖骨料取代率、稻壳灰掺量对透水混凝土的强度、透水性、抗冻性的影响。结果表明:水灰比为0.3、目标孔隙率为10%、废旧砖骨料取代率为40%、稻壳灰掺量为6%时,稻壳灰-废旧砖再生透水混凝土的性能更优,其抗压强度为11.28 MPa、劈裂抗拉强度为1.99 MPa、透水系数为0.56 cm/s、孔隙率为37.5%、50次冻融循环后抗压强度为3.74 MPa。

辅助胶凝材料对高浆骨比砂浆流变特性的影响

通过研究粉煤灰漂珠、硅灰、纳米二氧化硅及传统粉煤灰对高浆骨比砂浆的流变性能及力学性能影响。研究表明:(1)砂浆28d抗压抗折强度,随硅灰单掺掺量提高(至7.5%)而提高,继续增加至10%,强度不增反降;浆体流动性、屈服应力及低转速黏度则随掺量提高逐渐降低;高转速黏度随掺量先少量降低,掺量达到10%,黏度急速上升。(2)单掺漂珠(5%~25%),砂浆28d强度显著提高,但随掺量提高强度逐渐降低;屈服应力与高转速黏度随掺量提高而提高;流动度与低转速黏度也显著提高,但随掺量增加而降低。单掺粉煤灰对浆体强度提高程度有限,流动度则随掺量提高而提高。(3)复掺硅灰(5%)与漂珠(5%~25%),强度提高不明显,且随漂珠掺量提高而降低,屈服应力随掺量提高而提高,黏度先提高后降低。(4)外掺纳米二氧化硅(0.5%~2.5%)显著提高浆体黏度与屈服应力,并降低流动度,当掺量超过1.5%强度有所降低。因此,对高浆骨比砂浆,硅灰及漂珠掺量均宜控制在小掺量(5%),以获得较好的综合力学与流变性能。纳米二氧化硅可根据需求用以调控浆体流变性能,但需注意其对强度的影响。

含再生骨料和粉煤灰的多孔沥青混合料性能研究

文中研究了再生混凝土骨料(RCA)和C型粉煤灰对多孔沥青混合料整体性能的影响。试验室制备RCA和粉煤灰不同组合的混合料,测试分析多种性能参数,包括空隙率、渗透性、马歇尔稳定度、间接抗拉强度、水稳定性、宏观构造深度。结果表明,排水性沥青混合料掺入RCA或粉煤灰,其空隙率、渗透性和表面宏观构造深度略微降低。多孔沥青混合料用RCA替代10%的花岗岩集料,其稳定性、间接抗拉强度等性能降低。然而,混合料用粉煤灰进一步取代矿物填料,有助于抵消RCA的负面影响,RCA为10%时的混合料力学性能达到与对照混合料相当的水平。

级配再生细骨料及粉煤灰掺量对活性粉末混凝土性能影响

以0.26和0.28作为活性粉末混凝土的基础水胶比,用再生细集料全部取代石英砂,研究分维值D和20%、25%、30%粉煤灰掺量对RPC抗压强度、抗折强度的影响,并观察RPC的微观形貌。结果表明:随级配分维值上升,RPC流动度下降。级配分维值对RPC抗压强度、抗折强度有很大影响;标准养护下早期抗压/抗折强度会呈现先下降再上升的趋势,后期强度持续上升;常温养护下随级配分维值增加,抗压/抗折强度在不同的龄期均呈现上升趋势;各组RPC强度随粉煤灰掺量增加而不断下降;随着粉煤灰掺量增多,RPC水化产物基本相同,但内部微观结构呈现密实—疏松的变化趋势。

掺合料抑制碱骨料反应的试验研究

为了研究掺合料对骨料碱硅酸反应活性的抑制效果,选用具有碱硅酸反应活性的骨料,通过掺加不同比例的掺合料,采用砂浆棒快速法测试各组试件的膨胀率。结果表明,掺合料对骨料碱硅酸反应活性有较好的抑制效果,掺合料的掺量越大,抑制效果越明显;粉煤灰和矿粉的双掺抑制效果大于单掺掺合料。

粉煤灰及硅灰对再生粗骨料混凝土抗冲磨性能的影响研究

为探究再生混凝土采用不同再生粗骨料取代率时的抗冲磨性能差异,文中就粉煤灰及硅灰对再生粗骨料混凝土抗冲磨性能的影响进行研究。结果表明,随着再生骨料取代率提高,混凝土抗冲磨性能逐渐降低;硅灰的掺入有助于强化混凝土抗冲磨性能,而粉煤灰的掺入会对其产生不利影响;复掺粉煤灰和硅灰条件下,两者比例不同则混凝土抗冲磨性能所受影响也有不同,其中,掺加5%硅灰和15%粉煤灰时,再生混凝土具有良好抗冲磨性能且高于基准混凝土。

再生混凝土砌块抗压强度试验研究

文中主要针对不同掺量粉煤灰、钢纤维及再生骨料取代率对再生混凝土砌块抗压强度影响展开研究。结果表明,不同掺量的粉煤灰对混凝土强度产生明显负面影响,且粉煤灰掺量越大,抗压强度下降幅度越大,推荐粉煤灰掺量控制在15%~30%,能够在保持抗压强度达标的同时,降低材料造价;再生骨料抗压强度水平随再生骨料取代率的提升而逐渐降低,混凝土承载力极限值也随之逐渐降低。

粉煤灰协同制备轻骨料技术研究

使用粉煤灰、煤矸石、市政污泥等传统生活、工业固体废弃物作为原料进行了人工轻骨料的制备技术研究,对烧结温度分别为1100℃、1140℃、1180℃、1200℃、1220℃、1250℃条件下制备的轻骨料进行了抗压强度、吸水率和比表面积测定和分析。研究结果表明,粉煤灰、煤矸石、市政污泥可以协同制备轻骨料,五种成分的所有烧结陶粒轻骨料在1100℃~1220℃烧结范围内,抗压强度都满足国家标准要求,而烧结温度超过1250℃,会出现抗压强度骤减不满足国标要求的现象。在1200℃烧结温度下,粉煤灰为15wt%至35wt%的各成分陶粒轻骨料吸水率性能指标均优于国家标准,但比表面积逐渐减小,而粉煤灰含量为50wt%的陶粒轻骨料吸水率和比表面积都有降低。

粉煤灰不同掺加方式对再生骨料混凝土弹性模量的影响研究

为探究再生混凝土复掺矿粉和粉煤灰、单掺粉煤灰下弹性模量差异,文中就粉煤灰不同掺加方式对再生骨料混凝土弹性模量的影响展开研究。结果表明,掺入再生骨料的各组混凝土试件具有低于常规混凝土的弹性模量,单掺粉煤灰后混凝土弹性模量进一步降低。而复掺粉煤灰与矿渣后混凝土弹性模量与粉煤灰和矿渣掺入比例有关,其中粉煤灰掺量为10%、矿渣掺量为20%时试件具有较高弹性模量。对于复掺粉煤灰和矿渣的再生混凝土,其抗压强度与弹性模量之间具有良好相关性,并通过回归计算得到经验公式。

凝灰岩粉和粉煤灰对骨料碱活性抑制效果研究

基于岩相法和砂浆棒快速法(AMBT)针对某水电站骨料进行骨料碱活性反应(AAR)试验研究,分析了凝灰岩粉和粉煤灰对骨料碱-硅酸反应(ASR)抑制效果影响规律及机理。结果表明:该骨料属于有潜在ASR的活性骨料,其内部包含高应变石英等矿物成分,AMBT试件14 d时的膨胀率为0.173%,28 d时的膨胀率为0.295%。当凝灰岩粉掺量不超过20%(占水泥质量分数),粉煤灰掺量不低于10%时,可以显著的抑制ASR,AMBT试件28 d时的膨胀率均小于0.1%,在试件内部形成了致密的网络结构,未出现微观开裂现象,骨料界面处白色絮状物质显著减少,研究结果可为抑制ASR用掺合料提供参考。