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.

BOND PERFORMANCE EXPERIMENT FOR FLY ASH CONCRETE AND STEEL BAR

The impact of fly ash content on bond performance of steel bars and their surrounding concrete is studied by means of sticking strain gauges on steel bars. The average bond stress-slip curves, the steel strain-anchor location curves, and the bond stress-anchor position curves of the pullout specimens with various fly ash contents are obtained. Results indicate that the bond performance of concrete and steel bars can be improved and the distribution of steel strain along the anchorage length tends to be more uniform by adding fly ash in concrete specimens, and both ultimate bond stress and ultimate slip deformation increase the most when 20% of specimens′ content is fly ash.

Investigation of the medium calcium based non-burnt brick made by red mud and fly ash: durability and hydration characteristics

Red mud is a type of highly alkaline waste residue produced in the process of alumina smelting by the Bayer process.Based on the idea of medium calcium content,solid wastes such as red mud and fly ash were used to prepare non-burnt bricks;and the mass ratio of CaO/SiO2 was selected in the range of 0.88–1.42.Mechanical properties and durability were investigated with a compressive strength test.X-ray diffractometry(XRD),scanning electron microscope(SEM),and Fourier transform infrared spectroscopy(FTIR)techniques were used to characterize the hydration characteristic.The environmental performance was analyzed by Inductively Coupled Plasma Mass Spectrometry(ICP).The results indicated that the mechanical properties and the durability were optimal when the mass ratio of CaO/SiO2 was 1.23.The hydration products were mostly C–S–H gel,ettringite,Na4Ca(Si10All6)O32·12H2O and Ca3Al2(SiO4)(OH)8.They were responsible for the strength development,and the CaO/SiO2 mass ratio of 1.23 had the best polymerized structure.The results of an environmental performance test showed that the heavy metals in the raw materials were well-solidified in the brick.Therefore,this paper provides an effective solution for use of solid wastes in building material.

Effect of Fly Ash on the Electrical Conductivity of Concretes

The fly ash occasionally has high content of iron oxide and carbon that are good electrical conducting components. This paper investigates the effect of the fly ash used as mineral admixtures on the electrical conductivity of concretes. The electrical properties of concretes using 3 kinds of fly ash with different iron oxide contents have been studied. Experimental results show that at the same fly ash dosage the resistivity of concrete using fly ash with high content of iron oxide is slightly lower than that with low content of iron oxide. However, the concrete resistivity after 14d increases as fly ash dosage increases regardless of iron oxide content in fly ash.

Chloride binding and time-dependent surface chloride content models for fly ash concrete

Corrosion of embedded rebars is a classical deterioration mechanism of reinforced concrete structures exposed to chloride environments. Such environments can be attributed to the presence of seawater, deicing or sea-salts, which have high concentrations of chloride ion. Chloride ingress into concrete, essential for inducing rebar corrosion, is a complex interaction between many physical and chemical processes. The current study proposes two chloride ingress parameter models for fly ash concrete, namely： 1） surface chloride content under tidal exposure condition; and 2） chloride binding. First, inconsistencies in surface chloride content and chloride binding models reported in literature, due to them not being in line with past research studies, are pointed out. Secondly, to avoid such inconsistencies, surface chloride content and chloride binding models for fly ash concrete are proposed based upon the experimental work done by other researchers. It is observed that, proposed models are simple, consistent and in line with past research studies reported in literature.

镧-钙双金属凝胶微球对水中低磷含量的去除性能

以粉煤灰为基本骨架,将镧、钙双金属作为交联剂对海藻酸钠进行交联制备得到镧-钙双金属凝胶微球,并通过批量吸附实验和表征分析研究了镧-钙双金属凝胶微球对水中低含量磷的去除性能和去除机理。结果表明,镧-钙双金属凝胶微球具有不规则多孔结构,镧和钙2种金属被交联在了微球上,磷主要通过与微球上的La^(3+)和Ca^(2+)发生化学沉淀而被去除。随着微球投加量的增加,磷的去除率也随之增加;强酸性条件下微球的除磷效果较差;与磷共存的SO_(4)^(2-)和F^(-)会抑制微球对磷的吸附去除。微球对水体中低含量磷的吸附去除过程符合准2级动力学模型和Freundlich等温吸附模型,属于非均相、化学吸附过程。

粉煤灰、滑石粉及重钙粉对低含油废水除油研究

为处理水中低含量油,满足排水或膜过滤、离子交换等工艺进水水质要求,选用粉煤灰、滑石粉和重钙粉为吸附剂,去除油的性能。结果表明,在单因素实验中粉煤灰、滑石粉、重钙粉在投加20 g/L吸附剂,搅拌转速为200 r/min,吸附时间分别为60、45、45 min条件下,去除率可分别达到64.61%、57.66%、43.72%,除油速率大小顺序为粉煤灰>滑石粉>重钙粉。除油过程符合准2级动力学模型,Henry、Freundlich等温吸附模型拟合R^(2)在0.77~0.89。粉煤灰除油正交实验得出,在投加30 g/L吸附剂,以200 r/min转速搅拌120 min条件下除油效果最好,去除率为69.73%。搅拌转速影响最大,其次是投加量。

低钙粉煤灰掺量、水胶比和养护龄期对混凝土抗压强度的影响

本文对低钙粉煤灰掺量(0%、50%、70%、90%)、水胶比(0.38、0.44、0.50)和养护龄期(7 d、14 d、28 d)对混凝土抗压强度的影响进行了试验研究,并对试验结果进行了考虑交互作用的方差分析和回归分析,得到与试验结果吻合较好的经验公式,有一定工程参考价值。研究结果表明,低钙粉煤灰掺量、水胶比、养护龄期各因素单独对混凝土强度都有显著的影响,且双因素交互对混凝土强度也有显著的影响。掺加大量低钙粉煤灰可以减慢混凝土前7 d的强度增长,8~28 d强度增速下降也更平缓,强度发展的时间效应更显著;增大水胶比将减缓高掺量低钙粉煤灰混凝土在前7 d的强度增长,8~28 d强度增速下降也更急剧些;高掺量低钙粉煤灰混凝土抗压强度随着低钙粉煤灰掺量和水胶比的增大而减小,水胶比取0.38的70%低钙粉煤灰掺量混凝土的28 d抗压强度能达到C20以上,能够满足工程应用的需要。

Methods of Modifying the Brittle Behavior of Cementitious Composites

We put forward effective methods of increasing the tensile strain of cementitious composites with 2% PVA fiber and high fly ash content. The test results show that curing condition has a significantly effect on the tensile performance. It is approved that the specimens incorporated appropriate volume fraction rubber powder and lightweight aggregate greatly increase the tensile strain of composites at medium-term age, but indefinitely at long-term age. To a certain extent, EVA can limitedly enhance the tensile performance of comentitious composites owing to the formation of polymer membrane and the hindered hydration of cement.