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.

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.

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.

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.

复掺再生砂和超细粉煤灰对超高性能混凝土抗硫酸盐侵蚀性能的影响

为了研究再生砂超高性能混凝土(UHPC)的抗硫酸盐侵蚀性能,对掺再生砂和超细粉煤灰的超高性能混凝土进行了硫酸盐干湿循环侵蚀试验,测试了硫酸盐溶液侵蚀前后试件的抗压强度、相对动弹性模量、质量变化。通过离子滴定测定了不同侵蚀深度下硫酸根离子的分布,分析了再生砂和超细粉煤灰对硫酸根离子传输的影响。结果表明:经过90次硫酸盐干湿循环后,UHPC的耐侵蚀系数随着超细粉煤灰掺量的增加呈先增大后减小的趋势;超细粉煤灰掺量为20%(质量分数,下同)时,侵蚀全过程中UHPC的耐侵蚀系数、相对动弹性模量最大,硫酸根离子含量较低;再生砂掺量为50%时,UHPC在干湿循环45次之前的相对动弹性模量最大,相同深度下的硫酸根离子含量最低;复掺20%超细粉煤灰和50%再生砂的UHPC抗硫酸盐侵蚀性能最优。

富龙西江特大桥用超细粉体材料基预应力压浆料的制备及性能研究

以富龙西江特大桥为工程背景,研究了超细粉体材料的种类与掺量对压浆料的流动度性能、压力泌水率、自由膨胀率、抗压及抗折强度、抗氯离子渗透性能的影响。结果表明,超细粉煤灰的掺入可提升压浆料的流动度,提升压浆料的抗压强度,提升压浆料的抗硫酸盐侵蚀性能和抗氯离子渗透性能,但会导致压浆料压力泌水率的增加。硅灰的掺入可降低压浆料的流动度,显著提升压浆料的抗压强度,提升压浆料的抗硫酸盐侵蚀性能和抗氯离子渗透性能。两者混合使用可提升压浆料的综合性能。总体而言,超细粉煤灰和硅灰掺量分别为20%及5%时,压浆料的各项性能相对最优。

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.

超细粉煤灰对混凝土强度及水化产物的影响

对超细粉煤灰掺量为0～30％之间的混凝土抗压强度、硬化浆体水化产物中化学结合水和Ca（OH）2量的变化情况进行了分析。结果表明，超细粉煤灰掺入后能够充分发挥填充效应和火山灰活性，消耗水泥水化产物中的Ca（OH）2，降低水化产物中Ca（OH）2含量，且随水化龄期的延长，参与水化程度提高，能够提高混凝土的后期强度。

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.