矿物掺合料对混凝土抗氯离子渗透性的影响综述

矿物掺合料因对改善混凝土抗氯离子渗透性有着较为显著的作用而获得了研究者的广泛关注。综述了近年来国内外关于矿物掺合料对混凝土抗氯离子侵蚀能力影响的研究进展,分析并总结了粉煤灰、硅灰、矿渣等矿物掺合料单掺和复掺的情况下,对混凝土抗氯离子渗透性能的影响。同时,通过分析混凝土抗氯离子渗透性相关测试方法的优缺点,并对比不同研究者的测试结果,对需要进一步研究的相关问题提出了建议。     

高性能减水剂在C80混凝土中的试验研究

本文通过采用高性能减水剂进行了一系列的技术论证试验,利用本地原材料,大量地掺用矿物掺合料,成功配制了C80高强高性能混凝土,且成本较低。试验结果表明,高性能减水剂能够提高混凝土的施工性和硬化混凝土的物理力学性能及耐久性能。     

矿物掺合料对聚羧酸减水剂与水泥相容性的影响

高性能减水剂与水泥适应性差会导致混凝土流动性和坍落度损失过快,矿物掺合料将影响高性能减水剂与水泥的相容性。对比研究矿物掺合料种类和掺量对水泥净浆、砂浆和混凝土流动性的影响;采用TOC法测试了矿物掺合料对聚羧酸减水剂吸附量的影响;分析了矿物掺合料影响聚羧酸减水剂与水泥相容性的机理。结果表明,粉煤灰和矿渣对提高水泥净浆流动性具有一定的叠加效应,可用胶砂减水率的加权平均值进行量化;硅灰对水泥浆体流动性的不利影响远大于粉煤灰和矿渣的辅助减水分散作用,不利于改善聚羧酸减水剂与水泥的相容性;粉煤灰和矿渣增加聚羧酸减水剂在水泥体系中的吸附量;粉煤灰和矿渣对聚羧酸减水剂在混凝土中的减水分散效果有改善作用但不显著。     

矿物掺合料对水泥基材料耐海水侵蚀性能的影响研究

加入适当矿物掺合料是使水泥基材料达到高性能的重要手段之一。本课题从工程应用的角度出发,以磨细矿渣和磨细矿渣-粉煤灰复合掺合料为研究对象,着重研究了矿物掺合料对水泥基材料耐海水侵蚀性能的影响。     

不同环境中矿物掺合料混凝土抗硫酸盐侵蚀性能的研究进展

硫酸盐侵蚀是混凝土耐久性研究的热点之一。矿物掺合料的掺入改变混凝土内部的组成,细化了混凝土的孔结构,对混凝土抗硫酸盐侵蚀起着重要作用。掺合料的化学组成、细度、掺量等对混凝土抗硫酸盐侵蚀均有很大的影响。外界腐蚀环境的不同,矿物掺合料混凝土抗硫酸盐侵蚀的性能也有显著的差别。大量的研究表明,在连续浸泡的硫酸盐溶液中,矿物掺合料只要掺量适当能够提高混凝土抗硫酸盐侵蚀的能力。在干湿循环与硫酸盐溶液共同作用下,矿物掺合料混凝土抗硫酸盐侵蚀的能力有所争议,有些研究表明矿物掺合料能够提高干湿循环条件下混凝土抗硫酸盐侵蚀的能力;然而有些研究结果却呈现相反的结论,这需要进一步探索。     

矿物掺合料早期水化活性的测试和分析

本文采用环境扫描电子显微镜(ESEM)和热重-差热(TG-DTA)分析仪对磨细矿渣微粉、高钙粉煤灰、低钙粉煤灰的早期水化活性进行了系统测试和分析.理论和试验结果分析表明,掺合料取代水泥时,浆体早期抗压强度的提高取决于掺合料自身参与水化反应的速度和水化产物的数量.水化产物在掺合料颗粒表面沉积的速度和浆体中硅酸盐、铝酸盐水化产物的非蒸发水量随掺合料活性的提高而提高.掺合料活性按磨细矿渣微粉、高钙粉煤灰、低钙粉煤灰的顺序降低,将磨细矿渣微粉或高钙粉煤灰与低钙粉煤灰复合,可以克服低钙粉煤灰大掺量取代水泥时混凝土早期强度降低的缺陷,这是提高低钙粉煤灰在高强高性能混凝土中掺量的一个有效措施.     

再生混凝土纳米复合强化试验

本文对再生混凝土进行纳米复合强化试验研究,通过引入高活性纳米SiO2和纳米改性矿物掺合料,得到了纳米改性再生混凝土,研究了高活性纳米SiO2和纳米改性矿物掺合料对再生混凝土力学性能的影响,还研究了高活性纳米SiO2对再生混凝土抗氯离子渗透性能与抗渗性能的影响,为实际工程应用提供理论依据。研究结果表明:纳米SiO2与纳米改性矿物掺合料双掺,不仅能在一定程度上改善再生混凝土的力学性能,还能显著改善再生混凝土的抗氯离子渗透性能与抗渗性能,显示出良好的复合效果。     

合理掺入矿物掺合料对提高混凝土性能的可行性研究

利用"矿物掺合料在提高混凝土性能的应用"课题的研究成果,在施工实践中进行了大面积地推广应用,取得了显著的经济和社会效益。矿物掺合料的应用、制备已牵涉到水泥基材料科学研究的各个方面。在现代混凝土技术中,经过一定质量控制的矿物掺合料已成为高性能混凝土不可或缺的组分之一。本文通过对矿物掺合料研究历史和研究现状的分析,探讨了当前研究的主要缺陷及存在的问题,并展望了下一步的研究方向。     

矿物掺合料研究进展及存在的问题

矿物掺合料的应用、制备已牵涉到水泥基材料科学研究的各个方面.在现代混凝土技术中,经过一定质量控制的矿物掺合料已成为高性能混凝土不可或缺的组分之一.通过对矿物掺合料研究历史和研究现状的分析,探讨了当前研究的主要缺陷及存在的问题,并展望了下一步的研究方向.     

混杂纤维对大掺量矿物掺合料混凝土干燥收缩的影响

通过测定混凝土的长期干燥收缩值,研究了单掺聚丙烯(polypropylene,PP)纤维、聚酯纤维和钢纤维及其混杂技巧对大掺量矿物掺合料混凝土干燥收缩的影响.结果表明,大掺量矿物掺合料混凝土的干燥收缩比较大,纤维及混杂技巧有利于降低其干燥收缩,纤维的弹性模量越高,其抑制干燥收缩的效果越好;(0.05%PP纤维 0.05%聚酯纤维)的有机纤维混杂效果优于(0.1%PP纤维 0.7%钢纤维)和(0.1%聚酯纤维 0.7%钢纤维)的有机与无机纤维混杂;混杂纤维对混凝土干燥收缩的抑制效果与纤维之间的搭配有关.综合分析表明,(PP纤维 聚酯纤维)的二元混杂技术具有良好的工程应用价值.     

Use of nano-silica to increase early strength and reduce setting time of concretes with high volumes of slag

The effects of nano-silica (NS) on setting time and early strengths of high volume slag mortar and concrete have been experimentally studied. Effects of NS dosages, size and dispersion methods on strength development of high volume slag mortars were also investigated. A constant water-to-cementitious materials ratio (w/cm) 0.45 was used for all mixtures. The results indicate that the incorporation of a small amount of NS reduced setting times, and increased 3- and 7-day compressive strengths of high-volume slag concrete, significantly, in comparison to the reference slag concrete with no silica inclusion. Compressive strength of the slag mortars were increased with the increase in NS dosages from 0.5% to 2.0% by mass of cementitious materials at various ages up to 91 days. The strengths of the slag mortars were generally increased with the decrease in the particles size of silica inclusions at early age. Ultra-sonication of nano-silica with water is probably a better method for proper dispersion of nano-silica than mechanical mixing method.     

Evaluation of the consistency of fiber reinforced cementitious composites

The rheological properties of fresh concrete, mortar or cement paste are among the most important parameters when cementitious building materials are placed. New material designs, like high or ultrahigh performance concretes, include the addition of a high volume of fibers to the fresh mix influencing its workability properties. However, the analysis of the rheological properties of fiber reinforced cementitious composites is difficult. Conventional methods mostly do not apply, especially when a high fiber content and relatively stiff mixtures are used. For this reason, a new method was developed to evaluate the workability of fiber reinforced composites. This method was applied to carbon and PVA fiber reinforced high performance composites and was used to optimize the rheological properties of these composites for an application in a centrifugation casting process.     

Effect of mix design inputs,curing and compressive strength on the durability of Na2SO4-activated high volume fly ash concretes

This paper aims to advance research on the use in concrete of a high volume of fly ash, with a high loss on ignition value, aiding in sustainable low carbon footprint construction. To this end, the work explores the benefits that may be achieved in terms of long-term concrete performance from the incorporation of fly ash along with a chemical activator. Durability tests are performed on concrete with an activated hybrid cementitious system: Portland cement (PC) and high volume fly ash with sodium sulfate. The chloride diffusion coefficient significantly decreased over time for the activated system (50% PC - 50% fly ash with added sodium sulfate) compared to the control samples (100% PC and 80% PC - 20% fly ash) at the same water to cementitious material ratio. This behavior is particularly evident in samples cured under controlled laboratory conditions (100% RH and 23 °C). However, outdoor curing increases the permeability for all concretes. Long term carbonation is also investigated under natural exposure conditions, and samples that are cured outdoors exhibit a significant carbonation depth. The compressive strength is correlated with the durability parameters: the durability performance improves as the compressive strength increases, indicating that as is the case for Portland cement (but not always for alkali-activated binders), the microstructural factors which yield high strength are also contributing to durability properties.     

先进水泥及先进水泥基材料的研究进展

介绍了有关先进水泥和先进水泥基材料的探索和研究进展。消纳工业废渣的低环境负荷水泥技术、高胶凝性高钙水泥熟料体系的研究、高贝利特水泥的研究和应用、地聚合物的深入开发等成果反映了我国在水泥科学领域的突破。水泥基材料的研究进展主要体现在多因素协同作用下水泥基材料性能劣化和寿命预测的研究、大流动度自流平混凝土的研究、改善水泥基材料体积稳定性的研究、高延性纤维增强水泥基复合材料的研究方面。水泥和水泥基材料近期研究重点将主要集中在与节能减排、环保利废有关的新设备、新材料和新技术方面;水泥基材料的抗裂性和耐久性,功能性复合材料的开发也将是研究的重点。     

Numerical investigation on steel fibre reinforced cementitious composite panels subjected to high velocity impact loading

Steel fibre reinforced cementitious composite (SFRCC) panels are numerically investigated for their performances under high velocity impact of short projectiles. Numerical responses are obtained using advanced constitutive material model of Riedel–Hiermaier–Thoma (RHT) for cementitious materials and adopting appropriate modelling techniques. Effects of steel fibre volume and the thickness of panels on the impact performance are mainly highlighted in this paper. Various characteristics phenomenon during impact on cementitious composite panels namely, spalling, cracking, scabbing and perforation, are captured which is a difficult task. Scabbing is likely to occur when tensile stresses at the back face of the panel exceed dynamic tensile strength of the material. Various critical aspects in numerical modelling like boundary conditions, material input parameters, and handling severe distortion of the Lagrangian based finite elements are appropriately explained. Design chart is also developed to determine optimum fibre volume and thickness for an impact energy level up to 2.2 kJ. The numerically predicted impact responses are found to corroborate well with experimental results.     

水泥材料研究动向

环境负荷小的高性能低钙水泥和水泥代用材料的研究越来越热,有机高聚物和水泥的复合使用是水泥砼行业减耗,增效和改性的必要手段,国际标准的采用把各国水泥的研究、生产和贸易联在一起。中国水泥研究应不忘自身特点和自主产权。     

Printability and fire performance of a developed 3D printable fibre reinforced cementitious composites under elevated temperatures

ABSTRACT

To demonstrate printability and fire performance of 3D printable fibre reinforced cementitious materials at elevated temperatures, large-scaling printing and fire performance testing are required for engineering applications. In this work, a mixture design of 3D printable fibre reinforced cementitious composite (3DPFRCC) for large-scale printing was developed. A structure with dimensions of 78 × 60 × 90?cm (L × W × H) was printed by a gantry printer in 150?min, which demonstrates that the developed 3DPFRCC mixture possesses good buildability. The rheological property, setting-time, and mechanical properties under normal and elevated temperatures of the developed 3DPFRCC were then characterised. Final results indicate that the developed 3DPFRCC is suitable for engineering applications due to its good printability and mechanical properties under normal and elevated temperatures.     

A high performance fibre reinforced cement based plaster for retrofitting RC members

A high performance fibre-reinforced cementitious composite (HPFRCC) material is developed to be used for retrofitting reinforced concrete members. It can be applied to the face of a concrete member to the desired thickness as a wet mix or as an adhesively-bonded prefabricated slab or strip. The material is compatible with concrete and possesses favourable strength and ductility properties, desirable for seismic retrofit. It overcomes some of the problems associated with the current techniques based on externally bonded steel plates and fibre-reinforced polymer (FRP) laminates caused mainly by the mismatch of their tensile strength and stiffness with that of the concrete member being retrofitted. An extensive rheological analysis is undertaken to develop the appropriate mixes using different types and mix proportions of constituent materials including; fine steel fibres, fine quartz sand, silica fume, cement and superplasticizer. Much reduced amounts of steel fibres are used compared to the previous studies so that ordinary mixing procedures could be applied and a more cost-effective retrofitting material could be developed. Samples made of the optimum mixes are shown to posses very high compressive and tensile strengths and sufficient ductility for the composite plaster to be used externally for strengthening and seismic retrofitting of concrete members.     

钢筋增强超高韧性水泥基复合材料(RUHTCC)梁弯曲性能影响的几何参数分析

具有超高韧性新型随机PVA短纤维增强的水泥基复合材料(UHTCC)代替传统的具有准脆性应力软化特征的混凝土或纤维混凝土材料制作的钢筋(RUHTCC)受弯梁,可提高承载力,改善构件的延性,并具有良好的损伤演变能力,被认为是一种抗震性能较好的新型构件形式。除了配筋率和UHTCC拉压材料性能外,截面几何尺寸是影响其弯曲性能的一个重要因素。基于受弯理论分析和试验验证,采用该理论公式对截面几何尺寸(截面高度、宽度以及面积)的影响规律进行了系列分析。结果发现:对承载力,梁高度比宽度影响明显,而对承载力提高幅度和变形而言,随梁高的增加而减小,梁宽没有影响;对裂缝控制来说,只要梁下边缘的极限拉应变小于UHTCC材料的极限拉应变,截面尺寸的变化几乎不影响裂缝宽度的大小。并进一步针对RUHTCC梁的受弯设计提出了一些设计建议。