抗泥敏感性聚羧酸减水剂的研究进展

聚羧酸减水剂因具有低掺量、高减水及绿色环保等优点备受青睐,但在实际应用中也常伴有因混凝土骨料泥含量过高而导致的相容性差、减水率低及坍落度损失大等问题,抗泥敏感性差已成为制约聚羧酸减水剂向更广层面应用的重要现实问题之一。文中从聚羧酸减水剂发展现状与面临的泥敏感性入手,阐述了聚羧酸减水剂对水泥、黏土和水泥/黏土分散体系的作用机理,在此基础上总结概括了改善和提高聚羧酸减水剂抗泥敏感性的应对措施,并对抗泥敏感性聚羧酸减水剂未来发展与应用进行了预测和展望。     

聚羧酸混凝土减水剂的研究现状与发展趋势

聚羧酸减水剂的研发和推广是混凝土材料科学中的一个研究热点,推动混凝土材料向高强、高性能化不断发展.结合国内外资料综述了聚羧酸系高效减水剂的研究现状、作用杌理、合成方法,分析了聚羧酸减水剂结构与性能的关系,总结了当前研究与应用中存在的主要问题,展望了今后的发展趋势.     

聚羧酸系减水剂在高速铁路预制梁中的应用

该文针对鲁南高铁临沂东梁场对预应力梁混凝土的技术要求,以混凝土的工作性能、力学性能及耐久性能为目标,尤其以耐久性为核心,进行了C50预应力梁的混凝土配合比设计。通过采用性能优良的聚羧酸系高性能减水剂、低水胶比的技术路线,成功配制出高工作性能、良好的力学性能以及优异的耐久性能的预应力梁混凝土。最终该混凝土在临沂东梁场得到了成功的应用,取得了良好的效果。     

聚羧酸减水剂对混凝土结构影响

混凝土结构决定其性能。通过扫描电镜和压汞试验,表征和分析了聚羧酸减水剂对混凝土硬化水泥浆体、界面结构和水泥石孔结构的影响。结果表明,早龄期的混凝土硬化水泥浆体和界面结构裂纹较宽,裂缝较多,而龄期长则结构较密实;相同龄期掺有聚羧酸减水剂的混凝土硬化水泥浆体和界面过渡区结构裂缝数量、裂纹宽度均小于萘系减水剂;聚羧酸减水剂降低了水泥石的平均孔径,最可几孔径和孔隙率;少害孔和无害孔的含量多,而有害孔和多害孔含量少。聚羧酸减水剂对混凝土结构的作用优于萘系减水剂。     

聚羧酸高性能外加剂(聚羧酸系减水剂)在客运专线工程中的应用

聚羧酸高性能减水剂与其它高效减水剂相比,有许多突出的性能:低掺量(0.2%--0.5%)而发挥高的分散性能;保坍性好,90分钟内坍落度基本无损失;在相同流动度下比较时,延缓凝结时间较少;与水泥适应性强、混凝土收缩小等特点。由于它的诸多优点,致使在现在工程质量要求比较严苛的客运专线混凝土工程中会经常使用到。本文简单叙述了聚羧酸减水剂使用的优缺点和在客运专线上使用过程的案例和问题的处理方法。     

蒙脱土对聚羧酸减水剂的吸附行为研究

为揭示聚羧酸减水剂对砂石含泥量敏感机理,本实验研究了聚羧酸减水剂在蒙脱土上的吸附行为.采用紫外分光光度法,系统研究了聚羧酸减水剂溶液浓度、吸附时间和温度对蒙脱土吸附聚羧酸减水剂的过程及其吸附量的影响;利用Fourier红外光谱,表征分析了聚羧酸减水剂嵌入蒙脱土内部微观结构变化.结果表明:聚羧酸减水剂溶液浓度对蒙脱土层间吸附量影响较小;一定浓度的聚羧酸减水剂在蒙脱土表面的吸附量随吸附时间变化具有饱和吸附性;吸附时间小于90 min时,随时间延长,层间吸附量增大变化明显;吸附温度升高,聚羧酸减水剂在蒙脱土上的表面吸附和层间吸附量均增大;吸附聚羧酸减水剂后的蒙脱土,具有明显的减水剂特征吸收峰,聚羧酸减水剂嵌入了蒙脱土内部.聚羧酸减水剂在蒙脱土上的吸附为表面吸附和嵌入吸附.降低聚羧酸减水剂溶液浓度、缩短吸附时间、降低吸附温度,有利于减少聚羧酸减水剂在蒙脱土表面上的吸附;缩短吸附时间和降低吸附温度,可有效减少聚羧酸减水剂嵌入蒙脱土的驱动力,降低嵌入吸附量;最终达到提高聚羧酸减水剂对砂石含泥量适应性的目的.     

聚羧酸系减水剂在客运专线工程中的应用研究

介绍聚羧酸系减水剂在满足铁路客运专线高性能混凝土综合性能方面的能力和特点,分析了工程应用中使用聚羧酸系减水剂存在的一些问题。提出解决聚羧酸系减水剂与水泥的相容性问题以及保持聚羧酸系减水剂本身质量稳定性是目前该减水剂应用的关键。     

交联型聚羧酸减水剂的制备及性能研究

以异戊烯醇聚氧乙烯醚(TPEG?2400)、丙烯酸(AA)、丙烯酸羟乙酯(HEA)及氨基封端的聚乙二醇(H2 N?PEG?NH2)为主要原材料合成了一种微交联型(抗泥、保坍、减水)聚羧酸减水剂M42.探究了酸醚比、丙烯酸羟乙酯(HEA)的用量、抗泥单体氨基封端的聚乙二醇的用量对聚羧酸减水剂的影响.并通过红外光谱分析证实分子结构,采用红外光谱和热失重(TG)分析了M42在蒙脱土的表面吸附,采用XRD分析了蒙脱土对M42层间吸附的影响.最后,评价了M42对含蒙脱土的水泥净浆流动度、混凝土损失及抗压强度的影响.结果表明:当酸醚比为2.0,HEA和氨基封端的聚乙二醇的用量分别为大单体用量的2.9％和4.4％时,该产品同时具备抗泥、保坍及减水效果,综合性能优于市场同类产品.     

聚羧酸系高效减水剂的研究现状和应用前景

高效减水剂的研究已成为混凝土材料科学中的一个重要分支,并推动混凝土材料向高强、高性能化不断发展,其中聚羧酸系高效减水荆是新一代绿色高效减水剂的代表.结合国内外资料综述了聚羧酸系高效减水刑的研究现状、性能特点、分散稳定机理以及今后的发展方向.指出对聚羧酸系高效减水剂的基础理论研究还有待进一步加强;开发、合成、生产多元化和不同性能的系列聚羧酸系减水荆母体、多功能的聚羧酸系减水剂衍生产品,已成为当今聚羧酸系高效减水荆发展的必然趋势.     

聚羧酸减水剂的粘土耐受性研究进展

聚羧酸减水剂(PCE)因具有掺量低、减水率高、分散性能优异、功能可设计性强、制备过程绿色环保等优点在建设工程领域应用广泛。但是PCE与粘土矿物相互作用,尤其是蒙脱土(MMT)对PCE的有害吸附,使PCE的分散效果显著降低甚至完全丧失。为克服粘土对聚羧酸减水剂的负效应,从聚羧酸减水剂结构性能及其与粘土的作用机理入手,综述了近年来PCE的粘土耐受性研究进展和抑制粘土负效应的策略。通过粘土抑制剂复配、分子结构设计等手段提高PCE对粘土的适应性,为解决聚羧酸减水剂分散性能受制于粘土的技术难题提供基本思路。     

浅谈聚羧酸系减水剂在京沪高速铁路VI标段高性能混凝土的中应用

京沪高速铁路Ⅵ标段主要为桥梁工程,采用高性能混凝土结构,设计寿命100年。本文主要介绍了聚羧酸系减水剂在该工程中的应用,重点探讨了原材料选择、生产过程质量控制、高性能混凝土配合比设计及聚羧酸系减水剂在高性能混凝土施工中应注意问题,并指出高性能混凝土与普通混凝土的异同。     

SPS-8P-2型聚羧酸系泵送剂在中低强度等级预拌混凝土中的应用

SPS-8P-2聚羧酸系泵送剂经混凝土配合比研究和生产实践应用证实,可以在C20-C40预拌商品混凝土中应用,具有良好的工作性,混凝土配合比中的“浆骨比”是工作性的关键。     

减水剂合成新方法探讨一常温条件下减水剂的制作

本文介绍一种聚羧酸减水剂的合成工艺,与一般减水剂合成工艺不同的是．该工艺非常简单．只要将原料、催化剂按照一定顺序和比例加入到容器中搅匀,再保温6小时就能得到性能良好的聚羧酸减水剂产品。该工艺原料简单易得,设备更是简单,并且对实验用水的水质要求不高,可以直接使用一般的自来水。     

基于长江下游超细疏浚砂的碱激发矿渣混凝土力学性能

分析了长江下游航道超细疏浚砂的理化性质,并以超细疏浚砂为原料,设计了5种不同疏浚砂掺量的碱激发矿渣混凝土(AASC)配合比,研究了其流动性、抗压强度、劈拉强度和吸水率的变化.通过SEM、XRD和压汞(MIP)技术,分析了AASC的物相组成和微观结构.研究表明:长江下游航道的超细疏浚砂颗粒细度模数在0.1～0.5之间.随...     

商品混凝土在生产和浇筑过程中常见问题的处理方法

在商品混凝土的生产、交付和凝结硬化过程中,常常会遇到混凝土坍落度过小或过大、和易性差、缓凝、裂缝、强度不足、亏方等问题,有些问题处理不当,将会造成较大的经济损失,并且降低了企业的信誉。为了避免上述问题的发生,提高商品混凝土企业的信誉,特编写了此文作为借鉴或参考。     

交联型聚羧酸高性能减水剂的合成工艺研究

从分子结构设计的角度出发,选择了一种具有双官能团结构的功能单体参与聚羧酸高性能减水剂的主链结构的合成,通过正交设计试验研究制备了一系列具有交联结构的聚羧酸高性能减水剂。试验结果分析表明该减水剂具有更优的分散性能及对各种水泥的适应性,正交分析得到最优组合为MAA与单体E的摩尔比1．5,链转移剂用量0．25％,引发剂用量1．65％。     

机制砂配制路面混凝土的应用

本文通过对机制砂性能特点的研究,研究了机制砂混凝土配合比的设计原则。通过分析石粉含量对机制砂砂高性能混凝土在工作性和力学性能上的影响,确定石粉含量的范同;通过对机制砂和天然砂混凝土性能的对比试验,结果表明机制砂砂完全可以替代天然砂配制混凝土。     

Influences of superplasticizer modification and mixture composition on the performance of self-compacting concrete at varied ambient temperatures

The fresh behaviour of self-compacting concrete (SCC) at varying temperatures differs from that of normal vibrated concrete. This is because the rheology of SCC depends not only on degree of cement hydration, but also on the adsorption of superplasticizers – mostly polycarboxylate based polymers (PCE) -, which is affected by the time and hydration progress. Due to the variety of PCEs and mixture compositions for SCC a prediction of the rheology at varying temperatures is complicated. The charge densities of PCEs as well as the water to solid ratio in the paste are identified to be the main decisive parameters for robust fresh concrete properties.Rheometric concrete investigations with different SCC mixture compositions and varied anionic charge densities of the PCE were conducted. SCC which is rich in powder components showed robust performance at low temperatures while SCC with low powder content was favourable at high temperatures. High charge density PCE pointed out to be very robust at low temperatures but at high temperatures it significantly reduced the flow retention. Low charge density PCE could not generate self-compacting properties at low temperatures but retained the flow performance over sufficiently long time. Based on considerations about particle interactions and adsorption mechanisms of PCEs, the relevant processes are explained and options for the development of robust mixture compositions for individual temperature ranges are itemised.     

Effects of granulated blast furnace slag and superplasticizer type on the fresh properties and compressive strength of self-compacting concrete

This paper presents the results of an experimental investigation carried out to study the effect of granulated blast furnace slag and two types of superplasticizers on the properties of self-compacting concrete (SCC). In control SCC, cement was replaced with 10%, 15%, 20%, and 25% of blast furnace slag. Two types of superplasticizers: polycarboxylate based superplasticizer and naphthalene sulphonate based superplasticizers were used. Tests were conducted for slump flow, the modified slump test, V-Funnel, J-Ring, U-Box, and compressive strength. The results showed that polycarboxylate based superplasticizer concrete mixes give more workability and higher compressive strength, at all ages, than those with naphthalene sulphonate based superplasticizer. Inclusion of blast furnace slag by substitution to cement was found to be very beneficial to fresh self-compacting concrete. An improvement of workability was observed up to 20% of slag content with an optimum content of 15%. Workability retention of about 45 min with 15% and 20% of slag content was obtained using a polycarboxylate based superplasticizer; compressive strength decreased with the increase in slag content, as occurs for vibrated concrete, although at later ages the differences were small.     

Removal of As(III) in a column reactor packed with iron-coated sand and manganese-coated sand

The applicability of manganese-coated sand (MCS) and iron-coated sand (ICS) for the treatment of As(III) via oxidation and adsorption processes was investigated. Scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD) were used to observe the surface properties of the coated layer. In the batch adsorption, the adsorption rate of As(V) onto ICS was greater than that of As(III), and ICS showed a greater adsorption capacity for the removal of As(V) than As(III). From a bench-scale column test, a column reactor packed with both MCS and ICS was found to be the best system for the treatment of As(III) due to the promising oxidation efficiency of As(III) to As(V) by MCS and adsorption of As(V) by both MCS and ICS. From these bench-scale results, the treatment of synthetic wastewater contaminated with As(III) was investigated using a pilot-scale filtration system packed with equal amounts (each 21.5 kg) of MCS at the bottom and ICS on the top. The height and diameter of the column were 200 and 15 cm, respectively. As(III) solution was introduced into the bottom of the filtration system, at a speed of 5 × 10⁻³ cm s⁻¹, over 148 days. The breakthrough of total arsenic in the mid-sampling (end of the MCS bed) and final-sampling (end of the ICS bed) positions began after 18 and 44 days, respectively, and showed complete breakthrough after 148 days. Although the breakthrough of total arsenic in the mid-sampling position began after 18 days, the concentration of As(III) in the effluent was below 50 μg L⁻¹ for up to 61 days. This result indicates that MCS has sufficient oxidizing capacity for As(III), and 1 kg of MCS can oxidize 93 mg of As(III) for up to 61 days. When the complete breakthrough of total arsenic occurred, the total arsenic removed by 1 kg of MCS was 79.0 mg, suggesting MCS acts as an adsorbent for As(V), as well as an oxidant for As(III). From this work, a filtration system consisting of both MCS and ICS can potentially be used a new treatment system to simultaneously treat As(III) and As(V).