关于负温混凝土的受冻临界强度的探讨

本文对JGJ104—97《建筑工程冬期施工规程》、GB50119—2003《混凝土外加剂应用技术规范》和JC475—2004《混凝土防冻剂》中对负温混凝土的“受冻临界强度”进行了探讨。     

混凝土中聚羧酸外加剂的应用

聚羧酸系外加剂对于在高性能混凝土中的应用,已是人所共知的事情自混凝土广泛应用于建筑工程以来,混凝土技术的进步与外加剂的不断更新密不可分。在混凝土中掺人聚羧酸外加剂是提高混凝土耐久性和能提高使用寿命的有效技术途径。     

控制混凝土外加剂中释放氨，消除室内氨污染

2001年国家质量监督检验检疫总局根据国务院领导的指示和广大人民群众对室内环境污染的强烈反响,组织制定了“室内建筑装饰装修材料有害物质限量”十项强制性国家标准,《混凝土外加剂中释放氨的限量》为其中之一。一、标准制定的意义由于防冻剂产品的研究进展,使得在寒冷气候下的混凝土的制备、浇注、养护等取得显著的效果,从而使得冬季施工不必暂停,由此给建筑业创造了可观的经济效益。早期的防冻剂多以氯化钠为主,在人们认识到氯离子对钢筋的锈蚀作用后,改以尿素作为防冻剂的有效成分。尿素在混凝土中水解,生成NH3和CO2,氨气的挥发造成…     

浅析外加剂对混凝土的影响成因

在我国建筑行业不断发展的今天,我国的建筑工程在数量上以及质量上都有了非常大的提升和改进。在我国建筑工程施工建设的过程中,混凝土的用量以及质量直接影响着建筑工程的建筑质量以及使用质量,因此在进行混凝土施工的过程中,我们要对混凝土的施工质量给予格外的重视。作为建筑工程中使用量最大,同时也是用途施工最广的施工材料,混凝土施工材料是建筑工程施工中的一种常用施工材料。我们为了有效地提升混凝土的施工质量以及施工性能,我们要在混凝土的施工过程中添加相应的添加剂来改善混凝土的施工性能。本文主要针对外加剂对于混凝土的影响成因进行详细的阐述以及分析,希望通过本文的阐述以及分析能够有效地提升我国混凝土的施工质量,更加有效合理的提升外加剂的添加比例,同时也为我国的建筑工程施工质量的不断提升贡献力量。     

掺有减水剂的混凝土配合比设计要点

近几年来,外加剂已经成为混凝土组成材料中除水、水泥、砂、碎石以外的第五大材料,得到了广泛的应用。由于外加剂种类较多,性能各异,所以,掺有外加剂的混凝土的工作性好坏,都必须经过对比试验才能得知。     

混凝土的施工技术及质量控制分析

混凝土是水泥、砂、石、水、外加剂、掺合料等多组成分构成的一种性能多样化的材料,其性能不仅与组成材料的性能有直接关系,而且还与施工技术、所处环境及维护条件等有关。要在设计方法、施工技术以及维护要求等方面进一步研究,以促进我国混凝土结构技术的进一步发展。本文从混凝土对原材料的基本要求出发对混凝土在建筑工程中的施工要点及质量控制进行了详细的讨论。     

水泥混凝土外加剂与水泥适应性探讨

在混凝土、砂浆或净浆的制备过程中,掺入不超过水泥用量5％（特殊情况除外）,能对混凝土、砂浆或净浆的正常性能要求而改性的一种产品,称为混凝土外加剂。混凝土外加剂的开发应用,使混凝土逐渐朝绿色高性能混凝土方向发展。然而混凝土外加剂与水泥之间有时存在不相适应的状况,影响了外加剂的应用效果和混凝土的性能。本文从混凝士外加剂、水泥等方面入手,对水泥混凝土外加剂与水泥适应性的影响因素及使用过程中应注意的问题进行了探讨。     

公路水泥混凝土外加剂的应用研究

外加剂的应用是混凝土发展史上一次重大的技术变革,推动了混凝土科技事业的发展,促进了新的混凝土结构设计理论和施工技术的发展,同时应用外加剂可以显著改善混凝土的性能,减少水泥用量,降低混凝土成本,节约能源。所以,混凝土中外加剂的应用有着十分重要的技术和经济意义。目前,我国公路水泥混凝土工程建设规模很大,外加剂的使用也非常广泛。加入外加剂能改善水泥混凝土的性能,但同时由于外加剂的使用不当而导致水泥混凝土路面及桥涵结构的质量事故屡有发生,影响了公路工程的建设质量。有必要对公路工程中的常用外加剂进行综述。     

现代高性能混凝土的研究与发展

自混凝土开始被应用在建筑工程中以来,已经有一百多年的历史了。随着建筑对施工材料的性能要求越来越高,混凝土的性能也在不断的完善。目前,高性能混凝土的研究与应用已经开始引起人们的重视,现本文就主要针对现代高性能混凝土的相关内容进行简单研究探讨。     

商品混凝土的质量监理

商品混凝土主要是由水泥、集料、水以及根据需要掺入的外加剂和掺和料等组分按一定的比例,在集中搅拌站(厂)经计量,拌制后出售,并采用运输车在规定的时间内运至使用地点的混凝土拌合物。商品混凝土在建筑工程上的全面普及使用,其质量控制已成为监理工程师质量控制中的一项主要内容。     

Terminology,definition and classification of admixtures

The use of admixtures with the idea to modify certain properties of mortars and concretes, is as old as the use of cement itself. Already the Romans used blood, porkfat and milk as admixtures in their pozzolan-concrete, perhaps to increase the consistency of the fresh concrete. Although the Romans probably did not know this, blood is an AE agent and therefore it undoubtedly has helped to increase the durability of the Roman concrete. After the renewed invention of cement and concrete, admixtures in first instance were considered with suspicion, probably by unfavourable experiences with admixtures which were not tested well on their merites, and for which incorrect dosages played a part as well. The turning-point came about 30 years ago, when it was shown conclusively that admixtures which gave rise to air bubbles in concrete, led to an increased frost resistance. Consequently, air was accepted as an essential part of concrete. On the other hand, the criterion of maximum density gave rise to the development of fluidifiers and the first well-founded report on this type of admixture —as far as the author knows—was published in 1934 [1] by Rôs (EMPA, Zürich).     

Simulation of a temperature rise in concrete incorporating fly ash or slag

Granulated slag from metal industries and fly ash from the combustion of coal are among the industrial by-products and have been widely used as mineral admixtures in normal and high strength concrete. Due to the reaction between calcium hydroxide and fly ash or slag, compared with Portland cement, the hydration of concrete containing fly ash or slag is much more complex. In this paper, by considering the producing of calcium hydroxide in cement hydration and the consumption of it in the reaction of mineral admixtures, a numerical model is proposed to simulate the hydration of concrete containing fly ash or slag. The heat evolution rate of fly ash or slag blended concrete is determined from the contribution of both cement hydration and the reaction of mineral admixtures. Furthermore, a temperature rise in blended concrete is evaluated based on the degree of hydration of cement and mineral admixtures. The proposed model is verified with experimental data on the concrete with different water-to-cement ratios and mineral admixtures substitution ratios.     

大掺量矿物掺合料高性能混凝土在京沪高铁四标段中的应用

以京沪高速铁路为工程背景,试验研究了矿物掺合料（粉煤灰、粉煤灰-矿粉）对混凝土工作性能、力学性能和耐久性能的影响以及大掺量矿物掺合料高性能混凝土的配制技术。结合实际工程,介绍了大掺量矿物掺合料高性能混凝土原材料选择、配合比设计、施工工艺等方面的控制技术。     

炭纤维增强轻质矿粉混凝土的热电行为

炭纤维增强混凝土能用来感知温度,其因在于短炭纤维的P-型传导性引起的塞贝克(Seebeck)效应所致.通过测量添加炭纤维或矿质掺和物(飞灰、硅土粉)前后六种波特兰水泥基混凝土的热电功率,研究了炭纤维增强轻质混凝土热敏的能力及其矿质掺合物对Seebeck效应的影响.结果表明: 炭纤维增强轻质混凝土具有类似于炭纤维增强标准混凝土的Seebeck效应,只是Seebeck系数因掺合了矿粉而减低.掺有矿粉的炭纤维增强轻质混凝土可用作建筑物的热传感器.     

纳米碳纤维增强混凝土抗冻性能试验

对六种不同纳米碳纤维掺量的72个纳米碳纤维/混凝土试件进行了慢冻融循环试验,通过测量纳米碳纤维/混凝土经不同冻融循环次数作用后的抗剥落能力、质量损失率、相对动弹性模量和抗压强度损失率,研究了纳米碳纤维掺量对纳米碳纤维/混凝土抗冻性能的影响。另外进行了纳米碳纤维/混凝土的FE-SEM试验和压汞试验,分析了纳米碳纤维对纳米碳纤维/混凝土抗冻性能的微观改性机制。结果表明:纳米碳纤维通过改善混凝土的微观形貌,细化其孔隙结构,提高其整体性和密实度,显著改善了混凝土的抗冻性能;纳米碳纤维掺量为3vol%时,纳米碳纤维/混凝土的抗冻性能最佳。同普通混凝土相比,300次冻融循环后,纳米碳纤维/混凝土的相对动弹性模量提高了33.2%,抗剥落能力显著增强;相同冻融次数下,随着纳米碳纤维掺量的增加,纳米碳纤维/混凝土相对动弹性模量和抗压强度损失率均先增大后减小,质量损失率先减小后增大。但纳米碳纤维掺量最大为5vol%时,纳米碳纤维/混凝土的抗冻性能仍优于普通混凝土;冻融循环次数越多,纳米碳纤维对混凝土抗冻性能的改善作用越显著。      

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.     

Waste paint as an admixture in concrete

A significant volume of waste latex paint exists in New Zealand, with the rate of supply rapidly growing, prompting an investigation into the use of waste paint as a polymeric admixture in concrete due to similarities in chemical compositions of waste paint and polymeric admixtures. The objective of this study was to produce a blockfill mix capable of maintaining or improving the properties of the hardened material whilst increasing the efficiency of the construction process. The optimum dosage to achieve the required strength and workability was found to be approximately 12% replacement of mix water with waste paint, while the Modulus of Elasticity was found to be a function of compressive strength. Rheological testing indicated that regardless of paint concentration, the yield stress of the blockfill increased whilst the viscosity and separation rate decreased. It was established that waste latex paint was a suitable replacement for conventional admixtures in concrete masonry blockfill, resulting in maintained strength and improved workability.     

Corrosion Behaviour and Chloride Attack of Reinforcing Steel in Presence of Concrete Admixtures

Corrosion and electrochemical behaviour of reinforcing steel embedded in cement pastes with and without concrete admixtures used in Egypt to modify concrete properties have been studied. The influence of the admixtures on the corrosion resistance of the steel against chloride attack has been studied using impressed current and impressed voltage techniques. The results indicate that the type and concentration of the admixture used have an important effed on the extent of chloride induced corrosion of the steel. The mechanism of corrosion of steel due to chloride attack is discussed.     

Simultaneous effects of salted water and water flow on asphalt concrete pavement deterioration under freeze–thaw cycles

The presence of water flow on road surfaces may lead to early deterioration of bituminous pavements. The adverse impacts of various anti-freezing materials on road surface performance have drawn the attention of many researchers. However, the simultaneous effects of salted water and water flow on the deterioration of road surfaces, particularly under freeze–thaw conditions, have not been adequately addressed. This research aims to study the combined effects of water flow and anti-freezing materials, which are usually present in the vicinity of asphaltic pavements during freeze–thaw cycles, on asphalt concrete deterioration. Two sets of asphalt concrete samples were prepared and subjected to six exposure states. The samples were also tested in an abrasion test apparatus and subjected to normal and frictional forces. Marshall strength loss and weight loss of the samples were measured and the results were analysed. The results indicated that the combined effects of water flow and de-icers under freeze–thaw conditions intensified the deterioration of asphalt concrete.