预拌混凝土性能试验研究

本论文是通过试验来探讨在不同掺量的外加剂和粉煤灰作用下,不同坍落度对预拌混凝土性能影响的规律;考虑了不同掺量的粉煤灰混凝和外加剂对预拌混凝土坍落度的影响以及对其力学性能的影响,分析不同坍落度条件下,预拌混凝土的力学性能所反应的抗裂性能的优劣,为更加直观、准确的把握预拌混凝土工程的早期工作性能提供有效的依据。     

纵波波速与混凝土坍落度及贯入阻力之间相关性试验研究

预拌混凝土在工程中的应用越来越普遍,但其坍落度控制及凝结时间的确定却一直是有关建设施工单位需要考虑的问题。文章分别配置了水灰比为0.40,0.50和0.60的三组不同混凝土,对其早期纵波波速、混凝土坍落度、贯入阻力进行了测量,拟合了纵波波速与坍落度以及纵波波速与贯入阻力之间的关系,为利用纵波波速监测混凝土坍落度以及贯入阻力提供了指导。     

宜宾市举办预拌混凝土、预拌砂浆质量控制技术讲座

为了认真贯彻落实推广散装水泥相关政策精神,进一步提高宜宾市预拌混凝土、预拌砂浆生产、使用等环节从业人员的管理水平,确保建设工程质量,加快推动宜宾市散装水泥和预拌混凝土、预拌砂浆健康发展。经精心筹备,由宜宾市住建局主办,市散装办承办的第三期全市预拌混凝土、     

影响预拌混凝土质量若干问题的探讨

本文通过对影响预拌混凝土质量若干问题的原因分析,探讨了目前影响预拌混凝土质量的主要因素,并提出了部分应对措施供参考,希望通过各方的共同努力提高预拌混凝土质量。     

IHI公司搅拌楼计量控制装置

近年来,对搅拌楼的计量控制装置,不仅要求能稳定地供应预拌混凝土,而且还要能进行细致的质量管理,并能使整个搅拌楼节约劳动力。为满足这些要水,配置了水分计、浓度计,搅拌机内混凝土坍落度检测器,以及联机控制的外部计算机。以下,以日本的 IHI 公司搅拌楼的 MCSⅡ微机控制系统为例来说明。     

浅谈影响管片混凝土实际用水量的原因及控制方法

在管片混凝土的生产过程中,坍落度的控制得当与否将影响到预制管片的质量和生产周期,而其中实际用水量直接决定了混凝土的坍落度大小。文章通过对混凝土拌制过程中的各个环节进行分析,得出影响实际用水量的主要原因,并提出相应的控制办法,为生产优质混凝土管片提供参考。     

陶粒预处理对陶粒泡沫混凝土物理力学性能的影响

陶粒吸水会加速陶粒泡沫混凝土拌合物中泡沫的破灭,导致坍落度经时损失和表观密度显著增大。采用预湿、EVA乳液浸渍和憎水剂浸渍对陶粒进行预处理来降低陶粒的吸水量,并以陶粒泡沫混凝土的坍落度经时损失和表观密度表征泡沫的稳定性,对比3种预处理方式对陶粒泡沫混凝土物理力学性能的影响。结果表明:预湿处理可以改善泡沫的稳定性,保持混凝土的坍落度,降低表观密度和抗压强度;采用浓度5%和10%的EVA乳液处理陶粒可以提高混凝土的表观密度和抗压强度;采用20%的EVA乳液处理陶粒对表观密度和抗压强度的影响较小;陶粒憎水处理导致泡沫快速破灭,使陶粒泡沫混凝土的坍落度经时损失显著增大;制备陶粒泡沫混凝土时,更宜采用预湿处理方式。     

铜仁市预拌混凝土产业发展现状分析及建议

本论文以铜仁市预拌混凝土行业为分析对象,在分析生产企业的基本情况的基础上,依据局部区域内企业生产经营模式的差异情况以及预拌混凝土的特殊性,分析了铜仁市预拌混凝土行业现状及突出问题,并对其上下游产业链进行了相关分析,依此提出了优化方案,结合该地区预拌混凝土产业的实际情况,对现存在的问题进行科学研判,提出了推进高质量发展的建议.     

预拌砂浆在建筑工程中的应用

预拌砂浆是继预拌混凝土之后建筑业的又一项技术革新。本文阐述了预拌砂浆的技术优势,并针对当前预拌砂浆推广应用过程中存在的突出问题,提出了预拌砂浆在工程应用推广中的一些技术措施。     

基于环境作用下混凝土生命周期的评价

为客观评价预拌混凝土的环境影响,基于BEPAS(Building Environmental Performance Analysis System)评价系统,从六种混凝土的生产、施工、拆除三个阶段的资源和能源消耗基础数据收集入手,建立了各等级预拌混凝土的投入产出清单。依给出了基于6个模拟算例的混凝土框架结构的环境影响评价结果。单一预拌混凝土材料的环境影响随等级提高而上升,对于混凝土兼具环境表现和经济效果良好的特点。     

Effect of repeated dosages of superplasticizers on slump,strength and freeze-thaw resistance of concrete

Superplasticizers, when added to fresh concrete, cause large increases in its slump. However, this increase in slump is not sustained over long periods and within 60 minutes or so the concrete reverts to its original slump. In actual field applications of superplasticizers it may be necessary to add additional dosages to maintain the increased slump. This paper gives results of a laboratory investigation to determine the effect of repeated dosages of superplasticizers on workability, strength and durability of concrete. A series of air-entrained concrete mixes was made at a water/ cement ratio of 0.42 with a slump of 50 mm. Four commonly available superplasticizers were repeatedly added to the concrete, at the manufacture's recommended dosage rates, after completion of initial mixing. This was followed by additional mixing for 2 minutes. The properties of the fresh concrete were determined and test cylinders were cast after the addition of each dosage. Test prisms were also cast for strength and durability studies after the addition of the last dosage. The test results indicate that large increases in slumps of superplasticized concretes can be maintained for several hours by the addition of a second dosage. Apart from one instance, the addition of the third dosage is not considered desirable. The repeated additions of sulphonated melamine- and naphthalene-based superplasticizers caused substantial loss in entrained air content of the concrete; however, for concrete incorporating the lignosulphonate based superplasticizer, the reverse was true. The loss of entrained air adversely affected the performance of the concrete in freeze-thaw tests.     

Effect of absorption of limestone aggregates on strength and slump loss of concrete

Slump loss of concrete is very important in construction practice particularly with ready-mixed concrete. It is believed that slump loss occurs due to reduction of mixing water caused by aggregate absorption, evaporation, and cement hydration. In this study, the effect of absorption of limestone aggregates on the effective w/c ratio and on the strength and slump loss of concrete was investigated. It was found that the absorption of dry aggregates in all concrete mixes considered in this study occurred mainly in the first 15 min after the start of mixing and diminished substantially thereafter. The rate of slump loss of concrete was almost identical for mixes with dry and wet aggregates, even when setting time was extended. The results indicated that limestone aggregates used in this study with an absorption capacity of 1.3–1.9% by weight can absorb about 75% of their absorption capacity when mixed in concrete. The remaining 25% will add to the free water, thus increasing the effective w/c ratio. This phenomenon was demonstrated by the increased initial slump and decreased compressive strength of mixes with dry aggregates compared to those with wet aggregates.     

引气轻集料混凝土工作性和力学性能的研究

为配制高性能轻集料混凝土,研究了优质引气剂对大流动性轻集料混凝土的工作性及力学性能的影响规律.研究表明:引气剂对大流动性轻集料混凝土的坍落度的影响不大,对黏度影响较大;引气可减少离析、泌水及坍落度损失,明显改善轻集料混凝土拌合物的工作性能;一定范围内,引气对轻集料混凝土的力学性能有益;含气量小于5.5%时,抗压强度未降低,而是有所提高,提高幅度约3%～4%;含气量小于5.5%时,抗折强度提高,提高幅度约8%～10%.     

Modeling slump flow of concrete using second-order regressions and artificial neural networks

High-performance concrete (HPC) is a highly complex material, which makes modeling its behavior a very difficult task. Several studies have independently shown that the slump flow of HPC is not only determined by the water content and maximum size of coarse aggregate, but that is also influenced by the contents of other concrete ingredients. In this paper, the methods for modeling the slump flow of concrete using second-order regression and artificial neural network (ANN) are described. This study led to the following conclusions: (1) The slump flow model based on ANN is much more accurate than that based on regression analysis. (2) It has become convenient and easy to use ANN models for numerical experiments to review the effects of mix proportions on concrete flow properties.     

Filling ability and plastic settlement of self-compacting concrete

The use of self-compacting concrete (SCC) facilitates the placing of concrete by eliminating the need for compaction by vibration. Given the highly flowable nature of such concrete, care is required to ensure excellent filling ability and adequate stability. This is especially important in deep structural members and wall clements where concrete can block the flow, segregate and exhibit bleeding and settlement which can result in local defects that can reduce mechanical properties, durability and quality of surface finish.This paper shows results of an investigation of fresh properties of self-compacting concrete, such as filling ability measured by slump flow and flow time (measured by Orimet) and plastic fresh settlement measured in a columin. The SCC mixes incorporated various combinations of fine inorganic powders and admixtures. The slump flow of all SCCs was greater than 580 mm and the time in which the slumping concrete reached 500 mm was less than 3 s. The flow time was less than 5 s. The results on SCCs were compared to a control mix. The compressive strength and splitting tensile strength of SCCs were also measured.The effects of water/powder ratio, slump and nature of the sand on the fresh settlement were also evaluated. The volume of coarse aggregate and the dosage of superplasticizer were kept constant. It can be concluded that the settlement of fresh self-compacting concrete increased with the increase in water/powder ratio and slump. The nature of sand influenced the maximum settlement.     

Workability study of concretes made with recycled mortar aggregate

The use of recycled aggregates (RA) for concrete production usually involves a reduction of the workability as measured by slump. This reduction is mainly due to higher absorption rates, rough-textured surfaces and particles with quite irregular shape from RA. Besides that, the slump test is a static test, whose result is influenced by its own weight and by internal friction between particles. Because of that, recycled concrete workability is not well explained by the slump test. Thus, the main goal of this study is to assess the workability of concrete by varying: (1) workability tests (slump test, flow test and VeBe test); (2) the amount of fine and coarse RAs (0, 50 and 100 %); and, (3) the compensation index of RA absorption rates (60, 70, 80 and 90 %). Concrete compressive strength, at 28 days of age was also evaluated. It was observed that the flow test is the most suitable method for measuring the workability of recycled concrete. The results show that increasing the compensation index of RA absorption rate, there is an improvement of the workability of concrete and a reduction of compressive strength, which is related to the increase of the initial water content in mixtures.     

玄武岩-碳纤维/矿渣混凝土力学性能正交试验

应用正交试验法开展了16组玄武岩-碳纤维(BF-CF)/矿渣混凝土和1组C40级基准混凝土的塌落度、立方体抗压强度和劈裂抗拉强度试验,研究了BF、CF和矿渣三种因素对BF-CF/矿渣混凝土力学性能的影响。结果表明:BF-CF/矿渣混凝土立方体抗压强度和劈裂抗拉强度均高于C40基准混凝土,立方体抗压强度最大提高了21.0%,劈裂抗拉强度最大提高了35.3%。BF和CF的掺入均会减小混凝土的塌落度,BF对于塌落度的减小更加明显,BF对塌落度的最大降幅为67.1%;矿渣代砂率是影响BF-CF/矿渣混凝土立方体抗压强度的显著因素,随着矿渣代砂率的增大,立方体抗压强度先增大后减小,矿渣对立方体抗压强度的最大提高幅度为7.6%;BF是影响BF-CF/矿渣混凝土劈裂抗拉强度的显著因素,劈裂抗拉强度随BF体积率的增加而增大,BF对劈裂抗拉强度的最大增幅为12.0%,CF对劈裂抗拉强度的提升不明显。对正交试验的结果进行回归分析得出BF-CF/矿渣混凝土立方体抗压强度和劈裂抗拉强度预测模型,模型精度较高。