远距离运输混凝土坍落度损失与控制的试验研究

通过混凝土坍落度经时损失的原因分析，探讨了几种控制混凝土坍落度经时损失的方法。     

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。     

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。     

浅谈混凝土配合比中坍落度的重要性

混凝土出现已有200多年的历史,混凝土的作用在工程中的重要性是毋庸置疑的,随着近年来大坍落度混凝土的推广,本人经过在工地一线施工中的经验发现,混凝土坍落度对工程施工的重要性,并简单提出了在施工当中尽可能降低混凝土的坍落度。     

石屑在预拌混凝土中的应用研究

研究并利用石矿尾矿—作为预拌混凝土中的细集料拌制混凝土,从混凝土的力学性能、物理性能等进行相应的试验并用于生产。结果表明：在现有石矿的石屑情况下,把40％-60％的石屑作为混凝土的细集料来替代天然砂,是完全可行的,从而起到保护环境,节约资源的目的。     

高强混凝土制备研究

本文用普通原材料成功制备了８０ＭＰａ以上高强混凝土,研究了各种因素对混凝土的影响关系,探讨了解决坍落度损失的方法     

聚羧酸系减水剂在预拌混凝土中常见问题及分析

聚羧酸系减水剂作为一种新型的外加剂,具有减水率高、保塑性能好、水泥适应性强、混凝土收缩小等优点,但在掺入预拌混凝土的使用过程中,由于各种原因,引起混凝土的质量问题,合理选用使用原材料,提高聚羧酸类减水剂在预拌混凝土中的应用。     

建筑施工中混凝土结构裂缝分析

本文重点介绍了混凝土结构中常出现的裂缝等各种问题,通过分析来总结建筑经验,提供一定行之有效的方案措施。     

高强混凝土制备研究

本文用普通原材料成功制备了８０ＭＰａ以上高强混凝土，研究了各种因素对混凝土的影响关系，探讨了解决坍落度损失的方法。     

预拌混凝土质量控制措施分析

本文对预拌混凝土的生产、运输和浇注中的质量控制做了详细的分析,供大家参考。     

Control of slump loss in superplasticized concrete

The slump loss characteristics of concrete containing different amounts of sulphonated melamine formaldehyde (SMF) admixed with two types of polymers were investigated. The addition of 2% polymer to SMF retarded the slump loss. The setting times although retarded were found to satisfy the requirements of the ASTM standards. Addition of the polymer to a commercial superplasticizer formulation further extended its slump loss capability. The final setting times were within the limits specified by ASTM but the initial setting times were significantly higher than the specified ASTM limits. The control of slump loss in the presence of polymer may be related to the retarding action on the formation of ettringite from the C₃A+Gypsum reaction in cements.     

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。     

Rheology of fresh concrete: from measurements to predictions of casting processes

This paper tries to make a link between the measurements of the rheological properties of fresh concrete (yield stress and thixotropy) and casting processes. In the first part, methods allowing for the measurement of the yield stress of a given concrete without the use of a rheometer will be described. In a second part, a thixotropy model allowing for the prediction of the apparent yield stress of the material as a function of its flow history will be presented. Finally, in the last part, prediction methods of casting process will be presented. These methods can be considered as practical tools allowing for the prediction of formwork filling, pressure formwork or multilayer casting occurrence. Moreover, they contribute to bringing rheology from research and development into the field of practical applications. Dr Nicolas Roussel presented a lecture of this paper at the 2007 RILEM annual week in Ghent, Belgium, as he was awarded the 2007 Robert L’Hermite Medal in recognition of his work on rheology of concrete. The L’Hermite Award Committee for 2007 decided to recommend the prize to Dr Roussel in recognition of his extensive scientific work within rheology of concrete. In particular his physical analysis of concrete rheology and his ability to combine experimental and theoretical work are of high quality.     

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.     

Using aggregate flowability testing to predict lightweight self-consolidating concrete plastic properties

This paper presents the results of an experimental study on the flow properties of lightweight self-consolidating concrete (LWSCC) which utilizes a new test relating aggregate flow to concrete flow. Three types of LWSCC were tested containing differing proportions of lightweight and normal weight, coarse and fine aggregates, as well as a normal weight self-consolidating concrete (NWSCC) as a control. The flow properties of the aggregate mixes used in the LWSCC and NWSCC specimens were tested using a V-funnel. The concrete flow properties were also tested for comparison, as were the compressive and tensile strengths of the various mixtures. A relationship between the aggregate frictional resistance and the traditional concrete flowability tests—i.e., slump flow, J-ring, and T₅₀₀—was demonstrated. Compressive strengths were greater in LWSCC mixes that contained smaller sized coarse and normal weight aggregates. Finally, a design procedure is introduced that utilizes the aggregate frictional resistance, paste flow properties, and aggregate void ratio to predict the plastic properties of the concrete.     

Properties of cold bonded quarry dust coarse aggregates and its use in concrete

In this study, artificial coarse aggregates are prepared by a cold bonding technique. The waste materials, namely, fly ash and quarry dust, are used for the preparation of the cold bonded artificial aggregate. Portland cement is used as the binder material. The independent variables considered for the preparation of the artificial aggregate are cement and fly ash contents. The properties of the artificial aggregate are determined and regression models are proposed for predicting these properties. The strength and workability of concrete containing artificial aggregate is determined. The slump loss of concrete containing artificial aggregate is found to be gradual. The concretes with strengths of up to 30 MPa is prepared using artificial aggregates. The study promotes the use of waste material and supports sustainable construction practices.     

Influence of recycled aggregate on slump and bleeding of fresh concrete

The recycling of construction and demolition (C&;D) waste as a source of aggregates for the production of new concrete has attracted increasing interests from the construction industry. While the environmental benefits of using recycled aggregates are well accepted, some unsolved problems prevent this type of material from wide application in structural concrete. One of the major problems with the use of recycled aggregates in structural concrete is their high water absorption capacity which leads to difficulties in controlling the properties of fresh concrete and consequently influences the strength and durability of hardened concrete. This paper presents an experimental study on the properties of fresh concrete prepared with recycled aggregates. Concrete mixes with a target compressive strength of 35 MPa are prepared with the use of recycled aggregates at the levels from 0 to 100% of the total coarse aggregate. The influence of recycled aggregate on the slump and bleeding are investigated. The effect of delaying the starting time of bleeding tests and the effect of using fly ash on the bleeding of concrete are explored.     

Rheological properties considering the effect of aggregates on concrete slump flow

Rheology of concrete allows us to understand the flow behavior of concrete and further extend the quantitative evaluation of its construction performance. The use of a concrete rheometer is promising for the purpose, but sometimes limited high associated cost and procedure complexity. This study proposes a simulation-based model that correlates the slump flow test results to a concrete’s rheological properties, allowing quantitative evaluation through this simple method. The proposed model is based on single-fluid simulation using the volume-of-fluid method, with an extension to accommodate the partial segregation of coarse aggregates. Either the channel flow or the L-shaped panel filling of SCC is simulated using the rheological properties obtained by our model. Finally, the rheograph describing the self-compacting ability of SCC is updated.