Reuse of waste fresh concrete as a preceding mortar for concrete pumping constructions : Influence of chemical admixture.

A superplasticizer is a type of chemical admixture used to alter the workability (viscosity) of fresh concrete. The workability of fresh concrete is often of particular importance when the water-to-cement (w/c) ratio is low and a particular workability is desired. Reactive Powder Concrete (RPC) is a high-strength concrete formulated to provide compressive strengths exceeding 130MPa and made of primarily powders. RPC materials typically have a very low w/c, which requires the use of a chemical admixture in order to make the material workable for placing, handling and consolidating. Superplasticizer are commonly used for this purpose. Superplasticizers are developed from different formulations, the most common being Polynaphthalene Sulfonate (PNS), Polymelamine Sulfonate (PMS) and Polycarboxylate Ether (PCE). This study investigates the impact of various PNS based superplasticizers on the compressive strength and rheological performance of a RPC mixture. Six different types of PNS based superplasticizers were used; three of various compositional strengths (high, medium, low range) from a local provider, and three of the same compositional strengths (high, medium, low) from a leading manufacturer. Specific properties assessed were the superplasticizers viscosity, concrete workability through the mortar-spread test, concrete rheology, and 7, 14, and 28 day RPC compressive strengths. Two mixtures were produced with two w/cm (0.20 and 0.15), which would subsequently increase the amount of superplasticizer needed, from 34.7L/m3 to 44.5L/m3. The results show that the name brand high range composition produced the overall highest spread, lowest viscosity, and a highest compressive strength at all ages tested. However, the local provider outperformed the name brand in the mid and low range compositions. Additionally, the rheology test also demonstrated that the name brand high range, and RPC produced with the name brand high range, had a lower viscosity at all angular speeds than the others tested.

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Fresh Concrete Pumping Arrest Investigation for Thixotropy by a CFD Modelling Approach

RILEM Bookseries - Rheology and Processing of Construction Materials ◽

10.1007/978-3-030-22566-7_67 ◽

2019 ◽

pp. 580-587

Author(s):

Robin De Schryver ◽

Khadija El Cheikh ◽

Mert Y. Yardimci ◽

Karel Lesage ◽

Geert De Schutter

Keyword(s):

Fresh Concrete ◽

Cfd Modelling ◽

Concrete Pumping ◽

Modelling Approach

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Numerical Study on Concrete Pumping Behavior via Local Flow Simulation with Discrete Element Method

Materials ◽

10.3390/ma12091415 ◽

2019 ◽

Vol 12 (9) ◽

pp. 1415 ◽

Cited By ~ 3

Author(s):

Yijian Zhan ◽

Jian Gong ◽

Yulin Huang ◽

Chong Shi ◽

Zibo Zuo ◽

...

Keyword(s):

Discrete Element Method ◽

Fresh Concrete ◽

Numerical Study ◽

Flow Simulation ◽

Discrete Element ◽

Local Flow ◽

Pumping System ◽

Concrete Pumping ◽

Pipe Geometry ◽

Element Method

The use of self-consolidating concrete and advanced pumping system enables efficient construction of super high-rise buildings; however, risks such as clogging or even bursting of pipeline still exist. To better understand the fresh concrete pumping mechanisms in detail, the discrete element method is employed in this paper for the numerical simulation of local pumping problems. By modeling the coarse aggregates as rigid clumps and appropriately defining the contact models, the concrete flow in representative pipeline units is well revealed. Important factors related to the pipe geometry, aggregate geometry and pumping condition were considered during a series of parametric studies. Based on the simulation results, their impact on the local pumping performance is summarized. The present work demonstrates that the discrete element simulation offers a useful way to evaluate the influence of various parameters on the pumpability of fresh concrete.

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Establishment and verification of a contact model of flowing fresh concrete

Engineering Computations ◽

10.1108/ec-11-2017-0447 ◽

2018 ◽

Vol 35 (7) ◽

pp. 2589-2611

Author(s):

Yuan Zhao ◽

Zhennan Han ◽

Yali Ma ◽

Qianqian Zhang

Keyword(s):

Experimental Data ◽

Numerical Analysis ◽

Fresh Concrete ◽

Dynamic Performance ◽

Discrete Element ◽

Contact Model ◽

Two Phase ◽

Content Type ◽

Concrete Pumping ◽

Contact Models

Purpose The purpose of this paper is to establish a new dynamic coupled discrete-element contact model used for investigating fresh concrete with different grades and different motion states, and demonstrate its correctness and reliability according to the rheological property results of flow fresh concrete in different working states through simulating the slump process and mixing process. Design/methodology/approach To accurately express the motion and force of flowing fresh concrete in different working states from numerical analysis, a dynamic coupled discrete-element contact model is proposed for fresh concrete of varying strength. The fluid-like fresh concrete is modelled as a two-phase fluid consisting of mortar and aggregate. Depending on the contact forms of the aggregate and mortar, the model is of one of the five types, namely, Hertz–Mindlin, pendular LB contact, funicular mucous contact, capillary LB contact or slurry lift/drag contact. Findings To verify the accuracy of this contact model, concrete slump and cross-vane rheometer tests are simulated using the traditional LB model and dynamic coupled contact model, for five concrete strengths. Finally, by comparing the simulation results from the two different contact models with experimental data, it is found that those from the proposed contact model are closer to the experimental data. Practical implications This contact model could be used to address issues such as (a) the mixing, transportation and pumping of fresh concrete, (b) deeper research and discussion on the influence of fresh concrete on the dynamic performance of agitated-transport vehicles, (c) the behaviour of fresh concrete in mixing tanks and (d) the abrasion of concrete pumping pipes. Originality/value To accurately express the motion and force of flowing fresh concrete in different working states from numerical analysis, a dynamic coupled discrete-element contact model is proposed for fresh concrete of varying strength.

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Feasibility study of the reuse of waste fresh concrete as a preceding mortar for concrete pumping constructions.

Concrete Research and Technology ◽

10.3151/crt1990.13.1_33 ◽

2002 ◽

Vol 13 (1) ◽

pp. 33-42

Author(s):

Hajime Takano ◽

Yoshihisa Nakata ◽

Yoshinori Nara ◽

Torao Kemi

Keyword(s):

Feasibility Study ◽

Fresh Concrete ◽

Concrete Pumping

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Methods for Inhibition of Fluidity Loss of Concrete Mixed with Superplasticizers

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.680.370 ◽

2016 ◽

Vol 680 ◽

pp. 370-377

Author(s):

Wen Xian Zhu ◽

Zhen Ping Sun ◽

Yi Liu ◽

Dang Yi Li

Keyword(s):

Mineral Composition ◽

Fresh Concrete ◽

Raw Materials ◽

Cement Clinker ◽

Comprehensive Overview ◽

Mix Proportion ◽

Chemical Admixture

The slump loss of fresh concrete mixed with superplasticizers should be well controlled to ensure its transportation and pumping. In this paper, we describe a comprehensive overview of the mechanism of fluidity loss and then analyze the reason for the change. Researches show that the slump loss of fresh concrete is influenced by the mineral composition of cement clinker, the type and characteristics of aggregate, the species and dosage of admixture, the mix proportion and the construction environment, etc. Thus, a series of methods proven to be effective, such as adjustment of raw materials, adding methods of chemical admixture, synthesis of new types of superplasticizers, etc. have been proposed to solve the problems.

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