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International Concrete Abstracts Portal

Showing 1-5 of 168 Abstracts search results

Document: 

20-291

Date: 

November 1, 2021

Author(s):

Yu Liu, Rui Jing, Fengze Cao, and Peiyu Yan

Publication:

Materials Journal

Volume:

118

Issue:

6

Abstract:

The lubrication layer plays a governing role in predicting the pumpability of fresh concrete. The effects of aggregate content on the rheological properties and formation of the lubrication layer were determined from the measurements of the sliding pipe rheometer, tribometer, and mortar rheology. The performance indexes of fresh concrete, including its rheological properties and workability, were investigated in parallel to fully characterize the impact of aggregate content on the pumpability of concrete. The results show that there is an optimal sand-to-total aggregate ratio (sand ratio) that yields the best rheological properties of the lubrication layer and pumpability of concrete. They also improve with the increase in paste-aggregate (PA) ratio. The shearing degree of bulk concrete is affected by the aggregate content, which leads to different formation processes of the lubrication layer. The rheological properties and workability of concrete are improved with a moderate sand ratio and an increased PA ratio due to the change in thickness of the paste layer on the surface of aggregate particles. The thixotropy of concrete is affected by the aggregate content. Moreover, the formation of the lubrication layer and its rheological property evolution depend on the measurement systems.

DOI:

10.14359/51734147


Document: 

20-472

Date: 

November 1, 2021

Author(s):

Chandrasekhar Bhojaraju, Malo Charrier, and Claudiane M. Ouellet-Plamondon

Publication:

Materials Journal

Volume:

118

Issue:

6

Abstract:

A factorial experimental design plan was used to compare admixtures (high-range water-reducing admixture, viscosity-modifying agent, accelerator, calcium silicate hydrate [CSH] seeds, and nanoclay) in a cement and silica fume blend. Two methods were tested to measure the structuration rate: the constant velocity method and the creep recovery method. The measurements were performed with a rotational rheometer with a double-helical spiral geometry to reduce slippage. The evolution of yield stress and thixotropy of the mixtures at four resting times was evaluated, providing insight into the stress that the recently printed structure can withstand. The creep recovery method generally provides a higher static yield stress than the constant velocity method, except for the stronger mixtures, raising additional questions on the effect of the paste history on microstructural buildup mechanisms. When the extruder begins, shear is applied and the microstructure is broken, causing the dynamic yield stress to be lower than the static yield stress. The effect of the admixtures on thixotropy is discussed.

DOI:

10.14359/51734149


Document: 

20-433

Date: 

November 1, 2021

Author(s):

Sooraj A. O. Nair and Narayanan Neithalath

Publication:

Materials Journal

Volume:

118

Issue:

6

Abstract:

Three-dimensional (3D) printing of cement-based materials is carried out using extrusion, which requires a fundamental understanding of the non-Newtonian flow of pastes through capillaries, which is the focus of this paper. 3D-printable cementitious pastes, qualified using steady-state extrusion pressure, are subjected to multiple-speed extrusion tests under apparent shear rates that correspond to typical printing speeds. The true, non-Newtonian flow curves are obtained by carrying out the relevant end corrections, deconvoluting the apparent shear rate (or velocity) into its true and wall slip components and applying the Weissenberg-Rabinowitsch correction. An exponential relationship is observed between the slip velocity and the wall shear stress, which is used to determine the slip layer thickness. The velocity profiles in the capillary demonstrated the shear-thinning nature of the pastes and the existence of a plug-flow zone with invariant velocity, while the viscosity profiles showed the near-Newtonian response of the superplasticized paste at higher shear rates. The influence of printing speed, particle concentration, and the presence of superplasticizer on the slip layer thickness is explored. A particle-depleted slip layer could be beneficial in reducing the energy needed for printing but could have implications in interlayer bonding and durability. The flow characterization approach presented herein can be adopted to optimize the paste material design and printing characteristics for extrusion-based 3D printing.

DOI:

10.14359/51733110


Document: 

20-417

Date: 

November 1, 2021

Author(s):

Y. Tao, G. Vantyghem, K. Lesage, Y. Yuan, W. De Corte, K. Van Tittelboom, and G. De Schutter

Publication:

Materials Journal

Volume:

118

Issue:

6

Abstract:

Shotcrete used for rock tunnel linings calls for skilled technicians, which is the key aspect to control the rebound. Three-dimensional (3D) concrete printing of tunnel linings has the potential to reduce manual labor for construction workers and to eliminate rebound, especially at overhead positions. In this study, the sag resistance and bond properties of printable concrete for overhead applications were explored. Mixtures with the addition of redispersible polymer powders (RDPs) and cellulose ethers (CE) were formulated. Roughened concrete slabs were used to replace the tunnel wall rock. A tack test with a loading control mode and a stress growth test were performed. To verify the results of the tack test and the stress growth test, a 3D concrete printing test, involving upside-down printing against the lower face of a supported concrete slab, was performed afterward. Also, a pulloff test was performed to measure the bond strength of the printed layers in the hardened stage. The results showed that the sag resistance of printable concrete is related to two aspects: the adhesion at the interface and the shear resistance of the fresh material itself. The adhesion and shear resistance properties determined two different failure modes: adhesion failure and cohesion failure. The results also demonstrated that the tack test results were more consistent with the upside-down printing test results, compared to the stress growth test.

DOI:

10.14359/51733105


Document: 

20-456

Date: 

November 1, 2021

Author(s):

Girish Shamanna, Ajay Nagaraj, and Akanksha Achutha

Publication:

Materials Journal

Volume:

118

Issue:

6

Abstract:

The characterization and control of flow properties of present concrete are most critical due to the wide choice of ingredients with different characteristics. A rheological-based scientific approach is needed to overcome the deficiencies of empirical tests. This study has clearly brought out the effective use of the concrete shear box as an additional instrument in finding the rheological properties of very stiff to flowing concrete. The procedure for finding the rheological properties is unique and shows the existence of the limiting value of slump flow in using the Bingham model at a higher flowability of self-consolidating concrete. Results are consistent and clearly show a correlation between the slump flow and yield stress and the importance of the volume of paste and the use of multiple linear regression analysis in understanding the combined influence of ingredients. The study implies the design of self-consolidating concrete mixtures based on rheological properties for different slump flow values.

DOI:

10.14359/51734148


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