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International Concrete Abstracts Portal

Showing 1-5 of 140 Abstracts search results

Document: 

19-455

Date: 

March 1, 2021

Author(s):

Mohamed M. Sadek and Assem A. A. Hassan

Publication:

Materials Journal

Volume:

118

Issue:

2

Abstract:

This study evaluated the abrasion resistance for a number of lightweight self-consolidating concrete (LWSCC) incorporating coarse and fine lightweight expanded slate aggregates (LC or LF, respectively). The study also investigated the abrasion resistance before and after exposure to freezing-and-thawing cycles in the presence of deicing salt. The investigated parameters included different volumes of LC and LF aggregates, three binder contents (500, 550, and 600 kg/m3 [31.2, 34.3, and 37.5 lb/ft3]), and different types of concrete (LWSCC, lightweight vibrated concrete, and normal-weight self-consolidating concrete). Increasing the percentage of expanded slate aggregate decreased the abrasion resistance. Mixtures with LF showed higher strength-per-weight ratio and higher abrasion and salt-scaling resistance compared to mixtures with LC. Samples exposed to abrasion before salt scaling had higher mass losses due to salt scaling with an average of 26.8% compared to non-abraded ones. Higher mass loss was also observed in mixtures exposed to abrasion after the exposure to salt scaling with an average of 26% and 43.3% in the rotating-cutter and sandblasting abrasion tests, respectively.

DOI:

10.14359/51729325


Document: 

19-406

Date: 

March 1, 2021

Author(s):

Anvit Gadkar and Kolluru V. L. Subramaniam

Publication:

Materials Journal

Volume:

118

Issue:

2

Abstract:

Self-leveling concrete is developed with low-calcium alkali-activated fly ash (AAF) binder paste. The rheological behavior of AAF pastes with different compositions is evaluated. AAF pastes are proportioned with alkali-silicate activating solutions to ensure specific reactive oxide ratios for comparable geopolymer strength. The yield stress and the viscosity of the AAF binder paste vary with the silica content and the silica modulus (SiO2/Na2O mass ratio) in the alkali-silicate activating solution. The slump and flow behaviors of concrete mixtures made with AAF paste are evaluated. The requirements of the AAF binder characteristics, paste content, and aggregate packing for achieving self-leveling flow characteristics under gravity-induced flow are assessed. The transition from a frictional to a flow-type behavior in concrete mixtures depends on the AAF binder paste content. Self-leveling is achieved without the use of admixtures with an AAF binder paste of low yield stress and at a paste content of 45%. Improving the aggregate packing using the Fuller-Thompson curve and reducing the yield stress of the AAF binder paste increase the flow achieved in concrete mixtures. The specifications for cement-based self-consolidating concrete (SCC) are closely applicable for self-leveling AAF-based concrete.

DOI:

10.14359/51729324


Document: 

19-372

Date: 

January 1, 2021

Author(s):

Guilherme S. Araujo, Lui C. Iwamoto, Rosa C. C. Lintz, and Luisa A. Gachet

Publication:

Materials Journal

Volume:

118

Issue:

1

Abstract:

For the production of this lightweight concrete, expanded polystyrene (EPS) associated with expanded clay sintered lightweight aggregates were used to replace nature aggregates. Materials characterization tests were performed, as well as tests of the concrete in the fresh and hardened state. It is worth noting that the fresh tests displayed that the EPS concretes produced met the requirements of ABNT NBR 15823-1: 2017, classifying them as self-compacting. The hardened concrete tests observed the compressive strength, tensile strength, water absorption, void index, and specific mass. All concretes achieved resistances above 20 MPa, considered structural, and presented low specific mass, below 2000 kg/m3, classifying them as light concrete. Scanning electron microscopy (SEM) images allowed a better understanding of the microstructure, justifying the mechanical results obtained. The transition zone between the cement paste and the light aggregates, the number of voids in the cement paste, and the appearance of microcracks were considered.

DOI:

10.14359/51728280


Document: 

19-432

Date: 

November 1, 2020

Author(s):

Manar A. Al Fadul and Kevin R. Mackie

Publication:

Materials Journal

Volume:

117

Issue:

6

Abstract:

A model that simulates the two-dimensional (2-D) coupled heat and mass transfer phenomena in heated concrete is proposed. A fully implicit finite difference (FD) method was used in the discretization of the partial differential equations in both domain and time. The control volume approach was employed in the formulation of the FD equations, ensuring both local and global conservation properties are satisfied by the numerical solution. The solid, liquid, and gaseous (both air and vapor) phases are considered, including evaporation, condensation, and dehydration. The discretized equations of all species along with the temporal discretization of an interior node, surface node, and corner node are presented. Numerical case studies based on an object-oriented code for extremely rapid heating of concrete and nonsymmetric boundary conditions are validated against experimental results. Temperature, pressure, and moisture contours indicate the model’s ability to capture the complex 2-D behaviors of fire-exposed concrete over the entire flow domain.

DOI:

10.14359/51728122


Document: 

19-347

Date: 

September 1, 2020

Author(s):

Yusheng Zeng, Ser Tong Quek, Aiping Tang, and Xianyu Zhou

Publication:

Materials Journal

Volume:

117

Issue:

5

Abstract:

Freezing-and-thawing (F-T) resistance is a key parameter in evaluating the durability of concrete. The response of concrete under F-T environment varies depending on the mixture proportion and materials used. This paper focuses on the F-T behavior and damage resistance of normal-strength (NC), high-strength (HSC), high-performance (HPC), and ultra-high-performance (UHPC) concrete. The mechanisms causing F-T damage are discussed, specifically based on expansion of freezable water under negative temperature and thermal stress arising from differences in the coefficient of thermal expansion of cement and aggregates. To quantify damage, two parameters—namely, mass loss ratio (MLR) and relative dynamic elastic modulus (RDEM)—are compiled for different classes of concrete. Results show that UHPC exhibited much lower increase in MLR and reduction in RDEM than NC and HPC, respectively. The effects of F-T loading on other mechanical properties of concrete such as compressive strength, flexural strength, tensile strength and stress-strain relationship are also investigated in this paper as possible parameters to help characterize F-T resistance. It is found that F-T will decrease the peak stress but increase the peak strain, and the flexural strength has the fastest loss rate for NC, HPC, HSC and UHPC, respectively. As concrete under F-T environment is often exposed to chloride, the significance of sodium chloride (NaCl) concentration and chloride diffusion coefficient (CDC) on HSC and UHPC under NaCl solution are studied. UHPC exhibits better resistance on chloride diffusion after F-T action due to denser internal pore structure. To improve the F-T resistance of concrete, the performance of two supplementary cementitious admixtures, fly ash and silica fume, to partially replace cement are studied. Results show that the appropriate fly ash replacement of 10 to 30% or silica fume replacement of 5 to 10% is found to enhance the F-T resistance. In addition, introducing fibers such as PVA or PP can improve the F-T resistance significantly, although using the wrong proportion may have a negative effect. Using combined admixture of polyvinyl alcohol and polyethylene fiber with 1.5% volume in cement-based composites reduces strength degradation caused by F-T loadings.

DOI:

10.14359/51725781


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