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International Concrete Abstracts Portal

Showing 1-5 of 342 Abstracts search results

Document: 

18-512

Date: 

July 1, 2020

Author(s):

Mahdi Valipour and Kamal H. Khayat

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

Ultra-high-performance concrete (UHPC) can be vulnerable to variations in materials properties and environmental conditions. In this paper, the sensitivity of UHPC to changes in mixing, casting, curing, and testing temperatures ranging between 10 and 30 ± 2°C (50 and 86 ± 3.5°F) was investigated. The investigated rheological properties, mechanical properties, and shrinkage of UHPC are shown to be significantly affected by temperature changes. UHPC made with either binary or ternary binder containing fly ash (FA) or slag cement exhibited greater robustness than mixtures prepared with 25% silica fume. UHPC made with 60% FA necessitated the lowest high-range water-reducing admixture demand. With temperature increase, the yield stress of UHPC mixtures increased by up to 55%, and plastic viscosity decreased by up to 45%. This resulted in accelerating initial and final setting times by up to 4.5 and 5 hours, respectively. The increase of temperature from 10 to 30 ± 2°C (50 ± to 86 ± 3.5°F) led to a 10 to 75% increase in compressive, splitting tensile, and flexural strengths and modulus of elasticity and 15 to 60% increase in autogenous shrinkage.

DOI:

10.14359/51724613


Document: 

19-057

Date: 

May 1, 2020

Author(s):

A. Pczieczek, C. Effting, A. Schackow, I. Ribeiro Gomes, and D. V. Ferronato da Silva

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

This work aimed to analyze the physical and mechanical properties of mortar with the addition of fly ash and rubber concentrations used on building walls. The mortars had 5 and 10% of fine aggregate mass replaced by rubber and added fly ash in proportions of 10 and 20% according to the volume of cement. Ground fly ash addition in the mortar, in turn, increased the compressive strength by 18% at 28 days compared to the reference mortar, assuring a greater durability against sulfate attacks and presenting lower mass loss during exposure to sodium sulfate. The mortar containing 20% of ground fly ash and 5% of rubber presented tensile adhesion strength of 0.33 MPa at 65 days. A numerical simulation of the mortar microstructure was carried out using the finite element method to study its thermomechanical behavior. Stress distribution and cracking field of the model were also obtained.

DOI:

10.14359/51724594


Document: 

19-232

Date: 

May 1, 2020

Author(s):

Mohamed M. Sadek, Mohamed K. Ismail, and Assem A. A. Hassan

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

This study aimed to optimize the use of fine and coarse expanded slate lightweight aggregates in developing successful semi-lightweight self-consolidating concrete (SLWSCC) mixtures with densities ranging from 1850 to 2000 kg/m3 (115.5 to 124.9 lb/ft3) and strength of at least 50 MPa (7.25 ksi). All SLWSCC mixtures were developed by replacing either the fine or coarse normal-weight aggregates with expanded slate aggregates. Two additional normal-weight self-consolidating concrete mixtures were developed for comparison. The results indicated that due to the challenge in achieving acceptable self-consolidation, a minimum binder content of at least 500 kg/m3 (31.2 lb/ft3) and a minimum water-binder ratio (w/b) of 0.4 were required to develop successful SLWSCC with expanded slate. The use of metakaolin and fly ash were also found to be necessary to develop successful mixtures with optimized strength, flowability, and stability. The results also showed that SLWSCC mixtures made with expanded slate fine aggregate required more high-range water-reducing admixture than mixtures made with expanded slate coarse aggregate. However, at a given density, mixtures developed with expanded slate fine aggregate generally exhibited better fresh properties in terms of flowability and passing ability, as well as higher strength compared to mixtures developed with expanded slate coarse aggregate.

DOI:

10.14359/51722407


Document: 

19-205

Date: 

May 1, 2020

Author(s):

Rabab Allouzi, Aya Al Qatawna, and Toqa Al-Kasasbeh

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

Foamed concrete is currently studied to investigate its feasibility to be used structurally to produce a lightweight concrete mixture that is workable and has sufficient mechanical properties. This encouraged this research to design a foamed concrete mixture to be used in the construction industry. The main parameters that shall be satisfied for structural use are the workability, density less than 1900 kg/m3, and minimum cylinder compressive strength of 17 MPa (2500 ksi) based on ACI 213R. In this paper, 14 different foamed concrete mixtures are designed and tested to investigate their applicability. As fly ash quality affects foamed concrete permeability and as foamed concrete has low resistance to concentrated stresses, the proposed mixtures do not contain fly ash and are reinforced with polypropylene (PP) fibers. The effect of water-cement ratio (w/c), sand-cement ratio (s/c), PP fibers content, and the foam agent content are investigated. It is found that the compressive strength increases with the increase in density. The optimum s/c is 1:1, w/c is 0.4, and the PP fibers content is 1% by weight of cement. A relationship of splitting tensile strength relative to compressive strength is proposed.

DOI:

10.14359/51722405


Document: 

19-260

Date: 

May 1, 2020

Author(s):

Mohammed Farooq, Aamer Bhutta, and Nemkumar Banthia

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

Ambient-cured eco-friendly ductile geopolymer composites (EDGCs) with 2% uncoated polyvinyl alcohol (PVA) microfibers were developed using fly ash and slag hybrid binder in different proportions, natural sand, and sodium silicate and sodium hydroxide as alkaline activators. Two curing conditions, air-curing and water-curing at ambient temperature, were examined. Results showed that the 100% slag-EDGCs exhibited stiff workability, short setting time of 25 minutes, and provided highest compressive strength (82 to 85 MPa), while 100% fly ash-EDGCs had a long setting time of 4 hours and compressive strength was much lower (12 to 24 MPa). In terms of tensile stress-strain behavior, all EDGCs demonstrated a strain hardening response. The 100% fly ash-EDGCs had a low tensile strength around 3 MPa with high tensile strain capacity (>3%). On the other hand, 100% slag-EDGCs had much higher tensile strength (>5 MPa) with reduced ductility due to fiber rupture resulting from an over-optimal bond between the PVA fibers and EDGC matrix.

DOI:

10.14359/51724597


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