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International Concrete Abstracts Portal

Showing 1-5 of 327 Abstracts search results

Document: 

19-328

Date: 

July 1, 2020

Author(s):

Jedadiah F. Burroughs, Charles A. Weiss Jr., John E. Haddock, and W. Jason Weiss

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

This study presents the application of an analytical model to describe the rheological behavior of cement pastes containing silica fume at replacement rates of up to 30% by mass. The analytical model hypothesizes how water interacts with particles in a cementitious system. The coating thickness of water surrounding each particle in the system is estimated. This coating thickness is shown to correlate strongly with measured rheological properties when fit to the Herschel-Bulkley model. To calculate coating thickness, it is necessary to account for the water absorbed by nonhydraulic components in the system, whether aggregate, supplementary cementitious materials, or mineral. The results suggest that silica fume particles may be absorptive, and this absorption capacity, although small, must be considered when designing water-starved cementitious materials. The experimental investigation involved the rheological testing of three water-binder ratios (0.20, 0.30, 0.45), three silica fume replacement levels (10%, 20%, 30%), and eight different silica fume products.

DOI:

10.14359/51724626


Document: 

19-281

Date: 

July 1, 2020

Author(s):

Nader Ghafoori, Iani Batilov, and Meysam Najimi

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

The objective of this study was to evaluate the effectiveness of colloidal nanosilica (nS) as a nanomaterial and pozzolanic admixture to mitigate the deteriorative effects of sodium sulfate-based physical salt attack (PSA) on portland cement mortars. Mortar mixtures of an ASTM C150 Type II (<8% C3A) or a Type V (<5% C3A) portland cement were prepared with 0, 3, and 6% cement replacements with either nS or microsilica (mS). Test samples were subjected to 3 years of exposure under a constant or cyclic PSA-conducive environment. The PSA results were supported with additional water absorption, rapid sulfate ion permeability (RSPT), and porosimetry testing. The Type V cement mortars containing nS exhibited the most observable scaling and flaking under both conditions of PSA exposure. The addition and increase in cement replacement with nS had a clear detrimental effect to PSA resistance for both cement types and both types of PSA exposure. Results indicated nS reduces permeability and diffusion in mixtures of either cement type which, for PSA, the denser and more refined pore network proved conducive to higher damaging tensile stresses and distress. The larger the measured volume of permeable pore space through absorption, the less susceptible the mortars were to PSA, which is counterproductive to conventional good practice of designing high-durability concrete via reducing permeability and sorption, and increasing a mixture’s watertightness.

DOI:

10.14359/51725779


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: 

19-240

Date: 

May 1, 2020

Author(s):

Carolina Boschmann Käthler, Ueli Michael Angst, Karla Hornbostel, and Bernhard Elsener

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

Cracks in concrete are expected to accelerate the degradation of reinforced concrete—mainly reinforcement corrosion. Previous literature studies have shown that the initiation time can decrease due to cracks, whereas the accelerating effect on corrosion propagation has no clear experimental evidence. This paper critically assesses how different common experimental setups may influence the test results. It is found that, particularly, the exposure duration and condition, the water-binder ratio (w/b), and the crack width have an impact on the outcome of the experimental study about corrosion rates in cracked concrete. Hence, these parameters should be carefully considered when designing experiments to study the influence of cracks. Recommendations for future research work are given.

DOI:

10.14359/51722408


Document: 

19-244

Date: 

May 1, 2020

Author(s):

Hadi Bahmani, Davood Mostofinejad, and Sayyed Ali Dadvar

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

This study investigated the effects of different synthetic and mineral fibers and limestone powder on the mechanical properties of ultra-high-performance fiber-reinforced concrete (UHPFRC). For the purpose of this study, 16 mixture designs and 204 prism specimens were prepared and cured under either of wet or autoclave conditions. Measurements revealed that mixtures containing synthetic fibers recorded considerable compressive and flexural strengths close to the steel fiber-reinforced mixtures. Specimens reinforced with nylon fibers as the best fibers in this study exhibited a much better flexural performance in terms of flexural strength, deflection capacity, and post-peak ductility than did those containing ceramic and polyester fibers. Finally, specimens containing limestone powder recorded acceptable flexural strength, which was close to those only containing silica fume. The X-ray diffraction (XRD) test showed that limestone powder increased ettringite content due to the dilution effect at 180 days as the main reason for decreasing of compressive strength of mixtures.

DOI:

10.14359/51724596


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