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International Concrete Abstracts Portal

Showing 1-5 of 355 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: 

18-345

Date: 

July 1, 2020

Author(s):

Ashutosh G. Dabli, Abhay N. Bambole, and Kamalkishor M. Bajoria

Publication:

Materials Journal

Volume:

117

Issue:

4

Abstract:

The use of strain relief method is one of the most direct methods for determination of in-place stresses. In this method, a hole is drilled in the concrete member and the change in strain in the vicinity of the hole, on the surface of the member, is measured by means of electrical resistance strain gauges (ERSG). This change in strain due to drilling is used to assess the in-place stress in the member using constitutive relationship and calibration coefficient. This paper presents the experimental application of incremental hole drilling method (IHDM) in concrete under uniaxial stress. A small hole of 25 mm diameter and 40 mm deep was drilled incrementally to estimate the in-place stress in an axially loaded column with minimum damage. Dry drilling was used to eliminate the effect of swelling due to moisture (water) during the drilling. The experimental strain released was then correlated with an analytical solution using the theory of elasticity and finite element method (FEM). The excellent agreement of experimental results with analytical and numerical values of strain released suggests that IHDM can be conveniently used to evaluate in-place stresses in columns.

DOI:

10.14359/51724612


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: 

19-161

Date: 

March 1, 2020

Author(s):

Sarah Mariam Abraham and G. D. R. N. Ransinchung

Publication:

Materials Journal

Volume:

117

Issue:

2

Abstract:

A comprehensive analysis on the effect that fine fraction of reclaimed asphalt pavement (RAP) aggregates can produce on the fresh properties, strength, and durability characteristics of cementitious mixtures—that is, mortar and concrete—when used as partial or full replacement of natural fine aggregates (NA) is represented in this study. The replacements of NA were done by volume at 25, 50, 75, and 100% catering to the difference in specific gravity between the aggregates. The cement was also partially replaced by volume using silica fume and activated sugarcane bagasse ash (SCBA). To achieve this objective, effect of RAP aggregates was studied in both mortar and concrete. Although recycling is not a novel concept, altering the conventional mixture design and testing methodology whilst using RAP aggregates were looked into. The application of this study was focused upon rigid pavements, where flexural strength is of great importance. The mixtures considered did achieve the design flexural strength and protected the reinforcement from corrosion due to basic pH and absence of carbonation.

DOI:

10.14359/51722398


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