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International Concrete Abstracts Portal

Showing 1-5 of 133 Abstracts search results

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: 

18-284

Date: 

May 1, 2020

Author(s):

S. C. L. Lima, L. C. B. Costa, K. C. S. Defáveri, J. M. Franco de Carvalho, R. A. F. Peixoto, and G. J. Brigolini

Publication:

Materials Journal

Volume:

117

Issue:

3

Abstract:

The mining industry is responsible for various environmental problems, including the extraction of natural resources and the generation of a significant volume of waste. The use of such residues in the construction industry as supplementary cementitious material (SCM) is one possible solution to minimize its disposal and a way for both industries to improve their eco-efficiency. This research aims to study the pozzolanic potential of the residue generated in slate cutting, as well as to compare the current standard methods applied to verify the pozzolanic activity (strength activity index) and direct methods based on calcium hydroxide consumption. A milling study in a planetary ball mill was carried out to evaluate the effects of particle size distribution on reactivity. The pozzolanic activity was investigated based on current standard methods (strength activity index) and analytical evaluations. The results of calcium hydroxide consumption were obtained from simultaneous thermal analysis (thermogravimetric and thermal differential analysis) and X-ray diffraction. Conflicting results between the current standard and direct methods were observed. The tested specimens with low or inexpressive calcium hydroxide consumption presented a high-strength activity index, while the specimens that presented a higher calcium hydroxide consumption showed a strength activity index below the minimum values required by the current standards. The results pointed to the potential use of slate cutting waste and contributes to the discussions about the phenomena neglected by the current strength activity index standard.

DOI:

10.14359/51724611


Document: 

18-355

Date: 

November 1, 2019

Author(s):

Rafat Siddique, Malkit Singh, and Arpit Kumar Singhal

Publication:

Materials Journal

Volume:

116

Issue:

6

Abstract:

The use of unprocessed low-calcium wood ash as partial substitution of natural sand in manufacturing of concrete has been explored in the present study. X-ray diffraction (XRD) spectrum indicates the presence of amorphous as well as crystalline silica in unprocessed wood ash. The total composition of silica, alumina, and ferric of 92.93% qualifies the unprocessed wood ash to be used as pozzolanic material. Experimental tests were performed in laboratory for workability, strength, and durability properties of concrete incorporating 0, 5, 10, 15, and 20% wood ash as substitution of natural sand. It was observed that at a fixed water-cement ratio (w/c), the slump of concrete decreased on inclusion of unprocessed wood ash as partial substitution of natural sand. The compressive strength and splitting tensile strength of concrete mixtures made with unprocessed wood ash were lower than control concrete. The wood ash concrete mixtures, except the concrete mixture containing 5% unprocessed wood ash, displayed higher water absorption, sorptivity, and chloride-ion penetrability compared to control concrete. XRD analysis of powdered concrete specimens indicated no qualitative change in phase formation on incorporation of unprocessed wood ash.

DOI:

10.14359/51718052


Document: 

18-136

Date: 

November 1, 2019

Author(s):

Ashish Kumer Saha and Prabir Kumar Sarker

Publication:

Materials Journal

Volume:

116

Issue:

6

Abstract:

This study evaluates the acid resistance of cement mortar using granulated ferronickel slag (FNS) as fine aggregate and fly ash or ground FNS (GFNS) as a supplementary cementitious material (SCM). The deterioration was evaluated by visual inspection, and changes of mass and strength after immersion in 1% sulfuric acid solution for up to 180 days. Acid resistance was marginally reduced when 50% volume of sand was replaced by FNS. While the control specimens suffered significant spalling and strength loss, the use of fly ash or GFNS considerably reduced the deterioration. This is attributed to the formation of a protective zone and densification of microstructure by the pozzolanic reaction, as confirmed by strength activity index, permeable voids, thermogravimetric analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Overall, the specimens with FNS aggregate and GFNS or fly ash showed less deterioration than the control specimens after prolonged acid exposure.

DOI:

10.14359/51718051


Document: 

18-010

Date: 

November 1, 2019

Author(s):

Konstantinos Sotiriadis, Eleni Rakanta, Maria Eleni Mitzithra, George Batis, and Sotirios Tsivilis

Publication:

Materials Journal

Volume:

116

Issue:

6

Abstract:

The development of environmentally friendly cementitious materials, efficient in preventing chloride ingress and decreasing reinforcement corrosion risk, is significantly important for structural applications exposed to corrosive conditions. This paper investigates the effect of natural pozzolana, fly ash, blast-furnace slag, and metakaolin on the behavior of portland-limestone cement concretes and mortars during storage in chloride-sulfate and chloride solutions at 5°C (41°F). Acid- and water-soluble chloride contents, and apparent chloride diffusion coefficients, were determined in concretes. Reinforcement corrosion half-cell potential and current density, mass loss of steel reinforcing bars, and carbonation depth were monitored in mortars. The employment of mineral admixtures decreased chloride ingress and reinforcement corrosion during specimens’ exposure to chloride solution; however, the presence of sulfates in the corrosive environment prevented their improving effect. Mineral admixtures increased chloride binding and the resistance of concrete against chloride diffusion, while they also showed similar efficiency in preventing reinforcement corrosion. Sulfates facilitated chloride ingress, hindered chloride binding, and promoted reinforcement corrosion.

DOI:

10.14359/51716820


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