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Showing 1-5 of 52 Abstracts search results

Document: 

22-015

Date: 

January 1, 2023

Author(s):

Alaa M. Rashada and Yun Bai

Publication:

Materials Journal

Volume:

120

Issue:

1

Abstract:

The properties of sodium sulfate-activated ground-granulated blast-furnace slag (shortened as slag) pastes under carbonation attack were analyzed and compared with the uncarbonated specimens in this paper. A slag with two different finenesses—namely, 250 and 500 m2/kg—was activated by sodium sulfate at two concentrations (1 and 3% Na2O equivalent). After the initial 28 days of curing, the hardened pastes were carbonated in 5% CO2 and relative humidity (RH) of 65% at 20 ± 1°C for 2, 4, and 12 weeks. The carbonation depth, compressive strength, and pH value of the carbonated specimens were measured and compared with the uncarbonated counterparts exposed to a natural concentration of CO2. X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy were employed to characterize the reaction products and microstructure of both carbonated and uncarbonated alkali-activated slag (AAS) samples. The results indicated that the specimens prepared with the coarse slag and low Na2SO4 concentration (1% Na2O equivalent) showed the worst carbonation resistance. Increasing slag fineness has a leverage effect on increasing the carbonation resistance. However, increasing Na2SO4 concentration (3% Na2O equivalent) led to more notable carbonation resistance than increasing slag fineness. By combining the fine slag with high Na2SO4 concentration, almost no changes in the pH, carbonation depth, and compressive strength were noticed even after 12 weeks of carbonation, showing a superb resistance to carbonation attack.

DOI:

10.14359/51737291


Document: 

21-366

Date: 

May 1, 2022

Author(s):

Sara Seyedfarizani, Basem H. AbdelAleem, and Assem A. A. Hassan

Publication:

Materials Journal

Volume:

119

Issue:

3

Abstract:

This study aimed to investigate the effect of different curing conditions/temperatures on the compressive strength, flexural strength (FS), modulus of elasticity (ME), and abrasion resistance of concrete developed with different mixture compositions. The studied parameters included different water-binder ratios (w/b) (0.4 and 0.55), different coarse-to-fine aggregate ratios (C/F) (0.7 and 1.2), addition of steel fibers (SFs), and different supplementary cementitious materials (SCMs) (metakaolin [MK] and silica fume [SLF]). The developed mixtures were cured at four different curing conditions: moist curing (C1); air curing (C2); and cold curing, including +5°C curing (C3) and –10°C curing conditions (C4). The results indicated that the effect of curing concrete samples at cold curing conditions was more pronounced on FS results compared to all other mechanical properties results, in which the FS reduced by 23% and 41% at +5°C and –10°C curing conditions, respectively, compared to at the moist-curing condition. Despite the considerable enhancement in the mechanical properties and abrasion resistance when SFs or SCMs were used in the mixtures, cold curing of mixtures with SCMs or SFs significantly reduced this enhancement. The results also revealed that the rotating-cutter test results of the mixture with SFs were more affected by cold curing conditions than the sandblasting test results.

DOI:

10.14359/51734619


Document: 

21-022

Date: 

March 1, 2022

Author(s):

Alaa M. Rashad

Publication:

Materials Journal

Volume:

119

Issue:

2

Abstract:

The effect of a fixed ratio of different additives on the carbonation behavior of ground-granulated blast-furnace slag (shortened as slag) activated with a fixed concentration of Na2SO4 was investigated. Slag was activated by 1% (Na2O-equivalent) Na2SO4 (M0) and partially replaced with 10%, by weight, of one of the following additives: limestone powder (LS10), fly ash (FA10), portland cement (PC10), silica fume (SF10), metakaolin (MK10), and hydrated lime (HL10). The compressive strength values were measured and compared with those activated with the traditional common activators. After 28 days of curing, the pastes were exposed to 5% concentration of CO2 coupled with 20 ± 1°C and 65% surrounding temperature and relative humidity, respectively, for different durations of 2, 4, and 8 weeks. Compressive strength, pH value, and carbonation depth of carbonated specimens were determined and compared with noncarbonated ones exposed to the same conditions but at a natural CO2 concentration. The results were analyzed with special tools to determine the different phases. The results revealed that it is possible to increase the carbonation resistance of slag activated with Na2SO4 by using some additives. The specimens of LS10 exhibited the highest carbonation depth, while SF10 specimens exhibited the lowest carbonation depth. The remaining additives showed intermediate results between LS10 and SF10.

DOI:

10.14359/51734400


Document: 

20-528

Date: 

September 1, 2021

Author(s):

M. C. de Moraes, I. S. Buth, C. Angulski da Luz, E. A. Langaro, and M. H. F. Medeiros

Publication:

Materials Journal

Volume:

118

Issue:

5

Abstract:

Recently, alkali-activated cement (AAC) has been studied to partially replace portland cement (PC) to reduce the environmental impact caused by civil construction and the cement industry. However, with regard to durability, few studies have addressed the behavior of AAC. This study aimed to evaluate the performance of AAC made from blast-furnace slag with contents of 4 and 5% sodium hydroxide as an activator (Na2Oeq of 3.72% and 4.42%, respectively) when subjected to alkali-aggregate reaction (AAR). Length variation tests were carried out on mortar bars immersed in NaOH solution (1 N of NaOH, T = 80°C [176°F]) and on concrete bars (T = 60°C [140°F], RH = 95%); compressive strengths tests and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analyses were also made. Two types of PC were used as a comparison. The results showed good behavior of the AAC in relation to the AAR, with expansions lower than those established by the norm (34% of the limit) and without the finding of losses of mechanical resistance or structural integrity. The alkaline activator content had a small influence on the behavior of the AACs, in which the lowest amount of NaOH (4%) showed fewer expansions (only 15% of the limit established by the norm). Even for the highest activator content (5%), the results were good and comparable to those of PC with pozzolans, which is recommended for the inhibition of AAR.

DOI:

10.14359/51732937


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


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