scholarly journals Properties of Ambient-Cured Normal and Heavyweight Geopolymer Concrete Exposed to High Temperatures

Materials ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 740 ◽  
Author(s):  
Farhad Aslani ◽  
Zohaib Asif
Keyword(s):  
Mass Loss ◽  
High Temperatures ◽  
Offshore Structures ◽  
Normal Weight ◽  
Geopolymer Concrete ◽  
Coarse Aggregates ◽  
Residual Properties ◽  
New Type ◽  
Heavyweight Concrete ◽  
Underwater Structures

Ambient-cured heavyweight geopolymer concrete (HWGC) is a new type of concrete that combines the benefits of both heavyweight concrete (HWC) and geopolymer concrete (GC). HWGC provides proper protection from the sources that emit harmful radiations in medical and nuclear industries. Furthermore, HWGC may also be used in offshore structures for pipeline ballasting and similar underwater structures. In this study, heavyweight aggregates (magnetite) have been used and replaced by normal-weight coarse aggregates in GC at volume ratios of 50, 75, and 100% to attain heavyweight classification according to British standards. This study investigates the impacts of high temperatures on standard ambient-cured geopolymer concrete and ambient-cured HWGC through its residual properties regarding compressive and tensile strengths, mass loss, spalling intensity, and flexural strength. The residual properties were examined by heating 100 × 200 mm cylinder specimens to 100, 300, 600, and 900 °C. The results indicated that the maximum compressive strengths of 40.1 and 39.0 MPa were achieved by HWGC at 300 and 100 °C, respectively. The overall result shows that the strength of HWGC increases by increasing magnetite aggregate proportion, while the mass loss, intensity of spalling, and loss of strengths is proportional to temperature after a certain point. Minor spalling with holes and cracking was observed only at 900 °C in HWGC.

scholarly journals Development of Heavyweight Self-Compacting Concrete and Ambient-Cured Heavyweight Geopolymer Concrete Using Magnetite Aggregates

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1035 ◽  
Author(s):  
Afsaneh Valizadeh ◽  
Farhad Aslani ◽  
Zohaib Asif ◽  
Matt Roso
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Tensile Tests ◽  
Offshore Structures ◽  
Experimental Program ◽  
Geopolymer Concrete ◽  
Self Compacting Concrete ◽  
Coarse Aggregates ◽  
Maximum Compressive Strength ◽  
Heavyweight Concrete

Heavyweight self-compacting concrete (HWSCC) and heavyweight geopolymer concrete (HWGC) are new types of concrete that integrate the advantages of heavyweight concrete (HWC) with self-compacting concrete (SCC) and geopolymer concrete (GC), respectively. The replacement of natural coarse aggregates with magnetite aggregates in control SCC and control GC at volume ratios of 50%, 75%, and 100% was considered in this study to obtain heavyweight concrete classifications, according to British standards, which provide proper protection from sources that emit harmful radiations in medical and nuclear industries and may also be used in many offshore structures. The main aim of this study is to examine the fresh and mechanical properties of both types of mixes. The experimental program investigates the fresh properties of HWSCC and HWGC through the slump flow test. However, J-ring tests were only conducted for HWSCC mixes to ensure the flow requirements in order to achieve self-compacting properties. Moreover, the mechanical properties of both type of mixes were investigated after 7 and 28 days curing at an ambient temperature. The standard 100 × 200 mm cylinders were subjected to compressive and tensile tests. Furthermore, the flexural strength were examined by testing 450 × 100 × 100 mm prisms under four-point loading. The flexural load-displacement relationship for all mixes were also investigated. The results indicated that the maximum compressive strength of 53.54 MPa was achieved by using the control SCC mix after 28 days. However, in HWGC mixes, the maximum compressive strength of 31.31 MPa was achieved by 25% magnetite replacement samples. The overall result shows the strength of HWSCC decreases by increasing magnetite aggregate proportions, while, in HWGC mixes, the compressive strength increased with 50% magnetite replacement followed by a decrease in strength by 75% and 100% magnetite replacements. The maximum densities of 2901 and 2896 kg/m3 were obtained by 100% magnetite replacements in HWSCC and HWGC, respectively.

scholarly journals The Effect of Ordinary Portland Cement Substitution on the Thermal Stability of Geopolymer Concrete

Materials ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 2501 ◽  
Author(s):  
Hongen Zhang ◽  
Lang Li ◽  
Tao Long ◽  
Prabir Sarker ◽  
Xiaoshuang Shi ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Mass Loss ◽  
Residual Strength ◽  
Geopolymer Concrete ◽  
Sem Images ◽  
Sodium Aluminosilicate ◽  
Residual Properties ◽  
Original Strength ◽  
Sodium Aluminosilicate Hydrate ◽  
Heating Up

The influence of using cement on the residual properties of fly ash geopolymer concrete (FAGC) after exposure to high temperature of up to 800 °C was studied in terms of mass loss, residual compressive strength and microstructure. The mass loss was found to increase with the increase of exposure temperature, which is attributed to vaporization of water and dehydroxylation of sodium aluminosilicate hydrate (N-A-S-H) gels. The dehydroxylation of calcium silicate hydrate (C-S-H) gels and the disintegration of portlandite were responsible for higher mass loss ratio of FAGCs containing cement. The results showed that cement could increase compressive strength of FAGCs up to 200 °C, after which a significant reduction in residual strength was observed. It was found that FAGCs without cement yielded higher residual strength than the original strength after heating up to 600 °C. The observed increase of compressive strength up to 200 °C was attributed to the secondary geopolymerization which was evidenced in the scanning electronic microscopy (SEM) images.

scholarly journals A new screening test to evaluate the presence of oxidizable sulphide minerals in coarse aggregates

2021 ◽  
Author(s):  
Bassili Guirguis ◽  
Medhat Shehata
Keyword(s):  
Mass Loss ◽  
Screening Test ◽  
Room Temperature ◽  
Colour Change ◽  
Test Solution ◽  
Oxidizing Agent ◽  
Sulphide Minerals ◽  
Coarse Aggregates ◽  
Aggregate Sample ◽  
Simple Screening

A simple screening test was proposed in order to test coarse aggregates for their potential to cause damage when used in concrete due to the oxidation of sulphide phases. The test involves submerging an aggregate sample in an oxidizing agent and measuring the mass loss. Samples with no known oxidizable sulphides showed a mass loss of <1.0% after one week of testing at room temperature. Samples of oxidizable sulphides showed a mass loss higher than 3.5% and changes in the colour of the test solution. It is proposed that aggregates which achieve a mass loss of less than 0.50% and no colour change in the test solution be accepted.

Residual properties of recycled concrete after exposure to high temperatures

2019 ◽  
Vol 71 (15) ◽  
pp. 781-793 ◽  
Author(s):  
Zongping Chen ◽  
Jianjia Chen ◽  
Fan Ning ◽  
Yi Li
Keyword(s):  
High Temperatures ◽  
Recycled Concrete ◽  
Residual Properties

A study of the development of a new type of bulb bracket for offshore structures using suitable casting steel

2010 ◽  
Author(s):  
Tae-Won Kim ◽  
Chung-Gil Kang ◽  
Sang-Sik Park ◽  
F. Barlat ◽  
Y. H. Moon ◽  
...  
Keyword(s):  
Offshore Structures ◽  
New Type ◽  
Casting Steel

New Type of Defects Explored by Theory: Silicon Interstitial Clusters in SiC

2008 ◽  
Vol 600-603 ◽  
pp. 413-416
Author(s):  
Adam Gali ◽  
T. Hornos ◽  
Nguyen Tien Son ◽  
Erik Janzén
Keyword(s):  
Ab Initio ◽  
High Temperatures ◽  
Vibration Modes ◽  
Local Vibration ◽  
Ionization Energies ◽  
New Type ◽  
Carbon Interstitial ◽  
Small Clusters

We have studied the small clusters of silicon and carbon interstitials by ab initio supercell calculations in 4H-SiC. We found that silicon interstitials can form stable and electrically active complexes with each other or with a carbon interstitial. Local vibration modes and ionization energies were also calculated in order to help the identification of the defects. We propose that silicon interstitials can emit from these clusters at relatively high temperatures, which may play an important role in the formation of the DI center.

scholarly journals Residual Properties Analysis of Steel Reinforced Recycled Aggregate Concrete Components after Exposure to Elevated Temperature

2018 ◽  
Vol 8 (12) ◽  
pp. 2377 ◽  
Author(s):  
Zongping Chen ◽  
Rusheng Yao ◽  
Chenggui Jing ◽  
Fan Ning
Keyword(s):  
Elevated Temperature ◽  
Energy Dissipation ◽  
Mass Loss ◽  
Bearing Capacity ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Aggregate Concrete ◽  
Residual Properties ◽  
Significant Fluctuation ◽  
Capacity Degradation

The application of recycled aggregate concrete (RAC) has developed rapidly in recent years. But how to evaluate the residual properties of RAC after the fires is more beneficial to the further popularization and application of RAC. This paper presents the residual properties of RAC and steel reinforced recycled aggregate concrete (SRRAC) components after exposure to elevated temperature. A total of 176 specimens (120 rectangular prisms specimens, 24 SRRAC short columns and 32 SRRAC beams) were designed and tested after exposure to elevated temperature. The parameters were considered in the test, including replacement percentage of recycled coarse aggregate (0%, 30%, 50%, 70% and 100%) and exposure to different temperatures (20, 200, 400, 600 and 800 degrees centigrade). According to the test results, heat damage and residual properties of specimens were analyzed in detail, such as surface change, mass loss, bearing capacity degradation, stiffness degradation, ductility and energy dissipation of specimens under the elevated temperature. The results showed that a series of significant physical phenomena occurred on the surface of RAC and SRRAC components after exposure to elevated temperature, such as the color changed from green-grey to gray-white, chapped on the concrete surface after 400 degrees centigrade and the mass loss of concrete is less than 10%. The degradation of mechanical properties degenerated significantly with the increase of temperature, such as the strength of RAC, and compressive capacity, bending capacity, shear capacity and stiffness of SRRAC components, among that, the degradation of the strength of RAC was most obvious, up to 26%. The ductility and energy dissipation of SRRAC components were insignificant affected by the elevated temperature. Mass loss ratio, peak deformation and bearing capacity showed a slight increase trend with the increase of replacement percentage. But the stiffness showed significant fluctuation when replacement percentage was 70% to 100%. And the ductility and energy dissipation showed significant fluctuation when replacement percentage was 30% to 70%.

NDE/SHM of Underwater Structures: A Review

2012 ◽  
Vol 83 ◽  
pp. 208-216 ◽  
Author(s):  
P. Rizzo
Keyword(s):  
Natural Gas ◽  
Retaining Walls ◽  
Offshore Structures ◽  
Structural Failure ◽  
The People ◽  
Nondestructive Techniques ◽  
Water Mains ◽  
Oil And Natural Gas ◽  
Underwater Structures

Subsea infrastructures and broadly speaking any structure containing or surrounded by water such as water mains represent an important element of modern civilization. An arbitrary classification could consist of five groups: offshore structures that serve to extract oil or natural gas from the sea bead; communication cables; pipelines that carry oil and natural gas; naval vessels (ships and submarines); waterfront facilities such as piers, retaining walls, and docks. The occurrence of structural failure of any of these systems can have serious consequences for the people, the environment, and the economy. In this paper we describe the most important nondestructive techniques adopted to assess the health of offshore structures, pipelines, and marine facilities.

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