scholarly journals Composition and selected properties of low pH mortars and concretes for radioactive waste repositories

2020 ◽  
Vol 322 ◽  
pp. 01033
Author(s):  
An Cheng ◽  
Wei-Ting Lin ◽  
Sao-Jeng Chao ◽  
Hui-Mi Hsu
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Silica Fume ◽  
Spent Nuclear Fuel ◽  
Cementitious Materials ◽  
Low Ph ◽  
Engineering Properties ◽  
Filling Materials ◽  
Radioactive Waste Repositories ◽  
Waste Repositories

Conventional cementitious materials as tunnel supporting materials are utilised in the construction of the final repository for spent nuclear fuel. However, the use of cementitious material releases alkaline ions from pH12 to pH13 plumed into groundwater. Such a high pH is detrimental to the performance of the bentonite functioning, which may possibly enhance the dissolution and alteration of the fracture buffer and filling materials. Instead, low-pH cementitious materials are being developed for use in geological repositories. This study is aimed at evaluating the usability of low-pH cementitious materials containing 40% silica fume or composites blended with 20% silica fume and 40% fly ash. Engineering properties were analysed and verified through experimental research using the flow, compressive strength, pH measurement and hydraulic conductivity. Test results show that the replacement level with 40% of silica fume or 20% of silica fume and 40% of fly ash was suitable for the mixture of low-pH cementitious. Compared to the compressive strength and water permeability of ordinary cementitious, those of low-pH cementitious enhanced better engineered performances at the age of 91 days. The information is contributed us to establish the long-term durability and environmental requirements of disposal repositories in Taiwan.

Durability of Sustainable Self-Consolidating Concrete

2018 ◽  
Vol 765 ◽  
pp. 285-289
Author(s):  
Osama Ahmed Mohamed ◽  
Waddah Al Hawat ◽  
Omar Fawwaz Najm
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Silica Fume ◽  
Cementitious Materials ◽  
Chloride Penetration ◽  
Supplementary Cementitious Materials ◽  
Test Results ◽  
Self Consolidating Concrete ◽  
Human Footprint ◽  
Granulated Blast Furnace Slag

Supplementary cementitious materials such as fly ash, silica fume and ground granulated blast furnace slag (GGBS) have been used widely to partially replace cement in producing self-consolidating concrete (SCC). The production of cement is associated with emission of significant amounts of CO2 and increases the human footprint on the environment. Fly ash, silica fume, and GGBS are recycled industrial by-products that also impart favorable fresh and hardened properties on concrete. This study aims to assess the effect of the amounts of fly ash and silica fume on strength and chloride penetration resistance of concrete. Rapid Chloride Penetration Test (RCPT) was used to assess the ability of SCC to resist ingress of chlorides into concrete. SCC mixes with different dosages of fly ash and silica fume were developed and tested at different curing ages. Test results showed that replacing 20% of cement with fly ash produced the highest compressive strength of 67.96 MPa among all fly ash-cement binary mixes. Results also showed that replacing15% of cement with silica fume produced the highest compressive strength of 95.3 MPa among fly ash-cement binary mixes. Using fly ash and silica fume consistently increased the concrete resistance to chloride penetration at the early ages. Silica fume at all dosages results in low or very low levels of chloride penetration at all curing ages of concrete.

Development of an Alternative Cementitious Materials Based on Calcium Carbide Residue and Silica Fume

2021 ◽  
Vol 904 ◽  
pp. 435-440
Author(s):  
Thunthanut Inyai ◽  
Phongthorn Julphunthong ◽  
Panuwat Joyklad
Keyword(s):  
Compressive Strength ◽  
Portland Cement ◽  
Silica Fume ◽  
Ordinary Portland Cement ◽  
Raw Materials ◽  
Calcium Carbide ◽  
Cementitious Materials ◽  
Pozzolanic Reaction ◽  
Engineering Properties ◽  
Calcium Carbide Residue

The present study evaluated the engineering properties and microstructure of an alternative binder composed of calcium carbide residue and silica fume. The cementitious mechanisms of this alternative binder based on the pozzolanic reaction in raw materials. The ratio of calcium carbide residue and silica fume was decided based on the chemical composition of raw materials and their chemical reaction. The calcium carbide residue-silica fume mortar was prepared and tested for its compressive strength at several curing periods, with results then compared to conventional mortar made with ordinary Portland cement. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to investigate the microstructure of hardened mortars. The test results suggest that the compressive strength of calcium carbide residue-silica fume mortar continuously developed throughout the curing period. The relative compressive strength of calcium carbide residue-silica fume mortar reached 72.78% of the ordinary Portland cement mortar strength at 28 days curing age.

scholarly journals The Effect of Incorporating Ultra-Fine Spherical Particles on Rheology and Engineering Properties of Commercial Ultra-High-Performance Grout

Crystals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1040
Author(s):  
Wei-Ting Lin ◽  
Wen-Que Zhao ◽  
Yi-Hua Chang ◽  
Jiann-Shi Yang ◽  
An Cheng
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Silica Fume ◽  
High Performance ◽  
Hunan Province ◽  
Engineering Properties ◽  
Spherical Particles ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Volume Stability

In this study, ultra-fine spherical particles of silica fume and reactive ultra-fine fly ash were added to a mixture of commercial ultra-high-performance grout (UHPG) with the aim of enhancing the rheological properties, compressive strength, compactness, and permeability. This commercial UHPG study was conducted in collaboration with Triaxis Corporation (Changsha city, Hunan province, China). A water-to-binder ratio of 0.21 and a binder-to-fine aggregates ratio of 1.17 were used as fixed parameters, and the binders were a combination of type-II Portland cement, sulphoaluminate cement, silica fume, and reactive ultra-fine fly ash (RUFA). Polycarboxylate superplasticizer powder was used to control the rheology. The results revealed excellent compressive strength, volume stability, and resistance to chloride penetration. Mercury intrusion porosimetry and scanning electron microscopy tests revealed that the medium-sized RUFA particles with small silica fume particles completely filled the spaces between large cement particles to achieve optimal densification. This mixture also produced dense hydration and calcium-silicate-hydrates colloids, which filled the microstructures of the UHPG resulting in excellent engineering properties and durability. This commercially available UHPG mix responded to excellent compressive strengths approaching 120 MPa and exhibited good workability with a loss of slump-flow rate up to 33% after 60 min. It also exhibited very low abrasion resistance (0.5%), stable shrinkage and expansion rates (stabilization over 10 days), very low chloride diffusion coefficient (less than 0.1 × 10−14 m2/s) with a denser microstructure. This commercial UHPG (UHPG-120) has been developed to meet the needs of the market.

COMPRESSIVE STRENGTH AND THERMAL CONDUCTIVITY OF WATER AND AIR CURED PORTLAND CEMENT-FLY ASH-SILICA FUME MORTARS

2018 ◽  
Vol 17 (9) ◽  
pp. 2023-2030
Author(s):  
Arnon Chaipanich ◽  
Chalermphan Narattha ◽  
Watcharapong Wongkeo ◽  
Pailyn Thongsanitgarn
Keyword(s):  
Thermal Conductivity ◽  
Compressive Strength ◽  
Fly Ash ◽  
Portland Cement ◽  
Silica Fume

Sorption Mechanism of Carbon-14 by Hardened Cement Paste

1995 ◽  
Vol 412 ◽  
Author(s):  
K. Noshita ◽  
T. Nishi ◽  
M. Matsuda ◽  
T. Izumida
Keyword(s):  
Electrostatic Force ◽  
Cementitious Materials ◽  
Hardened Cement ◽  
Sorption Mechanism ◽  
Carbon 14 ◽  
Adsorption Sites ◽  
Radioactive Waste Repositories ◽  
Waste Repositories ◽  
Positively Charged

AbstractCarbon-14 sorption by cementitious materials should be enhanced to ensure the long term safety of radioactive waste repositories. The sorption mechanism of inorganic C- 14 (CO32- was investigated using batch sorption experiments and zeta potential measurements. The results suggested that C-14 was adsorbed onto the cement surface by an electrostatic force, due to the reaction between SiO2 and CaO contained in the cementitious composition. That is, SiO2 was originally negatively charged (SiO-) in cement, but became positively charged through the interaction of Ca2+. These positive sites on the SiO2 surface adsorbed inorganic C-14. Ordinary Portland cement (OPC) did not contain enough SiO2 compared with its CaO content to produce sufficient numbers of C-14 adsorption sites. The C-14 distribution coefficient (Kd) was increased from 2,000 to 7,000 mL/g by adding SiO2 to OPC.

Optimization of Concrete Porous Mix Using Slag as Substitute Material for Cement and Aggregates

2017 ◽  
Vol 865 ◽  
pp. 282-288 ◽  
Author(s):  
Jul Endawati ◽  
Rochaeti ◽  
R. Utami
Keyword(s):  
Compressive Strength ◽  
Blast Furnace ◽  
Fly Ash ◽  
Silica Fume ◽  
Blast Furnace Slag ◽  
Environmental Effect ◽  
Substitution Effect ◽  
Main Concern ◽  
Binder Material ◽  
Furnace Slag

In recent years, sustainability and environmental effect of concrete became the main concern. Substituting cement with the other cementitious material without decreasing mechanical properties of a mixture could save energy, reduce greenhouse effect due to mining, calcination and limestone refining. Therefore, some industrial by-products such as fly ash, silica fume, and Ground Iron Blast Furnace Slag (GIBFS) would be used in this study to substitute cement and aggregate. This substitution would be applied on the porous concrete mixture to minimize the environmental effect. Slag performance will be optimized by trying out variations of fly ash, silica fume, and slag as cement substitution material in mortar mixture. The result is narrowed into two types of substitution. First, reviewed from the fly ash substitution effect on binder material, highest compressive strength 16.2 MPa was obtained from mixture composition 6% fly ash, 3% silica fume and 17% grinding granular blast-furnace slag. Second, reviewed from slag types as cement substitution and silica fume substitution, highest compressive strength 15.2 MPa was obtained from mortar specimens with air-cooled blast furnace slag. It composed with binder material 56% Portland composite cement, 15% fly ash, 3% silica fume and 26% air-cooled blast furnace slag. Considering the cement substitution, the latter mixture was chosen.

scholarly journals Reliability of Unconventional Concrete: Improvement in Mix Design and Addition of Bacterial Admixture

2021 ◽  
Vol 9 (11) ◽  
pp. 136-149
Author(s):  
Burhan Afzal
Keyword(s):  
Carbon Dioxide ◽  
Compressive Strength ◽  
Bacillus Subtilis ◽  
Silica Fume ◽  
Carbon Dioxide Emissions ◽  
Substantial Reduction ◽  
Bacillus Sphaericus ◽  
Industrial Wastes ◽  
Engineering Properties ◽  
Environmental Damage

Abstract: Portland cement is used by the construction industries, which is known to be a heavy contributor of carbon dioxide emissions and environmental damage. Adding of industrial wastes like demolished old concrete OF structures, silica fume (SF) fly ash (FA) as additional cementing materials (SCMs) could result in a substantial reduction of the overall Carbon dioxide trace marks of the final concrete product. Use of these additional materials in construction industry especially in the making of concrete is highly challenging. Remarkable research efforts are needed to study about the engineering properties of concrete incorporating such industrial wastes. Present research is an effort to study the properties of concrete adding industrial wastes such as demolished concrete, FA and SF The improvement of properties of RCA concrete with the incorporation of two ureolytic-type bacteria, Bacillus subtilis and Bacillus sphaericus to improve the properties of RCA concrete. The experimental investigations are carried out by experts evaluate the improvement of the compressive strength, capillary water absorption and drying shrinkage of RCA concrete adding bacteria. Seven concrete mixes are manufactured using Portland slag cement (PSC) partially changed with SF ranging from 0 to 30%. The mix proportions were obtained as per Indian standard IS: 10262-2009 with 10% extra cement when SF is taken as per the above the construction practice by experts. Optimal dosages of SF for maximum values of compressive strength, tensile splitting strength and flexural strength at 28 days are determined. Keywords: Bacillus subtilis, Bacillus sphaericus, RCA, PSC, Silica Fume.

scholarly journals Research on Mechanical Performance & Behaviour of Geopolymer Concrete Subjected to Elevated Temperatures

2019 ◽  
Vol 8 (2S8) ◽  
pp. 883-887
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Silica Fume ◽  
Elevated Temperatures ◽  
Mechanical Performance ◽  
Geopolymer Concrete ◽  
Sem Images ◽  
Before And After ◽  
Alkaline Conditions ◽  
Compressive Strength Of Concrete

The investigative studies on mechanical performance & behaviour, of Geopolymer Concrete (GPC) before and after the exposure to elevated temperatures (of 200 0 C -1000 0 C with an increment of 100 0 C). Indicate that the GPC Specimens Exhibited better Compressive strength at higher temperatures than that of those made by regular OPC Concrete with M30 Grade. The chronological changes in the geopolymeric structure upon exposure to these temperatures and their reflections on the thermal behaviour have also been explored. The SEM images indicate GPC produced by fly ash , metakaolin and silica fume, under alkaline conditions form Mineral binders that are not only non-flammable and but are also non-combustible resins and binders. Further the Observations drawn disclose that the mass and compressive strength of concrete gets reduced with increase in temperatures.

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